Ross Island Lagoon—A Case Study for Confined Disposal of Contaminated Dredged Material, Portland, Oregon

The Ross Island investigation provides a case study for evaluating confined aquatic disposal (CAD) as a permanent disposal method for contaminated dredged material. Between 1992 and 1998, the Port of Portland (Port) disposed of dredged material in five CAD cells within Ross Island Lagoon, an active aggregate mining facility in the Willamette River at Portland, Oregon. Each disposal cell contains a few thousand to nearly 76,000 cubic meters (100,000 cubic yards) of maintenance-dredge material from various Port docks and slips. Although the Port received regulatory approval for disposal, subsequent regulatory and public interest led the Port to evaluate the disposals relative to human and environmental health and safety. The challenge faced by the project team was to evaluate possible human health and environmental risks several years after the dredged materials had been disposed. These challenges were compounded by the site operator's active reclamation and mining activities near the CAD cells in the intervening years.