Guest Opinion

What are the components of LOIS?

By Jon Holland

, Sep 25, 2008, Updated Oct 30, 2009 (3 Reader comments)

The Lake Oswego Interceptor Sewer is no electron supercollider in terms of complexity, but its design has received serious scrutiny by a team of engineers to ensure it provides reliable, long-term service. Last week’s column (by Joel Komarek, project director for the city of Lake Oswego’s LOIS project) addressed how the principles of gravity, thermal expansion and buoyancy are guiding the LOIS pipeline design.

This week, the focus is on interceptor component design and how the LOIS replacement will be stronger, more corrosion resistant, more flexible and more seismically resistant than the existing pipeline.

The sewer pipe: The design team evaluated a wide range of materials to find the most suitable for the environment (the lake) and for the contents it will carry (sewage). These materials included steel, ductile iron, polyvinyl chloride (PVC), carbon fiber reinforced resin, fiberglass, high density polyethylene (HDPE), and concrete.

The team determined that HDPE pipe is the ideal material:

It’s tough. A 50-year track record in severe marine environments demonstrates its impact resistance. Unlike more brittle materials, HDPE will not be damaged by the anchors from recreational boats on Oswego Lake.

It’s strong. Fifty-foot pipe lengths joined into 1,500-foot segments by heat fusion welding results in a continuous, jointless pipe, unlike the existing interceptor, which has a gasketed, push-on joint every 32 feet. The walls of the pipe are over 3-inches thick to resist more than 2.5 times the maximum water pressure for 100 years and to ensure that any nicks, cuts, or scrapes are structurally insignificant.

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