12815 19TH AVE SE 2018-01-02 MF Import

Proposed Stormwater Facilities •:• In order to avoid having to provide two separate relatively large stormwater facilities, SC PDS Staff (Randy Sleight/Ken Crossman/I20502) 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 No-Ptwesl 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. 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 Hvdrologic Calculations in Appendix A and the Prelinunory Drainage Plan in Appendix B. END SECTION I — SITE DRAINAGE NARRATIVE Targeted Drainage Report for Everett Public Schools Sihcr Lake Elementary Parking Lot Expansion By. Pent Engineering Secdo� 2 — Risk & Erosion Control January 6. 2003 Page 7 of 7