Abstract

Borehole-surface mise-à-la-masse (MALM) measurements were taken over time during a radial injection tracer experiment in partially saturated, fractured, Columbia River basalt. In this experiment an enhanced conductivity tracer stream was energized directly through a current electrode placed in the bottom of the injection well. A constant concentration tracer solution of potassium chloride was injected continuously above a perched water table at an average rate of 10 L/day under a constant hydraulic head for 34 days. An asymmetrical groundwater mound developed over time during which electrical potential measurements were taken to delineate migration of the tracer. A 15 by 15 array of porous pot electrodes (copper sulfate), located symmetrically about the centrally located injection well, was used for the borehole-surface MALM. Ratios of electrical potentials/baseline were contoured over time to delineate anomalies caused by the presence of tracer solution in the fractured basalt. Borehole-surface measurements delineated the lateral migration of tracer over time and presence of clay filled fractures.

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