Potential for groundwater pollution of the Floridan Aquifer : based upon surficial drainage, karst development, and overburden characteristics

Potential for Groundwater Pollution

of the Floridan Aquifer,

Based Upon Surficial Drainage, Karst

Development, and Overburden Characteristics,

Explanatory Text,

Barry F. Beck

Much of Florida's land surface is karst: a landscape characterized by
sinkholes, sinking streams, caves, and large springs. The characteristics of
this topography determine the path of the water that recharges the Floridan
Aquifer, and the movement ofwaterwithin the aquifer. The nature of the karst
topography also controls the route by which contaminants may reach the
aquifer and pollute our valuable ground-water supply. Because Florida relies
on ground water for its water supply more than any other state-approximately
90% of the water used in Florida is ground water-it is critical that we
understand the nature of karst and how it controls the potential for ground-
water pollutionn,
Karst topography occurs in Florida because limestone and dolomite underlie
the entire state and often occur at or near the surface. The Floridan Aquifer
comprises thousands of feet oflimestone and dolomite (a similar and related
rock) of Tertiary age. The discussion which follows, and the accompanying
maps, relate particular to this aquifer and do not refer to karst features which
may be forming on the younger limestones which are important aquifers in
S South Florida.
Limestone and dolomite are distinctly more soluble than other rocks. Over
millions of years the limestone underlying Florida has been riddled with
cavities created by the dissolving action of ground water. Primary pores,joints,
faults, and bedding planes have all been enlarged by dissolution creating a
3 dimensional network of interconnecting cavities The upper portion (ca.
30-35') of the limestone is most intensely dissolved and thereby most
permeable This zone has been called the epikarsticzone(Williams, 1985),The
process of dissolution is slow and complex and the enlarged drainage paths
throughout the aquifer have developed over millions of years. The process of
solution itself is not causing any significant changes within man's time frame.

ENLARGED FISSURES
ORHKARREN

ENLARGED MASTER JOINT
DRAINS WATER TO DEEPER
AQUIFER

Figure 1 : Generalized cross-section of the upper portion of the limestone and the
overlying sediment: the epikarstic zone (modified from Williams, 1 985).

During the last two million years, the Floridan peninsula has been
alternately exposed to weathering above sea level, or submerged by the sea
and covered with sediment. Due to the recent deposition of marine sediments,
dominantly sand and clay, the limestone in Florida is generally not exposed
and the karst terrane is referred to as a mantled karst. Because of the recent
interaction of sea level fluctuations, marine sedimentation, and surficial
erosion, Florida's karst topography can behdivided into four geomorphic zones
(Figure 2).

In the thinly mantled zone the limestone generally is overlain by less than
25' of clayey confining beds overlain by- less than 25' Of surficial sand.
However, in a few areas within this zone the cover thickness may be much
greater (circa 100'). particularly beneath the Brooksville Ridge and in
Southern Pinellas County. Where a continuous confining layer is present, a
surficial aquifer occurs in the sands. Along the west coast, from Pasco to Levy
Counties, the limestone is nearly bare, being overlain by less than 25' of cover
sediments In total. In the northern half of the thinly covered zone the sands
may overlie the limestone directly with no hydrologic separation.
In the zone of intermediate cover thickness the overlying sediments are
generally more than 50 thick and in the thickly covered zone the overburden
generally exceeds 175'. The limestone aquifer is confined in both zones,
usually by more than 50' o.f clayey, low permeability Hawthorn Group
sediments which in turn are overlain by younger, surficial sands. The
Hawthorn sediments also protect the aquifer from the downward leakage of
surface pollutants. The sands overlying the Hawthorn form a perched surficial
aquifer which often contains water of poor quality.
Within the intermediate zone there are a fewscattered areas, too small to be
shown in Figure 2, where erosion has thinned or removed the cover and
artesian springs are found. The boundary between intermediate and thick
cover was selected as 1 75' because 97% of all new sinkholes in the Orlando
area occur in areaswhere the cover is less than 1 75' thick (Wilson and others,
1 988) Thus, the intermediate zone is an area of active karst collapse, whereas
in the thickly covered zone this problem rarely effects the land surface today.
It is the relationship between the unconsolidated, surficial sediment,
sinkholes, the epikarstic zone, and the deeper Floridan Aquifer which
determines the potential for ground-water pollution in many areas of Florida.
In the thinly covered zone, sinkholes are often open directly to the water table.
In the area west of Gainesville these are vertically-walled pits in the limestone
which expose the ground water in the bottom. These are known to geologists
as cenotes. In many other areas, such as along the west coast from Pasco to
Citrus Counties, a more-or-less funnel-shaped depression in the sand may
connect to an open shaft in the limestone, or the collapsed sand may cover up
the limestone. Where the water table is close to the land surface, such
sinkholes will be water-filled. On the other hand, if the water table is deeper,
such as in the area west of Ocala, small sinkholes may be dry, even when the
limestone can be seen in the bottom. Older, broad, shallow sinkhole basins are
often dry because they usually do not intercept the water table. However,
throughout the thinly covered zone it is obvious that any contaminated water
which is allowed to drain directly into a sinkhole will quickly reach the ground
water in the aquifer and degrade the quality of the potable water supply,
In the zones of intermediate and thick cover a cap of low permeability
Hawthorn sediment generally protects the Floridan (limestone) Aquifer from
direct infiltration from the surface. However, throughout most of these zones,
karstic collapses have punctured the protective cap of Hawthorn strata. The
large sinkhole basins and circular lakes common in this area may be ancient
karst features caused by repeated collapse and erosion. Even the larger (one
mile or more) irregular lakes are often formed from several sinkholes which
have coallesced. Beneath these basins a vertical channel of permeable
sediment interconnects the surficial sands and the Floridan Aquifer (see
Figure 3)

EvaporatiOn Wellwater
A" E oSupply
-- Run off -
"Sand T / _

Clayeya __ _
Confining t~nti
Strata S G~f~e -te.1z ekge--

-- -- -/ --

Floridan
Aquifer

ZONE OF THIN COVER

COVER

ZONE OF THICK COVER

VERY THICK COVER,
YOUNGER LIMESTONE
AT SURFACE

ZONE OF

A-A' CROSS SECTION

Figure 2: Generalized map and cross-section of zones of karst geomorphology, as
related to the Tertiary limestones in Florida.

Figure 3: Leakage through the bottom of a sinkhole lake in Florida.

At many localities younger sediments may have completely covered ancient
sinkholes or lakes, obscuring them from detection However, the permeable
column of collapsed sediments still perforated the Hawthorn confining layer
providing an avenue for groundwater pollution, and also making the site
susceptible to reactivated collapse. In the zone of intermediate cover, sinkhole
collapse is still occurring today, opening direct pathways to the aquifer
In fact. mans modification of the local hydrologic conditions maytrigger or
induce collapse. The rate of infiltration from the surficial aquifer depends on
the elevation difference between the shallow water table in the surficial sand
and the potetiometric surface of the underlying limestone (Floridan) aquifer
Any changes which increase the difference may trigger sinkholes. The
creation of lakes, percolation ponds, or retention basins will raise the shallow
water table. The withdrawal (pumping) of water from the Floridan Aquifer will
lower the potentiometric surface. Both types of activities can cause sinkhole
collapse Of course, sinkholes also collapse sporadically under purely natural
conditions as part of the ongoing erosion process.
In the thickly mantled zone along the east coast, modern collapses are rare,
although large, ancient sinkholes are present. These probably formed origi-
nally during periods when sea level was lower, and ground-water levels and
the base level of erosion were also correspondingly lower. The breaks through
the Hawthorn Group still constitute a potential avenue for ground-water
pollution, although the impact of these features has not been investigated.
Within the zone of intermediate cover, some areas occur where erosion has
locally thinned the cover and the artesian pressure causes ground water to
discharge upward from the limestone, forming spring runs and streams. These
areas of thin cover are too small to show n Figure 2 In Central Florida many
spring-fed streams flow eastward into the St Johns River. Although the
limestone is close to the land surface, pollution is not now a significant
problem because water is discharging from the aquifer. However, if the
potentiometric surface is'lowered, these areas could become recharge sites
with potential contamination problems.
Surface streams also flow in many areas of the intermediate and thickly
covered zones, where the shallow water table is higher than the poten-
tiometric surface and is recharging the Floridan Aquifer slowly through the
low permeability Hawthorn confining strata. However, if buried sinkholes are
present, these breaks provide more direct avenues for rapid recharge or
contamination.
In southern Florida the cover over the Tertiary limestones is so thick (app.
1 ,000') that surface drainage is generally normal and karst is not a significant
factor with respect to pollution of the Floridan Aquifer. However, karsti.
features are developing on the younger, near surface limestones which are the
major aquifer in southeastern Florida

In northern Florida, some of the surface drainage flows westward or
southward, from the intermediate zone onto the thinly mantled zone. Where
surface drainage flows onto an area where the limestone is unconfined, the
flow disappears underground into the limestone aquifer at discrete sinking
points: stream sinks, swallets or ponors (see Figure 4). Much of this
subterranean flow reappears on the thinly covered zone as springs feed i ng the
Suwannee, Withlacoochee, or Santa Fe Rivers. In fact, several of the major
rivers, such as the Santa Fe, St. Mark's, and Aucilla, themselves sink and
reappear. In the latter cases, where a major stream sinks and resurges a short
distance away, there may becaves conveying the flow directly between the
two points. However, in the case of the numerous smaller sinking streams and
the more distant springs, it is probable that this point recharge disseminates
into diffuse flow through the aquifer, later to converge at the spring. Any
contamination reaching these sinking streams will flow directly into the
aquifer and has the potential to contaminate ground-water supplies over a
broad area.
From the foregoing discussion it is obvious that karstic processes aid land
forms are complex and highly variable from one area to another. It is also
obvious that these processes are a critical factor in evaluating the pollution
potential of the Florida Aquifer and protecting our valuable ground-water
s5upplii es..

31P00'

Figure 4: Cross-section showing surface drainage sinking as it passes from the
intermediate (right side) to the thinly covered zone. The Steep change in elevation at the
boundary is called the Cody Scarp. Modified from Ceryak, 1977.

30000'

3000'

82000'

References Cited
Ceryak, R., 1977, Hydrogeology of a river basin in a karst terrain-Alapaha
River-Hamilton County, Florida: Suwannee R. Water Mgt Dist Inf. Circ.,
SeriesIC-5, 20 p.
Williams P.W., 1 985, Subcutaneous hydrology and the development of doline
and cockpit karst: ZeitchriftWfur Geomorphologie N F., Bd. 29, Heft 4, p.
463-482.
Wilson, W.L., McDonald, K.M., Barfus, B.L., and Beck, B.F., 1988, Hydro
geologic factors associated with recent sinkhole development in the
Orlando area, Florida: Florida Sinkhole Research Institute Rpt. 87088-4,
University of Central Florida, Orlando, 104 p.

86 00'

Sources of Map Data
This series of fourteen maps was prepared from published data only. The
topography and drainage were interpreted from the U.S.G S 71 2' topographic
quadrangle maps. The inform ion on the geology and hydrologyvwas summarized
from various State, Federal, local, and professional publications. The data was not
verified in the field.
In assembling such composite data from maps of various scales, some error is
bound to occur in the precise placement of the margins. Further, in assigning the
various geohydrologic settings to one of eleven categories, some subjective
decisions must be made because all areas will not fit into a category perfectly.
Therefore, the reader is cautioned to use these maps as a starting point only and
to conduct more specific local investigations to confirm the precise site data.
These maps were prepared by professionals with due care. However, the
Florida Sinkhole Research Institute makes no warranty, express or implied, as to
the absolute validity of the data.

29000'

ADDITIONAL INFORMATION ON KARST IN FLORIDA
Beck, B.F., 1984, Sinkholes. Their geology, engineering and environmental
impact: Proceedings of the First Multidisciplinary Conference on
Sinkholes, Orlando Florida,: Rotterdam, Netherlands, A.A. Balkema,
Publisher, 429 p.
Beck,B.F.T, Ceryak R., Jenkins, D.T., Scott T.MN, and Spangler, D0P., 1985,
Karst hydrogeology of central and northern Florida: Rpt. 85-86-1 ,Florida
Sinkhole Research Institute, University of Central Florida, Orlando, 46 p.
Beck, B.F. and Sinclair, W.C., 1985, Sinkholes in Florida: an introduction Rpt.
85-86-4, Florida Sinkhole Research Institute, University of Central Florida
Orlando, 16 p.
Beck, B.F. and Wilson, W.L., 1 987, Karst hydrogeology. Engineering and
environmental applications: Proceedings of the Second Mivultidisciplinary
Conference on Sir'holes and the Environmental Impacts of Karst,
Orlando, Florida: Rotterdam, Netherlands, A.A. Balkema, Publisher, 429 p
Sinclair, VWVC 1982, Sinkhole development resulting from ground-water
withdrawal in the Tampa area, Florida: U:.S Geological Survey Water
Resources Investigations Rpt 81-50, 19 p.
Sinclair, W.C., Stewart, J W., Knutilla, R.L., Gilboy, A.E., and Miller, R.L, 1985,
Types of features and occurrence of sinkholes in the karst of west-central
Florida U.S. Geological Survey Water Resources Investigations Rpt. 85-
4/26..81 p.
Wilson, W.L., and Beck, B.F., 1 988, Evaluating sinkholes hazards in mantled
karst terrane, in N.Sitar (ed.) Geotechnical Aspects of Karst Terrains,
Geotechnical Special Publication No. 14, ASCE, New York, NY, p. 1-24.

7~---T

JACKSONVILL
No. 4 of 14 Sheets ir

v 1

APALACHICO
No. 5 of 14 Sheets

local, anc

Figure 3: Leakage through the bottom of a sinkhIolelake in Florida.

due care.
express c

At many localities younger sediments may have comp letelycovered ancient
sinkholes or lakes, obscuring them from detection. However, the permeable
column of collapsed sediments still perforates the Hawthtorrn confining layer
providing an avenue for groundwater pollution, and also making the site
susceptible to reactivated collapse: In the zone of intermediate cover, sinkhole
collapse isNstill occurring today, opening direct pathways to the aquier.
Inhfact, man's modificaion of the local hydirologic conditions nmay trigger or
induce collapse. The rate of infiltrationhfrom the surficial aqufer depends on
the elevation difference between theshallow water table in the surficial sanid
and the potetiormetric surface of the underlying limestone (Floridan) aquifer.
Any changes which increase the difference may trigger sinkholes. The
creation of lakes, percolation ponds, or retention basins will raise the shallow
water table. The withrawal(pumping) of water from the Floridan Aquifer will
lower the potentiometric surface. Both types of activities can cause sinkhoe
collapse. Of course, sinkholes also collapse sporadically under purely natural
conditions as part of the ongoing erosion process.
In the thickQlymantledpzone along the east coast, modern collapses are rare,
although large, ancient sinkholes are present These probably formed origi-
nallydurirng periods when sea level-was lower, and ground-water levels and
the base level oferosionvvere also correspondinglylower. The bralks though
the Havvthorn Groupstill constitute a potential avenue for ground-water
pollution, although the impact of thesefeatmures has notbeen investigated.
Within the zone of intermdiae cover some areas occur where erosionhas
lo-cally thinned the cover and te artesian pressue causes ground water to
discharge upwardnohmonthelimestone, forming spring runs and streasThese
areas of tbhn cover are too small to sh ow in Figure 2. I n Ce ntral Florida many
spring-fed streams flow eastward into the St. Johns Rivefr.Althlugh the
limestone is close to the land surface, pollution is not now a significant,
-problem because water is discharging from the aquifer However, if the
potentiometrec surface is lowered, these areas could become rechargesites.
with potential contamination problems.
Surface streams alsohflow in many areas ofOtheointernmeiiate and thickly
covered zones, where the shallow water tabie is higher than thmepoten-
tijometric surface and is recharging the Floridan Aquifer slowly through the
low permeablinty Hawthorn confining strata.However, if buried sinkholes are
present, these breaks provide -nmore direct avenues- for rapid recharge or
contamination.
In southern Florida theGcover over the Tertiary limestornes is so thick (app
1,001') thatsurface drainage is generally normal and karst is not a significant
factor"with respect to pollution of the Florndan Aquifer. However, karstic
features are developing on the younger, near surfaceli mestonesMwhich are the
major aquifers in southeastern Florida,

ADDITIONAL INFORMATION ON KARST IN FLORIDA
Beck, B.F., 1984, Sinkholes: Their geology, engineering and environmental
impact: Proceedinigs of the First Multidisciplinary Con-feren~ce on)
Sinkholes, Orlando, Florida,: Rotterdam, Netherlandrs.A.A. Balkema,
Pubi sher, 412 9 p.
;\Beck, B.,F., Ceryak R.,:JenkSD:T.,'SctT.,andSp e19
K arst hydrogeoQogy of central andnorthern Florida. Rpt. 85-86-1, Florida
Sinkhole Research Institute, University of Central Florida, Orlando, 46 p
Beck, B.F. and Smclair,WC, 1985. Sinkh^olesin Florida: an introduction: Rpt.
85-86-4, Florida Si nkhole Research Instit.ute, Universityof Cenral Florida,
Orlando, 1 ;6 p.
Beck,,B.F. and Whilsorn, W.L., 1987, Karst hydrogeology:Engineering and
environmental applications: Proceedings of the SeconidMultidisci^plnry
Conference on Sinklholes and the Environmentaln Impac ts of Karst,
Orlando, Florida: Rotterdam, Netherlands, A.A, Balkema, Publsher,429 p.
SSinclair, W.C., 1 982, Sinkhole development resulting from ground-water
withdrawals in the Tampa area, Florikda: U.S. Geological Survey Water
Resources Investigaations Rpt 81-50, 19 p.
Sinclair,WW.C. SewartJ.wiKnutil1aR L.,GilboyA.E ,andMiller,R L., 1985,
Types of features and occurrence of sinkholes in the karst of west-central
Florida: U.S. Geological Survey:Water Resources InvestigatiohnsRpt. 85-
4 2 6. 8 1 p.
WilsonV W;L. and Beck, B FP., 1988, Evaluating sinkholes hazards in mrantled-
karst terrane, in N. Sitar led.) Geotechnical Aspects of: KarstTerrains,
Geotechnical Special Pulblication No. 14, ASC(;ENewYork, NY, p. 1 -24.

)m the
n at the

Floridan
Aquifer

VERY THICK COVER,
YOUNGER LIMESTONE-----
AT SURFACE

ZONE OF

THIN
COVER

INTERMEDIATE
COVER

THICK
COVER

LOOSE
--SANDj

CLAYEY
HAWTHORNE STRATA

A-A'

Figure 2
related t

I

~4..

ENLARGED FISSURES
OR KARREN.

oc~~

~

Figure 4: Cross-section showing surface drainage sinking as it passes from the
intermediate (rightside) to the thinly covered zone. The steep change in elevation atthe
boundary is called the Cody Scarp. Modified from Ceryak, 1977.

0

NARROW FRACTURES_
iMPEDE INFILTRAT|OrF

karstic coll
large sinkh
karst featu

es have
basins
caused

DRAINS WATER TO
AQUIFER

Figure 3: Leakage through the bottom of a sinkhole lake in Florida.

ZONE OF

A A' CROSS SECTION

Figure 2: Generalized map and cross-section of zones of karst geomorphology, as
related to the Tertiary limestones in Florida.

At many localities younger sediments may have completely covered ancient
sinkholes or lakes, obscuring them from detection. However, the permeable
column of collapsed sediments still perforates the Hawthorn confining layer
S providing an avenue for groundwater pollution, and also making the site
susceptible to reactivated collapse. In the zone of intermediate cover, sinkhole
collapse is still occurring today, opening direct pathways to the aquifer.
S In fact, man's modification of the local hydrologic conditions may trigger or
induce collapse. The rate of infiltration from the surgical aquifer depends on
theelevation difference between the shallow water table in the surficial sand
and the potetiometric surface of the underlying limestone (Floridan) aquifer.
Any changes which increase the difference may trigger sinkholes. The
creation of lakes, percolation ponds, or retention basins will raise the shallow
water table. The withdrawal (pumping) of water from the Floridan Aquifer will
lower the potentiometric surface. Both types of activities can cause sinkhole
collapse. Of course, sinkholes aNso collapse sporadically under purely natural
conditions as part of the ongoing erosion process.
In the thickly mantled zone along the east coast, modern collapses are rare,
although large, ancient sinkholes are present These probably formed origi-
nally during periods when sea ievel was lower, and ground-water levels and
the base level of erosion were also correspondingly lower The breaks through
Sthe Hawthorn Group still constitute a potential avenue for ground-water
pollution, although the impact of these features has not been investigated.
... Within the zone of intermediate cover, some areas occur where erosionhas
locally thinned the cover and the arteSian pressure causes ground water to
discharge upwardfrom the limestone, forming spring runs and streams. These
areas ofthin cover are too small to show in Figure 2 inCentral Florida many
spring-fed streams flow eastward in0to the St. Johns River. Although the
limestone is close to the land surface, pollution is not now a significant
problem because water is discharging from the aquifer. However, if the
potentiometric surface is lowered, these areas could become recharge sites
with potential contamination problems.
Surface streams alsoflowin many areas of the intermediate and thickly
covered zones, where the shallow water table is higher than the poten-
tiometric surface and is recharging the Floridan Aquifer slowly through the
low permeability Hawthorn confining strata. However, if buried sinkholes are
present, these breaks provide more direct avenues for rapid recharge or
contamination.
In southern Florida the cover over the Tertiary limestones is so thick (app.
1, 000) that surface drainage is generally normal and karst is not a significant
factor with respect to pollution of the Floridan Aquifer. However, karstic
features are developing on the younger, near surface limestones which are the
major aquifers in southeastern Florida.

References Cited
Ceryak, R., 1977, Hydrogeology of a river basin in a karst terrain--Aapaha
River Hamilton County, Florida: Suwannee R. Water Mgt. Dist. Inf Circ.,
Series IC-5, 20 p.
Williams P.W., 1 985, Subcutaneous hydrology and the development of doline
and cockpit karst: Zeitchrift fur Geomorphologie N.F., Bd 29, Heft 4, p
463-482.
Wilson, W.L., McDonald, K.M., Barfus, B.L., and Beck, B.F., 1988, Hydro-
geologic factors associated with recent sinkhole development in the
Orlando area, Florida: Florida Sinkhole Research Institute Rpt. 87-88-4,
University of Central Florida, Orlando, 104 p.

Sources of Map Data
This series of fourteen maps was prepared from published, data only. The
topography and drainage were interpreted from the U.S G.S. 712' topographic
quadrangle maps. The information on the geology and hydrologywassummarized
from various State, Federal, local, and professional publications. The data was not
verified in the field.

In assembling such composite data from maps of various scales, some error is
bound to occur in the precise placement of the margins. Furtherinassigning the
various geohydrologic settings to one of eleven categories, some subjective
decisions must be made, because all areas will not fit into a category perfectly.
Therefore, the reader is cautioned to use these maps as a starting point only, and
to conduct more specific local investigations to confirm the precise site data

These maps were prepared by professionals with due care, However, the
Florida Sinkhole Research Institute makes no warranty, express or implied, as to
the absolute validity of the data.

ADDITIONAL INFORMATION ON KARST IN FLORIDA
Beck, B F., 1984, Sinkholes: Their geology, engineering and environmental
impact: Proceedings of the First Multidiscplinary Conference on
Sinkholes, Orlando, Florida, Rotterdam, Netherlands, A.A Balkema,
Publisher, 429 p.
Beck, BYF.Ceryak R., Jenkins, D.TA, Scott, T.M., and Spangler, D.P., 1985,
Karst hydrogeology of central and northern Florida: Rpt. 85-86-1, Florida
Sinkhole Research Institute, University of Central Florida, Orlando, 46p.
Beck, B.F. and Sinclair, W.C., 1985, Sinkholes in Florida: an introduction: Rpt.
85-86-4, Florida Sinkhole Research Institute, University of Centra! Florida,
Orlando, 1 6 p.
Beck, B.F. and Wilson, W.L., 1987, Karst hydrogeology: Engineering and
environmental applications: Proceedings of the Second Multidisciplinary
Conference on Sinkholes and the Environmental Impacts of Karst,
Orlando, Florida: Rotterdam, Netherlands, A.A. Balkemra, Publisher, 429 p.
Sinclair, W.C., 1982, Sinkhole development resulting from ground-water
withdrawal in the Tampa area, Florida: U.S. Geological Survey Water
Resources Investigations Rpt 81-50, 19 p.
Sinclair, W.C.,Stewart,J.W., Knutilla, R.L., Gilboy, A.E.,and Miller, R.L., 1985,
Types of features and occurrence of sinkholes in the karst of west-central
Florida: U.S. Geological Survey Water Resources Investigations Rpt 85-
4/26.81 p
Wilson, W.L., and Beck, B:F., 1988, Evaluating sinkholes hazards in mantled
karst terrane, in N. Sitar (ed,.) Geotechnical Aspects of Karst Terrains,
Geotechnical Special Publication No. 14, ASCE, New York, NY, p. 1-24.

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References Cited
Ceryak, R 1977, Hydrogeology of a river basin in a karst terrain-Alapaha
River-Hamnilton County, Florida: Suwannee R Water Mgt. Dist, inf. Circ.,
Series IC-5, 20 p.
Wilhlams P.W., 1985, Subcutaneous hydrology and the development of doline
and cockpit karst. Zeitchrift fur Geomorphologie N.F., Bd. 29, Heft 4, p.
463-482.
Wilson, W.L., McDornald, K.M., Barfus, B.I, and Beck, B.F., 1988, Hydro-
geologic factors associated cwlith recent sinkhole development in the
Orlando area, Florida Florida Sinkhole Research Institute Rpt. 87-88-4,
University of Central Florida, Orlando, 104 p.

Figure 1 : Generalized cross-section of the upper portion of the limestone and the
overlying sediment: the epikarstic zone (modified from'Williams, 1985).

Figure 3: Leakage through the bottom of a sinkhole lake in Florida.

ZONE OF

A-A' CROSS SECTION

Figure 2: Generalized map and cross-section of zones of karst geomorphology, as
related to the Tertiary limestones in Florida.

At many localities younger sediments may have completely covered ancient
sinkholes or lakes, obscuring them from detection. However, the permeable
column of collapsed sediments still perforated the Hawthorn confining layer
providing an avenue for groundwater pollution, and also making the site
susceptible to reactivatedcollapse.In the zoneof intermediate cover, sinkhole
collapse is still occurring today, opening direct pathways to the aquifer.
In fact, man's modification of the local hydrologic conditions may trigger or
induce collapse. The rate of infiltration from the surficial -aquifer depends on
the elevation difference between the shallow water table in the surficial sand
and the potetiometric surface of the underlying limestone (Floridan) aquifer.
Any changes which increase the difference may trigger sinkholes. The
creation of lakes, percolation ponds, or retention basins will raise the shallow
water table. The withdrawal (pumping) of water from the Floridan Aquifer will
lower the potentiometric surface. Both types of activities can cause sinkhole
collapse. Of course, sinkholes also collapse sporadically under purely natural
conditions as part of the ongoing erosion process.
In the thickly mantled zone along the east coast, modern collapses are rare,
although large, ancient sinkholes are present. These probably formed origi-
nally during periodsMwhen sea level was lower,)and ground-water levels and
thebase level of erosionwere also correspondingly lower.1Thebreaks through
the Hawthorn Group still constitute a potential avenue for ground-water
pollution, although the impact of these features has not been investigated.
Within the zone of intermediate cover, some areas occur where erosion has
local ly thinned the cover and the artesian pressure caUuses ground water to
discharge upward from the limestone, forming spri ng runs and streams. These
areas of thin cover are too small to show in Figure 2. In Central Florida many
spring-fed streams flow eastward into the St. Johns River. Although the
limestone is close to the land surface, pollution is not now a significant
problem because water is discharging from the aquifer. However, if the
potentiometric surface is lowered, these areas could become recharge sites
with potential contamination problems.
Surface streams also flow in many areas of the intermediate and thickly
covered zones, where the shallow water table is higher than the poten-
tiometric surface and is recharging the Floridan Aquifer slowly through the
low permeability Hawthorn confining strata. However, if buried sinkholes are
present, these breaks provide more direct avenues for rapid recharge or
contamination.
In southern Florida the cover over the Tertiary limestones is so thick (app.
1,000') that surface drainage is generally normal and karst is nrot a significant
factor with respect to pollution of the Floridan Aquifer. However, karstic
features are developing on the younger, near surface limestones which are the
major aquifers in southeastern Florida.

Sources of Map Data-

This series of fourteen maps was prepared from published data only. The
topography and drainage were interpreted from the U.S.G.S. 7 topographic
quadranglemaps. The information on the geology and hydrology was summarized
from various State, Federal, local, and professional publications. The data was not
verified in the field.

In assembling such composite data from maps of various scales, some error is
bound to occur in the precise placement of the margins. Further, in assigning the
various geohydrologic settings to one of eleven categories, some subjective
decisions must be made, because all areas will not fit into a category perfectly.
Therefore, the reader is cautioned to use these maps as a starting point only, and
to conduct more specific local investigations to confirm the precise site data.

These maps were prepared by professionals with due care. However, the
Florida Sinkhole Research Institute makes no warranty, express or implied, as to
the absolute validity of the data.

ADDITIONAL INFORMATION ON KARST IN FLORIDA
Beck, B.F., 1984, Sinkholes: Their geology, engineering and environmental
impact: Proceedings of the First Multidisciplinary Conference on
Sinkholes, Orlando, Florida,: Rotterdam, Netherlands, A.A. Balkema,
Publisher, 429 p.
Beck, B.F., Ceryak R., Jenkins, D.T., Scott, T.M., and Spangler, D.P., 1985,
Karst hydrogeology of central and northern Florida: Rpt. 85-86-1 Florida
Sinkhole Research Institute, University of Central Florida Orlando, 46 p.
Beck, B.F. and Sinclair, W.C., 1985, Sinkholes in Florida: an introduction: Rpt.
85-86-4, Florida Sinkhole Research Institute, University of Central Florida,
O rlando, 16 p.
Beck, B.F. and Wilson, W.L., 1987, Karst hydrogeology. Engineering and
environmental applications: Proceedings of the Second Multidisciplinary
Conference on Sinkholes and the Environmental Impacts of Karst,
Orlando, Florida: Rotterdam, Netherlands, A.A. Balkema, Publisher, 429 p.
Sinclair, W.C., 1982, Sinkhole development resulting from ground-water
withdrawal in the Tampa area, Florida: U.S. Geolog ical Survey Water
Resources Investigations Rpt 81-50, 119 p,
SirclairW.C.,Stewart,J.W.,Knutilla,R.L.,GilboyA.E., and Miller, R.L., 1985,
Types of features and occurrence of sinkholes in the karst of west-central
Florida: U.S. Geological Survey Water Resources Investigations Rpt. 85-
4/26. 81 p..
Wilson,W.L., and Beck, B.F., 1988, Evaluating sinkholes hazards in mantled
karst terrane, in N. Sitar (ed.) Gieotechnical Aspects of Karst Terrains,
Geotechnical Special Publication No. 14, ASCE, NewYork, NY, p. 1-24.

5

84 00. 2lAOO OOOOmE

)000 FEET *N(

.PRODUCED BY THE 1) S;GOLOCOI'C.AI SURVEY AND .THE NATIONAL
O.0FEAN: SURVEY, .' *" /. :
Base map. prepared by the De~fe~nse Mappng .Agency from raps dated
*I.947-48, NQ.S carts dated 1953, and aerail photographers taken 194.9-50
'Photographs field checked 195.4, Revised by .the U. Geological Survey
-fro~m aeia I .photogrnp ps tae 974 an o there source data Revised i Uonfra-
,tin not field checked Map edited 1975 ,'. ;*"*.*'
'Bathymetry, comipiled, by the; NationalU Oca Survey f romtde- oordiated
*hydrograpflc surveys Batby hetr c survey data. corrply wit Internato a
HMydrographlie Organization 'IHO.) Special.Pubricaton 44 acrura'c y t a dids
and/or standards .used, at the datea of the surv y..This inform ation; Is o
intendedU for navigationaI purpose's;
Mean .low water, (dotted) ,!rea ad mear high'water (solid) I ie compileo by:
N.OS..ron .tie-coordinated aerial photographs
.Offsh re protrac tion surely data, shownt i red, oixpildo by the Bu~reau of
Land Managemet;o Heavy hies indicate limits 'of DLV ;0ut'r r C of int
Shelf Protraucor 0 iagram dated January 27, 1976. The. prctrarte hs.o t this
mrap are not for Federalo fleai purposes; for soch purposes refer to fhe UfCS
.Official Protractinn Diagrars eaailable from the: Du~re'a of.'Land Mo anae

Transverse Mer at r Proje ction 1.0,POO-meter Uni~versal Transverse Mer-
cator grid,"zone 1.7 100,0.00-foot grid ticks based on Florida coordinate
.system, rorth: west, and east zoles 192.7 North Amverian Datumt Toplace
on the predicted N-ortt American Dafur 1983 onve the project ion 'ie 2.3
.meters .south' and 14 neters west- .' .*: . .
SLocatior of geodeti control estabished by governmenttagencies is 5' nro br
.orre~soondrng .l25.0 000-seal'e .Geodetic Crntrol Diagram.* :
There mae be private inholdingswithirnth~e bbudaries of the National or State
r servations shown on this map. '..

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ACES

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WCTURES
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I

ENLARGED FISSURES
OR KARREN

ENLARGED VIEW OF
DISSOLVED FRACTURES
(KARREN) WITH COVER

Potential for Groundwater Polltion

of the Floridan Aquifer,

Based Upon Surficial Drainage, Karst
Development, and Overburden Characteristics,

Explanatory Text

Barry F. Beck

Much of Florida's land surface is karst: a landscape characterized by
sinkholes, sinking streams, caves, and large springs. The characteristics of
this topography determine the path of the water that recharges the Floridan
Aquifer, and the movement of water within the aquifer. The nature of the karst
topography also controls the route by which contaminants may reach the
aquifer and pollute our valuable ground-water supply. Because Florida relies
on ground water for its water supply more than any other state--approximately
90% of the water used in Florida is ground water-it is critical that we
understand the nature of karst and how it controls the potential for ground-
water poHution.
Karsttopography occurs in Florida because limestone and dolomite underlie
the entire state and often occur at or near the surface. The Floridan Aquifer
comprises thousands of feet of limestone and dolomite (a similar and related
rock) of Tertiary age. The discussion which follows, and the accompanying
maps, relate particularytothis aquifer and do not refer to karst features which
may be forming on the younger limestones which are important aquifers in
South Florida.
Limestone and dolomite are distinctly more soluble than other rocks Over
millions of years the limestone underlying Florida has been riddled with
cavities created bythe dissolving action of groundwater. Primary pores, joints,
faults, and bedding planes haveall. been enlarged by dissolution creating a
30dimensional network of interconnecting cavities. The upper portion (ca.
30-35') of the limestone is most intensely dissolved and thereby most
permeable. This zone has been called theepikarstic zone (Williams, 1985). The
process of dissolution is slow and complex and the enlarged drainage paths
throughout the aquifer have developed over millions of years, The process of
solution itself is not causing any significant changes within man's time frame.

ENLARGED MASTER JOINT
DRAINS WATER TO DEEPER
AQUIFER

Sand

Figure 1: Generalized cross-section of the upper portion of tne limestone and the
overlying sediment: the epikarstic zone (modified from Williams, 1 985).

A-A' CROSS SECTION

Figure 2: Generalized map and cross-section of zones of karst geomorphology, as
related to the Tertiary limestones in Florida.

Clayey
Confining
Strata

Floridan
Aquifer

Figure 3: Leakage through the bottom of a sinkhole lake in Florida.

At many localities younger sediments may have completely covered ancient
sinkholes or lakes, obscuring them from detection. However, the permeable
column of collapsed sediments still perforates the Hawthorn confining layer
providing an avenue for groundwater pollution, and also making the site
susceptible to reactivated collapse. In the zone of intermediate cover, sinkhole
collapse is still occurring today, opening direct pathways to the aquifer.
In fact, man's modification of the local hydrologic conditions may trigger or
induce collapse. The rate of infiltration from the surficial aquifer depends on
the elevation difference between the shallow water table in the surficial sand
and the potetiometric surface of the underlying limestone (Floridan) aquifer.
Any changes which increase the difference may trigger sinkholes. The
creation of lakes, percolation ponds, or retention basins will raise the shallow
water table. The withdrawal (pumping) of water from the Floridan Aquifer will
lower the potentiometric surface. Both types of activities can cause sinkhole
collapse. Of course, sinkholes also collapse sporadically under purely natural
conditions as part of the ongoing erosion process.
In the thickly mantled zone along the east coast, modern collapsesare rare,
although large, ancientsinkholes are present. These probably formed origi-
nally during periods when sea level was lower, and ground-water levels and
the base level of erosion were also correspondingly lower. The breaks through
the Hawthorn Group still constitute a potential avenue for ground-water
pollution, although the impact of these features has not been investigated.
Within the zone of intermediate cover, some areas occur where erosion has
locally thinned the cover and the artesian pressure causes ground water to
discharge upward from the limestone, forming spring runs and streams These
areas of thin cover are too small to show in Figure 2. In Central Florida many
spring-fed streams flow eastward into the St. Johns River. Although the
limestone is close to the land surface, pollution is not now a significant
problem because water is discharging from the aquifer. However, if the
potentiometric surface is lowered, these areas could become recharge sites
with potential contamination problems.
Surface streams also flow in many areas of the intermediate and thickly
covered zones, where the shallow water table is higher than the poten-
tiometric surface and is recharging the Floridan Aquifer slowly through the
low permeability Hawthorn confining strata. However, if buried sinkholes are
present, these breaks provide more direct avenues for rapid recharge or
contamination.
In southern Florida the cover over the Tertiary limestones is so thick (app.
1 ,00Ou') that surface drainage is generally normal and karst is not a significant
factor with respect to pollution of the Floridan Aquifer. However, karstic
features are developing on the younger, near surface limestones which are the
major aquifers in southeastern Florida.

During the last two million years, the Floridan peninsula has been
alternately exposed to weathering above sea level, or submerged by the sea
and covered with sediment. Due to the recent deposition ofmarine sediments,
dominantly sand and clay, the limestone in Florida is generally not exposed
and the karst terrane is referred to as a mantled karst. Because of the recent
interaction of sea level fluctuations, marine sedimentation, and surficial
erosion, Florida's karst topography can be divided into four geomorphic zones
(Figure 2).

In the thinly mantled zone the limestone generally is overlain by less than
25' of clayey confining beds overlain by less than 25' of surficial sand.
However, in a few areas within this zone the cover thickness may be much
greater (circa 100'), particularly beneath the Brooksville Ridge and in
Southern Pinrielas County.Where a continuous confining layer is present, a
surficial aquifer occurs in the sands. Along the westcoast, from Pasco to Levy
Counties, the limestone is nearly bare, being overlain by less than 25' of cover
sediments in total. In the northern half of the thinly covered zone the sands
may overlieVthe limestone directly with no hydrologic separation.
In the zone of intermediate cover thickness the overlying sediments are
generally more than 50' thick and in the thickly covered zone the overburden
generally exceeds 175'. The limestone aquifer is confined in both zones,
usually by more than 50' of clayey, low permeability Hawthorn Group
sediments which in turn are overlain by younger, surficial sands. The
Hawthorn sediments also protect the aquifer from the downward leakage of
surface pollutants. The sands overlying the Hawthorn form a perched surficial
aquifer which often contains water of poor quality.
Within the intermediate zone there area few scattered areas,:too small to be
shown in Figure 2, where erosion has thinned or removed the cover and
artesian springs are found. The boundary between intermediate and thick
cover was selected as 175' because 97% of all new sinkholes inWthe Orlando .
area occur in areas where the cover is less than 1 75 thick (Wilson and others,
1 988). Thus, the intermediate zone is an area ofactive karst collapse, whereas
in theiphickly covered zone this problem rarely effects the land surface today.
It is the relationship between the unconsolidated, surficial sediment,
sinkholes the epikarstic zone, and the deeper Floridan Aquifer which
determines the potential for ground-water pollution in many areas of Florida.
In the thinly covered zone, sinkholes are often open directly to the water table.
In the area west of Gainesville these are vertically-walled pits in the limestone
which expose the ground water in the bottom. These are known to geologists
as cenotes. In many other areas, such as along the west coast from Pasco to
Citrus Counties, a more-or-less funnel-shaped depression in the sand may
connect to an open shaft in the limestone, or the collapsed sand may cover up
the limestone Where the water table is close to the land surface, such
sinkholes will be water-filled. On the other hand, if the water table is deeper,
such as in the area west of Ocala, small sinkholes may be dry, even when the
limestone can be seen in the bottom. Older, broad, shallowsinkhole basins are
often dry because they usually do not intercept the water table. However,
throughout the thinly covered zone it is obvious that any contaminated water
which is allowed to drain directly into a sinkhole will quickly reach the ground
water in the aquifer and degrade the quality of the potable water supply.
In the zones of intermediate and thick cover a cap of low permeability
Hawthorn sediment generally protects the Floridan (limestone) Aquifer from
direct infiltration from the surface. However, throughout most of these zones,
karstic collapses have punctured the protective cap of Hawthorn strata. The
large sinkhole basins and circular lakes common in this area may be ancient
karst features caused by repeated collapse and erosion. Even the larger (one
mile or more) irregular lakes are often formed from several sinkholes which
have coallesced. Beneath these basins a vertical channel of permeable
sediment interconnects the surficial sands and the Floridan Aquifer (see
Figure 3).

Figure 4: Cross-section showing surface drainage sinking as it passes from the
intermediate (right side) to the thinly covered zone. The steep change in elevation at the
boundary is called the Cody Scarp. Modified from Ceryak, 1977.

References Cited
Ceryak, R., 1977, Hydrogeology of a river basin in a karst terrain-Alapaha
River-Hamilton County, Florida: Suwannee R. Water Mgt. Dist Inf. Circ
Series IC 5, 20 p.
Williams P.W., 985, Subcutaneous hydrology and the development of doline
and cockpit karst Zeitchrift fur Geomorphologie N.F., Rd 29, Heft 4, p.
463-482.
Wilson, W.L\, McDonald, K M., Barfus, B.L, and Beck, B.F., 1988, Hydro-
geologic factors associated with recent sinkhole development in the
Orlando area, Florida: Florida Sinkhole Research Institute Rpt. 87-88-4,
University of Central Florida, Orlando, 104:p.

Sources of Map Data
This series of fourteen maps was prepared from published data only. The
topography and drainage were interpreted from the U.S.G.S. 712 topographic
quadrangle [naps. The information on the geology and hydrologywas summarized
from various State, Federal, local, and professional publications. The data was not
verified in the field.

In assembling such composite data from maps of various scales, some error is
bound to occur in the precise placement of the margins. Further, in assigning the
various geohydrologic settings to one of eleven categories, some subjective
decisions must be made, because all areas will not fit into a category perfectly.
Therefore, the reader is cautioned to use these maps as a starting point only, and
to conduct more specific local investigations to confirm the precise site data
These maps were prepared by professionals with due care. However, the
Florida Sinkhole Research Institute makes no warranty, express or implied, as to
the absolute validity of the data.

ADDITIONAL INFORMATION ON KARST IN FLORIDA
Beck, B.F., 1 984, Sinkholes: Their geology, engineering and environmental
impact: Proceedings of the First Multidisciplinary Conference on
Sinkholes, Orlando, Florida; Rotterdam, Netherlands, A.A Balkema,
Publisher, 429 p.
Beck, B.F., Ceryak R., Jenkins, D.T., Scott, T.M., and Spangler, O.P., 1985,
Karst hydrogeology of central and northern Florida: Rpt 85-86-d, Florida
Sinkhole Research Institute, University of Central Florida, Orlando, 46 p.
Beck, B.F. and Sinclair, W.C., 1 985, Sinkholes in Florida: an introduction: Rpt.
85-86-4, Florida Sinkhole Research Institute, University of Central Florida,
Orlando, 1 6 p.
Beck, B.F. and Wilson, W.L, 1987, Karst hydrogeology: Engineering and
environmental applications: Proceedings of the Second Multidisciplinary
Conference on Sinkholes and the Environmental Impacts of Karst,
Orlando, Florida: Rotterdam, Netherlands, A.A. Balkema, Publisher, 429 p.
Sinclair, W.C., 1982 Sinkhole development resulting from ground-water
withdrawal in the Tampa area, Florida: U.S. Geological Survey Water
Resources Investigations Rpt. 81-50, 19 p
Sinclair, W.C., Stewart, J.W., KnutiIa, R.L, Gilboy, A E., and Miller, R.L, 1985,
Types of features and occurrence of sinkholes in the karst of west-central
Florida: U.S. Geological Survey Water Resources Investigations Rpt 85-
4/26. 81 p.
Wilson, W.L and Beck, B.F., 1988, Evaluating sinkholes hazards in mantled
karst terrane, in N. Sitar (ed.) Geotechnical Aspects of Karst Terrains,
Geotechnical Special Publication No. 14, ASCE, New York, NY, p. 1-24.

In northern Florida, some of the surface drainage flows westward or
southward, from the intermediate zone onto the thinly mantled zone. Where
surface drainage flows onto an area where the limestone is unconfined, the
flow disappears underground into the limestone aquifer at discrete sinking
points: stream sinks, swallets or ponors (see Figure 4). Much of this
subterranean flow reappears on the thinly covered zone as springs feeding the
Suwannee, Withlacoochee, or Santa Fe Rivers In fact, several of the major
rivers, Such as the Santa Fe, St. Mark's, and Aucilla, themselves sink and
reappear. In the latter cases, where a major stream sinks and resurges a short
distance away, there may be caves conveying the flow directly between the
two points. However, in the case of the numerous smaller sinking streams and
the more distant springs, it is probable that this point recharge disseminates
into diffuse flow through the aquifer, later to converge at the spring. Any
contamination reaching these sinking streams will flow directly into the
aquifer and has the potential to contaminate ground-water supplies over a
broad area.
From the foregoing discussion it is obvious that karstic processes and land
forms are complex and highly variable from one area to another. It is also
obvious that these processes are a critical factor in evaluating the pollution
potential of the Florida Aquifer and protecting our valuable ground-water
supplies

BC 'I
H(A- (
V t~.L, (

ZONE OF

.0010

10 110
010

1010

I AL

Cr w

IrI

1 10

Potential for Groundwater Pollution

of the Floridan Aquifer,

Based Upon Surficial Drainage, Karst

Development, and Overburden Characteristics.

Explanatory Text

Barryv F. Beckk

Iijuch of Florida s land surface is fIar'sr a lar;asc:ape Charactermzed by,'
sinkholes sti-rrkinq streams caves, and la-ge sprnqgs The characteristic. '.I
this topography determine -l(he path of the water that recharges the Floccdanr
Aquifer and the movement of water within he a3Lquier The nature of rhe kars!
topography also controls the route v A hich ,[ontarinants may reach the
aquifer and polluh'e our valuable ground-water supply Because Florida :elies
on grcu d tcri -.aier for ts water :.u.pplv more than any othPr slatl- -pproxrnatelv
90'.: o) the walet used in FlormicJ 5. grouncitra waer- ir it, critical that w v
understand trhe nature of I arst and hcow i. controls the porter iial ior .cround-
wAjter p0ILtcirin
Karsi topiographv )ccJurs in Forida bec ads'- iriesione arnd dolomite underlie
the entire state a, nd,.I oieic ocnccr 3v or near iih-- surface Th'- Floridan ,.quilfter
corDrise's i.hoius-aids. of feet oft lin mestone and dolomite ia similar rind el-led
rcckh o Tertmar\ age The discu'flson which follow,.v. ,nd the accoiri panying
marps, relate pa;ticulary to o his aqJuifer and djo rnot re-ter io F aSt tfeatj ies \Vhich-
may be tfcrmring on the ycOLinqer i-nes;ornes whvvich are important aquifers in
South Florlda
Linestiori.-e ad doloIn-,- are i ::,tir,-,.' 'inore .oiuf ',le than oili-er rct'L5 Ove,
iml :- ,ii 'o ',- 3' lie lirnestione underlying rIJ Flionrida lis -, eeni rid led w l--i
ca'-.ties created hb, thir.- di .I SolL1nq aci[cfrhr t Jr)Lound .'ai. r. Priniar,' por-s oltnms
faimu ;. anr.l wedding plnets have all ieeri e ilar.:iedi l.y I s.Eoii.5 ition i l :r-ating-i
3.-dimrt-tisioni.i- neitwtrk of r tIIerh-'rnercitr-Q.q cavties Thie upper pori-,:r !ca.
" -- r c f f the lm'.-=.to-r.e.. is. rn i.-,i iiist iv ifs -Ol eT ai, d tht -Ib',c m-_.i
p(licrl'al:'ie rhis -r ,ie hrI lAb her canlerJ the ep ,.irsi' : zore.Vilim nism 1 9P615) Ti,:-
proces cii rmssouljtionr is .low and ,',r-,ipl,-,. -ncI inen -li.!ac qia% d drarnaqc e path'2
thi Oi 1_iJli':,i hli-e aq.i fel lihave irevelopted :,L I ?i ve m llcrii:. of v ear._z The uI',:. --;:, ,f
- i.oluiior itse- l rlno i urcic-irnq Il', sqiicf:'qtn [ if:!ati'4-n s V't.c irc m i ri-i s hime frarmi-'

ENLARGED FISSURES

ENLARGED VIEW OF
DISSOLVED FRACTURES
WARRENN) WITH COVER

ENLARGED MASTER JOINT
DRAINS WATER TO OEEPER
AQUIFFR

Figure 1 Gener.lized cras.s-section of the upper portion oi Ife limestone and the
overlying sediment. the epikarstic zone (modified from Willi3rtis, 1 981)

ZONE OF INTERMEDIATE____
COVER

ZONE OF THICK COVER.

VERY THICK COVER.
YOUNGER LIMESTONE
AT SURFACE

ZONE OF

A-A' CROSS SECTION

Figure 2. Generalized riArip and cross-sec tion of zones of koEst geomocrpholuog v, as
wilated to the Tertiary limestone in Floida

Liujril-, L [he lS't tv. o mri .iil \ears ilte Fi-ridari r:iiriular a has beei
CilIeiPinate1i iposied tc '/.'ere he-I nr4 aboi.,t sea level o' S, ii)-,iged b- ihe sea
and r over,-d wiih s, rnri e t r l I Due IC rhe iei: en[ depc.-,,t'ion ofl rmj,-rrire ;redri-.r- '
dof'rr[anrtl\ sa.i and c 'vy. t.h- ,i'n -S hm in i; V,-.rirl I.-a i ,enefE'all\ n'r t -1 'r"S. d
airid ith- kar;,I erra e 's refeired to a ic. anl.-..d k'.r:,.t B- eca[se- ':,f rh.- .-,ece."r'
nT, r':ric.r- n oi f "'-- .' level flul .'a.i na t.- ir .n [aiia ,ri.o anrid siurnii .31
-hI,.*:.r'* Firi ida s I.arst tc.p.:cji'a -\'iv .an.i t:e it,. 'I d t .d f r Qc o ,,r.iir,' r zi-?.
irFiqiir- 2l

Inr te mhinl'. ninzleu zone ihe limestone geneiall. ,is overlamr b\v le'_; l tia
`5' of caVey cirif;rnq beds 'overlain by less than 23 ,f surficial sa:id
Hc',wevet in a few .areas within this zone ithie. .tl,P\e' ihic.kries rnma be muI Lh
grei-ater (crca 1(0 i parrtc'.jlatlv Lieneath it,- ip Bi.'oks-ville Rodge rd II;
Sot'.ihern Pinellas :C'.-nr, '/Vhere a co- ininu-u-'. cu.fonf in .i la,,er is present a
surhicial aquifer occuJrs In irni sarnds. Along tie ,'.?st coast. Imrnm PasccO to Lev
Cnir.iies Iice lirneiorce is nearly / bare being -.ovet laini b',' !e's tihan 25 ot ccv-er
.sedirents i;n tol:ti In ltIe northern haIlf of the thitil covered zone the -ands
ma, o,',: rie t' p hi!T'e(rorEi directly vi'ch r io vdrroIlr._ sip-iratlrir
in th-e -one Qiif ini;errnediate cover thccl'rnEss 'he cverlyring sedimner'ls are
generally moire I han '' thiclk and in the t.hickl iv cov'ere'.! ;cin-e the ove ci.irl.e-
geri eralI,, exc-eds 1 75 Tr-e limnestorne aquiter i. confined in both zcnes.
usi.iaivliv br nore iiihan 50' of cla'ey i cv permeabili'y Haw:l-horn ,Gr)upj
seciri;'ent. wh"icl in turn r ii-) overiain by -unger. sUrficial sarnds The:-
Hawthorn sediments s pr:sLi teil the aqLI'er fron- i tthe d'cvrnward Ir-aF,age of
sLirlace polhit aril'S The sands overiying ihe iHaw-ih.: rn c' m a perched s .irfic, i31
aquifer which ,fifen contains wVater I: poor qrj Il,'t
A\/%jitI i t-i'n iI : it .I n ec 'ae zc' e t-ihere are, a fe 'i..' s,'a t r,.l ar e,-ta-. '- jE -'j .i:ll t. I .t,-
h','',ivr,'ii r" FI-,,liri' 2 -ri-re eiD.r inni h.7j thinrnei or irIPii\-,eJ th.-' -.:' :\',-.i at0!
ar'!--...ian pr'nrq! Fire ti.- nd T Ihe ounoar', be;vieei internedime and ciciii1k
(o'er '- a eiec.':ei as 1 75 b'e:iau. se r '',-c of -I .l! new .inknlis in ihe Orlianrdo
,r-ea oc. Ii ti n Jarc, *,.v.'-,vh \e thre c.\'over is Ie --:. tli'ai 1 75. th.-i'. k iV ;comr and ,Ciiler.
1 .'J1 ,. Thus c ti ie inter n 'li ,:c-i zone Is at' are .-A -, i -k.. : ir i I r.sllre _..,iw-ec eas1
iI, iie th1n ::l,-j. l o,, ri ; i,-, ihi, prrhbltjm rarI,, ettet'=- t 1e IiCnd si.r f:3ce tocda\,
It ls thle r.--iations:nip bil : e,' Iet e i r LI C Lcnrcl-iiiol.acited s' jrucf al ssed.ii&ent
_:nkholles th-e epikarstic zone and the deeper FloridaIn Aquifer which
deerm rei i'r t e pi- terifial tor jilound-w.atier Ipolli-cio-n nif ii\ areas cf Fhrijda
rIn the t-in'/ coveted zone: si-. ole' are ofler open d'rei.tl\ ) t he water tab:e
in the area 'vvesit c.f GanesvIle these are v-ertcicaII- aller! pipts': i in [he linesto'ie
v, ihi.'h e:po-,.,e t- -crcrid vxaiter in lhe t Ilitlorn Tnese are L rno'r-..r .c, geologic -is
a'-. ce 1c-,r in i enanIi\ otIher jrea;. such as aiong the west c'>,.-"r from Pasc ,-,n
Citruso C .iir -.s rore-cir-iest s f,.nr.el-.-Iha-LFd depuressoir in the f 'an:J itt-m,
c'ornerm t0 i an open _-hi-i fi in ilie I.restone cor the colla.:psed .and m -%\ cover up
he oe here the Fivneorrthe,, te hle ,s close ;o the lar.rJd slriface. ;cCh
sinkli.iles wvl! be water file Oi thi th ,tiher In- icJ i the wVaier table ;: dfeerer
sjch as in the area wvest oIfC OCrala. smil sinkholes mav lbe dv ev'-en .,!he-mn tne
lImestone carn he see r in the bi'-,toir,. Oluer broad, snaIllcvv.t sinkliole hasirs, re-
c-.tten Jr\ because ihc-'\ u ,j'i-,li do t-i it nterc-ept 1I-1 Vwater rihle I-, Howeve-r
fro .jhriHij t iti-e II-'irird, covered zone it i-. obvious. that a iC ..on imina'.ed v'atei
v,.hi.Ii ,; ailh:,owed to d'airi direcll\ into) a ; .nrikhole wIi qic.k-lv rea, t"- the aroLunr.-
i-at'-er in the a i.itet a-i ,nd degLjrade t- le clualmi`t o th, p liable .aater t..uppli ,
In th' ?,, z nes of ,rtermei.dite antd thitik l c'-r cap o V iov pel-i i'abiltv'
Hawihorn sedmirent qlener il|\ cprte, i m m-e Fldr',ati t Iir.estrr) Aqiucfer Irrinm
direct. infl t3i(Io friirnr trne) .url";':e Ho ,,vevter I1:rouighoult riT Mot f i these (zoine
k arstC ic cllapses -iave punctluied i1 pr l te1ecC v,'e cap cf Havwth,'rn shrat.i Thi
latrqe .;inilhole hrf r "as.nis .a d I c j r ,'u if lar. c,,': ,ni ,rc i- thi s -ea ma ir rrav oe .ar;.f'. nt
Ia ,i T tjAi l rt:- : -.. i ,js-'d by repealed collapse -u ri .i F \r i e 'i- i i t
_" -, P r _- o rl [ 1.,=r qh e r I :,- fr C -f
mi l- or more) irregul,3 lame ar r ohftn Irnrmed iro- tSe,,eial smik'noilts ji-!ilh
ha,-e co- lfeo,-,,cerd B- -ne-jih th'es.e basins a ',erri:.al c!ianiciei .'f p- erme.bie
S-,.irr,,inl ,ffnterconnec.t ithe urfh::ial .:ianJjs and Ihe Floridan Aqi.,r.-r isee
F-I:LIre 3).

Evaporation Wellwater
Eporation Supply

Cr 1.3 I'V ..-. __ -. ,.-
lrtun.ater FRcW *'w- .... .. ___
Confining----
C lay oy ^ P-ja~t4oIfle-WI^ ^^::=^
Strata ..Shcetet -Lea e
I ] I _ 4 : .. .. --

T . . ,--- .-,_' ._ .
SFlor I dn / "
Aquiler

T_ .

Figure 3. !.-akage through lice bi.ttom :.f a sinkhole lake in Florida

;.iaLliiie--, ir I c-.o*.-- L :'b.h.c iili] tl i1 -0 triii1 Jc-tett in t)TV-. a.-- i.- meri'.-' ihfe
r!:iflimr, oft11:1l, itcse.t .- :. j! ii:-In. still pt' htor~t.jie t" H A-:tliuorn Cci: iitnfll] t.-C,'i-r

fIn 'act. Iidrc e-. tnjcll'racriutn tl.' tcc iial l,.c~i~lc~iu.n mcidiiitics iti\ ti.]gt-r
tflcuc.e ( iflios~e T he rute rof i cf i fr.-i on fio ririIhe sujr f- ola cjqu'ir d.'renicds on
tt- -tl.ci'ahioii dcfferner,. betivecer ihel 9fallowv ^'lat.' tahie m [in I.- 5i crfci.3i sand~
.jincd the Lpctei-'mio ettic siirfac.- cj f hfre Lti'drrl\i iicf ~imI-.si:i'ri( (Fltiniiai) .iquifen
A'-4l, iC-cfnqt-' vii whU fincrSe thte differen-ce ma', trioqler cjikhc'ies The
*r-ratmor ot laLeS. r.piertcoat~lr poncds or retentmi:ii utjasiric? ncihl r.;>ist;* che' Siial1.>~i
v'"a-cter tabile The,.- w i icdJ'avnjIl ipc icipi ny ,1 v: ,;IA'f elr fr:im t Iie- F 1 r dan Aq.-\'l fritt'il!I
lowev.-r tr'tc- poiehnrtciflmtri;: strictae Both i\ cpes: of ati'.i'/ties. *:ari *:aise Si'ifk i-,tle
*ccllar-se Oit iciurs~e sirit~liiles? Jicci 1c:llapse- *-;|iorad aI.,i\ ijrier pc~r--i\ rc-iihtmc of
t:LbicJIltcicn. ,jS, pan 'i t[lie' cngnir:4 encl~mon prrticEss
rin ite~ i h k Iv cc i e 3 Zoi a. cc'_ q th'e... C,_ :as t c m.r'r 'a ... ... .e" fa-g .-- r-- rare
althCotCgl larcjt ;3iccer t s..r'ktcrl.5 ire- )rt-sel The;.e prohacvc!\ fci ed crigi-
na~illv durino pieriods; v.iher sead 'i-vie i was ic".''er a3nd gr LI iii !- V-,A t' C ].Vc'ls rnd
I.FIe ha:-? !e-e' oI C(Cc5'Cil "vjre also co ie-rti ii'Jii-l~i\'. lotaen 7 h- hct e-mLs hi i:'ipiq
tie q -ri GiL' cl i -rciih.le .4 pi'ie tidi avenue 1 q
r Foiiii(: r e i a lth .eah e imhr i.oi~g thie bot l u',:i.f ; a i. sbko elkein flri da-ug fi

'\'ll,,_....)i ln [ I-I 7 ,-_ l\,' .:. | :-I rl-.,-, di = i[.:e ^ in tl *- m z,^ i:,r~ i:t.l- l r n h i-i. r r-,-, ,'(|.:..-., h ,_,l**

i.: 'r, ., I, t; r -:,nedJ 8,,- S S,..'. cl" .:fc rv l v i .1rllmii ,a.=ea l> S._.f ,i- .ii.it ,-_r m ieiJj _-,' :I ,.'.,.l:-- i, ,
,!!.r ,,.- li-ar'i *Cy, l : i, tr.:. ihe, i i hll --_. ,'r,, l, rV nr. -iri i.rr u r hc'j r.r j t rre ,,n--,t T i-,,-.,,
lo .-- r nV ,A Hh trt: ,1'. e, -r,_ I r't io i -,-l! ro i -,m ir F r3, ..re 2 I- X C er'rth iF!.: t, i : 'k c :! i ,
r..'r tql-lc i d .'re,-, n n i :.-h t .r(.- c:-,:l ir i,_ e l Jr 1 .,rS. I. F: _-r .i- l r.tl r t _,j..!i hi
Isn,=i-.[i:,ne ci Flore h., iu ._-' i._rc'.. enr ir T-.,, ; an:,llclr'iio r ,- ro b;,[ ; .:, s .- t ,r'i t.:nac,
Lr[ .,-_,rcrle h,_-c a i..iS vva,":' i-,r i-,' .-i ,ini' i iii ii.i tri~ih l tll ^d ulel[,, H i ,,i, r \ !t [?L-
,,i rl iic c.'i'n tr c- mi.!, .,', in I.:I' i.'e i e c r [,-' pa,- l a_' -,id F.:i -. o ri-ir rH'hr arm,^ -,i t,-_
*.,.. ilh !:'i;. e n ti .-l :,-, t3 "I`1 .' t ,,f [, ,_,1.6:. i .;e m

ha~i:rVv:- r~tec t' *:Ilte' 1,h~ Flrl c qfitH' T r\n o. snti
:.,.,r;,Ce _Ire't'. ,l- ,cn ais:, filow iiL in._. l C are3-_i- ,:. f it-, c i'stier ieH':',le and h,,i-,!
Sir i .. ,ered zne;. l, n U [h-. ; a ,ii F-,,-, ,- Fr r.rhie -s h ,nr -iF Ihe po e -
[,,m-p'r~t? -.ulrfa.:e .sPnd IS rr'ii~arqtn.) ihe Fl,:,ridai' A,:i,.',f.r sio'.,..\ tr,!>ijjl'i tt_-
IOwv, perme'F-ahilii.i|',,'* ''/tihit:; n ,1c'i'I`h,1n irja,- How,,\e',,er !t h:Lirien :,,r-kh.ols are
,i~res,#nl tllese br,-_..i-.: r.''ri:',/i(.l ;(-.re du'ecli a'.;?r, ,Je 0 ,31. ,(:I'? r.._-cl'arg ,:,
cc, I c. T m l1.-11nn.
In _-,o: rrhej n F io ,_i [,e co.er u,,er tht_ Tertar\ lires',.,nes is so iI'i' iLi.
I o rri) a ull t ,,rface di aina i.-,- c-iriera i,, ,';-wii v31al :i I a, L ..- I s r,,l .3 I1gn i or,;it
a-.t.;r ,IIA- re.,pect t,-, i,..oilu i", or i h Florida, Aqu, ii rr ,'-lo Ue wer rsh.Th.-
te.0 )1r"- are dei 'h_,ia,-' ,:,e c r. rhe -, ,-Iug nqe," ne t. Iili 31 far eid I a ,t'i eS --,not ,:.-e i

o i,3-r qbife.rs in 5ou'l"ec';,ern Florid:

In northern F;ii oa scme- c' three urlace draljnagye ficOws. vVelwari or
s(..ijriward from i he internmediate .one onto the r-.Ily manle,'J zone. u .Vhere
3u.Fjrace drainageq lic.'vs i unto ar are'.i, w ere the Iime-sitone i ui-:oifirienrl t-ih-
t!:vv', disappear, undierg-round ito [1-1i IirnmsetcrIe aninfQer 3 1 dtS'Cret sInL. inq]
pc'rints Cstreaai sinks swallei:- ecr p>orn's Isee Fig.,re .1) Much ci tilis
s,.t.ter ra r >,- .: tiow i eaIpedrs on t1.-1,hiNly covered zone as spriings te.ed'ng i.-e
w'ivanne '.c '.Jithla-ooc!-.e or Sanr'a Fe Riiers In fa'r. several of thle i-.3aor
ro,ers such-i a rth' .ariFa F S S Mai .-I, and 'Auciiia iher.selvei sink and
reappea.r In the iarer w.a.ses v.here a major stream sinks c and reSLrges a short
distarice aivy ;v there inay be r ave. :crivevir'g, ihe I fl:'w dirc ti\, hetveerl Ihe
r'v. port': Hovwever in the case it rthe- nLIrIirI c';j 3 smaller sinkirt.q treatss a's d
the rr-.orr ,iisIari S iPi[QS. It IS probable tn:ait this pnrt in chargege dfiseme-iinalS
in'-i diftu.e 'lcA. throu)ii lh-_ aquifer later to conveic:e ati he spring An',
co.ntarnln.3.ton reaching thEst; sir.kriqr streak's wqI flciw ire.ct!\ iNio ,the
.jruiter and has the polential 't-, ,'ortaniinaia' grour',(-Wi ,e;r SupIl!es over a
broad area
Fromn the f,:.retgcirig dscuLssion it 's ob'.vious thal karstic proecses and land
lormns are crmrpie: and hiht-ly .,arIlil le trom one area o afnoth"I' It '. also
LubII:,iS that '..ee pro)cesses are a critical factr',r ,n Pjdiuadniq the po1iu.:
pcrt-nl.al ci the Floridri3 Aqufei anid l)rotecting our valuable .ro'und-v,/ar.er
s Ip jp3Ie

Figure 4. Cross-secton showing ;,jrface ,:drainage sinhirng as it passes from the
irteriediatei (right ;ide) to (ipe thinly covered zone. The steep change is elfevdtion .it the
boijncarv s13 called the Cody Scarp. Mod;fieci from Ceryak. 1977.

References Cited

i'- r',.-k 1977 H,1ru.g ,oluhg,\ '',! ri,_r tI--in in .1 i.rSi e r ii h--.,Ipaha
R.\r-'i -Hflaifhrin Ciioucr, FhI:,ril:a SuLI'.'aree F \A'aMet ryi, D.=i In C.,'
S ,-r.--- I( *5 '1:1 p
.V'il-i.s P \A 1 985 SubLcu iaIous. I-:\ ndr- iand the' de -Ilopiis rimt _.d(olnm-
andc cck:r-t katr.r 7 .et':;iit t, ir (Getlorrphol.Nie f F 8d 29 FlHIr 4 L'
463 .432
Wilsyn ,v L Mc:cnald YK P Barfu 6 .L and Becm; B F 19838:. Hvro-
geo':logicr: famt.-...s, ,"; -31 h;CIF-e(d 'i.,th recen; ".Lnm krok? d v- eloprnenf ir, the
irlando narea Florida Fli on Slic'1cle Re-.ear:h cInsi'tttle RLI. 67 3-f-
Ull .,n -t't.i \ c*-i Cerm ral Fl'rid:,r Orlai-ij.c I( 1C4 p

Sources of Map Data
i'-i. senie-. ',:f fLourtee,- ''i ipfS ',..3R Prepli .'Je Irci ,i -_uL,li-h d -'la.i oril\ The
l p,'-,i''*ln p-h\ ,.ird driirincl,' tv r_ ii, t-_-rpr,-',,,d tr,-,ii tt-.- Li S (G3 S 7' [i r d'. rarli',
qIa .iil-'anl' mapi' Te ii:crm.-trrnat'r r-on [henoi._ n .ri..:f h',drclogq', ,-as t LrrmirT.arie:l
trc;"i 31 r1JUS, Stdtet F'dc-:.ral l.,cal aiind prof.-% ,,i')i.-! puth.i tionris T e ,L-i it '.-'a- It
,...*r~l',. *rn the hiil-

ei r s' : -en-iihllt *" .Jti c1 c ri pr-,pc,' i[, d.lia fri onm a ,,i p-.i i ,:l ('-in il;:' s':.a -s .-,cri'i *rrcr is
Lic jiii d ij' .'i'L 11r Iri Ihi t- pre':,.e F'Ilch.-I eril t it l hi- i.ir jn,. rir liriter in -.'-:iiJ..li [[i-
,.,. r' iui.- ..- oh '.i ,',ciq*ii se-tii l_ ,. to o: e c,,f ,SIle,.'er *:;tueqIories .s'.,i :-Li!:leCiL.-
,:e.:',." 'irlIS I 'lbi he r;iiji- Lia-.,, us,' -ll nre-a- :vvill n it t ot ilti a c,.ie'j- .i, e ,if.cll- .
Thi -,.t,-r.. . thi ._ i i, er s L.,ti D l -n t t, h,.ice r...-Ib iIr Fraps .1.. .4 ':r;i l iif -int *l-, ,ritn
t,: ld L, I "I_ I r',O l 1 _S[ eI h," I ,- 101 a'.3 1 1n% e._.ll a, -.. ,--n,. f'rn i h.: .,e [i qe e .!

Thle.--;se maps were Pripretrd ci', prof-e.._i'rmc --.'.nith du.Je : Fl :I.lda Sinkl'ii-h e e,_-e,1,,-i1h lc ist [u i-mtr n :-sn x ;.-r.iriami- e pr'essi l.-_. oi Iili-:! as to
Ih,- .b'_'.l:Itl \-11- iliJ'.ld *, -A lih'' data

ADDITIONAL INFORMATION ON KARST IN FLORIDA
Be,.' L, B F I h"', '.I & ) ',:.i -.'_ T t-, ,- y ''o l j l'rj :n l'r ,.* 'Id e' t,, i."i, l ii
ir:' P.,. c :::t Frceed i,.i-; o- he Fi ;,i ijllliscirjlina:.r i.nt,-r.-r .nce : n
SitkII-,':. Orlandoj F 'i_-i, 3 Rt-, etrl:- r'; fJii'',r-;r '!A.- %. A B -i!,k7-c a
PnioItr.,,er 4o9 p,
Be,..k r (.Ce:\ak R j;i'- nsi, D T Scout T -I anoc Sp.a'.jle F' PF -1 -P..
I-.'rtr.i lr ,r-n.poceol,,,.\ o- cf ,.: ctr.,l r, ncor:t ,-rr F-lr',.i Rpt 85-8r'- 1 FlorccJ-_
Sin' I.Ie Resea c.l Ir st.it'ite jl'ii,.- r:srt, :. Cei 31 Floria OrIanco. .446 p
;,',,-k B F pnc Sinl.,ir \' ,. i 1 Sfle- ,n Fi,.rd an m o C .n Rpt
A -1 'rh i n- i arn'i m in tp c '"Jc i.i''fl rpt
;_'c-it-'8-- Flt:, S- khi.',,, ResearcI-' i rsIiLiie 'Ilni\'t-ih-,., :, Certr 1 FlI)r c'a
Ccrl i r hi i,. i li ,.i
Pe.* B F I /,'\.i,, V\'\ L. 7 F a7 Ir. ers ri i d) o ( A e o!o r E ncii n oe i n q d1-,
-ri,'i o-i .cr n ri,.. l 1L ,.:A i .ins -fr'c..:,eed. ,-J.c .I *-'t it-e Ser',.il f iuli Jsc',Jpl 'Iai ..
C r. 1 re rcr. ,e on '.,I -l d h- .i n\ .rc, r, enn ..r i I o-ip c ,f Kar.i
Oi laR-i::c Flr, da RoF.ct.-rd:i I NeI" i',-',lie nd i .41 B.jie,-.Cl j PubIsle.-l -4'2 p,
.-nn li /r A. C '' Sici-.hi'l-,I j dr'-\',!t,:[p ,rTi! r'--'ltu~ilcg fr:m ]..!,t'urd-c.. i rt-c
,mthdr..,ai r' trhe TanLpa area Flo '-Ja Ij Ge'-,.i..-:l Sir,.e iaier
R -,s'uurc:e. IneL tiq.iar:-ns Rp.t C1 -L0 l* I :, p
Sim lI- t/ C Slte.-vanr .I\J V ',' nii'.iila IR L Gii V A E a,-id iller. R L 1' '..5
Tt, reo '-t rea ut,-es and ioccurrepf 'e t ,hiri h.oles-, n he I f-l ,'I r .t ,.:i. t,, -.f-, rIItr,li
Fl-.i 'ra IJ ., t-eohiiiLli.ai Sl '-'-', ''V\-iie5 RFes':-' ii :e_ In,.er- ii_- tc ronsc Rpi. 35-
.-i c._' S l: p
\'V !o I -c'r vV L and -e,:t 6 F IF sP'C. Fi-' .ai;LJ, ,.iii. -in hi-oi 0.9" h'zars ,n m .-nri1izd
F;'rpt [--rra ;r IN Smtar Led I ': i,.'3I1 Aspe,-.tI of l", rsr Tri jins
iGei:techrica aSpcal PIh'li ication Nco 14 -SCE NeV'1 co'L NY p 1 -24-

I

Potential for Groundwater Pollution

of the Floridan Aquifer,

Based Upon Surficial Drainage, Karst
Development, and Overburden Characteristics,

Explanatory Text

Barry F. Bec'

Much of Fluri._la3's land surfaic:e is karst a landscapes characterized by
sinkholes sinking sireams caves and large springs. The. ch'aractnrisic.; of
this topography determine thle path of the waier that recharges !he Floridan
Aquifer. dnd the rno'.'eme-nt of water within he auiLter The nature oi thekarst
ti:.pirap-,Vi also controls the rou'e by Wiihich cortanimnarnts may reach the
aiLiifer arid polliit? o;ir '.alu bie grounId-wA'aier suppi, Becdiuse Florida relies
on ground water for its water supply more Than an, other slate--appro:ximna'telyi
SO'',, of the water used in Florida is around water--it is critical that we
Licdetrstand tne naltuie ol karst ,dnl how it controls the potential foi ground-
water pollu-r on
Karst topography o :curs in Florida because limestone and dolomite ir'jer lie
the entire state and often occur at or near thii- surface The Flor..Jar Aqifir
comprises thousands of ieet of Imn--pstone and dolomite (a sirmilar and related
Ic:k'i ot lertiary age T-e discussion which follows and the acc.omlarnving
maps, relate partiniilarv t.) this aquifer and do no! reler to karst features which
mav be forrning on thle younger r limrestones WvhiLh are importanr aquifers 'n
South Florida
Limeslon_-. and doiirlnlie t are distinctlyll\, moremi s i-.lJt-e an-l rI i ,er iiikS Ov-r
milliilns (of A ears lthe iini-,.t._n- iin-d.-,l inrgq Florida iha-, be'.c, riddled with
cc\',t- created lVt the disiol-.nq actin lnof qrc, indIvr atr Pi ini-at pores joins
faults and bedding planes have ail been Lnlaripcd li dsi.oluiCn cr-atinA a i
3 i-dim enblioial network of intierconr n ectl rij i:.q t'--: Ti i-, ipp'1-i porrto i ca
30-3: ) ,of ihe iriiine:.toni.- :s itoi.! irerid elv dissolved nd theEi.y rnisr
peo m "i ahtlh Tiizl'-,zr n-a1, ,3-,Ihe,--nc,lled ih ,-epil,,..:lrs.ir ,,:z ne!\..llh- lli,-l I-S Tti>.
prrci, -s' o.f ,'1 li .rilu- ionIr is _sio' i and ,,n:i-om pi-x ar, d i ie i t-enl,ir ed :Ir ._irla pai-th'
-hroin,.hiul[ tle aquifer ha\e devi elope,1 ,I:, r milliorns I-.,f i, i-drs The' prcic.,s of
solutiUor itself is not 'adiiSinig an',' ,,ignificant hii'nqe:i .','iiin m ''s linme -r [rin-i,

ENLARGED FISSURES
OR KARREN

NARROW FRACT
IMPEDE INFILTRi

rt l/
ENLARGED VIEW OF
DISSOLVED FRACTURES
WARRENN) WITH COVER

INWNX
. . .. . :

S E .'t ,, i .. '., ., -':' '
" "J '.- ""''

. '
fURES .... .
ATI01* :,9i..

S i^

ENLARGED MASTER JOINT
DRAINS WATER TO DEEPER
ACUIFER

Figure 1: Generalized cross.section of the upper portion of (ne limestone and the
overlying sediment- the epikarstic zone (mrnodifiedi from Wilhiamrn, 1985).

ZONE OF THIN COVER

COVER

ZONE OF THICK COVER

VERY THICK COVER,
YOUNGER LIMESTONE
AT SURFACE

ZONE OF

A-A' CROSS SECTION

Figure 2- Generalized map and cross -section ofzonesofkarsi geomorphology as
related to the Tertiary limestones in Florida

.DL~r~ly the -~last i*vv iIi wiliri ,erstli_-'Floridanri I-r'rSinslaliaS heern
aIeUrflateI l ,%, n.) ~.,1ir'I~~ s -a 1,-%-1 o ne~-dbyr vIh s,7
anil c'r-ve--red w~ith *'stm-d imfprfit D LJ it-,th& ri-',-Prit dp icP,ji on c. fl rir ,n -lI irt
dor~mai~ii t I. sand anid clay tfl 'Ii roe ,cr nFlorida it. ge nierdII jiiT X or .-
,-jf lh nijtIikar stt [:.i C ,jne i r-.? r r,-d to as aia nid ltrl -. arsi B--ca ust? cf the. ~i oc-ni ~
n,rit-ral:Eurilof s.-a lo-i.-! fI ut CnItIt. i-arinio si-'1iirInefl(atiim 3njf z'.Irficiaj

iFigiire 21

Ini- h, th~nl' n.;-jnjIld zonft- rnelinin-srcrie qentralIl overlain b less. iWan
25' of clavev coninring beds ok-trldarI h less ilar 215 of surricral szifld
However in 3 few areas witrhin this 2one trie Li [e UicInec,s am~wbt---uch-
qreater (circa 1100 ). parliculdirli beneath tchr- Bro-.,kstv;ille RidLPe, andi~ n
SOU11-1l-ri~ l Pmnellas Cc-uni. VWhere- a conltinutous confining layer ispraeseniI.a
burfic-al aCILI1f,r oizcurs in the ;ands. Along tile-west Gcoast, from Pasco it) L~ev
Counties". the Iim.iSri, jfloe s rearl Liart- tE-ing ov-erlair by less than 25 of co,,er
s(-~dinients inI total In the norrthern half of tlie thinli, covered zone the sands
fli3y OV.-rlie the lirnesione directly, with nio hv'drulogic 'zepararion
In 1the zone of witpiifIidiatC cover thic-kness tried. overlyiingsed'iments are
generally r-nore than 50' thick and inl tie thickl\ covered -Dn the -c'vrerbujr1de-n
tp-nFer3Ily HxcePi1s 1 75' The limestone aquiife~ris conflined in both ~"-
LVsua~l'V by inore. than 50 (.-f clavev low Vperm~labilit., Hav~jtliorn G.-rouip
-sedinierils vhinl iin turn are overliIn by VCoLIncle.r sUrfic al San~ds The
Ha~wthorn -::diml.-nts a1so pri)te-ct iti,riqi-,.t:,fr froirr the dclwnviard leakage. of
Stlrface p')IlI uianlts Tr'-I sarsansove-rIPini'L the KiHawhorn fi-irm a p.-'r( fled sur ficialI
jqli f~r whic h clfe~ri Q',f'td irltvater of pocir qual'itv
M.vintIin r.the' int7ri brInerliatone 2f~t here a -*1ty 7-r- aesI '- -l
shutI it~~.~ ~ it-, ly i rte2 ..~ .hprt- ir un 1i Iiirn.- (i*rr~ I t he ccLA'er and
ai lt~sia ri spr infl45. ri(-:,foujnd ITri. .)i~ri- rl'J ii i~..* .riierr h,Jia e and1thi ii
I~~~~~~~~~1 if~~ S~;l' ii 5l a uS.- j I a'I.I :~))n ew k v i,,- rh i L h
a r ea oc c ur i n aji --a --. vv i P r.I hlp-. rov er i S -s s I h a n 1 7 5' F ht i ';k I Vtl/I so n a n(. i urI i-P
10 8,- 1 T f1US: -, t-r, ri[Cer m eu i a .ZCf,:, n e8 sa r.a r tirif a c 'v,- 9 r srI c.oIIarpiss e kv h V- r p :I S
inf iicl- I -Iick i *, c-*v.-r.-iij ,oni-rh- Iis prohItL-m ~rareI Pt V(.tc I ,- itj lnd surfai-e titia,iv
It I:;is me relatlonsrlip betw.,-en the' uncon'soi~dated. surfic~iaI spdiriient.
qlnkholet, the e pikarstic zone arid The~ deep..-r Floridan Aquuiter vvhi'ch
di-ter mines the. potrental for *ground-water p:~ijollutonif n.inanarena-, (:,f Florida
In theti IiiliI\ ov.erii-dzojrl sinkholes are often upt-n direct 1v tot ip vaier rahk*:.
In jh~r: .rea %v-st of Garrpesoli. ir~iese arp ~ver tiall waJllecd pits iin h lmib-' i.jtone-
v'.,hich expr-I.e I he ground \,%are--r in the hoi rcuDiiti'esare' krnoven I0 )i_-0ICgYgSs
as cernot,-s In m-an%, other areas sucli as along the ivest coast' fromn Pasco to
Canris Cc'uni'es a ilore-ori-lss funnpi -sl-aped depe e r t.~S3n i
C(,irinect 'if.) an opensi Sifdt in the liip~lstofl.-. or itile coIlapsd sand may %-nktr up
ihp i&jriip,I(JIIP \A/her- the wait-r tablo is: It.S Pto ~[he lan d surface,. such
siflkt-lers %iItie water-F.Ii.dJ On the other hand. if the~ water table is dpep-p.r.
such as in the ar.-7a west of Ocala small sinikholes mnidy be dryr, even ,%ht-'n [It-~
lirnesuontcar-,he seenrit-,Ihe-' Lomtjri.Oldler broad shallow ,sink~hole basirns are~
:,ftpn ir' t)':ciauste they usijalj. do rnot intercept the water table Hr~w-:,,er
Ifirou'glliwitthe think\ coveredJ zone It iS n b 0Ii)LiG that an conttjrninated ~j vattir
which is alloweri t. drain dir~ctItl intc) a sinkri '':e vvill quick kI reach ith i- crojuri.
water in thp aquiter and dt-gradie the~ quality of the n-otable vvah-' Su-I'M
In tlh 2 zi~ie',. f intt-rnvdijze and thick cover a .:)cap oflow rwerrneaIbiijit\
Haw~xthorn .3s-din-i,'ni generdII pH i tects the Fiti d-.n (liir-~stcirwi) Aquiifer from
rdir~-~cin filtration fir. mii tot,,surtar. '-i H~.vi.k%.ve-r I Irc.ucJhrL1t rnv-Sl cf r hestezones,
kar'st'c collap:-,es ha',e P~r-iArctdr.[)h.:- prrote.-ti\ae cap of H -wvthuorn strata., Th-
larye- sinkliolet) l'irs and c-ircular lakes c~n-itnon inl this ;r, may be ancient
kar-31 features caused by~ repeated collapse and m-~rosio)n E%'en the~ larq7r (nnci-
mle .~ or mcre) irr.-g~LIar IljI(.- are ofter, forrneii~ frorn setrai sinkholes which
have call escr'ed Beneath tlh-s, basins a vertical channel r-f pe-irnmbah
.tadirn.:-nti inirc,,flhipcts the 31,urfic1ig sands 'and the Floridan Aquifer t:.e

Evaporation Well wat er

f75 supply

Sand ~ u t
G jroundmiter FLk7*
Cla-.yey- e ortt
Confining --- "SWfr1e~M~: Lek
Strata --- -

Floridan I
Aquifer

i -T

Figure 3: Leakage through the bctton-i of a sinkhole lake in Florida.

-~~~~~~~~~~~~rt. .ir.-priavi eatvr I :i~~-.- l tt. *.,t it, v Ioi.-le tel. coveresinkholer

i,'i .tll. [tirir:d th_- i~.,,i-r .i';d i0'- arr.:- i in pressure i diiuset- ,_4ri.ii id w ater to
ii-.-,-i^-rle 'J[,\. jrIfrom [lei- Irnmi- ii-n-_, formr ing .ir.iring I nin and -_.1 -,.im, The;r.-
areas of thin ,'.-r i i :.: r i i,,r l! i,: n:,,. ii Figure 2. lii Cerir,l FP :,-.1,.lai many
spring-fed streams flow :-,i d t ,i n in.. the Si Johns River. ,\il..:uih i,
liri-, it,_,ri, is close to the lan .,jrf -ii .- 0.lluiii:n ;.-w n:,t n ,w a .iari f;.:- r,
I.,Ildl-rn1 because water is, l'i_-;.:Pirutng 'rin -t 3ajiJt'-r However if the
potentiom etric :: irf.:f-- is i,.,.. r these .irpao ., ,:,: ll j .':. ':i -- :--i: ji .. ,i.- sites
with potential .: ,f irn,-tii,:,ii' problems.
Surface: sir-arms also flow in many areas .:'f th-e interm.:liaiL and thickly
covered zones, wnvire [ihe shallow water table is higher than ihe ooten-
,oini,i.c -,Lurfic.- anid is rechargring the Floridan Aquifer slowly through the
1:,,v perm at-fLibiltl\ Hl'.x i -,jrrl ,.i onfii-i'i,;ri %[r [ij '' er it turiea snknl h,_r' ,r
Lir-senlt hei'e breaks pr:,'di- -ii.:,re- d;r'e:t -avenu,-s for rppiid re:ih.rcge or
cni 'i minE a i.j'ri
In Sc,u[tnhrn Florida the cover over the Tertiary limestories is so thick (app.
1 000 I that surface drainage i- geriprall\ normal and karst is not a significant
factor with respect to ;.IolJlunon of liec Floridan -quit-ri towet-.r, karsti,
fi--Aturies are d-.-hlopii% ,.n rhe iirig-r, near r iffa e:- linmesor.i t, .ivilh arethe
major aquifers ir southeaste-rn Florida

In nimrherr1 FlorjrIId some of the~ surface drainage tiowrs vvetward or
soIutIhowarad frc)n th-11mi neririoiat-jItezone flf(o irE. tl~iml'nI mart ieu' zene WVVi'r
SUrface drainage flows onto: an jr,-a \vlere the iirr~estone Is tnrcornfintd h,7
flIoc vvd is~ap p e.ars'unde-rgrounld into:T, rh irriestorie aC]iLIter at di-,creje sinikin~g
points stream sinks svwaIleis or po'iors (see- Fiqure 4) Much -_f his
.:LIbre~rrafli-arI floW ,-r.-,pptars 'jr Iit-~rihin[,, covered zorie a,- spr i ncs h-edi rig Ih-
Sijwane~ \JrhI~co~h&. orSanta F,:-.Riv'ers inl fa~it 3evrIo r mar
n%~ rs, such ;,3 t he Santa IFe Sr Mari.,k and Aucilia. Ehems'ET-iveB knd
rpaL)pear In it-e latrter cases %v ee major strearn sinks anfd resuryet;a hcr
distarn . away. the-re may bLe raves riofv,vincJthe Ilo~p/d re-ctI\ between; r1ho
rtw( points Hovwever inl the case t? E ht-. nurrie.rou;s smaller sink~ing strea'ins and
Mel more distant spr'ing6 it is prorliabIP that triiipoinlt recharge dis-;n-iinatE-'
into diffujse flovu hrOiiq-_h jIh *JqUit Er later to c:nve~~rge 3t 'he spirng Afl
corItampnat~ofl racnhin4 thest sinkinq stre.arn-S \vilI f~cv ireC i\'rito [ih-
.-quifer and has th-e potentrial to c,:nranir'abo urtllimd -water supphtz5 ov~er a
broid area.
Pron'i rh-7 fore-gc-iritj di cusicj Cnit is Lb-oioIJs that karmirc pro(:ecses arnd 1,all(
forms are romp'e.-, .3nd highly Wci be from one are~a to arotioE-7-r-It ;z : dI$
ubv'iius that thesepsi ocesse-s are a critical~ factor in evaluating thp- poijurori1
pote 1 131 l of i'.-.F lo irda A(q itti r anid protect (ing amirval uable qrcJLInd -vva er

. ,. ',

Figure 4. Cross-section showing surfac- drainage sinking as it passes from the
intermediate (right side) to the thinly covered zone. The steep change in elevation at the
boundary is called thie Cody Scarp Modified from Cervak. 1977.

References Cited
Ceryak, R., 1977, H.dr,-,ge-,h,, ,f a1 river hain in a karst terrain--\lapa,_-:
Ri,,er- Hamilton C.oun[t, Florila Suwannee R. '"Vaier Mgt. Dist. Inf. Cir,-
Ser,, -r IC-5, 2_p
\,illiarns P vV I 95 SubcutaneouLs hydrology and the development of d:oline
and c,:cl,'pt k-i.rsL Zeitchrift fur G,-nmrirphologI-. j F., P.d. 29 Heft 4, p.
463--492
Wil-on WV L McDnrnald K M Barfus B L ard B,.-ck, B.F., 1'*:83 Hydro-
j-iol.:gic, lactors asso,-;iated ..it recPnI sinkl, hole development in th-
Orlando. area Fihiri,da Florida .3jnki,,:e Re.-_-:,rch Instiute Rpt. 87-88-4,
Uni, rr\ of Cenrral F!orijdd Orland,: 104 p

Sources of Map Data
Tliin series of fourteen maps was prepared from published data only. Th-
i,:.p.:' ,.-i'-,.h and drainage were interpreted from the U.S.G.S. 71/2 tO'-,,g-..yra,:-p,
qii._diran.-_li- inal'p,. Th. inf. rrmalit,,ri on-h, g-o :'I nI I\lrol.,g ',,a-, ;lii narzed
frront .arhi.Liu SIait- F_-d r ,- ial aI d:l n pr. ,f,-'s. _js : "',-i -,ui .l i Tii l,diia i,..ja not
ventr-hd inl ii ie Ilehl:i

In ".''semiilii SuL h i :ron-,poslte data fr. ,rnm map of \ iri:,Ll. S ''.a S some .-rr:.i is
bound Io i:I):Cur III Etie .precise pia.-e nent of the m ririnq Further, in .-iss nii;i,,) the
%.-iricois g.,:o.'?';itr,:.i,,g i(: ..,- iln.j.3 t, onei of eleven categories some uhijertiv,
decisions n',islt b in,i>,t- : Im -, .u._ls- all ,ir-a \', il not fit inol a ,:"- egj r',, perfc"I,
Ti'i?',-t,:.- the reader is t:aiut;i.'-d tu I, u. iht-.s. p.. a m :i *a- star iinii point ..il', and
to ,-on|iijii more sp cifr,: I:1:,0 "il\ '[ i 1iatu:,-, ., to '0 ifiriii -ie ir,-.:-cii e site data.
These n',[-,'' ,'v-r, pr'.par-d I.f1 .r,-,f-s- in. ,,.;i ih due care. However, the
Florida S'nkhole Research Institute makls ,n:, ,. inr[t -ipr...., ,r implied, a_ ,:,
the ab .,iiut.- 4luil' of the data.

ADDITIONAL INFORMATION ON KARST IN FLORIDA
Be-(:i B F., _1904 Sinklh. iei:, Their g ,-,i -ig\.q en '.iie,-rirq and etilvironmenirlt.l
iIi _'i. 1 Pro,:et-'ing.qj oijf ii.' Fii l, N jirildis,:plirilar .. ontererice o i
Sinkholes Orlando Florida,: R.)l'erdai' Netlherl.unJs ,A BiIlknma
Publisher 429 p
Beck F Cei\,,k R. .Jenkiri.,. ,T Scott, T rMA and Spanjler DP. 1985.
Kar.i h\idr-,,.eo-l,,',, ,:'t :-ntral and* northern Florida: PpE 85-86.- 1 Florida.
Sir Ikh:.le Re:-,air.:h Institute, University of Cernira! Flordi OrianI,,. 46 p
Beck, B.F. and Sinclair, W.C., 1985 Sinkhv,!,s in Fl,:,rili ,ain introlucii.'- Rpt
85-86-4, Fior.dAa Sinkh:;ieF Re.sar..:h Institute. Universityof Central Fliridd
Orlando, 16 p.
Be(: k B.F. and Wilson, '."V L 1957 Karst h,dr,:,qe.,:,ioq Engineering and
environmental appli>:Jiin_; F' oc, edJinq ,:,f the Se ,i,'-id MLJl I _,i'riprli,lJr1,
Conference o:in Siri'hole-. arnd the Enrunn',-riral Impacts of Kairsi
Orlanldo Florida Rc..itrjrdani N-iherland_; A A Balkemai Pihjliher 429p.
.zn,:ia ir '.C., 19.2, Sink-iile d j,-:-iopmjrnent ISulling Irom %i -Lr und-'".,.1,er
voitiidr..:i.\al in the Taimpad jrea Fi.,:rrd i! S GI eologri.- Sur-t_, kVaLt-r
Re-;,iir ,es Irn estigaiions Rp[ 31 -50. -I p.
Sinclair \NV C St,:wari, J \ Knutilla, R.L., Gilboy, A.E ond Mi,b-r R L 1935
T pes o l f-,aturl- and uo,:urrericci- ,:',f ::,iin holes in ith kars iof vuesi-,:er'iril
Floriid,,i S S. Ge,:10;g, wil S.ur\,e\ Water Res.urces Investigation.-. Rpt 85-
4 2G. 31 p.
\'il ,.,n iW .L., and Beck, B.F., 1988, E. aliiuaing -,,nl-holes az,'irdsl in m.lin[i.:-.j
t. ars[ terrane, in N. Sitar (ed.) Geot-,hriii;a! Ap: ct of Karst Tenramns
Ge-. tiC.hnicial Sp.-ecal Fubli,:a:iin No 14, ASCE, New York, NY p 1-24

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Mu'4.(to g'idJ tdck;

Potential for Groundwater Pollution

of -the Floridan Aquifer,

Based Upon Surficial Drainage, Karst

Development, and Overburden Characteristics,

Explanatory Text

Barry F. Beck

Much of Florida's land surface is karst: a landscape characterized by
sinkholes, sinking streams,, caves, and large springs. The characteristics of
this topography determine the path of the water that recharges the Floridan
Aquifer, and the movementof water within the aquifer. The nature of the karst
topography also controls the route by which contaminants may reach the
aquifer and pollute our valuable ground-water supply. Because Florida relies
on ground water for its water supply more than any other state-approximately
90% of the water used in Florida is ground water--it is critical that we
understand the nature of karst and how it controls the potential for ground-
water pollution.
Karst topography occurs inHFlorida because limestone and dolomite underlie
the entire state and often occur at or near the surface The Floridan Aquifer
comprises thousands of feet of limestone and dolomite (a similar and related
rock) of Tertiary age. The discussion which follows, and the accompanying
maps,relate particularytoQthis aquifer and do not refer to karst features which
may be forming on the younger limestones which are important aquifers in
South Florida.
Limestone and dolomite are distinctly more soluble than other rocks. Over
minions of years the limestone underlying Florida has been riddled with
cavities created by the dissolving action of ground water, Primary pores, joints,
faults, and bedding planes have all been enlarged by dissolution creating a
3-dimensional network of interconnecting cavities, The upper portion bca.
30,35') of the limestone is most intensely dissolved and thereby most
permeable. Thiszone has been called the epikarstic zone (Williams, 1 985). The
process of dissolution is slow and complex and the enlarged drainage paths
throughout the aquifer have developed over millions of years. The process of
solution itself is not causing any significant changes within man's time frame.

ENLARGED FISSURES

During the last two million years, the Fioridan peninsula has been
alternately exposed to weathering above sea level, or submerged by the sea
and covered with sediment. Due to the recent deposition of marine sediments,
dominantly sand and clay, the limestone in Florida is generally not exposed
and the karst terrane is referred to as a mantled karst. Because of the recent
interaction of sea level fluctuations, marine sedimentation, and surficial
erosion, Florida's karst topography can be divided into four geomorphic zones
(Figure 2)

In the thinly mantled zone the limestone generally is overlain by less than
25' of clayey confining beds overlain by less than 25' of surficial sand.
However, in a few areas within this zone the cover thickness may be much
greater (circa 100'), particularly beneath th Brooksville Ridge and in
Southern Pinellas County. Where a continuous confining layer is present, a
surficial aquifer occurs in the sands. Along the west coast, from Pasco to Levy
Counties, the limestone is nearly bare, being overlain by less than 25' of cover
sediments in total. In the northern half of the thinly covered zone the sands
may overiie the limestone directly with no hydrologic separation
In the zone of intermediate cover thickness the overlying sediments are
generally more than 50'thick and in the thickly covered zone the overburden
generally exceeds 175'. The limestone aquifer is confined in both zones,
usually by more than 50' of clayey, low permeability Hawthorn Group
sediments which in turn are overlain by younger, surficial sands The
Hawthorn sediments also protect the aquifer from the downward leakage of
surface pollutants. The sands overlying the Hawthorn form a perchedsurficial
aquifer which often contains water of poor quality
Within the intermediate zone there are a few scattered areas, too small to be
shown in Figure 2, where erosion has thinned or removed the cover and
artesian springs are found. The boundary between intermediate and thick
cover was selected as 1 75' because 97% of all new sinkholes in the Orlando
area occur in areas where thecoveris lessthan 175' thick (Wison and others,
1 988). Thus, the intermediate zone is an area of active karst collapse, whereas
in the thickly covered zone this problem rarely effects the land surface today.
It is the relationship between the unconsolidated, surficial sediment,
sinkholes, the epikarstic zone, and the deeper Floridan Aquifer which
determines the potential for ground-water pollution in many areas of Florida.
In the thinly covered zone, sinkholes are often open directly to the water table.
In thearea west of Gaindsville these are vertically-walled pits in the limestone
which expose the ground water in the bottom. These are known to geologists
as cenotes. In many other areas, such as along the west coast from Pasco to
Citrus Counties, a more-or-less funnel-shaped depression in the sand may
connect to an open shafthin the limestone, or the collapsed sand may cover up
the limestone. Where the water table is close to the land surface, such
sinkholes will be water-filled. On the other hand, if the water table is deeper,
such as in the area west of Ocala, small sinkholes may be dry, even when the
limestone can be seen in the bottom. Older, broad, shallowsinkhole basins are
often dry because they usually do not intercept the water table. However,
throughout the thinly covered zone it is obvious that any contaminated water
which is allowed to drain directly into a sinkhole will quickly reach the ground
water in the aquifer and degrade the quality of the potable water supply.
In the zones of intermediate and thick cover a cap of low permeability
Hawthorn sediment generally protects the Floridan (limestone) Aquifer from
direct infiltration from the surface. However, throughout most of these zones,
karstic collapses have punctured the protective cap of Hawthorn strata. The
large sinkhole basins and circular lakes common in this area may be ancient
karst features caused by repeated collapse and erosion. Even the Jarger (one
mile or more) irregular lakes are often formed from several sinkholes which
have coallesced. Beneath these basins a vertical channel of permeable
sediment interconnects the surficial sands and the Floridan Aquifer (see
Figure 3).

ENLARGED MASTER JOINT
DRAINS WATER TO DEEPER
AQUIFER

Sand

Figure 1I: Generalized cross-section of the upper portion of the limestone and the
overlying sediment: the epikarstic zone (modified from Williams, 1985).

ZONE OF

A-A' CROSS SECTION

Figure 2: Generalized map and cross-section of zones of karst geomorphology, as
related tothe Tertiary limestones in Florida,

Clayey
Confining
Strata

Floridan
AquIfer

Figure 3: Leakage through the bottom of a sinkhole lake in Florida

At many localities younger sediments may have completely covered ancient
sinkholes or lakes, obscuring them from detection. However, the permeable
column of collapsed sediments still perforates the Hawthorn confining layer
providing an avenue for groundwater pollution, and also making the site
susceptible to reactivated collapse. In the zone of intermediate cover, sinkhole
collapse is still occurring today, opening direct pathways to the aquifer.
In fact, man's modification of the local hydrologic conditions may trigger or
induce collapse. The rate of infiltration from the surficial aquifer depends on
the elevation difference between the shallow water table in the surficial sand
and the potetiometric surface of the underlying limestone (Floridan) aquifer.
Any changes which increase the difference may trigger sinkholes. The
creation of lakes, percolation ponds, or retention basins will raise the shallow
water table. The withdrawal (pumping) of waterfrom the Floridan Aquifer will
lower the potentiometric surface. Both types of activities can cause sinkhole
collapse. Of course, sinkholes alsocollapse sporadically under purely natural
conditions as part of the ongoing erosion process
In the thickly mantled zone along the east coast, modern collapses are rare,
although large, ancient sinkholes are present These probably formed origi-
nally during periods when sea level was lower, and ground-wacter levels and
the base level of erosion were also correspondingly lower. The breaks through
the Hawthorn Group still constitute a potential avenue for ground-water
pollution, although the impact of these features has not been investigated.
Within the zone of intermediate cover, some areas occur where erosion has
locally thinned the cover and the artesian pressure causes ground water to
discharge upward from the limestone, forming spring runs and streams These
areas of thin cover are too small to show in Figure 2. In Central Florida many
spring-fed streams flow eastward into the St. Johns River. Although the
limestone is close to the land surface, pollution is not now a significant
problem because water is discharging from the aquifer. However, if the
potentiometric surface is lowered, these areascould become recharge sites
with potential contamination problems.
Surface streams alsoH flow in mny areas of theintermediate andrthickly
covered zones, where the shallow water table is higher than the poten-
tiometric surface and is recharging the Floridan Aquifer slowly through the
low permeability Hawthorn confining strata. However, if buried sinkholes are.
present these breaks provide more direct avenues fo- rapid recharge or
contamination.
In southern Florida the cover over the Tertiary limestones is so thick (app
13,00O') that surface drainage is generally normal and karst is not a significant
factor with respect to pollution of the Floridan Aquifer. However, karstic
features aredeveloping on the younger, near surface limestoneswhich are the
major aquifers in southeastern Florida.

in northern Florida, some of the surface drainage flows westward or
southward, from the intermediate zone onto the thinly mantled: zone, Where
surface drainage flows onto an area where the limestone isunconfined, the
flow disappears underground into the limestone aquifer at discrete sinking
points: stream sinks, swallets or ponors (see Figure 4). Much of this
subterranean flow reappears on the thinly covered zone as springs feeding the
Suv.anmiee, Withlacoochee, or Santa Fe Rivers In fact, several of the major
rivers, such as the Santa Fe, St. Mark's, and Aucilla, themselves sink and
reappear.In the latter cases, where a major stream sinks and resurges a short
distance away, there may be caves conveying the flow directly between the
two points. However, in the case ofuthe numerous smaller sinking streams and
the more distant springs, itAis probable that this point recharge disseminates
into diffuse flow through the aquifer, later to converge at the spring. Any
contamination reaching these sinking streams will flow directly into the
aquifer and has the potential to contaminate ground-water supplies over a
broad area.
From the foregoing discussion it isobvious that karstic processes and land
torms are complex and highly variable from one area to another. It is also
obvious that these processes are a critical factor in evaluating the pollution
potential of the Florida Aquifer and protecting our valuable ground-water
supplies.

Figure 4: Cross-section showing surface drainage sinking as it passes from the
intermediate (right side) to the thinly covered zone. The steep change in elevation at the
boundary is called the Cody Scarp. Modified from Ceryak, 1977.

References Cited

Ceryak, R., 1977, Hydrogeology of a river basin in a karst terrain-Alapaha
River-Hamilton County, Florida: Suwannee R. Water Mgt,. Dist Wnf. Circ.,
Series IC5, 20 p.
Williams P.W., 1 985, Subcutaneous hydrology and the development of doline
and cockpit karst. Zeitchrift fur Geomorphologie N.F., Bd. 29, Heft 4, p
463-482.
Wilson, W'L McDonald, K.M., Barfus, B.L, and Beck, B.F., 1988, Hydro-
geologic factors associated with recent sinkhole development in the
Orlando area, Florida: Florida Sinkhole Research Institute Rpt. 87-88-4,
University of Central Florida, Orlando, 1 04 p.

,.3Sources of Map Data

This series of fourteen maps was prepared from published data only. The
topography and drainage were interpreted from the U S.G.S. 71 topographic
quadrangle maps. The information on the geology and hydrology was summarized
from various State, Federal, local, and professional publications. Thedata wasinot
verified in the field.

In assembling such composite data from maps of various scales, some error is
bound to occur in the precise placement of the margins. Further, in assigning the
various geohydrologic settings to one of eleven categories, some subjective
decisions must be made, because all areas will not fit into a category perfectly.
Therefore, the reader is cautioned to use these maps as a starting point only, and
to conduct more specific local investigations to confirm the precise site data.

These maps were prepared by professionals with due care. However, the
Florida Sinkhole Research Institute makes no warranty, express or implied, as to
the absolute validity of the data

ADDITIONAL INFORMATION ON KARST IN FLORIDA
Beck, B.F., 1 984, Sinkholes: Their geology, engineering and environmental
impact: Proceedings of the First Multidisciplinary Conference on
Sinkholes, Orlando, Florida,: Rotterdam, Netherlands, A.A. Baikema,
Publisher, 429 p.
Beck, B.F., Ceryak R., Jenkins, D.T., Scott, T M., and Spangler, D.P 1985,
Karst hydrogeology of central and northern Florida: Rpt. 85-86-1, Florida
Sinkhole Research Institute, University of Centra! Florida, Orlando, 46 p.
BeckB.F. and Sinclair, W.C., 1 985, Sinkholes in Florida an introduction: Rpt.
85-86-4, Florida Sinkhole Research Institute, University of Central Florida,
Orlando, 16 p.
Beck, B.F. and Wilson, W.L., 1987, Karst hydrogeology: Engineering and
environmental applications: Proceedings of the Second Multidisciplinary
Conference on Sinkholes:and the Environmewntalimpacts of Karst,
Qrlando, Florida: Rotterdam, Netherlands, A.A. Baema, Publisher, 429 p.
Sinclair, W.C., 1982, Sinkhole development resulting from ground-water
withdrawal in the Tampa area, Florida: U.S. Geological Survey Water
Resources Investigations Rpt. 81 50, 19 p
SinclairW.C., Stewart, J.W, KnutilaR.L., Gilboy, A.E,and Miller, R.L. 1985,
Types of features and occurrence of sinkholes in the karst of west-central
Florida U.S. Geological Survey Water Resources Investigations Rpt. 85-
4 26. 81 )p.
Wilson, W.L., and Beck, B.F., 1 988, Evaluating sinkholes hazards in mantled
karst terrane, in N. Sitar (ed.) Geotechnical Aspects of Karst Terrains,
Geotechnical Special Publlcation No. 14, ASCE, Nliew York, NY, p. 1 -24.

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Potential for Groundwater Pollution

of the Floridan Aquifer,

Based Upon Surficial Drainage, Karst

Development, and Overburden Characteristics,

Explanatory Text

Barry F. Beck

Much of Florida's land surface is karst: a landscape characterized by
sinkholes, sinking streams, caves, and large springs. The characteristics of
this topography determine the path of the water that recharges the Floridan
Aquifer, and the movement of water within the aquifer The nature of the karst
topography also controls the route by which contaminants may reach the
aquifer and pollute our valuable ground-water supply.;Because Florida relies
on ground water for itswater supply more than any other state--approximately
90% of the water used in Florida is ground water-it is critical that we
understand the nature of karst and how it controls the potential for ground-
water pollution.
Karst topography occurs in Florida because limestone and dolomiteunderlie
the entire state and often occur at or near the surface. The Floridan Aquifer
comprises thousands of feet of limestone and dolomite (a similar and related
rock) of Tertiary age. The discussion which follows, and the accompanying
maps, relate particularyto this aquifer and do not refer to karst features which
may be forming on the younger limestones which are important aquifers in
South Florida.
Limestone and dolomite are distinctly more soluble than other rocks. Over
millions of years the limestone underlying Florida has been riddled with
cavitiescreated bythe dissolving actionof groundwater. Primarypores,joints,
faults, and bedding planes have all been enlarged by dissolution creating a
3-dimensional network of interconnecting cavities. The upper portion (ca.
30-35') of the limestone is most intensely dissolved and thereby most
permeable. This zone has been called theepikarstic zone (Williams, 1985). The
process of dissolution is slow and complex and the enlarged drainage paths
throughout the aquifer have developed over millions of years The process of
solution itself is not causing any significant changes within man's time frame.

ENLARGED FISSURES
OR KARREN

During the last two million years, the Floridan peninsula has been
alternately exposed to weathering above sea level, or submerged by the sea
and covered with sediment. Due to the recent deposition ofCmarine sediments,
dominantly sand and clay, the limestone in Florida is generally not exposed
and the karst terrane is referred to as a mantled karst. Because of the recent
interaction of sea level fluctuations, marine sedimentation, and surficial
erosion, Florida's karst topography can be divided into four geomorphic zones
(Figure 2).

In the thinly mantled zone the limestone generally is overlain by less than
25' of clayey confining beds overlain by less than 25' of surficial sand.
However, in a few areas within this zone the cover thickness may be much
greater (circa 100'), particularly beneath the Brooksville Ridge and in
Southern Pinellas County. Where a continuous confining layer is present, a
surficial aquiferoccurs in the sands. Along the west coast, from Pascoto Levy
Counties, the limestone is nearly bare, being overlain by less than 25'of cover
sediments in total. In the northern half of the thinly covered zone the sands
may overlie the limestone directly with no hydrologic separation,
In the zone of intermediate cover thickness the overlying sediments are
generally more than 50' thick and in the thickly covered zone the overburden
generally exceeds 175'. The limestone aquifer is confined in both zones,
usually by more than 50' of clayey, low permeability H awthorn Group
sediments which in turn are overlain by younger, surficial sands. The
Hawthorn sediments also protect the aquifer from the downward leakage of
surface pollutants. The sands overlying the Hawthorn form a perched surficial
aquifer which often contains water of poor quality.
Within the intermediate zone there are a few scattered areas, too small to be
shown in Figure 2, where erosion has thinned or removed the cover and
artesian springs are found. The boundary between intermediate and thick
cover was selected as 175' because 97% of all new sinkholes in the Orlando
area occur in areas where the cover is less than 175' thick(Wilson and others,
1 988). Thus, the intermediate zone is an area of active karst collapse, whereas
in the thickly covered zone this problem rarely effects the land surface today.
It is the relationship between the unconsolidated, surficial sediment,
sinkholes, the epikarstic zone, and the deeper Floridan Aquifer which
determines the potential for ground-water pollution in many areas of Florida,
In the thinly covered zone, sinkholes are often open directlyto theater table.
In the area west of Gainesville these are vertically-walled pits in the limestone
which expose the ground water in the bottom. These are known to geologists
as cenotes. In many other areas, such as along the west coast from Pasco to
Citrus Counties, a more-or-less funnel-shaped depression in the sand may
connect to an open shaft in the limestone, orfthe collapsed sand may cover up
the limestone Where the water table is close to the land surface, such
sinkholes will be water-filled. On the other hand, if the water table is deeper,
such as in the area west of Ocala, small sinkholes may be dry, even when the
limestone can be seen in the bottom. Older, broad,/shallow sinkhole basins are
often dry because they usually do not intercept the water table. However,
throughout the thinly covered zone it is obvious that any contaminated water
which is allowed to drain directly into a sinkhole will quickly reach the ground
water in the aquifer and degrade the quality of the potable water supply.
In the zones of intermediate and thick cover a cap of low permeability
Hawthorn sediment generally protects the Floridan (limestone) Aquifer from
direct infiltration from the surface. However, throughout most of these zones,
karstic collapses havepunctured the protective cap of Hawthorn strata The
large sinkhole basins and circular lakes common in this area may be ancient
karst features caused by repeated collapse and erosion. Even the larger (one
mile or more) irregular lakes are often formed from several sinkholes which
have coallesced. Beneath these basins a vertical channel of permeable
sediment interconnects the surficial sands and the Floridan Aquifer (see
Figure 3).

ENLARGED MASTER JOINT
DRAINS WATER TO DEEPER
AQUIFER

Sand

Figure 1 : Generalized cross-section of the upper portion of the limestone and the
overlying sediment: the epikarstic zone (modified from Williams, 1985).

Clayey
Confining
Strata

Floridan
Aquifer

Figure 3: Leakage through the bottom of a sinkhole lake in Florida.

ZONE OF

A-"A' CROSS SECTION

Figure 2: Generalized map and cross-section of zones of karst geomorphology, as
related to the Tertiary limestones in Florida.

At many localities younger sediments may have completely covered ancient
sinkholes or lakes, obscuring them from detection. However, the permeable
column of collapsed sediments still perforates the Hawthorn confining layer
providing an avenue for groundwater pollution, and also making the site
susceptible to reactivated collapse. In the zone of intermediate cover, sinkhole
collapse is still occurring today, opening direct pathways to the aquifer.
In fact, man's modification of the local hydrologic conditions may trigger or
induce collapse. The rate of infiltration from the surficial aquifer depends on
the elevation difference between the shallow water table in the surficial sand
and the potetiometric surface of the underlying limestone (Floridan) aquifer.
Any changes which increase the difference may trigger sinkholes. The
creation of lakes, percolation ponds, or retention basins will raise the shallow
water table. The withdrawal (pumping) of water from the Floridan Aquifer will
lower the potentiometric surface. Both types of activities can cause sinkhole
collapse. Of course, sinkholes also collapse sporadically under purely natural
conditions as part of the ongoing erosion process.
In the thickly mantled zone along the east coast, modern collapses are rare,
although large, ancient sinkholes are present. These probably formed origi-
nally during periods when sea level was lower, and ground-water levels and
the base level of erosion were also correspondingly lower. The breaks through
the Hawthorn Group still constitute a potential avenue for ground-water
pollution, although the impact of these features has not been investigated.
Within the zone of intermediate cover, some areas occurwhere erosion has
locally thinned the cover and the artesian pressure causes ground water to
discharge upward from the limestone, forming spring runs and streams. These
areas of thin cover are too small to show in Figure 2. In Central Florida many
spring-fed streams flow eastward into the St. Johns River. Although the
limestone is close to the land surface, pollution is not now a significant
problem because water is discharging from the aquifer. However, if the
potentiometric surface is lowered, these areas could become recharge sites
with potential contamination problems.
Surface streams also flow in many areas of the intermediate and thickly
covered zones, where the shallow water table is higher than the poten-
tiometric surface and is recharging the Floridan Aquifer slowly through the
low permeability Hawthorn confining strata. However, if buried sinkholes are
present, these breaks provide more direct avenues for rapid recharge or
contamination.
In southern Florida the cover over the Tertiary limestones is so thick (app.
1 ,000') that surface drainage is generally normal and karst is not a significant
factor with respect to pollution of the Floridan Aquifer. However, karstic
features are developing on the younger, near surface limestone which are the
major aquifers in southeastern Florida.

In northern Florida, some of the surface drainage flows westward or
southward, from the intermediate zone onto the thinly mantled zone. Where
surface drainage flows onto an area where the limestone is unconfined, the
flow disappears underground into the limestone aquifer at discrete sinking
points: stream sinks, swallets or ponors (see Figure 4). Much of this
subterranean flow reappears on the thinly covered zone as springs feeding the
Suwannee, Withlacoochee, or Santa Fe Rivers. In fact, several of the major
rivers, such as the Santa Fe, St. Mark's, and Aucilla, themselves sink and
reappear.In the latter cases, where majorstream sinks and resurgesa short
distance away, there may be caves conveying the flow directly between the
two points. However, in the caseof the nrumeroussmaller sinking streams and
the more distant springs, it is probable that this point recharge disseminates
into diffuse flow through the aquifer, later to converge at the spring. Any
contamination reaching these sinking streams will flow directly into the
aquifer and has the potential to contaminate ground-water supplies over a
broad area.
From the foregoing discussion it is obvious that karstic processes and land
forms are complex and highly variable from one area to another. It is also
obvious that these processes are a critical factor in evaluating the pollution
potential of the Florida Aquifer and protecting our valuable ground-water
supplies.

Figure 4: Cross-section showing surface drainage sinking as it passes from the
intermediate (right side) to the thinly covered zone. The steep change in elevation at the
boundary is called the Cody Scarp. Modified from Ceryak, 1977.

References Cited

Ceryak, R., 1977, Hydrogeology of a river basin in a karst terrain-Alapaha
River-Hamilton County, Florida: Suwannee R. Water Mgt. Dist., Inf. Cirrc,
Series IC 5, 20 p.
Williams P.W., 1985, Subcutaneous hydrology and the development of doline
and cockpit karst: Zeitchrift fur Geomorphologie N.F., Bd. 29, Heft 4, p.
463-482.
Wilson, W.L., McDonald, K.M., Barfus, B.L., and Beck, B.F., 1988, Hydro-
geologic factors associated with recent sinkhole development in the
Orlando area, Florida: Florida Sinkhole Research Institute Rpt. 87-88-4,
University of Central Florida, Orlando, 104 p.

Sources of Map Data

This series of fourteen maps was prepared from published data only. The
topography and drainage were interpreted from the U.S.G.S. 7V2' topographic
quadrangle maps. The information on the geology and hydrologywas summarized
from various State, Federal, local, and professional publications.The data was not
verified in the field.

In assembling such composite data from maps of various scales, some error is
bound to occur in the precise placement of the margins Further, in assigning the
various geohydrologic settings to one of eleven categories, some subjective
decisions must be made, because all areas will not fit into a category perfectly.
Therefore, the reader is cautioned to use these maps as a starting point only, and
to conduct more specific local investigations to confirm the precise site data.

These maps were prepared by professionals with due care. However, the
Florida Sinkhole Research Institute makes no warranty, express or implied, as to
the absolute validity of the data.

ADDITIONAL INFORMATION ON KARST IN FLORIDA
Beck, B.F., 1984, Sinkholes Their geology, engineering and environmental
impact: Proceedings of the First Multidisciplinary Conference on
Sinknoles, Orlando, Florida,: Rotterdam, Netherlands, A.A. Balkema,
Publisher, 429 p.
Beck, B.F., Ceryak R., Jenkins, D.T., Scott, TNM., and Spangler, D.P., 1985,
Karst hydrogeology of central and northern Florida: Rpt. 85-86-1 Florida
Sinkhole Research Institute, University of Central Florida, Orlando, 46 p.
Beck, B.F. and Sinclair, W.C., 1985, Sinkholes in Florida: an introduction. Rpt.
85-86-4, Florida Sinkhole Research Institute, University of Central Florida,
Orlando, 16 p.
Beck, B.F. and Wilson, W.L, 1987, Karst hydrogeology: Engineering and
environmental applications: Proceedings of the Second Multidisciplinary
Conference on Sinkholes and the Environmental Impacts of Karst,
Orlando, Florida. Rotterdam, Netherlands, A.A. Balkema, Publisher, 429 p.
Sinclair, W.C., 1982, Sinkhole development resulting from ground-water
withdrawal in the Tampa area, Florida U.S. Geological Survey Water
Resources Investigations Rpt. 81-50, 19 p.
SiriclairW.C., Stewart, J.W., Knutilla, R.L., Gilboy, A.E., and Miller, R.L., 1985,
Types of features and occurrence of sinkholes in the karst of west-central
Florida: U.S. Geological Survey Water Resources Investigations Rpt. 85-
4/26. 8 p.
Wilson, W.L., and Beck, B.F., 1988, Evaluating sinkholes hazards in mantled
karst terrane, in N. Sitar (ed.) Geotechnical Aspects of Karst Terrains,
Geotechnical Special Publication No. 14, ASCE, New York, NY, p. 1 -24.

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Potential for Grondater Poltion

of the Floridan Aquifer,

Based Upon Surficial Drainage, Karst
Development, and Overburden Characteristics,

Expla natory 'Text

Baxry F. Beck

Much of Florda's land surface is karst: a landscape characterized by
sinkholes, sinlrking streams, ;caveand large springs. The characterstics of
this topography determine the path of the water that recharges the Floridan
Aquifer, and the movement ofwater within the aquifer. The nature oftthe karst
topographyalsoQcontrolsthe route' by which contaminantsemaylreach the
aquifer and pollute our valuable ground-water supply. Because Floridaorelies
on ground waterforits water supply more than any otherstate-approximately
90% of the water used in Florida is ground !wa ter--it is criticalthate
understand the natureof karst and how it controls the potential for gound-
water pollution
Karst topography occurs in Florida because lim-estone and dolomite underlie
theentire state and often occur at or near the surface. The Floridan Aquifer
co:mprisesthousandsof feeWof limestone and dolomite (a similarandrelated
rock) of Tertiary age.Thediscussion whichfollowsand theaccompanying
mapsrelate particularytothisaquifer and do not refer to karstfeatures ich
may be forming on the younger limestones which are important aquifers in
Sout h Forda.
Limesone anddolomite are distinctly more soluble than other rocks Over
millionsofyYears the limestone underlying Florida has been riddled with
cavities created bythe dissolving action of ground water. Primarypores, joints,
faults, and bedding planes have all been enlarged by dissolution creating a
3-dimension-al network of interconnecting cavities.The upper portion (ca.
30-35") of the limestone is most intensely dissolved and thereby most
Spermeable. This zone has been called theepikarsticzone(Williams, 1985) The
process of dissolution is slow and complex and the enlarged drainage paths
throughout the aquifer have developed over millions of years The process of
solution itself is not causing any significant changes within man'stimeframe.

ENLARGED FISSURES
OR WARREN

During the last two million years, the Floridan peninsula has been
alternately exposed toweathering above sea level, or submerged by the sea
and covered wthsedinent.Duetothe recent deposition ofmarine sediments,
dominantly sand and cay, the limestone in Florida is generally not expose
and the karst terranesreferredto as a mantled kast. Because of the recent
interaction of sea level fluctuations, marine sedimenritation, and surficial
erosion, Flcrida'skarst topography can bedividedinto four geomorhic zone
(Figure 2).

In thethhinlymrantled zone thelimestone generally is overlain by less than
25' of clayey confining beds overlain by less than 25 of surficial sand.
However, in a few areas within this zone e cver thickness may be uch
greater iirca 100' parlicuarlybeneat the Brooksvile Ridge and in
Sioutihern Pinellas CountyWhre a continues confining layer is present, a
surficial aquifer occurs in the sands. Along thewestcoastfrom Pasco to Levy
Counties, the limestoneisnearybare, being overlain by lessthan 25' of cover
sediments in total. In the northern half of the thinlycoveredzone the sands
may overie the limesonedirectly with no hydrologic separation.
In the zone of intermediatecover thickness the overlying ;edients are
generallymnore than 50' thick and in the thickly covered zone the overburden
generally exceeds 517. The limestone aqufer i confined in/both zones,
usually by more than 50' of clayey, low permeability Hawthorn Group
sediments which in turn are overlain by younger, surficial sands. The
Hawthorn sediments also protect the aquifer fromthe doward leakage of
surface pollutants.The sandsoveryingthe Hawthorn form a perched surficial
aquifer which often contains water of poor quality.
Within Ltheintenedatezonetheeareamfe scattered areas, too small to be
shown in Figure 2, where erosionhas thirnned or iremnoved the cover and
artesian springs are found. The boundary between intermediate and.thick
cover was selected as 175'because 97of all new sinkholes in the Orlando
area occur in areas where the cover is less than 175' thick(Wilson and others,
1 988). Thus, the intermediate zone is an area of active karst collapse, whereas
in the thickly covered zone thisproblem ra rely effects the land surface today
SIt is the relationship between the unconsolidated, surficial sediment,
sinkholes, the epikarstic zone, and the deeper Floridan Aquifer which
determines the potential for ground-water pollution in many areas of Florida.
In thethinly covered zone, sinkholes are often open directytothe watertable.
In the area west of Gainesvillethese arevertically-walled pits inthe limestone
which expose the ground water in the bottom. These are known to geologists
as cenotes. In many other areas, such as along the west coast from Pasco to
Citrus Counties, a more-or-less funnel-shaped depression in the sand may
connect to an open shaft in the limestone, or the collapsed sand may cover up
the limestone, Where the water table is close to the land surface, such
sinkholes will be watei-filled. On the other hand, if the water table is deeper,
such as in the area west of Ocala, small sinkholes may be dry, even when the
limestone can be seen in the bottom, Older, broad, shallowsinkhole basins are
often dry because they usually do not intercept the water table. However,
throughout the thinly covered zone it is obvious that any contaminated water
which is allowed to drain directly into a sinkhole will quickly reach the ground
water in the aquifer and degrade the quality of the potable water supply.
In the zones of intermediate and thick cover a cap of low permeability
Hawthorn sediment generally protects the Floridan (limestone) Aquifer from
direct infiltration from the surface. However, throughout most of these zones,
karstic collapses have punctured the protective cap of Hawthorn strata The
large sinkhole basins and circular lakes common in this area may be ancient
karst features caused by repeated collapse and erosion. Even the larger (one
mile or more) irregular lakes are often formed from several sinkholes which
have coallesced. Beneath these basins a vertical channel of permeable
sediment interconnects the surficial sands and the Floridan Aquifer (see
Figure 3).

ENLARGED MASTER JOINT
DRAINS WATER TO DEEPER
AQUIFER -

Figure 1 : Generalized cross-section of the upper portion of the limestone and the
overlying sediment: the epikarstic zone (modified from Williams, 1985).

ZONE OF THIN COVER-

ZONE OF INTERMEDIATE
COVER

VERY THICK COVER,
YOUNGER LIMESTONE
AT SURFACE

ZONE OF

A-A' CROSS SECTION

Figure 2: Generalized map and cross-section of zonesof karst geomorphology, as
related to the Tertiary limestones in Florida.

Figure 3: Leakage through the bottom of a sinkhole lake in Florida.

At many localities younger sediments may have completely covered ancient
sinkholes or lakes, obscuring them from detection. However, the permeable
column of collapsed sediments still perforates the Hawthorn confining layer
S providing an avenue for groundwater pollution, and also making the site
susceptible to reactivatedcollapse In the zone of intermediate cover, sinkhole
collapse is still occurring today, opening direct pathways to the aquifer
In fact, man's modification of the local hydrologic conditions maytrigger or
induce collapse. The rate of infiltration from the surficial aquifer depends on
S the elevation difference between the shallow water table in the surficial sand
and the potetiometric surface of the underlying limestone (Floridan) aquifer.
Any changes which increase the difference may trigger sinkholes. The
creation of lakes, percolation ponds, or retention basins will raise the shallow
water table. The withdrawal (pumping) of water from the Floridan Aquifer will
lower the potentiometric surface. Both types of activities can cause sinkhole
collapse. Of course, sinkholes also collapse sporadically under purely natural
conditions as part of the ongoing erosion process.
In thethickly mantled zone along the east coast, modern collapses are rare,
although large, ancient sinkholes are present. These probably formed origi-
nally during periods when sea level was lower, and ground-water levels and
the base level of erosion were a lso correspondingly lower The breaks through
the Hawthorn Group still constitute a potential avenue for ground-water
pollution, although the impact of these features has not been investigated.
Within the zone of intermediate cover, some areas occur where erosion has
locally thinned the cover and the artesian pressure causes ground water to
discharge upward from the limestone, forming spring runs and streams These
areas of thin cover are too small to show in Figure 2. In Central Florida many
spring-fed streams flow eastward into the St. Johns River. Although the
limestone is close to the land surface, pollution is not now a significant
problem because water is discharging from the aquifer However, if the
potentiometric surface is lowered, these areas could become recharge sites
with potential contamination problems.
Surface streams also flow in many areas of the intermediate and thickly
covered zones, where the shallow water table is higher than the poten-
tiometric surface and is recharging the Floridan Aquifer slowly through the
lowpermeability Hawthorn confining strata However, if buried sinkholes are
present, these breaks provide more direct avenues for rapid recharge or
contamination.
In southern Florida the cover over the Tertiary limestones is so thick (app.
1, 000') that surface drainage is generally normal and karst is not a significant
factor with respect to pollution of the Floridan Aquifer. However, karstic
features are developing on the younger, near surface limestones which are the
major aquifers in southeastern Florida.

In northern Florida, some of the surface drainage flows westward or
southward, from mthe intermediate zone onto the thinly mantled zone. Where
surface drainageflows onto an area where the limestone isunconfired, the
flovvcisappears underground into the limestone aquifer at discrete sinking
points: stream;nsinks, swallets;or ponors (see Figure 4). uch of this
subterranean flow reappears on the thinly covered zone as springs feeding the
Suwrannee,'Withlacoochee, or Santa Fe Rivers. In fact, several of the major
rivers, such as the Santa Fe, St. Mark's, and:Aucilla, themselves sink and
reappear.Indithe latter cases, where a major streamsinWks and resurgesa short
distance away" there may be caves conveying the flow directly between the
two points. However, in thecase of the numerous smaller sinking streamsarind
the mo:redistant springs, t is probable*that this pointrecharge diseminates
into diffuse flow through the aqufear, later to converge at the spring Any
contamination reaching these-sinking streaks will flow directly into the
aquifer and has the potential to containiate ground-water supplies over a
broad area.
From the foregoing discussion it IS obviouS that karstic processes and land
forms are complex and highly variable fromn one area to another. Itis alo
obvious that these processes are a critical factor in evaluating the pollution
potential of the Florida Aquifer and protecting our valuable ground-water
supplies.

Figure 4: Cross-section showing surface drainage sinking as it passes from the
intermediate (right side) to the thinly covered zone, The steep change in elevation at the
boundary is called the Cody Scarp. Modified from Ceryak, 1977.

SReferences Cited
Ceryak, R., 1977, Hydrogeology of a river basin in a karst terrain-Alapaha
River-Hamilton County, Florida: Suwannee R Water Mgt. Dist., nf. Circ,
SSeries IC-5, 20 p..
Williams P.W., 1985, Subcutaneous hydrology and the development of doline
and cockpit karst: Zeitchrift fur Geomorphologie N.F., Bd. 29, Heft 4 p
463-482. '
Wilson, WL, McDonald, K.M., Barfus, B.L., and Beck, B.F., 1988, Hydro-
geologic factors associated with recent sinkhole development in the
Orlando area, Florida: Florida Sinkhole Research Institute Rpt. 87-88-4,
University of Central Florida, Orlando, 104 p.

Sources of Map Data
This series of fourteen maps was prepared from published data only. The
topography and drainage were interpreted from the U.S.G.S. 712' topographic
quadrangle maps. The information on the geology and hydrology was summarized
from various State, Federal, local, and professional publications. The data was not
verified in the field.
In assembling such composite data from maps of various scales, some error is
bound to occur in the precise placement of the margins. Further, in assigning the
various geohydrologic settings to one of eleven categories, some subjective
decisions must be made, because all areas will not fit into a category perfectly
Therefore, the reader is cautioned to use these maps as a starting point only, and
to conduct more specific local investigations to confirm the precise site data.
These maps were prepared by professionals with due care. However, the
Florida Sinkhole Research Institute makes no warranty, express or implied, as to
the absolute validity of the data.

ADDITIONAL INFORMATION ON KARST IN FLORIDA
Beck, B.F., 1 984, Sinkholes: Their geology, engineering and environmental
impact: Proceedings of the First Multidisciplinary Conference on
Sinkholes, Orlando, Florida,: Rotterdam, Netherlands, AA Balkema,
SPublisher, 429 p.
Beck, BF., Ceryak R., Jenkins, D.T., Scott, TM., and Spangler, D.P., 1985,
Karst hydrogeology ofcentral and northern Florida: Rpt, 85-86-1, Florida
Sinkhole Research Institute, University of Central Florida, Orlando, 46 p.
Beck, B.F. and Sinclair, W.C., 1985, Sinkholes in Florida: an introduction: Rpt.
85-86-4, Florida Sinkhole Research Institute, University of Central Florida,
Orlando, 16[p.
Beck, B.F. and Wilson, W.L., 1987, Karst hydrogeology: Engineering and
environmental applications: Proceedings of the Second Multidisciplinary
Conference on Sinkholes and the Environmental Impacts of Karst,
Orlando, Florida: Rotterdam, Netherlands, A.A. Balkema, Publisher, 429 p.
Sinclair, W.C., 1982, Sinkhole development resulting from ground-water
withdrawal in the Tampa area, Florida: U.S. Geological Survey Water
Resources Investigations Rpt. 81-50, 19 p.
Sinclair, W.C., Stewart, J.W., KnutilHa, R.L, Gilboy,A.E.,,and Miller, R.L, 1985,
Types of features andoccurrence of sinkholes nthe karst of west-central
Florida: U.S. Geological Survey Water Resources Investigations Rpt 85-
4/26. 81 p
Wilson, W.L., and Beck, B.F., 1988, Evaluating sinkholes hazards in mantled
karst terrane, in N Sitar (ed ) Geotechnical Aspects of Karst Terrains,
Geotechnical Special Publication No. 14, ASCE, New York, NY, p. 1-24.

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	Composite sheet
	Daytona Beach
	Fort Pierce
	Gainesville
	Orlando
	Pensacola
	Tallahassee
	Tampa
	Tarpon Springs
	Valdosta

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