A portion of Lots 8 and 9, Block 1, Fountainhead Subdivision

PRELIMINARY DRAINAGE REPORT

Crescent View Academy 10855 E. Bethany Drive Aurora,

Prepared for: Crescent View Academy II, LLC 10958 E. Bethany Drive Aurora, Colorado 80014 303-745-2245 Contact: Anwar Zuraigt

Prepared by: Vermilion Peak Engineering LLC 1745 Shea Center Drive, 4th Floor Highlands Ranch, CO 80129 720-402-6070 Contact: Brian Krombein, PE, PLS

June 12, 2020 Job Number 19037

06/23/2020

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TABLE OF CONTENTS

Page 1.0 INTRODUCTION...... 4 Location Proposed Development 2.0 HISTORIC DRAINAGE ...... 4 Overall Basin Description Drainage Patterns Through Property Outfalls Downstream from Property 3.0 DESIGN CRITERIA ...... 5 List of References Hydrologic Criteria Hydraulic Criteria 4.0 DRAINAGE PLAN ...... 6 General Concept Specific Details 5.0 CONCLUSIONS ...... 8 Compliance with Standards Summary of Concept 6.0 LIST OF REFERENCES ...... 9

APPENDIX Hydrologic Computations Hydraulic Computations Copies of graphs, tables and nomographs used

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ENGINEER’S CERTIFICATION

This report for the preliminary drainage design of a portion of Lots 8 and 9, Block 1, Fountainhead Subdivision was prepared by me (or under my direct supervision) in accordance with the provisions of City of Aurora Storm Drainage Design and Technical Criteria and was designed to comply with the provisions thereof. I understand that the City of Aurora does not and will not assume liability for drainage facilities designed by others.

______Brian Krombein, PE, PLS Colorado Registered Professional Engineer No. 34294 For and on behalf of Vermilion Peak Engineering LLC

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1.0 INTRODUCTION

Location

The project site contains 1.00 acres and is located in the NW 1/4, Section 34, Township 4 South, Range 67 West of the 6th Principal Meridian in the City of Aurora, Arapahoe County, Colorado (see Vicinity Map). The property is platted as A portion of Lots 8 and 9, Block 1, Fountainhead Subdivision). It is bounded on the south by E. Bethany Drive and on the north, east and west by existing office buildings.

Proposed Development

The development at 10855 E. Bethany Drive contains an existing office building with associated parking areas and a small amount of landscaped areas. The disturbed area covers approximately 2,500 square feet. Proposed improvements include interior remodeling of the building, a small building expansion to contain only a new elevator and fire riser room, the addition of a one-way, paved drive aisle and sidewalk along the west side of the building and a new sidewalk connection to E. Bethany Drive.

According to FEMA flood insurance rate map 08005C0186K, dated December 17, 2010, this property lies within Zone X, which is defined as, "areas determined to be outside the 0.2% annual chance floodplain".

Soils on the site consist of Blakeland loamy sand, 1 to 20 percent slopes and Bresser- Truckton sandy loams, 3 to 5 percent slopes. They belong to Hydrologic Soil Group A.

The site impervious area will be increased by a total of 2,230 square feet which will increase the total site imperviousness from 78% to 83%.

2.0 HISTORIC DRAINAGE

Overall Basin Description The project site is located in the Cherry Creek drainage basin, with Cherry Creek being located approximately 1/4 mile southwest of the project site. This basin contains a mix of residential and commercial properties.

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Drainage Patterns Through Property In the existing condition site runoff drains either directly to Bethany Drive or through the adjacent office development to the west from where it drains to Bethany Drive. The proposed site improvements will not alter these existing drainage patterns. Runoff from 100% of the additional impervious areas will drain directly to Bethany Drive and not through neighboring properties. Concentrated drainage will not be allowed to flow over sidewalks.

No previous drainage reports were found that affect this property.

There are no existing wetland or irrigation facilities that affect the project site.

There are no offsite flows which affect the project site.

Outfalls Downstream from Property Once site runoff reaches Bethany Drive it drains westerly to public storm sewer inlets which collect runoff and convey it westerly then southerly in public storm sewer beneath Bethany Drive. Flows ultimately outfall to Cherry Creek a short distance southeast of the intersection of Havana Street and Dartmouth Avenue.

3.0 DRAINAGE DESIGN CRITERIA

List of References The hydrologic analysis and hydraulic design for this site is based upon criteria established in the City of Aurora Storm Drainage Design and Technical Criteria Manual and the Urban Storm Drainage Design Manual prepared by Mile High Flood District (MHFD).

Hydrologic Criteria The Rational Method was used to calculate peak runoff rates for the sub-basins during the 2-year and 100-year storm events. Basin imperviousness was obtained from Table 1 (City of Aurora), runoff coefficients were obtained from Table 1 (City of Aurora), rainfall intensities were obtained from Equation 5.5 (City of Aurora) using the 1-hour point rainfall data from Figures RA-1 and RA-6 (MHFD). Runoff velocities were obtained from Figure 1 (City of Aurora). Times of concentration were determined using form SF-2, and runoff flow

5 rates were determined using form SF-3. Runoff tables and calculations can be found in the appendices of this report.

None of the existing developments in the surrounding office park appear to contain onsite detention or water quality treatment. Although we could not find any previous drainage studies for this property it appears that detention and water quality were not required for this entire area due to its proximity to nearby Cherry Creek and Cherry Creek Reservoir.

Hydraulic Criteria Inlet sizing calculations are included in the appendix of this report. Hydraulic grade line calculations will be provided in the final drainage report.

4.0 DRAINAGE PLAN

General Concept

Site grading has been designed to direct runoff away from the building where it will sheetflow across the parking lots to curb and gutter which conveys flows to Bethany Drive. A new 5’ Type R inlet will be installed in the new drive aisle through the southwest corner of the property in order to collect a majority of onsite runoff. Collected flows will be routed through a mechanical water quality device then released into public storm sewer.

Specific Details

The project site has been analyzed as a single drainage basin for determination of historic and proposed runoff rates:

Basin H-1 (1.0 acres) contains the entire property in the existing condition. It contains building, pavement and landscaped areas. Runoff from Basin H-1 drains either directly to Bethany Drive or to the parking lot of the adjacent office building to the west, from which point it drains to Bethany Drive. The historic 2-year and 100-year flowrates at Design Point H1 are 2.2 cfs and 6.7 cfs. Upon reaching Bethany Drive runoff drains approximately 330 feet west to a public storm inlet in the north gutter from Bethany Drive. Public storm sewer conveys collected flows to a point of discharge into Cherry Creek approximately 1/4 mile to the southwest.

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Basin A (0.70 acres) contains the northwest two-thirds of the property. It contains building, pavement and landscaped areas. Runoff from Basin A drains to an on-grade, 5’ Type R inlet at Design Point 1. The proposed 2-year and 100-year flowrates at Design Point 1 will be 1.8 cfs and 5.5 cfs.

Basin B (0.30 acres) contains the southeast portion of the property. It contains pavement and landscaped areas. Runoff from Basin B drains directly to Bethany Drive as occurs in the existing condition. The proposed 2-year and 100-year flowrates at Design Point 2 will be 0.5 cfs and 1.6 cfs.

Runoff from the building expansion and a portion of the new concrete walk will drain across landscaped areas prior to sheetflowing into Bethany Drive. The remainder of the new impervious area will drain to the proposed 5’ Type R inlet at Design Point 1. Total site 2-year runoff rates will increase from 2.2 cfs to 2.3 cfs and 100-year rates will increase from 6.7 cfs to 7.1 fs.

We hereby request a variance from the typical requirement to provide additional detention volume due to an increase in impervious area. We offer the following support for this request: • Approximately 2,500 square feet of additional impervious area is proposed. • The proposed improvements are located in the lowest-elevation corner of the property with no area available to add detention facilities onsite. • It does not appear that any detention or water quality facilities currently exist to serve this entire commercial subdivision. • The proposed total site imperviousness is 83%. While we were unable to find an existing drainage study for this subdivision, it is reasonable to assume that the drainage infrastructure for this subdivision (downstream roadway and storm sewer) was designed with an assumed imperviousness of 95% for all of the lots in conformance with Table 1 of the COA drainage manual. Therefore, both the existing and proposed runoff rates are less than the area was originally designed to accommodate.

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We understand that the City of Aurora will require water quality treatment for a majority of the site including the additional impervious area. A vast majority of the site will not be disturbed and there is very limited area in the low (southwest) corner of the property. Therefore, the only viable water quality BMP for this application is a mechanical treatment device such as a Stormceptor by Contech. Our design includes the installation of a 5’ type R inlet to collect runoff from the new drive aisle through the southwest corner of the property. Private storm sewer will convey collected flows to a nearby Stormceptor which will then release treated stormwater through a proposed, public 18” RCP to the nearest public storm sewer located approximately 170 feet to the west.

5.0 CONCLUSIONS

Compliance with Standards This preliminary drainage report for a portion of Lots 8 and 9, Block 1, Fountainhead Subdivision has been prepared in compliance with the City of Aurora Storm Drainage Design and Technical Criteria and the Urban Storm Drainage Criteria Manual prepared by Mile High Flood District.

A variance has been requested to waive the requirement for additional detention or water quality improvements as part of the proposed site improvements.

Summary of Concept The drainage improvements recommended for this site will lead to a slight increase in site imperviousness and runoff rates. Drainage patterns will not be altered from the existing conditions. Runoff from the additional drive aisle and small building expansion will drain directly to Bethany Drive. The proposed development will not adversely impact downstream properties or drainage facilities.

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6.0 REFERENCES

1. City of Aurora Storm Drainage Design and Technical Criteria, City of Aurora, September 2010.

2. Federal Emergency Management Agency, Flood Insurance Rate Map, City of Aurora, Map No. 08005C0186K, December 17, 2010.

3. Urban Storm Drainage Criteria Manual, Mile High Flood District, Volume 1, Revised August 2018, September 2017, October 2019.

4. Department of Agriculture – Web Soil Survey, printed January 23, 2020, Soil Map – Arapahoe County, Colorado; http://websoilsurvey.nrcs.usda.gov/app/

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National Flood Hazard Layer FIRMette Legend

39°40'1.58"N SEE FIS REPORT FOR DETAILED LEGEND AND INDEX MAP FOR FIRM PANEL LAYOUT

Without Base Flood Elevation (BFE) Zone A, V, A99 With BFE or Depth Zone AE, AO, AH, VE, AR SPECIAL FLOOD HAZARD AREAS Regulatory Floodway 104°52'0.38"W 0.2% Annual Chance Flood Hazard, Areas of 1% annual chance flood with average depth less than one foot or with drainage areas of less than one square mile Zone X Future Conditions 1% Annual Chance Flood Hazard Zone X Area with Reduced Flood Risk due to OTHER AREAS OF Levee. See Notes. Zone X FLOOD HAZARD Area with Flood Risk due to Levee Zone D

NO SCREEN Area of Minimal Flood Hazard Zone X Effective LOMRs SITE OTHER AREAS Area of Undetermined Flood Hazard Zone D GENERAL Channel, Culvert, or Storm Sewer STRUCTURES Levee, Dike, or Floodwall

20.2 B Cross Sections with 1% Annual Chance 17.5 Water Surface Elevation

8 Coastal Transect Base Flood Elevation Line (BFE) Limit of Study Jurisdiction Boundary Coastal Transect Baseline OTHER Profile Baseline FEATURES Hydrographic Feature

Digital Data Available

No Digital Data Available MAP PANELS Unmapped Ü

The pin displayed on the map is an approximate point selected by the user and does not represent an authoritative property location.

This map complies with FEMA's standards for the use of digital flood maps if it is not void as described below. The basemap shown complies with FEMA's basemap accuracy standards The flood hazard information is derived directly from the authoritative NFHL web services provided by FEMA. This map was exported on 1/6/2020 at 11:20:07 AM and does not reflect changes or amendments subsequent to this date and 104°51'22.92"W 104°51'22.92"W time. The NFHL and effective information may change or become superseded by new data over time.

This map image is void if the one or more of the following map elements do not appear: basemap imagery, flood zone labels, USGS The National Map: Orthoimagery. Data refreshed April, 2019. legend, scale bar, map creation date, community identifiers, FIRM panel number, and FIRM effective date. Map images for Feet 1:6,000 39°39'33.88"N unmapped and unmodernized areas cannot be used for 0 250 500 1,000 1,500 2,000 regulatory purposes. Soil Map—Arapahoe County, Colorado 104° 51' 43'' W 104° 51' 40'' W

511840 511850 511860 511870 511880 511890 511900 39° 39' 50'' N 39° 39' 50'' N 4390480 4390480 4390470 4390470 4390460 4390460 4390450 4390450 4390440 4390440 4390430 4390430 4390420 4390420 4390410 4390410 4390400 4390400

Soil Map may not be valid at this scale. 4390390 4390390

39° 39' 47'' N 39° 39' 47'' N 511840 511850 511860 511870 511880 511890 511900

Map Scale: 1:464 if printed on A portrait (8.5" x 11") sheet. Meters N 0 5 10 20 30 104° 51' 43'' W 104° 51' 40'' W Feet 0 20 40 80 120 Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 13N WGS84

Natural Resources Web Soil Survey 1/23/2020 Conservation Service National Cooperative Soil Survey Page 1 of 3 Soil Map—Arapahoe County, Colorado

MAP LEGEND MAP INFORMATION

Area of Interest (AOI) Spoil Area The soil surveys that comprise your AOI were mapped at Area of Interest (AOI) 1:20,000. Stony Spot Soils Very Stony Spot Warning: Soil Map may not be valid at this scale. Soil Map Unit Polygons Wet Spot Enlargement of maps beyond the scale of mapping can cause Soil Map Unit Lines misunderstanding of the detail of mapping and accuracy of soil Other line placement. The maps do not show the small areas of Soil Map Unit Points contrasting soils that could have been shown at a more detailed Special Line Features Special Point Features scale. Blowout Water Features Streams and Canals Please rely on the bar scale on each map sheet for map Borrow Pit measurements. Transportation Clay Spot Rails Source of Map: Natural Resources Conservation Service Web Soil Survey URL: Closed Depression Interstate Highways Coordinate System: Web Mercator (EPSG:3857) Gravel Pit US Routes Maps from the Web Soil Survey are based on the Web Mercator Gravelly Spot projection, which preserves direction and shape but distorts Major Roads distance and area. A projection that preserves area, such as the Landfill Local Roads Albers equal-area conic projection, should be used if more Lava Flow accurate calculations of distance or area are required. Background Marsh or swamp Aerial Photography This product is generated from the USDA-NRCS certified data as of the version date(s) listed below. Mine or Quarry Soil Survey Area: Arapahoe County, Colorado Miscellaneous Water Survey Area Data: Version 15, Sep 12, 2019 Perennial Water Soil map units are labeled (as space allows) for map scales Rock Outcrop 1:50,000 or larger.

Saline Spot Date(s) aerial images were photographed: Oct 20, 2018—Oct 26, 2018 Sandy Spot The orthophoto or other base map on which the soil lines were Severely Eroded Spot compiled and digitized probably differs from the background imagery displayed on these maps. As a result, some minor Sinkhole shifting of map unit boundaries may be evident. Slide or Slip

Sodic Spot

Natural Resources Web Soil Survey 1/23/2020 Conservation Service National Cooperative Soil Survey Page 2 of 3 Soil Map—Arapahoe County, Colorado

Map Unit Legend

Map Unit Symbol Map Unit Name Acres in AOI Percent of AOI

BoE Blakeland loamy sand, 1 to 20 0.6 59.7% percent slopes BvC Bresser-Truckton sandy loams, 0.4 40.3% 3 to 5 percent slopes Totals for Area of Interest 1.0 100.0%

Natural Resources Web Soil Survey 1/23/2020 Conservation Service National Cooperative Soil Survey Page 3 of 3 Map Unit Description: Blakeland loamy sand, 1 to 20 percent slopes---Arapahoe County, Colorado

Arapahoe County, Colorado

BoE—Blakeland loamy sand, 1 to 20 percent slopes

Map Unit Setting National map unit symbol: 34xz Elevation: 4,600 to 5,800 feet Mean annual precipitation: 14 to 16 inches Mean annual air temperature: 46 to 48 degrees F Frost-free period: 135 to 155 days Farmland classification: Not prime farmland

Map Unit Composition Blakeland and similar soils: 90 percent Minor components: 10 percent Estimates are based on observations, descriptions, and transects of the mapunit.

Description of Blakeland Setting Landform: Hills Landform position (two-dimensional): Backslope Landform position (three-dimensional): Side slope Down-slope shape: Linear Across-slope shape: Linear Parent material: From the dawson formation eolian deposits Typical profile H1 - 0 to 14 inches: loamy sand H2 - 14 to 60 inches: loamy sand, loamy coarse sand, sand H2 - 14 to 60 inches: H2 - 14 to 60 inches: Properties and qualities Slope: 1 to 20 percent Depth to restrictive feature: More than 80 inches Natural drainage class: Somewhat excessively drained Runoff class: Low Capacity of the most limiting layer to transmit water (Ksat): High to very high (5.95 to 19.98 in/hr) Depth to water table: More than 80 inches Frequency of flooding: None Frequency of ponding: None Calcium carbonate, maximum in profile: 5 percent Available water storage in profile: High (about 10.7 inches) Interpretive groups Land capability classification (irrigated): 4e Land capability classification (nonirrigated): 6e Hydrologic Soil Group: A Ecological site: Deep Sand (R067BY015CO)

Natural Resources Web Soil Survey 1/23/2020 Conservation Service National Cooperative Soil Survey Page 1 of 2 Map Unit Description: Blakeland loamy sand, 1 to 20 percent slopes---Arapahoe County, Colorado

Hydric soil rating: No

Minor Components Valent Percent of map unit: 10 percent Hydric soil rating: No Data Source Information

Soil Survey Area: Arapahoe County, Colorado Survey Area Data: Version 15, Sep 12, 2019

Natural Resources Web Soil Survey 1/23/2020 Conservation Service National Cooperative Soil Survey Page 2 of 2 Map Unit Description: Bresser-Truckton sandy loams, 3 to 5 percent slopes---Arapahoe County, Colorado

Arapahoe County, Colorado

BvC—Bresser-Truckton sandy loams, 3 to 5 percent slopes

Map Unit Setting National map unit symbol: 34y5 Elevation: 4,500 to 6,800 feet Mean annual precipitation: 12 to 18 inches Mean annual air temperature: 46 to 52 degrees F Frost-free period: 125 to 180 days Farmland classification: Prime farmland if irrigated and the product of I (soil erodibility) x C (climate factor) does not exceed 60

Map Unit Composition Bresser and similar soils: 55 percent Truckton and similar soils: 30 percent Minor components: 15 percent Estimates are based on observations, descriptions, and transects of the mapunit.

Description of Bresser Setting Landform: Playas, drainageways, stream terraces Landform position (three-dimensional): Tread Down-slope shape: Linear Across-slope shape: Linear Parent material: Noncalcareous sandy alluvium and/or noncalcareous sandy eolian deposits Typical profile H1 - 0 to 6 inches: sandy loam H2 - 6 to 26 inches: sandy clay loam, clay loam H2 - 6 to 26 inches: sandy loam, coarse sandy loam, gravelly sandy loam H3 - 26 to 32 inches: loamy coarse sand, gravelly loamy sand H3 - 26 to 32 inches: H3 - 26 to 32 inches: H4 - 32 to 60 inches: H4 - 32 to 60 inches: Properties and qualities Slope: 3 to 5 percent Depth to restrictive feature: More than 80 inches Natural drainage class: Well drained Runoff class: Low Capacity of the most limiting layer to transmit water (Ksat): Moderately high to high (0.57 to 2.00 in/hr) Depth to water table: More than 80 inches Frequency of flooding: None Frequency of ponding: None Calcium carbonate, maximum in profile: 10 percent

Natural Resources Web Soil Survey 1/23/2020 Conservation Service National Cooperative Soil Survey Page 1 of 3 Map Unit Description: Bresser-Truckton sandy loams, 3 to 5 percent slopes---Arapahoe County, Colorado

Available water storage in profile: Very high (about 13.5 inches) Interpretive groups Land capability classification (irrigated): 3e Land capability classification (nonirrigated): 4e Hydrologic Soil Group: B Ecological site: Sandy Foothill (R049BY210CO) Hydric soil rating: No

Description of Truckton Setting Landform: Ridges Down-slope shape: Linear Across-slope shape: Linear Parent material: Eolian deposits Typical profile H1 - 0 to 5 inches: sandy loam H2 - 5 to 20 inches: sandy loam H3 - 20 to 60 inches: sandy loam, loamy sand, loamy coarse sand H3 - 20 to 60 inches: H3 - 20 to 60 inches: Properties and qualities Slope: 3 to 5 percent Depth to restrictive feature: More than 80 inches Natural drainage class: Well drained Runoff class: Very low Capacity of the most limiting layer to transmit water (Ksat): High (1.98 to 6.00 in/hr) Depth to water table: More than 80 inches Frequency of flooding: None Frequency of ponding: None Available water storage in profile: Very high (about 13.1 inches) Interpretive groups Land capability classification (irrigated): 3e Land capability classification (nonirrigated): 4e Hydrologic Soil Group: A Ecological site: Sandy Foothill (R049BY210CO) Hydric soil rating: No

Minor Components Nunn Percent of map unit: 8 percent Hydric soil rating: No Ascalon Percent of map unit: 7 percent

Natural Resources Web Soil Survey 1/23/2020 Conservation Service National Cooperative Soil Survey Page 2 of 3 Map Unit Description: Bresser-Truckton sandy loams, 3 to 5 percent slopes---Arapahoe County, Colorado

Hydric soil rating: No Data Source Information

Soil Survey Area: Arapahoe County, Colorado Survey Area Data: Version 15, Sep 12, 2019

Natural Resources Web Soil Survey 1/23/2020 Conservation Service National Cooperative Soil Survey Page 3 of 3

Version 4.05 Released March 2017 ALLOWABLE CAPACITY FOR ONE-HALF OF STREET (Minor & Major Storm) (Based on Regulated Criteria for Maximum Allowable Flow Depth and Spread) Project: 10855 E. Bethany Drive Inlet ID: DP 1

Gutter Geometry (Enter data in the blue cells) Maximum Allowable Width for Spread Behind Curb TBACK = 0.0 ft Side Slope Behind Curb (leave blank for no conveyance credit behind curb) SBACK = ft/ft Manning's Roughness Behind Curb (typically between 0.012 and 0.020) nBACK =

Height of Curb at Gutter Flow Line HCURB = 6.00 inches Distance from Curb Face to Street Crown TCROWN = 13.0 ft Gutter Width W = 2.00 ft Street Transverse Slope SX = 0.060 ft/ft Gutter Cross Slope (typically 2 inches over 24 inches or 0.083 ft/ft) SW = 0.083 ft/ft Street Longitudinal Slope - Enter 0 for sump condition SO = 0.030 ft/ft Manning's Roughness for Street Section (typically between 0.012 and 0.020) nSTREET = 0.016

Minor Storm Major Storm Max. Allowable Spread for Minor & Major Storm TMAX = 13.0 13.0 ft Max. Allowable Depth at Gutter Flowline for Minor & Major Storm dMAX = 6.0 6.0 inches Allow Flow Depth at Street Crown (leave blank for no) check = yes

MINOR STORM Allowable Capacity is based on Depth Criterion Minor Storm Major Storm

MAJOR STORM Allowable Capacity is based on Depth Criterion Qallow = 9.7 9.7 cfs Minor storm max. allowable capacity GOOD - greater than the design flow given on sheet 'Inlet Management' Major storm max. allowable capacity GOOD - greater than the design flow given on sheet 'Inlet Management'

UD-Inlet.xlsm, DP 1 6/12/2020, 12:20 PM INLET ON A CONTINUOUS GRADE Version 4.05 Released March 2017

Design Information (Input) MINOR MAJOR CDOT Type R Curb Opening Type of Inlet Type = CDOT Type R Curb Opening

Local Depression (additional to continuous gutter depression 'a') aLOCAL = 3.0 3.0 inches Total Number of Units in the Inlet (Grate or Curb Opening) No = 2 2

Length of a Single Unit Inlet (Grate or Curb Opening) Lo = 5.00 5.00 ft

Width of a Unit Grate (cannot be greater than W, Gutter Width) Wo = N/A N/A ft

Clogging Factor for a Single Unit Grate (typical min. value = 0.5) Cf-G = N/A N/A

Warning 1 Clogging Factor for a Single Unit Curb Opening (typical min. value = 0.1) Cf-C = 0.20 0.20 Street Hydraulics: OK - Q < Allowable Street Capacity' MINOR MAJOR Total Inlet Interception Capacity Q = 0.9 2.6 cfs

Total Inlet Carry-Over Flow (flow bypassing inlet) Qb = 0.0 0.0 cfs

Capture Percentage = Q a/Q o = C% = 100 100 %

UD-Inlet.xlsm, DP 1 6/12/2020, 12:20 PM Brief Stormceptor Sizing Report - Crescent View Academy Project Information & Location Project Name Crescent View Academy Project Number 28551

City State/ Province Colorado

Country United States of America Date 5/20/2020 Designer Information EOR Information (optional) Name Brian Krombein Name Company Vermilion Peak Engineering Company Phone # 720-402-6070 Phone # Email [email protected] Email

Stormwater Treatment Recommendation The recommended Stormceptor Model(s) which achieve or exceed the user defined water quality objective for each site within the project are listed in the below Sizing Summary table. Site Name Target TSS Removal (%) 85 TSS Removal (%) Provided 88 Recommended Stormceptor Model STC 450i The recommended Stormceptor Model achieves the water quality objectives based on the selected inputs, historical rainfall records and selected particle size distribution. Stormceptor Sizing Summary Stormceptor Model % TSS Removal Provided STC 450i 88 STC 900 93 STC 1200 93 STC 1800 94 STC 2400 95 STC 3600 96 STC 4800 97 STC 6000 97 STC 7200 98 STC 11000 98 STC 13000 99 STC 16000 99

Stormceptor Brief Sizing Report ±Page 1 of 2 Sizing Details

Drainage Area Water Quality Objective Total Area (acres) 0.7 TSS Removal (%) 85.0

Imperviousness % 51.0 Runoff Volume Capture (%) Rainfall Oil Spill Capture Volume (Gal) Peak Conveyed Flow Rate (CFS) Station Name STAPELTON Water Quality Flow Rate (CFS) State/Province Colorado Station ID # 2220 Up Stream Storage Years of Records 58 Storage (ac-ft) Discharge (cfs) Latitude 39°45'48"N 0.000 0.000 Longitude 104°52'10"W Up Stream Flow Diversion Max. Flow to Stormceptor (cfs) Particle Size Distribution (PSD) The selected PSD defines TSS removal Fine Distribution Particle Diameter Distribution Specific Gravity (microns) % 20.0 20.0 1.30 60.0 20.0 1.80 150.0 20.0 2.20 400.0 20.0 2.65 2000.0 20.0 2.65 Notes ‡Stormceptor performance estimates are based on simulations using PCSWMM for Stormceptor, which uses the EPA Rainfall and Runoff modules. ‡Design estimates listed are only representative of specific project requirements based on total suspended solids (TSS) removal defined by the selected PSD, and based on stable site conditions only, after construction is completed. ‡For submerged applications or sites specific to spill control, please contact your local Stormceptor representative for further design assistance. For Stormceptor Specifications and Drawings Please Visit: https://www.conteches.com/technical-guides/search?filter=1WBC0O5EYX

Stormceptor Brief Sizing Report ±Page 2 of 2