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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