Water: Contaminated Sediments
1997 Report to Congress Factsheet
Note: EPA no longer updates this information, but it may be useful as a reference or resource.
Fact sheet; January 1998
The U. S. Environmental Protection Agency (EPA)'s report to Congress on contaminated sediment identifies areas in the continental United States where sediment may be contaminated at levels that may adversely affect aquatic life and human health. The report was prepared in response to The Water Resources Development Act of 1992 which directed EPA to prepare a report to Congress on the environmental health of sediments in the nations waterways. It was prepared in conjunction with the National Oceanic and Atmospheric Administration (NOAA), the Army Corps of Engineers, and other federal, state, and local agencies. Data from 1980 to 1993 were used in preparing this report.
The report is based on existing data. It identifies 96 watersheds that contain areas of probable concern—most of which are already well-known to state and local government agencies and the general public. Areas of sediment contamination occur in coastal and inland waterways, in clusters around larger municipal and industrial centers, and in regions affected by agricultural and urban runoff. The data and the evaluation results are useful to local watershed managers to help identify local areas where additional analyses of water quality may be warranted, as well as the potential sources of contamination.
EPA's Report to Congress
The Incidence and Severity of Sediment Contamination in Surface Waters of the United States is the first comprehensive EPA analysis of existing sediment chemistry and related biological data to assess the national incidence and severity of sediment contamination. The 3-volume report describes areas where chemical contaminants are present at potentially harmful levels in river, lake, ocean, and estuary sediments and includes an assessment of the potential for associated adverse effects on human and aquatic life.
Study Approach and Data Evaluation
EPA assembled the largest set of sediment chemistry and related biological data ever compiled into a national database called the National Sediment Inventory. This database includes approximately two million records for more than 21,000 monitoring stations located in nearly 1,363 of the 2,111 watersheds in the continental United States. In developing this database, EPA sought data that were available in electronic format, represented broad geographic coverage, and represented specific sampling locations that were identified by latitude and longitude coordinates. There were also minimum data quality requirements for data to be included in the database.
The analysis approach called for EPA to identify watersheds where further study may be warranted. EPA used a weight-of-evidence approach recommended by national experts to review the sediment quality data at each station in the National Sediment Inventory and classified each station into one of three tiers based on the data recorded for that station:
- Tier 1: Adverse effects are probable;
- Tier 2: Adverse effects are possible, but expected infrequently; or
- Tier 3: There is no indication of associated adverse effects.
EPA then classified watersheds as areas of probable concern (or APCs) if they contained 10 or more Tier 1 stations and at least 75% of all sampling stations were categorized as either Tier 1 or Tier 2.
Report Findings and Considerations
EPA's evaluation of the data shows that sediment contamination exists in every region and state of the country and there are 96 areas (watersheds) of probable concern. More than two-thirds of these watersheds already have an active fish consumption advisory in place.
Water bodies affected include streams, lakes, harbors, nearshore areas, and oceans. At the Tier 1 level, PCBs, mercury, organochlorine pesticides, and polyaromatic hydrocarbons are the most frequent chemical indicators of sediment contamination.
Approximately 10% of the sediment underlying U.S. surface waters is sufficiently contaminated with toxic pollutants to pose potential risks to fish and to humans and wildlife who eat fish.
Much of the contaminated sediment in the U.S. was polluted years ago by such chemicals as DDT, PCB's, and mercury which have since been banned or restricted. However, they can persist for many years in the sediment, and continue to be a source of concern for the environment. Some other chemicals released to surface waters from industrial and municipal discharges and polluted runoff from urban and agricultural areas continue to accumulate to harmful levels in sediment.
Limitations of the Data
The evaluation is an effective screening-level assessment of sediment quality; however, the results of the study described in the report must be interpreted in the context of the data that are available. For example, some states appear to have greater incidence of sediment contamination than others, but this may only reflect the relative abundance of readily available electronic data and not necessarily the relative incidence of sediment contamination. Also, the characteristics of the data and the degree of certainty of the analysis does not allow an absolute determination of adverse effects on human health or the environment at any particular location. It is important to note, too, that further evaluation is required to confirm that sediment contamination at any given sampling station or within a particular watershed poses actual risks to aquatic life or human health.
Areas of Probable Concern
Based on the results of this study, EPA's primary recommendation is that state government agencies, in cooperation with EPA and other federal government agencies, should proceed with further evaluations of the 96 watersheds containing APC's — particularly those water body segments that had ten or more sampling stations classified by EPA as Tier 1 stations. These evaluations should focus on:
- Collecting and analyzing additional sediment chemistry and related biological data
- Further evaluating the potential for human health and ecological risk
- Identifying potential sources of contaminants, and determine whether potential sources are adequately controlled
Other EPA recommendations resulting from the evaluation are:
- Federal, state, and local government agencies should coordinate efforts to address sediment quality through watershed management programs.
- Future sediment monitoring programs should incorporate a weight-of-evidence approach and measures of chemical bioavailability into sediment monitoring programs.
- EPA should evaluate the National Sediment Inventory's coverage and capabilities and provide better access to information contained therein.
- EPA should develop better sediment monitoring and assessment tools.
EPA's Goals for Managing Contaminated Sediment
EPA has established four goals to manage the problem of contaminated sediment and is finalizing a strategy in the next three months to achieve them:
- Prevent the volume of contaminated sediment from increasing.
- Ban or restrict the use of toxic substances that cause contamination
- Control existing sources of contamination through strengthened water quality standards and permits
- Reduce the volume of existing contaminated sediment.
- Clean up existing contaminated sediment sites using Superfund and enforcement authorities
- Ensure that sediment dredging and dredged material disposal are managed in an environmentally sound manner.
- Release new guidance on improved testing standards for dredging and disposal of contaminated material in state waters
- Establish a national stakeholder group to review procedures for dredged material management in ocean waters
- Develop scientifically sound sediment management tools for use in pollution prevention, source control, remediation, and dredged material management.
- Improve the science to better understand the extent of sediment contamination problems and their impacts and to develop solutions