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Section 20: Radionuclides

There is no separate pathway for radionuclides. Rather, there are special considerations that come into play within each of the four pathways when radioactive substances are present.

Hazard Ranking System (HRS) Table 7.1 highlights where the differences are within the four pathways and the rest of Chapter 7 explains the differences.

If a site has both chemical and radioactive hazardous substances apply the HRS "as-is" for the chemical wastes and apply the special considerations in the evaluation of the radioactive wastes. 

Examine HRS Table 7.1 carefully as the "roadmap" to special considerations. 

Here is a brief summary of the differences:

  • Observed releases are different because a more statistical approach is taken for radionuclides.  Different sampling technology makes this possible.
  • Toxicity, ecotoxicity, persistence, and mobility values are calculated differently for radionuclides.  All you have to remember is to use Superfund Chemical Decision Matrix (SCDM).
  • Where there are both radioactive and chemical substances, the HRS provides that you use the highest value in selecting the most hazardous substance for a pathway.
  • Hazardous waste quantity is calculated for only tier A and B, based on curies rather than pounds.  If both radioactive and chemical substances are present in a source, the HRS provides a conversion that allows the two quantity values for the source to be added.
  • Targets are different only in that radiological benchmarks are used to establish Level I or Level II concentrations.  These benchmarks are in SCDM.

Even where there are differences in the treatment of radionuclides, those differences have been kept as parallel as possible to the HRS as you already know it.

20.1 Radionuclide Exclusion

  • CERCLA excludes a limited category of radioactive materials from the statutory definition of "release"
  • See the following sections of this training: Section 1.7 Statutory and Policy Exclusions; Section 1.7.2 Radioactive Materials 

  • Current EPA policy is not to list releases of radionuclides from facilities with current license issued directly by the NRC
    • NRC is responsible for requiring and overseeing cleanup of radioactive releases at these sites.
    • EPA has authority with NRC for the cleanup of mixed and chemical waste at such sites. 
  • Radionuclides are not part of a separate HRS pathway. Section 7 of the HRS rule contains directions for the HRS factors that must be evaluated differently if radioactive or mixed radioactive wastes are found on the site.

20.2 Likelihood of Release

The only difference for likelihood of release is found in an observed release by chemical analysis.

  • An observed release by direct observation remains the same.  You've simply documented the presence of a radionuclide in the material observed to be entering the ground water, surface water, or the air.
  • Potential to release remains the same.

Observed Release Criteria: HRS rule, Section 7.1.1, page 51663 to 51664

The criteria for an observed release by chemical analysis are different for naturally-occurring or ubiquitous radionuclides than for man-made radionuclides.

  • For naturally-occurring or ubiquitous radionuclides:
    • Measured concentrations of release samples must exceed either 2 standard deviations above mean site-specific background, or the upper-limit value for regional background in that type of sample. Plus, some portion of the increase must be attributable to the site.
    • For Man-made, non-ubiquitous radionuclides: Measured concentrations in release samples must equal or exceed the SQL for that radionuclide in that media and must be attributable to the site.
    • If a radionuclide is also attributable to neighboring sites, the measured concentration must also exceed 2 standard deviations above the mean concentration attributable to neighboring sites, or be 3 times the site-specific background, which ever is lower.
  • For the soil exposure pathway:
    • Radionuclides, like chemical wastes, must lie within the top 2 feet of the soil.
    • An exception is made gamma emitters.  For this highly-penetrating radiation, depth is not considered.
    • The gamma exposure rate must equal or exceed two times background and be measured with the survey instrument held 1 meter above the soil surface or 1 meter away from an aboveground source.

20.3 Waste Characteristics

Although the values for toxicity, ecotoxicity, persistence, and mobility are calculated differently, you will be able to find the values for the most common radionuclides already calculated for you in SCDM.

Hazardous waste quantity is based on activity content (curies) and is estimated for only Tiers A and B.

  • The HRS provides a cross-walk to convert activities into pound equivalents:
    • For Tier A, 1 curie is treated as 1,000 pounds of pure hazardous waste.
    • For Tier B, divide cubic yards of wastestream by 0.55 or gallons of wastestream by 110.
    • If a source contains both radioactive and non-radioactive hazardous substances, calculate a source hazardous waste quantity value for the radionuclides alone and for the chemical waste alone, then add the two values for that source.

20.4 Targets

Radionuclides have different benchmarks than chemical substances. These benchmarks have already been determined for you and are found in SCDM.

For the soil exposure pathway, gamma radiation that meets observed release criteria is considered to be Level I concentrations.

If both radionuclides and chemical substances meet observed release criteria at a sampling point and no single substance meets or exceeds a benchmark, you may use the I index (cancer risk) based on both types of substances. The J index is not used for radionuclides.

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