2002-07-25_AgendaPacket - Laserfiche WebLink

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,4~1£~ (~~~ ~~ ~f ~ ~~~ 1~ _ ~~~ ~ i l h s opes or ighly erodible soils and identify them on the site map. Describe any erosion and sedimentation control measures to be used during and after project construction. Erosion control measures as suggested by the MPCA's-Best Management Practices (BMPs), and as ~~ required by the NPDES Permits and the local governmental units would be installed to mitigate construction activity impacts. Storm water ponds will be constructed during the beginning of the construction sequence for each segment, to the extent practical. These measures will be specified in the contract documents and on the design plans, as applicable. The project will require a General Storm Water Permit from the Minnesota Pollution Control Agency which requires the incorporation of BMPs and a maintenance program to ensure they remain effective throughout the project. BMPs typically consist of silt fences, haybales, gravel construction entrances, slope grading methods, and turf restoration. 17. Water quality: surface water runoff a. Compare the quantity and quality of site runoff before and after the project. Describe permanent controls to mnnage or treat runoff. Describe any stormwater pollution prevention plans. The proposed project will generate an additional 1,580 cubic meters (1.3 acre-feet) of storm water runoff over the 2.6 kilometers (1.6 miles) of road improvements during a 10 year, 24 hour event. The project will generate an additional 2,092 cubic meters (1.7 acre-feet) of storm water runoff during a 100 year, 24 hour event- This estimate employs methodology of the U.S. Soil ' Conservation Service Technical Release No. 55. The quality of site runoff will be improved. due to proposed storm water treatment basins to be located in the roject area Th b i ill p . e as ns w intercept site runoff and remove pollutants and sediment prior to discharging into receiving waters. No ponding or treatment of site runoff occurs under the existing conditions. Traffic related pollutants consist of Copper, Lead, Zinc, and Phosphorus. A study conducted by the U.S. Environmental Protection Agency (EPA) titled, Results of the Nationwide Urban Runoff Program, December 1983, have identified the above pollutants as the predominant constituents in ~. highway runoff. Other common pollutants are Total Suspended Solids (TSS) and Chloride. TSS and Chloride are introduced into the highway runoff primarily from winter de-icing practices. The amounts vary depending upon the application rates and the number of ice/snowfall events in a given year. An effective means of reducing the amount of pollutants discharged into the receiving stream water body is to provide sedimentation ponds at the outfall of the storm sewers. b. Identify routes and receiving water bodies for runoff from the site; include major downstream water bodies as well as the immediate receiving waters. Estimate impact runoff on the quality of receiving waters. The Highway 49 project crosses the jurisdiction of three watershed districts/management organizations; the Rice Creek Watershed District (RCWD), the Grass Lake Watershed Management Organization, and the Vadnais Lake Area Watershed Management Organization (VLAWMO). One new storm water treatment pond is proposed for the project. Two existing storm water treatment ponds would be enlarged or modified. Stormwater from the subwatershed north of Tanglewood Drive (Drainage area 4A&B on Figure 7), which lies approximately 81% in the VLAWMO, 9% in the RCWD, and 10% in the Grass