Mainers interested in the question “how clean is clean?” – not to mention the Maine Department of Environmental Protection (DEP) – heavily rely on the Maine Remedial Action Guidelines (RAGs) for Sites Contaminated with Hazardous Substances when determining whether soils and groundwater require cleanup. The answer is important because human and environmental risks are at stake, and because cleanup can be costly and time-consuming. The RAGs are used under the Maine Uncontrolled Hazardous Substance Sites Law, the Voluntary Response Action Program (VRAP), Brownfields, Superfund/CERCLA, and RCRA/hazardous waste/corrective action programs.

In a change effective October 19, 2018, the revised risk-based RAGs for soil, sediment, indoor air, groundwater, and fish tissue now generally are based on the U.S. Environmental Protection Agency’s (EPA’s) approaches, including the agency’s detailed Risk Assessment Guidance for Superfund. These 2018 RAGs include numerical standards for ingestion, skin contact, and inhalation for soils, groundwater, and sediment exposures. They also provide numerical levels and indoor air exposures for residents and commercial workers. In a first, the 2018 RAGs also cover fish tissue ingestion by recreational anglers.

The RAGs have three main parts:

• The risk-based tables & narrative provide an alternative approach to undertaking a full risk assessment for common scenarios and routes of exposure. The tables are an efficient way to determine whether a site poses risk to public health, establish contaminant specific clean-up goals, and determine when sites are clear for reuse.

• The Technical Support Document describes how the RAG tables were developed using the EPA’s Regional Screening Levels (RSLs) calculator and provides the inputs that were used to derive the Maine RAG tables.

• The Supplemental Guidance for Conducting Site-Specific Risk Assessments contains the Maine-specific factors and protocols that should be used when developing a full risk assessment for a Maine site using EPA’s Risk Assessment Guidance for Superfund.

This switch to using EPA’s RSLs is a major change from working primarily with the Maine State Toxicologist to develop standards, and instead takes advantage of national, unified science efforts of EPA. It abandons the Maine “Maximum Exposure Guidelines” for drinking water and groundwater. For these reasons, many new RAGs are different from DEP’s recent standards. In addition, DEP adopted unique approaches for lead and per- and polyfluoroalkyl substances (PFAS). Importantly, the RAGs do not address “petroleum-only” contamination, ecological risk assessment, or radionuclides.

Beyond simply addressing numerical standards, the RAGs go into some detail on cleanup policies, including when exposure pathways (e.g., exposure to groundwater) may be excluded, what role environmental covenants can play, and when groundwater cleanup may be technically impracticable.

It is important to remember that the RAGs are guidance – not regulations – and are therefore not binding on DEP or the public. Further, the RAGs are intended to be conservative and used to simplify derivation of cleanup goals for sites and speed-up the decision-making process. Depending on the site, the contaminants, and potential exposures, it may be wise and cost-effective in the long run to develop a site-specific risk assessment, and forego using the numeric RAGs standards.