Portland, Oregon
In 2000, the USEPA added the Portland Harbor Superfund Site to the National Priorities List. The Gasco Sediments Site is an approximately 0.5 mile stretch on the West Side of the Lower Willamette River within the Portland Harbor Superfund Site. Multiple remediation methods are being evaluated in the Feasibility Study and implemented by NW Natural for the Gasco Sediments Site. Primary COCs include PAHs, VOCs, SVOCs, metals, and cyanide.
Sevenson performed this Pilot Study to determine the feasibility of construction methods and their impact to water quality for the remedial cleanup of contaminated sediments. For this Pilot Study, Sevenson self-performed the in-water ISS of overlapping columns to depths of 30-ft. below the mudline using a soil drill rig with an 8-ft. diameter drill bit. ISS was performed to a predetermined cement mixture design from the results of a bench treatability study performed in house. ISS was performed inside of a moonpool to control turbidity. There were no water quality exceedances during construction work. Generated swell was removed and stabilized using Portland cement. Prior to ISS, surveys were performed to identify surficial and buried debris that could impact the advancement of the augers into the sediment. Any potentially interfering debris was removed using a barge-mounted crane prior to drilling activities. Results were monitored to determine optimized construction means and methods in the field for full-scale ISS to be performed in the future.