DESCRIPTION: The City of Philomath completed an expansion of its existing wastewater treatment facility located south of the Marys River. The original facility included two lagoons covering ±40 acres that were built in the mid-1980’s. The recent improvements included construction of two new sewage treatment lagoons immediately north of the existing lagoons. The new lagoons have a combined footprint of ±38 acres and a normal maximum operating depth of 8 feet. The improvements also included new headworks and small, at-grade structures.
SERVICE: As part of the design team, Foundation Engineering completed a geotechnical investigation for all project elements. The new lagoons were successfully competed using a soil liner built with native clays. Evaluation of the permeability characteristics of the native soils was a primary focus of the geotechnical work and required extensive field exploration, and laboratory and field-testing. A critical geotechnical challenge was indentifying the extent and suitability of the native clays for liner construction as the two lagoons were being graded. Foundation Engineering provided on‑site observation, field infiltration testing, and consultation during lagoon berm and liner construction, and coordinated all of the materials testing.