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SPRG Frequently Asked Questions (FAQ)

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

  1. What are SPRGs?
  2. What are SPRGs used for?
  3. What are radionuclide slope factors (SF)?
  4. How should slope factors (SF) be used?
  5. How do SPRGs differ from Regional Removal Management Levels (RML)?
  6. How do SPRGs differ from cleanup standards?
  7. How often do you update the SPRG Table?
  8. Can I get a copy of a previous SPRG 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 SPRG Search page?
  11. How are the SPRG 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 SPRGs take into account field survey or laboratory analytical approaches?
  15. Are the SPRGs applicable to cleanup after a terrorist attack?
  16. Do the SPRGs 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. How do the ingestion and external SPRG values compare to the PRG values for soil?
  1. What are SPRGs?

    The recommended SPRGs (Preliminary Remediation Goals for Radionuclides in Outdoor Surfaces) presented on this site are risk-based concentrations, derived from standardized equations combining exposure information assumptions with EPA toxicity data that are used for Superfund/RCRA programs. They generally are considered by the Agency to be protective for humans (including sensitive groups) over a lifetime; however, recommended SPRGs are not always applicable to a particular site and do not address non-human health endpoints such as ecological impacts. The recommended SPRGs contained in the SPRG table are generic; that is, they are calculated without site-specific information. They may be re-calculated using site-specific data.

  2. What are SPRGs used for?

    They are often used for site "screening" and as initial cleanup goals, if appropriate. SPRGs are not de facto cleanup standards and should not be applied as such. The recommended SPRG'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 SPRGs, 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 SPRG calculations. Radionuclide concentrations above the SPRG would not automatically designate a site as "dirty" or trigger a response action; however, exceeding a SPRG suggests that further evaluation of the potential risks that may be posed by site contaminants generally is appropriate. SPRGs also can be useful tools for identifying initial cleanup goals at a site. In this role, SPRGs can provide long-term targets to use during the analysis of different remedial alternatives. By developing SPRGs early in the decision-making process, design staff may be able to streamline the consideration of remedial alternatives.

  3. What are radionuclide slope factors (SF)?

    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 (SF) 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 SPRGs differ from cleanup standards?

    SPRGs are not intended to be 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, much of 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 SPRG 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 typically is then documented in the Record of Decision.

  6. How do SPRGs differ from Regional Removal Management Levels (RML)?

    Risk-based RMLs for carcinogens generally are based on a 1 × 10-4 cancer risk. 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 SPRG calculator, we recommend either (1) multiply the SPRG results from either the tables on the SPRG "Download" page or the default option for the SPRG "Search" page by 100 or (2) select the site-specific option on the SPRG "Search" page and change the TR (target cancer risk) to 1.0E-4.

  7. How often do you update the SPRG 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 SPRG table?

    We do not distribute outdated copies of the SPRG table. Each new version of the table supersedes all previous versions. If you wish to maintain previous versions of the SPRGs 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 SPRG calculator.

    Land use Media Exposure Routes
    Oral Externala Inhalation
    Resident Dust Adult
    Child
    Adult
    Child
    All Ages
    Air NA All Ages Adult
    Child
    Indoor Worker Dust Adult Adult Adult
    Air NA Adult Adult
    Outdoor Worker Dust Adult Adult Adult
    Air NA Adult Adult
    Composite Worker Dust Adult Adult Adult
    Air NA Adult Adult

    NA = Not Applicable
    a. the external exposure routes include external exposure to ionizing radiation in dust and submersion in air.

  10. How can I select more than one isotope at a time in the SPRG 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 SPRG results converted to a mass basis?

    Appendix B of the Soil Screening Guidance for Radionuclides Technical Background Document presents a formula for converting SPRGs 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.


  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 SPRGs take into account field survey or laboratory analytical approaches?

    No, the SPRGs are a risk-based tool only. Determining the extent of contamination is a separate process during the 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 RPM to use the tools that are most appropriate for that situation. This analysis indicates that concentrations derived with the SPRG calculator that fall within the 10-4 to 10-6 excess lifetime cancer risk (ELCR) range are measurable.

  15. Are the SPRGs 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 SPRG calculator would be used only if site-specifically the optimization process chose to use a 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 SPRG exposure parameters to calculate site-specific SPRGs. The characteristics of an RDD or IND site may warrant the use of site-specific assumptions that differ from the SPRG defaults. The site manager should weigh the cost of collecting the data necessary to develop site-specific SPRGs with the potential for deriving a higher SPRG that provides an appropriate level of protection.

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

    Air SPRGs represent preliminary remediation goals for radionuclides on outdoor surfaces for outdoor air. The residential and indoor worker air SPRG values can be used to determine outdoor surfaces preliminary remediation goals that are detected in the outdoor air from a variety of sources. There are no SPRGs specific to the vapor intrusion pathway (i.e, for subsurface sources that may contribute to outdoor 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 in Buildings 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. How do the SPRG ingestion and external values for settled dust compare to the PRG values for soil?

    Some users have questioned why the proportion of risk from dust ingestion for external exposure with SPRGs is much greater than the proportion of risk from soil ingestion for external exposure with PRGs. The SPRG ingestion values are based on the transfer of dust to a receptor's hand and subsequent transfer of the dust from the hand to the receptor's mouth. The SPRG ingestion values are reported in units of square centimeters (area) and collected by surface wipe samples. The PRG ingestion values are based on the incidental ingestion of soil throughout the time period, regardless of the intake method. The PRG ingestion values are reported in units of grams (mass) and collected by digging and weighing samples. While the units of the ingestion SPRGs are different than the units of the ingestion PRGs, there is a correlation. If the mass of dust in an area is known, a SPRG can be converted to a PRG. This conversion factor is known as the dust mass loading factor with units of mass/area.

    Consider the Ra-226 indoor worker default ingestion PRG of 1.37 pCi/g and the indoor worker default ingestion SPRG of 0.000233 pCi/cm2 . Assume a dust mass loading factor of 0.17 mg/cm2 . The equation below shows the relationship.

    PRG 1.37 pCi/g x 1 g/1000 mg x 0.17 mg/cm2 = SPRG 0.000233 pCi/cm2 .

    In the report, Dust: A Metric for Use in Residential and Building Exposure Assessment and Source Characterization, dust loading factors are given that range from 0.05 to 99 g/m2 or 0.005 to 9.9 mg/cm2 . The dust loading factor used in the above equation was derived to fit the conversion between a PRG and SPRG and is well within the range of the values presented in the referenced report.

    The SPRG external values are based on ground plane exposure and the PRG external values are based on infinite soil volume exposure. Comparing ground plane to soil volume external route results is not valid for the following reasons:

    • The source thicknesses are different.
    • The PRG units are mass-based and the SPRG units are area-based.
    • The PRG equation is based on soil and the SPRG equation isn't based on any source matrix.