Monitoring radio-frequency heating of contaminated soils using electrical resistance tomography

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Authors:Ramirez, A. L.; Daily, W. D.
Corporate Authors:Lawrence Livermore National Laboratory, Livermore, CA, performer
Source:No.UCRL-ID-115373, 23p. Availability: National Technical Information Service, (703)605-6000, order number DE94007758NEG, Springfield, VA, United States
Publication Date:1993
Note:In English. Contract W-7405-ENG-48
Summary:Electrical resistance tomography (ERT) was used to monitor a radio-frequency heating process for the insitu remediation of volatile organic compounds from subsurface water and soil at the Savannah River Site, near Aiken, South Carolina. A dipole antenna located in a horizontal well in the unsaturated zone was used to heat a contaminated clay layer. The heat-induced changes were tomographically imaged by their effects on the formation electrical resistivity. The resistivity changes observed appear to be related to heating and vaporization of the pore water, formation of steam condensate, and infiltration of rainwater through the heated zones and adjacent areas. There is a clear asymmetry downward in the resistivity decreases associated with the heating process. The resistivity decreases observed in the vicinity of the heating well are believed to be caused by the heating and downward migration of warm water originally located within a radius of a few feet around the heating well; the magnitude of the change is between 10-20%. The decreasing resistivity implies an increasing rate of radio wave attenuation as heating progressed; therefore, the rate of energy deposition around the heating well increased while the penetration distance of the radio waves decreased. Saturation changes in the clay near the antenna during heating were estimated to be 50-55% based on the observed resistivity decreases. Resistivity changes observed at distances greater than 3 meters to one side of the antenna appear to be related to rainwater infiltration. We propose that gaps in near surface clay layers allow rainwater to migrate downward and reach the top of clay rich zone penetrated by the antenna borehole. The water may then accumulate along the top of the clay.
Subjects:Attenuation; Clastic sediments; Clay; Condensation; Controls; Electrical conductivity; Electrical methods; Geophysical methods; Ground water; Heat flow; Hydrology; Imagery; In situ; Monitoring; Organic compounds; Pollution; Pore water; Radio-wave methods; Rainfall; Remediation; Resistivity; Saturation; Sediments; Soils; Tomography; Volatile organic compounds; Volatiles; Water; Water vapor; Aiken County South Carolina; Aiken South Carolina; Savannah River Site; South Carolina; United States
Coordinates:N333400 N333400 W0814400 W0814400
Record ID:1998003096
Copyright Information:GeoRef, Copyright 2018 American Geosciences Institute. Reference includes data from NTIS database, National Technical Information Service, Springfield, VA, United States
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