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UNITED STATES DEPARTMENT OF THE INTERIOR
FLORIDA DEPARTMENT OF NATURAL RESOURCES
published by BUREAU OF GEOLOGY
GUIDE TO USERS OF GROUND WATER
IN BAY COUNTY, FLORIDA
James B. Foster
UNITED STATES GEOLOGICAL SURVEY
in cooperation with the
BUREAU OF GEOLOGY
FLORIDA DEPARTMENT OF NATURAL RESOURCES
This atlas provides information to Bay County home owners, well
drillers, and others who are interested in obtaining water from wells.
The atlas can be used to determine the approximate depth to the top of
the water bearing limestone (the Floridan aquifer) and to determine the
minimum length of casing required for a well tapping the limestone.
The approximate thickness of limestone that must be penetrated by a
well to assure an adequate yield, the location of water of good quality,
the yield of a well, the dissolved solids and selected minerals in the
water, and the types of rocks generally penetrated can also be
Bay County, in the Florida Panhandle, borders the Gulf of Mexico.
The county has an area of 861 square miles, including 114 square miles
of inland water area. Much of the county is forested. Its topography is
varied; it contains, in addition to lakes and streams, sand hills, coastal
sand dunes, wave-cut bluffs, and sinks.
Bay County, roughly triangular in shape, ranges in altitude from sea
level to about 240 feet in the northeast corner. The county is underlain
by water-yielding zones in both the sand and limestone strata. Although
the supply of ground water is abundant, little is being used at the
present time (1970). Numerous small-diameter wells supply water from
the sand aquifer and from the deeper limestone aquifer. The wells that
tap the sand are screened at the bottom of the casing; those that tap the
limestone are unscreened, and the casing terminates in the top of the
The sand overlying the limestone aquifer is variable in physical
character, with one or two recognizable water- bearing sections. A thick
clay bed separates the sand from the limestone aquifer.
The water-table aquifer is composed of sand and gravel with sandy
clay lenses. Its thickness is variable up to 140 feet along the coast.
Water levels range from 3 to 65 feet below land surface.
Six-inch-diameter wells may supply as much as 150 gpm (gallons per
minute). The Springfield area, the only area of large water use in Bay
County, has 12 industrial wells (8 to 18 inches in diameter) tapping
gravel beds of the water-table aquifer, which yield from 190 to 400
A shallow artesian aquifer, consisting of shell beds and limestone
lenses, underlies the coastal part of Bay County. Its permeable zones
are 10 to 25 feet thick and are generally between 80 and 170 feet
below land surface. Wells 2 to 6 inches in diameter that tap the shallow
artesian aquifer yield from 10 to 100 gpm. Water from the area
adjacent to the bays and the Gulf is not potable; chloride content is as
much as 1,400 mg/1 (milligrams per liter). A bed of sandy clay separates
the shallow artesian aquifer from the overlying water-table aquifer.
Water in the sand aquifers generally is soft but acidic (pH 5.5 to 6.5),
which makes it corrosive. It may contain high concentrations of iron,
making it unsuitable for domestic use. Along the coast and adjacent to
the bays, the sand contains saline water.
The limestone (Floridan) aquifer is the deepest fresh-water-bearing
stratum of the county. It is at sea level in the northeast and dips to
about 250 feet below sea level at the coast. Because of faulting, these
strata are offset as much as 100 feet near Panama City. Water levels
generally are not affected by the faulting, so that the water levels in
wells tapping the limestone aquifer are the same on both sides of the
faults. Water levels are highest in the northeast and lowest toward the
The only large-capacity wells now being used to withdraw water
from the limestone aquifer are 3 public-supply wells at the U.S. Navy
Mine Defense Laboratory, 2 at Long Beach Resort, 3 at West Panama
City Beach, and 2 at Lynn Haven. See the hydrologic map for well
locations. Two industrial wells are in operation at the Lansing Smith
Steam Plant north of St. Andrew Bay.
The height of water levels in wells is determined by water pressure in
the aquifer. Wells in which water rises above the top of the aquifer
tapped are artesian; if the pressure is great enough to lift the water
above land surface, the well flows. Such wells predominate in the
stream valleys of Bay County. The level to which water rises in artesian
wells establishes an imaginary surface (potentiometric surface), which is
not a level plane but, in Bay County, has about the same slope as the
surface of the limestone aquifer.
If wells are spaced too closely, heavy pumping can create severe
water-level declines, owing to mutual interference or overlapping
pumping effects. Properly constructed wells tapping a limestone aquifer
have casings set several feet into the limestone, tightly enough to avoid
movement of water between the limestone and sand aquifers. Properly
constructed wells tapping a sand aquifer are cased to the water-bearing
strata and screened in that strata with the appropriate screen-size for
maximum sediment-free water supply. Also, construction at the land
surface is adequate to prevent surface drainage into the well.
Use of the atlas is illustrated by considering an arbitrary well site
(identified by a square labeled W on all maps) on State Road 77 just
north of Vicksburg. On the map showing contours, this site is about
half-way between the 40- and 80- foot land-surface contours. The site
altitude, therefore, is some 60 feet above mean sea level. The altitude of
the top of the limestone aquifer (or the base of the clay) can be
determined similarly. W's location is 84 percent of the distance from
the zero contour to the minus-50 contour on the top of the limestone.
Hence, at W, the top of the limestone is estimated to be 84 percent of
minus 50, or 42 feet below sea level. The sum of these two vertical
distances, 60 feet above sea level and 42 feet below it, is the estimated
depth to the top of the limestone, 102 feet below land surface. A well
drilled here would thus require about 102 feet of casing, plus a few feet
additional to set the casing into the limestone. At site W, the water level
is an estimated 42 feet above sea level-the point is 40 percent of the
distance from the 40- to the 45-foot water-level contour-so that the
depth to water in a well at W, tapping the limestone aquifer, is
estimated to be 60 feet minus 42 feet, or 18 feet below land surface.
A properly developed well at W that penetrates as much as 135 feet
of the limestone aquifer could be expected to yield more than 20 gpm
per foot of drawdown, as shown on the map illustrating the areal
variation of water yield.
The depth below land surface at W for pump settings can be
estimated as follows: divide the pump capacity (in gallons per minute)
by 20 to find the number of feet that the water level in the well will
draw down during pumping; add this footage to the depth to water (18
feet); and add enough extra footage for natural fluctuations in the
water level from wet to dry years. Less than 8 feet in water-level change
may be expected as a result of annual variation in rainfall, but levels
may fluctuate seasonally as much as 30 feet in wells located near other
wells whose yields are very high.
Assuming installation of a pump with a capacity of 40 gpm at point
W-divide 40 by 20 for 2 feet of drawdown, which, added to the
18-foot static water level gives a 20-foot pumping level at 40 gpm; add
8 feet for variations in rainfall, and the total, 28 feet, is the depth for
proper pump setting. If nearby wells are heavily pumped, the extreme
30-foot seasonal fluctuation could be added instead of the 8 feet caused
by rainfall variation. The pump would then be set at a depth of 50 feet.
The water from a well at point W could be expected to contain the
following mineral concentrations, as illustrated by four maps: the
dissolved-solids map, 100-200 mg/I; the hardness map (hardness
expressed as calcium carbonate), 100-200 mg/1; the chloride map, less
than 50 mg/1; and the fluoride map, less than 0.5 mg/I. Wells that
penetrate the upper 50 feet or less of the limestone will probably yield
water with mineral concentrations on the low side of these ranges.
Additional information may be obtained from publications cited in
Edward E. Johnson, Inc.
1966 Ground water and wells: Saint Paul, Minnesota 55104.
Musgrove, R. H.
1965 (and Foster, J. B. and Toler, L. G.) Water resources of
Econfina Creek basin area in northwest Florida* Florida
Geol. Survey Rept. Inv. No. 41.
Musgrove, R. H.
1968 (and Foster, J. B. and Toler, L.G.) Water resource records
of the Econfina Creek basin area, Florida: Florida Div. of
Geol. Inf. Circ. No. 57.
Toler, L. G.
1964 (and Musgrove, R. H. and Foster, J. B.) Freshening of Deer
Point Lake, Bay County, Florida. Am. Water Works Assoc.
Journal, Vol. 56, no. 8, pp. 984-990.
U. S. Dept. of Health, Education, and Welfare
1962 Public Health Service drinking water standards: U. S.
Public Health Service Pub. No. 956 (1963).
1962 Manual of individual water supply systems U. S. Public
Health Service Pub. No. 24.
Sand, fine, brown to
white, some cloy
n C. )
Shell,sand and cloy i-r-F
Cloyey sand, block phosphorite -_ -
Cloy, green, fine
Limestone, grey to -
white, with interloyed -
beds of grey-green I -
cloy limestone -
Limestone. hard groy
Soft limestone, gray. I
block phosphorite s.ar-i. -
some limestone mu ,
I imestone, hord I I 1
RESISTIVITY IN OHM-METERS
10 20 30
I I II I I I I I I I I I I I
86-001 55 50' 45 40!' 35' 30' 25' e8521'
I ''' I I I I I I 1 1 1 i J-7-
50 to 100
100 to 150
D 150 to 200
I 200 to 250
The colored areas on each of these four maps show the expected
dissolved solids, hardness and concentrations of chloride and fluoride in
water that taps the upper part of the limestone aquifer. Each map
shows that the concentration of minerals being depicted is highest near
the coast. The mineral content reflected by the dissolved-solids
measurement includes calcium, magnesium, sodium, potassium,
bicarbonate, sulfate, and chloride. Other constituents are, of course,
included in the array of minerals dissolved in water but almost always
are present in small quantity. The U. S. Public Health Service standards
(1962) recommend 500 mg/I as the upper level of dissolved-solids
Graphic logs are one way to show the types of rocks and thicknesses
of strata. They are constructed from information obtained by careful
inspection of drill cuttings collected as a well is being drilled. The
accompanying graphic log is based on an examination of the cuttings
from a well 604 feet deep located southwest of Hathaway bridge.
There, limestone was penetrated at about 240 feet. The permeability of
the strata penetrated varies considerably, from "very poor" to "good."
Permeability determines the amount of water that can be pumped from
a well with a given amount of drawdown.
The water velocities in a nearby well, measured with a current meter,
indicated that virtually all the water comes from the limestone near the
300-foot zone identified as "good" on the relative permeability log.
The resistivity log, on the extreme right, indicates, among other
things, the electrical resistivity of the water in the limestone. If
resistivity of water is high, its mineral content is low. In the log shown,
the decrease in resistivity with depth indicates increasing mineral
content of the water. From 540 feet to the bottom of the well the
water is highly mineralized. This increase in mineral content (with
depth) persists throughout the county, although highly mineralized
water is 800 to 1,200 feet below land surface in other places.
Yields (in gallons per minute per foot of drawdown) are, in general,
least in wells that penetrate the upper part of the limestone aquifer near
the coast and increase greatly inland. This is shown by considering the
drawdown (due to pumping) required to produce a given yield. For
example, the water level in a well pumped at 20 gpm would be drawn
down less than 1 foot in the yellow area; I to 2 feet in the blue area; 2
to 4 feet in the green area; and 4 to 20 feet in the red area. At point
W, by drawing the water level down to the top of the limestone, 1,500
gpm could be withdrawn. To obtain the greatest yield possible from a
well in Bay County, it is necessary to develop the well properly: a
comprehensive description of methods and results of well development
is presented on pages 295-312 in Ground Water and Wells,published by
Edward E. Johnson, Inc., 1966.
Two different kinds of water-level fluctuations are shown by the
hydrograph for a well tapping the limestone aquifer. The seasonal
fluctuations, which produce the "saw tooth" pattern, are caused by
changes in pumping in the area and by the distribution of rain during
the year. The combined effect of rainfall and pumping determines the
extent of the variation of water level from the high in January to the
low in July. The second kind of fluctuation is the long- term decline in
level from 1946 to 1963. It reflects an annual increase in pumpage in
the Panama City area and the generally below normal rainfall of the
period except from 1957 to 1959, when the decline was interrupted by
above- average rainfall.
The water level rise caused by above-average rainfall in 1964-66 is
marked by the greater rise that began in January 1964, when pumping
ceased at the International Paper Company well field. The rapid water-
level rise of 1967 resulted from the July cessation of pumpage of the
city well fields in the St. Andrew and Millville sections of Panama City.
A geologic section can be drawn by using the graphic logs from a
series of wells drilled in a line. The geologic section portrays the types
of rocks and their thicknesses penetrated by wells drilled along the
section. The positions of the sections are shown on the water-hardness
map. The clay confining beds prevent movement of water between the
limestone aquifer and the overlying sand aquifer. The clay beds confine
the water in the limestone under artesian pressure sufficient to raise the
water level in wells above the top of the limestone. Locally, the
pressure is sufficient to raise the level above land surface.
As with dissolved solids, the hardest water is pumped from wells
along the coast. Water with a hardness of less than 60 mg/I is considered
soft; 60-120 mg/l, moderately hard; 120-200 mg/l, hard; and more than
200 mg/I is very hard.
In most of Bay County, water from the upper part of the limestone
aquifer contains less than 50 mg/I chloride, well below the 250 mg/I
limit recommended by the U. S. Public Health Service for drinking
U D U- UPTHROWN
WATER TABLE AQUIFER
SHALLOW ARTESIAN AQUIFER
* FLORIDAN AQUIFER
i, 0 5 10 MILES -
WEST VERTICAL SCALE EXAGGERATED EAST
In water from the limestone aquifer throughout most of the county,
fluoride content is less than 0.5 mg/l. The Public Health Service (1962)
establishes the maximum recommended limit of fluoride as 1.0 mg/I for
an area with an annual average maximum daily air temperature of 70.7
to 79.2 degrees F. Concentrations of 0.7 to 1.0 mg/I are considered
beneficial in the reduction of dental cavities.
Published by the Department of Natural Resources, 0U) O
Division of Interior Resources, Bureau of Geology. This a, 0
public document was promulgated at a cost of $1,416.50
or ($0.945) per copy for the purpose of disseminating
Water Resources data.
MAP SERIES NO. 46
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