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PT15 Contaminated Harbour and River Sediment
(PT249) Recent Sediment Investigations at the United Heckathorn Superfund Site, Richmond, California.
Kohn, N1, Evans, N1, White, C2, Lincoff, A2, 1 Battelle Marine Sciences Laboratory, Sequim, WA, USA2 U. S. Environmental Protection Agency, Region IX, San Francisco, CA, USA
ABSTRACT- Remedial dredging of pesticide-contaminated marine sediment from the United Heckathorn Superfund Site in Richmond, California, was conducted between September 1996 and March 1997. For the next five years, EPA conducted a post-remedial monitoring program consisting of annual collection of resident mussels and water samples for pesticide analysis. In October 1998, sediment DDT concentrations greater than the 0.590 mg/kg remediation goal were measured in Lauritzen Channel. Elevated DDT in sediment was confirmed in samples collected in November 1998, triggering an investigation into the extent of DDT recontamination in 1999. Furthermore, an increase in bioavailability of DDT to mussels in Lauritzen Channel was observed in 2001, the fourth year of post-remediation monitoring. Uncertainty about any trend in DDT bioavailability through five years of monitoring prompted EPA to continue the biomonitoring program for a sixth year (2003). The presence of elevated DDT in sediment throughout Lauritzen Channel triggered a two-phased source investigation study starting in 2002. Phase I identified a hotspot of DDT-contaminated sediment beneath a pier, embankment soils with elevated DDT concentrations, and a previously unidentified outfall pipe discharging into the intertidal zone of Lauritzen Channel. Phase II delineated the hotspot, investigated the depth to which bank soils were contaminated, and verified the outfall discharge. In channel sediment, DDT remained confined to unconsolidated surface sediment, which ranged in thickness from inches to about three feet, with an estimated volume of approximately 19,000 cubic yards.
Key words: pesticides, DDT, sediment
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