RI and Source Control Evaluation of Submerged Lands, Portland, Oregon

This is an RI, source control evaluation, and risk assessment project for Columbia Steel Casting Co. (CSCC)’s 85-acre industrial facility adjacent to the Columbia Slough in Portland, Oregon. The site is in the Oregon Department of Environmental Quality’s (DEQ) Voluntary Cleanup Program. Sediment, groundwater, and stormwater investigations are being conducted to characterize the nature and extent of contamination, determine if site-related chemicals may migrate to the Columbia Slough, and evaluate risks that chemicals in sediment may pose to potential human and ecological receptors. Chemicals of potential concern include metals, PAHs, PCBs, and dioxins/furans.

The CSCC property includes 35-acres of unimproved lowlands. A comprehensive investigation of lowland sediments was completed using both the incremental sampling methodology (ISM) and discrete sampling to characterize the nature and extent of sediment impacts. A variety of forensic methods were used to identify potential sources and responsible parties of PCBs and dioxins/furans in lowland sediment. Results of forensic analyses indicated that PCB impacts to the lowland were due to ubiquitous and regional legacy contamination in the Lower Columbia Slough, but dioxin/furan impacts were likely due to a historical local wood-treating operation.

An ERA was performed using sediment bioassays and Acid-volatile Sulfide/Simultaneously Extracted Metals (AVS/SEM) to evaluate risks that chemicals in sediment may pose to benthic invertebrates. Similarly, bioaccumulation modeling was used to evaluate risks that PCBs and dioxins in sediment may pose to local wildlife populations. Results of the ERA suggest that although unacceptable risks are not currently present, further evaluation of risks that dioxins/furans in sediment may pose to wildlife is warranted.

To better evaluate risks that dioxins may pose to wildlife, laboratory bioaccumulation tests with oligochaetes (worms) were used to estimate site-specific bioaccumulation of dioxins in the food chain. Site-specific sediment remedial action levels were developed using the bioaccumulation results. A sediment remedy was completed that included excavation and off-site disposal of sediment with high concentrations of dioxins along with application of a black carbon amendment to sequester dioxins in-situ.