Assessment of the chromium plume west of the 100-D/DR reactors

Sampling of the Columbia River substrate pore water in November 1995 revealed chromium concentrations in excess of 630 g/L in the river bed offshore of the 100-D/DR area. Shoreline drive point sampling at multiple depths also revealed chromium concentrations increasing with depth to a maximum of 869 g/L at approximately 3.05 m below the water table. Because the 1907-DR Process Sewer Outfall is located at the point where the highest concentrations of chromium were found, it was thought that the sewer outfall could be the source of chromium for these drive point and pore water samples. Historical records show that the outfall structure was demolished in fiscal year 1978. The area was then covered and leveled to blend in with the adjacent riverbank