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Risk Assessment

Regional Removal Management Levels (RMLs) User's Guide

 

The intention here is to provide updated lists of Regional Removal Management Levels for Chemicals (RMLs) to assist On Scene Coordinators (OSC’s), and others involved in decision-making concerning Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) removal actions at Superfund sites.

Here you will find generic, risk-based RMLs calculated using the latest toxicity values and exposure assumptions used by EPA’s Superfund program. The RMLs were developed by a cross-Regional workgroup of EPA risk assessors and removal site managers. The RMLs are based on the methods used to calculate EPA’s Regional Screening Levels (RSLs) for Chemical Contaminants.

The RMLs and methodology presented on this website will serve as an update to previous lists of Removal Action Levels (RALs) provided by EPA. The most recent list of RALs was published in 1998, and is outdated due to changes in Agency toxicity criteria and risk methodologies.

Previously, RALs were provided only for drinking water. This update provides RMLs for tap (drinking) water and soil, and is consistent with the Federal Superfund program’s risk assessment and risk management practices.

For proper application of the RMLs, please follow the instructions presented in this document. To ensure understanding of RML exposure scenarios review the RML user guide and frequently asked questions. The Generic RML Tables are provided but the RSL Calculator can also be used to generate RMLs.

Introduction

The increased use of EPA’s removal authority has been effective in accelerating the pace of cleanups and has contributed substantially to the number of projects reaching construction completion. Integrating the removal and remedial programs includes the use of related triggers for initiating action and common goals for site cleanup.

The Regional Removal Management Levels (RMLs) presented here are chemical-specific concentrations for individual contaminants in tap water and soil that may be used to support the decision for EPA to undertake a removal action. Although they are not necessarily health protective concentrations for chronic exposure, exceedance of an RML by itself does not imply that adverse health effects will occur.

Calculated RMLs should not be confused with or used as Preliminary Remediation Goals (PRGs), cleanup levels or cleanup standards required by the Applicable or Relevant and Appropriate Requirements (ARARs) under CERCLA. RMLs may be used to support the decision to undertake a removal action, but final cleanup levels should be selected to address the site-specific threat.

Methodology

The RMLs are based on exposure and risk assessment methods presented in the Risk Assessment Guidance for Superfund: Volume I, Human Health Evaluation Manual (Part B, Development of Risk-based Preliminary Remediation Goals) (RAGS Part B) and Soil Screening Guidance:

RAGS Part B and the Soil Screening Guidance use EPA toxicity values and exposure information to calculate risk-based screening levels. The relationship of Preliminary Remediation Goals (PRGs) to Regional Screening Levels (RSLs) and RMLs is discussed in more detail in the RMLs Frequently Asked Questions.

This website presents “generic” risk-based RMLs for individual chemical contaminants.

Generic RMLs are based on default exposure parameters and factors that represent Reasonable Maximum Exposure (RME) conditions for long-term/chronic exposures. Generic RMLs are provided for tap water and soil in a residential or industrial setting.

The target risk levels for calculating generic RMLs, are an extension of the Superfund program’s Role of the Baseline Risk Assessment in Superfund Remedy Selection Decisions” (OSWER Directive 9355.0-30) guidance which states:

Where the cumulative carcinogenic site risk to an individual based on reasonable maximum exposure for both current and future land use is less than 10-4 and the non-carcinogenic hazard quotient is less than 1, action generally is not warranted unless there are adverse environmental impacts. However, if Maximum Contaminant Levels (MCLs) or non-zero Maximum Contaminant Level Goals (MCLGs) are exceeded, action generally is warranted.

The guidance cited above describes conditions at a site where remedial action generally is not warranted. As such, the associated risk levels correspond to a cumulative site risk less than approximately 10-4 for exposure to multiple chemicals with potential carcinogenic effects and a Hazard Quotient (HQ) less than 1 for those chemicals with potential non-carcinogenic toxicity. On the other hand since RMLs may be used to support the decision to undertake a removal action at a site, they can correspond to higher risk levels and do not address cumulative risk from exposure to multiple chemicals.

Although exceeding MCLs does not trigger a removal action, once the Agency has determined the need for a removal action under CERCLA, typically MCLs should be attained to the extent practicable during the removal action considering the exigencies of the situation. In determining whether ARARs are practicable, the Agency may consider appropriate factors including the urgency of the situation and the scope of the removal action to be taken. For further information on ARARs in the removal action process, please refer to the guidance titled, “Superfund Removal Procedures: Guidance on the Consideration of ARARs During Removal Actions” (USEPA, 1991).

Once again, calculated RMLs are not meant to define protective levels and are not de facto cleanup levels. Thus, generic RMLs correspond to risk levels of approximately 10-4 and/or a Hazard Quotient of up to 3 for long-term exposure to individual chemicals at a site. A 10-4 risk level corresponds to the upper-end of EPA’s generally acceptable risk range of 10-6 to 10-4 as discussed in the National Contingency Plan (NCP), 40 CFR 300.430. The NCP gives no analogous recommended range for non-carcinogenic risks.

However, an HQ of 3 is generally considered a reasonable risk level for RMLs for non-carcinogenic chemicals based on the discussion of uncertainty included in EPA’s definition of the non-carcinogenic Reference Dose (RfD) and Reference Concentration (RfC). EPA defines the RfD and RfC as:

…an estimate (with uncertainty spanning perhaps an order of magnitude) of daily exposure to the human population (including sensitive subgroups) that is likely to be without an appreciable risk of deleterious effects during a lifetime...

It is unknown for any particular chemical where the RfD/RfC may fall within the order of magnitude range of uncertainty. As a science policy choice, OSWER places the RfD/RfC in the middle of a factor of ten uncertainty range; with a factor of three above and below (i.e., 0.3 to 3). As stated previously, action generally is not warranted at a site where the non-carcinogenic HQ is less than 1; whereas, action may be warranted where the non-carcinogenic HQ exceeds 1. Again, as a science policy choice to aid in prioritizing actions that may warrant the use of removal authority, an HQ of 3 was selected as the upper, target risk level for calculating non-cancer RMLs.

However, the generic RML tables provide risk-based values corresponding to an HQ of 1 and 3 as there may be site-specific and/or chemical specific circumstances where an HQ less than 3 may be more appropriate for calculating RMLs. For example, RMLs corresponding to an HQ of 1 may be more appropriate for those sites where multiple chemicals are present that have RfDs or RfCs based on the same toxic endpoint or where the toxicity of a chemical is such that exceeding the RfD/RfC, even slightly, warrants particular concern.

In addition to providing the user with a table of generic, risk-based RMLs, this website links to the Regional Screening Levels (RSLs) generic tables and the calculation tool which allows users to modify the standardized, default parameters to calculate site-specific RSLs and RMLs. The generic RSL table corresponds to risk levels of approximately 10-6 and/or an HQ of 1 for long-term exposure to individual chemicals at a site. It is recommended that if an OSC or other risk manager is calculating site specific RSLs or RMLs that a Regional risk assessor be consulted for assistance.

A risk assessor or risk manager may want to calculate RMLs based on short-term exposures. In this case, they would use the RSL calculation tool and reduce the 25 or 30-year default value for exposure duration and also replace the toxicity criteria and risk levels used for chronic exposures with values that are appropriate for the exposure duration and toxicity criteria selected.

Whether the user relies on generic RMLs or chooses to calculate site-specific RMLs, it is important to clearly demonstrate the equations and exposure parameters used in deriving RMLs at a site. A discussion of the assumptions used in the RML calculations should be included in the decision document where site specific RMLs are presented.

Comparison of site concentrations to RMLs is only one factor used in determining the need for a removal action at a site. While EPA's expectation is that removal actions are generally justifiable above the RML, EPA has the flexibility to determine that case-specific conditions do not warrant a removal action. For example, site-specific background or incomplete exposure pathways might indicate that a removal is not necessary, or that another mechanism for addressing the site is more appropriate. In such cases, EPA might refer the site for remedial action, or to a state or other authority, or might choose some other means of addressing the site.

Conversely, these generic values cannot account for all chemicals, exposure pathways or receptors that may be present at a site. Thus, a significant health threat may exist at a site even if none of the substances detected exceeds its numeric RML. Flexibility is provided so that additional site-specific factors can be considered like: threat of fire or explosion, exposures from other sources, exposures to multiple contaminants, population sensitivity, the finding of a public health hazard by the Agency for Toxic Substances and Disease Registry (ATSDR), and other factors not directly related to the contaminant concentration. Therefore, a removal action may be initiated if the risk/hazard at a site has been analyzed in detail and the analysis indicates that a serious risk/hazard is present due to site-specific factors.

It is always recommended that if an OSC or other risk manager has questions about RMLs, RSLs, and/or clean up levels that a Regional risk assessor be consulted for assistance.

  • Note: Radionuclide RMLs are not provided or addressed on this website, more information is available at EPA’s Preliminary Remediation Goals for Radionuclides Exit.
     
  • Note: No consideration is given to ecological effects in the values presented in this database tool. Therefore, ecological risk may need to be addressed separately when a removal action based on these RMLs is being considered.
     
  • Note: At this time, RMLs for air are not provided or addressed on this website.