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Ecological Risk Assessment

Frequently Asked Questions

Background Considerations

  1. Can I screen out potential contaminants of concern at the screening level based on background concentrations?
  2. Can I evaluate background concentrations as part of the uncertainty analysis?
  3. How do I handle contaminants that are present at background concentrations?

1. Can I screen out potential contaminants of concern at the screening level based on background concentrations?

EPA Region 3 BTAG regards comparison with background as a risk management function and not part of the risk assessment process. During the screening ecological risk assessment background data are not be used to eliminate areas from further risk assessment. Screening is a risk-based process and should not consider background or other policy-laden issues at this point.

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2. Can I evaluate background concentrations as part of the uncertainty analysis?

In general, only evaluations of site specific background concentrations are appropriate. The comparison of a benchmark or site concentration with U.S. background soil concentrations as a potential uncertainty is not appropriate. Regional background data may be appropriate for consideration if it is geographically limited to an area with similar soil, geology, and atmospheric deposition patterns as the site. Data from the eastern half of the country does not constitute regional data, nor does data from the northeastern US or state-specific data. For example, statewide background values for Pennsylvania encompass samples from glaciated and non-glaciated zones, as well as different meteorological conditions that would affect atmospheric fallout of contaminants.

It should be noted that naturally occurring and anthropogenic background sources are not to be differentiated; they are to be treated equally. When reliable site and contaminant-specific data are available, chemicals that are clearly not site related, but due to natural or anthropogenic background sources, may be identified in the uncertainty section of the baseline risk assessment (BERA) and identified for possible elimination as chemicals of concern (COC) during the risk management process.

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3. How do I handle contaminants that are present at background concentrations?

Where there are elevated concentrations of chemicals of potential concern due to background that may present an unacceptable risk to the environment, the risk from these chemicals should be quantified, if possible, in the risk assessment. Although these chemicals may not be called "COCs" in the risk assessment or the ROD, they none the less, should be evaluated. Even though EPA or the responsible party will not address these risks in the remedy selection process, Superfund believes that it has a responsibility to share this information with local and state authorities in the hope that they can take some action to reduce the risk from high background concentrations. EPA acknowledges that this approach can present issues in community involvement and encourages early community involvement and increased emphasis on risk communication.

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