Water: Contaminated Sediments
2004 Report to Congress Factsheet
We are releasing a report to Congress on "The Incidence and Severity of Sediment Contamination in Surface Waters of the United States, National Sediment Quality Survey: Second Edition." This report identifies areas in the United States where the sediment may be contaminated at potentially harmful levels. The report also assesses changes in sediment contamination over time for areas in the United States where we have enough data. The first National Sediment Quality Survey report was released in 1997, and this is the first update to that report.
The Water Resources Development Act of 1992 (WRDA) directs us, in consultation with the National Oceanic and Atmospheric Administration and the U.S. Army Corps of Engineers, to conduct a comprehensive program to assess the quality of aquatic sediments in the United States. WRDA also directs us to submit to Congress a report on the findings of that program. This report is an update to the 1997 National Sediment Quality Survey.
What does this report contain?
We evaluated sediment contaminant data at 19,398 sampling stations nationwide. Of these stations, we believe that 8,348 or 43% are probably associated with harmful effects on aquatic life or human health. Also, 5,846 stations or 30% are possibly associated with harmful effects on aquatic life or human health. And finally, 5,204 or 27% have no indication of associated harmful effects. The report identifies 96 watersheds where a higher proportion of sediments are contaminated at a level of concern for harmful effects. Our evaluation of historical sediment data from 1980 through 1999 tended to show either a decrease or no change in sediment contamination in most regions where data were available.
What are the report's limitations?
Two general types of limitations are associated with this report to Congress - limitations of the data and limitations of the evaluation approach. Limitations of the compiled data include:
- the mixture of data sets derived from different sampling strategies,
- incomplete sampling coverage,
- the age and quality of the data, and
- missing information, such as latitude and longitude.
The limitations of the evaluation approach include uncertainties in the tools used to assess sediment quality. Because of these limitations, this draft report assesses only those locations in the U.S. where exposure to contaminated sediments is likely to cause negative effects to human health and the environment. Since the data in this report come from non-random sampling and do not cover the entire country, it is not appropriate to use them to create a national estimate of contaminated sediments. Neither should results from the trend assessment be extrapolated to areas of the country where we did not have data.