Geophysical Investigations For Environmental Risk Assessments

Abstract

Geophysical techniques and surveys are useful for realistic site characterization, site monitoring strategies, and/or detection and mapping of contaminant plumes for verification of environmental risk assessments for nuclear waste facilities. The NRC staff has evaluated the role and applicability of geophysical techniques at three research field locations involving unsaturated, heterogeneous soils and fractured rock. The techniques evaluated included: (1) electroresistive tomography (ERT) to assess water flow through unsaturated, heterogeneous soils and fractured rock, to identify fracture aperture sizes that contribute to water migration and rapid fluxes, and to image three-dimensional resistivity within the zone bounded by the boreholes; (2) surface electromagnetic induction (EM) to detect changes in the apparent electrical conductivities from which water content changes can be inferred; and (3) multi-sensor capacitance probes (MCP) to determine temporal and spatial resolution of infiltration, deep percolation, and ground-water recharge in shallow heterogeneous soils. Specifics of the geophysical techniques and surveys used at the three sites are discussed and evaluated in the context of environmental risk assessments involving radionuclide transport. Key words: downhole geophysical methods, electromagnetic induction, electroresistive borehole tomography, environmental risk assessment, geophysical investigations, multi-sensor capacitance probe.