2300 KASCH PARK RD PAVEMENT MAINTENANCE AND RENOVATION 2022-02-17

MINIMUM REQUIREMENT NO. 1: PREPARATION OF STORMWATER SITE PLANS Stormwater site plans were prepared to meet the requirements of the 2012 SWMMWW. Refer to Section 5 for a detailed description of the stormwater design. MINIMUM REQUIREMENT NO. 2: CONSTRUCTION STORMWATER POLLUTION PREVENTION Since the proposed project includes more than 2,000 square feet of new plus replaced impervious surfaces, a Construction Stormwater Pollution Prevention Plan (SWPPP) in accordance with the 2012 SWMMWW requirement will be prepared by the contractor prior to the start of construction. Erosion and sedimentation that result from construction is addressed through the implementation of Temporary Erosion and Sedimentation Control (TESC) best management practices (BMPs). Refer to Section 8 of this report for additional information. MINIMUM REQUIREMENT NO. 3: SOURCE CONTROL OF POLLUTION Source control measures that are proposed are continued use of the oil/water separators that are currently installed. No new measures are proposed at this time. MINIMUM REQUIREMENT NO. 4: PRESERVATION OF NATURAL DRAINAGE SYSTEMS AND OUTFALLS The redeveloped target area will maintain the current drainage patterns of the site. All runoff will be mitigated on site by the existing oil/water separators and the detention vault, before being pumped to the updated water quality treatment system (see Minimum Requirement No. 6). Runoff from events exceeding the volume sent to the pump enter a 30-inch HDPE pipe and outfall to Wetland 3, located to the east of the site. See Section 5 for further details regarding conveyance and infiltration of runoff. MINIMUM REQUIREMENT NO. 5: ON -SITE STORMWATER MANAGEMENT The proposed design will maintain the existing oil/water separators and detention vault. See Section 5 for further details of on -site stormwater management. MINIMUM REQUIREMENT NO. 6: RUNOFF TREATMENT Prior to being released to Wetland 3, runoff will be treated on site by amending the current bioswale and then routing runoff to a water quality treatment vault by Contech. Refer to Section 6 for more information regarding water quality treatment. 4. Off -Site Analysis UPSTREAM DRAINAGE AREA The site is located within the Snohomish Water Resource Inventory Area (WRIA) No. 7. Previous construction on the site required an analysis that was completed by Reid Middleton, Inc in 1994 (see Appendix B). The site is made up of a large parking lot area and maintenance buildings. The total existing impervious area is 13.5 acres. It is bordered to the north of the site routed along Kasch Park Road. To the west, runoff falls into a wooded area (see Figure 4-1). This runoff is collected in a 24-inch HDPE pipe that routes runoff to the east across the southern portion of the parking lot and into Wetland 3. To the south of the parking lot area is the existing water quality swale. Immediately southwest of the bioswale is Wetland 3A, and to the south of the bioswale is Wetland 3B (see Figure 4-1). KPFF Consulting Engineers 6