Wastewater Treatment Plant Improvements
Outfall BOD and other demands called for sewage treatment improvements for this Columbia River Estuary site.
Improvements included three new diked, lined, and concrete surfaced sequencing batch reactors (SBR’s),
ultraviolet disinfection, outbuildings, pumps and piping. A new outfall was also installed with directional boring for over
4,000 feet under the marsh and tidal flats to the diffuser in the Columbia River channel.
GSI's thorough site evaluation included drilled borings, cone penetrometer test probes, and
digital instruments around the lagoons and outfall alignment. Our local experience enhanced
dike construction sequencing and surcharging, foundation bearing and earth pressures for
embedded treatment structures, and construction of a temporary, grid-reinforced access road over
wetlands (without vegetation removal to enhance restoration). GSI also provided experienced
observation of shoring and dewatering, as well as stabilization for the very soft tidally influenced