RML Frequently Asked Questions

Please search this page for answers to your questions before contacting technical support staff. Researching the questions and answers posted here will hopefully aid the reader in understanding some of the issues/questions that arise when using these RML tables.

1. What are RMLs?
2. EPA has provided previous guidance and lists of RALs, how does this approach differ?
3. How are RMLs used?
4. How do RMLs differ from Regional Screening Levels (RSLs), Preliminary Remediation Goals (PRGs) and site-specific cleanup levels?
5. What target risk levels are used in calculating RMLs?
6. What are the sources of toxicity values and chemical-specific parameters used to calculate RMLs?
7. Can EPA take a removal action if site concentrations are below the RML?
8. Can EPA decide not to take a removal action if site concentrations are above the RML?
9. How often do you update the RML Table?
10. Can I get a copy of a previous RML table?
11. Why are RMLs not provided for asbestos?
12. What is the Perchlorate value of 15 μg/L in the MCL column based on?
13. How do I apply the trihalomethane MCLs?
14. When should the RMLs for air be used?
15. What toxicity values are used for TCE?

1. What are RMLs?

   The Regional Removal Management Levels (RMLs) presented on this site are to support the decision for EPA to undertake a removal action under CERCLA. They are risk-based, although not necessarily protective for long term exposures, concentrations derived from standardized equations combining exposure assumptions with toxicity data from the Superfund program's hierarchy. The RMLs contained in the RML table are generic. In other words, they are calculated without site-specific information (e.g., the time-frame over which individuals may have been exposed to site contaminants). However, this website links to the Regional Screening Levels (RSLs) calculation tool which allows for the use of site-specific data to modify the generic RMLs.

2. EPA has provided previous guidance and lists of RALs, how does this approach differ?

   The most recent publically available list of RALs was published in 1998 and many are outdated due to changes in toxicity criteria and Agency risk methodologies. Previously, RALs were provided only for drinking water. This update provides RMLs for tap (drinking) water, air, and soil and is more in line with the Federal Superfund program’s risk assessment and risk management practices.

3. How are RMLs used?

   RMLs help identify areas, contaminants, and conditions where a removal action may be appropriate. Sites where contaminant concentrations fall below RMLs, are not necessarily “clean,” and further action or study may be warranted under the Federal Superfund program. In addition, sites with contaminant concentrations above the RMLs may not necessarily warrant a removal action dependent upon such factors as background concentrations, the use of site-specific exposure scenarios or other program considerations.

4. How do RMLs differ from Regional Screening Levels (RSLs), Preliminary Remediation Goals (PRGs) and site-specific cleanup levels?

   Risk-based RMLs, RSLs, PRGs, and site-specific cleanup levels can be viewed as part of a continuum of levels used to evaluate chemical concentrations at a site.

   

   RMLs are used to help define areas, contaminants and conditions that may warrant a removal action at a site. The generic RMLs are generally higher levels than those selected as final cleanup levels at sites where a remedial action may be required under Superfund authority. Thus, the RMLs are not de facto cleanup standards and should not be used as such. Sites where contaminant concentrations fall below RMLs, are not necessarily "clean," and further action or study may be warranted under the Federal Superfund program.

   Generally, RSLs are more conservative risk-based values for individual chemicals than RMLs. In the Federal Superfund program, "screening" refers to the process of identifying and defining areas, contaminants and conditions at a particular site that may be of potential concern or that do not require further Federal attention. Generally, at sites where contaminant concentrations fall below screening levels, no further action or study is warranted under the Federal Superfund program. Where contaminant concentrations equal or exceed screening levels, further study or investigation may be warranted, but not necessarily cleanup.

   PRGs are values that provide a reference point for establishing site-specific cleanup levels. There are two general sources of chemical-specific PRGs: 1) concentrations based on Applicable or Relevant and Appropriate Requirements (ARARs) such as Federal or State drinking water standards, and 2) risk-based concentrations. PRGs may then be used as the basis for developing final cleanup levels based on the nine-criteria analysis described in the National Contingency Plan [Section 300.430 (3)(2)(I)(A)]. The directive entitled “Role of the Baseline Risk Assessment in Superfund Remedy Selection Decisions” (OSWER Directive 9355.0-30) discusses the modification of PRGs to generate cleanup levels.

5. What target risk levels are used in calculating RMLs?

   Although generic RMLs, RSLs and PRGs are based on similar methodologies, RMLs are used to support the decision to take a removal action at a site; thus, risk-based RMLs are calculated using higher target risk levels than those for RSLs and PRGs. The “Role of the Baseline Risk Assessment in Superfund Remedy Selection Decisions” (OSWER Directive 9355.0-30) guidance 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 will be used to support the decision to undertake a removal action at a site, they correspond to higher risk levels and do not address cumulative risk. 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. Although exceeding an MCL does not trigger a removal action, once the Agency has determined the need for a removal action under CERCLA, ARARs, such as MCLs, shall be attained to the extent practicable during the removal action considering 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).

   There is no recommended range for non-carcinogenic risks. However, a range of uncertainty is discussed 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, OLEM 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 tables on this website 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.

6. What are the sources of toxicity values and chemical-specific parameters used to calculate RMLs?

   The toxicity values and chemical-specific parameters used in the RML calculator follow the same hierarchy as used in the EPA's Regional Screening Levels for Chemical Contaminants at Superfund Sites (RSL) calculator. Details of the toxicity value hierarchy can be found in section 2.3 of the RSL User's Guide. Details of the chemical-specific parameter hierarchy can be found in section 2.4 of the RSL User's Guide.  Below is a brief description of the toxicity hierarchy.

   In 2003, EPA's Superfund program revised its hierarchy of human health toxicity values, providing three tiers of toxicity values in a memo (PDF) (4 pp, 225 K). Three tier 3 sources were identified in that guidance, but it was acknowledged that additional tier 3 sources may exist. The 2003 guidance did not attempt to rank or put the identified tier 3 sources into a hierarchy of their own. However, when developing the calculator presented on this website, EPA needed to establish a hierarchy among the tier 3 sources. The toxicity values used as “defaults” in this calculator are consistent with the 2003 guidance.

   Users of this calculator wishing to consider using other toxicity values, including toxicity values from additional sources, may find the discussions and seven preferences on selecting toxicity values in the attached Environmental Council of States paper useful for this purpose (ECOS website EXIT, ECOS paper(DOC)).

   When using toxicity values other than tier 1, users are encouraged to carefully review the basis for the value and to document its use in decision documentation on a site.

7. Can EPA take a removal action if site concentrations are below the RML?

   Yes. While the purpose of the RMLs is to help define areas, contaminants and conditions that may warrant a removal action at a site, they do not cover every conceivable situation which EPA might need to address. On a case-specific basis, EPA may need to take action because of combinations of chemicals, chemical-specific factors, unusual site-specific circumstances, the finding of a public health hazard by ATSDR, ecological risk or other case-specific considerations.

8. Can EPA decide not to take a removal action if site concentrations are above the RML?

   Yes. 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 exposure scenarios 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 dealing with the site.

9. How often do you update the RML Table?

   The RML table will be updated following the updates to the RSL table which occurs approximately every 6 months. If new or updated toxicity values are available between the table updates, the RSL calculator can be used to determine any chemical specific RML. Please take note of the main page to identify when toxicity or exposure values have been recently updated.

10. Can I get a copy of a previous RML table?

    We do not distribute outdated copies of the RML table. Each new version of the table supersedes all previous versions. If you wish to maintain previous versions of the RMLs for a long-term project, you can download the entire table and save multiple versions with a time-stamp. If RMLs have been used in the decision to undertake a removal action, it is generally advisable that the administrative record for that decision contain documentation of the RMLs used (e.g., a time-stamped copy of the RMLs calculated).

11. Why are RMLs not provided for asbestos?

    There are no national default numbers available for asbestos concentrations in soil. Thus, the need for a removal action can only be determined on a site-specific basis. OLEM's Asbestos Technical Review Workgroup developed guidance for investigating and evaluating asbestos risk at sites: Framework for Investigating Asbestos-Contaminated Superfund Sites (OSWER Directive 9200.0-68).

12. What is the Perchlorate value of 15 μg/L in the MCL column based on?

    The value in the MCL column is a preliminary remedial goal (PRG) of 15 μg/L which was calculated by the Office of Solid Waste and Emergency Response in a January 8, 2009, guidance. As described in the OSWER (now known as OLEM) memorandum, the Agency has now issued an Interim Drinking Water Health Advisory (Interim Health Advisory) (USEPA, 2008) for exposure to perchlorate of 15 μg/L in water. A health advisory provides technical guidance to federal, state, and other public health officials on health effects, analytical methods and treatment technologies associated with drinking water contamination.

    The Interim Health Advisory for perchlorate was developed using EPA’s RfD of of 7E-04 mg/kg-day and representative body weight, as well as 90th percentile drinking water and national food exposure data for pregnant women in order to protect the most sensitive population identified by the National Research Council (NRC) (i.e., the fetuses of pregnant women who might have hypothyroidism or iodide deficiency).

    The NCP (40 CFR 300.430(e)(2)(A)(1)) provides that when establishing acceptable exposure levels for use as remediation goals (for a Superfund site), consideration must be given to concentration levels to which the human population, including sensitive subgroups, may be exposed without adverse effects over a lifetime or part of a lifetime, incorporating an adequate margin of safety. As a result of the publication of the Interim Health Advisory for perchlorate, OLEM recommends that where no federal or state applicable or relevant and appropriate (ARAR) requirements exist under federal or state laws, 15 μg/L (or 15 ppb) is recommended as the PRG for perchlorate when making CERCLA site-specific cleanup decisions where there is an actual or potential drinking water exposure pathway.

    However, where State regulations qualify as ARARs for perchlorate, the remediation goals established shall be developed considering the State regulations that qualify as ARARs, as well as other factors cited in the NCP (see 40 CFR 300.430(e)(2)(i)(ff)). Final remediation goals and remedy decisions are made in accordance with 40 CFR300.430 (e) and (f) and associated provisions.

    Preliminary remediation goals are the starting points in the development of final cleanup levels at sites. As at all sites addressed under the NCP, these goals may be modified, depending on physical characteristics of a site, State laws and guidance, and other site specific factors, such as additional exposure routes.

13. How do I apply the trihalomethane MCLs?

    The individual trihalomethanes (bromodichloromethane; bromoform; dibromochloromethane, chloroform) all have the MCL of 80 µg/L listed in the RSL table. However, 80 µg/L is the MCL for Total Trihalomethanes.

14. When should the RMLs for air be used?

    The residential and industrial air RML values can be used to compare to air concentrations that are detected in the air (e.g., indoor and outdoor) from a variety of sources to determine if a removal action may be warranted. The typical use of the air RMLs is expected to be for comparison to indoor air levels (e.g., vapor intrusion data). It is recommended that the user consult with a toxicologist and/or Regional risk assessor when using the air RMLs for decision making.

    In addition to long-term chronic, non-acute  scenarios, OSCs may respond in the early phases of emergency events where very short duration (acute) air benchmarks (TEELs, AEGLs, ERPGs) may be appropriate. These emergency exposure criteria for chemical air releases are published by both government and private entities (see EPA Emergency Response Air Monitoring Guidance Tables, 2012, Edition 3; DOE's Protective Action Criteria (PACs) at http://energy.gov/ehss/protective-action-criteria-pac-aegls-erpgs-teels-rev-27-chemicals-concern-march-2012. It is important to understand how each value is derived and who the values are meant to protect. Due to the different types of air release scenarios an OSC may encounter, and the difficulties inherent in choosing among these multiple criteria, OSCs and other risk managers should consult their Regional risk assessors and/or public health officials for help in selecting the most appropriate comparison values for their site-specific circumstances.

15. What toxicity values are used for TCE?

    It is recommended that a regional risk assessor be consulted when evaluating TCE in any medium especially when less than chronic exposure scenarios are considered. The Superfund program issued a Compilation of Information Relating of Early/Interim Actions at Superfund Sites and the TCE IRIS Assessment  memo in August 2014. Several regions have issued their own guidance as well.

    In order to make the calculator display the correct results for TCE, the standard cancer and mutagen equations needed to be combined. Since TCE requires the use of different toxicity values for cancer and mutagen equations, it was decided to make a toxicity value adjustment factor for cancer (CAF) and mutagens (MAF). The adjustments were done for oral (o) and inhalation (i). These adjustment factors are used in the TCE equation images presented in section 4 of the User's Guide. The equations used are presented below. The adjustment factors are based on the adult-based toxicity values and these are the cancer toxicity values presented in the Generic Tables.

    

    The calculator, if run in default mode, will now produce accurate TCE RMLs for all land uses. The old three step process is no longer necessary.