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Cross-Hole Complex Resistivity Survey For Pce At The Srs A-014 OutfallNormal access

Authors: Robert E. Grimm and Gary R. Olhoeft
Event name: 17th EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems
Session: DNAPL Studies
Publication date: 22 February 2004
Organisations: EEGS
Language: English
Info: Extended abstract, PDF ( 340.47Kb )

Summary:
Cross-hole complex-resistivity imaging of the vadose zone was performed at the A-014
Outfall at the Savannah River Site, Aiken, SC. Five vertical electrode arrays (VEAs) were
installed with ~15-ft separations in and around a suspected DNAPL source zone to depths of 72
feet. Amplitude and phase data were edited for quality and then inverted to form threedimensional
(3D) images of the target volume. The comparatively small magnitude of the
nonlinear resistivity Hilbert distortion allowed approximate linearized imaging of the 3D
distribution of these effects. Laboratory analysis of nearby soil contaminated in situ indicated
that the CR response to the PCE-clay reaction was maximized near 50 mHz. PCE occurrence
was predicted to track phase and Hilbert-distortion indicators. PCE concentrations were
measured at three drilling locations and were compared to predictions a receiver-operating
characteristic analysis. The optimum performance at 1000 mg/kg in situ PCE was >80%
detection (true positives) with <30% false alarms (false positives) at an effective resolution of 4
ft, ~1/3 of the interwell separation. The CR survey successfully predicted the general distribution
of PCE at parts-per-thousand concentrations, specifically widespread near-surface contamination
and a zone of discontinuous pods or stringers immediately below the source.

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