Interbay Pump Station, Forcemain, and Odor Control

The Interbay Pump Station, originally constructed in 1967, conveys wastewater flows from the Elliott Bay Interceptor system serving Seattle to King County’s regional West Point Wastewater Treatment Plant. It is King County’s highest-flow conveyance system pump station and handles most of the combined sewage/stormwater collected within Seattle city limits, including all of downtown.

Parametrix had designed an earlier upgrade to the pump station which brought the station to a capacity of 133 mgd. It improved reliability of operations with a new generator and electrical system; replaced the oldest pump, which was part of the original 1960s construction; and replaced two other pumps. Mechanical, electrical and control equipment was replaced, and the station was converted from engine driven to electrical motors, adding a 1750 kW diesel engine generator with a new building. The pump station has EPA Class 1 reliability, is 35 percent more efficient, and has eliminated most of its greenhouse gas emissions.

The related force main and odor control project replaced aging sewer pipes and added new odor control technology. The project will increase conveyance capacity to nearly 160 mgd. Work includes assessing existing conditions; replacing 36-inch twin force mains; rehabilitating twin 48-inch force mains, the discharge structure, and a 96-inch interceptor; and adding a 4,000 cfm odor control facility. Three-dimensional design facilitated communication and early decision-making with the team by enabling operations and maintenance staff and other stakeholders to better visualize the improvements. The project includes hydraulic transient modeling, force main condition assessment, and bypass pumping. Geotechnical modeling evaluated lateral spread, liquefaction, and piling.

Parametrix also provided wetland delineation and addressed significant permitting requirements with agencies including the Washington State Department of Ecology and U.S. Army Corps of Engineers. The team also obtained construction permits. Community relations involved coordination with the city park and commercial and residential neighbors. Parametrix is managing 48 tasks and 16 subconsultants. In addition to project management, design and permitting, Parametrix is providing project controls services including cost estimating, scheduling, risk management, and value-based decision analysis. The team tracked action items and logged decisions. They also developed a risk register with risk mitigation strategies. Workshops facilitated key decisions involving multiple project partners. Quality control and assurance used Bluebeam Sessions for this multi-firm, multidisciplinary design, with reviews at all major design milestones.  


King County

Seattle, WA


Gold Award – Complexity, ACEC Washington, 2015

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