FLORIDA GEOLOGICAL SURVEY


 Hydrostratigraphy

Introduction

 The hydrostratigraphic setting of the study
area varies from a locally exposed single aquifer
system in the north, to three aquifer systems in
the central and southern parts of the study area.
In the northern region, the FAS ranges from
variably confined to unconfined; clayey
sediments of the IAS/ICU or basal SAS are
locally present; IAS/ICU confining sediments
are present especially within the uplands and
ridges. The SAS, where present, is intersected
by numerous karst features (Trommer, 1987; see
also Plate 3) which may act as direct hydraulic
connection between the SAS and the FAS.
Increased permeability of the IAS/ICU occurs
where the Hawthorn Group sediments thicken
southward from central Hillsborough and Polk
Counties. In the central and southern regions,
the IAS/ICU collectively forms a thick confining
unit with intervening permeable zones that
separate the FAS from the SAS. As noted
earlier, the nomenclature applied herein is based
on aquifer system nomenclature as modified
from Florida Geological Survey Special
Publication 28 (see Hydrogeology, p. 17;
Appendix 2).

 Hydrogeological properties

 Numerous studies provide details on
hydrogeologic properties of aquifer systems in
the study area. For detailed information on
aquifer transmissivity, storativity, leakance
coefficients, etc., the reader is referred to USGS
publications (e.g., Ryder, 1985; Wolansky and
Corral, 1985; Metz, 1995; Yobbi, 1996;
Knochenmus, 2006), numerous SWFWMD
ROMP technical reports (e.g., Clayton, 1994,
1999; Gates, 2001; LaRoche, 2004); SWFWMD
hydrogeological studies (e.g., Barcelo and
Basso, 1993; Hancock and Basso, 1993; Basso,
2002, 2003) and especially the Southwest Florida
Water Management District (2006b) compilation:
"Aquifer Characteristics within the Southwest Florida
Water Management District, July 2005."

 To provide a general characterization of these


hydrogeologic parameters, two datasets are
statistically and graphically summarized in the
discussion of each aquifer system: 1) data in
Southwest Florida Water Management District
(2006b) that meet certain quality
assurance/quality control (QA/QC) standards6
and 2) results of more than 200 hydraulic
conductivity and total porosity analyses
measured at the FDEP-FGS on cores from
within the study area. Both datasets are
presented to represent laboratory and field-scale
conditions. The Southwest Florida Water
Management District (2006b) compilation
represents properties measured during aquifer
pumping and performance tests, while the
FDEP-FGS dataset represents matrix
permeability (vertical) and porosity of core
samples. In Florida's dual-porosity (e.g,
intergranular and conduit flow) heterogeneous
carbonate terrain, it is widely recognized that
permeability calculated from field-scale aquifer-
test data (e.g., Basso, 2002) may differ by orders
of magnitude from that of laboratory
measurements. These data summaries are
presented herein to characterize expected ranges
of these parameters for use in hydrologic models
and to provide a frame of reference for those
collecting hydrological data in the field or lab.
For further details on matrix permeability, as
well as discussion of its significance and
limitations, the reader is referred to Budd (2001,
2002) and Budd and Vacher (2004).

 In the descriptive statistics for each aquifer
system, standard parameters are summarized,
including mean, median, range, quartile values,
and number of analyses. Also included are
distribution descriptors: skewness, kurtosis and


6 QA/QC screening guidelines: 1) used data with
"acceptable" and "good" test-reliability scores as
defined and assigned in Southwest Florida Water
Management District (2006b); 2) avoided aquifer
tests where partial penetration was noted and no
corrections applied; 3) avoided tests where aquifer
penetration thicknesses were inconsistent with casing
and total depth data; 4) avoided use of well pairs in
which the observation well open interval differed
from the open interval in the test well by more than
15 percent; 5) avoided short-duration tests; and 6)
evaluated comments with respect to quality of test
data.