Sampling and analysis of sediments in dredged material from Wilma Uplands Disposal Site

Abstract

The Lower Granite Reservoir provides slack-water navigation for the Lewiston, Idaho, and Clarkston, Washington area. The levee system associated with the reservoir protects industrial, commercial, and residential areas from inundation of waters impounded behind the dam. Sediment deposition at the confluence of the Snake and Clearwater rivers has required frequent dredging events In past years, Including two recent events in 1986 and 1987. Dredged material from the 1986 and 1987 events was placed in three containment ponds located on the north bank of the Snake River, near River Mile 134.7. The ponds were used to hold approximately 400,000 cubic yards of dredged material removed from the port areas at the confluence of the Snake and Clearwater rivers. Prior to dredging, the river sediments were tested and found to be typical of non-contaminated sediment. Since that testing, dioxins and furans have been found in the effluent from a Kraft pulp mill in Lewiston that discharges directly into the confluence of the Snake and Clearwater rivers. The US Army Corps of Engineers (USACE) believed that dredged material placed in the containment ponds may contain contaminated levels of dioxins and furans. At their request, Battelle/Marine Sciences Laboratory (MSL) sampled sediments from these ponds and performed a chemical analysis.