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Environmental Indicators - Frequent Questions


  1. What are the RCRA Corrective Action Environmental Indicators (EIs)?

      The RCRA Corrective Action Environmental Indicators (EIs) are:

    • A means of evaluating and reporting on the acceptability of current site conditions (i.e., they are interim milestones and not final remedy or site closure goals).
    • An opportunity for facilities and regulators to show meaningful progress that is achievable in the near future.
    • A high priority within EPA and the #1 priority for the RCRA program.
    • Adopted by ECOS and equivalent to ASTSWMO cleanup measures.

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  2. How many RCRA CA EIs are there?

      There are two:

    • Current Human Exposures Under Control (a.k.a. "Human Exposure EI")
    • Migration of Contaminated Groundwater Under Control (a.k.a. "Groundwater EI")

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  3. What are the possible results (determinations) for the EIs?

      "YES" - conditions are "Under Control"
      "NO" - conditions are NOT "Under Control"
      "IN" - Insufficient information is available to determine if conditions are "Under Control"

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  4. What are the RCRA CA EI used for?

    These EIs are used to summarize and report on the site-wide environmental conditions at the RCRA CA Program's highest priority sites (i.e., those on RCRA Cleanup Baseline). These EIs are being used to track the RCRA program's progress on getting our highest priority contaminated sites under control and report to the Office of Management and Budget (OMB), U.S. Congress, and the public.

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  5. How are sites evaluated to see if they meet the RCRA CA EI?

    Known and suspected site (-wide) conditions are evaluated using a series of simple questions and flow-chart logic to arrive at a reasonably defensible determination (YES, NO, or IN). These questions (EI forms) were issued on Feb. 5, 1999 as Interim Final Guidance (PDF) (17 pp, 52K, About PDF)

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  6. Who makes the EI determinations and fills out the EI forms?

    The lead regulators for the site (Authorized State or EPA) make the EI determination. However, facilities or their consultants may assist EPA in the evaluation by providing information on the current environmental conditions and may even assist by filling out the EI forms and making recommendations for the determination.

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  7. How does the Human Exposures EI relate to traditional Risk Assessments?

    The Human Exposure EI is an assessment of actual current human risks and would typically take the form of a qualitative assessment of the completeness of exposure pathways, but may include a traditional Quantitative Risk Assessment.

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  8. How does the Groundwater EI differ from the Human Exposures EI?

    The Groundwater EI is strictly a resource protection measure and not a direct measure of human risk, and may include the assessment of the impacts of groundwater discharges to surface waters and surface water ecosystems.

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  9. Will EIs require additional investigations (beyond that typically required for CA)?

    No, since the EIs are small components of typical site corrective action final remedies, the EI should not require any additional investigations to be conducted. Although, the timing of when investigations, or stabilization actions, occur may be altered in order to demonstrate that site conditions are "Under Control" as soon a possible.

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  10. Is it necessary to complete an entire site investigation to show that human exposures are under control?

    No, human exposures can be considered "under control" if adequately protective controls are in place to prevent unacceptable exposures (i.e., cut pathways between humans and contamination) for the reasonably-expected worst-case conditions (in the un-investigated areas).

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  11. Are EI determinations a point-in-time determination, or do they have to be maintained to ensure they remain true through time?

    Yes, they are made in a point in time, and Yes, we are responsible to ensure that the EI determinations accurately report site conditions through time.

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  12. How do the Environmental Indicator determinations for Current Human Exposure under Control and Migration of Contaminated Groundwater relate to final remedy decisions at a RCRA corrective action facility?

    The environmental indicator determinations are a snapshot reflecting current conditions at a facility. The Human Exposure EI focuses on current exposure scenarios, and the Groundwater EI addresses the question of whether existing plumes of contaminated groundwater are continuing to expand above levels of concern. These determinations do not address whether corrective action is "complete" at the site, whether remedial long-term goals are met, or whether a site will be safe if land uses change in the future.

    As a result, overseeing agencies should not look at EI determinations at a facility as the "final" decision, and facility owner/operators should not interpret positive EI determinations as indicating that all corrective action obligations are met. In some cases, a facility that meets both Environmental Indicators may well need no further corrective action. But in many other cases, substantial work will be needed before a cleanup is complete. At some facilities, for example, current exposures may be cut off through interim measures, and groundwater migration may be under control, but more permanent measures (or more extensive site characterization) are needed to ensure that the site is safe for reasonably anticipated future uses. These measures would be addressed as part of longer term cleanup at the site.

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  13. How do I consider future land use in making an EI determination?

    An EI determination reflects current land use (and patterns of exposure). Potential future land uses are not relevant to the determination; instead, a positive EI determination is appropriate when current exposures are adequately under control. (Of course, when it's known that patterns of exposure or land use are about to change, the overseeing agency will likely take a more conservative approach, but this would be a special case.)

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Groundwater-to-Surface Water Interaction

  1. For the purpose of making a Groundwater Environmental Indicator determination, how do I address groundwater-to-surface-water interaction?

    In cases where groundwater is being discharged to surface water, you should, as a general matter, focus your groundwater environmental indicator evaluation on the question of whether or not contaminated groundwater is significantly impairing the quality of the surface water body. A positive environmental indicator determination would generally be appropriate where the groundwater is not significantly affecting the surface water body in a way that leads it to fail basic water-quality criteria.

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  2. What does the Groundwater Environmental Indicator deal with?

    The "Migration of Contaminated Groundwater Under Control" environmental indicator pertains to the physical migration (i.e., further spread) of contaminated groundwater and contaminants within groundwater (e.g., non-aqueous phase liquids or NAPLs). It also includes the interaction of contaminated groundwater with surface water.

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  3. What do we mean by a stabilized plume?

    A plume is stabilized if it remains within the "existing area of contaminated groundwater." A plume of contaminated groundwater could remain in its existing area if it is no longer expanding above levels of concern in the vertical or horizontal dimensions due to, for example, natural attenuation or engineered controls such as hydraulic containment and/or physical barriers. Alternatively, the plume of groundwater contamination might not be expanding within the geologic formation, but it might be discharging into a hydraulically connected surface water body. In such a situation, the plume of contaminated groundwater is not getting any bigger (i.e., the plume has "stabilized"), but it might or might not be "under control." The environmental indicator determination in such a setting would be based on whether or not the continued discharge of groundwater represented an unacceptable impact to the receiving surface water body.

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  4. Is the discharge of "contaminated" groundwater into surface water likely to be "insignificant?"

    In some cases, overseeing agencies are likely to be able to conclude that a release from groundwater into surface water will be "insignificant" - and therefore "under control" - based on the levels of contaminants in the groundwater, without consideration of the volume or flow of the surface water body. As a rule of thumb, we have found that, if the groundwater concentrations for all constituents are less than 10 times the appropriate surface water quality criteria for both human health and aquatic life, the current groundwater discharge should be "insignificant" for environmental indicator purposes. In this case, the regulator would conclude that the groundwater environmental indicator had been met (at least with respect to the discharge to surface water).

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  5. How do I deal with issues of historic sediment contamination when assessing the groundwater-to-surface-water pathway?

    In cases where groundwater is being discharged to surface water, you should, as a general matter, focus your groundwater environmental indicator evaluation on the question of whether or not contaminated groundwater is significantly impairing the quality of the surface water body. A positive environmental indicator determination would generally be appropriate where the groundwater is not affecting the surface water body in a way that leads it to fail basic water-quality criteria.

    In many cases, RCRA facilities are located near rivers or other water bodies characterized by historic sediment contamination. In such situations, the potential contribution of current groundwater discharge to sediment quality (and similarly, to the hyporrheic zone) would be beyond the scope of a groundwater environmental indicator determination. Instead, sediment quality issues would be dealt with as a part of the final remedy (or perhaps more broadly as part of an area-wide investigation).

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Contaminated Sediment

  1. In making a human health EI determination, how do I deal with releases to surface water that may be associated with contamination of fish above safe levels? How about contaminated sediment from runoff, direct discharges, etc., to which people may be exposed?

    It will generally be possible (for the purposes of a human health EI) to address concerns over possible contaminated fish consumption or direct human exposure to contaminated sediments through some combination of source control and exposure controls. For example, some RCRA facilities have been found to directly discharge contaminants into relatively small water bodies, leading to potential fish contamination. At some of these facilities, human health EIs were achieved through control of the discharges (e.g., water outflows and runoff), combined with access restrictions and signs warning against fishing. Other facilities may have contributed to broader water quality or sediment problems, which may have led to bioaccumulation of contaminants in fish. Again, we expect that measures to achieve the human health EI would focus on cutting off significant releases from the RCRA facility, perhaps combined with fish advisories or similar methods to reduce exposure where it is a concern.

    Again, it should be emphasized that achieving EIs does not necessarily mean that a facility has completed its corrective action obligations. In the situations described here, the final remedy is likely to require substantially more aggressive remedies, perhaps including direct cleanup of the contaminated sediment. In some cases, the remedy will likely take place as part of a broader area-wide cleanup.

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Contamination From off-Site Sources

  1. How do I address plumes of contaminated groundwater that originate from off-site sources in making a Migration of Contaminated Groundwater under Control EI determination at a RCRA facility?

    As stated in the February 5, 1999 guidance from the Office of Solid Waste, OSW (renamed Office of Resource Conservation and Recovery, ORCR, on January 18, 2009) on how to determine if a facility has met the RCRA Environmental Indicators, the Migration of Contaminated Groundwater under Control EI determination apples site-wide for all contaminated groundwater "subject to corrective action at or from the identified facility." Therefore, plumes that originate from off-site sources would not be subject to a RCRA groundwater EI determination for the RCRA facility in question. The overseeing agency, however, should ensure that such plumes are addressed as necessary through other regulatory actions.

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Vapor Intrusion

  1. What does USEPA recommend as the best way to address Vapor Intrusion for EI determinations in the time remaining before 2005?

    EPA recommends that its November 2002 Draft Guidance for Evaluating the Vapor Intrusion to Indoor Air Pathway from Groundwater and Soils be used to assess this pathway for the purpose of making RCRA EI determinations. Specifically, this would involve the use of the preliminary screening criteria in Tiers 1 and 2, and, if necessary, Tier 3 site-specific modeling for EI determinations. If scientific, site-specific models (such as the Johnson & Ettinger (1991) model spreadsheets found on the Superfund Program's website(www.epa.gov/superfund) or other appropriate models) do not indicate that the site has a potential to cause exposures above the applicable EI criteria (using site-appropriate input parameters), then this pathway should be considered to have been adequately screened for EI exposure assessment purposes. In such cases, we do not believe that confirmatory sampling will be necessary, for the purpose of making an EI determination.

    If Tier 3 models indicate a potential for exposure at levels above the applicable criteria, additional data gathering (e.g., sub-slab sampling or indoor air monitoring) or remediation may be needed to meet the human health environmental indicator.

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  2. What are the applicable criteria to use in determining whether the human health environmental indicator has been met for the vapor intrusion pathway?

    For the purpose of making Current Human Exposure under Control EI determinations with respect to vapor intrusion, EPA generally recommends the use of 10-5 levels for carcinogens (incremental individual lifetime cancer risk), and a Hazard Quotient (HQ) of 1 for non-cancer risks.) (For occupational settings, see question 3 below.)

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  3. How is vapor intrusion into occupational and other non-residential settings to be evaluated for RCRA EI determinations?

    Occupational settings where persons are in a working situation: Such settings could include workplaces where workers are handling hazardous chemicals (e.g., manufacturing facilities) similar to or different from those in the subsurface contamination, as well as other workplaces, such as administrative and other office buildings where chemicals are not routinely handled in daily activities. OSHA and EPA have agreed that OSHA generally will take the lead role in addressing occupational exposures. Therefore, EPA does not expect the November 2002 Vapor Intrusion Guidance to be used in such settings (i.e., primarily occupational). Nevertheless, we recommend that such facilities be notified of the potential for this exposure pathway and that they consider any potential exposure that may result.

    Nonresidential settings where persons are in a non-working situation: Nonresidential buildings may need to be evaluated where people (typically non-workers) may be exposed to hazardous constituents entering into the air space from the subsurface. This would include, for example, buildings where the general public may be present, e.g., schools, libraries, hospitals, hotels, and stores. In these situations we believe the November 2002 Vapor Intrusion Guidance may be appropriate, although we recommend appropriate adjustments be made for nonresidential exposure durations, the building specific air volumes and air exchange rates, as well as other relevant factors to be considered.

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  4. How is future land use considered in making a RCRA Current Human Exposure Under Control EI determination for vapor intrusion?

    Environmental Indicators reflect current, not future or potential, conditions. See response 13 in the "General" section above.

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