Establishing & Demonstrating Compliance with Derived Concentration Guideline Levels (DCGLs) for Subsurface Soil
J.W. Lively1 and J.S. Kirk2 (1MACTEC, Inc.; 2Nuclear Fuels Services, Inc.)
Many sites and facilities undergoing decommissioning have subsurface soils that are potentially impacted by radioactivity. The techniques and processes described in the Multi-Agency Radiation Site Survey and Investigation Manual (MARSSIM) apply to residual radioactivity deposited on building surfaces and in surface soils (MARSSIM specifically discounts its applicability to subsurface soils). In the absence of specific guidance designed for subsurface soils, many sites have attempted to apply derived concentration guideline levels (DCGLs) and final status survey techniques designed specifically for surface soils to these subsurface radiological constituents, typically resulting in significant over-excavation and cost escalation. Recent NRC decommissioning guidance (NUREG 1757) provides basic, overarching principles related to the development of, and compliance demonstration with, subsurface soils DCGLs. However, the guidance is very high level and does not direct the user in a practical way. A method for implementing the principles of NUREG 1757 to derive dose-based subsurface soil DCGLs has developed. The subsurface soil method also establishes a rigorous set of criterion-based data evaluation metrics (with analogs to the MARSSIM methodology) that can be used to demonstrate compliance with subsurface soil DCGLs. This paper describes the concepts and basis used to develop the dose-based subsurface soil DCGL method. The paper will show how the method can be used to demonstrate that higher concentrations of residual radioactivity in subsurface soils (as compared with surface soils) can meet the dose- or risk-based regulations. The technical basis for the method can be applied to a broad variety of sites with residual radioactivity in subsurface soils. Given the costly nature of soil surveys, excavation, and subsequent disposal of radioactive materials at a licensed facility, this new method offers the possibility of significant cost savings over the traditional approach of applying surface soil DCGLs to subsurface soils.