James W. Fowler Co. (JWF) is proud to be a part of the award-winning Georgetown Wet Weather Treatment Station – Conveyance Project. According to the Institute for Sustainable Infrastructure, “The $250 million Georgetown Wet Weather Treatment Station (GWWTS) in King County, Washington, has received the Envision® Platinum designation for sustainable infrastructure, awarded by the Institute for Sustainable Infrastructure (ISI). The project demonstrates its delivery of environmental, social, and economic benefits to the community. The GWWTS is the third Envision-recognized project in Washington State and the first to receive the Platinum award.” JWF served the project with the construction of underground diversion structures and four separate pipelines for conveying untreated combined sewer to the new treatment plant and treated effluent from the GWWTS to a new outfall in the Duwamish Waterway.
Constructed to control two existing sewer overflows, the project has the capability to treat up to 70 million gallons of combined rain and wastewater a day. It is projected the GWWTS will operate approximately 20 times per year preventing direct discharge of polluted runoff and raw sewage and allowing for cleaned stormwater to return to the river. The project improves overall water quality and habitats for the Duwamish River, a traditional fishing ground for the Muckleshoot and Suquamish Indian Tribes.
JWF was responsible for the demolition, dewatering, sewer bypassing, shoring, and excavation support systems. After initial set up, JWF, installed combined sewer and effluent pipelines that included 160-feet of 30–inch diameter and 1,300-feet of 60–inch diameter pipe. Also included were 150-feet of 8-foot by 4-foot pre-cast concrete pipe, the installation of a wet well, and control system upgrades. JWF also installed the associated manholes. The pipelines were tested, then backfilled and compacted. Upon pipeline installation completion, the team restored surface sidewalks, curbs, gutters, and provided necessary asphalt and cement concrete paving. In order to minimize impacts to residents, JWF ensured utility protection and relocation when needed. This included electrical, gas, sanitary sewers, combined sewers, storm drains, water mains, fire protection mains, fiber optics, among others. JWF worked closely with the Seattle Department of Transportation to ensure, reviews, and inspections were successfully completed.
JWF managed through unmarked utilities, a buried oil tank, unknown fiber optic cables, pipe support pile caps, and piped under drains. Fiber optic and unmarked electrical conduits interfered with the pipe ram launch pit and a large thrust block used for fire suppression interfered with the receiving pit. The team also discovered a high-pressure feeder main waterline under the railroad track that needed to be cut and capped before the commencement of work. These unexpected factors led to pipe alignment redesign, which led to the extended project duration as JWF waited for rail road permitting. Contaminated soil was also found to exceed the amount expected in the original plan. JWF installed pipes in tight alleyways with overhead wires and installed shoring without the use of cranes due to the overhead clearance. The team was conscientious of vibrations and sediments while installing effluent pipeline just 10–feet away from an unreinforced masonry building. Record breaking snow levels, cold weather, and wet summers caused inevitable weather delays.