A Subsurface Decision Model for Supporting Environmental Compliance (NUREG/CR-7021)

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Publication Information

Manuscript Completed: December 2009
Date Published: January 2012

Prepared by:
Robert Stewart
University of Tennessee
1416 Circle Park Drive
Knoxville, TN 37996

Dr. George Powers, NRC Project Manager

NRC Job Code N6232

Office of Nuclear Regulatory Research

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This document provides a geospatial modeling and decision framework for conducting a subsurface compliance survey and analysis for sites that have been remediated for radioactive contamination. This framework proposes a method to extend the Multi-Agency Site Survey Investigation Manual (MARSSIM) guidance, which only treats surface surveys, into the subsurface. It combines and organizes survey methods into a highly flexible sampling, modeling, and decision analysis approach that emphasizes the quality of decision making throughout the investigation. Major challenges face this goal, including lack of clear exposure mechanisms, inaccessibility of the subsurface, lack of comprehensive scans, and an increase in media complexity.

The US EPAs Triad model focuses on decision quality and methods that maximize available information, technologies, and expertise to address and mitigate sources of uncertainty. This document uses Triad to extend MARSSIM into the subsurface using a substantial and continually advancing set of tools including spatial analysis, modeling, and the GIS community. Recommendations are made on information that forms, updates, and evolves a spatial variation of the conceptual site model, called the Contamination Concern Map. This map focuses on the likelihood of exceeding a decision criterion at a local scale and directly addresses uncertainty in volume extent and location. The map matures over each major phase of the investigation and provides a decision framework. Results of this approach can inform investigators and regulators alike of a reasonable course of action in the final site assessment.

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