The URL can be used to link to this page

Home My WebLink AboutCOLLEGE EIGHT THIRTY - PDP - PDP150019 - REPORTS - STORMWATER-RELATED DOCUMENTSLID Conformance Report Date: November 10, 2015 Project: College Eight Thirty Project No. 574-006 Fort Collins, Colorado Attn: Stormwater Staff City of Fort Collins Stormwater Utility 700 Wood Street Fort Collins, Colorado 80521 Stormwater Staff: This letter serves to document conformance of the above referenced project with City of Fort Collins Low Impact Development (LID) requirements. In particular, the project is meeting Section 3.1 of the Fort Collins Stormwater Amendments to the Urban Drainage and Flood Control District Criteria Manual, including Section3.1 (a)(1) requiring that no less than 50% of any newly added impervious area be treated using one or more LID techniques and Section 3.1(a)(2) requiring that no less than 25% of all new paving use a permeable pavement technology that is considered an LID technique. Section 3.1(a)(1) The project as a whole is proposing 0.307 acres of new impervious area. This results in a minimum required LID treatment area of 0.154 acres. The project is providing 0.233 acres of impervious area treated by pavers (directly or indirectly), and is treating 0.021 acres of impervious areas using rain gardens. The total project area treated by LID techniques is 0.254 acres, which is 82.67% of the total new impervious area. There is also a small area of roof (0.018 acres) that is being released into a landscaped area within the public ROW that is not being counted towards the requirement but that does treat runoff, making the effective treatment percentage even higher. Section 3.1(a)(2) The project as a whole is proposing 2,076 sf of exposed impervious paving for parking. This results in a minimum required permeable paving area of 519 sf. The project has evaluated various areas for pavers, and has determined that the only appropriate location is the exposed area of paving. The total area of permeable pavers provided by the project is 2,076 sf, which is 100.0% of the total new paving. This greatly exceeds the requirement of 25%. An exhibit has been provided to illustrate the topics outlined. Please feel free to contact me if you have any questions. Sincerely, Andrew Reese Nicholas W. Haws, PE Project Engineer Project Manager. Sheet 1 of 2 Designer: Company: Date: Project: Location: 1. Basin Storage Volume A) Effective Imperviousness of Tributary Area, Ia Ia = 100.0 % (100% if all paved and roofed areas upstream of rain garden) B) Tributary Area's Imperviousness Ratio (i = Ia/100) i = 1.000 C) Water Quality Capture Volume (WQCV) for a 12-hour Drain Time WQCV = 0.40 watershed inches (WQCV= 0.8 * (0.91* i3 - 1.19 * i2 + 0.78 * i) D) Contributing Watershed Area (including rain garden area) Area = 434 sq ft E) Water Quality Capture Volume (WQCV) Design Volume VWQCV = 14 cu ft Vol = (WQCV / 12) * Area F) For Watersheds Outside of the Denver Region, Depth of d6 = in Average Runoff Producing Storm G) For Watersheds Outside of the Denver Region, VWQCV OTHER = 0.0 cu ft Water Quality Capture Volume (WQCV) Design Volume H) User Input of Water Quality Capture Volume (WQCV) Design Volume VWQCV USER = cu ft (Only if a different WQCV Design Volume is desired) 2. Basin Geometry A) WQCV Depth (12-inch maximum) DWQCV = 6 in B) Rain Garden Side Slopes (Z = 4 min., horiz. dist per unit vertical) Z = 4.00 ft / ft (Use "0" if rain garden has vertical walls) C) Mimimum Flat Surface Area AMin = 10 sq ft D) Actual Flat Surface Area AActual = 32 sq ft E) Area at Design Depth (Top Surface Area) ATop = 32 sq ft F) Rain Garden Total Volume VT= 16 cu ft (VT= ((ATop + AActual) / 2) * Depth) 3. Growing Media 4. Underdrain System A) Are underdrains provided? B) Underdrain system orifice diameter for 12 hour drain time i) Distance From Lowest Elevation of the Storage y = ft Volume to the Center of the Orifice ii) Volume to Drain in 12 Hours Vol12 = N/A cu ft iii) Orifice Diameter, 3/8" Minimum DO = N/A in Design Procedure Form: Rain Garden (RG) Andy Reese Northern Engineering September 9, 2015 College Eight Thirty South Rain Garden Choose One Choose One 18" Rain Garden Growing Media Other (Explain): YES NO UD-BMP_v3.02_South Raingarden.xls, RG 9/8/2015, 12:51 PM Sheet 2 of 2 Designer: Company: Date: Project: Location: 5. Impermeable Geomembrane Liner and Geotextile Separator Fabric A) Is an impermeable liner provided due to proximity of structures or groundwater contamination? 6. Inlet / Outlet Control A) Inlet Control 7. Vegetation 8. Irrigation A) Will the rain garden be irrigated? Notes: September 9, 2015 College Eight Thirty South Rain Garden Design Procedure Form: Rain Garden (RG) Andy Reese Northern Engineering Choose One Choose One Choose One Sheet Flow- No Energy Dissipation Required Concentrated Flow- Energy Dissipation Provided Plantings Seed (Plan for frequent weed control) Sand Grown or Other High Infiltration Sod Choose One YES NO YES NO UD-BMP_v3.02_South Raingarden.xls, RG 9/8/2015, 12:51 PM Sheet 1 of 2 Designer: Company: Date: Project: Location: 1. Basin Storage Volume A) Effective Imperviousness of Tributary Area, Ia Ia = 100.0 % (100% if all paved and roofed areas upstream of rain garden) B) Tributary Area's Imperviousness Ratio (i = Ia/100) i = 1.000 C) Water Quality Capture Volume (WQCV) for a 12-hour Drain Time WQCV = 0.40 watershed inches (WQCV= 0.8 * (0.91* i3 - 1.19 * i2 + 0.78 * i) D) Contributing Watershed Area (including rain garden area) Area = 434 sq ft E) Water Quality Capture Volume (WQCV) Design Volume VWQCV = 14 cu ft Vol = (WQCV / 12) * Area F) For Watersheds Outside of the Denver Region, Depth of d6 = in Average Runoff Producing Storm G) For Watersheds Outside of the Denver Region, VWQCV OTHER = 0.0 cu ft Water Quality Capture Volume (WQCV) Design Volume H) User Input of Water Quality Capture Volume (WQCV) Design Volume VWQCV USER = cu ft (Only if a different WQCV Design Volume is desired) 2. Basin Geometry A) WQCV Depth (12-inch maximum) DWQCV = 6 in B) Rain Garden Side Slopes (Z = 4 min., horiz. dist per unit vertical) Z = 4.00 ft / ft (Use "0" if rain garden has vertical walls) C) Mimimum Flat Surface Area AMin = 10 sq ft D) Actual Flat Surface Area AActual = 32 sq ft E) Area at Design Depth (Top Surface Area) ATop = 32 sq ft F) Rain Garden Total Volume VT= 16 cu ft (VT= ((ATop + AActual) / 2) * Depth) 3. Growing Media 4. Underdrain System A) Are underdrains provided? B) Underdrain system orifice diameter for 12 hour drain time i) Distance From Lowest Elevation of the Storage y = ft Volume to the Center of the Orifice ii) Volume to Drain in 12 Hours Vol12 = N/A cu ft iii) Orifice Diameter, 3/8" Minimum DO = N/A in College Eight Thirty North Rain Garden Design Procedure Form: Rain Garden (RG) Andy Reese Northern Engineering September 9, 2015 Choose One Choose One 18" Rain Garden Growing Media Other (Explain): YES NO UD-BMP_v3.02_North Raingarden.xls, RG 9/8/2015, 12:52 PM Sheet 2 of 2 Designer: Company: Date: Project: Location: 5. Impermeable Geomembrane Liner and Geotextile Separator Fabric A) Is an impermeable liner provided due to proximity of structures or groundwater contamination? 6. Inlet / Outlet Control A) Inlet Control 7. Vegetation 8. Irrigation A) Will the rain garden be irrigated? Notes: Design Procedure Form: Rain Garden (RG) Andy Reese Northern Engineering September 9, 2015 College Eight Thirty North Rain Garden Choose One Choose One Choose One Sheet Flow- No Energy Dissipation Required Concentrated Flow- Energy Dissipation Provided Plantings Seed (Plan for frequent weed control) Sand Grown or Other High Infiltration Sod Choose One YES NO YES NO UD-BMP_v3.02_North Raingarden.xls, RG 9/8/2015, 12:52 PM