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Integrated Geophysical Detection of DNAPL Source Zones

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Final rept. 1 Apr 1998-31 Jul 2001

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Identification of subsurface organic contamination, particularly dense nonaqueous phase liquids DNAPLs is one of the highest priorities - and among the most difficult - for remediation of numerous sites, including those of the DOD and DOE. Complex resistivity CR is the only geophysical method that has been demonstrated in the laboratory to have high sensitivity to organic compounds, by detecting responses indicative of clay-organic electrochemistry. However, direct detection of organics in the field has been elusive, in part due to the difficulty of obtaining robust measurements at very low contaminant levels in the presence of heterogeneous geological materials and cultural interference such as metallic utilities and remediation plumbing. This project sought to improve the capability to detect DNAPL by 1 better geophysical imaging of geological pathways that control DNAPL movement and 2 direct detection by detailed comparison of CR lab to field data using this improved imaging. For the first goal, algorithms were developed for the joint tomographic imaging of seismic and resistivity data. The method requires that an empirical relationship can be established between seismic and resistivity if values are ultimately tied to specific lithologies, then the final tomographic product can be an actual geological cross-section. Because shallow subsurface investigations are now commonly performed using a cone penetrometer CPTa new vibratory seismic source was developed to identify sites with clay-organic reactions measurable in the lab from core samples, perform reconnaissance field surveys, and proceed to detailed 2D or 3D cross-hole imaging.

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  • Seismic Detection and Detectors

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