Featuring an 11-million-gallon-per-day vertical flow wetland and associated pump station, pipelines, and other treatment-related elements, the wetlands are designed to remove ammonia that can be harmful to the fish and wildlife that live in the connecting Southern Wetlands.

Shannon & Wilson, Inc., was a subconsultant to Kennedy/Jenks Consultants, and was responsible for the geotechnical engineering of the Fernhill Western Wetlands predesign, design, and construction. The Portland office provided this project with knowledge of the local geologic and seismic conditions.

The subsurface conditions of the site are ideal for wetlands but created challenges when it came to the geotechnical design and earthwork construction of the project. Soft soils, high groundwater, seismic liquefaction settlement susceptibility, and varying excavation depths for the structures that make up the complex ammonia filter system meant that Shannon & Wilson needed to use ingenuity, judgment, and experience to meet Clean Water Services’ goals. Working with Clean Water Services and Kennedy/Jenks, Shannon & Wilson developed tailored solutions to settlement and dewatering issues, helped optimize the site layout to reduce expensive mitigation, and provided expert support during challenging winter construction. The results were cost-effective, geotechnically sound solutions for a complex site so that Clean Water Services could focus resources on the important treatment system portion of the project.