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201 S. Jackson St., Suite 505
Seattle, WA 98104-3855
Phone: 206-684-1280
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Puget Sound shoreline next to the West Point Treatment Plant, Seattle

Beach CSO map North Beach Pump Station and CSO Control Project

King County to upgrade wastewater facilities in South Magnolia to protect Puget Sound

As part of its mission to protect public health and the environment, King County is responsible for conveying and treating wastewater collected by 34 local city and sewer agencies, including the City of Seattle.

Upgrades needed to North Beach Facilities

King County has operated a pump station and sewer line in the North Beach area for more than 40 years. These aging facilities need to be upgraded to provide safe and reliable operations and capacity for the future. The North Beach Pump Station does not meet current county design standards or building and seismic codes. The station also has no odor control unit.

North Beach CSO project map and schedule
North Beach CSO Project Area
and Schedule
Also available as PDF file (617 KB)

The North Beach force main sewer conveys wastewater from North Beach Pump Station to the Carkeek Pump Station. From there, wastewater goes on to the West Point Treatment Plant. The pipe needs to be evaluated to determine its condition. Because of its location in the tidal area of Puget Sound, access to the pipe and maintenance are difficult. The existing single pipe may not provide adequate capacity for the future.

Reducing Combined Sewer Overflows (CSOs) at North Beach

During heavy rains when flows exceed the capacity of the sewer system, the system can overflow into Puget Sound at North Beach. When this happens, about 90 percent of the combined volume of the overflow is storm water and the rest is diluted sewage. These events are called combined sewer overflows, or CSOs. CSOs help to avoid sewer backups into homes and businesses and onto streets during storms. Between June 2000 and May 2007, the North Beach CSO discharged on average 9 times each year, a total of 2.2 million gallons per year.

CSOs are a public health and environmental concern because untreated wastewater and storm water may be discharged to Puget Sound during large storms. King County's goal is to reduce the number of CSOs each year, with a long-term goal of less than one untreated discharge per location per year to meet state regulations.

To protect Puget Sound and meet our goal, the county is identifying CSO control options for North Beach, West Seattle, and South Magnolia. These locations are top priority because people are most likely to come in contact with water during recreational activities such as swimming.

The map shows the area draining to North Beach and nearby facilities. At North Beach, CSO control options may include:

  • Storage of peak flows during large storms. Once the storm passes, flows would be sent to West Point Treatment Plant. This option would involve constructing a storage tank or pipe in the North Beach drainage basin.
  • Pumping more of the flows out of the basin by increasing the capacity of the North Beach Pump Station, force main, and downstream facilities.
  • Reducing flows of storm water and ground water into the wastewater collection system. The county will work with the City of Seattle to find ways to reduce flows into the city or county system.
  • Treatment of peak flows during large storms. This option would involve constructing a local CSO treatment facility in North Beach that would operate only a few times a year.

These options can be used alone or in combination, depending on local conditions at North Beach.

Schedule

  • Evaluate alternatives for reducing CSOs: 2007-2008
  • Predesign and environmental review: 2009-mid-2010
  • Final design & permitting: 2010-2011

  • Construction: 2012-2013

For more information