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Proposed Stormwater Facilities ❖ In order to avoid having to provide two separate relatively large stormwater facilities, SC PDS Staff(Randy Sleight/Ken Crossman/120502)has allowed the designation of a detention swap or equivalent area for the mitigation of increased peak flows from the Lot 7/South Access area. The Equivalent or Swap Area is the West Parking Lot. ❖ Flow Control of increased peak flows from the Northwest Parking Lot(Area A) &West Parking Lot(Swap Area)will be provided via 370 lineal feet of 96-inch detention pipe located within the fill prism of the new Northwest Parking Lot. Over 13,000 cubic feet of live/detention storage is being provided. ❖ Water Quality Treatment for pollutants generated from the Northwest and West Parking Lots will be provided via 370 lineal feet of 96-inch detention pipe located within the fill prism of the new Northwest Parking Lot. Over 5,300 cubic feet of dead/water quality storage is being provided.. ❖ Biological Treatment of pollutants generated from the Northwest and West Parking Lots will be provided via a media filter designed by Stormwater Management, Inc to treat the 6-month,24-hour design storm. •3 For Water Quality Treatment of Lot 7/South Access(Area B) and the South Parking Lot, flows from these areas are being routed via a new conveyance system to the existing biofiltration swale. See Hydrologic Calculations in Appendix A and the Preliminary Drainage Plan in Appendix B. END SECTION 1 —SITE DRAINAGE NARRATIVE Targeted Drainage Report for Everett Public Schools Section 2—Risk&Erosion Control Silver Lake Elementary Parking Lot Expansion January 6,2003 By: Perteet Engineering Page 7 of 7