Henderson Pump Station and M.L. King CSO Project
Overflows from the Henderson Relief Structure upstream of the Henderson Pumping Station and from the M.L. King Overflow Structure were discharging an estimated 30 to 60 million gallons of combined wastewater and stormwater into Lake Washington near a public beach and marina. An engineering evaluation of these overflow problems identified alternatives for eliminating these overflows, which included construction of a storage/treatment tunnel along with associated conveyance and pumping improvements at the Henderson Street Pumping Station. Through upgrades to the pump station, modifications to the overflows, and construction of new relief pipelines, the new Henderson/M.L. King system will eliminate the CSO events to Lake Washington. CSO flows will be diverted through the new conveyance system for storage and treatment prior to being discharged into the Duwamish River.
HDR provided predesign, design, and engineering services during construction for this project. Extensive evaluation of trenchless technologies and associated risks were performed during the design. Review of contractor proposals and observation of construction followed during the construction phase.