2235 LAKE HEIGHTS DR 2020-12-23 - Laserfiche WebLink

Thad Newport May 6,2019 21804s. a -age 2 of 6 City's NPDES Municipal Stormwater Permit. However, "recommended additional" BMPs are not required. Of particular importance on this site, considering the project's proximity to Silver Lake, are BMPs for Landscaping and LawnNegetation Management(S411). Response: Section 9.1.3—MR 3—Source Control of Pollution has been expanded to include applicable BMPs from Chapter 2 of Volume IV, including: good housekeeping, preventive maintenance, spill prevention and cleanup,applicable operational BMPs for landscaping,applicable operational BMPs for the use of pesticides, and applicable operational BMPs for vegetation management. Due to the nature of these BMPs,they are not shown on the plans. 4. MR #5—Onsite Stormwater Management: The Stormwater Site Plan for the project must clearly identify why each listed on-site stormwater management BMP (MR#5) is infeasible using the infeasibility criteria contained in the 2014 SWMMWW for each individual BMP. The presence of Alderwood Till soils (or other low permeability soils) is not, of itself, an infeasibility criteria because an infiltration rate of more than 0.3 inches per hour is considered a feasible infiltration rate for on-site stormwater management BMPS.The presence of perched groundwater may preclude the use of any of the infiltrating-type on-site stormwater management BMPs, but must be specifically checked and identified for each BMP against the specific BMP's infeasibility criteria. Compliance with BMP T5.13 is required and must be referenced in the report. Response: To address MR#5,the project utilizes post-construction soil quality and depth for lawn and landscaped areas, underdrained bioretention facilities for roof runoff(to the max extent feasible), and an underdrained bioretention facility for the other hard surfaces(new parking lot). Runoff from the new parking lot is treated by an underdrained bioretention facility.The City has agreed that this facility also addresses MR#5, bypassing permeable pavement. 5. MR #6—Runoff Treatment: Enhanced stormwater treatment is required for this project, which StormFilters do not provide. The City requires a GULD rating from Ecology for the level of stormwater treatment proposed with any proprietary device. Additional information can be found on Ecology's website at the following web address: https://ecologv.wa.00v/Regulations-Permits/Guidance-technical-assistance/Stormwater- permittee-quidance-resources/Emerging-stormwater-treatment-technologies The most current GULD approval from Ecology must be included in the Stormwater Site Plan if a proprietary device is used. This inclusion allows the City to go back and find out what Ecology's requirements were at the time of design if issues come up in the future. If the GULD requires the manufacturer to approve each device design or the project's site plan, the City will require a project-specific letter from the manufacturer which acknowledges their review and approval. Response: Per the Enhanced Treatment Menu in Chapter 3 of Volume V of the SMMWW,the project will utilize an underdrained bioretention facility for runoff