Are RSLs enforceable cleanup standards?

No. RSLs are screening tools, not cleanup standards, and EPA states this explicitly on the RSL website. A concentration above an RSL indicates the chemical warrants further evaluation - it does not require cleanup to the RSL value. Final cleanup levels at Superfund sites are developed through a site-specific risk assessment and documented in a Record of Decision (ROD).

How often are the RSL tables updated?

Approximately twice per year, typically in May and November. Updates reflect changes to toxicity values (from IRIS, PPRTVs, ATSDR, and other sources), exposure parameters, and chemical-specific properties. The EPA RSL 'What's New' page documents all changes between updates.

Should I use the THQ=1.0 or THQ=0.1 table?

Check with your EPA region or state program. Some regions use THQ=0.1 as the default for sites with multiple contaminants because the lower threshold accounts for cumulative risk from multiple chemicals. Other regions and most state programs use THQ=1.0 as the default for individual chemical screening. Both tables use the same target cancer risk of 1E-06.

Why is the RSL lower than the MCL for some chemicals?

RSLs are calculated purely from health-risk equations using toxicity values, standard exposure assumptions, and target risk levels. MCLs are set as close to the health-based Maximum Contaminant Level Goal (MCLG) as feasible, meaning they factor in treatment technology, analytical detection limits, and cost. For some chemicals, the purely risk-based RSL ends up lower than the feasibility-adjusted MCL.

Can I use RSLs at state-program sites?

It depends on the program. Some state programs (like Ohio's VAP) derive their own standards separately and do not use RSLs directly. Other states adopt RSLs as their default screening values. Some states reference RSLs but apply different target risk levels or exposure assumptions. Always check which standards apply under your specific state program.

Where can I find older versions of the RSL tables?

EPA does not distribute outdated tables. Each new version supersedes all previous versions. If you need historical tables for litigation or long-term projects, you can download and archive tables yourself when they are published, or submit a FOIA request to the Office of Land and Emergency Management.

EPA Regional Screening Levels (RSLs) Explained

What Are Regional Screening Levels?

Regional Screening Levels (RSLs) are risk-based concentrations developed by U.S. EPA for chemical contaminants at Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) sites - commonly known as Superfund sites. They provide comparison values for residential and commercial/industrial exposures to soil, air, and tap water (drinking water).

RSLs are the most widely referenced screening tool in environmental site assessment. Even outside the Superfund program, consultants routinely compare site data to RSLs during Phase II Environmental Site Assessments (ESAs), risk evaluations, and remediation planning. Many state programs reference RSLs directly or use similar risk-based methods to derive their own screening values.

The RSL tables are maintained by EPA and developed in partnership with the Department of Energy’s Oak Ridge National Laboratory (ORNL). They are the product of merging three legacy regional tables: the Region 3 Risk-Based Concentration (RBC) Table, the Region 6 Human Health Medium-Specific Screening Level (HHMSSL) Table, and the Region 9 Preliminary Remediation Goal (PRG) Table.

RSLs Are Not Cleanup Standards

This is the single most important thing to understand about RSLs, and EPA emphasizes it repeatedly: RSLs are screening thresholds, not cleanup levels.

If site concentrations are below RSLs, the chemical generally does not warrant further investigation for human health risk at that site. If concentrations exceed RSLs, it means the chemical needs a closer look - not that the site must be cleaned up to the RSL value.

Final cleanup levels at Superfund sites are developed through a site-specific process that considers the nine criteria outlined in the National Contingency Plan (NCP) and are documented in a Record of Decision (ROD). RSLs may serve as a starting point for Preliminary Remediation Goals (PRGs), but the final cleanup number often differs based on site-specific conditions, exposure pathways, land use, and feasibility.

For a broader discussion of how RSLs fit into the hierarchy of cleanup standards, see our guide: Cleanup Levels vs. Screening Levels vs. MCLs.

What the RSL Tables Cover

The generic RSL tables include screening levels for approximately 900 chemicals across several media:

Residential soil - exposure via ingestion, dermal contact, and inhalation of volatiles and particulates
Commercial/industrial soil - same pathways with different exposure assumptions (adult workers, shorter exposure duration)
Residential air - inhalation exposure for residents
Commercial/industrial air - inhalation exposure for workers
Tap water - ingestion and dermal exposure from drinking water
Soil-to-groundwater Soil Screening Levels (SSLs) - soil concentrations protective of underlying groundwater (based on a Dilution Attenuation Factor, or DAF, of 1 in the generic tables)

The tables also include Maximum Contaminant Levels (MCLs) where applicable, allowing side-by-side comparison of risk-based screening levels against enforceable drinking water standards.

The generic tables do not include screening levels for the ingestion of fish, outdoor worker, or indoor worker exposure pathways. These can be calculated using the RSL Calculator on a site-specific basis.

How RSLs Are Calculated

RSL values are calculated using standard risk assessment equations that combine toxicity values with default exposure assumptions.

Cancer Risk

For carcinogens, RSLs are calculated at a target cancer risk (TR) of 1 in 1,000,000 (1E-06). This means the RSL represents the concentration at which an individual exposed over a lifetime has an additional 1-in-a-million probability of developing cancer from that chemical.

The key inputs for carcinogenic RSLs are the oral slope factor (SFO) for ingestion pathways and the inhalation unit risk (IUR) for air pathways.

Non-Cancer Hazard

For non-carcinogens, RSLs are calculated at a target hazard quotient (THQ) of either 1.0 or 0.1. A THQ of 1.0 means the estimated exposure equals the reference dose (RfD) or reference concentration (RfC) - the level below which adverse health effects are not expected.

The THQ=0.1 table applies a tenfold safety factor and is used by some EPA regions at sites where multiple contaminants are present. The lower threshold accounts for cumulative hazard from simultaneous exposure to several chemicals. Check with your region or state program to determine which table applies.

When a chemical has both carcinogenic and non-carcinogenic toxicity values, the RSL tables present both the cancer-based and non-cancer-based screening level, and the lower (more protective) value drives the final RSL.

Mutagenic Mode of Action

For chemicals that cause cancer through a mutagenic mode of action (designated with “M” in the tables), EPA applies age-dependent adjustment factors (ADAFs) to account for increased susceptibility during early life. This adjustment produces lower RSLs for residential scenarios because childhood exposure is weighted more heavily.

The Toxicity Value Hierarchy

RSLs are only as good as the toxicity values underlying them. EPA uses a defined hierarchy of toxicity data sources, applied in the following priority order:

IRIS - EPA’s Integrated Risk Information System. The gold standard. IRIS values undergo extensive peer review and are the highest-tier toxicity data.
PPRTVs - Provisional Peer-Reviewed Toxicity Values, developed by EPA’s Superfund Health Risk Technical Support Center. Second tier. PPRTVs are archived when IRIS releases a profile for the same chemical.
OPP HHBPs - EPA Office of Pesticide Programs Human Health Benchmarks for Pesticides. Used for 51 pesticides where IRIS archived assessments in 2016.
ATSDR MRLs - Agency for Toxic Substances and Disease Registry Minimal Risk Levels. Both final and draft values are used (draft ATSDR values have undergone external peer review).
Cal EPA OEHHA - California EPA’s Office of Environmental Health Hazard Assessment values. Used when no higher-tier value is available.
PPRTV Appendix (Screening) Values - Lower confidence values from appendices to PPRTV documents. Designated with “X” in the tables rather than “P.”
HEAST - Health Effects Assessment Summary Tables. Legacy values, rarely the driving source for current RSLs.
Other sources - Including EPA Office of Water and Office of Research and Development values for special cases (such as PFOA, PFOS, and HFPO-DA).

The key column in the RSL tables indicates which source drives each chemical’s toxicity value. Understanding the hierarchy matters because lower-tier values carry more uncertainty, and a chemical’s RSL can change significantly when a higher-tier value is published.

Update Schedule and Recent Changes

RSL tables are updated approximately twice per year, typically in May and November. Updates may include:

New or revised toxicity values from any source in the hierarchy
Changes to exposure parameters or equations
Addition of new chemicals
Updates to chemical-specific properties (vapor pressure, Henry’s Law constants, etc.)
MCL additions or revisions

November 2024 Update (Most Recent as of March 2026)

Key changes in the November 2024 update included adding MCLs for six per- and polyfluoroalkyl substances (PFAS) compounds to the ion forms in addition to the acid forms already present: perfluorooctanoic acid (PFOA), perfluorooctanesulfonic acid (PFOS), perfluorohexanesulfonic acid (PFHxS), hexafluoropropylene oxide dimer acid (HFPO-DA, also known as GenX), perfluorononanoic acid (PFNA), and perfluorobutanesulfonic acid (PFBS). The lead action level in tap water was updated from 15 to 10 ug/L, and elemental phosphorus was added with a new CAS number assignment.

New toxicity values from PPRTV updates included 1-Methylnaphthalene (new screening chronic and subchronic RfD, RfC, and screening oral slope factor). Acrylonitrile received new draft subchronic and chronic RfD and subchronic RfC values from ATSDR.

RSL Calculator Availability

In February 2026, the RSL Calculator and the Vapor Intrusion Screening Level (VISL) Calculator were temporarily taken offline by EPA. Both tools were restored in mid-March 2026. During periods when the calculators are unavailable, the static generic tables remain accessible for download.

Which Table to Use

The RSL tables are published in two versions based on the target hazard quotient:

THQ=1.0 - Default for many state programs and for screening individual chemicals
THQ=0.1 - More conservative, used by some EPA regions as the default for sites with multiple contaminants

Both versions use the same target cancer risk of 1E-06.

The appropriate table depends on your regulatory context. If you are working under a specific state cleanup program, check that program’s guidance for which RSL table (if any) it references. For example, Ohio’s Voluntary Action Program (VAP) derives its own standards through CIDARS and does not directly adopt RSLs, though the underlying risk methodology is similar.

For federal Superfund work, confirm with the lead EPA region. Most regions default to the TR=1E-06 / THQ=0.1 table for multi-contaminant sites.

RSLs vs. State Standards

RSLs and state program standards often produce different numbers for the same chemical in the same medium. Common reasons include:

Different target risk levels - Some state programs use 1E-05 cancer risk instead of 1E-06
Different exposure assumptions - Exposure duration, body weight, ingestion rates, and other parameters may differ
MCL incorporation - Some states use the MCL as the default groundwater standard rather than a risk-based calculation, which can produce either higher or lower values
Different toxicity hierarchies - States may use different toxicity data sources or update on different schedules

When comparing site data to standards, always use the numbers from the regulatory program that actually governs your site. RSLs are a useful reference point, but they are not universally applicable.

Resources

EPA RSL Homepage - Main page with links to all resources
RSL Generic Tables - Download current tables in Excel and PDF
RSL Calculator - Generate site-specific screening levels
RSL User’s Guide - Detailed methodology and assumptions
RSL What’s New - Change log for each update
RSL Frequent Questions - EPA’s own FAQ