Volume II Eno River Watershed Improvement Plan Improvement Plan Durham, North Carolina December 2018

PREPARED FOR:

City of Durham Public Works Department Stormwater & GIS Services Division 101 City Hall Plaza, Third Floor Durham, North Carolina 27701 This page left blank intentionally Eno River Watershed Improvement Plan

City of Durham Stormwater & GIS Services Division Public Works Department 101 City Hall Plaza, Third Floor Durham, North Carolina 27701 This page left blank intentionally AECOM

Acknowledgments

The Eno River Watershed Improvement Plan represents the combined effort of staff from the City of Durham, AECOM, Kimley Horn and Associates, and Three Oaks Engineering.

City of Durham Team Paul Wiebke, Assistant Director, Public Works Kelly Hartman Sandra Wilbur, Project Manager Dana Hornkohl Lance Fontaine, Assistant Project Manager J.V. Loperfido Jonathan Baker Don O’Toole Christine Cailleret Laura Smith Charlotte Dawn Megan Walsh Erin Harrison Michelle Woolfolk

AECOM Team AECOM Technical Services of North Carolina Sujit Ekka, Project Manager Michelle Mayfield Brian Jacobson, Deputy Project Manager Karthik Narayanaswamy Matthew Burnette Alex Nice Diana Burke Hernan Rodriguez Brad Courtney Jason Sites Manasa Damera Zack Twigg Beth Kerby Cyndy Yu-Robinson

Kimley-Horn and Associates Three Oaks Engineering Beth Reed Tom Dickinson Jason Hartshorn Nathan Howell Andrew Jones Kate Monteith Sevick Jennifer Murphy Chris Sheats This page left blank intentionally AECOM

Table of Contents

Acronyms and Abbreviations ...... v 1 Introduction ...... 1-1 1.1 Background ...... 1-1 1.2 Goals ...... 1-2 1.3 Organization ...... 1-3 2 Watershed Assessment ...... 2-1 2.1 Watershed Characteristics ...... 2-1 2.1.1 Data Inventory ...... 2-1 2.1.2 Summary of Previous Studies...... 2-2 2.1.3 Hydrology...... 2-3 2.1.4 Topography ...... 2-4 2.1.5 Geology and Soils ...... 2-4 2.1.6 Floodplains ...... 2-5 2.1.7 Land Use and Impervious Cover ...... 2-6 2.2 Water Quality Conditions ...... 2-8 2.2.1 Surface Water Classifications...... 2-8 2.2.2 Water Quality Monitoring...... 2-9 2.2.3 Sediment Monitoring ...... 2-12 2.3 Watershed Impacts and Sources of Pollution ...... 2-13 3 Stream Inventory and Assessment and Project Opportunities ...... 3-1 3.1 Stream Field Inventory and Assessment Methodology ...... 3-1 3.2 Results of Stream Field Assessments ...... 3-1 3.3 Potential Stream Project Opportunities ...... 3-3 4 Stormwater Control Measure Inventory, Assessment, and Project Opportunities ...... 4-1 4.1 SCM Field Assessment Methodology ...... 4-1 4.2 Retrofit Opportunities to Existing SCMs ...... 4-2 4.3 Potential New SCMs ...... 4-4 5 Evaluation of Watershed Improvement Scenarios ...... 5-1 5.1 Pilot Study Areas ...... 5-1 5.2 Stormwater Management Modeling...... 5-1 5.3 Scenarios ...... 5-2 5.3.1 Scenario Methodology ...... 5-2 5.3.2 Scenario Results ...... 5-10 6 Prioritization of Watershed Improvement Projects...... 6-1 6.1 Prioritization Criteria ...... 6-1

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6.2 High-Priority Watershed Improvement Projects ...... 6-3 6.2.1 High-Priority SCM Projects...... 6-3 6.2.2 High Priority Stream Improvement Projects ...... 6-4 7 Public Outreach and Involvement ...... 7-1 7.1 Public Information Sessions ...... 7-1 7.1.1 First Public Information Session: March 21, 2017 ...... 7-1 7.1.2 Second Public Information Session: November 2, 2017...... 7-1 7.1.3 Third Public Information Session: July 31, 2018...... 7-2 7.2 Eno Watershed River Improvement Plan Webpage...... 7-3 7.3 Eno River Watershed Improvement Plan Social Media Updates ...... 7-3 7.4 Project Fact Sheets ...... 7-3 7.5 Educational Radio Spots ...... 7-3 7.6 Educational Videos ...... 7-4 8 Watershed Improvement Plan ...... 8-1 8.1 Recommended Strategies ...... 8-1 8.1.1 High-Priority SCM Projects...... 8-1 8.1.2 High-Priority Stream Improvement Projects ...... 8-1 8.1.3 Green Infrastructure and Low Impact Development Opportunities ...... 8-2 8.1.4 Protection and Preservation of High-Quality Streams ...... 8-2 8.1.5 Protection and Preservation of High-Quality Riparian Areas ...... 8-2 8.1.6 Continuation of City Programs and Practices ...... 8-3 8.2 Evaluating Progress ...... 8-5 9 References ...... 9-1

Figures Figure 2-1. Daily flow (mean and median) at USGS gage 02085070 and mean monthly precipitation at Raleigh-Durham International Airport (July 1996 to December 2016)...... 2-4 Figure 3-1. Example of a stream reach with an excellent overall stream condition rating ...... 3-2 Figure 3-2. Example of a stream reach with a poor overall stream condition rating: Reach 2038, located downstream of Danube Lane in ER11 ...... 3-2 Figure 4-1. Example of a retrofit opportunity in an existing dry pond (SCM 00060) ...... 4-3 Figure 4-2. Example of a retrofit opportunity to an existing wet pond (SCM 00055) ...... 4-3 Figure 4-3. Potential new SCM site in which a wet swale was recommended ...... 4-4

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Tables Table 1-1. USEPA’s nine key elements for watershed plans and corresponding section in the WIP...... 1-3 Table 2-1. Hydrologic soil groups ...... 2-5 Table 2-2. Projected land use change in the study area from existing to future conditions ...... 2-6 Table 2-3. Impervious cover and drainage area at City water quality monitoring locations ...... 2-8 Table 2-4. Water quality sampling stations in the Eno River watershed study area and dates of available monitoring data...... 2-10 Table 2-5. Water quality in the study area ...... 2-11 Table 2-6. Average WQI for Eno River watershed water quality monitoring stations ...... 2-12 Table 2-7. Summary of Eno River watershed pollution sources ...... 2-13 Table 2-8. Summary of potential nonpoint sources and impacts in the Eno River watershed ...... 2-15 Table 5-1. SCM removal efficiencies for TN, TP, and sediment ...... 5-3 Table 5-2. Water quality multipliers for existing SCMs ...... 5-4 Table 5-3. Recommended retrofits to existing SCMs ...... 5-6 Table 5-4. Potential new SCMs ...... 5-7 Table 5-5. Implementation factors used to assess GI-LID practices in Scenario 6 ...... 5-9 Table 5-6. Estimated change in TN, TP, and sediment annual loads for watershed improvement scenarios in the Eno River Watershed study area ...... 5-13 Table 5-7. Estimated TN, TP, and sediment annual load reductions for each practice evaluated in the Eno River watershed study area ...... 5-14 Table 6-1. Prioritization criteria with scoring ranges and weighting factors ...... 6-2 Table 6-2. High-priority SCM projects in the Eno River watershed...... 6-5 Table 6-3. High-priority stream projects in the Eno River watershed ...... 6-6 Table 8-1. Information used to track the effectiveness of controls in the Eno River watershed ...... 8-6

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Exhibits Exhibit 1 Watershed Overview Map Exhibit 2 Study Area Exhibit 3 Subwatersheds Exhibit 4 Eno River Canal Exhibit 5 Geology Exhibit 6 Hydrologic Soil Groups Exhibit 7 FEMA Floodplains Exhibit 8 Existing Land Use Exhibit 9 Future Land Use Exhibit 10 Impervious Cover Exhibit 11 NCDEQ Stream Classifications Exhibit 12 Monitoring Stations Exhibit 13 Inventory of Septic Systems, Sand Filters, and Sanitary Sewer Overflows Exhibit 14 Observed Water Quality Concerns Exhibit 15 Stream Quality Rating (RSAT) Exhibit 16 Stream Bank Erosion Exhibit 17 Potential Stream Projects Exhibit 18 Existing Stormwater Control Measures Evaluated Exhibit 19 Potential Retrofits to Existing Stormwater Control Measures Exhibit 20 Potential New Stormwater Control Measures Exhibit 21 Pilot Study Areas Exhibit 22 High Priority Stormwater Control Measures Exhibit 23 High Priority Stream Projects Exhibit 24 Stream Reaches Identified for Preservation

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Acronyms and Abbreviations

µg/L ...... microgram per liter NCIBI ...... North Carolina Index of Biotic Integrity BANCS ...... Bank Assessment for Non-Point Source NCWRC ...... North Carolina Wildlife Resources Consequences of Sediment Commission BEHI ...... Bank Erosion Hazard Index n.d...... no date BOD ...... biochemical oxygen demand NLCD ...... National Land Cover Database CAPP...... Critical Area Protection Plan NPDES ...... National Pollutant Discharge Elimination System CCC ...... Criterion Continuous Concentration NRCS ...... Natural Resources Conservation Service cfu ...... colony-forming unit NTU ...... Nephelometric Turbidity Unit CIP ...... capital improvement plan PAH ...... polycyclic aromatic hydrocarbon City ...... City of Durham PCSWMM ..... Personal Computer Storm Water DO ...... dissolved oxygen Management Model EMC ...... event mean concentration PID ...... Parcel Identification Number ESC ...... erosion and sediment control PSA...... Pilot Study Areas F/J-A ...... Falls/Jordan Critical Area ReGln ...... Residential Green Infrastructure F/J-B ...... Falls/Jordan Protected Area RSAT ...... Rapid Stream Assessment Technique FEMA ...... Federal Emergency Management SCM ...... stormwater control measure Agency SSO ...... Sanitary Sewer Overflow ft3/s ...... cubic feet per second TN ...... total nitrogen GI ...... Green Infrastructure TP...... total phosphorus GIS ...... Geographic Information Systems TSS ...... total suspended sediment HSG ...... hydrologic soil group UDO ...... Unified Development Ordinance I&I ...... infiltration and inflow UNCWI ...... Upper Neuse Clean Water Initiative LID ...... low impact development UNRBA...... Upper Neuse River Basin Association mg/L ...... milligrams per liter USACE ...... U.S. Army Corps of Engineers ml ...... milliliter USEPA ...... U.S. Environmental Protection Agency MS4 ...... Municipal Separate Storm Sewer System USGS ...... U.S. Geological Survey NCAC ...... North Carolina Administrative Code WASP ...... Water Quality Analysis Simulation Program NCDEQ ...... North Carolina Department of Environmental Quality WIP ...... Watershed Improvement Plan NCDOT ...... North Carolina Department of WQI...... Water Quality Index Transportation WS ...... water supply

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1 Introduction

Clean water is essential for the health of human implementation and tracking progress of the beings and the ecosystems that sustain wildlife, sustainability roadmap. The sustainability roadmap vegetation, and wetlands. To maintain clean water that was recently published (City of Durham, 2018a) within its city limits, the City of Durham (City) has is derived from the Strategic Plan and provides developed watershed plans to understand the priority strategies to meet the City goals. For condition of its waterbodies and watersheds and to example, the sustainability roadmap identifies identify the most effective ways of protecting and implementing green infrastructure practices as a improving water quality. strategy to protect and restore Durham’s natural resources and ecosystem. The watershed plans also allow the City to balance environmental, societal, and economic factors by These and other efforts to advance the City’s vision integrating water quality protection and restoration were recognized in 2017 when the City was certified with growth management. This balance is evident in as a 4-STAR Community for excellence in the City’s mission to “make Durham a great place to sustainability. The Sustainability Tools for Assessing live, work, and play” and its vision to “be a leader in and Rating (STAR) Community Rating System is the providing an excellent and sustainable quality of nation’s leading certification program for local life.” The City recently adopted the 2019-2021 sustainability. Strategic Plan that guides the vision and serves as an The City launched its watershed management action plan to achieve this mission. The Strategic program in 2007 to identify and prioritize projects Plan contains five specific goals that provide the that will improve water quality and watershed health. framework for implementing the Strategic Plan. Since 2007, the City has developed WIPs for the The City’s Stormwater & Geographic Information following watersheds: Ellerbe Creek (City of Durham. Systems (GIS) Services Division contributes to 2010), Third Fork Creek (City of Durham, 2012a), achieving the City’s vision by managing stormwater Northeast and Crooked Creek (City of Durham, and implementing land use best management 2013a), and Little Lick Creek (City of Durham, 2016a). practices that will protect and restore the streams, This document, the Eno River WIP, continues the rivers, and lakes in the City’s watersheds. City’s watershed program of protecting and The City’s Stormwater & GIS Services Division also restoring water quality. helps achieve the City’s strategic goal #5, Sustainable Natural and Built Environment, through 1.1 Background thoughtful planning and operations that ensure the The Eno River watershed is in the Upper Neuse River long-term viability of the City’s infrastructure, Basin in central North Carolina. The watershed facilities, and environment. covers 151 square miles and spans portions of This watershed improvement plan (WIP) aligns with Durham and Orange Counties (Exhibit 1). strategic goal #5, and the related objective to Approximately 11% (29 square miles or 18,561 acres) “Create a more Sustainable Durham”. This WIP of the entire watershed is within the city. addresses a few initiatives identified to attain this The unique history and natural beauty of the Eno objective such as increasing the amount of green River make the Eno River watershed a priority for infrastructure in the city, improving water quality land protection efforts of conservation groups such through stormwater and land use best practices, and

Eno River Watershed Improvement Plan, Volume II 1-1 AECOM as the Upper Neuse Clean Water Initiative (UNCWI) 1.2 Goals and the Eno River Association. The primary goal of the Eno River WIP is to provide a All of the streams in the watershed, including the comprehensive plan for achieving and maintaining mainstem Eno River, are currently meeting their high water quality and watershed health in the Eno designated uses, and none are on North Carolina’s River watershed study area (see Section 2.1 for a list of impaired waters (NCDEQ, 2016). description of the study area). However, the river flows into Falls Lake, an important Additional goals of the Eno River WIP are as follows: source of drinking water for the City of Raleigh. · Help the City address local water quality issues, Pollution from the Eno River watershed also reaches federal and state requirements under the City’s the lake. Portions of Falls Lake are listed as impaired National Pollutant Discharge Elimination System for turbidity and chlorophyll a (NCDEQ, 2016) and (NPDES) Municipal Separate Storm Sewer System the lake is classified as a Nutrient Sensitive Water (MS4) permit, and nutrient management (NCDEQ, 2018), which requires nutrient management strategies in the Upper Neuse River Basin due to excessive growth of microscopic and macroscopic vegetation. · Help the City prioritize and implement practices that will reduce nutrient loading to Falls Lake in The excessive growth of vegetation is largely the compliance with the Falls Lake Rules result of excess nutrients, primarily nitrogen and · Help the City achieve the goals set forth in their phosphorus. Uncontrolled plant and algae growth Strategic Plan and Sustainability Roadmap blocks sunlight, causes unsightly conditions, through helping to increase green infrastructure interferes with water treatment, and causes in the city and improving water quality through unpleasant taste and odor in drinking water. stormwater and land use best practices Falls Lake is subject to the Falls Lake Water Supply Developing the WIP included the following tasks: Nutrient Management Strategy (Falls Lake Rules) (NCDEQ, 2011). Approved by the North Carolina · Assessment of the existing water quality and Environmental Management Commission in 2010, health of the streams and aquatic habitats in the the Falls Lake Rules require municipalities and other Eno River watershed based on a review of existing governmental entities in the Falls Lake water supply watershed studies and reports, range of watershed to reduce nitrogen and phosphorus watershed datasets, and field investigations loading to the lake in an effort to reduce algal · Identification of the major impacts to the health growth in the lake. The rules include requirements of the watershed such as pollution from point and for new and existing development, agriculture, and nonpoint sources wastewater dischargers. The requirements in the · Identification of potential watershed Falls Lake Rules are currently under state review. The improvement projects such as pollution control city is working with other communities and measures, including stormwater control measures organizations through the Upper Neuse River Basin (SCMs), and stream restoration projects based on Association to provide additional monitoring and effectiveness in reducing pollutant loads, modeling that will re-evaluate the rules. regulatory considerations, and stakeholder goals The Eno River watershed is subject to the Falls Lake · Prioritization of the watershed improvement Rules because it is part of the Falls Lake water supply projects that were identified watershed (Durham City-County Planning · Development of partnerships with residents and Department, 2018). local watershed organizations and governmental agencies to promote the protection and

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enhancement of the water quality, aquatic · Volume I: Executive Summary. Project goals, habitats, and ecological function in the watershed watershed evaluation methods, results of the The WIP addresses the nine elements that are watershed improvement scenarios, recommended required in watershed plans by Section 319 of the projects, high-priority project fact sheets, and Clean Water Act. The elements are described in the next steps in evaluating progress. United States Environmental Protection Agency’s · Volume II: Improvement Plan. Summary of the (USEPA) Handbook for Developing Watershed Plans approach used to develop the WIP; data used to to Restore and Protect Our Waters (USEPA, 2008) and develop watershed models, stream and SCM are listed in Table 1-1. The table includes cross inventory and assessments; watershed references to the sections of the WIP that most improvement scenarios; watershed improvement directly correspond to each key element. Refer to project evaluation and prioritization; public Appendix O, Volume III of the WIP for the checklist. outreach and involvement efforts; The Eno River WIP also meets the North Carolina recommendations; implementation schedule; and Division of Mitigation Services requirements for local measurable milestones. watershed plans and thereby facilitates the · Volume III: Technical Appendices. Reports and implementation of watershed improvement projects memoranda with more detailed information on through mitigation funding. the technical approach used in development of the WIP than in Volume II, including field surveys 1.3 Organization and the development of modeling. The Eno River WIP is divided into three volumes, similar to other City watershed plans. The three volumes are:

Table 1-1. USEPA’s nine key elements for watershed plans and corresponding section in the WIP Element Description Section in WIP 1 Identify the causes and sources of pollution Vol. II, Sect. 2 2 Estimate pollutant loading into the watershed and expected management Vol. II, Sect. 5 measures and load reductions

3 Describe the management measures to achieve load reductions and identify the Vol. II, Sect. 5 critical areas in which those measures will be implemented and 6 4 Estimate the associated costs, amounts of technical and financial assistance needed, Vol. I; Vol. II, and the authorities needed to implement the plan Sect. 6 5 Implement a public information and education component that will be used to Vol. II, Sect. 7 enhance public understanding of the project

6 Provide a schedule for implementing the nonpoint source management measures Vol. II, Sect. 8 identified in the plan

7 Describe interim, measurable milestones for verifying whether nonpoint source Vol. II, Sect.8 management measures or other control actions are being implemented effectively 8 Describe a set of criteria that can be used to determine whether loading reductions Vol. II, Sect. 8 are being achieved over time and substantial progress is being made toward attaining water quality standards 9 Describe a monitoring plan to evaluate the effectiveness of the implementation Vol. II, Sect. 8 efforts over time, measured against the criteria established under Element 8

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2 Watershed Assessment

Section 2 summarizes the existing conditions in the bordered to the north by the Little River watershed watershed and provides an analysis of the water and to the south by the Ellerbe Creek watershed. quality concerns in the watershed and alternatives The Eno River watershed is home to six City parks for solving the concerns. Additional information on (West Point on the Eno, River Forest Park, Old Farm these topics is presented in the Eno River Watershed Road Park, Valley Springs Park, Holt School Road Assessment Report, which is provided in Volume III, Park, and Whippoorwill Park). Other public Appendix E, of this WIP. landmarks are the North Regional Library, Riverside The recommendations in Section 2 on addressing High School, Hillandale Elementary, and Sandy Ridge physical, chemical, and biological health are based Elementary. on an assessment of available data and the The study area for the Eno River WIP consists of the conditions in the watershed. portion of the Eno River watershed in Durham The key elements of the Eno River watershed County and the city (Exhibit 2). The study area assessment that are presented in Section 2 are as consists of 29 square miles (18,561 acres) and follows: extends from the Durham County/Orange County · Summary of recent watershed studies and reports boundary to the confluence of the Eno River and (Section 2.1.2) Little River. · Watershed hydrology, topography, geology, soils, For the purposes of the WIP, the study area was floodplains, and existing and future land use divided into 53 subwatersheds (ER01 through ER53) (Sections 2.1.3 to 2.1.7) based on surface hydrology, topography, and the existing stormwater infrastructure (Exhibit 3). The · Assessment of water quality and sediment subwatersheds range in size from 0.06 square miles monitoring data (Section 2.2) to 1.84 square miles. · Summary of watershed impacts, potential sources, and management recommendations (Section 2.3) Historically, many streams in the region were modified (e.g., impoundment, channelization, Field assessments and project opportunities related straightening). Steams in the Eno River watershed to streams and SCMs are presented in Sections 3 have been modified to benefit, for example, fords, and 4. mills, hydropower, and water supply reservoirs. One modification, the construction of a canal in the Eno 2.1 Watershed Characteristics River near Penny’s Bend, was verified on historical The Eno River watershed is located in the Upper property surveys (Exhibit 4). Neuse River Basin in the Central Piedmont Region of North Carolina. The watershed covers 151 square 2.1.1 Data Inventory miles and approximately 11% or 16 square miles are Information from local, state, and federal within Durham city limits. government agencies, private companies, and public The Eno River originates in Orange County and flows organizations was used to support the watershed southeast through Hillsborough and Durham to its analyses, inform the project team’s understanding of confluence with Falls Lake (Exhibit 1). In Durham water quality concerns, and prioritize SCMs and County, the Eno River flows from west to east and is other types of projects to address watershed concerns.

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Given the range and amount of available information City performed an aquatic vegetation survey in on the Eno River watershed, a Data Control Plan and 2013 for hydrilla, riverweed, and parrot feather as data catalog were developed to manage it. The Data part of a larger survey of the Eno River conducted Control Plan describes procedures used by the by the North Carolina State Parks, Eno River project team to manage GIS data, databases, Association, North Carolina Wildlife Resources spreadsheets, web applications, and other Commission (NCWRC), and North Carolina State information. The Data Control Plan is provided in University. Volume III, Appendix A, of this WIP. · Eno River Watershed Implementation Plan The data catalog is an inventory of the available Data Collection (City of Durham, 2014b). The City watershed-related data. The available data include conducted a comprehensive water quality study spatial data, tabular data, academic research, and for the Eno River watershed between July 2013 previous watershed studies performed in and near and June 2014 to fill data gaps in the City’s the Eno River watershed. Selected previous studies current monitoring program and provide a broad are summarized in Section 2.1.2. scale evaluation of aquatic health in the watershed to support the development of the 2.1.2 Summary of Previous Studies WIP. For this study, data was used from seven sites in the Eno River watershed, three on the Eno As noted in Section 1.1, the unique history and River mainstem and four located in tributaries to natural beauty of the Eno River make the Eno River the Eno River. These sites were monitored for one watershed a priority for land protection efforts of or more of the following: water chemistry, conservation groups such as the UNCWI and the Eno hydrology, sediment quality, and habitat. River Association. · Durham Comprehensive Plan (City of Durham, Recent reports on conservation efforts and aquatic 2017a). The Durham Comprehensive Plan outlines resource conditions in the Eno River watershed are the City’s long-term vision for how the summarized below and described in more detail in community would like to grow and develop, the Eno River Watershed Assessment Report (see including the City’s goals and vision on Volume III, Appendix E, of this WIP). Reports related conservation and the environment and actions to the Neuse River Basin and the Falls Lake Rules are needed to ensure that the City’s water, included because the Eno River watershed is in the wastewater, and stormwater facilities are well Upper Neuse River Basin and the watershed is maintained and adequate to support future subject to the Falls Lake Rules (see Section 1.1). development. · State of Our Streams (2004-2016) (City of · City of Durham Parks and Recreation Master Durham, 2018b). The City produces an annual Plan (City of Durham, 2013b). The three primary State of Our Streams Report to inform and goals in the master plan are connecting people engage citizens on watershed health. The report and places, improving sustainability, and includes a Water Quality Index (WQI) rating based optimizing current facilities. The Durham Trails on monitoring data on biochemical oxygen and Greenways Master Plan (City of Durham, demand (BOD), bacteria, nutrients, turbidity, and 2011) addresses these goals by outlining a metals. comprehensive trail system through the city, · Eno River Aquatic Vegetation Survey: including 14.5 miles of proposed greenway trails Submerged Aquatic Vegetation Survey for in the Eno River watershed. Hydrilla verticillata (hydrilla), Podostemum · Upper Neuse River Basin Stage II Falls Lake ceratophyllum (riverweed), and Myriophyllum Rules Reexamination Effort (UNRBA, 2018). The aquaticum (parrot feather) in the Eno River Upper Neuse River Basin Association (UNRBA) is near Durham, NC (City of Durham, 2014a). The developing tools to reevaluate the Falls Lake

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Nutrient Management Strategy (Falls Lake Rules). The U.S. Geological Survey (USGS) operates the To date, the effort has included evaluating following two gages in the study area: existing data for Falls Lake and associated · USGS gage 02085039 is at Cole Mill Road in tributaries, developing a framework for Durham County, east of the Orange County reexamining the Stage II strategy, estimating border. Daily stage is reported at this location. nutrient loads at Falls Lake, and reviewing existing · USGS gage 02085070 is downstream of the US models and recommendations for future studies. 501 bridge and approximately 0.2 miles · Upper Neuse Clean Water Initiative 2015–2045 downstream of the confluence of Crooked Run Conservation Strategy (UNCWI, 2015). The Creek and Eno River. Daily stage and daily strategy focuses on protecting land for drinking discharge are both reported at this location. This water resources in the Upper Neuse River Basin station has a drainage area of 141 square miles and includes a comprehensive conservation (approximately 93% of the total Eno River strategy for land protection. drainage area) and has been in operation since · Eno Journal (Eno River Association, n.d.). From 1963. 1973 to 2000, the Eno River Association published Over the past 20 years, the average annual nine volumes of the Eno Journal, which is focused streamflow has been 116 ft3/s. The mean daily flow on the environment, culture, and history of the at this location has ranged from a high of 234 ft3/s Eno River watershed. in March to a low of 43 ft3/s in August (Figure 2-1). · Eno New Hope Landscape Conservation Plan Average streamflow has varied considerably by (NCWRC, 2017). Through its Partners for Green season, with the highest flows in the winter and early Growth Program, NCWRC developed a landscape spring and lowest flows in the summer. conservation plan to protect critical habitat and In addition to the mean and median daily flow, provide connectivity between the Jordan Lake Figure 2-1, shows the mean monthly precipitation watershed, New Hope Creek (both in the Cape near the city. As can be seen, the temporal variation Fear River Basin), and the Eno River watershed in streamflow does not follow the temporal variation (Neuse River Basin). in precipitation, which is higher in the summer and lower in the winter. The counter-intuitive relationship 2.1.3 Hydrology between streamflow and precipitation is the result of The Eno River forms at the confluence of the East both higher evapotranspiration rates during the Fork Eno River and West Fork Eno River in northern summer and the presence of Triassic Basin geology Orange County. Two water supply reservoirs, Lake and soils (see Section 2.1.5). Orange and West Fork Eno Reservoir, are upstream Median and mean streamflow statistics highlight the of the confluence. relative impact that infrequent flow (high or low) The Eno River is 33 miles long from its origin at events have on understanding “typical” conditions in confluence of the East Fork Eno River and West Fork the stream. The median statistic is generally useful Eno River to its confluence with Little River. for understanding “typical” conditions in datasets Approximately 22 miles are in Orange County and that have asymmetrical distributions, such as the remaining 11 miles are in Durham County. Major streamflow, because it is less affected by extreme tributaries in the Durham County portion of the Eno events (e.g., very high flows). In contrast, the mean River watershed are Cub Creek, Crooked Run Creek, (or average) statistic is affected more by extreme and Warren Creek (Exhibit 1). events, which tend to skew the “typical” condition.

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Figure 2-1. Daily flow (mean and median) at USGS gage 02085070 and mean monthly precipitation at Raleigh-Durham International Airport (July 1996 to December 2016)

2.1.4 Topography 2.1.5 Geology and Soils The Eno River watershed is in the Piedmont Bedrock and surface deposits affect the quality and physiographic province of North Carolina. Elevation quantity of surface waters in the Eno River in the 151-square-mile watershed ranges from watershed. The western portion of the study area is approximately 249 feet at the confluence of Eno underlain by resistant metamorphic rock of the River with Little River to 757 feet in the headwaters. Carolina Slate Belt (Exhibit 5). The eastern portion of The watershed spans three ecoregions. A small the study area falls in the Triassic Basin, which is portion of the upper watershed is in the Southern composed of mostly sedimentary geology. The Outer Piedmont ecoregion. This ecoregion has lower Triassic Basin is composed of a mixture of elevations, less relief, and less precipitation than its conglomerates, sandstones, and mudstones, as well neighboring ecoregions. The landform class is as igneous dikes of Jurassic origin (Daniels et al., mostly dissected irregular plains with some rounded 1999). The Triassic Basin was formerly an inland sea hills and ridges. The central portion, and majority of consisting of sedimentary deposits of sandstone and the Eno River watershed, is in the Carolina Slate Belt siltstone. The rivers and streams in this region are ecoregion. This area is typically distinguished by generally flatter and slower moving with wider trellised drainage patterns. Streams tend to dry up, floodplains than in the western portion of the Eno and water yields to wells in this region are typically River watershed, but many years after deposition, low. The eastern portion of the watershed is in the the Durham Triassic sedimentary rocks were intruded Triassic Basins ecoregion. Local relief and elevations in places by molten diabase to create dikes and sills in the Triassic Basin are often less than in of very hard rock. Diabase is more resistant than the surrounding regions, and with rocks that are easier surrounding sandstones and siltstones and often to erode, stream valleys that cross the region tend to forms resistant ridges in the Triassic Basin (Bradley, widen (Griffith et al., 2002). 2007).

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The Carolina Slate Belt and Triassic Basin produce The Eno River watershed differs from neighboring soils with very different hydraulic properties. Carolina watersheds in the central and southern portions of Slate Belt soils typically have a moderate hydraulic the City’s jurisdiction in that it contains a much conductivity but are shallow or thin. The shallow soil higher percentage of well-drained soils. The soils thickness allows for minimal water storage in the present in other Durham watersheds such as Ellerbe surficial aquifer. Streams that drain areas of Carolina Creek, Little Lick Creek, and Third Fork Creek are Slate Belt soils often have no base flow during predominantly poorly drained. extended dry periods. The soils in the study area are classified as follows Triassic Basin soils are poorly drained and exhibit a (NRCS, 2017): low hydraulic conductivity (Dreps, 2011). · Group B: » 58% Additionally, Triassic Basin soils have a high shrink- · Group D: » 36% including undrained soils swell potential because of their clay composition. Because of these properties, the Triassic Basin soils · Group C/D: » 18% control both surface water and groundwater · Group C: » 4% hydrology in the area. The low infiltration rates result · Group B/D: » 4% in flashy streams with relatively high peak flows during storm events but low base flows due to poor · Group A or A/D: < 1% groundwater recharge (Dreps, 2011). Additional information on soil types, soil texture The Natural Resources Conservation Service (NRCS) HSG, and hydric soil indicators for the soils in the classifies soils into hydrologic soil groups (HSGs) Eno River watershed study area is presented in the based on infiltration rate and water storage capacity. Eno River Watershed Assessment Report (see Volume The four major HSGs are described in Table 2-1. Soils III, Appendix E, of this WIP) and in Exhibit 6. are often classified as a combination of two HSGs (A/D, B/D, or C/D) with the first letter representing 2.1.6 Floodplains drained areas and the second letter representing A floodplain is the low-lying ground adjacent to a undrained areas. river that is composed mainly of river sediments and is subject to flooding. Natural floodplain systems Table 2-1. Hydrologic soil groups offer many benefits including flood storage, erosion HSG Description control, enhanced water quality, groundwater Group A High infiltration rates and low runoff recharge, and increased biological habitat. potential; primarily well-drained sandy soils Floodplains allow stormwater to spread out, which reduces peak flows, and mitigates damage to Group B Moderate infiltration rates and runoff potential; consist primarily of moderate to existing infrastructure. Floodplains also support well-drained soils such as loams vegetation that filters sediment and nutrients during storm events (Wright, 2007). Group C Low infiltration rates and moderately high runoff potential; typically, sandy clays or The Eno River watershed floodplains (Exhibit 7) in clay loams Durham can generally be divided into two regions Group D Low infiltration rates and high runoff based on the physical characteristics of the two potential. Most D soils are clays and distinct underlying geologic formations described in contain a confining layer near the surface Section 2.1.5 (Carolina Slate Belt and Triassic Basin). or consist of shallow soils over bedrock. Evidence of the boundary, or fall line, between the Urban complex and gullied soils are also typically classified as Group D soils. geologic formations, can be seen from the Eno River and along trails near the US 501 bridge. Source: Natural Resources Conservation Service (n.d.) HSG = hydrologic soil group

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The river and tributaries west of US 501 are in the 2.1.7.1 Land Use Carolina Slate Belt and are typically steep and fast- Table 2-2 and Exhibits 8 and 9 present the existing moving with narrow, steep channel banks. The river and projected future land use in the study area. The and tributaries east of US 501 are in the Durham existing land use is primarily a mix of agriculture, Triassic Basin and are characterized by narrow banks parks and open space, and very low to low density with proportionally larger, wider, and flatter residential. floodplains. Large intrusions of resistant diabase ridges into erosive Triassic Basin sandstone and Based on the 2025 land use projection (City of siltstone cause the river to make sharp turns along Durham, 2016b), the primary development trend is its path eastward into Falls Lake. Such conditions the transition of agricultural and very low density have led to narrow banks with proportionally wider residential land to low density residential land. Most and flatter floodplains in sections of the Eno River. of the development is projected to occur in the upper portions of the Crooked Run Creek Additional information is presented in the Eno River subwatersheds and in the Warren Creek Watershed Assessment Report (see Volume III, subwatersheds (ER23 to ER29 and ER31 to ER38, Appendix E, of this WIP). respectively; see Exhibit 3).

2.1.7 Land Use and Impervious Cover Both commercial and industrial areas are projected to increase, but because together they currently Land use and land cover play a substantial role in occupy a small percentage of the study area (3% determining stream water quality, aquatic health, each in the existing land use), the projected land use and the hydrological response of a watershed. change is small. The projected decline in parks and Changes in land use can greatly impact the water open space in the future condition is due to the quality and aquatic habitat of surface waters. anticipated transition of vacant parcels (classified Generally, increases in development density under “parks and open space” in the existing negatively affect surface waters. condition) to residential land use categories in the

Table 2-2. Projected land use change in the study area from existing to future conditions Existing Land Use Future Land Use Projected Change

Land Use Description Acres Percent Acres Percent Acres Percent Agriculture 2,552 14% 159 1% –2,394 –94% Very Low Density Residential 2,717 15% 1,075 6% –1,642 –60% Low Density Residential 3,656 20% 8,338 45% 4,682 128% Medium Density Residential 2,232 12% 2,257 12% 25 1% High Density Residential 478 3% 445 2% –33 –7% Commercial 597 3% 766 4% 169 28% Institutional 490 3% 577 3% 88 18% Industrial 596 3% 916 5% 320 54% Parks and Open Space 3,611 19% 2,396 13% –1,215 –34% Roadways(1) 1,633 9% N/A N/A 0 0%

(1) Information necessary to project roadway land use N/A = not available in 2025 was insufficient. Source: City of Durham (2016b)

2-6 Eno River Watershed Improvement Plan, Volume II AECOM future condition. A detailed description of land use Most of the impervious cover occurs in evaluations and changes projected to occur in each subwatersheds south of the Eno River along the US subwatershed is presented in the Eno River 501 corridor. The subwatersheds (see Exhibit 3) Watershed Assessment Report (see Volume III, range from 0 to 35% impervious. The Warren Creek Appendix E, of this WIP). watershed upstream of Horton Road (subwatersheds ER34 to ER38) is approximately 23% impervious. The 2.1.7.2 Impervious Cover upstream watershed draining to the Cub Creek (subwatersheds ER07 to ER12) is approximately 33% Impervious area greatly affects both the hydrologic impervious. Crooked Run Creek watershed response of a watershed and the water quality of (subwatersheds ER23 to ER29) is approximately 9% surface waters. As impervious area increases, streams impervious with portions of the lower watershed at often exhibit higher peak flows and total volumes in 19% impervious. Other portions of the watershed response to storm events and also lower base flows. exhibiting high percentages of impervious cover Pollutants such as nutrients, bacteria, and heavy include the southwestern portion of the study area, metals deposited on impervious surfaces are with 21% to 24% impervious cover and catchments transported to streams through stormwater runoff and along the US 501 corridor with 23% to 29% leading to water quality degradation. Additionally, impervious cover. the high peak flows result in increases in shear stress. Sheer stress accelerates bank erosion and At approximately 12% impervious, the overall study stream scour, which are often a significant source of area is slightly less impervious than other watersheds sediment. in the city, including Ellerbe Creek (City of Durham, 2010), Third Fork Creek (City of Durham, 2012a), The impervious cover in the study area was Northeast and Crooked Creek (City of Durham, determined using the best available data for each 2013a), and Little Lick Creek (City of Durham, 2016a). type of impervious area. The sources of the data are provided in the Eno River Watershed Assessment Table 2-3 provides a summary of impervious area Report (see Volume III, Appendix E, of this WIP). and percentage associated with each of the City’s Based on 2013 to 2016 data, the impervious area in monitoring stations in the Eno River watershed. the larger study area is approximately 12%, and the A map displaying the impervious cover in the study impervious area in the city limits is approximately area is included as Exhibit 10. Volume III, Appendix E, 22%. of this WIP provides additional information on the impervious area in each subwatershed.

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Table 2-3. Impervious cover and drainage area at City water quality monitoring locations Impervious Area Drainage Station Stream Area (sq mi) Sq mi Percent(1) EN4.9ER Eno River 149 6.6 4.4% EN8.9ER Eno River 142 5.5 3.9% EN13.3ER Eno River 121 3.3 2.7% EN9.6CRC Crooked Run Creek 4.5 0.3 7.0% EN10.3WC Warren Creek 2.4 0.5 22.4% EN7.7ERT1 Unnamed Tributary 2.5 0.5 20.7% EN12.2ERT3 Unnamed Tributary 1.2 0.1 5.8% EN6.5CC Cub Creek 3.7 0.6 16.6%

(1 ) Only building footprints and roadways are included in estimating impervious area outside city limits. Other impervious areas, such as sidewalks and parking lots, were not available for this analysis. Additionally, nutrient loading associated with North Carolina Department of Transportation (NCDOT)-managed roadways and sidewalks are the responsibility of NCDOT. For these reasons, percentages provided for drainage areas not located entirely within city limits may underrepresent the actual impervious percentage.

The classifications of the surface water in the Eno 2.2 Water Quality Conditions River watershed study area are listed below and One of the goals of the Eno River WIP is to protect shown on Exhibit 11. areas of the watershed with healthy surface waters · Class C (Primary): All surface waters in the State of and improve areas of the watershed where there are North Carolina are subject to water quality water quality concerns. The starting point for standards associated with Class C uses, which achieving this goal is to determine the existing water include secondary recreation, fishing, wildlife, fish quality and compare it to water quality standards. consumption, and aquatic life propagation Section 2.2.1 provides the following: (NCDEQ, 2018). · Surface water classifications established by the · Class B (Primary): Waters are protected for all State of North Carolina and the City Class C uses with the addition of primary contact recreation. Portions of the Eno River upstream of · Water quality monitoring in the Eno River Roxboro Road are designated Class B (NCDEQ, watershed 2018). · Sediment sampling in the Eno River watershed · Water Supply IV (WS-IV; Primary): Waters used as water supply for drinking or culinary or food 2.2.1 Surface Water Classifications processing purposes that cannot feasibly meet The North Carolina Department of Environmental WS-I through WS-III standards, which are the Quality (NCDEQ) classifies surface waters in North most stringent (NCDEQ, 2018). The WS-IV Carolina according to the best uses of the surface classification includes two protection zones: a water, such as swimming, fishing, and drinking water critical area within 0.5 mile of the Falls Lake supply. The classifications are used to manage and normal pool and a protected area within 5 miles protect all streams, rivers, lakes and other surface of the Falls Lake normal pool. waters (NCDEQ, 2018).

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· Nutrient Sensitive Waters (Supplemental): Waters · ENR-8.3: UNRBA station near EN4.9ER and that require additional nutrient management J0810000 because of excessive microscopic and · ENR-23: UNRBA station near EN13.3ER macroscopic aquatic vegetation. The entire Neuse River Basin, which includes the Falls Lake and Eno Table 2-4 lists the water quality stations in the study River watersheds, is classified as a Nutrient area and the available monitoring data for the Sensitive Water. stations. Water quality data are also available through the City’s water quality website at 2.2.2 Water Quality Monitoring http://www.durhamwaterquality.org. The City, UNRBA, and NCDEQ maintain water quality In general, the data indicate better water quality in and biological monitoring stations in the Eno River the Eno River mainstem than in the contributing watershed study (see Exhibit 12). The stations are tributaries, which is largely a reflection of the larger listed below. portion of urban land uses in the smaller drainage areas. The monitoring station on Crooked Run Creek · EN4.9ER: City station on the Eno River at Snow at Latta Road demonstrates high bacteria and Hill Road; most downstream City station with a turbidity. Water quality in Warren Creek shows drainage area of approximately 149 square miles elevated concentrations of fecal coliform bacteria in · EN8.9ER: City station on the Eno River at the West all monitored years, low dissolved oxygen Point on the Eno Park upstream of Roxboro Road concentrations during 3 of the 6 monitored years, with a drainage area of approximately 142 square and elevated total nitrogen (TN) during 2 of the miles 6 monitored years. · EN13.3ER: City station on the Eno River at Cole The water quality concerns in the study area based Mill Road with a drainage area of approximately on the monitoring data are listed in Table 2-5. 121 square miles The City publishes a summary of the results of the · EN9.6CRC: City station on Crooked Run Creek at water quality monitoring performed by the City in an Latta Road near the confluence with the Eno River annual report titled State of Our Streams (City of with a drainage area of approximately 4.5 square Durham, 2016c) and combines the water quality miles measurements into a WQI. The State of Our Streams · EN10.3WC: City station on Warren Creek at reports are available at Horton Road with a drainage area of http://durhamnc.gov/708/State-of-Our-Streams. The approximately 2.4 square miles WQI is a numerical “grade” that ranges from 0 (poor) · EN7.7ERT1: City station on unnamed tributary to to 100 (excellent) and indicates the overall health of Eno River at Hebron Road with a drainage area of the City’s streams. In the 2016 report, the WQI was approximately 2.5 square miles based on the results of BOD, bacteria, nutrients, · EN12.2ERT3: City station on an unnamed tributary turbidity, and metals monitoring data. The City is to the Eno River at Sterling Drive; represents a currently revising the WQI methodology. drainage area of approximately 1.2 square miles Table 2-6 lists the average WQI for all of the years in · EN6.5CC: City station on Cub Creek near Stanley which it was computed for the five City water quality Road; limited data available; represents a stations in the Eno River watershed. The City drainage area of approximately 3.7 square miles combines the WQI values computed for all stations within a watershed to obtain a watershed WQI. In · J0770000 (JB007 benthic): NCDEQ station near the most recent State of our Streams report, the Eno EN8.9ER River watershed was assigned a WQI of 86 (City of · J0810000 (JB003 benthic): NCDEQ station near Durham, 2016c). Between 2004 and 2016, the WQI EN4.9ER for Eno River ranged between 86 and 99, averaged

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Table 2-4. Water quality sampling stations in the Eno River watershed study area and dates of available monitoring data Dates of Available Monitoring Data on Water Characteristics

Active/ Dissolved Fecal Benthic Station ID Agency Inactive Nitrogen Phosphorus Oxygen Turbidity Coliform Macroinvertebrates

EN4.9ER City Active 2004–2009, 2004–2009, 2004–2010, 2004–2010, 2004–2010, 2012, 1999–2012, 2014–2016 2012, 2014 2012, 2014 2012, 2014 2012, 2014 2014

EN8.9ER City Active 2004–2016 2004–2016 2004 – 2016 2004 – 2016 2004 – 2016 1999–2005, 2007–2012, 2014–2016

EN13.3ER City Active 2004–2010, 2004–2010, 2004–2010, 2004–2010, 2004–2010, 2012, N/A 2012, 2014, 2016 2012, 2014, 2016 2012, 2014, 2012, 2014, 2014, 2016 2016 2016

EN9.6CRC City Active 2009, 2012, 2009, 2012, 2008–2010, 2008–2010, 2008–2010, 2012, N/A 2014, 2016 2014, 2016 2012, 2014, 2012, 2014, 2014, 2016 2016 2016

EN10.3WC City Active 2008, 2010, 2008, 2010, 2008–2010, 2008–2010, 2008–2010, 2012, N/A 2012, 2014, 2016 2012, 2014, 2016 2012, 2014, 2012, 2014, 2014, 2016 2016 2016

EN7.7ERT1 City Inactive N/A N/A 2008 2008 2008 N/A

EN12.2ERT3 City Inactive N/A N/A 2008 2008 2008 N/A

EN6.5CC City Inactive 2013–2014 2013–2014 2013–2014 2013–2014 N/A N/A

J0770000 NCDEQ Active 1981–2016 1981–2016 1968–1975, 1970, 1975, 1968, 1970–1975, 1984, 1986, 1988, 1990, (JB007 benthic) 1981–2016 1981–2016 1981–1986, 1994– 1995, 2000, 2005, 2006, 2016 2010, 2015

J0810000 NCDEQ Active 1972, 1974– 1975–1980, 1968–1980, 1970, 1974– 1970, 1972–1980, 1985, 1991, 1995, 2000, (JB003 benthic) 1980, 1987–2016 1987–1996, 1986–2016 1980, 1987– 1994–2016 2005, 2006 2008–2016 2016

ENR-8.3 UNRBA Active 2014–2016 2014–2016 2014–2016 N/A N/A N/A

ENR-23 UNRBA Active 2014–2016 2014–2016 2014–2016 N/A N/A N/A

City = City of Durham NCDEQ = North Carolina Department of Environmental Quality N/A = not available UNRBA = Upper Neuse River Basin Association

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Table 2-5. Water quality in the study area Water Characteristic Water Quality Standard(1) Water Quality in Study Area

Dissolved oxygen (DO) Daily average not less than 5 mg/L and an instantaneous value DO measurements collected during 2008-2016 indicate good conditions at all of not less than 4 mg/L monitoring locations with the exception EN10.3WC where occasional occurrences of low DO were present during five of seven years with water quality data.

Fecal coliform bacteria Geometric mean less than 200 cfu/100 mL based on five Fecal coliform measurements collected during 2008-2016 indicate low bacteria consecutive samples during a 30-day period and does not concentrations throughout the Eno River mainstem and occasionally-elevated exceed 400 cfu/100 mL in more than 20% of the sample concentrations in Warren Creek (EN10.3WC) and Crooked Run Creek (EN9.6CRC). collected during the same period)

Turbidity 50 Nephelometric Turbidity Units (NTUs) Turbidity measurements collected during 2008-2016 indicate low concentrations are generally present in both the mainstem Eno River and monitored tributaries. The average annual turbidity concentration was below 50 NTUs for all stations.

Dissolved copper Water quality standard is defined using the Criterion Dissolved copper does not appear to be a problem pollutant in the Eno River Continuous Concentration (CCC), calculated to be 3.6 µg/L in watershed. The City’s ambient water quality monitoring program has collected water the Eno River.(2) samples with elevated copper levels in Warren Creek. These occurrences have been infrequent. In 2017, in-situ copper measurements at twenty predetermined locations within the Warren Creek subwatershed failed to detect the presence of copper.

Zinc Water quality standard is defined using the CCC calculated to Zinc does not appear to be a problem pollutant in the Eno River watershed. be 47.9 µg/L in the Eno River.(2)

Nutrients There are no numeric standards for total nitrogen (TN) or total The average TN concentration exceeded the Durham benchmark of 0.8 mg/L in phosphorus (TP) established or enforced by the State of North 1 out of 13 years at station EN8.9ER, 1 out of 10 years at station EN13.3ER (both in Carolina though the City applies a TN benchmark of greater 2004), and 2 out of 5 years at station EN10.3WC. The average TP concentration was than 0.8 mg/L but less than 1.0 mg/L and a TP benchmark of below the Durham benchmark of 0.08 mg/L for all years at all stations. less than 0.08 mg/L as part of its WQI.

Biochemical oxygen There are no numeric standards for BOD though the City The average BOD concentration was below 3 mg/L for all years at all stations. demand (BOD) applies a benchmark of greater than 2 mg/L but less than 4 mg/L as part of its WQI.

Chlorophyll a The North Carolina water quality standard for chlorophyll a is Chlorophyll a is not monitored or regulated in flowing streams such as the Eno not to exceed 40 µg/L. River. In 2008, downstream Falls Lake was placed on the 303(d) list for elevated chlorophyll a concentrations. Because the Eno River drains to the Falls Lake, nutrient management measures within the Falls Lake watershed encompass the Eno River watershed.

(1) Source: NCDEQ (2018b) cfu = colony-forming unit WQI = Water Quality Index (2) Calculated using the average hardness of 34 mg/L from all hardness samples collected at mg/L = milligrams per liter µg/L = microgram per liter the three City-maintained ambient monitoring locations along the Eno River. ml = milliliter

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Table 2-6. Average WQI for Eno River watershed water quality monitoring stations Average Number of Years Station Stream WQI of Data WQI Based On EN4.9ER Eno River 90 8 years EN8.9ER Eno River 93 13 years EN13.3ER Eno River 92 10 years EN9.6CRC Crooked Run Creek 89 4 years EN10.3WC Warren Creek 78 5 years

WQI = water quality index

92 (an “A” grade) and was the highest average WQI the sediment (City of Durham, 2014b). “Threshold for all watersheds in the city during that period (City effect concentration” is defined as “concentration in of Durham, 2018b). While a score of 92 indicates that media (surface water, sediment, soil) to which a plant water quality in the Eno River watershed is in overall or animal is exposed, above which some effect (or good condition, the lower scores at stations response) will be produced and below which it will EN9.6CRC and EN10.3WC indicate the potential for not” (USEPA, 2018). improvement in the Crooked Run Creek and Warren The Warren Creek subwatershed is also the only Creek subwatersheds. subwatershed in the study area that exhibited The average WQI scores for both the Crooked Run detectable concentrations of polycyclic aromatic Creek (89, a “B” grade) and Warren Creek (78, a “C” hydrocarbons (PAHs); the sediment samples showed grade) stations were negatively affected by high six of the eight PAH compounds that the samples fecal coliform bacteria counts and high turbidity were tested for. measurements. Elevated fecal coliform bacteria This Eno River water quality study (City of Durham, counts inhibit recreational opportunities, and high 2014b) concluded that there is an absence of acute turbidity values negatively impact water clarity. In toxicity concerns in sediment in Warren Creek; addition to elevated fecal coliform and turbidity however, exposure to chronic toxicity levels of values, the Warren Creek station is also impacted by chromium and PAHs is a potential concern for low DO values. Low DO values negatively impact benthic macroinvertebrates inhabiting stream aquatic life such as benthic macroinvertebrates and sediment. This study also concluded that elevated fish. chromium in sediment in Warren Creek does not appear to be adversely affecting overlying waters. 2.2.3 Sediment Monitoring The City performs source tracking and elimination As previously noted, the City conducted an extensive programs to address these and other metals water quality study for the Eno River watershed concerns throughout Durham’s watersheds. Recent between July 2013 and June 2014 that included examples include evaluations of pollutants in sediment sampling (City of Durham, 2014b). The wastewater produced from air conditioning cleaning sediment monitoring data revealed elevated operations in Durham (City of Durham, 2016d) and sediment chromium in Warren Creek at Horton Road evaluation of pollutants in wastewater generated by as well as at Snow Hill Road, the most downstream mobile car washing operations (City of Durham, site in the Eno River. The chromium concentrations 2014c). exceed the USEPA’s threshold effect concentration and indicate potentially toxic levels of chromium in

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2.3 Watershed Impacts and of elevated turbidity and fecal coliform bacteria and evidence of eroded banks are present throughout Sources of Pollution the study area, but the predominant impacts in the The USEPA defines nonpoint source pollution as study area are located in the Warren Creek and pollution that “results from land runoff, precipitation, Crooked Run Creek watersheds. Elevated fecal atmospheric deposition, drainage, seepage or coliform and low DO concentrations are common in hydrologic modification” (USEPA, 2017). Unlike point both Warren Creek and Crooked Run Creek, and source pollution, which may be linked to a discrete elevated chromium and PAH concentrations are source such as wastewater discharge from a pipe, documented in sediment samples in the Warren nonpoint source pollution is diffuse and comes from Creek watershed. a variety of natural and anthropogenic sources that The Eno River Watershed Assessment Report (see are carried by runoff as it flows to streams and Volume III, Appendix E, of this WIP) describes the waterbodies (USEPA, 2017). potential nonpoint sources identified during field The Eno River watershed exhibits overall good water investigations. Key source categories and watershed- quality (City of Durham, 2018c). Several indicators of specific concerns are presented in Table 2-7. A nonpoint source impacts are evident in water quality summary of potential nonpoint sources and impacts data and field assessments. Occasional occurrences in the Eno River watershed is presented in Table 2-8.

Table 2-7. Summary of Eno River watershed pollution sources Source Description Stormwater runoff · Increased impervious cover can result in increased stormwater runoff, higher peak flows, lower from impervious base flows, and reduced groundwater recharge. surfaces · Impervious cover accounts for approximately 12% of the study area. · The percentage of impervious cover in 18 of the 53 subwatersheds in the study area was found to be above 15%. · Eleven of the 25 subwatersheds in the southern portion of the study area have relatively large amounts of impervious cover that account for between 20 and 35% of their respective subwatershed areas. Animal waste · Animal waste deposits from both domestic house pets and wild animals such as deer and geese are potential sources of fecal coliform. · While additional information is needed, pet waste is a potential contributor to fecal coliform exceedances in the Eno River watershed.

Wastewater · Nutrients and fecal coliform associated with wastewater reduce water quality, contribute to collection systems growth of aquatic macrophytes, and reduce DO levels. · Annual loading from septic systems, sand filters, and sanitary sewer system overflows is estimated to be 2,829 lbs TN/yr and 357 lbs TP/yr within the City’s jurisdiction (see Volume III, Appendix E, of this WIP). · Water quality data collected in both the Crooked Run Creek and Warren Creek subwatersheds show elevated levels of fecal coliform bacteria. Approximately one third of septic systems (597 of 1813) and sand filters (49 of 141) in the study area are located in the Crooked Run Creek and Warren Creek subwatersheds (Exhibit 13). Approximately 20% of sanitary sewer overflows reported by the City within the study area between December 1999 and June 2016 were located in the Crooked Run Creek and Warren Creek subwatersheds.

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Table 2-7(cont.). Summary of Eno River watershed pollution sources Source Description Illicit discharges · Examples of illicit discharges include petroleum spills, improper disposal of yard waste, public sanitary sewer overflows, and cooking related wastes like oil, grease, and food that are discharged into storm drains or enter storm drains from overland runoff. · Field biologists noted evidence of illicit discharges while performing stream assessments in the Eno River watershed including a chemical odor from a surface pond, evidence of what appeared to be an oily substance on the water surface, and a sanitary sewer leak (see Exhibit 14). These observations were reported to the Public Works Department staff who investigate and resolve any illicit discharges. These illicit discharges are documented in the State of Streams Report. Streamflow · Beaver dams were noted as potential water quality concerns during stream assessments. impediments · While beaver dams may negatively impact flow and DO levels, they also provide positive effects in the management of legacy sediment. Legacy sediment · The historical record of mill dams on the Eno River suggests the presence of more than 30 gristmills during the 17th to 19th centuries on the Eno River (North Carolina State Parks, n.d.). · Legacy sediment associated with historical mill dams may be contributing to the total sediment load in the Eno River watershed (Wegmann et al., 2012 and Wegmann et al., 2013). Degraded riparian · Degraded riparian buffers result in increased bank erosion and sediment inputs to surface waters. buffer · In the Eno River watershed, field investigations identified more than 50,000 linear feet of stream in 35 reaches that would benefit from restoration, enhancement, or stabilization. Degraded habitat · The abundance and diversity of fish and benthic macroinvertebrates are impacted by the physical characteristics, substrate composition, and riparian area features of a stream. · Healthy stream habitat in the Piedmont physiographic province of North Carolina is characterized by a diversity of riffles and pools as well as healthy, riparian buffers that stabilize banks, moderate temperatures, and filter pollutants from overland runoff. · A 2014 assessment of watershed habitat in the Eno River watershed found that habitat scores were variable throughout the watershed, ranging from 50 in Cub Creek (EN6.5CC) to 92 in an unnamed tributary to the Eno River (EN12.2ERT3) (City of Durham, 2014). Habitat scores were strongly influenced by geology and land use in the watershed. Sites in the Triassic Sedimentary Basin generally scored low while those in the Slate Belt generally scored higher (City of Durham, 2014). In 2017, the City performed additional habitat assessments at two locations in the watershed, the Eno River mainstem at Guess Road and the Eno River mainstem at Sterling Drive, and found that the instream habitat at both locations was of excellent quality at those locations (see Volume III, Appendix M, of this WIP · Rapid Stream Assessment Technique (RSAT) assessments in the Eno River watershed revealed that, among the 49 stream miles assessed, 1% of streams are rated “excellent”, 41% are rated “good”, 53% are rated “fair”, and 5% are rated “poor” (Exhibit 15). The distribution of RSAT rating throughout the study area shows that the overall stream health is good, but that some areas in poor health.

DO = dissolved oxygen lbs TN/yr = pounds total nitrogen per year n.d. = no date

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Table 2-8. Summary of potential nonpoint sources and impacts in the Eno River watershed Identified Management Impact Potential Sources Indicator Supporting Documentation Recommendation Bacteria Leaking septic systems, sand filters, Fecal coliform Durham Water Quality Data Behavioral changes, programmatic SSOs and other sewage discharges, Portal(1) changes, sanitary sewer system animal waste, legacy sediment upgrades Sediment Stream bank erosion, legacy TSS, turbidity, BEHI, aquatic Durham Water Quality Portal,(1) Riparian buffer planting, improved sediment, improper ESC practices, habitat ratings field assessments ESC practices, behavioral changes degraded riparian buffer Increased Increased impervious surfaces, Incised streams, aquatic Discharge data(2) SCMs, riparian buffer plantings peak flows degraded riparian buffer, vegetation habitat ratings, increased removal frequency of high flow events Excess Impervious runoff, poorly Total N and Total P Field assessments, Falls Lake SCMs, environmental education, nutrients functioning septic systems, sand concentrations, chlorophyll a, Rules,(3) Eno River Watershed riparian buffer planting filters, SSOs and other sewage DO measurements, invasive Implementation Data discharges, degraded riparian buffer, aquatic macrophytes Collection,(4) Eno River Aquatic landscaping practices (fertilizer), Vegetation Survey,(5) NC animal waste, legacy sediment, soil, Invasive Plant Council atmospheric deposition, yard waste

Increased Impervious runoff, paint, roofing, Metals (Cu, Cr, Zn), NCIBI Durham Water Quality Portal, SCMs (bioretention and wet heavy metals brake pads, automobiles, metal ratings Eno River Implementation Data ponds), behavior changes workshops, geology, illicit Collection discharges, pesticides, algaecides, cooling water, atmospheric deposition Low DO Sewage, excess nutrients, sediment, DO measurements, NCIBI Durham Water Quality Portal, SCMs, riparian buffer planting, degraded riparian buffer, beaver ratings Northeast Creek Watershed beaver management, reconfiguring dams, low-head dams, illicit Modeling Services WASP problematic culverts, stream discharges, leaves, roadway culverts Modeling(6) restoration, baseflow augmentation

(1) http://www.durhamwaterquality.org BEHI = Bank Erosion Hazard Index N = nitrogen SSO = sanitary sewer overflow (2) USGS (n.d.) Cu = copper NCIBI = North Carolina Index of Biotic TSS = total suspended sediment (3) NCDEQ (2011) Cr = chromium Integrity WASP = Water Quality Analysis Simulation (4) City of Durham (2014b) DO = dissolved oxygen P = phosphorus Program (5) City of Durham (2014a) ESC = erosion and sediment control SCM = stormwater control measure Zn = zinc (6) City of Durham (2013c)

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3 Stream Inventory and Assessment and Project Opportunities

Streams play a vital role in both water quality and to prioritize restoration and enhancement watershed health. The physical condition of streams projects also controls the ecological benefits and suitable Stream assessments were performed in January 2017 aquatic habitat that they can provide. along 49 miles of stream that included 169 stream reaches. The field teams partitioned reaches at break 3.1 Stream Field Inventory and points based on continuity in channel conditions Assessment Methodology such as cross-sectional dimensions, riparian buffer condition, and sinuosity. Reaches continued until The total stream length in the study area is field teams determined an obvious change in stream 134 miles, based on the City’s stream hydrography type or level of impacts. GIS data. With support from City staff, field teams assessed existing stream channel conditions and The field teams performed two levels of stream riparian corridors and identified water quality assessments. Level 1 consisted of rapid, field-based problems as part of a stream inventory and data collection to meet objectives #1 through #5. assessment. The field teams also identified potential Level 2 assessments were performed on a subset of watershed improvement projects. The stream Level 1 streams and involved collecting more reaches that were assessed were identified and the detailed datasets to meet objective #6. The levels of assessment were determined using GIS methodology for both Level 1 and Level 2 data. The two levels were Level 1 (rapid) and Level 2 assessments is described in detail in the Stream (comprehensive). Assessment Field Plan (see Volume III, Appendix B, of this WIP). The six objectives of the stream assessment were as follows: 3.2 Results of Stream Field 1. Collect data on the physical condition of the streams and riparian buffers in the watershed Assessments 2. Identify stream reaches and riparian buffers in Section 3.2 provides a summary of the field stream need of restoration, enhancement, or assessment results. A detailed summary is provided preservation in the Eno River Watershed Assessment Report (see Volume III, Appendix E, of this WIP). 3. Identify sources of pollution along the stream corridors in the watershed Of the stream miles that were assessed, 1% were 4. Identify problems with public utilities that cross rated excellent, 41% were rated good, 53% were or are adjacent to streams rated fair, and 5% were rated poor. Figure 3-1 is an example of a stream reach with excellent overall 5. Collect information that would be needed for stream conditions, and Figure 3-2 is an example of a watershed modeling stream reach with poor overall stream conditions. 6. Collect detailed information on Level 2 stream Of the 44 subwatersheds in which streams were reaches that could be used to estimate assessed, 10 contained streams that received a RSAT streambank erosion rates, which could be used rating of poor (Exhibit 15).

Eno River Watershed Improvement Plan – Volume II 3-1 AECOM

Figure 3-1. Example of a stream reach with an excellent overall stream condition rating: Reach 2061 located at Infinity Road approximately 1,600 feet upstream of the confluence with Eno River in ER20

Figure 3-2. Example of a stream reach with a poor overall stream condition rating: Reach 2038, located downstream of Danube Lane in ER11

3-2 Eno River Watershed Improvement Plan, Volume II AECOM

In only 3 of the 10 subwatersheds, more than half of Enhancement II, bank stabilization, and preservation, the assessed stream length was rated poor. as defined by the U.S. Army Corps of Engineers Additionally, 26 of the subwatersheds contained (USACE) (USACE, 2003): streams with an RSAT rating of good. The entire · Stream restoration: Converts an unstable, length of the Eno River mainstem in the study area altered, or degraded stream corridor, including received an RSAT rating of good. The distribution of adjacent riparian buffers and floodplain, to its the RSAT rating throughout the study area shows natural, stable condition. Includes restoring a that the overall stream health is good but poor in naturally stable channel planform pattern, some localized areas (Exhibit 15). longitudinal profile (riffle/pool sequence) and The primary water quality concerns identified during channel cross section dimensions as well as the stream field assessments were debris dams and biological and water quality functions. threatened or exposed utilities. Beaver dams and Number of stream reaches identified for stream activity were prevalent along Warren Creek, Cub restoration projects: 10. Creek, and an unnamed tributary flowing into the · Enhancement I: Improvements to the stream Eno River. Debris dams have the potential to create channel and riparian zone that restore channel significant backwater conditions that increase the stability, water quality, and stream ecology. Re- risk of flooding, erosion, and water quality establishing channel cross-section dimensions impairment. and longitudinal profile are proposed, but Results of the Bank Erosion Hazard Index (BEHI) and restoration of channel pattern is not feasible or Near Bank Stress analysis indicated that of the 91 warranted. May also include other practices that stream reaches where Level 2 stream assessments provide improved water quality and ecological were performed, 62 reaches (approximately 12 benefits. stream miles) were found to have estimated Number of stream reaches identified for sediment yields of less than 20 tons/year (Exhibit 16). Enhancement I projects: 10. The remaining 29 reaches (approximately 13 stream · Enhancement II: Activities that improve channel miles) had estimated sediment yields of more than stability, water quality, and stream ecology but do 20 tons/year. Beaver activity was found to be present not include re-establishing the channel profile or in the two reaches with the largest sediment yield, pattern. May include re-establishment of the but it is unclear what effect their presence had on channel’s cross section as needed. May include estimated sediment yield. other practices that provide improved water quality and ecological benefits. 3.3 Potential Stream Project Number of stream reaches identified for Opportunities Enhancement II projects: 12. Opportunities to improve stream health throughout · Bank stabilization: In-place stabilization of an the study area were identified during the stream eroding streambank. Techniques include sloping inventory assessment. The opportunities are streambanks to a less vertical and more stable described in detail in the Stream Assessment Field angle, installing streambank revetments with Plan (Volume III, Appendix B, of this WIP). natural materials such as root wads or brush toe, Of the 169 stream reaches that were assessed by and revegetating banks and riparian buffers field crews, 65 were identified as potential stream without seeking to re-establish cross section improvement project opportunities (Exhibit 17). The dimensions. types of potential projects that were considered Number of stream reaches identified for bank were stream restoration, Enhancement I, stabilization projects: 3.

Eno River Watershed Improvement Plan – Volume II 3-3 AECOM

· Preservation: Establishing protection of adjacent to the stream necessary to ensure ecologically important streams (generally protection or enhancement of the overall stream. considered for high-quality streams) in perpetuity Number of stream reaches identified for by implementing protective mechanisms. May preservation projects: 30. include the protection of upland buffer areas

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4 Stormwater Control Measure Inventory, Assessment, and Project Opportunities

Field teams composed of staff from the AECOM 62 potential sites for new SCMs. The potential sites Team and the City completed an SCM inventory and were identified before the fieldwork through a GIS field assessment in November 2016 and identified pre-screening analysis. opportunities to improve the current level of A more detailed discussion of the GIS-based desktop stormwater and water quality treatment in the Eno analysis and field assessment methodology for both River watershed study area. The opportunities focus existing and potential new SCMs is available in the on retrofits or modifications to existing SCMs to SCM Inventory and Assessment Field Plan (see improve their function and water quality treatment Volume III, Appendix C, of this WIP). performance and on developed areas that are not currently receiving treatment but are suitable for new SCMs. 4.1 SCM Field Assessment Methodology The higher percentage of well-drained soils in the Eno River watershed compared to other Durham Field crews followed the procedures and protocols in watersheds allows the consideration of SCMs that the SCM Inventory and Assessment Field Plan (see promote infiltration and that are not feasible in other Volume III, Appendix C, of this WIP) and used tablets nearby watersheds. and forms that were developed in Survey 123 for ArcGIS software (Esri, n.d.) to collect the following The field crews did not focus on undeveloped areas information for each existing SCM and feature: of the watershed because future development will require on-site stormwater controls that comply with · SCM ID, subwatershed ID, date, surrounding land the Falls Lake Rules (NCDEQ, 2011) and the Unified use, HSG, receiving waterbody, and confirmation Development Ordinance (UDO) (Durham City- of SCM type County Planning Department, 2018) administered by · Photographs of individual SCM components and both the City and Durham County. the site A total of 140 SCMs were field-evaluated. The City · Physical measurements and information on SCM provided data on 128 existing SCMs in the Eno River components such as inlets, outlets, riser watershed. Of the 128 SCMs, 62 were recommended structures, and emergency spillways for further evaluation by field teams following a GIS- · Potential retrofits or modifications to improve based desktop pre-screening analysis (Exhibit 18). water quality treatment Field evaluations included an assessment of existing · Site constraints that would prevent installation or SCMs to evaluate retrofit opportunities and identify required maintenance activities for potential SCMs that were not functioning properly due to retrofits including potential conflicts with known design or maintenance issues. Field crews also utilities and infrastructure, proximity to inventoried and evaluated 16 existing features (4 dry jurisdictional streams or wetlands, access for ponds, 10 wet ponds, 1 level spreader, and construction and maintenance, encroachment on 1 stormwater wetland) that were not included in the to adjacent properties, and environmental City’s SCM database. Finally, field crews visited impacts or permitting requirements

Eno River Watershed Improvement Plan – Volume II 4-1 AECOM

· Evaluation of the current SCM condition and Field crews also identified and evaluated 4 dry functionality and an evaluation of any required or ponds, 10 wet ponds, 1 level spreader, and recommended maintenance activities 1 stormwater wetland. These 16 features are not in the City’s SCM database and are not referred to as Field crews visited each potential new SCM site to SCMs because it is not known whether they were verify the information identified during the GIS pre- designed as SCMs. screening process. Field crews assessed the following factors at each potential new SCM site: Field crews evaluated each existing SCM for · Site constraints not identified during the GIS pre- structure, volume, and add-on retrofits. Structural screening including potential conflicts with known retrofits focus on modifications to the SCM’s outlet utilities and infrastructure, proximity to structure. Modifications can include changing the jurisdictional streams or wetlands, access for elevation of the normal pool through a simple construction and maintenance, encroachment on control structure modification to provide additional to adjacent properties, and environmental storage volume or a complex redesign of an entire impacts or permitting requirements SCM to convert it to another type of SCM (e.g., converting a dry pond to a pocket wetland). · Potential new SCM type, length, and width of available area and a completed sketch of the Volume retrofits involve increasing the storage potential new SCM volume of an existing SCM so it can treat a larger volume of stormwater runoff or provide a longer · Contributing drainage area additions: primary and retention time. Volume retrofits typically require secondary options for small-scale (parcel-level) expanding the existing SCM’s footprint. SCMs that could be implemented to create a treatment train (series of SCMs) Add-on retrofits do not require changing the storage · Type of receiving waterway or waterbody volume or SCM footprint. These retrofits focus on enhancing the current water quality treatment · Site photographs: conditions at potential inlet capability by adding components such as a forebay, and outlet, conditions at potential discharge level spreader, or floating wetlands to existing SCMs. location, and a completed SCM sketch Of the 62 existing SCMs that field crews visited, 27 The results of the SCM inventory and assessment were determined to be candidates for retrofits and were documented in two GIS geodatabases—one for recommended for further evaluation. Additionally, of existing SCMs and another for potential new SCMs. the 16 existing features not in the City’s SCM The results and description of the retrofit database that field crews visited, 9 were determined opportunities to existing SCMs and features and new to be candidates for retrofits and recommended for SCM opportunities are summarized below. further evaluation. 4.2 Retrofit Opportunities The two most common retrofit opportunities are: to Existing SCMs · Converting an existing dry pond into a pocket wetland or constructed wetland (see Figure 4-1) The 62 existing SCMs in the Eno River watershed that · Water quality improvements to existing wet were evaluated by field crews included 31 dry ponds, 21 wet ponds, 6 bioretention cells, 3 stormwater ponds (see Figure 4-2) wetlands, and 1 sand filter. Of the 62 existing SCMs SCM performance can be less than optimal if the that were evaluated, 40 were in residential areas, 18 SCM design is older and less efficient, if the were in institutional areas (e.g., schools, churches, construction was poor, or maintenance is poor. Each libraries), 3 were in industrial areas, and 1 was in a existing SCM’s performance was evaluated during commercial area (Exhibit 19). the SCM Inventory and Assessment. Of the 62 existing SCMs that were evaluated by field crews, 20

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Figure 4-1. Example of a retrofit opportunity in an existing dry pond (SCM 00060). This dry pond could be converted to a pocket wetland to improve water quality treatment. Because there is ample space available at the site, the basin could be enlarged by increasing its length and width, which would allow for additional treatment capability.

Figure 4-2. Example of a retrofit opportunity to an existing wet pond (SCM 00055). Water quality improvement opportunities include (1) redesigning the control structure, (2) adding a level spreader to the outlet, (3) adding floating wetland islands, and (4) planting vegetation to stabilize/uptake nutrients.

Eno River Watershed Improvement Plan – Volume II 4-3 AECOM were identified as requiring maintenance to function bioretentions, 6 constructed wetlands, 4 pocket properly. The predominant maintenance concerns wetlands, 4 wet ponds, a dry pond, and a wet swale were overgrown vegetation and substantial amounts (Exhibit 20). of undesirable vegetation (mainly cattails). Poorly A treatment swale with wet conditions is a swale with managed vegetation can lower an SCM’s storage both swale and wetland functions (see Figure 4-3). capacity, obstruct flow, and reduce performance. The current Stormwater Control Measure Credit These SCMs were reported to City staff so SCM Document (NCDEQ, 2017) states that treatment owners could be notified to perform needed swales with wet conditions provide enhanced maintenance. removal and lower event mean concentrations 4.3 Potential New SCMs (EMCs) for TN and TP. Of the 62 potential new SCM sites visited by field Of the 24 potential new SCMs recommended for crews, 24 were determined to be suitable for a new further evaluation, 10 are in residential areas, 9 are in SCM. The 24 potential new SCM sites include 8 institutional areas, 3 are in industrial areas, and 2 are in a commercial area.

Figure 4-3. Potential new SCM site in which a wet swale was recommended. A treatment swale with wet conditions (wet swale) is a natural fit for this location because a ditch is already present. Construction of a wet swale would require minimal excavation and provide water quality benefits to the surrounding drainage area.

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5 Evaluation of Watershed Improvement Scenarios

One of the primary objectives of the Eno River WIP is selection of five pilot study areas (PSAs) which were to identify and prioritize improvement projects, used to support model development and application SCMs, and stream restoration opportunities that are through watershed management scenarios. critical to the protection and restoration of water Additional information on the PSA selection process quality in the Eno River and its tributaries and in is presented in the Eno River Watershed Assessment downstream Falls Lake. Report, which is provided in Volume III, Appendix E, of this WIP. As previously described, no water quality impairments are currently identified by NCDEQ in the Eno River and its tributaries, but portions of Falls 5.2 Stormwater Management Lake are impaired for turbidity and chlorophyll a, Modeling which have been linked to nutrient over-enrichment Information collected during the watershed field (NCDEQ, 2016). assessment was used to develop and calibrate a In 2010, the North Carolina Environmental Personal Computer Storm Water Management Management Commission approved the Falls Lake Model (PCSWMM) were used to help determine the Rules, which established a nutrient management projects that offer the greatest water quality benefit. strategy for Falls Lake that is designed to reduce Model results are presented in Section 5.3.2. algal growth in the lake (NCDEQ, 2011). Contributors The PCSWMM framework is a commercially available of nutrients to Falls Lake, including the City, are software system for running the U.S. Environmental required to reduce their loading of TN and TP to Protection Agency (USEPA) Storm Water restore water quality in the lake. Management Model version 5.1. PCSWMM was To assess the potential water quality benefits of selected because of its ability to simulate the SCMs and other practices, watershed management existing storm drainage system in the Eno River scenarios were developed and evaluated. Water watershed and estimate pollutant loadings and the quality improvement scenarios selected for this WIP transport of water quality constituents through the include practices that have demonstrated nutrient drainage system. reduction (referred to as “credit”) and are considered The primary goals of developing and using feasible in the Eno River watershed. PCSWMM for the Eno River watershed were to: · 5.1 Pilot Study Areas Develop a detailed model in the Durham County portion of the watershed that mimics the As described in Section 2.1, the study area was observed hydrology, hydraulics, and water quality divided into 53 subwatersheds based on surface conditions, and develop a less detailed model in hydrology, topography, and the existing stormwater the Orange County portion of the Eno River infrastructure. These subwatersheds were then watershed. categorized into seven groups based on land use, · Apply the model to estimate changes in pollutant projected development trends, impervious cover, loadings associated with various water quality dominant HSG, and the number and type of existing improvement scenarios and support the SCMs (Exhibit 21). This categorization led to the prioritization of SCMs for retrofit.

Eno River Watershed Improvement Plan – Volume II 5-1 AECOM

Additional information on the PCSWMM Additional information on the methods that were development and calibration is provided in Eno River used to evaluate the watershed improvement PCSWMM Model Development and Calibration (see practices is presented Section 5.3.1. Volume III, Appendix H, of this WIP). 5.3.1 Scenario Methodology 5.3 Scenarios Eight watershed improvement scenarios were Watershed scenarios were evaluated for the WIPs for evaluated for their benefits in nutrient and total Ellerbe Creek, Northeast and Crooked Creeks, Third suspended sediment (TSS) loading reduction at the Fork Creek and Little Lick Creek, and the results watershed scale. Scenarios 1 and 2 were used to provide valuable insights into practices that are assess the existing conditions in the watershed and feasible and cost-effective and provide the highest the change in loading associated with anticipated water quality benefit. changes in land use only. Scenario 3 builds on scenario 2 and scenarios 4 through 8 build on The PCSWMM model was used to evaluate potential scenario 3. project opportunities in five of the eight watershed improvement scenarios. The results of the modeling scenarios are presented in Section 5.3.2. 5.3.1.1 Scenario 1: Existing Land Use with Existing SCMs (Baseline Condition) Selecting the scenarios for the Eno River WIP began Scenario 1 represents the existing conditions in the by reviewing the modeling results in the Ellerbe watershed including the existing land use conditions Creek, Northeast and Crooked Creeks, Third Fork and water quality benefits provided by existing Creek and Little Lick Creek watersheds (see Volume SCMs. III, Appendix K, of this WIP). Next, the unique conditions in the Eno River watershed and current The existing land use condition in the study area for nutrient crediting in North Carolina were reviewed. Scenario 1 was based on the existing land use data Based on the modeling results, conditions in the Eno provided by the City (see Section 2.1.7). The existing River watershed, and nutrient crediting in North land use for the portion of the watershed in Orange Carolina, the following watershed improvement County was developed using the 2011 National Land practices were selected for evaluation in the Eno Cover Database (NLCD) (USGS, n.d.) and North River watershed: Carolina Department of Transportation (NCDOT) roadway data (NCDOT, n.d.). · Stormwater Performance Standards for New Development (City of Durham, 2012b) Because the two datasets had different classifications, the NLCD and NCDOT data were · Recommended SCM retrofits and new SCM reclassified to align the data with the City’s land use projects classification scheme. The reclassification is · Stream restoration projects described in Eno River PCSWMM Model Development · Green Infrastructure/Low Impact Development and Calibration (see Volume III, Appendix H, of this (GI-LID) WIP). For example, the City’s land use did not include · Land conservation a category for “forest,” so “forest” land use in Durham County was manually delineated based on a · Combination of Stormwater Performance review of aerial imagery. Manually delineated forest Standards for New Development, recommended areas in Durham County were primarily buffer areas SCM retrofits and new SCM projects, stream along streams. restoration projects, GI-LID, and land conservation The reclassification was also performed to assign hydrology parameters, such as Manning’s n and depression storage in pervious areas, and water

5-2 Eno River Watershed Improvement Plan, Volume II AECOM quality parameters, such as EMCs, to appropriate Field crews determined that 18 out of the 83 existing land uses. The manual reclassification was important SCMs included in PCSWMM were not functioning given the heavily forested nature of the watershed properly. If an existing SCM was determined to not because large tracts of contiguous forest produce be functioning properly because of a maintenance much different runoff and associated water quality issue such as sedimentation or overgrown than small tracts in residential areas. vegetation, a water quality multiplier from 0.25 to 0.80 was assigned depending on the SCM condition. A total of 83 existing SCMs consisting of 40 dry Assigning a SCM-specific water quality multiplier ponds, 30 wet ponds, 3 wetlands (constructed and allowed the model to account for the variability in pocket), and 10 bioretentions were included in the SCM performance relative to the SCM’s condition. modeling. In addition, 19 additional surface water The observed performance issues and water quality detention features were located while reviewing multipliers used in Scenario 1 are presented in aerial imagery and were also included in the model Table 5-2. as wet ponds. When properly designed, constructed, and maintained, these SCM types can achieve the Aerial imagery was reviewed to identify the pollutant removal efficiencies shown in Table 5-1. condition of the 19 additional wet ponds included in PCSWMM but were not assessed by field crews to Table 5-1. SCM removal efficiencies assign appropriate water quality multipliers. for TN, TP, and sediment Removal Efficiency (%) 5.3.1.2 Scenario 2: Future Land Use SCM Type TN TP Sediment with Existing SCMs Bioretention 35 45 85 Scenario 2 represents the future conditions in the Constructed Wetland 44 40 70 watershed assuming that no additional watershed improvement projects or pollution control measures Dry Pond 10 10 20 are added. Scenario 2 includes the future land use Pocket Wetland 44 40 70 conditions in the study area and the existing SCMs in Wet Pond 30 30 85 Scenario 1. To evaluate changes in the study area only, the land use for the portion of the watershed Wet Swale 30 30 85(1) outside the study area was not updated from Source: NCDEQ (2017a) Scenario 1. (1) NCDEQ SCM Credit Document (NCDEQ, 2017) does not define the total suspended sediment removal efficiency Scenario 2 establishes a baseline condition for the for a treatment swale (wet conditions); this value was set Eno River watershed study area under the future to equal that of a wet pond. land use condition. SCM = stormwater control measure TN = total nitrogen For Scenario 2, the land use distribution in the study TP = total phosphorus area was updated to the future land use condition, which required updating the impervious area for The 83 existing SCMs were evaluated during the each PCSWMM subcatchment in the study area. SCM field inventory and assessment. Based on Scenario 2 also assumed that routine maintenance observations during the field assessment, a water and repairs would be performed on the existing quality multiplier was assigned to each SCM to SCMs in Scenario 1 where performance issues were reflect its water quality performance. The water identified. Accounting for routine maintenance and quality multiplier was applied to the pollutant repairs was addressed in the model by updating the removal efficiencies presented in Table 5-1. A water water quality multiplier to 1.0 for the 18 existing quality multiplier of 1.0 was used for all SCMs that SCMs that were determined to not be functioning were observed to be properly designed, constructed, properly in Scenario 1. and maintained.

Eno River Watershed Improvement Plan – Volume II 5-3 AECOM

Table 5-2. Water quality multipliers for existing SCMs Sedimentation Water Forebay or Overgrown Quality SCM ID Subwatershed SCM Type Functioning? Present? Vegetation? Multiplier 00047 ER24 Dry Pond Yes N/A Yes 0.80 00106 ER31 Wet Pond Yes Yes Yes 0.80 00121 ER40 Wet Pond Yes Yes No 0.80 00138 ER11 Stormwater Yes Yes No 0.80 Wetland 00167 ER11 Wet Pond Yes Yes Yes 0.80 00190 ER06 Dry Pond Yes N/A Yes 0.80 00206 ER08 Dry Pond Yes N/A Yes 0.80 00207 ER11 Dry Pond Yes N/A Yes 0.80 00214 ER37 Wet Pond Yes Yes(1) Yes 0.80 00314 ER20 Wet Pond Yes Yes Yes 0.80 00322 ER21 Wet Pond No Yes No 0.25 00337 ER24 Wet Pond Yes Yes Yes 0.80 00365 ER25 Wet Pond Yes Yes No 0.80 00527 ER33 Dry Pond Yes N/A Yes 0.80 00528 ER33 Dry Pond Yes N/A Yes 0.80 00753 ER40 Dry Pond Yes N/A Yes 0.80 13113 ER46 Wet Pond Yes No No 0.80 13247 ER12 Wet Pond Yes No Yes 0.80

(1) Forebay is present but not functioning

5.3.1.3 Scenario 3: Future Land Use with on-site SCMs and the purchase of off-site nutrient Stormwater Performance Standards credits. for New Development Implementing Scenario 3 required identifying new Scenario 3 was developed to assess the impact of development parcels and adjusting the TN and TP implementing the City’s Stormwater Performance export rates for these parcels to account for on-site Standards for New Development Ordinance (City of treatment that will be accomplished as a result of the Durham, 2012b). The ordinance requires that areas City’s ordinance. of new development and redevelopment not exceed To determine the new development area that would the following unit area loading rates: 2.2 lbs/ac/yr for be required to meet the water quality standards, the TN and 0.33 lbs/ac/yr for TP. To meet these water existing land use and future land use conditions in quality performance standards, developers have the the study area were compared. The following option of using on-site SCMs or a combination of changes were considered new development in the study area:

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· Vacant or undeveloped (parcels classified as 5.3.1.4 Scenario 4: Stormwater agriculture, forest, parks and open space, vacant, Performance Standards for New or very low density residential) greater than 1.0 Development with Recommended acre that are expected to convert to low density SCM Retrofits and New SCM residential land use type Projects · Vacant or undeveloped (parcels classified as Scenario 4 expands on Scenario 3 by determining agriculture, forest, parks and open space, vacant, the annual pollutant load reduction that could be or very low density residential) greater than 0.5 achieved on a watershed scale by implementing the acre that are expected to convert to any other proposed existing SCM retrofit projects and urban land use type (commercial, industrial, potential new SCM projects identified in the study institutional, medium density residential, or high area. In the SCM inventory and assessment (see density residential) Section 4), 29 existing SCMs were recommended for Approximately 5,960 acres, or approximately one- further evaluation of potential retrofits. Additionally, third of the study area, were identified that will be 9 features not in the City’s SCM database were also required to meet the performance standards during recommended for further evaluation of potential the development process. retrofits. The existing SCMs and features are listed in Table 5-3. Similar to the evaluation performed for the Little Lick WIP (City of Durham, 2016a), it was assumed that Existing SCM retrofit projects were incorporated into 50% of the required reduction for the ordinance will PCSWMM by updating the existing SCM be achieved through on-site SCMs and the representation in Scenario 3, which involved remaining 50% of the required reduction will be updating the stage-storage curve, stage discharge achieved by purchasing off-site nutrient credits. curve, and pollutant removal efficiencies for each existing SCM with a proposed retrofit. Scenario 3 model inputs were developed by comparing the existing nutrient export rate to the The 24 potential new SCMs recommended in Section water quality standard for new development parcels 4 (listed in Table 5-4) were added to PCSWMM for in the study area. If a new development parcel Scenario 4. A conceptual design was created for each exceeded the water quality standard loading rate, new SCM that is proposed in the study area. The the amount that it exceeded the standard was conceptual designs were developed and modeled reduced by 50%. This methodology was used to using HydroCAD version 10.0 software and Soil account for the 50% of load reduction that will occur Conservation Service methodology to ensure that on site. proposed SCMs would be designed to the City’s design standards. Though redevelopment areas are also subject to the For existing wet ponds and water retention features City’s ordinance, they were not considered in identified by field crews, Eno River WIP only Scenario 3 because redevelopment is not expected recommends building of a sediment forebay and to be significant in the study area. adding floating wetland islands as a retrofit option. However, installation of internal berms above the permanent pool should be explored as an option to retrofit existing wet ponds in the future WIPs.

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Table 5-3. Recommended retrofits to existing SCMs Existing SCM Existing Potential Structural or Feature ID SCM Type or Volume Retrofit Potential Add-On Retrofits ER_SCM_00023 Dry Pond Convert to pocket wetland Install internal berm to increase flow path ER_SCM_00047 Dry Pond Convert to constructed Install internal berm to increase flow path wetland ER_SCM_00055 Wet Pond Redesign outlet structure Add level spreader; add floating wetland islands; plant vegetation to stabilize or uptake nutrients ER_SCM_00060 Dry Pond Convert to pocket wetland — ER_SCM_00068 Dry Pond Convert to pocket wetland — ER_SCM_00082 Dry Pond Convert to bioretention — ER_SCM_00083 Dry Pond Convert to bioretention — ER_SCM_00084 Dry Pond Convert to pocket wetland — ER_SCM_00085 Dry Pond Convert to pocket wetland Install internal berm to increase flow path ER_SCM_00086 Dry Pond Convert to pocket wetland Install internal berm to increase flow path ER_SCM_00097 Dry Pond Convert to pocket wetland — ER_SCM_00114 Dry Pond Convert to pocket wetland Add level spreader ER_SCM_00138 Wetland Redesign constructed wetland Install internal berm to increase flow path ER_SCM_00152 Wet Pond Redesign outlet structure Add floating wetland islands; plant vegetation to stabilize or uptake nutrients

ER_SCM_00167 Wet Pond Redesign outlet structure Add floating wetland islands; add riprap or stabilize inlet; add upflow filter ER_SCM_00190 Dry Pond Convert to pocket wetland Install internal berm to increase flow path ER_SCM_00191 Dry Pond Convert to pocket wetland Install internal berm to increase flow path ER_SCM_00206 Dry Pond Convert to constructed Install internal berm to increase flow path wetland

ER_SCM_00207 Dry Pond Convert to constructed Install internal berm to increase flow path; add level wetland spreader ER_SCM_00271 Dry Pond Convert to constructed Install internal berm to increase flow path wetland ER_SCM_00321 Dry Pond Convert to pocket wetland Install internal berm to increase flow path ER_SCM_00332 Dry Pond Convert to pocket wetland Install internal berm to increase flow path ER_SCM_00337 Wet Pond Convert to constructed Add upflow filter wetland ER_SCM_00417 Dry Pond Convert to pocket wetland Add level spreader ER_SCM_00448 Dry Pond Convert to constructed Add level spreader wetland

ER_SCM_00454 Dry Pond Convert to pocket wetland Install internal berm to increase flow path

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Table 5-3(cont.). Recommended retrofits to existing SCMs Existing SCM Existing Potential Structural or Feature ID SCM Type or Volume Retrofit Potential Add-On Retrofits ER_SCM_00455 Wet Pond Redesign outlet structure Build sediment forebay; add floating wetland islands ER_SCM_00753 Dry Pond Convert to constructed Install internal berm to increase flow path wetland ER_SCM_00767 Dry Pond Convert to pocket wetland Install internal berm to increase flow path ER_SCM_ENO0101 Wet Pond Redesign outlet structure and Build sediment forebay; add floating wetland rebuild dam islands

ER_SCM_ENO0102 Wet Pond Redesign outlet structure and Add floating wetland islands rebuild dam

ER_SCM_ENO0108 Wet Pond Redesign control structure Build sediment forebay; add riprap or stabilize inlet ER_SCM_ENO0109 Wet Pond Redesign control structure Build sediment forebay; add floating wetland islands ER_SCM_ENO0111 Dry Pond Redesign control structure Add riprap or stabilize inlet ER_SCM_ENO0112 Wet Pond Redesign control structure Build sediment forebay; add floating wetland islands

ER_SCM_ENO0113 Dry Pond Convert to pocket wetland Install internal berm to increase flow path ER_SCM_ENO0114 Dry Pond Convert to pocket wetland Install internal berm to increase flow path ER_SCM_ENO0115 Wet Pond — Build sediment forebay; add floating wetland islands

Table 5-4. Potential new SCMs SCM Drainage SCM Drainage New SCM ID New SCM Type Area (ac) New SCM ID New SCM Type Area (ac) ER_SCM_ENO0117 Constructed Wetland 18 ER_SCM_ENO0144 Bioretention 3 ER_SCM_ENO0122 Bioretention 5 ER_SCM_ENO0148 Pocket Wetland 5 ER_SCM_ENO0123 Wet Swale 12 ER_SCM_ENO0149 Constructed Wetland 6 ER_SCM_ENO0124 Bioretention 4 ER_SCM_ENO0151 Constructed Wetland 9 ER_SCM_ENO0127 Bioretention 25 ER_SCM_ENO0154 Constructed Wetland 9 ER_SCM_ENO0128 Wet Pond 17 ER_SCM_ENO0156 Constructed Wetland 22 ER_SCM_ENO0133 Bioretention 5 ER_SCM_ENO0160 Pocket Wetland 4 ER_SCM_ENO0136 Wet Pond 22 ER_SCM_ENO0169 Pocket Wetland 17 ER_SCM_ENO0137 Wet Pond 9 ER_SCM_ENO0170 Pocket Wetland 7 ER_SCM_ENO0138 Bioretention 11 ER_SCM_ENO0171 Constructed Wetland 8 ER_SCM_ENO0139 Dry Pond 8 ER_SCM_ENO0176 Bioretention 2 ER_SCM_ENO0142 Bioretention 4 ER_SCM_ENO0177 Wet Pond 6

Eno River Watershed Improvement Plan – Volume II 5-7 AECOM

5.3.1.5 Scenario 5: Stormwater The quantity of prevented sediment for Protocol 1 Performance Standards for New was estimated using the Bank Assessment for Non- Development with Stream Projects Point Source Consequences of Sediment (BANCS) Method (Rosgen, 2001). A detailed description of the Scenario 5 was developed to quantify the annual methodology and calculations used to develop this pollutant load reductions that could be achieved on scenario us provided in Volume III, Appendix K, of a watershed scale by implementing the proposed 35 this WIP. stream projects identified by the field crews during the stream inventory and assessment (see Section 3). The estimated project efficiency was assumed to be The assessment resulted in a recommendation that 50% for sediment, TN, and TP, which is based on the approximately 9.6 miles of stream projects in the Chesapeake Bay Program’s assumption that stream study area be evaluated further. projects are not 100% effective in preventing stream bank erosion and that sediment transport occurs While urban stream restoration is recognized as an naturally in stable stream reaches (Chesapeake Bay eligible practice for nutrient crediting under the Program, 2014). Chesapeake Bay Nutrient TMDL framework, this practice is not currently recognized by NCDEQ for crediting in North Carolina. For this reason, annual 5.3.1.6 Scenario 6: Stormwater pollutant load reductions for TN, TP, and sediment Performance Standards for New were determined using methodology developed by Development with Green the Chesapeake Bay Program (2014) with Infrastructure and Low Impact modifications for the North Carolina Piedmont Development Nutrient Loading Measures Technical Report (Tetra Scenario 6 was developed to quantify the annual Tech, 2013). Because PCSWMM is not well suited for pollutant load reductions that could be achieved on simulating stream processes, Scenario 5 was a watershed scale if GI-LID practices were installed in performed using Microsoft Excel. The following developed areas that lack stormwater controls. assumptions were used when estimating the Scenario 6 is similar to Scenario 4 except that GI-LID pollutant removal achieved through implementing practices are distributed throughout developed the individual stream projects: portions of the study area as opposed to the central Stream reaches proposed for restoration could location of traditional SCMs such as dry ponds, wet achieve the pollutant reductions for Protocol 1: ponds, and stormwater wetlands. Credit for Prevented Sediment during Storm Flow The western portion of the study area is underlain by and Protocol 2: Credit for Instream and Riparian resistant metamorphic rock of the Carolina Slate Belt. Nutrient Processing during Baseflow (Chesapeake The eastern portion of the study area falls in the Bay Program, 2014). Triassic Basin, which is composed of mostly Stream reaches proposed for Enhancement I, sedimentary geology. The Carolina Slate Belt and Enhancement II (USACE, 2003), and bank Triassic Basin produce soils with very different stabilization could achieve the pollutant reductions hydraulic properties. Carolina Slate Belt soils typically for Protocol 1: Credit for Prevented Sediment during have a moderate hydraulic conductivity while Triassic Storm Flow (Chesapeake Bay Program, 2014) only. Basin soils are poorly drained and exhibit a low No stream projects were credited for Protocol 3: hydraulic conductivity (Dreps, 2011). The Eno River Credit for Floodplain Reconnection Volumes during watershed differs from neighboring watersheds in Storm Flow (Chesapeake Bay Program, 2014) the central and southern portions of the City’s because it would require detailed design information jurisdiction in that it contains a much higher for each potential stream project. percentage of well-drained soils. The soils present in other Durham watersheds such as Ellerbe Creek,

5-8 Eno River Watershed Improvement Plan, Volume II AECOM

Little Lick Creek, and Third Fork Creek are in each land use category that would implement GI- predominantly poorly drained. The assumptions LID practices. For low density residential and concerning GI-LID that are described below were medium density residential land uses, this intended to help the City evaluate how practices that implementation factor was calculated using data rely on infiltration may be better suited in areas from the City’s Residential Green Infrastructure underlain by the Carolina Slate Belt. Analysis (ReGIn Analysis) for the Eno River watershed (City of Durham, 2017b). The implementation factors Green infrastructure encompasses many different for high density residential and commercial land practices. Due to the presence of soils with low uses are estimates based on visual assessment conductivity in some portions in the Eno River review of aerial imagery, and previous experience. In watershed, green infrastructure practices are not practice, implementation across land uses is appropriate in all areas of the watershed. For this dependent on additional feasibility factors such as reason, the following assumptions were used to site-level physical conditions, utility constraints, and determine the number of GI-LID objects and the property owner cooperation. percentage of impervious area that GI-LID objects would treat in the study area: Table 5-5. Implementation factors used to assess · No GI-LID will be implemented in areas already GI-LID practices in Scenario 6 receiving treatment by an SCM. No GI-LID will be Hydrologic Soil Group implemented in a new development area. These Land Use A and B C and D areas are subject to the City’s Stormwater Performance Standards for New Development Commercial 7% 5% (City of Durham, 2012b). High Density Residential 17% 15% · No GI-LID will be implemented for the following Medium Density Residential 22% 20% land uses: agriculture, forest, parks and open Low Density Residential 25% 23% space, water, institutional, industrial, roads, and very low density residential. Because the Eno River watershed study area is · Residential areas will receive rain gardens, and comprised of approximately 62% well-drained soils commercial areas will receive bioretentions. (HSG A and B soils) and GI-LID practices are both · All feasible GI-LID practices identified in this easier to implement and more effective in well- analysis would be fully implemented in residential drained soils, a 2% bonus was added to the and commercial locations identified. This implementation factor for each land use for portions assumption likely results in a higher quantity of of the watershed with well-drained soils. For each feasible locations. Typically, the number of catchment impervious areas associated with each feasible locations decreases after site-level land use and soil type combination were multiplied evaluation due to issues such as utility conflicts by the implementation factors (Table 5-5) to assign and lack of property owner cooperation. to identify the area treated by GI-LID and number of · The extent to which GI-LID practices are GI-LID devices/catchment. successfully implemented in the watershed depends on soil and existing land use type 5.3.1.7 Scenario 7: Stormwater (described below and presented in Table 5-5) as Performance Standards for New well as other site-level feasibility factors such as Development with Land property owner cooperation and unforeseen Conservation utility conflicts. Riparian buffers along streams in the study area An implementation factor for each land use was provide many benefits to the health of the determined to assign the fraction of impervious area watershed. The City’s Critical Area Protection Plan

Eno River Watershed Improvement Plan – Volume II 5-9 AECOM

(CAPP) (see Volume III, Appendix F, of this WIP) NCDEQ to finalize the applicable credits are identifies privately owned parcels with high-quality ongoing. Based on discussions with the City1, land riparian buffers that could be prioritized for conservation credits for protected parcels in the Eno conservation or protection to preserve the benefits River watershed were conservatively assigned as to water quality and watershed health. 0.62 lbs/ac/yr for TN and 0.061 lbs/ac/yr for TP. As part of the WIP, the CAPP was updated to include Scenario 7 was performed in Microsoft Excel outside a list of priority parcels and areas marked for PCSWMM. protection in the Eno River watershed. The parcels and areas include “keystone” and “urban gem,” 5.3.1.8 Scenario 8: Combined Nonpoint which are defined as follows: Source Pollution Projects · Keystone properties are the highest priority Scenario 8 is a combination of Scenarios 3, 4, 5, 6, parcels identified for protection in each and 7 to assess the combined benefit of the watershed that can expand high-quality riparian Stormwater Performance Standards for New areas that are already protected, such as existing Development (City of Durham, 2012b), retrofits to parks, or that could serve as parcels around which existing SCMs and new SCMs, stream projects, GI- larger protected areas might be built. LID controls, and land conservation. The modeling · Urban gem properties contain high-quality approaches described for Scenarios 3, 4, 5, 6, and 7 riparian areas in heavily urbanized portions of were combined to generate the results for each watershed that are isolated or lack Scenario 8. connectivity to other protected open spaces. Although urban gem properties do not qualify as 5.3.2 Scenario Results keystone properties, they have characteristics that Results of the watershed improvement scenarios, are deemed worthy of protecting. presented in Table 5-6 and Table 5-7, suggest that A total of 45 keystone and 3 urban gem properties nutrients and TSS will increase based on projected were identified in the study area. The properties total changes in future land use, but that these increases 986 acres, or approximately 5%, of the study area. can be reduced by implementing management Because portions of the parcels are already required practices. Table 5-6 and Table 5-7 present the to be conserved per the existing Neuse River Buffer changes in load within the study area as calculated Rules (50-foot buffer on all perennial and from the model output at stations EN4.9ER and intermittent streams) (NCDEQ, 2000), nutrient credit EN13.3ER. can only be claimed for the portion of the parcels TN and TP loads within the study area are expected that is not already required to be conserved, to increase approximately 12.5% and 0.7%, resulting in 841 acres of conservation-eligible land respectively, based on future land use projections from the parcels identified in the CAPP. and the implementation of current new Scenario 7 was developed to quantify the annual development standards. New development pollutant reduction that could be achieved on a standards applied to the future land use condition watershed scale if the keystone and urban gem are shown to provide a 6.7% reduction in TN load parcels were protected. Although NCDEQ has not and a 7.2% reduction in TP load compared to total established water quality credits for land load present under the future land use condition. conservation, conversations between the UNRBA and When evaluating the incremental change in load

1 Sandra Wilbur, Watershed Planning and Implementation Section Head, City of Durham, oral communication, May 29, 2018.

5-10 Eno River Watershed Improvement Plan, Volume II AECOM associated with the future land use condition with model for the Eno River study area. As previously and without new development standards, New noted, urban stream restoration is recognized as an development standards reduce the incremental TN eligible practice for nutrient crediting under the load change associated with new development by Chesapeake Bay Nutrient TMDL framework; however, 40% (reducing the change in load from 11,526 lb/yr this practice is not currently recognized by NCDEQ to 6,986 lb/yr) and incremental TP load change for crediting in North Carolina. associated with new development by 90% (reducing The methodology used to estimate load reductions the change in load from 722 lb/yr to 58 lb/yr). from implementing stream projects required the Of the six watershed improvement practices that following assumptions: (1) uniform and continuous were evaluated (see Section 5.3 ), those practices stream bank height along the entire reach, (2) with the highest benefit are described below. continuous stream bank erosion rates along the entire reach, (3) continuous soil bulk density along Total Nitrogen. Stream projects were found to the entire reach, and (4) a single value for soil bulk provide the highest TN reduction (15.1%) in total density. The methodology is intended to be used as load exported from the study area under the future a high-level planning tool, and detailed evaluations land use condition. Stream projects were followed by of individual stream projects require more detailed GI-LID which provides approximately 1.9% reduction, field data than what was collected during the field SCM projects which provide 1.7%; and land assessments as part of this WIP. The full nutrient conservation, which provides approximately 0.8% methodology and process has not been approved by reduction in TN loads present under the future land NCDEQ. use condition. The planning-level cost to implement streams · Total Phosphorus. Stream projects were found projects is more than $28 million. When compared to provide the highest reduction (16.3%) in total to the cost of implementing recommended SCM load exported from the study area under the projects ($29 million) stream projects represent a future land use condition. Stream projects were better value and should be prioritized over SCM followed by GI LID and SCM projects, both of projects based on higher pollutant reductions which provide approximately 2.0%, and land gained for a similar cost. Costs associated with conservation, which provides approximately 0.6% stream projects and SCMs are based on gross reduction in TP loads present under the future assumptions and should be used for high-level land use condition. planning only. · Total Suspended Solids. Stream projects were found to provide the highest reduction in TSS While formal nutrient load credits have not been (6,476,096 lb/yr) relative to the baseline condition assigned to land conservation by NCDEQ, this (Section 5.3.1.5), followed by proposed SCM practice was evaluated in the Eno River watershed projects, which provide approximately 4.7% based on assumed credits above those initially reduction in load and GI-LID, which provide proposed by NCDEQ. Results of this evaluation approximately 4.0% reduction in TSS loads demonstrate that, compared to other management present under the future land use condition. practices, land conservation will likely provide relatively small nutrient reduction credit under the Though stream projects were found to provide the Falls Lake nutrient management strategy. While this highest overall benefit for TN, TP, and TSS, the result is important with respect to compliance with assumptions required to calculate the water quality the rules, land conservation provides an array of benefits warrant additional investigation. The other benefits and ecosystem services that are estimated reduction in annual sediment loading outside the scope if this WIP and that are considered from stream projects is higher than the average by the City when selecting or supporting watershed annual sediment load simulated with the PCSWMM improvement practices. Given the uncertainty

Eno River Watershed Improvement Plan – Volume II 5-11 AECOM associated with the credits calculated under Scenario 7, land conservation should be reevaluated after NCDEQ has assigned nutrient credits to this practice.

5-12 Eno River Watershed Improvement Plan, Volume II AECOM

Table 5-6. Estimated change in TN, TP, and sediment annual loads for watershed improvement scenarios in the Eno River Watershed study area Total Nitrogen Total Phosphorus Total Suspended Sediment

Incremental Relative Incremental Relative Incremental Relative Watershed Annual Load Change(1) Difference(1) Annual Load Change(1) Difference(1) Annual Load Change(1) Difference(1) Management Scenario (lb/yr) (lb/yr) (%) (lb/yr) (lb/yr) (%) (lb/yr) (lb/yr) (%) 1 ELU 55,885 — — 8,429 — — 1,111,882 — — 2 FLU 67,411 +11,526 +20.6% 9,151 +722 +8.6% 1,448,357 +336,475 +30.3% 3 FLU and NewDStds 62,871 +6,986 +12.5% 8,488 +58 +0.7% — — — 4 FLU, NewDStds, and SCM 61,707 +5,821 +10.4% 8,301 –128 –1.5% 1,380,829 +268,947 +24.2% Projects(2) 5 FLU, NewDStds, and Stream 52,689 –3,196 –5.7% 6,998 –1,432 –17.0% — — — Projects(3) 6 FLU, NewDStds, and 61,590 +5,705 +10.2% 8,301 –128 –1.5% 1,390,144 +278,262 +25.0% GI-LID(2) 7 FLU, NewDStds, and Land 62,350 +6,465 +11.6% 8,437 +7 +0.1% — — — Conservation(4) 8 FLU, NewDStds, SCM 49,723 –6,162 –11.0% 6,574 –1,855 –22.0% — — — Projects, Stream Projects, GI-LID, and Land Conservation

(1) Incremental change and relative difference are based on a comparison to Scenario 1, which represents the baseline condition. (2) New development standards for sediment are not included. (3) Implementing stream projects results in a reduction of 6,476,096 lb/yr sediment relative to the baseline condition. The methodology used to estimate load reductions from implementing stream projects required the following assumptions: (1) uniform and continuous stream bank height along the entire reach, (2) continuous stream bank erosion rates along the entire reach, (3) continuous soil bulk density along the entire reach, and (4) a single value for soil bulk density. The methodology is intended to be used as a high-level planning tool, and detailed evaluations of individual stream projects require more detailed field data than what was collected during the field assessments as part of this WIP. For these reasons, annual sediment loads for stream projects are not included in this table. (4) Sediment credits are not assigned to land conservation. “—" = not applicable lb/yr = pounds per year ELU = existing land use NewDStds = Stormwater Performance Standards for New Development FLU = future land use SCM = stormwater control measure GI-LID = green infrastructure – low impact development

Eno River Watershed Improvement Plan – Volume II 5-13 AECOM

Table 5-7. Estimated TN, TP, and sediment annual load reductions for each practice evaluated in the Eno River watershed study area Annual Load Reduction

Total Nitrogen Total Phosphorus Total Suspended Sediment Watershed Management Practice lb/yr Percent lb/yr Percent lb/yr Percent Stormwater Performance Standards 4,540 6.7% 663 7.2% — — for New Development(1) Structural Stormwater Control 1,164 1.7% 186 2.0% 67,528 4.7% Measure Projects(2) Stream Projects(2),(3) 10,182 15.1% 1,490 16.3% — — Green Infrastructure – Low Impact 1,281 1.9% 187 2.0% 58,213 4.0% Development(2)

Land Conservation(2),(4) 521 0.8% 51 0.6% — —

(1) Annual load reduction percentages are based on a comparison to Scenario 2, which represents the future land use condition without stormwater performance standards for new development. (2) Annual load reductions (lb/yr) are based on a comparison to Scenario 3, which represents the future land use condition with stormwater performance standards for new development. (3) Implementing stream projects results in a reduction of 6,476,096 lb/yr sediment relative to the baseline condition. Please see discussion in Section 5.3.2 of Volume II of this WIP. (4) Sediment credits are not assigned to land conservation. “—" = not applicable lb/yr = pounds per year

5-14 Eno River Watershed Improvement Plan, Volume II AECOM

6 Prioritization of Watershed Improvement Projects

A total of 97 potential watershed improvement direct comparison of scores for SCM projects, both projects were identified as feasible through field retrofits to existing SCMs and new SCM projects, and assessments, hydrologic and hydraulic modeling, stream projects among watersheds. The 14 criteria and water quality modeling. The projects consist of were divided into the following six categories: 38 retrofits to existing SCMs, 24 new SCM projects, · Water quality treatment: Amount of pollutant and 35 stream projects. All of the projects would be removed and the associated cost-effectiveness. beneficial, but the type of benefit, level of benefit, and cost vary widely. · Habitat and biological integrity: Benefit to the ecological function of a stream and the stream’s Section 6 summarizes the evaluation and ability to support aquatic life. prioritization of the potential watershed · Stream bank protection: Ability of a potential improvement projects to identify the projects that project to reduce erosion of stream banks during would provide the most benefit cost-effectively. The high flows. evaluation provides the City with a systematic and transparent method for implementing the most · Community enhancement: Benefits a potential beneficial projects in the Eno River watershed and project would have on the surrounding also in Durham’s other watersheds when ranked with community such as property protection, project opportunities in previous WIPs. neighborhood acceptance, opportunities for public education, and proximity to schools, parks, 6.1 Prioritization Criteria and open space. · Prioritization is generally expressed through an Implementation issues: Difficulty and cost of evaluation of benefits gained per dollar invested. implementing a project, including issues such as The selection of prioritization criteria for the Eno property ownership, site accessibility for River WIP began by considering the following: construction, operations and maintenance, compatibility with existing City programs, · Water quality problems observed in the Eno River permitting requirements, and potential watershed environmental impacts. · Criteria listed in the Falls Lake nutrient strategy · Public safety and public property (NCDEQ, 2011) considerations: Amount of flood protection or · The USEPA’s watershed planning process (USEPA, reduction. 2008) Each criterion was assigned a raw score ranging from · Criteria used in the City’s previous WIPs 0 to 5, with 0 indicating no benefit and 5 indicating a The project team determined that the criteria that significant benefit (see Table 6-1). The raw scores for were used in previous WIPs achieved the Eno River each criterion were adjusted using a weighting factor WIP objectives. Using similar criteria facilitates a to create a weight-adjusted score. The weighting

Eno River Watershed Improvement Plan – Volume II 6-1 AECOM

Table 6-1. Prioritization criteria with scoring ranges and weighting factors Score Weighting Results of Score x Category Criteria Range Factor Weighting Factor Water quality Nitrogen 0 – 5 2 0 – 10 treatment Phosphorus 0 – 5 2 0 – 10 Sediment 0 – 5 1.5 0 – 7.5 Fecal coliform 0 – 5 1.5 0 – 7.5 Habitat and Habitat/biology 0 – 5 3 0 – 15 biological integrity Stream bank Stream bank protection 0 – 5 2 0 – 10 protection Community Property protection 0 – 5 1 0 – 5 enhancement Property owner and 0 – 5 1 0 – 5 neighborhood acceptance

Public education 0 – 5 1 0 – 5 Implementation Property ownership 0 – 5 1 0 – 5 issues Accessibility for construction and 0 – 5 1 0 – 5 operations and maintenance City program compatibility 0 – 5 1 0 – 5 Permitting/adverse environmental 0 – 5 1 0 – 5 impacts Public safety and Public safety and public property 0 – 5 1 0 – 5 public property considerations

Total Possible Score 0 – 100 factor allowed individual criteria to be more Nutrient Loading Measures Technical Report (Tetra significant in the evaluation than others. Tech, 2013). For SCM projects, prioritization involved a review of the estimated implementation cost, Factors were weighted to reflect that one criterion including design, permitting, construction, and may be more important in one watershed than annual maintenance. The average annual pollutant another. Though the raw scores for projects can vary, removal for each SCM project was generated using the weighting factor for each criterion remains the PCSWMM. same. Additional information on the methodology of determining a project’s raw scores is provided in A Microsoft-based Excel tool was used to estimate Prioritization of Proposed Watershed Improvement costs associated with proposed SCMs and streams Projects (see Volume III, Appendix J, of this WIP). projects. The City developed the tool as part of the Ellerbe Creek WIP (City of Durham, 2010). The City For stream projects, prioritization involved has maintained the tool through regular updates to evaluating the water quality benefits for TN, TP, and adjust for current market prices. The tool was sediment using the methodology developed by the updated for the Eno River WIP before applying it to Chesapeake Bay Program (2014) with modifications projects in the Eno River watershed. The total capital for the North Carolina Piedmont based on the cost for each SCM and stream project was based on protocol outlined in the North Carolina Piedmont

6-2 Eno River Watershed Improvement Plan, Volume II AECOM total costs associated with construction, engineering, islands. ER_SCM_ENO0102 appears to be a relict surveying, permitting, and administrative, land SCM that is not in the City’s SCM database. acquisition, and annual maintenance. · ER_SCM_ENO0101: Redesign a 0.8-acre improperly functioning wet pond at Riverside 6.2 High-Priority Watershed High School to improve its water quality benefit Improvement Projects by rebuilding the dam embankment, constructing a sediment forebay, and adding floating wetland The feasible watershed improvement projects were islands. ER_SCM_ENO0101 appears to be a relict evaluated based on the prioritization criteria SCM that is not in the City’s SCM database. described in Section 6.1. Based on the evaluation, 15 high-priority SCM projects and 15 high-priority · ER_SCM_00047: Convert an existing 0.2-acre dry stream projects were selected. pond at George L. Carrington Middle School into a constructed wetland to improve its water quality The high-priority SCM projects consist of 12 retrofits benefit. Conversion to a constructed wetland will to existing SCMs and 3 new SCM projects. The high- require enlarging the pond by increasing the priority stream improvement projects consist of 7 length and width and adding internal reaches proposed for restoration, 6 reaches baffles/berm. proposed for Enhancement I, and 2 reaches · ER_SCM_ENO0123: Proposed 0.04-acre proposed for Enhancement II. treatment swale with wet conditions off Cedar The high-priority SCM projects are described in Ridge Way that will treat stormwater runoff from Section 6.2.1, and the high-priority stream projects a multi-family residential area. are described in Section 6.2.2. · ER_SCM_00167: Modify an existing 0.2-acre wet pond in a commercial area off North Roxboro 6.2.1 High-Priority SCM Projects Street to improve its water quality benefits by The 15 high-priority SCM projects are described redesigning the control structure, adding riprap below and in Table 6-2 and shown on Exhibit 22. or stabilizing the inlet, adding floating wetland · ER_SCM_00060: Convert an existing 0.3-acre dry islands, and adding an upflow filter. pond in a residential common area at the end of · ER_SCM_00152: Modify an existing 0.3-acre wet Eagles Nest Drive into a pocket wetland to pond in an industrial area off Old Oxford Road to improve its water quality benefits. Conversion to a improve its water quality benefit by redesigning pocket wetland will require enlarging the pond by the control structure, adding floating wetland increasing the length and width. islands, and planting vegetation to · ER_SCM_00055: Modify an existing 0.4-acre wet stabilize/uptake nutrients. pond in a commercial area off Medical Park Drive · ER_SCM_ENO0113 and ER_SCM_ENO0114 to improve its water quality benefits by - ER_SCM_ENO0113: Convert an existing redesigning the control structure, adding a level 0.08-acre dry pond in a residential area near spreader at the outfall, adding floating wetland the end of Coke Court in Croasdaile Village islands, and planting vegetation to into a pocket wetland to improve its water stabilize/uptake nutrients. quality benefit. Conversion to a pocket · ER_SCM_ENO0102: Redesign a 0.2-acre wetland will require dredging within the improperly functioning wet pond at Riverside existing footprint and adding internal High School to improve its water quality benefit baffles/berm. ER_SCM_ENO0113 appears to be by rebuilding the dam embankment, constructing a relict sediment basin that is not in the City’s a sediment forebay, and adding floating wetland SCM database.

Eno River Watershed Improvement Plan – Volume II 6-3 AECOM

- ER_SCM_ENO0114: Convert an existing water quality benefit. Conversion to a constructed 0.03-acre dry pond in a residential area near wetland will require enlarging the pond by the end of Coke Court in Croasdaile Village increasing the length and width and adding into a pocket wetland to improve its water internal baffles/berm. quality benefit. Conversion to a pocket · ER_SCM_00332: Convert an existing 0.4-acre dry wetland will require dredging within the pond in a residential area off Cedar Ridge Way existing footprint and adding internal into a pocket wetland to improve its water quality baffles/berm. ER_SCM_ENO0114 was not a benefit. Conversion to a pocket wetland will high-priority project but is adjacent to and require dredging within the existing footprint and could be combined with ER_SCM_ENO0113 to adding internal baffles/berm. reduce project costs. ER_SCM_ENO0114 · ER_SCM_00321: Convert an existing 0.4-acre dry appears to be a relict sediment basin that is pond in a residential area off Cedar Ridge Way not in the City’s SCM database. into a pocket wetland to improve its water quality · ER_SCM_00023: Convert an existing 0.2-acre dry benefit. Conversion to a pocket wetland will pond in a residential area near the end of Kinross require dredging within the existing footprint and Court into a pocket wetland to improve its water adding internal baffles/berm. quality benefit. Conversion to a pocket wetland will require enlarging the pond by increasing the 6.2.2 High Priority Stream length and width and adding internal Improvement Projects baffles/berm. The 15 high-priority stream improvement projects · ER_SCM_ENO0170: Proposed 0.09-acre pocket are described below and in Table 6-3 and are shown wetland near the intersection of North Roxboro in Exhibit 23. Street and Macwood Drive that will treat stormwater runoff from a parking lot and athletic · Stream Restoration: Proposed for seven highly- fields at Northern High School. degraded stream reaches within the Eno River watershed for a total of 10,761 feet. · ER_SCM_ENO0148: Proposed 0.2-acre pocket wetland at Hillandale Elementary School that will · Stream Enhancement – Level I: Proposed for six treat stormwater runoff from a parking lot and degraded reaches within the Eno River watershed athletic fields. for a total of 10,482 feet. · ER_SCM_00206: Convert an existing 0.4-acre dry · Stream Enhancement – Level II: Proposed for pond in a residential area near the end of Fanning two degraded reaches within the Eno River Way into a constructed wetland to improve its watershed for a total of 4,567 feet.

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Table 6-2. High-priority SCM projects in the Eno River watershed Annual Load Total Project SCM Reduction (lbs/yr) Total Capital Prioritization Sub- Drainage Costs (2018 Score Project ID Project Description watershed Area (ac) TN TP Sediment Dollars)(1) (100 Max) ER_SCM_00060(2) Convert Existing Dry Pond to Pocket Wetland — 8 24 3 632 $249,000 82.5 ER_SCM_00055 Water Quality Improvements to an Existing Wet Pond ER11 8 32 7 3,153 $282,000 81.0 ER_SCM_ENO0102 Water Quality Improvements to an Existing Wet Pond ER41 13 37 7 1,802 $346,000 81.0 ER_SCM_ENO0101 Water Quality Improvements to an Existing Wet Pond ER39 28 88 18 4,560 $661,000 78.0 ER_SCM_00047 Convert Existing Dry Pond to Constructed Wetland ER24 6 17 3 983 $248,000 77.5 ER_SCM_ENO0123 New Wet Swale ER38 12 12 2 893 $130,000 75.5 ER_SCM_00167 Water Quality Improvements to an Existing Wet Pond ER11 15 43 9 4,900 $271,000 70.0 ER_SCM_00152 Water Quality Improvements to an Existing Wet Pond ER07 13 34 7 3,774 $247,000 70.0 ER_SCM_ENO0113 – Convert Two Adjacent Existing Dry Ponds to One ER38 6 17 2 794 $217,000 69.5 ER_SCM_ENO0114(3) Pocket Wetland ER_SCM_00023(2) Convert Existing Dry Pond to Pocket Wetland — 7 16 2 838 $267,000 68.5 ER_SCM_ENO0170 New Pocket Wetland ER20 7 12 2 680 $312,000 67.5 ER_SCM_ENO0148 New Pocket Wetland ER35 5 16 3 928 $330,000 65.5 ER_SCM_00206 Convert Existing Dry Pond to Constructed Wetland ER08 12 16 2 849 $328,000 65.5 ER_SCM_00332 Convert Existing Dry Pond to Pocket Wetland ER38 6 12 2 662 $180,000 65.5 ER_SCM_00321 Convert Existing Dry Pond to Pocket Wetland ER39 11 18 2 377 $253,000 65.5

Totals 156 392 70 25,824 $4,321,000

(1) Total capital costs consist of administrative, engineering, surveying, permitting, land acquisition, construction, and construction administration costs and 20 years of annual maintenance. (2) ER_SCM_00060 and ER_SCM_00023 are located within City limits near the Orange County and Durham County boundary in a small portion of the study area outside of the 53 subwatersheds that were used to support pilot study area selection and modeling decisions. Additional information is presented in in Volume III, Appendix E, of this WIP. (3) ER_SCM_ENO0113 and ER_SCM_ENO0114 are adjacent SCMs and could be combined into a single project. This would reduce cost relative to implementing two individual projects. In the table, the drainage area, annual load reductions, and cost have been combined for the two projects. The score is for the project that scored higher (ER_SCM_ENO0113).

Eno River Watershed Improvement Plan – Volume II 6-5 AECOM

Table 6-3. High-priority stream projects in the Eno River watershed Annual Load Stream Total Capital Total Project Reduction (lbs/yr) Sub- Reach Costs Prioritization Project ID Project Description watershed Length (ft) TN TP Sediment (2018 Dollars)(1) Score (100 Max) ER_STREAM_2019 Stream Restoration ER32 4,938 3,346 320 1,392,863 $2,920,000 83.5 ER_STREAM_2072 Enhancement I ER23 2,146 147 38 165,061 $1,051,000 76.4 ER_STREAM_1021(2) Enhancement I ER38 2,621 293 76 329,693 $1,199,000 72.5 ER_STREAM_2039(3) Stream Restoration ER10 1,935 3,010 628 2,732,600 $1,162,000 70.5 ER_STREAM_2075(4) Stream Restoration ER05 480 204 3 12,684 $319,000 69.5 ER_STREAM_1026 Enhancement I ER35 1,870 47 12 52,969 $890,000 68.7 ER_STREAM_2038(3) Enhancement I ER11 1,654 728 188 818,024 $1,349,000 67.5 ER_STREAM_2013 Enhancement II ER37 2,847 56 14 62,559 $1,160,000 65.9 ER_STREAM_2053(5) Enhancement I ER17 664 33 9 37,382 $330,000 63.4 ER_STREAM_2042(6) Stream Restoration ER08 921 179 3 12,326 $827,000 61.5 ER_STREAM_2045(4) Stream Restoration ER07 745 268 1 5,427 $449,000 61.5 ER_STREAM_1086 Stream Restoration ER41 800 165 1 6,318 $488,000 58.5 ER_STREAM_2041(6) Stream Restoration ER08 942 243 2 9,054 $846,000 57.5 ER_STREAM_2054(5) Enhancement II ER17 1,720 147 38 165,335 $572,000 57.3 ER_STREAM_1023(2) Enhancement I ER38 1,526 43 11 48,417 $699,000 56.5

Totals 25,810 8,911 1,346 5,850,711 $14,261,000

1) Total capital costs consist of administrative, engineering, surveying, permitting, land acquisition, construction, and construction administration costs and 20 years of annual maintenance. (2) ER_STREAM_1021 and ER_STREAM_1023 are adjacent reaches and could be combined into a single project. This would reduce cost relative to the cost of two individual projects. (3) ER_STREAM_2039 and ER_STREAM_2038 are adjacent reaches and could be combined into a single project. This would reduce cost relative to the cost of two individual projects. (4) ER_STREAM_2075 extends beyond the length provided in the table. Field assessment of the reach was stopped due to beaver activity. This reach is a part of the old Eno River bend prior to construction of the Eno River Canal. If this project is considered, the entire Eno River bend area should be reassessed. Additionally, ER_STREAM_2075 could be combined with ER_STREAM_2045 to form a single project. These reaches are on the same stream but separated by one large parcel (Hanson Aggregates Southeast – Parcel Identification Number: 178019). (5) ER_STREAM_2053 and ER_STREAM_2054 are adjacent reaches and could be combined into a single project. This would reduce cost relative to the cost of two individual projects. (6) ER_STREAM_2042 and ER_STREAM_2041 are adjacent reaches and could be combined into a single project. This would reduce cost relative to the cost of two individual projects.

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7 Public Outreach and Involvement

Public involvement is a critical component of the the room. Several handouts were available and watershed improvement planning process. Residents educational posters were set up for viewing until the bring local knowledge that informs the watershed meeting began. The session was called to order by planning process. Their input is invaluable in the meeting facilitator. A slide show was used to developing a comprehensive plan. present project background, a progress update, and future steps. The City used a public engagement process to inform the public, key stakeholders such as the Eno 7.1.1 First Public Information Session: River Association, staff from City departments, and elected officials. Tools included a City-hosted project March 21, 2017 webpage, three public information sessions, three The first public information session introduced project fact sheets that provides progress updates, residents to the project background and the City’s and social media updates to communicate and watershed planning program. The presentation solicit feedback from the public. Three videos that included water quality challenges and the federal focused on various stormwater messages were also and state regulations (e.g., NPDES Permit, Falls Lake produced. Rules) that drive the watershed planning program. The City has a diverse population, and the Eno River Presenters stated the goals of the Eno River WIP and watershed has a significant Spanish-speaking the progress that had been made in the first 9 population. The City developed a project fact sheet months of the project, which included visits by in Spanish and stormwater messages that were scientists and engineers to SCMs and stream sites broadcast on a Spanish radio channel. These efforts where potential improvement had been deemed are discussed further below. possible during a desktop evaluation. The preliminary results from the field visits were 7.1 Public Information Sessions discussed, and feedback from residents was solicited. Three public information sessions were hosted Attendees asked questions during and after the between 2017 and 2018. The sessions were held at presentation to clarify information. The next steps in key milestones to provide an update on the project the process were discussed. progress and receive input from attendees on After the presentation, the session reverted to an important topics. The sessions were typically held in open-house format. Attendees visited the poster evenings at public locations that were easily stations and engaged with the City staff and accessible. Attendees included residents, consultants to provide feedback. representatives from local nonprofit and environmental organizations, City staff, and The 18 attendees included 4 City staff and 3 staff members of the consulting team. from the consultant team. All of the sessions followed a town hall style with 7.1.2 Second Public Information open house formats in the beginning and end of the Session: November 2, 2017 meeting to allow interaction between City staff and The second public information session was similar to attendees. Both City staff and members of the the first. It began as an open-house style, then consultant team welcomed the attendees to the converted to town-hall format for the presentation, meeting at a sign-in station set up at the entrance of and then reverted to an open-house format. The

Eno River Watershed Improvement Plan, Volume II 7-1 AECOM slide show recapped the first meeting (regulatory - Project implementation issues background and SCM and fieldwork results) and · Several respondents indicated concern about the proceed with the results of a fish study and aquatic following potential pollution discharges in the vegetation study that were conducted in the Eno watershed: River to help determine water quality. The - Plastic/trash pollution (10 respondents) presentation also included the approach to computer modeling and prioritizing the SCM and - Sediment pollution from construction sites (5 stream restoration projects, the next steps in the respondents) project. An interactive game focusing on - Sewer overflows (4 respondents) environmental science knowledge of the Eno River - Industrial pollution (3 respondents) was available for the children in attendance. · Three respondents expressed concern about The 19 attendees included four City staff and three swimming staff from the consultant team. · The City used several outlets to advertise the A survey was available online to residents from project. Survey responses suggested that most October 15, 2017, to November 15, 2017 (before and people heard about the project through the after the meeting), and at the meeting in electronic following outlets, from highest to lowest based and paper formats. on the frequency cited in survey responses: The survey questions were aimed at understanding - Facebook the residents’ use of Eno River’s recreational - City email and press release opportunities and their perception of the water quality in the Eno River watershed. A total of 86 - Neighborhood listserv responses were received and are summarized as - Other nonprofit newsletter follows: - Twitter · Nearly 75% of respondents spend significant - Newspapers amounts of time in the watershed. Approximately · Two of the most popular ideas for enhancing 50% of the respondents live in the watershed and reporting of pollution issues were installing signs approximately 25% work in the watershed. near trailheads (7 respondents) and using a · Approximately 50% of the respondents enjoy the phone application (6 respondents). outdoors in the Eno River watershed at least once a week while several are out as many as five times The survey provided insightful information for the a week. project team in understanding how respondents use and value water resources in the Eno River · The primary reasons for visiting the Eno River are watershed. nature/hike, walking dogs, running, swimming, paddling, fishing, camping, and other events. 7.1.3 Third Public Information Session: · Respondents ranked the criteria that were July 31, 2018 proposed for watershed improvement projects as The third and final public information session was follows (in order of importance): hosted on July 31, 2018 at the Durham County - Water quality benefits Regional Library. The goal of this final session was to - Habitat and biological integrity present the results of watershed modeling, SCM and - Stream bank protection stream restoration project prioritization, watershed management scenarios, and overall project - Community enhancement recommendations. - Public safety and public property

7-2 Eno River Watershed Improvement Plan, Volume II AECOM

The meeting format started in an open-house style 7.2 Eno Watershed River and was attended by residents, representatives from local environmental organizations, elected officials, Improvement Plan Webpage and City staff and consultants. Approximately 24 The City is providing a dedicated webpage for the attendees (18 people signed in) participated in the Eno River WIP (http://durhamnc.gov/2890/ Eno- meeting, included six City staff and four staff from River-Watershed-Improvement-Plan). The webpage the consultant team. was updated regularly during the project life between 2016 and 2018 to provide the public with The meeting transitioned to a town-hall format for a important schedule updates, field activities, and PowerPoint presentation during which the City and project milestones. The webpage has links to the consultant project managers provided a brief recap slide shows from the public information sessions, of the project background and field work completed project factsheets and key project reports. in earlier stages of the project. Results from the survey conducted during the second public meeting were also discussed. Results and recommendations 7.3 Eno River Watershed from the draft WIP were presented, which included Improvement Plan Social the following: Media Updates · Stream and SCM project prioritization and the The City used social media platforms such as costs to implement these projects. Facebook · Summary of pollutant reduction benefits (https://www.facebook.com/durhamncstormwater/) associated with several watershed management and Twitter to publish key updates on the project scenarios that were evaluated. and stormwater management and volunteer events. After the presentation, the meeting transitioned to The Twitter handle for the City, managed under an open-house format during which time attendees @DurhamStormH2O, was used to share important engaged with the City staff and consultants, project updates as well as links to videos when reviewed project posters and documents, and released for public. provided feedback to the project team. To facilitate this discussion the following materials were available 7.4 Project Fact Sheets at the meeting for public review: Three project factsheets were developed for Eno · A one-page final project factsheet along with River watershed improvement project to provide a copies of the fact sheets made available during summary of project progress and key findings. The the first two public meetings. first fact sheet was developed in both English and Spanish to reach the diverse population in the · Project documents including CAPP, Fish Survey watershed. The two-page factsheets were developed Report, Aquatic Macrophyte Report, Watershed in coordination with each public information session Assessment Report, and draft of the WIP were and were available at the sessions and later on the also made available for public review. project webpage. · A variety of project posters illustrating various features of the watershed, including locations of 7.5 Educational Radio Spots SCMs and stream restoration opportunities. A radio spot was developed in Spanish and A final survey was conducted to evaluate the broadcasted on the channel La Ley 101.1FM to reach effectiveness of public outreach and information the Spanish-speaking population. The radio message sessions performed during the project. was focused on best practices when using paint brushes to prevent paint pollution from entering

Eno River Watershed Improvement Plan, Volume II 7-3 AECOM storm drains and streams. The recorded message is · “Proper Paint Disposal” highlights the importance available at: https://durhamnc.gov/2890. of managing paint pollution by providing simple tips such as washing brushes indoors and 7.6 Educational Videos properly disposing of paint cans. This video is available at the following link: The consultant team helped the City develop the https://youtu.be/UOEpBtx5QL0?list=PL5760F8572 following three high-quality videos for the public BE4AD39. outreach and education effort: · “Green Stormwater Infrastructure” promotes the · “The River Starts in your Backyard” introduces the practice of green stormwater infrastructure and concept of a watershed and how the daily displays some of the key projects and activities of residents have the potential to convey partnerships developed by the City. This video is pollutants to a stream or river if not managed available at the following link: properly. The video provides simple tips for https://youtu.be/um2dRkrxUEY. homeowners such as pet waste cleanup, checking sewer leaks, and planting native vegetation to The videos and those developed previously by the prevent backyard pollutants from getting washed City are available at the following link: into waterways. This video is available at the https://www.youtube.com/playlist?list=PL5760F8572 following link: https://youtu.be/CdgevXy5cyM. BE4AD39.

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8 Watershed Improvement Plan

Achieving and maintaining water quality goals and At this time, the City’s authority to implement watershed health in the Eno River watershed will watershed-specific or local stormwater requirements depend on the implementation of measures such as is limited. North Carolina General Statue 143-214.7 pollution controls, management practices, and (NC Session Law 2014-90) restricts local government strategies designed to mitigate the bacteria, stormwater programs from imposing increased sediment, nutrient, metals, low DO, and flow impacts stormwater controls beyond what is required by the described in Section 2.3. state or federal government. These measures will achieve water quality goals and 8.1.1 High-Priority SCM Projects restore and maintain the physical, chemical, and biological integrity of the receiving waterbodies by: Stormwater controls and retrofits reduce the contribution of pollutants from stormwater and · Reducing or avoiding pollutant inputs to mitigate the hydraulic impacts of runoff from receiving waters developed surfaces. These controls help reduce the · Controlling discharges that could alter natural existing impacts of increased peak flows, excess hydrology nutrients, metals, and low DO described in Section · Mitigating other stressors that may contribute to 2.3. Through field assessments, hydrologic and impairment hydraulic modeling, and water quality modeling, 38 Each WIP developed by the City describes strategies retrofits to existing SCMs and 24 new SCM projects that are tailored to address the unique challenges were identified as feasible watershed improvement and concerns that are present in each watershed. As projects. The top 15 SCM projects are presented in described in this section and in NPDES annual Section 6.2. reports, the City already implements multiple practices and programs throughout the Eno River 8.1.2 High-Priority Stream and other city watersheds. WIP recommendations Improvement Projects are prioritized across all city watersheds based on Degraded streams typically lack diversity in aquatic current and anticipated City initiatives and regulatory habitat and fauna and may have increased levels of obligations. streambank erosion that contribute to higher sediment loading and lower DO concentrations. 8.1 Recommended Strategies Stream degradation may be the product of past The City is currently implementing a number of channelization, “flashy” hydrology due to increased projects and programs that will protect and enhance impervious cover, lack of buffer, or upstream the Eno River. The recommendations presented in pollution. this section build on these initiatives and highlight Stream restoration is the re-establishment of the additional opportunities for future consideration. general structure, function, and self-sustaining The City recognizes that watershed protection behavior of the stream. Many restoration projects requires creative water quality improvement projects feature aspects of the natural channel design and effective partnerships and, as a result, actively method such as modification of channel dimension, partners with state and local agencies, watershed pattern, and profile. Stream enhancement and associations, and stakeholder groups in working to stream stabilization are narrower in scope than protect the Eno River watershed.

Eno River Watershed Improvement Plan, Volume II 8-1 AECOM stream restoration and focus on improving the LID treatment practices will likely not be floodplain and streambank areas, respectively. implemented on all 831 sites. Through field assessments, hydrologic and hydraulic PCSWMM results show that using green modeling, and water quality modeling, 35 stream infrastructure and LID controls reduces TN by 1.9%, projects were identified as feasible watershed TP by 2.0%, and TSS by 4.0 compared to Scenario 3 improvement projects. The top 15 stream projects (Future Land Use with Stormwater Performance are presented in Section 6.2. Standards for New Development Ordinance).

8.1.3 Green Infrastructure and Low 8.1.4 Protection and Preservation of Impact Development High-Quality Streams Opportunities High-quality streams provide watershed benefits Green infrastructure combines elements of the including diverse habitat, natural pollutant filtering, natural environment and traditional stormwater and protection from storm flows (Young et al., 2016). drainage systems to improve water quality and Preservation involves establishing protection of restore ecosystems. The City implements green ecologically important streams (generally considered infrastructure practices by incorporating them into for high-quality streams) in perpetuity by larger City projects through research projects and implementing protective mechanisms, such as grants, partnerships with local organizations, and by acquisition, conservation easements, or restrictive working with other City departments. covenants. Preservation may include the protection of upland buffer areas adjacent to the stream The City recently published the Sustainability necessary to ensure protection or enhancement of Roadmap (City of Durham, 2018a) which identified the stream. implementing green infrastructure practices as a strategy to protect and restore Durham’s natural Preservation of high-quality streams has been shown resources and ecosystem. Low Impact Development to have greater success in maintaining aquatic (LID) is implemented through the Stormwater functions and to be less expensive than stream Performance Standards for Development (City of restoration (Young et al., 2016). Durham, 2012b) and the Durham City-County UDO A total of 30 stream reaches were identified for (Durham City-County Planning Department, 2018). preservation projects in the study area (Exhibit 24). Green infrastructure practices are not appropriate in all areas of the watershed due to the presence of 8.1.5 Protection and Preservation of soils with low conductivity in some areas. The High-Quality Riparian Areas evaluation of green infrastructure opportunities in Stream buffers protect and maintain vegetative the Eno River watershed involved field evaluation of systems along streams and provide biological and a GIS-based ReGIn analysis that was conducted hydrologic benefits by diffusing and treating previously under a separate contract (see the Eno stormwater runoff. While a significant portion of the River Watershed Assessment Report in Volume III, riparian buffers along the mainstem of the Eno River Appendix E, of this WIP). The field assessment area and tributaries are already protected through public included 1,915 parcels in the watershed that were ownership or development restrictions, additional selected from census blocks that scored highest in opportunities for protection exist. the ReGIn analysis. Of the 1,915 parcels, field crews identified 831 as potential sites to locate a rain The City’s CAPP identifies privately owned parcels garden or downspout disconnection retrofit. Many with high-quality riparian buffers that could be of these potential sites are located on private prioritized for conservation or protection to preserve property. For this reason, green infrastructure and these benefits to water quality and watershed health.

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As part of the WIP, the CAPP was updated to include A complete list of keystone properties and urban a list of priority parcels and areas marked for gems identified in the Eno River watershed is protection in the Eno River watershed. A total of 45 provided in Volume III, Appendix F, of this WIP. keystone and 3 urban gem properties were identified in the study area. Eight of the 45 keystone 8.1.6 Continuation of City Programs properties are in the Warren Creek subwatershed. and Practices The two highest scoring keystone properties in the The City’s Stormwater & GIS Services Division is Warren Creek subwatershed (Parcel Identification actively engaged in a number of activities that Number [PID] 177587 and 177597) contain multiple improve and protect watershed and water quality streams draining to Warren Creek and are conditions in the Eno River watershed. As part of the contiguous parcels less than 500 feet from the West City’s MS4 permit requirements, the City reports Point on the Eno city park. Five of the proposed SCM annually on how it is implementing the following projects are in the identified keystone properties permit requirements: public education and outreach; (ENO 0129, ENO 0135, ENO 0157, ENO 0165, and public participation and involvement; illicit discharge, ENO 0166). detection, and elimination; post-construction runoff; Ten of the 45 keystone properties are in the Crooked municipal pollution prevention and good Run Creek subwatershed. Most of the keystone housekeeping; industrial inspection; and water properties throughout the Crooked Run Creek quality monitoring and assessment (City of Durham, subwatershed are currently vacant parcels or are 2016e). Together, these activities help the City adjacent to homeowner’s associations or manage stormwater and reduce pollutants of institutional developments. Two large keystone concern in the Eno River watershed. properties (PID 182907 and 183002) in the Crooked Examples of ongoing City initiatives in the Eno River Run Creek subwatershed are adjacent to the George watershed include: L. Carrington Middle School and provide a unique opportunity for conservation adjacent to an existing · UNRBA and Falls Lake nutrient reevaluation. public school. One new SCM retrofit opportunity The mission of the UNRBA is to preserve the (ER_SCM_00047) and one SCM project water quality of the Upper Neuse River Basin (ER_SCM_ENO0176) are on the school’s property. through innovative and cost-effective pollution reduction strategies and to constitute a forum to The three urban gem properties identified in the cooperate on water supply issues within the watershed provide opportunities for headwater Upper Neuse River Basin. As an active UNRBA stream protection immediately upstream of member, the City supports these objectives and identified keystone properties. By incorporating ongoing efforts to reevaluate the current nutrient these urban gems into the conservation plans, the management strategy, update watershed and lake City has an opportunity to preserve entire stream models, evaluate alternative regulatory options, reaches draining directly to the Eno River. and examine jurisdictional load allocations. In the context of nutrient rule compliance in North · Illicit discharge detection and elimination. An Carolina, land conservation practices do not illicit discharge is a discharge that conveys currently have an established nutrient credit. NCDEQ unauthorized substances to the stormwater is in the process of developing an accounting and drainage system. The City identifies and mitigates crediting mechanism for riparian buffer non-stormwater discharges and illegal dumping improvements. Upon completion, it is anticipated of materials through routine inspections and that opportunities to partner on riparian buffer monitoring as well as investigation following improvement projects may be incentivized. observations or complaints, reliance on regulatory measures for abatement and enforcement, and

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remedial construction of illicit connections where and aquatic plant data in Ellerbe Creek and the necessary. Eno River. · Post-construction runoff control. Post- The City maintains a Water Quality Web Portal construction controls are designed to reduce (http://www.durhamwaterquality.org) where the potential pollutant and hydrological impacts public can access existing water quality data. associated with built-upon areas through the use Results of water quality and biological monitoring of SCMs that treat runoff or through site design are also presented in the City’s Annual State of that employs LID or GI principles to reduce the Streams Report, and characterization of the water volume of runoff. The Stormwater and GIS through the WQI is presented for each Services Division of the Public Works Department monitoring station. reviews development plans and administers · Wastewater treatment improvements. Both standards for post-construction SCMs in centralized and decentralized systems require accordance with the City's stormwater regular maintenance to avoid failure and impacts performance standards for development. As to water quality. Older sanitary sewer lines may required under Section F of their NPDES have significantly high rates of infiltration and stormwater permit, the City manages an SCM inflow (I&I) (water entering the sewer line) and inspection program that requires annual exfiltration (untreated sewage leaching into the inspection reports of permitted structural SCMs, soil and groundwater). Excessive I&I can cause the performed by a qualified professional. volume of the sewage transported to exceed the · Watershed protection ordinances. The City’s design capacity of the system, producing sewer UDO includes natural resource protections overflows. Failing septic systems and sand filters (Durham City-County Planning Department, can also be a source of fecal coliform bacteria, 2018). City Articles 8 and 12 of the UDO address nutrients, and BOD. The City will continue environmental protection and outline standards scheduled I&I inspections, rehabilitation, and to protect and conserve natural resources, other collection system improvements ($37.9 minimize future flooding, and minimize impacts million budgeted in FY 2019). to natural resources by future development. Part · Stormwater research. Stormwater research of the Eno River is in the Falls Lake Water Supply provides information to improve the Watershed and therefore has more stringent understanding of the pollutants in stormwater buffer protections than waters that are not and the controls that can be used to mitigate the designated for drinking supply. Riparian buffer impacts. Ongoing research on SCMs such as algal protection zones are 150 feet on perennial flow-way technologies, regenerative stormwater streams and 100 feet on intermittent streams conveyance, permeable pavement, and others located in Falls/Jordan Critical Area (F/J-A). helps the City better understand the pollutant Falls/Jordan Protected Area (F/J-B) require 100 removal effectiveness of these SCMs within the feet on perennial and 50 feet (100 feet high City’s unique geology, soils, and climate. density) for intermittent streams. Stormwater research is also used to support · Water quality and biological monitoring. The recommendations for site selection, design, City performs water quality and biological installation, and maintenance activities. monitoring at five stations in the Eno River · Flood prevention and mitigation. Portions of watershed study area and has collected data from the Eno River watershed, particularly downstream additional stations as part of watershed studies. of US 501 near the Old Farm and River Forest The City collects benthic macroinvertebrate and neighborhoods and upstream of Penny’s Bend, aquatic habitat assessment data in the watershed are highly prone to flooding. The Old Farm and and, in conjunction with this WIP, collected fish River Forest neighborhoods were developed and

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annexed prior to floodplain regulation. After and septic system maintenance can also lead to Hurricane Fran in 1996, the City purchased and behavior changes that reduce bacteria, sediment, preserved 12 residential floodplain properties in nutrient, and heavy metal impacts in the Eno River these neighborhoods as open space. During the watershed. City staff are regularly engaged in same period, the City acquired numerous large direct and indirect education that includes tracts of Eno River floodplain in this area to engagement of select audiences, provision of preserve them for open space and recreation. educational materials, demonstration of best The City manages a flood warning gage practices, and solicitation of feedback and monitoring system for the Old Farm and River involvement. Forest neighborhoods. The system is used to · Collaboration among City departments. The inform road closure and other safety-related City is coordinating several projects that have the decisions made by Durham County Emergency potential to affect water quality in the Eno River Management. The City and Durham County watershed. Project examples include the Eno River Emergency Management also participate in and Outfall Phase II (Water Management), Warren help maintain the Eno-Haw Regional Hazard Creek Trail (Parks and Recreation, General Mitigation Plan (Alamance County et al., 2015) Services, and Transportation), Warren Creek and regularly apply for Federal Emergency Stream Restoration (Public Works), and Warren Management Agency (FEMA) hazard mitigation Creek Pollutant Source Tracking (Public Works). grants. The City was recently awarded a grant to mitigate 10 additional flood-prone properties in 8.2 Evaluating Progress various locations of the city. The mitigation Progress toward protecting water quality in the Eno actions include acquisition, open space creation, River and its tributaries is taking place through an and a residential building elevation for high-risk adaptive management framework in which new structures in floodplains. information is used to inform actions needed to The frequency and magnitude of flooding events protect or restore water quality. The adaptive in the Eno River watershed correspond in part to management process begins with implementing and land use changes and new development. To tracking existing controls, programs, and practices alleviate current and potential future increased that improve water quality (Section 8.1). Through impacts, the City should continue to maintain the monitoring and assessment of conditions in the Eno-Haw Regional Hazard Mitigation Plan watershed, the City assesses the effectiveness of (Alamance County et al., 2015), allowing the City these controls and progress toward achieving the to continue to apply for FEMA hazard mitigation desired water quality conditions. This information is grants. The City should also financially support then used to adjust project implementation plans as the operation and maintenance of USGS rainfall needed. and streamflow gages that are used as the basis Current monitoring and assessment tools used to for the Eno River flood warning system. protect the Eno River watershed and implement · Environmental education programs. City staff nutrient management strategies for Falls Lake are routinely educate the public on stormwater- presented in Table 8-1. Because the Eno River is related topics. This education helps to inform the currently achieving its designated uses, no additional public about the importance of stormwater controls are required to address water quality quality, reduce pollution at its source by changing concerns within the Eno River watershed beyond attitudes and behaviors, and create a body of those required to comply with Falls Lake nutrient support for local stormwater initiatives. management strategy. Encouraging the proper application of lawn fertilizer, landscape practices, pet waste disposal,

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Table 8-1. Information used to track the effectiveness of controls in the Eno River watershed Implementation Category Collected or Reported Information Schedule Water quality Ambient water chemistry is collected monthly at five locations in the Eno Monthly River watershed, and WQI and water quality analyses are reported annually in monitoring and the City’s State of Our Streams Report (City of Durham, 2018b). Water quality annual reporting data are available through the City’s web portal (http://www.durhamwaterquality.org). Chemical water quality monitoring is also performed by NCDEQ and UNRBA (ends 2018) throughout the Eno River watershed. Benthic community Biological data including benthic macroinvertebrate data have been collected Every other year and freshwater by the City and NCDEQ. The City has collected benthic macroinvertebrate mussels data at two stations on the Eno River. Freshwater mussels have been assessed by NCDEQ. Fish community The City conducted quantitative and qualitative fish surveys at four sites in the 2017 Eno River in 2017. This information will serve as a reference and baseline for future surveys. Aquatic vegetation The City performed an aquatic vegetation survey for invasive aquatic plants in 2013 and 2016 the Eno River (City of Durham, 2014a). Surveys have also been performed by the Eno River Association, NC Wildlife Resource Commission, and NC State University (Eno River Hydrilla Management Task Force, 2018). Nutrient loading Portions of the Falls Lake Watershed Analysis Risk Management Framework 2018 and future (WARMF) model, including the Eno River watershed, were updated in 2018. updates The model provides nutrient loading and source characterization for the Eno River watershed. Future updates will be used to support the Falls Lake Nutrient Management Strategy. Sediment chemistry The City conducted a comprehensive water quality study for the Eno River 2014 watershed between July 2013 and June 2014 that included sediment sampling (City of Durham, 2014b). This information will serve as a reference and baseline for future sediment sampling. Streamflow and Streamflow and stage are recorded at three USGS gage locations along the Ongoing flooding Eno River mainstem. The City manages a flood warning gage monitoring system for portions of the Eno River watershed. SCM retrofits The City maintains a database of all SCMs installed by the City or others Ongoing with within the city under the Stormwater Performance Standards for frequent updates Development Ordinance (City of Durham, 2012b) as well as completed SCMs that were not installed under these requirements.

SCM retrofits The City tracks potential or proposed SCM retrofits and new SCMs identified Ongoing with (potential) through watershed planning studies and on an annual basis, selects projects frequent updates for CIP funding. SCM maintenance The City tracks SCM inspection and maintenance actions for all SCMs. Ongoing with frequent updates GI-LID Development The City tracks the implementation of and GI-LID practices throughout the Ongoing with city. frequent updates

CIP = capital improvement plan SCM = stormwater control measure GI-LID = green infrastructure – low impact development WQI = Water Quality Index

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9 References

Alamance County, Orange County, and Durham County. 2015. Eno-Haw Regional Hazard Mitigation Plan. Prepared by Eno-Haw Hazard Mitigation Planning Team. Accessed June 28, 2018, at https://orangecountync.gov/672/Eno-Haw-Regional-Hazard-Mitigation-Plan. Bradley, P.J. 2007. A Geologic Adventure Along the Eno River. North Carolina Geological Survey Information Circular 35. Chesapeake Bay Program. 2014. Recommendations of the Expert Panel to Define Removal Rates for Individual Stream Restoration Projects. Prepared by Tom Schueler and Bill Stack, Center for Watershed Protection. City of Durham. 2010. Ellerbe Creek Watershed Improvement Plan. Prepared by Brown and Caldwell. Accessed June 28, 2018, at https://durhamnc.gov/954/Ellerbe-Creek-Watershed-Improvement-Plan. City of Durham. 2011. Durham Trails and Greenways Master Plan. Durham City-County Planning Department. Accessed June 28, 2018, at http://nc-durham.civicplus.com/DocumentCenter/View/3445/Durham-Trails-and- Greenways-Master-Plan-2011-PDF?bidId=. City of Durham. 2012a. Durham Third Fork Creek Watershed Management Plan. Accessed June 30, 2018, at https://durhamnc.gov/970/Third-Fork-Creek-Watershed-Improvement-P. City of Durham. 2012b. Stormwater Performance Standards for Development. Durham City Code, Chapter 70, Article X, Sections 70-736 through 70-749. Accessed June 29, 2018, at https://library.municode.com/nc/durham/codes/code_of_ordinances?nodeId=PTIICOOR_CH70UT_ARTXSTPEST DE. City of Durham. 2013a. Northeast and Crooked Creek Watershed Improvement Plan. Prepared for the City of Durham. Prepared by Brown and Caldwell. City of Durham. 2013b. City of Durham Parks and Recreation Master Plan. Accessed June 27, 2018, at http://durhamnc.gov/DocumentCenter/View/7496/DPR-Master-Plan-2013. City of Durham. 2013c. Northeast Creek Watershed Modeling Services WASP Modeling. Prepared for City of Durham Stormwater & GIS Services. City of Durham. 2014a. Eno River Aquatic Vegetation Survey: Submerged Aquatic Vegetation Survey for Hydrilla verticillata (hydrilla), Podostemum ceratophyllum (riverweed), and Myriophyllum aquaticum (parrot feather) in the Eno River near Durham, NC. Department of Public Works. Accessed June 27, 2018, at http://nc- ipc.weebly.com/eno-river-hydrilla-project.html. City of Durham. 2014b. Eno River Watershed Implementation Plan Data Collection. Department of Public Works. Accessed June 27, 2018, at https://durhamnc.gov/DocumentCenter/View/5748/EnoRiverRFPaddendum1f. City of Durham. 2014c. Evaluation of Pollutants in Wastewater Generated by Mobile Car Washing Operations. Department of Public Works. City of Durham. 2016a. Little Lick Creek Watershed Improvement Plan. Department of Public Works. Accessed June 30, 2018, at https://durhamnc.gov/960/Little-Lick-Creek-Watershed-Plan. City of Durham. 2016b. Future Land Use Map. Durham City-County Planning Department. Received May 23, 2016. City of Durham. 2016c. State of Our Streams 2016. Public Works Department.

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City of Durham. 2016d. Evaluation of Pollutants in Wastewater Produced from Air Conditioning Cleaning Operations in Durham, NC. Department of Public Works. Water Quality Report # 14-001. Accessed October 1, 2018, at https://durhamnc.gov/DocumentCenter/View/16309/AC-Coil-Cleaning-Study-Report-FINAL-92116- reduced?bidId=. City of Durham. 2016e. City of Durham Stormwater Management Program Plan. Department of Public Works. City of Durham. 2017a. Durham Comprehensive Plan. Durham City-County Planning Department. Accessed June 27, 2018, at https://durhamnc.gov/346/Comprehensive-Plan. City of Durham. 2017b. Technical memorandum on Cluster Selection Criteria, GIS Analysis, & Program Recommendations. Small Scale Residential Stormwater Control Retrofits in Durham (City contract #13499). Department of Public Works, Durham, NC. City of Durham. 2018a. Roadmap to Sustainability. Accessed August 22, 2018, at https://durhamnc.gov/822/Sustainability-Energy-Management. City of Durham. 2018b. “State of our Streams”. Public Works Department. Accessed August 22, 2018, at http://durhamnc.gov/708/State-of-Our-Streams. City of Durham. 2018c. “Water Quality Web Data Portal: City of Durham.” Public Works Department. Accessed July 26, 2018, at http://www.durhamwaterquality.org. Daniels, R.B., S.W. Buol, H.J. Kleiss, and C.A. Ditzler. 1999. Soil Systems in North Carolina. Technical Bulletin 314. Raleigh: North Carolina State University. Dreps, C.L. 2011. Water Storm Dynamics and Water Balances of Two Piedmont North Carolina Headwater Catchments. Master’s thesis, North Carolina State University. Durham City-County Planning Department. 2018. Unified Development Ordinance. Accessed June 29, 2018, at https://durham.municipal.codes/UDO. Eno River Association. n.d. “Journals.” Accessed on October 3, 2017, at https://www.enoriver.org/store/journals. Eno River Hydrilla Management Task Force. 2018. “Eno River Hydrilla Management Project.” Accessed on June 27, 2018, at http://nc-ipc.weebly.com/eno-river-hydrilla-project.html. Esri. n.d. “Survey123 for ArcGIS.” Accessed on June 30, 2018, at https://www.esri.com/ products/survey123. Griffith, G.E., J.M. Omernik, J.A. Comstock, M.P. Schafale, W.H. McNab, D.R. Lenat, T.F. MacPherson, J.B. Glover, and V.B. Shelburne, V.B. 2002. Ecoregions of North Carolina and South Carolina (color poster with map, descriptive text, summary tables, and photographs): Reston, Virginia, U.S. Geological Survey (map scale 1:1,500,000). Accessed on June 12, 2018, at ftp://newftp.epa.gov/EPADataCommons/ORD/Ecoregions/nc/ncsc_front.pdf. NCDEQ (North Carolina Department of Environmental Quality). 2000. Neuse River Basin: Nutrient Sensitive Waters Management Strategy: Protection and Maintenance of Existing Riparian Buffers. (15A NCAC 02B. 0233). Accessed June 28, 2017, at http://reports.oah.state.nc.us/ncac/title%2015a%20- %20environmental%20quality/chapter%2002%20- %20environmental%20management/subchapter%20b/15a%20ncac%2002b%20.0233.pdf. NCDEQ. 2011. Falls Water Supply Nutrient Strategy. 15A NCAC 02B .0275 – .0282 and amended .0235 and .0315. Accessed June 29, 2018, at https://deq.nc.gov/about/divisions/water-resources/water-planning/nonpoint- source-planning/falls-lake-nutrient-strategy. NCDEQ. 2016. Final 2016 Category 5 Assessments -303(d). Accessed July 11, 2018, at https://files.nc.gov/ncdeq/Water%20Quality/Planning/TMDL/303d/2016/2016_NC_Category_5_303d_list.pdf.

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NCDEQ. 2017. Stormwater Control Measure Credit Document. Accessed June 27, 2018, at https://files.nc.gov/ncdeq/Energy%20Mineral%20and%20Land%20Resources/Stormwater/BMP%20Manual/SS W-SCM-Credit-Doc-20170807.pdf. NCDEQ. 2018. “Classifications and Standards.” Accessed June 27, 2018, at https://deq.nc.gov/about/divisions/water-resources/planning/classification-standards. NCDOT (North Carolina Department of Transportation). n.d. “North Carolina Dept. of Transportation (NCDOT) Data.” Accessed June 30, 2018, at https://connect.ncdot.gov/resources/gis/Pages/GIS-Data-Layers.aspx. NCWRC (North Carolina Wildlife Resources Commission). 2017. Eno-New Hope Landscape Conservation Plan. Green Growth. Wildlife and Natural Resources Stewardship in Planning. North Carolina State Parks. n.d. “Eno River State Park.” Accessed May 25, 2017, at https://www.ncparks.gov/eno-river-state-park/activities. NRCS (Natural Resource Conservation Service). n.d. “Updated Hydrologic Soils Group (HSG) Questions and Answers.” Accessed June 30, 2018, at https://www.nrcs.usda.gov/wps/PA_NRCSConsumption/download?cid=stelprdb1262857&ext=pdf. Rosgen, D. 2001. A Practical Method of Computing Stream Bank Erosion Rate. Proceedings of the Seventh Federal Interagency Sedimentation Conference. Vol. 2, pp. II – 9-15, March 25-29, 2001, Reno, NV. Soil Survey Staff, Natural Resources Conservation Service, United States Department of Agriculture. Web Soil Survey. Accessed May 17, 2017, at https://websoilsurvey.sc.egov.usda.gov/app/WebSoilSurvey.aspx. Tetra Tech. 2013. North Carolina Piedmont Nutrient Load Reducing Measures Technical Report. Prepared for Piedmont Triangle Regional Council, NC Division of Water Quality and Nutrient Science Advisory Board BMP Subcommittee. UNCWI (Upper Neuse Clean Water Initiative). 2015. Upper Neuse Clean Water Initiative 2015–2045 Conservation Strategy. Accessed June 29, 2018, at https://issuu.com/rebeccahankins/docs/2015- 2045_conservation_strategy?workerAddress=ec2-54-226-101-238.compute-1.amazonaws.com. UNRBA (Upper Neuse River Basin Association). 2018. “UNRBA Stage II Falls Lake Rules Reexamination Effort.” Accessed June 27, 2018, at https://www.unrba.org/reexamination. USACE (U.S. Army Corps of Engineers). 2003. Stream Mitigation Guidelines. Accessed July 5, 2017, at http://portal.ncdenr.org/c/document_library/get_file?uuid=ab4ccad4-5cbe-45f3-979f- ab3fe35d21a1&groupId=61581. USEPA (U.S. Environmental Protection Agency). 2008. Handbook for Developing Watershed Plans to Restore and Protect our Waters. EPA 841-B-08-002. Available at https://www.epa.gov/sites/production/files/2015- 09/documents/2008_04_18_nps_watershed_handbook_handbook-2.pdf. USEPA. 2017. “Polluted Runoff: Nonpoint Source Pollution. What is Nonpoint Source?” Accessed October 2, 2017, at https://www.epa.gov/nps/what-nonpoint-source. USEPA. 2018. “Ecological Risk Assessment - Glossary of Terms.” Accessed June 27, 2018, at https://archive.epa.gov/reg5sfun/ecology/web/html/glossary.html. USGS (U.S. Geological Survey). n.d. “National Land Cover Database (NLCD) Land Cover Collection.” Accessed June 30, 2018, at https://catalog.data.gov/dataset/national-land-cover-database-nlcd-land-cover-collection. USGS. n.d. “USGS 02085070 Eno River near Durham, NC. Peak Streamflow for North Carolina.” Accessed September 10, 2018, at https://nwis.waterdata.usgs.gov/nc/nwis/peak/?site_no=02085070&agency_cd=USGS.

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Wright, J.M. 2007. “Floodplain Natural Resources and Functions.” In Floodplain Management: Principles and Current Practices. Accessed July 17, 2017, at https://training.fema.gov/hiedu/docs/fmc/chapter%208%20- %20floodplain%20natural%20resources%20and%20functions.pdf. Wegmann, Karl W., C.L. Osburn, R. Q. Lewis, I.M. Peszlen and H. Mitasova. 2013. Legacy Sediments and Stream Water Quality: Estimating Volume, Nutrient Content, and Stream Bank Erosion in 303(d)-Impaired Waterways of the North Carolina Piedmont. Report No. 435. Water Resources Research Institute of The University of North Carolina. Accessed August 24, 2018, at https://repository.lib.ncsu.edu/bitstream/handle/1840.4/8190/NC- WRRI-435.pdf?sequence=1&isAllowed=y. Wegmann, Karl W., R.Q. Lewis, and M.C. Hunt. 2012. Historic mill ponds and piedmont stream water quality: Making the connection near Raleigh, North Carolina. In Eppes, M.C., and Bartholomew, M.J., eds., From the Blue Ridge to the Coastal Plain: Field Excursions in the Southeastern United States: Geological Society of America Field Guide 29, p. 93–121, doi:10.1130/2012.0029(03). Accessed August 24, 2018, at https://www.researchgate.net/publication/234402580_Historic_mill_ponds_and_piedmont_stream_water_quality _Making_the_connection_near_Raleigh_North_Carolina. Young, Ben, Lydia Olander, and Amy Pickle. 2016. “Use of Preservation in North Carolina Wetland and Stream Mitigation.” NI WP 17-04. Durham, NC: Duke University. Accessed June 29, 2018, at https://nicholasinstitute.duke.edu/sites/default/files/publications/ni_wp_17-04_0.pdf.

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