Hydrogeologic Assessment of Shallow Clastic and Carbonate Rock Aquifers
in Hendry and Collier Counties, Southwest Florida
By Charles E. Brown, Richard K.
Krulikas, and Daniel L. Brendle
ABSTRACT
Direct-current electrical
resistivity data were collected from 109 vertical electrical sounding sites
in Hendry and Collier Counties, southwestern Florida. Selected direct-current
electrical resistivity surveys, together with available borehole geologic
and geophysical data, were used to determine the approximate areal extent
of the shallow clastic aquifers composed of thick sands and carbonate lithologies.
Results indicated that a complex pattern of shallow sands, clays, and carbonate
lithologies occur throughout the area. Buried channel sands were found as
deep as 50 meters below land surface in some places. The channels contain
unconsolidated fine-to medium-grained quartz sand interbedded with sandy
limestone, shell fragments, and gray-green sandy clay.
Both surface and
borehole geophysical techniques with lithologic data were necessary to approximately
locate and define layers that might behave as confining layers and to locate
and define the extent of any buried sand aquifers. The borehole geophysical
data were used to analyze the zones of higher resistivity. Direct-current
electrical resistivity data indicated the approximate location of certain
layer boundaries. The conjunctive use of natural gamma and short- and long-normal
resistivity logs was helpful in determining lithologic effects. Geohydrologic
sections were prepared to identify potential locations of buried channels
and carbonates containing fresh water. Buried channel sands and carbonate
rock sections were identified in the subsurface that potentially may contain
freshwater supplies.
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