PFAS 101

The information on this page provides information about Environmental Protection Agency’s (EPA’s) Regional Screening Levels (RSLs) included in Department of Defense (DoD) investigations of per-and polyfluoroalkyl substances (PFAS) conducted under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA). Assistant Secretary of Defense for Energy, Installations, and Environment memorandum, “Investigating Per- and Polyfluoroalkyl Substances within the Department of Defense Cleanup Program,” January 17, 2025, provides the updates to the screening values that the Department uses for PFAS investigations and are based on EPA’s November 2024 RSL update.

EPA establishes RSLs for many chemicals addressed under CERCLA. RSLs reflect chemical-specific concentrations for individual contaminants in air, drinking water, and soils that, if exceeded, may warrant further investigation. RSLs for PFAS continue to change as new toxicity values are used to refine existing RSLs or develop new RSLs for additional PFAS.

When EPA updates the RSLs for PFAS, the Department evaluates and incorporates the updated RSLs, as appropriate, into DoD investigations. PFAS screening levels that are derived from final, peer reviewed toxicity values are taken from EPA’s RSL table and incorporated into DoD environmental cleanup investigations to determine if a remedial investigation is needed. Unless there is only one PFAS present or the conceptual site model (CSM) can demonstrate that a target hazard quotient (THQ) of 1.0 is appropriate, sites with multiple PFAS must use residential soil or tap water RSLs set at a target risk of 1E-06 or a THQ of 0.1 for initial screening purposes.

Additional information about how RSLs are used in cleanup is available on the EPA website at https://www.epa.gov/risk/regional-screening-levels-rsls.

Table 1: RSLs Included in DoD Investigations of PFAS

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