Abstract: Detection of a Clay Aquiclude by Means of Surface Electrical Resistivity

DAO, THANH, C. and ROBERT M. NEGRINI

A clay aquiclude has been detected under a Kern County landfill based on an electric log from a nearby well. Landfill expansion may depend on the continuity of the aquiclude under the proposed area of expansion. In this study we investigate the feasibility of using surface electrical resistivity as a cost-effective method to determine the extent of the clay aquiclude.

The Schlumberger arrangement was used for three soundings. From these soundings, apparent resistivity vs. electrode spacing plots were constructed which are crude estimates of true resistivity vs. depth. Two of these lines were characterized by a high signal to noise ratio. Subtle relative dips to lower resistivity, 10-40 ohm-meters in magnitude, are observed in both lines at electrode spacings of 60-250 meters. This reproducible feature may be attributable to the low resistivity clay aquiclude.

Computer modeling demonstrated that the relative resistivity values and the corresponding electrode spacing of the aforementioned subtle dips are consistent with the synthetic data modeled with a 25 to 35 feet thick low resistivity unit. This unit has the same depth as the clay aquiclude shown by the electric log. We conclude that the surface electrical resistivity method is feasible as a means of investigation at this site.

Search and Discovery Article #90945©1997 AAPG Pacific Section Meeting, Bakersfield, California