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A new Peak PRG output option has been added. Please see the What's New page for details.

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. What are radionuclide slope factors (SF)?
  4. How should slope factors (SF) be used?
  5. How do PRGs differ from Regional Removal Management Levels (RML)?
  6. How do PRGs differ from cleanup standards?
  7. How often do you update the PRG Table?
  8. Can I get a copy of a previous PRG table?
  9. What ages and exposure routes are considered in each land use?
  10. How can I select more than one isotope at a time in the PRG Search page?
  11. How are the PRG results converted to a mass basis?
  12. How are the residential exposure durations (EDs) determined for carcinogenic (age-adjusted) exposures?
  13. How can I get the calculator results or the other web pages to print on one page?
  14. Do the PRGs take into account field survey or laboratory analytical approaches?
  15. Are the PRGs applicable to cleanup after a terrorist attack?
  16. Do the PRGs factor inhalation from Radon vapor intrusion?
  17. What is the preferred citation for information taken from this website?
  18. Where else can I go for toxicity studies (values) not on this site?
  19. Do the fish tissue and/or soil PRGs apply to wet-weight or dry-weight data?
  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 Calculation 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. Exceeding a PRG, however, suggests that further evaluation of the potential excess lifetime cancer risk (ELCR) 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. What are radionuclide slope factors?

    Slope factors (SFs), for a given radionuclide, represent the excess lifetime cancer risk (ELCR) equivalent per unit intake (i.e., ingestion or inhalation) or external exposure of that radionuclide. These SFs are used to convert a radionuclide concentration in soil, air, water, or foodstuffs to a radiation ELCR. SFs are also called risk coefficients.

  4. How should slope factors be used?

    The primary use of slope factors (SFs), also called risk coefficients, is to compute the excess lifetime cancer risk (ELCR) resulting from site-related exposures. This is accomplished by multiplying the route-specific SF by the chronic daily intake (CDI) of each radionuclide of potential concern for each route of exposure.

  5. How do PRGs differ from Regional Removal Management Levels (RMLs)?

    Risk-based RMLs for carcinogens generally are based on a 1.0E-04 excess lifetime cancer risk (ELCR). RMLs 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 RMLs based on the PRG calculator, we recommend either (1) change the TR (target risk) to 1.0E-4 on the calculator main page or (2) multiply the PRG results from the default tables on the PRG "Download" page by 100 to convert 1.0E-06 PRGs to 1.0E-04 PRGs. 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.

  6. 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.

  7. How often do you update the PRG Table?

    The tables are updated when new toxicity values become available, exposure parameter values change, or a model is updated that impacts the default calculator results. There is no set schedule for these updates. Please take note of the "What's New" page to identify when these updates are incorporated.

  8. 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.

  9. What ages and exposure routes are considered in each land use?

    The following table lists the land uses, media, and receptor ages utilized in the PRG calculator.

    Land use Media Exposure Routes
    Oral Externala Inhalation
    Resident Soil Adult
    Child
    Adult
    Child
    All Ages
    Tapwater Adult
    Child
    Adult
    Child
    All Ages
    Air NA All Ages Adult
    Child
    Fish All Ages NA NA
    Recreator Soil/Sediment Adult
    Child
    Adult
    Child
    All Ages
    Surface Water Adult
    Child
    Adult
    Child
    NA
    Air NA All Ages Adult
    Child
    Game & Fowl
    Consumption
    All Ages NA NA
    Farmer Soil Adult
    Child
    Adult
    Child
    All Ages
    Tapwater Adult
    Child
    Adult
    Child
    All Ages
    Air NA All Ages Adult
    Child
    Biota
    Consumption
    Adult
    Child
    NA NA
    Outdoor Worker Soil Adult Adult Adult
    Air NA Adult Adult
    Indoor Worker Soil Adult Adult Adult
    Air NA Adult Adult
    Composite Worker Soil Adult Adult Adult
    Air NA Adult Adult
    Construction Worker Soil Adult Adult Adult
    Air NA Adult Adult
    Soil to Groundwater Soil Adult
    Child
    Adult
    Child
    All Ages

    NA = Not Applicable
    a. The external exposure routes include: external exposure to ionizing radiation in soil, submersion in air, and immersion in water.

  10. 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.
  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 to convert PRGs in pCi/g to mg/kg and also a formula to convert 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.


  12. How are the residential exposure durations (EDs) determined for carcinogenic (age-adjusted) exposures?

    Residential exposure duration (EDres) is set at 26 years, according to an OSWER directive based on the 2011 version of the Exposure Factor's Handbook. When evaluating carcinogenic exposure, intakes are age-adjusted to account for exposure as a child and an adult within the 26 years. The OSWER directive sets child exposure at 6 years (EDres-c). Therefore, EDres - EDres-c = 20 years of adult exposure (EDres-a). For this tool, child intakes are used with EDres-c and adult intakes are used for EDres-a.

  13. How can I get the calculator results or the other web pages to print on one page?

    Output links for PDF and Spreadsheet files can be found at the top of the calculator results page. The HTML results are not suited for formatting to print on a single page but are rather designed for ease of use on the screen.

  14. 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. 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 for remedial decision data to 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. This analysis indicates that concentrations derived with the PRG calculator that fall within the 10-4 to 10-6 excess lifetime cancer risk (ELCR) range are measurable.

  15. 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 uses 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 the optimal process for the late-phase was a Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) approach. 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 that 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.

  16. Do the PRGs factor inhalation from Radon vapor intrusion?

    Air PRGs represent preliminary remediation goals for indoor and outdoor air. The residential and industrial air PRG values can be used to determine preliminary remediation goals that are detected in the air (e.g., indoor and outdoor) from a variety of sources. There are no PRGs specific to the vapor intrusion pathway (i.e, for subsurface sources that may contribute to indoor air contamination). EPA's recommended Radon Vapor Intrusion Screening Level tool can be found online here. For guidance on vapor intrusion assessment, see EPA's Vapor Intrusion Site. The OSWER Technical Guide For Assessing And Mitigating The Vapor Intrusion Pathway From Subsurface Vapor Sources To Indoor Air (OSWER Publication 9200.2-154; June 2015) can be found there among other resources and information.

  17. What is the preferred citation for information taken from this website?

    United States Environmental Protection Agency. Preliminary Remediation Goals for Radionuclide Contaminants at Superfund Sites. (insert date accessed and url).

  18. 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.

  19. Do the fish tissue and/or soil PRGs apply to wet-weight or dry-weight data?

    The fish PRGs represent the concentration that can be consumed at the rate indicated in the Technical Background Document. Therefore, wet or dry weight is not an inherent assumption of the PRG numbers. Rather, users of the Table should consider whether their population of interest is more likely to consume the fish using a preparation method that is better simulated by a wet or dry weight. (For example, consumption of raw or fried fish would be more likely represented by wet weight, whereas consumption of smoked or dried fish might be better represented by dry weight.) In other words, the use of a site-specific sample as wet or dry weight should be governed by its representativeness for the population of interest. The PRG Calculator does not provide default fish PRGs under residential. If the fish scenario is selected under residential, the calculator will automatically switch to site-specific mode. On the next page, the user is required to enter a site-specific fish consumption rate. The previous default fish intake rate of 54,000 mg/day from the Standard Default Exposure Factors has been removed. Intake rates can be found in the 2011 Exposure Factors Handbook. Please consult your Regional risk assessor when determining appropriate fish consumption rates. The soil PRGs are based on dry weight, because the soil intake rates are based on dry weight. Most soil data is typically reported as dry weight. As always, please consult your Regional risk assessor when applying the PRGs to site-specific data.