9900 19TH AVE SE WINCO FOODS 2025-03-27

JSACIVIL Englncenng I Plonning I Monogement Proposed Solution No. 2: Backwater Valve: JSA recommends mitigating the unintended flooding of the Silverlake Professional Center by installing a backwater valve in the structure shown below preventing backwater of the outfall system from discharging into the Silverlake Parking lot during routine flooding events. Proposed Backwater Valve Location in Overflow system It is acknowledged that when the overflow system Is in a backwater condition, this proposed backwater valve will prevent the Silverlake Professional Park from discharging without the use of Pump Station No. 1. However, we are not aware of a time where Pump Station No.1 has not functioned during these flood events. In addition, the following mitigation measures are also in place: o Silverlake Professional Center has installed their own pump system which discharges into 16u Avenue; from there, runoff enters into the lower pond and ultimately into the bypass system downstream of the proposed backwater valve. o Aqualis will remain on call for stormwater maintenance.Therefore, if a situation occurs where Pump Station No.1 and the Silverlake Professional Center pump station are not functioning properly, Aqualis can provide temporary pumping until the permanent Pump Stations can be fixed. 20220125 1 4of6