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Home My WebLink About6617 S. COLLEGE AVE. - BASIC DEVELOPMENT REVIEW - BDR150011 - SUBMITTAL DOCUMENTS - ROUND 3 - EROSION CONTROL LETTER/REPORT■ STORMWATER & EROSION CONTROL REPORT FOR KIND CARE 6617 SOUTH COLLEGE AVENUE FORT COLLINS, COLORADO 80525 Project Number 2360-15 October 10, 2015 Revised April 10, 2016 Prepared for: 6617 South College 6617 South Coll Fort Collins, C' Prep y: Forbes Engineering 2908 Cherly Street Fort Collins, CO 80524 Phone: (970) 295-4874 TABLE OF CONTENTS PAGE CERTIFICATION 1 I. GENERAL LOCATION AND DESCRIPTION A. Site Location 2 B. Description of Property 2 C. Flood Hazards 2 II. DRAINAGE BASINS AND SUB -BASINS A. Major Basin Description 3 B. Sub -basin Description 3 III. DRAINAGE ANALYSIS CRITERIA A. Regulations 3 B. Hydrological Criteria 4 IV. DRAINAGE FACILITY & DESIGN A. General Proposed Concept 4 B. Specific Drainage Design Details 4 V. EROSION CONTROL DESIGN A. General Proposed Concept 5 B. Specific Erosion Control Details 5 VI. CONCLUSIONS 6 VII. REFERENCES 6 VIII. APPENDICES 7 CERTIFICATION: I hereby certify that this preliminary stormwater plan & report for the Kind Care site development located at 6617 South College Avenue was prepared by me and meets or exceeds the criteria in the City of Fort Collins Stormwater Management Manual. Kevin Forbes Registered Professional Engineer State of Colorado No. 35265 1 4 4 4 LI It It I. GENERAL LOCATION AND DESCRIPTION A. Site Location The Kind Care Site Development is located in the Northeast quarter of Section 14, Township 6 North, Range 69 West of the 6th Principal Meridian, County of Larimer, State of Colorado. The property lies on the west side of US Highway 287 (South College Avenue) approximately 100 feet south of West Trilby Road. See Vicinity Map in the Appendix. B. Description of Property j Currently, the property area is approximately 141,957 square feet (3.26 acres). Of this 6175 square feet will to be dedicated to US Highway 287, leaving 135,782 square feet (3.12 acres) as the site development area. The lot is currently developed for commercial use with two businesses on site. The west portion contains .a gravel yard, an open shed and a 9200 square foot building used as an office/warehouse. The east portion contains the Kind Care business which is made up of three buildings, a gravel parking area, an asphalt drive and various concrete walks and pads. Landscaping borders the project site on all sides. Other than a very small portion of landscaping located at the northwest corner of the property, the site has a very slight slope towards the east (approximately 1 %). Currently there isn't any detention on the site although it appears that because of the shallow grade there has been an uncertain amount of surface run-off that pools along the landscaping area along the east side of the property. The soil classification for the Site is a Fort Collins loam (3-5% slopes). Fort Collins loams belong to the hydrologic soil group B, as assigned by the Natural Resources Conservation Service. Run-off is moderate and the hazards of wind and water erosion are slight to moderate. Depth to seasonal high water table is greater than 6 feet. C. Flood Hazards The Site does not lie within any floodplain. No known drainage studies exist for this Site and there are no wetlands associated with the Site. 2 II. DRAINAGE BASIN AND SUB -BASINS A. Major Drainage Basin The property is located southwest of and drains into the Stone Creek Basin which is part of the Fossil Creek Drainage Basin. The property drains into the west street gutter system of South College Ave which enters the stormwater system and the intersection of Trilby & College. From there stormwater run-off is transported to Stone Creek. No adverse effects to the Stone Creek Basin are anticipated with this development. B. Sub -Basins Both the existing & proposed drainage for the site is broken up into 3 sub - basins (see historic & developed drainage sub -basin maps in the appendix). Sub -basin A contains the majority of the site and is located in the southern portion of the property. It is fairly flat with an average slope of 1 % towards the east. The outfall is at the landscaping area along the west side of College Ave. Sub -basin B lies in the northwest portion of the property and also slopes east at a 1 % slope. The outfall for Sub -basin B is into an existing pipe system that spills into Sub -basin A. Sub -basin C is located in the northeast portion of the property, it slopes east at an approximate grade of 2% with a non -concentrated sheet flow release into the west gutter system of South College Ave. The difference between the historic and developed sub -basins concerns the areas of the sub -basins only with a larger portion directed towards and into Sub -basin A as a result of the new building roof lines. III. DRAINAGE ANALYSIS CRITERIA A. Regulations The analysis of the storm drainage system for this project was prepared in accordance with the criteria set forth in the City of Fort Collins Stormwater Criteria Manual and the Urban Drainage and Flood Control District's Urban Storm Drainage Criteria Manual (USDCM). B. Hydrological Criteria 1. Design Rainfall Intensity -Duration -Frequency Table for City of Fort Collins 2. Runoff Method Rational 3. Design Storms a. Minor 2-year b. Major 100-year IV. DRAINAGE FACILITY & DESIGN A. General Proposed Concept As expressed in the sub -basin descriptions, the change between the historic and developed drainage patterns is minimal. Existing drainage patterns will be maintained and utilized as well as a portion of the existing pipe system. Surface stormwater run-off will be detained and released at the historic flow rate of 2.84 cfs into the west gutter system of South College Avenue. Additional volume in the detention pond has been added to account for the water quality capture volume. The WQCV has been calculated at 1846 cubic feet. B. Specific Drainage Design Details Erosion control measures will be utilized when the over -lot grading commences and during the demolition and construction of the buildings in order to mitigate erosion and control sediment. Standard Best Management Practices will include, but are not limited to, the use of perimeter silt fencing, a vehicle tracking mat, as well as permanent seeding and an outlet filter in the detention pond. The detention pond will serve as a sediment trap during construction with a filter at the outlet structure and pipe provided. This will last until the end of the site improvements at which time the detention pond will be permanently seeded and the outlet structure will be completed. 11 4 :1 0 V. EROSION & SEDIMENT CONTROL A. General Proposed Concept p o cept Volumes and Areas Impacted The proposed development will disturb approximately 44,540 square feet (1.02 ac) on -site and approximately 4077 square feet off -site. Some of the Site will be graded with topsoil & gravel stripped and stockpiled. The total quantity of cut from the detention pond has been estimated to be 540 cubic yards. Because the cuts exceed the fill, some will be exported from the Site. Erosion and Sediment Control Measures The erosion control measures for the site are shown on the Erosion Control Plans (Sheets C4.0 & C4.1). The construction entrance will be at the curb cut along College Avenue; ,a vehicle tracking mat and concrete washout area will be provided for on -site. Any and all stock piles for excess cut shall be maintained with a silt fence around its base. Other graded areas will be left in rough surface condition until covered with planting and wood or stone mulch. Silt fencing will be installed at the perimeter of the site and at the top of detention area as appropriate to intercept and detain sediment from runoff leaving the site. Other measures utilized in order to control sediment during construction include rock sock bags at curb cuts, curb inlets and at the detention pond outlet structure, as well as permanent seeding in the detention area. Rip rap will be installed as needed at the northern pipe inlet as well as a rock filter installed at the detention pond outlet structure in order to reduce/prevent erosion. It Schedule The construction schedule is as follows: • Install perimeter controls and construction entrances / VTC • Detention pond with outlet structures, outlet protection (rock filter), and downstream inlet protection (rock socks). • Permanent seeding in detention areas. • Site Grading, subgrade preparation and foundation excavation. • Install base course and rough surface all exposed soil areas. Utility construction — install storm water pipe system. • Footing & foundation installation. • Paving and landscaping. • Removal of Erosion Control Measures. B. Specific Erosion Control Details Permanent Stabilization Measures Permanent stabilization measures include permanent seeding, water quality plates on outlet structures & outlet protection. See construction plans for specifications. Stormwater Management Considerations Stormwater will sheet flow from the building areas toward the ponds. Ponds will be constructed early in the development process, including the bioretention/rain garden feature, outlet structures with water quality plates, rock socks and permanent seeding. The pond will also provide post - development stormwater quality control, as will grass -lined swales and permanent landscaping. All areas that will not be intercepted at ponds will be protected with silt fence during construction. Construction Materials and Equipment The contractor shall store all construction materials and equipment and shall provide maintenance and fueling of equipment in confined areas on site. Maintenance The erosion control measures will be inspected weekly during construction. Silt fence, rock socks and curb inlet protection will be cleaned of excessive sediment if necessary. Rock socks will be checked for undermining and bypass and repaired or expanded as needed. Mulching of bare soils will be checked regularly and areas where it was lost or damage will be remulched within seven working days when needed. Cost Estimate The estimated cost of the erosion control measures is $3,175. A detailed spreadsheet is attached to this report. VI. CONCLUSIONS Stormwater Management Conclusion A high water (no build) line has been added to the drainage map that delineates the 100 year watershed elevation with a 1 /2 foot freeboard. The closest building is approximately 45 feet away & 2.32 feet above this line and will not be affected by the 100 year storm water detention or run-off. The analysis of the storm drainage system for this project was completed in accordance with the criteria set forth in the City of Fort Collins Stormwater Criteria Manual and the USDCM. No adverse affects to surrounding properties are anticipated from the proposed improvement of this site. Erosion Control Conclusion The Erosion and Sediment Control Plan has been placed in the City of Fort Collins file for this project. The plan appears to fulfill the City of Fort Collins criteria for erosion control. It is understood that additional erosion control measures may be needed if unforeseen erosion problems occur or if the submitted plan does not function as intended. The requirements of this plan shall run with the land and be the obligation of the land owner until 7 such time as the plan is properly completed, modified or voided. Details for the erosion control measures can be found on sheets C4.0 and C4.1 of the construction plans. VII. REFERENCES 1. Urban Storm Drainage Criteria Manual Volumes I and 2, Urban Drainage and Flood Control District, June 2001, and Volume 3, September 1999. 2. City of Fort Collins Stormwater Criteria Manual, City of Fort Collins Stormwater Department, 2009. 3. Soil Survey of Larimer County Area, Colorado, U.S. Department of Agriculture, Soil Conservation Service and Forest Service, December, 1980. In IN 14 14 8 0 VIII. APPENDICES 1. Vicinity Map Existing Site Conditions Existing Drainage Sub -basins 2. Proposed Site Development Layout Developed Drainage Sub -basins 3. Existing Stormwater Run-off Calculations Proposed Stormwater Run-off Calculations 4. Detention Pond Volume Calculations 5. Pipe Capacity Calculations 6. Erosion Control Worksheets 7. Tables & Figures 8. Erosion & Sediment Control Escrow Calculations 9. Developed Drainage Plan (insert) 10. Erosion Control Plans (insert) G� VICINITY MAP 8c EXISTING SITE CONDITIONS PORTNER , RE'ERVOIR , t•— / LL O �40co 4 LT 12 W TRILBY ROAD w 15 �/ SITE ROBERT Q J/ W i BENSON m 1 i LAKF, Q � J LCR 32 p CARPENTER ROAD VICINITY MAP SCALE 1 " = 2000' A A A x A A K--x --- a--m--m i --w-w R -- a LANDSCAPE I EMT.BIDG. WO%" CEX WOOD HEX BLDG 2t W mat W ONCijIIIII PA �D , 1 IIIASPHALT _ 7t r19.440 sr ASPHAO L fast sr I NC WALK PATIO 457 g i II 212' O 0.9R GRAVEL YARD TCO:PAN WPC i 29.840 SF J I ( I `\ GRA 2 SF � � 1 023 YAM SF I ` \ EX CURB & GUTTER EXISTING IMPERVIOUS AREA EXHIBIT EXISTING NOT TO SCALE CONDITIONS CONCRETE 1155 SF ASPHALT 19,440 SF PERCENT IMPERVIOUS VALUES ROOFS 14,929 SF Percent BASED ON THE FOLLOWING WOOD DECKS 330 SF Impervious 40.7% Character Percent GRAVEL 52,505 SF of Surface Impervious OPEN 47,423 SF Streets TOTAL 135.782 SO FT Paved 100 Gravel 40 Walks 90 Roofs 90 Lawns 0 KIND CARE SITE DEVELOPMENT BY: KEF DATE: 4/12/16 'a, MARRAZZAAAK m IF SUD -DASIN D INFORMATION: SUB -BASIN C INFORMATION: B AREA - 0.45 ACRES AREA - 0.38 ACRES IMPERVIOUSNESS - 25.1% rc IMPERVIOUSNESS - 27.9% C5-0.41 05-0.42 0.45 0.51 Cl00 - 0.51 C10o - 0.52 02; 0.32 CFS GRASS SWALE 02 - 0.29 CFS 0100 0.38 0.52 - 1.42 CFS 78' O 1.98% 0100 - 1.28 CFS 338' O 0.96% 1.53' VERT. DROP 3•23' `ERT• DROP 207' O 1.9X 4' VERT. DROP 67' O 2.5X \ / 204 1.68' VERT. DROP PIPE SYSTEM 35` �= y \42' O 2.4X OROP I j I I I I I I I I a I I I I \a I I \............... ........... i \---- - --- ----------------- _ i \ _...... _--- ___--- ---- —�/ L------------------------------------�..J SUB -BASIN A INFORMATION: EXISTING DRAINAGE SUB -BASINS AREA - 2.29 ACRES NOT TO SCALE AIMPERVIOUSNESS - 46.6% Op DESIGN POINT DESIGNATION C5 - 0.50 2.29 0.63 C100 - 0.63 02 - z.06 CFS KIND CARE SITE DEVELOPMENT A A=SUB-BASIN DESIGNATION Q100 - 9.38 CFS B=AREA IN ACRES C=100 BY: KEF DATE: 2/20/16 B RUNOFFR COEFFICOIENT