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Underground pipeline storage for CSO control in North Beach
North Beach CSO basin project area
N.W. Blue Ridge Drive (looking northeast)
Existing conditions
Proposed underground storage pipeline (cross section). View larger image (PDF).
How the underground pipeline storage facility works to control CSOs(PDF)
King County plans to design and build an underground storage pipeline in the right-of-way in N.W. Blue Ridge Drive and Triton Drive N.W. This facility will store about 230,000 gallons of peak flows when the North Beach Pump Station reaches maximum capacity. After storms have passed, an underground pump will transfer stored flows to the pump station for conveyance to King County’s Carkeek Wet Weather Treatment Facility for transfer to West Point Treatment Plant or onsite treatment.
How community input informed the decision process
Beginning in March 2010, King County presented three proposals for CSO control in North Beach. The county’s project team hosted a public meeting and provided a presentation to the Blue Ridge community, affected by two of the alternatives with proposed siting in Blue Ridge Park. The project team provided a half-day Technical Information Session in June to respond to specific community concerns and questions in more detail. People provided feedback at a public meeting, on the Web, and by email, mail, and phone to project staff. In July, the team presented the proposed alternatives to members of the Pipers Creek Watershed Council. (View meeting calendar page for public meeting agendas, presentations and handouts.)
King County’s project team used input from the community along with a range of selection factors and updated technical information to evaluate the three alternatives. Community questions and concerns related to project design and construction will be carried forward as King County continues to work with the North Beach community throughout the design and construction phase.
North Beach CSO Control Project - underground pipeline storage
The recommended proposal involves an underground diversion structure that will convey peak flows to an underground storage pipeline in N.W. Blue Ridge and Triton Drive N.W. This option for CSO control provides a number of benefits:
- A single facility located outside of the shoreline zone
- Low level of complexity to operate and maintain
- Similar to other King County facilities
- Will not locate any facility in Blue Ridge Park
- Supported by the community
Project elements include:
- An underground diversion structure located on King County property
- Approximately 325 lineal feet of 12-foot diameter underground storage pipeline installed in the right-of-way
- Small underground pumps to discharge stored flows after storms have passed
- A pipe connecting the storage tank to the influent sewer
- Odor control and electrical facilities located on King County’s North Beach Pump Station property
- Access hatches in the right-of-way spaced along the storage pipeline
What is next:
- King County continues to work with the North Beach community throughout the design and construction phase
- Exact location will be determined during the design phase
- Many opportunities to be involved in this project are still to come. In early 2011, the State Environmental Policy Act (SEPA) review of the recommended proposal will begin with a threshold determination and formal comment period.
- Construction of the new system, expected to take up to 2 years, is expected to begin by December, 2013. After construction, all affected areas will be restored.
- Periodic maintenance (about every 3-5 years) where street closures may be required.
What we heard from North Beach stakeholders
Community members provided King County with a robust level of input during the alternatives evaluation process. The project team received over 200 communications providing feedback on alternatives.We heard: - The majority of respondents supported the recommended alternative, with strong concerns from most people about alternatives involving Blue Ridge Park.
- Project neighbors posed questions and concerns about construction impacts and expressed a desire for King County to work closely with them during project design.
- People expressed concerns about costs and impacts involved in a proposed alternative to replace the existing North Beach pump station and forcemain.
- Community members wanted to understand King County’s plans for the existing facilities if they are not replaced as part of the North Beach CSO Control Project.
New project site launched March 2011 North Beach CSO control project -- underground storage pipeline
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