FLORIDA GEOLOGICAL SURVEY


3) hydrogeologic characteristics of the samples
(e.g., estimated porosity and permeability,
hydraulic continuity between lithostratigraphic
units), 4) potentiometric data from nested
monitor wells, and 5) in the absence of other
data, correlation to lithostratigraphic units.
Application of the first four methods is highly
preferred; the majority of this data originates
from ROMP wells.

 Contacts between aquifer systems can be
very subtle or abrupt depending on the
hydrogeologic properties of the rocks and
sediments. When only lithologic material from
a borehole is available on which to base an
aquifer-system boundary, further complications
arise. Preferential removal of clay-sized
particles, either during drilling or sample
archiving (e.g., sorting during material transfer
or washing of cuttings), tend to bias toward
interpretations of higher sample permeability.

 Delineation of the basal contact of the SAS is
perhaps the most susceptible to the
aforementioned bias. If the contact is based
solely on estimates of hydrogeologic properties
of lithologic data, misrepresentation of clay
content, especially in borehole cuttings may
result in the interpretation of a preferentially
deep base of the SAS. This issue may become a
factor where the SAS may include sediments as
old as the upper Hawthorn Group. On the other
hand, permeable sands along the top of the upper
Peace River Formation in Manatee County (Tom
Scott, personal communication, 2006) comprise
the lower part of the SAS. If there is reason to
believe that the two units (Hawthorn and post-
Hawthorn Group sediments) are hydraulically
connected, both would be considered part of the
SAS. Alternatively, sandy clays overlying clay-
rich Hawthorn Group sediments would be
considered part of the IAS/ICU (assuming
sufficient lateral extent). Further south, the
Tamiami Formation is included within both the
SAS and IAS/ICU.

 Noting the above exceptions, the lateral
extent of the IAS/ICU broadly corresponds to
the extent of Hawthorn Group sediments, except
where those sediments are part of the FAS (e.g.,
the Tampa Member [Arcadia Formation] along
the upper reaches of the Hillsborough River).
For consistency, in areas where the IAS/ICU is


mapped owing to sufficient lateral continuity,
the SAS is mapped over the same extent. In
areas where the SAS and IAS/ICU are
discontinuous, the FAS is generally
characterized as unconfined to semi-confined
(see Hy ,,, i'ui gi ph 1 ', p. 52, for more detail).

 Figure 8 represents a compilation of
hydrogeological data to provide correlation
between hydrostratigraphic units and
lithostratigraphic units. In most areas, the
correlation is readily apparent, such as the
relation between the top of the Suwannee
Limestone in Sarasota County with the top of the
FAS. In another example, the Tampa Member
(Arcadia Formation) is hydraulically connected to
the FAS in Pinellas County and therefore
comprises the uppermost part of the FAS. The
correlations, however, are not always
straightforward, such as the area denoted as
"variable" (Suwannee Limestone and Nocatee
Member, Arcadia Formation) in DeSoto County
(Figure 8).
 Cross-Section Construction

 Detailed lithologic descriptions, gamma-ray
logs and hydrologic data comprise the bulk of the
information used to develop the cross sections.
The dominant sources of information for cross-
section control are SWFWMD ROMP wells;
FDEP-FGS wells were included to fill out
appropriate data-point coverage for the cross
sections. Where no lithologic data was available,
borehole geophysical logs were used. Of these
geophysical logs, gamma-ray logs were the most
readily available and generally useful for
correlative purposes within the study area.
Gamma-ray logs were included in the cross
sections to allow comparison of the gamma-ray
signatures relative to each stratigraphic unit. The
following discussion outlines the methods used
for construction of the cross sections for this
study.

Topography

 Topographic profiles were included on each
cross section to facilitate comparison of surface
morphologies with subsurface stratigraphy. Data
used to construct these profiles was taken from U.S.
Geological Survey 1:24,000 (7.5 minute) quadrangle
maps. The profiles include selected anthropogenic
features, cultural boundaries and landforms.