Date of Award

12-1999

Degree Name

Master of Science

Department

Geological and Environmental Sciences

Department

Geosciences

First Advisor

Dr. William A. Sauck

Second Advisor

Dr. Estella Atekwana

Third Advisor

Dr. Daniel Cassidy

Access Setting

Masters Thesis-Open Access

Abstract

Vertical Resistivity Probes (VRPs) are being increasingly used in a variety of applications where detailed vertical resistivity information in both the vadose and saturated zones is needed. All the different possible array types and spacings must be calibrated for the effect of the 2" (outer diameter) insulating PVC cylinder on which the electrodes are mounted. Apparent resistivities must be corrected by calibration factors. Varying the installation parameters greatly influences the measured apparent resistivity because of the disturbed annulus and the composition of the backfill materials. Bentonite slurry is necessary for the installations to keep the electrodes in good contact with the formation. However, leaches ions into the formation with the passage of time loses ions to the formation by diffusion or leaching, causing resistivities to increase. The equilibration time for this annular filling is thus important to document, if repeat readings of resistivity are to be interpreted properly. Properly calibrating for array geometry, and correcting for temporal changes in the bentonite-based annular space filling, allow for very useful resistivity or conductivity information to be extracted from these probes.

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