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Cleanup Levels vs. Screening Levels vs. MCLs - What's the Difference?

What MCLs, RSLs, PRGs, and state cleanup standards mean, where they come from, and when to use each one. A plain-language guide for environmental professionals.

Published March 23, 2026 10 min read

Why This Matters

Environmental regulatory standards go by a lot of names - MCLs, RSLs, PRGs, screening levels, action levels, cleanup levels, generic standards. These terms get used interchangeably in conversation, but they are not the same thing. Each one comes from a different regulatory context, serves a different purpose, and carries different legal weight.

Using the wrong number in the wrong context can mean either over-remediating a site (expensive and unnecessary) or under-protecting human health (a liability and ethical problem). This guide explains what each term means, where it comes from, and when it applies.

MCLs - Maximum Contaminant Levels

An MCL (Maximum Contaminant Level) is an enforceable drinking water standard established under the Safe Drinking Water Act (SDWA). MCLs are set by EPA’s Office of Water and apply to public water systems - the water utilities that deliver drinking water to communities.

MCLs are not purely risk-based numbers. They are set through a process that considers both health risk and feasibility. EPA first establishes a Maximum Contaminant Level Goal (MCLG) - the concentration below which there is no known or expected health risk, with an adequate margin of safety. For carcinogens, the MCLG is typically zero.

EPA then sets the MCL as close to the MCLG “as feasible,” factoring in the best available treatment technology, analytical detection limits, and cost. This means the MCL is a compromise between what is health-protective and what is achievable in practice.

Not all contaminants have MCLs. EPA has established MCLs for roughly 90 contaminants. Many chemicals encountered at contaminated sites - including most SVOCs (Semi-Volatile Organic Compounds), many pesticides, and most metals beyond the common ones - do not have MCLs.

Key points about MCLs: they apply to public water systems, they are legally enforceable, they factor in feasibility (not just health risk), and they are updated infrequently compared to risk-based values.

RSLs - Regional Screening Levels

RSLs (Regional Screening Levels) are risk-based concentrations calculated by EPA’s Superfund program for use at CERCLA (Comprehensive Environmental Response, Compensation, and Liability Act) sites. They cover contaminants in soil, air, and tapwater for both residential and commercial/industrial land use scenarios.

RSLs are purely risk-based. They are calculated using standard risk assessment equations that combine toxicity values with default exposure assumptions. The default RSL tables use a target cancer risk of 1 x 10^-6 (one additional cancer case per million exposed people) and a target hazard quotient (HQ) of 1 for non-cancer effects.

RSLs are screening thresholds, not cleanup standards. Their purpose is to help site managers quickly identify which chemicals at a site may need further evaluation. If a detected concentration is below the RSL, the chemical generally does not warrant further investigation for that exposure pathway. If the concentration is above the RSL, it means “look harder” - not “clean up to this number.”

Because RSLs are purely risk-based and do not consider treatment feasibility, they can be lower than MCLs for the same chemical. This is a common source of confusion.

RSLs are updated approximately twice per year (spring and fall) as new toxicity values become available. The RSL tables and an online calculator are maintained by EPA at epa.gov/risk/regional-screening-levels-rsls.

Cleanup Levels

A cleanup level is the actual concentration a site must achieve to satisfy the applicable regulatory program. This is the number that matters at the end of the day - it determines how much contamination must be removed, treated, or managed.

Cleanup levels are not a single national standard. They are determined by the regulatory program governing the site and can come from several sources:

Generic program standards - Many state cleanup programs publish tables of numeric standards for common contaminants. Ohio’s VAP (Voluntary Action Program) publishes generic numerical standards in its CIDARS (Chemical Information Database and Applicable Regulatory Standards) database. These function as default cleanup levels within the VAP framework. Other states have similar tables under their own programs.

Site-specific risk assessments - When generic standards don’t fit a site’s conditions, a property-specific risk assessment (PSRA) can derive custom cleanup levels based on actual site conditions, exposure pathways, and receptor populations. These are typically less restrictive than generic standards because they replace conservative default assumptions with measured data.

ARARs - At Superfund sites, cleanup levels must consider Applicable or Relevant and Appropriate Requirements (ARARs), which include standards from other federal and state environmental laws. MCLs are a common ARAR for groundwater at Superfund sites.

Record of Decision (ROD) - At federal Superfund sites, the final cleanup levels are documented in the ROD after a nine-criteria analysis that considers protectiveness, compliance with ARARs, cost, implementability, and other factors.

The critical thing to understand is that “cleanup level” is a site-specific outcome, not a lookup table. The number depends on the regulatory program, the exposure scenario, the land use, and sometimes the specific negotiations between the responsible party and the regulatory agency.

State Program Standards

Most environmental work in the United States happens under state programs, not federal Superfund. Each state has its own cleanup program with its own set of numeric standards. These standards function as cleanup levels within that state’s regulatory framework.

State standards are typically derived from risk-based calculations similar to those used for RSLs, but they may use different exposure assumptions, different toxicity sources, different target risk levels, or they may incorporate MCLs as a floor or ceiling.

For example, Ohio’s VAP calculates its Unrestricted Potable Use Standard (UPUS) for groundwater as the lower of the risk-based concentration and the MCL. This means the UPUS will never be higher than the MCL (when one exists), but it may be lower for chemicals where the risk-based number is more restrictive.

Different states can have different standards for the same chemical in the same medium because they use different assumptions in their calculations. This is one of the reasons state-by-state standards references (like the ones on this site) are valuable - there is no single national cleanup table.

PRGs - Preliminary Remediation Goals

PRGs (Preliminary Remediation Goals) are used at federal Superfund sites as the starting point for developing final cleanup levels. PRGs are often based on RSLs but may be modified using site-specific data from the Remedial Investigation/Feasibility Study (RI/FS).

PRGs become final cleanup levels after the nine-criteria analysis described in the National Contingency Plan (NCP). The final cleanup levels are documented in the ROD. In practice, PRGs are an intermediate step between generic screening values and site-specific cleanup standards.

RMLs - Regional Removal Management Levels

RMLs (Regional Removal Management Levels) are a less commonly encountered set of values used to evaluate whether a removal action (an emergency or time-critical response) is warranted at a site under CERCLA. RMLs are calculated using the same methodology as RSLs but with higher target risk levels (10^-4 cancer risk instead of 10^-6), reflecting the shorter-term exposure scenarios typical of removal actions.

RMLs are not cleanup levels. They are decision triggers - concentrations above an RML suggest that conditions may warrant an EPA removal action. Concentrations below RMLs do not mean a site is “clean.”

How They Relate to Each Other

These values exist on a spectrum from conservative screening to enforceable standards:

RSLs are the most conservative screening values (lowest concentrations) for most chemicals because they are purely risk-based with no feasibility adjustment.

MCLs are enforceable drinking water standards that apply specifically to public water systems. They are a common benchmark but only apply directly to drinking water.

State program standards are the numbers most consultants work with day-to-day. They may incorporate MCLs, use RSL-like risk calculations, or derive values through their own methods.

Cleanup levels are the final, site-specific numbers documented in a regulatory decision. They may equal any of the above or be derived independently through a site-specific risk assessment.

RMLs are the highest thresholds (least conservative) and serve only as removal action decision triggers.

A Concrete Example - Benzene in Groundwater

To illustrate how the same chemical can have different numbers in different contexts:

MCLG: 0 ug/L - The health-based goal. Benzene is a known carcinogen, so the goal is zero.

MCL: 5 ug/L - The enforceable drinking water standard. Treatment technology can reliably achieve this level, and it represents an acceptable balance of risk and feasibility.

RSL (tapwater): 0.46 ug/L - The purely risk-based screening level at 10^-6 cancer risk (November 2024 RSL table). Lower than the MCL because it doesn’t consider feasibility.

Ohio VAP UPUS: 5 ug/L - Ohio’s generic groundwater standard. The VAP takes the lower of the MCL and the risk-based value, but for benzene the MCL of 5 ug/L is used because the VAP’s risk-based calculation at the 10^-5 target risk level produces a value higher than the MCL.

Ohio BUSTR Closure Action Level (groundwater): 0.005 mg/L (5 ug/L) - BUSTR’s closure screening level for benzene in groundwater. Same numeric value as the MCL in this case, but derived through BUSTR’s own framework.

All five numbers are “benzene in groundwater.” The right one to use depends entirely on which regulatory program applies to your site.

Frequently Asked Questions

Are RSLs enforceable cleanup standards?

No. Regional Screening Levels are screening thresholds, not enforceable standards. A concentration above an RSL means the chemical warrants further evaluation - it does not automatically require cleanup to the RSL value. Final cleanup levels at Superfund sites are developed through a site-specific process and documented in a Record of Decision.

Can I use RSLs as cleanup levels?

RSLs are sometimes used as preliminary remediation goals at Superfund sites, but they are not intended to be used directly as final cleanup levels without site-specific evaluation. Some state programs use RSLs as their default screening values, while others (like Ohio's VAP) derive their own program-specific standards. Always check which standards apply under your specific regulatory program.

Why is the RSL sometimes lower than the MCL for the same chemical?

RSLs are calculated purely from health risk equations without considering treatment feasibility, detection limits, or cost. MCLs are set as close to health-based goals as feasible, meaning they factor in what water treatment technology can realistically achieve. For some chemicals, the purely risk-based number (RSL) ends up lower than the feasibility-adjusted number (MCL).

Which number should I use for my site?

It depends on the regulatory program governing your site. If you're working under a state voluntary cleanup program, use that program's published standards. If you're at a federal Superfund site, your regional EPA office will direct the process. If you're doing preliminary screening for a property transaction, RSLs are a common starting point. When in doubt, consult with the applicable regulatory agency or a qualified environmental professional.

What is the difference between an MCL and an MCLG?

A Maximum Contaminant Level Goal (MCLG) is the non-enforceable, health-based goal - the concentration below which there is no known or expected health risk. A Maximum Contaminant Level (MCL) is the enforceable standard, set as close to the MCLG as feasible considering treatment technology, cost, and detection limits. For carcinogens, the MCLG is typically zero, while the MCL is a non-zero number that treatment can realistically achieve.