WP20 Contaminated Harbor and River Sediment
Wednesday, 16 November 2005: 8:00 AM - 6:30 PM in Exhibit Hall

(PAR-1117-830860) 23-acre multilayer sediment cap in dynamic riverine environment using organoclay as adsorptive capping material.

Parrett, K¹, Blischke, H ¹, ¹ Oregon Department of Environmental Quality, Portland, Oregon, USA

ABSTRACT- The McCormick and Baxter Creosoting Company was founded in 1944 to produce treated wood products. The site is located along the Willamette River in Portland, Oregon. From 1945 to 1969, creosote-contaminated waste water and cooling water were discharged directly into the Willamette River. Creosote was identified in sediment at as much as 90 feet below the mudline and also found to be seeping into the river from upland source areas. The selected sediment remedy required capping areas that contain contaminant concentrations above human health and ecological risk-based protective levels, or that exhibit significant toxicity to biological organisms in the near surface. Surface water, groundwater, and transition zone water samples were collected in September 2002 and 2003 and crayfish tissue sampling was conducted in 2003. Results from these investigations and previous site investigation data were used to determine appropriate construction for the sediment cap as well as providing baseline conditions prior to cap installation. The sediment cap was installed during the summer of 2004. The footprint encompasses 23 acres and consists of 2 to 5 feet of sand with an average grade of 2.5 horizontal to 1 vertical. Approximately 131,000 tons of sand was placed over contaminated sediment and 600 tons of organoclay were placed over the creosote seep areas as an active capping material to prevent premature breakthrough of the creosote. Articulated concrete block armoring was placed over the shore and shallow water portions of the cap and rock was used as armoring over the remaining portion of the cap. The project was conducted collaboratively with EPA, NOAA, and local American Indian Tribes. Much of the work needed to be completed within a narrow Endangered Species Act -mandated fish in-water construction window. The design included considerations for enhancing fish habitat and protection.

Key words: sediment cap, organoclay, creosote