CC PACKET 01161996 - Laserfiche WebLink

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01/02/96 17: 15 V612 937 5822 I;ESTI OOD PRO SN'S 4L 012 DRAFT--Silver Lake Center EAW Page 10 January 2, 1996 The uppermost bedrock units In the vicinity of the site are Platteville and Glenwood Formations, which consist of flne-gralned dolostone and limestone underlain by thin,green, sandy shale. The depth to bedrock in the vicinity of the site is approximately 100 feet. The regional groundwater flow direction in the glacial outwash deposits and the uppermost bedrock aquifer(St.Peter Sandstone)In the vicinity of the site is generally south- southwestward The s/te=specific groundwater flow direction was not determined during this Investigation. 17. Erosion and Sedimentation Give the acreage to be graded or excavated and the cubic yards of soil to be moved: acres: Phase 1 Approximately 12.1 acres of the site will be graded. Phase 2+ Approximately 33.7-38.7 acres of the site will be graded. cubic yards: Phase 1 Approximately 60,000 cubic yards. Phase 2+ Approximately 55,000 cubic yards. Describe any steep slopes or highly erodible soils and identify them on the site map. Describe the erosion and sedimentation measures to be used.durhig and after construction of the project. The slte is currently 96+percent impervious,non-erodible,and has gradual slopes. All site grading and erosion control activities are subject to Rice Creed Watershed District(RCWD)and National Pollutant Discharge Elimination System(NPDES) permits and will comply with pertinent requirements as described In the required Grading and Erosion Control Plan which will likely Incorporate the following Best Management Practices(BMP): . 1. Silt fence installed at the construction limits prlor.to the Initiation of earth work and maintained until all exposed soil is'stabilized. 2. Periodic street cleaning: 3. Rock construction entrance.* 4. Erosion control for stockpile areas,where appropriate. 5. Energy dissipation,such as riprap,Installed at the outfalls of culverts on the stormwater ponds. Because the site lacks steep slopes and the above-mentioned BMPs will be Implemented,adverse Impacts from construction-related sediment and erosion'are not expected to significantly Increase long- term,off-site sediment loading over the level currently generated on this site. Permanent eroslori control will consist of pavement and limited sod areas. No erodible soils or steep slopes will be exposed. Permanent sedimentation and water quality basins will be incorporated into the design of the project. These features are described in greater detail in the next section. 18. Water Quality-Surface Water Runoff a. Compare the quantity and quality of site runoff before and after the project. Describe methods to be used to manage and/or treat runoff. The results indicate that the project will reduce.peak runoff rates from the existing conditions for both the interim and ultlmate redevelopment proposal. The results predict a 26 percent reduction in phosphorus runoff fr'in the 54 acre tributary watershed(a small portion of the drainage area Is outside the subject property)following the construction of the first three ponds(Phase 1). The Inclusion of the fourth basin-will result in further stormwater discharge rate reductions and will provide a 45 percent total reduction in phosphorus discharge relative to existing conditions. Westwood Professional Services, Inc. W