20142014 AANNUALNNUAL RREPORTEPORT ONON AACTIVITIESCTIVITIES

CherryCherry CreekCreek BasinBasin WaterWater QualityQuality AuthorityAuthority

March 31, 2015 2014 Annual Report on Activities Cherry Creek Basin Water Quality Authority

Cherry Creek Basin Water Quality Authority Chuck Reid, Manager CliftonLarsonAllen LLP 8390 E. Crescent Parkway, Suite 500 Greenwood Village, CO 80111 Phone: 303-779-4525 Email: [email protected]

PREPARED BY:

Leonard Rice Engineers, Inc. William P. Ruzzo, P.E., L.L.C. GEI Consultants, Inc. JRS Engineering Consultant LLC Cherry Creek Land Use Agencies and Utilities Cherry Creek Stewardship Partners

TABLE OF CONTENTS

TABLE OF CONTENTS ...... i LIST OF FIGURES ...... iii LIST OF TABLES ...... iv LIST OF MAPS ...... iv CONTROL REGULATION 72 REPORTING REQUIREMENTS CHECKLIST ...... v LIST OF ACRONYMS AND ABBREVIATIONS ...... vii EXECUTIVE SUMMARY ...... ES-1 1 The Authority ...... 1-1 1.1 Regulatory History ...... 1-2 1.2 Financial Matters ...... 1-5 1.3 Web Links to the Authority ...... 1-6 2 Description of Cherry Creek Reservoir Watershed ...... 2-1 2.1 Cherry Creek Reservoir Model ...... 2-2 2.2 Public Information and Education by Authority and Partners...... 2-3 3 Point Sources ...... 3-1 3.1 Limits and Data Summary Requirements for Phosphorus and Nitrogen ...... 3-5 3.2 Monthly Phosphorus Concentrations ...... 3-7 3.3 Monthly Nitrogen Concentrations ...... 3-10 3.4 Permit Compliance ...... 3-11 3.5 Permit Renewal Timing and Process ...... 3-12 3.6 Other Point Source Discharge Permits in the Watershed ...... 3-13 3.7 Onsite Wastewater Treatment Systems ...... 3-15 3.8 Approved Site Applications ...... 3-16 3.8.1 Authority’s Role in Site Application Process ...... 3-17 3.9 Effectiveness in Reducing Nutrient Concentrations ...... 3-18 4 Regulated Stormwater Source Controls ...... 4-1 4.1 MS4 General Permit Renewal Process ...... 4-3 4.2 Sediment and Erosion Control Permits ...... 4-3 4.3 Adoption and Implementation of BMPs by Local Governments ...... 4-3 4.4 Construction BMPs ...... 4-4 4.5 Post-Construction BMPs ...... 4-4 4.6 Flood Control Facilities Retrofitting, Inspection, and Maintenance Actions ...... 4-6 4.7 Effectiveness in Reducing Phosphorus Concentrations ...... 4-7 4.8 Funding of Regulated Stormwater Projects ...... 4-10 i 4.9 Monitoring of Regulated Stormwater Projects ...... 4-10 4.10 Public Information and Education Actions of MS4s ...... 4-10 5 Other Nonpoint Sources ...... 5-1 5.1 Update list of PRFs Implemented ...... 5-1 5.2 Overview of PRFs to Date ...... 5-5 5.3 Floodplain Preservation/Conservation Easements ...... 5-9 5.4 Monitoring of PRFs ...... 5-9 5.5 PRF Effectiveness in Reducing Phosphorus Concentrations ...... 5-9 5.5.1 Cottonwood Creek Peoria Pond ...... 5-11 5.5.2 Cottonwood Creek Reclamation and Perimeter Pond ...... 5-13 5.5.3 McMurdo Gulch Stream Reclamation ...... 5-15 5.6 Funding of PRFs and Nonpoint Source Projects ...... 5-15 5.7 Annual Inspection of PRFs ...... 5-16 6 Riparian and Wetlands Protection ...... 6-1 6.1 Regulatory Protection ...... 6-1 6.2 Land Development Activities ...... 6-2 6.3 Protection, Enhancement, and Restoration Actions ...... 6-2 7 Monitoring ...... 7-1 7.1 Sampling Sites ...... 7-1 7.2 Reservoir Water Quality ...... 7-3 7.2.1 2014 Reservoir Water Quality ...... 7-3 7.3 2014 Reservoir Inflows – Outflows and Total Phosphorus Loads ...... 7-10 7.4 Reservoir Management Strategy ...... 7-12 7.5 2014 Phytoplankton and Cyanotoxins ...... 7-13 7.6 Long-Term Phytoplankton ...... 7-14 7.7 Zooplankton ...... 7-16 7.8 Water Quality in Cherry Creek from a Watershed Perspective ...... 7-17 7.8.1 Nutrients ...... 7-18 7.9 Proposed Modifications to Monitoring Program ...... 7-23 7.10 CDPHE WQCD Data Call ...... 7-23 8 Watershed Plan Implementation ...... 8-1 8.1 Priorities and Implementation Strategies ...... 8-3 References ...... R-1 Appendices

ii LIST OF FIGURES

Figure 1-1: Estimated 2014 Revenues ...... 1-5 Figure 2-1: Initial model bathymetry development ...... 2-3 Figure 2-2: Reservoir Model Schedule ...... 2-3 Figure 3-1: Summary of 2014 Total Phosphorus Maximum Reported Data ...... 3-9 Figure 3-2: Summary of 2014 Total Inorganic Nitrogen Maximum Reported Data ...... 3-10 Figure 4-1: Land Use Development Applications Reviewed by Authority, 1997-2014 ...... 4-9 Figure 4-2: Types of Development Projects Reviewed by Authority In 2014 ...... 4-9 Figure 5-1: Base Flow Total Phosphorus Concentrations for Cottonwood Creek, 1996-2014 ...... 5-10 Figure 5-2: Storm Flow Total Phosphorus Concentrations for Cottonwood Creek, 1996-2014...... 5-11 Figure 5-3: Average Total Suspended Solids 2009-2014 for Cottonwood-Peoria Pond PRF ...... 5-12 Figure 5-4: Flow-weighted Total Phosphorus (µg/L) 2009-2014 for Cottonwood Creek-Peoria Pond PRF ...... 5-12 Figure 5-5. Average Total Suspended Solids 2009-2014 for Cottonwood Creek-Perimeter Pond PRF ...... 5-14 Figure 5-6: Flow-weighted Total Phosphorus (µg/L) 2009-2014 for Cottonwood Creek Perimeter Pond PRF ...... 5-14 Figure 7-1: Chlorophyll A (µG/l) Concentrations in Cherry Creek Reservoir, 2014 WY ...... 7-4 Figure 7-2: Seasonal Mean (July to September) Chlorophyll A Concentrations Measured in Cherry Creek Reservoir, 1987 to 2014 ...... 7-5 Figure 7-3: Soluble Reactive Phsophorus and Chlorophyll A Concentrations Measured in Cherry Creek Reservoir, 2014 WY ...... 7-6 Figure 7-4: Dissolved Inorganic Nitrogen and Chlorophyll A Concentrations Measured in Cherry Creek Reservoir, 2014 WY ...... 7-7 Figure 7-5: Seasonal Mean (July to September) Total Phosphorus Concentrations (µG/L) Measured in Cherry Creek Reservoir, 1992-2014 ...... 7-7 Figure 7-6: Seasonal Mean (july to September) Total Nitrogen Concentrations (µG/L) Measured in Cherry Creek Reservoir, 1987 - 2014 ...... 7-8 Figure 7-7: Temperature Profiles Recorded During Continuous Monitoring at Site CCR 2 COE Inflows During 2014 ...... 7-9 Figure 7-8: Dissolved Oxygen (MG/L) Profiles Recorded During Routine Monitoring at Site CCR 2 in 2014 WY ...... 7-10 Figure 7-9: Percent Relative Biovolume of Algal Groups for Each Routine Photic Zone Composite Sample Collected in Cherry Creek Reservoir, 2014 ...... 7-14 Figure 7-10: Percent Algal Biovolume of Major Taxonomic Groups in Cherry Creek Reservoir from 2009 through 2014 ...... 7-16 Figure 7-11: Total Density of Zooplankton Groups and Chlorophyll a Concentration by Sample Date in Cherry Creek Reservoir, 2014 CY ...... 7-17 Figure 7-12: Total Phosphorus Concentration Measured at Cherry Creek Surface Water Stations Castlewood, CC-1, CC-4, and CC-9 ...... 7-18 Figure 7-13: Nitrate Concentration MeAsured at Surface Water Stations Castlewood, CC-1, CC-4, and CC-9 ..... 7-19 Figure 7-14: Choloride Concentration Measured at Surface Water Stations Castlewood, CC-1, CC-4, and CC-9 ...... 7-22 Figure 7-15: Sulfate Concentration Measured at Surface Water Stations Castlewood, CC-1, CC-4, and CC-9 ..... 7-23

iii LIST OF TABLES

Table 1-1: Authority Members ...... 1-4 Table 1-2: Authority TAC Members ...... 1-4 Table 1-3: New and Updated Reference Documents ...... 1-6 Table 3-1: Cherry Creek Watershed Wastewater Facilities and Permit Expiration Dates ...... 3-1 Table 3-2: Regulation 72 Discharge Limits for Phosphorus ...... 3-5 Table 3-3: Summary of Total Phosphorus Permit Limits and Data 2014 ...... 3-6 Table 3-4: Summary of Total Inorganic Nitrogen Permit Limits and Data 2014 ...... 3-7 Table 3-5: 2014 Point Source Phosphorus Monthly Concentration ...... 3-8 Table 3-6: 2014 Point Source Total Inorganic Nitrogen ...... 3-11 Table 3-7: Workplan Schedule for Renewal of General and Individual Permits ...... 3-12 Table 3-8: Total Phosphorus Concentration Ranges reported by other PERMITTED POINT source dischargers in the cherry creek basin ...... 3-13 Table 4-1. Summary of Stormwater Permit, Inspection, and Enforcement Actions ...... 4-5 Table 5-1: CCBWQA Summary of Recommended Pollutant Reduction Facilities 2015-2024 Budget Projections ($1000) ...... 5-3 Table 5-2: CCBWQA Summary of Recommended Pollutant Reduction Facilities 2015-2024 Budget Projections ($1000) ...... 5-4 Table 5-3: 2014 Annual Inspection Report of PRFs at Cherry Creek State Park ...... 5-17 Table 7-1: Normalized Phosphorus Loads, Exports, and Flow-Weighted Phosphorus Concentrations for Cherry Creek Reservoir, 1992 to 2014 ...... 7-11 Table 7-2. Regulation 85 Monitoring for Instream Phosphorus Concentrations Submitted to Date ...... 7-20 Table 7-3. Regulation 85 Monitoring for Instream Nitrogen Concentration Submitted to Date ...... 7-21

LIST OF MAPS

Section Map 1-1: Entities Within the Cherry Creek Reservoir Watershed Boundaries ...... 1 Map 2-1: Cherry Creek Reservoir Watershed Boundaries ...... 2 Map 3-1: Locations of Wastewater Treatment Facilities ...... 3 Map 3-2: Other Point Source Discharge Permits ...... 3 Map 3-3: Onsite Wastewater Treatment Systems ...... 3 Map 4-1: Municipal Separate Storm Sewer Systems ...... 4 Map 4-2: Land Use Development Applications Reviewed by Authority, 2013 ...... 4 Map 7-1: Monitoring Sites ...... 7

iv CONTROL REGULATION 72 REPORTING REQUIREMENTS CHECKLIST

This report is being submitted to both the Colorado Water Quality Control Commission and the Water Quality Control Division on or before March 31, 2015, in fulfillment of the reporting requirements of Regulation No. 72 – Cherry Creek Reservoir Control Regulation (Regulation 72). The following list shows where the reporting requirements of the Cherry Creek Reservoir Control Regulation can be found in this report. Reporting information includes all requirements of Regulation 72, effective November 30, 2012. Cross Reference between Regulation 72 Reporting Requirements and Annual Report Section Reservoir/Watershed Public information and education by Authority and Partners (§72.6(2)) ...... 2.2 Point Source Controls (§72.9(1)(a) & §72.9(1)(e)) ...... 3 Phosphorus concentrations (§72.9(1)(a)) ...... 3.1,3.2 Permit violations (§72.9(1)(a)) ...... 3.4 Approved site applications (§72.9(1)(a)) ...... 3.9 Effectiveness in reducing nutrient concentrations (§72.9(1)(a)) ...... 3.10 Regulated Stormwater Controls (§72.9(1)(b) & (§72.9(1)(e)) ...... 4 Sediment and erosion control permit, inspection, and enforcement actions (§72.9(1)(b)) ...... 4.2 Construction BMPs inspection and enforcement actions (§72.9(1)(b)) ...... 4.4 Permanent BMPs construction, inspection, and maintenance actions (§72.9(1)(b)) ...... 4.5 Flood control facilities retrofitting, inspection, and maintenance actions (§72.9(1)(b)) ...... 4.6 Effectiveness in reducing phosphorus concentration (§72.9(1)(b)) ...... 4.7 Funding of nonpoint source control projects (§72.9(1)(b)) ...... 4.8 Monitoring of nonpoint source control projects (§72.9(1)(b)) ...... 4.9 Public information and education actions of MS4s (§72.9(1)(b)) ...... 4.10 Nonpoint Source Controls (§72.9(1)(c) & (§72.9(1)(e)) ...... 5 Updated list of PRFs implemented (§72.3)...... 5.1 Floodplain preservation/conservation easements (§72.6(6)) ...... 5.3 Effectiveness in reducing phosphorus concentration (§72.9(1)(c)) ...... 5.6 Funding of PRFs (§72.9(1)(c)) ...... 5.7 Monitoring of PRFs (§72.9(1)(c)) ...... 5.5 Riparian and Wetlands Protection (§72.9(1)(d)) ...... 6 Protection, enhancement, and restoration actions (§72.9(1)(d)) ...... 6.1 Water Quality Monitoring (§72.9(1)(e)) ...... 7 Reservoir water quality and inflow volumes (§72.8.1) ...... 7.2, 7.3 Alluvial water quality (§72.8.2) ...... Appendix Surface water quality (§72.8.2(a)) ...... 7.7 Point sources (§72.8.1) ...... 3 PRF monitoring (inflow and outflow nutrient concentrations) (§72.8.2(b)) ...... 5.5 Proposed modifications to monitoring program (§72.8.3) ...... 7.8

v Program Effectiveness (§72.9(2) & §72.9(1)(e)) ...... 3.10, 4.7, 5.5 Status of compliance with discharge limits and conditions ...... 3.4 Recommendations on new/proposed expansion of facilities (§72.9(1)€) ...... 5.1 Updated list of planned PRFs with implementation schedule (§72.6.1€) ...... 5.1, 5.2 Recommendations for improving water quality (§72.9(1)€) ...... 8 Proposed special water quality investigative studies (§72.8.4) ...... 8 Financing of nonpoint source projects (§72.9(2)) ...... 5.6 Regulated stormwater permit requirements (§72.9(2)) ...... 4.2, 4.4, 4.5 Adoption and implementation of BMPs by local governments (§72.9(2)) ...... 4.3 Reduction of phosphorus concentrations into the reservoir by the MEP (§72.9(2)) ...... 7.2

Photo Credits: Chris Muller, Jojo La, Jessica DiToro, Katie Fendel, Jim Swanson, Bill Ruzzo, Casey Davenhill, Cherry Creek Partners, Craig Wolf

vi LIST OF ACRONYMS AND ABBREVIATIONS

2014 Annual Report 2014 Annual Report on Activities ac-ft Acre-feet ACWWA Arapahoe County Water & Wastewater Authority Authority Cherry Creek Basin Water Quality Authority BMP Best Management Practice Board Board of Directors of Cherry Creek Basin Water Quality Authority CCR Colorado Code of Regulations CCSP Cherry Creek State Park CDOT Colorado Department of Transportation CDPHE Colorado Department of Public Health and Environment

CDPS Colorado Discharge Permit System CIP Capital Improvement Project COE U.S. Army Corps of Engineers Commission Colorado Water Quality Control Commission CPW Colorado Parks and Wildlife C.R.S. Colorado Revised Statutes CSU Colorado State University DESC Drainage, Erosion, and Sediment Control Division Colorado Water Quality Control Division DOC Dissolved Organic Carbon DOLA Dog Off-Leash Area DMR Discharge Monitoring Report ECHO Enforcement & Compliance History Online EDB Extended Detention Basin EPA U.S. Environmental Protection Agency ESCP Erosion and Sediment Control Plan GEI GEI Consultants, Inc. GESC Grading, Erosion, and Sediment Control lbs/yr Pounds per Year LID Low Impact Development µg/L Micrograms per Liter

m Meter MDCIA Minimize Directly Connected Impervious Areas mg/kg Milligrams per Kilogram (dry weight)

vii mg/L Milligrams per Liter MGD Million Gallons per Day MEP Maximum Extent Practicable MS4 Municipal Separate Storm Sewer System MWAT Maximum Weekly Average Temperature NOA Notice of Authorization O&M Operation and Maintenance OWTS Onsite Wastewater Treatment Systems Partners Cherry Creek Stewardship Partners PCWRA Plum Creek Water Reclamation Authority PJMD Parker Jordan Metropolitan District PWSD Parker Water and Sanitation District

PRF Pollutant Reduction Facility Regulation 31 The Basic Standards and Methodologies for Surface Water (5 CCR 1002-31)

Classifications and Numeric Standards for South Platte River Basin, Laramie Regulation 38 River Basin, Republican River Basin, Smoky Hill River Basin (5 CCR 1002-38)

Regulation 61 Colorado Discharge Permit System Regulations (5 CCR 1002-61) Regulation 72 Cherry Creek Reservoir Control Regulation (5 CCR 1002-72) Regulation 85 Nutrients Management and Control Regulation (5 CCR 1002-85) SBR Sequencing Batch Reactor SEMSWA Southeast Metro Stormwater Authority SRP Soluble Reactive Phosphorus TAC Technical Advisory Committee of the Cherry Creek Basin Water Quality TCHD Tri-County Health Department TDP Total Dissolved Phosphorus TDS Total Dissolved Solids TIN Total Inorganic Nitrogen TMAL Total Maximum Annual Load TN Total Nitrogen TOC Total Organic Carbon TP Total Phosphorus TSS Total Suspended Solids UDFCD Urban Drainage and Flood Control District

USGS U.S. Geological Survey WWTF Wastewater Treatment Facility WY Water Year

viii

2014 ANNUAL REPORT ON ACTIVITIES

EXECUTIVE SUMMARY

Purpose

The Cherry Creek Basin Water Quality Authority (Authority) was created in 1988 to improve, protect, and preserve the water quality of Cherry Creek and Cherry Creek Reservoir and to achieve and maintain state water quality standards. The 2014 Annual Report on Activities (2014 Annual Report) gives a status report on activities and reviews progress made by the Authority toward attaining water quality standards in 2014. This report is submitted in fulfillment of the Authority's obligation to report annually to the Colorado Water Quality Control Commission (Commission) and Water Quality Control Division (Division).

Statutory and Regulatory Basis

The Authority’s statutory and regulatory requirement to protect water quality can be divided into two parts: Cherry Creek watershed, namely Cherry Creek and tributaries above the reservoir, and Cherry Creek Reservoir. Water quality standards for Cherry Creek Reservoir and its tributaries are contained in Regulation 38 (Classifications and Numeric Standards for South Platte River Basin, Laramie River Basin, Republican River Basin, Smoky Hill River Basin, effective 12/31/2012). In addition to Regulation 38, the Cherry Creek Reservoir Control Regulation (Regulation 72) was adopted in 1985, to direct actions designed to attain the phosphorus water quality standard that was adopted for the reservoir in 1984. In 2009, the Commission revised the chlorophyll a standard1 to align more with conditions feasible to achiee in the future, and modified the implementing Regulation 72 accordingly. Regulation 72 was last updated in 2012 to further protect the uses and water quality of Cherry Creek Reservoir. There are also local regulations, as well as education programs, that are implelmented to control nonpoint sources. Taken together, these state and local regulations provide a mechanism for protecting the quality of Cherry Creek Reservoir.

1 The Commission changed the standard from phosphorus to chlorophyll a in 2000. ES - 1

Regulation 72 provides the basis for implementation of control measures to protect Cherry Creek Reservoir's quality, and is based on state/local partnerships for controlling nutrients, including phosphorus. Upon its initial adoption of Regulation 72, the Commission found that controls for both point and nonpoint sources of phosphorus are essential to protect the quality and uses of Cherry Creek Reservoir over the long term. In 2009, the Commission placed an emphasis on other nutrients (specifically nitrogen) as well as phosphorus, expanded Regulation 72 to require monitoring for both nitrogen and phosphorus, which the Authority has been doing since its inception. Regulation 72 requires measures necessary to reduce the inflow total phosphorus and nutrient concentrations to Cherry Creek Reservoir to be implemented throughout the watershed. In addition, point source controls and discharge effluent limitations are specified in Regulation 72. This regulation also contains requirements for regulated and other nonpoint sources, including implementation of Pollutant Reduction Facilities (PRFs) and Best Management Practices (BMPs). The history of Control Regulation 72 demonstrates the complexity and uncertainty of measures and programs to preserve water quality in the reservoir. Some initial strategies and approaches were found to be beneficial while others required modifications based on data collection and analysis. This overall approach is the foundation of the scientific method: the hypothesis was that controlling total phospohrus loads from point and nonpoint sources will preserve and protect reservoir water quality. Data collected since 1982 suggest that reservoir water quality has not improved, but may have been prevented from becoming worse through watershed programs and efforts of the Authority and its members. The hypothesis today, after 30-years of implementing point source, NPS, and regulated stormwater controls, has not changed significantly: controlling nutrient concentrations from point and nonpoint sources will preserve and protect water quality of the reservoir. Although the Authority continues to implement watershed controls with indications of some success, focus has shifted to better understanding the complex dynamics of the reservoir ecological system by developing a hydrodynamic reservoir model. While still in its development stages, a thorough data review has shown that other factors besides inflow nutrient loads may be important in effecting water quality dynamics in the reservoir. In other words, “It’s complicated!”

Pollutant Reduction Facilities

Implementation of watershed measures and controls has resulted in substantial water quality improvements in Cherry Creek Reservoir tributaries. In Water Year 2014 (WY2014), the annual median total phosphorus (TP) concentration in one tributary, Cottonwood Creek just upstream of Cherry Creek Reservoir, was 48 µg/L. Concentrations at this location have been reduced to a long-term (1995-2014) median annual base flow concentration of 69 µg/L2. TP concentrations in Cherry Creek have been controlled closer to background levels, in spite of unprecedented growth in the watershed. The

2 However, the CC-10 long-term median storm flow concentration is approximately 5 times greater (360 µg/L). ES - 2

Statement of Basis and Purpose for Regulation 72 recognizes 200 µg/L as the background instream phosphorus level. Recently completed stream reclamation projects have further reduced TP concentrations in Cherry Creek itself. The WY2014 TP concentration of Cherry Creek just upstream of the reservoir was 197 µg/L, compared to the long-term (1995-2014) median base flow concentration of 213 µg/L. Exceptionally high TP concentrations in another tributary, McMurdo Gulch, have been reduced by about 15% percent through a stream reclamation project, although both upstream and downstream annual median TP concentrations (340 µg/L and 300 µg/L, respectively) are still above the 200 µg/L background value. Finally, in WY2014 the annual median total nitrogen (TN) concentrations in Cherry Creek and Cottonwood Creeks, just upstream of the reservoir, were 885 µg/L and 1208 µg/L. It is important to note, however, that Cherry Creek at the EcoPark monitoring site (about 5 miles upstream from the reservoir) had a WY2014 annual median TN concentration about twice the level at the mouth (1660 µg/L vs. 885 µg/L). This indicates that the TN levels are apparently decreasing as the creek flows downstream; this may be related to denitrification, but the Authority has not evaluated the relative percentage of nirtorgen species.

Wastewater Treatment Plants

The six wastewater treatment facilities (WWTFs) that discharge in the basin also continue to achieve notable phosphorus removal. All WWTFs met their permit limit for phosphorus, which for nearly all of the discharges is 50 µg/L (30-day average)3. Again, this is one-quarter of the instream designated background level of 200 µg/L. In addition, there were 40 other permitted point source dischargers in the Cherry Creek basin in 2014, most of whom were certified under general permits. Some of the general permits now include a TP limit of 50 µg/L for discharges to the Cherry Creek basin (e.g., COG604000-Hydrostatic Testing and COG070000-Special Trade Contractors). There was also one drinking water facility with an individual permit (CO0047589-Arapahoe County Water and Wastewater Authority’s Joint Water Purification Plant). This permit contains a TP limit of 200 µg/L, as required by Regulation 72 for drinking water plant discharges.

Municipal Separate Storm Sewer Systems (MS4) Programs

There are eight permittees covered by the Cherry Creek Reservoir Basin MS4 General Permit (COR080000) and nine entities permitted under the Non-Standard MS4 General Permit (COR070000). Regulation 72 contains a number of requirements, that are in addition to requirements included in Regulation 61 (Colorado Discharge Permit System Regulations), that the State shall incorporate into any stormwater permit issued to an MS4 in the Cherry Creek

3 Two WWTFs which are permitted or authorized to use their treated effluent for irrigation have limits that vary from the 50 µg/L permit limit. The TP limits that apply to these 2 outfalls are 250 µg/L as a 30-day average (Stonegate Village Metropolitan District WWTF) and 500 µg/L as a 90- day average (Meridian Metropolitan District WWTF). ES - 3

watershed. Stringent requirements have been developed for construction site stormwater runoff and post- construction stormwater management in new development and redevelopment. Different levels of BMPs are required, depending on which of the Authority’s three development tiers a project falls under. For example, all Tier 3 development and redevelopment must include post-construction BMPs that provide a Water Quality Capture Volume designed to capture and treat, at a minimum, the 80th percentile runoff event. Other required activities include public education and outreach targeting nutrient sources and special requirements for stream preservation areas.

Reservoir’s Response to Watershed Improvement Actions

In spite of water quality improvements in tributary streams, chlorophyll a concentrations in the reservoir again exceeded 18 µg/L. This is the fifth consecutive year that the seasonal mean chlorophyll value has exceeded the standard of 18 µg/L. As a result, the reservoir is not attaining the site specific chlorophyll a standard based on an allowable exceedence frequency of once in five years. The Authority has implemented new programs and procedures in 2014 to further understand reservoir dynamics and to make greater progress towards meeting the reservoir standard. In 2008, the Authority implemented the reservoir destratification management program that was designed to increase the circulation of the water column, to promote a greater exchange of dissolved oxygen at the surface layer, and to circulate the reaerated water into the deeper depths of the reservoir. A goal of this management strategy is to increase the dissolved oxygen concentrations near the water/sediment interface, which should help reduce the internal phosphorus loading component of the reservoir (AMEC, 2005). The sediment phosphorus load accumulates over time from external and internal sources, including from within the reservoir (e.g., settled algae and detritus), and is geochemically transformed and released when the sediment surface becomes anoxic (Nurmberg and LaZerte 2008). This internal release of phosphorus facilitates the growth of all algae; thus, by reducing the internal load, algae growth should be reduced too. The destratification system was also designed to vertically mix algae and to disrupt the suitable habitat of large filamentous cyanobacteria which have the ability to regulate their buoyancy, fix atmospheric nitrogen, and rapidly grow at the surface of the reservoir. In theory, when these design considerations are placed in the context of each other, the destratification system should have reduced chlorophyll a concentrations, both seasonal

ES - 4

means and peak values, and helped to achieve the site specific chlorophyll a standard while protecting the beneficial uses of the reservoir. However, after operating the destratification system for a period of six years, the reservoir appeared to have reached a new condition characterized by internal nutrient loading and higher than expected algal biomass (chlorophyll a) conditions that resulted in the standard being exceeded 4 out of the last 5 years of the destratification system’s operation. Note that the standard was met for the first 2 years of the system’s operation, which began in 2008. A laboratory change in 2009 resulted in different methods used for counting phytoplankton data, which produced results that were not comparable to the previous years’ results. This confounded the comparison of algae species composition and density (cell count) data before and after the 2009 change. Note that in previous years’ Annual Reports, the cell count data were displayed in “pie charts”. These charts showed a substantial reduction in cyanobacteria from 2009 onward. However, the Authority has since concluded that it is incorrect to directly compare the cell count data from the two different labs using different methods and to infer that the destratification system has reduced the number of cyanobacteria cells.

Also, because the new lab also provides biovolume results (which the previous lab would not provide), biovolume data were only available for the reservoir during operation of destratification. As a result, the destratification system was not operated in 2014 to reassess the phytoplankton community dynamics in the absence of aeration and to better understand whether the destratification system was vertically mixing the algae and disrupting the suitable habitat for undesirable large filamentous cyanobacteria. Whereas the previous objectives of the annual monitoring study remain, two special studies were included in 2014 to better understand the potential concern for cyanotoxins (which can be produced by some cyanobacteria under certain conditions) in the context of beneficial uses and to better understand organic carbon dynamics in the system. The 2014 data will also be used to inform the development of the reservoir hydrodynamic model currently in progress.

2014 has been a year for the Authority to ask tougher questions regarding our programs. Whereas watershed control measures appear to be improving water quality in Cherry Creek and its tributaries, these improvements have yet to bring the reservoir into consistent compliance with the standard. Reservoir water quality is being driven by more than external nutrient loading and the reservoir model will help the Authority better understand how to improve water quality. The Authority is still learning, and adjusting our programs to improve results.

ES - 5

2014 ANNUAL REPORT ON ACTIVITIES

1 THE AUTHORITY The Cherry Creek Basin Water Quality Authority (Authority) was formally created in 1988 by the Colorado State Legislature by statute (see Colorado Revised Statues (C.R.S.) 25-8.5-101 et seq.). The Authority was created as a quasi-municipal corporation and political subdivision of the state, and was provided with specific powers (see box below). The Authority is tasked with improving, protecting, and preserving the water quality of Cherry Creek and Cherry Creek Reservoir and preserving waters for recreation, fisheries, water supplies, and other beneficial uses. The Legislature established the Authority to benefit the inhabitants and landowners within the basin by preserving water quality in both Cherry Creek and Cherry Creek Reservoir, and to benefit the people of the State of Colorado by preserving waters for recreation, fisheries, water supplies, and other beneficial uses. The Authority develops water quality management strategies to: (1) minimize point, nonpoint, and regulated stormwater pollutant source nutrient contributions; (2) implement pollutant reduction programs; and (3) monitor water quality to evaluate progress. Together, these strategies create an effective water quality management approach.

PARTIAL LIST OF GENERAL STATUTORY POWERS OF THE AUTHORITY (C.R.S. 25-8.5-111) . “Develop and implement, with such revisions as become necessary in light of changing conditions, plans for water quality controls for the reservoir, applicable drainage basin, waters, and watershed, to achieve and maintain the water quality standards” . “Conduct pilot studies and other studies that may be appropriate for the development of potential water quality control solutions” . “Develop and implement programs to provide credits, incentives, and rewards within the Cherry Creek basin plan for water quality control projects” . “Recommend the maximum loads of pollutants allowable to maintain the water quality standards” . “Recommend erosion control and urban runoff control standards and conduct educational programs regarding such controls in the basin” . “Recommend septic system [OWTS] maintenance programs” . “Acquire, lease, rent, manage, operate, construct, and maintain water quality control facilities or improvements for drainage, nonpoint sources, or runoff within or without the Authority boundaries”

(In addition, the Authority has contractual, administrative and financial powers.)

1-1

1.1 Regulatory History 1982 A Clean Lakes Study of Cherry Creek Reservoir identified phosphorus as the major nutrient causing algal productivity, potentially leading to eutrophication with potential negative impacts to beneficial uses of the reservoir. 1984 The Colorado Water Quality Control Commission (Commission) first adopted a water quality standard for the reservoir in 1984. The following year, the Commission adopted a control regulation (Regulation 72, the Cherry Creek Reservoir Control Regulation) for the reservoir to provide a mechanism for protecting the quality of Cherry Creek Reservoir using a model based upon 1982 hydrologic conditions. 1990 In 1990/1991, the Commission established a Total Maximum Annual Load (TMAL) of total phosphorus (TP) that could enter the reservoir and still maintain the phosphorus standard and established a total phosphorus limit for dischargers of 0.05 milligrams per liter (mg/L), the lowest level technically attainable. 2000 The Commission adopted a new standard for the protection of Cherry Creek Reservoir in 2000. This standard, a maximum of 15 micrograms per liter (μg/L) of chlorophyll α during the growing season from July to September, with a phosphorus goal of 40 μg/L was determined to be protective of the uses of the reservoir. An amended control regulation to implement the new water quality standard and protect the designated uses was adopted the following year, based on a phased TMAL approach. 2009 Based on findings from thirteen studies completed as part of the phased TMAL, the Authority recommended, and the Commission adopted, a revised water quality standard (seasonal mean chlorophyll α of 18 μg/L). The control regulation was also modified in 2009. These changes to Regulation 72 included establishment of a concentration-based nutrient management approach, removal of all TMAL-related components, a discharge effluent limit for drinking water plant discharges of 0.20 mg/L total phosphorus, and establishment of a 3-tiered system for stormwater quality measures for new development and redevelopment. 2012 The Comission adopted amendments to Regulation 72 regarding stormwater permit requirements, based on recent studies and information, to help improve the effectiveness of the Regulation 72 stormwater program. The changes provided consistency between state and federal stormwater requirements in Regulation 72 and the Colorado Discharge Permit System Regulation (Regulation 61).

1-2

Today’s Authority

C.R.S. 25-8.5-105 defines the Authority’s membership. The following entities are designated as members of the Authority:

• Douglas and Arapahoe shall each have one member (El Paso and Elbert Counties are not included in the statutory definition of the Authority boundaries); • Each municipality that has property within the Authority’s boundaries shall have one member; • The special districts that own and operate wastewater treatment services in the Cherry Creek basin shall collectively be represented by a single member of the Authority; • A total of seven members shall be appointed by the governor to represent sports persons, recreational users, and concerned citizens. There are currently two counties and eight municipalities within the boundaries; however, not all have appointed Board members. Of the Governor’s appointees, at least two are to be from sporting or recreational MAP 1 – 1 MAP OF ENTITIES WITHIN THE CHERRY CREEK organizations that have members RESERVOIR WATERSHED BOUNDARIES who use the reservoir; at least two from citizen or environmental organizations interested in preserving water quality with members who use the reservoir or reside in the basin; and at least three must have professional backgrounds in or professional training regarding water quality issues.

1-3

TABLE 1-1: AUTHORITY MEMBERS

Maximum Current Entity Type Number of Number of Members Members County 2 2 (Arapahoe, Douglas) Municipality 8 6 (Aurora, Castle Pines, Castle Rock, Centennial, Foxfield, Greenwood Village, Lone Tree, Parker) Special Districts (represents all water and wastewater service district providers) 1 1 Appointed by the Governor 7 6 Total members of Authority Board 18 16

Board and TAC

The Authority has a Board of Directors (Board) and a Technical Advisory Committee (TAC). According to the statute, each Authority member (other than the Governor’s appointees) shall appoint a representative to serve on the Board. (C.R.S. 25-8.5-106(2)). The Authority’s bylaws state that county, municipal, and special district members may each appoint one representative to serve on the TAC, and the Board can appoint other individuals who represent educational or public interest groups, and/or local governments that are not members of the Authority, and have an interest in stormwater drainage and water quality within the Cherry Creek basin to the TAC. The role of the TAC is to consider and report to the Board on matters of a scientific or technical nature. Under the bylaws, possible roles may include assistance with technical and scientific matters, development and submission of referral comments, review and provision of comments/recommendations on 401 and 404 permit applications, and review and provision of comments/recommendations on local government decisions including rezoning, subdivisions, special projects, new rules and regulations, and other duties. The current makeup of the Board and TAC are shown in Table 1-1 and Table 1-2; note that the Towns of Castle Pines and Foxfield municipality positions are currently vacant. TABLE 1-2: AUTHORITY TAC MEMBERS

Number of Entity Type Members County (Arapahoe and Douglas) 2 Municipality 6 (Aurora, Castle Rock, Centennial, Greenwood Village, Lone Tree, and Parker) Special Districts 1 Board-appointed (TAC Chair, SEMSWA, Partners, USACOE, CPW, TCHD, CDOT, and UDFCD) 8 Total Members of TAC 17

1-4

1.2 Financial Matters The Authority levies property taxes (one-half mill) on all taxable property within the Authority’s boundaries (C.R.S. 25-8.5-111(p)(I)). The Statute also allows the Authority to establish rates, tolls, fees, charges, and penalties for functions, services, facilities, and Authority programs. The total annual revenue from these sources shall not exceed 30 percent of the annual Authority budget. Agricultural lands are exempt from the collection of these fees. Current development fees include $60 per single family residence and $0.04 per square foot of impervious area in commercial and multi-family developments. Wastewater fees are $0.25 per 1,000 gallons of treated wastewater discharged in the Cherry Creek basin. The Authority also receives user fees from Cherry Creek State Park visitors. These fees are subject to review and approval by the Colorado Parks and Wildlife Board and add an additional $3 on annual passes and $1 on single-day passes. The relative percentages of the estimated revenues for 2014 are shown in Figure 1-1 below.

Property Tax -73.2%

State Park Fees - 8.1%

Development Fees - 7.0%

Wastewater Surcharges - 5.6% Other - 6.1%

FIGURE 1-1: ESTIMATED 2014 REVENUES

The 2014 budget included about $2.1 million in revenues: about $1.5 million from property taxes, $175,000 from State Park user fees, $150,000 from building permit fees, $120,000 from wastewater surcharges, and the rest from miscellaneous income.

The Authority’s 2014 budgeted expenditures were approximately $3 million (the Authority may spend funds from its reserves for large capital projects). Expenditures and revenues are often not matched each calendar year because implementation and timing of project costs for the capital improvement program can vary significantly from year to year. The statute mandates that the Authority spend at least 60% of the annual authorized revenues on the construction and maintenance of Pollutant Reduction Facilities (PRFs). The remaining 40% is allocated towards monitoring, special studies, planning documents, technical reports or memoranda, and administrative costs. Again, because expenditures and revenues are not matched each calendar year, the Authority interprets the 60/40 split referenced above as a multi-year mandate and does not account for this in any one year.

1-5

1.3 Web Links to the Authority In 2014, the Authority launched its new website that features new design, and added content and information. The website now hosts basin information including the Authority’s vision and mission, Board and TAC members, and the bylaws. The website is a central location where reports, maps, financials, meetings minutes, and board and TAC packets can be found. The website also contains information about current, pending, and completed projects, including summaries of Pollutant Reduction Facilities and other basin projects. The website can be found at: www.cherycreekbasin.org . In 2014, the Authority created or updated several documents that serve as references for the status of water quality in Cherry Creek Reservoir, guidelines and educational material on water quality best management practices (BMPs) and PRFs, technical sources on various aspects of water quality, and watershed planning and management strategies. These are listed in Table 1-3. TABLE 1-3: NEW AND UPDATED REFERENCE DOCUMENTS

2012 Cherry Creek Basin Water Quality Authority Watershed Plan (Chapter 7 [Annual Action Plans] updated in 2014) (Multi-year plan for watershed management) 2013 Annual Report of Activities by the Cherry Creek Basin Water Quality Authority (Update on activities completed by the Authority in 2013, submitted to Commission in March 2014) 2014 Annual Inspection of Pollutant Reduction Facilities (PRFs) (Inspection of PRFs constructed by the Authority to assess whether PRFs are functioning as designed and to identify routine, restorative, and rehabilitative maintenance needs) 2015 – 2024 10-Year Capital Improvement Projects (CIP) Plan (Summary of potential pollutant reduction facilities) Monthly CIP Status Reports to Board (Summary of 2014 progress on capital improvement projects, updated twice each month) Cherry Creek Reservoir 2014 Water Year Aquatic Biologic-Nutrient Monitoring Study and Cottonwood Creek Pollutant Reduction Facilities Monitoring Report.

The Authority has continued to consolidate and maintain its environmental and water quality data in a relational database management system, made available through a password–protected website. The CCBWQA Data Viewer website is located at the following address: http://lre-projects.com/CCBWQA/. The website is used by members of the Authority and consultants and outside entities for data evaluation and review. The database was queried to respond to the Colorado Department of Public Health and Environment (CDPHE) data call for the 2015 Rulemaking Hearing.

1-6

2014 ANNUAL REPORT ON ACTIVITIES

2 DESCRIPTION OF CHERRY CREEK RESERVOIR WATERSHED The Cherry Creek watershed is one of the most important and prominent components of the Denver metropolitan area. Cherry Creek meets the South Platte River in the heart of Denver and connects communities in Denver, Arapahoe, and Douglas Counties. The creek has been used for hundreds of years by Native Americans, trappers, traders, and settlers, and much of the land was used for agriculture, especially during the late 1800s through the 1930s. Landmarks and reminders of the watershed’s rich history can still be readily found throughout the watershed and within the state parks and agricultural operations. One such site is Castlewood Dam, located in Castlewood Canyon State Park in the upper watershed. The dam was originally built in response to Cherry Creek flooding Denver in 1864. Castlewood Dam was first build in 1890, then failed in 1892. It was then rebuilt, and failed again in 1933, bursting after several days of torrential rain. The flood was the worst in Colorado’s recorded history at that time, destroying a great number of buildings in Denver, including the Rocky Mountain News building, the Methodist Church, and City Hall. Eight Denver residents lost their lives along with a great number of livestock. Following this dam failure, Cherry Creek Dam was constructed and Cherry Creek Reservoir was created in 1948, to protect downstream areas from floods as had been experienced in the past. The reservoir is owned and operated by the U.S. Army Corps of Engineers (COE) and has a surface area of approximately 852 acres. This infrastructure was successful in reducing damages during the 1965 Denver flood by storing all flows in the creek upstream of the reservoir. In 1959, recreational demands on the reservoir from the growing urban population led to the creation of the Cherry Creek State Recreation Area, Colorado’s first state park. Today the park is one of Colorado’s busiest. In 2013, there were an estimated 3 million visitors at Cherry Creek Dam State Park.

2-1

Boundaries of the Authority

The Authority’s enabling legislation defines the boundaries of the Authority as being limited to Arapahoe and Douglas Counties. About 386 square miles of land and 600 miles of riparian stream corridors are encompassed within the Authority boundaries. Land use within the watershed varies from highly rural in the upper watershed to dense residential in the lower watershed and around the reservoir. Note that the Cherry Creek Reservoir Control Regulation defines the boundaries of the watershed to also include lands within El Paso and Elbert Counties: “all lands that drain into the following: (a) the mainstream of Cherry Creek, from the source of East and West Cherry Creek to the inlet of Cherry Creek Reservoir (Segment 1), including alluvial groundwater; (b) Cherry Creek Reservoir (Segment 2), including alluvial groundwater; (c) all tributaries to Cherry Creek, including wetlands and alluvial groundwater, from the sources of East and West Cherry Creeks (parts of Segment 4); and all lakes and reservoirs in the Cherry Creek Reservoir watershed”. 2.1 Cherry Creek Reservoir Model In 2014, a comprehensive reservoir water quality model was initiated to better understand complex relationships among the biotic and abiotic components of the reservoir. The model will be used to MAP 2-1: MAP OF CHERRY CREEK RESERVOIR further evaluate water quality and WATERSHED BOUNDARIES ecological conditions of the reservoir under different hydrologic scenarios, and to evaluate the potential effects of alternative management strategies , both within the reservoir and the watershed, to meet beneficial uses and numeric standards. The model will also help to better understand the mechanisms behind changes in chlorophyll a concentrations, especially in recent years.

2-2

CE-QUAL-W2 was chosen for the hydrodynamic model. Data acquisition and data analyses were completed in 2014, with a focus on chlorophyll a concentrations and influencing factors including biological response parameters (cyanobacteria and/or other algal groups, other tropic levels, e.g., zooplankton, fish). Other parameters include chemical/physical/biologic parameters (D.O., pH, clarity, temperature), predictive input variables (phosphorus, nitrogen, TOC/DOC, TSS, TDS), external and internal loads, and variable hydrological inputs (including reservoir destratification system inputs). The following tasks are planned for completion of FIGURE 2-1: INITIAL MODEL BATHYMETRY the model: (1) model development, calibration, DEVELOPMENT validation (2) management scenarion identification (3) management scenario evaluation, and (4) model documentation and training. The modeling is projected to be completed by December 2015.

FIGURE 2-2: RESERVOIR MODEL SCHEDULE

2.2 Public Information and Education by Authority and Partners Pursuant to Regulation 72, the Authority is tasked with developing and implementing a public information and education program. This program is to focus on the prevention of pollution from sources that could be mobilized during storm events from present and future activities as well as measures that could abate known nonpoint source pollution. Areas for abatement are to include, but are not limited to, general agricultural and silvicultural practices, onsite wastewater treatment systems, large lot development greater than one acre, and other potential nutrient sources. The Authority fulfills this regulatory taskiing by partially funding and utilizing the service of the Cherry Creek Stewardship Partners (Partners).

2-3

The Partners are an association of a broad range of stakeholders actively promoting effective stewardship and providing education and outreach activities in the Cherry Creek Reservoir watershed. The Partners emerged from the first Cherry Creek Reservoir Watershed Forum held in the fall of 1999. The Partners bring together representatives from: . Land use jurisdictions, . State and federal resource management agencies, . Conservation, recreation, and historic preservation groups, . Business communities, and . Interested citizens. In 2004, the Partners, aided by funding and staff provided by the Authority, developed a comprehensive and coordinated education strategy and action plan on a reservoir watershed scale entitled the “Cherry Creek Basin Water Stewardship and Education Initiative”. This plan contains a compilation of the key education and public involvement goals, strategies, and activities aimed at engaging the community in active stewardship of Cherry Creek basin, including parks, open space, trails, and tributaries within the watershed. The purpose of the Education Initiative is to describe the approach recommended by the Partners and the Authority to promote active stewardship in the basin. The purpose of active stewardship is to preserve, protect, and restore water quality, wildlife habitat, recreational opportunities, and the natural function of the watershed. In coordination with key stakeholders in the Cherry Creek watershed, the Education Initiative makes recommendations and identifies next steps for the development and implementation of a public information and education outreach program for the Cherry Creek watershed that meet the regulatory requirements of Regulation 72 and the objectives identified in Cherry Creek Basin Watershed Plan.

2014 Highlights

In 2014, the Cherry Creek Stewardship Partners celebrated 15 years of providing a forum for active engagement with the natural resources of the Cherry Creek watershed. Over the years the Partners have continued to build relationships with land use agencies, businesses and individuals who find value

2-4

and enjoyment from living and working near Cherry Creek. Building on the assessment and recommendations identified in the Cherry Creek Basin Water Stewardship and Education Initiative, the Partners engage with schools, stormwater permit holders, Colorado Division of Parks and Wildlife, and other scientific and cultural organizations to bring a water quality message to a wide range of events and meetings. By maintaining established relationships and building new ones, the Partners leverage outreach opportunities and respond to feedback from participants to develop new activities and events. The Partners organize and sponsor a wide variety of activities in the Cherry Creek Reservoir watershed that support water quality goals. In 2014, Partners’ events included over 40 public activities and approximately 4,900 participants. Education and Outreach The Cherry Creek Stewardship Partners bring watershed science to numerous schools and other groups in the Cherry Creek Basin. In 2014, over 10,000 contact hours were logged by the Partners working with students ranging from 2nd graders to professional educators through classroom presentations and workshops at Community College of Aurora and Metropolitan State University of Denver.

In 2014, the Partners ‘made history’ by expanding its partnership with the Cherry Creek Valley Historical Society and Red Hawk Ridge Elementary School adjacent to the Cherry Creek Valley Ecological Park. Helping to build an imaginative play area and developing a program to bring young people in safe and active contact with their watershed was a ‘high water mark’ this year. The Authority has been a sponsor of the Denver Metropolitan Regional Science Fair since 2007. This event included more than 500 students, grades 6 though 12, from the seven-county Denver metropolitan area. Sanjna Bhartiya, 11th grade, Cherry Creek High School received the Cherry Creek Basin Water Quality Authority Award and a $100 cash prize for her project: “Effectiveness of Soil Types as a Buffer to Excess Nutrients in Runoff Water.”

2-5

PRF and Water Quality Education The Partners invite bird and wildlife fans to walk the Cherry Creek trails that have become valuable connections in the community. By visiting various parks and stream segments, participants are educated about the effects and benefits of stream stabilization and riparian buffers created by the joint effort of the Cherry Creek Basin Water Quality Authority, the Urban Drainage and Flood Control District and local stormwater and land use agencies. Expert birders, botanists, and bio-engineers visit the sites that have become important to maintaining a diverse ecosystem and create quality of life opportunities for recreation and education. The Right Message at the Right Time and Place Bringing a positive message to park users about how their behavior impacts their investment has allowed the Partners to engage the public in fun and effective outreach. The success of Partner events over the past 15 years is the result of joint efforts and strong relationships maintained over time.

Annual Stewardship Partners Conference This event is supported by the Authority and many others as a way to bring the broad range of watershed interests together to learn from one another. Since 1999, the Annual Stewardship Partners Conference has highlighted topics of interest for people who live and work in the Cherry Creek watershed. This year the Partners celebrated 15 years of active stewardship with presentations ranging from technical review of significant projects to comparison of education and outreach efforts on a local and a global level.

2-6

2014 ANNUAL REPORT ON ACTIVITIES

3 POINT SOURCES Wastewater treatment facilities (WWTFs) in the basin provide phosphorus removal by using advanced wastewater treatment processes followed by land application or direct discharge. Some of the WWTFs also must treat to remove nitrogen to meet permit limits. Several facilities within the Cherry Creek Reservoir watershed provide centralized wastewater treatment service. One point source discharger (Plum Creek Water Reclamation Authority) is located outside the watershed but can apply some of its treated effluent as irrigation water within the watershed. Wastewater and industrial process wastewater sources are limited in the amounts of phosphorus they can discharge to the Cherry Creek Reservoir watershed. Regulation 72 requires phosphorus concentration-based limits for point source dischargers. All major wastewater treatment plants treating wastewater in the Cherry Creek basin have current discharge permits or Notices of Authorization (NOA) to discharge to land. Expiration dates for all current domestic wastewater treatment facilities’ permits are shown in Table 3-1 below. Locations of these wastewater treatment facilities can be seen on Figure 3-1 on the next page, and information on each WWTF is presented in this chapter. TABLE 3-1: CHERRY CREEK WATERSHED WASTEWATER FACILITIES AND PERMIT EXPIRATION DATES

Design Does Permit or NOA Permit Expiration Permittee Capacity Comments Have Phosphorus Number Date (MGD) Concentration Limits? Arapahoe County Water CO0040681 3.6 01/31/2018 Active Yes & Wastewater Authority Pinery Water & CO0041092 2.0 10/31/2016 Active Yes Sanitation District Parker Water & CO0046507 4.0 01/31/2017 Active Yes Sanitation District Meridian Metropolitan NOA, Reg.84 District 1.5 10/31/2016 Active Yes (COE-024000) Stonegate Village Metro CO0040291 1.1 10/31/2016 Active Yes District Plum Creek Water CO0038547 6.44 10/31/2017 Active Yes Reclamation Authority Note: Data obtained from EPA's ECHO (Enforcement & Compliance History Online) Detailed Facility Reports, December 2014 search as well as updated Permits provided by Water Quality Records Center, CDPHE December 2014.

3-1

MAP 3–1: MAP SHOWING LOCATIONS OF WASTEWATER TREATMENT FACILITIES

3-2

Arapahoe County Water and Wastewater Authority

The Arapahoe County Water and Wastewater Authority primarily serves properties located in Arapahoe County. In addition to Arapahoe County, this Authority also serves Highfield Business Park, a small area in the northwest corner of Parker’s Urban Growth Area.

Pinery Water and Wastewater District

The Pinery Water and Wastewater District serves residential and commercial users located within the Subdivision of Pinery in Parker. In 1965, the District was formed as the “Denver Southeast Suburban Water and Sanitation District” and now serves about 4,000 residential customers, as well as 88 large irrigator and commercial customers in the basin as the Pinery Water and Wastewater District.

Parker Water and Sanitation District

The Parker Water and Sanitation District serves the majority of the residents in Parker along with many residents outside of the town. The current wastewater treatment facility is developed to accommodate peak flows at “ultimate” buildout. The facility uses advanced wastewater treatment proceses to remove not only conventional pollutants, but also algae promoting nutrients like nitrogen and phosphorus.

3-3

Meridian Metropolitan District

The Meridian Metropolitan District was formed in 1976, to serve development within the Meridian International Business Center. The District operates its own wastewater treatment plant, which also provides water and sewer service to two adjoining connectors (South Meridian and North Meridian Metropolitan Districts).

Stonegate Village Metropolitan District

Stonegate Village Metropolitan District provides wastewater services for District residents, Lincoln Park Metropolitan District, Compark Business Campus, and Potomac Metropolitan District. The Stonegate Village Metropolitan

District is bound by the Cottonwood Water and Sanitation District on the north, Jordan Road on the east, Chambers Road on the west, and north of Mainstreet to the South. This District began reconstruction of its wastewater treatment plant in June 2014 to better meet water quality standards in Cherry Creek. The project is expected to be completed in October 2015 and to cost $13.4 million.

Plum Creek Water Reclamation Authority

The Plum Creek Water Reclamation Authority Wastewater Treatment Facility is a biological nutrient removal process with a permitted capacity of 6.44 million gallons per day. The water is screened, oxidized in two 3.23 million gallon oxidation ditches which utilize both anaerobic and anoxic zones for nitrification, denitrification, and biological phosphorus removal. The water then is treated in secondary clarifiers to separate microorganisms from the water. The water is then sent through a flocculation tank, two tertiary cloth media filters, and then disinfected with UV light. The Plum Creek Water Reclamation Authority can apply some of its treated effluent as irrigated water in the Cherry Creek basin.

3-4

3.1 Limits and Data Summary Requirements for Phosphorus and Nitrogen In 2001, Regulation 72 was amended, in part to include monitoring of nutrients, rather than only phosphorus. Previously, the main emphasis of watershed sutdies related to nutrient transport had been on the development of monitoring programs to provide information on the annual transport of phosphorus at various points along Cherry Creek. The Commission expanded the monitoring program to include an empahsis on nitrogen as well as phosphorus. Thus, data on both phosphorus and nitrogen are included in this chapter where available, as well as in Chapter 7 (Monitoring). Regulation 72 defines discharge limits for Total Phosphorus (TP) for various facilities, as shown in Table 3-2 below. There are no discharge limits required under Regulation 72 for nitrogen.

TABLE 3-2: REGULATION 72 DISCHARGE LIMITS FOR PHOSPHORUS

30-Day Average1 Total Discharge Phosphorus Limit (mg/L) Wastewater Facilities/Industrial Process Wastewater Sources with Direct Discharges ≤0.05 Drinking Water Treatment Facilities (see section 3.6 of this report) ≤ 0.2 Discharges Using Land Application and Relying on a Return Flow Factor ≤ 0.052 Dischargers Using Land Application and Relying on Lysimeters ≤ 1.0 1 Total phosphorus limit is a 30-day average, unless a 90-day average is approved by the Division at the request of the discharger 2 The 30-day flow-weighted average phosphorus concentration must be ≤ 0.05 mg/L total phosphorus divided by the land application return flow factor

Discharger limits for those using land application meet the 0.05 mg/L total phosphorus limitation are calculated using the volume of water land applied, its concentration, plant and soil uptake rates, and return flows. For example, Stonegate Village Metropolitan District has a return flow factor of 20%. Therefore, its discharge phosphorus limit is calculated to be 0.25 mg/L (0.05/0.20 = 0.25 mg/L; see footnote 2 to Table 3-2, above). Meridian Metropolitan District has been issued a Notice of Authorization (NOA) under Regulation 84 – Reclaimed Water Control Regulation to reuse its treated effluent for irrigation by approved users. Meridian’s discharge limits were calculated using a return flow factor of 10%, resulting in a limit of 0.50 mg/L phosphorus. Current Colorado Discharge Permit System (CDPS) permits require all WWTFs in the basin to monitor for phosphorus. Table 3-3 on the next page presents phosphorus concentration-based limits and 30-day average and maximum reported concentrations from October 2013 through September 2014 for the wastewater dischargers. Note that Meridian Metropolitan District’s approved limit is a 90-day average (See footnote 1 to Table 3-2, above).

3-5

TABLE 3-3: SUMMARY OF TOTAL PHOSPHORUS PERMIT LIMITS AND DATA 2014

30-day Avg. Total Phosphorus Maximum Reported Total Phosphorus Limit (mg/L) 30-day Avg. Total Facility Permit Limit Violation? Phosphorus Concentration (Note Meridian has a 90-day (yes/no) average) (mg/L)

Arapahoe County Water & ≤ 0.05 0.045 No Wastewater Authority Pinery Water & Sanitation ≤ 0.05 0.043 No District ≤ 0.05

(Outfall 002A-NT: Combined No Discharge No North and South WRFs Discharge Parker Water & Sanitation to Regional Reservoir) District ≤ 0.05

(Outfall 003A: Combined North 0.041 No and South WRFs Discharge to Sulfur Gulch) Meridian Metropolitan (no 30-day reporting ≤ 0.5 2 (90-day Avg) No District requirements in NOA) 1 ≤ 0.25 2 0.03 No Stonegate Village (Outfall 001A) Metropolitan District ≤ 0.05 0.03 No (Outfall 002A)

Plum Creek Water ≤ 0.05 0.02 No Reclamation Authority (Outfall 007A) 1 Total phosphorus limit is a 30-day average, unless a 90-day average is approved by the Division at the request of the discharger 2 The flow-weighted average phosphorus concentration must be ≤ 0.05 mg/L total phosphorus divided by the land application return flow factor Note, State and EPA records did not contain DMR for Meridian for September 2014.

3-6

Three wastewater treatment facilities in the basin currently have TIN limits of 10 mg/L in their current discharge permits (Pinery, Parker, and Stonegate). Table 3-4 below shows Total Inorganic Nitrogen (TIN) limits and reported 30-day average concentrations from October 2013 through September 2014 for the wastewater facilities. TABLE 3-4: SUMMARY OF TOTAL INORGANIC NITROGEN PERMIT LIMITS AND DATA 2014

Facility Daily Maximum Total Inorganic Daily Maximum Reported Nitrogen Permit Limit Nitrogen (TIN) Limit (mg/L) Total Inorganic Nitrogen Violation? (yes/no) (TIN) Concentration (mg/L) Arapahoe County Water & (no TIN limit) -- -- Wastewater Authority Pinery Water & Sanitation 10 9.03 No District 10

(Outfall 002A-NT Combined North No Discharge No and South WRFs Discharge to Parker Water & Sanitation Regional Reservoir) District 10

(Outfall 003A Combined North and 12.0 Yes South WRFs Discharge to Sulfur Gulch) Meridian Metropolitan (no TIN limit) -- -- District

Stonegate Village 10 5.7 No Metropolitan District (Outfall 002A) (no TIN limit for discharges to Plum Creek Water Cherry Creek Basin from Outfall -- -- Reclamation Authority 007A)

3.2 Monthly Phosphorus Concentrations Table 3-5 and Figure 3-1 summarize monthly phosphorus concentrations in the effluent for each wastewater treatment plant, based on monthly Discharge Monitoring Reports (DMRs). All dischargers were consistently below their phosphorus discharge limits in 2014. In addition, all of dischargers are well below the average flow-weighted 0.200 mg/L phosphorus concentration goal for all inflows to the reservoir. This goal was supported in the 2009 hearing by the Authority to help attain the chlorophyll standard.

3-7

TABLE 3-5: 2014 POINT SOURCE PHOSPHORUS MONTHLY CONCENTRATION

Month Average Monthly Phosphorus Discharge Concentrations to Cherry Creek Basin

Parker Water & San Pinery Stonegate Village Plum Meridian Arapahoe District Water & Metropolitan District Creek Metro County San Water District Water & District Recl Wastewater 1 (monthly Auth Auth Outfall Outfall (monthly Outfall Outfall mg/L) 002A-NT 003A mg/L) 001A 002A Outfall (monthly 007A mg/L) (monthly (monthly (monthly (monthly mg/L) mg/L) mg/L) mg/L) (monthly mg/L) No No Oct 0.033 0.031 0.02 0.02 N/A 0.010 Discharge Discharge No No Nov 0.025 0.043 0.03 0.02 N/A <0.010 Discharge Discharge No No Dec 0.035 0.037 0.03 0.02 0.07 <0.010 Discharge Discharge No No Jan 0.037 0.032 0.02 0.02 N/A 0.029 Discharge Discharge No No Feb 0.034 0.028 0.03 0.02 N/A <0.010 Discharge Discharge No No Mar 0.035 0.039 0.03 0.02 0.04 0.041 Discharge Discharge No Apr 0.041 0.041 0.03 0.02 0.02 N/A 0.030 Discharge No May 0.031 0.031 0.01 0.02 0.02 N/A 0.017 Discharge No No Jun 0.024 0.032 0.03 0.02 0.05 0.012 Discharge Discharge No No Jul 0.029 0.037 0.02 0.02 N/A 0.020 Discharge Discharge No Aug 0.027 0.032 0.02 0.01 0.02 N/A 0.023 Discharge

No Not Sep 0.019 0.039 0.02 0.02 0.01 0.045 Discharge Reported

1The Plum Creek Wastewater Authority dischargse in the Cherry Creek Reservoir watershed area through reuse irrigation.

3-8

0.080

0.070

0.060

0.050

0.040 (mg/L) 0.030

0.020

0.010

Total Concentration Phosphorus -Avg Reported 30-day Maximum 0.000 Oct. Nov. Dec. Jan. Feb. Mar. Apr. May Jun. Jul. Aug. Sep.

Parker W&S (003A) Pinery W&S Stonegate Metro Dist. (001A) Stonegate Metro. Dist. (002A) Plum Creek Water Recl. Auth. Meridian W&S Arapahoe County WW Auth.

FIGURE 3-1: SUMMARY OF 2014 TOTAL PHOSPHORUS MAXIMUM REPORTED DATA

3-9

3.3 Monthly Nitrogen Concentrations Table 3-6 and Figure 3-2 summarizes the monthly total inorganic nitrogen concentrations in the effluent for each wastewater treatment plant that is required to monitor for TIN and report in its monthly DMR. All facilities that had TIN discharge limits were in compliance with those limits in Water Year (WY) 2014, with one exception. Parker Water and Sanitation District reported a value of 12.0 mg/l TIN in March 2014. The TIN data are required to be reported as daily maximums. At the beginning of the month, aeration rates were changed in the activated sludge basin in an attempt to control foaming. The first sample of the month resulted in a high ammonia value, which contributed to a high TIN value. The lab informed operations immediately of the result and the aeration was adjusted; however, the biological process took a day to respond. After this, all remaining ammonia and TIN values were below limits for the month.

14.0

12.0

10.0

8.0

tration - Daily Reported Maximum 6.0 (mg/L)

4.0

2.0

0.0 Total Inorganice Nitrogen Concen Nitrogen Total Inorganice Oct. Nov Dec. Jan. Feb. Mar. Apr. May Jun. Jul. Aug. Sep. .. Parker W&S (003A) Pinery W&S Stonegate Metro Dist. (001A)

FIGURE 3-2: SUMMARY OF 2014 TOTAL INORGANIC NITROGEN MAXIMUM REPORTED DATA

3-10

TABLE 3-6: 2014 POINT SOURCE TOTAL INORGANIC NITROGEN

Month Average Monthly TIN Discharge Concentrations to Cherry Creek Basin

Parker Water & San District Pinery Stonegate Village Plum Creek Meridian Arapahoe County Water & Metropolitan District Water Recl Metro Water & San Auth1 District Wastewater Auth Outfall 002A- Outfall District Outfall Outfall NT 003A 001A 002A (monthly (monthly (monthly mg/L) (monthly mg/L) mg/L) (monthly (monthly mg/L) (monthly (monthly mg/L) mg/L) mg/L) mg/L)

Oct No Discharge 8.8 9.03 N/A 4.9 N/A N/A N/A Nov No Discharge 8.6 8.01 N/A 5.7 N/A N/A N/A Dec No Discharge 8.3 7.43 N/A 4.0 N/A N/A N/A Jan No Discharge 8.7 7.23 N/A 5.6 N/A N/A N/A Feb No Discharge 8.4 8.21 N/A 4.2 N/A N/A N/A Mar No Discharge 12.0 7.83 N/A 4.2 N/A N/A N/A Apr No Discharge 9.0 5.81 N/A 4.5 N/A N/A N/A May No Discharge 8.4 7.45 N/A 4.2 N/A N/A N/A

No Jun No Discharge 8.4 7.36 N/A N/A N/A N/A Discharge No Jul No Discharge 8.6 7.90 N/A N/A N/A N/A Discharge Aug No Discharge 8.1 8.99 N/A 3.6 N/A N/A N/A Sep No Discharge 7.4 8.33 N/A 5.4 N/A N/A N/A

1The Plum Creek Water Reclamation Authority discharges to the Cherry Creek basin through reuse irrigation. 3.4 Permit Compliance Regulation 72 requires that the Annual Report identify wastewater facility permit violations. In 2014, no permits were in violation of phosphorus concentration limits. For 2014, the six wastewater treatment facilities all were within the effluent limits included in their current permits. The wastewater treatment facilities are removing substantial amounts of phosphorus, especially the forms of phosphorus that are readily available for algal or bacterial uptake in the reservoir ; i.e., soluble reactive phosphorus (SRP). The WWTFs with TIN limits were also in compliance during 2014, with the one exception noted above.

3-11

3.5 Permit Renewal Timing and Process The CDPHE prepares permit work plan schedules for the planned renewal of general and individual permits. The renewal of individual permits is expected to occur in 2016 for the South Platte River Basin dischargers. The following table is the anticipated General Permit Work Plan Schedule. TABLE 3-7: WORKPLAN SCHEDULE FOR RENEWAL OF GENERAL AND INDIVIDUAL PERMITS

General Permit Name Permit Number Expiration Year1 Planned Renewal Year2 Sewage Systems Domestic Waste Water Treatment Plant with Chronic COG588000 2018 2018 Low Flow Design Domestic Waste Water COG589000 2018 2018 Treatment Facilities Domestic Septic Treatment COX620000 2006 n/a3 Systems Domestic Onsite Systems ISDS COX621000 2012 tbd Domestic Onsite Systems OWTS COX622000 2012 tbd No Wells Domestic Discharges Land COX631000 2012 tbd Disposal Domestic Discharges Land COX632000 2012 tbd Treatment Domestic Discharges Land COX633000 2012 tbd Treatment Agronomic Rate Construction Construction Dewatering COG070000 2018 2018 Stormwater Construction COR030000 2012 2015 MS4 Sector MS4 Cherry Creek Reservoir COR080000 2013 tbd Basin MS4 Non-Standard COR070000 2013 tbd MS4 Standard COR090000 2013 tbd MS4 Phase I COS000000 2014 tbd 1 Permits Expiration Year - When a general permit expires and is not renewed, it is Administratively Continued, allowing coverage under that general permit to continue until the renewed permit is issued. 2 Planned Renewal Year - This designates the year in which the Division plans on renewing a general permit. The actual completion of the renewal depends on time restraints, resource availability, and emergency requests or requirements. 3 Permit will be terminated once existing permit coverage is terminated or converted to new permit coverage. 4 Originally proposed to be combined with COR090000 MS4 Standard Permit

3-12

3.6 Other Point Source Discharge Permits in the Watershed There are several other permitted point source discharges in the watershed as shown in Map 3-2. Data were retrieved from EPA’s Enviromapper and ICIS databases for NPDES-permitted facilities with active permits during 2014. There were 40 other point source discharge permits4 that were active in the watershed in 2014. Of these 40 permits, 19 contain total phosphorus reporting requirements. Table 3-8 shows summarizes the ranges of total phosphorus data reported to date for those permittees that actually had discharges. (Note, many of the permittees only reported “no discharge”.) These values give an indication of the levels of phosphorus that could be expected from certain types of operations.

TABLE 3-8: TOTAL PHOSPHORUS CONCENTRATION RANGES REPORTED BY OTHER PERMITTED POINT SOURCE DISCHARGERS IN THE CHERRY CREEK BASIN

Permit No. Facility Name Permit Type Total Phosphorus Concentration Range (mg/L)

COX621026 DirectTV Castle Rock Broadcast Center General Permit: Discharge to 0.04-1.54 Groundwater

COG073345 South Water Reclamation Facility General Permit: Special Trade 0.14-0.87 Contractors COG0047589 Joint Water Purification Plant Individual Permit: Water 0.01-0.182 Supply COG603027 Parker WSD DW Wells General Permit: Heavy 0.01-0.228 Construction COG072642 Parker North WRF General Permit: Special Trade 0.16-0.22 Contractors COG072611 South Metro Medical Campus General Permit: Heavy 0.01-0.1 Construction COG074567 Arapahoe Road over Cherry Creek Special Trade Contractors 0.00-0.14

4 These include permits for 2 discharges to groundwater, 1 construction sand and gravel operation, 11 special trade contractors, 2 ready-mixed concrete operations, 4 non-extractive industries stormwater, 1 land application operation, 4 water treatment facility permits (ACCWA, Stonegate, and PWSD Rueter-Hess WTP), 3 heavy construction operations, 3 air/water/solid waste management entities, 1 hydrostatic testing permit, 1 machine tools/metal forming facility, 1 airport, 1 surgical/medical instruments entity, 1 facility listed as an “unpermitted facility”, and 4 unspecified permit types.

3-13

During 2014, there was one permitted drinking water treatment plant in the Cherry Creek basin in 2014, which was required to meet a 30-day average total phosphorus discharge limit of 0.2 mg/L under the 2009 changes to Regulation 72. Arapahoe County Water and Wastewater Authority Joint Water Purification Plant (CO0047589) discharges waste backwash water from its water purification plant to Windmill Creek. This permit was amended in 2010 to increase the phosphorus concentration limit to 0.2 mg/L, consistent with the new Regulation 72 limit. In 2014, ACCWA reported no discharge for all reporting periods.

Colorado also has a general permit, COG641000, which covers water treatment plants that do not have individual permit coverage. The Stonegate Village Metropolitan District Water Treatment Facility is covered by this permit to discharge to Cherry Creek (COG641142). Stonegate reported no discharges from this facility for each quarter in 2014. This permit will expire September 30, 2015 and does not include any phosphorus discharge limits for facilities in the Cherry Creek basin; only monitoring and reporting are required. The Authority recommends that this permit incorporate the new 30-day average total phosphorus limitation of 0.2 mg/L for water treatment plant dischargers in the Cherry Creek basin. Parker Water and Sanitation District has also obtained coverage for its new Rueter-Hess water treatment plant under this general permit (COG641168); the permit certification was issued August 28, 2014. The permit authorizes discharges to Newlin Gulch. The Rueter-Hess WTP reported no discharges for the third and fourth quarters of 2014.

There are also a number of general discharge permits MAP 3–2: MAP SHOWING OTHER POINT issued and operating within the watershed in addition to SOURCE DISCHARGE PERMITS the wastewater permits discussed earlier in this section and the MS4 general discharge permits discussed in Chapter 4. In 2014, there were 22 other general permits in the basin that included the 7 permits that contain phosphorus limits listed in Table 3.8. The phosphorus concentrations for these facilities ranged from 0.00-1.54 mg/L.

The latest construction dewatering permit, issued 3/1/2013, includes a total phosphorus limit of 0.05 mg/L and requires phosphorus monitoring. All construction dewatering permits issued under the new

3-14

permit should include the phosphorus limits and monitoring requirements. The commercial outdoor washing permit also contains phosphorus limits and monitoring. This permit expired in 2012; limits and monitoring should be retained (and enforced) when it is renewed.

3.7 Onsite Wastewater Treatment Systems On July 1, 2014, the Tri-County Health Department Board of Health updated Regulation No. O-14 for onsite wastewater treatment systems (OWTS) in Adams, Arapahoe, and Douglas Counties. The new regulation:

• Requires a higher level of training for OWTS professionals. • Requires all septic tank manufactures become certified by CDPHE. • Recognizes and provides higher incentives for the use of Higher Level Treatment Systems, which achieve substantial verifiable pollutant reduction and can be installed on difficult sites. • Include procedures for CDPHE acceptance of proprietary OWTS. • Requires operation and maintenance permits. • Requires more rigorous site characterization and design for all OWTS. • Continues to implement two Regulation 72 requirements; 1) no MAP 3–3: MAP OF ONSITE WASTEWATER TREATMENT new OWTS may be constructed in SYSTEMS the 100-year floodplain, and 2) new systems installed in sand or loamy sand soil or with percolation rates < 15 minutes/inch require additional phosphorus removal. The Authority supported Regulation 0-14. The approved regulation can be downloaded at the following link: www.tchd.org/documentcenter/view/1947.

3-15

3.8 Approved Site Applications As the designated regional water quality management agency for the Cherry Creek Reservoir watershed, the Authority reviews Applications forSite Location Approval (site applications) for domestic wastewater treatment works, including lift stations. Reviews of site location applications address protection of Cherry Creek Reservoir and the watershed with respect to phosphorus and nitrogen, general water quality, protection of downstream water quality for to protect water supplies, and adequacy of proposed design processes and capacity to protect water quality. As required by Regulation 72, the Authority must report on approved site applications annually. Applications for Site Location Approval are reviewed in conformance with the following documents: . Cherry Creek Reservoir Control Regulation 72; . Emergency Response Plan Criteria for the Cherry Creek Reservoir Watershed (Authority, March 2002); . Regulation 22, “Site Location and Design Approval Regulations for Domestic Wastewater Treatment Works” (Commission, September 2009); . Metro Vision Clean Water Plan: “Wastewater Utility Plan Guidance” (Denver Regional Council of Governments, March 2007); and . Policy WPC-DR-1, “Design Criteria for Domestic Wastewater Treatment Works” (Colorado Water Quality Control Commission, effective Date: September 15, 2012). In 2014, two site applications were received by the Authority. The first site application was submitted by Meridian Metropolitan District for Lift Station H. The proposed lift station is to be located in the Stepping Stone Subdivision, part of the Meridian International Business Center Planned Development 8th Amendment. The lift station will provide service to 283 single-family homes, 242 multi-family homes, and 44 acres of commercial development. The lift station is designed to convey wastewater from the development to the existing Lift Station G. After

3-16

review of the site application, the Cherry Authority provided a conditional approval dependent upon: verification that infiltration and inflow will not cause any part of the lift station to be under-sized, the final design addresses concerns of expansive soils in the area, differential flow metering be placed on each force main, and the emergency response plan be updated to provide further detail in case of an emergency. The second site application was submitted by Rocking Horse Partners, LLC for the Rocking Horse Lift Station that will serve the western portion of the Rocking Horse development. Upon completion of the lift station, ownership of the lift station will be transferred to Aurora Water. The lift station is proposed to server 1,249 single- family homes and a community center. The lift station will transfer the flows from the development to the Aurora Creek Side Interceptor. The wastewater treatment entity will be Metro Wastewater Reclamation District. After review of the site application, the Authority was concerned that the limited emergency response time provided by emergency storage may not provide enough time to respond to a failure alarm and provide a remedy prior to a spill to the adjacent regional storm water detention pond. The Authority discussed concerns with the design engineer and the design was modified to provide additional emergency response time adequate for Aurora Water to respond to an alarm and provide a remedy prior to overflow.

3.8.1 AUTHORITY’S ROLE IN SITE APPLICATION PROCESS

In 2014 the Authority continued to review site applications for wastewater facilities. Wastewater facilities required to submit site applications include: new domestic wastewater treatment facilities; increasing or decreasing the design capacity of an existing wastewater treatment facility; facilities constructing or expanding interceptor sewers eligible for certification or interceptor sewers not eligible for certification; and lift stations. CDPHE reviews wastewater facilities and must approve the facility prior to the start of construction of the facility. The process CDPHE uses for approval of wastewater facilities includes site applications, process design report, basis of design reports, and final design documents. CDPHE only requires approval signatures from outside agencies during the site application portion of the approval process. The site application is designed to collect information about the site, owner, operator, and a 30 percent concept design. The Authority’s directive to review site applications that are submitted within the Cherry Creek Basin stems from section 208 of the Clean Water Act. Site applications for wastewater facilities are to be reviewed by 208 planning agencies designated by the Governor of Colorado. The 208 planning agency

3-17

that serves the Cherry Creek Basin (the Denver Regional Council of Governments) is not currently active in Water Quality Planning, and is therefore not currently reviewing site applications for wastewater facilities. DRCOG previously designated the Authority as the Management Agency for our Basin. Thus, the Authority reviews on all site applications except for 208 planning agency-certified interceptors and site application amendments for a disinfection change only. An in-kind replacement does not require a site application as long as it does not increase or decrease capacity. The Authority focuses the review of the site application on the potential for an illicit discharge from the facility. The review identifies the purpose and background of the facility; identifies potential overflow causes; reviews operation and maintenance practices; reviews features to prevent overflows; and reviews the emergency preparedness plan. Due to the difficulty of reviewing all of the above items with just a 30 percent concept level, correspondence is usually required with the design engineer. In most cases, a conditional approval is provided based on the conceptual level of the plans provided. The Authority also reviews the site applications for additional requirements set forth in the Cherry Creek Basin Water Quality Authority Cherry Creek Basin Reservoir Watershed Site Application Review Process Emergency Response Plan Criteria. 3.9 Effectiveness in Reducing Nutrient Concentrations The control requirements placed on the point source dischargers described above were effective in reducing or controlling phosphorus concentrations to the watershed and reservoir. All wastewater treatment plants met their phosphorus discharge limits, which are designed to help meet the reservoir standard and the requirements of the Regulation 72 control program. In addition, wastewater treatment facilities that have total inorganic nitrogen limits in their permits also met their limits in 2014, with only one exception. It is also noted that the required effluent limits for total phosphorus concentrations discharging from wastewater facilities and industrial process wastewater sources (i.e., for most dischargers, less than 0.05 mg/L total phosphorus concentration as a 30-day average) are significantly less than the flow-weighted total phosphorus concentrations currently entering the reservoir. Actual concentrations discharged by wastewater treatment plants were consistently below their limits and well below the 0.200 mg/L flow- weighted phosphorus concentration goal. For 2014, the flow-weighted influent concentration of all sources to the reservoir was 0.190 mg/L, and the 1992-2014 median was 0.200 mg/L, both at or below the phosphorus concentration goal.

3-18

2014 ANNUAL REPORT ON ACTIVITIES

4 REGULATED STORMWATER SOURCE CONTROLS Regulated stormwater is stormwater runoff that discharges to State Waters (including reservoirs, streams, and groundwater) from regulated entities, such as commercial and industrial facilities, and municipal separate storm sewer systems (MS4s). MS4s are storm sewer systems that are owned or operated by a state, city, town, county, district, or association having jurisdiction over stormwater management. There is one MS4 with an individual permit in the Cherry Creek Basin, the City of Aurora. There are eight permittees covered by the general MS4 permit (COR080000) for discharges in the Cherry Creek basin: . Douglas County . Greenwood Village . Arapahoe County . Town of Parker . Town of Castle Rock Utilities Department . City of Lone Tree MAP 4-1: MAP OF MUNICIPAL SEPARATE STORM SEWER . SEMSWA SYSTEMS . Castle Pines North Non-standard MS4s are regulated separate storm sewer systems that discharge from entities other than municipalities and counties (e.g., State Parks, metropolitan districts). There are nine non-standard MS4s permitted within the Cherry Creek basin: . Goldsmith Metro District . Heritage Hills Metropolitan District . Greenwood South Metropolitan District

4-1

. Castle Pines Metropolitan District . Meridian Metropolitan District . Castle Pines North Metropolitan District . Stonegate Village Metro District Water Treatment Facility . Cherry Creek State Park . Lincoln Park Metropolitan District These entities are covered by COR070000, which expired on March 9, 2013, and was administratively extended. The Colorado Department of Transportation also has a MS4 permit. Regulated stormwater sources are subject to the Colorado Discharge Permit System Regulations (Regulation 61). Larger sources were originally regulated under the EPA’s Stormwater Phase I Rule (1990), which covered entities with populations over 100,000 and other significant dischargers. The City of Aurora and CDOT were the only Cherry Creek Basin entities that were included under Phase I. In 1999, the Stormwater Phase II Rule expanded the Phase I Rule to include several of the land use agencies that are part of the Authority. The Phase II Rule requires small MS4s to, at a minimum, adopt BMPs for six minimum control measures, implement them to the maximum extent practicable (MEP), identify measurable goals for control measures, show an implementation schedule of activities or frequency of activities, and define the entity responsible for implementation. These requirements fit closely with the current programs in the Cherry Creek watershed as required by Regulation 72. The six minimum requirements are:

. Public education and outreach

. Public involvement/participation

. Illicit connections and discharge detection and elimination

. Construction site stormwater runoff control

. Post-construction stormwater management in development/redevelopment

. Pollution prevention/good housekeeping for municipal operations

Phase II MS4s in the Cherry Creek Basin currently have coverage under General Permit COR080000, “Stormwater Discharges Associated with Cherry Creek Reservoir Drainage Basin Municipal Separate

4-2

Storm Sewer Systems”. This permit incorporates relevant requirements of Regulation 72. More detailed information on implementation for each Phase II MS4 permittee can be found in the Stormwater Annual Reports that Phase II MS4s are required to submit to the Division by March 10 of every year. Phase II MS4 permittees must conduct an annual review of their stormwater programs including an assessment of compliance with measurable goals for each of the six program areas, the results of any monitoring, and plans for stormwater activities in the next year. Regulation 72 also spells out several requirements that are in addition to Regulation 61 requirements. These additional requirements are to be applied to regulated stormwater discharges. These include stringent watershed-specific requirements for MS4 permits, including public education and outreach efforts that target nutrient sources, detailed construction site controls, and tiered post-construction stormwater management requirements for new development and redeveloped areas, with special requirements for stream preservation areas (§72.7). 4.1 MS4 General Permit Renewal Process The CDPHE is currently renewing general permits (COR090000 and COR080000) for discharges associated with MS4s. The Authority has participated in the public meeting process, attended stakeholder meetings, and made comments during the public notice process. 4.2 Sediment and Erosion Control Permits Regulation 72 requires that an Erosion and Sediment Control Plan (ESCP) must be submitted to and approved by the local MS4 entity. All land use agencies in the basin require that an erosion and sediment control plan be submitted and approved prior to the start of any new land-disturbance activity. Land- disturbance activities include clearing, grading, or excavation of land; construction, expansion, or alteration of a residential, commercial, or industrial site or development; and construction of public improvements and facilities (e.g., roads, airports, and schools). Erosion and sediment control requirements during construction for each agency under the stormwater Phase I and II requirements are complementary to the programs required under Regulation 72. 4.3 Adoption and Implementation of BMPs by Local Governments

4-3

All MS4s in the watershed have adopted stormwater regulations setting requirements for construction and post-construction BMPs for new development and redevelopment projects within their jurisdictions that are consistent with Regulation 72 requirements. 4.4 Construction BMPs

The Authority’s “Stormwater Permit Requirements The Regulation 85 Discharge Guidance Document” recommends implementation of Assessment Data Report: substantive BMP measures to control the quality of stormwater runoff from land disturbances on private In June of 2012 the Commission and public property. In addition, the requirements adopted Regulation #85 Nutrients establish the minimum construction and post- Management Control Regulation, construction BMPs in the reservoir watershed for all which include requirements for MS4s new development activities. All land use agencies regarding public education and maintain design standards or refer to the Urban outreach, prevention and good Drainage and Flood Control District (UDFCD) design housekeeping for municipal standards for construction BMPs to limit the amount operations, and data gap reporting. of sediment that enters the watershed during the For the data gap report, MS4 construction activities within the basin. permittees or group(s) of permittees Table 4-1 shows BMP data from the land use agencies were required to submit a report to with all or a portion of their jurisdiction located within the Division by October 31, 2014. The the Cherry Creek basin. Data for the Cherry Creek reports were to document the basin is provided for the number of construction sites availability of existing data and active during 2014, number of construction BMP provide a gap analysis that identifies inspections, number of enforcement actions taken, the need for additional monitoring to number of permanent BMPs, and number of determine appropriate nitrogen and inspections and enforcement actions for permanent phosphorus contributions to State BMP sites. Waters from MS4s. 4.5 Post-Construction BMPs The Cherry Creek Basin MS4s

The Guidance Document described above also participated in a Data Gap Analysis includes requirements for post-construction control of Report prepared for the Colorado stormwater quality. All regulated new development Stormwater Council and UDFCD to and redevelopment projects must submit a post- meet the requirements of Regulation construction BMP plan to the MS4 agency for review 85. and approval prior to commencing land-disturbance activities. Again, as for construction BMPs, each land use agency maintains design standards or refers to UDFCD design standards for permanent BMPs. Plans for permanent BMPs are reviewed by the local land use agency prior to the start of construction.

4-4

TABLE 4-1. SUMMARY OF STORMWATER PERMIT, INSPECTION, AND ENFORCEMENT ACTIONS

Land Use Agency Construction Construction BMPs Permanent BMPs Sites Total Sites Number of Number of Number of Number of Number of Inspections Enforcement Actions BMPs (or Inspections Enforcement BMP Sites) Actions Constructed Arapahoe County 66 505 19 5 6 0 GESC-37 violations GESC – 205 GESC-1849 3 – Stop Work Douglas County 79 1 0 DESC - 749 DESC - 3548 DESC – 55 violations 2 – Stop Work City of Aurora 51 219 35 0 251 0 City of 60 583 18 2 8 0 Centennial/SEMSWA City of Greenwood 0 0 0 36 21 0 Village City of Lone Tree 12 116 13 0 0 0 City of Castle Pines 13 100 9 0 4 2 Town of Castle Rock 895 3984 1128 11 350 0 Town of Parker 61 368 79 12 305 0 # not # not # not # not CDOT # not provided # not provided provided provided provided provided 1 This number includes 3 private BMPs and 22 public municiple BMPs.

4-5

The Water Quality Control Commission has adopted the following three-tiered approach to stormwater management for post-construction development and redevelopment in the Cherry Creek Reservoir watershed. The level of required post-construction BMPS increases for the higher tiers (e.g., tier 3).

Development and Redevelopment Tiers: Tier 1: Any land disturbance <1 acre that is independently developed, and which results in <500 square feet of imperviousness for new development or <500 square feet of increased imperviousness for redevelopment. Tier 2: Any land disturbance <1 acre that is independently developed, and which results in >500 but <5,000 square feet of imperviousness for new development or >500 square feet and <5,000 square feet of increased imperviousness for redevelopment, including disturbances of existing impervious areas. Tier 3: Any land disturbance >1 acre that is independently developed, or which results in ≥5,000 square feet of imperviousness for new development or ≥5,000 square feet of increased imperviousness for redevelopment, including disturbances of existing impervious areas.

4.6 Flood Control Facilities Retrofitting, Inspection, and Maintenance Actions The Authority supports the retrofitting of stormwater facilities in order to address any potential water quality issues identified through monitoring and reporting of existing facilities. One of the priority items identified during the Watershed Plan effort was the opportunity to retrofit detention ponds for the control of nutrients and other pollutants. Table 4-1 shows the number of inspection and maintenance actions taken in 2014, which includes

retrofitted facilities.

4-6

4.7 Effectiveness in Reducing Phosphorus Concentrations The Commission has previously concluded that point source, nonpoint source, and regulated stormwater controls for total phosphorus are successfully reducing total phosphorus concentrations in stormwater and surface water flows to the reservoir. This is supported by ongoing monitoring being conducted both upstream and downstream of the PRFs, which effectively measures the cumulative benefits of BMP implementation in the upstream watershed. The data confirm that the BMPs and other controls placed on regulated stormwater continue to be effective. Watershed and reservoir modeling results have shown that, although population growth and surface flows have increased in the basin, the total phosphorus concentration in the inflow to the reservoir has remained relatively constant. In addition to the controls required by Regulation 72 for regulated stormwater sources, the Authority also ensures implementation of effective BMPs through other activities. The Authority serves as a referral agency in the land use application process for local land use agencies within the Cherry Creek Reservoir watershed. When a land use agency receives a land use or development application, a copy is sent to the Authority for review. The Authority then has the opportunity to comment on the potential water quality impacts of the proposed application prior to approval of site plans and to determine whether the proposed project complies with Regulation 72 and Authority’s Guidelines. The Authority reviews land development applications, for the inclusion of construction (temporary) and post- MAP 4-2: MAP OF LAND USE construction (permanent) stormwater quality BMPs for DEVELOPMENT APPLICATIONS REVIEWED land disturbances in the Cherry Creek Watershed. Map 4-2 BY AUTHORITY, 2014 provides a summary of the number of 2014 referrals by land use agency. Figure 4-1 provides a review of the number of land use and development applications that the Authority has received annually since March 1997.

4-7

The Authority’s review of applications for land use changes in the Cherry Creek Reservoir watershed provides the following benefits:

. A better understanding of where and how development is occurring in the Cherry Creek Reservoir watershed. Currently, the bulk of development is occurring in the central reservoir watershed around Douglas County, Town of Parker, City of Aurora, and City of Centennial in several tributaries that previously were undeveloped. This pattern points to the need to focus on preventing or minimizing erosion in the tributaries by stabilizing the tributary drainage ways simultaneously with, if not in advance of, development.

. A better understanding of how well developers are complying with Authority requirements and improved communication with the land use agency personnel. Currently, the Authority’s review comments are integral to the development process, and a negative response from the Authority has resulted in positive changes to the land use application.

. An opportunity for the Authority to work more closely with developers during initial stages of land use planning to identify projects where water quality enhancements and alternate BMPs are appropriate.

The number of land use referrals has risen substantially in 2014 and is comparable to development in years before the 2008 economic downturn. In 2014, the Authority received 153 referrals. The most land use applications submitted were from the Town of Parker, although there were significant application submittals from Douglas County, the City of Centennial, and Arapahoe County. The type of land use for project referrals received in 2014 included residential, commercial, planned urban development, open space or parks, highways and bridges, and other (airport, parking lots, transmission line, WWTF, lift station, etc.). Figure 4-2 shows the distribution of land use for the referrals received in 2014. The Authority took no exception to most projects that were received. For the projects for which the Authority took exception, the Authority worked with the land use agency and engineering consultants to recommend improved stormwater quality controls and compliance with Regulation 72.

4-8

FIGURE 4-1: LAND USE DEVELOPMENT APPLICATIONS REVIEWED BY AUTHORITY, 1997-2014

FIGURE 4-2: TYPES OF DEVELOPMENT PROJECTS REVIEWED BY AUTHORITY IN 2014

4-9

4.8 Funding of Regulated Stormwater Projects For new development and redevelopment projects within the jurisdictional boundaries of the land use agencies, the developer or land owner is generally held responsible for planning, constructing, operating, and maintaining construction and post-construction BMPs (unless the MS4 accepts operations and maintenance (O&M) responsibilities). The developer must make any necessary repairs to construction BMPs after a defect or need for repair is discovered. For permanent BMPs, the Post- Construction BMP plan requirement is to address the design, construction, and long-term operation and maintenance. The plan must contain procedures for maintaining and inspecting the facility on a regular basis to ensure the continued effectiveness of the BMPs. The plan also requires commitments from the responsible agency or owner that it will continue to maintain the BMPs once the facilities are complete. The plan must also contain provisions to access the BMPs for operation, maintenance, and inspection by the public entities by easement or other legal means of access. The Authority supports the use of Low Impact Development (LID) features that can be both protective of water quality and cost-saving for developers. An example of this is the recent adoption in Regulation 72 of a new Runoff Reduction Practices BMP that relies on LID strategies and Minimizing Directly-Connected Impervious Areas (MDCIA) to promote onsite storage and infiltration, which can be cost-effective for new developments. 4.9 Monitoring of Regulated Stormwater Projects The Commission requires the Authority to monitor and maintain all PRFs for nutrient control (PRF monitoring is further discussed in Chapter 5.) The Commission also concluded that individual monitoring of BMPs need not occur because PRF monitoring upstream and downstream of the project effectively measures the cumulative benefits of BMP implementation in the upstream watershed. PRF monitoring results are discussed in Section 5.5. In addition to Authority monitoring, MS4s are required to report separately to the Division (as part of their annual reports) on any monitoring data collected and analyzed to assess the effectiveness of stormwater controls in reducing the discharge of pollutants. 4.10 Public Information and Education Actions of MS4s In partnership with Arapahoe County, the Southeast Metro Stormwater Authroity (SEMSWA) is leading the Stormwater Permittees for Local Awareness of Stream Health (SPLASH) Group. The SPLASH Group works together to provide public educational outreach, opportunities for public participation, and staff training to increase awareness of each person’s role in protecting water quality.

4-10

SPLASH installed a giant straw in Cherry Creek as a way to remind and encourage residents to “Think about your drink: What can you do at your home, school, and business to protect water that use everyday? Rain that falls on imprevious (hard) surfaces such as streets and parking lots can pick up trash, oil, lawn fertilizer, pet waste and other polluntants as it travels. These pollutants are carried to the storm water drainage system, which drains directly into our local water bodies,

untreated. Polluted rain runoff, or stormwater compromises the quality of the water that is ued for drinking other uses.” SPLASH also hosts and sponsors number of events year round including relay races, volunteer days, and school presentaions. For more information on SPLASH: http://www.splashco.org/home.html. In 2014, Aurora Water’s Water World Program offered free water presentations for local schools. Programs ranged from “If I Was a Fish” for preschoolers to more technical topics such as “Reclaimed Water” and “Careers in Water” for highschoolers. In addition to in class presentations they also offered field trips for grades 3-12. Field Trips included tours of the Water and Wastewater Treatment Plants, and Water Quality Testing at the AWQUA Lounge. For more information: https://www.auroragov.org/cs/groups/public/documents/document/018172.pdf.

4-11

2014 ANNUAL REPORT ON ACTIVITIES

5 OTHER NONPOINT SOURCES Nonpoint source stormwater controls consist of Pollutant Reduction Facilities (PRFs) constructed by the Authority and similar type projects constructed PRFs are defined in Regulation by local governments. These are water quality 72 as “projects that reduce measures, such as stream reclamation, shoreline stabilization, detention, wetlands, and others that nonpoint source pollutants in otherwise provide water quality benefits for the stormwater runoff that may reservoir, reduce pollutants carried by stormwater also contain regulated from existing and future land disturbances. PRFs stormwater. PRFs are are different from the BMPs that are implemented by local land use agencies (i.e., MS4s) under the structural measures that regulated stormwater program discussed include, but are not limited to, previously in Section 4. The difference between detention, wetlands, PRFs and BMPs is formally recognized in the definitions in Regulation 72. filtration, infiltration, and other technologies with the PRFs are selected based on a prioritization method considering cost/benefit and other factors that primary purpose of reducing include quantitative and qualitative assessments pollutant concentrations and Authority consideration of all reasonable entering the reservoir or that evaluation criteria. Evaluation criteria include protect the beneficial uses of estimates of pollution reduction, economic baselines, expected timeframe for benefits to be the reservoir.” seen, cost, and potential downstream impacts. 5.1 Update list of PRFs Implemented In accordance with statuatory requirements, the Authority must spend at least 60 percent of its annual budget on design, construction, operation, and maintenance of PRFs. This was accomplished in 2014. To implement this requirement, the Authority conducts a multi-year Capital Improvement Program (CIP) planning process to identify PRF construction projects. Potential PRFs are first identified and evaluated, and costs are estimated over the life of design and construction for each project. The next step is development of a list of all potential PRFs (called the master PRF list), which includes capital, operation, and maintenance costs compared with potential benefits in terms of phosphorus reduction. As pollution reduction opportuntieis are identified during the year, they are evaluated at the conceptual level to determine costs and beneftis. If project costs and benefits appear to be reasonable, the TAC recommends to the Board that the project be included on the master PRF list. Once the Board approves the project for inclusion on the master list, any future work towards design and construction, which also must be authorized by the Board, is considered to be part of capital expenses of the Authority. The next

5-1

step is to select the best projects from the master list of PRFs to be included on the CIP list. In 2014, the Authority expanded the previous year’s 5-year CIP to a 10-year CIP in an effort to better plan for and manage the CIP program.

Cost/ Benefit Master Analysis PRF List

10-Year CIP List

Fund and Build

The TAC evaluates projects annually on the master list and forwards recommendations to the Board for inclusion on the 10-year CIP. The Board then annually selects projects from the 10-year CIP, based on recommendations from the TAC and subject to available funds. The PRFs completed to date, ongoing PRFs, and the 10-year plan PRFs are listed in Tables 5-1 and 5-2, and in section 5.2 below. Tables 5-1 and 5-2 provide a summary of recommended PRFs for 2015-2024, and estimated capital costs which include engineering, construction, administration, and contingency. Design costs include technical feasibility design, construciton observation and adminstrative costs. Prior year oligated funds are accumulative expenditures for the project, based on previous years accounting and estimate of current year expenses. This budget in Table 5-1 is the TAC recommendation. The funds allocated to each project are subject to further board approval, and the CIP is included in the Board’s budget adopted annually in November. Where noted, some funds have been previously obligated to the specific project by the Board. Projects completed in prior years are not shown.

5-2

TABLE 5-1: CCBWQA SUMMARY OF RECOMMENDED POLLUTANT REDUCTION FACILITIES 2015-2024 BUDGET PROJECTIONS ($1000)

Current Project Budget 3 Proposed 2015 201 201 2018 201 202 202 2022 2023 202 Budget 6 7 9 0 1 4 Project

Project Title 1 No. 2 Prior Year Total Total Total Total Total Total Total Total Total Total Total Capital Portion Portion Design Capital Obligated Funds Authority Authority Residual PRF Costs PRF Costs Residual CAPITAL CCB-5.4 Cherry Creek Stream Stabilization at $1776 $1176 $200 11% $255 $200 $- $- $- $- $- $- $- $- $200 $- $- $- Main street (Parker) CCB-5.6 Cherry Creek Stream Stabilization at $1447 $1447 $304 21% $900 $304 $- $- $- $- $- $- $- $- $304 $- $- $- Lincoln Avenue (Parker) CCB-5.11 Cherry Creek Stream Stabilization at $900 $900 $255 28% $ $- $- $- $- $- $- $- $- $- $- $- $- Norton Open Space (Parker) CCB-5.14 Cherry Creek Stream Reclamation- $12,172 $12,172 $3043 25% $50 $2143 $60 $- $60 $300 $400 $500 $500 $383 $- $- $- $- CCSP to EcoPark (Ph II to V)

Cherry Creek Stream Reclamation – $2227 $2227 $2227 100% $- $2227 $- $- $- $150 $- $- $- $- $- $300 $900 $427 CCSP Ph I CCB-6.4 Piney Creek Stream Stabilization at $8402 $8402 $2101 25% $- $2051 $- $500 $500 $500 $500 $551 $- $- $- $- $- $- Caley Ave. Reach 6 & 7 (Liverpool) CCB-16 Stream Corridor Preservation $100 $100 $100 100% $- $100 $- $- $- $- $- $- $- $- $- $- $- $- CCB-17.4 East Boat Ramp Shoreline Stabilization $70 $70 $70 100% $- $70 $- $- $- $- $- $- $20 $50 $- $- $- $- Phase II CCB-17.5 East Shade Shelter Shoreline $50 $50 $50 100% $50 $- $- $- $- $- $- $20 $30 $- $- $- $- Stabilization Phase II CCB-17.6 West Shade Shelter Shoreline $950 $950 $950 100% $- $950 $- $- $- $- $- $- $150 $300 $500 $- $- $- Stabilization PRF CCB-17.7 Tower Loop Shoreline Stabilization $90 $90 $90 100% $70 $- $- $- $150 $- $- $20 $70 $- $- $- $- Phase II

CCB-19 Non-Point Pollutant Management $100 $100 $100 100% $ $100 $- $- $- $- $- $- $- $- $- $- $- $100

CCB Interview PRF Signage at 12-Mile Park $16 $16 $16 100% $ $16 $- $16 $16 $- $- $- $- $- $- $- $- $- (2 signs) & West Boat Ramp (1 sign) SUB-TOTALS $ $$$$$8915$60$516 $576

5-3

TABLE 5-2: CCBWQA SUMMARY OF RECOMMENDED POLLUTANT REDUCTION FACILITIES 2015-2024 BUDGET PROJECTIONS ($1000)

Current Project Budget 3 Proposed 2015 2016 2017 2018 2019 2020 2021 2022 2023 2024 Budget

Project No. Project Title 1 2 Prior Year Total Total Total Total Total Total Total Total Total Total Total Capital Portion Portion Design Capital Obligated Funds Authority Authority Residual PRF Costs PRF Costs Residual OPERATIONS AND MAINTENANCE Rehabilitation Categories

OM- Shop Creek Inlet Rehabilitation $20 $20 $20 100% $20 $20

OM- Frame Restoration & Sign $25 $25 $14 56% $14 $14 $14

OM- Cottonwood Wetlands Outlet Maint $9 $9 $9 100% $9 $9 $9 SUB-TOTALS $23 $43 $43 Restorative Categories OM-1.1 Cottonwood Creek - Regrade $6 $6 $6 100% $- $6 $- $6 $6

OM- Emergency or Unplanned Repairs $- $- $- 100% $- $- $50 $50 $50 $50 $50 $50 $50 $50 $50 $50 $50

OM- Mtn/Lake Loop- Grading at Boat $3 $3 100% $3 $3 $3 House

OM- Tree/Shrub Planting 100% $- $8 $8 $8 $8 $8

OM- East Shoreline Flood Restoration $11 $11 $11 100% $11 $11 $11 SUB-TOTALS $- $28 $- $78 $78 $58 $58 $50 $50 $50 $50 $50 $50 $50 Routine Categories

OM-7 Reservoir Destratification $90 $90 $90 100% $- $35 $- $85 $85 $90 $96 $101 $107 $112 $118 $124 $130 $136

OM-14.1 PRF Weed Control $26 $26 $26 100% $- $34 $- $34 $34 $36 $38 $41 $42 $44 $46 $49 $51 $54

OM-14.2 PRF Reseeding at CCSP $39 $39 $39 100% $- $45 $- $45 $45 $45 $45 $45 $45 $45 $45 $45 $45 $45

OM- ERO Annual Reports $7 $7 $7 100% $- $7 $7 7 $7 $7 $7 SUB-TOTALS $171 $- $171 $171 $178 $186 $194 $194 $201 $209 $218 $226 $235 SUB-TOTAL O&M $222 $- $292 $292 $236 $244 $244 $244 $251 $259 $268 $276 $285 GRAND TOTAL $9137 $60 $808 $868 $1186 $1144 $1295 $1104 $1084 $1263 $1168 $1176 $812

5-4

5.2 Overview of PRFs to Date The Authority has completed 23 PRF projects in the basin since 1989 and has several specific PRF projects in the 10- year plan. The Authority’s initial PRF focus area concentrated in Cherry Creek State Park along the shoreline and gradually moved upstream and outside of the Park limit. Funding for PRFs from 1989-1999 was provided 100 percent by the Authority due to the location of the first PRFs in the Cherry Creek State Park. However, as the Authority moves its focus area upstream, joint funding from municipalities and other stakeholders has augmented the funds available and reduced the percentage paid by the Authority for individual PRFs.

PRFs Completed to Date: • Shop Creek • Cottonwood Wetlands • Quincy Drainage • East Shade Shelter • East Boat Ramp • East Shoreline extension • Tower Loop • Dixon Grove • Cottonwood\Peoria Pond • Bowtie Property Acquisition • Piney Creek Stream Reclamation at Buckley Road • Cottonwood Creek Reclamation Phase I & II • CC Reservoir Destratification System • CC Stream Reclamation at EcoPark • CC Stream Reclamation at Eco-Park • McMurdo Gulch Stream Reclamation • Cottonwood Creek Stream Reclamation at Easter Ave • Cottonwood Creek Peoria Trib, Ponds C3 & C4 • CC Stream Reclamation at 12-Mile Park Phase I & II • Parker Jordon Centennial Open Space • Mountain & Lake Loop Shoreline Stabilization • CC Stream Reclamation – Reach 5, drop structure 14 • West Boat Ramp Parking Lot In Progress PRFs: • CC Stream Reclamation at Hess Road (Country • CC Stream Reclamation at Norton Open Space Meadows) • Cherry Creek Stream Reclamation at Shop Creek Trail • CC Stream Reclamation – CCSP to EcoPark – O&M activities (multiple segments) 10– year Plan: • East Boat Ramp Shoreline Stabilization Phase II • East Shade Shelter Shoreline Stabilization Phase II • West Shade Shelter Shoreline Stabilization • CC Stream Reclamation @ Main Street (Parker) • CC Stream Reclamation @ Lincoln Avenue (Parker) • Piney Creek Stream Reclamation upstream of Tower Road • CC Stream Reclamation Reach 2 •

5-5

2014 Pollutant Reduction Facilities (PRF) Summary

Over the course of the Authority’s history, it has spent more than $13 million on capital projects and pollutant reduction facilities. Prior to 2010, Cherry Creek Reservoir was under a total maximum annual load (TMAL) limitation for phosphorus. Since capital projects and PRFs originally focused on reduction of phosphorus loads discharged into the reservoir, projected loads and treatment, and estimated pounds of phosphorus removal are estimated. Currently there is no TMAL; instead the control strategy identified in Regulation No. 72 is to minimize nutrient (phosphorus and nitrogen) concentrations. Therefore, capital improvement projects and PRFs are still evaluated, in part, on phosphorus removal per year for consistency between all projects. The following are brief descriptions of the 2014 projects and in-progress projects. For a full description of each project see Appendices.

Cherry Creek Stream Reclamation CCSP to Eco Park, Reach 5

Cherry Creek in this project area is a 20 to 50 foot wide sandy channel bed with incised banks between three and eight feet tall. There is major erosion and degradation of stream banks and contains exposed-at-grade utility lines. The upper limit of this project will tie into the Cherry Creek Stream Reclamation at Eco Park project that was completed in 2013. The Authority has partnered with UDFCD, City of Aurora, and SEMSWA to complete this project and it is estimated that approximately 38 lbs/year of phosphorus will be removed annually as a result of this project. Stream reclamation for this corridor includes 2,200 linear feet of improvements downstream of Eco Park. The construction of a drop structure (Drop Structure #14) was completed in the fall of 2014 for this area, anchoring the lower end of Reach 5. The channel improvements for the remaining length of Reach 5 are scheduled for construction in 2015-2016.

Cherry Creek Stream Reclamation at Hess Road

This project is located in Parker, and begins immediately downstream of Hess Road, and extends for a distance of approximately 4,200 linear feet. Cherry Creek in this area is a 20 to 50 foot wide sandy channel bed with incised banks between three and ten feet tall. The creek has eroded four to six feet deep and threatens sensitive riparian areas and wildlife habitat as well as existing trails

5-6

and utilities. The Authority has partnered with the Town of Parker, Douglas County, and UDFCD to improve the stream and mitigate the existing erosion and prevent future erosion on Cherry Creek. Design objectives include raising the channel bed, widening the low flow channel, providing a secondary channel through most of the reach, adding riffle drops and sculpted concrete drop structures, creating wetland benches adjacent to the low flow channel, improving riparian areas and improving overall water quality. Construction of the project began in October 2014. It is estimated that approximately 72 lbs/year of phosphorus will be removed as a result of this project. The construction of the project is scheduled for completion in spring 2015.

Cherry Creek Stream Reclamation at Norton Farms Open Space

This project is located in Parker, immediately upstream of the Cherry Creek Stream Reclamation Project at 17- Mile House beginning at the Arapahoe / Douglas County Line. The Authority has partnered with the Town of Parker and UDFCD on this project that extends upstream for a distance of approximately 2,500 linear feet in length and ties into the Cherry Creek Improvements project that was completed in 2008 within the Cottonwood subdivision. Cherry Creek, in the project area, has eroded four to six feet deep and threatens sensitive riparian areas and wildlife habitat as well as existing trails and utilities. Construction will begin in the fall of 2015 and be completed in 2016. The project will include grade control/drop structures, bank stabilization, raising the channel bed, widening the low flow channel, adding riffle drops, creating wetland benches adjacent to the low flow channel, and improving riparian areas. This construction will mitigate the existing erosion and prevent future erosion on Cherry Creek and will provide water quality benefits to the basin. It was estimated that these improvements will remove approximately 38 lbs of phosphorus per year from Cherry Creek.

Cherry Creek Stream Stabilization at 12-Mile Park, Phase II (the Dog Off Leash Area DOLA Park Project)

This project is located near the southeast corner of the CCSP, along the “big- bend”, adjacent to the dog off-leash area. The off-leash dog park is located along the east side of Cherry Creek and has over 100 acres in the 12-Mile Area. Severe damage to bank vegetation and channel erosion were observed throughout the area where people, dog, and horse activity was concentrated.

5-7

In addition, in 2010, the right bank of Cherry Creek breached, causing the creek to change course through the downstream cottonwood grove, damaging the wetlands. In 2014, the stream stabilization at 12-Mile Park was completed and had over 550 visits (Phase II). The east bank of the dog park area was repaired and groundwater wetlands were restored to help prevent erosion. It was estimated that a total of 52 lbs/year of phosphorus will be removed as a result of this project.

Cherry Creek Reservoir West Boat Ramp Retrofit

In 2014, the Authority resolved a direct discharge into Cherry Creek Reservoir by retrofitting the West Boat Ramp area, specifically to improve water quality of the direct discharge runoff from paved vehicle/boat trailer parking lot. The pre-retrofit conditions did not contain treatment or attenuation for the runoff and stormwater was directly discharged into the reservoir from approximately 4.1 acres of parking lot and 0.3 acres from the boat ramp. The retrofit maximized water quality treatment and had no adverse impacts to flood storage volume, Cherry Creek Dam, or the Marina. Improvements included rerouting direct discharges to the existing water quality facility. The retrofit provides water quality enhancements, energy dissipation, improved aesthetics of the structures, and promotes vegetative growth. Improvements were also made to the existing water quality pond, which included: . Modified design to account for increased tributary area o Existing = 0.80 acres o Proposed = 4.94 acres . Maximized water quality enhancement o Required 6,186 cf storage o Provided 8,550 cf storage . Provided water quality treatment for the entire West Boat Ramp parking and ramp area . Promoted infiltration and vegetation growth . No fill within the permanent flood pool of the reservoir . No flooding of adjacent areas

5-8

5.3 Floodplain Preservation/Conservation Easements The Water Quality Control Commission recognizes protection of floodplain, riparian corridor, and other environmentally sensitive lands through public acquisition or conservation easements and restoration of the same lands for nutrient control through erosion control, revegetation, or other means, to control nutrients. The Authority and local governments may collaborate with other entities in pursuing easements, ownerships, and rights to protect the streams, riparian corridors, tributaries, and wetlands in the Cherry Creek watershed. In the past, the Authority was a founding partner in the acquisition of 21.5 acres of land at the confluence of Piney Creek and Cherry Creek whose shape resembled a bowtie and was hence called the Bowtie Property. The purchase was a joint effort between the City of Centennial, Arapahoe County, the UDFCD, the Trust for Public Lands, and the Authority and preserved the channel and riparian corridor of Piney Creek from future development, and returned an existing developed area into open space park. 5.4 Monitoring of PRFs The Authority continued its annual PRF monitoring program in 2014. PRF monitoring is conducted on Cottonwood Creek at sites above and below both the Peoria Pond PRF and the Perimeter Pond PRF. Monitoring data for these two PRFs are found in Figures 5-1 through 5-3. Shop Creek and Quincy Drainage PRFs have also been monitored for effectiveness since 2000. The Authority also monitors McMurdo Gulch and more recently Cherry Creek mainstem at the downstream limits of the EcoPark Project. This monitoring is discussed below.

5.5 PRF Effectiveness in Reducing Phosphorus Concentrations PRF effectiveness is gauged by monitoring the concentration of phosphorus and suspended solids and the phosphorus loading upstream and downstream of each facility. Evaluation of the effectiveness of the entire Cottonwood Creek Stream Reclamation Reach was performed using the data collected at the existing PRFs both upstream and downstream of the reclamation reach. Two PRFs, the Cottonwood Creek-Peoria Wetland System (upstream) and the Cottonwood Creek-Perimeter Pond, in conjunction with the stream reclamation

5-9

between these two wetlands, operate very effectively as a “treatment train” along Cottonwood Creek. Their effectiveness in reducing both phosphorus and sediment concentrations is discussed below. The Cottonwood Creek Stream Reclamation Project, which is paired with two wetland detention systems (PRFs), continues to be effective in reducing the suspended solids and total phosphorus load to the Reservoir. This effort, combined with the wastewater treatment plants’ effort to achieve the 50 µg/L total phosphorus permit limits are believed to be the reasons behind the significant reduction in baseflow phosphorus concentrations in Cottonwood Creek over time (Figure 5-1).

FIGURE 5-1: BASE FLOW TOTAL PHOSPHORUS CONCENTRATIONS FOR COTTONWOOD CREEK, 1996- 2014

A similar, but more pronounced trend for reduction in storm-flow phosphorus concentration over time is shown in Figure 5-2 for Cottonwood Creek inflows entering the Reservoir. Completion of the stream reclamation in 2008 shows the most dramatic reduction in concentrations, demonstrating how sensitive phosphorus concentrations can be for unstable stream conditions. Note that the Cottonwood Creek Stream Reclamation Project and its associated PRFs reduces the median total phosphorus concentrations, which are less than the interim warm water stream value for phosphorus of 170 ug/L, even during storm flow events. The Authority has relied on its PRF efficiency data in Cottonwood Creek to expand its watershed management efforts to other tributaries in the Cherry Creek Basin. Currently, the Authority monitors water qualtiy conditions McMurdo Gulch (~20 miles upstream of the Reservoir) to document the efficiency of the McMurdo Stream Reclamation Project. Since 2012, the McMurdo Gulch Stream Reclamation project has shown to be effective at reducing total phosphorus and total suspended solids downstream of the stream reclamation project (GEI 2015). The Authority also monitors the water quality conditions downstream of the EcoPark Stream Reclamation Project located on the mainstem of

5-10

Cherry Creek (~4 miles upstream of the Reservoir). In 2015, the Authority is partnering with the Urban Drainage and Flood Control District, Southeast Metro Stormwater Authority, City of Aurora, and Douglas County to establish a new monitoring station on Piney Creek to begin documenting water quality conditions prior to construction of Piney Creek Stream Reclamation Project.

Restoration of Cottonwood Wetlands Pond

FIGURE 5-2: STORM FLOW TOTAL PHOSPHORUS CONCENTRATIONS FOR COTTONWOOD CREEK, 1996- 2014

5.5.1 COTTONWOOD CREEK PEORIA POND

The 2014 WY flow-weighted phosphorus concentration upstream of the Cottonwood Creek-Peoria Pond PRF was 145 μg/L, while the flow-weighted concentration downstream of the system was 135 μg/L. This represents a 7 percent decrease in flow-weighted total phosphorus concentrations downstream of the PRF. Over the life of the project, the PRF shows an average 18% reduction in the flow-weighted total phosphorus concentration at the downstream monitoring site. Total suspended solids also showed a substantial decrease downstream of the PRF, being reduced by 41 percent. This PRF underwent sediment removal maintenance in 2008, and continues to be very efficient in reducing phosphorus and sediment from Cottonwood flows. This PRF was also particularly effective at reducing the total suspended solids and total phosphorus load during storm events during 2014. During the storm event on April 24, 2014, this PRF removed over half of the total suspended solids and 40% or more of the total phosphorus load being carried down the creek. During the July 5,

5-11

2014 storm, this PRF removed approximately 53% of the total suspended solids and 40% of the total phosphorus in Cottonwood Creek flows. The 2014 upstream and downstream average total suspended solids and total phosphorus concentrations are compared to the previous five years in Figures 5-3 and 5- 4. The raw data for these figures can be found in the 2014 GEI Monitoring Report, which is included in the Appendix of this report.

150

100

50 % Change Downstream 0 Upstream Downstream -50

-100

% Change Downstream Concentration (mg/L) Concentration Downstream % Change 2009 2010 2011 2012 2013 2014

FIGURE 5-3: AVERAGE TOTAL SUSPENDED SOLIDS 2009-2014 FOR COTTONWOOD-PEORIA POND PRF

300

250

200

150

100

50 % Change Downstream 0 Upstream Downstream -50

% Change Downstream Concentration (mg/L) Concentration Downstream % Change -100 2009 2010 2011 2012 2013 2014 FIGURE 5-4: FLOW-WEIGHTED TOTAL PHOSPHORUS (µG/L) 2009-2014 FOR COTTONWOOD CREEK- PEORIA POND PRF

5-12

5.5.2 COTTONWOOD CREEK RECLAMATION AND PERIMETER POND

In 2008, the Cottonwood Creek Reclamation Project was completed. It relocated the channel to its historic location and substantially reduced the amount of erosion by widening the channel and dissipating the flow energy through this reach. This channel stabilization and reclamation project has greatly reduced the amount of phosphorus in flows entering Cherry Creek Reservoir.

In 2012, the control gate for the outlet weir structure at the Perimeter Pond (Site CT-2) was left partially open during restoration of the wetlands in 2012 and resulted in extremely high discharge values during storm events as compared to both the previous years’ values and the upstream Site CT-1. Therefore, the weir equation for Site CT-2 was not used to estimate discharge for the Cottonwood Perimeter PRF in 2013. Instead the Site CT-1 discharge was substituted to estimate flow-weighted concentrations.

In 2014, streamflow at CT-1 was greatly affected by a beaver dam, which caused inundation of the monitoring site in mid-summer which altered the hydrology throughout the reach.

The 2014 WY flow-weighted phosphorus concentration upstream of the Cottonwood Creek Reclamation and Perimeter Pond PRF was 112 μg/L, while the flow-weighted concentration downstream of the system was 81 μg/L for baseflow. This represents a 28 percent decrease in flow-weighted total phosphorus concentrations downstream of the PRF. Total suspended solids also showed a substantial decrease downstream of the PRF, being reduced by 61 percent. This PRF was also particularly effective at reducing the total suspended solids and total phosphorus load during multiple storm events during 2014. During the storm event on September 5, 2013, this PRF removed approximately 90% of the total suspended solids and 84% of the total phosphorus from Cottonwood Creek flows. 2014 upstream and downstream average total suspended solids and total phosphorus concentrations are compared to the previous 5 years in Figures 5-5 and 5-6. The raw data for these figures can be found in the 2014 GEI Monitoring Report, which is included in the Appendix of this report.

5-13

80

60

40

20 % Change Downstream 0 Upstream Downstream

-20

-40

-60

(mg/L) Concentration Downstream % Change -80 2009 2010 2011 2013 2014

FIGURE 5-5. AVERAGE TOTAL SUSPENDED SOLIDS 2009-2014 FOR COTTONWOOD CREEK-PERIMETER POND PRF

140 120 100 80 60

40 % Change 20 Downstream

0 Upstream Downstream -20 -40 -60

(µg/L) Concentration Downstream %Change -80 2009 2010 2011 2013 2014

FIGURE 5-6: FLOW-WEIGHTED TOTAL PHOSPHORUS (µG/L) 2009-2014 FOR COTTONWOOD CREEK PERIMETER POND PRF

5-14

5.5.3 MCMURDO GULCH STREAM RECLAMATION

Due to foreseeable erosion issues, given residential development along McMurdo Gulch, the Town of Castle Rock, with support from the Authority, implemented a stream reclamation project along three miles of stream between the Cobblestone Ranch and Castle Oaks subdivisions. In January 2012, two water quality monitoring sites were established on McMurdo Gulch, one site approximately 150 m upstream of the McMurdo Gulch Stream Reclamation Project Boundary (MCM-1), and one site approximately 80 m upstream of the Castle Oaks Drive Bridge crossing of McMurdo Gulch (MCM-2), near the North Rocky View Road intersection. Data from these monitoring sites provide background nutrient concentrations in a watershed that is planned for future development and also provide a comparative data set to evaluate the water quality benefits of stream reclamation in smaller tributaries to Cherry Creek. Base flow water quality samples were collected on a monthly basis at sites MCM-1 and MCM-2 during the 2014 WY. Total phosphorus concentrations at Site MCM-1 ranged from 266 to 564 μg/L with a WY median concentration of 340 μg/L. Total phosphorous concentrations at Site MCM-2 were reduced compared to Site MCM-1 and ranged from 177 to 335 μg/L with a WY median concentration of 300 μg/L. Total suspended solids concentrations were slightly greater at the downstream location (Site MCM-2) with a WY median total suspended solids concentration of 11.6 mg/L, as compared to 5.7 mg/L at the upstream site (MCM-1). Because Site MCM-1 is located upstream of the McMurdo Gulch Stream Reclamation Project Boundary and Site MCM-2 is located downstream of the PRF, the reduction in phosphorus from Site MCM-1 to Site MCM-2 indicates that the stream reclamation project is reducing total phosphorus concentrations in McMurdo Gulch, even though the total suspended solids data shows mixed results. 5.6 Funding of PRFs and Nonpoint Source Projects The Authority either funds or co-funds PRFs and other nonpoint source projects together with other agencies through taxes, fees, and wastewater surcharges. Funding varies year to year. As noted earlier in this chapter, the 10-year CIP (Tables 5-1 and 5-2) identifies various cost components for the PRFs including design, capital, land acquisition, water augmentation requirements, and operations and maintenance costs. The Authority’s portion of the total costs for co-funded projects can be seen in the 10-year CIP. These costs are then spread out over a multi-year period for longer-range planning purposes, subject to available Authority funds. In addition, these tables show the amount spent (and obligated) to date by the Authority for the various PRFs that have been completed or that are in progress.

5-15

For 2015, the Authority is projecting a budget of $868,000 for capital improvements and O&M for projects shown in Tables 5-1 and 5-2. The Authority plans and budgets for multiple year projects, from concept through construction processes, and projects it will have funds to plan for and implement the projects shown in the 10-year CIP. Implementation and timing of projects can vary from year to year; projects are sometimes funded through capital reserves. The Capital Project and Maintenance Status Report is updated monthly for the TAC and Board meetings. It provides a brief summary of ongoing capital and maintenance projects, as well as current and planned activities for each. 5.7 Annual Inspection of PRFs The 2014 annual inspection of pollutant reduction facilities (PRF) constructed by the Authority was conducted on August 12th and 18th. The conclusions and recommendation of the 2014 annual inspection are: 1) All PRF’s are generally performing as designed, but some routine, rehabilitative and restorative maintenance activities are recommended and are planned for 2015 and beyond. 2) Noted erosion areas will be included in the 2015 budget for restoration. 3) Signage upgrade, repair, and replacement needs will be included in the 2015 budget. 4) The projected total O&M cost as the result of this inspection is $156,000 as compared to the 2014 budget of $82,600. Weed control and re- vegetation budget estimates are included in the 2015 projected costs. 5) Weed control and reseeding work can be more readily accomplished by using the Park vendors for seeding and for weed control. 6) It is recommended that the Authority develop a capital maintenance program that prequalifies contractors and sets unit prices for materials and labor to facilitate smaller routine and restorative maintenance projects, rather than bidding the work for each project.

5-16

TABLE 5-3: 2014 ANNUAL INSPECTION REPORT OF PRFS AT CHERRY CREEK STATE PARK

PRF Action Estimate of Cost to Authority Routine cleaning of trash rack & removal of woody vegetation. Replace $16,000 trash rack. Monitor water quality performance. Routine cleaning of trash rack. Replace trash rack. Monitor water quality Shop Creek Wetlands $4,000 Channel performance and seepage. Herbicide application. $1,050 Paint frames and replace signs. $4,000 Revegetate bare areas. Perform weed control measures and CCSP to continue operations to control prairie dogs. Mowing & herbicide $31,200 Cottonwood Creek application. Phase I & II Clean out pipe and verify operation. $800 Regrade area downstream of the bridge and revegetate the area. $5,000 Weed control scheduled in 2014. Additional re-vegetation and weed $20,700 control planned for 2015. Cottonwood Perimeter Install boulder edge and aggregate for maintenance pad above water Road Wetlands $8,500 surface. Paint frames and replace signs $3,800 Cherry Creek at 12-Mile Perform weed control and reseeding work. Annual Report. $7,000 Park Phase I Cherry Creek at 12-Mile Perform weed control and re-vegetation work including seeding, $22,400 Park Phase II additional shrubs, signage and temporary construction fence. Mtn/Lake Loop Regrade area adjacent to boathouse to divert water to grass area and continue with weed control and re-vegetation. Annual Reporting. Shrub $14,650 replacement. East Boat Ramp Monitor condition. Include additional shoreline stabilization in 5-yr CIP $800 budget. Repair area below the north curbout. East Shade Shelter Monitor condition. Include additional shoreline stabilization in 5-yr CIP $5,700 budget. Fill area under the paved access Repair undercut and eroded areas. $4,500 Tower Loop Paint frame and replace signs. $3,100 General Signage Paint frames and replace signs. $3,400 Total $156,600

5-17

2014 ANNUAL REPORT ON ACTIVITIES

6 RIPARIAN AND WETLANDS PROTECTION Wetlands and riparian areas occur as natural buffers between the uplands and Cherry Creek, Cherry Creek Reservoir, and its tributaries. They act as natural filters of nonpoint source pollutants,which include sediment, nutrients,and pathogens, and can play a significant role in managing adverse water quality impacts in the basin. In addition, wetlands and riparian areas can help decrease the need for costly stormwater and flood protection facilities. The functions of wetlands and riparian areas include water quality improvement; stream shading; flood attenuation; shoreline stabilization; ground water exchange; and habitat for aquatic, semiaquatic, terrestrial, and migratory species. Loss of these areas allows for a more direct contribution of pollutants to receiving waters. The pollutant removal functions associated with wetlands and riparian area vegetation and soils combine the physical process of filtering and the biological processes of nutrient uptake and denitrification and may stabilize the recharge of shallow aquifers in a manner that supports streamflows of longer natural duration. Wetlands and riparian areas can play a critical role in reducing pollution by intercepting surface runoff, subsurface flow, and certain ground water flows, which can process, remove, transform, and store sediment, nitrogen, phosphorus, and some heavy metals.

6.1 Regulatory Protection Regulation 72 recognizes the importance of protecting floodplains, riparian corridors, and other environmentally sensitive lands through public acquisition or conservation easement. Restoration of the same lands to reduce nutrients entering the channel by controlling erosion through re-vegetation, or other means, is encouraged. Riparian areas and wetlands are protected in the Cherry Creek basin by Regulation 72 as Stream Preservation Areas, providing special standards and procedures for land disturbances in riparian or wetland areas. Stream Preservation

6-1

Areas are defined as those areas within the Cherry Creek watershed that transport a higher percentage of stormwater runoff and associated pollutants to the water system and reservoir. Stream Preservation Areas include; Cherry Creek Reservoir, all of Cherry Creek State Park, surface drainage and discharges to the park within 100 feet of the park boundary, lands overlying the Cherry Creek 100-year floodplain, and all lands within 100-year floodplain of Cherry Creek tributaries, as defined by the Urban Drainage and Flood Control District.

Regulation 72 requires additional Best Management Practices (BMPs) for all land disturbances within a Stream Preservation Area which includes construction and post- construction BMPs. Examples of such BMPs include, constructed wetlands basins, sand filter basins, porous landscape detention, and porous pavement detention. Wetlands and riparian areas are also federally protected as Waters of the United States under section 404 of the Clean Water Act. Land disturbances that include discharge of dredged or fill material to wetlands must obtain authorization for the discharge from the United States Army Corps of Engineers.

6.2 Land Development Activities In 2014, the Authority reviewed all land development activities in the basin for point and non-point source pollutant impacts, water quality considerations, and activities in Stream Preservation Areas that may have affected wetlands and riparian areas. The Authority reviewed 14 land development activities that occurred in a Stream Preservation Area and provided comments to the land use agency. The type of projects included residential construction, stormwater drainage easement, a recreation center expansion, transportation construction, stream reclamation, utility line, and a lift station. The Authority recommended construction and post-construction BMPs in compliance with Regulation 72 to protect wetlands and riparian areas. 6.3 Protection, Enhancement, and Restoration Actions In the Cherry Creek basin, wetlands and riparian areas have been affected by construction, filling, channelization, urbanization, and the construction of the reservoir. Urbanization in the basin has increased the rate, volume, duration, and frequency of runoff during storm events, resulting in significantly higher stream erosion rates than from undisturbed watersheds. Urban runoff was identified

6-2

as a major contributor of phosphorus loads to the reservoir during the Clean Lake Study of Cherry Creek Reservoir, degrading the water quality. The Authority has implemented protection, enhancement, and restoration actions in the basin for channel or stream stabilization, and has quantified the amount of nutrient reduction as a result of these projects. Channel or stream stabilization means the activities used to minimize erosion and sedimentation within a surface water or stormwater-runoff conveyance. Channel or stream stabilizations are designed based on hydrology of the tributary watershed that factors in storm runoff rate, volume, frequency, and duration from projected future development conditions. Stabilization activities in the basin include excavation and re-grading; placement of fill; construction of check structures, drop structures, and channel bed and bank protection measures; and placement of vegetation that protects the channel area of the conveyance. Channel or stream reclamation also means additional measures or enhancements to channel or stream stabilization that typically include riparian and floodplain vegetation plantings and construction of channel cross-sections that result in more frequent connection and flooding of the overbank area. Riparian vegetation promotes filtration of fine particles with attached nutrients, and over-bank flooding promotes additional filtration and, to some extent, infiltration, both of which reduce nutrient loads and concentrations. Therefore, the benefits from stream reclamation include the reduction in sediment and nutrients (i.e., phosphorus and nitrogen) transport from the main channel, as well as reduction in nutrient loads from riparian and floodplain vegetation through more frequent floodplain inundation. The design of channel and stream reclamation projects must also recognize the fact that urban development in the watershed has significantly altered the hydrologic regime.. The protection, enhancement, and restoration actions of the Authority have reduced nutrient contributions to the reservoir and have provided recreational and aesthetic value to the watershed. One of the main focuses of the Authority is re-integrating the stream channel and floodplain along the corridor of Cherry Creek and its tributaries. By reconnecting the channel and floodplain, more frequent storm flows spill out of the channel onto the riparian and floodplain area, thus reducing stream velocities and increasing

6-3

filtration/infiltration on the overflow banks. Revegetation along the corridor with grasses, shrubs, and trees provide an aesthetic corridor buffer and promote enhanced riparian habitat.Re-establishment of riparian habitat also benefits many animal species that rely on riparian areas for at least part of their lives. The following measures have been implemented in the basin:

. Reduction of stream flow velocities in certain areas in the basin by reducing longitudinal channel grade and constructing drop structures that anchor the channel and floodplain cross-section. These structural components stabilize both the channel and buffer area (between the outer edges of the floodplain and the channel) against continued channel and riparian area degradation.

. Maintenance of long-term stability and water quality benefits in the basin, and channel geometry based on storm flows that reflect changes in watershed hydrology due to urbanization. Watershed development increases frequency, duration, and magnitude of storm runoff, all factors which influence channel geometry. When channel geometry is based on runoff from an urban watershed, the design approach is more appropriately referred to as reclamation, instead of restoration (i.e., pre-urbanized geometry). If an urban stream is “restored” instead of “reclaimed”, there is a greater risk of failure because the restored channel will eventually change geometry to reflect increased runoff from an urban watershed.

. Incorporation of trails has been incorporated along and across the corridor in many areas which encourage public use and connectivity with the stream corridor amenities and neighborhoods. Recreation trails also serve as access locations for routine channel maintenance activities that help preserve flood control and water quality protection benefits of channel reclamation. Often, the trail crossings become part of the drop structures used to reduce longitudinal channel grades, thereby integrating flood control, water quality, and recreation benefits into a multi-purpose project.

6-4

The Authority encourages local governments to collaborate with other entities in pursuing easements, ownerships, and rights to protect the streams, riparian corridors, tributaries, and wetlands in the Cherry Creek watershed. As part of its Watershed Plan efforts, described in other sections of this report, the Board and TAC jointly prioritized future work plan efforts, choosing among several identified likely pollutant sources and management strategies that could be implemented. The highest ranking priority, by far, was stream erosion and the need to continue to implement erosion control strategies. Management options chosen to prevent and control stream erosion that have received the most support from Authority include: . Protecting riparian zones through stream buffer programs; . Being preemptive and performing stream reclamation projects before the streams are eroded due to development (i.e., before they “unravel”); and . Studying the impacts of water development and increasing alluvial well withdrawals on riparian vegetation. It is believed that if stream reclamation projects can be identified and the channels protected before they unravel, the reclamation approach can be more surgical with improvements that are constructed in specifically identified locations at less cost of an entire stream reclamation project. The following projects are examples of riparian and wetland restoration in the Cherry Creek basin.

McMurdo Gulch

The McMurdo Gulch stream restoration project consisted of restoring and stabilizing nine areas along 3 miles of McMurdo Gulch. Stabilization measures consisted of a combination of ungrouted boulder drop structures, void-filled rock channel lining, and buried riprap bank projection. The McMurdo Gulch project was authorized under an Army Corps of Engineers Nationwide Permit. The project impacted 2.21 acres of Waters of the U.S. including 1.03 acres of wetlands. Mitigation

6-5

for the project impacts was required and included planting wetland, riparian, and upland seed mixes in the disturbed areas. Wetland plugs were harvested and transplanted within the restored wetlands areas, and sandbar willow stakes and fascines were harvested from local areas and planted in the project area. The stream restoration activities and mitigation have created conditions favorable for the establishment of wetland vegetation along McMurdo Gulch within the project area.

Cherry Creek Ecological Park

The Cherry Creek Ecological Park project area was severely degraded, banks were eroded resulting in steep slopes and material sloughing, and there was lateral channel migration. This resulted in the loss of wetlands and upland vegetation due to lowering of the water table by the streambed erosion. A combination of a natural bio-engineering approach connecting the streambed to the overbanks and a more engineered approach where topography constrains the channel were used. In some locations, essentially all of the existing channel bank and riparian vegetation had to be removed and replanted due to the substantive changes in channel geometry necessary to accommodate topographic and floodplain limitations. The project was designed to raise the streambed and reestablish the water table to prevent further loss of vegetation and to restore and enhance wetland and riparian functions of Cherry Creek.

Cherry Creek Stream Stabilization at 12-Mile Park

The 12-Mile Park project area had severe damage to bank vegetation and channel erosion throughout the area where human, dog, and horse activity was concentrated. Stream stabilization to this area was completed in 2014 and included repair of the east bank of the dog park area, and repairs to groundwater wetlands, which help prevent erosion. In 2014, the Cherry Creek Basin Water Quality Authority was awarded the Colorado’s Best of 2014 honor award for outstanding achievement on this project by the Colorado Association of Stormwater and Floodplain Managers.

6-6

2014 ANNUAL REPORT ON ACTIVITIES

7 MONITORING The Authority continued to implement its routine annual water quality monitoring program in the Cherry Creek Reservoir and basin, which has been monitored since 1992. The program monitors reservoir and tributary water quality, inflows and outflow, loads and export, surface and groundwater quality in the watershed, and PRF effectiveness. In the summer of 2008, the Authority implemented a destratification system to help reduce internal nutrient loading, reduce available habitat for nuisance filamentous cyanobacteria, and to ultimately reduce algal biomass (chlorophyll a) in the reservoir. The destratification system was operated seasonally through 2013 with mixed results. In 2013, the Authority began development of a hydrodynamic reservoir model to better understand the mechanisms that affect algae growth with and without destratification management. In 2014, the destratification system was not operated specifically to examine, in the absence of continuous mixing, the response of the algae community in terms of composition, biovolume and biomass, using the current lab. The Authority changed the algae laboratory it used in 2009, resulting in different algae methodologies used before and after 2009. Also, the destratification system first became operational in 2008. All algae data collected for the pre-destratification period was analyzed by the previous lab. Thus, in 2014, the Authority collected data for a year without destratification using its current lab and algae analysis methods. This was done for comparative purposes, and to assit the reservoir modeller with interpretation of previous data. Baseline and supplemental cyanotoxin monitoring data were also collected during 2014 to document conditions without destratification. 7.1 Sampling Sites In 2014, water quality sampling routinely occurred at the same three sites in Cherry Creek Reservoir (Map 7-1) and along a transect to help spatially evaluate dissolved oxygen conditions. The reservoir tributary inflows (Cherry Creek and Cottonwood Creek ) were monitored just upstream of the reservoir and flows at the dam outlet were monitored to develop an annual water balance and phosphorus mass balance for the reservoir. The Authority continued to monitor sites upstream and downstream of its PRFs on Cottonwood Creek and McMurdo Gulch to evaluate their effectiveness of reducing suspended solids and phosphorus. In 2013, the Authority established a new monitoring site on the mainstem of Cherry Creek at EcoPark to evaluate the stream reclamation project in the same context.Watershed monitoring included an additional seven surface water sites along Cherry Creek, from Castlewood Canyon to Cherry Creek Reservoir and seven alluvial groundwater well locations from Franktown to Cherry Creek Reservoir . A comprehensive Annual Monitoring Report provides additional discussion of

7-1

the Authority’s 2014 baseline and supplemental monitoring activities, along with site locations and sampling frequency ; the body of this report is included in the Appendix.

MAP 7-1: MAP OF MONITORING SITES

7-2

7.2 Reservoir Water Quality Presented below is a summary of water quality conditions measured in Cherry Creek Reservoir during the 2014 water year (WY), including a summary of the past 23 years of monitoring. The 2014 flows, loads, and flow-weighted concentrations are based on the WY designation (October 2013 - September 2014); all historical flows, loads, and flow-weighted concentrations represent WY conditions. Additonal data and analyses are available in the 2014 Annual Monitoring Report in the Appendix.

7.2.1 2014 RESERVOIR WATER QUALITY

In 2014, the July through September mean chlorophyll a content in Cherry Creek Reservoir was 24.4 µg/L, which exceeded the site-specific standard of 18 µg/L. This is the fifth consecutive year when the seasonal mean chlorophyll a content has exceeded the standard. As a result, the reservoir is not in attainment of the site-specific chlorophyll a standard, given an allowable exceedance frequency of once in five years. The 2014 WY flow-weighted total phosphorus concentration for all of the sources of inflow to the reservoir was 190 µg/L. This concentation is less than the Authority’s goal for a flow-weighted total phosphorus concentration of 200 µg/L for sources of inflow, which is essentially the same as the background phosphorus concentration observed in the upper portion of the watershed.

7.2.1.1 Chlorophyll a

The annual pattern of chlorophyll a concentrations was quite variable throughout the 2014 WY. From October 2013 through September 2014, chlorophyll a concentrations ranged from 6.1 µg/L in late June to 43.3 µg/L in mid-February (Figure 7-1), with a 2014 WY mean chlorophyll a concentration of 23.4 μg/L. During the summer, the reservoir experienced three peak algal bloom events characterized by relatively high chlorophyll a concentrations (i.e., > 30 µg/L). In early June, a nuisance filamentous cyanobacteria bloom responded to optimal growing conditions (i.e., water temperature, nutrients, and sunlight) in the reservoir and raised concerns regarding the protection of the recreational uses. The bloom continued for approximately two weeks when the population suddenly crashed (died off) in late June following a wind-driven mixing event for the reservoir. By contrast, the reservoir experienced a “clear water” phase just prior to the June bloom, and achieved its highest clarity since 1988. The algal blooms in July responded in similar fashion to the cyanobacteria bloom, yet more beneficial algal species (cryptophytes and diatoms) were responsible for these events. During the regulatory growing season, chlorophyll a concentrations averaged 34.6 µg/L in

7-3

July, and 19.3 µg/L for August and September which resulted in a seasonal mean concentration of 24.4 µ/L.

FIGURE 7-1: CHLOROPHYLL A (µG/L) CONCENTRATIONS IN CHERRY CREEK RESERVOIR, 2014 WY

7.2.1.2 Long-Term Chlorophyll a Concentrations

The long-term chlorophyll record shows considerable variability and there is no trend in the seasonal mean chlorophyll a concentration over time (Figure 7-2). Patterns in the data may correspond to different annual conditions (e.g. dry summer, 2002; wet summers, 2007 and 2009) or reservoir destratification management (2008-2013). It is noted that the reservoir met the cholorophyll a standard from 1989 through 1996, and did not meet the standard from 1997 through 2004. More recently, the standard was met from 2005 through 2009 but not from 2010 through 2014. Based on the 95% confidence intervals shown on Figure 7-2, there is a measurable difference between these two recent periods (2005-2009 and 2010-2014)5. The years when the destratification system was operated are also shown on

5 In addition, Hydros Consulting (one of the Authority’s consultants), using 3 different statistical tests (two-sample t test, Wilcoxon-Mann- Whitney rank sum test, and the Markov-Chain-Monte-Carlo permutation test, showed that the July-September average chlorophyll a value for 2014 is statistically lower than the value computed for 2010. (Memorandum dated February 3, 2015 from Hydros Consulting Inc. to Leonard Rice Engineers.)

7-4

Figure 7-2. In the summer of 2008, the seasonal operation of the reservoir destratification system began and continued through 2013. In 2014, the destratification system was not operated specifically to examine the phytoplankton community dynamics in terms of composition, biovolume, and biomass (chlorophyll a) in the absence of continuous mixing by the destratification system. Under destratification management, the latter period from 2010 through 2013 represented a new set of conditions for the reservoir. The 2010 seasonal mean chlorophyll a concentration (31.0 µg/L) represents the highest seasonal level observed during destratification operation, and highlights the propensity of algae to respond to optimal growing conditions. The 2011 through 2013 seasonal mean chlorophyll a concentration averaged 28.6 µg/L, and is considerably greater than the chlorophyll a standard. While the destratification system was not operated in 2014, the chlorophyll a concentration remained relatively high at 24.4 µg/L.

Period of Destratification

FIGURE 7-2: SEASONAL MEAN (JULY TO SEPTEMBER) CHLOROPHYLL A CONCENTRATIONS MEASURED IN CHERRY CREEK RESERVOIR, 1987 TO 2014

7.2.1.3 Bioavailable Phosphorus and Nitrogen

The reservoir continues to experience internal nutrient loading, and as a result, the algal community responds to the influx of soluble reactive phosphorus (SRP) and dissolved inorganic nitrogen (DIN) that is released from the sediment. Internal nutrient loading occurred from approximately late May though late August (i.e., 7 m SRP and DIN) and was facilitated by the low dissolved oxygen concentrations (i.e., <2 mg/L) near the water/sediment interface. The nuisance filamentous cyanobacteria population responded quickly to the release of SRP in late May (Figure 7-4). Cyanobacteria are unique in terms of

7-5

their nutrient requirements because they do not need a balanced supply of phosphorus and nitrogen to grow well. Cyanobacteria can fix atmoshperic nitrogen to supplement their DIN requirements rather than incorporating nitrogen from the water. The internal release of DIN (Figure 7-4) began later than the SRP release and the peak concentrations were observed when the nuisance filamentous cyanobacteria bloom was crashing and the cryptophyte – diatom bloom was beginning in July. A combination of both SRP and DIN nutrient release from the sediment facilitated the algal blooms in July. There was no indication of SRP or DIN limitation during the summer 2014; although the data revealed a rapid uptake of SRP in the photic zone in mid-July which corresponded to the algal bloom (Figure 7-4).

FIGURE 7-3: SOLUBLE REACTIVE PHSOPHORUS AND CHLOROPHYLL A CONCENTRATIONS MEASURED IN CHERRY CREEK RESERVOIR, 2014 WY

7-6

FIGURE 7-4: DISSOLVED INORGANIC NITROGEN AND CHLOROPHYLL A CONCENTRATIONS MEASURED IN CHERRY CREEK RESERVOIR, 2014 WY

7.2.1.4 Long-Term Total Phosphorus and Total Nitrogen

Routine monitoring data collected since 1987 indicates a general increasing pattern in summer mean total phosphorus concentrations in the upper three meters (i.e., photic zone) of the reservoir (Figure 7- 5). In 2014, the July through September (seasonal) mean concentration of total phosphorus was 87 μg/L, and it is similar to the long-term median value of 89 µg/L. The 2011, 2012, and 2013 seasonal mean total phosphorus concentrations reflect the more uniform reservoir conditions created under destratification management as well as the phosphorus incorporated into algal biomass. These three years (2011, 2012, and 2013) exhibited the highest seasonal mean TP concentration on record; based on a comparison of 95% confidence intervals, there was a notable decrease in 2014 (see Figure 7-5). The 2014 seasonal mean total phosphorus concentration is typical of Reservoir conditions absent the destratification system and reflects the variable algal biomass conditions observed during the July to September period. When the 2014 Reservoir total phosphorus conditions are placed in the context of the Commission’s interim total phosphorus value for lakes and reservoirs (> 25 acres), the seasonal total phosphorus concentration (87 µg/L) was slightly greater than the interim value (83 µg/L).

Period of Destratification

FIGURE 7-5: SEASONAL MEAN (JULY TO SEPTEMBER) TOTAL PHOSPHORUS CONCENTRATIONS (µG/L) MEASURED IN CHERRY CREEK RESERVOIR, 1992-2014

The seasonal mean total nitrogen concentrations in the photic zone have remained relatively stable over the monitoring period and show no long-term trend. In 2014, the July through September mean total nitrogen concentration was 904 μg/L (Figure 7-6), and it slightly less than the long-term median value of 914 µg/L. When the 2014 Reservoir total nitrogen conditions are placed in the context of the commission’s interim total nitrogen value for lakes and reservoirs (> 25 acres), the seasonal mean total nitrogen concentration (904 μg/L) was slightly less than the interim value (910 µg/L), while the long- term median concentration is slightly greater than the interim value.

7-7

Period of Destratification

FIGURE 7-6: SEASONAL MEAN (JULY TO SEPTEMBER) TOTAL NITROGEN CONCENTRATIONS (µG/L) MEASURED IN CHERRY CREEK RESERVOIR, 1987 - 2014

7.2.1.5 Temperatures and Dissolved Oxygen

The Authority maintains an array of thermistors to evaluate thermal conditions in the reservoir as well as to examine factors that contribute to periods of low dissolved oxygen conditions in the reservoir. In addition, the Authority generally performs over 100 temperature and dissolved oxygen profiles of the water column to document conditions. Based on the thermistor data, the reservoir experienced 46 days of thermally stratified conditions in 2014 (Figure 7-7) which is greater than the average number of days (24 days) that the reservoir was thermally stratified when the destratification system was operating. The reservoir continued to show periods of thermal stratification, typically the result of weather events, which corresponded to periods of low dissolved oxygen conditions near the water/sediment interface and facilitated internal nutrient loading. When the reservoir temperature conditions are placed in the context of the temperature standards for Warm Water lakes and reservoirs, the reservoir was in attainment of both the acute and chronic temperature standards for the summer months (insufficient winter data).

7-8

FIGURE 7-7: TEMPERATURE PROFILES RECORDED DURING CONTINUOUS MONITORING AT SITE CCR 2 COE INFLOWS DURING 2014

The reservoir dissolved oxygen conditions were evaluated in the context of the warm water dissolved oxgyen standard of 5 mg/L for lakes and reservoirs. The reservoir (i.e., 0.5 – 2 m layer) was in attainment of the dissolved oxygen standard in 99 of the 100 profiles collected from the reservoir, with the single excursion (4.2 mg/L) occuring in late August following a storm event. Low dissolved oxygen conditions (i.e., <2 mg/L) near the bottom of the reservoir began in mid-May and persisted throughout most of the summer months until early September (Figure 7-8). The peak dissolved oxygen conditions observed in the upper layers of the Resevoir in June, July and August are closely coupled with algae photosynthesis and the release of oxygen as a metabolic by-product. As with other years, low dissolved oxygen was observed near the bottom of the reservoir. An initial review of the dissolved oxygen isopleths for 2012 (GEI, 2013, Figure 14) and 2014 (GEI, 2015, Figure 15) show the conditions in 2012, a year with destratification, may have been worse that in 2014 (Memorandum dated February 3, 2015 from Hydros Consulting to Leonard Rice Engineers, Inc.).

7-9

FIGURE 7-8: DISSOLVED OXYGEN (MG/L) PROFILES RECORDED DURING ROUTINE MONITORING AT SITE CCR 2 IN 2014 WY

7.3 2014 Reservoir Inflows – Outflows and Total Phosphorus Loads A primary objective of the Authority’s monitoring program is to document the various sources of phosphorus and nitrogen that can limit or enhance algal growth in a reservoir, either within the reservoir (internal loading) or from outside the reservoir (external loading). Fish and plankton excrement, direct sediment re-supply, and the decay of organic matter are all internal sources of nutrients in a reservoir. Based on modeling efforts, net internal phosphorus loading to Cherry Creek Reservoir has been estimated to be 2,000 lbs/yr. Other studies evaluating internal loading using a variety of methodologies suggest phosphorus loading ranges between 810 lbs/yr and 1,590 lbs/yr, and alluvial phosphorus loads of approximately 1,170 lbs/yr. External sources of nutrients include inflow from streams and precipitation, which carry nutrients from soil erosion, agricultural and municipal runoff, treated wastewater, and airborne particulates. Phosphorus loading was determined for several primary sources and exports in 2014, including the tributary streams Cherry Creek and Cottonwood Creek, and the reservoir outflow (export) as summarized in Table 7-2. Total phosphorus loading to the reservoir from surface flows of Cherry Creek and Cottonwood Creek was estimated at 6,075 lbs for the 2014 WY (Table 7-1). The annual flow-weighted phosphorus concentrations from surface flows of Cherry Creek and Cottonwood Creek were 235 µg/L and 72 µg/L, respectively. When the other two sources of inflow, precipitation and alluvium, are considered, the external total phosphorus load and flow-weighted phosphorus concentration for all sources of inflow to the reservoir were 7,419 lbs and 190 µg/L, respectively, during the 2014 WY (Table 7-1). The reservoir retained 3,011 lbs of phosphorus in 2014 and discharged 4,408 lbs through the outlet structure (i.e., export). The flow-weighted total phosphorus concentration in the outlfow was 119 µg/L.

7-10

TABLE 7-1: NORMALIZED PHOSPHORUS LOADS, EXPORTS, AND FLOW-WEIGHTED PHOSPHORUS CONCENTRATIONS FOR CHERRY CREEK RESERVOIR, 1992 TO 2014

Loads and Exports Flow-weighted Concentrations Cherry Cherry Cottonwood External Reservoir Cottonwood External Reservoir Creek Water Creek Creek Flow- Flow- Export Flow- Creek Load Load1 Export Flow- Year Load weighted weighted weighted (lbs/yr) (lbs/yr) (lbs/yr) weighted (lbs/yr) (µg/L) (µg/L) (µg/L) (µg/L) 1992 3,024 334 4,796 1,328 270 170 246 91 1993 1,521 229 3,162 1,000 251 187 198 92 1994 2,525 168 3,907 964 248 88 196 73 1995 2,064 1,396 5,556 1,366 189 203 178 63 1996 2,548 600 4,509 1,382 232 332 208 87 1997 2,131 616 4,299 1,129 264 184 200 88 1998 10,007 1,838 13,574 4,139 279 178 237 81 1999 10,495 1,290 16,403 6,388 268 135 234 102 2000 11,801 1,379 14,582 4,113 312 159 265 83 2001 6,283 2,101 10,068 5,524 257 130 198 127 2002 2,091 438 3,746 1,971 221 88 171 107 2003 6,199 1,052 9,359 4,774 287 138 229 140 2004 4,307 1,640 7,377 2,682 247 157 201 96 2005 8,757 1,347 11,518 3,964 247 120 208 78 2006 3,568 1,224 6,174 3,251 231 132 187 115 2007 15,987 2,072 19,601 7,891 295 149 254 115 2008 7,254 832 9,384 4,785 205 84 177 104 2009 13,591 936 16,052 9,483 276 62 218 148 2010 12,049 1,037 14,488 7,880 239 78 200 115 2011 7,341 652 9,301 4,114 263 81 212 108 2012 5,531 588 7,462 3,478 244 91 200 118 2013 6,043 846 8,588 3,378 294 59 190 120 2014 5,567 509 7,419 4,408 235 72 190 119

Mean 6,551 1,005 9,188 3,887 255 134 209 103 Median 6,043 936 8,588 3,964 251 132 200 104 1Includes ungaged residual load

7-11

7.4 Reservoir Management Strategy In 2008, the Authority implemented the reservoir destratification management strategy based upon aeration to control nuisance algal growth (large filamentous cyanobacteria). The destratification system was designed, in part, to reduce the periods of thermal stratification as well as to reduce suitable habitat conditions for large filamentous cyanobacteria by vertical mixing6. Over time, it was estimated that, by oxygenating the bottom sediments, the destratification system could reduce the internal phosphorus load to approximately 50 percent of historical conditions by limiting the periods of stratification (AMEC 2005). In addition, the destratification system was anticipated to reduce both the seasonal mean and peak annual chlorophyll a concentrations in the reservoir by controlling nuisance cyanobacteria blooms. The uncertainty associated with these objectives lies both in the timing (when) and magnitude (how) of potential benefits that the reservoir might experience. From 2008 through 2013, the Reservoir revealed mixed results when placed in the context of design objectives for the destratification system. The temperature data indicate that the periods of thermal stratification were reduced when the destratification system was operated, yet dissolved oxygen conditions near the bottom remained conducive (i.e., <2 mg/L) for internal nutrient loading. As a result, the internal nutrient loading continued to supply bioavailable SRP and DIN that facilitated algal production. Despite the destratification system’s apparent inability to completely mix oyxgenated water all the way to the bottom of the reservoir, the system did sufficiently mix the bioavailable nutrients released from the sediment into the photic zone for uptake by algae. This mixing created more uniform conditions in the reservoir and facilitated the growth of algae as indicated by the elevated chlorophyll a levels during the growing season. This highlights the propensity of algae to respond to optimal growing

6 Note that the destratification system was originally designed to achieve the following goals: 1) reduce the release of phosphorus and nitrogen nutrients from the bottom sediments into the water column of the reservoir in a typical year by 810 lbs/yr and 1140 lbs/yr, respectively; 2) decrease the seasonal mean (July-Sept) chlorophyll a concentrations by approximately 8 µg/L under typical year conditions; 3) decrease annual peak chlorophyll a concentrations by up to 30 µg/L; 4) increase dissolved oxygen concentrations in the deepest and most vulnerable zones of the reservoir into the range of 5 mg/L; and 5) reduce the production of blue-green algae by making the habitat of the reservoir less suitable for the production of blue-green algae via vertical mixing. (AMEC Earth & Environmental, Inc., Alex Horne Associates, Hydrosphere Resource Consultants, Inc. (December 5, 2005). Feasibility Report Cherry Creek Reservoir Destratification).

7-12

conditions (see Section 7.2.1.2). There has also been uncertainty regarding the destratification system’s ability to control nuisance cyanobacteria. This was confounded by a change in the algal identification laboratory that occurred in 2009, which resulted in algal identification being performed differently by each laboratory. The change in laboratories (2009) coincided closely with the initiation of operation of the destratification system (2008). At the request of the reservoir modeling consultant, the Authority decided to not operate the destratification system in 2014. That way, it could specifically examine the response of the nuisance cyanobacteria and the rest of the algae community in terms of both composition and biovolume as well as biomas (i.e., chlorophyll a), both with and without destratification utilizing the same laboratory. The algal biovolume data are discussed herein because it provides information relative to the size and density of the algae taxa, as well as provides more information relative to chlorophyll a (algal biomass). 7.5 2014 Phytoplankton and Cyanotoxins One of the objectives of the destratification system is to reduce the suitable habitat conditions for large filamentous cyanobacteria by vertical mixing which should disrupt their ability to efficiently grow near the surface of the reservoir and fix nitrogen from the atmosphere. These types of cyanobacteria can produce toxins that inhibit the growth of competing algae, inhibit grazing by zooplankton that rely on algae as a food source, and harm other beneficial uses. Historically, the nuisance chlorophyll a levels (i.e., > 30 µg/L) during the summer were associated with cyanobacteria blooms7. Starting on June 13, 2014 (after the bloom began), the Authority implemented a cyanotoxin (anatoxins, microcystins, saxitoxins, cylindrospermopsin) monitoring program to document toxin concentrations within the main body of the reservoir and at the swim beach area on a weekly basis, including other opportunistic areas depending upon the visual presence of cyanobacteria. During the summer months of 2014, the reservoir experienced three events when chlorophyll a concentrations were greater than 30 µg/L (Figure 7-1). The event in early June was dominated by nuisance filamentous cyanobacteria (Anabaena flos-aquae) which accounted for 84% of the total algal biovolume (Figure 7-9). During this event, the filamentous cyanobacteria grew extremely well and created a visually dense layer of cyanobacteria near the surface of the reservoir. On June 10th, the microcystin concentrations in the main body of the reservoir were 10 µg/L, which is on the threshold of low to moderate risk for

7 This has also been noted in other locations. For example, the Maryland Department of the Environment found that exceedances of a 30 µg/L chlorophyll a threshold are associated with a shift to cyanobacteria assemblages (MDEP, 2012). Similar findings were made for lakes in Minnesota, where all high risk microcystin concentrations were associated with chlorophyll a greater than 30 µg/L, while moderate risk microcystin toxin levels were not encountered until blooms exceeded 30 µg/L (Lindon and Heiskary (200*) and Lindon and Heiskary (2009)).

7-13

recreational contact based on the World Health Organization guidelines. In days following the initial bloom, the microcystin concentrations were <1 µg/L which posed no concern from a recreational standpoint. However, on June 17th, the cyanobacteria bloom drifted along the face of the dam and accumulated a very dense layer which posed a high risk for recreational contact based on a microcystin concentration of 24 µg/L. All other toxin concentrations were reported as non-detects during the bloom. On June 23th, a wind-driven mixing event completely mixed the reservoir from the surface to the bottom and caused the cyanobacteria bloom to crash (die off). In days following the cyanobacteria crash, the clarity of the reservoir greatly increased to a Secchi depth of 3.7 m which is the deepest depth recorded for the reservoir and all of the cyanotoxin levels were reported as non-detects. The nuisance cyanobacteria remained at very low or non-detect levels for the remainder of the summer season. The other two blooms that exhibited chlorophyll a concentrations greater than 30 µg/L were dominated by diatoms (51%) and cryptophytes (32%) in early July and by dinoflagellates (77%) in late July. These algae are considered more beneficial in terms of a food source for zooplankton and fish, and posed no risk to recreational contact. Reservoir conditions that contributed to these algae blooms are discussed in the 2014 Annual Monitoring Report in the Appendix.

Cryptophytes Diatoms Chrysophytes Dinoflagellates Cyanobacteria Euglenoids Chlorophytes

100

80

60

40

20 Percent Relative Biovolume

0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

FIGURE 7-9: PERCENT RELATIVE BIOVOLUME OF ALGAL GROUPS FOR EACH ROUTINE PHOTIC ZONE COMPOSITE SAMPLE COLLECTED IN CHERRY CREEK RESERVOIR, 2014

7.6 Long-Term Phytoplankton In previous years, phytoplankton density data were compared for time frames with and without destratification. In hindsight, however, given the laboratory change, we now recognize it was inappropriate to compare the data from the two different labs and conclude that the destratification system resulted in a reduction cyanobacteria cell counts. Thus, the years from 2009 through 2014 will be evaluated, as they represent a period of consistent methodologies, with (2009-2013) and without

7-14

(2014) destratification. In 2014, cryptomonads, diatoms, and green algae remained numerically dominant algal types in terms of algae biovolume (Figure 7-10). These taxonomic algal groups are a preferred food source over cyanobacteria by zooplankton and fish. From 2009 through 2014, algal percent relative biovolume has been variable among the years (Figure 7-10). Reservoir conditions in 2009 were different from the other years in the sense that the seasonal mean chlorophyll a concentration was low (13.2 µg/L) compared to other years with destratification when concentrations ranged from 24.1 µg/L to 31µg/L (Figure 7-2). From 2010 through 2013 when chlorophyll a concentrations remained relatively high (i.e., ~28 µg/L), the relative biovolume data showed more variability with diatoms, euglenoids, and cyanobacteria (Figure 7-10). The relative biovolume for both cryptomonads and green algae were consistent during this period. In terms of biovolume, cyanobacteria accounted for 17.4%, 4.2%, 18.5%, and 5.3% over the four year period from 2010 to 2013, respectively. Total biovolume data for 1984 to 2014 are found in Table E-3, Appendix E, of the GEI Annual Monitoring Report, which is included as an Appendix to this report. In 2014, some algae groups revealed biovolume conditions that were slightly different than the previous 4 years, yet most of the algae groups revealed conditions within the range of conditions previously observed. In 2014, the green algae revealed greater percentages for both density and biovolume as compared to previous years, while the same metrics for the diatoms were both less than the previous years. Cyanobacteria relative percent density (2.2%) and biovolume (15%) were both in the range of conditions previously observed for the reservoir. Based on Hydros Consulting’s analysis of algal species data from 2009 to 2014, when the same lab was analyzing the data, comparisons were made between years with the destratification system on (2009-2013) and off (2014). Biovolume and density data were analyzed over three different time periods: annual (calendar) year; June – September; and July – September. Hydros concluded that, using these metrics, there is no evidence of cyanobacteria reductions with the use of the destrification system. Also, Hydros compared the one-time July, 16, 2010 results analyzed by the Authority’s previous lab (C.U. Center for Limnology) with pre-2009 results also analyzed by this same lab. Hydros stated it could not conclude that an overall reduction in cyanobacteria has occurred with the use of the existing destratification system operating under current operational parameters. (Memorandum dated February 3, 2015 from Hydros Consulting Inc. to Leonard Rice Engineers, Inc.) The response of the algal community, including nuisance cyanobacteria, to destratification management or its absence is continuing to be studied by the Authority. The Authority will be evaluating the mechanisms and effects that various reservoir conditions have on the biological assemblages as well as the other beneficial uses of the reservoir during its Reservoir Model Project.

7-15

Destratification management may take a considerable amount of time to reduce the sediment oxygen demand and effectively control internal nutrient loading which facilitates the summer algal production.

Cryptophytes Diatoms Chrysophytes Dinoflagellates Cyanobacteria Euglenoids Chlorophytes Miscellaneous 100

80

60

40

20 Percent Biovolume Relative

0 2009 2010 2011 2012 2013 2014 Data are representative of biological production year (calendar year rather than water year). FIGURE 7-10: PERCENT ALGAL BIOVOLUME OF MAJOR TAXONOMIC GROUPS IN CHERRY CREEK RESERVOIR FROM 2009 THROUGH 2014

7.7 Zooplankton Zooplankton density ranged from 139 organisms/L in late March to 1,239 organisms/mL which occurred in early July 2014 (Figure 7-11). Over the WY, the zooplankton assemblage contained a total of nine zooplankton crustacean species—seven cladocerans and two copepods with immature copepodids and nauplius—and nine species of rotifers were collected during the 15 sampling events (Appendix E). There was one species that was collected during all sampling events: a relatively smaller cladoceran (Bosmina longirostris). The immature copepods (copepodids and nauplius) were also observed during all 15 sampling events. The copepod (Diacyclops thomasi) was collected at 14 of the 15 sampling events (Appendix E). Bosmina longirostris have been found to be the dominant cladoceran in other eutrophic lakes (Harman et al. 1995). One rotifer (Keratella cochlearis) was collected during 12 of the 15 sampling events and one cladoceran (Daphnia sp.) was collected during 11 of the 15 sampling events. Cladocera were low in abundance throughout the late winter and early spring; however, they became relatively abundant during mid-May through July 2014. Copepods did comprise the majority of the zooplankton assemblage during most sampling events (Figure 7-11). Both the copepods and rotifers substantially increase their density during the early July algal bloom that was comprised mainly of diatoms and cryptomonads. While the zooplankton assemblage showed some response to the algal assemblages and biomass, there is no statistical correlation between the zooplankton density and chlorophyll a (surrogate for algal biomass). Similarly, there was no correlation between zooplankton density and algal density or algal biomass.

7-16

FIGURE 7-11: TOTAL DENSITY OF ZOOPLANKTON GROUPS AND CHLOROPHYLL A CONCENTRATION BY SAMPLE DATE IN CHERRY CREEK RESERVOIR, 2014 CY

Ideally, the pattern between zooplankton density and chlorophyll a (algal biomass) should be inversely related, as herbivorous zooplankton could theoretically affect algal biomass via grazing pressure, provided planktivorous fish are not suppressing the zooplankton populations (Harman et al. 1995). However, in Cherry Creek Reservoir, the increased abundance of gizzard shad has likely increased the grazing pressure on the zooplankton assemblage, thereby reducing the zooplankton density and reducing their ability to effectively control the algal assemblage. Notably, the cladoceran – Daphnia lumholtzi – was observed in the Reservoir from early August through November 2014. This species is considered an Aquatic Nuisance Species (ANS) and was also observed in 2011 and 2012. This species has two relatively long spines on the head and tail which may affect fish that feed on zooplankton, plus this species may out-compete other native cladocera for resources. 7.8 Water Quality in Cherry Creek from a Watershed Perspective The Authority’s watershed monitoring program includes, in addition to the monthly sites used to monitor PRFs (See Chapter 5 and Map 7-1), seven other surface water sites along the mainstem of Cherry Creek from Castlewood Canyon downstream to the reservoir that are sampled biannually. Monitoring data from four key sites are presented herein – Castlewood Canyon (upstream background), CC-1, CC-4, and CC-9. Site CC-1 is located on Cherry Creek at the confluence with McMurdo Gulch, downstream of Castle Rock. Site CC-4 is located downstream of the confluence with Sulphur Gulch and Parker Water and Sanitation South (PWSD) wastewater treatment facility discharges. Site CC-9 is located just upstream of the reservoir near the Perimeter Road within the park boundary. The distance from the Castlewood Canyon site to the reservoir is approximately 25 miles (see Map 7-1). By comparing differences in concentrations at each of these surface flow stations, the changes in water quality resulting from urbanization can be observed. Little or no change in concentrations can be interpreted as maintaining water quality conditions through the urban corridor, while reduction in

7-17

concentrations indicated that watershed control measures may be improving water quality, and increases in concentrations may indicate other influences outside regulatory control.

7.8.1 NUTRIENTS

The total phosphorus concentrations from 1994 through 2014 show that concentrations entering the reservoir (CC-9) are nearly identical to concentrations representaive of “background” conditions in the watershed at the Castlewood and CC-1 sites (Figure 7-11). Total phosphorus is the measure of the combined impact from total dissolved phosphorus, soluble reactive phosphorus, and particulate forms of phosphorus. The data show typical seasonal variability during the years prior to 2003 when monthly sampling occurred, and that variability is still evident in the more recent years when biannual samples were collected. The data collected at Site CC-4 from 2011 through 2015, showing much lower phosphorus concentrations in the downstream of Sulphur Gulch and the PWSD discharge, reveals the influence of the wastewater discharge on the total phosphorus concentrations in the stream (i.e., less than the other sites), yet as flows continue downstream to the reservoir the concentration increases (i.e., CC-9). In Cherry Creek, a sandy alluvial plains stream, the mixing of surface waters and shallow groundwater results in similar total phosphorus concentrations between both water sources. Water quality controls in the watershed appear to be maintaining or improving total phosphorus levels over time.

FIGURE 7-12: TOTAL PHOSPHORUS CONCENTRATION MEASURED AT CHERRY CREEK SURFACE WATER STATIONS CASTLEWOOD, CC-1, CC-4, AND CC-9

Nitrogen is a nutrient found in several forms (e.g., ammonium (NH4), nitrite (NO2), and nitrate (NO3)), with nitrate being the most important relative to algal production in Cherry Creek. The Authority’s nitrate-nitrogen data from 1994 through 2014 (Figure 7-12) shows that concentrations entering the reservoir (~0.500 mg/L) are greater than “background” conditions (0.050 mg/L) at sites Castlewood and CC-1, but have remained relatively stable over the period of record. The data collected at Site CC-4 (downstream of PWSD) shows the influence of the higher nitrate concentrations in the wastewater

7-18

discharge on surface water nitrate concentrations (i.e., greater than other sites), and since 2002 there has a been an increasing trend in nitrate concentrations at this site. It is important to note that concentrations at Site CC-9 are significantly less than at CC-4, which highlights the ability of the stream corridor to reduce nitrate. This process (dentirification) is a microbially-mediated process that reduces nitrate to nitrite and eventually to nitrogen gas (N2). In essence, the stream is functioning well in terms of nitrate reduction and efforts to maintain or even improve this ecological function, especially related to stream habitat and bank restoration should help maintain this function.

FIGURE 7-13: NITRATE CONCENTRATION MEASURED AT SURFACE WATER STATIONS CASTLEWOOD, CC-1, CC-4, AND CC-9

7.8.1.1 Regulation 85 and Instream Nutrient Monitoring Data

Regulations 85 requires the implementation of a nutrient monitoring program for wastewater treatment plant dischargers. Cherry Creek basin WWTs are required to monitor for total phosphorus and total inorganic nitrogen upstream, downstream, and in the effluent of the effluent prior to discharge.

The instream Regulation 85 data are included here for comparative purposes. Nutrient monitoring results are to be submitted by April 15th of each year, so data are not yet available for January through September 2014. Regulation 85 upstream and downstream nutrient data were available for three of the five WWTFs located in the basin (Parker

7-19

Water and Sanitation District, Pinery Water & Sanitation District, and Arapahoe County Water and Wastewater Authority) and can be found in Tables 7-2 and 7-3 for all available data to date.

Table 7-2. Regulation 85 Monitoring for Instream Phosphorus Concentrations Submitted to Date

Month Reg. 85 Reported Average Monthly Total Phosphorus Concentrations

Arapahoe County Water & Parker Water & Sanitation District Pinery Water & Sanitation District Wastewater Authority Upstream of Upstream of Downstream of Upstream of Downstream of Downstream of WWTF WWTF WWTF WWTF WWTF WWTF (monthly (monthly (monthly mg/L) (monthly mg/L) (monthly mg/L) (monthly mg/L) mg/L) mg/L) Feb-14 Not Available Not Available 0.171 0.09 Not Available Not Available Mar-13 0.115 0.105 0.119 0.137 <0.010 0.049 Apr-13 0.145 0.105 0.127 0.146 0.034 0.067 May-13 0.16 0.145 0.25 0.298 0.018 0.064 Jun-13 0.125 0.13 0.154 0.087 <0.010 <0.010 Jul-13 0.06 0.23 Not Available 0.044 <0.010 <0.010 Aug-13 0.05 0.135 Not Available 0.044 0.072 0.081 Sep-13 0.155 0.255 0.197 0.15 <0.010 0.029 Oct-13 0.75 0.175 0.121 0.052 <0.010 <0.010 Nov-13 0.115 0.12 0.119 0.056 0.016 0.011 Dec-13 0.12 0.12 0.12 0.054 <0.010 0.02

7-20

Table 7-3. Regulation 85 Monitoring for Instream Nitrogen Concentration Submitted to Date

Month Reg. 85 Reported Average Monthly Total Inorganic Nitrogen Concentrations

Arapahoe County Water & Parker Water & Sanitation District Pinery Water & Sanitation District Wastewater Authority

Downstream Upstream of Downstream of Upstream of TN Upstream of TN Downstream of WWTF WWTF WWTF WWTF WWTF (monthly of WWTF (monthly (monthly (monthly (monthly mg/L) mg/L) (monthly mg/L) mg/L) mg/L) mg/L)

Feb-13 Not Available Not Available 0.68 6.76 Not Available Not Available Mar-13 1.42 2.25 0.45 1.91 0.16 2.4 Apr-13 1.41 2.9 0.39 3.92 0.56 0.44 May-13 1.27 2.52 0.85 2.61 0.11 0.81 Jun-13 6.68 2.2 0.41 8.17 Not Detected 0.11 Jul-13 8.81 1.37 Not Available 9.27 Not Detected 0.23 Aug-13 8.2 3.16 Not Available 8.39 0.052 0.5 Sep-13 3.73 1.21 0.35 5.99 Not Detected 0.37 Oct-13 4.74 2.27 0.2 8.08 0.15 1.4 Nov-13 1.89 2.69 0.28 8.09 0.27 3.1 Dec-13 3.48 3.65 0.22 5.74 1.3 3.5

7.8.1.2 Chloride and Sulfate

Chloride is a chemical compound often found in de-icing agents used to control roadway ice and is also utilized in water softeners for in-home use. Chloride concentrations from 1994 through 2014 are shown in Figure 7-13 for the same sites. The data show that chloride concentrations have remained realtively consistent in the upper watershed, although a slight increasing trend is observed over the 20 year period. From 1995 thorugh 2001, the chloride concentrations at sites CC-4 and CC-9 remained relatively consistent from year to year with a slight increase in concentration observed further downstream near the reservoir (i.e., culmination of the watershed). Beginning in 2002, the chloride concentrations began increasing in the watershed likely due to a combination of both urban development and the corresponding use of de-icing agents in the watershed. Over the last five years, chloride concentrations have significantly increased at Site CC-9 before entering the reservoir. This trend was noted in a recent Colorado Department of Transporation Report and a U.S. Geological Survey (USGS) study (Corsi et al. 2015) documenting the increasing chloride concentrations within the Cherry Creek Basin. Both studies attribute the increasing chloride concentrations to the use of road de-icing agents – especially magnesium chloride. The USGS study noted that chloride concentrations have outpaced the rate of urbanization in many watersheds, and that the runoff from winter time use of de-icing agents and other potential sources of chlorides is likely stored in the shallow alluvium and slowly released throughout the

7-21

year. This trend indicates the need for waterhsed controls for de-icing agents through education and use-specific BMPs (requirement of Control Regulation 72).

FIGURE 7-14: CHOLORIDE CONCENTRATION MEASURED AT SURFACE WATER STATIONS CASTLEWOOD, CC-1, CC-4, AND CC-9

Sulfates may be the result of wastewater treatment practices used to reduce phosphorus from discharge. Sulfate concentrations are shown from 1994 through 2014 (Figure 7-14) and indicate the influence of wastewater treatment downstream of Site CC-4 when compared to background concentrations at sites Castlewood and CC-1. Sulfate concentrations continue to increase near the reservoir and both sites (CC-4 and CC-9) reveal increasing concentrations over time. In recent years, sulfate concentrations at Site CC-9 are approaching the 250 mg/L water quality standard for water supply use.

7-22

FIGURE 7-15: SULFATE CONCENTRATION MEASURED AT SURFACE WATER STATIONS CASTLEWOOD, CC-1, CC-4, AND CC-9

7.9 Proposed Modifications to Monitoring Program The Authority recently revised its baseline sampling and analsysis plan and quality assuranace project plan (SAP/QAPP) and will be adding a water quality sampling site on Piney Creek immediately upstream of the confluence with Cherry Creek. This site will document baseline water quality conditions prior to the stream reclamation project on Piney Creek and continue to monitoring post-project conditions. The Authority will also evaluate the pros/cons of operating or not operating the destratification system in 2015 to document the effects of the system on Cherry Creek Reservoir, or the lack thereof. It was suggested by Hydros that the Authority consider sending algae samples to another lab that can report picoplankton and biovolume (while continuing to send samples to its current lab) to obtain site-specific data for Cherry Creek Reservoir (Memorandum dated January 15, 2015, from Hydros Consulting to GEI). This would allow further comparison of data using the two different methods (filtration and settling), similar to the evaluation completed for the July 16, 2010 sample, as described in Section 7.6, page 7-23. 7.10 CDPHE WQCD Data Call In January of 2014, the Division sent out a request for water quality data for the South Platte River Basin for the 2015 triennial review. The data request was for all biological, physical, chemical, and other related data collected throughout the river basin including data from Cherry Creek, Cherry Creek Reservoir and its tributaries. The Authority submitted over 30,000 records of water quality data to the Division using the Division data submittal template. The Authority used its relational database management system to compile and query the requested dataset. Water quality data was provided for all available data for the last ten year period at all monitoring sites including the Cherry Creek monitoring stations (CC-1-9), Cherry Creek Reservoir (CCR1-3, transects, outlet), Cottonwood Creek, McMurdo Gulch, Shop Creek, and various monitoring wells (MW 1-9).

7-23

2014 ANNUAL REPORT ON ACTIVITIES

Our Vision: Water quality in Cherry Creek Reservoir and Watershed that optimizes beneficial uses for the public.

8 WATERSHED PLAN IMPLEMENTATION The Authority began updating its Watershed Plan in 2014. The Watershed Plan was created to serve as a living document to define the pathway to meeting all of our goals and reaching our long-term vision. The overarching goal is preservation of the beneficial uses of the reservoir and streams. This can be viewed as a keystone; all of the Authority’s activities described in this Annual Report are intended to help achieve this goal. The final chapter in the Plan is perhaps the most important chapter. It identifies priorities and an implementation strategy. Proposed action plans are shown for the next few years. Every year, progress is evaluated as part of the Annual Report. The action plans are updated as needed to reflect shifting priorities and to incorporate new knowledge about the reservoir and watershed. The 2014 Action Plan is shown on the next page.

8-1

2014 Proposed Action Plan

Planning and Evaluation Tools Implementation

Build reservoir model to evaluate role of sediments Select, develop, calibrate, & validate reservoir model in nutrient recycling and effects on beneficial uses

By July 2014, identify path forward for Initiate next steps for fate & transport model (e.g., RFP, stream/alluvial fate and transport model contractor selection, partner(s) identification)

Complete GIS-based analyses to "quantify” other Continue to implement CIP projects nutrient contributions (e.g., agriculture, golf courses) as input to stream fate and transport model

Continue to coordinate with CPW on food chain Continue to identify & implement stream reclamation condition/management strategies as related to projects before they “unravel”, and that promote beneficial use protection stream connectivity

Using sediment cores, estimate nutrient release Continue to implement all Reg. 72 requirements and all rates, and releases rate for other related chemicals MS4 permit terms

Develop stream buffer program (including stream Support stream buffer programs for riparian area barriers for animals) protection

Develop educational materials: nutrient reductions Continue watershed monitoring and reservoir programs for agricultural operations to document PRF/stream reclamation results

Identify how member entities are regulating riparian corridors

8-2

8.1 Priorities and Implementation Strategies The 2014 Proposed Action Plan was used by the Authority to guide its 2014 activities. The following hightlights some of our accomplishments during 2014:

. Role of Sediments: In 2014, a comprehensive reservoir water quality model was initiated to better understand the complex relationships among the biotic and abiotic components of the reservoir. This includes evaluating the role of sediments with respect to nutrient recycling and beneficial uses. Next steps: The Authority reservoir modeling committee has identified next steps to evaluate sediment diagenesis functions of the water quality model and will begin calibration of this portion of the model in early 2015.

. Reservoir Model: The reservoir model consultant recommended that CE-QUAL-W2 be used to model Cherry Creek Reservoir. Tasks competed in 2014 include initial review and compilation of water quality, hydrometeorological, and other data; development of the model grid; completion of model thermal simulation calibration runs; investigations to increase understanding of what drives thermal response; and development of an aerator grid for the model.

. Quantify Other Potential Nutrient Contributions: In 2014, a technical plan and scope was developed to complete GIS-based analyses to “quantify” potential nutrient contributions from agricultural lands and animals, golf courses, and airport for inputs into the stream fate and transport model. Next steps: This analysis planned to start in 2015.

. Estimate Nutrient Release Rates using Sediment Cores: Sediment cores were collected from the reservoir and analyzed for nutrients and related parameters (e.g., iron), to assist with calculation of site-specific sediment nutrient inputs.

8-3

. Develop Educational Materials: An educational brochure was developed to help agricultural operations in the Cherry Creek watershed reduce nutrient contributions. It identifies Best Management Practices for operations including livestock grazing, tilled cropland, irrigated and non-irrigated hay land, sod businesses, tree nurseries, and greenhouse operations. The audience is agricultural operators in the basin.

. Continue to Implement CIP Projects: In 2014, the Authority and its partners continued to implement CIP projects including completion of the Cherry Creek Stream Stabilization at 12 Mile Park, in coordination with State Park’s Dog-Off Leash Area (DOLA) Management Plant (see Section 5.2).

. Continue to Identify and Implement Stream Reclamation Projects: The Authority continues to seek and implement stream reclamation projects before the stream “unravels” as development occurs. An example project includes McMurdo Gulch. Projects that promote stream connectivity are also priority projects. Another priority area is to promote longitudinal stream connectivity. An example of this is the Cherry Creek Stream Reclamation Project from Cherry Creek State Park to EcoPark (Phases I to V). Next steps: The design of this project is planned for 2015.

. Continue Watershed and Reservoir Monitoring Program: The Authority continues its monitoring program to document PRF/stream reclamation results and evaluate compliance with water quality standards (see Chapter 7). In 2014, the Authority updated its sampling and analysis plan/quality assurance project plan for the routine monitoring program, including updated documentation of sampling locations, processes, and procedures. The update also included regulatory requirements for sampling, periodic updates and review standards, purposes, and objectives.

. Develop Path Forward for Stream/Alluvial Fate and Transport Model: During 2014, the technical team evaluated potential modeling options for a fate and transport model for Cherry Creek and possibly other tributaries. A preliminary recommendation to consider the use a model similar to QUAL2K was made by the technical team. Next steps: In 2015, the TAC plans to document the pros and cons of QUAL2K and others types of models and identify data needs for such a model to ensure the appropriate data are available to develop and calibrate the model.

THESE ACTIVITIES HELP THE AUTHORITY BETTER UNDERSTAND

THE DYNAMICS OF THE RESERVOIR

AND WATERSHED.

8-4

2014 ANNUAL REPORT ON ACTIVITIES

REFERENCES

AMEC Earth & Environmental, Inc., Alex Horne Associates, and Hydrosphere Resource Consultants, Inc. December 2005. Draft Feasibility Report Cherry Creek Reservoir Destratification. AMEC Earth & Environmental, Inc., Alex Horne Associates, Hydrosphere Resource Consultants, Inc. (December 5, 2005). Feasibility Report Cherry Creek Reservoir Destratification AMEC Earth & Environmental, Inc., Alex Horne Associates, and Hydrosphere Resource Consultants, Inc. October 2005. Draft Feasibility Report Cherry Creek Reservoir Destratification. Berg, Joe. "Baseflow Stream Channel Design: An Approach to Restoration that Optimizes Resource Values and Ecosystem Services." Water Resources IMPACT , September 2009: Vol. 11 No. 5. Board of Health of Tri-County Health Department. "Regulation No. I-11 individual sewage Disposal Systems." July 1, 2011. Center for Watershed Protection. (n.d.). Irreducible Pollutant Concentrations Discharged from Stormwater Practices. Watershed Protection Techniques , pp. Technical Note #75: 2(2): 369-372. Cherry Creek Basin Water Quality Authority. (2013). 2012 Annual Report of Activities. Cherry Creek Basin Water Quality Authority. (2011). Stormwater Permit Requirements Guidance Document . Cherry Creek Basin Water Quality Authority. (2011). Stream Reclamation, Water Quality Benefit Evaluation - Interim Status Report. Cherry Creek Basin Water Quality Authority. October 2012. Cherry Creek Basin Water Quality Authority Watershed Plan 2012. Cherry Creek Stewardship Partners. (2004). Cherry Creek Basin Water Stewardship and Education Initiative. Cherry Creek Basin Water Quality Authority. February 2000. Cherry Creek Reservoir Watershed Stormwater Quality Requirements. Cherry Creek Basin Water Quality Authority. March 2002. Emergency Response Plan Criteria for the Cherry Creek Reservoir Watershed. Cherry Creek Basin Water Quality Authority. August 2003. Cherry Creek Reservoir Watershed Plan 2003. Cherry Creek Basin Water Quality Authority. 2013. 2013 Annual Inspection of Pollutant Reduction Facilities. Cherry Creek Basin Water Quality Authority. 2013. 2013 Capital Improvement Projects. Cherry Creek Stewardship Partners. January 2011. Cherry Creek Stewardship Partners 2010 Annual Report. Colorado Water Quality Control Commission. March 2009. Regulation No. 72 – Cherry Creek Reservoir Control Regulation. Colorado Water Quality Control Commission. June 2004. Regulation No. 22 – Site Location and Design Approval Regulations for Domestic Wastewater Treatment Works. Colorado Water Quality Control Commission. September 2012. Regulation No. 85 – Nutrients Management Control Regulation. Colorado Water Quality Control Commission. September 2012. Policy WPC-DR-1, Design Criteria for Domestic Wastewater Treatment Works. Colorado Water Quality Control Commission. January 2013. Regulation No. 31 – The Basic Standards and Methodologies for Surface Water. Colorado Water Quality Control Commission. June 2013. Regulation No. 43 – On-site Wastewater Treatment System Regulation Colorado Water Quality Control Commission. (2008). Policy 96-1, Design Criteria Considered in the Review of Wastewater Treatment Facilities.

R-1

Colorado Water Quality Control Commission. Regulation No. 61 - Colorado Discharge Permit System Regulations. Corsi,S.R., L.A. De Cicco, M.A. Lutz, and R.M. Hirsch. 2015. River Chloride Trends in Snow-Affected Urban Watersheds: Increasing Concentrations Outspace Urban Growth Rate and are Common Among All Seasons. Science of the Total Environment, 508:488-497. Denver Regional Council of Governments. October 2000. Lift Station Report Guidance and Checklist. Denver Regional Council of Governments. January 2003. Metro Vision 2020 Clean Water Plan: Wastewater Utility Plan Guidance. Denver Regional Council of Governments. March 2007. Metro Vision Clean Water Plan: Wastewater Utility Plan Guidance/ GEI Consultants, Inc. 2015. Cherry Creek Reservoir 2014 Annual Aquatic Biological and Nutrient Monitoring Study and Cottonwood Creek Phosphorus Reduction Facility Monitoring. GEI Consultants, Inc. 2013. Cherry Creek Reservoir 2012 Annual Aquatic Biological and Nutrient Monitoring Study and Cottonwood Creek Phosphorus Reduction Facility Monitoring. GEI. "Annual Reservoir Monitoring Report." 2015. DRAFT Cherry Creek Reservoir 2013 Water Year Aquatic Biological and Nutrient Monitoring Study and Cottonwood Creek Pollutant Reduction Facilities Monitoring. John C. Halepaska and Associates, Inc. 2008. West Cherry Creek Background Phosphorus Report – Special Study. Knowlton, M.R., and J.R. Jones. 1993. Limnological Investigations of Cherry Creek Lake. Final report to Cherry Creek Basin Water Quality Authority. Lewis, W.M., J. H. McCutchan, and J.F. Saunders. 2005. Estimation of Groundwater Flow into Cherry Creek Reservoir and its Relationship to the Phosphorus Budget of the Reservoir. Prepared for the Cherry Creek Basin Water Qualtiy Authority. Lindon, M.J. and S.A. Heiskary. 2009. Blue-green Algal Toxin (Microcystin) Levels in Minnesota Lakes. Lake and Reservoir Management 25:240-252. Lindon, M.J. and S.A. Heiskary. 2008. Blue-green Algal Toxin (Microcystin) Levels in Minnesota Lakes. Environmental Bulletin No. 11. Minnesota Pollution Control Agency, St. Paul, MN. Maryland Department of the Environment. 2012. Guidelines for Interpreting Dissolved Oxygen and Chlorophyll a Criteria in Maryland’s Seasonally-Stratified Water Supply Reservoirs. Memorandum dated November 14, 2014 from Colorado Parks and Wildlife (Mindi May) to Cherry Creek Basin Water Quality Authority (Chuck Reid) re: Phytoplankton Analysis. Memorandum dated January 15, 2015 from Hydros Consulting (Jean Marie Boyer) to GEI (Craig Wolf) re: Algal Species Data for Cherry Creek Reservoir. Memorandum dated February 3, 2015 from Hydros Consulting (Jean Marie Boyer) to Leonard Rice Engineers (Katie Fendel) re: Recommendation Regarding Cherry Creek Reservoir Destratification System Operations in 2015. Nürmberg, G., and LaZerte, B. 2008. Cherry Creek Reservoir Model and Proposed Chlorophyll Standard. Prepared for the Cherry Creek Basin Water Quality Authority. Tri-County Health Department. July 2011. Regulation No. I-11 - Individual Sewage Disposal Systems. U.S. Environmental Protection Agency. December 2013. Enforcement and Compliance History Online. Detailed Facility Reports.

R-2

APPPENDICES

GEI 2014 Mointoring Report

Consulting Engineers and Scientists

Cherry Creek Reservoir 2014 Water Year Aquatic Biological Nutrient Monitoring and Pollutant Reduction Facilities Monitoring

Submitted to: Cherry Creek Basin Water Quality Authority Clifton Larson Allen LLP 8390 East Crescent Parkway, Suite 500 Greenwood Village, CO 80111-2814

Submitted by: GEI Consultants, Inc. Ecological Division 4601 DTC Boulevard, Suite 900 Denver, CO 80237

March 2015 Project 062450

Table of Contents

Executive Summary ...... i ES 1.1 Temperature and Dissolved Oxygen ...... i ES 1.2 Total Phosphorous in Cherry Creek Reservoir ...... ii ES 1.3 Chlorophyll a ...... ii ES 1.4 Phytoplankton ...... ii ES 1.5 Zooplankton ...... iii ES 1.6 Total Phosphorous in Streams ...... iii ES 1.7 Mass Balance/Net Loading of Phosphorous to the Reservoir ...... iii ES 1.8 Pollutant Reduction Facility Effectiveness ...... iv ES 1.9 Special Study: Cyanotoxin Monitoring ...... v ES 1.10 Special Study: Organic Carbon Monitoring ...... v

1. Historical Perspective ...... 1

2. Study Area ...... 4 2.1 Sampling Sites ...... 4 2.1.1 Cherry Creek Reservoir ...... 4 2.1.2 Cherry Creek ...... 6 2.1.3 Cottonwood Creek ...... 7 2.1.4 McMurdo Gulch ...... 8

3. Methods ...... 9 3.1 Sampling Methodologies ...... 9 3.1.1 Reservoir Sampling ...... 9 3.1.2 Stream Sampling ...... 10 3.1.3 Surface Hydrology ...... 11 3.2 Laboratory Procedures ...... 11 3.2.1 Nutrient Laboratory Analysis ...... 11 3.2.2 Biological Laboratory Analysis ...... 12 3.3 Evaluation of Long-Term Trends in Cherry Creek Reservoir ... 12

4. Results and Discussion ...... 14 4.1 Reservoir Water Quality ...... 14 4.1.1 2014 WY Transparency ...... 14 4.1.2 Long-Term Secchi Transparency Trends in Cherry Creek Reservoir ...... 14 4.1.3 2014 WY Temperature and Dissolved Oxygen ...... 15 4.1.4 2014 WY Nutrients ...... 26 4.1.5 Long-Term Phosphorus Trends in Cherry Creek Reservoir ..... 28 4.1.6 2014 WY Chlorophyll a Levels ...... 30 4.1.7 Long-term Chlorophyll a Trends in Cherry Creek Reservoir .... 31

GEI Consultants, Inc. i March 2015 2014 Cherry Creek Monitoring Report

4.2 Reservoir Biology ...... 32 4.2.1 2014 Phytoplankton ...... 32 4.2.2 Long-Term Phytoplankton ...... 37 4.2.3 2014 Zooplankton ...... 39 4.3 Stream Water Quality ...... 41 4.3.1 2014 WY Phosphorus Concentrations in Streams ...... 41 4.3.2 Long-Term Trends in Phosphorus Concentrations in Cherry Creek Reservoir Tributaries ...... 42 4.3.3 Long-Term Trends in Phosphorus Concentrations in Cherry Creek Reservoir Alluvium ...... 47 4.4 Reservoir Phosphorus Loads and Export ...... 47 4.4.1 Phosphorus Load from Tributary Streams ...... 48 4.4.2 Phosphorus Export from Reservoir Outflow ...... 48 4.4.3 Phosphorus Load from Precipitation ...... 49 4.4.4 Phosphorus Load from Alluvium ...... 50 4.4.5 Mass Balance/Net Loading of Phosphorus to the Reservoir .... 50 4.5 Effectiveness of Pollutant Reduction Facilities ...... 53 4.5.1 Cottonwood Creek Peoria Pond ...... 53 4.5.2 Cottonwood Creek Perimeter Pond ...... 55 4.5.3 McMurdo Stream Reclamation ...... 57 4.6 2014 WY Special Studies ...... 57 4.6.1 Cyanotoxin Monitoring in Cherry Creek Reservoir ...... 57 4.6.2 TOC and DOC Analyses in Cherry Creek Reservoir and Tributaries ...... 59

5. References ...... 61

List of Tables Table 1: Sampling trips per sampling period, 2014 WY...... 9 Table 2: Number of storm samples collected from tributary streams to Cherry Creek Reservoir, 2014 WY. See Appendix C for sample dates...... 11 Table 3: Parameter list, method number, and detection limits for chemical and biological analyses of water collected from Cherry Creek Reservoir and tributaries...... 12 Table 4: Comparison of water year mean and July through September mean phosphorus, nitrogen, and chlorophyll a levels in Cherry Creek Reservoir, 1988 to 2014...... 29 Table 5: Density (#/mL) of phytoplankton and total number of taxa for routine photic zone composite samples representative of the three samples sites on Cherry Creek Reservoir, and for opportunistic grab/composite samples in other Reservoir locations, 2014 CY...... 34 Table 6: Comparison of median base flow and median storm flow concentrations of total phosphorus (TP) and total suspended solids (TSS) in tributaries to Cherry Creek Reservoir, 2014 WY...... 41 Table 7: Comparison of base flow median WY total phosphorus (TP) and soluble reactive phosphorus (SRP) concentrations for CC-10 and CT-2 from 1995 to 2014...... 43 Table 8: Comparison of storm flow median WY total phosphorus (TP) and soluble reactive phosphorus (SRP) concentrations for CC-10 and CT-2 from 1995 to 2014...... 44

GEI Consultants, Inc. ii March 2015 2014 Cherry Creek Monitoring Report

Table 9: Normalized phosphorus loads and export (lbs/year) for Cherry Creek Reservoir, 1992 to 2014 WY...... 49 Table 10: Flow-weighted phosphorus concentrations (µg/L) for Cherry Creek Reservoir, 1992 to 2014 WY...... 51 Table 11: Historical total phosphorus and total suspended solids concentrations and total phosphorus loads upstream and downstream of the Cottonwood Creek  Peoria Pond, 2002 to 2014 WY...... 54 Table 12: Historical total phosphorus and total suspended solids concentrations and total phosphorus loads upstream and downstream of the Cottonwood Creek Perimeter Pond, 1997 to 2014 WY...... 56 Table 13: Total organic carbon (TOC) and dissolved organic carbon (DOC) concentrations in Cherry Creek Reservoir and tributaries (CC-10 and CT-2), February through September 2014...... 60

GEI Consultants, Inc. iii March 2015 2014 Cherry Creek Monitoring Report

List of Figures Figure 1: Sampling sites on Cherry Creek Reservoir and selected streams, 2014...... 5 Figure 2: Sampling sites on McMurdo Gulch, 2014...... 6 Figure 3: Patterns for mean whole-reservoir Secchi depth, 1% transmissivity, and chlorophyll a in Cherry Creek Reservoir, 2014 WY...... 14 Figure 4: Whole-reservoir seasonal mean (July through September) Secchi depth (m) measured in Cherry Creek Reservoir. Error bars represent a 95% confidence interval for each mean...... 15 Figure 5: Temperature (°C) recorded at depth during routine monitoring at CCR-1 during the 2014 WY...... 16 Figure 6: Dissolved oxygen (mg/L) recorded at depth during routine monitoring at CCR-1 during the 2014 WY. The dissolved oxygen basic standards table value for Class 1 warm water lakes and reservoirs is provided for comparison (5 mg/L)...... 16 Figure 7: Temperature (°C) recorded at depth during routine monitoring at CCR-2 during the 2014 WY...... 17 Figure 8: Dissolved oxygen (mg/L) recorded at depth during routine monitoring at CCR-2 during the 2014 WY. The dissolved oxygen basic standards table value for Class 1 warm water lakes and reservoirs is provided for comparison (5 mg/L)...... 17 Figure 9: Temperature (°C) recorded at depth during routine monitoring at CCR-3 during the 2014 WY...... 18 Figure 10: Dissolved oxygen (mg/L) recorded at depth during routine monitoring at CCR-3 during the 2014 WY. The dissolved oxygen basic standards table value for Class 1 warm water lakes and reservoirs is provided for comparison (5 mg/L)...... 18 Figure 11: Relative thermal resistance to mixing gradients and temperature profiles for Cherry Creek Reservoir, June – September, 2014...... 20 Figure 12: Daily mean temperature (°C) recorded at depth for CCR-1 based on 15-minute interval data collected by temperature loggers, with USACE inflow in 2014. Shaded areas denote periods of thermal stratification...... 21 Figure 13: Daily mean temperature (°C) recorded at depth for CCR-2 based on 15-minute interval data collected by temperature loggers, with USACE inflow in 2014. Shaded areas denote periods of thermal stratification...... 22 Figure 14: Daily mean temperature (°C) recorded at depth for CCR-3 based on 15-minute interval data collected by temperature loggers, with USACE inflow in 2014. Shaded areas denote periods of thermal stratification...... 22 Figure 15: Dissolved oxygen conditions in Cherry Creek Reservoir for three dates based on transect profile data during the 2014 WY...... 23 Figure 16: Oxidation reduction potentials (ORP) in Cherry Creek Reservoir for three dates based on transect profile data during the 2014 WY. The ORP scales for each transect are all relative to each other within and among sampling events...... 25 Figure 17: Annual pattern of photic zone total phosphorus, total nitrogen and USACE inflow in Cherry Creek Reservoir, 2014 WY...... 27 Figure 18: Soluble phosphorus concentrations recorded for the photic zone and at depth during routine monitoring during the 2014 WY at CCR-2...... 28 Figure 19: Seasonal mean (July through September) total phosphorus concentrations (μg/L) measured in Cherry Creek Reservoir, 1987 to 2014. Error bars represent a 95% confidence interval for each mean...... 28 Figure 20: Concentration of chlorophyll a (μg/L) in Cherry Creek Reservoir, 2014 WY. Error bars represent a 95% confidence interval around each mean. Highlighted area denotes the seasonal period for the chlorophyll a standard...... 30 Figure 21: Seasonal mean (July through September) concentrations of chlorophyll a (μg/L) measured in Cherry Creek Reservoir, 1987 to 2014. Error bars represent a 95%

GEI Consultants, Inc. iv March 2015 2014 Cherry Creek Monitoring Report

confidence interval around each mean. The Reservoir destratification system was operated from 2008 through 2013...... 31 Figure 22: Percent relative density of algal groups for each routine photic zone composite sample collected in Cherry Creek Reservoir, 2014 CY...... 33 Figure 23: Percent relative biovolume of algal groups for each routine photic zone composite sample collected in Cherry Creek Reservoir, 2014 CY...... 36 Figure 24: Percent algal density of major taxonomic groups in Cherry Creek Reservoir from 2009 through 2014, by CY...... 39 Figure 25: Percent algal biovolume of major taxonomic groups in Cherry Creek Reservoir from 2009 through 2014, by CY...... 39 Figure 26: Total density of zooplankton groups and chlorophyll a concentration by sample date in Cherry Creek Reservoir, 2014 CY...... 40 Figure 27: Base flow and storm flow total phosphorus concentrations measured at CC-10, 1994 to 2014...... 45 Figure 28: Base flow and storm flow soluble reactive phosphorus concentrations measured at CC-10, 1994 to 2014...... 45 Figure 29: Base flow and storm flow total phosphorus concentrations measured at CT-2, 1996 to 2014...... 46 Figure 30: Base flow and storm flow soluble reactive phosphorus concentrations measured at CT-2, 1996 to 2014...... 46 Figure 31: Total dissolved phosphorus and soluble reactive phosphorus concentrations measured at MW-9, 1994 to 2014...... 47 Figure 32: Mass balance diagram of phosphorus loading in Cherry Creek Reservoir, 2014 WY...... 52 Figure 33: Cyanotoxin analyses for Cherry Creek Reservoir, June through September 2014...... 59

List of Photos Photo 1: Cyanobacteria bloom at Site CCR-2 on 6/10/14 (10 µg/L microcystins)...... 58 Photo 2: Cyanobacteria bloom along the dam face (near the tower outlet structure) on 6/17/14 (25 µg/L microcystins)...... 58

List of Appendices Appendix A: Cherry Creek Reservoir Sampling and Analysis Plan Appendix B: 2014 WY Reservoir Water Quality Data Appendix C: 2014 WY Stream Water Quality and Precipitation Data Appendix D: 2014 WY Streamflow, Rainfall, Phosphorous Loading Calculations and Final Inflow and Load Data Normalized to the U.S. Army Corps of Engineers Inflow Data Appendix E: 2014 Biological Data

GEI Consultants, Inc. v March 2015 2014 Cherry Creek Monitoring Report

List of Acronyms & Abbreviations ac acres ac-ft acre-feet ANOVA analysis of variance APHA American Public Health Association CCBWQA Cherry Creek Basin Water Quality Authority CDPHE Colorado Department of Public Health and Environment CEC Chadwick Ecological Consultants, Inc. cfs cubic feet per second CPW Colorado Parks and Wildlife CWQCC Colorado Water Quality Control Commission CY calendar year DM daily maximum DRCOG Denver Regional Council of Governments ed.(s) editor(s) ft feet GEI GEI Consultants, Inc. ha hectare JCHA John C. Halepaska & Associates, Inc. KAPA Denver/Centennial Airport km kilometer lb pound m meter mg milligram mg/L milligrams per liter mL milliliter mo month mph miles per hour mV millivolt MWAT maximum weekly average temperature ORP oxidation reduction potential PAR photosynthetically active radiation PRF pollutant reduction facilities Reservoir Cherry Creek Reservoir TDP total dissolved phosphorus TMAL total maximum annual load TMDL total maximum daily load TN total nitrogen TP total phosphorus TSS total suspended solids SRP soluble reactive phosphorus µg/L micrograms per liter USACE U.S. Army Corps of Engineers USGS U.S. Geological Survey WY water year yr year

GEI Consultants, Inc. vi March 2015 2014 Cherry Creek Monitoring Report

1. Historical Perspective

An inter-governmental agreement was executed in 1985 by several local governmental entities within the Cherry Creek basin to form the Cherry Creek Basin Water Quality Authority (CCBWQA). The CCBWQA was created for the purpose of coordinating and implementing the investigations necessary to maintain the quality of water resources of the Cherry Creek basin while allowing for further economic development. Based on a clean lakes water study (Denver Regional Council of Governments [DRCOG] 1984), the Colorado Water Quality Control Commission (CWQCC) set standards for phosphorus, and a total maximum daily load (TMDL) for phosphorus. The Reservoir was classified as Class 1 Warm Water for aquatic life, with an in-lake phosphorus standard of 35 micrograms per liter (μg/L) and seasonal mean chlorophyll a goal of 15 μg/L. Subsequently, a phosphorus TMDL was prepared for Cherry Creek Reservoir (Reservoir) allocating loads among point sources, background sources, and nonpoint sources with a total maximum annual load (TMAL) of 14,270 pounds (lbs) total phosphorus.

The Cherry Creek Basin Master Plan (DRCOG 1985), approved by the CWQCC in 1985, was adopted in part as the “Regulations for Control of Water Quality in Cherry Creek Reservoir” (Section 4.2.0, 5C.C.R.3.8.11). An annual monitoring program (In-Situ, Inc. 1986, as amended, Advanced Sciences, Inc., 1994a and 1994b) was implemented at the end of April 1987 to assist in the assessment of several aspects of the Master Plan. These monitoring studies have included long-term monitoring of: 1) nutrient levels within the Reservoir and from tributary streams during base flows and storm flows; 2) nutrient levels in precipitation; and 3) chlorophyll a levels within the Reservoir.

In September 2000, following a hearing before the CWQCC, the standard for Cherry Creek Reservoir (Regulation #38) was changed to a seasonal July to September mean value of 15 μg/L of chlorophyll a to be met 9 out of 10 years, with an underlying total phosphorus goal of 40 μg/L, also as a July to September mean value. In addition, the limit for wastewater effluent total phosphorus concentration was set at 50 µg/L, to be met as a 30-day mean value. In May 2001 at the CWQCC hearing, the Control Regulation (#72) was adopted for the Cherry Creek Reservoir, which maintained the annual TMAL of 14,270 lbs/year as part of a phased TMDL for the Reservoir. During the March 2009 Rulemaking Hearing, Regulations 38 and 72 were again refined to reflect the most current feasibility-based chlorophyll a standard and flow-weighted inflow total phosphorus goal for Cherry Creek Reservoir. The current chlorophyll a standard is 18 µg/L with an exceedance frequency of once in 5 years. The control regulation changed from a phosphorus load-based TMAL to a flow-weighted concentration such that the annual flow-weighted total phosphorus concentration goal is 200 µg/L for all combined sources of inflow to the Reservoir.

GEI Consultants, Inc. 1 March 2015 2014 Cherry Creek Monitoring Report

From 1993 to 1998, Dr. John Jones of the University of Missouri contributed greatly to the Cherry Creek Reservoir annual monitoring program (Jones 1994 to 1999, 2001), and assisted with the transition of the program to Chadwick Ecological Consultants, Inc. (CEC) in 1994. Results of the aquatic biological and nutrient analyses have been summarized in annual monitoring reports (CEC 1995 to 2006). In 2006, CEC merged with GEI Consultants, Inc. (GEI), and continues to perform the annual monitoring duties of Cherry Creek Reservoir (GEI 2007, 2008b, 2009 to 2013). The present study was designed to continue the characterization of the relationships between nutrient loading (both in-lake and external) and Reservoir productivity. The specific objectives of this annual monitoring study include the following:

 Determine baseflow and stormflow concentrations for nitrogen and phosphorus fractions in tributary inflows, as well as concentrations in Cherry Creek Reservoir and the outflow.

 Determine the hydrological inflows and nutrient loads entering Cherry Creek Reservoir, including Reservoir exports. These data provide the necessary information to calculate flow-weighted nutrient concentrations for the Reservoir.

 Determine biological productivity in Cherry Creek Reservoir, as measured by algal biomass (chlorophyll a concentration). In addition, determine species composition of the algal assemblages to characterize the types of algae responsible for chlorophyll a, and determine zooplankton species composition to better characterize the plankton community.

 Evaluate relationships between the biological productivity and nutrient concentrations within Cherry Creek Reservoir and total inflows.

 Assess the effectiveness of pollutant reduction facilities (PRFs) on Cottonwood Creek, McMurdo Gulch and Cherry Creek to reduce phosphorus loads into the Reservoir.

 Assess the effectiveness of the destratification system in minimizing periods of thermal stratification, increasing the dissolved oxygen concentrations in the deepest water layers, reducing the internal nutrient release of phosphorus and nitrogen from the sediments, reducing peak and seasonal mean chlorophyll a concentrations, and reducing the production of cyanobacteria via vertical mixing.

In 2008, the CCBWQA implemented a new Reservoir destratification management strategy that was designed to increase the circulation of the water column, to promote a greater exchange of dissolved oxygen at the surface layer, and to circulate the reaerated water into the deeper depths of the Reservoir. A goal of this management strategy is to increase the dissolved oxygen concentrations near the water/sediment interface which should help reduce the internal phosphorus loading component of the Reservoir (AMEC 2005). The sediment

GEI Consultants, Inc. 2 March 2015 2014 Cherry Creek Monitoring Report

phosphorus load accumulates over time from external sources, including from the Reservoir, and is geochemically transformed and released when the sediment surface becomes anoxic (Nürnberg and LaZerte 2008). This internal release of phosphorus facilitates the growth of all algae; thus by reducing the internal load, algae growth should be reduced too. In addition, a goal of the design of the destratification system was to vertically mix algae and to disrupt the suitable habitat of large filamentous cyanobacteria which have the ability to regulate their buoyancy, fix atmospheric nitrogen, and rapidly grow at the surface of the Reservoir. In theory, when these design considerations are placed in the context of each other, the destratification system should have reduced chlorophyll a concentrations and helped to achieve the site-specific chlorophyll a standard while protecting the beneficial uses. However, after operating the destratification system for a period of 6 years, the reservoir appeared to have reached a new state of conditions that was characterized by internal nutrient loading and higher than expected algal biomass (chlorophyll a) conditions that resulted in the seasonal mean chlorophyll a concentration being exceeded 4 out of the 6 years. In addition, a laboratory change in 2009 resulted in phytoplankton data that was different than historical data which confounded the comparison of algae species composition data. As a result, the destratification system was not operated in 2014 to reassess the phytoplankton community dynamics in the absence of aeration and to better understand whether the destratification system was vertically mixing the algae and disrupting the suitable habitat for large filamentous cyanobacteria. The objectives of the annual monitoring study remained the same as stated above; although two special studies were included to better understand the potential concern for cyanotoxins in the context of beneficial uses and to better understand organic carbon dynamics in the system. The 2014 data will also be used to inform the development of the Reservoir hydrodynamic model.

GEI Consultants, Inc. 3 March 2015 2014 Cherry Creek Monitoring Report

2. Study Area

Cherry Creek was impounded in 1948 and the dam was completely finished in 1950 by the U.S. Army Corps of Engineers (USACE) to protect the City of Denver from flash floods that originated in the 995 square kilometers (km2) (385 square miles) drainage basin. The CCBWQA performed a bathymetric survey in November 2013, and the Reservoir surface area was 875 acres (ac) at the multipurpose storage pool elevation of 5,550 feet (ft). The volume of the Reservoir was 13,522 acre-feet (ac-ft). The Reservoir and surrounding state park has also become an important recreational site, providing activities that include fishing, boating, swimming, bicycling, bird watching, and walking.

2.1 Sampling Sites

Sampling during the 2014 WY was routinely conducted at 12 sites, including three sites in Cherry Creek Reservoir, eight sites on tributary streams, and one site on Cherry Creek downstream of the Reservoir (Figures 1 and 2). In addition to these routine monitoring sites, 10 transect sites (D1 to D10) were established from the approximate mid-point of the dam extending perpendicular across the destratification zone in the Reservoir, as well as three continuous temperature logging sites near the routine reservoir monitoring sites. The routine sampling sites are summarized below.

2.1.1 Cherry Creek Reservoir

CCR-1 This site is also called the Dam site, and was established in 1987. Site CCR-1 corresponds to the northwest area within the lake (Knowlton and Jones 1993). Sampling was discontinued at this site in 1996 following determination that this site exhibited similar characteristics to the other two sites in this polymictic Reservoir. Sampling recommenced in July 1998 at the request of consultants for Greenwood Village.

CCR-2 This site is also called the Swim Beach site, and was established in 1987. Site CCR-2 corresponds to the northeast area within the lake (Knowlton and Jones 1993).

CCR-3 This site is also called the Inlet site and was established in 1987, corresponding to the south area within the lake (Knowlton and Jones 1993).

GEI Consultants, Inc. 4 March 2015 2014 Cherry Creek Monitoring Report

Figure 1: Sampling sites on Cherry Creek Reservoir and selected streams, 2014.

GEI Consultants, Inc. 5 March 2015 2014 Cherry Creek Monitoring Report

Figure 2: Sampling sites on McMurdo Gulch, 2014.

2.1.2 Cherry Creek

CC-7 (EcoPark) This site was established in 2013 on Cherry Creek at the downstream boundary of Cherry Creek Valley Ecological Park (EcoPark). This site is approximately 1.7 kilometers (km) upstream of Arapahoe Road, and serves to monitor water quality conditions downstream of the EcoPark Stream Reclamation Project (PRF). This site also provides more accurate flow estimates in this reach of Cherry Creek.

CC-10 This site was originally established in 1987 on Cherry Creek near the historic U.S. Geological Survey (USGS) Melvin gage, approximately 3.5 km upstream of the Reservoir (roughly due west of the intersection of Parker Road and Orchard Road). This location is in an area of Cherry Creek that frequently becomes dry during summer months as a result of the natural geomorphology and alluvial pumping for domestic water supply (John C. Halepaska & Associates, Inc. [JCHA] 1999 and 2000).

In 1995, this site was relocated farther downstream between the Perimeter Road and the Reservoir, approximately 800 meters (m) upstream of the Reservoir. This site was moved still farther downstream in 1996, just upstream of the confluence with Shop Creek and closer to the Reservoir. In 1999, it was moved below the confluence with Shop Creek

GEI Consultants, Inc. 6 March 2015 2014 Cherry Creek Monitoring Report

to eliminate the effect of a stream crossing on the site’s hydrograph. Since 1995, Cherry Creek has been monitored in a reach with perennial flow, allowing for more accurate monitoring of water quality and surface flow in Cherry Creek before entering the Reservoir. Historically, this site has been referred to as CC or CC-I (i.e., CC-Inflow), but was renamed Site CC-10 in 1997 to place it in context with concurrent monitoring in Cherry Creek mainstem upstream of the Reservoir (JCHA 1999 to 2007).

CC-O This site was established in 1987 on Cherry Creek downstream of Cherry Creek Reservoir and upstream of the Hampden Avenue- Havana Street junction in the Kennedy Golf Course near the historical USGS gage (06713000). In 2007, Site CC-O (also identified as Site CC-Out @ I225) was relocated immediately downstream of the dam outlet structure and serves to monitor the water quality of the Reservoir outflow.

2.1.3 Cottonwood Creek

CT-P1 This site was established in 2002 and is located just north of where Caley Avenue crosses Cottonwood Creek, and west of Peoria Street. This site monitors the water quality of Cottonwood Creek before it enters the Peoria Pond PRF, also created in 2001/2002 on the west side of Peoria Street.

CT-P2 This site was established in 2002 and is located at the outfall of the PRF, on the west side of Peoria Street. The ISCO stormwater sampler and pressure transducer is located inside the outlet structure. This site monitors the effectiveness of the PRF on water quality.

CT-1 This site was established in 1987 where the Cherry Creek Park Perimeter Road crosses Cottonwood Creek. It was chosen to monitor the water quality of Cottonwood Creek before it enters the Reservoir. During the fall/winter of 1996, a PRF, consisting of a water quality/detention pond and wetland system, was constructed downstream of this site. As a result of the back-flow from this pond inundating this site, this site was relocated approximately 250 m upstream near Belleview Avenue in 1997. In 2009, this site was relocated approximately 75 m upstream of the Perimeter Road as it crosses Cottonwood Creek, due to the stream reclamation project. This site is now approximately 200 m upstream of the PRF.

CT-2 This site was established in 1996 and was originally located downstream of the Perimeter Pond on Cottonwood Creek. The ISCO pressure transducer and staff gage was located in a section of the stream relatively unobstructed by vegetation, and approximately 50 m downstream of the PRF. However, over the years the growth of vegetation considerably increased along the

GEI Consultants, Inc. 7 March 2015 2014 Cherry Creek Monitoring Report

channel, creating problems with accurately determining stream flow. Eventually, when no accurate and reliable streamflow measurements could be performed in 2003, other locations were evaluated. In August 2004, the pressure transducer and staff gage were relocated inside of the outlet structure for the PRF to mitigate problems associated with streamflow measurements by providing a reliable multilevel weir equation. In 2013, modifications to the PRF overflow elevation and the partial closure of the downstream control gate changed the relationship of the multilevel weir equation, resulting in unreliable stream flow estimates. In April 2014, the weir and overflow elevations were surveyed and the control gate was fully opened, and adjustments were made to the weir equations accordingly. Water quality samples are collected from the outlet structure as well. This site monitors the effectiveness of the PRF on Cottonwood Creek water quality and provides information on the stream before it enters the Reservoir.

2.1.4 McMurdo Gulch

MCM-1 This site was established in 2012 on McMurdo Gulch, approximately 150 m upstream of the McMurdo Gulch Stream Reclamation Project boundary. This site is also 120 m upstream of the confluence with an unnamed tributary that receives runoff from the Castle Oaks Subdivision. This site serves as the upstream monitoring location for the McMurdo Gulch Stream Reclamation Project.

MCM-2 This site was established in 2012 on McMurdo Gulch, approximately 80 m upstream of the Castle Oaks Drive Bridge crossing of McMurdo Gulch, near the North Rocky View Road intersection. This site serves as the downstream monitoring location for the McMurdo Gulch Stream Reclamation Project. This site is located within the project boundary, and consistently maintained base flows, whereas the reach further downstream was often dry due to surface flow becoming subsurface.

GEI Consultants, Inc. 8 March 2015 2014 Cherry Creek Monitoring Report

3. Methods

3.1 Sampling Methodologies

Field sampling protocols and analytical methods used for monitoring the Reservoir and stream sites as outlined in the Cherry Creek Reservoir Sampling and Analysis Plan (GEI 2008a; Appendix A).

3.1.1 Reservoir Sampling

The general sampling schedule included regular sampling trips to the Reservoir at varying frequencies over the annual sampling period, as outlined below, with increased sampling frequency during the summer growing season (Table 1). A total of 22 reservoir sampling events were conducted during the 2014 WY. The December 2013 and January 2014 sampling events were not performed due to unsafe ice conditions. During 15 of the 22 sampling events on the Reservoir, three main tasks were conducted, including: 1) determining water clarity, 2) collecting physicochemical depth profiles, and 3) collecting water samples for chemical and biological analyses. During the remaining 7 out of 22 sampling events on the reservoir, only cyanotoxin samples, physiochemical depth profiles and water clarity were collected for a special study that was initiated in summer 2014. This special study was conducted to evaluate changes in cyanobacteria and cyanotoxins because the destratification system was not operated in 2014.

Table 1: Sampling trips per sampling period, 2014 WY. Sampling Period Frequency Planned Trips/Period Actual Trips/Period Oct - Apr Monthly 7 5 May - Sept Bi-Monthly 10 17 Total 17 22

3.1.1.1 Water Clarity

Transparency was determined using a Secchi disk and LI-COR quantum sensors (ambient and underwater). Detailed methods of both instruments can be found in the Sampling and Analysis Plan (Appendix A).

3.1.1.2 Profile Measurements

A Hydrolab MS5 Surveyor and Sonde was used for the collection of dissolved oxygen, temperature, conductivity, pH, and oxidation reduction potential (ORP) profile measurements from the surface to the bottom of the Reservoir.

GEI Consultants, Inc. 9 March 2015 2014 Cherry Creek Monitoring Report

3.1.1.3 Water Sampling

Water samples for nutrient, phytoplankton, zooplankton, chlorophyll a, and suspended solids analyses were collected at the three Reservoir sites. Data collected from each site during a single sampling event (i.e., three replicate samples), are averaged to provide a whole-reservoir mean estimate for each parameter. Sample event means are then used to calculate annual or seasonal mean values for key parameters such as chlorophyll a and total phosphorus and to facilitate comparison with regulatory standards and goals that apply to the Reservoir. Depending upon the distributional characteristics of each parameter, annual values may be compared to either the long-term mean or median value. Secchi depth and chlorophyll a are two parameters that reveal normal distributions, thus it is more appropriate to compare annual values with the long-term mean. Conversely, the total phosphorus data exhibit a log normal distribution; therefore it is more appropriate to compare annual values to the long-term median value. The Sampling and Analysis Plan (Appendix A) outlines the detailed methods used to collect lake water samples, as well as the laboratory methods in sample handling and preparation.

3.1.1.4 Cyanotoxin Data

Two cyanotoxin samples were collected from the Reservoir during each sampling event from early June to late September. One sample was collected a composite of the three photic zone samples (sites CCR-1, CCR-2, and CCR-3). Each photic zone consisted of equal volumes of water collected from the surface, 1m, 2m and 3m depths. This sampling regime is the same process used for collecting the phytoplankton sample, so the data are comparable. A second sample was also collected as a surface water grab sample from the Swim Beach water area. In addition, four “worse-case” surface water grab samples were collected from different locations within the reservoir where the nuisance algal bloom conditions existed. All samples were submitted to GreenWater Laboratories for analysis of the following cyanotoxins: anatoxins, microcystins, cylindrospermopsins, and saxitoxins.

3.1.1.5 Fish Population Data

Historically, this monitoring study has also reviewed fish stocking and population data collected by the Colorado Parks and Wildlife (CPW). The most recent fish population survey was conducted in the late summer 2014by the CPW (personal communication with Paul Winkle, CPW). However, these data were not available to GEI at the time of finalizing the 2014 Cherry Creek Monitoring Report.

3.1.2 Stream Sampling

3.1.2.1 Base Flow Sampling

Base flow stream sampling was conducted on a monthly basis (12 events) in coordination with the routine Reservoir sampling trips to Cherry Creek Reservoir. This sampling was performed to characterize base flow conditions, which corresponds to the low-flow ambient

GEI Consultants, Inc. 10 March 2015 2014 Cherry Creek Monitoring Report

samples collected in past studies. Monthly samples are assumed to be representative of non-storm, base flow periods on Cherry Creek, Cottonwood Creek, and McMurdo Gulch.

3.1.2.2 Storm Sampling

Storm events sampled at the inflow sites on Cherry Creek and Cottonwood Creek characterize non-base flow conditions during the sampling season (Table 2). A detailed outline of storm sampling protocols can be found in the Sampling and Analysis Plan (Appendix A). Storm samples were not collected on McMurdo Gulch.

Table 2: Number of storm samples collected from tributary streams to Cherry Creek Reservoir, 2014 WY. See Appendix C for sample dates. Sites

EcoPark CC-10 CT-P1 CT-P2 CT-1 CT-2 Number of Storm Samples 6 6 7 7 7 7

3.1.3 Surface Hydrology Pressure transducers attached to ISCO Series 6700 or 6712 flowmeters measured and recorded water levels (stage) at six sites on the two tributaries to Cherry Creek Reservoir (Figure 1). These flow meters are programmed to record water level data on 15-minute intervals year round. Streamflow (discharge) was estimated at CC-10, CT-1, and CT-P1 using a stage-discharge relationship developed for each stream site. For sites CT-2, CT-P2, and EcoPark, where the flow meters are located inside or connected to the concrete outlet structure, multi-level orifice and weir equations were used to estimate discharge. Periodic stream discharge measurements were collected during a range of flow conditions using a Marsh McBirney Model 2000 flowmeter to develop the stage-discharge relationships. For a complete description of streamflow determination, see Appendix D.

In 2012, a modification to the Site CT-2 outlet works structure and dam embankment occurred during maintenance to the PRF system which altered the flow characteristics inside the weir. In April 2014, the weir was surveyed and it was observed that the control gate was partially closed. The weir equations were modified to account for the effects of the partially closed gate. The gate was fully opened at this time and the weir equations were adjusted again for unobstructed flow.

3.2 Laboratory Procedures 3.2.1 Nutrient Laboratory Analysis Physicochemical and biological analyses from the Reservoir and stream water quality samples were performed by the GEI analytical laboratory (Table 3). Quality Assurance/ Quality Control protocols for the low level nutrient analyses were performed by the GEI Laboratory, with all results being reported in Appendix B.

The methods for these analyses, with appropriate QA/QC procedures, are available from GEI.

GEI Consultants, Inc. 11 March 2015 2014 Cherry Creek Monitoring Report

Table 3: Parameter list, method number, and detection limits for chemical and biological analyses of water collected from Cherry Creek Reservoir and tributaries. Parameter Method Detection Limit Total Phosphorus QC 10-115-01-4-B 2 μg/L Total Dissolved Phosphorus QC 10-115-01-4-B 2 μg/L Soluble Reactive Phosphorus QC 10-115-01-1-T 2 μg/L Total Nitrogen QC 10-107-04-4-B 2 μg/L Total Dissolved Nitrogen QC 10-107-04-4-B 2 μg/L Ammonium Ion QC 10-107-06-2-A 3 μg/L Nitrate and Nitrite QC 10-107-04-1-C 2 μg/L TSS APHA 2540D 4 mg/L TVSS APHA 2540E 4 mg/L Chlorophyll a APHA 10200 H (modified) 0.1 μg/L Phytoplankton APHA 10200 C.2 -- Zooplankton APHA 10200 G -- APHA = American Public Health Association, 1998.

3.2.2 Biological Laboratory Analysis

Biological analyses of the Reservoir phytoplankton samples were conducted by Aquatic Analysts, Friday Harbor, Washington. Aquatic Analysts performed phytoplankton identification and enumeration and biovolume (µm3) per unit volume [#/milliliter (mL)], while GEI performed the chlorophyll a concentrations (µg/L). Water’s Edge Scientific LLC, Baraboo, Wisconsin performed zooplankton identification, enumeration, and biomass (µg/L). Cyanotoxin samples were analyzed by GreenWater Laboratory, Palatka, Florida; when toxin levels were greater than recommended thresholds, the laboratory also identified and enumerated the types of cyanobacteria present which likely produced the toxins.

3.3 Evaluation of Long-Term Trends in Cherry Creek Reservoir

Long-term seasonal trends were evaluated for Secchi depth, chlorophyll a, and total phosphorus using whole-reservoir mean values from 1987 to 2014 and linear regression analysis (described below). Additionally, 95% confidence intervals provided information on data dispersal around the mean annual values. These analyses were used to determine whether there was significant increasing or decreasing trends in Secchi depth, total phosphorus, and chlorophyll a levels over time.

Comparisons of biological and physical parameters for each site were conducted using NCSS 2007 statistical software (Hintze 2009). Basic descriptive statistics were used to evaluate the distributional characteristics of the data, and to determine whether a variable required transformation to meet the basic assumptions of normality or whether outliers existed in the data. Logarithmic transformations were used to increase the symmetry of the data about the mean, approximating a normal distribution. If the transformation did not improve normality, the untransformed data were used in subsequent analyses.

GEI Consultants, Inc. 12 March 2015 2014 Cherry Creek Monitoring Report

The least-squares linear regression was used to estimate slope, with analysis of variance (ANOVA) being used to determine if the slope was significantly different than zero. A probability of < 0.05 was used to indicate statistical significance. In the cases of the linear regressions, the R2 value provided a measure of how well the variance is explained by the regression equation. R2 values measure the proportion of total variation that is explained or accounted for by the fitted regression line (i.e., it is a measure of the strength of the relationship with the observed data).

GEI Consultants, Inc. 13 March 2015 2014 Cherry Creek Monitoring Report

4. Results and Discussion

4.1 Reservoir Water Quality

4.1.1 2014 WY Transparency

The whole-reservoir mean Secchi depth varied from 0.69 m in mid-October to 3.19 m in late June (Figure 3). The seasonal (July through September) whole-reservoir mean Secchi depth was 1.10 m (Figure 4). The depth at which 1% of photosynthetically active radiation (PAR) penetrated the water column (i.e., photic zone depth) ranged from 1.89 m in mid-October to a maximum depth 5.70 m in late June (Figure 3). The greatest level of whole-reservoir chlorophyll a concentration of 43.3 µg/L was observed in mid-February 2014, beneath the ice cover, while the next greatest level was observed in early June 2014 (37.5 µg/L, Figure 3). The water clarity observed on June 24th was the deepest recorded Secchi depth (3.2 m) for the Reservoir since data collection began in 1987, and occurred immediately after the crash of a large filamentous cyanobacteria population which resulted in the peak chlorophyll a concentration in early June. The water clarity in late May (1.5 m) facilitated the rapid growth of the cyanobacteria population along with other Reservoir conditions such as temperature and nutrients.

Figure 3: Patterns for mean whole-reservoir Secchi depth, 1% transmissivity, and chlorophyll a in Cherry Creek Reservoir, 2014 WY.

4.1.2 Long-Term Secchi Transparency Trends in Cherry Creek Reservoir In general, seasonal mean (July through September) Secchi depths increased from 1987 to 1996, then decreased in 1997 at which time they have been relatively stable until the past few years (Figure 4). The 2014 seasonal whole-reservoir mean Secchi depth was 1.10 m, which is greater than the present long-term (1987 to present) mean value of 0.95 m. In terms of water

GEI Consultants, Inc. 14 March 2015 2014 Cherry Creek Monitoring Report

clarity, the 2014 Reservoir conditions were very similar to historical conditions (i.e., prior to 2008) in the absence of destratification management.

Figure 4: Whole-reservoir seasonal mean (July through September) Secchi depth (m) measured in Cherry Creek Reservoir. Error bars represent a 95% confidence interval for each mean.

4.1.3 2014 WY Temperature and Dissolved Oxygen Analysis of past Cherry Creek Reservoir temperature profiles indicates that stratification typically occurs when there is greater than 2°Celsius (C) difference between the surface and bottom water temperatures (Jones 1998). Differences of less than 1°C between the surface and bottom waters indicate mixing (Jones 1998). This criterion is generally supported by the classical definition of a thermocline, as being the layer with the greatest rate of change in temperature or dt/dz greater than 1°C/m. However, given the relatively shallow nature of the Reservoir and the temperature-density relationships, the Reservoir can become stratified even though the greatest rate of change may be less than 1°C. In addition, relative thermal resistance to mixing (RTRM) can be used to evaluate stratification as a function of temperature differentials in the water column (Wetzel 2001). Dissolved oxygen profiles are also used to evaluate periods of stratification when temperature differences are less than 1°C.

Water temperatures during routine profile measurements in the Reservoir ranged from 1.1°C immediately beneath the ice cover in mid-February 2014 to 24.5°C at the surface in mid-July 2014 (Figure 5, Figure 7, and Figure 9). Temperature profile data showed a fairly well-mixed reservoir in early spring with increasing stratification starting in mid-May 2014 (Figure 5, Figure 7, and Figure 9).

From October 2013 to mid-May 2014, the dissolved oxygen concentrations remained greater than 5 milligrams per liter (mg/L) throughout the water column (Figures 6, 8, and 10). From mid-May through September, the deeper 5-7 m layers and water/sediment interface were

GEI Consultants, Inc. 15 March 2015 2014 Cherry Creek Monitoring Report

consistently below 5 mg/L (Figures 6, 8, and 10). The dissolved oxygen standard for warm water lakes is 5.0 mg/L and is applicable to the 0.5 m to 2.0 m layers of the Reservoir. However, when summer water temperatures increase, the deeper, cooler water becomes more important for fish refuge and if dissolved oxygen conditions are less than 5.0 mg/L, the Reservoir conditions become less conducive for fish. The periodic peaks in dissolved oxygen concentrations near the surface (Figures 6, 8, and 10) are indicative of algal production and the release of oxygen during photosynthesis, as well as influence from wind- driven mixing events.

Figure 5: Temperature (°C) recorded at depth during routine monitoring at CCR-1 during the 2014 WY.

Figure 6: Dissolved oxygen (mg/L) recorded at depth during routine monitoring at CCR-1 during the 2014 WY. The dissolved oxygen basic standards table value for Class 1 warm water lakes and reservoirs is provided for comparison (5 mg/L).

GEI Consultants, Inc. 16 March 2015 2014 Cherry Creek Monitoring Report

Figure 7: Temperature (°C) recorded at depth during routine monitoring at CCR-2 during the 2014 WY.

Figure 8: Dissolved oxygen (mg/L) recorded at depth during routine monitoring at CCR-2 during the 2014 WY. The dissolved oxygen basic standards table value for Class 1 warm water lakes and reservoirs is provided for comparison (5 mg/L).

GEI Consultants, Inc. 17 March 2015 2014 Cherry Creek Monitoring Report

Figure 9: Temperature (°C) recorded at depth during routine monitoring at CCR-3 during the 2014 WY.

Figure 10: Dissolved oxygen (mg/L) recorded at depth during routine monitoring at CCR-3 during the 2014 WY. The dissolved oxygen basic standards table value for Class 1 warm water lakes and reservoirs is provided for comparison (5 mg/L).

GEI Consultants, Inc. 18 March 2015 2014 Cherry Creek Monitoring Report

Relative thermal resistance to mixing (RTRM) was calculated to evaluate stratification as a function of density gradients in the water column. From June through September 2014 the RTRM gradients in the deeper water are minimal, with the exception of July 3rd and August 7th (Figure 11). The RTRM values for the 4 to 6 m layers on these dates indicate the water column was only weakly stratified. Greater RTRM values were observed in the upper layers of the Reservoir on June 12th, July 10th, July 31st, and September 11th (Figure 11). These values are limited to the upper layers and indicate solar heating in the top portion of the water column and are not indicative of typical stratification in the water column. However, the RTRM condition observed on June 12th indicates a resistance to mixing near the surface which also corresponds to the Anabaena-flos aquae bloom that was observed from June 9th through June 23rd. This condition likely related to the bloom or at least facilitated the bloom given the relatively strong resistance to mixing near the surface (0 to 2 m). Despite the low levels of thermal stratification and low RTRM which indicate a well-mixed Reservoir for most of the growing season, the sediment oxygen demand (SOD) remained very high. This indicates that even a few centimeters of anoxic bottom water is sufficient for creating a reducing environment and internal load release of nutrients.

By the second sampling event in May 2014, dissolved oxygen concentrations began decreasing at depths greater than 6 m with values less than the upper threshold (2 mg/L) conducive for internal loading at the sediment boundary. These conditions in the deep layers of the Reservoir, at this time of year, may pose relatively little harm to the warm water biological community, because the upper layers remained well oxygenated. However, deep water anoxia (< 2 mg/L) at the sediment boundary created favorable conditions for internal nutrient loading for several weeks during the summer period.

On June 10th, dissolved oxygen profiles indicated that the water column had become mixed with dissolved oxygen concentrations ranging from 11.4 mg/L at the surface to 5.0 mg/L at the sediment boundary (Figure 6, Figure 8, and Figure 10). By June 24th, dissolved oxygen concentrations once again began decreasing at depths greater than 6 m with values less than the upper threshold (2 mg/L). This deep water anoxia continued throughout the Reservoir until August 26th (Figure 6, Figure 8, and Figure 10).

Reservoir profiles were also evaluated to determine the attainment of the dissolved oxygen standard. Over the course of the monitoring year, 100 vertical water column profiles were collected in the Reservoir. For each profile, the 1 m and 2 m dissolved oxygen values were averaged and evaluated for attainment of the Class 1 Warm Water table value standard (5 mg/L) for lakes and reservoirs that are greater than 5 m deep (CDPHE 2011). The Reservoir was in attainment of the dissolved oxygen standard for 99 of 100 profiles. The single exceedance occurred on August 26th, 2014 with a minimum average dissolved oxygen value of 4.2 mg/L which occurred at Site CCR-3; followed a storm event that occurred the day before. During the July to September growing season, the average dissolved oxygen concentration of the upper layer was 7.8 mg/L for all vertical profiles.

GEI Consultants, Inc. 19 March 2015 2014 Cherry Creek Monitoring Report

Figure 11: Relative thermal resistance to mixing gradients and temperature profiles for Cherry Creek Reservoir, June – September, 2014.

GEI Consultants, Inc. 20 March 2015 2014 Cherry Creek Monitoring Report

4.1.3.1 Continuous Temperature Monitoring On April 15, 2014, temperature loggers were deployed for monitoring the efficiency of the destratification system at mixing the water column. Using the > 2°C difference criteria from the surface to the bottom, Cherry Creek Reservoir was evaluated for periods of stratification using the continuous temperature record at depths for all three Reservoir sites from April 15th to November 4th (Figure 12, Figure 13, and Figure 14). Due to a deployment issue, temperature data was not recorded at the 1 m layer for the three Reservoir sites from April 15th through June 24th; therefore, temperature data from the 2 m layer was used to assess Reservoir stratification during that timeframe. The Reservoir exhibited several periods of thermal stratification, but days of thermal stratification did vary slightly by site throughout the monitoring period and not all sites were stratified on the exact same dates (Figure 12, Figure 13, and Figure 14). Overall, the Reservoir exhibited several periods of thermal stratification that occurred from approximately April 21st - April 24th, May 3rd - May 9th, May 18th – June 5th, June 13th – June 14th, June 21st – June 22nd, June 25th – June 27th, June 30th – July 4th, July 2nd – July 3rd, July 9th – July 11th, August 1st – August 4th, August 12th – August 13th, and September 18th – September 21st (Figure 12, Figure 13, and Figure 14). From April 15th through November 1st the Reservoir was stratified for approximately 46 days. This is a greater number of stratification events compared to 2013, and is likely due to the fact that the destratification system was not in operation during 2014. The temperature standards for Class I Warm Water lakes and reservoirs are 29.5°C (acute, ac) and 26.3°C (chronic, ch) for summer months and 14.8°C (ac) and 13.2°C (ch) for winter months (CDPHE 2011). The Reservoir daily maximum (ac) and weekly average temperatures did not exceed the warm water standards during the summer months.

Figure 12: Daily mean temperature (°C) recorded at depth for CCR-1 based on 15-minute interval data collected by temperature loggers, with USACE inflow in 2014. Shaded areas denote periods of thermal stratification.

GEI Consultants, Inc. 21 March 2015 2014 Cherry Creek Monitoring Report

Figure 13: Daily mean temperature (°C) recorded at depth for CCR-2 based on 15-minute interval data collected by temperature loggers, with USACE inflow in 2014. Shaded areas denote periods of thermal stratification.

Figure 14: Daily mean temperature (°C) recorded at depth for CCR-3 based on 15-minute interval data collected by temperature loggers, with USACE inflow in 2014. Shaded areas denote periods of thermal stratification.

GEI Consultants, Inc. 22 March 2015 2014 Cherry Creek Monitoring Report

4.1.3.2 Dissolved Oxygen and Oxidation-Reduction Potential Transect

The water quality transect was established in the Reservoir originating from approximately the mid-point of the dam and extending southward across the Reservoir, towards the inlet region (see Figure 1). As part of the destratification monitoring program, water column dissolved oxygen and oxidation reduction potential profiles were continued to be collected at 10 locations along the transect and the nearby Site CCR-3 location (D-10), on three sample dates (Figure 15). These data help document the areal extent of low dissolved oxygen and reducing conditions near the water/sediment interface. Low dissolved oxygen conditions (i.e., < 2 mg/L) facilitate the internal release of soluble nutrients that promotes algae growth during the summer.

Figure 15: Dissolved oxygen conditions in Cherry Creek Reservoir for three dates based on transect profile data during the 2014 WY.

GEI Consultants, Inc. 23 March 2015 2014 Cherry Creek Monitoring Report

During the first sample date on June 24th, the Reservoir was well oxygenated (i.e., > 5 mg/L) from the surface down to a depth of approximately 4 m (Figure 15). This pattern was consistent from D1 near the dam to D10, at which point the maximum Reservoir depth became shallower. The average dissolved oxygen concentration for the 1 m and 2 m depths along the transect was 6.3 mg/L indicating the Reservoir was in attainment of the dissolved oxygen standard. Low dissolved oxygen conditions (<2 mg/L) were evident in the lower portion of the Reservoir (6 m, 7 m, and bottom), and this zone continued to expand higher into the water column by mid-July (Figure 15; Appendix B). The average dissolved oxygen concentration for depths from 6 m to the bottom was 1.44 mg/L.

The July 22nd transect profiles documented the continued expansion of the anoxic zone upward into the water column (Figure 15). The average dissolved oxygen concentration of the 1 m and 2 m layer values along the transect was 9.7 mg/L which indicated the Reservoir was in attainment of the warm water standard (5 mg/L). The dissolved oxygen concentrations in the upper portion of the Reservoir were greater during this sampling event versus the June 24th event (Figure 15). The lower portion of the Reservoir showed anoxic conditions (<2 mg/L) for most sites at the 6 m, 7 m, and the water-sediment interface. The average dissolved oxygen concentration for these depths was 0.79 mg/L.

The last transect profile was collected on August 19th and showed decreased dissolved oxygen concentrations in the Reservoir in the upper layer (1 m and 2 m); however, dissolved oxygen concentrations in the deeper layers of the Reservoir was improved compared to the two previous sampling events (Figure 15). The average dissolved oxygen concentration for the 1 m and 2 m depths along the transect was 6.6 mg/L indicating the Reservoir was in attainment of the dissolved oxygen standard. The extent of the anoxic zone in the bottom portion of the Reservoir decreased dramatically from the previous two sampling events (Figure 15). The average dissolved oxygen concentration at these depths was 3.16 mg/L which is a large increase from the previous sampling events.

Oxidation reduction potential (ORP) measurements are used to quantify the exchange of electrons that occur during oxidation-reduction reactions (redox reactions), with electrical activity being reported in millivolts (mV), very similar to a pH probe. At the water-sediment boundary layer, microbial organisms facilitate the chemical reactions but do not actually oxidize or reduce the compounds. The redox reactions provide energy for microbial cells to carry out their metabolic processes (Wetzel 2001). The combination of microbial organisms and redox reactions are responsible for the breakdown of organic matter and development of anoxic conditions near the sediment boundary in reservoirs during the summer, and as a result soluble nutrients (nitrogen and phosphorus) are released as well as other forms of iron, manganese and sulfur.

In Cherry Creek Reservoir, the water column ORP measurements will often range between 100 to 300 mV depending upon the seasonal conditions. On any given date, the water column ORP conditions, from the surface waters down to approximately the 6 m layer, will be relatively uniform because there is sufficient dissolved oxygen in the water column to maintain

GEI Consultants, Inc. 24 March 2015 2014 Cherry Creek Monitoring Report

compounds in their most oxidized state. However, when anoxic conditions exist at depths greater than 6 m or near the water-sediment interface, the redox potential will sharply decrease, often ranging from -200 to 0 mV, indicating conditions that facilitate internal nutrient loading as well as other elemental releases. When reviewing ORP profile measurements (Figure 16), the occurrence of a sharp inflection point (i.e., low or negative values) in the profile indicates where conditions are favorable for redox reactions to occur.

Figure 16: Oxidation reduction potentials (ORP) in Cherry Creek Reservoir for three dates based on transect profile data during the 2014 WY. The ORP scales for each transect are all relative to each other within and among sampling events.

GEI Consultants, Inc. 25 March 2015 2014 Cherry Creek Monitoring Report

The June 24th ORP conditions near the water-sediment interface do not indicate a strong reducing environment such as observed on July 22nd, yet the dissolved nutrient conditions near the bottom indicate loading was occurring. The August 19th ORP conditions were also less indicative of a strong redox condition near the bottom, and dissolved nutrient conditions show that loading was considerably less than the June 24th sampling event.

The oxidation-reduction potential profiles on July 22nd indicate that conditions were favorable for a reducing environment at the water-sediment interface (Figure 16). This interface acts as a barrier to the free exchange of soluble phosphorus between water and sediment, and when conditions are favorable (e.g., anoxic-reducing environment) phosphorus is released (i.e., internal load) at rates as much as 1,000 times faster than during well oxygenated conditions (Horne and Goldman 1994). Although the rate of exchange of nutrients (mainly phosphorus) at this interface remains unknown for Cherry Creek Reservoir, the internal loading component of the Reservoir has been estimated to account for approximately 25% of the cumulative total phosphorus load from 1992 to 2006 (Nürnberg and LaZerte 2008).

4.1.4 2014 WY Nutrients

Monitoring at Cherry Creek Reservoir has focused on the concentrations of phosphorus and nitrogen, because these inorganic nutrients are often the contributing or limiting factor in the growth of algae (Cole 1979; Horne and Goldman 1994; Wetzel 2001; Cooke et al. 1993). Excessive amounts of these nutrients in aquatic systems often result in algal blooms that create aesthetic problems as well as potentially unsuitable conditions for aquatic life. An imbalance in the nitrogen and phosphorous relationships (i.e., ratios) can result in one element limiting algal growth, or both could be limiting at different times of the year. Ultimately, the nutrient concentrations need to be relatively less to greatly reduce algal biomass as measured by chlorophyll a.

During the 2014 WY, the photic zone mean concentration of total phosphorus ranged from 40 to 130 μg/L with an overall water year mean of 86 μg/L. The seasonal (July through September) photic zone mean concentrations ranged from 40 to 120 μg/L (Figure 17), with a seasonal mean of 87 μg/L. In May and June 2014, storm-induced external loads likely contributed to the total phosphorus content within the photic zone; however, other factors such as internal loading and algal uptake also affected the seasonal pattern.

GEI Consultants, Inc. 26 March 2015 2014 Cherry Creek Monitoring Report

400 200 Total10 (µg/L) Nitrogen ×

USACE Inflow (µg/L) Phosphorus Total Total Phosphorus 300 Total Nitrogen 150

200 100 Inflow (af/d) 100 50

0 0 Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct

Figure 17: Annual pattern of photic zone total phosphorus, total nitrogen and USACE inflow in Cherry Creek Reservoir, 2014 WY.

Patterns in soluble reactive phosphorus concentrations collected during profile sampling at Site CCR-2 showed a well-mixed Reservoir from October to mid-May (Figure 18). There was an extended period of nutrient release from bottom sediments from mid-May through late August as revealed by the pattern of increasing total phosphorus concentrations for 7 m layer as compared with concentrations observed at the same layers during the spring and late fall periods (Figure 18). The period of internal phosphorous loading shows a substantial increase in phosphorus at the 7 m depth from mid-June to mid-August. During this period, the soluble reactive phosphorus fraction in the 7 m water layer accounted for approximately 57 to 85% of the total phosphorus content, also supporting evidence that phosphorus was being released from the sediment during that time.

During 2014, the aeration system was not operating in the Reservoir because the CCBWQA decided to re-evaluate phytoplankton dynamics in the absence of aeration to provide more information for the Reservoir model development. In previous years when the aeration system was operational, there was more consistency within the upper layers due to the upward diffusion of phosphorus from the sediment layer at approximately 7 m, and the eventual circulation within the upper layers by the aeration system. In terms of nutrient concentrations, the aeration system appears to create a well-mixed layer from the surface down to approximately the 6 m depth (GEI 2013), which is slightly above the aerator heads (approximately 0.75 m above the sediment). However, this consistency in the upper layers of the Reservoir was not as apparent during June through September 2014, as in recent years when the destratification system was operating.

Photic zone total nitrogen mean concentrations ranged from 583 to 1,258 µg/L, with a 2014 WY average of 951 µg/L (Figure 17). During the July through September period, the photic zone total nitrogen concentration also ranged from 583 to 1,184 µg/L, with a mean concentration of 904 µg/L (Figure 17).

GEI Consultants, Inc. 27 March 2015 2014 Cherry Creek Monitoring Report

Figure 18: Soluble phosphorus concentrations recorded for the photic zone and at depth during routine monitoring during the 2014 WY at CCR-2.

4.1.5 Long-Term Phosphorus Trends in Cherry Creek Reservoir Routine monitoring data collected since 1987 indicates a general increasing pattern in summer mean concentrations of total phosphorus in the photic zone of the Reservoir (Figure 19). In 2014, the July through September mean concentration of total phosphorus was 87 μg/L. This value is less than last year’s 125 µg/L concentration, and it is equal to the long-term median value of 87 µg/L (Table 4). Regression analyses performed on 1997 to 2014 seasonal mean total phosphorous data indicates a significant (p = 0.006) increasing trend. The 2014 seasonal mean total phosphorus concentration is within the range of historical conditions absent aeration (i.e., prior to 2008) and reflect the variability observed in the algal biomass data (i.e., chlorophyll a). The 2011, 2012, and 2013 seasonal mean concentrations also reflect the more uniform conditions observed in the algal biomass data. Algal biomass or its relative phosphorus content is included in the total phosphorus fraction which is apparent in the total phosphorus data.

Figure 19: Seasonal mean (July through September) total phosphorus concentrations (μg/L) measured in Cherry Creek Reservoir, 1987 to 2014. Error bars represent a 95% confidence interval for each mean.

GEI Consultants, Inc. 28 March 2015 2014 Cherry Creek Monitoring Report

Table 4: Comparison of water year mean and July through September mean phosphorus, nitrogen, and chlorophyll a levels in Cherry Creek Reservoir, 1988 to 2014. Total Nitrogen (μg/L) Total Phosphorus (μg/L) Mean Chlorophyll a (μg/L) Year WY Jul-Sep WY Jul-Sep WY Jul-Sep 1988 902 1,053 52 49 21.8 31.8 1989 803 828 45 39 8.5 5.6 1990 600 -- 58 55 2.3 8.6 1991 1,067 1,237 86 56 9.7 9.8 1992 931 970 52 66 12.2 17.4 1993 790 826 55 62 12.6 14.8 1994 1,134 1,144 53 59 11.4 15.4 1995 910 913 46 48 12.7 15.6 1996 889 944 35 62 13.4 18.2 1997 981 1,120 70 96 16.4 22.2 1998 763 880 77 89 18.4 26.6 1999 709 753 76 81 21.6 28.9 2000 774 802 80 81 22.3 25.1 2001 764 741 84 87 26.0 26.1 2002 825 858 70 74 21.7 18.8 2003 987 1,121 83 90 22.7 25.8 2004 929 977 85 102 19.1 18.4 2005 916 990 93 116 16.3 17.1 2006 874 914 96 87 13.7 14.7 2007 880 716 108 118 21.4 12.6 2008 795 800 92 118 15.8 16.6 2009 1,173 1,236 85 98 12.4 13.2 2010 925 974 92 101 23.6 31.0 2011 904 987 110 154 25.6 26.7 2012 891 923 114 141 24.0 27.1 2013 995 983 101 125 24.8 26.8 2014 951 904 86 87 23.4 24.4 Mean 891 946 77 87 17.5 20.0 Median 902 937 83 87 18.4 18.4

GEI Consultants, Inc. 29 March 2015 2014 Cherry Creek Monitoring Report

4.1.6 2014 WY Chlorophyll a Levels

The annual pattern of chlorophyll a concentrations was quite variable throughout the 2014 WY. From October 2013 through September 2014, chlorophyll a concentrations ranged from 6.1 µg/L to 43.3 µg/L with a 2014 WY mean chlorophyll a concentration of 23.4 μg/L (Figure 20). During the regulatory growing season (July through September) 5 of the 6 Reservoir mean chlorophyll a concentrations were greater than 18 µg/L standard (Figure 20), and showed considerable variability early in the growing season. The July through September seasonal mean chlorophyll a concentration was 24.4 µg/L, with a peak seasonal reservoir mean concentration of 34.8 µg/L. The winter (February) under ice chlorophyll a level was the highest observed concentration and was followed by the transitional period from a winter to a spring algae assemblage which resulted in a decreasing chlorophyll a pattern. This pattern is typical of historical conditions, absent the destratification system, when Reservoir conditions typically resulted in the lowest chlorophyll a concentrations in June. While the Reservoir again revealed the lowest observed chlorophyll a concentration in June, this event was preceded by a cyanobacteria bloom (Anabaena flos-aquae) that resulted in 37.5 µg/L of chlorophyll a. A wind-driven mixing event caused the cyanobacteria population to crash just prior to sampling the Reservoir on June 24th. Following the cyanobacteria population crash in late June, different algae assemblages resulted in the high chlorophyll a concentrations in July which are very similar to the cyanobacteria driven event. Based solely on chlorophyll a concentrations, the June and July events are the nearly identical, yet different algae assemblages were responsible for the same level of chlorophyll a. A late July storm event, again affected Reservoir conditions which caused the shift in chlorophyll a concentrations; though not as drastic as observed in late June. Chlorophyll a concentrations averaged 19.3 µg/L in late summer (August and September).

Figure 20: Concentration of chlorophyll a (μg/L) in Cherry Creek Reservoir, 2014 WY. Error bars represent a 95% confidence interval around each mean. Highlighted area denotes the seasonal period for the chlorophyll a standard.

GEI Consultants, Inc. 30 March 2015 2014 Cherry Creek Monitoring Report

4.1.7 Long-term Chlorophyll a Trends in Cherry Creek Reservoir

Since 1987, there is no significant increasing or decreasing trend in the seasonal mean chlorophyll a concentration over time (Figure 21); although patterns in the data correspond to different annual conditions (e.g. dry summer, 2002; wet summers, 2007 and 2009) or different reservoir management strategies (2008-2013). In the summer of 2008, the seasonal operation of the Reservoir destratification system began and continued through 2013. In 2014, the destratification system was not operated to specifically examine the phytoplankton community dynamics in terms of both composition and biomass (chlorophyll) to the absence of continuous mixing by the destratification system. Under destratification management, the period from 2010 through 2013 represented a new state of conditions for the Reservoir. The 2010 seasonal mean chlorophyll a concentration (31.0 µg/L) represents the highest seasonal level observed during destratification operation or for the history of the Reservoir, and highlights the propensity of algae to respond to optimal growing conditions. The 2011 through 2013 seasonal mean chlorophyll a concentrations averaged 28.6 µg/L, and were considerably greater than the chlorophyll a standard. While the destratification was not operated in 2014, the chlorophyll a concentration remained relative high at 24.4 µg/L and is statistically indistinguishable from the previous 4 years.

For regulatory assessment purposes (i.e. 303d listing), the site-specific chlorophyll a standard has two assessment components – a numeric level and an allowable exceedance frequency. In essence, the Reservoir is allowed to exceed the numerical standard one time over a 5-year sequential period. The 2014 seasonal mean chlorophyll a concentration represents the fifth consecutive year the Reservoir has exceeded the numeric standard, as well as the allowable exceedance frequency (Figure 21).

50 Compliance Period 40

(µg/L) 30 a

20

Chlorophyll a

Chlorophyll Chlorophyll Standard = 18 µg/L 10

0 1987 1989 1991 1993 1995 1997 1999 2001 2003 2005 2007 2009 2011 2013

Figure 21: Seasonal mean (July through September) concentrations of chlorophyll a (μg/L) measured in Cherry Creek Reservoir, 1987 to 2014. Error bars represent a 95% confidence interval around each mean. The Reservoir destratification system was operated from 2008 through 2013.

GEI Consultants, Inc. 31 March 2015 2014 Cherry Creek Monitoring Report

4.2 Reservoir Biology

4.2.1 2014 Phytoplankton

The 2014 summer season represented conditions in the reservoir absent the influence of the destratification system. More specifically, the destratification system was not operated to evaluate the response of the algae assemblages and to establish conditions without aeration under the current phytoplankton analyst (Aquatic Analysts). Given the absence of continuous mixing, there were stakeholder concerns regarding the potential development of large filamentous cyanobacteria which may also produce cyanotoxins. As such, additional opportunistic phytoplankton samples were collected during the summer to document the June cyanobacteria bloom in different areas of the Reservoir, including the swim beach area.

During the routine sampling events, the phytoplankton total density in the photic zone composite samples (CCR-1, CCR-2, and CCR-3) ranged from 838 #/mL on June 24th to 15,489 #/mL on October 14th (Table 5). These samples are representative of the algal populations that were present within the upper 3 m of the water column at the time of sampling. The number of algal taxa present during each of these sampling events ranged from 8 on February 11th, to 31 on May 13th. A number of opportunistic samples were collected from June 10th through June 24th to document the cyanobacteria bloom. On June 9th, GEI was notified that an algae bloom was occurring in the Marina area as well as the other parts of the Reservoir; therefore, multiple surface water samples were collected on June 10th in addition to the routine photic zone composite sample. The CCR-1 and CCR-2 surface composite sample and the CCR-2 surface sample revealed total phytoplankton densities of 52,234 #/mL and 62,999 #/mL, respectively, and with a total of 10 taxa each. The Marina surface water sample revealed a total density of 9,020 #/mL, and 14 total taxa. In both open water surface samples, Anabaena flos-aquae (large filamentous cyanobacteria containing gas vacuoles) accounted for greater than 96% of the algae identified, and greater than 80% of the algae identified in the Marina surface water sample. The differences observed in the Anabaena flos-aquae density between the photic zone composite sample (1,481 #/mL) and other surface water samples (50,102 #/mL and 61,590 #/mL) highlights this species ability to rapidly grow at the surface by regulating their buoyancy via their gas vacuoles (Table 5). On June 13th, GEI also received a request from the CCBWQA to collect additional samples, prior to the weekend, to document conditions of the cyanobacteria bloom. Samples were collected from Site CCR-2, the Marina, and the swim beach area with phytoplankton total density ranging from 3,178 #/mL to 9,020 #/mL. Cyanobacteria accounted for more than 73% of the individuals identified in the swim beach and Site CCR-2 samples and 40% of the individuals identified in the Marina sample. On June 17th, the cyanobacteria bloom had accumulated along the face of the dam and created a visually dense layer of biomass on the surface of the Reservoir. A single surface water sample was collected from near the outlet tower, and represented a worse-case scenario for the cyanobacteria bloom. Cyanobacteria density was 226,402 #/mL and represented over 98% of the algae identified in the sample.

GEI Consultants, Inc. 32 March 2015 2014 Cherry Creek Monitoring Report

During this cyanobacteria bloom, cyanotoxin samples were also collected (Section 4.6.1) and analyzed by GreenWater Laboratory and when cyanotoxins were present the laboratory identified and enumerated the cyanobacteria in the sample to help document the species likely responsible for the toxins. While these samples were not preserved (toxin analyses require raw water) and identified using a different phytoplankton method, their results are consistent with Aquatic Analysts. For example, GreenWater Laboratory reported a cyanobacteria density of 54,807 #/mL for the CCR-2 surface water sample collected on June 10th (Appendix E) while Aquatic Analysts reported a cyanobacteria density of 61,590 #/mL for the same sample. Similarly, GreenWater Laboratory reported a cyanobacteria density of 133,411 #/mL for Dam surface water sample collected on June 17th, while Aquatic Analysts reported a cyanobacteria density of 226,402 #/mL for the same sample.

Based on the calendar year, the assemblage was dominated in terms of density by chlorophytes (green algae, 47%), with cryptomonads and diatoms being the next most abundant taxonomic groups at 30% and 16%, respectively (Figure 22). In 2014, the relative percent density of cyanobacteria was 2.2%. In February, green algae were the dominant algal group (81%) followed by cryptomonads (15%). In March, cryptomonads were the dominant algal group (72%) followed by green algae (12%). Green algae abundance was variable throughout 2014; however, they were relatively abundant throughout many of the sampling events (Figure 22). Cryptomonads were especially abundant during the March, late June, and early July sampling events (Figure 22).

Cryptophytes Diatoms Chrysophytes Dinoflagellates Cyanobacteria Euglenoids Chlorophytes

100 Crytophytes Diatoms Chrysophytes Dinoflagellates Cyanobacteria Euglenoids Chlorophytes Unidentifed Flagellate 80

60

40

20 Percent Relative Density Relative Percent

0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Figure 22: Percent relative density of algal groups for each routine photic zone composite sample collected in Cherry Creek Reservoir, 2014 CY.

GEI Consultants, Inc. 33 March 2015 2014 Cherry Creek Monitoring Report

Table 5: Density (#/mL) of phytoplankton and total number of taxa for routine photic zone composite samples representative of the three samples sites on Cherry Creek Reservoir, and for opportunistic grab/composite samples in other Reservoir locations, 2014 CY. Taxonomic Group Sample Green Cyano- Golden Dino- Crypto- Unidentified Total Total Date Diatoms Algae bacteria Algae Euglenoid flagellate monads Flagellate Density Taxa Routine Photic Zone Composite Samples (CCR1,2,3) 2/11/2014 113 6,089 -- 56 -- 113 1,128 -- 7,498 8 3/12/2014 349 476 -- 159 -- 127 2,985 32 4,129 16 4/15/2014 593 902 -- 155 26 26 1,469 26 3,196 21 5/13/2014 413 1,766 -- 413 113 38 639 -- 3,383 31 5/27/2014 204 1,923 204 58 -- -- 2,272 -- 4,661 22 6/10/2014 152 1,063 1,481 ------1,367 38 4,100 15 6/24/2014 19 173 29 ------617 -- 838 11 7/08/2014 1,298 1,298 45 45 -- -- 4,295 -- 6,980 14 7/22/2014 674 1,611 -- -- 29 703 293 -- 3,309 28 8/05/2014 671 900 18 -- 53 106 441 -- 2,188 25 8/19/2014 1,162 726 -- -- 18 18 236 -- 2,161 21 9/02/2014 2,553 1,830 ------681 -- 5,063 23 9/16/2014 1,718 4,209 ------86 172 -- 6,185 22 10/14/2014 569 8,542 -- 114 114 342 5,581 228 15,489 18 11/04/2014 2,182 7,032 -- 364 121 242 2,667 -- 12,609 22 Opportunistic Grab/Composite Samples 6/10/2014a 82 1,394 50,102 ------656 -- 52,234 10 6/10/2014b 70 634 61,590 ------705 -- 62,999 10 6/10/2014c 150 1,353 9,772 ------902 -- 12,177 13 6/13/2014b 50 752 7,316 ------902 -- 9,020 14 6/13/2014c 68 1,128 1,264 ------683 34 3,178 16 6/13/2014d 117 933 5,132 ------467 -- 6,648 15 6/13/2014e 237 576 2,713 ------170 -- 3,696 14 6/17/2014f -- 2,706 226,402 ------902 -- 230,010 5 6/24/2014d 31 194 31 ------398 -- 654 10 a CCR-1 and CCR-2 surface b CCR-2 surface c Marina surface d CCR-2 photic composite e Swim beach surface f Dam surface

GEI Consultants, Inc. 34 March 2015 2014 Cherry Creek Monitoring Report

When the size (e.g., biovolume) of each alga is considered during each routine photic zone composite sample (Figure 23), green algae were the most dominant algal group (28%) observed over the course of the year, followed by cryptophytes (22%) and diatoms (17%). Both the dinoflagellates and cyanobacteria accounted for approximately 15% of the total algal biovolume. Patterns in algal biovolume show typical seasonal succession patterns of many temperate lakes and reservoirs with cryptomonads and diatoms being most abundant in the spring, while green algae were abundant throughout the year and comprising a larger component of the assemblage in winter and fall.

In February 2014, the green algae (Chlamydomonas sp.), and the flagellated cryptomonad algae (Cryptomonas erosa) were the most abundant in terms of biovolume and density. In March, the biovolume of green algae decreased substantially and cryptomonads were the dominant algal group. In the Rocky Mountain region, cryptomonads appear to prefer colder water (Kugrens and Clay 2003) which explains their abundance in late winter and spring. This could partially explain the increased density of cryptomonads during the sampling events. In April, cryptophytes continued to be dominant in terms of density; however, the diatoms (Astrionella formosa and Stephanodiscus astraea minutula) were dominant in terms of biovolume. In early May, Scenedesmus quadricauda (green algae) was the most abundant species in terms of density, but Cryptomonas erosa continued to dominant biovolume. In late May, the cryptomonad (Rhodomonas minuta) was the most abundant species in terms of density, while the cyanobacterium (Anabaena flos-aquae) comprised a larger percentage of the biovolume.

Factors contributing to the cyanobacteria bloom in June were evident in the data collected during the May 27th sampling event. The May 27th temperature and dissolved oxygen profiles and the CCR-2 7m soluble reactive phosphorus data all indicated that thermal stratification was present and that internal phosphorus loading was beginning to occur. When these data are considered in the context of the phytoplankton biovolume data, the Reservoir conditions were conducive for the subsequent algal bloom in June. On May 27th, a cyanobacterium (Anabaena flos-aquae) accounted for 41% of the total algal biovolume, and by June 10th their biovolume accounted for 84% of the total biovolume. Anabaena flos-aquae is a filamentous cyanobacterium whose trichome is composed of many individual cells, including a gas- vacuole, to form one physiological entity that has the ability to fix atmospheric nitrogen (Komárek et al. 2003). These physiological characteristics allowed this species to grow very rapidly at the surface of the Reservoir and create a visible algal biomass layer that covered much of the Reservoir surface. Following their population crash in late June, A. flos-aquae accounted for 11% of the biovolume, while cryptomonads (Cryptomonas erosa and Rhodomonas minuta) became the most dominant taxa in terms of biovolume at 72%. Other cyanobacteria taxa were present during the routine sampling events from late May through early August which included Aphanizomenon flos-aquae and Aphanothece sp. (picoplankton) but their biovolume accounted for less than 2.6% and 0.1% of the total algal biovolume, respectively. The cyanobacteria (e.g., Aphanizomenon flos-aquae and Anabaena flos-aquae)

GEI Consultants, Inc. 35 March 2015 2014 Cherry Creek Monitoring Report

typically dominate late summer algal assemblages (Whitton and Potts 2000; James et al. 1992; Padisák 1985, Konopka and Brock 1978; Pollingher 1987) which makes the A. flos-aquae bloom in early June unique, including for Cherry Creek Reservoir.

During late July, the algal assemblage was transitioning from a diatom – cryptomonad dominated community to one dominated by dinoflagellates (77%), in terms of biovolume. In early August, the algal assemblage was more balanced when euglenoids (11%), cryptophytes (16%), diatoms (17%), green algae (22%), and dinoflagellates (31%) contributed more evenly to the total biovolume. From late August through September, the algal assemblage again transitioned to assemblages dominated (i.e., biovolume) by diatoms and green algae. These observed successional patterns of algal dominance are closely coupled with reservoir conditions such as cooler water temperature during the spring followed by the warmer water and longer photoperiod conditions of the summer and the cool down during the fall. In addition, nutrient resources are a key component to the successional pattern as well as the ability of each taxon to outcompete other taxa for the resources. Other biological factors such as zooplankton and forage fish grazing influence the algal succession pattern too.

The relative density and biovolume of algae is largely a response to bottom-up factors that promote growth such as inorganic nutrients, light, temperature, and pH which are closely coupled with top-downs factors such as predation (i.e., zooplankton grazing), life history traits (i.e., cyst production) and outflow (Pollingher 1987). The bottom-up factors were evident during the summer season when internal phosphorus loading began in May.

Cryptophytes Diatoms Chrysophytes Dinoflagellates Cyanobacteria Euglenoids Chlorophytes

100

80

60

40

20 Percent Relative Biovolume Percent Relative

0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Figure 23: Percent relative biovolume of algal groups for each routine photic zone composite sample collected in Cherry Creek Reservoir, 2014 CY.

A key aspect in the algal successional patterns is that cyanobacteria were only dominant during a few weeks in late-May and early June (Figures 22 and 23). Only 14 days after the

GEI Consultants, Inc. 36 March 2015 2014 Cherry Creek Monitoring Report

cyanobacteria bloom was observed on June 10th, this group comprised less than 5% of the assemblage in terms of density and approximately 27% in terms of biovolume.

In the event of reduced top-down pressure such as low zooplankton grazing, the algal assemblage can maximize their relative density given the influence of the bottom-up factors. It is unlikely that the zooplankton population was able to effectively exert top-down controls on the algal population during the summer 2014 conditions. The large gizzard shad (forage fish) population may be over-grazing the zooplankton population such that algae growth remained unchecked during their peak growing period. Communities dominated by large zooplankton populations tend to show reduced algal biomass yields as these herbivores effectively reduce the number of algae in the water column (Sarnelle 1992; Mazumder 1994; Mazumder and Lean 1994). These patterns are not observed in the Reservoir. However, this relationship can be affected by the relative biomass (e.g., size) of the individual algae. For example, if the algal assemblage is dominated by filamentous or colonial cyanobacteria, zooplankton will preferentially graze on more palatable and preferred algae such as diatoms, cryptomonads, and green algae (Vanni and Temte 1990). This condition was apparent during early July when the zooplankton assemblage responded to the more palatable algae – diatoms and cryptomonads.

In 2014 the Reservoir exhibited high biomass levels (i.e., chlorophyll a) at various periods throughout the year. In February 2014, the high chlorophyll a concentration of 43.3 µg/L was associated with primarily with the high density and biovolume of Chlamydomonas sp. (green algae). In early June 2014, the high chlorophyll a concentration of 37.5 µg/L was associated with the high density and biovolume of Anabaena flos-aquae (cyanobacteria, 84%). The chlorophyll a concentration in late June decreased to 6.1 µg/L which was associated with the crash of the cyanobacteria bloom and subsequent low algal density in the Reservoir (838 #/mL, Table 5). Following this marked decrease in the chlorophyll a concentration, high chlorophyll a concentrations were observed during both July sampling events (34.5 and 34.8 µg/L). These chlorophyll a concentrations were associated with the increased density and biovolume of Melosira ganulata (diatom), Cryptomonas erosa (cryptomonad) and Peridinium cinctum (dinoflagellate).

4.2.2 Long-Term Phytoplankton

In previous years, phytoplankton data was compared based on the pre- and post-aeration system timeframe; however, due to circumstances in 2009 there was a change in laboratory regarding the phytoplankton analyses. This laboratory change confounded the pre/post destratification results regarding algal density. After extensive discussion about the datasets and laboratory methodologies, it was determined that the differences resulted in data not directly comparable. The methodological differences centered on each laboratory’s ability to document picoplankton to the genus/species level and to document biovolume estimates for all types of algae. Neither laboratory was able or is able to document both types of information. The current laboratory provides both density and biovolume data to adequately

GEI Consultants, Inc. 37 March 2015 2014 Cherry Creek Monitoring Report

characterize the large filamentous cyanobacteria which are the “algae of concern” and which destratification management is designed to control or reduce. The current laboratory also provides both density and biovolume data that adequately characterizes the algae assemblage to document which types of algae contribute to the chlorophyll a concentration (algae biomass), as well as providing data suitable for modeling purposes.

Therefore, phytoplankton data collected prior to 2009 are not discussed in the context of long-term phytoplankton analyses, and the focus has shifted to the period from 2009-2014 with the current laboratory. This period contains 5 years of data with destratification and one year without destratification (2014).

From 2009 through 2014, algal percent relative density has been variable among the years (Figure 24). Reservoir conditions in 2009, were different from the other years in the sense that seasonal mean chlorophyll a concentration was low (13.2 µg/L) compared to other years under aeration when concentrations have ranged from 24.1 µg/L to 31µg/L. In 2009, the cryptomonads dominated algal abundance (45%), and were followed by diatoms (23%) and green algae (22%) (Figure 24), yet in terms of biovolume, the diatoms comprised the largest percentage (60%) of the community (Figure 25). In 2009, the cyanobacteria density accounted for 0.7% of the community, and their relative biovolume accounted for 2.2% of the community. From 2010 through 2013, there was more consistency with respect to their relative densities among the three dominant types of algae (cryptomonads, diatoms, and green algae; Figure 24); although the relative biovolume data showed more variability with diatoms, euglenoids, and cyanobacteria (Figure 25). The relative biovolume for both cryptomonads and green algae were consistent during this period. In terms of biovolume, cyanobacteria accounted for 17.4%, 4.2%, 18.5%, and 5.3% over the four year period from 2010 to 2013.

In 2014, some algae groups revealed density and biovolume conditions that were slightly different than the previous 4 years, yet most of the algae groups revealed conditions within the range of conditions previously observed. In 2014, the green algae revealed greater percentages for both density and biovolume as compared to previous years, while the same metrics for the diatoms were both less than the previous years. Cyanobacteria relative percent density (2.2%) and biovolume (15%) were both in the range of conditions previously observed for the Reservoir.

GEI Consultants, Inc. 38 March 2015 2014 Cherry Creek Monitoring Report

Cryptophytes Diatoms Chrysophytes Dinoflagellates Cyanobacteria Euglenoids Chlorophytes Miscellaneous 100

80

60

40

20 Percent Relative Density Relative Percent

0 2009 2010 2011 2012 2013 2014

Figure 24: Percent algal density of major taxonomic groups in Cherry Creek Reservoir from 2009 through 2014, by CY.

Cryptophytes Diatoms Chrysophytes Dinoflagellates Cyanobacteria Euglenoids Chlorophytes Miscellaneous 100

80

60

40

20 Percent Biovolume Relative

0 2009 2010 2011 2012 2013 2014

Figure 25: Percent algal biovolume of major taxonomic groups in Cherry Creek Reservoir from 2009 through 2014, by CY.

4.2.3 2014 Zooplankton

Zooplankton density ranged from 139 organisms/L in late March to 1,239 organisms/mL which occurred in early July 2014 (Figure 26). Over the WY, the zooplankton assemblage contained a total of nine zooplankton crustacean species—seven cladocerans and two copepods with immature copepodids and nauplius—and nine species of rotifers were collected during the

GEI Consultants, Inc. 39 March 2015 2014 Cherry Creek Monitoring Report

15 sampling events (Appendix E). There was one species that was collected during all sampling events: a relatively smaller cladoceran (Bosmina longirostris). The immature copepods (copepodids and nauplius) were also observed during all 15 sampling events. The copepod (Diacyclops thomasi) was collected at 14 of the 15 sampling events (Appendix E). Bosmina longirostris have been found to be the dominant cladoceran in other eutrophic lakes (Harman et al. 1995). One rotifer (Keratella cochlearis) was collected during 12 of the 15 sampling events and one cladoceran (Daphnia sp.) was collected during 11 of the 15 sampling events (Appendix E). Cladocera were low in abundance throughout the late winter and early spring; however, they became relatively abundant during mid-May through July 2014. Copepods did comprise the majority of the zooplankton assemblage during most sampling events (Figure 26). Both the copepods and rotifers substantially increase their density during the early July algal bloom that was comprised mainly of diatoms and cryptomonads. While the zooplankton assemblage showed some response to the algal assemblages and biomass, there is no statistical correlation between the zooplankton density and chlorophyll a (surrogate for algal biomass). Similarly, there was no correlation between zooplankton density and algal density or algal biomass.

Figure 26: Total density of zooplankton groups and chlorophyll a concentration by sample date in Cherry Creek Reservoir, 2014 CY.

Ideally, the pattern between zooplankton density and chlorophyll a (algal biomass) should be inversely related, as herbivorous zooplankton could theoretically affect algal biomass via grazing pressure, provided planktivorous fish are not suppressing the zooplankton populations (Harman et al. 1995). However, in Cherry Creek Reservoir, the increased abundance of gizzard shad has likely increased the grazing pressure on the zooplankton assemblage, thereby reducing the zooplankton density and reducing their ability to effectively control the algal assemblage. Notably, the cladoceran – Daphnia lumholtzi – was observed in the Reservoir from early August through November 2014. This species is considered an Aquatic Nuisance Species (ANS) and was also observed in 2011 and 2012.

GEI Consultants, Inc. 40 March 2015 2014 Cherry Creek Monitoring Report

This species has two relatively long spines on the head and tail which may affect fish that feed on zooplankton, plus this species may out-compete other native cladocera for resources. 4.3 Stream Water Quality

4.3.1 2014 WY Phosphorus Concentrations in Streams

The median annual total phosphorus concentration for base flow conditions ranged from 36 µg/L at Site CT-P1 to 340 μg/L at Site MCM-1 (Table 6). The median seasonal (July through September) base flow total phosphorous concentration was greater than the annual median concentration at all three Cherry Creek sites (sites CC-10, CC-Out @ I225, and EcoPark) and three of the four Cottonwood Creek sites (sites CT-P1, CT-P2 and CT-1; Table 6). The seasonal median concentration of total phosphorous was 1 μg/L less than the median annual phosphorous concentration at Site CT-1 (Table 6). The seasonal median concentration of total phosphorus ranged from 49 μg/L at Site CT-P1 to 500 μg/L at Site MCM-1. At all stream sites, except McMurdo Gulch, where storm samples are not collected, the storm flow total phosphorous concentration was greater than concentrations during base flow conditions. The annual median storm flow total phosphorous concentrations ranged from 97 μg/L at Site CT-2 to 472 μg/L at Site CC-10 (Table 6).

Table 6: Comparison of median base flow and median storm flow concentrations of total phosphorus (TP) and total suspended solids (TSS) in tributaries to Cherry Creek Reservoir, 2014 WY. Base Flow Storm Flow July - September Annual Annual TP TSS TP TSS TP TSS Stream/Site (µg/L) (mg/L) (µg/L) (mg/L) (µg/L) (mg/L) Cherry Creek EcoPark 133 15 122 8 472 155 CC-10 213 7 197 11 326 84 CC-Out @ I225 154 13 98 12 -- -- Cottonwood Creek CT-P1 49 16 36 10 240 123 CT-P2 68 20 38 13 189 58 CT-1 74 31 69 24 174 59 CT-2 47 12 48 15 97 23 McMurdo Gulch MCM-1 500 -- 340 6 -- -- MCM-2 305 7 3001 12 -- --

1 Outlier concentration (1.342 µg/L) was removed for assessment purposes.

GEI Consultants, Inc. 41 March 2015 2014 Cherry Creek Monitoring Report

Total suspended solids were generally consistent across all sites during base flow conditions during the 2014 WY. The annual median annual total suspended solids concentrations for base flow conditions ranged from 6 mg/L at MCM-1 to 24 mg/L at CT-1 (Table 6). The median seasonal (July through September) base flow total suspended solids concentrations were greater at five of the seven sites compared to the annual median concentrations, and ranged from 7 mg/L at Site CC-10 to 31 mg/L at Site CT-1.. At all stream sites, with the exception of McMurdo Gulch sites, the storm flow total suspended solids concentration was greater than concentrations during base flow conditions. The annual median storm flow total suspended solids concentrations ranged from 23 mg/L at Site CT-2 to 155 mg/L at Site CC-10 (Table 6).

4.3.2 Long-Term Trends in Phosphorus Concentrations in Cherry Creek Reservoir Tributaries

Long-term patterns (1995 to 2014) in total phosphorus and soluble reactive phosphorus concentrations were evaluated for the two main tributary sites (CC-10 and CT-2) to Cherry Creek Reservoir, for both base flow and storm flow conditions. The long-term median annual base flow total phosphorus concentration for Cherry Creek (Site CC-10) is 207 µg/L and (Table 7), with storm flow concentrations being approximately 74% greater with a median phosphorous concentration of 360 µg/L (Table 8). In Cottonwood Creek (Site CT-2), the long-term median annual base flow total phosphorus concentration is 69 µg/L; however, the long-term median storm flow concentration is approximately 2.5 times greater (175 µg/L). The long-term median soluble reactive phosphorus fraction in base flows for Cherry Creek were approximately 79% of the long-term median total phosphorus concentrations, while soluble reactive phosphorus fractions in Cottonwood Creek (Site CT-2) have been approximately 16% of total phosphorus concentrations.

In the Colorado regulatory proceedings there is precedence for only considering the last 5 years of data in the hearing for standard levels because conditions may change over time. Therefore, median values for the most recent 5-year period have been provided for comparison to long-term statistics (2010 through 2014, Tables 7 and 8). In Cottonwood Creek, total phosphorous concentrations have decreased (Tables 7 and 8) due to the CCBWQA’s efforts in stream reclamation to reduce erosion, reductions in nutrient discharges from point sources and other storm management practices implemented within the watershed. In Cherry Creek, the long-term metrics are very similar to the last 5 years of data, with exception of the storm flow metrics. In the last 5 years, storm flow total phosphorous and soluble reactive phosphorus concentrations have increased by approximately 50 µg/L when compared to the long-term metric. However, the maximum storm flow total phosphorus and soluble reactive phosphorous concentrations have decreased over the years (Figures 27 and 28).

Base flow total phosphorus and soluble reactive phosphorus concentrations revealed significant (p < 0.001) decreasing trends during base flow conditions at site CC-10 and CT-2 over time

GEI Consultants, Inc. 42 March 2015 2014 Cherry Creek Monitoring Report

(Figures 27 through 30). The observed decreasing trend and greatly reduced variability in soluble reactive phosphorus concentrations at Site CT-2 from 1995 to 2014 is the result of the effectiveness of the PRFs near the Perimeter Road and Peoria Street, along with the stream reclamation project along Cottonwood Creek. There is a seasonal pattern in phosphorus concentration at all sites, which is not specifically addressed in the trend analysis.

Table 7: Comparison of base flow median WY total phosphorus (TP) and soluble reactive phosphorus (SRP) concentrations for CC-10 and CT-2 from 1995 to 2014. CC-10 CT-2 Water Year TP (µg/L) SRP (µg/L) TP (µg/L) SRP (µg/L) 1995 218 169 -- -- 1996 145a 153a 97 77 1997 176 170 108 64 1998 291 231 108 66 1999 258 200 94 39 2000 247 195 83 24 2001 239 168 84 22 2002 191 144 69 13 2003 213 158 83 13 2004 214 164 92 8 2005 200 163 66 10 2006 162 134 67 7 2007 217 160 65 11 2008 200 143 69 5 2009 176 129 50 6 2010 217 168 61 7 2011 226 165 56 7 2012 181 147 56 6 2013 181 141 53 7 2014 197 176 48 12 Median (1995-2014) 213 164 69 11 Median (2010-2014) 197 165 56 7 a Results for total phosphorus and soluble reactive phosphorus are obtained independently and are within the 10% analytical error rate for all data used to calculate the median annual value.

GEI Consultants, Inc. 43 March 2015 2014 Cherry Creek Monitoring Report

Table 8: Comparison of storm flow median WY total phosphorus (TP) and soluble reactive phosphorus (SRP) concentrations for CC-10 and CT-2 from 1995 to 2014. CC-10 CT-2 Water Year TP (µg/L) SRP (µg/L) TP (µg/L) SRP (µg/L) 1995 181 161 -- -- 1996 323 270 336 160 1997 402 316 391 221 1998 378 277 314 108 1999 348 247 118 58 2000 673 274 277 93 2001 293 172 209 33 2002 251 171 175 21 2003 365 171 204 35 2004 285 237 208 35 2005 354 187 175 26 2006 477 221 259 74 2007 366 195 230 27 2008 271 207 79 14 2009 378 180 78 24 2010 307 178 97 24 2011 409 197 113 29 2012 471 210 110 19 2013 414 197 60 16 2014 326 171 97 8 Median (1995-2014) 360 197 175 29 Median (2010-2014) 409 197 97 19

GEI Consultants, Inc. 44 March 2015 2014 Cherry Creek Monitoring Report

Figure 27: Base flow and storm flow total phosphorus concentrations measured at CC-10, 1994 to 2014.

Figure 28: Base flow and storm flow soluble reactive phosphorus concentrations measured at CC-10, 1994 to 2014.

GEI Consultants, Inc. 45 March 2015 2014 Cherry Creek Monitoring Report

Figure 29: Base flow and storm flow total phosphorus concentrations measured at CT-2, 1996 to 2014.

Figure 30: Base flow and storm flow soluble reactive phosphorus concentrations measured at CT-2, 1996 to 2014.

GEI Consultants, Inc. 46 March 2015 2014 Cherry Creek Monitoring Report

4.3.3 Long-Term Trends in Phosphorus Concentrations in Cherry Creek Reservoir Alluvium

In April 2014, monthly sampling began at Site MW-9 to better characterize the alluvial nutrient concentrations upstream of the Reservoir, and to provide additional information for the Reservoir model development. Monthly total phosphorous concentrations ranged from 168 to 202 µg/L with a median concentration of 195 µg/L which is greater than the long-term median of 190 µg/L (1994-2014).

Alluvial phosphorus data for Site MW-9 were used to estimate the alluvial phosphorus load component, as summarized in Appendix D (JCHA 2001 through 2010; GEI 2012 - 2014). Total dissolved phosphorus is used as a surrogate to total phosphorus, because the alluvium filters out the particulate fraction common to surface water. Alluvial total dissolved phosphorus concentrations show a significant (p < 0.001), increasing trend over time (1994 to 2014) at Site MW-9 (Figure 31).

Figure 31: Total dissolved phosphorus and soluble reactive phosphorus concentrations measured at MW-9, 1994 to 2014.

4.4 Reservoir Phosphorus Loads and Export

Nutrients that limit or enhance algal growth in Cherry Creek Reservoir have many sources, both within the Reservoir (internal loading) or from outside the Reservoir (external loading). The direct release of nutrients from sediment, fish and plankton excrement, and the decay of organic matter are all internal sources of nutrients in a reservoir (Horne and Goldman 1994). However, the release of soluble reactive phosphorus from sediment during anoxic water conditions accounts for approximately 2,000 pounds per year (lbs/yr) in Cherry Creek Reservoir (Nürnberg and LaZerte 2008). Other studies evaluating internal loading from the

GEI Consultants, Inc. 47 March 2015 2014 Cherry Creek Monitoring Report

sediments suggest lower estimates of internal phosphorus loading ranging between 810 lbs/yr and 1,590 lbs/yr (AMEC et al. 2005).

External sources of nutrients include flow from streams, direct precipitation and the alluvium, which carry nutrients from soil erosion, agricultural and residential runoff, treated wastewater, and airborne particulates. While both phosphorus and nitrogen are potentially important, past studies have concluded that Cherry Creek Reservoir was generally phosphorus limited (DRCOG 1985). However, a more recent nutrient enrichment study by Lewis et al. (2004) indicated that nitrogen was often the primary limiting nutrient in Cherry Creek Reservoir during the growing season.

Phosphorus (unlike nitrogen) does not have a gas phase. Thus, phosphorus concentrations cannot be reduced by interactions with the atmosphere or gases within the water column. For these reasons, efforts in past years and during the present study have focused on phosphorus loading and flow-weighted phosphorus concentrations. Total phosphorus loads were determined for several primary sources, including the tributary streams Cherry Creek, Shop Creek, and Cottonwood Creek, as well as from precipitation and alluvium, as summarized in Appendix D. The flow-weighted concentrations represent the relationship between the total annual phosphorus load divided by total annual flow at a site.

4.4.1 Phosphorus Load from Tributary Streams

Monthly base flow phosphorus concentrations, along with the annual storm flow median concentration were applied to their respective flow to estimate loads for each stream site. Stream flows that were greater than the 90th percentile of all flows measured during the respective year and for that site were categorized as storm flows. The greatest proportion (75%) of the normalized total phosphorus load to the Reservoir was from Cherry Creek mainstem flows (5,567 lbs). Cottonwood Creek accounted for 7% of the phosphorus load, or 546 lbs. During the 2014 WY, the total phosphorus load to Cherry Creek Reservoir from tributary streams was 6,076 lbs (Table 9).

4.4.2 Phosphorus Export from Reservoir Outflow

The total outflow from Cherry Creek Reservoir as measured by the USACE was 13,648 ac-ft in 2014 (Appendix D). Monthly total phosphorus data collected from Site CC-Out @ I225 near the dam outlet was used to estimate the phosphorus export at 4,408 lbs/yr for the Reservoir in 2014 (Table 9).

GEI Consultants, Inc. 48 March 2015 2014 Cherry Creek Monitoring Report

Table 9: Normalized phosphorus loads and export (lbs/year) for Cherry Creek Reservoir, 1992 to 2014 WY. Stream & Cherry Cherry Cottonwood Ungaged Creek Direct Cherry Net Creek Creek Residual Alluvial Precipitation External Creek External Water Year Load Load Load Load Load Load Export Load 1992* 3,024 334 3,620 750 360 4,796 1,328 3,468 1993 1,521 229 1,750 1,024 313 3,162 1,000 2,162 1994 2,525 168 2,692 874 271 3,907 964 2,943 1995 2,064 1,396 3,886 992 608 5,556 1,366 4,190 1996 2,548 600 3,147 935 353 4,509 1,382 3,126 1997 2,131 616 2,747 1,008 447 4,299 1,129 3,171 1998 10,007 1,838 11,925 1,033 449 13,574 4,139 9,434 1999 10,495 1,290 14,830 1,033 540 16,403 6,388 10,015 2000 11,801 1,379 13,180 1,034 368 14,582 4,113 10,469 2001 6,283 2,101 8,627 1,033 408 10,068 5,524 4,544 2002 2,091 438 2,530 913 303 3,746 1,971 1,776 2003 6,199 1,052 7,868 1,033 457 9,359 4,774 4,584 2004 4,307 1,640 5,965 1,034 379 7,377 2,682 4,695 2005 8,757 1,347 10,104 1,033 382 11,518 3,964 7,554 2006 3,568 1,224 4,792 1,033 349 6,174 3,251 2,923 2007 15,987 2,072 18,189 1,033 379 19,601 7,891 11,710 2008 7,254 832 8,085 1,015 283 9,384 4,785 4,599 2009 13,591 936 14,584 1,033 435 16,052 9,483 6,569 2010 12,049 1,037 13,086 1,003 399 14,488 7,880 6,609 2011 7,341 652 7,992 1,024 285 9,301 4,114 5,187 2012 5,531 588 6,119 1,020 323 7,462 3,478 3,984 2013 6,043 846 7,164 1,033 391 8,588 3,378 5,210 2014 5,567 508 6,076 1,033 310 7,419 4,408 3,011 Median (1992-2014) 6,043 936 7,164 1,033 379 8,588 3,964 4,584 Median (2010-2014) 6,043 652 7,164 1,024 323 8,588 4,114 5,187 * 1992 WY totals are calculated using January through September data.

4.4.3 Phosphorus Load from Precipitation

During the 2014 WY, a total of 14.3 inches of precipitation was recorded at the KAPA meteorological station located at Centennial Airport. When scaled to the areal extent of the Reservoir (875 acres), precipitation accounted for a total of 1,045 ac-ft of inflow to the Reservoir. The long-term (1995 to 2014) median total phosphorus concentration of 109 μg/L was used to calculate the 2014 WY total phosphorus load of 310 lbs/yr. This long-term median total phosphorous concentration represents a combination of dry fall and precipitation as measured near the Reservoir. The long-term median total phosphorus load from precipitation events collected from 1992 to 2014 is 379 lbs (Table 9).

GEI Consultants, Inc. 49 March 2015 2014 Cherry Creek Monitoring Report

4.4.4 Phosphorus Load from Alluvium

During the 2014 WY, the alluvial inflow constant was 2,000 ac-ft/yr (see Appendix D). The long-term (1994 to 2014) median total dissolved phosphorus concentration of alluvial flows from Site MW-9 is 190 µg/L. The alluvial phosphorus load to the Reservoir was estimated to be 1,033 lbs in 2014 (Table 10).

4.4.5 Mass Balance/Net Loading of Phosphorus to the Reservoir

The USACE calculates daily inflow to Cherry Creek Reservoir as a function of change in storage (i.e., reservoir volume) based on: 1) changes in reservoir level; 2) measured outflow; 3) precipitation; and 4) evaporation. This method for calculating reservoir volume accounts for groundwater inflow via alluvium, but does not directly quantify the flow. GEI monitors surface water inflow to the Reservoir using gaged stations on the three main surface inflows, Cherry Creek, Cottonwood Creek, and Shop Creek. Given the differences in the two methods for determining inflow, combined with the potential for unmonitored multiple Cherry Creek channels in the wetlands adjacent to the Reservoir, unmonitored surface flow (i.e., Belleview and Quincy drainages), and the potential for the USACE calculations to underestimate dam leakage (Lewis and Saunders 2002), an exact match between USACE and GEI calculated inflows is not expected.

During the 2014 WY, the USACE calculated inflow was 14,352 ac-ft/yr, while GEI calculated stream inflow was 14,181 ac-ft/yr (Appendix D). To compare these two inflow values, the USACE inflow was adjusted for precipitation (1,045 ac-ft/yr) and alluvial inflows (2,000 ac-ft/yr), which resulted in an adjusted USACE inflow of 11,308 ac-ft/yr. The difference between the adjusted USACE inflow and the GEI stream inflow was -2,874 ac-ft of water. This water volume difference was reapportioned between Cherry Creek (78%), Cottonwood Creek (22%). Flow-weighted total phosphorus concentrations for Cherry Creek and Cottonwood Creek were used to calculate the combined reapportioned load of -1,663 lbs (Appendix D).

Following the water balance normalization process, flow from Cherry Creek and Cottonwood Creek accounted for a total phosphorus load of 6,076 lbs to the Reservoir during the 2014 WY (Figure 32). The alluvial inflow contributed 1,033 lbs of phosphorus, with precipitation events contributing 310 lbs to the Reservoir. The total external load of phosphorus to the Reservoir in 2014 WY was 7,419 lbs (Figure 32).

The Reservoir outflow phosphorus load was estimated to be 4,408 lbs. The flow-weighted total phosphorus concentration for all external sources of inflow to the Reservoir is 190 µg/L and the flow-weighted export concentration for the Reservoir is 119 µg/L (Table 10). The difference of 71 µg/L was retained by the Reservoir. The net external phosphorus load to the Reservoir was 3,011 lbs during the 2014 WY.

GEI Consultants, Inc. 50 March 2015 2014 Cherry Creek Monitoring Report

Table 10: Flow-weighted phosphorus concentrations (µg/L) for Cherry Creek Reservoir, 1992 to 2014 WY. Cottonwood Cherry Creek Creek Inflow Outflow Flow-weighted Flow-weighted Flow-weighted Flow-weighted Water Year Concentration Concentration Concentration Concentration 1992 270 170 246 91 1993 251 187 198 92 1994 248 88 196 73 1995 189 203 178 63 1996 232 332 208 87 1997 264 184 200 88 1998 279 178 237 81 1999 268 135 234 102 2000 312 159 265 83 2001 257 130 198 127 2002 221 88 171 107 2003 287 138 229 140 2004 247 157 201 96 2005 247 120 208 78 2006 231 132 187 115 2007 295 149 254 115 2008 205 84 177 104 2009 276 62 218 148 2010 239 78 200 115 2011 263 81 212 108 2012 244 91 200 118 2013 291 59 190 120 2014 231 73 190 119 Median (1992-2014) 251 132 200 104 Median (2010-2014) 244 78 200 118

GEI Consultants, Inc. 51 March 2015 2014 Cherry Creek Monitoring Report

Figure 32: Mass balance diagram of phosphorus loading in Cherry Creek Reservoir, 2014 WY.

GEI Consultants, Inc. 52 March 2015 2014 Cherry Creek Monitoring Report

4.5 Effectiveness of Pollutant Reduction Facilities 4.5.1 Cottonwood Creek Peoria Pond The effectiveness of the Cottonwood Creek Peoria Pond is gaged by monitoring the concentrations of phosphorus and total suspended solids, and determining the flow-weighted phosphorus concentrations upstream and downstream of the facility. Notably, the loads and flows used to evaluate the effectiveness of the PRF are not affected by the “normalization” of GEI inflow to USACE inflow values for Cherry Creek Reservoir. The ISCO at Site CT-P1 was lost during the September 2013 storm event and was replaced on January 21, 2014; therefore, PRF efficiency in terms of flow-weighted total phosphorous was based on the months of February through December 2014.

This PRF continues to be effective in reducing the amount of total suspended solids and total phosphorus as stream flow passes through this system. The total suspended solids were reduced by approximately 41% in 2014, with the long-term average showing a 28% reduction. The flow-weighted total phosphorus concentration upstream and downstream of the PRF was 145 µg/L and 135 µg/L, respectively, which indicates efficiency in removing phosphorus from flow (Table 11). Over the life of the project, the PRF shows approximately an average 18% reduction in the flow-weighted total phosphorus concentration at the downstream site.

This PRF was particularly effective at reducing the total suspended solids and total phosphorous load during multiple storm events during the 2014 WY. During the April 24, 2014 storm event, the inflow total suspended solids concentration at Site CT-P1 was 207 mg/L while the outflow total suspended solids concentration at Site CT-P2 was 92 mg/L. Similarly, the total phosphorous concentration entering the PRF during the storm event was 654 µg/L while the outflow concentration was 371 µg/L. During this storm event the PRF removed approximately 56% of the total suspended solids and 43% of the total phosphorous in Cottonwood Creek flows. During the storm event on July 15, 2014, the inflow total suspended solids concentration at Site CT-P1 was 462 mg/L while the outflow total suspended solids concentration at Site CT-P2 was 220 mg/L. The total phosphorous concentration entering the PRF during this storm event was 660 µg/L while the outflow concentration was 396 µg/L. During this storm event the PRF removed approximately 53% of the total suspended solids and 40% of the total phosphorous in Cottonwood Creek flows.

GEI Consultants, Inc. 53 March 2015 2014 Cherry Creek Monitoring Report

Table 11: Historical total phosphorus and total suspended solids concentrations and total phosphorus loads upstream and downstream of the Cottonwood Creek  Peoria Pond, 2002 to 2014 WY. Sampling Sites Percent Change Parameter Water Year CT-P1 CT-P2 Difference Downstream 2002 81 74 -7 -9 2003 30 33 3 10 2004 104 51 -53 -51 2005 50 53 3 6 2006 13 13 0 0 2007 78 41 -37 -47 Mean Total 2008* 36 34 -2 -6 Suspended Solids (mg/L) 2009 48 27 -21 -44 2010 34 26 -8 -24 2011 48 30 -18 -38 2012 121 55 -66 -55 2013 97 35 -62 -64 2014 66 39 -27 -41 Mean 62 39 -23 -28 2002 142 118 -24 -17 2003 117 109 -8 -7 2004 132 132 0 0 2005 129 119 -10 -8 2006 146 140 -6 -4 2007 156 120 -36 -23 Flow-weighted Total Phosphorus 2008* 128 92 -36 -28 Concentration 2009 114 83 -31 -27 (µg/L) 2010 106 96 -10 -9 2011 153 131 -22 -14 2012 193 127 -66 -34 2013 267 113 -154 -58 2014 145 135 -10 -7 Mean 148 117 -32 -18 * Eight months of operation.

GEI Consultants, Inc. 54 March 2015 2014 Cherry Creek Monitoring Report

4.5.2 Cottonwood Creek Perimeter Pond

The effectiveness of the Cottonwood Creek storm water Perimeter Pond in reducing phosphorus loads to the Reservoir is similarly gaged by comparing data from sites upstream and downstream of the PRF (Table 12). The total suspended solids were reduced by approximately 61% in 2014, with the long-term average showing a 32% reduction. The flow-weighted total phosphorus concentration upstream and downstream of the PRF was 112 µg/L and 81 µg/L, respectively, which indicates a high efficiency in removing phosphorus from flow (Table 12). Over the life of the project, the PRF shows approximately an average 23% reduction in the flow-weighted total phosphorus concentration at the downstream site.

This PRF was particularly effective at reducing the total suspended solids and total phosphorous load during multiple storm events during the 2014 WY. During the September 5, 2014 storm event, the inflow total suspended solids concentration at Site CT-1 was 444 mg/L while the outflow total suspended solids concentration at Site CT-2 was 44 mg/L. Similarly, the total phosphorous concentration entering the PRF during the storm event was 478 µg/L while the outflow concentration was 76 µg/L. During this storm event the PRF removed approximately 90% of the total suspended solids and 84% of the total phosphorous in Cottonwood Creek flows.

In 2014, streamflow at Site CT-1 was greatly affected by the construction along the Perimeter Road and the bridge work over Cottonwood Creek. In addition, a beaver dam inundated the monitoring site in mid-summer which altered the hydrology throughout the reach. In terms of accurately measuring stream flow at this site, the months from February through June 2014 represented “typical” base flow and storm flow conditions. Data collected during this period were used to evaluate the efficiency of the PRF.

GEI Consultants, Inc. 55 March 2015 2014 Cherry Creek Monitoring Report

Table 12: Historical total phosphorus and total suspended solids concentrations and total phosphorus loads upstream and downstream of the Cottonwood Creek Perimeter Pond, 1997 to 2014 WY. Sampling Sites Percent Change Parameter Water Year CT-1 CT-2 Difference Downstream 1997 207 87 -120 -58 1998 311 129 -182 -59 1999 267 68 -199 -75 2000 96 64 -32 -33 2001 79 43 -36 -46 2002 150 86 -64 -43 2003 83 58 -25 -30 2004 156 128 -28 -18 2005 123 65 -58 -47 Average Total 2006 31 20 -11 -35 Suspended Solids (mg/L) 2007 93 64 -29 -31 2008* 31 59 28 90 2009 31 32 1 3 2010 33 33 0 0 2011 48 30 -18 -38 2012 NA NA NA NA 2013 57 21 -36 -63 2014 56 22 -34 -61 Mean 109 59 -50 -32 1997 485 183 -302 -62 1998 311 176 -135 -43 1999 143 129 -14 -10 2000 266 161 -105 -39 2001 163 146 -17 -10 2002 124 105 -19 -15 2003 193 124 -69 -36 2004 194 149 -45 -23

Flow-weighted 2005 141 120 -21 -15 Total Phosphorus 2006 165 135 -30 -18 Concentration (µg/L) 2007 170 148 -22 -13 2008* 87 86 -1 -1 2009 70 61 -9 -13 2010 77 77 0 0 2011 101 81 -20 -20 2012 NA NA NA NA 2013 119 59 -62 -52 2014 112 81 -31 -28 Mean 172 119 -53 -23 * Nine months of operation.

GEI Consultants, Inc. 56 March 2015 2014 Cherry Creek Monitoring Report

4.5.3 McMurdo Stream Reclamation

Using a proactive approach to control stream erosion along McMurdo Gulch, before extensive land use development occurs along McMurdo Gulch, the town of Castle Rock and the CCBWQA implemented a stream reclamation project along three miles of stream between the Cobblestone Ranch and Castle Oaks subdivisions. Once the reclamation activities were completed in fall 2011, two water quality monitoring sites were established by CCBWQA. Site MCM-1 was established in January 2012 on McMurdo Gulch, approximately 150 m upstream of the McMurdo Gulch Stream Reclamation Project Boundary. This site is also 120 m upstream of the confluence with an unnamed tributary that receives runoff from the Castle Oaks Subdivision. This site serves as the upstream monitoring location for the McMurdo Gulch Stream Reclamation Project. Site MCM-2 was also established in January 2012 on McMurdo Gulch, approximately 80 m upstream of the Castle Oaks Drive Bridge crossing of McMurdo Gulch, near the North Rocky View Road intersection. This site serves as the downstream monitoring location for the McMurdo Gulch Stream Reclamation Project. This site is located within the project boundary, and consistently maintained base flows, whereas reaches further downstream were dry due to flow going subsurface.

Base flow water quality samples were collected on a monthly basis at sites MCM-1 and MCM-2) during the 2014 WY. Total phosphorous concentrations at Site MCM-1 ranged from 266 to 564 µg/L with a WY median concentration of 340 µg/L. Total phosphorous concentrations at Site MCM-2 were reduced compared to Site MCM-1 and ranged from 177 to 335 µg/L2 with a WY median concentration of 300 µg/L. Total suspended solids concentrations were slightly greater at the downstream location (Site MCM-2) with a WY median total suspended solids concentration of 11.6 mg/L, as compared to 5.7 mg/L at the upstream site (MCM-1).

Because Site MCM-1 is located upstream of the McMurdo Gulch Stream Reclamation Project Boundary and Site MCM-2 is located downstream of the PRF, the reduction in phosphorous from Site MCM-1 to Site MCM-2 indicates that the stream reclamation project is reducing total phosphorous concentrations in McMurdo Gulch, although the total suspended solids data shows mixed results.

4.6 2014 WY Special Studies

4.6.1 Cyanotoxin Monitoring in Cherry Creek Reservoir

Owing to the CCBWQA’s decision to not operate the destratification system in 2014, there were concerns that nuisance cyanobacteria would proliferate in the absence of aeration, and potentially impact the recreational beneficial use. Cyanobacteria are often associated with

2 Outlier concentration (1.342 µg/L) was removed for assessment purposes.

GEI Consultants, Inc. 57 March 2015 2014 Cherry Creek Monitoring Report

nuisance algal blooms, and can produce toxins that inhibit growth of competing algae as well as inhibit grazing by zooplankton that rely on algae as a food source. The most common cyanobacteria genera that are known to produce toxins and have been observed in Cherry Creek Reservoir include Anabaena, Aphanizomenon, Microcystis, and Planktothrix. Over the past 10 years, Anabaena sp. have been observed in 51 of the 148 phytoplankton samples collected, Aphanizomenon sp. in 36 samples, Planktothrix sp. in 4 samples, and Microcystis sp.in 3 samples. The historical context for both Anabaena and Aphanizomenon occurrence provided bases to monitor for cyanotoxins given the concern for potential nuisance cyanobacteria growth in the absence of aeration. Coincidentally, while the CCBWQA was developing a cyanotoxins monitoring program, the Reservoir began showing signs of a cyanobacteria bloom in early June 2014. On June 10th filamentous algae was visible on the surface at CCR-2 and a cyanotoxin sample was collected (Photo 1). Based on the World Health Organization microcystins thresholds for recreational water contact, there was a moderate human health risk at CCR-2 on June 10th (10 µg/L ELISA and 9.3 µg/L LC-MS; Figure 33). During the June 13th sampling event, cyanotoxin samples were collected at CCR-2, the Marina, and the Swim Beach. Microcystins levels were <1.0 µg/L for all of these samples and posed a very low human risk (Figure 33). On June 17th, the cyanobacteria bloom was reported along the dam face of the Reservoir (Photo 2). GEI personnel walked the face of the dam in the late morning of June 17th, and documented that the bloom was more pronounced near the Reservoir outlet tower. A surface grab sample was collected from what appeared to represent the worse-case scenario for the bloom (Photo 2). Based on the World Health Organization microcystins thresholds for recreation, there was a high risk to human health as well as for other animals that used this area of the Reservoir on June 17th (24 µg/L ELISA and 15.3 LC-MS; Figure 33).

Photo 1: Cyanobacteria bloom at Site CCR-2 Photo 2: Cyanobacteria bloom along the on 6/10/14 (10 µg/L microcystins). dam face (near the tower outlet structure) on 6/17/14 (25 µg/L microcystins).

Beginning on June 24th, two cyanotoxin samples were collected on a weekly basis (photic composite sample from CCR-1, CCR-2, and CCR-3), and a surface grab sample at the Swim Beach. A total of 20 out of the 27 samples were recorded as a non-detect for cyanotoxins

GEI Consultants, Inc. 58 March 2015 2014 Cherry Creek Monitoring Report

(Figure 33). The remaining 7 samples were all ≤ 0.29 µg/L for microcystins which indicates a very low risk to human health, including the samples collected at the swim beach.

Figure 33: Cyanotoxin analyses for Cherry Creek Reservoir, June through September 2014.

4.6.2 TOC and DOC Analyses in Cherry Creek Reservoir and Tributaries

For reservoir model development purposes, total organic carbon (TOC) and dissolved organic carbon (DOC) concentrations were measured at the Reservoir and two tributaries (Cherry Creek (CC-10) and Cottonwood Creek (CT-2)) from February through September 2014 (Table 13). TOC concentrations ranged from 5.7 mg/L in mid-May to 7.5 mg/L in late July in the photic zone at CCR-2, and DOC concentrations ranged from 4.8 mg/L in mid- March to 6.2 mg/L in late July (Table 13). During February through September 2014, TOC and DOC concentrations at CCR-2 Photic averaged 6.6 and 5.4 mg/L, respectively.

From April through September 2014, TOC and DOC concentrations were monitored at the bottom of Reservoir near the water-sediment interface (CCR-2 7M; Table 13). TOC concentrations ranged from 5.8 mg/L in mid-May to 6.7 mg/L in late June and early July at CCR-2 7M, and DOC concentrations ranged from 4.7 mg/L in mid-May to 6.1 mg/L in late July (Table 13). During April through September 2014, TOC and DOC concentrations at CCR-2 7M averaged 6.3 and 5.3 mg/L, respectively. These concentrations are similar to the TOC and DOC concentrations recorded in the photic zone at CCR-2 (Table 13).

GEI Consultants, Inc. 59 March 2015 2014 Cherry Creek Monitoring Report

Table 13: Total organic carbon (TOC) and dissolved organic carbon (DOC) concentrations in Cherry Creek Reservoir and tributaries (CC-10 and CT-2), February through September 2014. Sample Date Sample Location TOC (mg/L) DOC (mg/L) DOC/TOC (%) 2/11/2014 CCR-1 Photic 6.1 5.6 91.80 2/11/2014 CCR-2 Photic 6.1 5.9 96.72 2/18/2014 CT-2 7.2 6.5 90.28 2/18/2014 CC-10 3.9 3.8 97.44 3/12/2014 CCR-2 Photic 7.1 4.8 67.61 3/13/2014 CT-2 10.0 7.7 77.00 3/13/2014 CC-10 3.9 3.5 89.74 4/15/2014 CCR-2 Photic 6.8 4.9 72.06 4/15/2014 CCR-2 7M 6.6 4.8 72.73 4/17/2014 CT-2 7.5 5.6 74.67 4/17/2014 CC-10 4.5 3.6 80.00 5/13/2014 CCR-2 Photic 5.7 5.3 92.98 5/13/2014 CCR-2 7M 5.8 4.9 84.48 5/20/2014 CT-2 6.5 5.3 81.54 5/20/2014 CC-10 4.6 3.8 82.61 5/27/2014 CCR-2 Photic 6.7 5.0 74.63 5/27/2104 CCR-2 7M 6.1 4.7 77.05 6/10/2014 CCR-2 Photic 6.1 5.2 85.25 6/10/2014 CCR-2 7M 5.8 4.9 84.48 6/16/214 CT-2 7.5 6.6 88.00 6/16/2014 CC-10 5.2 4.7 90.38 6/24/2014 CCR-2 Photic 7.3 5.6 76.71 6/24/2014 CCR-2 7M 6.7 5.5 82.09 7/07/2014 CT-2 7.5 6.5 86.67 7/07/2014 CC-10 3.8 3.5 92.11 7/08/2014 CCR-2 Photic 6.6 5.5 83.33 7/08/2014 CCR-2 7M 6.7 5.6 83.58 7/22/2014 CCR-2 Photic 7.5 6.2 82.67 7/22/2014 CCR-2 7M 6.5 6.1 93.85 8/04/2014 CT-2 7.1 5.7 80.28 8/04/2014 CC-10 4.6 4.3 93.48 8/05/2014 CCR-2 Photic 6.5 5.6 86.15 8/05/2014 CCR-2 7M 6.2 5.4 87.10 8/19/2014 CCR-2 Photic 6.5 5.5 84.62 8/19/2014 CCR-2 7M 6.4 5.7 89.06 9/02/2014 CCR-2 Photic 6.4 5.1 79.69 9/02/2014 CCR-2 7M 5.8 4.9 84.48 9/03/2014 CT-2 5.7 4.8 84.21 9/03/2014 CC-10 4.1 3.4 82.93 9/16/2014 CCR-2 Photic 6.3 5.4 85.71 9/16/2014 CCR-2 7M 6.2 5.6 90.32

GEI Consultants, Inc. 60 March 2015 2014 Cherry Creek Monitoring Report

5. References

Advanced Sciences, Inc. 1994a. Cherry Creek Basin, Annual Water-Quality Monitoring Report, 1993 Water Year. Project No. 8970. Prepared for the Cherry Creek Basin Water Quality Authority.

Advanced Sciences, Inc. 1994b. 1993 Cherry Creek Basin Water Quality Authority Contract: Project 8790. Exhibits A through H (amended).

AMEC, Earth and Environmental, Inc., Alex Horne Associates, and Hydrosphere Resource Consultants, Inc. 2005. Cherry Creek Reservoir Destratification. Feasibility report prepared for the Cherry Creek Basin Water Quality Authority.

American Public Health Association (APHA). 1998. Standard Methods for the Examination of Water and Wastewater, 20th Edition. Prepared and published jointly by the American Public Health Association, American Water Works Association, and Water Pollution Control Federation, Washington, DC.

Barkoh, A. and L.T. Fries. 2010. Aspects of the Origins, Ecology, and Control of Golden Alga (Pyrmnesium parvum): Introduction to the Featured Collection. Journal of the American Water Resources Association (JAWRA) 46(1): 1-5

Carpenter, S. R., J. F. Kitchell, and J. R. Hodgson. 1985. Cascading trophic interactions and lake productivity. Bioscience 35:634-639.

Chadwick Ecological Consultants, Inc. (CEC). 1995. Cherry Creek Reservoir Annual Aquatic Biological and Nutrient Monitoring Study, 1994. Prepared for the Cherry Creek Basin Water Quality Authority.

Chadwick Ecological Consultants, Inc. (CEC). 1996. Cherry Creek Reservoir Annual Aquatic Biological and Nutrient Monitoring Study, 1995. Prepared for the Cherry Creek Basin Water Quality Authority.

Chadwick Ecological Consultants, Inc. (CEC). 1997. Cherry Creek Reservoir Annual Aquatic Biological and Nutrient Monitoring Study, 1996. Prepared for the Cherry Creek Basin Water Quality Authority.

Chadwick Ecological Consultants, Inc. (CEC). 1998a. Analysis of Phosphorus Loads to Cherry Creek Reservoir. Prepared for the Cherry Creek Basin Water Quality Authority.

Chadwick Ecological Consultants, Inc. (CEC). 1998b. Cherry Creek Reservoir Annual Aquatic Biological and Nutrient Monitoring Study, 1997. Prepared for the Cherry Creek Basin Water Quality Authority.

GEI Consultants, Inc. 61 March 2015 2014 Cherry Creek Monitoring Report

Chadwick Ecological Consultants, Inc. (CEC). 1999. Cherry Creek Reservoir 1998 Annual Aquatic Biological and Nutrient Monitoring Study. Prepared for the Cherry Creek Basin Water Quality Authority.

Chadwick Ecological Consultants, Inc. (CEC). 2000. Cherry Creek Reservoir 1999 Annual Aquatic Biological and Nutrient Monitoring Study. Prepared for the Cherry Creek Basin Water Quality Authority.

Chadwick Ecological Consultants, Inc. (CEC). 2001. Cherry Creek Reservoir 2000 Annual Aquatic Biological and Nutrient Monitoring Study. Prepared for the Cherry Creek Basin Water Quality Authority.

Chadwick Ecological Consultants, Inc. (CEC). 2002. Cherry Creek Reservoir 2001 Annual Aquatic Biological and Nutrient Monitoring Study. Prepared for the Cherry Creek Basin Water Quality Authority.

Chadwick Ecological Consultants, Inc. (CEC). 2003. Cherry Creek Reservoir 2002 Annual Aquatic Biological and Nutrient Monitoring Study and Cottonwood Creek Phosphorus Reduction Facility Monitoring. Prepared for the Cherry Creek Basin Water Quality Authority.

Chadwick Ecological Consultants, Inc. (CEC). 2004. Cherry Creek Reservoir 2003 Annual Aquatic Biological and Nutrient Monitoring Study and Cottonwood Creek Phosphorus Reduction Facility Monitoring. Prepared for the Cherry Creek Basin Water Quality Authority.

Chadwick Ecological Consultants, Inc. (CEC). 2005. Cherry Creek Reservoir 2004 Annual Aquatic Biological and Nutrient Monitoring Study and Cottonwood Creek Phosphorus Reduction Facility Monitoring. Prepared for the Cherry Creek Basin Water Quality Authority.

Chadwick Ecological Consultants, Inc. (CEC). 2006. Cherry Creek Reservoir 2005 Annual Aquatic Biological and Nutrient Monitoring Study and Cottonwood Creek Phosphorus Reduction Facility Monitoring. Prepared for the Cherry Creek Basin Water Quality Authority.

Cole, G. A. 1979. Textbook of Limnology, 2nd Edition. The C.V. Mosby Company, St. Louis, MO.

Colorado Division of Public Health and Environment (CDPHE). 2010. Water Quality Control Division Prehearing Statement, Regulation #31 Rulemaking Hearing: June 7, 2010.

GEI Consultants, Inc. 62 March 2015 2014 Cherry Creek Monitoring Report

Colorado Department of Public Health and Environment (CDPHE). 2011. Section 303(d) Listing Methodology: 2012 Listing Cycle. Water Quality Control Division, Denver, CO.

Cooke, D. C., E. B. Welch, S. A. Peterson, and P.R. Newroth. 1993. Restoration & Management of Lakes & Reservoirs, 2nd Edition. Lewis Publishers, Boca Raton, FL.

Denver Regional Council of Governments (DRCOG). 1984. Cherry Creek Reservoir Clean Lakes Study. Denver Regional Council of Governments, Denver, CO.

Denver Regional Council of Governments (DRCOG). 1985. Cherry Creek Basin Water Quality Management Master Plan. Prepared in Cooperation with Counties, Municipalities, Water and Sanitation Districts in the Cherry Creek Basin and Colorado Department of Health.

GEI Consultants, Inc. (GEI). 2007. Cherry Creek Reservoir 2006 Annual Aquatic Biological and Nutrient Monitoring Study and Cottonwood Creek Phosphorus Reduction Facility Monitoring. Prepared for the Cherry Creek Basin Water Quality Authority.

GEI Consultants, Inc. (GEI). 2008a. Cherry Creek Reservoir Aquatic Biological and Nutrient Sampling and Laboratory Analyses, Sampling, Analysis, and Quality Assurance Work Plan. April 2008. Prepared for the Cherry Creek Basin Water Quality Authority.

GEI Consultants, Inc. (GEI). 2008b. Cherry Creek Reservoir 2007 Annual Aquatic Biological and Nutrient Monitoring Study and Cottonwood Creek Phosphorus Reduction Facility Monitoring. Prepared for the Cherry Creek Basin Water Quality Authority.

GEI Consultants, Inc. (GEI). 2009. Cherry Creek Reservoir 2008 Annual Aquatic Biological and Nutrient Monitoring Study and Cottonwood Creek Phosphorus Reduction Facility Monitoring. Prepared for the Cherry Creek Basin Water Quality Authority.

GEI Consultants, Inc. (GEI). 2010. Cherry Creek Reservoir 2009 Annual Aquatic Biological and Nutrient Monitoring Study and Cottonwood Creek Phosphorus Reduction Facility Monitoring. Prepared for the Cherry Creek Basin Water Quality Authority.

GEI Consultants, Inc. (GEI). 2011. Cherry Creek Reservoir 2010 Annual Aquatic Biological and Nutrient Monitoring Study and Cottonwood Creek Phosphorus Reduction Facility Monitoring. Prepared for the Cherry Creek Basin Water Quality Authority.

GEI Consultants, Inc. (GEI). 2012. Cherry Creek Reservoir 2011 Annual Aquatic Biological and Nutrient Monitoring Study and Cottonwood Creek Phosphorus Reduction Facility Monitoring. Prepared for the Cherry Creek Basin Water Quality Authority.

GEI Consultants, Inc. (GEI). 2013. Cherry Creek Reservoir 2012 Annual Aquatic Biological and Nutrient Monitoring Study and Cottonwood Creek Phosphorus Reduction Facility Monitoring. Prepared for the Cherry Creek Basin Water Quality Authority.

GEI Consultants, Inc. 63 March 2015 2014 Cherry Creek Monitoring Report

GEI Consultants, Inc. (GEI). 2014. Cherry Creek Reservoir 2013 Annual Aquatic Biological and Nutrient Monitoring Study and Cottonwood Creek Phosphorus Reduction Facility Monitoring. Prepared for the Cherry Creek Basin Water Quality Authority.

Harman, C. D., D. R. Bayne, and M. S. West. 1995. Zooplankton trophic state relationships in four Alabama-Georgia reservoirs. Lake and Reservoir Management, 11:4 299-309.

Havens K. E. 2008. Cyanobacteria blooms: effects on aquatic ecosystems. Advanced Experimental Medical Biology, 619:733-47.

Hintze, J. L. 2009. NCSS and PASS. Number Cruncher Statistical Systems, Kaysville, UT.

Horne, A. J. and C. R. Goldman. 1994. Limnology. McGraw-Hill Company, NY.

In-Situ, Inc. 1986 (as amended). Cherry Creek Reservoir and Cherry Creek Basin Monitoring Program, Southeastern Denver Metropolitan Area, Colorado: Proposal No. 4405. Prepared for the Cherry Creek Basin Authority, December 3 (with later modifications).

James, W. F., W. D. Taylor, J. W. Barko. 1992. Production and vertical migration of Ceratium hirundinella in relation to phosphorus availability in Eau Galle Reservoir, Wisconsin. Canadian Journal of Fisheries and Aquatic Sciences 49:694-700.

John C. Halepaska & Associates, Inc. (JCHA). 1999. 1998 Annual Report, Phase I Baseline Water Quality Data Collection Study for the Upper Cherry Creek Basin. Prepared for the Cherry Creek Basin Water Quality Authority, Project No. 5601:6.

John C. Halepaska & Associates, Inc. (JCHA). 2000. 1999 Annual Report, Phase I Baseline Water Quality Data Collection Study for the Upper Cherry Creek Basin. Prepared for the Cherry Creek Basin Water Quality Authority.

John C. Halepaska & Associates, Inc. (JCHA). 2001. 2000 Annual Report, Baseline Water Quality Data Collection Study for the Upper Cherry Creek Basin. Prepared for the Cherry Creek Basin Water Quality Authority.

John C. Halepaska & Associates, Inc. (JCHA). 2002. 2001 Annual Report, Baseline Water Quality Data Collection Study for the Upper Cherry Creek Basin. Prepared for the Cherry Creek Basin Water Quality Authority.

John C. Halepaska & Associates, Inc. (JCHA). 2003. 2002 Annual Report, Baseline Water Quality Data Collection Study for the Upper Cherry Creek Basin. Prepared for the Cherry Creek Basin Water Quality Authority.

John C. Halepaska & Associates, Inc. (JCHA). 2004. 2003 Annual Report, Baseline Water Quality Data Collection Study for the Upper Cherry Creek Basin. Prepared for the Cherry Creek Basin Water Quality Authority.

GEI Consultants, Inc. 64 March 2015 2014 Cherry Creek Monitoring Report

John C. Halepaska & Associates, Inc. (JCHA). 2005. 2004 Annual Report, Baseline Water Quality Data Collection Study for the Upper Cherry Creek Basin. Prepared for the Cherry Creek Basin Water Quality Authority.

John C. Halepaska & Associates, Inc. (JCHA). 2006. 2005 Annual Report, Baseline Water Quality Data Collection Study for the Upper Cherry Creek Basin. Prepared for the Cherry Creek Basin Water Quality Authority.

John C. Halepaska & Associates, Inc. (JCHA). 2007. 2006 Annual Report, Baseline Water Quality Data Collection Study for the Upper Cherry Creek Basin. Prepared for the Cherry Creek Basin Water Quality Authority.

John C. Halepaska & Associates, Inc. (JCHA). 2008. 2007 Annual Report, Baseline Water Quality Data Collection Study for the Upper Cherry Creek Basin. Prepared for the Cherry Creek Basin Water Quality Authority.

John C. Halepaska & Associates, Inc. (JCHA). 2009. 2008 Annual Report, Baseline Water Quality Data Collection Study for the Upper Cherry Creek Basin. Prepared for the Cherry Creek Basin Water Quality Authority.

John C. Halepaska & Associates, Inc. (JCHA). 2010. 2009 Annual Report, Baseline Water Quality Data Collection Study for the Upper Cherry Creek Basin. Prepared for the Cherry Creek Basin Water Quality Authority.

Jones, J. R. 1994. Report on Cherry Creek Reservoir, Summer 1993. Report to Cherry Creek Basin Water Quality Authority.

Jones, J. R. 1995. Report on Cherry Creek Reservoir, Summer 1994. Report to Cherry Creek Basin Water Quality Authority.

Jones, J. R. 1996. Report on Cherry Creek Reservoir, 1995 Sampling Season. Report to Cherry Creek Basin Water Quality Authority.

Jones, J. R. 1997. Report on Cherry Creek Reservoir, 1996 Sampling Season. Report to Cherry Creek Basin Water Quality Authority.

Jones, J. R. 1998. Report on Cherry Creek Reservoir, 1997 Sampling Season. Report to Cherry Creek Basin Water Quality Authority.

Jones, J. R. 1999. Report on Cherry Creek Reservoir, 1998 Sampling Season. Report to Cherry Creek Basin Water Quality Authority.

Jones, J. R. 2001. Report on Cherry Creek Reservoir, 1992-2001 and Historical Data. Report to Cherry Creek Basin Water Quality Authority.

GEI Consultants, Inc. 65 March 2015 2014 Cherry Creek Monitoring Report

Konopka, A. and T. D. Brock. 1978. Effect of temperature on blue-green algae (Cyanobacteria) in Lake Mendota. Applied and Environmental Microbiology 36:572-576.

Knowlton, M. R., and J. R. Jones. 1993. Limnological Investigations of Cherry Creek Lake. Final report to Cherry Creek Basin Water Quality Authority.

Komárek, J., H. Kling, and J. Komáaková. 2003. Filamentous Cyanobacteria. Pp 117-196 in Wehr, J. D. and R. G. Sheath (eds.). Freshwater Algae of North America: Ecology and Classification. Academic Press, Burlington, MA.

Kugrens, P. and B. L. Clay. 2003. Cryptomonads. Pp. 715-755 in Wehr, J. D. and R. G. Sheath (eds.). Freshwater Algae of North America: Ecology and Classification. Academic Press, Burlington, MA.

Lewis, W. M., and J. F. Saunders. 2002. Review and Analysis of Hydrologic Information on Cherry Creek Watershed and Cherry Creek Reservoir. Prepared for the Cherry Creek Basin Water Quality Authority.

Lewis, W. M., J. F. Saunders, and J. H. McCutchan. 2004. Studies of Phytoplankton Response to Nutrient Enrichment in Cherry Creek Reservoir, Colorado. Prepared for Colorado Department of Public Health and Environment, Water Quality Control Division.

Lewis, W. M., J. H. McCutchan, and J. F. Saunders. 2005. Estimation of Groundwater Flow into Cherry Creek Reservoir and its Relationship to the Phosphorous Budget of the Reservoir. Prepared for the Cherry Creek Basin Water Quality Authority.

Mazumder, A. 1994. Phosphorus-chlorophyll relationships under contrasting zooplankton community structure: potential mechanisms. Canadian Journal of Fisheries and Aquatic Sciences 51:401-407.

Mazumder, A. and D. R. S. Lean. 1994. Consumer dependent responses of lake ecosystems to nutrient loading. Journal of Plankton Research 16:1567-1580.

Nürnberg, G., and LaZerte, B. 2008. Cherry Creek Reservoir Model and Proposed Chlorophyll Standard. Prepared for the Cherry Creek Basin Water Quality Authority.

Padisák, J. 1985. Population dynamics of the freshwater dinoflagellate Ceratium hirundinella in the largest shallow lake of Central Europe, Lake Balaton, Hungary. Freshwater Biology 15:43-52.

Pollingher, U. 1987. Freshwater ecosystems, in Taylor, F. J. R. (ed.). The Biology of Dinoflagellates. Blackwell Science, Malden, MA.

Sarnelle, O. 1992. Nutrient enrichment and grazer effects on phytoplankton in lakes. Ecology 73:51-56.

GEI Consultants, Inc. 66 March 2015 2014 Cherry Creek Monitoring Report

United States Environmental Protection Agency (USEPA). 2001. Methods for Collection, Storage and Manipulation of Sediments for Chemical and Toxicological Analyses: Technical Manual. EPA 823-B-01-002, U.S. Environmental Protection Agency, Washington, DC.

Vanni, M. J., and J. Temte. 1990. Seasonal patterns of grazing and nutrient limitation of phytoplankton in a eutrophic lake. Limnology and Oceanography 35:697-709.

Vanni, M. J., and C. D. Layne. 1996. Nutrient recycling and herbivory as mechanisms in the top-down effect of fish on algae in lakes. Ecology 78:21-40.

Vanni, M. J., C. D. Layne, and S. E. Arnott. 1996. Top-down trophic interactions in lakes: effects of fish on nutrient dynamics. Ecology 78:1-20.

Wetzel, R. G. 2001. Limnology, 3rd Edition. Academic Press, San Diego, CA.

Whitton, B. A. and M. Potts (eds.). 2000. The Ecology of Cyanobacteria: Their diversity in time and Space. Kluwer Academic, Boston, MA.

Wright, R. T. 1964. Dynamics of a Phytoplankton Community in an Ice-Covered Lake. Limnology and Oceanography 9:163-178.

GEI Consultants, Inc. 67 March 2015 2014 Cherry Creek Monitoring Report

Biological Data

APPENDIX E PAGE E-1

Table E-1: Quantity and size of fish stocked in Cherry Creek Reservoir, 1985 to 1995. 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 Black crappie Size (inches) 5 ------Number 7,234 ------Blue catfish Size (inches) ------3 -- 3 -- Number ------9,000 -- 21,000 -- Bluegill Size (inches) -- 1 0.2 ------Number -- 111,968 70,000 ------Channel catfish Size (inches) 2 to 8 4 4 3 3 3.5 3 4 4 4 4 Number 116,784 25,594 25,600 16,000 10,316 25,599 13,500 13,500 13,500 23,625 18,900 Cutthroat trout Size (inches) -- 6 ------9 -- Number -- 52,228 ------9,089 -- Flathead catfish Size (inches) ------1 -- Number ------148 -- Largemouth bass Size (inches) -- -- 5 5 6 ------Number -- -- 10,000 10,000 8,993 ------Rainbow trout Size (inches) 8 to 12 2 to 18 2 to 26 9.5 8 to 22 9 to 15 9 to 10 9.5 9.5 9 to 18 9 to 20 Number 75,753 414,136 129,715 293,931 79,919 74,986 79,571 101,656 92,601 62,615 139,242 Tiger musky Size (inches) -- 5.5 7 8 -- 8 5 to 8 7 9 8 8 Number -- 4,723 4,000 4,500 -- 2,001 6,500 4,940 4,500 900 4,500 Walleye Size (inches) 0.3 0.3 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 Number 2,346,000 1,734,000 1,760,000 1,760,000 1,352,000 1,400,000 1,300,000 2,600,000 2,600,000 2,600,000 2,600,000 Wiper Size (inches) -- 0.2 -- -- 0.2 1 1 10 1 1 to 4 1 Number -- 80,000 -- -- 99,000 8,996 9,000 15,520 9,003 26,177 4,500 Yellow perch Size (inches) 2 ------Number 90,160 ------APPENDIX E PAGE E-2

Table E-1 (cont.): Quantity and size of fish stocked in Cherry Creek Reservoir, 1996 to 2006. 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 Black crappie Size (inches) ------2.5 Number ------300 Channel catfish Size (inches) 3 3 4 3.5 4.1 3.5 -- 2.5 2.5 2.2 2.8 Number 8,100 13,500 7,425 13,500 13,500 13,500 -- 33,669 13,500 14 13,500 Cutthroat trout Size (inches) 9.5 3 to 9 ------Number 85,802 22,907 ------Largemouth bass Size (inches) ------2.1 Number ------195 Northern pike Size (inches) ------Number ------46 ------Rainbow × cutthroat hybrid Size (inches) ------10.6 Number ------5,600 ------7,895 Rainbow trout Size (inches) 4 to 22 10 to 24 11 10 to 19 -- 10 to 19 10 10.5 10.5 10.4 10.8 Number 163,007 74,525 59,560 32,729 -- 23,065 13,900 30,111 43,553 43,248 47,150 Snake River cutthroat Size (inches) ------16.1 Number ------204 Tiger musky Size (inches) 7 6 7 7 8 7 7 ------Number 3,500 4,500 4,000 3,000 4,086 4,000 4,000 ------Walleye Size (inches) 0.2 0.2 1.5 0.2 0.2 0.2 0.2 0.3 0.3 0.3 0.2 Number 3,202,940 2,600,000 40,000 2,400,000 2,400,000 2,400,000 2,519,660 4,136,709 2,874,100 2,579,939 2,788,825 Wiper Size (inches) 1 1 1.3 1.3 ------0.2 2.1 Number 8,938 9,000 9,000 9,000 ------200,000 5,000 APPENDIX E PAGE E-3

Table E-1 (cont.): Quantity and size of fish stocked in Cherry Creek Reservoir, 2007 to 2012. 2007 2008 2009 2010 2011 2012 Black crappie Size (inches) -- -- 1.4 -- 1.1 to 1.2 0.7 to 1.8 Number -- -- 5,000 -- 97,399 41,541 Channel catfish Size (inches) 3 -- 3.3 2.7 3.4 2.5 to 6.6 Number 9,360 -- 3,780 13,500 9,450 11,750 Cutthroat trout Size (inches) ------12.5 to 14.7 15.1 -- Number ------1,562 200 -- Rainbow × cutthroat trout Size (inches) -- 9.7 ------Number -- 4,001 ------Rainbow trout Size (inches) 10 10.1 4.8 9.6 to 17.7 10.1 to 10.9 10.1 to 17.0 Number 37,709 11,588 12,287 11,038 28,029 29,872 Size (inches) 12 -- 10.2 9.8 to 10.2 10.6 -- Number 4,800 -- 29,759 39,200 1,737 -- Size (inches) -- -- 13-Jan ------Number -- -- 18-Apr ------Walleye Size (inches) 0.3 0.2 0.2 0.2 to 1.1 0.2 0.23 Number 4,300,000 3,992,572 4,012,800 4,264,512 4,001,400 4,001,400 Size (inches) 1 -- 1.3 -- -- 1 Number 7,998 -- 14,998 -- -- 15,000 Wiper Size (inches) 1.5 -- -- 1.6 -- -- Number 4,600 -- -- 8,000 -- -- APPENDIX E PAGE E-4

Table E-2: 2014 Cherry Creek Reservoir phytoplankton data represented in numbers per mililter (#/mL). 2014 11-Feb 12-Mar 15-Apr 13-May 27-May 10-Jun 24-Jun 8-Jul 22-Jul 5-Aug 19-Aug 2-Sep 16-Sep 14-Oct 4-Nov Bacillariophyta Centrales Coscinodiscus sp. ------29 -- 54 43 86 -- -- Cyclotella meneghiniana ------59 35 ------Cyclotella stelligera ------38 -- -- 264 106 236 511 344 -- -- Melosira ambigua ------29 ------Melosira distans alpigena ------38 ------Melosira granulata ------1,253 ------121 Melosira granulata angustissima ------75 ------Stephanodiscus astraea minutula -- 127 129 -- -- 38 -- -- 176 229 127 170 86 -- 364 Stephanodiscus hantzschii -- 32 52 75 29 76 10 45 59 247 635 596 1,031 569 1,576 Pennate Amphora ovalis -- 32 ------Amphora perpusilla -- 32 ------Asterionella formosa 56 64 155 38 29 ------43 ------Cymbella naviculiformis ------29 ------Diatoma tenue ------29 ------Fragilaria construens ------38 ------18 ------Fragilaria pinnata -- 32 ------18 ------121 Fragilaria vaucheriae ------18 ------Gomphonema olivaceum -- 32 ------Gomphonema subclavatum ------18 ------Navicula sp. ------38 ------Navicula cryptocephala veneta ------35 ------Navicula viridula ------29 -- 18 ------Nitzschia acicularis -- -- 52 ------596 ------Nitzschia capitellata ------213 86 -- -- Nitzschia dissipata -- -- 26 38 ------Nitzschia palea ------10 ------18 ------Nitzschia paleacea -- -- 180 ------29 -- 18 340 ------Synedra radians ------38 87 ------Synedra rumpens ------86 -- -- Synedra ulna 56 -- -- 38 ------43 ------Chlorophyta Ankistrodesmus falcatus 56 159 129 113 -- 76 39 89 117 141 73 43 387 1,594 1,940 Aphanothece sp. ------Botryococcus braunii ------45 ------Chlamydomonas sp. -- 127 52 29 38 -- -- 59 88 454 43 86 683 606 Chodatella wratislawiensis -- -- 129 38 ------114 485 Cosmarium sp. ------59 ------Crucigenia crucifera ------10 -- -- 35 -- 128 43 -- -- Crucigenia quadrata -- -- 52 38 146 76 -- -- 29 35 36 170 1,546 1,025 485 Crucigenia tetrapedia ------38 -- -- 29 35 18 128 172 456 -- Nephrocytium sp. ------38 ------Oocystis lacustris -- -- 77 75 117 190 10 -- 117 35 ------Oocystis pusilla -- -- 52 188 291 494 29 403 205 71 18 43 86 -- 121 Pediastrum boryanum ------58 -- -- 45 59 ------Pediastrum duplex ------19 89 29 ------Scenedesmus abundans -- -- 26 75 146 38 -- -- 88 18 36 255 344 797 242 Scenedesmus acuminatus -- -- 77 75 ------88 53 -- -- 129 569 727 Scenedesmus bijuga ------67 ------902 -- -- Scenedesmus quadricauda -- 127 155 526 845 76 -- 537 527 318 91 553 43 1,139 242 Selenastrum minutum -- 64 155 376 58 ------35 -- 128 -- 569 364 Sphaerocystis schroeteri ------38 29 ------59 -- -- 43 -- 114 -- Tetraedron minimum ------150 146 38 -- 45 88 -- -- 213 430 1,139 1,697 Tetraedron regulare ------38 29 -- -- 45 59 35 -- -- 43 -- -- Tetrastrum staurogeniaforme ------29 ------85 -- 342 121 Chrysophyta Chromulina sp. ------38 ------114 121 Chrysococcus rufescens -- 127 ------121 Kephyrion sp. -- 32 -- 113 ------121 Kephyrion littorale -- -- 155 263 58 ------Lagynion sp. ------45 ------Rhodomonas minuta 338 858 1,237 226 2,098 797 77 2,729 117 194 182 170 129 4,328 1,576 APPENDIX E PAGE E-5

Table E-2 (cont.): 2014 Cherry Creek Reservoir phytoplankton data represented in numbers per mililter (#/mL). 2014 11-Feb 12-Mar 15-Apr 13-May 27-May 10-Jun 24-Jun 8-Jul 22-Jul 5-Aug 19-Aug 2-Sep 16-Sep 14-Oct 4-Nov Cyanobacteria Anabaena flos-aquae ------146 1,481 29 45 ------Aphanizomenon flos-aquae ------18 ------Aphanothece ------58 ------Euglenophycota Euglena sp. ------38 ------29 ------Trachelomonas crebea ------121 Trachelomonas hispida -- -- 26 38 ------18 ------Trachelomonas scabra ------35 18 -- -- 114 -- Trachelomonas volvocina ------38 ------Pyrrophycophyta Ceratium hirundinella ------43 -- -- Dinobryon sertularia 56 ------Glenodinium sp. 113 127 26 38 ------205 53 18 -- -- 342 242 Peridinium cinctum ------498 53 -- -- 43 -- -- Cryptophyta Cryptomonas erosa 789 2,128 232 413 175 569 540 1,566 176 247 54 511 43 1,253 1,091 Unidentified Flagellate Unidentified flagellate -- 32 26 -- -- 38 ------228 -- Total Density (cells/mL) 1,466 4,129 3,196 3,383 4,661 4,100 838 6,980 3,309 2,188 2,161 5,063 6,185 15,489 12,609 Total Taxa 7 17 22 31 22 16 11 14 28 25 21 23 22 19 22 APPENDIX E PAGE E-6

Table E-3: Total reservoir phytoplankton density (cells/mL) and number of taxa in Cherry Creek Reservoir, 1984 to 2014 1984 1985 1986 1987 1988 1989 1991 1992 1993 1994 1995 1996 Blue-Green Algae Density 71,780 66,496 99,316 168,259 155,180 273,175 307,691 77,516 15,708 10,015 18,194 16,599 Taxa 7 7 6 18 24 24 14 16 7 3 7 9 Green Algae Density 5,864 11,760 25,595 11,985 19,177 55,415 18,688 41,899 1,198 314 355 738 Taxa 11 10 13 58 76 66 46 48 16 2 11 11 Diatoms Density 1,776 3,863 5,428 10,677 12,880 9,311 4,160 1,243 946 194 2,189 2,354 Taxa 6 4 7 34 30 31 21 11 15 2 15 13 Golden-Brown Algae Density -- 7 125 469 56 505 821 93 158 3 63 249 Taxa -- 1 1 6 4 7 5 4 1 1 2 4 Euglenoids Density 514 135 208 251 276 108 89 23 231 196 304 409 Taxa 2 1 1 9 9 6 3 5 2 1 2 3 Dinoflagellates Density -- 13 19 19 83 28 23 54 -- 31 5 21 Taxa -- 1 1 2 4 3 2 2 -- 1 2 4 Cryptomonads Density 1,513 718 1,113 1,090 2,689 1,689 628 529 332 450 919 1,104 Taxa 2 3 3 6 4 5 2 3 1 1 1 1 Miscellaneous Density ------Taxa ------Total Density (#/mL) 81,447 82,992 131,804 192,750 190,341 340,231 329,773 121,357 18,573 11,203 22,029 21,474 Total Number of Taxa 28 27 32 133 151 142 93 89 42 11 40 45 APPENDIX E PAGE E-7

Table E-3 (cont.): Total reservoir phytoplankton density (cells/mL) and number of taxa in Cherry Creek Reservoir, 1984 to 2014. 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 Blue-Green Algae Density 19,716 44,951 15,263 164,290 148,691 941 54,114 165,677 79,154 665,696 1,266,765 1,124,197 Taxa 10 11 8 19 12 3 21 27 19 19 21 19 Green Algae Density 2,461 1,809 898 43,881 33,217 1,973 55,190 56,236 189,777 1,358,248 563,344 1,531,579 Taxa 18 18 18 71 56 27 70 75 66 63 63 67 Diatoms Density 1,109 628 838 12,019 5,256 978 2,026 1,720 3,610 32,036 60,127 27,681 Taxa 8 18 16 34 22 24 22 26 24 21 21 17 Golden-Brown Algae Density 227 56 -- 391 1,346 34 44 57 335 542 2,380 6,270 Taxa 2 2 -- 14 13 3 5 5 4 5 3 3 Euglenoids Density 838 698 1,252 126 91 22 308 24 39 1,549 1,303 259 Taxa 3 3 1 6 4 3 9 11 8 10 10 11 Dinoflagellates Density -- 18 45 80 157 193 20 57 60 330 595 722 Taxa -- 2 2 8 6 5 3 5 6 5 5 3 Cryptomonads Density 1,487 1,393 559 2,472 2,851 355 3,282 3,158 3,293 40,511 61,037 35,962 Taxa 1 1 1 4 6 4 8 8 9 12 9 11 Miscellaneous Density ------1,923 5,714 15 1,294 164 2,014 4,855 73,435 53,330 Taxa ------1 1 1 3 6 6 6 7 8 Total Density (#/mL) 25,838 49,553 18,855 225,182 197,323 4,511 116,278 227,093 278,282 2,103,767 2,028,986 2,780,000 Total Number of Taxa 39 55 46 157 120 70 141 164 142 141 139 139 APPENDIX E PAGE E-8

Table E-3 (cont.): Total reservoir phytoplankton density (cells/mL) and number of taxa in Cherry Creek Reservoir, 1984 to 2014. Long- 2009 2010 2011 2012 2013 2014 term Blue-Green Algae Density 332 4,177 1,136 2,648 731 1,776 60,305 Taxa 3 6 3 2 2 3 10 Green Algae Density 10,733 19,202 26,055 23,851 21,270 32,506 20,236 Taxa 20 22 23 20 21 23 23 Diatoms Density 11,609 13,975 39,654 24,186 16,380 12,669 4,708 Taxa 25 30 21 34 22 30 21 Golden-Brown Algae Density 246 587 1,895 1,304 6,371 16,363 292 Taxa 4 3 4 3 5 6 4 Euglenoids Density 83 272 570 1,802 1,308 474 266 Taxa 3 4 4 5 7 5 4 Dinoflagellates Density 4,497 2,556 6,253 1,158 326 1,857 60 Taxa 4 3 1 2 3 4 3 Cryptomonads Density 22,277 16,794 14,850 12,130 7,930 9,787 2,081 Taxa 2 2 2 2 2 1 3 Miscellaneous Density ------94 -- 323 1,923 Taxa ------1 -- 1 3 Total Density (#/mL) 49,777 57,563 90,413 67,173 54,316 75,755 86,703 Total Number of Taxa 61 70 58 68 62 73 70 APPENDIX E PAGE E-9

Table E-4: 2014 Cherry Creek Reservoir zooplankton. 2014 11-Feb 25-Mar 15-Apr 13-May 27-May 10-Jun 24-Jun 8-Jul 22-Jul 5-Aug 19-Aug 2-Sep 16-Sep 14-Oct 4-Nov Cladocera Bosmina longirostris 29.6 13.9 17.3 33.6 82.3 94.7 36.7 133.8 28.3 21.9 11.8 6.6 12.1 12.8 10.0 Daphnia ambigua ------2.4 6.2 6.2 4.9 ------Daphnia lumholtzi ------47.9 14.2 4.5 5.1 2.8 2.9 Daphnia parvula ------0.6 -- 0.1 -- 0.1 Daphnia rosea ------1.1 5.3 ------Daphnia sp. -- -- 0.4 7.0 14.2 74.8 19.9 26.1 1.4 -- -- 0.2 0.2 0.6 0.1 Pleuroxus sp. ------0.9 ------Skistodiaptomus pallidus 1.2 ------0.9 0.4 10.2 65.5 3.3 0.2 0.1 0.2 2.8 4.2 Copepod Diacyclops thomasi 36.7 73.3 53.5 12.5 2.7 21.2 5.8 34.0 1.8 1.2 -- 0.04 0.4 1.3 1.6 Immature instar (copepodid) 110.2 46.8 15.0 67.8 35.4 50.0 11.9 25.0 5.3 10.7 3.5 5.0 8.1 12.2 7.3 Mesocyclops edax ------4.9 -- 7.9 ------0.04 0.1 0.4 0.1 Nauplius 62.8 2.7 -- 154.8 179.1 31.0 65.5 526.4 148.6 74.9 61.3 52.0 47.1 58.7 38.9 Rotifer Ascomorpha ovalis ------8.8 ------Asplanchna sp. 5.8 ------0.4 -- 34.9 90.7 9.3 1.5 1.8 1.4 3.2 1.4 Brachionus angularis ------39.8 8.4 10.5 1.2 0.7 2.1 1.1 0.7 Brachionus calyciflorus -- -- 33.3 ------Brachionus sp. ------1.8 ------Conochiloides sp. -- 0.9 327.0 ------2.2 0.9 37.2 0.6 ------Keratella cochlearis 0.9 0.9 -- 4.4 31.8 8.4 2.2 278.7 4.9 -- 0.3 0.4 -- 2.1 75.0 Keratella quadrata -- 0.9 -- 0.4 1.3 -- 42.5 6.6 ------Polyarthra sp. -- -- 3.6 1.3 0.4 -- -- 48.7 -- 0.6 1.2 13.1 -- 8.1 6.0 Total Concentration (#/mL) 247.2 139.3 450.1 285.4 360.0 291.9 226.5 1238.9 274.3 209.7 94.9 84.4 76.9 106.3 148.3 Total Number of Taxa 6 6 6 9 11 8 10 13 9 9 9 11 10 11 12 APPENDIX E PAGE E-10

Table E-5: 2014 Routine weekly cyanotoxin sampling events (values in µg/L) Anatoxin-A Cylindrospermopsin CCR 1,2,3 Comp Swim Beach CCR 1,2,3 Comp Swim Beach Date Result D.L. Method Result D.L. Method Date Result D.L. Method Result D.L. Method 6/13 ------ND 0.05 LC-MS/MS 6/13 ------ND 0.1 ELISA 6/24 ------ND 0.05 LC-MS/MS 6/24 ------ND 0.1 ELISA 7/1 ND 0.05 LC-MS/MS ND 0.05 LC-MS/MS 7/1 ND 0.1 ELISA ND 0.1 ELISA 7/8 ND 0.05 LC-MS/MS ND 0.05 LC-MS/MS 7/8 ND 0.1 ELISA ND 0.1 ELISA 7/16 ND 0.05 LC-MS/MS ND 0.05 LC-MS/MS 7/16 ND 0.1 ELISA ND 0.1 ELISA 7/22 ND 0.05 LC-MS/MS ND 0.05 LC-MS/MS 7/22 ND 0.1 ELISA ND 0.1 ELISA 7/29 ND 0.05 LC-MS/MS ND 0.05 LC-MS/MS 7/29 ND 0.1 ELISA ND 0.1 ELISA 8/5 ND 0.05 LC-MS/MS ND 0.05 LC-MS/MS 8/5 ND 0.1 ELISA ND 0.1 ELISA 8/12 ND 0.05 LC-MS/MS ND 0.05 LC-MS/MS 8/12 ND 0.1 ELISA ND 0.1 ELISA 8/19 ND 0.05 LC-MS/MS ND 0.05 LC-MS/MS 8/19 ND 0.1 ELISA ND 0.1 ELISA 8/26 ND 0.05 LC-MS/MS ND 0.05 LC-MS/MS 8/26 ND 0.1 ELISA ND 0.1 ELISA 9/2 ND 0.05 LC-MS/MS ND 0.05 LC-MS/MS 9/2 ND 0.1 ELISA ND 0.1 ELISA 9/9 ND 0.05 LC-MS/MS ND 0.05 LC-MS/MS 9/9 ND 0.1 ELISA ND 0.1 ELISA 9/16 ND 0.05 LC-MS/MS ND 0.05 LC-MS/MS 9/16 ND 0.1 ELISA ND 0.1 ELISA 9/23 ND 0.05 LC-MS/MS ND 0.05 LC-MS/MS 9/23 ND 0.1 ELISA ND 0.1 ELISA Mycrocystin Saxitoxin CCR 1,2,3 Comp Swim Beach CCR 1,2,3 Comp Swim Beach Date Result D.L. Method Result D.L. Method Date Result D.L. Method Result D.L. Method 6/13 ------0.20 0.15 ELISA 6/13 ------ND 0.05 ELISA 6/24 ------ND 0.15 ELISA 6/24 ------ND 0.05 ELISA 7/1 ND 0.15 ELISA ND 0.15 ELISA 7/1 ND 0.05 ELISA ND 0.05 ELISA 7/8 ND 0.15 ELISA ND 0.15 ELISA 7/8 ND 0.05 ELISA ND 0.05 ELISA 7/16 ND 0.15 ELISA ND 0.15 ELISA 7/16 ND 0.05 ELISA ND 0.05 ELISA 7/22 0.21 0.15 ELISA ND 0.15 ELISA 7/22 ND 0.05 ELISA ND 0.05 ELISA 7/29 0.24 0.15 ELISA 0.29 0.15 ELISA 7/29 ND 0.05 ELISA ND 0.05 ELISA 8/5 ND 0.15 ELISA 0.27 0.15 ELISA 8/5 ND 0.05 ELISA ND 0.05 ELISA 8/12 ND 0.15 ELISA ND 0.15 ELISA 8/12 ND 0.05 ELISA ND 0.05 ELISA 8/19 ND 0.15 ELISA ND 0.15 ELISA 8/19 ND 0.05 ELISA ND 0.05 ELISA 8/26 0.16 0.15 ELISA ND 0.15 ELISA 8/26 ND 0.05 ELISA ND 0.05 ELISA 9/2 ND 0.15 ELISA ND 0.15 ELISA 9/2 ND 0.05 ELISA ND 0.05 ELISA 9/9 ND 0.15 ELISA 0.16 0.15 ELISA 9/9 ND 0.05 ELISA ND 0.05 ELISA 9/16 ND 0.15 ELISA 0.18 0.15 ELISA 9/16 ND 0.05 ELISA ND 0.05 ELISA 9/23 ND 0.15 ELISA ND 0.15 ELISA 9/23 ND 0.05 ELISA ND 0.05 ELISA APPENDIX E PAGE E-11

Table E-6: 2014 Opportunistic cyanotoxin sampling events(values in µg/L) Anatoxin-A CCR-2 CCR-2 Surface CCR-2 Photic DAM Marina Date Result D.L. Method Result D.L. Method Result D.L. Method Result D.L. Method Result D.L. Method 6/10 ND 0.05 LC-MS/MS ------6/13 ------ND 0.05 LC-MS/MS ND 0.05 LC-MS/MS ------ND 0.05 LC-MS/MS 6/17 ------ND 0.05 LC-MS/MS ------6/24 ------ND 0.05 LC-MS/MS ------Cylindrospermopsin Date CCR-2 CCR-2 Surface CCR-2 Photic DAM Marina 6/10 ND 0.1 ELISA ------6/13 ------ND 0.1 ELISA ND 0.1 ELISA ------ND 0.1 ELISA 6/17 ------ND 0.1 ELISA ------6/24 ------ND 0.1 ELISA ------Mycrocystin Date CCR-2 CCR-2 Surface CCR-2 Photic DAM Marina 6/10 10.0 0.15 ELISA ------6/10 9.3 -- LC-MS ------6/13 ------0.70 0.15 ELISA 0.40 0.15 ELISA ------0.20 0.15 ELISA 6/17 ------25.00 0.15 ELISA ------6/24 ------0.20 0.15 ELISA ------Saxitoxin Date CCR-2 CCR-2 Surface CCR-2 Photic DAM Marina 6/10 ND 0.05 ELISA ------6/13 ------ND 0.05 ELISA ND 0.05 ELISA ------ND 0.05 ELISA 6/17 ------ND 0.05 ELISA ------6/24 ------ND 0.05 ELISA ------APPENDIX E PAGE E-12

Table E-7: 2014 Cherry Creek Reservoir cyanobacteria identification and enumeration based on cyanotoxin presence (species units/mL.) 2014 Cyanobacteria 10-Jun 17-Jun 24-Jun Aphanizomenon flos-aquae -- 280 -- Aphanizomenon sp. 30 -- 6 Aphanocapsa sp. -- -- 7 Cyanophyte spp. -- 266 53 Dolichospermum cf. crassum -- -- 9 Dolichospermum cf. flos-aquae -- 132,865 219 Dolichospermum flos-aquae ------Dolichospermum spp. 54,777 -- --

PRF Summaries

Summary of Pollutant Reduction Facilities (PRF)

Shop Creek

Cottonwood Wetlands

Quincy Drainage

Shoreline Stabilization

Cottonwood/Peoria Pond

Bowtie Property Acquisition

Piney Creek Stream Reclamation at Buckley Road

Cottonwood Creek Reclamation Phase I & II

Cherry Creek Reservoir Destratification System

Cherry Creek Stream Reclamation at PJCOS

Cherry Creek Stream Reclamation at Eco-Park

McMurdo Gulch Stream Reclamation

Cottonwood Creek Stream Reclamation at Easter Avenue

Cottonwood Creek Peoria Trib., Ponds C3 & C4

Cherry Creek Stream Reclamation at 12-Mile Park, Phase I

Cherry Creek Stream Reclamation at 12-Mile Park, Phase II

Mountain & Lake Loop Shoreline Stabilization Shop Creek

The Problem The Cherry Creek Reservoir Clean Lakes Study (DRCOG 1984) identified that Reservoir water quality and its uses were moderately impaired and that phosphorus was the limiting nutrient. To protect the water quality of Cherry Creek, the Water quality Control Commission (WQCC) originally set an in-lake phosphorus standard of 35-g/l (1985) and subsequently changed the standard to 15- g/l chlorophyll a (2000). A maximum phosphorus concentration of 40-g/l was set as the goal. The Cherry Creek Control Regulation (December 2004), requires the implementation of best management practices (BMP) for all new development and pollutant reduction facilities throughout the watershed (PRF). PRF are typically larger scale BMP with expressed purpose of reduction phosphorus loads to Cherry Creek Reservoir and are primarily constructed with Authority funds.

Shop Creek - One Solution In the 1980’s, an urbanizing watershed of 550-acres within the City of Aurora was causing severe erosion to a small drainage channel (Shop Creek) within Cherry Creek State Park. Soils were also being carried into the Park from upstream development and ending up in the Reservoir, along with other associated pollutants, particularly phosphorus.

The City of Aurora worked with the Urban Drainage & Flood Control District, the Cherry Creek Basin Water Quality Authority and Cherry Creek State Parks to develop a demonstration project for treatment of phosphorus. To maximize phosphorus removal from storm runoff, detention, retention and wetlands were combined in series to provide a “treatment train” (see photo at left). The detention area located upstream of Parker Road (not shown) removes coarse sediment. The retention area (photo below) furthers sedimentation and particulate phosphorum removal. The series of seven wetlands even greater phosphorus removal, including dissolved phosphorus.

From the Park prospective, the solution complements park values, aesthetics, recreational access, wildlife habitat, low maintenance.

Technical Data  Watershed area 550 acres  Imperviousness of 40%, of which 75% is hydraulically connected.  Permanent pool of 4.8 acre feet, which is 0.10 inches of runoff from entire watershed or 0.26 inches from impervious areas. Aerial View of Shop Creek (Muller Engineering)

 Surcharge above permanent pool of 9.1-acre feet, providing detention for 0.2 inches of runoff from entire watershed.  Outlet empties 90% of surcharge volume in 30-hours.  Total of 3.5-acres of wetlands.  One year storm event velocity of 1-fps.  Six drop-structures constructed from soil cement.

Performance Regular sampling occurs upstream, downstream of retention pond and downstream of wetlands. In addition to phosphorus (total and dissolved), samples analyzed for nitrates, nitrites, nitrogen, copper, iron, manganese, zinc, alkalinity, chemical oxygen demand, and total suspended solids. Long term performance for phosphorus is shown in the chart below. Sampling upstream and within the wetlands was discontinued in 2000.

Other Pollutant Reduction Facilities (PRF) The Authority has constructed and is operating, maintaining and monitoring eight major PRFs in the Cherry Creek Reservoir watershed. A ninth facility, Cottonwood Creek Restoration, began construction in 2004.

ShopCreekFlyer-v2, 01/08/13 Shop Creek Detention/wetlands System

1000 CEC, 1998. Cherry Creek Reservoir 1997 Annual Aquatic Biological and Nutrient Monitoring Study

100

Station SC-1, Pond influent Long Term Average Performance (1994 to present) Station SC-2, pond effluent, Through Pond: 36% wetlands influent Through Wetlands: 45% Station SC-3, Wetlands Through System: 65% Annual Total Phosphorus Loads (pounds) effluent

10 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 Water Year

 Cottonwood Creek/Perimeter Rd. This PRF is similar to directly discharge into the lake. The projects include East Shop Creek, except that the initial retention basin for Side Shade Shelter (1996) and the Tower Loop (1999) Cottonwood Creek is much larger to accommodate the projects (see photo at left). larger runoff volume from the 7,500-acre drainage area. Also, Cottonwood Creek is followed by a single wetland. The Recreation Component Multiple uses for PRF are vital to their success and provisions  Quincy Drainage. This PRF captures runoff from the for recreation are key to many projects. The before (photo 530-acre drainage basin and quickly infiltrates the runoff left) and after (next page) photos illustrate the Tower Loop through the sandy alluvium. Native grasses typical of a area, a PRF constructed in 1999. Tower Loop is a very semi-arid climate populate the pond. Typically, no popular fishing area and controlling public access was a key surface flows are discharged from this PRF during factor in the design. Recreation was enhanced by providing baseflow conditions and discharges during precipitation “fishing pods” events have been limited. A mission of the Authority is public education regarding Tower Loop Erosion before Construction (Ruzzo) impacts of urban runoff on water quality of Cherry Creek. By providing or enhancing recreation opportunities for PRF, the Authority also enhances its opportunities to educate the public about urban runoff pollution.

Most of the PRF’s constructed by the Authority to date have included signage prepared by professional park planners. For instance, along Shop Creek several kiosks have been installed explaining the need and benefits of the project.

The Authority was also recently awarded a Section 319, information and education Grant from EPA. The Authority will work with Cherry Creek State Park Staff to increase the general awareness regarding the importance of BMPs in Cherry Creek Reservoir to gain public support and participation in protecting water quality.

Shoreline Protection Projects. The Authority has an ongoing Cherry Creek Basin program of projects to protect the shoreline of the Reservoir, The Cherry Creek Reservoir watershed covers 386 square thereby limiting sediment and attached phosphorus that miles of the Front Range corridor, extending upstream to the ShopCreekFlyer-v2 Palmer Divide. The basin drains northward from elevation of Cherry Creek. The Plan identifies projects, called reaching approximately 7,700 feet near Colorado Springs, to pollutant reduction facilities (PRF) that include enhanced 5,600 feet at the Reservoir. Topography within the watershed BMP (i.e.: detention, retention, wetlands, filtration), in- is quite variable – consisting of pinyon pine covered hillsides, stream and in-lake controls, and shoreline and stream short grass prairie, and canyons, such as those found in bank protection. PRFs provide levels of protection Castlewood Canyon State Park. beyond permanent BMPs by also targeting other pollutants such as sediment, nitrogen, and metals. PRF measures also provide a net environmental benefit by improving riparian health and wildlife habitat. The Authority funds PRF by collecting fees and taxes.

 Operations and Maintenance Plan. The Authority is developing a long-term program to insure that technical measures continue to serve their purpose. The goal of the plan is to insure physical integrity and proper hydraulic function for PRF. The plan will identify specific requirements for PRF that address maintenance access, safety and convenience, aesthetic and recreation requirements.

Aerial View of the Reservoir (USACE)

The Reservoir was impounded in 1950, creating the 860-acre lake and a 3,500 acre State Park.

Precipitation averages from 13” at the Reservoir to 18” at the divide with long-term maximums ranging from 22” to 33”. Annual storm runoff has varied over the last 15-years from a low of 5,000 acre feet to a high of 27,700 acre feet in 1999. Tower Loop with Enhanced Recreation Features (Ruzzo) Phosphorus loads have also varied widely with watershed hydrology, ranging from a low of 4,500 pounds to a high of 18,800 pounds.

Cherry Creek Basin Water Quality Authority The CCBWQA is a quasi-municipal corporation and political subdivision of the State that has primary responsibility for water quality in the Cherry Creek Basin. The Authority is specifically empowered to develop and implement plans for water quality controls for the Reservoir and watershed. The watershed management strategy of the Authority includes:

 Regulations. Stormwater Quality Regulations (Regulations) have been adopted by the Authority (2000). The purpose is to implement, monitor, and enforce technical measures (BMP) to reduce sediments and nutrients reaching Cherry Creek and Cherry Creek Reservoir. The Regulations establish minimum requirements for BMP that address construction erosion (temporary measures) and water quality enhancement for completed developments (permanent measures).

 Planning. The Authority has adopted (1999) a Storm Drainage Quality Plan to further protect the water quality ShopCreekFlyer-v2 Cottonwood Wetlands

Presented in this memorandum is a summary of the Cottonwood Wetlands Pollutant Reduction Facility (PRF) Rehabilitation project (Cottonwood Wetlands PRF or Project.

BACKGROUND AND PURPOSE

The Cottonwood Wetlands PRF1 was constructed by the Authority around 1997 for the purpose of trapping sediment from the highly eroded Cottonwood Creek channel within the Park boundaries to prevent sediment and attached pollutants from entering the Reservoir. This project was followed by the Cottonwood\Peoria Wetlands (2001) and the first Phase of Cottonwood Creek reclamation (2004) within the Park. See Figure 1, Site Map.

Despite these upstream stabilization measures, routine monitoring of the inflow and outflow phosphorus loads beginning in 1997 showed that by 2005, the “…effectiveness of the pond system was greatly reduced2. Restoration of Cottonwood Wetlands

1 Previously referred to as the Cottonwood Perimeter Road Pond in earlier Authority documents. 2 Chadwick Ecological Consultants, Inc. March 2006. Cherry Creek Reservoir 2005 Annual Aquatic Biological-Nutrient Monitoring Study and Cottonwood Creek Phosphorus Reduction Facility Monitoring. 1

ProjectSummaryMemo-CottonwoodWetlands December 27, 2012 was identified as a necessary project in the 2005 annual inspection report3 and included in the Authority’s 5-year CIP budget. However, rehabilitation of the Cottonwood Wetlands was delayed until the upstream reaches of Cottonwood Creek from West Lakeview Road (aka perimeter road) to Peoria Street were stabilized to minimize additional sedimentation of the Cottonwood Wetlands PRF.

Phase II of Cottonwood Creek Reclamation was finished in 2008 completing reclamation of the 2.2-miles of highly eroded channel within the Park boundary. The Authority then began preparing plans for rehabilitation of the Cottonwood Wetlands in 2008 by retaining Muller Engineering Company4 to prepare final plans and construction documents.

INVESTIGATION PHASE – Clay Pigeon Debris

During design of the rehabilitation project, clay pigeons were found at the site in early 2009. Some types of clay pigeons are classified as a solid waste since they contain polynuclear-aromatic hydrocarbons (PAH). In discussions with the Colorado Department of Public Health and Environment (CDPHE) it was determined that only material containing clay pigeons disturbed during construction must be removed and disposed in a qualified landfill. It is not necessary to remove clay pigeons from the entire project site, if they are left undisturbed. Therefore, the Authority redesigned the Cottonwood Wetlands PRF to minimize excavation in areas of the project where clay pigeons were known to exist in order to reduce cost of offsite, landfill disposal.

The area affected by the PRF and clay pigeon debris is owned by the US Army Corps of Engineers (Corps) and is in the possession of CPW pursuant to a long term lease. The Figure 2 - Clay Pigeon Debris Authority could not assume responsibility for removing waste material from property it does not own, especially since the placement of that material resulted from the actions of third parties over whom the Authority had no control. Because the PRF could not be rehabilitated until the clay pigeons were removed and because of economies of scale, contractor scheduling issues and other matters of contract administration, rehabilitation of the PRF and the removal of the clay pigeons was determined to be best treated as an integrated project and managed by a single owner, CPW.

DESIGN APPROACH

The primary purpose of the Project was to restore the sedimentation function of the PRF, which had become clogged with sediment since construction reducing water quality benefits. However, to avoid damaging the existing cottonwood, sedge, cattail, and rush wetlands that had become

3 William P. Ruzzo, PE, LLC April 25, 2005. Annual Inspection of PRF’s at Cherry Creek State Park. 4 October 1, 2008. Agreement for Engineering Design Services – Cottonwood Wetlands Project.

ProjectSummaryMemo-CottonwoodWetlands 2 December 27, 2012 established since construction, the main creek channel was realigned to avoid existing wetlands, which also avoided the known clay pigeon areas. In addition, the main channel was aligned to create a serpentine pathway with localized pools through the pond area to maximize the contact between storm runoff and the existing and newly planted vegetation further improving water quality. These modifications are illustrated in Figure 3 below where the green color represents existing wetlands.

Rehabilitation of the Project did not restore the original sedimentation capacity because of the reduced pond surface area occupied by wetlands. However, the modifications discussed above were considered to offset reduction in sedimentation capacity, particularly since the upstream channel was now stabilized reducing future sediment transport into the Project. Figure 3 General Project Plan

FUNDING AGREEMENT

Because of the shared responsibility by both parties for the Project, the Authority and CPW entered into a funding agreement in September 2011 to share project costs. Key provisions of the agreement included:

1. Both parties allocated funds for the project to cover all costs, including PRF rehabilitation and clay pigeon removal and disposal.

2. CPW pays for all costs associated with removal and proper, off-site disposal of clay pigeon debris.

3. The Authority pays for all costs associated with rehabilitation of the Cottonwood Creek Wetlands PRF.

4. CPW and the Authority already incurred expenses related to the project that were not their responsibility and therefore each party receives credit for the expenses when determining how the final project costs will be shared. The construction contract administration and quantities have been developed to clearly separate PRF rehabilitation costs from clay pigeon disposal costs.

5. The project was constructed per plans prepared for and approved by the Authority.

ProjectSummaryMemo-CottonwoodWetlands 3 December 27, 2012

The funding agreement was amended (First Amendment) on April 16, 2012 to adjust expected project costs due to greater quantities of sediment that needed to be removed.

PROJECT MANAGEMENT

CPW agreed to manage construction of the project and, with approval of the Authority, contracted with the Authority’s consultant to provide construction observation services to oversee the rehabilitation of the Cottonwood Wetlands PRF. CPW managed project bidding and construction contracting paying all project costs from a separate State account initially funded by the State. The Authority provided overall project guidance and direction related to rehabilitation of the PRF working cooperatively with CPW throughout construction. After completion of the Project and all project costs were accounted for, the Authority reimbursed CPW for the balance of the Authority’s cost share.

CONSTRUCTION

A single bid was received for the Project and opened on November 22, 2011. Since the bid amount of $326,7815 compared favorable to the engineer’s opinion of probable cost ($337,267) adjusting for increased sediment removal costs, the Project was awarded to 53-Corporation, LLC of Castle Rock. The notice to proceed with construction was issued on January 17, 2012.

To facilitate sediment removal, the pond was drained starting October 7, 2011 which revealed that the pond had experienced greater sedimentation than previously estimated and would require more excavation and sediment removal. During construction of the Project, the Authority also had another project6 under construction within Cherry Creek State Park by 53-Corporation, which needed earth materials. After determining the suitability of the sediment for use in the 12-Mile Park project, the Authority directed the contractor to haul sediment from the Cottonwood Wetlands project and place it at the 12-Mile Park project to reclaim the wetlands damaged during breach of the Cherry Creek channel. This exchange of material between projects reduced costs to import materials for the two projects and export materials Figure 4 - Beginning excavation from the Park to preserve flood storage volume7.

5 Amount includes the base bid and optional work but not clay pigeon removal. 6 Cherry Creek Stream Reclamation at 12-Mile Park – Phase I 7 William P. Ruzzo, PE, LLC July 26, 2012. Tower Loop, Cottonwood Wetlands, and Cherry Creek @ 12- Mile Park

ProjectSummaryMemo-CottonwoodWetlands 4 December 27, 2012

In late May of 2012, it was discovered that the original dam embankment for the Cottonwood Wetlands PRF was constructed from 0.5 to 1.5-feet below the design elevation. The contractor was issued a change order to raise the embankment to the original design elevation. On June 6, 2012 a significant storm event occurred over Cottonwood Creek and lower Cherry Creek basin that resulted in minor flood damages at the Cottonwood Wetlands project8. The investigation concluded that if the dam embankment had not been raised,”…it is likely that the dam would have overtopped resulting in significant damage downstream of the dam and to the Cottonwood Wetlands project.”

The Cottonwood Wetlands project TOTAL PROJECT COSTS Total Authority CPW was complete as of July 9, 2012. Preliminary Engineering $ 39,750.00 $ 39,750.00 -$ Final Design Engineering $ 29,637.00 $ 10,607.50 $ 19,029.50 Final project costs and allocation of Construction Engineering $ 93,494.50 $ 80,761.00 $ 12,733.50 costs between the Authority and Construction $306,805.66 $ 289,089.32 $ 17,716.34 CPW are shown in the adjacent table. Environmental testing $ 810.20 -$ $ 810.20 The cost allocated to CPW represents Total $470,497.36 $ 420,207.82 $ 50,289.54 the final costs to remove and dispose clay pigeons disturbed as the result of the Project. CPW originally received an estimate of $90,000 to just characterize the solid and hazardous9 wastes on the site, which costs did not include any removal of clay pigeon debris.

SEDIMENT SAMPLES Prior to construction, samples of the sediment were obtained and tested for total phosphorus content10. The average total phosphorus (TP) concentration of 744 mg/kg for the Cottonwood Wetlands is consistent with the Authority’s results for sediment removed from the Cottonwood Peoria Street wetlands (average of 743 mg/kg). TP concentrations in sediment ponds are approximately 50% higher than found in stream bed and stream banks, which are typically around 500-mg/kg.

WATER QUALITY BENEFITS

Water quality benefits of the Cottonwood Wetlands have been documented in the Authority’s annual report of activities to the Water Quality Control Commission required by Control Regulation No. 72. The Authority collects data upstream and downstream of the Cottonwood Wetlands and the Cottonwood Peoria Wetlands which allows each segment of the treatment train

8 William P. Ruzzo June 7, 2012. Preliminary Report on the June 6, 2012 Flood Event on Recent Completed PRFs in Cherry Creek State Park. 9 Since clay pigeon debris was found there was a possibility that lead from the shot would also be found. Samples of the sediment containing clay pigeons were tested and found to be less than maximum contaminant limits. 10 William P. Ruzzo, January 12, 2012. Cottonwood Wetlands PRF Rehabilitation – Soil Phosphorus Content.

ProjectSummaryMemo-CottonwoodWetlands 5 December 27, 2012

(i.e.: Cottonwood\Peoria Pond, Cottonwood Creek Reclamation, and Cottonwood Wetlands) to be evaluated independently.

The Annual Report for 201111 shows that, prior to rehabilitation of the Cottonwood Wetlands, the 2011, flow weighted total phosphorus (TP) into the Project was 101-ug/l and discharged from the Project was 81-ug/l. Measurements during 2012 showed that TP12 discharged from the Project varied from 87-ug/l to 36-ug/l which is a noticeable improvement in water quality. It is also noted that the discharge TP is less than the proposed in-stream standard for TP, which is 170-ug/l.

11 CCBWQA March 31, 2012. Annual Report on Activities Cherry Creek Basin Water Quality Authority. 12 One measurement taken in March 2012 during construction resulted in a TP of 156-ug/l.

ProjectSummaryMemo-CottonwoodWetlands 6 Quincy Drainage

BACKGROUND AND PURPOSE The Quincy Drainage Detention (Project) is located in the east part of Cherry Creek State Park (see Figure 1) and consists of a small earth embankment that doubles as a paved park trail (Photo 1) with a pipe outlet and trash rack (Photo 2). The Project, which drains approximately 527 acres1, was constructed in 1995 at a capital cost of $219,000. To create the detention area, the park trail was relocated to the west around the Cottonwood grove and elevated to create an embankment2.

PROJECT PARTNERS AND FUNDING Quincy Drainage Detention was funded in total by the Authority and was a cooperative effort with Figure 1 Location Map Cherry Creek State Park.

WATER QUALITY BENEFITS Quincy Drainage Detention temporarily detains stormwater which allows for particulate matter (i.e.: pollutants) to settle out in the storage area, which is also a Photo 1 – Park Trail Cottonwood grove. In addition, because the native soils in the detention area are relatively pervious, the Project rarely experiences a discharge through the outlet because the storm runoff infiltrates into the alluvium, providing even Photo 2 – Pond Outlet greater water quality benefits.

1 Boyle Engineering Corporation June 1985. Outfall System Planning Quincy Drainage & Shop Creek. 2 Personal communication with Jim Wulliman of Muller Engineering Co., formerly PM for Project with CH2MHill.

ProjectSummaryMemo-QuincyDrain.docx

1 Shoreline Stablization East Shade Shelter, East Boat Ramp, Tower Loop, and Dixon Grove

Presented in this memorandum is a summary of the early (pre 2000) shoreline stabilization pollutant reduction facilities (PRFs, see Figure 1 Location Map).

BACKGROUND AND PURPOSE The Authority began constructing shoreline stabilization PRFs in 1996 with the East Shade Shelter and East Boat Ramp projects, which were followed by the Tower Loop and Dixon Grove projects in 1999 (see Figure 1 PRF Location Map). The most recent project at Mountain and Lake Loop was completed in 20131 and design of the West Shade Shelter PRF is projected for 2016. To date, the total cost of shoreline PRF’s exceeds $1,214,000.

The dominant shoreline stabilization method is to use riprap and large boulders supplemented with willow, bushes, trees, and other suitable vegetation plantings. See Photos 1, 2, and 3. Runoff from parking lots is addressed by creating wetland retention areas (see Photo 1) or infiltration areas that filter pollutants in the runoff minimizing the discharge into the reservoir. Figure 1 – Location Map The earlier shoreline PRF’s placed large boulders, typically 36” or larger, along the water’s edge with the top of the boulder about 18” above the normal maximum water surface (i.e.: 5550 feet) in the Reservoir. For the Tower Loop project (Photo 3), boulders were stacked two and three high creating a wall that raised the fishing platforms constructed along the steep shoreline slope.

1 See separate project summary report.

ProjectSummaryMemo-EarlyShorelinePRF.docx

1 January 13, 2014

The boulder sizes exceed rock sizes needed to protect the shoreline from wave erosion. However, it was observed during some winter and early spring periods that ice forces were able to move and displace some large Photo 1 East Boat Ramp Photo 2 East Boat Ramp boulders at the east shoreline projects and, for Tower Loop, resulted in failure of the boulder walls. The impact of ice forces on shoreline erosion was investigated and changes to the design approach have evolved over the years. See report2 for findings and recommendations regarding the Authority’s approach.

PROJECT PARTNERS AND FUNDING

Figure 3 Tower loop All PRFs within the limits of Cherry Creek State Park are designed, constructed, and maintained by the Authority without funding assistance from other local governments.

WATER QUALITY BENEFITS Shoreline stabilization projects qualify as PRF because they minimize the quantity of soil, with attached phosphorus and other pollutants, eroded along the edge of the reservoir that become deposited directly into the lake. In many cases, shoreline erosion and pollutant discharges to the reservoir are aggravated by parking lots that discharge pollutants directly to the reservoir. Discharges from parking areas are directed to wetland detention areas or infiltration retention areas to immobilize pollutants. Erosion is primarily the result of

wave and ice Photo 4 Extreme Bank Erosion forces acting on the shoreline soils, but also from pedestrian and domestic animal uses that destroy vegetation exposing bare soils that are more readily eroded. Examples of shoreline erosion at Cherry

Creek are shown on the Photos 4 and 5.

CONCLUSIONS Stabilization of the reservoir shoreline continues to be a priority Photo 5 Typical Bank Erosion PRF for the Authority as it represents the “first line of defense” when managing pollutant discharges into the Reservoir.

2 William P. Ruzzo, PE, LLC November 11, 2013. Shoreline PRF Design Approach at Cherry Creek Reservoir.

2 Cottonwood/Peoria Pond

BACKGROUND AND PURPOSE

The Cottonwood\Peoria Pond was part of a regional master plan prepared for multiple governmental agencies1 lead by UDFCD. The Project is located just outside of the Park boundary but within the Corps of Engineers flowage easement (see Figure 1, General Location Map).

Design was started in 1997 but was put on hold until the spring of 2000 due to right-of-way and annexation requirements for the roadway portion of the project. Design was completed in 2001. Construction was underway by July 2001 and the final “punch-list” was issued in April 2003.

PROJECT PARTNERS AND FUNDING

Funding for the project was contributed by the UDFCD (~$280,000), Arapahoe County (~$280,000), Greenwood Village (~$250,000), CCBWQA ($200,000), and a private developer2, Figure 1 - General Location Map

1 Agencies represented at the meetings included Arapahoe County, Greenwood Village, Arapahoe Water and Wastewater Authority, Cherry Creek State Park, U.S. Army Corps of Engineers, and the CCBWQA. Also represented was Cooper Investments and Southfield Park. 2 Participation by the Landmark \Cooper Investments on behalf of Cherry C reek Vista was due, in part, to development requirements to make roadway and waterway improvements along Peoria Street

ProjectSummaryMemo-CtnwdPeoriaPond.docx 1 December 26, 2013

Landmark/Cooper ($373,000). Total project cost was approximately $1,500,000 including construction services.

DESIGN APPROACH

The Cottonwood\Peoria Pond provides flood protection and water quality benefits for Cherry Creek State Park and Cherry Creek Reservoir through a sediment basin, wetlands, and temporary storage or runoff (i.e.: water quality capture volume) from a tributary area of 7.8-square miles.

Since the project is part of a watershed master plan for drainage and storm water quality, the design tributary area for water quality is 500-acres.

The Project also provides detention and water quality for the Southfield Park runoff in the Peoria Tributary B and a storm sewer from the Cherry Creek Vista development (see Figure 2 to the left). For flood control purposes, the Project provides 31.5-acre feet Figure 2 - Project Area Schematic of storage with a maximum release of 4,400-cubic feet per second (cfs) during the 100-year flood.

The design is based on the extended detention basin (EDB) approach, which has surcharge volume and a “micro pool”. 11.6- acre-feet of surcharge volume is provided with a maximum release of 15-cfs. This volume is equivalent to 0.28-inches of runoff from 500-acres. The design criteria for an EDB are 40-hour release of the capture volume. Base flow channel in Cottonwood Creek is very sinuous to increase contact time for sediment control.

The creek improvements were designed to emulate the meandering character of the upstream Cottonwood Creek channel, lush with wetland and riparian vegetation. The construction of the facility rehabilitated the unsightly project area, which had been used for years Photo 1 - Meandering Channel

2 December 26, 2013

as a dumping ground for broken-up concrete and other rubble. Other features include a bike trail and crossing of Peoria Street through the box culverts under the street. Other trails along the wetlands perimeter provide a nature experience.

The improvements were designed to facilitate ongoing maintenance. A bypass system of gates and pipes allows Cottonwood Creek base-flows to be diverted around the facility during maintenance operations and a local electric power panel enables night operation of quiet electric pumps to dewater the sediment basin and micro-pool. An underwater rock bench provides a stable platform for an excavator and dump truck to work from as sediments are removed from the basin. A comprehensive Operations and Maintenance Manual was prepared to guide maintenance crews

WATER QUALITY BENEFITS

Water quality benefits were not calculated by the Authority for Cottonwood\Peoria Pond prior to design and construction. As part of the Authority’s 2007 operations and maintenance plan for PRF’s, the Authority contributed $6,000 to UDFCD in support of removing sediment accumulated in the Cottonwood Creek Peoria pond. The contribution was for sediment sampling and analysis of the phosphorus content in the sediment by GEI3. The measurements by GEI show average total phosphorus content in the sediment basin to be 743-mg/kg of which 3-mg/kg is extractable phosphorus available for plant uptake. A final quantity Photo 2 - Vegetation Established of sediment removed from the project was not provided to the Authority therefore, an estimate of cost per pound was not prepared. However, the Authority’s experience has been that sediment removal and disposal projects have very low cost per pound of phosphorus amounts when compared to stream reclamation projects.

Photo 3 - Mature Project Site

3 GEI, March 21, 2008. Peoria Pond Phosphorus Results. Email communication from Craig Wolf.

3 Bowtie Property Acquistion

BACKGROUND AND PURPOSE In 2002, the Authority was approached by the Trust for Public Lands (TPL) to participate in the acquisition of the Bow-Tie Property for the purpose of “…preservation of open space and creation of parks in the Cherry Creek Corridor from Castle Wood Canyon to Cherry Creek’s confluence with the South Platte River1.

The Bow-Tie Property is adjacent to Cherry Creek State Park in the northeast ¼ of Section 19, Range 67 West Township 5 South (see Figure 1 Location Map). The property is 21.4 acres in size, of which 16.4 acres is floodplain and the remaining area is upland. The Bow-Tie Property is also adjacent to land owned by Arapahoe County, which includes a detention pond for the Prairie Creek Subdivision north of Piney Creek. Figure 1 – Location Map PROJECT PARTNERS AND FUNDING Acquisition of the Bow-Tie Property was a joint effort between the Authority, City of Centennial, Urban Drainage and Flood Control District, Colorado Parks Department2, Arapahoe County, and The Trust for Public Land. The multi-party agreement was signed in early 2003 during a late-winter snow storm event that stranded at least one member of the signing party.

1 The Trust for Public Land January 11, 2002. Letter from Douglas M. Robotham to Jim Worley, Cherry Creek Basin Water Quality Authority. 2 Now Colorado Parks and Wildlife.

ProjectSummaryMemo-BowtieProperty.docx 1 January 13, 2014

Agency3 Contribution In addition to the Authority’s right to construct Cherry Creek Basin Water Quality $350,000 water quality related improvements along Cherry Authority Creek and Piney Creek, the Authority’s City of Centennial $260,000 contribution included $100,000 for the property Urban Drainage & Flood Control District $50,000 and water rights for an alluvial well, a Denver Colorado State Parks $99,000 Basin well, easements for ingress and egress, and Arapahoe County $100,000 all the related pumps, equipment, pipelines and TOTAL $859,000 appurtenances. The Authority is currently evaluating future uses of these wells related to the Authority’s business of protecting water quality in Cherry Creek. As the result of the Bow-Tie proect, the Authority has included stream corridor preservation in the capital improvement program (CIP) since 2002.

WATER QUALITY BENEFITS Protection of the floodplain, riparian corridor and other environmentally sensitive lands through public acquisition or conservation easement and restoration of the same lands for nutrient control through erosion control, revegetation or other means is identified by the Water Quality Control Commission (WQCC) as a nonpoint source nutrient control measure4.

The Authority evaluated the Bow-Tie Property Acquisition for water quality benefits using two different approaches. The first was based on construction of wetlands at the confluence of Cherry Creek and Piney Creek5. This analysis suggested that with a capital cost of $826,200, land costs of $300,000 and annual O&M of $6,400, the projected annual phosphorus costs could be from $300 to $400, based on an annual phosphorus reduction of 235-pounds. The second approach evaluated the acquisition based on preventing a portion of the property from being developed into single family housing6. A finding of this analysis was that development of approximately 9-acres would increase phosphorus loads by around 2.5-times over preserving the land as open space. This increase takes into account that the development would be required to implement post-construction best management practices (BMP) that could reduce phosphorus loads by 50% annually.

CONCLUSIONS Although the Bow-Tie Property Acquisition was the first and only Authority PRF that was based on preservation of floodplain and riparian corridor, the Authority continues to include in its CIP budget funds for future acquisitions to take advantage of the opportunity which can occur on short notice.

3 Trust for Public Land, August 28, 2003. Tying the Bow at Cherry Creek State Park. Press Release 4 CDPHE, Water Quality Control Commission November 30, 2012. Cherry Creek Reservoir Control Regulation. @72.6.6. See Statement of Basis, Specific Statutory Authority and Purpose (May 2001). 5 Ruzzo, William P. and McGregor, Dr. Robert F. November 5,2002. Updated Analysis of Bow Tie Property. 6 William P. Ruzzo, PE. January 28, 2002. Bow Tie Property – Phosphorus Contribution from Developed Land.

2 Piney Creek Stream Reclamation at Buckley Road

Presented in this memorandum is a summary of the Piney Creek stream stabilization project at Buckley Road, which was the Authority’s first participation in stabilizing or reclaiming a degraded stream channel for water quality purposes.

BACKGROUND AND PURPOSE During development of the Watershed Plan 20001, stream stabilization was given high priority as a PRF due in part to phosphorus content in sediment. This was not a new concept as controlling erosion in streams was recommended in the 1985 watershed plan2 and continued in the 1989 revision3.

In Watershed Plan 2000, Piney Creek was considered a high priority due to rapid development in the watershed and its close proximity to the Reservoir. The cost for stream stabilization in Piney Creek was extracted from the stabilization plan for Piney Creek4 funded in part by the UDFCD. The 1989 plan costs were updated for inflation but street and utility costs were not included. These adjustments resulted in $5,915,0005 capital cost for 17.4 miles of stabilization. At that time, it was assumed that the Authority would participate at a 1/3 level as a means of accelerating the implementation of stream stabilization measures by local jurisdictions. The total capital costs for the recommended PRFs in the Watershed Plan 2000 were $17,394,000, which included the $5,915,000 for Piney Creek.

EVALUATION OF STREAM STABILIZATION During development of the 2002 CIP at 2001 TAC meetings (which included some Board members) the Authority’s participation in stream stabilization was discussed at length. It was argued that although stabilization was important to managing water quality in the Reservoir, local jurisdictions would share in the costs through the UDFCD, thereby allowing the Authority to fund other priority PRFs.

1 CCBWQA June 2000. Watershed Plan 2000 2 DRCOG, September 1985. Cherry Creek Basin Water Quality Management Master Plan, 3 CCBWQA November 1989. Cherry Creek Basin Water Quality Management Master Plan (Revised 1989). 4 Greenhorne & Omeara 1989. Stream Stabilization and Major Crossing Planning. 5 CCBWQA 2000, p5-10

ProjectSummaryMemo-PineyCreekProjects 1 November 13, 2013

However, it was also determined by the TAC that the Authority could participate in stream stabilization to the extent that improvements go beyond stabilization and include reclamation of the stream corridor. The reclamation concept results in more frequent “connection” between flow in the main channel and flow in the floodplain, which results in more infiltration and filtration of storm runoff. Reclamation, which also includes the impacts of increased runoff from urbanization, was considered to provide additional, quantifiable phosphorus reduction benefits and, therefore, should be an Authority focus6. This argument was applied to Piney Creek and lower Cottonwood Creek stabilization projects that were subsequently included in the 2002 CIP.

PROJECT PARTNERS AND FUNDING The Authority contributed $118,000 (~6%) to the Piney Creek stream stabilization at Buckley Road whose total costs was $1,853,000 and included engineering and construction costs. The Project construction, which was a joint effort between UDFCD, Arapahoe County, and the Authority, began in November 2003 and was completed around May 2004.

DESIGN APPROACH The approach to stabilization of Piney Creek included the construction of 8-sheet pile reinforced drop structures to flatten the grade along with re-vegetation of the stream banks. The design cross section allowed for more frequent connection between the base flows and the channel overbank. The shallower longitudinal grade in conjunction with the sheet pile cutoff wall that forced the shallow ground water to the surface allowed for more rapid and more extensive wetland development.

WATER QUALITY BENEFITS Although the Authority concluded that stream stabilization of Piney Creek would result in water quality benefits7, an approach to quantify the benefits in terms of phosphorus reduction had not been developed at the time the project was approved. Therefore, no calculations of phosphorus reduction benefits were performed.

6 William P. Ruzzo, P.E., April 2, 2002. Piney Creek Stream Stabilization 2002 CIP. Memorandum to CCBWQA Technical Advisory Committee. 7 Ibid.

2 Cottonwood Creek Reclamation Phase I & II

The Problem The Cherry Creek Reservoir Clean Lakes Study (DRCOG 1984) identified that Reservoir water quality and its uses were moderately impaired and that phosphorus was the limiting nutrient. To protect the water quality of Cherry Creek, the Water quality Control Commission (WQCC) set an in-lake, seasonal chlorophyll a standard of 15-g/l and set a phosphorus goal of 40-g/l (2000, 2001). The Cherry Creek Control Regulation (2004), requires the implementation of best management practices (BMP) for all new development and pollutant reduction facilities throughout the watershed (PRF). PRF are typically larger scale BMP constructed by the Authority that reduce phosphorus loads to the Reservoir.

Urbanization of the Cottonwood Creek watershed (8.5 square miles) greatly increased during 1980’s and continues today. Urbanization increases the rate, frequency, duration and magnitude of storm runoff, all of which increases erosion of the streambed and banks. This erosion is evident in the adjacent photo, which shows that the Creek had degraded up to 10-feet within Cherry Creek State Park. These soils, along with other associated pollutants, particularly phosphorus, are being carried into the Reservoir, degrading its quality. Soils were also being carried into the Park from upstream development and ending up in the Reservoir.

Flood History Cottonwood Creek through Cherry Creek State Park has a history of flood events that have severely eroded the channel bed and banks and confined it to a narrow section beginning at Peoria Street (see photo above). Flooding has been reported in the past at the intersection of Peoria Street and Belleview Avenue, and within the shooting range, most recently in August 2004. Previous farming activities have apparently relocated the lower portion of the channel up on a ridge through the shooting center, rather than in the valley, which has altered the flood plain.

Stream Stabilization – One Solution The Cottonwood Creek Stream Reclamation project extends from Peoria Street to the Perimeter Road within Cherry Creek State Park. This reach constitutes phase III and IV of the four phase improvements for Lower Cottonwood Creek. Phase I was the perimeter road wetlands constructed in 1996 and Phase II was the Peoria Street extended detention basin, completed in 2003. Phase III stream reclamation-Peoria Street to the confluence with Lone Tree Creek-was completed in 2004. Phase IV-confluence to the Perimeter Road-is scheduled to begin construction in 2006.

The primary purpose of stream stabilization (Phase III and IV) is to reduce erosion of the streambed and stream banks. Phase III and IV will also enhance growth of wetland and riparian vegetation, will attract wildlife, and will provide passive recreation opportunities, all of which are important objectives in the design approach.

The proposed design concept will go beyond simply stabilizing the Creek in place. Improvements will re-create, as closely as possible, a natural, well-vegetated, functional stream system that establishes close ties between its baseflow channel and its broad, flat floodplain overbanks (see picture at left).

CotnwdCreekFlyer-v2.doc, 9/16/2005 Water Quality Benefits Cottonwood Creek will be reclaimed as a meandering, shallow prairie stream that will overtop with fairly frequent storm events, allowing over-banks and secondary channels to dissipate flood flows, thereby reducing velocities and erosive forces. Hydrologic conditions will be conducive to the regeneration of cottonwoods, willows, and other natural riparian species along the channel. This additional vegetation will further help to slow down flood flows, reinforce channel banks, enhance water quality, and provide other environmental benefits. In an attempt to quantify the phosphorus reduction benefits, the Authority has estimated the reduction in phosphorus from stream stabilization and the additional floodplain area and wetlands.

1. Stream Bank Stabilization. The improved stream will increase the length from 11,600 linear feet, with a sinuosity of 1.37 to 14,260 feet, with a sinuosity of 1.74. Authority estimates for stream stabilization (both banks for Cottonwood Creek only) is approximately 210 pounds of phosphorus per mile for 2.19 miles, per year or around 460 lbs.

2. Flood Plain Area. Existing 2-year floodplain width is 5.3 acres, which will increase to over 80 acres. This will increase the riparian corridor area from 4.4- to 24.9 acres and provide for greater infiltration and filtration by vegetation. Estimates were made of long term phosphorus removal by inundating the floodplain for various flood frequencies, based on dynamic, particle-settling theory. These estimates resulted in a long-term average 1.0 lbs/P per acre/year of floodplain, or around 70 pounds per year.

3. Riparian Wetlands. The existing channel has less than 0.5 acres of riparian wetlands, which are primarily associated with limited channel bottom. The project will widen the channel and increase the frequency of riparian flooding. These improvements are expected to increase riparian wetland areas by 20-acres and immobilize from 200-lbs annually (i.e.: about 10-lbs/ac/yr).

4. Annual Phosphorus Reduction Total of all components is 460 + 70 + 200 = 730 pounds P.

Cottonwood Creek Reclamation Phase 1 was completed in early August 2004 with the first flood occurring on August 18, 2004. Based on water-marks at Peoria Street, the peak flow entering the newly constructed channel was estimated to be 1400 cfs, which compares to the projected 100-year event of 4,000cfs. The photo below shows the restored creek during the flood event. The success of the project is attributed to the "low-energy" design. This approach flattens the channel slope decreasing velocity (kinetic energy) and allows the flood to spread over larger areas, increasing flow area and decreasing velocity.

Additional Information Information about the Cherry Creek Basin Water Quality Authority can be obtained from our recently created website at www.cherrycreekbasin.org

CotnwdCreekFlyer-v2.doc, 9/16/2005 Cherry Creek Reservoir Destratification System

The Cherry Creek Basin Water Quality Authority (Authority) has been implementing watershed- based, best management practices (BMP) and constructing pollution reduction facilities (PRF) for many years to protect the beneficial uses of Cherry Creek Reservoir. However, the chlorophyll a standard (15-g/l) was not being met from 1996 through 2005, but was met in 2006 and 2007. In addition, there is a trend in water quality improvement since 2002 (see Figure 17 below from the annual monitoring report). Note that the horizontal dashed line represents average value and not the standard). In addition, the phosphorus goal (40-g/l) has only been met once in 1989 and has been on an upward trend for a number of years (see Figure 15 below).

The 2004 special study1 of in-lake nutrient enrichment indicated that nitrogen is the limiting nutrient for algae growth. Dr. Lewis also noted that “reduction in phosphorus concentrations sufficient to induce phosphorus deficiency in the phytoplankton of year 2003 would involve decreases in upper water column concentrations of at least 50%, or about 30 g/L”. What this means is that controlling algal growth by reducing nutrients in the Cherry Creek watershed alone is very difficult and that algae must also be controlled “…based on non-nutrient factors”, according to Dr. Lewis

Even though the Authority and others have implemented watershed controls with some success, watershed controls alone are not sufficient nor are the phosphorus reductions timely enough to control algae growth in the near future. Therefore, the need for supplemental strategies to control algae growth, such as in-lake management, became more apparent.

Dr. Lewis found that during periods when the reservoir was not being naturally mixed by wind activity, then algal growth activity was at its highest. He determined that the most practical approach

1 Lewis, Willam M. Saunders, James F III, and McCutchan, James H. Jr. January 22, 2004. Studies of Phytoplankton Response to Nutrient Enrichment in Cherry Creek Reservoir, Colorado.

ProjectSummaryMemo Final.doc 1 June 10, 2008

to controlling this growth would be to artificially mix the reservoir. Since the reservoir is relatively shallow, it can usually be mixed by normal wind activity. Several times throughout the year, however, extended periods of hot, dry and windless weather cause the lake to stop mixing and to stratify. This stratification not only causes anoxic (lack of oxygen) conditions at the bottom of the reservoir, but also allows blue-green algae to bask in the sunlight on the surface of the reservoir, fixing all the nitrogen they need from the air. And, with plenty of phosphorus in the water, they can reproduce explosively. Thus, an algae bloom is created.

As a result, the Authority considered in-lake management techniques that could be beneficial to reducing chlorophyll a, as well as nutrients and dissolved oxygen (DO) concentrations in the near term. Dr. Lewis suggested destratification (mixing) as a method to address internal loading and other factors that increase algal growth and therefore, chlorophyll a and phosphorus and nitrogen concentrations. It was noted that watershed management is a necessary component of the Watershed Plan 20032 and both BMPs and PRFs should continue to be implemented. The continuation of these programs was also a condition for the approval of the Department of Natural Resources for the installation of the aeration system.

INVESTIGATION PHASE

The Authority then had prepared a conceptual investigation3 to identify other lake mixing projects, the pros and cons of aeration for mixing, and the order of magnitude of cost. The investigation concluded that aeration is used in local lakes (e.g., Bear Creek Lake, McClellan Reservoir, Coors lakes and Quincy Reservoir) with varying degrees of success and complexity of the systems, with the simplest systems performing with greater reliability than more complex systems. The projected capital, design, and administration costs were around $700,000.

TECHNICAL FEASIBILITY

The Authority then authorized by contract with AMEC Earth and Environmental (AMEC) dated August 3, 2005 a more detailed investigation4 to further identify technical feasibility and costs. After

2 Cherry Creek Basin Water Quality Authority 2003. Cherry Creek Reservoir Watershed Plan 2003. 3 Brown and Caldwell, May 4, 2004. Conceptual Investigation of Reservoir Destratification for Cherry Creek Reservoir 4 AMEC Earth and Environmental May 5, 2005. Feasibility Report for Cherry Creek Reservoir Destratification.

2 June 10, 2008 a eight month investigation and evaluation that included representatives of Cherry Creek State Park, the Army Corps of Engineers, the Colorado Division of Wildlife and representatives of the fishing and boating community, the AMEC team recommended the installation of a submerged mixing system in the 330 acre portion of the reservoir which is greater than 16 feet deep. The primary objectives for the mixing system were to:

. Destratify and strongly mix the deepest portions of the reservoir, . Vertically mix algae to compromise their habitat and reduce production of blue-green algae, and . Oxidize of the deep bottom sediments to reduce the release of nutrients from the sediments into the water column.

The estimated capital costs were projected to be up to $700,000.

FINAL DESIGN AND CONSTRUCTION

The Authority then authorized final design and construction of the AMEC recommended focused mixing system by contract amendment approved by the Board on February 16, 2006. The final design was completed in September 2006 and estimated the construction costs were $810,400. The project was awarded in separate contracts to supply the compressor and aeration line, underwater installation, above water installation and other miscellaneous items, which is summarized in the table below.

Item Cost Summary of Destratification Project Investigation, Design & Administration Capital Costs Technical Feasibility Report $70,000 Final Design and Construction $93,000 To supply the air to the diffusers, a Management distribution line was placed partially Administration $9,000 across the face of the dam and covered Sub-Total Investigation, Design, Admin $172,000 with a berm large enough for maintenance Construction access. The berm was enlarged during Compressor Purchase $58,500 construction to become a portion of a Hydraulic Hose and Fittings $243,100 formal trail across the entire face of the Underwater Construction $142,500 dam at the request of Colorado Division Above Water construction $478,600 of Parks. The extra cost of $150,000 to Power Installation $12,000 enlarge the berm was reimbursed to the Aerator System Inspection and Adjustment $11,400 Authority by the Department of Natural Sub-total $946,100 Resources. Less enlarged trail costs in the amount5 $150,000 Net Construction $796,100 The destratification system was substantially completed by December 14, TOTAL CAPITAL COSTS $968,100 2007 and the official start up of the system took place on April 4, 2008. Subsequent to the official start up modifications were made to the compressor building, consisting of duct work to improve the heat ventilation and compressor cooling, installing the extra aerator assemblies, and additional inspection and adjustment of existing aerator assemblies. This work, which is part of the annual operations and maintenance budget, was approximately $15,000.

3 June 10, 2008

HOW DOES THE SYSTEM WORK?

The destratification system works by pumping air into the bottom of the Reservoir at a rate of 200 to 250 standard cubic feet per minute (SCFM) at a pressure of 51 pounds per square inch gage (psig). The 125 Hp compressor used to deliver this air is housed in a 19 by 17 foot block building with a metal roof near the Marina and has a rated maximum capacity of 455 SCFM. The reserve capacity of the compressor is available for enlargement of the in-lake portion of the system in the future if that proves to be desirable. The air passes through over 40,000 feet of 1-1/4 inch hydraulic hose leading to 102 air diffusers placed at the bottom of the deepest part of the reservoir, which is greater than 16-feet and covers 350-acres of the 850-acre total surface area. These diffusers are expected to move about 1,000,000 gallons of water per minute (approximately 4,400 acre feet per day) which will “turn-over” the mixing zone about once per day.

HOW WILL IT BE DETERMINED IF THE SYSTEM WORKS?

The aeration and mixing system was designed to meet the following program objectives:

1) Reduce the release of phosphorus and nitrogen nutrients from the bottom sediments into the water column of the reservoir in a typical year by 810 lbs/yr and 1,140 lbs/yr, respectively, 2) Decrease the seasonal mean (July-September) chlorophyll a concentrations by approximately 8 ug/L under typical year conditions, 3) Decrease annual peak chlorophyll a concentrations by up to 30 ug/l, 4) Increase dissolved oxygen concentrations in the deepest and most vulnerable zones of the reservoir into the range of 5 mg/L, and 5) Reduce the production of blue-green algae by making the habitat of the reservoir less suitable for the production of blue-green algae via vertical mixing.

The ultimate test of whether destratification and mixing works will be the reduction of algae biomass and density as measured by chlorophyll a and species identification and enumeration, particularly the blue-green species cyanobacteria. The more immediate test will be to determine if the reservoir stays mixed throughout the algae growing season from May through October, as measured by the vertical temperature and dissolved oxygen profile of the water column.

During the regular growing season, the authority contracts with GEI\Chadwick Division to conduct bi- monthly sampling in the reservoir at three locations. During each sampling episode on the reservoir, three main tasks were conducted, including: 1) determining water clarity; 2) collecting depth profile measurements for temperature, dissolved oxygen, and pH conductivity; and 3) collecting water samples for chemical and biological analyses. In anticipation of construction of the destratification system, the Authority had GEI install three temperature arrays consisting of Onset HOBO® Water Temp Pro data loggers in the deepest part of the reservoir. These data loggers recorded temperature measurements on 15-minute intervals for each 1 meter water layer. This monitoring program was continued in 2008 to determine how well the reservoir stays mixed and may be extended beyond 2008.

In addition to the temperature loggers at the three monitoring sites, GEI will also perform monthly Oxidation Reduction Potential (ORP) profiles along a transect through the deep water zone, including measurements near the water/sediment surface during the July to September period. The sample locations and transect will be consistent with locations previously established by AMEC during their destratification feasibility study.

4 Cherry Creek Stream Reclamation at PJCOS

BACKGROUND

In 2008, reclamation of Cherry Creek from the Bronco’s Parkway trailhead to the pedestrian bridge (see Figure 1) was in preliminary design by J3 Engineering under contract with the Parker Jordan Metro District (PJMD). Project partners included SEMSWA, City of Centennial, and Arapahoe County Open Space. The Authority inspected the Project area and found the channel to be in a severe state of degradation (see Photo 1, next page). Observations included: extensive bed erosion (i.e.: “down cutting”); bank erosion resulting in steep slopes and material sloughing; lateral channel migration; damage from vehicle crossing the stream at several locations; and loss of wetlands and upland vegetation due to lowering of the water table by the bed erosion. The Project was added to the Authority’s capital improvement program (CIP) in 2008 and the Authority began monitoring the design in late 2009 through 2010. The Authority assessed the water quality benefits of the project and determined the Project meets Authority goals for stream reclamation. On March 8, 2010, the PJMD requested Figure 1 - Location Map funding assistance from the Authority which led to a reimbursement agreement with the PJMD dated June 17, 2010 to provide $56,000 for design purposes.

ProjectSummaryMemo-PJCOS 1 March 19, 2013

On February 8, 2011, the PJMD requested construction funding assistance from the Authority, which was formalized in a participation agreement with PJMD dated June 16, 2011 in the amount not to exceed $586,8711. Construction began in September 2011 and was substantially complete by July 2012. DESIGN APPROACH

Because of the severity of the channel degradation, areas of extreme topographical constraints, and floodplain regulations limiting increases in flood elevations, the approach to the Project reach resulted in a more formal approach to reclamation of Cherry Creek. For instance, essentially all of the existing channel bank and riparian vegetation had to be removed and replanted due to substantive changes in channel geometry necessary to accommodate topographic and floodplain limitations. The preferred design approach for reclamation is to retain and protect as much of the existing vegetation as possible, minimizing disturbances and improving the chances of re-vegetation success. Drop structures necessary to flatten and control longitudinal grade are grouted boulder drop types Photo 1 - Pre-Project with sheet pile cut-off walls to protect the structure from damages during larger flood events. The preferred approach for reclamation conveys the mean flood event in a narrower channel that uses riffle- pool structures constructed entirely from rock and to allow rarer floods to spread out into a large floodplain, which lowers velocities, allowing more filtration and infiltration. Because each project is unique, more formal drop structures (i.e.: grouted boulder and sculpted concrete) are often used in reclamation projects where additional channel “anchoring” is deemed necessary by site constraints and greater risks of damages from the more rare flood events. The Project was designed to raise the channel bed and reestablish the water table to prevent further down cutting, erosion, and subsequent sediment transport on Cherry Creek2. The goal of the channel improvement portion of the project was to restore and enhance the aquatic, wetland, and riparian Photo 2 - Post project drop structure functions and values of Cherry Creek, and to construct a wider and flatter floodplain by reshaping and raising the channel invert an average of 5 feet throughout the project area. This was accomplished by reshaping the main channel of Cherry Creek; constructing a secondary channel; laying back the upper channel banks; and installing five grouted-

1 The Authority’s financial contribution to the Project was limited to components of the Project that provided water quality benefits. The total project cost that provided water quality benefits was found to be $3,017,253. 2 U.S. Army Corps of Engineers, September 14, 2011. Department of the Army Permit No. NOW-2009-02909 Parker Jordan Open Space Cherry Creek Restoration Project.

2 March 19, 2013 boulder drop structures, one vertical sheet pile drop structure with an integrated low-water pedestrian crossing, and seven types of bank protection. The proposed drop structures and bank protection measures include varying types of bioengineered and hard treatments. In addition to the improvements along the main channel, an overflow channel was constructed along the inside of a bend of Cherry Creek to reduce the stream pressure along the banks of the main channel during frequent flooding events (e.g., 2-year events) and reconnect the water table with portions of the floodplain. The overflow channel is about 1,200 feet long and constructed along the remnants of a historical channel on the east side of Cherry Creek. A sloping grouted-boulder drop structure was constructed at the downstream end of the overflow channel to transition the elevation to match the elevation of the main channel. Photo 3 - Post project with side channel Seven different types of bioengineered bank protection were installed along the realigned/reshaped Cherry Creek channel throughout the project area. The protection types were designed to meet site- specific needs through the project reach. The protection types are unique for straight sections, inside and outside bends, bend-way weirs, and for the secondary channel. CONSTRUCTION ISSUE

During construction, localized dewatering (i.e.: groundwater pumping) was necessary in order to construct drop structures in dry conditions, which is a common practice in stream reclamation projects. The State Engineer’s Office (SEO) rules for water well construction3 includes construction dewatering wells and requires that a notice of intent (NOI) be filed with the SEO prior to dewatering activities, which the contractor had failed to do. The construction site was inspected by the SEO and it was determined that the dewatering practices resulted in consumptive use (i.e.: water loss through evaporation and transpiration or resulted in a time-lag before returning to the source). The contractor was required to file an NOI, modify the dewatering practices to prevent consumptive use, prepare and file a temporary substitute water supply plan (SWSP) and augment for the consumptive use. The contractor also modified the construction BMPs to minimize water losses during conveyance and treatment activities to reduce sediment in the water, such as using pipes for transport, covered tanks for sediment removal from construction water, and eliminating land-application of construction water. Whereas not all stream reclamation projects will result in consumptive use of ground or surface water, there is a greater likelihood that augmentation water will be needed for future stream reclamation projects. The Authority is currently investigating if the “Bowtie4” property water rights can be used to augment consumptive uses from construction activities, which also includes evaporative losses from practices that

3 Office of the State Engineer January 1, 2005. Rules and Regulations for Water Well Construction, Pump Installation, Cistern Installation, and Monitoring and Observation Hole/Well Construction. 4 The Bowtie property is located at the confluence of Cherry Creek and Piney Creek and is named after the shape of the property that was acquired by local governments as a stream corridor preservation activity. The Authority participated in the acquisition and received the water rights associated with a shallow and a deep, pre-senate bill 319 well.

3 March 19, 2013 reduce sediment discharges caused by construction activities. The investigation may also include using the water rights for temporary, supplemental watering of new vegetation. JUNE 6, 2012 FLOOD EVENT

Prior to the June 6, 2012 flood event, the majority of the construction effort had been completed but final inspection had yet to occur and final acceptance had not been granted. The improvements included low water crossing, drop structures, bendway weirs, bank stabilization measures, secondary channel construction and stabilization, erosion control protection, vegetation installation, and the majority of final stabilization of the disturbed construction area. Due to the size and magnitude of the Project, it was built in multiple phases. As a result, the project had a varying range of Photo 4 Post project flood June 6, 2012 stabilization and vegetation establishment at the time of the flood. Phase 1 had the most advanced stage of re-vegetation in the low flow terrace due to its completion occurring at the beginning of March. Phase 3 vegetation was installed only 2-3 weeks prior to the event; therefore, seedling germination and establishment was minimal. The impact of the flood event on the Project was analyzed5, concluding that: … stream reclamation project of Cherry Creek within PJCOS experienced an estimated 2-year storm event6 on the evening of June 6th through the morning of June 7th. This storm occurred at a time when the project was vulnerable since vegetation was not fully established or in some cases minimal growth of vegetation occurred and portions of the project were not completed (i.e. erosion control blanket staked, vegetation installed). Although this storm even caused damages to the project, the integrity of the channel improvements functioned as intended in the design. Minor damages occurred to isolated areas of the structural components (drop structures, bendway weirs, grouted boulder edge walls). Minor to moderate damage occurred in vegetated areas and the general observation was that areas planted from February to mid-April functioned much better than portions more recently seeded and blanketed. Most stream reclamation projects are designed to minimize, not eliminate, flood damages during events up to and including the 1% chance (i.e.: 100-year event) and therefore some damages are expected. The projects are most vulnerable, however, during the period before adequate vegetation becomes established to protect the channel from erosion. The design includes measures, such as biologs, riprap, and blanket, to temporarily protect the more critical sections of the channel, such as the toe of slope and the main channel bank.

5 J3 Engineering Consultants and The Restoration Group, Inc. June 20, 2012. Documentation of the June 6th and 7th Flood Event on Cherry Creek through the Cherry Creek Low Water Crossing South of Arapahoe Road. 6 The estimated flood peak discharge was 1,700-cfs at the Project.

4 March 19, 2013

The PJCOS project was tested by a flood event at its most critical time and yet received relatively minimal damages, which the Authority believes is evidence that the approach to stream reclamation is technically sound. WATER QUALITY BENEFITS

An assessment of the water quality benefits for the entire Project was made by the Authority7. The Project was found to lower stream velocities, channel shear, and stream power from values prior to reclamation, all of which minimize the transport of sediment and associated pollutants. It was also determined that the channel was in an extremely unstable state that resulted in erosion rates that were over 140-times rates that were considered “typical” for Cherry Creek.

Stream stabilization benefits and evaluation procedures have been documented in the Authority’s Stream Reclamation Interim Report8. Benefits include reductions in sediment and other pollutant loads and concentrations, including phosphorus and nitrogen. These benefits are supported by Authority data, literature research, and quantitative analysis.

7 William P. Ruzzo, PE, LLC December 27, 2010. Cherry Creek Stream Reclamation at PJCOS Modified Design 8 CCBWQA Technical Advisory Committee, June 16, 2011. Stream Reclamation, Water Quality Benefit Evaluation – Interim Report.

5 Cherry Creek Stream Reclamation at Eco-Park

BACKGROUND AND PURPOSE: In October 2009, UDFCD and SEMSWA entered into an Intergovernmental Agreement (IGA) for design of Cherry Creek stream reclamation improvements at Eco Park. In April 2010, upon SEMSWA's request, the Authority entered into an IGA with SEMSWA to participate in funding the project following the Authority's inspection and analysis of the Project area and hydrologic data. The project area is approximately 4,850 linear feet long and connects to the downstream end of the Parker Jordan Centennial Open Space stream reclamation project. The Project site is shown on Figure 1 - Area Map.

The Authority's inspection of the Project area found the channel to be in a severe state of degradation (i.e., "down cutting"); bank erosion resulting in steep slopes and material sloughing; lateral channel migration and loss of wetlands and upland vegetation due to lowering of the water table by the streambed erosion.

The Authority assessed the water quality benefits of the project and determined the Project meets the Authority's goal for stream reclamation. The Project was added to the Authority's Capital Improvement Plan in 2010 and the Authority began monitoring the project design performed by Muller Engineering through 2010 and 2011. On April 15, 2010 the Authority entered into an IGA with SEMSWA for design finds in the amount of $56,000. On May 19, 2011 the Authority approved contributing $905,000 of the total Project cost and entered into an agreement with SEMSWA, dated effective on December 31, 2011. Figure 1 - Area Map

EXISTING CONDITIONS: Urbanization and the resulting increase in the rate, frequency, duration and magnitude of stormwater runoff accelerated degradation of the streambed and banks. Typical pre-project conditions are shown on Photos 1, 2 and 3 documenting that Cherry Creek has degraded up to 10-feet within the streambed.

Photo 1 - Existing Condition Photo 2 - Existing Condition Photo 3 - Existing Condition DESIGN APPROACH: Because of the severity of the channel degradation, areas of topographical constraints and floodplain regulations limiting increases in flood elevations, the approach to reclamation of this reach is a combination of a natural bioengineering approach connecting the streambed to the overbanks and a more engineered approach where topography constrains the channel. In some locations essentially all of the existing channel bank and riparian vegetation had to be removed and replanted due to the substantive changes in channel geometry necessary to accommodate topographic and floodplain limitations. In several areas the preferred design approach for stream reclamation was used whereby much of the existing vegetation was retained and protected, minimizing disturbances and improving the chances of revegetation success.

Hand sculpted concrete drop structures, as shown on Photo 4, are incorporated into the project to flatten and control the longitudinal grade, with sheet pile cut-off walls to protect the structure from damages during the larger flood events. Riffle-pool structures, constructed entirely of rock, were constructed in the channel to aide in conveyance of the mean flood event in the narrower channel. Larger floods in these areas then spread over the broader floodplain, This design approach lowers the runoff velocities allowing for more filtration and infiltration.

The Project was designed to raise the streambed and reestablish the water table to prevent further loss of vegetation and down cutting, erosion and sediment transport. The overall project goal was to restore and enhance the aquatic, wetland and riparian functions of Cherry Creek.

CONSTRUCTED PROJECT: Two bids were advertised for this project. The first was for construction of four sculpted concrete drop

structures and the second was for the stream Photo 4 - Sculpted Concrete Drop reclamation work. Bids for the project were opened on August 15, 2012. The successful bidders, ECI Site Construction (stream reclamation) and Naranjo Civil Constructors (sculpted concrete drops), were awarded contracts in the combined amount of $3,607,351.60. Two notices to proceed were issued for September 24, 2012. The work was substantially complete on September 9, 2013. The final project cost totaled $3,780,899.37.

The Project included secondary channels in two locations, three sculpted concrete drops, one sculpted concrete splitter drop, one lateral weir drop, and six riffle drops. The sculpted concrete splitter drop, located closest to the the Eco Park trail access bridge over Cherry Creek provides for an interactive creek crossing, see Photo 5.

The lateral drop weir and the sculpted concrete splitter drop each divert stream flows into a secondary channel section as the water level in Cherry Creek rises to the diversion invert elevation. This design feature allows for the stream flow to widen out into two channels and further reduce velocities. The secondary channels are beneficial for reconnection of the water table with portions of the floodplain. Six different types of bioengineered bank protection details were installed along the realigned/reshaped channel through the project. The bank protection types were unique for

Photo 5 - Sculpted Drop Creek Crossing

straight sections, inside bends, outside bends and for the secondary channel. As part of the revegetation efforts the project included installation of:

 28 acres of seeding.  10,315 grass plugs.  11,281 willow stakes.  217 trees.  824 shrubs.

A flow monitoring and sampling station was installed near the lower end of the project to provide a data collection point for the Authority as shown on Photo 6. This data collection point is one of a series used by the Authority along Cherry Creek to monitor nutrient loading and stream flows within the Cherry Creek Basin.

Photo 6 - New Monitoring/Sampling Station

September 14, 2013 Storm Event: On Sunday September 14, 2013 the upper reaches of Cherry Creek received heavy rainfall that at its peak was measured at approximately 1,000 cfs.

An on-site inspection followed that found that all major structures designed and installed to control the minor and significant storm runoff events each functioned as expected. None were damaged or adversely impacted. The upper banks where the revegetation work had not re-established itself yet, received the majority of the damage. Seeded areas had eroded, upper bank material was displaced and low areas filled in. Crusher fine trails were washed out in specific locations where runoff was concentrated. The project team quickly assessed the damage and the project consultant prepared an overall restoration plan. Restoration work began promptly to repair areas impacted by the flooding. It was anticipated that the flood damages would have been minimal if the project vegetation had a season or two to establish itself. This is confirmed following a brief site visit to the Parker Jordan Centennial Open Space project immediately upstream of Eco Park. It is strong testimony that bioengineering design works for stream reclamation after the vegetation is established.

Photos 8, 9, 10 and 11 show some of the typical damage from the storm.

Photo 8 - Flooding Damage Photo 9 - Flooding at a Trail Crossing

Photo 10 - Flooding Damage Photo 11 - Flooding Damage

WATER QUALITY BENEFITS: An assessment of the water quality benefits for the entire project was made by the Authority1 as part of the ongoing water quality analysis of all projects listed on the 5-year capital improvement program. Based on the outcome of this assessment it is calculated that 117 lbs of phosphorus per year will be eliminated from being transported downstream from the Eco Park stream reclamation improvements. The project was found to lower stream velocities, channel shear and stream power from that found prior to reclamation, all which minimizes the transport of sediment and pollutants.

1 Water Quality Benefits of Shoreline Stabilization Memorandum, dated October 23, 2008; William P. Ruzzo, P.E., LLC McMurdo Gulch Stream Reclamation

Presented in this memorandum is a summary of the McMurdo Gulch Stream Reclamation, which was jointly funded by the Town of Castle Rock and the Authority. Project design occurred during 2009 and 2010 and construction was completed in 2011 at a cost of ~ $1,178,000 for the 2.84-mile reach.

BACKGROUND AND PURPOSE

A reclamation plan for McMurdo Gulch, a major tributary to Cherry Creek in the upper watershed, was developed in 2009 and 2010 and implemented in 2011 under the sponsorship of the Town of Castle Rock and the Authority. Although relatively undeveloped at the time of the study, there are significant plans for further build-out in the McMurdo Gulch watershed, making the timing of the reclamation plan advantageous to implement a proactive approach to protect the gulch and reduce sediment and nutrient loads into Cherry Creek in advance of increased stormwater runoff and degradation. It is believed that implementing measures to protect the gulch before the onset of severe erosion will be more cost effective and more favorable to downstream water quality than reacting after increased runoff has a chance to degrade the gulch.

ProjectSummaryMemo-McMurdo Final 1 November 16, 2011

INVESTIGATION PHASE

McMurdo Gulch is a western tributary to Cherry Creek that has a watershed area of 6.5 square miles. The entire McMurdo Gulch channel is approximately 6.7 miles long from the headwaters to the confluence with Cherry Creek. The McMurdo Gulch Reclamation Project study reach accounts for roughly 2.84 miles of channel length and is centrally located in the basin. Over the 2.84 mile project reach, the characteristics of McMurdo Gulch vary significantly. The project reach has three distinct channel reaches: upstream, middle, and downstream. The average gradient through the three reaches varies between 1.3 and 2.0%.

In all three reaches there is evidence of active erosion (see Picture 12 below). The impacts of this erosion were most evident in the lower reaches. Part of this is due to the change in soil characteristics and vegetative cover, which are comprised mainly of sand and cobbles that are more susceptible to erosive forces. Also, in many areas along the channel, erosion has been caused by off- road vehicles crossing and running down the center of the channel.

In addition to the proactive channel reclamation aspect of the work, Castle Rock and the Authority also included watershed requirements for existing and new development (MEC 2011- b). For the existing developments, the detention ponds are to be modified to include Excess Urban Runoff Volume (EURV), which is believed to provide greater water quality benefits than minimum requirements of Control Regulation No. 72 (i.e.: extended detention basin). For future development, the minimum requirement would include EURV for detention facilities. Figure 2 above illustrates the anticipated increase in watershed imperviousness as development occurs in McMurdo Gulch (MEC 2011c).

DESIGN APPROACH

Although the channel erosion discovered during field visits to McMurdo Gulch was considered minor, the project sponsors decided on a proactive approach in reclaiming the degrading areas prior to severe erosion taking place (MEC 2011a). As more development occurs in the upstream portions of the basin, flow rates will increase, which will likely increase erosion within the channel.

ProjectSummaryMemo-McMurdo Final 2 November 16, 2011

A reclamation plan was developed consisting of stabilizing eroded sections of the channel with a combination of boulder cascade drop structures, rock lining, bioengineered bank protection, and riparian vegetation. The proposed improvements are segmented in nine improvement reaches within the 2.84 mile project reach: Reach A through Reach I. The improvement reaches cover a total of approximately 4,000 lineal feet and they are separated by reaches with no improvements since they are currently not eroding.

A unique approach to grade control structures, called boulder cascades, were designed to mimic a natural boulder channel characteristic of streams observed in the Rocky Mountains. The structures are comprised of a combination of loose boulders and void-filled riprap. The boulder cascades range from 1 to 4 feet in drop height and the bottom width varies from 10-feet to 35- feet. The structures contain a 6% longitudinal slope down the face of the structures and extend 2.5-feet up each channel bank at a 4:1 side slope. The side slopes are buried with topsoil and covered with erosion control blanket.

The drop dimensions are not intended to provide a specific capacity, but instead are intended to work with the geometry of the existing channel and surrounding areas. In areas where a series of boulder cascades are to be constructed in close proximity to one another, a stable longitudinal slope of 0.6% was used between structures. The photo (MEC 2011) at the left shows a completed structure with wetland vegetation growing before the project was completed.

WATERSHED PLAN

A watershed plan was evaluated to control peak discharges from developed areas to levels similar to or less than pre-development conditions over the whole spectrum of storm events -- from frequent small events to large flood-producing storms (MEC 2011b). At the least, it is anticipated that implementing full-spectrum detention in the watershed (and retrofitting existing detention facilities) to control runoff will reduce the level of improvements required for stream reclamation and will slow the pace of degradation such that funding resources can more easily keep up with the required improvements. At best, it may be found that watershed-wide full-spectrum detention may eliminate the need for capital improvements in some stream reaches.

The initial flow-control plan was focused on the Castle Oaks Subdivision, since in the near term this community contains the largest concentration of impervious area that will drain into the critical reaches of McMurdo Gulch. Eight existing Castle Oaks detention facilities, shown in Figure 4 on the following page, were evaluated for potential retrofitting. Five of these facilities were designed with outlet structures that control the 10 year and 100 year flow rates, one facility was designed to capture and slowly release only the water quality capture volume (WQCV), and two facilities were designed to control the WQCV and the 10 year and 100 year events.

ProjectSummaryMemo-McMurdo Final 3 November 16, 2011

In addition to these recommended retrofit improvements, it is essential that future detention ponds implemented as part of new development be designed as full-spectrum detention facilities and modeled to ensure that runoff levels remain close to pre-developed. Initial coordination between the Town of Castle Rock, Douglas County, and Authority took place during the design process to define a common requirement of implementing full-spectrum detention for all future development within the basin. The findings and recommendations of the detention retrofit investigation are found in MEC 2011b.

FUNDING

In December 2009, the Town of Castle Rock and the CCBWQA entered into a memorandum of understanding (MOU) to jointly participate in the McMurdo Gulch stream reclamation project. This project was originally identified in the Authority’s capital improvement projects list for 2009. In 2010 Muller Engineering Company was retained by Castle Rock to develop a design for McMurdo Gulch. Throughout this design process the design team, made up of representatives of the Town of Castle Rock and the Authority, maximized the total reach length designed to allow for flexibility in construction.

In the fall of 2010 a request for proposals was sent to four construction contractors that are experienced in this type of work. The low bidder was 53 Corporation with a low bid of $1,099,818. This bid was significantly lower than the engineer’s estimate of $1,531,549. A summary of project funding is shown on the following table:

SUMMARY OF PROJECT COSTS

EXPENDITURES AMOUNT MONITORING Engineering Services $ 291,800 Beginning in 2012, the Authority will Construction $ 1,178,200 take grab samples from surface flows on Total Costs $ 1,470,000 a monthly basis and analyzed for FUNDING CONTRIBUTIONS physicochemical parameters, such as Town of Castle Rock $ 840,000 nutrients and suspended solids, and Cherry Creek Basin Water Quality Authority$ 630,000 identified as either base flow or storm flow samples. Samples will be obtained at the upstream and downstream end of the McMurdo

ProjectSummaryMemo-McMurdo Final 4 November 16, 2011

Gulch project. The sampling is intended to identify if the proactive, surgical approach to stream reclamation will control sediment and nutrients to pre-development levels in the watershed.

WATER QUALITY BENEFITS

Stream reclamation is beneficial to Summary of Water Quality Benefits water quality in the stream and in the Reservoir (CCBWQA 2011). Stream McMurdo Item reclamation reduces sediment and other Gulch

pollutant loads and concentrations, Project Length (mi) = 2.84 including phosphorus and nitrogen. Project Capital Costs = $ 1,470,000 Load and concentration reductions Project Cost per mile =$ 517,600 during base and storm flow conditions Stream Reclamation Water Quality Benefits (lbs/mi/yr) = 90 Project Annual Water Quality Benefits (lbs/yr) = 255.6 can occur by reducing flow velocities, Capital Recovery Factor (4% 35-years) = 0.053577 providing greater areas for filtration Annualized Capital Cost =$ 78,800 and infiltration of stormwater and, to Annual O&M Cost =$ 28,400 some extent, through increases in Project Annual Unit Cost ($/lb) =$ 419 Baseline Project Life (yr) = 35 dissolved oxygen. This finding is also Project Life Time Costs =$ 2,464,000 supported by literature search of other Project Life Time Water Quality Benefits (lb) = 8946 strategies used by watershed Project Life Time Unit Costs ($/lb) =$ 275 organizations to improve runoff water Notes: 1. Project length includes stabilized reaches and reaches quality and several years of Authority without improvements water quality data collected to evaluate 2. Analysis based on "simplified method". See Stream PRFs, particularly Cottonwood Creek. Reclamation Report. 3. Values in "blue" are input variables. 4. Costs include design, construction, and construction services. For each pollutant reduction facility (PRF) that the Authority considers for funding and as a minimum, simplified calculations of water quality benefits, as measured by cost per pound of phosphorus immobilized, are prepared. The calculations for McMurdo Gulch are provided in the table above.

Project costs for McMurdo Gulch are Comparison of Project Unit Costs also compared to two other Authority Cottonwood McMurdo EcoPark Item sponsored project, Cottonwood Creek Creek Gulch Project and Eco Park project (see table on the Project Length (ft) 13900 15000 7300 left). Cottonwood Creek project lies Total Projected Cost1 $ 2,405,300 $ 1,470,000 $ 3,829,950 Project Cost per mile $ 913,700 $ 517,400 $ 2,770,200 entirely within Cherry Creek State Park Annual Project Cost2 $ 128,900 $ 78,800 $ 205,200 and was completed in 2008 solely with Annual P Reduction Benefit (lbs/year) 237 256 124 Annual Cost per Pound of P $ 540 $ 310 $ 1,650 Authority funds. Cherry Creek Stream Authority Contribution $ 2,405,300 $ 630,000 $ 905,000 Reclamation at Eco Park is scheduled to Authority funding amount (%) 100.0% 42.9% 23.6% Authority annual cost per pound P $ 544 $ 132 $ 390 begin construction in 2012 and is a joint effort between the Authority, Notes: 1. Stream Reclamation Costs only, no education or recreation costs. SEMSWA, Urban Drainage & Flood 2. Based on 4% for 35-years and not including maintenance Control District, and Arapahoe County. The table illustrates that the proactive approach to stream reclamation cost per mile is substantially less than Cottonwood Creek or Eco Park projects and, potentially costs less per pound of phosphorus immobilized.

ProjectSummaryMemo-McMurdo Final 5 November 16, 2011

REFERENCES

1. CCBWQA Technical Advisory Committee June 16, 2011. Stream Reclamation Water Quality Benefit Evaluation – Interim Status Report.

2. Muller Engineering Company August 30, 2011a. McMurdo Gulch Reclamation Project Stream Reclamation Improvements Design.

3. Muller Engineering Company September 2, 2011b. McMurdo Gulch Reclamation Project Detention Facility Retrofit Improvements Design

4. Muller Engineering Company September 6, 2011c. McMurdo Gulch Reclamation Template

5. PBS&J December 2006. Final McMurdo Gulch Major Drainageway Master Plan.

ProjectSummaryMemo-McMurdo Final 6 Cottonwood Creek Stream Reclamation at Easter Avenue

Presented in this memorandum is a summary of the Cottonwood Creek Stream Reclamation between Easter Avenue and Briarwood Avenue (Cottonwood @ Easter Avenue, Project, see Figure 1 Location Map).

BACKGROUND AND PURPOSE

The Cottonwood @ East Avenue project is part of a watershed master plan1 prepared under the guidance of the Urban Drainage & Flood Control District for SEMSWA and Douglas County. The Project is approximately 0.42-miles long following the creek thalweg and the drainage area is 5.47-square miles at Briarwood Avenue. SEMSWA began design for the reclamation of the Project reach in 2006 at which time detailed topographic information was obtained. Construction of the project was delayed until 2010 during which time additional erosion in the reach has occurred. Project Reach The Cottonwood\Easter Project was reviewed by the TAC in May 2007 at the request of the U.S. Army Corp of Engineers because of a 404 permit application by SEMSWA. Because SEMSWA’s design approach to stream stabilization was consistent with the Authority’s water quality goals and objectives, the Cottonwood Project was included in the Authority’s 2008 Master PRF list by the TAC.

The Master PRF List shows the 2600 foot long Figure 1 – Location Map project to contribute 50-lbs/year of phosphorus to Cherry Creek Reservoir based on typical erosion rates of silty clayey channels. Capital costs were

1 Muller Engineering Company August 2010. Cottonwood Creek (Downstream of Lincoln Avenue) Outfall Systems Plan Conceptual Design Report.

[email protected] 1 January 8, 2014

estimated to be $1,350,000 with an annualized cost of $105,000 including maintenance. Assuming 90% efficiency, the Cottonwood @ Easter Avenue Project would immobilize 45-lbs per year of phosphorus at an annual cost of $2,332 per pound. There are over 30 projects on the Master CIP list with annual cost per pound estimates ranging from as little as $300 to over $3,000, a tenfold variation. The average value is approximately $1,200 and the median value is approximately $400.

PROJECT PARTNERS AND FUNDING

The Authority partnered with SEMSWA through a Memorandum of Understanding (MOU) in 2010 to provide $338,000 for the construction of the Cottonwood @ Easter Avenue project. The MOU was one of the first intergovernmental agreements between the Authority and local governments for the construction of pollutant reduction facilities (PRFs) such as stream reclamation.

WATER QUALITY BENEFITS

The Authority supports the reclamation of streams in the watershed because reclamation provides water quality benefits by reducing erosion and immobilizing pollutants in the channel by filtering them through riparian vegetation. These benefits have been demonstrated by PRF monitoring, literature reviews, and the TAC’s investigations¹. Because of rapid urbanization in Cottonwood Creek watershed, channel degradation had resulted in significant erosion far beyond assumed average or typical conditions for other streams (see Figure 2), rendering the 2006

topographic survey out of date.

To determine how much the erosion would impact earth quantities that might require design changes, SEMSWA commissioned an additional topographic survey in 2010 and prepared comparative cross sections. The Authority then analyzed the changes in the stream channel geometry using the two topographic surveys for the project. The Authority evaluated the 31 cross sections to estimate the amount of erosion that had occurred during the four year period. Figure 2 – Example of Extensive Erosion Each section was reviewed to determine the change in cross section area related to stream flow erosion. The eroded area was estimated using the following criteria:

1. Change in cross section area was limited to the main channel area, a lateral distance around 80-feet.

2. Where it appeared that bank material sloughed into the channel bed but had not been eroded, the sloughed area of the bank was not included in the erode area calculation since the material is still in the channel bottom.

3. Some cross sections showed that the 2010 topography was higher than 2006 topography, which may be interpreted as deposition or perhaps channel shifting. No erosion was assumed for these sections.

2 January 8, 2014

Table 1 below summarizes the calculations performed to estimate the amount of erosion that had occurred over the period from start of design to start of construction.

Table 1 – Channel Erosion Estimate

Total Erosion 2623 cubic yards When compared to other channel erosion rates, the Project Length 0.42-miles (thalweg) Cottonwood @ Easter Avenue results show that the erosion Erosion Duration 4-years Erosion Rate 1574 cy/mi/yr rate for the four year period was extremely high when, as Sediment Density 90 pcf shown in Table 2. Ward Branch and Stroubles Creek are Erosion Rate 1912 Tons/mi/yr results from areas outside of Colorado that were found in the literature.

The four-year rate for the Cottonwood @ Table 2 – Comparison of Stream Erosion Rates Easter Avenue project is about 10 times what (tons/mile/year) was estimated for Cottonwood Creek within Cherry Creek State Park – which occurred Cottonwood Creek over a period of 50 or more years - and about Cherry Easter to Stroubles Ward Branch 19-times the rate the Authority currently uses Creek State Briarwood Creek to approximate sediment loads from an Park unstable stream system (i.e.: 100 tons/mi/yr). 182 1912 610 164 It is likely, however, that Briarwood to Easter Avenue reach would not continue at this rate for an extended period of time.

The Authority also obtained sediment samples and had them tested for total phosphorus content. Total phosphorus concentrations ranged from 431 to 910 mg/kg with an average of 573-mg/kg. This translates to average total phosphorus in the samples of 1.0-lbs P per ton of sediment, which is consistent with the Authority’s estimated value for calculating water quality benefits.

Conclusions

The analysis and comparison suggests that when bank sloughing (or wasting) occurs, the sediment loads increase dramatically over normal stream bank and bed erosion rates. The significant increase in sediment loads – and associated pollutants - further demonstrates the importance of stabilizing and reclaiming stream systems well before the condition worsens such as the Easter to

Briarwood reach.

Reclamation of the reach of Cottonwood Creek between Easter Avenue and Briarwood will reduce channel bed/bank erosion and pollutant loads to Cherry Creek Reservoir. Figure 3 – Reclaimed Reach of Cottonwood Creek

3 Cottonwood Creek Peoria Trib., Ponds C3 & C4

Presented in this memorandum is a summary of the Cottonwood Creek Tributary B Airport Ponds East and West (Peoria Tributary B Airport Ponds East and West, Project, see Figure 1 Location Map).

BACKGROUND AND PURPOSE

A Conceptual Design Report for the Cottonwood Creek watershed was prepared for SEMSWA, Douglas County, and the UDFCD in 2010 (called OSP)1. An OSP provides a watershed wide plan that addresses drainage, flood control, and storm water quality impacts from urbanization. The Authority Project provided input to the OSP as a stakeholder by attending progress meetings and commenting on draft documents. The final OSP recommendation included a total of 26 existing, retrofitted, or new regional detention/water quality facilities with 23 of the sites providing excess urban runoff volume2 (EURV), including modifications to Tributary B Airport West Dam and Airport East Dam to include EURV (see Figure 1).

In early 2010, the TAC investigated the Airport’s storm water management plan (SWMP) with attention towards evaluation of the Airports deicing management program. The airport uses propylene glycol and in the past ethylene glycol as deicing agents which have high biological and Figure 1 – Location Map chemical oxygen demands (BOD and COD) that reduce oxygen in receiving waters. High total suspended solids (TSS) concentrations have also been

1 Muller Engineering Company August 18, 2010. Cottonwood Creek (Downstream of Lincoln Avenue) Outfall Systems Plan Conceptual Design Report. 2 Providing EURV in a water quality pond is believed to provide additional water quality benefits beyond Authority minimum requirements, which is extended detention basin (EDB).

ProjectSummaryMemo-CtnwdTribBPonds.docx 1 January 8, 2014

detected in the runoff. The Authority provided comments to the Airport expressing concerns that the SWMP did not adequately address pollutant discharges, specifically glycol COD, BOD, and TSS. The Authority offered to work with the Airport and, as a result, also provided suggestions to the Airport regarding the SWMP, many of which were incorporated into the final Airport SWMP.

PROJECT PARTNERS AND FUNDING

In 2010, the Authority Board adopted the 2011 – 2014, 5-year capital improvement budget (CIP) that included the Peoria Tributary B Airport Ponds East and West CIP, based in part on the OSP recommendations and the need to address deicing runoff from the airport. At that time, it was assumed that the Authority would partner with the Airport and SEMSWA to fund the project, which consisted of modification to two existing ponds at a cost $523,000 with the Authority providing of $131,000 (25%).

In March 2011, the Authority was requested to provide comments on construction plans being prepared by the Airport’s consultant who was designing improvements to Airport Ponds East and West that included combining the two ponds and providing EURV water quality capture volume. The Airport was modifying the east and west detention ponds per the OSP as a mitigation measure for the FAA directed, safety-related-widening of the nearby runway.

Representatives of the Airport and their consultant attended the October 6, 2011 TAC meeting and reported that the total project cost estimate for the ponds is around $1,500,000, including design, construction, and permitting. The FAA provided $1,200,000 and the Airport provided $134,000 plus the land value. The Authority contribution of $131,000 constitutes 8.7% of the total project cost.

WATER QUALITY BENEFITS Construction of the Peoria Tributary B Airport Ponds East and West will prevent sediment and nutrients in runoff from Centennial Airport from entering Cottonwood Creek and protect water quality and beneficial uses of Cherry Creek Reservoir. The project will also help to maintain higher levels of dissolved oxygen in Cottonwood Creek and the Reservoir3 and is also part of a comprehensive watershed approach to manage water quality.

Figure 2 shows the pond outlet which was modified to include a rock filter. Water quality sampling and testing by Arapahoe County has identified the natural presence of rust colored bacteria in the storm drainage system at Easter Avenue which includes runoff from Centennial Airport. Research by the Authority suggested that naturally occurring Figure 2 – Pond Outlet bacteria can reduce glycol concentrations and that other airports have incorporated similar treatment for deicing runoff. Authority recommended modifications to the Airport pond incorporates small, angular rock in the swale and at the outlet to simulate a “trickling filter” common in wastewater treatment.

3 Until very recently, the Reservoir was on the 303(d) list for dissolved oxygen, which was a concern to the Authority.

2 Cherry Creek Stream Reclamation at 12-Mile Park, Phase I

Presented in this memorandum is a summary of the first phase of the Cherry Creek Stream Reclamation at 12- Mile Park (Project). The second and final phase of the Project, which is scheduled to begin construction in the fall of 2013, will be summarized in an addendum or separate memorandum.

BACKGROUND AND PURPOSE

In 2007, Cherry Creek State Park (Parks) and the Authority inspected the reach of Cherry Creek along the “big-bend” in the Creek adjacent to the dog off-leash area near the south east area of the Park. Severe damage to bank vegetation and channel erosion were observed throughout the area where people, dog, and horse activity were concentrated (see Photo 1). The Authority evaluated the water quality impacts from these activities and decided to investigate the technical feasibility of stabilizing the channel banks. Funds for investigation were included in the 2008 capital improvement program (CIP). On January 2008, the Authority met with Parks to discuss coordination between the Parks construction of a formal dog off-leash area (DOLA) and the Authority’s channel stabilization measures. The parties agreed to a design approach that would integrate stream stabilization measures with DOLA users by controlling access to the Photo 1 - Cherry Creek 01-28-2008 creek and creating a larger vegetated buffer between the creek and the fenced-in DOLA for water quality purposes, but also to continue allow dogs and people to access the creek for recreation purposes in the same areas as existed at that time. Through 2008 and 2009, the Parks conducted a public process to review the DOLA improvement plans.

ProjectSummaryMemo-12-MilePark-Phase I 1 January 28, 2013

The Authority advertised for engineering consultants to prepare a stream reclamation plan for the entire reach of the Project (see Figure 1) and contracted with CH2M Hill for the work on May 20, 2010. Prior to selection of a consultant, the right bank of Cherry Creek breached causing the creek to change course through the downstream cottonwood grove, damaging the wetlands which is evident in Photo 2. Therefore, the engineering contract included a task to develop an immediate solution to repair the breached right-bank.

CH2M Hill provided a draft alternative evaluation report1 and recommended permanent repairs to the breached bank area, dividing the Project into two phases. The Authority then amended the CH2M Hill contract on January 20, 2011 for final design of the breach area (Phase I) and again on October 1, 2011 for bidding and construction services.

DESIGN APPROACH

The overall design approach is best described as “stabilization” rather than “reclamation”. First, no improvements are required along the left bank (looking downstream), which is a heavily vegetated, stable, wetlands and uplands area. Second, because the right bank is so high (up to 8-feet), reconnection of the channel and the floodplain is impractical along the right bank. However, because of the intensive use of the right bank of Cherry Creek by the DOLA users, stabilization measures were limited to “harder” structures such as rock toe and timber access points. The new and existing vegetated bank areas also require ingress/egress protection using various types of barriers such as fencing along the top of bank installed as part of the DOLA project. The final plans, however, include eight separate creek-access areas along the right bank constructed from boulders and/or timber to allow DOLA users to have the same experience as prior to DOLA and stream stabilization improvements.

Photo 2 - Wetlands damage from breach

1 CH2M Hill April 2011. Cherry Creek at 12- Mile Park DRAFT Alternatives Evaluation Report

2 January 28, 2013

CONSTRUCTION

Bids for the Project were opened on October 31, 2011 and the construction contract was issued to 53- Corporation, LLC of Castle Rock on December 8, 2011 in the amount of $227,588. The notice to proceed was issued for January 23, 2012 and work was substantially complete as of June 6, 2012. Final project costs, which included additional work to restore the damaged wetlands, are $236,778.

Repair to the breach along the right bank included a combination of a boulder toe wall (Photo 3) and sheet-pile cut-off wall along the upper bank (Photo 4).

During work on the 12-Mile Park Project, the Authority also had another project under construction by 53-Corporation within Cherry Creek State Park which had excess earth materials. After determining the suitability of the sediment Photo 3 - Boulder Toe Wall for use in the 12-Mile Park project, the Authority directed the contractor to haul sediment from the Cottonwood Wetlands project and place it at the 12- Mile Park project to reclaim the wetlands damaged during breach of the Cherry Creek channel. This exchange of material between projects reduced costs to import materials for the 12-Mile Park project and export materials from the Park to preserve flood storage volume2. Photo 5 shows the restored wetlands and Photo 6 shows the restored right bank of Cherry Creek that had breached.

Photo 4 - Sheet Pile Cut-Off Wall

Photo 5 - Restored Wetlands

Photo 6 - Restored Breach Area

2 William P. Ruzzo, PE, LLC July 26, 2012. Tower Loop, Cottonwood Wetlands, and Cherry Creek @ 12-Mile Park

3 January 28, 2013

June 6, 2012 Flood Event

At the time of inspection (~ noon 6-7-12), the flows in Cherry Creek had begun to recede. Photo 6 above is looking downstream at the right bank where the creek previously was breached. The high flow debris-line is clearly visible just to the right of the water surface. The top of newly restored bank is along the wooden fence posts. This clearly shows that the flood did not breach the repaired bank at the breach area. Analysis by CH2M Hill of the debris line using HEC-RAS developed for the Project suggests that peak flow on June 6, 2012 reached values near 2,000-cfs.

Photo 7 shows the downstream end of the project where the grade was tied back into existing grade in front of the trees. The existing channel bank did overtop in this area, outside of the project limits, then flowed back into the project area and did result in some localized erosion. The area downstream of the breach (to the right of the photo) showed minor erosion and sedimentation and possibly some seeded areas were impacted.

Preliminary conclusion is that the project experienced minor local erosion damage and can be repaired during Phase II of the project at a minor cost. It is also my opinion that if the breach had not been repaired, the environmental damage in the breach area would have Photo 7 - Bank Overflow Area been extended wider and further downstream damaging other wetlands and far exceeding the minimal damages observed.

WATER QUALITY BENEFITS

An assessment of the water quality benefits for the entire Project was made by the Authority3. Water quality benefits from the combined 12-Mile Park and DOLA projects (combined projects) fall into one of two categories, stream stabilization or recreation management.

Stream stabilization benefits and evaluation procedures have been documented in the Authority’s Stream Reclamation Interim Report4. Benefits include reductions in sediment and other pollutant loads and concentrations, including phosphorus and nitrogen. These benefits are supported by Authority data, literature research, and quantitative analysis.

The 12-Mile Park Stream Reclamation Plan also addresses the dispersed runoff from the DOLA by including a swale along the top of the east bank of Cherry Creek. This BMP is intended to capture minor storm events from the DOLA and provide filtration and infiltration treatment of the runoff. Because of the breach that occurred in the right bank of Cherry Creek, the 12-Mile Park project also includes repairs and restoration of Cherry Creek and the damaged wetland area.

3 William P. Ruzzo, PE, LLC May 25, 2011. Cherry Creek Stream Reclamation at 12-Mile Park – Water Quality Benefits and Costs. 4 CCBWQA Technical Advisory Committee, June 16, 2011. Stream Reclamation, Water Quality Benefit Evaluation – Interim Report.

4 January 28, 2013

The Park’s DOLA project includes extensive improvements, relative to water quality, such as perimeter fencing, controlled access to Cherry Creek, and waste management practices. In addition to management of the dog use area, the overall DOLA project includes modifications to the horse boarding area, which is adjacent to the DOLA area on the west and south. The principal modification to the horse area, relative to water quality, will be an updated manure management plan.

The analysis by the Authority suggests that when concentrated nutrient (phosphorus) sources are addressed, along with stream reclamation, the water quality benefits are significantly increased, and can reduce water quality protect costs. This supports the Authority’s approach of also addressing local sources of nutrients, when partnering with others on stream reclamation projects.

5 Cherry Creek Stream Reclamation at 12-Mile Park, Phase II

Presented in this memorandum is a summary of the second and final phase of the Cherry Creek Stream Reclamation at 12-Mile Park (Project). The first phase of the project, was substantially completed on June 6, 2012. The Cherry Creek Stream Reclamation @ 12-Mile Park Phase I - Project Summary Memorandum1 highlights the initial project observations, details, investigations and findings.

BACKGROUND AND PURPOSE: In 2007, Cherry Creek State Park (Parks) and the Authority inspected the reach of Cherry Creek along the “big-bend” in the Creek adjacent to the dog off-leash area near the south east area of the Park. This area is shown on Figure 1 - Location Map.

Severe damage to bank vegetation and channel erosion were observed throughout the area where people, dog, and horse activity were concentrated. The Authority evaluated the water quality impacts from these activities and decided to investigate the technical feasibility of stabilizing the channel banks. The parties agreed to a design approach that would integrate stream stabilization measures with DOLA users by controlling access to the creek and creating a larger vegetated buffer between the creek and the fenced-in DOLA for water quality purposes, but also to continue to allow dogs and people to access the creek for recreation purposes in the same areas as existed at that time.

The Authority contracted with CH2M Hill to perform the design and construction phase services for the Phase II project through an amendment to the Cherry Creek Stream Reclamation Phase I project

1 William P. Ruzzo, PE, LLC January 28, 2013, Cherry Creek Stream Reclamation @ 12-Mile Park Phase I - Project Summary Memorandum. 6013 E. Briarwood Drive - Centennial, CO 80112 (303) 726-5577 JRS Engineering Consultant, LLC – Cont. Cherry Creek State Park - Cherry Creek Stream Reclamation 12-Mile Park Phase II October 21, 2014 - Page 2

contract. This continuity provided a seamless transition in project design as well as continuity to integrate the Phase II project character and detail into those of the Phase I project.

EXISTING CONDITIONS: The Phase II project limits were comprised of two distinct reaches. The upstream reach is characterized by a secondary channel to Cherry Creek, fed by groundwater. The downstream reach is an active channel bank to Cherry Creek.

The Authority's investigation during Phase I found that areas along the east bank of Cherry Creek were severely eroded with minimal existing vegetation and included topography typified by steep, almost vertical, slopes, see Photo 1. Other areas along the Project were not as steep; however, the bank was experiencing severe erosion from park user access, see Photo 2. Photo 1 - Steep Creek Banks

Each reach was heavily used by both visitors and their dogs with challenges encountered to safely access the water's edge.

Large existing trees were characteristic to the shoreline and a valued component of the DOLA as seen in Photo 3. The Phase II project incorporated bank stabilization features that preserved existing trees and vegetation along the corridor.

Photo 2 - Limited Secondary Channel Access

Photo 3 - Existing Trees

6013 E. Briarwood Drive - Centennial, CO 80112 (303) 726-5577 JRS Engineering Consultant, LLC – Cont. Cherry Creek State Park - Cherry Creek Stream Reclamation 12-Mile Park Phase II October 21, 2014 - Page 3

DESIGN APPROACH: Consistent with the Phase I project, the overall design approach for the Phase II Project is best described as “stabilization” rather than “reclamation”. No improvements are required along the left bank (looking downstream), which is a heavily vegetated, stable, wetlands and uplands area.

Since the right bank is so high (up to 14-feet), reconnection of the channel and the floodplain is impractical along the right bank. However, because of the intensive use of the right bank of Cherry Creek by the DOLA users, stabilization measures were limited to “harder” structures such as rock toe and timber access points. Photos 4 through 10 depict the completed improvements.

Photo 4 - Connection with the Phase I Project

The newly constructed sloped banks are protected by a layer of void-filled rip-rap covered by topsoil and seeded vegetation. Fencing was installed along the top of bank as part of the DOLA project to

Photo 5 - Top of Bank Pedestrian Trail & Fence control access to Cherry Creek.

Controlled access is provided by eight separate creek-access points along the creek bank constructed from boulders and timbers allowing DOLA users safe and convenient water access. Additionally, existing trees were protected and incorporated into the stream stabilization improvements.

Overall, nearly 6,000 cubic yards of earthen material was hauled off-site during the Project.

Photo 6 - Timber / Boulder Access Point

6013 E. Briarwood Drive - Centennial, CO 80112 (303) 726-5577 JRS Engineering Consultant, LLC – Cont. Cherry Creek State Park - Cherry Creek Stream Reclamation 12-Mile Park Phase II October 21, 2014 - Page 4

Photo 7 shows the constructed stream stabilization improvements along the bank at the existing tree shown previously in Photo 3. Tree preservation along the Project corridor provides instant shade and ambiance to the Project.

Photo 7 - Access Beach @ Existing Tree

Photo 8 - New Access to Beach @ Existing Tree

Photo 9 - Beach Access to the Secondary Channel

Photo 10 - Stabilized Slope (seeded & blanketed)

CONSTRUCTED PROJECT: Bids for the project were opened on August 22, 2013. The successful bidder, 53 Corporation, was awarded the contract in the amount of $873,992.00. The notice to proceed was issued for October 30, 2013. The work was substantially complete on June 2, 2014. The final project cost totaled $876,694.20. 53 Corporation was also the contractor for the Phase I project, bringing additional continuity and experience to the Project.

6013 E. Briarwood Drive - Centennial, CO 80112 (303) 726-5577 JRS Engineering Consultant, LLC – Cont. Cherry Creek State Park - Cherry Creek Stream Reclamation 12-Mile Park Phase II October 21, 2014 - Page 5

PROJECT AWARD: Following completion of project construction, the project was submitted to the Colorado Association of Stormwater and Floodplain Mangers as an entry for their annual awards program. Five projects were submitted for the awards program, three were presented and the Cherry Creek Stream Reclamation at 12-Mile Park project received the "Honor Award for Outstanding Achievement" following its presentation at the conference.

WATER QUALITY BENEFITS: An assessment of the water quality benefits for the entire project was made by the Authority2. Water quality benefits from the combined 12- Mile Park (Phases I and II) fall into one of two categories, stream stabilization or recreation management.

.As stated in the Cherry Creek Stream Reclamation @ 12-Mile Park Phase I - Project Summary Memo3: "Stream stabilization benefits and evaluation procedures have been documented in the Authority's Stream Reclamation Interim Report4. Benefits include reductions in sediment and other pollutant loads and concentrations, including phosphorus and nitrogen. These benefits are supported by Authority data, literature research and quantitative analysis.

The 12-Mile Park Stream Reclamation Plan also addresses the dispersed runoff from the DOLA by including a swale along the top of the east bank of Cherry Creek. This BMP is intended to capture minor storm events from the DOLA and provide filtration and infiltration treatment of the runoff."

2 William P. Ruzzo, PE, LLC May 25, 2011. Cherry Creek Stream Reclamation at 12-Mile Park - Water Quality Benefits and Costs. 3 William P. Ruzzo, PE, LLC January 28, 2013. Cherry Creek Stream Reclamation @ 12-Mile Park Phase I - Project Summary Memorandum. 4 CCBWQA Technical Advisory Committee, June 16, 2011. Stream Reclamation, Water Quality Benefit Evaluation - Interim Report. 6013 E. Briarwood Drive - Centennial, CO 80112 (303) 726-5577 Mountain and Lake Loop Shoreline Stabilization

BACKGROUND AND PURPOSE: The Cherry Creek Reservoir Shoreline Stabilization Mountain and Lake Loop Alternative Development and Analysis (Project) was part of the Authority's 2008 Capital Improvement Program (2008 CIP) which was developed to identify and to prioritize activities and projects necessary to achieve water quality standards in Cherry Creek Reservoir. The project area is located on the southwest side of the reservoir as shown on Figure 1 - Area Map. The project site covers approximately 6.5 acres including the area between the foot trail and the shoreline and approximately 2,300 feet of shoreline, see Figure 2. The project objectives include construction of shoreline and bank stabilization measures that: 1. Minimize sediment from wind, rain, ice, surface runoff, wave action and park user access reaching the reservoir. 2. Minimize water quality impacts from two parking lots and other impervious surface runoff. 3. Integrate and enhance the proposed uses within Cherry Creek State Park.

Figure 1 - Area Map

Figure 2 - Project Site

EXISTING CONDITIONS: Wave action, wind, ice push and shoreline users have each contributed to erosion of the reservoir shoreline and major cut banks. This point along the shoreline is exposed to wind and wave actions during every season of the year. As the ice cover breaks up each spring, the north wind pushes ice to the south shore and in particular this point. Typical pre-project conditions are shown on Photos 1, 2 and 3.

Photo 1 - Existing Condition Photo 2 - Existing Condition Photo 3 - Existing Condition DESIGN APPROACH: The overall design approach is best described as "stabilization" rather than "reclamation". In 2008 the Authority performed an in depth assessment of the water quality benefits of shoreline stabilization1. This assessment concluded that phosphorus reduction from shoreline stabilization differs from stream bank stabilization, primarily because shorelines are impacted by additional erosive forces besides storm runoff, including wave and wind forces as well as recreation impacts. The conclusion of this assessment is that, over the long term, shoreline stabilization is expected to reduce phosphorus concentrations into the reservoir from pre-project conditions and likely would reduce phosphorus concentrations to a level consistent with the Authority's goal of 0.20-mg/l.

The assessment also concluded that , based on historical data, for the majority of the time( ≈80% ) the water surface of the reservoir varied within one foot plus/minus of the normal recreational pool (Elevation 5550 ). And, the water level remained within two feet of the normal recreational pool over 95 percent of the time. Thus the shoreline stabilization work for this project will be implemented between the elevations of 5548 and 5552.2

The vertical banks were trimmed back to provide manageable vegetated slopes, the shoreline in critical areas was armored with boulders, shoreline point locations were enhanced to protect adjacent shorelines from the prevailing winds, recreation access to beach areas was enhanced, crusher fine trails were created and pedestrian access was directed to the trails using strategically located heavy rail fence; a park standard detail. Runoff from the parking lots was collected and directed into infiltration basis where the storm water is filtered through a select material that allows rapid infiltration.

CONSTRUCTED PROJECT: Bids for the project were opened on July 24, 2012 and the construction contract was issued to 53- Corporation LLC of Castle Rock on August 16, 2012 in the amount of $750,436.29. The notice to proceed was issued for September 13, 2013 and the work was substantially complete on June 7, 2013. The final project cost, which included watering of the trees, shrubs and turf totaled $725,121.97.

Construction of the boulder point with riprap bank protection provides armoring at the Lake Loop point. The boulders were anchored on the reservoir side with Type H riprap sloping at a 3:1 grade into the water. This detail pushes any ice upward and onto the top of the boulders rather than displacing them. A photo of the constructed point is shown as Photo 4 - Constructed Lake Loop Point.

The shape and location of the point (at Lake Loop and at Mountain Loop) protects adjacent shoreline from the direct prevailing winds and wave action.

The beach areas were re-established along the shoreline for recreational uses. The beach areas along the Mountain and Lake Loop project are in continual use by park users for picnics, fishing or a day in the sun as well as providing a convenient location to launch kayaks and long boats.

Photo 4 - Constructed Lake Loop Point 1 Water Quality Benefits of Shoreline Stabilization Memorandum, dated October 23, 2008; William P. Ruzzo, P.E., LLC 2 Recent water rights administration and weather patterns have resulted in more fluctuations in the reservoir pool level. For future projects, the limits of protection are anticipated to be greater.

Photo 5 - Constructed Mountain Loop Point Photo 6 - Beach Area

Infiltration basins were incorporated at both the Mountain Loop parking lot and the Lake Loop parking lot. These BMP's are intended to capture minor storm events from the parking lot and provide filtration and infiltration treatment of the runoff. Photo 7 shows an infiltration basin in action at Lake Loop.

September 14, 2013 Storm Event: On Sunday September 14, 2013 the upper reaches of Cherry Creek received heavy rainfall that at its peak ; the upstream flows were measured at approximately 1,000 cfs. Prior to this event, the water level in Cherry Creek Reservoir was 3.6 feet below normal th recreation pool (WSL at 5546.4). On September 16 Photo 7 - Infiltration Basin @ Parking Lot the reservoir water level was at 5553.2.

An on-site inspection followed on September 18th that found moderate erosion of the trails and graded areas above the upper limit for design ( Elevation = 5552 ) based on the 2008 reservoir water level assessment findings . The boulders and armored structures were not impacted by the flood stage. Following that review, a restoration plan has been completed and construction is anticipated this fall / winter to restore the site to its post construction condition. Photos 8 and 9 show some of the typical damage from the storm.

Photo 8 - Trail Damage Photo 9 - Sand Deposition on Trail & Vegetation

WATER QUALITY BENEFITS: An assessment of the water quality benefits was made in 2008 by the Authority3 as part of the ongoing water quality analysis of projects on the 5-year capital improvement program. Based on the outcome of this assessment it is calculated that 54 lbs of phosphorus per year will be eliminated from directly entering the reservoir from the shoreline improvements. Additionally the discharge of sediment and other pollutants from the two parking lots is also minimized from entering the reservoir by the infiltration basins.

3 Water Quality Benefits of Shoreline Stabilization Memorandum, dated October 23, 2008; William Ruzzo, P.E.