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Waste and Cleanup Risk Assessment

Dose Compliance Concentrations for Radionuclides in Outdoor Surfaces (SDCC)

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SDCC 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 SDCCs?
  2. What are SDCCs used for?
  3. What are radionuclide slope factors?
  4. How should slope factors be used?
  5. What dose-based radiation standards may be applicable or relevant and appropriate requirements (ARARs)?
  6. How do PRGs differ from cleanup standards?
  7. How often do you update the SDCC Table?
  8. Can I get a copy of a previous SDCC 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 SDCC Search page?
  11. How are the SDCC results converted to a mass basis?
  12. How do the SDCC ingestion and external values for settled dust compare to the DCC values for soil?
  13. What is the preferred citation for information taken from this website?
  14. Where else can I go for toxicity studies (values) not on this site?
  1. What are SDCCs?
  2. The recommended SDCCs (Dose Compliance Concentrations for Radionuclides in Outdoor Surfaces) presented on this site are dose-based concentrations, derived from standardized equations combining exposure information assumptions with EPA dose conversion factors, 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 SDCCs are not always useful for a particular site and do not address non-human health endpoints such as ecological impacts. The recommended SDCCs contained in the SDCC table are generic; that is, they are calculated without site-specific information. They may be re-calculated using site-specific data.

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

  5. What are radionuclide slope factors?

    Slope factors (SFs), for a given radionuclide, represent the risk 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 risk.

  6. How should slope factors be used?

    The primary use of SFs is to compute risk resulting from site-related exposures for comparison with radiation protection standards that are determined to be ARARs. This is accomplished by multiplying the exposure estimates (i.e., the intake of each radionuclide of concern via inhalation and ingestion and the duration of exposure and concentration of each radionuclide of concern in environmental media for external exposure) by the appropriate SF values for that exposure pathway and radionuclide.

  7. What dose-based radiation standards may be applicable or relevant and appropriate requirements (ARARs)?
  8. IIn some cases, cleanup levels may be derived based on compliance with ARARs. Attachment A, "Likely Federal Radiation Applicable or Relevant and Appropriate Requirements (ARARs)", of OSWER Directive 9200.4-18 (U.S. EPA 1997a) provides guidance to use federal standards that have often been selected as ARARs that may be either applicable or relevant and appropriate for particular site-specific conditions. NOTE: EPA has determined that NRC decommissioning requirements (e.g., 25 or 100 mrem/yr dose limits) under 10 CFR 20 Subpart E should generally not be used to establish cleanup levels under CERCLA, even when these regulations are ARARs.

  9. How do SDCCs differ from cleanup standards?
  10. SDCCs 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 SDCC 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.

  11. How often do you update the SDCC Table?
  12. The recommended SDCC 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.

  13. Can I get a copy of a previous SDCC table?
  14. We do not distribute outdated copies of the SDCC table. Each new version of the table supersedes all previous versions. If you wish to maintain previous versions of the SDCCs for a long-term project, you can download the entire table and save multiple versions with a time-stamp.

  15. What ages and exposure routes are considered in each land use?
  16. The following table lists the land uses, media, and receptor ages utilized in the SDCC 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.

  17. How can I select more than one isotope at a time in the SDCC Search page?
  18. 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.
  19. How are the SDCC results converted to a mass basis?
  20. Appendix b of the Soil Screening Guidance for Radionuclides Technical Background Document presents a formula for converting SDCCs 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.


  21. How do the SDCC ingestion and external values for settled dust compare to the DCC values for soil?
  22. Some users have questioned why the proportion of dose posed by dust ingestion for external exposure with SDDCs is much greater than the proportion of dose from soil ingestion for external exposure with DCCs. The SDCC 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 SDCC ingestion values are reported in units of square centimeters (area) and collected by surface wipe samples. The DCC ingestion values are based on the incidental ingestion of soil throughout the time period, regardless of the intake method. The DCC ingestion values are reported in units of grams (mass) and collected by digging and weighing samples. While the units of the ingestion SDCCs are different than the units of the ingestion DCCs, there is a correlation. If the mass of dust in an area is known, a SDCC can be converted to a DCC. This conversion factor is known as the dust mass loading factor with units of mass/area.

    Consider the Ra-226 indoor worker default ingestion DCC of 9.88 pCi/g and the indoor worker default ingestion SDCC of 0.00168 pCi/cm2 . Assume a dust mass loading factor of 0.17 mg/cm2 . The equation below shows the relationship.

    DCC 9.88 pCi/g x 1 g/1000 mg x 0.17 mg/cm2 = SDCC 0.00168 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 DCC and SBDCC and is well within the range of the values presented in the referenced report.

    The SDCC external values are based on ground plane exposure, and the DCC 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 DCC units are mass-based and the SDCC units are area-based.
    • The DCC equation is based on soil and the SDCC equation isn't based on any source matrix.
  23. What is the preferred citation for information taken from this website?
  24. United States Environmental Protection Agency. Dose Compliance Concentrations for Radionuclide Contaminants on Outdoor Surfaces at Superfund Sites. (insert date accessed and url).

  25. Where else can I go for toxicity studies (values) not on this site?
  26. 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.

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