An approach for looking at sediment quality on a national perspective

Abstract

Sediment quality analyses are conducted for specific reasons and most for some type of regulatory purpose. These purposes could include support for: sediment remediation, dredged material disposal, and sediment monitoring. One such sediment monitoring effort in the United States is to fulfill the requirements set forth in the Water Resources Development Act of 1992 (WRDA). This Act requires EPA to develop the National Sediment Quality Survey, a national evaluation of sediment quality in the United States. The first report was prepared in 1997 and described the incidence and severity of sediment contamination nationwide. The first update to this report was recently released (USEPA, 2004) and is designed to be a screening-level assessment for the identification of potentially contaminated sediments. While there are many challenges to assessing sediment contamination on a localized area, these are drastically magnified at a national scale. One of the biggest challenges was the reliance on existing sediment quality data (mostly with only a single line of evidence reported—sediment chemistry), not collected with the WRDA mandate in mind and providing a limited spatial coverage for most watersheds. Out of the nearly 20,000 stations evaluated in this report (using data from 1990 to 1999), 70% had data available for sediment chemistry only that precluded a weight-of-evidence approach at these stations. Therefore, sediment quality guidelines (SQGs—both empirical and mechanistic) were a primary tool for assessing sediment quality. Other sediment quality benchmarks used in this report included theoretical bioaccumulation potential (TBP), sediment toxicity, and tissue residues. To develop benchmarks for classifying sediments according to possible hazard, some assumptions were made that may not reflect site-specific conditions. While recognizing the inherent limitations of the data and the assessment approach, this is a viable approach to broad scale sediment assessments.