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Preliminary Remediation Goals for Radionuclides (PRG)

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PRG Frequently Asked Questions (FAQ)

This page presents many questions asked by site users and responses. Please search this page for answers to your questions prior to contacting technical support staff. Researching the questions and answers posted here will greatly reduce the time it takes for you to solve many problems that arise from calculating and using this PRG site.

  1. What are PRGs?
  2. What are PRGs used for?
  3. How do PRGs differ from cleanup standards?
  4. How do PRGs differ from Removal Action Levels (RALs)?
  5. How often do you update the PRG Table?
  6. Can I get a copy of a previous PRG table?
  7. Where else can I go for toxicity studies (values) not on this site?
  8. How can I select more than one isotope at a time in the PRG Search page?
  9. Do the PRGs take into account field survey or laboratory analytical approaches?
  10. Are the PRGs applicable to cleanup after a terrorist attack?
  11. How are the PRG results converted to a mass basis?
  1. What are PRGs?

    Preliminary Remediation Goals (PRGs), presented on this site, are risk-based concentrations for the Superfund/RCRA programs. PRGs are derived from standardized equations combining exposure information assumptions with toxicity data. They are considered by the Agency to be protective for humans (including sensitive groups), over a lifetime. However, PRGs are not always applicable to a particular site and do not address non-human health endpoints such as ecological impacts. The PRGs contained in the PRG table are generic; that is, they are calculated without site-specific information. They may be re-calculated using site-specific data. Cancer slope factors (SFs) used are provided by the Center for Radiation Protection Knowledge. The main report is Calculations of Slope Factors and Dose Coefficients and the tables of slope factors are in a separate appendix.

  2. What are PRGs used for?

    They are used for site "screening" and as initial cleanup goals if applicable. PRGs are not de facto cleanup standards and should not be applied as such. The PRG's role in site "screening" is to help identify areas, contaminants, and conditions that do not require further federal attention at a particular site. Generally, at sites where contaminant concentrations fall below PRGs, no further action or study is warranted under the Superfund program, so long as the exposure assumptions at a site match those taken into account by the PRG calculations. Chemical concentrations above the PRG would not automatically designate a site as "dirty" or trigger a response action. However, exceeding a PRG suggests that further evaluation of the potential risks that may be posed by site contaminants is appropriate. PRGs are also useful tools for identifying initial cleanup goals at a site. In this role, PRGs provide long-term targets to use during the analysis of different remedial alternatives. By developing PRGs early in the decision-making process, design staff may be able to streamline the consideration of remedial alternatives.

  3. How do PRGs differ from cleanup standards?

    PRGs are not de facto cleanup standards, however, they could be used to establish final cleanup levels for a site after a proper evaluation takes place. In the Superfund program, this evaluation is carried out as part of the nine criteria for remedy selection outlined in the National Oil and Hazardous Substances Pollution Contingency Plan (NCP). Once the nine criteria analysis is completed, the PRG may be retained as is, or modified (based on site-specific information) prior to becoming established as a cleanup standard. This site-specific cleanup level is then documented in the Record of Decision.

  4. How do PRGs differ from Removal Action Levels (RALs)?

    Risk-based RALs for carcinogens generally are based on a 1 × 10-4 cancer risk. RALs typically are used to help define areas, contaminants and conditions that may warrant an emergency or a time-critical removal action at a site. To develop RALs based on the PRG calculator, we recommend either (1) multiply the PRG results from either the tables on the PRG "Download" page or the default option for the PRG "Search" page by 100; or, (2) select the site-specific on the PRG "Search" page and change the TR (target cancer risk) to 1.0E-4. Most of the radionuclides under the Soil to Groundwater scenario use MCLs as a target protective level so these two methods for adjusting PRG results would not apply.

  5. How often do you update the PRG Table?

    The PRG database is updated when new toxicity values are presented by the EPA. This is generally done monthly. However, there may be times when more than one month passes without the release of updated toxicity values. Please take note of the "What's New" page to identify when toxicity values are updated.

  6. Can I get a copy of a previous PRG table?

    We do not distribute outdated copies of the PRG table. Each new version of the table supersedes all previous versions. If you wish to maintain previous versions of the PRGs for a long-term project, you can download the entire table and save multiple versions with a time-stamp.

  7. Where else can I go for toxicity studies (values) not on this site?

    Many other websites host toxicity information from other countries and other government agencies similar to this EPA site. The Risk Assessment Information System (RAIS) at http://rais.ornl.gov/ presents toxicity values and toxicity study information. Websites of other governmental agencies are also useful. Call the U.S. EPA Superfund Health Risk Technical Support Center at (513) 569-7300 and ask for toxicity values. Call the ATSDR Information Center toll-free at 1-888-422-8737 for toxicity values and profiles.

  8. How can I select more than one isotope at a time in the PRG Search page?

    To select more than one isotope you can:

    1. left click and hold the button down while dragging the mouse pointer up and down through the isotope list,
    2. hold the control (Ctrl) key down while left clicking on the isotopes desired or
    3. click in the "Select All" box to the bottom right of the isotope list.
  9. Do the PRGs take into account field survey or laboratory analytical approaches?

    No, the PRGs are a risk-based tool only, except for the Soil to Groundwater scenario which is usually based on MCLs. The approach to determining the extent of contamination is a separate process during the Remedial Investigation or Feasibility Study (RI/FS) and remedial design processes. It is important that data that support remedial decisions be of known and acceptable quality. The determination of what data are needed is a site-specific decision and it is the responsibility of the Remedial Project Manager (RPM) to use the tools that are most appropriate for that situation. Here is an analysis that indicates that PRG calculator derived concentrations that fall within the 10-4 to 10-6 risk range are measurable.

  10. Are the PRGs applicable to cleanup after a terrorist attack?

    Responses to radiological and nuclear terrorist incidents, is addressed in an August 1, 2008, guidance issued by the Department of Homeland Security (DHS) in the Federal Register (Vol. 73, No. 149, pp 45029 - 45049), Planning Guidance for Protection and Recovery Following Radiological Dispersal Device (RDD) and Improvised Nuclear Device (IND) Incident. The DHS guidance envisions using Operational Guidelines from the Department of Energy to guide the early and intermediate phases of response to an RDD and an IND. Under the guidance, the late-phase generally would utilize an optimization process to site-specifically decide on an approach for addressing the remaining residual contamination. Normally, the PRG calculator would be used only if site-specifically the optimization process chose to use a Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) approach for the late-phase. As at a CERCLA site, the user at an RDD or IND site can choose to modify the standard default PRG exposure parameters to calculate site-specific PRGs. The characteristics of an RDD or IND site may warrant the use of site-specific assumptions which differ from the PRG defaults. The site manager should weigh the cost of collecting the data necessary to develop site-specific PRGs with the potential for deriving a higher PRG that provides an appropriate level of protection.

  11. How are the PRG results converted to a mass basis?

    Appendix B of the Soil Screening Guidance for Radionuclides Technical Background Document presents a formula for converting PRGs in pCi/g to mg/kg and also a formula for converting pCi/L to mg/L. The equation is reproduced here with similar conversions for mg/m3 and mg/cm2.


    The derivation of the 2.8 × 10-12 and the 2.8 × 10-15 conversions are presented below.


    Combination of the derivation of the conversions with the isotope-specific half life and atomic weight is presented here.


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