We tested a prototype capacitive-conductivity borehole
tool in a shallow, unconfined aquifer with coarse, unconsolidated
sediments and very-low-conductivity water at the Boise
Hydrogeophysical Research Site BHRS. Examining
such a high-resistivity system provides a good test for the capacitive-
conductivity tool because the conventional induction-
conductivity tool known to have limited effectiveness
in high-resistivity systems did not generate expressive well
logs at the BHRS. The capacitive-conductivity tool demonstrated
highly repeatable, low-noise behavior but poor correlation
with the induction tool in the lower-conductivity portions
of the stratigraphy where the induction tool was relatively
unresponsive. Singular spectrum analysis of capacitive-
conductivity logs reveals similar vertical-length scales
of structures to porosity logs at the BHRS.Also, major stratigraphic
units identified with porosity logs are evident in the
capacitive-conductivity logs. However, a previously unrecognized
subdivision in the upper portion of one of the major
stratigraphic units can be identified consistently as a relatively
low-conductivity body i.e., an electrostratigraphic unit
between the overlying stratigraphic unit and the relatively
high-conductivity lower portion — despite similar porosity
and lithology in adjacent units. The high repeatability and
resolution and the wide dynamic range of the capacitive-conductivity
tool are demonstrated here to extend to high-resistivity,
unconsolidated sedimentary aquifer environments.