BULLETIN NO. 68


 SUMMARY

 The hydrogeologic framework of the
Southwest Florida Water Management District
region described in this report is spatially
characterized through a series of 32 maps (plates
and figures) and 34 cross sections. Lithologic,
hydrologic and geophysical data from more than
1050 wells comprise a database of subsurface
elevations and thicknesses for nine
lithostratigraphic and four hydrostratigraphic
units represented in these maps and cross
sections. Elevations of unit boundaries for most
of the wells used in the maps and cross sections
have been confirmed through visual inspection
of cores and cuttings by the authors and those
acknowledged in this report. Additional data on
which the maps and cross sections are based are
incorporated from peer-reviewed reports and
interpreted from geophysical logs and existing
lithologic descriptions. The lithostratigraphic
units are discussed in terms of age, lithology,
mineralogy, common fossils, sedimentary
structures, porosity/permeability, contact
relations with other units, facies changes, spatial
distribution (vertical and lateral), gamma-ray log
responses, hydrostratigraphic unit correlations
and depositional environments.
Hydrostratigraphic units are similarly discussed
in terms of spatial distribution, regional and
local hydraulic characteristics, hydrogeologic
properties and correlation with lithostratigraphic
units.

 Among the challenges that exist when
creating subsurface stratigraphic maps based on
well data is the need to balance three factors: 1)
accuracy of the interpolated contours relative to
the data on which each map is based, 2) the
implicit resolution of the map, which is depicted
by the contour interval and the degree of
perturbations in the contours and 3) an accurate
regional characterization of the unit being
mapped. For example, a map that is 100 percent
accurate with respect to elevations or
thicknesses may overemphasize local anomalies
such as karst features. Although a small
percentage of wells represent these anomalous
elevations, the wells also represent an
infinitesimal fraction of the total number of
anomalous features in the mapped surface. In


other words, thousands of paleosink features
may exist in the top of a carbonate unit;
however, less than five percent of the wells in
the database may have encountered one of these
features. Hence, a regional-scale map would be
more representative of the true regional
character of the surface (or thickness) if the local
anomalies had less influence on the interpolated
surface. Moreover, a highly accurate map may
also result in jagged, irregular contours, which
may imply changes in elevation (or thickness) at
a scale that is not justified by the distribution
and density of the well data.

 To achieve an appropriate balance of the
aforementioned factors, an iterative process of
data evaluation, sample inspection, data
interpretation, and spatial and statistical analysis
was completed. For the final maps, kriging was
used to interpolate map surfaces, which were
then corrected as needed for consistency with
land surface and other mapped units. The
interpolated surfaces were then smoothed to
reflect the regional character of each mapped
unit. The surface interpolations also provide
GIS coverages that can be applied in
groundwater flow models and 3D applications.

 The cross sections focus on data from cores,
with an emphasis on those collected through the
SWFWMD Regional Observation and Monitor-
well Program (ROMP). Data from geophysical
logs as well as cores and cuttings archived in the
Florida Geological Survey sample repository
were used to fill gaps in the cross-section well
coverage. Of the 34 cross sections, nine trend
approximately north-south, averaging
approximately 60 mi (-96 kilometers) in length,
while the remaining sections generally trend
east-west and average approximately 35 mi (-56
km) in length. Graphical representation of
borehole data from 149 wells used in the cross
sections include lithostratigraphic and
hydrostratigraphic boundaries and cross-well
correlations, lithology, mineralogy and gamma-
ray log response. Each section also includes
topographic profiles labeled with selected
anthropogenic features.

 The relationship between lithostratigraphic
and hydrostratigraphic units is straightforward in
many parts of the study area; however, the