Portland, Oregon
The PGM sediment site includes a river reach of 800 ft. along the western side of the Willamette River in downtown Portland. The remedial action addressed contaminated sediments in submerged land adjacent to the former PGM upland site. The submerged lands are owned by the State of Oregon and managed by the Oregon Department of State Lands. The PGM site was used to produce manufactured gas between 1860-1913. Primary waste products associated with PGM site operations include oil, tar, and purifier waste. Primary COCs included PAHs, TPH, BTEX, free cyanide, and metals.
Sevenson mechanically dredged contaminated sediment and performed extensive debris removal using a specialized mechanical long reach dredge equipped with an environmental clamshell bucket. Sediments were dewatered and amended with Portland cement. During dredging operations, crews unexpectedly encountered live unexploded WW2 munitions and explosives of concern (MEC), both incendiary and high explosive rounds. The job was shut down and Sevenson immediately hired a third party MEC contractor, wrote a detailed plan and was up and running within two weeks. Sevenson set up safety procedures, established blast impact areas, and setbacks from public contact. A total of 367 rounds of MEC were found, recovered, and removed from site during remediation and disposed of by the Department of Defense (DoD)
Upon completion of dredging, Sevenson then placed both a multi layered engineered protective cap consisting of sand and Granular Activated Carbon and carbon amended sand for enhanced monitored natural attenuation to address any residual contamination in the dredged area. Sevenson completed this project, even with the delays, still ahead of schedule and under budget when calculating the DoD’s contribution for the cost of the MEC. Additionally, this project was completed with no water quality exceedances during construction work.