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9601 SE 36th Street
Mercer Island, WA 98040
Phone: 206.275.7608
Fax: 206.275.7814
Email: publicworks@mercer. . .
Hours: 7:00 AM - 3:30 PM (Mon-Fri)
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City of Mercer Island / Public Works / Sanitary Sewer Utility / Mercer Island's Sanitary Sewer

Mercer Island's Sanitary Sewer

Clogged Pipe
Clogged Pipe
The City of Mercer Island recently spent more than $20 million to upgrade the sewer line in Lake Washington that runs along the northwest shore of Mercer Island. This Lake Line collects sewer flows from all parts of the Island and conveys it to pump stations, which then deliver our Islandís sewage to a King County Wastewater Treatment Plant.
 
Because the Lake Line is located in the Lake, it is continuously exposed to cold temperatures, especially during winter months. This means that when fats, oil and grease (FOG) enters the Lake Line, it can easily congeal and get stuck. This accumulated FOG can clog the line over time. Removal by City staff is challenging because of the pipeís location offshore and limited access.
 
A Proven Problem
 
In November 2010, the City of Mercer Island had some sampling done to test the levels of FOG in our sanitary sewer system.
  • Maximum FOG levels recommended by the Washington Department of Health (DOH) in residential wastewater: 20 to 25 mg/L
  • Average total FOG concentration for Mercer Island: 40 mg/L
  • Maximum recorded FOG concentration for Mercer Island:  77 mg/L
FOG concentration levels above 50 mg/L have been reported to negatively impact sewer collection and wastewater treatment plant operations by increasing collection system cleaning frequency. Mercer Islandís levels of 40 to 77 mg/L certainly fall in this range.
 
Note that the FOG testing was done during the peak holiday season of Thanksgiving, within a residential area development with no significant commercial facilities (e.g., restaurants) present. Even so, Mercer Islandís measured FOG exceeds recommended levels. 





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Parametrix Report 03-08-11.pdf

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