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~- <br />t; STORMWATER MANAGEMENT PLAN (SWMP) <br />f ~. AND EROSION AND SEDIMENT CONTROL REPORT <br />FOR <br />' ' ST. VRAIN LAKE GRADING IMPROVEMENT PLANS <br />i~ <br />Page 5 <br /> Stormwater Discharge Permit and other applicable regulations. It is <br /> anticipated that construction activity for the residential development of <br /> phase 1 will begin immediately after the lake grading has been <br /> completed. <br /> F. Site Area <br /> The proposed lake grading portion of the site consists of approximately 277 <br />`" acres more or less. The current plan is to perform the grading required to <br />. , enhance the two existing lakes located north of St. Vrain River. <br /> G. Runoff Coefficients and Soils <br /> The pre-construction 100-year runoff coefficient ('C' value) is approximately <br />' I 0.50 and the post-construction runoff coefficient is approximately 0.51 <br />t because a majority of the site wiii be park and open space. Soil data for the <br /> subject property was obtained from the United States Department of <br />"' Agriculture Soil Conservation Service (SCS) Soil Survey of Arapahoe <br />- ~ Counfy, Colorado. Soils consist of three types: Aquo(Is gravelly <br /> substratum, Colby Loam and Tassel Fine Sandy Loam. The three types of <br />1 soil are classified within the hydrologic soil group 'B' or 'C.' Runoff in these <br />- I types of soils is medium. The erosion hazard is moderate. <br />- ~ H. Existing Vegetation <br />. ~ The site generally slopes in a southeast direction to the two existing lakes <br /> located north of the St. Vrain River with slopes ranging from 2% to 20%. <br />` ~ Areas that are not significantly impacted by agricultural use are currently <br />. ~ covered by approximately 60%-65% of vegetative growth (distributed <br /> uniformly). This growth consists of natural grasses and other native <br />' ' vegetation. Vegetative growth of areas that are significantly impacted by <br /> agricultural use are dependent on the agricultural schedule. <br />, I. Potential Pollution Sources <br /> Potential pollution sources at the project site include sediment, <br /> equipmenUvehicle washing, vehicle maintenance and fueling, paint, <br /> solvents, wood treated products, petroleum products, waste storage and <br />i ; disposal, and off-site sediment transport from vehicle tracking. Many <br /> chemicals typically associated with construction activities are considered <br />' ' potential pollutants. The table below lists many of these pollutants. Careful <br />i ~ handling, storage, and application of these materials reduce the likelihood <br />;, <br /> <br />