Cross‐borehole resistivity tomography of a pilot‐scale, in‐situ vitrification test

Abstract

Direct current (dc) cross‐borehole resistivity measurements were used to monitor the melting and solidification processes of an in‐situ vitrification (ISV) experiment at Oak Ridge National Laboratory (ORNL) in Tennessee. Six boreholes, 6-m deep, were augured around the ISV site, and five electrodes implanted in each hole. Three sets of crosswell, pole‐pole resistivity data were collected: prior to the melt phase, immediately after power shut‐off, and after the melt zone had solidified and returned to ambient temperature. These three sets of data were inverted using a conjugate‐gradient scheme to produce conductivity images of the melt phase and the vitrified end products. The images obtained depend quite strongly on the model weighting function applied to the inversion. With an optimum weighting function based on a priori spatial constraints, the resistivity images delineate the melt zone and provide a reasonable indication of its geometry. The resistivity data support, but do not require, the existence of the melt zone.