Lane Construction Low Bidder on Seattle Ship Canal CSO Tunnel

Lane Construction was the lowest of seven bidders for Seattle Public Utilities’ (SPU) Ship Canal Water Quality Project (SCWQP). Lane submitted a bid of $254.9 million. Other bidders included Kiewit-McNally JV ($297.2 million), Traylor-Shea JV ($320.7 million), Tunnel Storage JV ($335.9 million), Barnard Walsh ($336.3 million), Michels ($344 million), and Kenny Construction ($356.9 million). The engineer’s estimate was $218 million.

SCWQP is being delivered in response to an EPA Consent Decree, and under a Joint Project Agreement between SPU and King County, with the goal of limiting combined sewer overflows (CSOs) in the Seattle neighborhoods of Ballard, Fremont, Queen Anne, and Wallingford to no more than one overflow per year on average for each of the seven affected outfalls. Achieving this goal will keep nearly 80 million gallons of polluted water out of Seattle waterways each year, as these affected outfalls currently average more than 130 overflows per year.

The SCWQP program is composed of multiple projects, the two largest being the Tunnel Storage and the Tunnel Effluent Pump Station (TEPS) projects. The Tunnel Storage project is the central feature of SCWQP and includes a 14,000-ft long (4,267 m) storage tunnel with an internal diameter of 18.83 ft (5.74 m) and a storage capacity of 29.2 million gallons. Combined sewage flows are intercepted and sent to the tunnel via a series of new diversion structures, which route them to one of five new drop structures. Connecting the drop structures to the new 80- to 110-ft deep (24.4-33.5 m) tunnel requires five shafts with diameters ranging from 11 to 86 ft (3.4-26.2 m), and depths up to 110 ft; an approximately 650-ft long (198 m), 94-in. ID (2,390 mm) curved microtunnel beneath the Lake Washington Ship Canal; and two short conventionally mined adits, each having a finished internal diameter of 8 ft (2.4 m).

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The tunnel will be excavated using a pressurized-face tunnel boring machine (TBM), which will be launched from the west end of the tunnel alignment and driven through glacially overconsolidated soils under groundwater pressures up to 3 bar. The shafts are all located in soft ground, and will be constructed using drilled shaft, secant pile, and slurry wall techniques. Upon completion of the tunnel and upstream facilities, the TEPS, a 12 mgd pump station, will be constructed within the TBM launch shaft and will serve to pump the stored wastewater from the tunnel to King County’s West Point Wastewater Treatment Plant via existing infrastructure.

Contractor mobilization was anticipated for late 2019. Final design for the TEPS contract is underway and anticipated to be complete by mid-2020. McMillen Jacobs Associates is the prime consultant for SPU.

Source: Information for this article came from the City of Seattle website and the McMillen Jacobs Associates website.

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