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STATE OF FLORIDA
DEPARTMENT OF ENVIRONMENTAL PROTECTION
Virginia Wetherell, Executive Director





DIVISION OF ADMINISTRATIVE AND TECHNICAL SERVICES
Mimi Drew, Director of Technical Services





FLORIDA GEOLOGICAL SURVEY
Walter Schmidt, State Geologist and Chief





OPEN FILE REPORT 61





LITHOSTRATIGRAPHIC AND HYDROSTRATIGRAPHIC CROSS SECTIONS THROUGH
PINELLAS AND HILLSBOROUGH COUNTIES, SOUTHWEST FLORIDA

By

Richard Green, P.G. #1776, Jonathan D. Arthur and David DeWitt


FLORIDA GEOLOGICAL SURVEY
Tallahassee
in cooperation with the Southwest Florida Water Management District
1995

ISSN 1058-1391


to OF FLRIDA i.-'










LITHOSTRATIGRAPHIC AND HYDROSTRATIGRAPHIC CROSS SECTIONS THROUGH
PINELLAS AND HILLSBOROUGH COUNTIES


Richard Green' P.G. 1776, Jonathan D. Arthur1 P.G. 1149, and David DeWitt2 P.G. 1626

'Florida Geological Survey, Tallahassee, Florida, and 2Southwest Florida Water
Management District, Brooksville, Florida


INTRODUCTION

A cooperative program exists between
the Southwest Florida Water Management
District (SWFWMD) and the Florida Geological
Survey (FGS) to construct geologic and
hydrogeologic cross sections throughout the
16 county SWFWMD region. The purpose
of the program was to delineate the extent
of lithostratigraphic and hydrostratigraphic
units within the region to aid in the manage-
ment and protection of ground-water
resources. In order to systematically
accomplish these goals, the project was
subdivided into three phases, each with
separate study areas: Phase I included the
southwest region of the District, from Pinellas
and Hillsborough to Charlotte Counties; Phase
II included the northwest part of the District,
from Levy and Marion to Pasco Counties; and
Phase III included the southeastern portion
of the District, encompassing all areas not
covered in Phases I and II. Regional
lithostratigraphy of Eocene through Miocene
formations, gamma-ray log characteristics of
these formations and aquifer-system
delineation within each study area were the
primary focuses of the cross sections. Most
of the data used to construct the cross
sections were taken from wells drilled as part
of the SWFWMD Regional Observation and
Monitor-Well Program (ROMP; Gomberg,
1975). In areas where ROMP data were not
available, borehole data from the FGS and the
United States Geological Survey (USGS) were
utilized.


Interim reports on each project phase
will be released as FGS Open File Reports
(OFR). The present interim report, one of two
reports on the Phase I region, covers Pinellas
County, Hillsborough County, and part of
Manatee County. The second OFR produced
for Phase I includes Manatee, Sarasota and
Charlotte Counties (Arthur et al., 1995).
Similar reports for the Phase II and III regions
will also be forthcoming. Three east-west
cross sections across Pinellas and Hillsborough
Counties and three north-south cross sections
through the study area are presented in this
report. The east-west cross sections spanning
this region extend inland from the coast an
average of 31 miles. Figure 1 is a location
map for the cross sections (Plates 1 through
6).

CROSS SECTION CONSTRUCTION

Detailed lithologic descriptions, gamma-
ray logs and hydrologic data comprise the bulk
of the information used to develop the cross
sections shown in Plates 1 through 6. The
dominant source of information for cross-
section control points are SWFWMD ROMP
wells. In areas where ROMP data are limited,
however, supplemental wells are included to
provide appropriate data-point coverage.
There are cases where the only available
borehole data are geophysical logs (i.e,, no
lithologic data are available). Of these
geophysical logs, gamma-ray logs are the most
readily available and useful for correlative
purposes within the study area. Gamma-ray
logs are included in the cross sections to allow













R 15E 16E 17E I R18192021E R1 I R1 E E E E E 22 E
'" S -- ...-. ~--- ---------r------- ---------- -------------. -----


B lW-7795 PE3 E lW-7032)


A W- 12943


L OM TR \
W-15204 TR 12-3 I0)
W-15W-15204494
B( Nj^-S' w -'52 \934 C

WRAP 2-D 4
W-16574
W-16576

TR 172 ) W)7-14668 HILLSBOROUGH CO. (y.
TR 13-2X I R
W-16197

PINELLAS CO. / I 19
I W 7672 0 0
V,



I W-16618 L,4
PI-32 ROMF
-5001T ROMP 4
4 1 6-15642 W- -W-16456-







SCALE MANATEE CO.
MILES M A FU
012345 E) F
01 34 67 TR 8-1 W-1 6740
KILOMETERS W-15826 f --

R 16 E I R 17 E i R 18 E R 19 E R 20 E R 21 E R 22 E


Figure 1. Location map for cross sections in Plates 1 through 6.


FGS070194









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.
Topographic profiles are included on
each cross section to facilitate comparison
of surface morphologies with subsurface
stratigraphy. Data used to construct these
profiles were taken from U.S. Geological
Survey 1:24,000 (7.5 minute) quadrangle
maps. Profiles are plotted above the cross
sections, along with selected anthropomorphic
features, cultural boundaries and landforms.

Lithology

For each well, a stratigraphic column
was generated using existing lithologic data.
In cases where no description (or one of poor
quality) was available, borehole samples (core
and/or cuttings) were described for this study.
Hatching patterns depict primary lithologies
in the columns, with accessory minerals
shown on the right of the columns as text
codes. Figure 2 lists the definitions of
mineralogic and lithologic codes and patterns.
Accessory-mineral codes are generally the
same as those used in the FGS lithologic data-
base (the Well Log Data System; GeoSys, Inc.,
1992). The listed order of the accessory
mineral codes does not always imply relative
abundance since percentages of these minerals
were not provided in the lithologic descriptions
in many cases. For accessory sand (greater
than five percent quartz + phosphate), where
the percentages were available from the
lithologic descriptions, the hatching pattern
reflects sand content as a stippled overlay.
If the amount of accessory sand-sized minerals
is less than five percent, the accessories are
listed in the text codes.
Comparison of the degree of lithologic
detail between boreholes clearly shows a
correlation with the type of material available
for description. In general, more detail exists
for the cores. Table 1 provides a listing of
well-site information and sample type (e.g.,


cores, cuttings or both) available for this
study.
Bed thicknesses on the stratigraphic
columns are limited to no less than five feet
due to graphical constraints. There are several
examples where lithologies and accessory
minerals have been averaged over a five to
10 foot interval to accommodate these
requirements. Lithologic descriptions for all
wells used in this study are available from the
Florida Geological Survey or the Southwest
Florida Water Management District.


Gamma-ray logs

Available gamma-ray logs are plotted
to the right of each stratigraphic column on
the cross sections. These logs facilitate
delineation of formational boundaries and
allow comparison of gamma-ray activity
between the various lithostratigraphic and
hydrostratigraphic units. Gilboy (1983) and
Miller (1986) have both used this approach.
Their cross sections, however, do not provide
detailed lithology or topographic profiles. The
phosphatic nature of the sediments comprising
the Hawthorn Group, allowed gamma-ray logs
to be quite successful for the delineation of
stratigraphic units.
The "signal quality" of these logs varies
from poor to very good. This variation is
primarily due to non-ideal instrument settings,
the most common of which are the time
constant (TC) and full scale. The TC is a
setting used to average gamma-ray activity
over a given period of time during a borehole
reading. On logs where the trend is very
smooth, the TC is probably set too high,
whereas, in cases where the log response is
extremely erratic, the TC was probably set
too low. The full scale, which results from
the rate and variable span settings, should
be adjusted to provide good contrast between
the gamma-ray peaks and the background
count rates. In addition, except for
anomalously high gamma-ray peaks, the full
scale should be set to avoid peak truncation.



























oooooooooooooooc


GRAVEL







SAND








SILT








CLAY


LIMESTONE






FINE MEDIUM COARSE

DOLOSTONE






FINE MEDIUM COARSE

INTERBEDDED LIMESTONE AND DOLOSTONE


MEDIUM


COARSE


+aa + aanan+ + +
CHERT SHELL BED + + + +GYPSUM


CHERT SHELL BED GYPSUM


CODES


MICRITE T

SAND C

PHOSPHATE GRAVEL Sh

PHOSPHATE SAND D


ORGANIC

SPAR

IRON STAIN
QUARTZ

ANHYDRITE
CHERT


L
H

NO SPL


SILT

CLAY

SHELL

DOLOSTONE

LIMESTONE
HEAVY MINERALS

NO SAMPLE


G GYPSUM

Py PYRITE
K GLAUCONITE


SSurFlcla aquifer system







SIntermediate aquifer system/




oridoconfining unite



Floridan aquifer system


Figure 2: Explanation of hatching patterns
and codes used in Plates 1 through 6.














Table 1. Borehole data on all wells used in this study. Footnotes are in parentheses.


WELL ID SITE NAME
(1)

A-A'

W-12943 N/A (5)


N/A EAST LAKE


W-7795 N/A


N/A DUNDEE


W-3428 N/A


N/A PEBBLE CRE


W-7032 N/A


B-B'

W-15204 TR 14-2


W-15494 TR 12-3


W-16574 WRAP 2D


W-14668 TR 11-2


W-16576 DV-1


C-C'

W-50015 PI-32


W-15642 TR 9-3


W-16618 TR 9-2


W-16456 ROMP 49


W-14386 ROMP 48


TOWNSHIP, RANGE,
SECTION (2)


T27S R15E S25 A


T29S R16E S10 AC


T27S R17E S06 DB


T27S R18E S09 CA


T27S R18E S12 AD


T27S R20E S07 AA


T27S R22E S06 DB




T28S R15E S25 BA


T28S R18E S31 DB


T28S R18E S35


T29S R19E S23 BB


T29S R21E S04


T32S R16E S10


T31S R19E S32


T31S R19E S22


T31S R20E S25


T31S R22E S31


LAT/LONG TD (BLS) ELEVATION GAMMA-RAY
(3) (NGVD) (4) LOG


28 06 37
82 45 46

28 08 52
82 41 43

28 09 46
82 38 05

28 09 01
82 31 04

28 08 52
82 27 30

28 09 21
82 21 01

280959
82 08 30



28 01 32
82 45 28

280005
823205

28 00 33
82 28 49

275705
8222 11

27 59 26
821234



274304
8241 17

274418
82 25 37

274554
822338

27 45 46
821516

274427
82 08 37


1700


774


510


693


320


482


400




604


540.5


1180


589


850




1438


785


1260


1575


925


SAMPLE WORKED BY:
TYPE


X CUTTINGS


X N/A


CORE


X N/A


CORE


X N/A


CUTTINGS


CORE


CUTTINGS/
CORE

CUTTINGS


CORE


CUTTINGS/
CORE



CUTTINGS


CUTTINGS


CUTTINGS/
CORE

CUTTINGS/
CORE

CUTTINGS


K. KING


N/A


C.COLEMAN


N/A


C. COLEMAN


N/A


C. COLEMAN




G.HENDERSON


G. HENDERSON
J.DECKER

M. CLAUSEN
(CH2M HILL)

UNKNOWN


G. KINSMAN




UNKNOWN


J. DECKER


J. DECKER


J. DECKER &
G. KINSMAN

G.STRASSER


Footnotes:


(1) Well ID is FGS "W" number.
(2) Section quarters are coded as A= NW 1/4; B= NE 1/4; C= SW 1/4; D= SE 1/4.
(3) TD total depth; BLS below land surface in feet.
(4) NGVD National Geodetic Vertical Datum of 1929 (in feet).
(5) N/A Not applicable.













Table 1. (Continued).

WELL ID SITE NAME


TOWNSHIP, RANGE, LAT/LONG TD


SECTION (2)


(BLS)
mI


ELEVATION GAMMA-RAY SAMPLE WORKED BY:


N( GVD) (4) LOG


TYPE


D- D'

W-12943


W-15204


W-16197


W-50015


E-E'

N/A


W-16574


W-7672


W-15826


F-F

W-7032


W-16576


W-16456


W-16740


Footnotes:


N/A


TR 14-2


TR 13-2X


PI-32




DUNDEE


WRAP 2D


N/A


TR 8-1




N/A


DV-1


ROMP 49


ROMP 39


T27S R15E S25 A


T28S R15E S25 BA


T29S R16E S32 CD


T32S R16E S10 AB




T27S R18E S09 CA


T28S R18E S35


T30S R18E S22


T33S R18E S30 AA




T27S R22E S06 DB


T29S R21E S04


T31S R20E S25 BB


T33S R21E S19 AC


X CUTTINGS K. KING


X CORE G.HENDERSON


X CUTTINGS/ J. CLAYTON
CORE

X CUTTINGS UNKNOWN


28 06 37
82 45 46

28 01 32
82 45 28

27 54 30
824314

274304
82 41 17



28 09 01
82 31 04

28 00 33
82 28 49

27 51 27
82 29 40

27 34 58
82 32 47



28 09 59
82 08 30

27 59 26
821234

27 45 46
821516

27 35 21
821505


1700


604


677.5


1438




693


1180


1000


1260




400


850


1575


1013


N/A


M. CLAUSEN
(CH2M HILL)

CHRISTOPHER


TOM SCOTT




C. COLEMAN


G. KINSMAN


J. DECKER &
G. KINSMAN

JIM CLAYTON
DOUG RAPPUHN


(1) Well ID is FGS "W" number.
(2) Section quarters are coded as A= NW 1/4; B= NE 1/4; C= SW 1/4; D= SE 1/4.
(3) TD total depth; BLS below land surface in feet.
(4) NGVD National Geodetic Vertical Datum of 1929 (in feet).
(5) N/A Not applicable.


N/A


CUTTINGS


CUTTINGS


CORE




CUTTINGS


CUTTINGS/
CORE

CUTTINGS/
CORE

CORE


YLV IIVI ~I \INGVQ (4) LOG ---









Other factors that limit the utility of the logs
include unknown log history (e.g., the older
logs may have been run through casing in all
or part of the borehole) and logs that reflect
instrument "drift" or a slowly changing base-
line. Most of the logs shown on the cross
sections were run at a logging speed of 20
to 25 feet/minute.
The intensity units shown on the logs
(horizontal axis) are in counts per second
(CPS). Due to inconsistency between logs
with respect to different logging-parameter
settings and borehole characteristics (e.g.,
depth of casing and lack of caliper logs to
determine wash out of poorly consolidated
units), it is not possible to quantitatively
compare the logs shown in Plates 1 through
6. The logs are very useful, however, in the
identification of correlative "packages" of
gamma-ray peaks and for comparison of the
overallgamma-raysignaturewithinformational
units.

Delineation of boundaries

Formations

Delineation of formational boundaries
is based on inspection of available borehole
samples (cores and/or cuttings) by geologists
from SWFWMD, the FGS, or both. Formation
boundaries are primarily based on lithologic
character. Gamma-ray logs and fossil
assemblages are used only to supplement the
lithologic descriptions in the determination
of the boundaries. The following general
comments pertain to the lithostratigraphic
contacts shown on Plates 1 through 6. In
cases where distinctly different lithologies of
two lithostratigraphic units are interlayered,
the top of the uppermost occurrence of the
underlying unit is used as the formation
"contact." In determining the position of
formational members (e.g., Tampa Member
of the Arcadia Formation) within the section,
a conservative approach was taken: when
a unit has characteristics of both the member
and the broader formational unit, the sequence


is shown as part of the formation
(undifferentiated). Where there exists
uncertainty regarding the exact position of
the formation boundary, or when the boundary
is inferred within an interval of poor or no
sample recovery, a dashed rather than solid
line is shown. Dashed contacts are also drawn
where only a gamma-ray log was used and
no samples were available for inspection. In
cases where sample quality is poor, as is
sometimes true with cuttings, the gamma-ray
logs become more important in the determina-
tion of formational boundaries.
Lithostratigraphic units shown on the
cross sections include the Avon Park Forma-
tion through the Hawthorn Group. Strati-
graphic relationships, ages, extent and
nomenclature of post-Miocene units within
the southwest Florida region are complicated
(Scott and Allmon, 1992) and their delineation
is not within the scope of this study. On a
regional basis, the post-Hawthorn Group units
are components of the surficial aquifer system.
For the purposes of this study, the various
post-Miocene units are combined as
undifferentiated sand and clay (UDSC) or
undifferentiated sand, clay and shells (UDSS).

Aquifer systems

Generalized aquifer-system delineations
are shown on the cross sections (Plates 1
through 6) as hydrostratigraphic columns to
the left of the lithologic columns. Hatching
patterns used in the hydrostratigraphic
columns identify the three aquifer systems
present in the study area (Figure 2). Delinea-
tion of the aquifer systems is based on
available hydrogeologic data collected during
drilling. Criteria for delineation of
hydrostratigraphic units include
hydrogeological characteristics of the samples
(e.g., porosity types, measured and estimated
permeability) and observed changes in
potentiometric-head levelsbetween permeable
rock units, both during drilling and in
completed monitor wells at the sites. Where
reliable hydrogeologic data are not available,






Plate 1. Cross section A-A', Pinellas/Hlltsborough Counties



SR17E I RIE RSE RISE RISE R20E
-E $1


WEST


RME | M6E


A









W-12943


0 30 60 0 s5 50
SGA A I I I
G4mA MA c 4A4M (CPS)


- 50



-10 0



-150 -









-Em -
-200



-2 -

















-S.-
-300



-350



-400



-450



-s.

-500 -

-550



-600



-650



- 700



-750







-8o0













-I1.
-1000



-1050 -


R



R





R





T.O -170 LS


150 4
40

100 30
20
50
10
0 0

10

- s0 -1



I- 40


EASTLAKE W-7795 DUNDEE W-3428 PEBBLE CREEK


0o-


EAST


UDSC


W-7032


150 40

100 - 30
80

50 0
010


10
- 50

FEET )ITERS


15 4
40


ARCADIA FM.





SUVANNEE
LIMESTONE


ms













M
[ch






N
N


Irp
Krh


aN
MS

NR SPL


*Ay
K
MR
MA
K&R

MK
W


OCALA
LIMESTONE


RILES
0 05 1 2 3 4 5
I os I I


00o51 3 4 5 6 7 7
KILDIETERS
HOizDONT SCALE

RTICAL EXGGERATWH IS 115.9 T S
HOumIZNTAL SCALE


rn5070294


AVON PARK
FORMATION


- 240


50-



0-







so -



150 -











-300 -



-350 -



-400 -



-450 -

















-M-
-500-













-700-



-750-







-100-











-100


S-- 0


--320


--320






VEST Plate 2, Cross section B-B', Pinellas/HIllsborough Counties EAST
RaSE RsE R16E ImR7E R17EE R18E RIBE R9E 19E R20E RE R1E







- 10 TR 14-2 TR 12-3 WRAP 2D TR 11-2 DV-1 -
0 00 300 400 50

V-15204 V-15494 V-16574 V-14668 V-16576


SAPEACE RIVER GAA cp
FM. UDSC tm
100 0 -0 100 1

00 n0
50- SF T o o ---
ED HARBO-DAY 0 T t
t -- 2 o m a m e s 1
-m 1 -A 21D
p UDSC "---- C G 0 AM R GAM A FPM.

'L a OF "
Ss ITH-RN GRP. o UDS TAMPA MBR.

ra G TAMPA a BR. ARCADIA FM -



-50- 0 a0 SUVANNEE 1 -
5 FORMATION E





-s E SUVANNEE -
-eso ARCADIA FM. L T -50






Sa LIMESTONE




Ss M LIMESTONE



0 --B MEMRNo Stt DCALA $ -A sA FM. -5 s--









Ms O AVON PARK a aMATION
,-E fU -0 -
- -m -240 HnNU S .MU. '
























-mKa -K C -"m
40EK SUWANNEE 40








C 7N -5-
-eP -- -L
c N L IMESTONE -AV R

TLIMESTONIOE N0 -0 -
MAORIZsmTAL OCALA


SLIMESTONE -I
- 0a F -- -OaA 0
R LIMESTONE LIET
NO M OCALA A- 400o- 2

--450 ----140.-4-!M 140


-LIMESTONESO--


SAVON PARKF






-700 MILES N_70
0 0.5 1 0 3 4 5 -m
-750- 0 1 -03 3-m45 7i

KCL.DETERS OI
-240 HOIZONTAL SCALE-
---EIL EXARATIO]N r IS BOA TIMES
ORI Z O SCALE

S-T
GoD M -sm-









-450 --320 D --_L-n

TM -LIM






WEST


PLate 3, Cross section C-C', Pinettas/HILlsborough Counties


RIUE R7E


RIBE RgE


RI7E I RIE


MANGROVE
POINT i


R9E R20E SEAI D R20EI R R IE R22E
SEATIOARD
C DAS m IRAH HURRAH C
ffi --C


VOLF
RMNCH


TR 9-3 TR 9-2

W-15642 W-16618


- 20








- 20



- 40


v ~RTICAL
2. 1 TIMES


T0J~ -143' NGVK


a un 30

GAMMA (CPS>








S a ARCADIA
FORMATION





i TAMPA
MEMBER OF
Sch ARCADIA
FORMATION










SSUWANNEE
LIMESTONE









ch



OCALA
LIMESTONE












SAVON PARK
FORMATION o 0.5 1

S0 1 2 3
SAMPLED FOR
URANRUM ANALYSES HRI3


10 -


L- -
METERXS
- 40



- 30


ROMP 49

W-16456


AMA













a4
S7a W















ch




DA



IN
C
cM
aI












s



r.


a








i4
i 7 8


i je]i--^ ^


ROMP 48

V-14386


- 30 -L
-,
FEET ITE
r 4


0 100 2O0 300 420

GAN1A - -SO.-__0 -




3 -
o-


UDSC
0 I15 300 450
GAM CCPS)
PEACE RIVER
C.AT FORMATION



rp ARCADIA
FORMATION

















c ARCALIMESTONE
CAOALA























iL LIMESTONE
T--- --- --






m
KT


















F LIRMATIONE















P





TJ44 -0 3L'


'~;';~:
~'
.;~j~













a oo ao 30 400 no
cmam acm
OH
P -=T











































N












L
CS


S.A



PTIN






CAN























L


T.IL -1s7' UIs


-33-


-400 -


-M -


-700 -


- m -


--eM


FGS070494


PI-32

W-50015


so -

0 -



FmT


- 1 -


- 100 -


w

UV^
TAMPA
K11" MEMBER OF
ARCADIA
FORMATION











: : v SUVANNEE
LIMESTONE














DCALA
LIMESTONE



ITI e


MILES
2 3

3 4 5
:IL[ETERS
ZONTAL SCALE

EXAGGERATION
SHORIZMNTAL


-00-


-6-0 -200
-an -O


-SO 4- -eo


-9w'


- - pb=F-Ff


R]



AVON PARK
FORMATION

onw1


- 30 -1







NORTH PLate 4. Cross section D-D', PinetLas County SOUTH
T27S T8a5 TEiS TESS T T30S T30S T31S T31S T32S

D a CLEV SEAARD M
SEEK COASCOAST R JOE '

10- LA~GE" 10X 0


10 --

T TES W-12943 V-15204 o -16197 W-50015 FEET METERS
E 0 30 a CMW ACm
50- 2
oo -


,- -O iM I ON -20
Gnna a aM a oa ws xo0-
0m O 40I NI160E10 0 I I
UDSC UDSC ...... M
--'".TAMPA m UDSS o
.... MEMBER ri THORN GRP.
'' W ARADIA UNDI FF
50 FO~ F-RMATION -:- 0 -



-40 ;-:i - .0
PTAMPA. .HAWTHORN GRPs.
MR MEMBER OF UNDIFF. .

-ARCADIA ARCADIA L 0 -

--0 R PORTION || 0 1 FORMATION N 4

-u1so ...
TAMPA30
69-K-R s MEMBER OF c
BUN-KD ARCADIA Ch --
SUANNEE FORMATION


SLIMESTNE LIMESTONE
-100KtCCh -1


4....-120K SUVANNEE I-0-

c-4 30 T-430 -
LIMEST..E LIMESTONE ,',',','






-14 I
B- N




ODCALAA
-LLIMESTNEESTON

KCODCALA
-650 - AVON PARK LIMESTONErC5,0','',,,
FORMATION s, -



-2 40
-7am -M L.S900 -






.I 1, I AVON PARK
-860 0.0.s51 2 3 4 5s 7 8 FORMATION


-90 --n0 V 0RCAL EXA AERATION Is 978 TIES9 -
KAIF" HORIZM'TAL SCALE



-10 -00 .... .ST_ -o1000 -




-n0120. --10 -10
- -100 t --4










TeS jT29


Plate 5. Cross section E-E', Hitsloorough/Manatee Counties

i T9rS I TM T30S | T3IS T3 T3a


LAKE COAST RR ____
LAK E SEA BA RD

-_L I CAST RR


T32 TS33 SEABARD
COAST RR


SOUTH
E'


TAWPA DAY


T DUNDEE WRAP 2D TR 8-1

e as so W7 V-16574 W-7672 V-15826


\ TAMPA MB-R,
OF
,NRCADIA FM.


N


SUVANNEE
LIMESTONE


AVON PARK
FORMATION


0 SO 100
o I Ic o

GAMMA CPB
UDSC
---. PEACE RIVER FMI


AVON PARK
FORMATION


0 0 10050 -
GWA (CPS)


UDSC


ARCADIA

FORMATION


KCh

KR

KAS

NO sPL
KWAS

KR.s

KR


KR
WU





KR
KR




IOR.

NO SPL

NO SP.


OCALA

LIMESTONE


NO SPL
LAR





L
L.lp


Up HORIZONTAL SCALE
PAM MILES
KSPfI 00a 1 3 4 5
UWp I 1. 1 1 I I
Ij 0051 2 3 4 5 6 7 8
KILOMETERS

VERTICAL EXAGGERATION IS 125.7 TDIE
HORIZONTAL SCALE


TA 120 LS


- -e4o


-1050 -3pg


-1100 -


-340


--340


NORTH

E


T27S I T8S


LAKE RV
STARVATEN ,


0 --

2a -


to


FE -



FEET r ETES


- 50




- 650

- Ln


-650 -20


-am


- 850 -2.


-150


-1000


-10o0 -3-


-u50


I I










NORTH R ROlE

F

SEAIWD


Plate 6,
TEtS Tl9S



@ C?5 @


K IOTS
RIDa


Cross section F-F', HIllsborough/Manatee Counties

m s rT T3SrT31S
SERWARD
SEIATRD CST RR\
COAST RR I


40




1 10

0 0






150
-


0


















100
S-60







- 100 -







-m---


V-7032


T31S JIT


T32SIT33s SOUTH

MS FORK IE

aI RIVER 'R


ROMP 49
W-16456 o no o00 o 40o so

I m I I IC
cmNA IEPV


ROMP 39
V-16740


T.Di -157' LS


DV-1
V-16576


-a2 -

-=-

-30 -



-30 -



-400-



-4S0











- son -




-700



-750


- -140




- -I0




--1M


- -240


150






S10








40



150




0 0




-5 n


100 -

--40




ISO -







--00

-
-3-10
-00



-450 - -460


-40o
-140o






-so













-30B
-1-0 0

-7-0




-7 50


-0-40

--a





IN
-I0



-Um





-1 --0

_1SnO -o


--321









aquifer delineations are based primarily on
lithology and compared with hydrostratigraphy
established at adjoining data points in the
cross section. A summary of aquifer intervals
for cross section data points is given in Table
2. Descriptions of the hydrogeologic
properties of aquifer systems present in the
study area is presented in an ensuing section
entitled Hydrostratigraphy.

LITHOSTRATIGRAPHY

The deepest boreholes used in this
study penetrate Middle Eocene lithostrati-
graphic units. Following is a discussion of
lithologic characteristics of Middle Eocene and
younger units and their general gamma-ray
log characteristics, which are shown in the
cross sections (Plates 1 through 6). Table
3 summarizes the tops of these units relative
to National Geodetic Vertical Datum of 1929
(NGVD).

Eocene Series

Avon Park Formation

The Middle Eocene Avon Park Forma-
tion (Miller, 1986) underlies all of Pinellas,
Hillsborough, and Manatee counties. Its
lithology is generally comprised of tan to buff
dolostones and dolomitic limestones with
occasional organic-rich laminations. The
uppermost portion of the Avon Park Formation
within the study area is, however, a very light-
orangeto yellowish-gray calcarenitic limestone
with variable amounts of organic-rich
laminations and dolomite. Porosity in this
formation is generally intergranular in the
limestone section. Fracture porosity in the
dolostone is common, as well as
intercrystalline porosity in the sucrosic
textures. Pinpoint vugs and fossil molds are
present to a lesser extent. The most diagnos-
tic fossils include the foraminifers Dictyoconus
americanus and Coskinolina floridana. The
echinoid Neolaganum (Peronella) dalli is
common within the upper portions of the unit.
The Lower to Middle Eocene


(Braunstein and others, 1988) Oldsmar
Limestone is subjacent to the Avon Park
Formation in this region. Miller (1986) reports
the base of Middle Eocene rocks (approxi-
mately the base of Avon Park Formation) at
depths ranging from -1700 to -2400 feet
NGVD. The Avon Park Formation varies in
thickness beneath Pinellas, Hillsborough, and
Manatee Counties, ranging from approximately
1250 feet in northeastern Manatee County
to 1500 feet in Pinellas County (Miller, 1986).
According to Miller (1986), the top of the
formation is between -500 and -900 feet
NGVD; however, the present study has found
this horizon at higher levels, the shallowest
being -226 feet NGVD (Plates 1 and 6). The
Avon Park Formation is unconformably
overlain by the Ocala Limestone.
Gamma-ray log response for the Avon
Park Formation is somewhat different from
that of the overlying Ocala Limestone. In
general, Avon Park lithologies give rise to a
more variable signal with a slightly higher
background count rate. This variability is
probably due to the dolomite content. In some
cases, near the top of the Avon Park a set
of diagnostic gamma-ray peaks occur, which
may be a response to the presence of organic
laminations in the uppermost part of the
section. These organic may contain elevated
amounts of uranium, which would cause
increased gamma-ray activity.

Ocala Limestone

The Upper Eocene Ocala Limestone,
first named by Dall and Harris (1892), consists
of white to light-gray to light-orange limestone
with a diverse fossil assemblage. More
specifically, the lithology of this formation
ranges from a weathered wackestone to
packestone with a variable amount of
calcilutite matrix (chalky) in the upper
portions, to a biogenic packstone to grainstone
in the central and lower portions of the unit.
Trace amounts of organic, clay and variable
amounts of dolomite are also present.
Porosity is variable within this unit and is
generally moldic and intergranular with













Table 2. Upper boundaries of aquifer-system units within the study area; datum is NGVD, units are in feet.


SURFICIAL AQUIFER INTERMEDIATE AQUIFER FLORIDAN AQUIFER
SYSTEM SYSTEM/CONFINING UNIT SYSTEM


WELL ID


A-A'

W-12943
W-7795
W-3428
W-7032

B- B'

W-15204
W-15494
W-16574
W-14668
W-16576

C-C'

W-50015
W '5642
W-16618
W-16456
W-14386

D-D'

W-12943
W-15204
W-16197
W-50015

E-E'

W-16574
W-7672
W-15826

F-F'


NOT OBSERVED
NOT OBSERVED
NOT OBSERVED
NOT OBSERVED


N. PINELLAS INJ. WELL NO. 1






ROMP TR 14-2
ROMP TR 12-3
NW HILLSBOROUGH WRAP 2D
ROMP TR 11-2
ROMP DV-1



PI-32 TEST HOLE ST. PETE WWTP
ROMP TR 9-3
ROMP TR 9-2
ROMP 49
ROMP 48



N. PINELLAS INJ. WELL NO. 1
ROMP TR 14-2
ROMP TR 13-2X
PI-32 TEST HOLE ST. PETE WWTP



NW HILLSBOROUGH WRAP 2D

ROMP TR 8-1


SITE NAME


NOT OBSERVED
32
1
-73



-2
NOT OBSERVED
-24



NOT OBSERVED
92
68
50


W-7032
W-16576
W-16456
W-16740


ROMP DV-1
ROMP 49
ROMP 39


-13
-7
-107
-198


64
32
-203
-251












Table 3. Upper boundaries of lithostratigraphic units delineated in cross sections for this report; datum is
NGVD, units are in feet. All estimated contacts are indicated by brackets.

i HAWTHORN
WELL ID SITE NAME AVON PARK OCALA SUWANNEE GROUP ARCADIA TAMPA PEACE RIVER UDSC/UDSS
FORMATION LIMESTONE LIMESTONE (UNDIFF.) FORMATION MEMBER FORMATION THICKNESS

A-A'

W-12943 -443 -323 -53 -13 -13 30
GAMMA EASTLAKE [-452] [-318] [-6] [5] [5] [34]
W-7795 -433 -293 12 28 [28] 9
GAMMA DUNDEE [-442] [-264] [16] [31] [31] [28]
W-3428 -212 23 31 31 37
GAMMA PEBBLE CREEK [-329] [-179] [33] [41] [41] [4]
W-7032 -226 -76 54 64 64 20

B-B'

W-15204 TR 14-2 -455 -99 32 -12 -12 67
W-15494 TR 12-3 -432.5 -157.5 [-6.5] -16.5 -16.5 43.5
W-16574 WRAP 2D -470 -342 [-159.5] -2 -27 -27 55
W-14668 TR 11-2 -473 -318 -100 8 -7 -7 22
W-16576 DV-1 -415 -232 -41 22 22 91 21

C C'

W-50015 PI-32 -758 -570 -338 -78 -189 85
W-15642 TR 9-3 -757 -517 -277 [-22] -147 -12 20
W-16618 TR 9-2 -684 -444 -243 -40 -106 -23 36
W-16456 ROMP 49 -679 -429 -233 30 -93 68 78
W-14386 ROMP 48 -683 -453 -198 [62] -53 [98.5] 3.5

D-D'

W-12943 -443 -323 -53 -13 -13 30
W-15204 TR 14-2 -455 -99 32 -12 -12 -
W-16197 13-2X -546 -201 -22 -106 -106 -
W-50015 PI-32 -758 -570 -338 -78 -189 85

E-E'

GAMMA DUNDEE [-442] [-264] [16] [31] [31] [28]
W-16574 WRAP 2D -470 -342 [-159.5] -2 -27 -27 55
W-7672 -520 -240 -105 -20 -20 40
W-15826 TR 8-1 -940 -627 -365 -20 -250 35


F-F'

W-7032 -226 -76 54 64 64 20
W-16576 DV-1 -415 -232 -41 22 22 91 21
W-16456 ROMP 49 -679 -429 -233 30 -93 68 78
W-16740 ROMP 39 -840 -592 -388 -58 -264.5 [67.5] [57.5]








occasional macrofossil molds. This formation
contains characteristic fossils such as the
foraminifera Lepidocyclina spp., Nummulites
(Operculinoides) and echinoids such as
Eupatagus antillarum. Other fossils observed
in the unit include pelecypods, bryozoans,
gastropods and rare Rotulina (Spirolina)
vernoni.
The Ocala Limestone is typically bound
by unconformities. Depths to the top of the
formation range from approximately -76 to
-627 feet NGVD (Plates 1 through 6).
Analysis of well cuttings and cores selected
for this study indicates that the Ocala
Limestone, which averages 195 feet thick,
ranges in thickness from 120 feet in the
northern part of the study area (Plate 1) to
313 feet in the southern part (Plate 5). The
dip of the Ocala Limestone in this area is
approximately 0.1 to 0.2 degrees towards
the southwest.
Relative to the overlying Suwannee
Limestone and the underlying Avon Park
Formation, the gamma-ray signature for the
Ocala Limestone is muted, with consistently
low background rates and a characteristic lack
of peaks. In cases where the Ocala is
dolomitized, the gamma-ray logs may exhibit
a slightly higher and more sporadic baseline.

Lower Oligocene Series

Suwannee Limestone

The lithology of the Lower Oligocene
Suwannee Limestone (Cooke and Mansfield,
1936) ranges from a light-gray to yellowish-
gray packestone to grainstone. These
carbonates are variably moldic with trace
amounts of sand and clay within the upper
portions. Trace amounts of chert and organic
occur throughout the unit. A dolostone or
dolomitic limestone layer, approximately 10
to 20 feet thick, commonly occurs within the
lower one-third of the unit in the study area.
Fossils in the unit include gastropods,
pelecypods, echinoids (e.g., Rhyncholampus
gouldii), abundant miliolids and other benthic
foraminifers including Coskolina floridana and


Dictyoconus cookei.
This formation unconformably overlies
the Ocala Limestone and is unconformably
overlain by Hawthorn Group sediments. It
should be noted that, in some cases, the upper
Suwannee lithologies appear to grade upward
into the Hawthorn Group. Where the two
lithologies are intercalated, the uppermost
occurrence of the older formation is selected
as the formational "boundary." The top of
the Suwannee Limestone occurs between
+ 54 and -388 feet NGVD. The unit thickens
to the south and west, ranging from 130 to
356 feet and averaging approximately 219
feet (Plates 1 through 6). The dip of the
Suwannee Limestone is approximately 0.1
degrees toward the southwest.
The Suwannee Limestone is character-
ized by a gamma-ray signature which has an
overall higher background rate than the
underlying Ocala Limestone. In addition, there
exists much more variability in its signature
from bed to bed relative to the Ocala Lime-
stone. This variability in the gamma-ray
signature is probably due to variable dolomite
and organic content from bed to bed within
the formation. The lower portion of the
Suwannee is generally more variable than the
upper portions of the unit with respect to its
gamma-ray response. Although the gamma-
ray log is generally useful for providing
corroborative evidence for the
lithostratigraphic boundary between the
Eocene Oligocene carbonates, the utility of
the logs for determination of the upper bound-
ary of the Suwannee Limestone is not always
as straightforward. For example, where the
Tampa Member of the Arcadia Formation is
in contact with the Suwannee Limestone,
gamma-ray signatures for the two units are
quite similar, both in their background count
rates and distribution of peaks.
Another consistent observation in the
gamma-ray logs is the presence of a 50- to
100-foot thick interval of high gamma-ray
activity within the central to lower portions
of the Suwannee Limestone. The gamma-ray
log for the Pebble Creek borehole (Plate 1)
and W-16574 (Plate 2) are exceptions, where








the interval is in the upper part of the unit.
This interval varies in thickness and depth and
apparently does not correlate with a given
stratigraphic horizon. This suggests that the
high-gamma activity interval may be post-
depositional in origin.

Lower Oligocene to Pliocene Series

Hawthorn Group

Hawthorn Group sediments (Scott,
1988) are Lower Oligocene (Wingard and
others, 1993, 1994, 1995) Lower Pliocene
(Covington, 1993; Missimer and others, 1994)
in age and generally consist of phosphatic
siliciclastics (sands, silts and clays) and
carbonates. These sediments in Pinellas,
Hillsborough, and Manatee Counties lie
unconformably above the Suwannee Lime-
stone. In the study area, the Hawthorn Group
consists of the Arcadia Formation, the Peace
River Formation and undifferentiated Hawthorn
Group. Also observed in the region is the
Tampa Member of the Arcadia Formation.
Overall, the top of the Hawthorn Group occurs
from + 100 to -106 feet NGVD, and ranges
in thickness from less than 10 feet to
approximately 345 feet (Plates 1 through 6).
Unconsolidated post-Pliocene sediments lie
unconformably above the Hawthorn Group
throughout the study area.

Arcadia Formation

The Lower Oligocene to Middle
Miocene (Wingard and others, 1995) Arcadia
Formation (undifferentiated)isayellowish-gray
to light-olive gray, clayey carbonate with
highly variable amounts of quartz sand and
sand-size to gravel-size phosphate. Highly
dolomitic layers occur throughout the
formation and many of the finer-grained
carbonate beds are dolomitic. Some of the
descriptions on which the stratigraphic
columns are based did not always note the
presence of dolomite/dolostone. Upon re-
inspection of samples during this study,
however, it was noted that many of the "clay"


units are comprised of fine-grained dolomite
with a subordinate clay matrix. Scott (1988)
reports that most of the carbonate in this
formation is dolomite.
The Upper Oligocene (Wingard and
others, 1993) to Lower Miocene Tampa
Member of the Arcadia Formation is white
to yellowish gray in color, and ranges from
a wackestone to packestone with varying
micrite, quartz sand and clay (Scott, 1988).
Minor phosphate, dolomite and chert are also
observed. Porosity of this unit is generally
intergranular and moldic.
The top of the Arcadia Formation
ranges from +65 to -105 feet NGVD, and
ranges in thickness from less than 10 to 345
feet. In the southern part of the study area,
(Plate 3) where the Tampa Member is not
equal to the entire thickness of the Arcadia
Formation, the Tampa Member top occurs
at -50 to -190 feet NGVD and averages 140
feet thick. In other locations, the top of the
Tampa Member is equivalent to the top of the
Arcadia Formation.

Peace River Formation

The Middle Miocene to Lower Pliocene
(Covington, 1993; Missimer and others, 1994)
Peace River Formation is comprised of
yellowish gray to olive gray, interbedded
sands, clays and carbonates with the
siliciclastic component being dominant (Scott,
1988). Variable amounts of phosphate sand
and gravel, as well as occasional carbonate
beds, are interspersed throughout the unit.
This formation is limited to the central and
southern portions of the study area.
The top of the Peace River Formation
varies between +98 to -12 feet NGVD, and
the unit attains thicknesses of up to 70 feet
along the eastern margin of Hillsborough
County (Plate 2). The cross sections illustrate
cases where the described lithologic package
is clearly part of the Hawthorn Group, but
further subdivision of the unit is limited by
sample quality and lack of stratigraphic
control. In these cases, only the Hawthorn
Group (undifferentiated) is delineated (Plates








2 and 4 ).
Gamma-ray signatures in the Hawthorn
Group are highly variable. In the study area,
the overall signature in the Arcadia Formation
and the Peace River Formation is similar, with
both having well-defined peaks and higher
backgrounds than the underlying Tampa
Member. This similarity is atypical because
the gamma-ray signature of the Peace River
Formation in other areas is usually more
subdued than that of the Arcadia Formation
(undifferentiated).
In the study area, the Arcadia Forma-
tion generally contains an interval of numerous
peaks whereas the Peace River is limited to
three peaks or less, which in some cases are
at least two times greater than the maximum
Arcadia peaks. Very high magnitude gamma-
ray peaks in the Peace River Formation occur
in the easternmost wells (Plates 2 and 3),
which may be indicative of the Bone Valley
Member of the Peace River Formation (i.e.,
responding to abundant phosphorite). Due
to limited samples and variable sample quality,
the Bone Valley Member is not delineated on
the cross sections. Scott (1988) shows the
western subcrop limit of the Bone Valley
Member to occur in the area.
As a general rule, the gamma-ray
signature for the Tampa Member of the
Arcadia Formation is relatively subdued in
comparison to the undifferentiated Arcadia
Formation. In some cases, the gamma-ray
response of the Tampa Member is variable,
with sets of moderate-intensity peaks.
Relative to the Suwannee Limestone, the
Tampa Member gamma-ray log occasionally
has higher background levels.

Post-Hawthorn Group

Undifferentiated Sands and Clays

Post-Hawthorn Group sediments occur
throughout the study area and range in
thickness from approximately 5 to 85 feet
(Plates 1 through 6). These sediments are
primarily comprised of varying proportions
of sand, shell and clay. Lithostratigraphic


units in this sequence can include the Ft.
Thompson and Caloosahatchee Formations.
Variable amounts of organic and re-worked
phosphate may occur in these sediments as
well.
Gamma-ray activity is variable in these
sediments; however, moderate basal peaks
are observed in some logs, possibly reflecting
deposits of re-worked phosphorite. In the
cross sections, straight line (zero baseline)
gamma-ray signals at the top of some of the
logs indicate a lack of data collected over the
interval shown.

Uranium-Reconnaissance Analyses

Reconnaissance U-series isotopic
analyses of four core samples from the
Suwannee Limestone in a core from
Hillsborough County (W-16618) were
performed to further evaluate the above
observations. The results of these analyses
are presented in Table 4.
Two methods were utilized to analyze
these four samples: 1) acid-dissolution of the
carbonate fraction of each sample, and 2)
leaching of splits from each of the samples
with a 0.2 normal solution of potassium
carbonate. Green (1994) provides more
detailed information on these methods.
The acid-dissolution method was
utilized in order to obtain uranium concen-
tration and 234U/238U activity ratio of the acid-
soluble fraction of the samples, which allows
comparison with expected values. The
234U/238U activity ratio of a sample is expected
to be 1.0 (secular equilibrium) after approxi-
mately one million years of time have passed
since the deposition of the uranium in the
sediments (Osmond and Cowart, 1976).
Given that the samples analyzed were all from
the Suwannee Limestone, their 234U/238U
activity ratios were expected to be in equilibri-
um. Several of the samples analyzed had
activity ratios less than unity (Table 4),
indicating that uranium has been mobilized
in these sediments within the last one million
years.
In general, the average U concentration













Table 4. Uranium geochemical data for selected samples from W-16618 (TR 9-2), Hillsborough Co., Florida.


SAMPLE
DEPTH
(FEET NGVD)


WT. PERCENT
INSOLUBLE
RESIDUE


URANIUM
SPIKE YIELD
(PERCENT)


URANIUM
(234/238)
ACTIVITY RATIO


ACTIVITY
RATIO
ERROR


URANIUM
CONCENTRATION
(ug/g)


URANIUM
CONCENTRATION
ERROR


SAMPLES DISSOLVED IN MIXTURE OF 8 NORMAL NITRIC AND HYDROCHLORIC ACIDS

1.40 49.2 1.00 0.01 8.86 0.16 N/A
2.10 52.7 0.98 0.01 6.94 0.10 N/A
12.1 22.0 0.89 0.01 29.7 0.70 N/A
8.40 36.5 0.96 0.02 2.93 0.06 N/A

SAMPLES LEACHED 24 HOURS WITH 0.2 NORMAL SOLUTION OF POTASSIUM CARBONATE


53.4
43.9
1.0
44.0


0.53
0.44
0.59
0.85


0.03
0.02
0.03
0.06


0.03
0.04
0.52
0.01


8.0
21.2
32.3
5.8


* NOTE: The low yield of spike for this sample makes the data for Uranium concentration questionable.


-368.0
-382.5
-392.0
-425.0



-368.0
-382.5
-392.0
-425.0


LEACHABLE
URANIUM
(PERCENT)








in limestone is approximately 1 part per million
(ppm; Osmond and Cowart, 1976). Table 4
shows that the average uranium concentra-
tion in the four samples analyzed from the
Suwannee Limestone is 12.1 ppm. This
indicates that there has been significant
enrichment in uranium in these samples
relative to average limestones. The analytical
methods used, however, cannot determine
if the uranium was emplaced during the
deposition of the limestone, or if the high
uranium content is due to some sort of post-
depositional enrichment process.
It is interesting to note that the sample
with the highest uranium concentration also
has a high organic content. Uranium is
immobile under reducing conditions and mobile
under oxidizing conditions. Therefore, if a
uranium-rich water were to come into contact
with an organic-zone within the sediments,
the uranium could become reduced, leading
to precipitation of a secondary coating of
uranium on the aquifer matrix (Osmond and
Cowart, 1976). Conversely, if an oxidized
source of ground water were to come into
contact with such a secondary coating of
uranium in an aquifer, the uranium could
potentially be re-mobilized into the ground
water.
In order to test the mobility of the
uranium, leaching experiments were performed
on splits of each of the samples. Green
(1994) demonstrated that a solution of 0.2
normal potassium carbonate could effectively
leach uranium from carbonates without
fractionating the uranium. Leaching
experiments performed on these four samples
indicated that the uranium associated with
this zone is relatively mobile. The "percent
leachable uranium" listed in Table 4 represents
the amount of leachable uranium relative to
the total uranium present in the sample. This
value gives an approximation of uranium
mobility in a given sample is under laboratory
oxidizing conditions. The leaching data for
the samples from 382.5 feet and 392 feet
below land surface indicate that the uranium
present can be highly mobile under oxidizing
conditions. This observation should be


considered in the design of groundwater
storage and recovery programs, where
relatively oxygen-rich waters are injected into
the subsurface for later recovery. If a source
of relatively mobile uranium is present in the
aquifer, then the oxygenated water could
potentially re-mobilize the uranium into the
stored water.
For a more detailed discussion of
leaching of uranium-rich carbonates and the
significance of low 234U/238U activity ratios
of the leached uranium, see Green (1994).
Further investigation of this uranium-enriched
zone in the Suwannee Limestone is the subject
of planned research.

HYDROSTRATIGRAPHY

The hydrostratigraphy of the study area
consists of a variably complex, two- and three-
layer aquifer system. The three aquifers
present in descending order are the surficial
aquifer system (SAS), the intermediate aquifer
system/intermediate confining unit (IAS/ICU),
and the Floridan aquifer system (FAS;
Southeastern Geological Society, 1986). The
relationship between geologic formations and
hydrostratigraphic units in the study area is
shown in Plates 1 through 6. Correlation
between aquifer systems and geologic
formations generally coincides with
lithostratigraphic boundaries established on
the cross sections.
The SAS is composed of unconsoli-
dated plastic (and locally, carbonate) deposits
that are generally referred to as post-Hawthorn
Group undifferentiated sand and clays. As
noted above, these sediments may include
all or parts of the Pleistocene Fort Thompson
and Caloosahatchee Formations, as well as
Pleistocene-Holocene marine terrace deposits.
Clays present in the base of the SAS most
likely represent reworked Hawthorn Group
sediments.
The IAS/ICU is composed of
interbedded clays and carbonates of the Peace
River Formation, and some carbonates of the
undifferentiated Arcadia Formation and the
Tampa Member. The IAS/ICU in the study








area is generally restricted to the Hawthorn
Group sediments, although post-Hawthorn
confining (clay) beds may locally occur above
the carbonates of the IAS/ICU.
The FAS, the principle artesian aquifer
in the region, is primarily a carbonate aquifer
which includes all or part of the Tampa
Member (Arcadia Formation), and all of the
Suwannee Limestone, Ocala Limestone, and
Avon Park Formation.
Hydrostratigraphy in the study area
varies from a simple two-aquifer system in
the northern portion of the study area (Plate
1), where the FAS is directly overlain by sedi-
ments of the SAS, to a more complex system
in the southern portion of the study area,
where two confined aquifers are present
below the SAS. The FAS in the northern
portion of the map area exists as a poorly
confined or semi-confined artesian aquifer,
where siliciclastic sediments of the upper
Hawthorn Group become thin and discontinu-
ous. The SAS is also intersected by numerous
karst features (Trommer, 1987) in which
sinkholes may act as direct conduits between
the SAS and the FAS. Increased
hydrogeologic importance of the IAS/ICU
occurs where the Hawthorn Group sediments
thicken from north to south, overlying regional
southwest-dipping carbonate rock sequences
of the FAS (Plates 4 through 6). Permeable
carbonates interbedded with lower permeabili-
ty clastics within the Hawthorn Group
facilitate artesian conditions within the
IAS/ICU. Collectively, the IAS/ICU forms a
thick confining unit separating the FAS from
the SAS in the southern region of the study
area.

Surficial Aquifer System

The surficial aquifer system (SAS)
occurs throughout the study area and is
composed primarily of unconsolidated quartz
sand with variable amounts of shell, clay,
phosphate, and organic material. Thickness
of the SAS ranges from ten feet in the
northern region of the study area to 80 feet
in areas of southern Pinellas and Hillsborough


Counties. Delineation of the SAS in the cross
sections is based on water level measurements
collected during drilling, and on interpretation
of lithology from well cuttings and/or core
samples.
The SAS is normally identified by the
presence of a phreatic water level that is
distinct from potentiometric water levels
occurring in deeper confined aquifer systems.
A surficial or "water table" aquifer may occur
where there are sufficient confining materials
such as clay at the base of the unconsolidated
sediments, or if hardpan intervals within the
surficial sand provides a permeability barrier,
resulting in a "perched" water table.
Hydrostratigraphic correlation of the
SAS with geologic units in the study area
places the system in the post-Hawthorn
undifferentiated sands and clays (UDSC). The
base of the aquifer generally coincides with
the first occurrence of clay at the top of the
Peace River Formation (Hawthorn Group).
Where the Peace River Formation is absent
in the northern portion of the study area
(Plate 1), the SAS directly overlies the FAS.
Sandy clays typically form the base of the
SAS, providing some hydraulic separation
between the SAS and the FAS, but the
stratigraphic columns shown in Plate 1 do not
detail the presence of clay. This is probably
due to either poor-quality well samples or no
samples being collected from the
unconsolidated surficial sediments.
Discrete monitor wells constructed in
both the SAS and the FAS at the western
wellsite (W-12943), cross section A-A' of
Plate 1, indicate head differences between
the two aquifer systems (Coffin and Fletcher,
1992, p. 177-178). Other complimentary
pairs of monitor wells in the area of cross
section A-A' support the presence of a
surficial aquifer system "water table" that is
distinguishablefrom FASpotentiometriclevels,
suggesting some degree of confinement exists
between the two aquifer systems. The
thickness and continuity of this intermediate
confining unit is highly variable across the
northern region of the study area (Sinclair,
1981; Ryder and others, 1980). A thin








sequence of clay coupled with existing karst
features increases the hydraulic connection
and recharge potential between the SAS and
the underlying artesian aquifers. The SAS
in central and southern regions of the study
area is relatively isolated from the FAS by
intervening siliciclastics and low-permeability
carbonates that comprise the IAS/ICU.
Localized areas of karst terrain will increase
the potential for recharge from the SAS to
both the IAS and FAS.

Intermediate Aquifer System/Intermediate
Confining Unit

The intermediate aquifer system (IAS)
and intermediate confining unit (ICU) occur
across most of the study area, except in the
vicinity of cross section A-A' (Figure 1).
Hydrogeologic properties of the IAS/ICU are
highly variable, due to lithologic variations
and complex interbedding typical of the
Hawthorn Group sediments. The IAS/ICU is
primarily contained within the Hawthorn
Group, although some post-Hawthorn
siliciclastics may also occur in the uppermost
portions of the ICU. Parts of the Tampa
Member may not be included in the IAS/ICU
if vertical hydraulic connection exists between
the Tampa Member and the Suwannee
Limestone of the Floridan aquifer system.
The heterogeneous nature of the
IAS/ICU makes hydrostratigraphic correlation
between well sites difficult. Detailed site-
specific hydrogeologic data exists for most
sites where core drilling was conducted, but
variables such as well-casing depth, length
of uncased wellbore, and the composition of
borehole fluids can affect the parameters being
measured. Relative changes in water levels
measured in the well during drilling can be
correlated with core samples to identify
permeable zones within the IAS/ICU, or the
contact between the IAS/ICU and the
underlying FAS. Interpolating these observa-
tions between data points on the cross-section
maps is not practical due to limitations on
vertical scale resolution, and the reliability of
the drilling data. Therefore the IAS/ICU, as


depicted on the hydrostratigraphic columns,
is treated as a complete system of variably
interbedded permeable sections and confining
units within the Hawthorn Group.
The IAS/ICU in the study area is
present as a confining unit in the central study
area depicted in Plate 2, and also along the
western coastal area, shown in the north-
south cross section through Pinellas County
(Plate 4). Sediments comprising the ICU in
these two sections are composed primarily
of low-permeability clays and carbonates of
the Peace River and upper Arcadia Formations.
In these cross sections, permeable limestone
of the Tampa Member forms the uppermost
section of the Floridan aquifer system.
Several factors influence the effective-
ness of the ICU in restricting hydraulic
connection between the SAS and the Floridan
aquifer system. For example, the thickness
and mineral composition of the ICU are
important in the west and central portions
of the study area. An increased sand compo-
nent within the clays generally limits the
effectiveness of those beds as confining units.
Fracturing can also have a substantial effect
on the effectiveness of the ICU. Although
fractures have been observed in core samples
within this hydrostratigraphic unit, their
cumulative affect on the confining nature of
the ICU is difficult to quantify without field
studies. The occurrence of karst features may
also provide a more direct path for localized
downward movement of ground water through
the ICU in this region.
Permeable carbonate beds in the Peace
River Formation, and all or portions of the
Tampa Member make up the IAS in the
southern region of the study area (Plate 3).
Less permeable limestones in the lower Tampa
Member separate the IAS from the underlying
FAS. The base of the IAS/ICU generally
coincides with the stratigraphic top of the
Suwannee Limestone in this area, but
permeable beds in the lowermost Tampa
Member are included in the FAS where
hydraulic connection exists.









Floridan Aquifer System

The Floridan aquifer system (FAS),
which is present throughout the study area,
is composed of heterogenous Lower Eocene
to Lower Miocene carbonate rocks. In the
study area, the FAS is typically considered
an artesian aquifer having a distinct
potentiometric water level based on wells
open to the system. The top of the FAS is
generally placed at the first occurrence of
vertically persistent carbonates below
siliciclastic materials of the SAS and IAS/ICU.
The base of the FAS is identified by the
presence of vertically and laterally persistent
evaporite (e.g., gypsum and anhydrite) beds
of regional extent (Southeastern Geological
Society, 1986). These evaporites comprise
the sub-Floridan confining unit, which
underlies the FAS throughout the region.
The top of the FAS occurs near land
surface in the northern part of the study area,
and dips to over 200 feet below land surface
in the southern portion. The base of the FAS
occurs in the lower Avon Park Formation
where bedded or interstitial evaporites retard
vertical movement of water. The stratigraphic
column for W-12943 (Plates 1 and 4) extends
to the base of the FAS at depth of about 980
feet below NGVD. Average thickness of the
FAS is approximately 1100 feet in the study
area (Wolansky and Garbode, 1981).
A large degree of vertical anisotropy
exists in the Floridan aquifer system (Ryder
and others, 1980; Ryder, 1981) due to
variations in grain size and other lithologic
controls such as fossil content, diagenesis,
and cementation. Vertical variations in
porosity and permeability cannot be resolved
at the level of detail and scale depicted on
the cross-section plates. Variations in
hydraulic properties are present where
changes in lithologic properties occur within
formations or at formation contacts. Data
presented by Arthur and others (1995)
indicate that lower permeability lithologies
in the FAS have vertical hydraulic conductivity
values on the order of 10'4 feet/day, whereas
the more permeable rocks have vertical


hydraulic conductivity values on the order of
101- feet/day.


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