| August 20, 2002
News Release The King County Wastewater Treatment Division is scheduled to begin construction Sept. 4 of a $45 million, 2-mile-long sewer project in the Rainier Beach neighborhood of Seattle. The Henderson/M.L. King CSO Project will improve water quality in Lake Washington by providing major new protection from combined sewer overflows, or CSOs. A CSO is caused when stormwater and sewage combine during extreme storms and overload the sewer system. Construction will include tunneling, open-trench pipeline installation, pump station improvements and two flow-regulation structures along South Henderson Street, 42nd Avenue South and South Norfolk Street. Limited activities--including surveying, utility location and preconstruction photography--will occur in the first month. Construction will take about 30 months. The sewer system in the Rainier Beach area is more than 50 years old. This project will protect public health and the environment by reducing overflows and providing improved storage and treatment capacity for in a new huge tunnel. Currently, 15 to 30 overflows occur each year from the Rainier Beach area into Lake Washington. The 14-foot-diameter wastewater storage tunnel will be 30 to 100 feet underground beneath 42nd Avenue. During storms, the 3,100-foot-long tunnel will hold combined stormwater and sewage until the flows can reach King County's wastewater treatment plants in Renton and Seattle. When extreme storms overload the sewer system, the new tunnel will provide primary sewage treatment before discharge through an existing combined sewer outfall to the Duwamish River at South Norfolk Street. One of several similar sewer improvement projects under way in the Puget Sound area, the Henderson/M.L. King project is an example of King County's stewardship in safeguarding water quality while providing improvements to urban communities. Working with City of Seattle Public Utilities, the Wastewater Treatment Division of King County's Department of Natural Resources and Parks is managing the project. Tri-State Construction Inc. of Bellevue is King County's contractor for the project. King County is working with the contractor and the city to minimize construction impacts to residents, pedestrians, businesses and motorists. Construction will take place in the public right-of-way--along city streets. It will require heavy construction equipment, installation of pipelines in trenches, tunnel construction and related earth moving. The project will be completed in segments. To minimize disruption, King County has considered the needs of the Rainier Beach community in planning this project. The project team has met with businesses, residents and community groups in the area, including Rainier Beach High School, to gather information and explain details. For safety and to reduce impacts to businesses, residents, motorists and pedestrians, the construction contractor will provide flaggers and signs described in a traffic plan and approved by the City of Seattle. Information about project schedule and activities will continue to be available to community members. Updates will be hand-delivered, mailed and placed at signposts along the construction route. People can also call the project's construction hot line at (206) 684-1251, send an e-mail message to hendersoncso@kingcounty.gov or visit the project Web site at http://dnr.metrokc.gov/wtd/henderson-cso/. King County's Wastewater Treatment Division protects public health and the environment by serving 16 cities, 16 sewer districts and more than 1.4 million residents in King, Snohomish and Pierce counties. Tunnel construction The storage and treatment tunnel will run parallel to Martin Luther King Jr. Way beneath the undeveloped public right-of-way along 42nd Avenue South. Construction will begin in early October and take about 16 months. Work will advance north from South Norfolk Street to Henderson Street. Because work will be deep underground, impacts to the community will be minimal--mostly in areas near two new wastewater flow-regulator structures. King County and its contractor will work closely with neighbors to minimize disturbances. Flow regulator structures The contractor will also build a tunnel inlet regulator at the intersection of 42nd Avenue South and South Fairbanks Street. This structure will serve as the north portal for the storage and treatment tunnel, one of two openings to the major tunneled portion of this project. It will manage the flow of combined underground storm and wastewater. Work to complete the facility will take about 14 months. At the same time, the contractor will build a tunnel outlet regulator at the south tunnel portal at 42nd Avenue and South Norfolk Street. Besides construction of the flow regulators, work began in early 2002 on upgrading King County's existing Henderson Pump Station at Seward Park Avenue South and South Henderson Street. Work there is expected to be complete in early 2004. Open-trench construction Open-trench pipeline work is expected to begin in early spring 2003. The contractor will install a pipeline along South Norfolk Street, mostly by open-trench construction. The pipeline will begin at the intersection of Norfolk Street and East Marginal Way South, and move eastward to the intersection of 42nd Avenue South and Norfolk Street. Installation of the 72-inch pipeline will take about six months In June 2003, work will begin on open-trench pipelines along South Henderson Street. Work will run eastward from Renton Avenue South. The pipeline will end near the Atlantic City boat launch at South Seward Park Avenue South and South Henderson Street. Sewers have overflowed there into Lake Washington during major storms. The contractor will use heavy equipment to build an open trench in the center of Henderson Street. To reduce disturbances to the community, work crews will dig the trench in sections to install new pipelines 20 inches and 42 inches in diameter. Crews will backfill and restore sections of the street as work progresses. Crews will work west along Henderson Street to just past Martin Luther King Jr. Way South at 42nd Avenue South. Work along Henderson Street will take about six months. Detours including lane and street closures will be necessary in the immediate area of the work. Flaggers and signs will aid pedestrians, motorists and businesses as needed. 'Microtunnels' Several smaller-diameter tunnels--called "microtunnels"--will be built under South Fairbanks Street, South Henderson Street and the South Norfolk Street right-of-way. The tunnels will range in diameter from 42-72 inches and connect to the open-trenched pipelines. Microtunneling, remote-controlled from the ground surface, will be used in areas where the pipeline is more than 20 feet deep and to go under Martin Luther King Jr. Way, Interstate 5 and the railroad tracks. This work will be carried out about the same time as the open-trench pipeline work. Related Information
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