Applications For Capacitively Coupled Resistivity Suvreys In Florida

Abstract

The use of capacitively coupled resistivity (CCR) as a geophysical method has historically been of limited use in Florida due to the shallow water table and the time necessary to make multiple passes to collect resistivity data at depth. The induced current used by CCR instruments is stronger and can penetrate to greater depth if the surface materials are resistive, because the voltage measured at the receiver equals the current in the transmitter multiplied by the resistivity of the earth materials. The presence of shallow groundwater increases conductivity thereby reducing the CCR signal strength. The availability of a multi-channel CCR instrument, the Ohm-Mapper by Geometrics, Inc. has eliminated the need for multiple passes for a study. Subsurface Evaluations, Inc. has investigated two applications for multi-channel CCR surveys in Florida: 1. CCR has been successfully used to delineate buried depressions in sandy upland areas producing results remarkably similar to ground penetrating radar (GPR) data but easier to interpret; and 2. CCR has been successfully tested on road projects for identifying shallow deleterious soil conditions such as clay and peat lenses that might be missed by a standard drilling program and that are not readily detectable by GPR.