| October 17, 2003
News Release
Daylighting of the 14-foot, 8-inch inside-diameter tunnel marks an important milestone for King County's two-year Henderson/ML King CSO Project. When completed, the project will reduce sewer overflows to Lake Washington, improve water quality, and add capacity and the ability to convey, store and treat wastewater and stormwater. When needed during extreme storms, the tunnel will provide disinfection, screening and dechlorination. The central part of King County's sewer project, the 3,100-foot-long tunnel has been built from 30 to 109 feet below 42nd Avenue South in Seattle. Mining has occurred south to north along 42nd Avenue, which runs parallel to Martin Luther King Jr. Way South between South Norfolk Street and South Fairbanks Street. The sewer system in the Rainier Beach community is more than 50 years old. Each year, 15 to 30 overflows totaling an estimated 30 million to 60 million gallons of combined wastewater and stormwater occur in the area and reach Lake Washington. Tunneling for the storage facility was undertaken with an earth-pressure-balance tunnel boring machine made by Lovat Tunneling Equipment Inc of Toronto. The machine was used two years ago on King County's similar Mercer Street Tunnel for the Denny Way CSO Project in Seattle. The tunnel represents about 30 percent of the project's two-mile alignment, which also includes five other smaller tunnels that range from 42 to 72 inches in diameter. Four of the project's six tunnels, including the large-diameter storage and treatment tunnel, intersect in two deep shafts that are 43 feet in diameter and 80 to 85 feet deep. The deep shafts are at South Henderson Street and 42nd Avenue South. King County's Wastewater Treatment Division has extensive experience building tunnels. Its projects include the Mercer Street Tunnel, recently completed tunnels for the Eastside and South Interceptor pipelines in Renton and Kent, the Fort Lawton Tunnel to the West Point Treatment Plant in Magnolia and the West Seattle Tunnel. Long deep tunnels are also planned for the proposed Brightwater treatment system serving north King County and south Snohomish County. To control flows in the Henderson/MLK tunnel, the contractor is building two flow regulator structures at the north and south portals of the storage and treatment tunnel. Other project pipelines, ranging in size from 20 to 72 inches, are being installed in open-cut trenches. King County is also upgrading its Henderson Pump Station to carry additional flows away from Lake Washington west along South Henderson Street to the new storage and treatment tunnel. The Wastewater Treatment Division of King County's Department of Natural Resources and Parks is managing the project. NW Boring/Kenny JV of Woodinville is the tunneling subcontractor to prime contractor, Tri-State Construction Inc. of Bellevue. Jacobs Engineering is providing construction management services, and HDR is the project designer. The Wastewater Treatment Division protects public health and the environment by serving 18 cities, 15 sewer districts and more than 1.4 million residents in King, Snohomish and Pierce counties. The regional utility now operated by King County has been preventing water pollution for nearly 40 years. Related Information
|
|
Links to external sites do not constitute endorsements by King County. |
Mining for King County's 4-million-gallon wastewater storage and treatment tunnel in Rainier Beach will end Oct. 20, when it breaks through a steel-reinforced concrete wall into an open receiving shaft, 80-feet deep and 43 feet in diameter.
News Releases