A range of environmental chemical contaminant concentrations may exist throughout impacted areas that represent a conceptual range of risk management decisions and responses. At one end are levels of high contamination that clearly warrant a response action; at the other end are levels that are below health concerns. For some chemicals, chemical contaminant screening levels, such as the EPA Regional Screening Levels (RSLs), can identify the lower bound of the contaminant concentration spectrum — levels below which there is little or no concern for adverse health effects for the variety of exposure pathways that may impact potential site occupants (Figure 4). Appropriate remediation/cleanup goals for a particular site likely fall within this range depending on site-specific conditions.
These chemical-specific and site-specific screening levels can be used to help define the areas requiring further investigation and potential remediation; they can also help to evaluate the capabilities of field and laboratory-based analytical equipment and techniques that may be used to guide the decontamination efforts. Screening levels may be derived using risk-based methods; they may be based on natural or anthropogenic background levels of chemical constituents, or they may be based on other site-specific considerations.
Methods for deriving site-specific environmental exposure guidelines have been developed by EPA and others that can be applied to a variety of environmental contamination scenarios. Exposure guidelines that have a variety of applications during the response are discussed in Section 4 and Appendix A.
