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Lake Oswego Interceptor Sewer


Lake Oswego Interceptor Sewer---Large


Lake Oswego Interceptor Sewer, Lake Oswego, OR

World’s first buoyant gravity sewer.


The original 1960’s lake interceptor was undersized and corroding and would collapse in an earthquake. The City of Lake Oswego needed an affordable, minimally disruptive, long-term fix to ensure reliable sewer service to its 37,000 residents. The first-ever buoyant gravity sewer pipeline is the answer.


  • Serpentine pipe alignment allows expansion/contraction and maintains tight grade control through wide-ranging lake temperatures.
  • 29,000 feet of 18- to 42-inch HDPE sewer and buoyancy pipe installed.
  • 428 wire rope tethers and steel ground anchors drilled through 200 feet of sediment into underlying bedrock hold the system 15-20 feet beneath the lake surface.
  • Six submerged buoyant stainless steel manholes, accessed via removable aluminum caissons, allow inspection and maintenance.
  • Completed on schedule ahead of the summer recreation season, 10 percent under budget, and with broad public support.
  • System flexibility maximizes seismic resistance.
  • HDPE, stainless steel hardware, and cathodically protected piling control corrosion.
  • Robust system is expected to serve Lake Oswego for a century or more.


  • Project Entrant/Design Engineer/Construction Manager: Brown and Caldwell
  • Project Owner: City of Lake Oswego
  • General Contractors: Advanced American Construction (lake full contract)
  • JW Fowler (lake down contract)

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