BULLETIN NO. 68


 Evaluation of the regional slope of the
MFCU, lithologic similarities between the units,
and sparse data for unit II lead to an alternate
interpretation: unit II north of Manatee and
Hardee Counties may correlate with unit VI
south of these counties (Figure 39). In this
interpretation, isolated MFCU facies occur
approximately 400 ft (122 m) above the lower
MFCU unit in southwestern Highlands and
western Charlotte Counties. Plate 59 and Figure
39 (bottom half) reflect this latter interpretation.
Wells that encountered both MFCU facies (II
and VI) are represented by green symbols (Plate
59) and are labeled with the elevation of the
shallower discontinuous MFCU facies, which is
informally referred to as the "middle to upper
Avon Park confining unit." Data in Miller
(1988) indicate a high permeability zone
between the base of the "middle to upper Avon
Park confining unit" and the MFCU as mapped
herein within all wells containing both of
Miller's MFCU facies (II and VI).

 Based on comparison of Plate 38 with
Miller's (1986) Middle Eocene isopach, the
MFCU as defined and mapped in this study
generally occurs within the lower half of the
Avon Park Formation. Exceptions to the
generalization include Marion, Osceola and
Pinellas Counties, where the MFCU occurs
within the upper third of the Avon Park
Formation. Several cross sections contain wells
that penetrate the MFCU (e.g., Plates 7, 9, 21,
29, 30 and 34). In the northwestern part of the
study area, the elevation of the MFCU is
generally deeper than -400 ft (-122 m) MSL.
The unit dips southward to depths below -2100
ft (-640.1 m) MSL in Charlotte County. South
of the study area, Reese (2000) mapped the
"dolomite-evaporite unit in the middle confining
unit" of the FAS, recognizing the significance of
dense unfractured dolostones in his study area.
He also notes that this unit may locally be
considered the top of the MFCU, which is
generally supported by the MFCU surface in
Plate 59. It is possible that the few wells with
shallower elevations in Reese's (2000)
"dolomite evaporite unit" map are related to
the discontinuous "middle to upper Avon Park
confining unit" described herein.

 Presence of the MFCU is debatable for two
regions within the eastern half of the study area.


Throughout most of Marion County (including
parts of Alachua, Sumter and Lake Counties),
the MFCU is inferred. Borehole cuttings from
multiple wells in the area show no evidence of
gypsum/anhydrite; however, anomalously high
sulfate concentrations (some exceeding 500
mg/L; Sacks, 1996) in FAS groundwater
samples suggest the MFCU may be present. As
such, this area is denoted on Plate 59 as "MFCU
inferred based on water quality data." In eastern
Polk County, Miller (1986) mapped the MFCU;
however, available well control (this study and
Miller, 1988), as well as water quality data for
the area, yields no direct evidence that it is
present. Sprinkle (1989) and Katz (1992) report
relatively low sulfate concentrations (< 50
mg/L) within the UFA in the area. To
emphasize this uncertainty the MFCU in this
area is labeled "MFCU possibly absent: limited
data" (Plate 59).

 Hydraulic conductivity analyses of MFCU
rocks were not completed for this study;
however, data exists in SWFWMD and
consultant's reports. For example, Hickey
(1982) reports hydraulic conductivities ranging
from 1.1 ft/day to 6.0x10-7 ft/day (3.8x10-4 to
2. lxl0 10 cm/sec) based on core representing the
"lower confining bed" (greater than -1000 ft
[-305 m] MSL) in Pinellas County. To provide
characterization of MFCU hydraulic
conductivity and total porosity, data has been
compiled from three injection well sites:
Knight's Trail, Sarasota County, (Law
Environmental, Inc., 1989), Burnt Store
Utilities, Charlotte County, (ViroGroup, Inc.,
1995) and Punta Gorda, Charlotte County, (City
of Punta Gorda, Water Resource Solutions, Inc.,
and Boyle Engineering Corporation, 2001).
Data from Stewart (1966) and Hickey (1982)
and Montgomery Watson Americas (1997) are
also included. Hydraulic conductivity (Kv) for
the 21 MFCU cores analyzed in these studies
range from 1.5x10-'1 ft/day to 1.Oxl0-6 ft/day
(5.3x10-' to 3.53x10-10 cm/sec), with a median
value of 1.84x10-3 ft/day (6.5x10-7 cm/sec;
Figure 40). Total porosity for these samples
average 17.2 percent (median = 19.6 percent)
and range from 5 percent to 30 percent (Figure
41). Basso (2002) reports Kh values ranging
from .002 to .04 ft/day (7.06x10-07 to 1.4x105
cm/sec). Transmissivity data range from 0.08 to
2.9 ft2/day (0.86 to 31.2 m2/day).