BULLETIN NO. 68


the Anderson-Darling test for normality. In the
Anderson-Darling test, the A2 value is the test
statistic for normality; if the probability (P-
value) is greater than 0.05, the data are normally
distributed. Graphical summaries of the
hydrogeological data include histograms, box
plots and 95 percent confidence interval range
charts. The histograms include a log-normal
curve fit for all parameters except for the
porosity data and SAS vertical hydraulic
conductivity. The vertical (y) axis on the
histograms reflects the total number of analyses
(N), which are listed in each statistical summary.
Units for each parameter are listed in the figure
header. The horizontal (x) axis of the box plots
corresponds to the histogram x-axis. Asterisks
in the box plots denote statistical outliers.

Surficial aquifer system

 The surficial aquifer system (SAS) is
predominately comprised of Late Pliocene to
Holocene sediments and is contiguous with land
surface. This hydrostratigraphic unit occurs
throughout the study area, with the exception of
two hydrogeologic settings: 1) where an
unobstructed vertical hydraulic connection exists
between surficial sediments and the FAS (e.g.,
unconfined FAS) and 2) where the very low-
permeability sediments of the Hawthorn Group
(e.g., Peace River Formation) locally occur at or
near land surface (e.g., SAS absent and FAS is
confined). This latter setting occurs in the
central and southern Polk Upland physiographic
province (Figure 6). The extents of either of
these settings are too localized or disturbed by
mining to delineate accurately within the scale
and scope of this project. The SAS generally
consists of unconsolidated quartz sand with
variable amounts of shell, clay, phosphate and
organic material. Shell content in the SAS
increases significantly toward the southern part
of the study area (Vacher et al., 1993; see also
"UDSS" comprising the SAS in the
southernmost cross sections [e.g., Plates 18,
19]). Excluding the ridges, thickness of the SAS
averages -30 ft (-9 m). Along the Lake Wales
Ridge in the southeastern part of the study area,
SAS thicknesses range to more than 300 ft (99.4
m) (Plates 26 and 55). In the southern region,
the areas with relatively thick SAS generally


correspond to localities where the permeable
upper Tamiami Formation sediments are
included within the SAS.

 The SAS is delineated in areas where
laterally extensive, sufficiently confining clayey
sediments of the IAS/ICU occur beneath
unconsolidated surficial sediments. In parts of
the northern region, the SAS locally may
directly overly the FAS. Iron-cemented zones
("hardpan") and intermittent basal clays may
result in a "perched" water table or local SAS-
like unit. On the other hand, basal confinement
breached by sinkholes or fractures precludes
characterizing much of the northern region as a
laterally extensive and functional SAS due to
lack of regional hydraulic continuity. In this
hydrogeologic setting, delineation of the SAS
becomes subjective. To account for such areas,
a hachured pattern is included on Plate 55 to
reflect "discontinuous basal confinement of the
SAS." It is noteworthy that this subjective
delineation could also be applied to the northern,
significantly karstified part of the Brooksville
Ridge; however, in recognition of available data
and to maintain consistency with the IAS/ICU,
the SAS is delineated in this area.

 Groundwater w ithdrawals from the SAS are
minimal compared to that of the IAS/ICU or
FAS. Based on data from Marella (2004), the
SAS yielded between 1 percent and 5 percent of
total groundwater withdia%%als in Charlotte,
Citrus, Levy, Marion, and Sumter Counties
during 2000. In Lee County, the SAS comprised
more than 55 percent of total w ithdiaals
(Marella, 2004). Each of the remaining counties
in the study area withdrew less than 1 percent
groundwater from the SAS (Marella, 2004).

 Throughout the study area, the local water
table mimics topography (Sepulveda, 2002;
Arthur et al., in review). Elevation of the water
table varies widely throughout the study area,
ranging to more than 175 ft (53.3 m) MSL
(Arthur et al., in review). Along much of the
Lake Wales Ridge, such as in the Intraridge
Valley (Figure 6) the water table is often less
than 10 ft (3.0 m) below land surface. The water
table in other parts of the Lake Wales Ridge, as
well as other upland areas, can exceed 50 ft
(15.2 m) below land surface. Movement of SAS