FLORIDA GEOLOGICAL SURVEY


groundwater is dynamic, due to complex
interactions between recharge, discharge
(including pumping and mining operations),
runoff, infiltration, evapotranspiration and
seepage to and from underlying aquifers
(Lewelling et al., 1998). Evidence from paired
monitor wells confirms local semi-permeable
hydrologic connection between the SAS and
FAS in parts of the Lake Wales Ridge due in
part to interaquifer connectivity through sinks or
paleosinks (Tihansky et al., 1996). Depending
on hydraulic conditions, karst density, and the
leakance of basal SAS clays (or IAS/ICU clays),
the SAS may locally recharge the FAS in parts
of the northern study area. Local pumping,
rainfall events, seasonal and climatic variations
add to the complex dynamics of this
relationship.

 Surface-water/groundwater interactions are
evident throughout the study area, such as
coastal springs and base flow in rivers and
streams. An outstanding example of these
dynamic interactions occurs within the Peace
River basin. Along the upper part of the basin,
maximum river-flow losses exceed 11 million
gallons per day (4.2x107 liters per day), locally
recharging underlying aquifers due to a
downward head gradient, riverbed sinkholes and
inferred buried subsidence structures (Lewelling
et al., 1998). Further downstream in the lower
part of the basin, the river receives intergranular
(rather than karst-related) seepage from the SAS
and possibly the IAS/ICU (Lewelling et al.,
1998). Understanding such surface-
water/groundwater interactions is essential
toward the establishment of effective minimum
flows and levels (MFL) and total maximum
daily loads (TMDL). Some karst-related
features, however, do not affect these
interactions. For example, the closed
topographic depressions in eastern Sarasota
County (Plate 3) are likely "sags" formed due to
the dissolution of carbonate shell material (Sam
Upchurch, personal communication, 2004).
These sags likely do not function as preferential
recharge path% a% s from the SAS to underlying
aquifer systems.
 Correlation of the SAS with lithostratigraphic
units in the study area generally places the
system within post-Hawthorn Group sediments.
In the northern region, these Pliocene and


younger sands and clays are undifferentiated
(UDSC). Along the eastern region, the
sediments correlate with the Cypresshead
Formation. Further south, the Ft. Thompson,
Caloosahatchee and Tamiami Formations
comprise most of the SAS. Basal SAS clays
may represent low-permeability undifferentiated
Hawthorn Group sediments, or re-worked
Hawthorn Group sediments in the northern and
central region. In the central and eastern
regions, the base of the SAS generally coincides
with the top of the Peace River Formation
(Hawthorn Group); however, relatively clean
sands of the Peace River Formation comprise
part of the SAS in localized areas (e.g., W-
14382 [ROMP 23], Plate 17). In the southern
region, the base of the SAS not only overlies the
Peace River Formation, but also the fine-grained
dolostones of the Arcadia Formation (parts of
western/coastal Manatee and Sarasota Counties)
and middle-Tamiami clays (e.g., southeastern
Charlotte and Lee Counties; Reese, 2000;
Weinberg and Cowart, 2001). Note however,
that Missimer and Martin (2001) report two
aquifers within the SAS in Lee County, the
lowermost being the "Lower Tamiami Aquifer;"
whereas researchers such as Knochenmus and
Bowman (1998) and Torres et al. (2001) place
the entire Tamiami Formation within the
IAS/ICU. The relation between the Tamiami
Formation and hydrostratigraphic units from Lee
County north to Sarasota County warrants
further investigation.

 Vadose-zone hydrogeologic characteristics of
the SAS can be approximately inferred from a
comparison of environmental geology and soil
permeability maps (Figures 4 and 18,
respectively). Patterns in both of these maps
roughly correlate with major geomorphic
provinces (Figure 6). The most permeable soils
and shallow sand-dominated sediments or
carbonate lithologies are located in the Coastal
Swamps, Gulf Coastal Lowlands, the Lake
Wales Ridge, whereas some of the least
permeable soils occur along the southern extent
of the Brooksville Ridge and parts of the
Western Valley.

 In the northern region, surficial deposits may
be missing, having been eroded away and
exposing limestone at the surface (e.g.,