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

JSACIVIL EnglneeMg I Planning I Management pipe to be installed 0.14' below the lowest CO. This installation error was causing stormwater in the lower pond to bubble out of the 161 Avenue CB's prior to entering the intended overflow system. Ultimately, leading to frequent flooding of 161 Avenue. See the link in Section 3i for additional information. In April 2020, the overflow was lowered to the Intended design elevation. COMPLETED MITIGATION - UPPER POND BERM In addition, it was determined the upper pond was installed with an elevation along the southern retaining wall of the pond approximately 2' lower than the overflow standpipe. This installation error caused the upper pond to overflow back down into 1(i Avenue, further exaggerating the flooding problems. See the link in Section 31 for additional information and photos of overflow below. In April 2020, a berm was installed to Prevent this unintended overflow. Photo of unintended overflow Photo of unintended overflow Down 10100 ST Se The overall system outfall was installed approximately 4' above the intended design outfall elevation. The initial modeling of the system with the incorrect outlet elevation shows the Hydraulic Grade Line (HG L) pushing water out of the lowest CO in the system, which is located in the Silverlake Professional Parking Center, during routine flooding events. See the link in Section 31 for additional information. JSA has identified the following options as potential solutions: • Proposed Solution No. 1: Easement/ Outfall Modification: We believe this outfall was installed at an elevation higher than the original design due to actual elevations at the property line being higher than expected and the need for an easement from the adjacent property owner to reach the lower elevations. It is our understanding that the site to the north is currently going through a permit review process. If it is possible for the City to obtain the easement necessary to reach the Intended outlet elevation as a condition of their permitting, Wini could modify the outfall to reflect the original design intent. 2022 0125 1 3 of 4