12815 19TH AVE SE 2018-01-30 - Laserfiche WebLink

Proposed Area Calculations ❖ Approximately 44%and 56%of the Proposed PDA is impervious and pervious respectively. ❖ The project will cause a net new impervious increase of 16,700 square feet(0.38 Acres/3%). About 1/3 of this 16,700 square feet is Non Pollution Generating Impervious Surface(NPGIS)and 2/3 is Pollution Generating Impervious Surface (PGIS). ❖ Approximately 21%of the Proposed PDA is Pollution Generating Impervious Surface(PGIS). This represents a net increase of 2%(9,800 sf). ❖ Approximately 32%of the Proposed PDA is Pollution Generating Pervious Surface (PGPS). This represents a net decrease of 3%(16,700 sf). See Proposed Area Calculations in Appendix A. Redevelopment 24.30.025 SCC The Silver Lake Elementary Parking Lot Expansion Project meets threshold requirements for Redevelopment as specified in SC24.30.025, and as communicated by PDS Staff (Randy Sleight/Ken Crossman) on December 5, 2002. ❖ Water Quantity Treatment-Detention facilities have been provided to adequately meet requirements of 24.30.025(1). Flow control is being provided for mitigation of increased peak flows from New and Replaced surfaces. The Director has not imposed additional flow control requirements for this project. For water quantity control calculations,predeveloped site conditions have assumed forested cover and a volume correction factor of 1.3 has been applied. ❖ Water Quality Treatment-The project cannot feasibly provide water quality treatment for the entire site per 24.30.025(2)b. A Drainage Variance Request has been submitted under separate cover. In summary,water quality treatment has been provided to the maximum extent feasible for all of the new and replaced areas plus two other existing parking lots —the West Parking Lot and the South Parking Lot-respectively. In addition, many previously untreated pollution generating areas are being relocated or demolished as a result of the new construction including the child care building, the northwest parking lot and the north parking lot. Approximately 89%(237,000 sf) of the PGIS and PGPS will be treated with facilities provided during playfield upgrades in 1998 and with facilities provided with this parking lot expansion. Approximately 11%(30,000 sf)of the pollution generating areas will remain untreated. They include the west building with built up asphalt roof(17,300 sf),the south access road(8,600 sf), and some of the proposed northwest parking lot landscape areas(estimated 4,000 sf). As described in the Variance Request,these areas can neither be economically treated nor physically connected in a reasonably feasible manner. 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 5 of 7