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Electrical resistivity imaging of conductive plume dilution in fractured rock |
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| Authors: | Robin E Nimmer James L Osiensky Andrew M Binley Kenneth F Sprenke Barbara C Williams |
| Institution: | (1) Hydrology Program, Department of Geological Sciences, University of Idaho, P.O. Box 443022, Moscow, ID 83844-3022, USA;(2) Department of Geological Sciences, University of Idaho, P.O. Box 443022, Moscow, ID 83844-3022, USA;(3) Department of Environmental Science, I.E.N.S., Lancaster University, Lancaster, LA1 4YQ, UK;(4) Present address: Department of Biological and Agricultural Engineering, University of Idaho, P.O. Box 440904, Moscow, ID 83844-0904, USA |
| Abstract: | Electrical resistance tomography (ERT) was used to monitor a conductive plume dilution experiment that was conducted in fractured basalt in order to assess its applications in this type of fractured-rock environment. Tap water was injected into an injection well for 34 days to dilute a pre-existing potassium chloride (KCl) plume at a site in Idaho, USA. No further fluids were introduced artificially during a 62-day monitoring period. Both surface ERT and cross-borehole ERT were used to monitor dilution and displacement of the plume. A square grid of land-surface electrodes was used with the surface ERT. Three-dimensional images of surface ERT delineated areas of increased and decreased resistivities. Increasing resistivities are attributed to dilution/displacement of the KCl solution by tap-water invasion or the influx of seasonal recharge. Decreasing resistivities resulted from redistribution of residual KCl solution. Cross-borehole ERT was conducted between the injection well and each of seven surrounding monitoring wells. Polar plots of the injection-well resistivity data in the direction of each monitoring well delineate specific locations where tap water seeped from the injection well via preferential flow paths determined by time-dependent resistivity increases. Monitoring-well data indicate locations of clustered and isolated regions of resistivity changes. |
| Keywords: | Fractured rocks Basalt Tracer tests Electrical resistance tomography Plume |
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