Advancing Electrical Geophysical Characterization of DNAPL-Contaminated Fractured Rock Aquifers(PPT)

摘要

There is a need to better characterize contaminated aquifers in fractured rock and to determine the fate of remediation injections away from boreholes. A synthetic cross borehole electrical resistivity study was conducted within a fractured rock setting representing the Naval Air Warfare Center (NAWC), New Jersey, which is contaminated with trichloroethylene (TCE), cis-1,2-dichloroethene (DCE), and vinyl chloride (VC). Four boreholes and two fracture seams, assumed to be the dominant electrical and hydraulically conductive pathways, were explicitly modeled within an unstructured tetrahedral mesh. Parallel processing was used to handle the large number of mesh elements associated with modeling such small-scale features. To simulate field conditions, 5% random noise was added to all synthetic datasets. Five 3D inversions were performed on the synthetic data, each with different regularization constraints. We began with an uninformed smoothness-constrained inversion, to which a priori information was incrementally added. We found major improvements when (1) smoothness regularization constraints were relaxed (or disconnected) along boreholes and fractures, (2) a homogeneous conductivity was assumed along boreholes, and (3) borehole and packer conductivity constraints were applied. Incorporating this information has the potential to improve imaging of fracture location, orientation, and changes in electrical conductivity distribution due to remediation injections.