The system was deficient due to hydraulic capacity limitations, corrosion and deterioration of the pipe, and seismic vulnerabilities. The in-lake portion of Lake Oswego Interceptor Sewer (LOIS) included approximately 11,300 feet of at-grade or buried pipeline, 5,800 feet of pile-supported pipe, and 9,700 feet of buoyant pipeline tied down by drilled anchors.

Shannon & Wilson provided geotechnical services through alternatives evaluation and preliminary and final design. In the final design, we completed geotechnical explorations and in situ testing and built a complex 3-D GIS model using borings, geophysics, as-built records, and paleo flood geomorphology interpretation to predict subsurface conditions and estimate depths to competent materials. Toward the end of the design phase, the project converted to a conventional design/bid/build model, and we provided final design recommendations and geotechnical specifications. We provided ongoing construction services for all phases of work, leading to the project being completed on schedule and under budget.