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Material Information
- Title:
- Water resource studies ground water resources of the Naples area, Collier County, Florida ( FGS: Report of investigations 11 )
- Series Title:
- ( FGS: Report of investigations 11 )
- Creator:
- Klein, Howard
- Place of Publication:
- Tallahassee
- Publisher:
- [s.n.]
- Publication Date:
- 1954
- Language:
- English
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- 64 p. : illus. ; 28 cm.
Subjects
- Subjects / Keywords:
- Groundwater -- Florida ( lcsh )
Water-supply -- Florida -- Collier County ( lcsh ) City of Naples ( flgeo ) Collier County ( flgeo ) Water wells ( jstor ) Pumping ( jstor ) Groundwater ( jstor )
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- Funding:
- Report of investigations (Florida Geological Survey) ;
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- University of Florida
- Holding Location:
- University of Florida
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- The author dedicated the work to the public domain by waiving all of his or her rights to the work worldwide under copyright law and all related or neighboring legal rights he or she had in the work, to the extent allowable by law.
- Resource Identifier:
- 021692238 ( aleph )
01723525 ( oclc ) AER8192 ( notis ) a 54009800 ( lccn )
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STATE OF FLORIDA
STATE BOARD OF CONSERVATION
Charlie Bevis, Supervisor
FLORIDA GEOLOGICAL SURVEY
?Herman Qunter, Director
REPORT OF INVESTIGATIONS No. 11
WATER RESOURCE STUDIES
GROUND-WATER RESOURCES OF
THE NAPLES AREA, COLLIER COUNTY, FLORIDA
By
(0 Howard Klein
* Ground Water Branch
U.S. GEOLOGICAL SURVEY
Prepared By The UNITED STATES GEOLOGICAL SURVEY
*In cooperation with the
FLORIDA GEOLOGICAL SURVEY and the
CITY OF NAPLES
TALLAHASSEE, FLORIDA 1954
AG.
CULTURAL
FLORIDA STATE BOARD A OF
CONSERVATION
CHARLEY E. JOHNS
Acting Governor
R. A. GRAY NATHAN MAYO
Secretary ol State Commissioner of Agriculture
J. EDWIN LARSON THOMAS D. BAILEY
Treasurer Superintendent Public Instruction
CLARENCE M. GAY RICHARD ERVIN
Comptroller Attorney General
CHARLIE BEVIS
Supervisor ol Conservation
LETTER OF TRANSMITTAL
June 15, 1954
Mr. Charlie Bevis, Supervisor
Florida State Board of Conservation Tallahassee, Florida
Dear Mr. Bevis:
Second only to sunshine in value, the State's water resources are an important and necessary item in a progressive economy. The Florida Geological Survey has been collecting water data since its organization in 1907 and joined forces with the U. S. Geological Survey in these studies beginning in 1980. This report on the ground-water resources of the Naples area, Collier County, Florida, prepared by Howard Klein, Geologist of the U. S. Geological Survey, is a portion of the studies undertaken by the two geological surveys.
'It is a pleasure to publish this report as Report of Investigations No. 11, part of a continuing series of Water Resource Studies.
Respectfully,
Herman Gunter, Director
Printed by ROSS PRINTING COMPANY, TALLAHASSEI, FLORIDA
CONTENTS
Page
A bstract 1...................................... ................ 1
Introduction ................................................... 2
Purpose and scope ........................................... 2
Acknowledgm ents ........................................... 4
Location and general features of area ........................... 4
Geography and topography .................................. 4
Clim ate ........ ............................................ 6
Test-well drilling .............................................. 7
Geologic formations and their water-bearing properties ............ 8
General conditions ................................... 8
M iocene series ............................................... 8
Tampa formation .............................. .......... 8
Hawthorn form ation ...................................... 9
Tamiami form ation ...................................... 9
Pleistocene and Recent series ..............................11
Anastasia and Fort Thompson(?) formations ............... 12
Pamlico sand and later deposits ........................... 13
G round water ................................................. 13
Principles of ground-water occurrence ......................... 13
Hydrologic properties of aquifers ............................. 15
Nonartesian aquifer ...................................... 15
D ischarge ....... ..................................... 16
R echarge ........ ..................................... 17
Shallow artesian aquifer ................................. 18
D ischarge ....... ..................................... 19
R echarge ........ ..................................... 19
Principal artesian aquifer ................................ 22
W ater-level fluctuations ..................................... 26
Salt-water encroachment .................................... 30
Contamination in nonartesian aquifer ................. 31
Contamination in shallow artesian aquifer .................. 35
Quality of water ............................................. 36
Quantitative studies ........................................ 42
Ground-water use ........................................... 50
Summary ..... ............... ........................ 52
W ell logs ....................................................... 61
Bibliography .................................................. 63
ILLUSTRATIONS
Figure Page
1. Map of Florida showing location of the Naples area in Collier County .. ...... ................. .............. 3
2. Naples area showing location of wells and location of geologic sections ........ &... ............................. 5
3. North-south geologic section, A-A', through the Naples well field ................. ............. Between 10 and 11
4. West-east geologic section, B-B', across Naples area ......... 11
5. Hydrograph of daily high and low water levels in well 107 showing the correlation of ground-water levels with
rainfall ....................... ...................... 20
6. Hydrograph of daily high and low water levels in well 88 showing the correlation of ground-water levels with
rainfall ................................................ 21
7. Contour map of water levels in the Naples area, February 12, 1952, showing the effect of concentrated pumping
in the golf course .............................. .... .... 23
8. Contour map of water levels in the Naples area, March 12, 1952 ...................... ...................... . 24
9. Contour map of water levels in the Naples area, May 27, 1952 .................... .......... . ....... ....... 25
10. Contour map showing the effect of well-field pumping on
water levels in the Naples area, February 11, 1952 ......... 27 10a. Pumping and nonpumping water-level profiles along
North PFifth Avenue across the Naples peninsula, February 11-12, 1952 .. .......... ........... ......... 29
11. Contour map showing the effect of well-field pumping on
water levels in the Naples area, May 26, 1952 ............. 31
12. Naples area showing maximum chloride concentration in
water from wells of various depths, analyzed during
course of investigation .................................. 41
13. Drawdown observed in wells 33 and 107 during pumping
test on Naples well field, August 7, 1952 .................. 45
14. Composite drawdown graph for wells 33 and 107 during pumping test on Naples well field, August 7, 1952 .......... 46 15. Expected drawdowns at various distances from a well pumping at a constant rate of 1,000 gpm after selected
time intervals ................................... .... 47
TABLES
Table Page 1, Average monthly temperature in degrees F, at Naples, and a comparison of average monthly rainfall, in inches
at Naples and Bonita Springs ............................ 7
2. Chloride concentration in water samples from selected w ell at N aples ............................................ 34
3. Analyses of water from selected wells at Naples ............... 38
4. Results of pumping tests on wells in the shallow artesian aquifer at Naples ...... ....... ......... ... .............. 43
5. Pumpage from Naples well field in millions of gallons per m onth ........................... ........... ......... . 51
6. Water levels, in feet, referred to mean sea level .............. 55
7, Records of selected wells at Naples ...................... 58
vii
GROUNDWATER RESOURCES
OF THE NAPLES AREA, COLLIER COUNTY, FLORIDA
By
HowAnn KLEIN
ABSTRACT
Two shallow aquifers are the sources of fresh-water supplies in the Naples area. The upper aquifer is under nonartesian conditions; it extends from the land surface to a depth of 32 to 55 feet below mean sea level. It is composed of the Pamlico sand and the Anastasia formation of Pleistocene age and a portion of the upper part of the Tamiami formation of late Miocene age. The upper aquifer is tapped by several small, private irrigation wells and also by wells used to supplement the municipal supply. The lower fresh-water aquifer is under artesian pressure and is penetrated about 50 feet below mean sea level in the city well field, where it extends to at least 80 feet below mean sea level. The lower aquifer is much thicker north of the city well field. It lies entirely within the Tamiami formation. It supplies water to most of the city supply wells and to all the large irrigation wells in the vicinity. The movement of water between the aquifers is impeded by 5 to 20 feet of semi-impermeable marl of the Tamiami formation.
Differences in the chemical quality of the water from the two aquifers are slight. Samples of the water from the lower aquifer in uncontaminated areas contain less than 250 parts per million (ppm) of dissolved solids and also have a hardness less than 250 ppm. Water from the upper aquifer usually contains slightly more' dissolved solids than does that from the lower aquifer. Periodic chloride analyses showed that some salt-water encroachment has occurred in both aquifers in areas adjacent to the Gulf of Mexico and in the southern part of the city.
Pumping tests indicate that the lower fresh-water aquifer has a coefficient of transmissibility of about 92,000 gallons per day per foot and a coefficient of storage of about 0.001. The maximum rate of pumping from the aquifer is governed by the amount that groundwater levels can be lowered before salt water moves into the area of pumping. By applying data computed from pumping tests, it was determined that the aquifer, as now developed by means of the city wells and other Wlls of substantial yield, will not support
2 FLORIDA GEOLOGICAL SURVEY
heavy withdrawals for a period of more than 1 day during dry periods. It is essential that wells of large yield which means, essentially, those in the city well field be shut down daily to allow recovery of water levels, if salt-water encroachment is to be averted. Additional ground-water supplies could be obtained from the thick, permeable parts of both fresh-water aquifers in the area north of the present well field.
INTRODUCTION
PURPOSE AND SCOPE
Because of the rapid growth in both the seasonal and the permanent population of Naples, Collier County, Fla., the residents and city officials were faced with a problem of maintaining an adequate water supply. They recognized the necessity for a ground-water survey on the basis of which steps could be taken to protect the present water supply, and to determine the most feasible means of increasing water supplies to meet expanding demands. The city estimated that its present water-plant facilities should provide for an anticipated population of 12,000 to 15,000, or more than 30 million gallons of water per month. The peak monthly output to date was 12.3 million gallons, in March 1952.
In view of the ever-threatening possibility of salt-water encroachment from the Gulf of Mexico into the well field, and the experience of the previous salting of the old municipal well field in the southern part of the city, the Naples City Council requested the United States Geological Survey to investigate the ground-water resources of the area, and to determine the ground-water potential of the aquifers that might be used for the future development of water supplies for municipal and other uses.
Field work started in August 1951 and was continued intermittently through August 1952. A partial inventory of the existing wells was made, elevations of measuring points for water-level measurements were determined by spirit level, and a schedule of well-water sampling for chloride analyses was set up.
The investigation was under the general supervision of A. N. Sayre, Chief, Ground Water Branch, U. S. Geological Survey, and Herman Gunter, Director, Florida Geological Survey; immediate supervision was given by N. D. Hoy, District Geologist, U. S. Geological Survey, Miami, Fla. The Florida Survey and the Federal Survey
REPORT OF INVESIGATIONS No. 11 8
have been cooperating in general investigations of the geology and ground water of the State since 1930.
Julia Gardner, paleontologist of the U. S. Geological Survey, examined and identified fossil specimens and indicated tentative geologic ages for them. Chemical analyses of water samples were made by the Quality of Water Branch, U. S. Geological Survey.
The data of this report will be incorporated in a later report covering the ground-water resources of Collier County (fig. 1). The need for such a report is shown by the increased use of ground water for agricultural and municipal purposes within the county.
The principal sources of published information pertinent to western Collier County are in the form of brief references incorporated
I,*y *. "** *,-- ** -.. -- - ..
"'C IERi
' NAPLES
EVEROLADES
0 20 4,0 6,0 80 IO MILES
PIGURE 1. Map Of Florida showing location of the Naples area in Collier County.
4 FLORIDA GEOLOGICAL SURVEY
in Florida Geological Survey Bulletins 18 (Mansfield, 1939), 27 (Parker and Cooke, 1944), and 29 (Cooke, 1945), and in WaterSupply Papers 319 (Matson and Sanford, 1913), 596-G (Collins and Howard, 1928), and 773-C (Stringfield, 1936). In addition, some quality-of-water data have been collected by the U. S. Geological Survey during more recent years. No detailed ground-water studies had been made in Collier County prior to the present investigation.
ACKNOWLEDGMENTS
The investigation was greatly aided by the cooperation of residents and business establishments who supplied much valuable data and permitted water sampling of wells. F. M. Lowdermilk, City Manager, W. B. Uihlein, Chairman of the Naples Water Committee, and W. F. Savidge, Water Plant Superintendent, gave valuable assistance during the survey. J. P. Maharrey of Fort Myers and Chisholm Rivers of Naples, well drillers, supplied data on water wells in the area. A. D. Miller and Claude Storter of the Naples Co. granted permission for drilling a test well on company property and permitted frequent water sampling of wells at the Naples Golf Course. J. G. Sample and H. H. McGee permitted the running of a pumping test using the irrigation wells in J. G. Sample's citrus grove.
LOCATION AND GENERAL FEATURES OF THE AREA
GEOGRAPHY AND TOPOGRAPHY
The area covered by this report includes the city of Naples (fig. 1) and adjacent parts of Collier County. The larger part of the city of Naples, (fig. 2) is on a small peninsula which separates Naples Bay and the Gordon River from the Gulf of Mexico. The remainder of the city includes small areas east of the bay and the river. The peninsula is more than 1% miles wide at the northernmost reaches of the Gordon River and tapers southward to a point at Gordon Pass where Naples Bay joins the Gulf of Mexico.
The surface elevation on the peninsula ranges from 15 to 25 feet above sea level in the north and north-central portions and slopes off gradually to the south and east and more abruptly at the Gulf beach. The southern extremity of the peninsula and the areas bordering Naples Bay and the Gordon River are relatively flat with an average elevation of about 5 feet. During severe storms and excessively high tides sea water moves into Naples Bay and the Gordon River, flooding areas adjacent to the bay and portions of the southern
*REPORT OF INVESTIGATIONS No. 11 5
* 82
/ *e
/ /
//
/6 7 36 62
-V, GO-- -..4@75.// / @J @74
60
*97 5TH sAV E\ 3 NOT... 66
B 0 7 6 %B@5
1040g 31 32 $
,, 101 A'6"
yg0 1301
'67
26.
* LOCATION F'GOLOGIC
,TH' A O T / E IO '
AVE I SCALE IN FEET64
'st- SOUSOT 8oo
'" 114 -- 0 0 I
PzXGURE i2. Naples area showing location of wells and location-.of geologic
sect i..
AVTH OU 63
$ tosoXLNTO
0gy g WELLR
CITY SUPLYANNOHE BROAD SOUTH WLSO AG IL
WELLUPPDWT
RECORDING CAGE
4A
LOCATION OF, GEOLOGIC* SECTION
GR2.Naples area showing locatiori of ells* and lcto fgooi nGURE 2. c' sections.f golgi
6 FLORIDA GEOLOGICAL SURVEY
part of the peninsula. The Gulf side is protected by a beach ridge which extends along the coast.
The peninsula is entirely blanketed by a permeable terrace sand, the surface of which has been altered by winds and by washing of heavy rains. The drainage of the area is chiefly underground because rainfall rapidly percolates into the sandy mantle. Places of low elevation are locally covered by a thin layer of sand mixed with muck that is being formed by the decay of vegetation. The area is marked by small natural and artificial lakes or ponds which receive some overland runoff, as do the Gulf of Mexico and Naples Bay, during short periods of heavy rainfall. The land just east of the beach ridge in the northern part of the city is swampy and remains inundated throughout much of the year.
The lower part of the peninsula is dissected to some extent by drainage ditches and dredged-out boat basins. They are avenues of possible extended salt-water encroachment.
CLIMATE
The climate at Naples is subtropical and the humidity is usually high. The average annual temperature as shown by discontinuous records of the U. S. Weather Bureau is 75.80 F., and the warmest weather occurs during July and August. Table 1 shows monthly and yearly averages of temperatures and rainfall at the Naples station and rainfall at the Bonita Springs station, about 15 miles north of Naples.
The average annual rainfall at Naples and Bonita Springs, from discontinuous U. S. Weather Bureau records, is 52.19 inches and 54.30 inches, respectively. The heaviest. rains occur during the period June-October, inclusive. The greatest yearly rainfall on record at Naples was 71.47 inches in 1947. During June of that year a total of 17.79 inches of rain was recorded. However, the rainfall throughout 1947, even during ordinarily dry months, was unusually high. The year of lowest rainfall on record was 1944 with 30.93 inches.
Rainfall in this portion of the Gulf coast is not evenly distributed areally but is localized, as shown by table 1. Although the stations are relatively close, appreciable variations are noted in monthly totals, especially during months of heavy rainfall.
REPORT OF INVESTIGATIONS No. 11 7
TABLE 1
Average monthly temperature, in degrees F, at Naples, and a
comparison of average monthly rainfall, in inches, at Naples and Bonita Springs
Month Temperature' Rainfall2 Naples Naples Bonita Springs Jan ......................................... 67.2 1.15 1.20
Feb ......................................... 67.6 0.82 0.83
M ar ....................................... 70.6 1.38 1.21
April ........................................ 75.9 2.57 1.84
May .......................................... 77.5 3.41 3.55
June ........................................ 82.0 8.88 8.78
July .......................................... 83.3 7.88 11.04
Aug ......................................... 84.0 7.71 10.00
Sept. ....................................... 82.8 9.67 9.42
Oct ......................................... .. 77.9 5.56 4.02
Nov ......................................... 72.5 2.10 1.34
Dec ......................................... 68.6 1.06 1.07
Yearly average ...................... 75.8 52.19 54.30
1 Discontinuous record 1942-50, U. S. Weather Bureau. 2 Discontinuous record 1943-50, U. 8. Weather Bureau.
TEST-WELL DRILLING
Five 2-inch test wells, drilled under contract at Naples early in 1952, furnished information on the general subsurface geology of the area. In addition, they were and will continue to be used to gather data on ground-water-level fluctuation and for determining the extent of salt-water encroachment from Naples Bay and the Gulf of Mexico.
Three of the test wells, nos. 116, 117, and 118 (fig. 2), were drilled to depths comparable to those of the city supply wells. Well 116, drilled to 62 feet below mean sea level, is at the southwest corner of South Golf Drive and Third Street, about 1,300 feet inland from .the Gulf of Mexico. Well 117, drilled to 72 feet below mean sea level, is on Fifth Avenue North, east of the Tamiami Trail and approximately 1,500 feet west of the Gordon River. Well 118, just west of the water plant, was drilled to 64 feet below mean sea 'level. With such a distribution of test wells the municipal well field is encircled by observation wells so that, by means of periodic sampling, any extension of present salt-water encroachment may be detected. None of the above tests showed any indication of salt-water encroachment.
Wells 119 and 123 were drilled to determine the depth at which salt water occurs. Well 119, in the approximate center of the well field, was drilled to 105 feet below mean sea level, at which depth a pronounced increase in chloride was detected. Well 123, drilled to 145 feet below mean sea level, 0.7 mile north of the Naples Golf
8 FLORIDA GEOLOGICAL SURVEY
Course in an area only slightly effected by pumping, showed no evidence of salt water. These wells similarly will serve as waterlevel and chloride-sampling observation wells.
During the course of test drilling, specimens of the penetrated material were collected, usually at 5-foot intervals, and examined. Each time a permeable rock layer was penetrated the well was pumped, and water samples were collected for chemical analyses including chloride. Water samples from materials of low permeability were collected with the bailer and were analyzed for chloride content only.
GEOLOGIC FORMATIONS AND THEIR
WATER.BEARING PROPERTIES GENERAL CONDITIONS
The strata underlying the Naples area to a depth of about 600 feet range in age from Miocene to Recent; however, strata of Pliocene age apparently are missing. Deeper rocks older than Miocene contain water of poor quality and are not discussed in this report.
MIOCENE SERIES
Formations of Miocene age are the oldest strata penetrated by water wells in the Naples area. The Miocene series in the area includes the Tampa formation, Hawthorn formation, and Tamiami formation of early, middle, and late Miocene age, respectively.
TAMPA FORMATION1
The Tampa formation, as defined by Cooke (1945, pp. 111-113), overlies the Suwannee limestone of Oligocene age and is gradational with the overlying Hawthorn formation.
sandy limestone and calcareous sandstone are the chief components of the Tampa formation. The sand, predominantly quartz, may occur either disseminated in the matrix of the limestone or in thin beds or pockets. The Tampa formation forms a part of the principal artesian aquifer which underlies much of Florida and southeastern Georgia (Stringfield, 1936, pp. 122-128) and for which Parker (1951, p. 819) proposed the name Floridan aquifer. The Tampa formation is permeable and is one of the major sources of irrigation water in counties bordering the Gulf coast north of Collier County. The top of the Tampa formation occurs between 600 and 640 feet below sea level at Fort Myers and the formation ranges from 80 to 120 feet
1 The geologic nomenclature used in this report conforms to the nomenclature of the Florida Geological Survey. It conforms also to that of the U. 8. Geological Survey with the exception that the Tampa formation is used instead of Tampa limestone.
REPORT OF INVESTIGATIONS No. 11 9
in thickness (Hoy and Schroeder, 1952). It is possible that well 115 (fig. 2), drilled to a depth of 540 feet, penetrates the Tampa formation. The formation yields only salty water in this and adjacent areas.
HAWTHORN FORMATION
Rocks younger than the Tampa and older than late Miocene in age are referred to the Hawthorn formation by Cooke (1945, p. 144) and Vernon (1951, pp. 186-187).
The Hawthorn formation is composed chiefly of gray-green clay, silt, and fine sand and interbedded limestone and shell marl. Permeable limestone and shell beds in the lower part of the formation are regarded as the uppermost part of the principal artesian aquifer (Stringfield, 1936, p. 130), and are the probable sources of the deep, freely flowing artesian wells at Naples. The overlying clay and silt sections, however, are relatively impermeable and separate the water of the principal artesian aquifer from the shallow artesian beds, such as the shallow confined aquifer of the Naples area. At Fort Myers the top of the Hawthorn formation occurs at depths between 40 aand 55 feet below the land surface. At Goodland, south of Naples, the top of the Hawthorn formation lies between 150 feet and 270 feet below the land surface. By projection, the clay and silt of the Hawthorn should be encountered at a depth of about 170 feet in the Naples area. The formation is about 400 feet thick in this area. None of the test wells at Naples were deep enough (maximum depth 157 feet) to penetrate material which appeared to be of Hawthorn age.
TAMIAMI FORMATION
All materials of late Miocene age in southern Florida are assigned to the Tamiami formation by Parker (1951, p. 823); thus the upper part of the Hawthorn formation of Parker and Cooke (1944, pp. 98112), the Tamiami formation, and Mansfield's (1939, p. 8) Buckingham limestone and Tamiami limestone are incorporated as a unit the Tamiami formation.
The macrofossil content of test-well samples has been studied from depths ranging from 20 feet to 70 feet. Julia Gardner states: "No species have been determined from the Tamiami fauna, but the general character of the assemblage is uniform: Pecten, Anomia, Ostrea, and Balanus, all of them fragmented, possibly from the surf on the old Tamiami reef." The samples contained Giycymeris sp. and Turritella sp. of a pattern common to the upper Miocene of Florida.
The Tamiami formation is composed primarily of light-tan and
10 FLORIDA GEOLOGICAL SURVEY
gray fossiliferous sandy limestone and interbedded gray-green sandy and shelly marl. Although not precisely located, the top of the formation at Naples generally occurs between 15 feet and 30 feet below mean sea level. The Tamiami formation may be more than 125 feet thick at Naples.
The upper part of the Tamiami formation is composed predominantly of beds or lenses of soft, relatively impermeable greenishgray marl and minor beds of gray permeable limestone. The marly sediments generally are poorly sorted and act as a semi-impervious barrier or confining bed which retards the vertical movement of ground water. This relatively impermeable zone ranges in thickness from 5 feet to 20 feet and is apparently thickest in the Naples wellfield area.
Data from drillers' logs and from recent test drilling indicate that the first thick permeable limestone that underlies the confining bed is the most persistent fresh-water-bearing rock in the Naples area. This limestone is the main aquifer and is sufficiently thick that a well penetrating it will have at least 5 to 10 feet of open-hole finish. The upper surface of this permeable rock occurs at approximately 50 feet below mean sea level at the municipal well-field area and apparently slopes very gently toward the Gulf.
Wells 119 and 123 are of sufficient depth to furnish more complete information concerning the hydrologic properties of deeper parts of the Tamiami formation. The greatest permeability in well 119 was at the intervals between 50 to 61 feet and 70 to 74 feet below mean sea level. Below 74 feet unconsolidated material, which occurs as thin beds of calcareous sand or cavity fillings in the limestone, and dense limestone beds reduce the permeability. If well 119 can be used as an index of the general conditions at the well field, a depth of 80 to 85 feet below mean sea level is the maximum to which supply wells in that vicinity may be drilled. Not only is there a decrease in permeability with greater depth, but there is also an increase in salinity of the ground water.
North of the well field, as data from well 123 show, the lower part of the Tamiami formation to a depth of 145 feet below sea level is composed of limestone of varying degrees of cementation. This thick rock zone is a possible source of large quantities of fresh Water. The limestone is riddled with solution cavities which are usually filled with loose sand. When penetrated by drilling, the loose material slumps or caves, but can be bailed or pumped clear.
48
FLORIDA GEOLOGICAL SURVEY Report of Investigations No. 11
A A'
123
I 116 119 10 ig
"118
SNONARTESIAN A 0 UIFER
20 "-rRESH WATER
SHELLS
30
-,4
40 BED
50
- 60
-0 SHALLOW ARTESIAN AQUIFER
I-.
80
EXPLANATION
- 90
SAND
M .ARL
100 SHELLS, MARINE LIMESTONE
A
110 / 123
116/ CROSS SECTION A-A'
120 o SHOWING PROJECTION OF S WELL 116 ONTO NORTH\STOUTH LINE. SEE FIG. 2 119 FOR LOCATIONS. 130 SCALE IN FEET
500 0 500 1,000 li
140 A'
FIGURE 3. North-south geologic section, A-A', through the Naples well field.
V4
REPORT OF INVESTIGATIONS No, 11 11
Rapid changes in lithology are noted in a horizontal direction as well as vertically. These variations may be either gradational or fairly abrupt. A thickness of limestone or shelly marl at a certain depth in one test well may be no indication that a corresponding bed will be present at a comparable depth in another well. However, the thicker permeable limestone layers are fairly consistent throughout the area and may be tentatively correlated from one well to another (figs. 3 and 4).
PLEISTOCENE AND RECENT SERIES
Deposits of Pliocene age are not known to occur in the Naples area. In describing the faunal assemblage from a sample taken at
B B'
10 116 119
ASL MSL
NONARTESIAN AQUIFER 10
FRESH
WATER
t4J SHELLS
A 20
,4
tI)
c o
30
1J k
40 C N I NNE
o60 SHALLOW ARTESIAN AQUIFER
k 70
E X PL AN A T ION
80 SAND
MARL
SSHELLS, MARINE
90 LIMESTONE
, CALE IN FEET.
oo500 0 o500 1,000
100FIGURE 4. West-east geologic section -B, across Naples area
PFIGURE 4. West-east geologic section B-B'. across Naples area.
12 FLORIDA GEOLOGICAL SURVEY
28 feet from test well 119 Julia Gardner states: "None of the species listed would be out of place in either a Pliocene or a Pleistocene fauna. However, the assemblage is unlike any I have seen from the Pliocene. Very few of the dominant species of the Caloosahatchee (Pliocene) are present." The assemblage collected at 28 feet from well 119 includes:
Anadara sp.; juvenile. Group of A. transversa (Say) but relatively wider.
Carditamera floridana Conrad? juvenile
Bellucina aminata Dall
Cardium sp.
Chione (Chione) canceUllata (Linnaeus)
Chione (Timoclea) qrus (Holmes)
Ervilia? sp. juvenile
Corbula (Caryocorbula) barrattiana C. B. Adams
Diodora alternata (Say)
Turritella tips
Young Columbellids?
Nassarius vibex (Say)
Olivella sp. cf. O. mutica (Say)
Turrids juvenile
In the absence of contrary information, the deposits containing the fauna listed are included in the Pleistocene series in this report.
Rocks of known Pleistocene age in Naples and vicinity are the Anastasia formation, the Fort Thompson formation or an equivalent, and the Pamlico sand. The Recent series is represented by black mucky sands.
ANASTASIA AND FORT THOMPSON (?) FORMATIONS
The Anastasia formation represents materials deposited during part of Pleistocene time. In the Naples area it is composed of lightcream to light-gray sandy limestone and gray to tan shelly, sandy marl containing an abundance of Chione cancellate. The limestone of the Anastasia formation thickens eastward where its top occurs at higher elevations than at the center of the Naples area. It seems apparent that the Anastasia formation originally covered the Naples area, but was subjected to beach erosion and was partially removed prior to the deposition of the surface sand.
A thin bed of shelly marl overlies the limestone beds of the Anastasia in many places. In places the marl contains small fragile shells of gastropods (snails) of fresh-water origin. It may represent
REPORT OF INVESTIGATIONS No. 11 18
or be equivalent to part of the Fort Thompson formation, which was deposited during one of the glacial stages of the Pleistocene.
The Anastasia formation exhibits a lack of uniformity in deposition similar to that of the Tamiami formation. The only correlatable unit is a hard fossiliferous tan to gray limestone which is the shallowest water-bearing limestone in the Naples area. According to information received from well drillers, this limestone bed of the Anastasia formation is often encountered within 10 feet of the surface in adjacent areas east of the Gordon River and causes very difficult drilling. In test well 117 this stratum occurs 20 feet below the surface and is about 15 feet thick. The same hard limestone was noted in well 123 between 36 and 44 feet below the surface. It is reported that this water-producing rock was penetrated at about 28 feet in well 110, but the precise thickness there is not known. In the western and southern parts of the peninsula the rock is very thin or missing as a result of erosion during pre-Pamlico time.
PAMLICO SAND AND LATER DEPOSITS
The Naples area is entirely blanketed by the terrace deposits of the Pamlico sand which in places is mixed with Recent black mucky sands. The altitude of the terrace is everywhere less than 25 feet. The Pamlico sand is composed of fine to medium sand, the base of which lies at a depth of 10 to 15 feet below mean sea level. The uppermost material is white or light gray medium-grained quartz sand which grades downward to highly colored rust-brown finegrained quartz sand. The color is apparently the result of the vertical migration of organic materials in percolating ground water. The components of the Pamlico sand are sufficiently well sorted to permit the ready intake of rainfall and to allow easy downward percolation. The Pamlico sand will supply small quantities of water to shallow sand-point wells.
GROUND WATER
PRINCIPLES OF GROUND-WATER OCCURRENCE
Ground water is stored in .the openings, solution cavities, and pore spaces within the consolidated and unconsolidated materials of the earth's crust. The openings or voids between particles vary in size because of the nonhomogeneous character of the sediments. The frequency and the size of the openings determine the porosity, which is expressed as the ratio of the volume of the interstices to the volume of rock mass (Meinzer, 1923, p. 19). Clay is one of the most porous
14 FLORIDA GEOLOGICAL SURVEY
of all natural earth materials, but is also one of the least permeable. Permeability in water-bearing materials is the property of transminitting water under a gradient.
Well sorted, unconsolidated sands or silts, regardless of the size of the components, are highly porous but the permeability varies with the size of the pores. Admixtures of particles of various sizes such as sandy clay, marly sand, or shelly marl may be of low porosity and are of low permeability because the smaller grains occupy the voids between large grains. In consolidated rocks, porosity and permeability may be reduced by the filling of openings with cementing material.
Clay, marl, or fine sand, although highly porous, are capable of transmitting only small quantities of ground water. Coarse sand or gravel and cavernous limestone, however, transmit ground water with great facility. The consolidated rock layers underlying Naples are highly permeable because the network of interconnected solution cavities permit the ready movement of water. Any natural geologic formation that transmits water in sufficient quantities to supply a well is called an aquifer.
All the water that supplies the wells in the Naples area is derived from local rainfall. Not all of the rainfall, however, percolates through the surface sand to the water table, the remainder being lost by evaporation and transpiration or by overland runoff into the Gordon River, Naples Bay, and the Gulf of Mexico. The water table is the surface below which earth materials are completely saturated.
Ground water that is, water below the water table moves laterally under gravitational influence from points of recharge to points of artificial discharge such as wells, and to places of natural discharge such as springs, lakes or streams. It is this natural groundwater discharge that largely maintains streamflow and lake levels d(luring dry periods.
The water table is an undulating surface conforming in a general way to the topography of the land, being higher under hills than under valleys. It fluctuates seasonally, rising during seasons of heavy rain and falling during periods of low rainfall. It fluctuates also in response to many other forces such as evaporation, transpiration, and pumping from wells.
An aquifer that is not overlain by impermeable material contains water under nonartesian or unconfined conditions. The water in a
REPORT OF INVESTIGATIONs No. 11 15
well penetrating an unconfined aquifer will not rise above the point where the water was encountered in drilling the well. The shallow aquifer at the Naples well field is a nonartesian aquifer because the overlying materials are permeable. The aquifer is tapped by many wells, such as well 110, and the water level in each well is a measure of the altitude of the water table in that immediate area.
Where ground water has moved laterally into permeable material that is overlain by a relatively impervious cover, it is said to occur under artesian (confined) conditions. The water level in a well penetrating an artesian aquifer will rise above the top of the aquifer to a point that is the approximate measurement of the pressure head. The pressure head is due to the weight of the water at higher elevations in the aquifer. The water level of an artesian aquifer is known as the piezometric surface, and wherever it is above the land surface, wells tapping the aquifer will flow. The piezometric surface of an artesian aquifer fluctuates in response to the same forces that affect the water table, and also in response to forces like earthquakes, passing trains, and hurricanes and other storms, that generally do not affect the water table directly (Parker and Stringfield, 1950).
HYDROLOGIC PROPERTIES OF THE AQUIFERS
Ground-water supplies in the Naples area occur in three separate aquifers having different water levels and water quality. These are designated as: (1) nonartesian aquifer containing water under watertable or unconfined conditions; (2) shallow aquifer containing water under artesian conditions; and, (3) principal artesian aquifer (Floridan aquifer) containing saline water under artesian conditions.
NONARTESIAN AQUIFER
The nonartesian aquifer in the Naples area is usually composed of the Pamlico sand, the Anastasia formation, and that part of the Tamiami formation which overlies the main confining marl. The permeability of the aquifer is highest in the vicinity of wells 110, 116, 117, and 123, as in these areas the section between the surface sand and the confining bed is composed almost entirely of cavernous limestone which remains open after penetration. In these areas limestone of the Anastasia formation is immediately underlain by consolidated parts of the upper part of the Tamiami formation. Regardless of the difference in geologic age of the rocks the entire section is a single, connected, unconfined, hydrologic unit. In other areas such as at wells 118 and 119 and over much of the northern part of the well field the nonartesian aquifer is least productive because
16 FLoIDA GEOLOGICAL SURVEY
limestone beds are very thin or missing and the aquifer consists mainly of sand and marl.
The base of the nonartesian aquifer is an undulating surface ranging in depth from about 32 feet below mean sea level in the south to 55 feet in the north. The aquifer is the source of water for several small privately owned irrigation wells and for public-supply well 110.
Discharge
Ground-water losses from the nonartesian aquifer occur naturally by seepage and evapotranspiration, and by pumping from wells. Considerable discharge undoubtedly occurs through submarine seeps where the aquifer crops out beneath the Gulf and Naples Bay. Losses through seepage are greatest during periods of high rainfall when ground-water levels are highest. Another part of the seepage loss occurs where nonartesian water percolates downward through the less permeable confining bed to the lower fresh-water aquifer. Also of major importance is the quantity of water lost through evaporation and transpiration. Ground-water losses due to evaporation and transpiration are greatest when the water table is high and decrease as the water table declines. Losses resulting from these natural processes greatly exceed the quantity of water withdrawn from the aquifer by pumping from wells.
When water is pumped from a well penetrating the nonartesian aquifer, the dewatering of the material causes a rapid lowering of the water table in the immediate vicinity of the well, thus establishing a hydraulic gradient toward the well. The water table assumes the form of an inverted cone centered at the discharge point. As pumping continues at a constant rate, the water table at the well declines progressively but at a slowly decreasing rate, until a point of near-equilibrium is reached in the vicinity of the well whereby the rate of discharge is balanced by an equal amount of water being transmitted to the center of withdrawal. At the same time, the cone of depression or cone of influence (Meinzer 1923, p. 61) spreads so that the water table is lowered at greater distances from the well; thus, water from more distant parts of the aquifer is being diverted to the pumped area. As pumping proceeds, the water table continues its slow decline and the cone of depression spreads farther unless recharge is made available to the aquifer. If recharge is sufficient to balance withdrawals, the spreading of the cone progresses no farther, and the water level at the pumped well remains essentially constant. An additional deepening and spreading of the cone would result if the pumping rate
RiEPORT OF INVESTIGATIONS No. 11 17
were to increase or if another nearby well in the aquifer started pumping. When pumping from the well ceases, the water level immediately starts to recover, rapidly at first, then at a slowly decreasing rate to a point of essentially the original nonpumping level. The rate at which drawdown and recovery proceed in the vicinity of a well depends in part upon the permeability of the aquifer. Pumping from material of high permeability produces a small drawdown with a wide shallow cone of depression; in material of low permeability a narrow deep cone develops.
Because the peninsula is bounded on the west, south, and east by bodies of salt water, these must be considered as the boundaries of the shallow aquifer, for an excessive lowering of the water table in these extreme areas would result in drawing in salt water laterally. To the north, however, the aquifer is of much greater areal extent.
Recharge
The main recharge to the nonartesian aquifer is that part of the total rainfall that percolates downward to the zone of saturation. A general rise in the water table at Naples occurs when rain falls in the immediate vicinity of the city. Rainfall to the north and east may or may not effect the water table in the city itself. The relatively flat topography and the permeable sandy cover throughout the area permit little surface runoff and the largest drainage is underground. It is possible that during high water stages some water is recharged to the aquifer from the Gordon River. This seepage would occur only for a short interval because as the stream level is lowered the water would drain back into the stream and the normal streamward gradient of the water table would be restored.
When the effect of pumping nonartesian wells (lowering of the water table) reaches an area where natural surface-water or groundwater discharge occurs into the Gulf of Mexico, Naples Bay, or Gordon River, some of the water normally lost through this discharge would be diverted toward the pumped area; thus rejected recharge and normally wasted water would be salvaged. The water levels in the shallow lakes at Naples and in the swampy area to the north denote the height of the water table in those areas. If the spreading of the cone of influence were to include any of these lakes, the water level in that lake would lower slowly owing to the fact that its water was being moved toward the pumping area. The diversion of normally rejected water retards the spreading of the cone of depression.
During dry periods some recharge occurs through the seepage of
18 FLORIDA GEOLOGICAL' SURVEY
irrigation water to the water table. The amount thus supplied is small because evaporation and transpiration rates increase during dry times.
SHALLOW ARTESIAN AQUIFER
The top of the shallow artesian aquifer at Naples occurs between 40 and 70 feet below mean sea level. Exclusive of well 110 it is the source of water for all city supply wells and also the source for several privately owned irrigation wells including the large-diameter wells at the golf course (wells 78, 79, 80, 136, fig. 2), and J. G. Sample's citrus grove (wells 71, 72, 73, 74, 98, fig. 2). Well 110 whose bottom is 32 feet below mean sea level, and the lower 12 feet of which is uncased shows no evidence of hydraulic connection between the nonartesian and shallow artesian aquifers; the water level in the well shows no fluctuation when the pumps are being turned on and off in the remainder of the field. From this fact and from test-drilling data it is certain that in the well field the nonartesian and shallow artesian aquifers are separated by a confining bed or beds.
Different conditions appear to exist south of the well field and in areas of the eastern part of the peninsula. Test well 118 penetrated a series of beds or lenses of slightly permeable sandy marl and thin layers of permeable limestone beneath the nonartesian aquifer. It is possible that some interconnection exists between the two fresh-water aquifers, so that south of the well field their entire thickness may be a single hydrologic unit. In support of this speculation is the fact that each time a highly permeable zone was encountered during drilling well 118, the water level in the well remained at the level of the water table. This cannot be considered conclusive evidence, however, because the land-surface and water-table elevations are lower in the south and the water-table elevation approaches the elevation of the water surface in the shallow artesian aquifer. East of the well field also, the confining layer becomes thinner and thus may permit increased movement of water between aquifers. In well 117 the water table was 0.5 foot higher than the piezometric surface and in wells 116 and 123 the water table ranged from 2 to 3 feet higher than the piezometric surface of the shallow artesian aquifer.
Material overlying an artesian aquifer may either effectively confine or partially confine the water in the aquifer. Effective confinement is produced by impermeable beds, but slightly permeable confining beds retard rather than prevent percolation of water (Meinzer, 1923, p. 40). Probably the confining material in much of the Naples area is of the slightly permeable type and produces artesian groundwater heads.
REPORT OF INVESTIGATIONS No. 11 19
Discharge
The effects produced by withdrawing water from an artesian well are similar to those produced in a nonartesian well. However, discharge from an artesian well results in a lowering of the pressure at the well rather than an actual dewatering of the aquifer. Water is released from storage, owing to the compaction or squeezing of sediments when the artesian pressure is lowered, and to slight expansion of the water itself. The basic principle of the cone of influence remains in effect, but the drawdown and spreading of the cone occur at a more rapid rate because the amount of water released from storage per unit area is much smaller than the amount that drains from the pores of the rocks when the water table is lowered.
During periods of low rainfall the water table in the southern part of the Naples area declines to elevations below the pressure surface of the shallow artesian aquifer. A pressure differential is then set up whereby water may move from the lower aquifer to the higher aquifer, especially in areas where the confining layer is thinnest or most permeable. The rate at which the movement occurs will depend on the gradient between the aquifers, but in general the seepage will be small. During normal times the water table is above the piezometric surface of the shallow artesian aquifer, and any movement through the confining bed is downward into the artesian aquifer.
A part of the ground water lost from the shallow artesian aquifer is also due to natural seepage. The aquifer slopes off to the west and the south, extending for an undetermined distance beneath the Gulf of Mexico. The discharge occurs by upward seepage through the confining bed, or by direct discharge where and if the aquifer crops out on the floor of the Gulf.
Recharge
The shallow artesian aquifer accepts recharge from rainfall in Naples and vicinity, and as seepage from overlying water-bearing beds that may, in some cases, be at a considerable distance from the city. Figures 5 and 6 are hydrographs of wells 107 and 88, respectively, showing the correlation between water levels and rainfall. Both wells penetrate the shallow artesian aquifer and their water levels respond to rainfall in the area. The water levels in well 107 are effected by well-field pumping so that the plotted points in figure 5 represent daily highs and lows throughout most of 1948 and the first three months of 1949. Appreciable rainfall at Naples is always accompanied by a rise in the water level in shallow artesian wells. Such rises in the water level may be the result of recharge percolating
20 FLORIDA GEOLOGICAL SURVEY to the aquifer, or may be due to the pressure effects from the weight of water added to the nonartesian aquifer. An attempt was made to correlate the occurrence of rainfall at Bonita Springs, 15 miles
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REPORT OF 'INVESTIGATIONS No. 11 21
north of Naples, with rises in water levels at Naples, but no definite conclusion could be drawn. Slight rises on the hydrograph (as for example on February 9, 1948) might be correlated with rain at Bonita
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22 FLORIDA GEOLOGICAL SURVEY
Springs when no rainfall was recorded at Naples, but these rises may be due instead to a decrease in barometric pressure. Figure 6 is a similar correlation of rainfall with water levels at well 88. The water level in this well is influenced by tides and shows plots of daily highs and lows.
Seepage of ground water from the nonartesian aquifer through the confining layer to the shallow artesian aquifer is one of the sources of recharge. Although proceeding at a relatively slow rate, seepage occurs over a wide area and may be substantial. The lowering of pressure which accompanies pumping from the shallow artesian aquifer. increases the gradient between the nonartesian and the shallow artesian aquifers, and more rapid inter-aquifer seepage results. Seepage rates vary from place to place owning to differences in gradient between the two aquifers and in thickness and permeability of the confining layer.
A part of the recharge enters the shallow artesian aquifer in an undetermined area north or northeast of Naples where the aquifer is probably overlain by permeable sand. The source of recharge from the north is indicated by the general southward direction of groundwater flow.
PRINCIPAL ARTESIAN AQUIFER
The upper part of the principal artesian aquifer underlying the Naples area and vicinity is composed of limestone of the Tampa formation and permeable limestones and shell beds in the lower part of the overlying Hawthorn formation (Stringfield, 1936, p. 132). Well 115 drilled to a depth of 540 feet, is the deepest artesian well of record in the Naples area, and may penetrate the Tampa formation. The piezometric surface in this well is about 20 feet above the land surface. Stringfield (1936, p. 166) lists a 400-foot well at the Naples Hotel as penetrating the Hawthorn formation. The piezometric surface in this well measured 18 feet above the land surface in 1934.
A higher water-bearing limestone occurs within the Hawthorn formation and yields water to wells ranging in depth from about 200 feet to 250 feet. The piezometric surface in tightly cased wells at these depths is approximately at the land surface. This limestone may be a poorly connected part of the principal artesian aquifer or it might possibly be a separate artesian system.
Recharge to the artesian aquifer occurs where it is at or near the surface, as in central Florida, and in areas where sinkholes penetrate the Hawthorn formation, as in Polk County (Stringfield, 1936, pp.
REPORT OF INVESTIGATIONS No. 11 23
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SC.5- WATER-LEVEL CONTOUR CONTOUR INTERVAL, 0.1 FOOT ,... S'TH SC L IN F E
FIGURE 7. Contour map of water levels in the Naples area, February 12, 1952,
showing the effect of concentrated pumping in the golf course.
24 FLORIDA GEOLOGICAL SURVEY
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REPORT OF INVESTIGATIONS No. 11 25
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26 FLORIDA GEOLOGICAL SURVEY
146-148, pl. 12). Water levels in wells 'penetrating the principal artesian aquifer show seasonal fluctuations in and near recharge areas that are due to variations in rainfall. However, rainfall at Naples does not affect the artesian pressure in wells tapping the aquifer. Water from the flowing wells is of little economic importance to the area because it contains about 2,000 ppm of chloride.
WATER-LEVEL FLUCTUATIONS
Water levels in the shallow artesian wells at Naples respond to recharge by rainfall and discharge by pumping, fluctuate with changes in atmospheric pressure, and are affected by tides in the Gulf of Mexico. On occasions, water levels in these wells are disturbed by distant earthquake shocks.
Figures 7, 8, and 9 are contour maps showing water levels in the Naples area on different dates (table 6), when the municipal wells were not pumping. It is apparent from the relatively uniform head that the water is derived from the same aquifer regardless of the divergence in the depth of the wells. The piezometric surface has a slight but regular gradient to the south, indicating recharge from the north and discharge to the south. The contours in general appear to conform to the topography of the area, which is more typical of nonartesian than of artesian conditions. However, it is understandable because, as mentioned, seepage occurs through the confining bed and the heads of both shallow aquifers tend to become equalized. Water-level measurements for the contour maps were made after recovery from pumping was essentially complete. A cone of influence has formed north of the well field (fig. 7) as a result of pumping irrigation wells 79 and 80 at the total rate of 500 gallons per minute. This withdrawal concentrated within a small area is reflected by the lowering of water levels in the northernmost city supply wells.
Figures 10 and 11 are water-level contours in the Naples area after several hours of pumping in the city well field, and represent water levels at periods of peak withdrawals during the winter season and after a long period of drought in the spring. Figure 10a, in addition, shows pumping and nonpumping water-level profiles across the peninsula on February 11-12, 1952, and demarks the position of the Gulf tide at the time of the measurements. Measuring water levels in pumped wells is generally not accepted procedure because, owing to loss of head (well loss) as water enters and moves up a well, the water level at the well does not reflect the true water level in the vicinity. However, if the head losses in all wells are assumed to be
REPORT OF INVESTIGATIONS No. 11 27 l.
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2 5- WATERF.LEVEL CONIOUR CONTOUR INTERVAL, 0.25 rOOT
1 LqII SCALE IN FEET
FzaURE. 10. Contour m4p showing the effect of well-field pumping on water
levels in the Naples area, February 11, 1952.
28 FLORIDA GEOLOGICAL SURVEY
the same, a map based on pumping water levels indicates the general attitude of the piezometric surface and the adjustments in the direction of ground-water flow. The adjustments are noted at the north end of the well field, where the higher contour lines bend southward, suggesting that recharge enters from the north.
Long-range water-level records are not available for the Naples area; therefore no yearly comparisons can be made. The only useful data are presented in the hydrographs in figures 5 and 6 and the measurements in table 6 from which the contour maps were prepared. These data show the seasonal rise and decline of water levels, and in addition they show in a general way the difference in water levels in shallow artesian wells and wells penetrating the nonartesian aquifer such as well 110.
Throughout part of the year the water table in the southern part of the well field is higher than the shallow artesian head, at times being half a foot to a foot higher. During the period December through May the water table declines more rapidly than the artesian level, so that after the long period of low rainfall and high evapotranspiration the nonartesian aquifer in the southern part of the well field is drained to a point where the water-table elevation falls below the artesian head. At the end of May 1952 the water table ranged between 0.75 and 1.0 foot lower than the artesian water level in the Naples well field. However, in areas of higher ground elevation the water table remains higher than the artesian head throughout the year. During May 1952 the water table in the northern part of the well field ranged from 1 foot to 1.5 feet higher than the artesian level.
Tidal fluctuations in the Gulf of Mexico are reflected in the water levels in nonartesian wells near the shoreline and in shallow artesian wells at greater distance from the shore. Ground-water fluctuations due to tides are caused in three ways (Brown, 1925, p. 50): (1) by transmission of pressure through the pore spaces and cavities which connect the well to the Gulf; (2) by changes in the rate of normal ground-water flow from the aquifer to the Gulf; and, (3) by deformation of the material resulting from alternate loading and unloading on the earth's crust. The principle is the same in the first two, the main difference being the rate at which the ground-water level fluctuations occur. The effect of the deformation of sediments may or nmay not contribute to ground-water fluctuations; the amount of effect produced depends upon the competence of the limestone.
From the short period of tidal data available at Naples, a maximum
REPORT OF INVESTIGATIONS No. 11 29
range of about 4 feet between high and. low tides has been recorded in the Gulf. The water level in well 88 fluctuates with tides and lags approximately 12 hours. The daily fluctuation ranges from 0.2 to
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30 FLORIDA GEOLOGICAL SURVEY
0.7 foot, but some of the effect is due to nearby pumping. The maximum range in daily fluctuation recorded at well 130 was 0.9 foot. The water level in this well also is influenced to some extent by well-field pumping. Although not definitely established, it is probable that the effect of tides reaches the municipal supply wells.
SALT-WATER ENCROACHMENT
Salt-water encroachment into the fresh-water aquifers may occur from two sources: (1) direct movement inland from the Gulf of Mexico and from Naples Bay; and, (2) upward contamination from salt water which occurs at greater depth. The salt water at depth exists either trapped in the sediments at the time of deposition, or as water that entered the sediments at times when the sea covered the Naples area during Pleistocene time.
The quantity of water that can be drawn from the fresh-water aquifers in the Naples area is governed by the amount that groundwater levels can be lowered without producing accelerated vertical movement of high-chloride water from underlying sources or lateral movement from the Gulf or Naples Bay. Because of a lower specific gravity, the fresh-water body floats on top of the salt water, and the depth to the salt water is related to the height of the fresh water above mean sea level. This relationship, which is simply that of a U-tube whose 2 limbs contain liquids of different density, is referred to as the Ghyben-Herzberg principle (Brown, 1925, pp. 16-17) and is expressed as:
t
h .
g-1
where h is the depth of fresh water below mean sea level, t is the fresh-water level in feet above mean sea level and g is the specific gravity of the salt water. If it is assumed that the specific gravity of the sea water is 1.025, a common value, then for each foot of fresh water which occurs above sea level, 40 feet of fresh water extends below mean sea level. The relationship applies strictly only to static conditions, and is modified under dynamic conditions. However, the departure is not large enough to invalidate the principle for practical use.
CONTAMINATION IN NONARTESIAN AQUIFER
The formula is directly applicable to the nonartesian aquifer which is relatively permeable throughout and extends outward beneath the Gulf of Mexico and Naples Bay. An average fresh-water head of 1.5 feet above mean sea level is sufficient to prevent salt-water en-
REPORT OF INVESTIGATIONS No. 11 31
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FIGUPE 11. Contour map showing the effect of well-field pumping on water
levels in the Naples area, May 2.6, 1952.
32 FLORIDA GEOLOGICAL SURVEY
croachment to a depth of 60 feet below mean sea level. Therefore, this aquifer with a maximum depth of 55 feet below sea level is protected in areas where the water-table elevation is 1.5 feet or more above mean sea level. In fringe areas adjacent to the Gulf and Naples Bay the water table slopes off to near-sea-level elevations, permitting salt water to enter the aquifer for short distances inland. This movement has not been excessive. In the southern part of the city, where land elevations average about 5 feet, the water table lies at low elevations. The various boat basins dug in this area have lowered the water table still farther so that salt water has contaminated the area south of Broad Avenue South. Fresh ground water is available in this part of Naples only in very shallow wells during periods of heavy rainfall, at which time fresh water exists as a thin lens floating on the salt water. Wells in these fringe areas cannot be pumped heavily or continuously because salt water would be drawn in after a short time.
Elsewhere in the city the water table has remained at sufficient height to prevent major contamination. It must be recognized, however, that pumping from the aquifer at present is very small as compared with that from the main (shallow artesian) aquifer, the largest losses occurring from natural seepage and evaporation. If pumpage were to increase with the advent of many new irrigation, municipal, or industrial wells, the water table would be lowered to a point where salt-water contamination would result and would pose a major threat.
The extent of lowering of the water table during the months December through May is the factor that determines the safe rate of withdrawal from the nonartesian aquifer. During this period the water table reaches its lowest levels during the year because of minimum rainfall, high evapotranspiration, and increased pumping from small irrigation wells; thus the probability of sea-water encroachment is greatest.
Under present conditions at Naples, the decline of the water table during critical times is widespread and gradual. Pumping is scattered throughout the area so that no pronounced centers of withdrawal exist and no large cones of depression are developed. Over-all declines are very slow but progressive. Therefore, if the water table remained long enough below the point of salt water-fresh water balance, the salt-water encroachment would occur slowly but on a broad front. However, there is a considerable lag between the time of lowering the fresh-water head and the resultant movement of salt water. It is
REPORT OF INVESTIGATIONS No. 11 33
probably the over-all, not the short-time, water level that controls the salt water-fresh water 1:40 ratio.
The water level in well 110 was about 3 feet above mean sea level on March 12, 1952, but by May 27, after a period of little rainfall, the water level fell to 1.25 feet above sea level. This water-table elevation is at the point where a further lowering of 0.25 foot would permit salt water to move inland from the fringe areas into the lower part of the aquifer. As encroachment into the nonartesian aquifer occurred, the lower fresh-water aquifer would become exposed to contamination owing to recharge through the confining cover at times when the piezometric surface was below the water table.
The concentration of chloride in areas near the Gulf and Naples Bay is influenced by tides, increasing at high tides and decreasing at low tides, and by storms. When ground-water levels inland are high, only a narrow segment of land adjacent to the Gulf and Bay is affected. As the ground-water level falls, a progressively wider lateral zone is subject to fluctuation in chloride. A high tide of 2.5 feet above mean sea level was recorded on September 2, 1951, and on October 2, during a squall, a high of 3.1 feet above mean sea level occurred. Along vith the flooding of the southern part of Naples, sea water backed up into the Gordon River and raised the water levels in tributaries, causing salty water to flow laterally into the permeable materials.
The water from several wells tapping the nonartesian aquifer was analyzed for chloride content and showed low concentrations denoiing little salt-water movement (see tables 2, 7, and fig. 12). Water samples were collected also from the bottom of the various lakes in the area, and along the Gordon River. The chloride concentration in the lakes ranged from 5 parts per million at the lake south of the golf course to about 1,420 ppm at the lake west of the well field between First and Third Streets. The latter lake drains to the Gulf through a control at First Street and Fifth Avenue North. Prior to the installation of the control the lake may have been subject to some reverse flow from the Gulf during very high tides or during dry times when the water table approached mean sea level. The high chloride content in this lake is probably due to the accumulation of sea water which became land locked prior to the installation of the dam.
34 FLORIDA GEOLOGICAL SURVEY
TABLE 2
Chloride concentration in water samples from selected wells at Naples
Depth of well,
Well In feet, Date Chloride No. below land surface ppm
76 65 Aug. 8, 1951 560 Nov. 2,1951 565 Nov. 26, 1951 610 Jan. 4, 1952 665 Feb. 28, 1952 510 Apr. 14, 1952 705
May 27, 1952 735
99 60 Sept. 26, 1951 253
Jan. 18, 1952 400 Apr. 14, 1952 528 May 27, 1952 500
100 42 Sept. 26, 1951 102 Jan. 18, 1952 96 Apr. 29, 1952 93 May 27, 1952 118
105 83 Sept. 26, 1951 110 Nov. 2, 1951 101 Nov. 26, 1951 103
Jan. 18, 1952 126 Feb. 28, 1952 133 Apr. 14, 1952 130 May 27, 1952 133
119 611 Jan. 15, 1952 14
80 Jan. 16, 1952 17 100 Jan. 16, 1952 181 103 Jan. 17, 1952 210 108 Jan. 17, 1952 452 113 Jan. 17, 1952 550 Feb. 28, 1952 605 Apr. 15, 1952 605 May 27, 1952 615
124 55+ Mar. 11, 1952 105
Apr. 30, 1952 113 June 4, 1952 127 SChloride samples collected at various depths during drilling.
The Gordon River was sampled from the Tamiami Trail bridge crossing to a point about 2 miles upstream. The samples, which were collected during high tide when the chloride concentration is highest, increased southward from 11,500 ppm to 13,400 ppm. The ground-water levels at the time of collection (February 12, 1952) were relatively high for that part of the year so that during normal years the chloride would probably show a still higher concentration. Little encroachment has occurred in areas adjacent to the Gordon River because the river is shallow, and its floor is silted up and
REPORT OF INVESTIGATIONS No. 11 85
clogged with organic matter. Also, the water table in areas adjacent to the river probably has remained sufficiently high to retard encroachment.
CONTAMINATION IN SHALLOW ARTESIAN AQUIFER
The elevation of the piezometric surface in the shallow artesian aquifer, rather than the water table in the nonartesian aquifer, controls the depth at which salt water occurs in the lower fresh-water aquifer. The maximum depth of the municipal wells is 93 feet below mean sea level; therefore, an average fresh-water head of more than 2.25 feet above mean sea level is required to retard the movement of the salt front in the shallow artesian aquifer. As noted during the controlled drilling of test well 119 (table 2), the chloride concentration in the artesian aquifer increased markedly at about 92 feet below mean sea level (100 feet below land surface). At the time of drilling, the nonpumping water level in supply wells at the well field stood at an average elevation of about 2.5 feet above mean sea level. The depth at which high chloride actually occurred and the depth at which high chloride content is predicted from the Ghyben-Herzberg formula apparently check to within a few feet.
The water samples taken in the interval between 100 feet and 113 feet below the land surface in well 119 were collected with a bailer because the rock material was too low in permeability to supply sufficient water to a pump. This indication of low permeability suggests the possibility that the brackish water at that depth might represent Pleistocene sea water trapped in sediments of low permeability.
The lower fresh-water aquifer as penetrated in test well 123 is composed almost entirely of limestones of variable permeability from about 70 feet to 145 feet below mean sea level. The water level in this well at the time of drilling was about 4 feet above mean sea level. Highly mineralized ground water was not" encountered at the bottom of the well. Therefore, it may be assumed that the Ghyben-Herzberg principle applies throughout the Naples area.
The aquifer underlies the entire Naples area and extends westward beneath the Gulf of Mexico, possibly cropping out at an undetermined distance from the shoreline. Salt-water contamination apparently has taken place along the western fringe and in the southern part of the area, and chloride analyses from well 105 (table 2) indicate slight encroachment in the lower part of the aquifer west of the well field. Encroachment in the south and in the vicinity of
36 FLORIDA GEOLOGICAL SURVEY
the Gulf is the result of direct lateral movement of sea water into the aquifer and perhaps some seepage from the contaminated parts of the nonartesian aquifer through the confining bed. The deeper contamination in the aquifer inland probably is due in part to lateral movement and also to upward migration of highly mineralized water which remained trapped in the deep sediments at the time of deposition or has become trapped since.
The salt water interface is a fluctuating front that slowly advances inland, or rises from below the aquifer, when ground-water levels fall owing to pumping or low rainfall; conversely, it slowly moves seaward and is depressed when fresh-water levels rise. Maximuin seasonal encroachment occurs during January through May when the decline in fresh-water levels, due to the lack of recharge by rainfall, is further accelerated by the near-capacity operation of municipal and irrigation wells. If sufficient recharge is not available to balance the quantity withdrawn, a persistent, slow, inland, and upward movement of the salt front occurs.
The hydrograph in figure 6 shows the reason for the salt-water contamination in the south. The average water levels for January and April 1952 were about 1.6 feet above mean sea level and were further lowered during May 1952. If the estimated average water level through April and May was 1.5 feet, then salt water would occur at 60 feet below sea level. The measured depth of well 88 is 73 feet below sea level; thus, the well penetrates a contaminated portion of the aquifer (table 7).
Wells 76, 99, 105, and 119, (table 2) are excellent index wells for observing changes in chloride. The water samples from well 76, near the Gulf, show an over-all increase in chloride content. The progressive increase in chloride as noted in the analyses of samples from well 105 gives evidence of definite movement of brackish water into the lower portion of the aquifer. This well, located midway between the Gulf and the well field, and well 119 at the well field, are good indices to determine the extent of salt-water encroachment in the lower part of the aquifer.
QUALITY OF WATER
Eighteen ground-water samples were collected at Naples for complete or partial chemical analyses. The principal chemical constituents found in these samples are given in table 3. Four of the analyses are of water from the nonartesian aquifer, and the remainder represent water from the shallow artesian aqunifer.
REPORT OF INVESTIGATIONS No. 11 37
Few major variations are noted in the water from the two aquifers except in fringe areas near the salt-water bodies and inland at depths greater than 100 feet below mean sea level where the water becomes relatively highly mineralized. The high mineralization is due primarily to an increase in sodium and calcium chloride and bicarbonate, which is accompanied by an increase in hardness. High mineralization occurs in both aquifers in the southern part of the city. In the fringe areas and in the southern part of Naples the mineralization is probably due to sea water mixing with fresh ground water. However, the high mineral content noted in the sample from the bottom of well 119 at a depth of 113 feet, may represent Pleistocene sea water trapped in relatively impermeable material. This is suggested by the fact that the principal cation in this sample is calcium whereas the principal cation in the water from wells 76, 88, and 99 is sodium. The high calcium content and the increase in total hardness may denote alteration of Pleistocene sea water trapped in relatively impermeable limy sediments. Also, the increase in silica content may signify a difference in the original composition of the Pleistocene sea water, as compared with modern sea water.
Ground-water samples taken from wells more distant from sources of contamination contained less than 250 ppm of dissolved solids. The dissolved-solids content of the nonartesian water is apparently higher than that of the water from the lower fresh-water aquifer.
Water having a hardness of less than 60 ppm is rated as soft; between 60 and 120 ppm, moderately hard; and 120 to 200 parts, hard. Water having a hardness of more than 200 ppm ordinarily requires softening for most uses. Ground water from the well-field area has a hardness of less than 200 ppm, most of which is due to calcium bicarbonate and is removable by means of relatively simple treatment. Hardness tends to increase to the east and south of the well field.
Iron in quantities of more than a few tenths of one ppm is an objectional constituent in water (Collins and Howard, 1928, p. 181). In addition to causing a disagreeable taste, it quickly discolors plumbing fixtures and other objects with which it comes in contact to a reddish-brown color. Many home owners in the Naples area have experienced this discoloration on their property. The content of iron seldom can be predicted. It differs from place to place and may also vary with depth in the same location. Iron in water to be used for public consumption can be removed by aeration and filtration. The results for iron in table 3 represent iron in solution and do not in-
TABLE 3
Analyses of water from selected wells at Naples
(All results are in parts per million except those for color, pH, and specific conductance)
Well 76 Well 88 Well 99 Well 105 Well 111 Well 112
Silica (SiO ) ...................................... 7.2 7.8 8.7 ............ 9.4 12.0
Iron (Fe) 1 .......................................... 2.3 1.9 2 1.9 0.04 0.48
Calcium (Ca) .................................... 117 102 134 92 62 61
Magnesium (Mg) .............................. 27 30 9.1 6 4 3
Sodium (Na) ...................................... 309 273 172 ) 10 7.7
Potassium (K) ................................. 6 6 1.5 68 0.5 0.8
Carbonate (Co03) ......................... 0 0 0 0 0 0
Bicarbonate (HCO3) ....................... 300 250 250 224 206 198
Sulfate (804) ................................... 45 56 24 17 6.5 6
Chloride (Cl) ................................... 558 508 368 142 12 10
Fluoride (F) .................................... 0.1 0 0 ............ 0.4 0.2
Nitrate (NO3) .................................. 1.2 1.1 1.1 0.5 0.5 0.6
Dissolved solids ................................. 1,370 1,230 967 ........... 220 212
Total hardness as CaCO, ................ 402 378 372 254 171 164
Color ................................................... 160 110 110 120 27 26
pH ........ ....................................... 7.5 7.4 7.4 7.5 7.9 7.6
Specific conductance
(micromhos at 25 C.) ................. 2,250 2,040 1,580 821 332 316
Date of collection ............................. Mar. 26, 1953 Mar. 26, 1953 Mar. 26, 1953 Mar. 26, 1953 Aug. 16,1951 Aug. 16, 1951
Depth of sample (feet
below land surface) .................... 65 78 60 83 76 68
Aquifer ............................................... Artesian Artesian Artesian Artesian Artesian Artesian
TABLE 3- continued
Well 116 Well 116 Well 117 Well 117 Well 117 Well 118 F.G.S. W-3046* F.G.S. W-3046 F.G.S. W-3041 F.G.S. W-3041 F.G.S. W-3041 F.G.S. W-3040
Silica (SiO2) ...................................... ............ 17 ............ ............ 11.0 ............
Iron (Fe) .............--- .......................... ............ 0.29 ........................ 0.02 ...........
alc (Ca) .................................... ............ 62 ........................ 59 ............
Magnesium (Mg) ............................. ............ 6.4 ........................ 4.5 ............
Sodium (Na) ..........---.........................) 8.6 8
0 um (K) ............ ...................... j26 0.3 7.2 9.4 0.8 49
Potinaeium ( C ) ------ .............................. 0 0.30 0.8
-------.(O3 ----------------------- 0 0 0 0 0 0
arbonate (HCOs) ......................... 200 218 238 252 197 314
(ate (SO4) .........................--......... 5.5 3.5 4.5 4.5 3.5 4.5
C~oride(C)-------------------------------81 41 16
i de (01) .................................... 28 13 14 11 11 62
de (P ) ...................................... ............ 0.4 ........................ 0.5 ............
ait (NO3) .....................--............... 0.5 0.5 0.3 0.8 0.5 1
Dissolved sois--------------------4
I solved solids ................................ .............. 240 ............ ............ ............ ............
Total hardness as CaCO, ................ 152 181 204 212 166 244
Color ----------.......................................... ............ 22 ............ ............ 22 ............
H -....................................................... 7.5 7.9 7.6 7.8 7.9 7.7
Specific conductance
(micromhos at 25 C.) .................. 379 355 390 401 320 644
-Date of collection .............................. Jan. 3, 1952 Jan. 4,1952 Jan. 5, 1952 Jan. 9, 1952 Jan. 10, 1952 Jan. 11, 1952
Depth of sample (feet
below land surface) ....--................ 30-36 62-70 23 23-40 63-78 40
Aquifer ................................................ Nonartesian Artesian Nonartesian Nonartesian Artesian Nonartesian
1 Rock cuttings are filed in the sample library of the Florida Geological Survey, Tallahassee, Florida, under this number.
Co
TABLE 3 continued
Well 118 Well 118 Well 119 Well 119 Well 119 Well 124 P.G.S. W-3040 F.G.S. W-3040 F.G.S. W-3042 P.G S. W-3042 P.G.S. W-3042
Silica (SiO 2) ..................................... ............ 11.0 ............ 34.0 ............
Iron (Fe) .......................................... ............ 0.10 ............ ............ 0.00 0.15
Calcium (Ca) ................... ............... .... ......... 69 ............ ............ 181 76
Magurnesium (Mg) .............................. ........... 3 ....................... 29 5
Sodium (Na) ......................................17 0.6 4.4 7.6 125 70
Potassium (K) .................................. 0.6 3.4
Carbonate (COs) ............................. 0 0 0 0 0 0
Bicarbonate (HCO) ....................... 262 218 142 200 246 204
Sulfate (804) ................................... 4.5 4.5 1.0 2.5 6.5 4.0 0
Chloride (01) ................................... 25 15 8.5 14 448 135
PFluoride (F) ...................................... ............ 0.1 ........................ 0.1 ...........
Nitrate (NO.) .................................. 0.9 0.5 0.2 0.3 0.5 0.5
Dissolved solids ................................. ............ 241 ....................... 963 ............
Total hardness as CaCO0 ................ 216 184 120 170 570 210
Color ................................. ................... ............ 45 ........................ 29 19
pH ........................................................ 7.7 7.8 8.0 8.2 7.7 7.6
Specific conductance
(micromhos at 25 C.) .................. 456 368 238 339 1,740 747
Date of collection ........................... Jan.11,1952 Jan. 14, 1952 Jan.15, 1952 Jan. 16,1952 Jan. 17,1952 Mar. 26,1953
Depth of sample (feet
below land surface) .................... 46 70 62 80 113 55
Aquifer ............................................... Artesian Artesian Artesian Artesian Artesian Artesian
: Iron in solution at time of analysis.
REPORT OF INVESTIGATIONS No. 11 41
848
01
'4
Ik
S *34
r 43
Got
44
6B5 12
C71*
*I*
o0
"13 AVEOU
t ow:n EXPLANATION
WEE
C*.
CITY SUPPLY AND OTHER WELLS OF LARGE YIELD
WELL EQUIPPED WITH B OAD A -- RECORDING GAGE 714
UPPER NUMBER IS CHLORIDE CONCENTRATION (PPM) LOWER NUMBER IS WELL DEPTH (FEET BELOW LAND SURFACE )
I ~ sou H.SuT
15N SO UT SCALE IN FEET
40 0 400 0 BOG 1,000
FIGURE 12. Naples area showing maximum chloride concentration in water
from wells of various depths, analyzed during course of investigIYaUPiYANnOHE
42 FLORIDA GEOLOGICAL SURVEY
elude iron that may have precipitated after the water was pumped from the well.
The pH indicates the degree of acidity or alkalinity of the water. Figures below 7.0 denote increasing acidity, and above 7.0 indicate increasing alkalinity. The pH of samples at Naples were between 7.5 and 8.2, the greater alkalinities generally occurring in the deeper water.
Chloride analyses were taken of samples from several wells throughout the Naples area. These are listed in tables 2 and 7 and are shown in figure 12, with the depth below land surface from which the samples were collected.
QUANTITATIVE STUDIES
Three separate pumping tests were made on selected wells tapping the shallow artesian aquifer at Naples. From water-level changes reflected in observation wells during the tests, the coefficients of transmissibility and storage were computed. The determinations of the transmissibility and storage coefficients were made by the application of the nonequilibrium method developed by Theis and described by Wenzel (1942, pp. 87-90), and also by the method described by Cooper and Jacob (1946, pp. 526-534).
The coefficient of transmissibility is a determination of the capacity of an aquifer to transmit water. It is expressed as the quantity of water, in gallons per day, that will move through a vertical section of the aquifer one foot wide under a hydraulic gradient of one foot per foot (Theis, 1938, p. 892). The coefficient of storage expresses the capacity of the aquifer to store water, and is the amount of water, in cubic feet, that will be released from a vertical section of the aquifer one foot square when the water level is lowered one foot (Theis, 1938, p. 894).
Computations are based on the following assumptions: (1) the aquifer is without limit in a lateral direction; (2) the aquifer is homogeneous throughout and transmits water with equal ease in all directions; (3) the aquifer is bounded above and below by impervious material; and, (4) no recharge enters the aquifer, and the well pumped for the test constitutes the only discharge from the aquifer. The characteristics of the main aquifer at Naples do not satisfy the requirements of an ideal aquifer. It is heterogeneous throughout, it is capped by slightly permeable marl, it is limited by the proximity of the Gulf, and receives recharge both from the area to the north and from the
REPORT OF INVESTIGATIONS No. 11 43
overlying material. However, the determinations for transmissibility and storage give some valuable indications of the capacities of the aquifer.
The first pumping test was performed on August 24, 1951 at the municipal well field whereby well 58 was pumped for 6Y2 hours at the rate of 62 gallons per minute. The test was of short duration due to limited storage facilities. Water-level measurements were taken at frequent intervals in wells 57 and 59 which are 437 feet and 609 feet, respectively, from the pumping well. Two minutes after pumping started the drawdown in water levels was reflected in well 57, and after nine minutes was noted in well 59. Total drawdowns at the completion of the test were 0.42 foot in well 57 and 0.3 foot in well 59. A recording gauge on well 107, about 2,500 feet south of the pumped well registered a total drawdown of 0.25 foot and the effect of pumpage reached this well after an interval of 20 or 25 minutes. The comparatively rapid response of water levels in observation wells and the magnitude of the computed coefficient of storage indicate the existence of artesian conditions at the well field. Table 4 lists the results of this test and subsequent tests.
On May 6-7, 1952 a pumping test was run on the 6-inch irrigation wells at the J. G. Sample citrus grove. Well 72 was pumped for 11 hours at the rate of 250 gpm, and then shut off to permit recovery of the water level. Frequent water-level measurements were made for both drawdown and recovery in wells 71, 73, 74, and 98 which range from 575 feet to 1,075 feet from the pumped well. The effect of pumping was reflected immediately in well 71. Total drawdowns after 11.hours ranged from 1.88 feet in well 71 to 0.79 foot in well 98. After 12 hours of recovery the water level returned to its pre-pumping elevation.
TABLE 4
Results of pumping tests on wells in the shallow artesian aquifer at Naples
Coefficient of Coefficient
Well transmissibility, of storage, REMARKS No. T, gpd/ft. S
33 92,000 .0014 Entire city field pumping. 107 92,000 .00096 do. 57 83,000 .00038 Well 58 pumping. 59 71,000 .0010 do. 71 100,000 .00015 Well 72 pumping. 71 96,000 .00025 Recovery after pumping well 72.
73 116,000 .00057 do.
74 129,000 .0004 do.
98 91,000 .0011 Well 72 pumping.
44 FLOlIDA GEOLOGICAL SURVEY
Evidence of fluctuations in pumping rates was noted in plotting curves for drawdown and recovery levels in observation wells. Drawdown measurements during the test were effected by uncontrolled variations of pumping in the grove and were influenced by withdrawals at the municipal well field and the golf course. Also affecting the water levels during tests were fluctuations due to tides. Therefore, figures for transmissibility and storage computed from drawdown measurements may not be as accurate as those determined from the recovery test. Conditions during recovery were more constant except that after approximately two hours, the effect of shutting down of the city field was noted. The effect of the shutting down of the city field immediately increases the quantity of water available for recharge with the result of more rapid recovery. Recovery then proceeded as if an imaginary well at the city field were recharging water into the aquifer at the same rate that the well field was pumping previously. By computation the distance from the pumped well at the grove to the image well was 4,240 feet. If it is assumed that the approximate center of pumping at the well field (figs. 10 and 11) is well 33 the scaled distance between the two wells is about 4,000 feet.
Water samples were collected from well 72 throughout the duration of pumping. Analyses of these samples did not indicate any trend toward an increase in the concentration of chloride.
The final quantitative test was made on August 6, 1952, using the city supply wells. The entire well field was operated at full capacity for five hours. The average pumping rate for the duration of the test was 616 gpm from 20 wells. Well 33 was not pumped during the test but was used to observe water-level changes in the northern part of the well field. An automatic gage was installed on well 107 to record water levels in the southern part of the field. The results of this test were undoubtedly the most accurate and are indicative of the conditions throughout the entire well field while in operation, with no outside influences to effect water levels with the possible exception of tidal influence.
The curves in figure 13 are plots of the drawdown in water levels as observed in wells 33 and 107 during this test. From these changes in water levels, computations were made to determine the composite effect that the pumping wells produced on levels in the observation wells after selected time intervals. These values are plotted for both wells in figure 14 as specific drawdown (s/Q) against the logarithmic mean of the distance (r2/t).
REPORT OF INVESTIGATIONS No. 11 45
0.0
0.5
1. O
1.5
c 2.0
WELL 33 WELL /01
25
3.0
50 100 ISO 200 250 300 TIME IN MINUTES AFTER PUMPING STARTED
FIouRF, 13. Drawdown observed in wells 33 and 107 during pumping test on
Naples well field, August T, 1952.
Transmissibility and storage coefficients were then determined by the following formulas (Cooper and Jacob, 1946, p. 528): T- 2,303 Q
4 I As
2.25 T to
r2
where T = transmissibility, s drawdown in feet, Q discharge of well in gpm, S -- storage, r distance in feet from discharge well to observed water levels, and t = time in days. The slopes of the lines showing the composite drawdowns in observation wells after various
46 FLORIDA GEOLOGICAL SURVEY
1-4
z
o
p _. .. ... ... .. ..-... .. .
0)
* t oo
C'd
4
0
0.'
intervals (fig. 14) are parallel or very nearly parallel; thus the computed transmissibility for each is 92,000 gpd per foot. However, the offset.of the lines denotes a value of .00096 for the storage coefficient in well 107 as compared with .0014 in well 33. In comparing these results with those of previous tests, the cofficient of transmissibility
REPOrT OF INVESTIGATION No. 11 47
falls within the same magnitude but the storage coefficient is higher. The average transmissibility for the August 1951 and May 1952 tests was about 98,000 gpd per foot and the average storage coefficient was .0006.
Figure 15 presents a series of curves that represent expected drawdowns at various distances from a pumped well after selected time intervals. The pumpage is arbitrarily placed at 1,000 gpm or less than twice the present rate of pumping in the Naples well field. The curves are plotted from the Theis (1935) formula using a coefficient of transmissibility of 92,000 gpd per foot and a storage coefficient of .001. If it is assumed that a single well is discharging at 1,000 gpm at the location of well 33, the drawdown at a point 2,800 feet west of the well (edge of Gulf) after 24 hours of pumping would be 1.7 feet. This computation for drawdown is the predicted drawdown if the aquifer transmits water with equal facility in all directions with the assumption that no recharge is available to the aquifer.
The following is a list of theoretical predicted drawdowns, as taken from the graph, at various distances from a single well in the main aquifer pumping 1,000 gpm:
DISTANCE IN FEET FROM PUMPED WELL
0 0 0
o0 0 0 o 0 0 0 0 0 0 0 6
4 4
FIGURE 15. Expected drawdowns at various distances from a well pumping at a constant rate of 1,000 gpm after selected time intervals.
I ,0 .
0- <..
T
0 Y. Z /I
,2 ....... ...../00'0
$0I
10 0 ..
Foa.14, Epce rwon tvros itne rmawl upn
48 FLOIDA GEOLOGICAL SURVEY
Distance Drawdown (feet)
(feet) after
1 day 2 days
200 ..................................................................... 8.25 9.03
500 ..................................................................... 5.95 6.75
1,000 ..................................................................... 4.22 5.02
2,000 .................................................................... 2.51 3.32
3,000 .................................................................... 1.55 2.38
5,000 ................................................................... 0.73 1.30
The foregoing computations are based on the supposition that only a single well is pumping at a constant rate. If withdrawals were distributed over 10 wells, each pumping 100 gpm, and spaced 400 feet apart along the center line of the well field, the predicted drawdown after one day at the edge of the Gulf would be 1.56 feet or 0.15 foot less drawdown than if the total withdrawal came from one well.
Under present operating conditions at the well field, 21 wells pump a total of 500 gpm from the shallow artesian aquifer or an average of 24 gpm per well. Being proportional to the rate of output, the predicted drawdown at the Gulf beach after 24 hours is computed at 0.78 foot or slightly less, due to the wider distribution of wells.
In analyzing the accuracy of the chosen coefficients of transmissibility and storage used in figure 15, a predicted drawdown is compared with an actual measured drawdown. On May 26, 1952 the measured drawdown in well 117, 2,000 feet east of the center of the well-field pumpage, was 0.6 foot after 10 hours of operation at 500 gpm. A predicted drawdown of 0.73 foot was computed after 12 hours and less than 0.7 foot after 10 hours. Thus, the actual drawdown and the predicted lowering check to within less than 0.1 foot.
With this relatively accurate comparison between measured and anticipated drawdowns it was assumed that the Theis method of computing pumping test data was sufficient for practical purposes. Some departure in the coefficient of transmissibility would result by using the method described by Jacob (1946 pp. 198-205), in which leakage from the confining bed is taken into account. Owing to the fact that the pumping tests were of short duration the ground-water contribution to the aquifer in the form of vertical leakage is probably relatively small, and thus would produce only a slight deviation from the Theis curve.
As is often the case during dry periods, the irrigation wells at the golf course and the citrus grove pump water at the same time
REPORT OF INVESTIGATIONS No. 11 49
the city well field is operating at peak. This arrangement sets up three distinct centers of pumpage in the area. The point where the three cones of influence intersect (greatest accumulated drawdown) is the theoretical center of pumpage of the three withdrawal areas. Employing figure 15 for varying distances, the point of greatest mutual interference between the three centers is located about 100 feet east of a line connecting wells 33 and 79, midway between the two wells. Assuming that 500 gpm is withdrawn from a single well at each center, the accumulated drawdown at the theoretical point of greatest interference would be 4.16 feet after 12 hours and
5.33 feet after 24 hours.
The maximum amount of water that can be pumped from the Naples area without endangering the quality of the ground water is the safe yield of the aquifer. The nearest source of salt water is the Gulf of Mexico and is considered the boundary of the aquifer. It has been previously determined that a line of 10 wells each pumping 100 gpm at the well field would produce a drawdown of 1.56 feet at the edge of the Gulf after 24 hours. From the short period of water-level data and from figure 9, the nonpumping water level at the well field ranged from 2.0 feet to 2.5 feet above mean sea level at the end of May 1952 after an extended dry period, and sloped off to 1.5 feet near the western edge of the peninsula. Using this range in water levels as a low or a near low of record it is readily seen that after 24 hours of continuous pumping at 1,000 gpm the ground-water level at the western edge of Naples would decline to mean sea level, and after 12 hours at the same rate the water level would fall to 0.8 foot above mean sea level.
The lowering of ground-water levels to mean sea level at the Gulf indicates that the safe yield of the aquifer is being exceeded. This is not meant to imply that as soon as the fresh-water head falls below the critical 2.0 foot level set up by the Ghyben-Herzberg formula, the well field will be immediately contaminated. Actually salt water moves first into the lower part of the aquifer and along the fringes of the peninsula. The movement of ground water is naturally slow, depending upon the gradient, so that contamination would occur gradually but probably with a considerable time lag. If lowering were induced by pumping over a period of days, the encroachment would be accelerated due to the steeper ground-water gradient. However, when pumping stops, rising fresh-water levels force the salt water interface back toward its original position. Thus, the safe yield of the aquifer may be exceeded only for short periods.
50 FLORIDA GEOLOGICAL SURVEY
If exceeded over long periods the aquifer will become permanently contaminated.
GROUND-WATER USE
In the several years prior to 1945 the development of the Naples area remained nearly static. Ground-water withdrawals were small and supplies were relatively undeveloped. A large percentage of water was pumped from privately owned wells. One 6-inch well and two 4-inch wells west of the water plant, ranging in depth from 80 to 84 feet, produced the water supply for the city. The wells eventually yielded brackish water because of close spacing and excessive local lowering of the ground-water levels. The present water-supply system was developed in 1945 when the rapid growth of the city of Naples created a demand for a dependable water supply. The supply was obtained from 10 wells of 3-inch diameter, tapping the shallow artesian aquifer, each equipped with a small centrifugal pump. Pumpage was restricted to not more than 30 gpm from each well. The wells were spaced about 400 feet apart so that the pumping effect was distributed over a relatively large area and drawdowns were slight. With the large increase of population from 1946 to 1951, 12 additional wells were drilled. Eleven of these are 4 inches in diameter and penetrate the shallow artesian aquifer; the last, well 110, is a 6-inch well developed in the nonartesian aquifer. Similarly, the pumping rates of these wells are restricted so that average outputs are usually below 30 gpm per well during peak seasons. The spacing of these wells is also approximately 400 feet. The entire well field is spread over an area of about 65 acres.
Figures of total pumpage from the well field are available since 1946 and are presented in table 4. The peak months of water usage are December through April which coincides with the height of the tourist season. During these months the population at Naples nearly doubles. In addition, this is a period of low rainfall and increasing need for irrigation water.
Irrigational use is one of the largest drains on the ground water supplies. Most private homes in the area irrigate with small-diameter wells that penetrate either the nonartesian or the shallow artesian aquifer. Approximately 100 of these wells are in operation during the period of low rainfall, and even when they are pumped only 3 or 4 hours daily their combined pumpage amounts to a considerable percentage of the total groundwater withdrawal. In the southern part of the city the shallow aquifers produce salty water and the
TABLE 5
Pumpage from Naples well field in millions of gallons per month
Year Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec. o
1946 .............. ...... ...... ...... 4.802 2.40 1.58 1.82 1.82 1.41 2.54 2.41 2.12 0
1947 ............ 3.48 3.78 4.37 3.92 3.05 1.60 1.64 1.94 1.65 1.97 2.59 3.33
1948. ............. 3.42 4.93 6.31 3.86 3.56 3.24 2.15 1.95 2.41 3.44 5.76 5.52 "
1949 ....... 6.83 7.16 7.71 5.54 4.37 2.43 2.39 2.51 2.24 2.76 3.28 5.04
1950 .........7.02 6.86 8.60 7.20 5.503 4.44 3.08 3.48 4.12 3.99 5.15 4.624
1951 ............. 6.505 7.506 9.30 5.71 7.46 6.70 3.87 3.84 3.77 4.20 7.22 9.07
1952 .............. 11.55 9.79 12.327 11.27 9.09 5.68 5.15 8.04 5.18 4.62 8.38 10.04
0
Figures are approximate.
2 Twelve wells in operation. SEstimate. 0 Thirteen wells in operation.
5 Fifteen wells in operation.
* Seventeen wells in operation.
7 Twenty-two wells in operation.
52 FLORIDA GEOLOGICAL SURVEY
municipal supply is used for irrigation as well as household needs. A few residents in this area have reverted to partial irrigation from flowing wells penetrating the principal artesian aquifer. According to some owners this high-chloride water is fairly satisfactory for irrigating some grasses.
The largest withdrawal of water for irrigation is made at the golf course, which is supplied by pumping three 6-inch wells (wells 78, 79, and 80) and one 8-inch well (well 136) that penetrate the shallow artesian aquifer. These wells are piped together into a single system serviced by one pump of 500- to 600-gpm capacity. When irrigation is required, the wells operate 5 to 8 hours per day. To be noted again in figure 7 is the marked effect produced in the northern part of the well field by the heavy pumping in the golf course area.
Considerable quantities of water for irrigation are pumped from five 6-inch wells at the J. G. Sample citrus grove in the eastern part of the city. Each well is capable of yielding 200 to 300 gpm from the shallow artesian aquifer, and during dry seasons some of the wells may pump continuously for 3 or 4 days.
SUMMARY
In the Naples are and most of Collier County the principal artesian aquifer contains salty water. At the town of Everglades near the southern edge of Collier County, however, the principal artesian aquifer yields water containing less than 300 ppm of chloride to some flowing wells. The shallow artesian and nonartesian aquifers yield fresh water to wells at shallow depths throughout most of the county and are used for irrigation, domestic, and public supplies. In the vicinity of Ochopee, 35 miles southeast of Naples, and much of the area south of the Tamiami Trail, the shallow aquifers contain salty or brackish water.
The shallow artesian aquifer at Naples is composed of part of the Tamiami formation, and in northwestern Collier County it includes shell beds in the upper part of the Hawthorn formation. The less permeable marls of the Tamiami formation form a confining layer above the shallow artesian aquifer. At present few data are available for north-central and east-central Collier County concerning the variation in depth, thickness, and capacities of the freshwater aquifers.
REPORT OF INVESTIGATIONS No. 11 53
With the exception of the city of Naples, no area in Collier County shows any indication of overdraft of the ground-water reserves. The original municipal well field at Naples was abandoned after the shallow ground water in the southern part of the city became salty because of heavy pumping and declining ground-water levels. The present well field is similarly subject to contamination, and sampling of ground water reveals that some encroachment of salt water has taken place in the lower part of the shallow artesian aquifer. Pumping tests indicate that, because of the proximity of salt water, the safe yield of the shallow artesian aquifer can be exceeded only for short periods of pumping, and that contamination will occur during dry periods if ground-water levels are not permitted to recover sufficiently each day.
As existing well-field facilities have already reached peak capacity, further development has been proposed for the area to the north, in the direction indicated by the test-drilling program. Of prime importance in the development of additional ground-water supplies is a location where the pumping will have the least effect on the ground-water levels in the present area of withdrawal, and to obtain water from the nonartesian aquifer as well as the shallow artesian aquifer. Results of pumping tests and predictions of drawdowns in wells provide data useful in locating and spacing new wells penetrating the shallow artesian aquifer. These data, however, probably are not indicative of the aquifer as a whole. This fact is borne out by the variation in the results of various pumping tests.
The most favorable sites for additional ground-water supplies are in areas where: (1) the aquifers are thickest; (2) pumping will least affect water levels in the present well field; (3) there is least danger of salt-water contamination (farthest from the source of salt water); and, (4) ground-water levels remain sufficiently high throughout the year to prevent salt-water encroachment. These areas, so far as known at this time, include sites 0.7 mile to a mile north or northeast of the golf course.
Dredging of boat basins in the southern part of the city has caused lowering of the ground-water levels in that area, thus permitting accelerated salt-water encroachment. The digging of drainage canals results in a rapid decline of ground-water levels, which may extend back into the recharge areas. Drainage ditches have caused serious problems of salt-water encroachment in other parts of south Florida, notably in the Miami area.
54 FLORIDA GEOLOGICAL SURVEY
Much valuable information concerning the capacities and the development of the fresh-water aquifers in Collier County can be gained through the continuous gathering of such basic data as waterlevel fluctuations, changes in chloride concentration, and pumpage records. Water-level observations in both equifers made on a continuing basis, and regular chloride analyses of water from key wells taken at the beginning and end of periods of well-field pumping, more frequently during critical months, will permit determining the extent of overdevelopment of the ground-water resources, the quantity of usable ground water available, and the approximate position of the salt-water front.
REPORT OF INVESTIGATIONS No. 11 55
TABLE 6
Water levels, in feet, referred to mean sea level (p denotes pumping level)
Well Date Water Well Date Water No. level No. level
24 11-12-51 0.91p 31 11-12-51 0.78p 11-26-51 0.66p 11-26-51 0.46p
11-27-51 3.41 11-27-51 3.47
3-12-52 3.02 2-11-52 0.16p 5-26-52 -0.87p 2-12-52 3.14 5-27-52 2.11 3-12-52 3.04 5-26-52 -1.18p
25 11-12-51 0.93p 5-27-52 2.14 11-26-51 0.65p
11-27-51 3.37 32 11-12-51 0.55p
2-11-52 0.16p 11-26-51 0.20p
2-12-52 3.10 11-27-51 3.33
3-12-52 3.00 3-12-52 2.89
5-26-52 -1.26p 5-26-52 -1.32p
5-27-52 2.11 5-27-52 2.09
26 11-12-51 0.59p 33 11-12-51 -0.37p 11-26-51 0.30p 11-26-51 -0.58p
11-27-51 3.38 11-27-51 3.64
2-11-52 0.30p 2-11-52 -1.63p
2-12-52 3.08 2-12-52 3.21
3-12-52 2.99 3-12-52 3.18 5-26-52 -2.96p
27 2-11-52 0.50p 5-27-52 2.27
2-12-52 3.13
3-12-52 3.04 56 11-12-51 1.11p 5-26-52 -0.91p 11-26-51 0.89p 5-27-52 2.07 11-27-51 3.72 2-11-52 0.60p
2-12-52 3.22
28 11-12-51 0.78p 3-12-52 3.25
11-26-51 0.50p 5-26-52 -0.80
11-27-51 3.38 5-2-52 .
2-11-52 0.67p 5-27-52 2.33
2-12-52 3.08 57 11-12-51 1.65p 3-12-52 2.99 11-26-51 1.31p
5-26-52 -1.41p 11-27-51 3.72
5-27-52 2.12 2-11-52 1.071p 2-12-52 3.20
29 11-12-51 0.70P 3-12-52 3.24
11-26-51 0.39p 5-26-52 -0.35p 11-27-51 3.41 5-27-52 2.34
2-11-52 0.26p
2-12-52 3.09 58 11-12-51 0.93p 3-12-52 3.02 11-26-51 0.66p 5-26-52 -1.01 11-27-51 3.57
5-27-52 2.13 2-11-52 0.36p 2-12-52 3.14
30 11-12-51 0.97p 3-12-52 3.11
11-26-51 0.69p 5-26-52 -0.96p
11-27-51 3.58 5-27-52 2.23
2-11-52 0.64p
2-12-52 3.21 59 11-12-51 1.88p 3-12-52 3.14 11-26-51 1.69p 5-26-52 -0.77p 11-27-51 3.84
5-27-52 2.21 2-11-52 1.62p
.56 FLOIRIDA GEOLOGICAL SURVEY
TABLE 6- continued
Well Date Water Well Date Water No. level No. level
2-12-52 3.16 108 11-12-51 2.18 3-12-52 3.32 11-26-51 1.90 5-26-52 0.06p 11-27-51 3.655 5-27-52 2.44 2-11-52 1.79 2-12-52 3.28
60 11-12-51 1.55p 3-12-52 3.22
11-26-51 1.63p 5-26-52 -0.57p
11-27-51 3.95 5-27-52 2.17
2-11-52 1.46p
2-12-52 3.12 109 11-12-51 1.77 3-12-52 3.45 11-26-51 1.47 5-26-52 0.01p 11-27-51 3.42
5-27-52 2.55 2-11-52 03.72p 2-12-52 3.15
3-12-52 3.02
61 11-12-51 1.41p 5-26-52 -1.02p
11-26-51 1.64p 5-27-52 2,06
11-27-51 4.04
2-11-52 1.18p 110 11-12-51 3.73
2-12-52 3.02 11-28-51 3.60 3-12-52 3.53 11-27-51 3.61
5-26-52 -0.31p 2-11-52 3.28p 2-12-52 3.53
62 11-12-51 2.08p 3-12-52 2.98
11-26-51 2.05p 5-26-52 0.71p
11-27-51 3.98 5-27-52 1.25
2-11-52 1.51p
2-12-52 3.12 111 11-12-51 1.71
3-12-52 3.47 11-26-51 1.41 5-26-52 1.02 11-27-51 3.56
5-27-52 2.58 2-11-52 1.30 2-12-52 3.21
78 11-12-51 1.58 3-12-52 3.31
5-26-52 --0.17
11-26-51 3.32 5-27-52 2-0.18
11-27-51 4.17 5-27-52 2.18
2-11-52 3.17 112 11-12-51 2.06 2-12-52 2.30 11-26-51 1.78 3-12-52 3.43p 11-27-51 371
5-26-52 1.60 2-11-52 1.OOp 5-27-52 2.74 2-12-52 3.16
3-12-52 3.21
79 11-12-51 -4.81p 5-26-52 0.37p
11-26-51 3.31 5-27-52 2.34
11-27-51 4.15
2-11-52 3.17 116 2-11-52 3.02
2-12-52 -1.07p 2-12-52 2.85 3-12-52 3.59 3-12-52 3.19
5-26-52 1.58 5-26-52 1.78 5-27-52 1.12p 5-27-52 2.38
REPORT OF INVESTIGATIONS No. 11 57
TABLE 6 continued
Wll Date Water Well Date Water No. level No. level
117 2-11-52 1.89 5-26-52 1.22
2-12-52 2.40 5-27-52 1.57
3-12-52 2.21
5-26-52 0.87 119 2-11-52 0.80 5-27-52 1.47 2-12-52 0.90 5-26-52 -.0.31
5-27-52 1.74
118 2-11-52 2.38 2-12-52 2.58 123 5-26-52 2.67 3-12,52 2.30 5-27-52 3.36
TABLE 7
Records of selected wells at Naples
Year Dia- Casing
Well PLa. Sample Owner Driller com- Depth meter depth Chloride Use, REMARKS No. LAbrary No. pleted (ft. I iin. I ft. I ppm. Date
24 City of Naples J. Maharrey 1945 73 3 71 43 8- 7-51 P.S. See table 6 25 do. do. 1945 73 3 71 43 8- 7-51 P.S. do. 26 do. do. 1945 62 3 58 28 8- 7-51 P.S. do. 27 do. do. 1945 75 3 71 28 7-31-46 P.S. do.
41 8- 7-51
28 do. do. 1945 63 3 60 28 7-31-46 PUS. do.
25 8- 7-51
29 do. do. 1945 63 3 60 28 8- 7-51 P.. do. 30 do. do. 1945 63 3 60 17 8- 7-51 P.S. do. 31 do. do. 1945 73 3 71 28 8- 7-51 P.S. do. 32 do. do. 1945 98 3 92 63 12-31-52 P.S. do. 33 do. do. 1945 95 3 93 13 8- 7-51 PS. See tables 4, 6 and figs. 13, 14
38 J. L. Kirk A. Cooper 1951 42 2 40 168 8- 9-51 Irr. 56 City of Naples J. taharrey 1949 74 4 67 16 8- 7-51 P.S. See table 6 57 do. do. 1949 76 4 65 12 8-7-51 P.S. See tables 4 and6 58 do. do. 1950 75 4 69 P.S. do. 59 do. do. 1950 88 4 83 15 8- 7-51 P.S. do. 60 do. do. 1950 92 4 88 13 8- 7-51 P.S. See table 6 61 do. do. 1950 82? 4 78 12 8- 7-51 P.S. do. 62 do. do. 1950 70+- 4 70 12 8- 7-51 P.S. do. 63 J. Prince --.. 1930 27 11/2 .... 19 11-26-51 Dom.
64 Naples J. Maharrey 1950 65-70 3 .... 19 11-26-51 Ind.
Supply Co. 28 1-18-52 65 J. Pulling Jenkins 1939 33 4 26? Irr. 66 do. do. 1939 33 4 26 irr. 67 do. do. 1939 33 2 30 32 8- 8-51 Stock 68 City of Naples J. Mabarrey 1950 90 4 75 11 11-26-51 School 13 5-27-52
69 W. R. Rosier J. Pulling 1951 63 1!2 60 25 8- 8-51 Dom. 70 Trail's End .......... 1951 75 4 70 29 11-26-51 Irr.
Motel
71 J. G. Sample J. Maharrey 1945 60+ 6 .... .... ............ Irr. See table 4
72 do. do. 1945 52+ 6 .... 34 5- 6-52 Irr. do. 73 do. do. 1949 43-+ 6 .. 41 8-23-51 Irr. do.
TABLE 7- continued
Year Dia- Casing
Well Fla. Sample Owner Driller corn- Depth meter depth Chloride Usex REMARKS
- No. Library No. pieted (ft.) (in.) (:t.) ppm. Date
74 do. do. 1949 50+ 6 .... ............ Irr. do.
75 do. do. 1949 62+ 6 .... Irr. 76 Tibbett Estate J. Townshend 1950 65 2 60 .... ............ Irr. See tables 2 and 3
77 Fleischmann do. 1950 55 2 50 364 8- 8-51 Irr. -.
Estate 362 4-29-52 78 Naples Co. J. Maharrey 1930 .... 6 .... 14 8- 8-51 Irr. See table 6
12 3- 6-52
79 do. do. 1930 .... 6 .... 24 3-12-52 II:. do.
80 do. do. 1930 63 6 .... 14 5-27-52 Irr. Composite sample with well 79
81 City Ice Co. 1930 73 3 70 Ind. 82 Neopolitan C. Rivers 1951 63 3 60 18 8- 8-51 Dom., Enterprises Irr. 83 L. A. Oricks do. 1949 52 2 50 19 8- 8-51 Irr.
31 5-27-52
86 R. Lehman .......... 1936 72 2 70 18 8- 9-51 Irr.
87 City Ice Co. --........ ........ 73 3 70 .... ............ Ind.,
Irr.
88 do. .......... 1922 78 4 .... 458 4-15-52 Obs. See fig. 6, table 3
465 5-27-52
97 B. W. Morris C. Rivers 1950 46? 3 .... 58 8-22-51 Irr.
48 5-27-52 2 98 J. G. Sample J. Maharrey 1949 52+ 6 .... 43 8-23-51 Irr. See table 4 99 A. D. Miller A. Cooper 1950 60 2 .... .... I'rr. See tables 2 and 3
100 J. E. Turner J. Townshend 1950 42 2 40 .... Irr. See table 2 .01 C. J. Sumarall .......... 1949 42 11/2 40 15 9-26-51 Irr.
102 R. 0. Clark A. Cooper 1950 42 2 40 14 9-26-51 Irr. 103 H. C. Peterson do. 1950 42 2 40 113 9-26-51 Irr.
80 4-29-52
104 W. T. Truesdale do. 1951 63 2 60 27 9-26-51 Irr.
34 5-27-52
105 do. do. 1951 83 2 78 ........ Irr. See tables 2 and 3
106 W. Storter J. Townshend 1949 45 11 /4 .... 442 9-26-51 Irr. 107 City of Naples J. Maharrey 1951 66 3 60 .... ............ Obs. See figs. 5, 13, 14 and
table 4
TABLE 7- continued
Year Dm- Casing
Well Pla. Sample Owner Driller com- Depth meter depth Chloride Use- REARZS No. Library No. pleted ft. in. ,ft. ppm. Date
108 City of Naples J. Maharrey 1951 71 4 59 16 10-11-51 P.S. See table 6 109 do. do. 1951 .. 4 .. 31 10-12-51 P.S. do.
110 do. do. 1951 40 6 27 15 10-12-51 P.S. do.
16 4-30-52
111 do. do. 1951 77 4 74 .... ............ P.S. See tables 3 and 6
112 do. do. 1951 68 4 66 .... ............ P.S. do.
114 Belding P. Duke 1951 245 4 235 4510 11-13-51 Irr. Water level slightly above land surface
115 City of Naples J. Maharrey 1939 540 5 300 2300 11-13-51 Fire Water level approx. 20 2160 3-24-52 ft. above land surface 116 W-3046 U. S. Geological Miller Bros. 1952 71 2 62 .... ............ Obs. Test well; see log and
Survey tables 3 and 6 117 W-3041 do. do. 1952 78 2 63 .... ............ Obs. do.
118 W-3040 do. do. 1952 70 2 69 .... ............ Obs. do.
119 W-3042 do. do. 1952 113 2 112 .... ............ Obs. Test well; see log and
tables 2, 3, and 6 0
123 W-3045 do. do. 1952 157 2 97 .... ............ Obs. Test well; see log and
table 6
124 A. DiMeola C. Rivers 1949 35+ 11 / 50 .... ............ Dom., See tables 2 and 3
Irr.
125 H. M. McClaskey A. Cooper 1951 40+ 11/2 40 318 4-29-52 Irr.
242 5-27-52
126 H. C. Sherier do. 1951 42 1Y2 40 16 4-29-52 Irr.
17 5-27-52
127 L. P. Grimes do. 1951 46 1 .... 214 4-29-52 Irr.
192 5-27-52
128 R. L. Williams J. Maharrey 1951 60? 2 .... 27 4-29-52 Irr. 129 F. W. Dreher C. Rivers 1951 40+ 1% 40 34 4-29-52 Irr. 130 W-3044 U. S. Geological Miller Bros. 1952 71 6 69 148 6-10-52 Obs. Recording gage Survey
136 Naples Co. J. _Maharrey 1952 90 8 84+ ... ............ Irr.
Z P.S.--Publlc Supply
Irr.-In~gation Do.-Domestic Ind.C-Indstratl
Obs.--Observation
REPORT OF INVESTIGATIONS No, 11 61
WELL LOGS
WELL 116
(P.G.S. Sample Library No. W-3046) Southwest corner of Third Street and South Golf Drive, Naples, Florida Depth, in feet,
Description below land surface
Sand, quartz, fine to medium, white to tan, becoming brown
in lower part ............................. ......... ..................... 0- 20
Sand, quartz, fine to very fine, brown ........................................ 20- 25
Limestone, sandy, fossiliferous, tan to gray; permeable....... 25- 42 Marl, sandy, tan to gray; becomes very shelly in lower part.... 42 52 Lim estone, sandy, gray ................................................................. 52- 55
M arl, sandy, white to gray ........................................................... 55 61
Limestone, sandy, fossiliferous, gray; permeable..................... 61 70
Sand, marly, fine to medium, gray .................................. ........... 70 71
WELL 117
(F.G.S. Sample Library No. W-3041) North side of Fifth Avenue, North, east of Tamiami Trail, just
west of Atlantic Coast Line Railroad, Naples, Florida.
Depth, in feet,
Description below land surface
Sand, quartz, fine to medium, white to tan grading to
brown at base ................................. ............ .............. 0- 15
Sand, quartz, very shelly, white to tan; with few freshwater gastropod shells ........................................................... 15- 19
Limestone, sandy, fossiliferous, very hard, tan; permeable.. 19 34 Limestone, sandy, fossiliferous, tan to gray, softer than
above; permeable ................................................................... ... 34 40
Sand, fine, shelly, gray to greenish ............................................... 40 45
Limestone, sandy, gray, fossiliferous .......................... ............. 45 47
Sand, marly, shelly, gray to greenish ....................................... 47 54
Lim estone, sandy, gray ....................... ................................. 54 57
Marl, sandy, shelly, gray to green ...... .. ............ ............... 57- 64
Limestone, sandy, fossiliferous, gray to tan; permeable .......... 64 78
WELL 118
(F.G.S. Sample Library No. W-3040) Five hundred feet west of Naples water plant, Naples, Florida.
Depth, in feet,
Description below land surface
Sand, quartz, fine to medium, white to gray becoming rustbrown in lower part ............................................................0. 21
Limestone, sandy, shelly, tan ...................................... ...... ..... 21- 22
Sand, fine, marly, very shelly, tan to cream .............................. 22 34
Sand, tan, fine, very shelly....................................................... 34 38
Limestone, sandy, fossiliferous, gray to tan; permeable........ 38 40 Marl, sandy, very shelly, gray to tan .................................... 40- 45
Limestone, sandyi fossiliferous, gray; permeable ............. 45- 47
62 FLORIDA GEOLOGICAL SURVEY
Marl, sandy, very shelly in lower part, gray ............................ 47- 54
Lim estone, sandy, gray .................................................................. 54- 56
M arl, very sandy, gray ................................................................... 56 64
Limestone, sandy, fossiliferous, gray, hard; permeable ........ 64- 70
WELL 119
(F.G.S. Sample Library No. W-3042) Depth, in feet,
Description below land surface
Fifty feet west of well 31, Naples well field, Naples, Florida. Sand, quartz, fine to medium, white to tan, changing to
brown in lower part ............................................................... 20
Marl, sandy, shelly, tan to cream ............................................... 20- 25
Limestone, sandy, shelly, tan to gray ........................................ 25- 27'
Sand, quartz, shelly, fine, tan to gray ......................................... 27 32
Limestone, sandy, fossiliferous, tan to gray ............................... 32 38
Marl, sandy, shelly, gray to green .............................................. 38 56
Limestone, sandy, fossiliferous, gray; permeable .................. 56- 71
Marl, sandy, gray, with thin interbed of soft limestone ........ 71 78 Limestone, sandy, fossiliferous, gray; permeable .................. 78- 83
Marl, very sandy, gray to green, becoming cream to white in
lower part; contains thin interbeds of hard, fossiliferous
lim estone ................................................................................... 83 113
WELL 123
(F.G.S. Sample Library No. W-3045) Seven-tenths mile north of South Golf Drive, and 150 feet west
of Tamiami Trail in city dump area, Naples, Florida.
Depth, in feet,
Description below land surface
Sand, quartz, medium to fine, white to tan, grading to rustbrown in lower 10 feet ........................................................... 26
Lim estone, sandy, shelly, tan .................................................... 26 28
M arl, very sandy, shelly, tan ......................................................... 28- 32
Marl, similar to above, contains fresh-water gastropods ........ 32 34 Sand, quartz, medium, shelly, tan ............................. ................. 34- 36
Limestone, sandy, fossiliferous, tan to gray, very hard;
perm eable ................................................................................... 36 44
Limestone, very sandy, tan, soft, contains few fossils; permeable .............................................................................................. 44 54
Limestone, partially cemented, sandy, shelly, tan to light
green .......................................................................................... 54 60
Marl, very sandy and shelly, gray to green .............................. 60- 63
Limestone, sandy, fossiliferous, gray to green; a sand-filled
cavity at 69 feet; permeable ................................................... 63 71
Marl, sandy, very shelly, gray to green; heaves badly ........... 71- 82
Limestone, sandy, fossiliferous, cream to white; permeable.... 82- 107 Marl, sandy, cream to white; occurs as a cavity filling or
thin bed ....................................................................................... 107 109
Limestone, sandy, slightly fossiliferous, cream to yellowishgreen; with cavity fills or thin interbels of marl or cal-
REPORT OF INVESTIGATIONS No. 11 63
careous sand ............................................................................. 109 138
Marl, sandy, cream; as cavity filling or thin bed ..................... 138- 141
Limestone, partly cemented, sandy, fossiliferous, and cream
m arl, sandy ............................................................................... 141 157
BIBLIOGRAPHY
BROWN, J. S.
1925 A study of coastal ground water with special reference to Connecticut: U. S. Geol. Survey Water-Supply Paper 537, pp. 14-17,
34-37, 49-53.
COLLINS, W. D.
1928 (and HOWARD, C. S.) Chemical character of waters of Florida:
U. S. Geol. Survey Water-Supply Paper 596-G, pp. 181-185. COOKE, C. WYTHE (also see PARKER, G. G.)
1945 Geology of Florida: Florida Geol. Survey Bull. 29, pp. 111-113,
144, 210-212, 238-243.
COOPER, H. H.
1946 (and JACOB, C. E.) A generalized graphical method for evaluating
formation constants and summarizing well-field history: Am.
Geophys. Union Trans., vol. 27, no. IV, pp. 526-534. HoY, N. D.
1952 (and SCHROEDER, M. C.) Geology and ground-water resources of
Lee and Charlotte Counties, Florida: (unpublished manuscript in
preparation).
JACOB, C. E.
1946 Radial flow in a leaky artesian aquifer: Am. Geophys. Union
Trans., vol. 27, no. 2, pp. 198-205. MANSFIELD, W. C.
1939 Notes on the upper Tertiary and Pleistocene mollusks of penin* sular Florida: Florida Geol. Survey Bull. 18, pp. 11-16. MATSON, G. C.
1913 (and SANFORD, SAMUEL) Geology and ground waters of Florida:
U. S. Geol. Survey Water-Supply Paper 319. MEINZER, .O. E.
1923 Outline of ground-water hydrology: U. S. Geol. Survey WaterSupply Paper 494, pp. 17-28, 32-50, 60-63.
1932 The occurrence of ground water in the United States with a discussion of principles: U. S. Geol. Survey Water-Supply Paper
489, pp. 2-8, 28, 52-53.
PARKER, G. G.
1944 (and COOKE, C. WYTHE) Late Cenozoic geology of Southern Florida, with a discussion of the ground water: Florida Geol. Survey
Bull. 27, pp. 56-67, 74-75.
1950 (and STRINGFIELD, V. T.) Effects of earthquakes, trains, tides,
winds, and atmospheric pressure changes on water in the geologic formations in southern Florida: Econ. Geology, vol. 45, no. 5,
pp. 441-460.
64 FLORIDA GEOLOGICAL SURVEY
1951 Geologic and hydrologic factors in the perennial yield of the
Biscayne aquifer: Jour. Amer. Water Works Assn,, vol. 43, no.
10, p. 819.
STRINGFIELD, V. T. (also see PARKER, 0. G.)
1936 Artesian water in the Florida peninsula: U.S. Geol. Survey WaterSupply Paper 773-C, pp. 127-132, 146-148, 166-167, and pl. 12. THIS, C. V.
1935 The relation between the lowering of the piezometric surface and
the rate and duration of discharge of a well using ground-water
storage: Am. Geophys. Union Trans.. pp. 519-524.
1938 The significance and nature of the cone of depression in groundwater bodies: Econ. Geology vol. 33, no. 8, p. 894. VERNON, R. 0.
1951 Geology of Citrus and Levy Counties, Florida: Florida Geol. Survey Bull. 33, pp. 186-187.
WENZEL, L. K.
1942 Methods for determining permeability of water-bearing materials:
U. S. Geol. Survey Water-Supply Paper 887, pp. 87-90.
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STATE OF FLORIDA STATE BOARD OF CONSERVATION Charlie Bevis, Supervisor FLORIDA GEOLOGICAL SURVEY Herman Gunter, Director REPORT OF INVESTIGATIONS No. 11 WATER RESOURCE STUDIES GROUND-WATER RESOURCES OF THE NAPLES AREA, COLLIER COUNTY, FLORIDA By ( Howard Klein Ground Water Branch U.S. GEOLOGICAL SURVEY Prepared By The UNITED STATES GEOLOGICAL SURVEY In cooperation with the FLORIDA GEOLOGICAL SURVEY and the CITY OF NAPLES TALLAHASSEE, FLORIDA 1954
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AGQ. CULTURAL FLORIDA STATE BOARD OF CONSERVATION CHARLEY E. JOHNS Acting Governor R. A. GRAY NATHAN MAYO Secretary of State Commissioner of Agriculture J. EDWIN LARSON THOMAS D. BAILEY Treasurer Superintendent Public Instruction CLARENCE M. GAY RICHARD ERVIN Comptroller Attorney General CHARLIE BEVIS Supervisor of Conservation
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LETTER OF TRANSMITTAL June 15, 1954 Mr. Charlie Bevis, Supervisor Florida State Board of Conservation Tallahassee, Florida Dear Mr. Bevis: Second only to sunshine in value, the State's water resources are an important and necessary item in a progressive economy. The Florida Geological Survey has been collecting water data since its organization in 1907 and joined forces with the U. S. Geological Survey in these studies beginning in 1930. This report on the ground-water resources of the Naples area, Collier County, Florida, prepared by Howard Klein, Geologist of the U. S. Geological Survey, is a portion of the studies undertaken by the two geological surveys. 'It is a pleasure to publish this report as Report of Investigations No. 11, part of a continuing series of Water Resource Studies. Respectfully, Herman Gunter, Director
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Printed by ROSS PRINTING COMPANY, TALLAHASSEK, FLORIDA
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CONTENTS Page Abstract ..................... ............ .......... 1 Introduction ........................... ................. .... .2 Purpose and scope ....... ................................... 2 Acknowledgments ............................. .............. 4 Location and general features of area ........................... 4 Geography and topography ................................. 4 Clim ate .......................... ...................... .... 6 Test-well drilling ......................................... ..... 7 Geologic formations and their water-bearing properties ............ 8 General conditions .............. .................... ., ... 8 Miocene series .......... ....... .......... .. ..... .. 8 Tampa formation ....................................... 8 Hawthorn formation ...................................... 9 Tamiami formation ..................................... 9 Pleistocene and Recent series ................................ 11 Anastasia and Fort Thompson(?) formations ............... 12 Pamlico sand and later deposits .......................... 13 Ground water .............................................. 13 Principles of ground-water occurrence ........................ 13 Hydrologic properties of aquifers .............................. 15 Nonartesian aquifer ....................................... 15 Discharge ........................................... 16 Recharge .............................................. 17 Shallow artesian aquifer ................................. 18 D ischarge ........................ ................... .19 Recharge ......................................... .19 Principal artesian aquifer ................................. 22 Water-level fluctuations ..................................... 26 Salt-water encroachment ........................ .......... 30 Contamination in nonartesian aquifer ............... .31 Contamination in shallow artesian aquifer .................. 35 Quality of water ................. .................. 36 Quantitative studies ..................................... 42 Ground-water use .......................................... 50 Summary ........... .................. ............ 52 W ell logs .......................................... .. ....... .61 Bibliography ................................................ .63
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ILLUSTRATIONS Figure Page 1. Map of Florida showing location of the Naples area in Collier County ...... .............................. 3 2. Naples area showing location of wells and location of geologic sections ......... , ............................. 5 3. North-south geologic section, A-A', through the Naples well field .......... ... ... ............ .etween 10 and 11 4. West-east geologic section, B-B', across Naples area ......... 11 5. Hydrograph of daily high and low water levels in well 107 showing the correlation of ground-water levels with rainfall .................. ...... ...................... 20 6. Hydrograph of daily high and low water levels in well 88 showing the correlation of ground-water levels with rainfall .......... ................................... .21 7. Contour map of water levels in the Naples area, February 12, 1952, showing the effect of concentrated pumping in the golf course ..................................... .23 8. Contour map of water levels in the Naples area, March 12, 1952 .................. ................ ............ .24 9. Contour map of water levels in the Naples area, May 27, 1952 ................... ................ ... ....... .25 10. Contour map showing the effect of well-field pumping on water levels in the Naples area, February 11, 1952 ......... 27 10a. Pumping and nonpumping water-level profiles along North Fifth Avenue across the Naples peninsula, February 11-12, 1952 .......... ... ................... .29 11. Contour map showing the effect of well-field pumping on water levels in the Naples area, May 26, 1952 ............. 31 12. Naples area showing maximum chloride concentration in water from wells of various depths, analyzed during course of investigation ................................. .41 13. Drawdown observed in wells 33 and 107 during pumping test on Naples well field, August 7, 1952 .................. 45 14. Composite drawdown graph for wells 33 and 107 during pumping test on Naples well field, August 7, 1952 .......... 46 15. Expected drawdowns at various distances from a well pumping at a constant rate of 1,000 gpm after selected time intervals ..................... ...... ..... ....... .47 TABLES Table Page 1. Average monthly temperature in degrees F, at Naples, and a comparison of average monthly rainfall, in inches at Naples and Bonita Springs ............................ 7 2. Chloride concentration in water samples from selected w ell at N aples ............................................ 34 3. Analyses of water from selected wells at Naples ............... 38 4. Results of pumping tests on wells in the shallow artesian aquifer at Naples ....... ..... .. ,.. , .. .. ....... .... .43 5. Pumpage from Naples well field in millions of gallons per m onth .... ...................................... ..... 51 6. Water levels, in feet, referred to mean sea level ............... 55 7. Records of selected wells at Naples ........... ......... .. 58 vii
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GROUND.WATER RESOURCES OF THE NAPLES AREA, COLLIER COUNTY, FLORIDA By HowAnR KLEIN ABSTRACT Two shallow aquifers are the sources of fresh-water supplies in the Naples area. The upper aquifer is under nonartesian conditions; it extends from the land surface to a depth of 32 to 55 feet below mean sea level. It is composed of the Pamlico sand and the Anastasia formation of Pleistocene age and a portion of the upper part of the Tamiami formation of late Miocene age. The upper aquifer is tapped by several small, private irrigation wells and also by wells used to supplement the municipal supply. The lower fresh-water aquifer is under artesian pressure and is penetrated about 50 feet below mean sea level in the city well field, where it extends to at least 80 feet below mean sea level. The lower aquifer is much thicker north of the city well field. It lies entirely within the Tamiami formation. It supplies water to most of the city supply wells and to all the large irrigation wells in the vicinity. The movement of water between the aquifers is impeded by 5 to 20 feet of semi-impermeable marl of the Tamiami formation. Differences in the chemical quality of the water from the two aquifers are slight. Samples of the water from the lower aquifer in uncontaminated areas contain less than 250 parts per million (ppm) of dissolved solids and also have a hardness less than 250 ppm. Water from the upper aquifer usually contains slightly more' dissolved solids than does that from the lower aquifer. Periodic chloride analyses showed that some salt-water encroachment has occurred in both aquifers in areas adjacent to the Gulf of Mexico and in the southern part of the city. Pumping tests indicate that the lower fresh-water aquifer has a coefficient of transmissibility of about 92,000 gallons per day per foot and a coefficient of storage of about 0.001. The maximum rate of pumping from the aquifer is governed by the amount that groundwater levels can be lowered before salt water moves into the area of pumping. By applying data computed from pumping tests, it was determined that the aquifer, as now developed by means of the city wells and other wells of substantial yield, will not support
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2 FLORIDA GEOLOGICAL SURVEY heavy withdrawals for a period of more than 1 day during dry periods. It is essential that wells of large yield -which means, essentially, those in the city well field -be shut down daily to allow recovery of water levels, if salt-water encroachment is to be averted. Additional ground-water supplies could be obtained from the thick, permeable parts of both fresh-water aquifers in the area north of the present well field. INTRODUCTION PURPOSE AND SCOPE Because of the rapid growth in both the seasonal and the permanent population of Naples, Collier County, Fla., the residents and city officials were faced with a problem of maintaining an adequate water supply. They recognized the necessity for a ground-water survey on the basis of which steps could be taken to protect the present water supply, and to determine the most feasible means of increasing water supplies to meet expanding demands. The city estimated that its present water-plant facilities should provide for an anticipated population of 12,000 to 15,000, or more than 30 million gallons of water per month. The peak monthly output to date was 12.3 million gallons, in March 1952. In view of the ever-threatening possibility of salt-water encroachment from the Gulf of Mexico into the well field, and the experience of the previous salting of the old municipal well field in the southern part of the city, the Naples City Council requested the United States Geological Survey to investigate the ground-water resources of the area, and to determine the ground-water potential of the aquifers that might be used for the future development of water supplies for municipal and other uses. Field work started in August 1951 and was continued intermittently through August 1952. A partial inventory of the existing wells was made, elevations of measuring points for water-level measurements were determined by spirit level, and a schedule of well-water sampling for chloride analyses was set up. The investigation was under the general supervision of A. N. Sayre, Chief, Ground Water Branch, U. S. Geological Survey, and Herman Gunter, Director, Florida Geological Survey; immediate supervision was given by N. D. Hoy, District Geologist, U. S. Geological Survey, Miami, Fla. The Florida Survey and the Federal Survey
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REPORT OF INVESIGATIONS No. 11 3 have been cooperating in general investigations of the geology and ground water of the State since 1930. Julia Gardner, paleontologist of the U. S. Geological Survey, examined and identified fossil specimens and indicated tentative geologic ages for them. Chemical analyses of water samples were made by the Quality of Water Branch, U. S. Geological Survey. The data of this report will be incorporated in a later report covering the ground-water resources of Collier County (fig. 1). The need for such a report is shown by the increased use of ground water for agricultural and municipal purposes within the county. The principal sources of published information pertinent to western Collier County are in the form of brief references incorporated , r .w f " \ .-/ ' \ " S-1 0E Z -,V -,.i . 0 2 40 60 0 0 MILS o '. .... ...., FIGURE 1. Map of Florida showing location of the Naples area in Collier County. Counity.
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4 FLORIDA GEOLOGICAL SURVEY in Florida Geological Survey Bulletins 18 (Mansfield, 1939), 27 (Parker and Cooke, 1944), and 29 (Cooke, 1945), and in WaterSupply Papers 319 (Matson and Sanford, 1913), 596-G (Collins and Howard, 1928), and 773-C (Stringfield, 1936). In addition, some quality-of-water data have been collected by the U. S. Geological Survey during more recent years. No detailed ground-water studies had been made in Collier County prior to the present investigation. ACKNOWLEDGMENTS The investigation was greatly aided by the coopeiation of residents and business establishments who supplied much valuable data and permitted water sampling of wells. F. M. Lowdermilk, City Manager, W. B. Uihlein, Chairman of the Naples Water Committee, and W. F. Savidge, Water Plant Superintendent, gave valuable assistance during the survey. J. P. Maharrey of Fort Myers and Chisholm Rivers of Naples, well drillers, supplied data on water wells in the area. A. D. Miller and Claude Storter of the Naples Co. granted permission for drilling a test well on company property and permitted frequent water sampling of wells at the Naples Golf Course. J. G. Sample and H. H. McGee permitted the running of a pumping test using the irrigation wells in J. G. Sample's citrus grove. LOCATION AND GENERAL FEATURES OF THE AREA GEOGRAPHY AND TOPOGRAPHY The area covered by this report includes the city of Naples (fig. 1) and adjacent parts of Collier County. The larger part of the city of Naples, (fig. 2) is on a small peninsula which separates Naples Bay and the Gordon River from the Gulf of Mexico. The remainder of the city includes small areas east of the bay and the river. The peninsula is more than 1% miles wide at the northernmost reaches of the Gordon River and tapers southward to a point at Gordon Pass where Naples Bay joins the Gulf of Mexico. The surface elevation on the peninsula ranges from 15 to 25 feet above sea level in the north and north-central portions and slopes off gradually to the south and east and more abruptly at the Gulf beach. The southern extremity of the peninsula and the areas bordering Naples Bay and the Gordon River are relatively flat with an average elevation of about 5 feet. During severe storms and excessively high tides sea water moves into Naples Bay and the Gordon River, flooding areas adjacent to the bay and portions of the southern
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REPORT OF INVESTIGATIONS No. 11 5 / * .82 / *1` // 606 / @ 5/ B S06 7 36 62 \,\ 0 os i J3 8'6 "' I I I \I ® I Ito $90 TRL lo 6 * ' *"*, yo WELL EVPPENO WITH66 * * LOCATON FGOLOG 10 TH CTAVE SCALE IN FET ' 1*114 .-0 -0 I -I -0 UREI. Naples area showig locaton of wells and locationof geologic si THo 63 I03 9 WELL |CITY SUPPLY AND OTHER \ SOU -H WELLS OF UARHE YIELD 1LOCATION OF, GEOLOGIC \ \SECTION 15T AVH E.. OU T H SCALE IN FEET GURE 2. Naples area showing locatiori of ells and location of geologic ::2 ; 'wo nfsections. geologic
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6 FLORIDA GEOLOGICAL SURVEY part of the peninsula. The Gulf side is protected by a beach ridge which extends along the coast. The peninsula is entirely blanketed by a permeable terrace sand, the surface of which has been altered by winds and by washing of heavy rains. The drainage of the area is chiefly underground because rainfall rapidly percolates into the sandy mantle. Places of low elevation are locally covered by a thin layer of sand mixed with muck that is being formed by the decay of vegetation. The area is marked by small natural and artificial lakes or ponds which receive some overland runoff, as do the Gulf of Mexico and Naples Bay, during short periods of heavy rainfall. The land just east of the beach ridge in the northern part of the city is swampy and remains inundated throughout much of the year. The lower part of the peninsula is dissected to some extent by drainage ditches and dredged-out boat basins. They are avenues of possible extended salt-water encroachment. CLIMATE The climate at Naples is subtropical and the humidity is usually high. The average annual temperature as shown by discontinuous records of the U. S. Weather Bureau is 75.80 F., and the warmest weather occurs during July and August. Table .1 shows monthly and yearly averages of temperatures and rainfall at the Naples station and rainfall at the Bonita Springs station, about 15 miles north of Naples. The average annual rainfall at Naples and Bonita Springs, from discontinuous U. S. Weather Bureau records, is 52.19 inches and 54.30 inches, respectively. The heaviest rains occur during the period June-October, inclusive. The greatest yearly rainfall on record at Naples was 71.47 inches in 1947. During June of that year a total of 17.79 inches of rain was recorded. However, the rainfall throughout 1947, even during ordinarily dry months, was unusually high. The year of lowest rainfall on record was 1944 with 30.93 inches. Rainfall in this portion of the Gulf coast is not evenly distributed areally but is localized, as shown by table 1. Although the stations are relatively close, appreciable variations are noted in monthly totals, especially during months of heavy rainfall.
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REPORT OF INVESTIGATIONS No. 11 7 TABLE 1 Average monthly temperature, in degrees F, at Naples, and a comparison of average monthly rainfall, in inches, at Naples and Bonita Springs Month Temperature1 Rainfall2 Naples Naples Bonita Springs Jan ........................................ 67.2 1.15 1.20 Feb ................... ...................... 67.6 0.82 0.83 Mar ........................................ 70.6 1.38 1.21 April ........................................ 75.9 2.57 1.84 M ay ........................................ 77.5 3.41 3.55 June ....................................... 82.0 8.88 8.78 July ......................................... 83.3 7.88 11.04 Aug ......................................... 84.0 7.71 10.00 Sept. ....................................... 82.8 9.67 9.42 Oct ....................................... 77.9 5.56 4.02 Nov ........................................ 72.5 2.10 1.34 Dec ......................................... 68.6 1.06 1.07 Yearly average ..................... 75.8 52.19 54.30 1 Discontinuous record 1942-50, U. S. Weather Bureau. 2 Discontinuous record 1943-50, U. 8. Weather Bureau. TEST-WELL DRILLING Five 2-inch test wells, drilled under contract at Naples early in 1952, furnished information on the general subsurface geology of the area. In addition, they were and will continue to be used to gather data on ground-water-level fluctuation and for determining the extent of salt-water encroachment from Naples Bay and the Gulf of Mexico. Three of the test wells, nos. 116, 117, and 118 (fig. 2), were drilled to depths comparable to those of the city supply wells. Well 116, drilled to 62 feet below mean sea level, is at the southwest corner of South Golf Drive and Third Street, about 1,300 feet inland from .the Gulf of Mexico. Well 117, drilled to 72 feet below mean sea level, is on Fifth Avenue North, east of the Tamiami Trail and approximately 1,500 feet west of the Gordon River. Well 118, just west of the water plant, was drilled to 64 feet below mean sea 'level. With such a distribution of test wells the municipal well field is encircled by observation wells so that, by means of periodic sampling, any extension of present salt-water encroachment may be detected. None of the above tests showed any indication of salt-water encroachment. Wells 119 and 123 were drilled to determine the depth at which salt water occurs. Well 119, in the approximate center of the well field, was drilled to 105 feet below mean sea level, at which depth a pronounced increase in chloride was detected. Well 123, drilled to 145 feet below mean sea level, 0.7 mile north of the Naples Golf
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8 FLORIDA GEOLOGICAL SURVEY Course in an area only slightly effected by pumping, showed no evidence of salt water. These wells similarly will serve as waterlevel and chloride-sampling observation wells. During the course of test drilling, specimens of the penetrated material were collected, usually at 5-foot intervals, and examined. Each time a permeable rock layer was penetrated the well was pumped, and water samples were collected for chemical analyses including chloride. Water samples from materials of low permeability were collected with the bailer and were analyzed for chloride content only. GEOLOGIC FORMATIONS AND THEIR WATER-BEARING PROPERTIES GENERAL CONDITIONS The strata underlying the Naples area to a depth of about 600 feet range in age from Miocene to Recent; however, strata of Pliocene age apparently are missing. Deeper rocks older than Miocene contain water of poor quality and are not discussed in this report. MIOCENE SERIES Formations of Miocene age are the oldest strata penetrated by water wells in the Naples area. The Miocene series in the area includes the Tampa formation, Hawthorn formation, and Tamiami formation of early, middle, and late Miocene age, respectively. TAMPA FORMATION1 The Tampa formation, as defined by Cooke (1945, pp. 111-113), overlies the Suwannee limestone of Oligocene age and is gradational with the overlying Hawthorn formation. sandy limestone and calcareous sandstone are the chief components of the Tampa formation. The sand, predominantly quartz, may occur either disseminated in the matrix of the limestone or in thin beds or pockets. The Tampa formation forms a part of the principal artesian aquifer which underlies much of Florida and southeastern Georgia (Stringfield, 1936, pp. 122-128) and for which Parker (1951, p. 819) proposed the name Floridan aquifer. The Tampa formation is permeable and is one of the major sources of irrigation water in counties bordering the Gulf coast north of Collier County. The top of the Tampa formation occurs between 600 and 640 feet below sea level at Fort Myers and the formation ranges from 80 to 120 feet 1The geologic nomenclature used in this report conforms to the nomenclature of the Florida Geological Survey. It conforms also to that of the U. 8. Geological Survey with the exception that the Tampa formation is used instead of Tampa limestone.
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REPORT OF INVESTIGATIONS No. 11 9 in thickness (Hoy and Schroeder, 1952). It is possible that well 115 (fig. 2), drilled to a depth of 540 feet, penetrates the Tampa formation. The formation yields only salty water in this and adjacent areas. HAWTHORN FORMATION Rocks younger than the Tampa and older than late Miocene in age are referred to the Hawthorn formation by Cooke (1945, p. 144) and Vernon (1951, pp. 186-187). The Hawthorn formation is composed chiefly of gray-green clay, silt, and fine sand and interbedded limestone and shell marl. Permeable limestone and shell beds in the lower part of the formation are regarded as the uppermost part of the principal artesian aquifer (Stringfield, 1936, p. 130), and are the probable sources of the deep, freely flowing artesian wells at Naples. The overlying clay and silt sections, however, are relatively impermeable and separate the water of the principal artesian aquifer from the shallow artesian beds, such as the shallow confined aquifer of the Naples area. At Fort Myers the top of the Hawthorn formation occurs at depths between 40 and 55 feet below the land surface. At Goodland, south of Naples, the top of the Hawthorn formation lies between 150 feet and 270 feet below the land surface. By projection, the clay and silt of the Hawthorn should be encountered at a depth of about 170 feet in the Naples area. The formation is about 400 feet thick in this area. None of the test wells at Naples were deep enough (maximum depth 157 feet) to penetrate material which appeared to be of Hawthorn age. TAMIAMI FORMATION All materials of late Miocene age in southern Florida are assigned to the Tamiami formation by Parker (1951, p. 823); thus the upper part of the Hawthorn formation of Parker and Cooke (1944, pp. 98112), the Tamiami formation, and Mansfield's (1939, p. 8) Buckingham limestone and Tamiami limestone are incorporated as a unit -the Tamiami formation. The macrofossil content of test-well samples has been studied from depths ranging from 20 feet to 70 feet. Julia Gardner states: "No species have been determined from the Tamiami fauna, but the general character of the assemblage is uniform: Pecten, Anomia, Ostrea, and Balanus, all of them fragmented, possibly from the surf on the old Tamiami reef." The samples contained Glycymeris sp. and Turritella sp. of a pattern common to the upper Miocene of Florida. The Tamiami formation is composed primarily of light-tan and
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10 FLORIDA GEOLOGICAL SURVEY gray fossiliferous sandy limestone and interbedded gray-green sandy and shelly marl. Although not precisely located, the top of the formation at Naples generally occurs between 15 feet and 30 feet below mean sea level. The Tamiami formation may be more than 125 feet thick at Naples. The upper part of the Tamiami formation is composed predominantly of beds or lenses of soft, relatively impermeable greenishgray marl and minor beds of gray permeable limestone. The marly sediments generally are poorly sorted and act as a semi-impervious barrier or confining bed which retards the vertical movement of ground water. This relatively impermeable zone ranges in thickness from 5 feet to 20 feet and is apparently thickest in the Naples wellfield area. Data from drillers' logs and from recent test drilling indicate that the first thick permeable limestone that underlies the confining bed is the most persistent fresh-water-bearing rock in the Naples area. This limestone is the main aquifer and is sufficiently thick that a well penetrating it will have at least 5 to 10 feet of open-hole finish. The upper surface of this permeable rock occurs at approximately 50 feet below mean sea level at the municipal well-field area and apparently slopes very gently toward the Gulf. Wells 119 and 123 are of sufficient depth to furnish more complete information concerning the hydrologic properties of deeper parts of the Tamiami formation. The greatest permeability in well 119 was at the intervals between 50 to 61 feet and 70 to 74 feet below mean sea level. Below 74 feet unconsolidated material, which occurs as thin beds of calcareous sand or cavity fillings in the limestone, and dense limestone beds reduce the permeability. If well 119 can be used as an index of the general conditions at the well field, a depth of 80 to 85 feet below mean sea level is the maximum to which supply wells in that vicinity may be drilled. Not only is there a decrease in permeability with greater depth, but there is also an increase in salinity of the ground water. North of the well field, as data from well 123 show, the lower part of the Tamiami formation to a depth of 145 feet below sea level is composed of limestone of varying degrees of cementation. This thick rock zone is a possible source of large quantities of fresh water. The limestone is riddled with solution cavities which are usually filled with loose sand. When penetrated by drilling, the loose material slumps or caves, but can be bailed or pumped clear.
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FLORIDA GEOLOGICAL SURVEY Report of Investigations No. 1 A A' 123 S--------116 119 S118 .I 'SL ___ M_ __ _ MSL o NONARTESIAN AQUIFER S20 '-FRESH WATER SHELLS 30 -,4 S40 gED -6o 50 a .y, , i .5 * 70 SHALLOW ARTESIAN AQUIFER S80 EXPLANATION -90 A 116 / CROSS SECTION A-A' 120 o SHOWING PROJECTION OF \ WELL 116 ONTO NORTHSSOUTH LINE. SEE FIG. 2 119 FOR LOCATIONS. 130 SCALE IN FEET 500 ' 500 1,000 118 1140 A' FIGURE 3. North-south geologic section, A-A, through the Naples well field. V ...» , ...
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REPOHT OF INVESTIGATIONS No, 11 11 Rapid changes in lithology are noted in a horizontal direction as well as vertically. These variations may be either gradational or fairly abrupt. A thickness of limestone or shelly marl at a certain depth in one test well may be no indication that a corresponding bed will be present at a comparable depth in another well. However, the thicker permeable limestone layers are fairly consistent throughout the area and may be tentatively correlated from one well to another (figs. 3 and 4). PLEISTOCENE AND RECENT SERIES Deposits of Pliocene age are not known to occur in the Naples area. In describing the faunal assemblage from a sample taken at B B' 0 116 119 10I MS_ _____________ __ _______ MSL NONARTESIAN AQUIFER FRESH WATER t4J SHELLS A 20 30 t00 0 N F t.A 60 SHALLOW ARTESIAN A AQUIFER k 70 EXPLANATION 80 [ SAND MARL 9 SHELLS, MARINE 90 LIMESTONE SCALE IN FEET o500 0 o00 1,000 100 FIGURE 4. West-east geologic section B-B', across Naples area.
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12 FLORIDA GEOLOGICAL SURVEY 28 feet from test well 119 Julia Gardner states: "None of the species listed would be out of place in either a Pliocene or a Pleistocene fauna. However, the assemblage is unlike any I have seen from the Pliocene. Very few of the dominant species of the Caloosahatchee (Pliocene) are present." The assemblage collected at 28 feet from well 119 includes: Anadara sp.; juvenile. Group of A. transversa (Say) but relatively wider. Carditamera floridana Conrad? juvenile Bellucina aminata Dall Cardium sp. Chione (Chione) cancellata (Linnaeus) Chione (Timoclea) qrus (Holmes) Ervilia? sp. juvenile Corbula (Caryocorbula) brrattiana C. B. Adams Diodora alternata (Say) Turritella tips Young Columbellids? Nassarius vibex (Say) Olivella sp. cf. 0. mutica (Say) Turrids juvenile In the absence of contrary information, the deposits containing the fauna listed are included in the Pleistocene series in this report. Rocks of known Pleistocene age in Naples and vicinity are the Anastasia formation, the Fort Thompson formation or an equivalent, and the Pamlico sand. The Recent series is represented by black mucky sands. ANASTASIA AND FORT THOMPSON (?) FORMATIONS The Anastasia formation represents materials deposited during part of Pleistocene time. In the Naples area it is composed of lightcream to light-gray sandy limestone and gray to tan shelly, sandy marl containing an abundance of Chione cancellata. The limestone of the Anastasia formation thickens eastward where its top occurs at higher elevations than at the center of the Naples area. It seems apparent that the Anastasia formation originally covered the Naples area, but was subjected to beach erosion and was partially removed prior to the deposition of the surface sand. A thin bed of shelly marl overlies the limestone beds of the Anastasia in many places. In places the marl contains small fragile shells of gastropods (snails) of fresh-water origin. It may represent
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REPORT OF INVESTIGATIONS No. 11 13 or be equivalent to part of the Fort Thompson formation, which was deposited during one of the glacial stages of the Pleistocene. The Anastasia formation exhibits a lack of uniformity in deposition similar to that of the Tamiami formation. The only correlatable unit is a hard fossiliferous tan to gray limestone which is the shallowest water-bearing limestone in the Naples area. According to information received from well drillers, this limestone bed of the Anastasia formation is often encountered within 10 feet of the surface in adjacent areas east of the Gordon River and causes very difficult drilling. In test well 117 this stratum occurs 20 feet below the surface and is about 15 feet thick. The same hard limestone was noted in well 123 between 36 and 44 feet below the surface. It is reported that this water-producing rock was penetrated at about 28 feet in well 110, but the precise thickness there is not known. In the western and southern parts of the peninsula the rock is very thin or missing as a result of erosion during pre-Pamlico time. PAMLICO SAND AND LATER DEPOSITS The Naples area is entirely blanketed by the terrace deposits of the Pamlico sand which in places is mixed with Recent black mucky sands. The altitude of the terrace is everywhere less than 25 feet. The Pamlico sand is composed of fine to medium sand, the base of which lies at a depth of 10 to 15 feet below mean sea level. The uppermost material is white or light gray medium-grained quartz .sand which grades downward to highly colored rust-brown finegrained quartz sand. The color is apparently the result of the vertical migration of organic materials in percolating ground water. The components of the Pamlico sand are sufficiently well sorted to permit the ready intake of rainfall and to allow easy downward percolation. The Pamlico sand will supply small quantities of water to shallow sand-point wells. GROUND WATER PRINCIPLES OF GROUND-WATER OCCURRENCE Ground water is stored in .the openings, solution cavities, and pore spaces within the consolidated and unconsolidated materials of the earth's crust. The openings or voids between particles vary in size because of the nonhomogeneous character of the sediments. The frequency and the size of the openings determine the porosity, which is expressed as the ratio of the volume of the interstices to the volume of rock mass (Meinzer, 1923, p. 19). Clay is one of the most porous
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14 FLORIDA GEOLOGICAL SURVEY of all natural earth materials, but is also one of the least permeable. Permeability in water-bearing materials is the property of transmitting water under a gradient. Well sorted, unconsolidated sands or silts, regardless of the size of the components, are highly porous but the permeability varies with the size of the pores. Admixtures of particles of various sizes such as sandy clay, marly sand, or shelly marl may be of low porosity and are of low permeability because the smaller grains occupy the voids between large grains. In consolidated rocks, porosity and permeability may be reduced by the filling of openings with cementing material. Clay, marl, or fine sand, although highly porous, are capable of transmitting only small quantities of ground water. Coarse sand or gravel and cavernous limestone, however, transmit ground water with great facility. The consolidated rock layers underlying Naples are highly permeable because the network of interconnected solution cavities permit the ready movement of water. Any natural geologic formation that transmits water in sufficient quantities to supply a well is called an aquifer. All the water that supplies the wells in the Naples area is derived from local rainfall. Not all of the rainfall, however, percolates through the surface sand to the water table, the remainder being lost by evaporation and transpiration or by overland runoff into the Gordon River, Naples Bay, and the Gulf of Mexico. The water table is the surface below which earth materials are completely saturated. Ground water -that is, water below the water table -moves laterally under gravitational influence from points of recharge to points of artificial discharge such as wells, and to places of natural discharge such as springs, lakes or streams. It is this natural groundwater discharge that largely maintains streamflow and lake levels during dry periods. The water table is an undulating surface conforming in a general way to the topography of the land, being higher under hills than under valleys. It fluctuates seasonally, rising during seasons of heavy rain and falling during periods of low rainfall. It fluctuates also in response to many other forces such as evaporation, transpiration, and pumping from wells. An aquifer that is not overlain by impermeable material contains water under nonartesian or unconfined conditions. The water in a
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REPORT OF INVESTIGATIONS No. 11 15 well penetrating an unconfined aquifer will not rise above the point where the water was encountered in drilling the well. The shallow aquifer at the Naples well field is a nonartesian aquifer because the overlying materials are permeable. The aquifer is tapped by many wells, such as well 110, and the water level in each well is a measure of the altitude of the water table in that immediate area. Where ground water has moved laterally into permeable material that is overlain by a relatively impervious cover, it is said to occur under artesian (confined) conditions. The water level in a well penetrating an artesian aquifer will rise above the top of the aquifer to a point that is the approximate measurement of the pressure head. The pressure head is due to the weight of the water at higher elevations in the aquifer. The water level of an artesian aquifer is known as the piezometric surface, and wherever it is above the land surface, wells tapping the aquifer will flow. The piezometric surface of an artesian aquifer fluctuates in response to the same forces that affect the water table, and also in response to forces like earthquakes, passing trains, and hurricanes and other storms, that generally do not affect the water table directly (Parker and Stringfield, 1950). HYDROLOGIC PROPERTIES OF THE AQUIFERS Ground-water supplies in the Naples area occur in three separate aquifers having different water levels and water quality. These are designated as: (1) nonartesian aquifer containing water under watertable or unconfined conditions; (2) shallow aquifer containing water under artesian conditions; and, (3) principal artesian aquifer (Floridan aquifer) containing saline water under artesian conditions. NONARTESIAN AQUIFER The nonartesian aquifer in the Naples area is usually composed of the Pamlico sand, the Anastasia formation, and that part of the Tamiami formation which overlies the main confining marl. The permeability of the aquifer is highest in the vicinity of wells 110, 116, 117, and 123, as in these areas the section between the surface sand and the confining bed is composed almost entirely of cavernous limestone which remains open after penetration. In these areas limestone of the Anastasia formation is immediately underlain by consolidated parts of the upper part of the Tamiami formation. Regardless of the difference in geologic age of the rocks the entire section is a single, connected, unconfined, hydrologic unit. In other areas such as at wells 118 and 119 and over much of the northern part of the well field the nonartesian aquifer is least productive because
PAGE 24
16 FLO)IDA GEOLOGICAL SUHVEY limestone beds are very thin or missing and the aquifer consists mainly of sand and marl. The base of the nonartesian aquifer is an undulating surface ranging in depth from about 32 feet below mean sea level in the south to 55 feet in the north. The aquifer is the source of water for several small privately owned irrigation wells and for public-supply well 110. Discharge Ground-water losses from the nonartesian aquifer occur naturally by seepage and evapotranspiration, and by pumping from wells. Considerable discharge undoubtedly occurs through submarine seeps where the aquifer crops out beneath the Gulf and Naples Bay. Losses through seepage are greatest during periods of high rainfall when ground-water levels are highest. Another part of the seepage loss occurs where nonartesian water percolates downward through the less permeable confining bed to the lower fresh-water aquifer. Also of major importance is the quantity of water lost through evaporation and transpiration. Ground-water losses due to evaporation and transpiration are greatest when the water table is high and decrease as the water table declines. Losses resulting from these natural processes greatly exceed the quantity of water withdrawn from the aquifer by pumping from wells. When water is pumped from a well penetrating the nonartesian aquifer, the dewatering of the material causes a rapid lowering of the water table in the immediate vicinity of the well, thus establishing a hydraulic gradient toward the well. The water table assumes the form of an inverted cone centered at the discharge point. As pumping continues at a constant rate, the water table at the well declines progressively but at a slowly decreasing rate, until a point of near-equilibrium is reached in the vicinity of the well whereby the rate of discharge is balanced by an equal amount of water being transmitted to the center of withdrawal. At the same time, the cone of depression or cone of influence (Meinzer 1923, p. 61) spreads so that the water table is lowered at greater distances from the well; thus, water from more distant parts of the aquifer is being diverted to the pumped area. As pumping proceeds, the water table continues its slow decline and the cone of depression spreads farther unless recharge is made available to the aquifer. If recharge is sufficient to balance withdrawals, the spreading of the cone progresses no farther, and the water level at the pumped well remains essentially constant. An additional deepening and spreading of the cone would result if the pumping rate
PAGE 25
REPORT OF INVESTIGATIONS No. 11 17 were to increase or if another nearby well in the aquifer started pumping. When pumping from the well ceases, the water level immediately starts to recover, rapidly at first, then at a slowly decreasing rate to a point of essentially the original nonpumping level. The rate at which drawdown and recovery proceed in the vicinity of a well depends in part upon the permeability of the aquifer. Pumping from material of high permeability produces a small drawdown with a wide shallow cone of depression; in material of low permeability a narrow deep cone develops. Because the peninsula is bounded on the west, south, and east by bodies of salt water, these must be considered as the boundaries of the shallow aquifer, for an excessive lowering of the water table in these extreme areas would result in drawing in salt water laterally. To the north, however, the aquifer is of much greater areal extent. Recharge The main recharge to the nonartesian aquifer is that part of the total rainfall that percolates downward to the zone of saturation. A general rise in the water table at Naples occurs when rain falls in the immediate vicinity of the city. Rainfall to the north and east may or may not effect the water table in the city itself. The relatively flat topography and the permeable sandy cover throughout the area permit little surface runoff and the largest drainage is underground. It is possible that during high water stages some water is recharged to the aquifer from the Gordon River. This seepage would occur only for a short interval because as the stream level is lowered the water would drain back into the stream and the normal streamward gradient of the water table would be restored. When the effect of pumping nonartesian wells (lowering of the water table) reaches an area where natural surface-water or groundwater discharge occurs into the Gulf of Mexico, Naples Bay, or Gordon River, some of the water normally lost through this discharge would be diverted toward the pumped area; thus rejected recharge and normally wasted water would be salvaged. The water levels in the shallow lakes at Naples and in the swampy area to the north denote the height of the water table in those areas. If the spreading of the cone of influence were to include any of these lakes, the water level in that lake would lower slowly owing to the fact that its water was being moved toward the pumping area. The diversion of normally rejected water retards the spreading of the cone of depression. During dry periods some recharge occurs through the seepage of
PAGE 26
18 FLORIDA GEOLOGICAAL SURVEY irrigation water to the water table. The amount thus supplied is small because evaporation and transpiration rates increase during dry times. SHALLOW ARTESIAN AQUIFER The top of the shallow artesian aquifer at Naples occurs between 40 and 70 feet below mean sea level. Exclusive of well 110 it is the source of water for all city supply wells and also the source for several privately owned irrigation wells including the large-diameter wells at the golf course (wells 78, 79, 80, 136, fig. 2), and J. G. Sample's citrus grove (wells 71, 72, 73, 74, 98, fig. 2). Well 110 whose bottom is 32 feet below mean sea level, and the lower 12 feet of which is uncased shows no evidence of hydraulic connection between the nonartesian and shallow artesian aquifers; the water level in the well shows no fluctuation when the pumps are being turned on and off in the remainder of the field. From this fact and from test-drilling data it is certain that in the well field the nonartesian and shallow artesian aquifers are separated by a confining bed or beds. Different conditions appear to exist south of the well field and in areas of the eastern part of the peninsula. Test well 118 penetrated a series of beds or lenses of slightly permeable sandy marl and thin layers of permeable limestone beneath the nonartesian aquifer. It is possible that some interconnection exists between the two fresh-water aquifers, so that south of the well field their entire thickness may be a single hydrologic unit. In support of this speculation is the fact that each time a highly permeable zone was encountered during drilling well 118, the water level in the well remained at the level of the water table. This cannot be considered conclusive evidence, however, because the land-surface and water-table elevations are lower in the south and the water-table elevation approaches the elevation of the water surface in the shallow artesian aquifer. East of the well field also, the confining layer becomes thinner and thus may permit increased movement of water between aquifers. In well 117 the water table was 0.5 foot higher than the piezometric surface and in wells 116 and 123 the water table ranged from 2 to 3 feet higher than the piezometric surface of the shallow artesian aquifer. Material overlying an artesian aquifer may either effectively confine or partially confine the water in the aquifer. Effective confinement is produced by impermeable beds, but slightly permeable confining beds retard rather than prevent percolation of water (Meinzer, 1923, p. 40). Probably the confining material in much of the Naples area is of the slightly permeable type and produces artesian groundwater heads.
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REPORT OF 'INVESTIGATIONS No. 11 19 Discharge The effects produced by withdrawing water from an artesian well are similar to those produced in a nonartesian well. However, discharge from an artesian well results in a lowering of the pressure at the well rather than an actual dewatering of the aquifer. Water is released from storage, owing to the compaction or squeezing of sediments when the artesian pressure is lowered, and to slight expansion of the water itself. The basic principle of the cone of influence remains in effect, but the drawdown and spreading of the cone occur at a more rapid rate because the amount of water released from storage per unit area is much smaller than the amount that drains from the pores of the rocks when the water table is lowered. During periods of low rainfall the water table in the southern part of the Naples area declines to elevations below the pressure surface of the shallow artesian aquifer. A pressure differential is then set up whereby water may move from the lower aquifer to the higher aquifer, especially in areas where the confining layer is thinnest or most permeable. The rate at which the movement occurs will depend on the gradient between the aquifers, but in general the seepage will be small. During normal times the water table is above the piezometric surface of the shallow artesian aquifer, and any movement through the confining bed is downward into the artesian aquifer. A part of the ground water lost from the shallow artesian aquifer is also due to natural seepage. The aquifer slopes off to the west and the south, extending for an undetermined distance beneath the Gulf of Mexico. The discharge occurs by upward seepage through the confining bed, or by direct discharge where and if the aquifer crops out on the floor of the Gulf. Recharge The shallow artesian aquifer accepts recharge from rainfall in Naples and vicinity, and as seepage from overlying water-bearing beds that may, in some cases, be at a considerable distance from the city. Figures 5 and 6 are hydrographs of wells 107 and 88, respectively, showing the correlation between water levels and rainfall. Both wells penetrate the shallow artesian aquifer and their water levels respond to rainfall in the area. The water levels in well 107 are effected by well-field pumping so that the plotted points in figure 5 represent daily highs and lows throughout most of 1948 and the first three months of 1949. Appreciable rainfall at Naples is always accompanied by a rise in the water level in shallow artesian wells. Such rises in the water level may be the result of recharge percolating
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20 FLORIDA GEOLOGICAL SURVEY to the aquifer, or may be due to the pressure effects from the weight of water added to the nonartesian aquifer. An attempt was made to correlate the occurrence of rainfall at Bonita Springs, 15 miles 4-4 0 bo OS 4 " ° IL/ N N t 7) .T N 7: 0 N i 0 U) 0 0 A 9IJI 1.3. NI 73337 O34l34 MO-If 13 J H ^3A1 U3VM
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REPORT OF INVESTIGATIONS No. 11 21 north of Naples, with rises in water levels at Naples, but no definite conclusion could be drawn. Slight rises on the hydrograph (as for example on February 9, 1948) might be correlated with rain at Bonita I---------------------I 0 g4 oto ___ ,,, ___ .., ___ L'.. 'SW 0. OJAV...4.M A N/I 77A77 .,JVM H 'NfO/VJ0 d/3&d0 <=2£ : 4 7:= Ulde I d-
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22 FLORIDA GEOLOGICAL SURVEY Springs when no rainfall was recorded at Naples, but these rises may be due instead to a decrease in barometric pressure. Figure 6 is a similar correlation of rainfall with water levels at well 88. The water level in this well is influenced by tides and shows plots of daily highs and lows. Seepage of ground water from the nonartesian aquifer through the confining layer to the shallow artesian aquifer is one of the sources of recharge. Although proceeding at a relatively slow rate, seepage occurs over a wide area and may be substantial. The lowering of pressure which accompanies pumping from the shallow artesian aquifer. increases the gradient between the nonartesian and the shallow artesian aquifers, and more rapid inter-aquifer seepage results. Seepage rates vary from place to place owning to differences in gradient between the two aquifers and in thickness and permeability of the confining layer. A part of the recharge enters the shallow artesian aquifer in an undetermined area north or northeast of Naples where the aquifer is probably overlain by permeable sand. The source of recharge from the north is indicated by the general southward direction of groundwater flow. PRINCIPAL ARTESIAN AQUIFER The upper part of the principal artesian aquifer underlying the Naples area and vicinity is composed of limestone of the Tampa formation and permeable limestones and shell beds in the lower part of the overlying Hawthorn formation (Stringfield, 1936, p. 132). Well 115 drilled to a depth of 540 feet, is the deepest artesian well of record in the Naples area, and may penetrate the Tampa formation. The piezometric surface in this well is about 20 feet above the land surface. Stringfield (1936, p. 166) lists a 400-foot well at the Naples Hotel as penetrating the Hawthorn formation. The piezometric surface in this well measured 18 feet above the land surface in 1934. A higher water-bearing limestone occurs within the Hawthorn formation and yields water to wells ranging in depth from about 200 feet to 250 feet. The piezometric surface in tightly cased wells at these depths is approximately at the land surface. This limestone may be a poorly connected part of the principal artesian aquifer or it might possibly be a separate artesian system. Recharge to the artesian aquifer occurs where it is at or near the surface, as in central Florida, and in areas where sinkholes penetrate the Hawthorn formation, as in Polk County (Stringfield, 1936, pp.
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REPORT OF INVESTIGATIONS No. 11 23 OL URSE lA\99 2.9 \ 3.0 Av \ \ \ \ \ \ \ o \\ 1 ·dl SXPLANATION I 2.5WATER-LEVEL CONTOUR CONIOUR !NTERVAL, 0.1 FOOT II b E " " 5 W T R EV. .Tso, .\..-" I SCALE IN FEET FIGURE 7. Contour map of water levels in the Naples area, February 12, 1952 showing the effect of concentrated pumping in the golf course. IMaRE~ onorma f IV l~l i hn" 17ae Fbuay1, 92
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24 FLORIDA GEOLOGICAL SURVEY i -----* ---_-_ _ ..4j /o / 2.5WATER-LEVEL CONTOUR CONTOUR INTERVAL, 0.1 FOOT .U H / S CA L E IN -F 9 T ,500 00 FIGURE 8. Contour map of water levels in the Naples area, March 12, 1952.
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REPORT OF INVESTIGATIONS No. 11 25 i ' 2 1 4' EXpLANATIONG 21 5' WATCR*LEVEL CONTOUR soU r H e .| ICONTOUR INTERVAL, 0.I rOOT \\ SCL IN EET . SA r .GEN 5R L\ ,, G 9 OAT AVE. SO UT l500u; .ay 152,. FIGURES 9. 001ur IR&D ·Of water levels in t~he Nnanleannrean May 27 11ows
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26 FLORIDA GEOLOGICAL SURVEY 146-148, pl. 12). Water levels in wells 'penetrating the principal artesian aquifer show seasonal fluctuations in and near recharge areas that are due to variations in rainfall. However, rainfall at Naples does not affect the artesian pressure in wells tapping the aquifer. Water from the flowing wells is of little economic importance to the area because it contains about 2,000 ppm of chloride. WATER-LEVEL FLUCTUATIONS Water levels in the shallow artesian wells at Naples respond to recharge by rainfall and discharge by pumping, fluctuate with changes in atmospheric pressure, and are affected by tides in the Gulf of Mexico. On occasions, water levels in these wells are disturbed by distant earthquake shocks. Figures 7, 8, and 9 are contour maps showing water levels in the Naples area on different dates (table 6), when the municipal wells were not pumping. It is apparent from the relatively uniform head that the water is derived from the same aquifer regardless of the divergence in the depth of the wells. The piezometric surface has a slight but regular gradient to the south, indicating recharge from the north and discharge to the south. The contours in general appear to conform to the topography of the area, which is more typical of nonartesian than of artesian conditions. However, it is understandable because, as mentioned, seepage occurs through the confining bed and the heads of both shallow aquifers tend to become equalized. Water-level measurements for the contour maps were made after recovery from pumping was essentially complete. A cone of influence has formed north of the well field (fig. 7) as a result of pumping irrigation wells 79 and 80 at the total rate of 500 gallons per minute. This withdrawal concentrated within a small area is reflected by the lowering of water levels in the northernmost city supply wells. Figures 10 and 11 are water-level contours in the Naples area after several hours of pumping in the city well field, and represent water levels at periods of peak withdrawals during the winter season and after a long period of drought in the spring. Figure 10a, in addition, shows pumping and nonpumping water-level profiles across the peninsula on February 11-12, 1952, and demarks the position of the Gulf tide at the time of the measurements. Measuring water levels in pumped wells is generally not accepted procedure because, owing to loss of head (well loss) as water enters and moves up a well, the water level at the well does not reflect the true water level in the vicinity. However, if the head losses in all wells are assumed to be
PAGE 35
REPORT OF INVESTIGATIONS No. 11 27 .J I-L U // \ O/FI0 /'' %'60 CENTA Lr S WAT. _E C-L COO L II SCALE IN FEET QO r4 FIGUR. 10. Contour m4p showing the effect of well-field pumping on water levels in the Naples are, February 11 1952. 151q. SCALE IN FEET r levels'In the Naples area, I1-Feb ua I I I952.
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28 FLORIDA GEOLOGICAL SURVEY the same, a map based on pumping water levels indicates the general attitude of the piezometric surface and the adjustments in the direction of ground-water flow. The adjustments are noted at the north end of the well field, where the higher contour lines bend southward, suggesting that recharge enters from the north. Long-range water-level records are not available for the Naples area; therefore no yearly comparisons can be made. The only useful data are presented in the hydrographs in figures 5 and 6 and the measurements in table 6 from which the contour maps were prepared. These data show the seasonal rise and decline of water levels, and in addition they show in a general way the difference in water levels in shallow artesian wells and wells penetrating the nonartesian aquifer such as well 110. Throughout part of the year the water table in the southern part of the well field is higher than the shallow artesian head, at times being half a foot to a foot higher. During the period December through May the water table declines more rapidly than the artesian level, so that after the long period of low rainfall and high evapotranspiration the nonartesian aquifer in the southern part of the well field is drained to a point where the water-table elevation falls below the artesian head. At the end of May 1952 the water table ranged between 0.75 and 1.0 foot lower than the artesian water level in the Naples well field. However, in areas of higher ground elevation the water table remains higher than the artesian head throughout the year. During May 1952 the water table in the northern part of the well field ranged from 1 foot to 1.5 feet higher than the artesian level. Tidal fluctuations in the Gulf of Mexico are reflected in the water levels in nonartesian wells near the shoreline and in shallow artesian wells at greater distance from the shore. Ground-water fluctuations due to tides are caused in three ways (Brown, 1925, p. 50): (1) by transmission of pressure through the pore spaces and cavities which connect the well to the Gulf; (2) by changes in the rate of normal ground-water flow from the aquifer to the Gulf; and, (3) by deformation of the material resulting from alternate loading and unloading on the earth's crust. The principle is the same in the first two, the main difference being the rate at which the ground-water level fluctuations occur. The effect of the deformation of sediments may or may not contribute to ground-water fluctuations; the amount of effect produced depends upon the competence of the limestone. From the short period of tidal data available at Naples, a maximum
PAGE 37
REPORT OF INVESTIGATIONS No. 11 29 range of about 4 feet between high and low tides has been recorded in the Gulf. The water level in well 88 fluctuates with tides and lags approximately 12 hours. The daily fluctuation ranges from 0.2 to C) I LII 7-3M --_bD 0 a 11VU1 IWVIWVl -0 LI1 1313 00IX3tl .i 7 I H 2C 1T13M --------.;^ o t4 " . 3NII 3UOH8 73WS' 01 I3UY3J3Y 133d NI '73A37 Vh1VM
PAGE 38
30 FLORIDA GEOLOGICAL SURVEY 0.7 foot, but some of the effect is due to nearby pumping. The maximum range in daily fluctuation recorded at well 130 was 0.9 foot. The water level in this well also is influenced to some extent by well-field pumping. Although not definitely established, it is probable that the effect of tides reaches the municipal supply wells. SALT-WATER ENCROACHMENT Salt-water encroachment into the fresh-water aquifers may occur from two sources: (1) direct movement inland from the Gulf of Mexico and from Naples Bay; and, (2) upward .contamination from salt water which occurs at greater depth. The salt water at depth exists either trapped in the sediments at the time of deposition, or as water that entered the sediments at times when the sea covered the Naples area during Pleistocene time. The quantity of water that can be drawn from the fresh-water aquifers in the Naples area is governed by the amount that groundwater levels can be lowered without producing accelerated vertical movement of high-chloride water from underlying sources or lateral movement from the Gulf or Naples Bay. Because of a lower specific gravity, the fresh-water body floats on top of the salt water, and the depth to the salt water is related to the height of the fresh water above mean sea level. This relationship, which is simply that of a U-tube whose 2 limbs contain liquids of different density, is referred to as the Ghyben-Herzberg principle (Brown, 1925, pp. 16-17) and is expressed as: t h . g-1 where h is the depth of fresh water below mean sea level, t is the fresh-water level in feet above mean sea level and g is the specific gravity of the salt water. If it is assumed that the specific gravity of the sea water is 1.025, a common value, then for each foot of fresh water which occurs above sea level, 40 feet of fresh water extends below mean sea level. The relationship applies strictly only to static conditions, and is modified under dynamic conditions. However, the departure is not large enough to invalidate the principle for practical use. CONTAMINATION IN NONARTESIAN AQUIFER The formula is directly applicable to the nonartesian aquifer which is relatively permeable throughout and extends outward beneath the Gulf of Mexico and Naples Bay. An average fresh-water head of 1.5 feet above mean sea level is sufficient to prevent salt-water en-
PAGE 39
REPORT OF INVESTIGATIONS No. 11 31 I 75 S-1.50 00020.75 .00 0. \l \. .\1\\e _ I_\ \ f1.\ 00 / / X A 60.1 25WATER-LEVEL CONTOUR \ \0.00 C IT.V 0 2 OT SOUT E XPLANATION 2 5--ý WATER-LEVEL CONTOUR CONTOUR INTERVAL. 0 25 FOOT S TH V O--_SCALE IN FEET 5 6-:o--5 .. --o -f0ooo FIGUPE 11. Contour map showing the effect of well-field pumping on water levels in the Naples area, May 26. 1952.
PAGE 40
32 FLORIDA GEOLOGICAL SURVEY croachment to a depth of 60 feet below mean sea level. Therefore, this aquifer with a maximum depth of 55 feet below sea level is protected in areas where the water-table elevation is 1.5 feet or more above mean sea level. In fringe areas adjacent to the Gulf and Naples Bay the water table slopes off to near-sea-level elevations, permitting salt water to enter the aquifer for short distances inland. This movement has not been excessive. In the southern part of the city, where land elevations average about 5 feet, the water table lies at low elevations. The various boat basins dug in this area have lowered the water table still farther so that salt water has contaminated the area south of Broad Avenue South. Fresh ground water is available in this part of Naples only in very shallow wells during periods of heavy rainfall, at which time fresh water exists as a thin lens floating on the salt water. Wells in these fringe areas cannot be pumped heavily or continuously because salt water would be drawn in after a short time. Elsewhere in the city the water table has remained at sufficient height to prevent major contamination. It must be recognized, however, that pumping from the aquifer at present is very small as compared with that from the main (shallow artesian) aquifer, the largest losses occurring from natural seepage and evaporation. If pumpage were to increase with the advent of many new irrigation, municipal, or industrial wells, the water table would be lowered to a point where salt-water contamination would result and would pose a major threat. The extent of lowering of the water table during the months December through May is the factor that determines the safe rate of withdrawal from the nonartesian aquifer. During this period the water table reaches its lowest levels during the year because of minimum rainfall, high evapotranspiration, and increased pumping from small irrigation wells; thus the probability of sea-water encroachment is greatest. Under present conditions at Naples, the decline of the water table during critical times is widespread and gradual. Pumping is scattered throughout the area so that no pronounced centers of withdrawal exist and no large cones of depression are developed. Over-all declines are very slow but progressive. Therefore, if the water table remained long enough below the point of salt water-fresh water balance, the salt-water encroachment would occur slowly but on a broad front. However, there is a considerable lag between the time of lowering the fresh-water head and the resultant movement of salt water. It is
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REPORT OF INVESTIGATIONS No. 11 33 probably the over-all, not the short-time, water level that controls the salt water-fresh water 1:40 ratio. The water level in well 110 was about 3 feet above mean sea level on March 12, 1952, but by May 27, after a period of little rainfall, the water level fell to 1.25 feet above sea level. This water-table elevation is at the point where a further lowering of 0.25 foot would permit salt water to move inland from the fringe areas into the lower part of the aquifer. As encroachment into the nonartesian aquifer occurred, the lower fresh-water aquifer would become exposed to contamination owing to recharge through the confining cover at times when the piezometric surface was below the water table. The concentration of chloride in areas near the Gulf and Naples Bay is influenced by tides, increasing at high tides and decreasing at low tides, and by storms. When ground-water levels inland are high, only a narrow segment of land adjacent to the Gulf and Bay is affected. As the ground-water level falls, a progressively wider lateral zone is subject to fluctuation in chloride. A high tide of 2.5 feet above mean sea level was recorded on September 2, 1951, and on October 2, during a squall, a high of 3.1 feet above mean sea level occurred. Along vith the flooding of the southern part of Naples, sea water backed up into the Gordon River and raised the water levels in tributaries, causing salty water to flow laterally into the permeable materials. The water from several wells tapping the nonartesian aquifer was analyzed for chloride content and showed low concentrations denoting little salt-water movement (see tables 2, 7, and fig. 12). Water samples were collected also from the bottom of the various lakes in the area, and along the Gordon River. The chloride concentration in the lakes ranged from 5 parts per million at the lake south of the golf course to about 1,420 ppm at the lake west of the well field between First and Third Streets. The latter lake drains to the Gulf through a control at First Street and Fifth Avenue North. Prior to the installation of the control the lake may have been subject to some reverse flow from the Gulf during very high tides or during dry times when the water table approached mean sea level. The high chloride content in this lake is probably due to the accumulation of sea water which became land locked prior to the installation of the dam.
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34 FLORIDA GEOLOGICAL SURVEY TABLE 2 Chloride concentration in water samples from selected wells at Naples Depth of well, Well In feet, Date Chloride No. below land surface ppm 76 65 Aug. 8, 1951 560 Nov. 2, 1951 565 Nov. 26, 1951 610 Jan. 4, 1952 665 Feb. 28, 1952 510 Apr. 14, 1952 705 May 27, 1952 735 99 60 Sept. 26, 1951 253 Jan. 18, 1952 400 Apr. 14, 1952 528 May 27, 1952 500 100 42 Sept. 26, 1951 102 Jan. 18, 1952 96 Apr. 29, 1952 93 May 2', 1952 118 105 83 Sept. 26, 1951 110 Nov. 2, 1951 101 Nov. 26, 1951 103 Jan. 18, 1952 126 Feb. 28, 1952 133 Apr. 14, 1952 130 May 27, 1952 133 119 611 Jan. 15, 1952 14 80 Jan. 16, 1952 17 100 Jan. 16, 1952 181 103 Jan. 17, 1952 210 108 Jan. 17, 1952 452 113 Jan. 17, 1952 550 Feb. 28, 1952 605 Apr. 15, 1952 605 May 27, 1952 615 124 55+ Mar. 11, 1952 105 Apr. 30, 1952 113 June 4, 1952 127 ' Chloride samples collected at various depths during drilling. The Gordon River was sampled from the Tamiami Trail bridge crossing to a point about 2 miles upstream. The samples, which were collected during high tide when the chloride concentration is highest, increased southward from 11,500 ppm to 13,400 ppm. The ground-water levels at the time of collection (February 12, 1952) were relatively high for that part of the year so that during normal years the chloride would probably show a still higher concentration. Little encroachment has occurred in areas adjacent to the Gordon River because the river is shallow, and its floor is silted up and
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REPORT OF INVESTIGATIONS No. 11 85 clogged with organic matter. Also, the water table in areas adjacent to the river probably has remained sufficiently high to retard encroachment. CONTAMINATION IN SHALLOW ARTESIAN AQUIFER The elevation of the piezometric surface in the shallow artesian aquifer, rather than the water table in the nonartesian aquifer, controls the depth at which salt water occurs in the lower fresh-water aquifer. The maximum depth of the municipal wells is 93 feet below mean sea level; therefore, an average fresh-water head of more than 2.25 feet above mean sea level is required to retard the movement of the salt front in the shallow artesian aquifer. As noted during the controlled drilling of test well 119 (table 2), the chloride concentration in the artesian aquifer increased markedly at about 92 feet below mean sea level (100 feet below land surface). At the time of drilling, the nonpumping water level in supply wells at the well field stood at an average elevation of about 2.5 feet above mean sea level. The depth at which high chloride actually occurred and the depth at which high chloride content is predicted from the Ghyben-Herzberg formula apparently check to within a few feet. The water samples taken in the interval between 100 feet and 113 feet below the land surface in well 119 were collected with a bailer because the rock material was too low in permeability to supply sufficient water to a pump. This indication of low permeability suggests the possibility that the brackish water at that depth might represent Pleistocene sea water trapped in sediments of low permeability. The lower fresh-water aquifer as penetrated in test well 123 is composed almost entirely of limestones of variable permeability from about 70 feet to 145 feet below mean sea level. The water level in this well at the time of drilling was about 4 feet above mean sea level. Highly mineralized ground water was not' encountered at the bottom of the well. Therefore, it may be assumed that the Ghyben-Herzberg principle applies throughout the Naples area. The aquifer underlies the entire Naples area and extends westward beneath the Gulf of Mexico, possibly cropping out at an undetermined distance from the shoreline. Salt-water contamination apparently has taken place along the western fringe and in the southern part of the area, and chloride analyses from well 105 (table 2) indicate slight encroachment in the lower part of the aquifer west of the well field. Encroachment in the south and in the vicinity of
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36 FLORIDA GEOLOGICAL SURVEY the Gulf is the result of direct lateral movement of sea water into the aquifer and perhaps some seepage from the contaminated parts of the nonartesian aquifer through the confining bed. The deeper contamination in the aquifer inland probably is due in part to lateral movement and also to upward migration of highly mineralized water which remained trapped in the deep sediments at the time of deposition or has become trapped since. The salt water interface is a fluctuating front that slowly advances inland, or rises from below the aquifer, when ground-water levels fall owing to pumping or low rainfall; conversely, it slowly moves seaward and is depressed when fresh-water levels rise. Maximuin seasonal encroachment occurs during January through May when the decline in fresh-water levels, due to the lack of recharge by rainfall, is further accelerated by the near-capacity operation of municipal and irrigation wells. If sufficient recharge is not available to balance the quantity withdrawn, a persistent, slow, inland, and upward movement of the salt front occurs. The hydrograph in figure 6 shows the reason for the salt-water contamination in the south. The average water levels for January and April 1952 were about 1.6 feet above mean sea level and were further lowered during May 1952. If the estimated average water level through April and May was 1.5 feet, then salt water would occur at 60 feet below sea level. The measured depth of well 88 is 73 feet below sea level; thus, the well penetrates a contaminated portion of the aquifer (table 7). Wells 76, 99, 105, and 119, (table 2) are excellent index wells for observing changes in chloride. The water samples from well 76, near the Gulf, show an over-all increase in chloride content. The progressive increase in chloride as noted in the analyses of samples from well 105 gives evidence of definite movement of brackish water into the lower portion of the aquifer. This well, located midway between the Gulf and the well field, and well 119 at the well field, are good indices to determine the extent of salt-water encroachment in the lower part of the aquifer. QUALITY OF WATER Eighteen ground-water samples were collected at Naples for complete or partial chemical analyses. The principal chemical constituents found in these samples are given in table 3. Four of the analyses are of water from the nonartesian aquifer, and the remainder represent water from the shallow artesian aquifer.
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REPORT OF INVESTIGATIONS No. 11 37 Few major variations are noted in the water from the two aquifers except in fringe areas near the salt-water bodies and inland at depths greater than 100 feet below mean sea level where the water becomes relatively highly mineralized. The high mineralization is due primarily to an increase in sodium and calcium chloride and bicarbonate, which is accompanied by an increase in hardness. High mineralization occurs in both aquifers in the southern part of the city. In the fringe areas and in the southern part of Naples the mineralization is probably due to sea water mixing with fresh ground water. However, the high mineral content noted in the sample from the bottom of well 119 at a depth of ,113 feet, may represent Pleistocene sea water trapped in relatively impermeable material. This is suggested by the fact that the principal cation in this sample is calcium whereas the principal cation in the water from wells 76, 88, and 99 is sodium. The high calcium content and the increase in total hardness may denote alteration of Pleistocene sea water trapped in relatively impermeable limy sediments. Also, the increase in silica content may signify a difference in the original composition of the Pleistocene sea water, as compared with modern sea water. Ground-water samples taken from wells more distant from sources of contamination contained less than 250 ppm of dissolved solids. The dissolved-solids content of the nonartesian water is apparently higher than that of the water from the lower fresh-water aquifer. Water having a hardness of less than 60 ppm is rated as soft; between 60 and 120 ppm, moderately hard; and 120 to 200 parts, hard. Water having a hardness of more than 200 ppm ordinarily requires softening for most uses. Ground water from the well-field area has a hardness of less than 200 ppm, most of which is due to calcium bicarbonate and is removable by means of relatively simple treatment. Hardness tends to increase to the east and south of the well field. Iron in quantities of more than a few tenths of one ppm is an objectional constituent in water (Collins and Howard, 1928, p. 181). In addition to causing a disagreeable taste, it quickly discolors plumbing fixtures and other objects with which it comes in contact to a reddish-brown color. Many home owners in the Naples area have experienced this discoloration on their property. The content of iron seldom can be predicted. It differs from place to place and may also vary with depth in the same location. Iron in water to be used for public consumption can be removed by aeration and filtration. The results for iron in table 3 represent iron in solution and do not in-
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TABLE 3 Analyses of water from selected wells at Naples (All results are in parts per million except those for color, pH, and specific conductance) Well 76 Well 88 Well 99 Well 105 Well 111 Well 112 Silica (SiOg) ..................................... 7.2 7.8 8.7 ............ 9.4 12.0 Iron (Pe) 1 ......................................... 2.3 1.9 2 1.9 0.04 0.48 Calcium (Ca) .................................... 117 102 134 92 62 61 Magnesium (Mg) ............................ 27 30 9.1 6 4 3 Sodium (Na) .................................... 309 273 172 ) 10 7.7 Potassium (K) .............................. 6 6 1.5 68 0.5 0.8 Carbonate (CO0) .............................. 0 0 0 0 0 0 Bicarbonate (HCO) ...................... 300 250 250 224 206 198 Sulfate (SO4) .................................. 45 56 24 17 6.5 6 Chloride (C1) ................................... 558 508 368 142 12 10 Fluoride (F) ................................ 0.1 0 0 ............ 0.4 0.2 Nitrate (NO3) .................................. 1.2 1.1 1.1 0.5 0.5 0.6 Dissolved solids ................................ 1,370 1,230 967 ........... 220 212 Total hardness as CaCO, ................ 402 378 372 254 171 164 Color .............................................. 160 110 110 120 27 26 pH ......... ..................................... ..7.5 7.4 7.4 7.5 7.9 7.6 Specific conductance (micromhos at 25 C.) ................ 2,250 2,040 1,580 821 332 316 Date of collection ............................ Mar. 26, 1953 Mar. 26, 1953 Mar. 26, 1953 Mar. 26, 1953 Aug. 16,1951 Aug. 16, 1951 Depth of sample (feet below land surface) .................... 65 78 60 83 76 68 Aquifer .................................. Artesian Artesian Artesian Artesian Artesian Artesian
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TABLE 3 continued Well 116 Well 116 Well 117 Well 117 Well 117 Well 118 F.G.S. W-3046* F.G.S. W-3046 F.G.S. W-3041 F.G.S. W-3041 F.G.S. W-3041 F.G.S. W-3040 Silica (SiO ) .................................... ............ 17 ........... ........... 11. ............ Iron (Fe) ............. ......................... ........... 0.29 ............ ............ 0.02 ........... Calci m (Ca) ................................... ............ 62 ............ ......... 59 ............ Magnesium (Mg) .................................... 6.4 ........................ 4.5 ............ Sodium (Na) .........---......................... 8.6 8 Potassium (K) ................................. 0.3 7.2 94 0.8 itaronae (C ,) --.............................. 0 0 0 0 0 crbonate (HCOs) ..-.---............... 200 218 238 252 197 314 uate (84) ................................ 5.5 3.5 4.5 4.5 3.5 4.5 C~oride(C)--------------------------------81 41 16 de () ....................................28 13 14 11 11 62 orii de (P) -'........................ 0.4 ............ ............ 0.5 ............ irat (NO) .................................. 0.5 0.5 0.3 0.8 0.5 1 D issolved solids ....--.................... ................... 240 ................................... ............ Total hardness as CaCO3 ................ 152 181 204 212 166 244 Color ---...................................................... 22 ............ ............ 22 ............ pH -...--.............................................. 7.5 7.9 7.6 7.8 7.9 7.7 Specific conductance (niicromhos at 25 C.) .................. 379 355 390 401 320 644 -Date of collection .............................. Jan. 3, 1952 Jan. 4, 1952 Jan. 5, 1952 Jan. 9, 1952 Jan. 10, 1952 Jan. 11, 1952 Depth of sample (feet below land surface) .................... 30-36 62-70 23 23-40 63-78 40 Aquifer ................................................ Nonartesian Artesian Nonartesian Nonartesian Artesian Nonartesian 1 Rock cuttings are filed in the sample library of the Florida Geological S urvey, Tallahassee, Florida, under this number. CO
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TABLE 3continued Well 118 Well 118 Well 119 Well 119 Well 119 Well 124 F.G.S. W-3040 F.G.S. W-3040 F.O.S. W-3042 P.G S. W-3042 P.G.S. W-3042 Silica (S O ) ..................................... ............ 11.0 ........... .34.0 ............ Iron (Fe) ... ........... .... .............................. 0.10 ............ ............ 0.00 0.15 Calcium (Ca) ........................................... 6.............. ............ 181 76 M agnesium (M g) .............................. ............ 3 ......................... 29 5 Sodium (Na) .................... ......17 0.6 4. 7.6 15 70 Potassium (K) .................................. 0.6 3.4 Carbonate (CO) ............................ 0 0 0 0 0 0 Bicarbonate (HCO,) -........................ 262 218 142 200 246 204 Sulfate (SO ) .......................... .. 4.5 4.5 1.0 2.5 6.5 4.0 Chloride (C1) ................................. .. 25 15 8.5 14 448 135 Fluoride ( ) ...................................... ............ 0.1 ........................ 0.1 ........... Nitrate (NO.) .................................. 0.9 0.5 0.2 0.3 0.5 0.5 Dissolved solids .... .......................................... 241 ..................... .963 ............ Total hardness as CaCOs ................ 216 184 120 170 570 210 Color ................................................. ............ 45 ........... ........... 29 19 pH ........................................................ 7.7 7.8 8.0 8.2 7.7 7.6 Specific conductance (micromhos at 25 C.) ................... 456 -368 238 339 1,740 747 Date of collection .......................... Jan. 11,1952 Jan. 14,1952 Jan. 15, 1952 Jan. 16,1952 Jan. 17,1952 Mar. 26,1953 Depth of sample (feet below land surface) .................... 46 70 62 80 113 55 Aquifer .............................................. Artesian Artesian Artesian Artesian Artesian Artesian 1Iron in solution at time of analysis.
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REPORT OF INVESTIGATIONS No. 11 41 ' 34 Sr 43 q/ .I Q _4 \\1 \ V 40 L 74 137 CITY SUPPLY AND OTHER \UPPER NUMBER IS CHLORIDE CONCENTRATION (PPM) LOWER NUMBER IS WELL _. DEPTH (FEET OFELOW LAND SURFACE ) 15 I SUT SCALE IN FEET 14 000 0 BG 1,000I FIGURE 12. Naples area showing maximum chloride concentration in water from wells of various depths, analyzed during course of investi04510 $00 0 500 1,000 FIGUE 1. Nalesareashoing~~x ium hlorde oncetraion l2-45e
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42 FLORIDA GEOLOGICAL SURVEY elude iron that may have precipitated after the water was pumped from the well. The pH indicates the degree of acidity or alkalinity of the water. Figures below 7.0 denote increasing acidity, and above 7.0 indicate increasing alkalinity. The pH of samples at Naples were between 7.5 and 8.2, the greater alkalinities generally occurring in the deeper water. Chloride analyses were taken of samples from several wells throughout the Naples area. These are listed in tables 2 and 7 and are shown in figure 12, with the depth below land surface from which the samples were collected. QUANTITATIVE STUDIES Three separate pumping tests were made on selected wells tapping the shallow artesian aquifer at Naples. From water-level changes reflected in observation wells during the tests, the coefficients of transmissibility and storage were computed. The determinations of the transmissibility and storage coefficients were made by the application of the nonequilibrium method developed by Theis and described by Wenzel (1942, pp. 87-90), and also by the method described by Cooper and Jacob (1946, pp. 526-534). The coefficient of transmissibility is a determination of the capacity of an aquifer to transmit water. It is expressed as the quantity of water, in gallons per day, that will move through a vertical section of the aquifer one foot wide under a hydraulic gradient of one foot per foot (Theis, 1938, p. 892). The coefficient of storage expresses the capacity of the aquifer to store water, and is the amount of water, in cubic feet, that will be released from a vertical section of the aquifer one foot square when the water level is lowered one foot (Theis, 1938, p. 894). Computations are based on the following assumptions: (1) the aquifer is without limit in a lateral direction; (2) the aquifer is homogeneous throughout and transmits water with equal ease in all directions; (3) the aquifer is bounded above and below by impervious material; and, (4) no recharge enters the aquifer, and the well pumped for the test constitutes the only discharge from the aquifer. The characteristics of the main aquifer at Naples do not satisfy the requirements of an ideal aquifer. It is heterogeneous throughout, it is capped by slightly permeable marl, it is limited by the proximity of the Gulf, and receives recharge both from the area to the north and from the
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REPORT OF INVESTIGATIONS No. 11 43 overlying material. However, the determinations for transmissibility and storage give some valuable indications of the capacities of the aquifer. The first pumping test was performed on August 24, 1951 at the municipal well field whereby well 58 was pumped for 6Y2 hours at the rate of 62 gallons per minute. The test was of short duration due to limited storage facilities. Water-level measurements were taken at frequent intervals in wells 57 and 59 which are 437 feet and 609 feet, respectively, from the pumping well. Two minutes after pumping started the drawdown in water levels was reflected in well 57, and after nine minutes was noted in well 59. Total drawdowns at the completion of the test were 0.42 foot in well 57 and 0.3 foot in well 59. A recording gauge on well 107, about 2,500 feet south of the pumped well registered a total drawdown of 0.25 foot and the effect of pumpage reached this well after an interval of 20 or 25 minutes. The comparatively rapid response of water levels in observation wells and the magnitude of the computed coefficient of storage indicate the existence of artesian conditions at the well field. Table 4 lists the results of this test and subsequent tests. On May 6-7, 1952 a pumping test was run on the 6-inch irrigation wells at the J. G. Sample citrus grove. Well 72 was pumped for 11 hours at the rate of 250 gpm, and then shut off to permit recovery of the water level. Frequent water-level measurements were made for both drawdown and recovery in wells 71, 73, 74, and 98 which range from 575 feet to 1,075 feet from the pumped well. The effect of pumping was reflected immediately in well 71. Total drawdowns after 11.hours ranged from 1.88 feet in well 71 to 0.79 foot in well 98. After 12 hours of recovery the water level returned to its pre-pumping elevation. TABLE 4 Results of pumping tests on wells in the shallow artesian aquifer at Naples Coefficient of Coefficient Well transmissibility, of storage, REMARKS No. T, gpd/ft. S 33 92,000 .0014 Entire city field pumping. 107 92,000 .00096 do. 57 83,000 .00038 Well 58 pumping. 59 71,000 .0010 do: 71 100,000 .00015 Well 72 pumping. 71 96,000 .00025 Recovery after pumping well 72. 73 116,000 .00057 do. 74 129,000 .0004 do. 98 91,000 .0011 Well 72 pumping.
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44 FLOlIDA GEOLOGICAL SURVEY Evidence of fluctuations in pumping rates was noted in plotting curves for drawdown and recovery levels in observation wells. Drawdown measurements during the test were effected by uncontrolled variations of pumping in the grove and were influenced by withdrawals at the municipal well field and the golf course. Also affecting the water levels during tests were fluctuations due to tides. Therefore, figures for transmissibility and storage computed from drawdown measurements may not be as accurate as those determined from the recovery test. Conditions during recovery were more constant except that after approximately two hours, the effect of shutting down of the city field was noted. The effect of the shutting down of the city field immediately increases the quantity of water available for recharge with the result of more rapid recovery. Recovery then proceeded as if an imaginary well at the city field were recharging water into the aquifer at the same rate that the well field was pumping previously. By computation the distance from the pumped well at the grove to the image well was 4,240 feet. If it is assumed that the approximate center of pumping at the well field (figs. 10 and 11) is well 33 the scaled distance between the two wells is about 4,000 feet. Water samples were collected from well 72 throughout the duration of pumping. Analyses of these samples did not indicate any trend toward an increase in the concentration of chloride. The final quantitative test was made on August 6, 1952, using the city supply wells. The entire well field was operated at full capacity for five hours. The average pumping rate for the duration of the test was 616 gpm from 20 wells. Well 33 was not pumped during the test but was used to observe water-level changes in the northern part of the well field. An automatic gage was installed on well 107 to record water levels in the southern part of the field. The results of this test were undoubtedly the most accurate and are indicative of the conditions throughout the entire well field while in operation, with no outside influences to effect water levels with the possible exception of tidal influence. The curves in figure 13 are plots of the drawdown in water levels as observed in wells 33 and 107 during this test. From these changes in water levels, computations were made to determine the composite effect that the pumping wells produced on levels in the observation wells after selected time intervals. These values are plotted for both wells in figure 14 as specific drawdown (s/Q) against the logarithmic mean of the distance (r2/t).
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REPORT OF INVESTIGATIONS No. 11 45 0,0 0.5 1. O 1.5 c 2.0 -WELL 33 WELL /017-. 25 3.0 50 100 150 200 250 300 TIME IN MINUTES AFTER PUMPING STARTED FIGURa, 13. Drawdown observed in wells 33 and 107 during pumping test on Naples well field, August ', 1952. Transmissibility and storage coefficients were then determined by the following formulas (Cooper and Jacob, 1946, p. 528): T= 2303 Q 4l As S2.25 T to r2 where T = transmissibility, s -drawdown in feet, Q -discharge of well in gpm, S -storage, r t distance in feet from discharge well to observed water levels, and t = time in days. The slopes of the lines showing the composite drawdowns in observation wells after various
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46 FLORIDA GEOLOGICAL SURVEY -4 *C o 40 intervals (fig. 14) are parallel or very nearly parallel; thus the computed transmissibility for each is 92,000 gpd per foot. However, the offset.of the lines denotes a value of .00096 for the storage coefficient o -___. .-._ ..-----_ -_._. _ __ __ ----3 "'-0 ---------__ _o 0 2 0 0 0 0 in well 107 as compared with .0014 in well 33. In comparing these results with those of previous tests, the cofficient of transmissibility
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REPORT OF INVESTIGATIONS No. 11 47 falls within the same magnitude but the storage coefficient is higher. The average transmissibility for the August 1951 and May 1952 tests was about 98,000 gpd per foot and the average storage coefficient was .0006. Figure 15 presents a series of curves that represent expected drawdowns at various distances from a pumped well after selected time intervals. The pumpage is arbitrarily placed at 1,000 gpm or less than twice the present rate of pumping in the Naples well field. The curves are plotted from the Theis (1935) formula using a coefficient of transmissibility of 92,000 gpd per foot and a storage coefficient of .001. If it is assumed that a single well is discharging at 1,000 gpm at the location of well 33, the drawdown at a point 2,800 feet west of the well (edge of Gulf) after 24 hours of pumping would be 1.7 feet. This computation for drawdown is the predicted drawdown if the aquifer transmits water with equal facility in all directions with the assumption that no recharge is available to the aquifer. The following is a list of theoretical predicted drawdowns, as taken from the graph, at various distances from a single well in the main aquifer pumping 1,000 gpm: DISTANCE IN FEET FROM PUMPED WELL 0 0 0 S0 0 0 0 0 0 0 0 8 0 08 6 § 0S 14 FIGURE 15. Expected drawdowns at various distances from a well pumping at a constant rate of 1,000 gpm after selected time intervals.
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48 FLORIDA GEOLOGICAL SURVEY Distance Drawdown (feet) (feet) after 1 day 2 days 200 .......... ........................................................... 8.25 9.03 500 .............................................. ....................... 5.95 6.75 1,000 ..................................................................... 4.22 5.02 2,000 ..................................................................... 2.51 3.32 3,000 ......................................... ............................ 1.55 2.38 5,000 ................................................................ 0.73 1.30 The foregoing computations are based on the supposition that only a single well is pumping at a constant rate. If withdrawals were distributed over 10 wells, each pumping 100 gpm, and spaced 400 feet apart along the center line of the well field, the predicted drawdown after one day at the edge of the Gulf would be 1.56 feet or 0.15 foot less drawdown than if the total withdrawal came from one well. Under present operating conditions at the well field, 21 wells pump a total of 500 gpm from the shallow artesian aquifer or an average of 24 gpm per well. Being proportional to the rate of output, the predicted drawdown at the Gulf beach after 24 hours is computed at 0.78 foot or slightly less, due to the wider distribution of wells. In analyzing the accuracy of the chosen coefficients of transmissibility and storage used in figure 15, a predicted drawdown is compared with an actual measured drawdown. On May 26, 1952 the measured drawdown in well 117, 2,000 feet east of the center of the well-field pumpage, was 0.6 foot after 10 hours of operation at 500 gpm. A predicted drawdown of 0.73 foot was computed after 12 hours and less than 0.7 foot after 10 hours. Thus, the actual drawdown and the predicted lowering check to within less than 0.1 foot. With this relatively accurate comparison between measured and anticipated drawdowns it was assumed that the Theis method of computing pumping test data was sufficient for practical purposes. Some departure in the coefficient of transmissibility would result by using the method described by Jacob (1946 pp. 198-205), in which leakage from the confining bed is taken into account. Owing to the fact that the pumping tests were of short duration the ground-water contribution to the aquifer in the form of vertical leakage is probably relatively small, and thus would produce only a slight deviation from the Theis curve. As is often the case during dry periods, the irrigation wells at the golf course and the citrus grove pump water at the same time
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REPORT OF INVESTIGATIONS No. 11 49 the city well field is operating at peak. This arrangement sets up three distinct centers of pumpage in the area. The point where the three cones of influence intersect (greatest accumulated drawdown) is the theoretical center of pumpage of the three withdrawal areas. Employing figure 15 for varying distances, the point of greatest mutual interference between the three centers is located about 100 feet east of a line connecting wells 33 and 79, midway between the two wells. Assuming that 500 gpm is withdrawn from a single well at each center, the accumulated drawdown at the theoretical point of greatest interference would be 4.16 feet after 12 hours and 5.33 feet after 24 hours. The maximum amount of water that can be pumped from the Naples area without endangering the quality of the ground water is the safe yield of the aquifer. The nearest source of salt water is the Gulf of Mexico and is considered the boundary of the aquifer. It has been previously determined that a line of 10 wells each pump:ing 100 gpm at the well field would produce a drawdown of 1.56 feet at the edge of the Gulf after 24 hours. From the short period of water-level data and from figure 9, the nonpumping water level at the well field ranged from 2.0 feet to 2.5 feet above mean sea level at the end of May 1952 after an extended dry period, and sloped off to 1.5 feet near the western edge of the peninsula. Using this range in water levels as a low or a near low of record it is readily seen that after 24 hours of continuous pumping at 1,000 gpm the ground-water level at the western edge of Naples would decline to mean sea level, and after 12 hours at the same rate the water level would fall to 0.8 foot above mean sea level. The lowering of ground-water levels to mean sea level at the Gulf indicates that the safe yield of the aquifer is being exceeded. This is not meant to imply that as soon as the fresh-water head falls below the critical 2.0 foot level set up by the Ghyben-Herzberg formula, the well field will be immediately contaminated. Actually salt water moves first into the lower part of the aquifer and along the fringes of the peninsula. The movement of ground water is naturally slow, depending upon the gradient, so that contamination would occur gradually but probably with a consideralle time lag. If lowering were induced by pumping over a period of days, the encroachment would be accelerated due to the steeper ground-water gradient. However, when pumping stops, rising fresh-water levels force the salt water interface back toward its original position. Thus, the safe yield of the aquifer may be exceeded only for short periods.
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50 FLORIDA GEOLOGICAL SURVEY If exceeded over long periods the aquifer will become permanently contaminated. GROUND-WATER USE In the several years prior to 1945 the development of the Naples area remained nearly static. Ground-water withdrawals were small and supplies were relatively undeveloped. A large percentage of water was pumped from privately owned wells. One 6-inch well and two 4-inch wells west of the water plant, ranging in depth from 80 to 84 feet, produced the water supply for the city. The wells eventually yielded brackish water because of close spacing and excessive local lowering of the ground-water levels. The present water-supply system was developed in 1945 when the rapid growth of the city of Naples created a demand for a dependable water supply. The supply was obtained from 10 wells of 3-inch diameter, tapping the shallow artesian aquifer, each equipped with a small centrifugal pump. Pumpage was restricted to not more than 30 gpm from each well. The wells were spaced about 400 feet apart so that the pumping effect was distributed over a relatively large area and drawdowns were slight. With the large increase of population from 1946 to 1951, 12 additional wells were drilled. Eleven of these are 4 inches in diameter and penetrate the shallow artesian aquifer; the last, well 110, is a 6-inch well developed in the nonartesian aquifer. Similarly, the pumping rates of these wells are restricted so that average outputs are usually below 30 gpm per well during peak seasons. The spacing of these wells is also approximately 400 feet. The entire well field is spread over an area of about 65 acres. Figures of total pumpage from the well field are available since 1946 and are presented in table 4. The peak months of water usage are December through April which coincides with the height of the tourist season. During these months the population at Naples nearly doubles. In addition, this is a period of low rainfall and increasing need for irrigation water. Irrigational use is one of the largest drains on the ground water supplies. Most private homes in the area irrigate with small-diameter wells that penetrate either the nonartesian or the shallow artesian aquifer. Approximately 100 of these wells are in operation during the period of low rainfall, and even when they are pumped only 3 or 4 hours daily their combined pumpage amounts to a considerable percentage of the total groundwater withdrawal. In the southern part of the city the shallow aquifers produce salty water and the
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TABLE 5 Pumpage from Naples well field in millions of gallons per month1 Year Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec. o 1946 .............. ...... ...... ...... 4.802 2.40 1.58 1.82 1.82 1.41 2.54 2.41 2.12 0 1947 .............. 3.48 3.78 4.37 3.92 3.05 1.60 1.64 1.94 1.65 1.97 2.59 3.33 1948 ---............. 3.42 4.93 6.31 3.86 3.56 3.24 2.15 1.95 2.41 3.44 5.76 5.52 1949 ........... 6.83 7.16 7.71 5.54 4.37 2.43 2.39 2.51 2.24 2.76 3.28 5.04 1950 ........ 7.02 6.86 8.60 7.20 5.503 4.44 3.08 3.48 4.12 3.99 5.15 4.624 1951 .............. 6.505 7.506 9.30 5.71 7.46 6.70 3.87 3.84 3.77 4.20 7.22 9.07 S 1952 ..............11.55 9.79 12.327 11.27 9.09 5.68 5.15 8.04 5.18 4.62 8.38 10.04 SFigures are approximate. STwelve wells in operation. SEstimate. 0 SThirteen wells in operation. 5 Fifteen wells in operation. e Seventeen wells in operation. 7 Twenty-two wells in operation. CA
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52 FLORIDA GEOLOGICAL SURVEY municipal supply is used for irrigation as well as household needs. A few residents in this area have reverted to partial irrigation from flowing wells penetrating the principal artesian aquifer. According to some owners this high-chloride water is fairly satisfactory for irrigating some grasses. The largest withdrawal of water for irrigation is made at the golf course, which is supplied by pumping three 6-inch wells (wells 78, 79, and 80) and one 8-inch well (well 136) that penetrate the shallow artesian aquifer. These wells are piped together into a single system serviced by one pump of 500to 600-gpm capacity. When irrigation is required, the wells operate 5 to 8 hours per day. To be noted again in figure 7 is the marked effect produced in the northern part of the well field by the heavy pumping in the golf course area. Considerable quantities of water for irrigation are pumped from five 6-inch wells at the J. G. Sample citrus grove in the eastern part of the city. Each well is capable of yielding 200 to 300 gpm from the shallow artesian aquifer, and during dry seasons some of the wells may pump continuously for 3 or 4 days. SUMMARY In the Naples are and most of Collier County the principal artesian aquifer contains salty water. At the town of Everglades near the southern edge of Collier County, however, the principal artesian aquifer yields water containing less than 300 ppm of chloride to some flowing wells. The shallow artesian and nonartesian aquifers yield fresh water to wells at shallow depths throughout most of the county and are used for irrigation, domestic, and public supplies. In the vicinity of Ochopee, 35 miles southeast of Naples, and much of the area south of the Tamiami Trail, the shallow aquifers contain salty or brackish water. The shallow artesian aquifer at Naples is composed of part of the Tamiami formation, and in northwestern Collier County it includes shell beds in the upper part of the Hawthorn formation. The less permeable marls of the Tamiami formation form a confining layer above the shallow artesian aquifer. At present few data are available for north-central and east-central Collier County concerning the variation in depth, thickness, and capacities of the freshwater aquifers.
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REPORT OF INVESTIGATIONS No. 11 53 With the exception of the city of Naples, no area in Collier County shows any indication of overdraft of the ground-water reserves. The original municipal well field at Naples was abandoned after the shallow ground water in the southern part of the city became salty because of heavy pumping and declining ground-water levels. The present well field is similarly subject to contamination, and sampling of ground water reveals that some encroachment of salt water has taken place in the lower part of the shallow artesian aquifer. Pumping tests indicate that, because of the proximity of salt water, the safe yield of the shallow artesian aquifer can be exceeded only for short periods of pumping, and that contamination will occur during dry periods if ground-water levels are not permitted to recover sufficiently each day. As existing well-field facilities have already reached peak capacity, further development has been proposed for the area to the north, in the direction indicated by the test-drilling program. Of prime importance in the development of additional ground-water supplies is a location where the pumping will have the least effect on the ground-water levels in the present area of withdrawal, and to obtain water from the nonartesian aquifer as well as the shallow artesian aquifer. Results of pumping tests and predictions of drawdowns in wells provide data useful in locating and spacing new wells penetrating the shallow artesian aquifer. These data, however, probably are not indicative of the aquifer as a whole. This fact is borne out by the variation in the results of various pumping tests. The most favorable sites for additional ground-water supplies are in areas where: (1) the aquifers are thickest; (2) pumping will least affect water levels in the present well field; (3) there is least danger of salt-water contamination (farthest from the source of salt water); and, (4) ground-water levels remain sufficiently high throughout the year to prevent salt-water encroachment. These areas, so far as known at this time, include sites 0.7 mile to a mile north or northeast of the golf course. Dredging of boat basins in the southern part of the city has caused lowering of the ground-water levels in that area, thus permitting accelerated salt-water encroachment. The digging of drainage canals results in a rapid decline of ground-water levels, which may extend back into the recharge areas. Drainage ditches have caused serious problems of salt-water encroachment in other parts of south Florida, notably in the Miami area.
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54 FLORIDA GEOLOGICAL SURVEY Much valuable information concerning the capacities and the development of the fresh-water aquifers in Collier County can be gained through the continuous gathering of such basic data as waterlevel fluctuations, changes in chloride concentration, and pumpage records. Water-level observations in both equifers made on a continuing basis, and regular chloride analyses of water from key wells taken at the beginning and end of periods of well-field pumping, more frequently during critical months, will permit determining the extent of overdevelopment of the ground-water resources, the quantity of usable ground water available, and the approximate position of the salt-water front.
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REPORT OF INVESTIGATIONS No. 11 55 TABLE 6 Water levels, in feet, referred to mean sea level (p denotes pumping level) Well Date Water Well Date Water No. level No. level 24 11-12-51 0.91p 31 11-12-51 0.78p 11-26-51 0.66p 11-26-51 0.46p 11-27-51 3.41 11-27-51 3.47 3-12-52 3.02 2-11-52 0.16p 5-26-52 -0.87p 2-12-52 3.14 5-27-52 2.11 3-12-52 3.04 5-26-52 -1.18p 25 11-12-51 0.93p 5-27-52 2.14 11-26-51 0.65p 11-27-51 3.37 32 11-12-51 0.55p 2-11-52 0.16p 11-26-51 0.20p 2-12-52 3.10 11-27-51 3.33 3-12-52 3.00 3-12-52 2.89 5-26-52 -1.26p 5-26-52 -1.32p 5-27-52 2.11 5-27-52 2.09 26 11-12-51 0.59p 33 11-12-51 -0.37p 11-26-51 0.30p 11-26-51 -0.58p 11-27-51 3.38 11-27-51 3.64 2-11-52 0.30p 2-11-52 -1.63p 2-12-52 3.08 2-12-52 3.21 3-12-52 2.99 3-12-52 3.18 5-26-52 -2.96p 27 2-11-52 0.50p 5-27-52 2.27 2-12-52 3.13 3-12-52 3.04 56 11-12-51 1.11p 5-26-52 -0.91p 11-26-51 0.89p 5-27-52 2.07 11-27-51 3.72 2-11-52 0.60p 2-12-52 3.22 28 11-12-51 0.78p 3-12-52 3.25 11-26-51 0.50p 5-26-52 -0.80 11-27-51 3.3 5-2-52 -02.3380 2-11-52 0.67p 5-27-52 2.33 2-12-52 3.08 57 11-12-51 1.65p 3-12-52 2.99 11-26-51 1.31p 5-26-52 -1.41p 11-27-51 3.72 5-27-52 2.12 2-11-52 1.07p 2-12-52 3.20 29 11-12-51 0.70p 3-12-52 3.24 11-26-51 0.39p 5-26-52 -0.35p 11-27-51 3.41 5-27-52 2.34 2-11-52 0.26p 2-12-52 3.09 58 11-12-51 0.93p 3-12-52 3.02 11-26-51 0.66p 5-26-52 -1.01 11-27-51 3.57 5-27-52 2.13 2-11-52 0.36p 2-12-52 3.14 30 11-12-51 0.97p 3-12-52 3.11 11-26-51 0.69p 5-26-52 -0.96p 11-27-51 3.58 5-27-52 2.23 2-11-52 0.64p 2-12-52 3.21 59 11-12-51 1.88p 3-12-52 3.14 11-26-51 1.69p 5-26-52 --0.77p 11-27-51 3.84 5-27-52 2.21 2-11-52 1.62p
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56 wFLOIIDA GEOLOGICAL SURVEY TABLE 6continued Well Date Water Well Date Water No. level No. level 2-12-52 3.16 108 11-12-51 2.18 3-12-52 3.32 11-26-51 1.0O 5-26-52 0.06p 11-27-51 3.65 5-27-52 2.44 2-11-52 1.79 2-12-52 3.28 60 11-12-51 1.55P 3-12-52 3.22 11-26-51 1.63p 5-26-52 -0.57p 11-27-51 3.95 5-27-52 2.17 2-11-523 1.46p 2-12-52 3.12 109 11-12-51 1.77 3-12-52 3.45 11-26-51 1.47 5-26-52 0.01p 11-27-51 3.42 5-27-52 2.55 2-11-52 0.72p 2-12-52 3.15 3-12-52 3.02 61 11-12-51 1.41p -26-52 --1.02p 11-26-51 1.64p 5-27-52 2,06 11-27-51 4.04 2-11-52 1.18p 110 11-12-51 3.73 2-12-52 3.02 11-26-51 3.60 3-12-52 3.53 11-27-51 3.61 5-26-52 -0.31p 2-11-52 3.28p 2-12-52 3.53 62 11-12-51 2.08p 3-12-52 2.98 11-26-51 2.05P 5-26-52 0.71p 11-27-51 3.98 5-27-52 1.25 2-11-52 1.51p 2-12-52 3.12 111 11-12-51 1.71 3-12-52 3.47 11-26-51 1.41 5-26-52 1.02 11-27-51 3.56 5-27-52 2.58 2-11-52 1.30 2-12-52 3.21 78 11-12-51 1.58 3-12-52 3.31 5-26-52 -0.17 11-26-51 3.32 5-27-52 0.18 11-27-51 4.17 2 2 21 2-11-52 3.17 112 11-12-51 2.06 2-12-52 2.30 11-26-51 1.78 3-12-52 3.43p 11-27-51 3/71 5-26-52 1.60 2-11-52 .OOp 5-27-52 2.74 2-12-52 3.16 3-12-52 3.21 79 11-12-51 -4.81p 5-26-52 0.37p 11-26-51 3.31 5-27-52 2.34 11-27-51 4.15 2-11-52 3.17 116 2-11-52 3.02 2-12-52 -1.07p 2-12-52 2.85 3-12-52 3.59 3-12-52 3.19 5-26-52 1.58 5-26-52 1.78 5-27-52 1.12p 5-27-52 2.38
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REPORT OF INVESTIGATIONS No. 11 57 TABLE 6 -continued W611 Date Water Well Date Water No. level No. level 117 2-11-52 1.89 5-26-52 1.22 2-12-52 2.40 5-27-52 1.57 3-12-52 2.21 5-26-52 0.87 119 2-11-52 0.80 5-27-52 1.47 2-12-52 0.90 5-26-52 -.0.31 5-27-52 1.74 118 2-11-52 2.38 2-12-52 2.58 123 5-26-52 2.67 3-12-52 2.30 5-27-52 3.36
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TABLE 7 Records of selected wells at Naples Year DiaCasing Well Pla. Sample Owner Driller comDepth meter depth Chloride Use1 RMARKS No. Library No.. pleted (ft. imn.» I ft. ppm. Date 24 City of Naples J. Maharrey 1945 73 3 71 43 87-51 PS. See table 6 25 do. do. 1945 73 3 71 43 87-51 PS. do. 26 do. do. 1945 62 3 58 28 87-51 P.S. do. 27 do. do. 1945 75 3 71 28 7-31-46 P.S. do. 41 87-51 28 do. do. 1945 63 3 60 28 7-31-46 P.S. do. 25 87-51 29 do. do. 1945 63 3 60 28 87-51 PS. do. 30 do. do. 1945 63 3 60 17 87-51 PJS. do. 31 do. do. 1945 73 3 71 28 87-51 P.S. do. 32 do. do. 1945 98 3 92 63 12-31-52 P.S. do. 33 do. do. 1945 95 3 93 13 87-51 PS. See tables 4, 6 and figs. 13, 14 38 J. L. Kirk A. Cooper 1951 42 2 40 168 89-51 Irr. 56 City of Naples J. Maharrey 1949 74 4 67 16 87-51 P.S. See table 6 57 do. do. 1949 76 4 65 12 87-51 P.S. See tables 4 and 6 58 do. do. 1950 75 4 69 P.S. do. 59 do. do. 1950 88 4 83 15 87-51 P.S. do. 60 do. do. 1950 92 4 88 13 87-51 P.S. See table 6 61 do. do. 1950 82? 4 78 12 87-51 P.S. do. 62 do. do. 1950 7044 70 12 87-51 P.S. do. 63 J. Prince .... 1930 27 11 .... 19 11-26-51 Dom. 64 Naples J. Maharrey 1950 65-70 3 .... 19 11-26-51 Ind. Supply Co. 28 1-18-52 65 J. Pulling Jenkins 1939 33 4 26? Irr. 66 do. do. 1939 33 4 26 Irr. 67 do. do. 1939 33 2 30 32 88-51 Stock 68 City of Naples J. Mabarrey 1950 90 4 75 11 11-26-51 School 13 5-27-52 69 W. R. Rosier J. Pulling 1951 63 1/2 60 25 88-51 Dom. 70 Trail's End .......... 1951 75 4 70 29 11-26-51 Irr. Motel 71 J. G. Sample J. Maharrey 1945 60+ 6 .... .... ........... Irr. See table 4 72 do. do. 1945 52+ 6 .... 34 56-52 Irr. do. 73 do. do. 1949 436 .41 8-23-51 Irr. do.
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TABLE 7continued Year DiaCasing Well Fla. Sample Owner Driller cornDepth meter depth Chloride Use1 REMARKS -No. Library No. .pieted (ft.) (in.) (ft.) ppm. Date 74 do. do. 1949 50+ 6 .... ........... Irr. do. 75 do. do. 1949 62+ 6 .... Irr. 76 Tibbett Estate J. Townshend 1950 65 2 60 ... .......... Irr. See tables 2 and 3 77 leischmann do. 1950 55 2 50 364 88-51 Irr. Estate 362 4-29-52 78 Naples Co. J. Maharrey 1930 .... 6 .... 14 88-51 Irr. See table 6 12 36-52 79 do. do. 1930 .... 6 .... 24 3-12-52 It:. do. 80 do. do. 1930 63 6 ... 14 5-27-52 Irr. Composite sample with well 79 o 81 City Ice Co. ... .1930 73 3 70 .. .....Ind. I 82 Neopolitan C. Rivers 1951 63 3 60 18 88-51 Dom., Enterprises Irr. 83 L. A. Oricks ' do. 1949 52 2 50 19 88-51 Irr. 31 5-27-52 86 R. Lehman .......... 1936 72 2 70 18 89-51 Irr. 87 City Ice Co. .................. 73 3 70 .... ............ Ind., Irr. In-. 88 do. .......... 1922 78 4 .... 458 4-15-52 Obs. See fig. 6, table 3 465 5-27-52 97 B. W. Morris C. Rivers 1950 46? 3 .... 58 8-22-51 Irr. 48 5-27-52 98 J. G. Sample J. Maharrey 1949 52+ 6 .... 43 8-23-51 Irr. See table 4 99 A. D. Miller A. Cooper 1950 60 2 ... .... Irr. See tables 2 and 3 100 J. E. Turner J. Townshend 1950 42 2 40 .... Irr. See table 2 1.01 C. J. Sumarall .......... 1949 42 1 1 40 15 9-26-51 Irr. 102 R. O. Clark A. Cooper 1950 42 2 40 14 9-26-51 Irr. 103 H. C. Peterson do. 1950 42 2 40 113 9-26-51 Irr. 80 4-29-52 104 W. T. Truesdale do. 1951 63 2 60 27 9-26-51 Irr. 34 5-27-52 105 do. do. 1951 83 2 78 .. ......... Irr. See tables 2 and 3 106 W. Storter J. Townshend 1949 45 11/4 .... 442 9-26-51 Irr. 107 City of Naples J. Maharrey 1951 66 3 60 .... .......... Obs. See figs. 5, 13, 14 and table 4
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TABLE 7continued Year DACasing Well Pla. Sample Owner Driller comDepth meter depth Chloride Use1 REARKS No. Library No. pleted kft. in. ft. ppm. Date 108 City of Naples J. Maharrey 1951 71 4 59 16 10-11-51 P.S. See table 6 109 do. do. 1951 .4 ... 31 10-12-51 P.S. do. 110 do. do. 1951 40 6 27 15 10-12-51 P.S. do. 16 4-30-52 111 do. do. 1951 77 4 74 ... ............ PS. See tables 3 and 6 112 do. do. 1951 68 4 66 ............ PS. do. 114 Belding P. Duke 1951 245 4 235 4510 11-13-51 Irr. Water level slightly above land surface 115 City of Naples J. Maharrey 1939 540 5 300 2300 11-13-51 Fire Water level approx. 20 ! 2160 3-24-52 ft. above land surface 116 W-3046 U. S. Geological Miller Bros. 1952 71 2 62 ... ............ Obs. Test well; see log and Survey tables 3 and 6 117 W-3041 do. do. 1952 78 2 63 .... ............ Obs. do. 118 W-3040 do. do. 1952 70 2 69 ... ............ Obs. do. 119 W-3042 do. do. 1952 113 2 112 .... ............ Obs. Test well; see log and F tables 2, 3, and 6 0 123 W-3045 do. do. 1952 157 2 97 .... ............ Obs. Test well; see log and table 6 124 A. DiMeola C. Rivers 1949 55+ 1 Y 50 .... ............ Dom., See tables 2 and 3 Irr. 125 H. M. McClaskey A. Cooper 1951 40 + 1/2 40 318 4-29-52 Irr. 242 5-27-52 126 H. C. Sherier do. 1951 42 1Y2 40 16 4-29-52 Irr. 17 5-27-52 127 L. P. Grimes do. 1951 46 1Y .... 214 4-29-52 Irr. 192 5-27-52 128 R ..Williams J. Maharrey 1951 60? 2 .... 27 4-29-52 Irr. 129 F. W. Dreher C. Rivers 1951 40+ 1Y 40 34 4-29-52 Irr. 130 W-3044 U. S. Geological Miller Bros. 1952 71 6 69 148 6-10-52 Obs. Recording gage Survey 136 Naples Co. J. Marharrey 1952 90 8 84+ .. ............ Irr. Z PS.-Publc Supply Irr.-Irrigation Dom.-Domestic nd.-mIndstrial O -O--Observaton
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REPORT OF INVESTIGATIONS No, 11 61 WELL LOGS WELL 116 (P.G.S. Sample Library No. W-3046) Southwest corner of Third Street and South Golf Drive, Naples, Florida Depth, in feet, Description below land surface Sand, quartz, fine to medium, white to tan, becoming brown in lower part ................... .... ... ....... .................... 020 Sand, quartz, fine to very fine, brown ........................................ 2025 Limestone, sandy, fossiliferous, tan to gray; permeable........ 25 -42 Marl, sandy, tan to gray; becomes very shelly in lower part.... 42 -52 Limestone, sandy, gray ........................ ............................ 255 Marl, sandy, white to gray .......................................... ........ 5561 Limestone, sandy, fossiliferous, gray; permeable...................... 6170 Sand, marly, fine to medium, gray ...... ......................................... 70 -71 WELL 117 (F.G.S. Sample Library No. W-3041) North side of Fifth Avenue, North, east of Tamiami Trail, just west of Atlantic Coast Line Railroad, Naples, Florida. Depth, in feet, Description below land surface Sand, quartz, fine to medium, white to tan grading to brown at base .......... .... ..... ........................................... 0 -15 Sand, quartz, very shelly, white to tan; with few freshwater gastropod shells ................................................... ... 15 -19 Limestone, sandy, fossiliferous, very hard, tan; permeable.. 19 34 Limestone, sandy, fossiliferous, tan to gray, softer than above; permeable ........... ................................. ........... 34 -40 Sand, fine, shelly, gray to greenish ............................................. .40 -45 Limestone, sandy, gray, fossiliferous ................................ 4547 Sand, marly, shelly, gray to greenish ...................................... 4754 Limestone, sandy, gray .................. ..................................... 4 -57 Marl, sandy, shelly, gray to green ............................................ 7 -64 Limestone, sandy, fossiliferous, gray to tan; permeable ........ 64 -78 WELL 118 (F.G.S. Sample Library No. W-3040) Five hundred feet west of Naples water plant, Naples, Florida. Depth, in feet, Description below land surface Sand, quartz, fine to medium, white to gray becoming rustbrown in lower part ................................................ ......... 0 -21 Limestone, sandy, shelly, tan ..... ................................ ............ 2122 Sand, fine, marly, very shelly, tan to cream ........................... 2234 Sand, tan, fine, very shelly .............................. ............. ..... 34 -38 Limestone, sandy, fossiliferous, gray to tan; permeable........ 38-40 Marl, sandy, very shelly, gray to tan ..................................... .40 -45 Limestone, sandy, fossiliferous, gray; permeable .................... 4 -47
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62 FLORIDA GEOLOGICAL SURVEY Marl, sandy, very shelly in lower part, gray .......................... 47 -54 Limestone, sandy, gray .................................................. ........... 54 -56 M arl, very sandy, gray ............................................................... 56 -64 Limestone, sandy, fossiliferous, gray, hard; permeable ........ 6470 WELL 119 (F.Q.S. Sample Library No. W-3042) Depth, in feet, Description below land surface Fifty feet west of well 31, Naples well field, Naples, Florida. Sand, quartz, fine to medium, white to tan, changing to brown in lower part ............................................................ 0 -20 Marl, sandy, shelly, tan to cream ........................................... .2025 Limestone, sandy, shelly, tan to gray ............ ......................... 2527' Sand, quartz, shelly, fine, tan to gray ....................................... .27 -32 Limestone, sandy, fossiliferous, tan to gray .............................. 32 -38 Marl, sandy, shelly, gray to green .......................................... 3856 Limestone, sandy, fossiliferous, gray; permeable ................ 5671 Marl, sandy, gray, with thin interbed of soft limestone ........ 71 -78 Limestone, sandy, fossiliferous, gray; permeable .................. 78-83 Marl, very sandy, gray to green, becoming cream to white in lower part; contains thin interbeds of hard, fossiliferous lim estone .................................................................................. 83 -113 WELL 123 (F.O.S. Sample Library No. W-3045) Seven-tenths mile north of South Golf Drive, and 150 feet west of Tamiami Trail in city dump area, Naples, Florida. Depth, in feet, Description below land surface Sand, quartz, medium to fine, white to tan, grading to rustbrown in lower 10 feet ........................................ ......... .026 Limestone, sandy, shelly, tan .................................................... .2628 Marl, very sandy, shelly, tan .................................... ........... 28 -32 Marl, similar to above, contains fresh-water gastropods ........ 32 -34 Sand, quartz, medium , shelly, tan ............................................. 34 -36 Limestone, sandy, fossiliferous, tan to gray, very hard; perm eable .................................................................................. 36 -44 Limestone, very sandy, tan, soft, contains few fossils; permeable .................................................... ..................................... 44 -54 Limestone, partially cemented, sandy, shelly, tan to light green ................................................. .................................... 54 -60 Marl, very sandy and shelly, gray to green ............................ 60 -63 Limestone, sandy, fossiliferous, gray to green; a sand-filled cavity at 69 feet; permeable ................................... ........ 63 -71 Marl, sandy, very shelly, gray to green; heaves badly ........... 7182 Limestone, sandy, fossiliferous, cream to white; permeable.... 82 -107 Marl, sandy, cream to white; occurs as a cavity filling or thin bed ..................................................................................... 107 -109 Limestone, sandy, slightly fossiliferous, cream to yellowishgreen; with cavity fills or thin interbeds of marl or cal-
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REPORT OF INVESTIGATIONS No. 11 63 careous sand .............................................................................. 109 -138 Marl, sandy, cream; as cavity filling or thin bed .................... 138 -141 Limestone, partly cemented, sandy, fossiliferous, and cream m arl, sandy ........................................................................... 141 -157 BIBLIOGRAPHY BROWN, J. S. 1925 A study of coastal ground water with special reference to Connecticut: U. S. Geol. Survey Water-Supply Paper 537, pp. 14-17, 34-37, 49-53. COLLINS, W. D. 1928 (and HOWARD, C. S.) Chemical character of waters of Florida: U. S. Geol. Survey Water-Supply Paper 596-G, pp. 181-185. COOKE, C. WYTHE (also see PARKER, G. G.) 1945 Geology of Florida: Florida Geol. Survey Bull. 29, pp. 111-113, 144, 210-212, 238-243. COOPER, H. H. 1946 (and JACOB, C. E.) A generalized graphical method for evaluating formation constants and summarizing well-field history: Am. Geophys. Union Trans., vol. 27, no. IV, pp. 526-534. HOY, N. D. 1952 (and SCHROEDER, M. C.) Geology and ground-water resources of Lee and Charlotte Counties, Florida: (unpublished manuscript in preparation). JACOB, C. E. 1946 Radial flow in a leaky artesian aquifer: Am. Geophys. Union Trans., vol. 27, no. 2, pp. 198-205. MANSFIELD, W. C. 1939 Notes on the upper Tertiary and Pleistocene mollusks of penin* sular Florida: Florida Geol. Survey Bull. 18, pp. 11-16. MATSON, G. C. 1913 (and SANFORD, SAMUEL) Geology and ground waters of Florida: U. S. Geol. Survey Water-Supply Paper 319. MEINZER, .O. E. 1923 Outline of ground-water hydrology: U. S. Geol. Survey WaterSupply Paper 494, pp. 17-28, 32-50, 60-63. 1932 The occurrence of ground water in the United States with a discussion of principles: U. S. Geol. Survey Water-Supply Paper 489, pp. 2-8, 28, 52-53. PARKER, G. G. 1944 (and COOKE, C. WYTHE) Late Cenozoic geology of southern Florida, with a discussion of the ground water: Florida Geol. Survey Bull. 27, pp. 56-67, 74-75. 1950 (and STRINGFIELD, V. T.) Effects of earthquakes, trains, tides, winds, and atmospheric pressure changes on water in the geologic formations in southern Florida: Econ. Geology, vol. 45, no. 5, pp. 441-460.
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64 FLORIDA GEOLOGICAL SURVEY 1951 Geologic and hydrologic factors in the perennial yield of the Biscayne aquifer: Jour. Amer. Water Works Assn,, vol. 43, no. 10, p. 819. STRINGFIELD, V. T. (also see PARKER, 0. G.) 1936 Artesian water in the Florida peninsula: U. S. Geol. Survey WaterSupply Paper 773-C, pp. 127-132, 146-148, 166-167, and pl. 12. THEIS, C. V. 1935 The relation between the lowering of the piezometric surface and the rate and duration of discharge of a well using ground-water storage: Am. Geophys. Union Trans.. pp. 519-524. 1938 The significance and nature of the cone of depression in groundwater bodies: Econ. Geology vol. 33, no. 8, p. 894. VERNON, R. 0. 1951 Geology of Citrus and Levy Counties, Florida: Florida Geol. Survey Bull. 33, pp. 186-187. WENZEL, L. K. 1942 Methods for determining permeability of water-bearing materials: U. S. Geol. Survey Water-Supply Paper 887, pp. 87-90.
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