ML21208A218
| ML21208A218 | |
| Person / Time | |
|---|---|
| Issue date: | 07/15/2021 |
| From: | Cynthia Barr NRC/RES/DRA |
| To: | |
| Aird, Thomas - 301 415 2442 | |
| Shared Package | |
| ML21208A206 | List: |
| References | |
| Download: ML21208A218 (9) | |
Text
Subsurface Soil Surveys Public Workshop Cynthia Barr Senior Risk Analyst July 15, 2021
Development of Derived Concentration Guideline Levels (DCGLs or clean-up levels) for Subsurface Residual Radioactivity
Surface versus Subsurface DCGLs
- What is surface soil?
- Typically top 6 inches, but
- Dependent on what can be scanned and
- Dose modeling assumptions
- Typically, different radionuclides and pathways will dominate dose for surface versus subsurface soils
- it is important to understand the importance of source parameters such as area, thickness and depth of residual radioactivity to dose through sensitivity analysis
Surface versus Subsurface DCGLs
- Soil Depth (Important Pathways)
- Surface (external radiation, incidental ingestion, inhalation)
- Intermediate (plant)
- Deep subsurface (groundwater dependent pathways)
Multiple DCGLs
- Potential need for multiple DCGLs
- Vertical heterogeneity and sensitivity of dose results to depth and thickness (i.e., significantly different DCGLs for surface versus subsurface residual radioactivity)
- Various contaminated media (buildings; surface and subsurface soils; groundwater or surface water; and streambed sediments)
Multiple DCGL Considerations
- Challenges associated with applying multiple DCGLs
- Survey of soils for reuse in an open excavation (when and how to survey)
- Soil layers are in close contact with each other making accounting of residual radioactivity difficult
- Lack of guidance on conduct of MARSSIM statistical tests for multiple soil layers.
- Potential scenarios that could re-distribute residual radioactivity to the surface should be considered.
Scenarios for Buried Radioactivity
- Two conceptual models can be considered
- No soil cover
- Soil cover 7
Groundwater Considerations
- In some cases, enough time has elapsed that existing groundwater contamination is present
- The contribution to dose associated with the existing groundwater contamination should be considered
- Biosphere or dose modeling can be used to determine the dose per unit groundwater concentration to determine the contribution of existing groundwater contamination to dose
Thank you!