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STATE OF FLORIDA
DEPARTMENT OF NATURAL RESOURCES
Harmon Shields, Executive Director
DIVISION OF RESOURCE MANAGEMENT
Charles M. Sanders; Director
BUREAU OF GEOLOGY
Charles W. Hendry, Jr., Chief
REPORT OF INVESTIGATIONS NO. 72
HYDROLOGIC CONCEPTS OF ARTIFICIALLY
RECHARGING THE FLORIDAN AQUIFER IN
EASTERN ORANGE COUNTY, FLORIDA--
A FEASIBILITY STUDY
Darwin D. Knochenmus
UNITED STATES GEOLOGICAL SURVEY
in cooperation with the
BUREAU OF GEOLOGY
FLORIDA DEPARTMENT OF NATURAL RESOURCES
CENTRAL AND SOUTHERN FLORIDA FLOOD CONTROL DISTRICT
REUBIN O'D. ASKEW
BRUCE A. SMATHERS
Secretary of State
PHILIP F. ASHLER
RALPH D. TURLINGTON
Commissioner of Education
ROBERT L. SHEVIN
GERALD A. LEWIS
Commissioner of Agriculture
HARMON W. SHIELDS
LETTER OF TRANSMITTAL
Bureau of Geology
August 28, 1975
Governor Reubin O'D. Askew, Chairman
Florida Department of Natural Resources
Tallahassee, FL 32304
Dear Governor Askew:
The Bureau of Geology of the Division of Resource Management, Florida
Department of Natural Resources, is publishing as its Report of Investiga-
tions No. 72, a study, "Hydrologic Concepts of Artificially Recharging the
Floridan Aquifer in Eastern Orange County, Florida-A Feasibility Study",
by Darwin D. Knochenmus, of the U. S. Geological Survey.
Artificial recharge of the Floridan Aquifer is a most important water
management tool in that it captures rainfall that otherwise would run off or
be lost by evapotranspiration. This means of increasing the amount of water
in storage and available for development from the Aquifer is one that will
be looked at in substantially more detail in many areas of the State of Florida
in the near future.
Charles W. Hendry, Jr., Chief
Bureau of Geology
Completed manuscript received
May 7, 1975
Printed for the
Florida Department of Natural Resources
Division of Resource Management
Bureau of Geology
Abstract ................................................................................. ... ........... ........ 1
Introduction ......................................................... ................................................. ........................................ 2
Purpose and Scope .................................. ........................... 2
Acknowledgments ....................................................................... 3
Geography ..... ............................................................................... 3
Location ................................................................................. ........... 3
C lim a te .... ................................... ........................................................................... .......................... 3
Topography .............................................................................. ... 5
Drainage ..................................................... ................ .......... ................. 5
H ydrologic system ................................ ........ ............ ... .............................. 7
Hydrogeologic framework ...................................................... ..... 7
Hydrology of surficial water .............................. ...--... .... .. ....... 13
R rainfall ........................................... .................................. ............................................................. 13
E vapotranspiration ................ ........ ....... ..................................... ................ 13
Runoff ....................... ............... .... ................. 13
Infiltration and aquifer storage .....................~............................................ 14
W after quality ........................... .............. ...................... ............. .......... .. 14
Hydrologic concepts of artificial recharge ..... ................ ............ ..... 17
Source of recharge water ............................... ..... .... .... .... .... ............ 17
Schemes for capturing water from potential losses ......... ........ ................... 19
Surface impoundments ..................................................................................... .. 19
C onnector w ells .................................... .. ..... .......... ... ............. .... ............... .............. 21
E valuation of scheme es .............................. .................................. .......... ................................ 21
Capture of w after ................................... ...................................... ............................. ............... 21
Land utilization ............................................................ .......... .............. 21
W after treatm ent ............................................................ .................... ............. ...... 24
L and acquisition ..... .............. ....... .. ............................................. ........ 24
Analysis of a connector-well network .................................. ..... 24
Operational connector wells ..... ................. .. ............... ............ ............ 32
Water-quality considerations ............................ ............... ....................... .... 32
Subsequent withdrawal of recharged water ...... .. .... ....... 33
Summary and conclusions ..................... ............ ............................ .... ....... 33
R references cited .................................................................... ....................................... 36
1. Location map of eastern Orange County 4
2. Map showing drainage basin boundaries and physiographic
divisions ______ 6
3. Hydrogeologic sections across eastern Orange County 8
4. Hydrographs of wells tapping the nonartesian, shallow arte-
sian and Floridan aquifer near Bithlo ...... .. 9
5. Map showing depth to the top of the Floridan aquifer ....... 11
6. Potentiometric map of the Floridan aquifer at normal condi-
tions, July 1961 12
7. Map showing areal distribution of average annual water losses
through evapotranspiration and runoff. 1____..._.. 15
8. Map of the dissolved-solids concentration of water in the upper
part of the Floridan aquifer, 1960-62 16
9. Map showing area of inundation and contributing area of sur-
face impoundment scheme 20
10. Schematic sectional view of a connector well between nonar-
tesian and Floridan aquifers 22
11. Contour map of head difference between nonartesian and
Floridan aquifers 23
12. Schematic curve illustrating the capture-drawdown function_ 25
13. Diagrammatic plan view and section showing the physical con-
cepts of a connector-well network ._____ 27
14. Graph for determining well spacing in a square-grid connector-
well network 28
1. Chemical analyses of water from various environments in east
Orange County 18
2..Well spacing 1, well discharge Q, and number of wells per
square mile Nwfor upper and lower limits of transmissivity T,
capture rate Co, effective drawdown se, and available draw-
down sw, and for well radii rwof 0.25 and 0.5 foot 30
HYDROLOGIC CONCEPTS OF ARTIFICIALLY
RECHARGING THE FLORIDAN AQUIFER IN
EASTERN ORANGE COUNTY, FLORIDA-
A FEASIBILITY STUDY
Darwin D. Knochenmus
Artificial recharge in eastern Orange County is worth consideration. The
hydrologic system is suitable for gravity flow through a network of connector
wells to recharge the Floridan aquifer from the nonartesian aquifer. Also, the
Floridan aquifer needs the additional fresh water to prevent migration of
brackish water into the area as rates of withdrawal are increased.
The hydrologic system cycles about 55 inches of rainfall per year of which
10 to 15 inches runs off, 40 to 45 inches evapotranspires, and 0 to 2 inches
recharges the Floridan aquifer. The hydrogeologic framework consists of a
nonartesian aquifer that is separated from the underlying Floridan aquifer
by a confining layer. The water table in the nonartesian aquifer is near land
surface and as much as 30 feet above the altitude of the potentiometric surface
of the Floridan aquifer. Dissolved-solids concentration of water in the non-
artesian aquifer is less than that of the water in the Floridan.
The supply of water for artificially recharging the Floridan through a
network of connector wells that also tap the nonartesian aquifer could be
derived from the capture of potential water losses evapotranspiration and
runoff. This recharge water would be replaced in the nonartesian aquifer by
the capture of rainfall that otherwise would run off or be lost to evapotrans-
piration. However, the water table must be lowered before capture can occur.
Systematically lowering the water table requires a network of connector
wells. The spacing of the wells in the network depends on the transmissivity of
the nonartesian aquifer, the available drawdown in the connector well, the
well radius, and the capture-drawdown function. The average thickness of the
nonartesian aquifer is 50 feet and its average transmissivity is estimated to be
between 125 and 625 ft2 per day (feet squared per day). The capture rate
is estimated to be between 0.5 and 1.5 feet per year with an effective draw-
down between 5 and 10 feet. The well spacing for a network of fully penetrat-
ing 6-inch connector wells would be 2,220 feet for an aquifer having a trans-
missivity of 625 ft2 per day, a capture rate of 0.5 foot per year, and an effec-
tive drawdown of 5 feet. A higher capture rate would require additional wells
and closer spacing.
The relation between the amount of capture and amount of drawdown,
presently unknown, is a critical parameter in the analysis of connector-well
recharge. An investigation of the capture-drawdown function in eastern
Orange County would appear to be a logical step to provide the needed data.
BUREAU OF GEOLOGY
PURPOSE AND SCOPE
The largest dependable source of water in central Florida is the Floridan
aquifer. Its water quality grades from fresh in the central region to brackish
near the coast. The occurence of brackish water has forced coastal cities to
find other less dependable sources such as lakes or shallow ground water. The
city of Cocoa, in order to obtain a dependable source of water, drilled their
public supply wells 25 miles inland where the aquifer contains fresh water.
In that part of east-central Florida where the water in the Floridan aquifer
changes in quality from fresh to brackish, the terrain is swampy and of low
relief. Potential ground-water recharge in this water-logged area is lost by
surface runoff and evapotranspiration. If these water losses could be reduced
and that water used to artificially recharge the aquifer, the transitional zone
would be displaced toward the coast and greater amounts of fresh water could
be withdrawn. With the availability of greater amounts of fresh water, coastal
cities would not have to drill new wells farther and farther inland to satisfy
growing demands, and legal conflicts between local governments over water
rights would be reduced.
The purpose of this report is to present the hydrologic concepts involved
in artificially recharging the Floridan aquifer through connector wells by
gravity flow and to formulate and evaluate models of various connector-well
The investigation was limited to eastern Orange County. an area whose
general hydrology is known from previous investigations. There, a 1-year
feasibility study need be concerned primarily with assembling and analyzing
all readily available hydrologic and geologic information as it relates to arti-
ficial recharge. Eastern Orange County is considered an appropriate study
area also because it is experiencing water problems associated with increased
withdrawals from the Floridan aquifer. The dearth of geologic information on
near-surface deposits made it necessary to drill some shallow test holes. Twelve
test holes were drilled and about 100 cores were taken for laboratory analyses
of aquifer characteristics.
The specific objectives of this investigation were to determine the quantity,
quality, source and areal extent of water lost from the area by surface runoff
and evapotranspiration; the quantity, quality and areal extent of water in the
surficial sediments; the quantity of water that might be available for recharge;
the means of inducing recharge; the areas most hydrologically favorable for
construction of recharge works; and the probability of recharge water re-
maining in storage as a discrete volume for future recovery.
The feasibility study in eastern Orange County should have transfer value
to other coastal areas in east-central Florida because many have similar
hydrologicc systems and are in need of increasing their supply of fresh water.
REPORT OF INVESTIGATION NO. 72
This report was prepared by the U. S. Geological Survey in cooperation
with the Central and Southern Florida Flood Control District. The investiga-
tion was under the direct supervision of Joel O. Kimrey, Chief, Winter Park
Subdistrict and general supervision of Clyde S. Conover, District Chief, Water
Resources Division, U. S. Geological Survey.
Personnel of the U. S. Geological Survey who contributed significantly to
the project were: Peter Bush, hydraulic engineer, James Holly, engineering
technician, who provided assistance during the test drilling program, Hilton
Cooper, research engineer, and Stavros S. Papadopulos, research hydrologist,
who provided valuable assistance in formulating and evaluating the mathe-
matical models of the aquifer system.
To all who contributed to the project, the author expresses his sincere
The study area encompasses about 300 square miles between latitude 280
20' and 28040' and longitude 81o00' and 81015' in eastern Orange County.
This area lies east of Orlando and west of the St. Johns River (fig. 1.) There
is very little development in the eastern part of the county except in the north-
ern sector along State Highway 50 where small businesses and subdivisions
are spreading eastward from Orlando. Most of the area is in pine woods and
cypress heads where major land use is forestry and natural pasture. A few
sections in the vicinity of Wewahootee Road and Econlockhatchee River have
recently been developed for grain farming and citrus. In this same general
area the city of Cocoa has a well field for their municipal supply (fig. 1).
Orange County is in the north-central climatic division of Florida as
segmented by the Environmental Data Service for the collection of climatic
records. Complete temperature and rainfall records are collected at the Or-
lando station and supplementary rainfall records are collected at Bithlo and
The area has a subtropical climate; its average annual temperature is 220C
(710F) and its average rainfall is slightly more than 51 inches. These aver-
ages are computed from long-term records for the normal climatic period
(1931-60) at Orlando. Eastern Orange County may have slightly more rainfall
than Orlando as is suggested from a comparison with shorter-term records at
.I I -- -- -.
L 1 1) I1 1 (
1i i r '
Eastern Orangci PD
County or 'd
City of Co
n well ,
LINE OF HYDROGEOLOGIC SECTION
( SEE FIGURE 3 )
Figure 1.-Location map of eastern Orange County.
I b I 4 M It t Ik
REPORT OF INVESTIGATION NO. 72 5
Records have been collected at Bithlo for the last 12 years (1960-71) and
during that time annual rainfall has averaged about 4 inches more than at
Orlando. For the same 12 years, the average annual rainfall at Orlando has
been equal to the long-term average of 51 inches.
Rain on the area is not distributed equally with time. About 60 percent
falls in June, July, August, and September, at an average rate of 7-8 inches
Eastern Orange County was included in the Coastal Lowlands division of
Cooke's (1939) generalized physiographic description of Florida. Puri and
Vernon (1964), while describing the landforms of Florida in greater detail,
called the section of the Coastal Lowlands that includes most of eastern Orange
County, the Osceola Plain. It extends from the central highlands eastward
to the coastal lowlands. The study area is wholly within the Osceola Plain ex-
cept for a small part along the St. Johns River that is in the Eastern Valley
This gently sloping plain is highest, just over 90 feet above msl (mean sea
level), along a north-south line of rolling hills which form a drainage divide
between the Little Econlockhatchee and Econlockhatchee Rivers. From the
divide the land slopes westward to an altitude of 40 feet in the Little Econlock-
hatchee River valley and eastward to an altitude of 30 feet in the Econlock-
hatchee River valley. The divide between the Econlockhatchee drainage and
the St. Johns River basin is a flat plain with altitudes just over 75 feet.
The landforms, such as the gently rolling hills, the sloping plains, the river
valleys and the escarpment separating the Osceola Plain from the Eastern
Valley are all aligned parallel to the Atlantic Coast suggesting a coast-related
The principal form of drainage is by surface streams, but due to a poorly
developed system the area is wet and swampy much of the time. The most
poorly developed part of the drainage system, and therefore the wettest, is
along the broad basin divides. The St. Johns River forms the east boundary
of Orange County and 45 percent of the study area drains eastward through
small tributaries directly into the St. Johns. Thirty percent-in the middle of
the study area-drains to the north by the Econlockhatchee River. The north-
western section-14 percent-is drained to the north by the Little Econlock-
hatchee River and the southwestern section-11 percent-to the south by the
headwaters of the Kissimmee River (fig. 2),
c o u N r r
10 05' 81000' 55'
Figure 2.-Map showing drainage basin boundaries and physiographic
REPORT OF INVESTIGATION NO. 72
The Osceola Plain is dissected in varying degree by these four drainage
systems. The small tributaries to the St. Johns River flow through the eastern
edge of the Osceola Plain, cut through the escarpment and debouch into the.
swamps of the Eastern Valley. The valleys of the Econlockhatchee and Little
Econlockhatchee Rivers become more dissected near the north edge of the
county as the streams flow northward out of swamps in the south. Dissection
is least where the headwaters of the Kissimmee consist of north trending
elongate swamps separated by slightly raised knobs of land.
The hydrogeology in eastern Orange County is simple. The groundwater
system consists of a nonartesian aquifer lying above the Floridan aquifer but
separated from it by a thick confining layer (fig. 3). Within the confining
layer are discontinuous shell beds, sand lenses and limestone layers which
form secondary artesian aquifers. The hydrogeologic sections on figure 3
were adapted from the geologic sections of Lichtler and others (1968, fig. 6).
The nonartesian aquifer extends throughout the area and ranges in thick-
ness from 40 to 80 feet. At land surface the aquifer material is a fine sand
which becomes progressively finer grained with depth until the material is
predominantly clay at which point it is appropriately classified as a confining
bed. Generally at depths below 20 feet the aquifer contains layers which con-
sist partly, or in some cases, entirely of shells. The layers that consist predomi-
nantly of shells have the greatest permeability of any of the material in the
nonartesian aquifer. Permeability is a measure of the ease with which a por-
ous medium can transmit a fluid-in this case water. The sand in the upper
part of the aquifer is the second most permeable material, after which the
permeability decreases with depth as the clay content increases. The geologic
age of the materials comprising the nonartesian aquifer ranges from Holocene
to upper Miocene (Lichtler, 1968).
Except under the areas of greatest relief and highest altitude, the water
table in the nonartesian aquifer is generally within 5 feet of the land surface
and fluctuates within this range (fig. 4). This high water table in combination
with the flat terrain creates a very wet and swampy area.
Water-level declines are small and primarily the result of evapotranspira-
tion as surface drainage is not greatly incised, and downward leakage is
The confining layer that separates the nonartesian aquifer from the Flori-
dan aquifer ranges in thickness from 60 to 300 feet (fig. 3). It is composed
8 BUREAU OF GEOLOGY
S PUalmtarine Sater.
VEL .- ...... LEVEL
CONFINING .. AYER...
NONARTESIAN AQUIFER .
a200' F D- FLORIDAN AQUIFER 200'
VERTICAL EXAGGERATION X 106
0 I 3 4 S MILES
B gWa Table 0 0 Patentiooltric Surface u B
r r s te u d m t o w f t Florida n Aq uifer
NONAII ESIAN --AQUIFER
....-- .. = ......'.-... .- : -- -
myc -FLORIDAN AQUIFER 300
Figure 3 --Hydrogeologic sections across eastern Orange County.
principally of a mixture of sand, shell and clay, all of the Hawthorn Formation
af Mocene age. Where the sand and shell constitute discrete strata within the
ranfiing layer they yield water to wells. These strata are referred to collec-
tively as the secondary artesian aquifers. One such shell bed is 25 feet thick.
The finer-grained strata of the confining layer and of the material above it
retard the downward movement of water from the nonartesian aquifer to the
Floridan. In the artesian-flow area along the St. Johns River the confining
layer retards the upward movement of water from the Floridan aquifer.
The contact between the nonartesian aquifer and the confining layer is
transitional: the beds become finer grained with depth. Thus the placement of
the contact on figure 3 was arbitrarily selected, depending upon the degree
of fine-grained material. The lower contact, that with the Floridan aquifer, is
placed at the top of the Eocene limestones. In a few places 5 to 10 feet of
I (SHALLOW ARTESIAN AQUIFER)
(SHAL (FLORIDAN AQUIFER)
Floridan aquifer near Bithlo.
Flogoridan aquifer near Bithlo.
BUREAU OF GEOLOGY
limestone at the base of the Hawthorn Formation is hydraulically part of the
The potentiometric level of the secondary artesian aquifer fluctuates slight-
ly less than 5 feet, similar to the magnitude of the fluctuation in the non-
artesian aquifer (fig. 4). Response of the potentiometric surface to rainfall
is less rapid than the response of the water table but in general, both rise and
decline similarly during wet and dry seasons.
The Floridan aquifer is the principal aquifer in the area, both in its
hydraulic capability and areal extent. It is highly permeable and large wells
may yield as much as 4,000 gpm (gallons per minute). The aquifer consists
of nearly 2,000 feet of dolomitic limestone of Eocene age (Lichtler and others,
1968). Solutional processes in this limestone have produced a highly cavern-
ous aquifer having a high secondary permeability. Solution of the carbonate
minerals has not been uniform throughout the aquifer and in central Orange
County two major producing zones, 150 to 600 feet and 1,100 to 1,500 feet,
separated by a less permeable zone, have been mapped. In eastern Orange
County, most wells penetrate only the upper producing zone as the lower zone
contains brackish water. In water samples from a 1,350-foot salinity monitor-
ing well of the city of Cocoa, chloride concentration has been as high as 1,400
milligrams per liter.
The depth to the top of the Floridan aquifer ranges from 100 to 350 feet
fig. 5). Near the Seminole County line the overburden is about 100 feet thick
and increases to its maximum thickness in the southeast part of the area. This
increasing depth to the top of the aquifer corresponds to the increasing thick-
ness of the confining layer.
The Floridan aquifer is artesian; thus water in the aquifer is under ar-
tesian pressure and its potentiometric surface is above the top of the aquifer.
(The level to which the water will rise in a tightly cased well open to the
aquifer constitutes its potentiometric surface). The potentiometric surface of
the FIoridan aquifer fluctuates about 10 feet (fig. 4) or about twice the mag-
nitude of fluctuation of the potentiometric surface of the nonartesian aquifer.
The altitude of the potentiometric surface of the Floridan is highest on the
west side of the area and the surface slopes toward the St. Johns River (fig.
6.) The general slope of the land surface is greater than the slope of the
potentiometric surface, thus the potentiometric surface intersects land surface
along the escarpment of the Osceola Plain (fig. 2) and rises above it toward
the St. Johns River. Therefore, the area east of the escarpment is one
of artesian flow. (fig. 6).
DEPTH IN FEET BELOW LAND SURFACE TO
TOP OF FLORIDAN AQUIFER
In u No N au TUNY6
FL9 7Th2Yt r'
E X P L A N ACTION
), I SHOWS ALTITUDE OF POTENTIOMETRIC SURFACE)
I, ,i CONTOUR INTERVAL 5 FEET
DATUM IS MEAN SEA LEVEL.
(AREAS OF ARTESIAN FLOW)
0 ; a 3 4 MILES
81'15' 10 05 8100 55 8050'
Figure 6.-Potentiometric map of the Floridan aquifer at normal conditions,
REPORT OF INVESTIGATION NO. 72
HYDROLOGY OF SURFICIAL WATER
In this report, surficial water means water that occurs at or near the land
surface. It includes rainfall, water lost from the area by runoff and evapo-
transpiration, water stored on the land surface, and shallow ground water.
Most of the surficial water in eastern Orange County is derived directly
from rainfall. Minor amounts are derived from streamflow in the St. Johns
River and surface inflow from the Econlockhatchee River swamp in Osceola
County. It is estimated that the average annual rainfall in the eastern part of
the county is about 55 inches, slightly more than at Orlando.
The path water follows after it has fallen as rain is very dependent upon
antecedent moisture conditions. If enough rain has fallen so that the water
table is at the land surface, rain is stored on the land surface in swamps from
which it evaporates or runs off- overland. After a dry period when the water
table is several feet below the land surface, rain will infiltrate the land surface
and be stored in the nonartesian aquifer from which it evaporates, transpires,
or discharges to streams as base flow. The rate at which water is lost from the
area through evapotranspiration is much greater when water is stored on the
surface than when it is stored in the subsurface.
The greatest loss of water from the area is through evapotranspiration. It
is estimated that 70 percent of rainfall on Orange County (36 inches per
year) is returned to the atmosphere (Lichtler and others, 1968). In the east-
ern part of the county where wetlands and a high water table prevail, evapo-
transpiration is believed to be slightly more than 70 percent, or from 40 to 45
inches per year.
The second largest water loss occurs through surface runoff which has
been estimated by Anderson (Lichtler and others, 1968) at 10 inches per year
for Econlockhatchee and Little Econlockhatchee River basins. The 10 inches
of runoff represents an average value for the entire basin. It is estimated that
as much as 15 inches per year runs off areas adjacent to streams where sec-
ondary and tertiary drainage lines have developed. Runoff is much less from
interbasin areas (basin divides) where little or no drainage lines have devel-
oped. Less runoff from interbasin areas is also inferred from the fact that
these are also the wet and swampy areas where water remains on the surface
until it evaporates.
The average annual water loss from evapotranspiration plus surface run-
off is probably nearly uniform throughout the area: areas having lower rates
BUREAU OF GEOLOGY
of surface runoff have higher rates of evaporation. The areal distribution of
water losses in percent of rainfall is shown in figure 7.
INFILTRATION AND AQUIFER STORAGE
The infiltration capacity of the surficial sand is as high as 3.5 inches per
hour (Powell and Lewis in Lichtler and others, 1968). This rate will accom-
modate most rain intensities and probably could be sustained except for aqui-
fer storage limitations. The water table does not decline much more than 5
feet below land surface and less than that in some periods (fig. 4). Normally
the water table would be only 2 to 3 feet below land surface. Three feet of
unsaturated aquifer would hold about 10 inches of water. This amount of
water falls in a normal 45-day period during the wet summer season.
At the beginning of the wet season the nonartesian aquifer is quickly re-
charged to capacity and then begins to reject recharge. Between rains and
during dry season, water is discharged from the nonartesian aquifer to supply
evapotranspiration and base flow streams. In most places a little water perco-
lated downward through the nonartesian aquifer and confining-layer to re-
charge the underlying Floridan aquifer. This recharge probably amounts to
less than 3 percent of annual rainfall.
In a general way the water in the hydrologic system increases in dissolved:
solids concentration with depth. The water in the Floridan aquifer also in-
creases in dissolved-solids concentration toward the east; that is, to the St.
Johns River (fig. 8).
Surface water, in the upper part of the hydrologic system, contains the
smallest quantity of dissolved solids. It is generally soft, somewhat acidic,
highly colored, and each dissolved constituent is low in concentration. This
discussion does not pertain to the St. Johns River, for the river includes water
from other hydrologic systems outside the area. Summaries of the chemical
analyses of water from Econlockhatchee and Little Econlockhatchee Rivers
are given in table 1. Even though surface water is low in dissolved-solids con-
centration, its range in concentration is greater than in the nonartesian aqui-
fer. This greater range in water in streams is related to the flow characteristics
of the streams. During high flow, the water in streams is derived predomi-
nantly from overland flow. In chemical character it is similar to rainfall but
its quality is slightly inferior because as the water flows over the land surface
it picks up dissolved and suspended material. The organic matter included in
the suspended material forms complexes which color the water. At low flow
or base flow the water in the streams is derived from the nonartesian aquifer
and its dissolved-solids concentration is greater than during high flow.
I trowl#AVY A
*t f' %k
*__ I i 4Y
TIP 1 P11
I) Vr y
Figure 7.-Map showing areal distribution of average annual water losses
through evapotranspiration and runoff.
S R M I N O L V C O U N T Y
7,:.-'T-"r r -tA.--.. -i* --t. T+n, "r "
^ [ ^
aC U N T
I 19 I I I I
amin r wr ri
.-~. --. ~.-~1.
r~rriu I I- lli -n L`~J ~I
Water loss not determl
S I L. area of artesian flow
'0 3 MILES
to 1,,, II I
tv ,.* "* *-lrr
''0 8 .'^ ~ 'C T 9 0 1. A
"-s>/ 1 Oa~ rdL CB IRrf O L
*-rr -* --1.1 --I Irrl I e IY -I
Average annual water loss In
percent of rainfall
Top number refers to water
loss through evapotranspiratic
L Bottom number refers to water
loss through surface runoff,
A / I ;I",
Contour line shows content of
dissolved solids in milligrams pr
Figure 8.-Map of the dissolved-solids concentration of water in the upper part
of the Floridan aquifer, 1960-62.
REPORT OF INVESTIGATION NO. 72
The chemical character of the water in the nonartesian aquifer is generally
similar to the water in streams except that the water is harder, contains more
dissolved solids, and is less colored. The variation in water quality at a par-
ticular site is small with respect to time but does vary with respect to different
zones in the aquifer. In the upper part where the material is predominantly
sand, the water is soft, low in dissolved-solids concentration, neutral, and
slightly colored. At depths where shell beds occur, the water is hard from the
presence of calcium and magnesium ions, is alkaline, and is less colored.
Chemical analyses of water from two wells that tap shell beds in the
secondary artesian aquifer indicate that the water is almost as highly min-
eralized as the water in the Floridan aquifer in the western part of the study
area (fig. 8). The dissolved-solids concentration in the water from the shell
beds is as high as 400 mg/i (milligrams per liter), although the chloride
concentration is much lower than that in the Floridan aquifer.
In the western part of the study area, water in the Floridan aquifer has a
dissolved-solids concentration of 200 mg/l. It becomes progressively poorer
in quality toward the east until near the St. Johns River the dissolved-solids
concentration is greater than 2,000 mg/1 (fig. 8). The limit of dissolved-
solids concentration suggested by the Public Health Service (1962) for drink-
ing water is 500 mg/1. The 500-mg/l line runs down through the middle of
the study area and indicates the transitional zone between fresh and brackish
water. Water-quality maps of Lichtler and others (1966) indicate that water
of poor quality has migrated westward under the influence of pumping of
wells in the vicinity of the Cocoa well field. However, more recent studies
(Tibbals, 1973) indicate that the salty water has migrated upward from
depth rather than laterally. Thus, the salt water intrusion in the Cocoa well
field is a local phenomenon and its effects do not extend outward from the
well field in any direction for any significant distance. The balance between
fresh and brackish water in the aquifer is delicate in the well-field vicinity.
HYDROLOGIC CONCEPTS OF ARTIFICIAL RECHARGE
SOURCE OF RECHARGE WATER
In the humid eastern United States, rainfall is sufficient to supply water
for artificial recharge. However, in eastern Orange County 95 to 100 percent
of the rainfall is lost from the area by evapotranspiration and stream runoff
(fig. 7). For an artificial recharge scheme to be effective it must include a
means of salvaging water that otherwise would be lost and must also include
a means of placing it underground beyond the reach of evapotranspiration.
Table 1,-Chemical analyses of water from various environments in eastern Orange County,
Namfoz} Sampl' B peplflo
woo-% % 6 Wionuotanc all
Name or Sample 1 (mi romho depth
1 No D (test)
llvir i IIIt llh 10 511. 7/113 0.0 8a1
:;1 1 -iiilyto 1)
hlihrii. liver ir. J15 liOniilyses)
2aM3SN01n04N 7 1 ,701 0, ,.73
ZBl241NU10 13.,3 Iu'll l1 .4/70 3,1 .4.2 .00 .7!1
2H321NO8l llin17,l I 311,11:1 1.0 4.5
21'lSTNO411431,9ll l o11/ 1 7.0 2 0
2n2107N0110 4:10. 1 III 1 020 .70
2 N03 11NllNl042.1 7 '71 3.8 100
S 112IN118111115'L. 1' 0113 2, 00
11'301itlNU 111 H 2 7' 1 7.1 i1
0l2BiO10N11104045,4 7I. '71 3,0 0
,2H2a3)ON(I114,l 7/1/71 0.7 1.2
10/03. 4/70 12. 18 .00 47, 107. 120 1.10.0.
I '(1.4/70 18 .0 03. 112 8.4 .,7
(11 llm ilyiel)
2H:1107NII 111141.1 4 27/70
3Hl!41NIIH0n10532,1 4 21/70
28'3114NOI0501311.1 5 12/00
2828147N0B10117.1 4 21/70
242320INnR11 1710,l 56/1/00
292348HN01H'51147.1 4 27 '70
,.a .0 8 10 12 1 .0 I 0 833
5,0.0.0 .1 ., 00. 1004 .0 ?1.0 8.0. 11 .0 .1 .0. 1.0 107 1111 84 1832
7,4 1.2 78 11n .0 .2 ais
.o 1 17 4 2.4 12 .0 1 4 .7
11. 0 .7 21 ,0 1 .4 .0 2 182
0, 4 15 ,0 is .0 ,0
4.3 .0 .0 211
a1 9:.0 238 nil 41 ,0 3J11 240
38 0.11 40 8:3 9 2 I I ,0 295 00
24 1.3 48 I 44 0 140 35
Secondary Artesian aquifer
184.13 .D -2 7 1 382 2 0 0 ...2 2.02 ,00 -. 130 921..400 1 70.310
10.0 10 ,0, .,*..311 .0. .4 15.18 .10 0 9 7 70 0 17. 1 710 .00
7.2 7.4 1.0
II! 35 1.9
65 360 13
3 I 8 1 1.3
8,8 I Ia I 1,3
,.0 38 2,1
27 102 380
l1i 0.0 s0
202-118 18.104.22.168 .s10
170 7,0 8
74 8,6 80
309 7.8 45
127 01. 50
30 ,0 5
510.090 2 ,07 8,28 0 .0
380.800 7.o.8.4 0.10
120 8,8 1o
1114 40 n13
018 2 08 000
218 00 00
230 .4 21
200 50 54
204 a1 348
1 Sample taken from water tap, maybe contaminated from plumbing.
.0 SO 0,8..87
5.4 ld0 ,6.4.8
0.0 0 6.4
1, .0 n,
0,0.,8 0.0. 1,3
.0..4 .0 .8
I i I
REPORT OF INVESTIGATION NO. 72
SCHEMES FOR CAPTURING WATER FROM POTENTIAL LOSSES
The two most readily conceived schemes for capturing potential water
losses are those that involve impoundments and (or) shallow ground-water
withdrawals. In both schemes, water losses are reduced because: (1) impound-
ing water behind a dam in a surface reservoir will reduce runoff and (2)
lowering the water table in the nonartesian (shallow) aquifer will reduce
both runoff and evapotranspiration. The water impounded on the surface or
withdrawn from the nonartesian aquifer by lowering its water level would
serve to supply the wells used for artificial recharge to the Floridan aquifer.
The surface impoundment concept envisions dams constructed across the
major streams to reduce runoff during high flow and to retain this water
until it is artificially recharged to the Floridan aquifer. For example, con-
structing a dam across the Econlockhatchee River just upstream of State
Highway 50 large enough to hold a 20-foot head of water would create a
reservoir having the capacity of 20,000 acre-feet. A mean monthly discharge
of 20,000 acre-feet or more occurs on the Econlockhatchee River at Highway
50 at least once each year, thus supplying sufficient water in 1 month to refill
a reservoir of this capacity. Therefore, at least 20,000 acre-feet is available
each year for recharge. This is equivalent to about 4.5 inches of water per
year from the entire contributing area. If dams were constructed on the other
streams, it is estimated that a comparable amount of water per unit area could
Because of the low relief, the total acreage necessary for surface reservoirs
would be quite large. For instance, when the hypothetical reservoir on the
Econlockhatchee River is full, it would inundate 7 percent of the total drain-
age area (fig. 9). This 7 percent, of course, would have no other use because
the time of inundation would be dictated by the weather conditions.
A variation of the surface impoundment scheme envisions the contain-
ment of water in off-stream swampy areas of the basin divides during exces-
sive rainfall. These constitute the area shown on figure 7 that has the highest
rate of evapotranspiration- 87 percent of rainfall. Excess water that nor-
mally runs off could be contained in the area by levees which would increase
surface storage in the swamps. Through a network of canals and ditches the
water could be channeled to the deeper depressions. The amount of water that
would be captured by this scheme is estimated to be 2 to 3 inches per year.
Most of the water that normally runs off this area, estimated at 5 inches per
year, could be captured but about one half of it would be lost to evapotrans-
piration before the water could be utilized for recharge.
i ,-.-- .---
Area Inundated when water
level Is 50 feet above mean
^ ^ 0
Figure 9.-Map showing area of inundation and contributing area of surface
REPORT OF INVESTIGATION NO. 72
The second scheme for capturing water for artificial recharge-lowering
water levels-involves the use of connector wells. These are wells that are open
to both the nonartesian and Floridan aquifers and act to short circuit the flow
through the confining layer (fig. 10). Water in the nonartesian aquifer would
move laterally to the connector well, flow down through the well and recharge
the Floridan aquifer. Under natural conditions, water would percolate very
slowly, if at all, through the confining bed to the Floridan aquifer. The con-
nector-well concept, where water flows by gravity from an upper aquifer to a
lower one will woik only when the water table of the nonartesian aquifer is
higher than the altitude of the potentiometric surface of the Floridan aquifer.
The areal distribution of the head difference in eastern Orange County is
shown on figure 11.
As water from the nonartesian aquifer flows downward through the con-
nector well, the water table declines. This decline reduces evapotranspiration
and creates additional storage in the aquifer which allows for greater infiltra-
tion, thus capturing water which would have run off or evapotranspired. Sys-
tematically lowering the water table over a specified area requires a network
of connector wells. The actual rate of capture of water relative to the extent of
lowering of the water table is not known. However, capture rates can be
assumed for evaluation of the connector well scheme.
EVALUATION OF SCHEMES
In both the surface impoundment and connector well schemes, the method
of introducing water into the Floridan aquifer is the same. This method con-
sists of the gravity flow of water through a well bore from either a surface
water body or shallow aquifer to the Floridan aquifer. The difference in
schemes is in the method of capturing water for recharge and in the hydro-
logic advantages and disadvantages.
The connector-well scheme has hydrologic advantages which make it more
desirable than the surface impoundment scheme as a means of artificial
CAPTURE OF WATER
Connector wells capture water that would be lost by evapotranspiration as
well as from runoff, whereas an impoundment scheme would only decrease
surface runoff and, probably, would even increase evapotranspiration.
The land used for a connector-well installation can also be developed for
both urban and agricultural use; whereas the need for numerous reservoirs
BUREAU OF GEOLOGY
---i-- --!-- "" ." : .
U I POTENTIOMETRIC SURFACE
S ( FLORIDAN AQUIFER)
( NOT TO SCALE )
Figure 10.-Schematic sectional view of a connector well between nonartesian
and Floridan aquifers.
i M I N 0 L E C U N T Y
u .1 '''*. .
i Hart ay
D C E L
OS CO L A
I '' *-
Figure 11.-Contour map of head difference between nonartesian and Floridan
EXPL ANAT ION
HEIGHT OF WATER TABLE ABOVE POTENT-
IOMETRIC SURFACE OF FLORIDAN AQUIFER
- = .
... Z : -
I J I
BUREAU OF GEOLOGY
in a surface impoundment scheme would preclude any other use of the land
because of the wide fluctuation in water level which would occur in a recharge
project. A connector-well scheme would also dewater some areas that are
now waterlogged making them suitable for land development.
Recharge water in a connector-well scheme does not require treatment.
The nonartesian aquifer would act as a large sand filter to purify and produce
water similar in chemical character to water naturally recharged in other
parts of the county. Recharge water from a surface impoundment requires
treatment to avoid introducing suspended material and bacteria into the
The cost of land for connector-well sites would be much less than the
cost of land for reservoirs.
ANALYSIS OF A CONNECTOR-WELL NETWORK
From general hydrologic concepts it was concluded that the connector-
well scheme has more benefits than the surface impoundment scheme. But
before such a system can be deemed feasible for a given area, it is necessary
to analyze the hydraulic relationships of a connector-well network.
The infiltration capacities that exist in eastern Orange County are high
enough to make capture of water possible if storage space can be created in
the nonartesian aquifer. The discharge of water to connector wells will lower
the water table and thus provide storage space in the nonartesian aquifer.
The number of wells needed to lower the water table enough to make the
project feasible is dependent upon the transmissivity of the nonartesian aqui-
fer, the available drawdown in the well, and the rate of capture.
For a given set of atmospheric and geologic conditions, the rate of capture
is a function of the depth to the water table. As the depth to water increases,
the rate of capture will increase until the maximum capture rate is attained
at which point further drawdown will not affect the capture rate (fig. 12).
The drawdown that is associated with a particular rate of capture is the effec-
tive drawdown. A schematic model of the physical concepts of capture, draw-
down, and contributing area of a connector-well network is shown on figure
If there is available drawdown in the well, the drawdown in the aquifer
will continue until discharge to the well equals the rate of capture, after
which time no additional water is withdrawn from storage and the discharge-
REPORT OF INVESTIGATION NO. 72
Figure 12.-Schematic curve illustrating the capture-drawdown function.
BUREAU OF GEOLOGY
drawdown relation is said to be in a steady-state condition. A numerical
analysis of the drawdown from a connector-well network in the nonartesian
aquifer under steady-state conditions has been developed by Papadopulos and
Cooper (written commun., 1973). This analysis uses the Dupuit-Forchheimer
assumption of horizontal flow to the well. Deviation from this ideal condition
may result in less accurate calculations of drawdown in the immediate vicinity
of the well, especially if the drawdown is large compared to the thickness of
the aquifer. However, equations derived on the basis of this assumption have
been shown to be exact for discharge calculations (Hantush, 1962).
In a square-grid network the area contributing water to an individual
connector well is a square with sides equal to the well spacing. If the network
is designed to provide maximum capture with the least number of wells, the
wells are placed at a spacing J such that the minimum drawdown, which oc-
curs at a point equidistant from the four nearest wells, is equal to the effective
drawdown s. (fig.13).
An equation relating drawdown in the well sw, effective drawdown se,
aquifer thickness ho, transmissivity T, maximum capture rate Co, and well
radius r, with the well spacing e for a network of fully penetrating con-
nector wells with negligible well losses, is given by Papadopulos and Cooper
(written common., 1973):
s 2 -2
[(s 2ho ) (Se- 2h )IT
Cor2 = f (/r,)
0 r o 1 2nrrw
f (1/r) + I [cosh n, cos (-1)n]
2rrw n=l n n sinh nmr -
If the parameters on the left side of the equation are known, the well
spacing .1 can be determined graphically from a plot of //r, against
f( A/r,) as shown on figure 14. With this spacing the discharge of each
connector well will be Q= Co2.
Of the various parameters in the "well-spacing" equation, capture and
effective drawdown (se) in the drawdown-capture function are quantitatively
the least known. The transmissivity of the nonartesian aquifer has not been
measured directly but is estimated from indirect methods. Aquifer thickness
and available drawdown in the well have been determined. For those par-
ameters whose values are not explicitly known, a range of values representing
a reasonable upper and lower limit are used in the analysis.
REPORT OF INVESTIGATION NO. 72
Figure 13.-Diagrammatic plan view and section showing the physical con-
cepts of a connector-well network.
Io 3 I I I I I I II-......-........... I I I I l I1 1 1 I I I
106 o107 108
2 2 2
f(A/r,) [(a /2h.o) (-s 8/2h)] T/C ro
Figure 14.--Graph for determining well spacing in a square-grid connector.
REPORT OF INVESTIGATION NO. 72
Estimates of the capture rate range from 0.5 to 1.5 feet per year. These
rates would produce 38,200 ft3 per day (0.3 mgd) and 114,600 ft3 per day
(0.9 mgd) of recharge water per square mile. Ripple and others (1972),
using theoretical approaches, determined the relation between evaporation
rates and water-table depths in the southwestern United States for given
meteorological and bare soil conditions. For a given set of these conditions
the evaporation rate decreases from 0.31 cm (centimenters) per day (3.7
feet per year) for a water-table depth of 200 cm (7.9 feet) to 0.10 cm per
day (1.2 feet per year) for a depth of 250 cm (9.8 feet). Therefore it does
not seem improbable that the rate of capture of water that otherwise would
be lost by evapotranspiration and runoff could be between 0.5 and 1.5 feet
Calculations of well spacing, discharge per well and number of wells per
square mile using the upper and lower limits for each of the hydraulic par-
ameters and well radii of 0.25 and 0.50 ft are given in table 2. As the well
spacing equations and these calculations indicate, well spacing increases as the
transmissivity and the difference between available and effective drawdown
increases, and as the rate of capture and well radius decrease. However, the
effect of well radius is relatively small. The reduction in the number of wells
per square mile for larger diameter wells is small and on an areal basis the
cost of the slightly greater number of small wells would be less than the cost
of a smaller number of large wells. Therefore, connector-well networks de-
signed with wells of the smallest practical diameter would be sufficient.
The average transmissivity of the nonartesian aquifer is estimated to be
between 125 ft2 per day and 625 ft2 per day. To justify these estimates, sam-
ples of the aquifer material were collected for laboratory analysis of grain
size and vertical hydraulic conductivity. The median grain size of the material
in the nonartesian aquifer is 0.15 millimeter. Grains having this diameter
are classified as fine sand (Johnson and others, 1966).
Various investigators have related soil class to hydraulic conductivity with
some success. Todd (1959) shows a general relationship in which fine sand
ranges in hydraulic conductivity from 10-1 to 20 feet per day. A relationship
between median grain size and permeability of alluvial sediments from the
Arkansas River Valley indicates- a hydraulic conductivity of about 5 feet per
day for fine sand (Bedinger, 1961). Well sorted, very fine sand may have a
hydraulic conductivity as high as 25 feet per day (Davis, 1970). The fine
sands of the nonartesian aquifer are fair to well sorted, thus it is not un-
reasonable to estimate a hydraulic conductivity between 2 and 12 feet per day
for these sediments. Laboratory determinations of vertical hydraulic conduc-
tivity range from 0.02 to 20 feet per day for the aquifer materials. The rela-
30 BUREAU OF GEOLOGY
Table 2.-Well spacing/, well discharge Q, and numbers of wells per square
mile N,, for upper and lower limits of transmissivity T, capture
rate C, effective drawdown Se, and
well radii r, of 0.25 and 0.5 foot.
available drawdown s,, and for
T C, se f(1/rW) / Q N,
(ft /day) (ft/year) (ft) dimensionlesss) (ft) (ft3/day) (per mi2)
125 0.5 5 2.044 x 107 1.040 1,480 26
125 .5 10 1.424 x 107 880 1,060 36
125 1.5 5 6.813 x 106 630 1,630 71
125 1.5 10 4.745 x 106 530 1,150 100
625 .5 5 1.022 x 108 2,220 6,750 6
625 .5 10 7.118 x 107 1,870 4,790 8
625 1.5 5 3.407 x 107 1,330 7,270 16
625 1.5 10 2.373 x 107 1,120 5,160 23
125 .5 5 5.110 x 106 1,090 1,630 24
125 .5 10 3.559 x 106 920 1,160 33
125 1.5 5 1.703 x 106 660 1,790 64
125 1.5 10 1.186 x 106 560 1,290 89
625 .5 5 2.555 x 107 2,320 7,370 6
625 .5 10 1.779 x 107 1,960 5,260 8
625 1.5 5 8.517 x 106 1,390 7,940 15
625 1.5 10 5.931 x 106 1,170 5,630 21
125 .5 5 2.957 x 107 1,240 2,110 19
125 .5 10 2.336 x 107 1,110 1,690 23
125 1.5 5 9.855 x 106 740 2,250 51
125 1.5 10 7.787 x 106 670 1,840 63
625 .5 5 1.478 x 108 2,640 9,550 4
625 .5 10 1.168 x 108 2,360 7,630 6
625 1.5 5 4.928 x 107 1,580 10,260 12
625 1.5 10 3.893 x 107 1,410 8,170 15
r,= 0.5 ft
125 .5 5 7.391x 106 1,300 2,320 17
125 .5 10 5.840 x 106 1,160 1,840 21
125 1.5 5 2.464 x 106 780 2,500 46
125 1.5 10 1.947 x 106 700 2,010 57
625 .5 5 3.696 x 107 2,760 10,440 4
625 .5 10 2.920 x 107 2,470 8,360 5
625 1.5 5 1.232 x 107 1,650 11,190 11
625 1.5 10 9.733 x 106 1,480 9,000 13
REPORT OF INVESTIGATION NO. 72
tion between vertical and horizontal conductivity is not known but generally
horizontal conductivity is greater. The laboratory values also imply that the
estimated values are reasonable.
The thickness of the nonartesian aquifer is 50 feet and the available
drawdown under present conditions is about 25 feet. However, the maximum
drawdown could be 50 feet if the potentiometric surface of the Floridan aqui-
fer were lowered 25 feet or to the bottom of the nonartesian aquifer. It is
unlikely, however, that in the foreseeable future pumpage from the Floridan
aquifer will increase to a degree that will lower its potentiometric surface by
an additional 25 feet. Evaluation of equations that describe nonsteady flow
to multiaquifer wells (Papadopulos, 1966) indicates that because of the large
differences in the transmissivities of the nonartesian and the Floridan aquifer,
the water level in a connector well will stand very close to the potentiometric
surface of the Floridan aquifer. The availability of drawdown will therefore
be affected if pumpage from the Floridan aquifer does not increase to counter-
act the build-up that could be caused by the recharge. However, the needs for
increase in pumpage is small, about 200 gpm for each 6 inches of capture
over 1 square mile.
The well spacing, discharge per well and number of wells per square mile,
for fully penetrating wells with negligible well losses, are calculated in exam-
ple 1, below, for a given set of hydraulic parameters.
Given: C = 1.0 foot per year = 2.74 X 10-3 feet per day
sw = 25 feet
Se = 5 feet
T = 400 ft2 per day
ho = 50 feet
r, = 0.25 ft.
[ (25-- )-(5- )] X 400
f/r) 2.74 X 10-3 X 0.0625
= 3.27 X 107
From figure 14
./rw = 5.2 X 10
and = 5.2 X 103 X 0.25 =1300 ft
BUREAU OF GEOLOGY
Discharge per well
Q = CP2 = 2.74 X 10-3 X 1.69 X 106
Q =4630 ft3 per day
Number of wells per square mile
Q per sq. mi. 7.64 X 10D
N, = Q per well 4.63 X 103
N, = 17 wells on 1,300 foot centers.
OPERATIONAL CONNECTOR WELLS
The connector-well concept has been utilized in other areas and hydrogeo-
logic systems as a basis for designing recharge works. In Anchorage, Alaska,
the U. S. Geological Survey experimented with a well connecting a shallow
plastic aquifer to two deeper artesian aquifers (Cederstrom and others, 1964).
The shallow aquifer is hydraulically connected to a creek. By lowering the
water table, the rate at which water from the creek infiltrated the aquifer was
increased. The additional water captured flowed into the connector well. The
recharge operation was not as successful as anticipated due to the decrease
in the rate at which the two artesian aquifers accepted the water. Recharge
began at a rate of 135 gpm but diminished to 55 gpm after 5 months. The
authors attributed the reduction in recharge rate to incomplete development
of the well and clogging of the deeper aquifer with silt from the shallow
Another experimental connector-well installation by the U. S. Geological
Survey is located southwest of Orlando, Florida, in western Orange County.
At this site the hydrologic system consists of a thin surficial sand aquifer
separated by a confining layer (thick hardpan) from an intermediate sand
aquifer, both of which are separated from the deeper Floridan aquifer by a
thick confining layer. This experiment has been operational for about 18
months and the data to 1972 indicate that the flow through the well
has stabilized at about 13 gpm. Drawdown has reached 6 feet in an observation
well 105 feet from the connector well and that taps the sand aquifer. (Written
common, 1972, Frank Watkins, U. S. Geological Survey).
WATER QUALITY CONSIDERATIONS
Pumping from the Floridan aquifer at an ever increasing rate in an area
where the quality of the water is marginal to begin with has caused the quality
to degrade still farther. If water of good quality were recharged to the Flori-
dan, withdrawal could be increased without degrading water quality. Thus,
it becomes important that only fresh water be used for recharge.
REPORT OF INVESTIGATION NO. 72 33
The source of water for recharge .is the nonartesian aquifer. This water has
a chloride concentration less than 25 mg/1 (milligrams per liter), hardness
less than 100 mg/1 (except in shell beds) and sulfate less than 5 mg/l. In
contrast, in the Cocoa well field where quality is marginal, water from the
Floridan aquifer has a chloride concentration as high as 500 mg/1, hardness
480 mg/1, and sulfate 190 mg/1. The nonartesian water is more acidic than
the Floridan which would probably have the desirable effect of increasing its
permeability. The only constituent that may be undesirable and whose geo-
chemistry would need investigating is iron. The iron concentration of the
nonartesian water appears to be high in some areas (table 1). The slightly
colored water would be no trouble; after recharge had been in operation for
a time water would move downward more rapidly through the soil zone and
the amount of color would probably decrease.
SUBSEQUENT WITHDRAWAL OF RECHARGED WATER
The purpose of most recharge operations is to store potable water in an
aquifer for subsequent withdrawal. No recharge operation is successful if the
recharged water or a mixture thereof cannot be retrieved. Several recharge-
withdrawal experiments were made in the Cocoa well field to investigate the
retrievability of the water after injection into the Floridan aquifer (Tibbals,
Water for the recharge experiment was obtained from a secondary arte-
sian aquifer. The water had a chloride concentration of about 20 mg/1. The
Floridan aquifer normally contains water whose chloride concentration is in
excess of 500 mg/1. After five recharge-withdrawal experiments, Tibbals con-
cluded that a buffer zone between the fresh and salty water could be estab-
lished and that greater amounts of the recharged water were recovered on each
successive experiment. On the fifth experiment, 68 percent of the actual water
recharged was recovered before the chloride concentration of the mixture that
was being withdrawn reached 250 mg/1. On a volume basis, 75 percent of the
quantity recharged was withdrawn before the chloride concentration of the
mixture reached 250 mg/1 and the experiment was terminated. The four
previous cycles were also terminated when the chloride concentration of the
discharge water reached 250 mg/l.
SUMMARY AND CONCLUSIONS
Artificial recharge in eastern Orange County is a worthwhile considera-
tion. Not only is the hydrologic system suitable for gravity flow through a well
to recharge the Floridan aquifer but there is also the need for additional
fresh water in the Floridan in this area. The present rate of withdrawal from
BUREAU OF GEOLOGY
the Cocoa well field puts a stress on the aquifer such that brackish water has
migrated upward into the pumped zone of the aquifer in the eastern section of
The hydrologic system cycles about 55 inches of rainfall per year, of which
10 to 15 inches runs off, 40 to 45 inches evapotranspires and 0 to 2 inches
recharges the Floridan aquifer. With such a large supply to and loss from the
area, there is a sufficient source of water for artificial recharge. The hydro-
geologic framework also enhances the feasibility of artificial recharge. It
consists of a surficial (nonartesian) aquifer separated from the underlying
Floridan aquifer by a confining layer. The water table in the nonartesian
aquifer stands as much as 30 feet above the altitude of the potentiometric
surface of the Floridan aquifer. The water in the nonartesian aquifer is gen-
erally soft and low in dissolved-solids concentration whereas water in the
FIoridan aquifer, especially where quality is marginal, is very hard and has
a chloride concentration as high as 500 mg/1.
The supply of water for artificial recharge could be derived from a net-
work of connector wells capturing water currently lost from the area. The
network would consist of wells hydraulically connecting the nonartesian and
FIoridan aquifers. Because the water table in the nonartesian aquifer is higher
than the potentiometric surface of the Floridan aquifer, water would flow
into the wells from the nonartesian aquifer, down the wells and into the Flori-
dan. Hydrologic advantages to the connector-well scheme make it more desire-
able means for recharging water to the Floridan aquifer. These advantages
are: only one device (well) need be constructed for capturing water and in-
jecting it to the Floridan aquifer; runoff and evapotranspiration losses are
both reduced; hydrologic change to the environment is less; and the water
needs no treatment before it is injected.
The water table must be lowered before capture can succeed. The amount
of lowering caused by flow to a connector well is controlled by the available
drawdown, the transmissivity of the nonartesian aquifer, and the rate of cap-
ture. The available drawdown is limited under present conditions by the dif-
ference in head between the water table and the potentiometric surface of the
Floridan aquifer. The ultimate available drawdown, however, would be equal
to just slightly less than the thickness of the nonartesian aquifer. The trans-
missivity of the nonartesian aquifer is estimated to be between 125 and 625
ftz per day. These values are considered reasonable from indirect correlations
with grain size and laboratory permeability determinations.
Calculations from a numerical model developed by Papadopulos and
Cooper (written commun., 1973) indicate that for a capture rate of 1.0 foot
per year and an effective drawdown of 5 feet, 6-inch fully penetrating con-
REPORT OF INVESTIGATION NO. 72
nector wells located in a square-grid network should have spacing of
1,300 feet. The corresponding recharge rate would be 4,630 ft8 per day per
well or about 0.57 mgd per square mile. Higher capture rates would require
additional wells and closer spacings, and the flow to each well would be
slightly higher. Greater effective drawdowns would require closer well spac-
ings and consequently a greater number of wells and a lower recharge rate
From recharge-withdrawal experiments in the Cocoa well field, Tibbals
(1972) concluded that a buffer zone between the fresh and salty water could
be established and that a greater amount of the recharged waters was re-
covered on each successive experiment.
The conclusion of this study is that it is feasible to capture surficial waters
and recharge them to the Floridan aquifer in eastern Orange County by using
a connector well.
The critical parameters used in the numerical analysis are the transmis-
sivity of the nonartesian aquifer and the capture-drawdown function. Verifica-
tion of the values of transmissivity used in the analysis can be obtained from
proven field test procedures (Boulton, 1963; Prickett, 1965). However, veri-
fication of the capture drawdown function is more difficult to obtain.
As a succeeding phase in this artificial recharge study, a connector well
and associated observation wells could be installed. Through the use of this
installation an experiment tould be conducted to obtain the empirical data on
capture rate and drawdown distribution. From the empirical data the capture-
drawdown function would be investigated. If a relationship between capture
and drawdown can be determined, the potential for artificial recharge by
means of a connector well system can be evaluated for other areas.
36 BUREAU OF GEOLOGY
Bedinger, M. S., 1961, Relation between median grain size and permeability in
the Arkansas River valley, Arkansas: U. S. Geol. Survey Prof. Paper
424-C, p. 31-32.
Boulton, N. S., 1963, Analysis of data from nonequilibrium pumping tests
allowing for delayed yield from storage: Proc. Inst. Civil Engineers
(London), v. 26, no. 6693.
Cederstrom, D. J., Trainer, Frank W., and Waller, Roger M., 1964, Geology
and ground-water resources of the Anchorage area, Alaska: U. S. Geo-
logical Survey Water-Supply Paperi1773, p. 63-68.
Cooke, C. Wythe, 1945, Geology of Florida: Fla. Geol. Survey Bull. 29, 339 p.
Davis, Stanley N., and DeWeist, Roger, J. M., 1966, Hydrogeology: New York,
John Wiley and Sons, Inc., p. 374-417.
Hantush, M. S., 1962, Validity of the Dupuit-Forchheimer well-discharge for-
mula: Jour. Geophys. Research, v. 67, no. 6, p. 2417-2420.
Johnson, A. I., Moston, R. P., and Versaw, S. F., 1966, Laboratory study of
aquifer properties and well design for an artificial-recharge site: U. S.
Geol. Survey Water-Supply Paper 1615-H, 42 p.
Lichtler, W. F., and Joyner, B. F., 1966, Availability of ground water in
Orange County, Florida: Fla.. Geol. Survey Map Ser. 21
Lichtler, W. F., Anderson, Warren, and Joyner, B. F., 1968, Water resources
of Orange County, Florida: Fla. Geol. Survey Rept. of Inv. 50, 150 p.
Papadopulos, Stavros S., 1966, Nonsteady flow to multiaquifer wells: Am.
Geophys. Union; Jour. Geophys. Research, v. 71, no. 20, p. 4791-4797.
Prickett, T. A., 1965, Type-curve solution to aquifer tests under water-table
conditions: Ground Water, v. 3, no. 3.
Puri, H. S. and Vernon, R. 0., 1964, Summary of the geology of Florida and
a guidebook to the classic exposures: Fla. Geol. Survey Spec. Pub. 5,
RippIe, C. D., Rubin, Jacob, and van Hylckama, T. E. A., 1972, Estimating
steady-state evaporation rates from bare soils under conditions of high
water table: U. S. Geol. Survey Water-Supply Paper 2019-A p. 1-39.
Tibbals, C. H., 1972, Temporary storage of fresh water in a saline aquifer by
use of wells- a field experiment: Short papers on the Eighth American
Water Resources Conference, St. Louis, Mo., Oct. 30- Nov. 2.
Tibbals, C_ H., and Frazee, J. M., 1973, Hydrologic investigations in the Cocoa
well-field area, Orange County, Florida: U. S. Geol. Survey, report in
Todd, David K., 1959, Ground Water Hydrology: New York, John Wiley and
Sons, Inc., p. 336.
U. S. Dept. Health, Education and Welfare, 1962, Public Health Service drink-
ing water standards: Pub. No. 956, 33 p.
3 1262 04709 8339
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