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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.

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