Using Mise-à-la-Masse to Delineate the Migration of a Conductive Tracer in Partially Saturated Basalt

Robin Nimmer received a Bachelor of Science degree in Geology from the University of Wisconsin-Milwaukee and a Master of Science degree in hydrology from the University of Idaho. She currently is working on a Ph.D. in Geology from the University of Idaho. Robin's research interests include groundwater contamination and remediation and the use of geophysics as a hydrologic tool.

James L. Osiensky has been a Hydrogeology faculty member for the University of Idaho since 1988. Osiensky's current research interests include, the application of hydrogeophysics to environmental problems, point and non-point source ground water contamination, ground water resource evaluation, aquifer testing in heterogeneous environments, and ground water modeling.

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.