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STATE OF FLORIDA
DEPARTMENT OF NATURAL RESOURCES
Randolph Hodges, Executive Director





DIVISION OF INTERIOR RESOURCES
Robert O. Vernon, Director




BUREAU OF GEOLOGY
C. W. Hendry, Jr., Chief




REPORT OF INVESTIGATIONS NO. 68




HYDROGEOLOGIC ASPECTS OF A PROPOSED SANITARY
LANDFILL NEAR OLD TAMPA BAY, FLORIDA




By
R. N. Cherry and D. P. Brown





Prepared by the
U. S. GEOLOGICAL SURVEY
in cooperation with
BUREAU OF GEOLOGY
FLORIDA DEPARTMENT OF NATURAL RESOURCES
and the
CITY OF CLEARWATER


Tallahassee, Florida
1974







DEPARTMENT
OF
NATURAL RESOURCES



REUBIN O'D. ASKEW
Governor


RICHARD (DICK) STONE
Secretary of State




THOMAS D. O'MALLEY
Treasurer




FLOYD T. CHRISTIAN
Commissioner of Education


ROBERT L. SHEVIN
Attorney General




FRED O. DICKINSON, JR.
Comptroller




DOYLE CONNER
Commissioner of Agriculture


W. RANDOLPH HODGES
Executive Director





LETTER OF TRANSMITTAL


Bureau of Geology
Tallahassee
December 17, 1973


Honorable Reubin O'D. Askew, Chairman
Department of Natural Resources
Tallahassee, Florida 32304

Dear Governor Askew:

The Department of Natural Resources, Bureau of Geology, is publishing as
its Report of Investigation No. 68 the report entitled, "Hydrogeologic Aspects
of a Proposed Sanitary Landfill near Old Tampa Bay, Florida," by R. N. Cherry
and D. P. Brown of the U. S. Geological Survey.

The use of a sanitary landfill for solid-waste disposal overcomes some of
the serious health and esthetic problems that are associated with open-dump
disposal. However, unless the landfill site is selected and properly operated with
respect to the hydrologic environment, leachate from the landfill site may
contaminate the water resources of the area.

This study of a particular sanitary landfill site is published in order to
provide guidelines which may be incorporated in evaluating other potential
sanitary landfill sites.

Respectfully yours,




C. W. Hendry, Jr., Chief
Bureau of Geology












































Completed manuscript received
November 9, 1973
Printed for the
Florida Department of Natural Resources
Division of Interior Resources
Bureau of Geology
by
Ambrose the Printer, Inc.
Jacksonville, Florida

Tallahassee
1974

iv






CONTENTS

Page
Abstract .. ........ ... .. ...................... ........ 1
Introduction ................ ................................. 2
Purpose and scope .. ................ .......... ..... 2
Acknowledgments .......... ....... .................. 3
Geography ...................... ...... ................ 3
Hydrogeology ....................... ................... 3
Shallow aquifer .......................................... 3
Confining layer .................... .................. 14
Floridan aquifer .. ............................ ....... 16
Stream s ............. ........ ................... .... 19
Evaluation of the proposed landfill site . . . ..... ...... 20
Summary ................... ..................... ...... 22
Selected references... ................... .............. 25





ILLUSTRATIONS

Figure Page
I. Map of proposed landfill and data-collection sites... ...... 4

2. Topographic map of the proposed sanitary landfill site and adjacent area. .. 5

3. Diagram showing the thickness of shallow aquifer and confining layer over-
lying the Floridan aquifer in the proposed sanitary landfill site. .... 9

4. Geohydrologic sections through the proposed sanitary landfill site area. .. 11

5. Map showing generalized water-level contours of the shallow aquifer in and
near the proposed sanitary landfill site, May 1971. .. . 12

6. Map showing water-level contours in the shallow aquifer in the proposed
sanitary landfill site, May 1971. ...... ...... .............. 13

7. Structure contours on top of Floridan aquifer in and near the proposed
sanitary landfill site. ... ... ...................... .. 17

8. Map of the potentiometric surface of the Floridan aquifer in and near the
proposed sanitary landfill site, May 1971. . . . ..... 18





TABLES


Table Page
1. General information concerning test, observation, and domestic wells in the
proposed sanitary landfill area .. ... .. . . 6

2. Laboratory analyses and description of materials in the confining layer from
test well 3. ........ .. ..... .................... 15

3. Evaluation of the proposed site according to Stewart's and Hanan's criteria. 21


























































































































































































































































































































1






HYDROGEOLOGIC ASPECTS OF A PROPOSED SANITARY
LANDFILL NEAR OLD TAMPA BAY, FLORIDA


By
R. N. Cherry and D. P. Brown


ABSTRACT

The proposed sanitary landfill site for the city of Clearwater is in
east-central Pinellas County near Old Tampa Bay. The area of the site is about
320 acres.

The site is about 50 feet above mean sea level and is partly drained by two
unnamed streams. One stream is a tributary of the Lake Tarpon outfall canal;
the other stream, a tributary of Bishop Creek, drains into the north end of Old
Tampa Bay.

The two aquifers in the area are a shallow aquifer, which is composed of
sand containing a limestone zone, and the Floridan aquifer, which is composed
of limestone. At the site of the proposed landfill, the two aquifers are separed,
on the average, by 35 feet of clay, that forms a confining layer of low vertical
permeability. The head difference between the shallow and Floridan aquifers is
40 feet, and the rate of vertical movement within the proposed landfill site from
the shallow aquifer through the, clay layer to the underlying Floridan aquifer is
estimated to be 32,000 gallons per day in an area of 320 acres.



In the area of the proposed site, water moves laterally through both
aquifers from west to east toward Old Tampa Bay. Water levels in the shallow
aquifer within the proposed landfill site are less than 5 feet below land surface
and range from about 30 to 60 feet above sea level. The potentiometric surface
of the Floridan aquifer within the proposed landfill site ranges in elevation from
about 6 to 10 feet above sea level.


The horizontal flow through the shallow aquifer from the proposed
landfill site is estimated to be 314,000 gallons per day. The two streams at the
site intercept about 190,000 gallons of ground water per day. The remainder,
124,000 gallons per day, moves as horizontal flow through the shallow aquifer
toward Old Tampa Bay. At the estimated theoretical rate of horizontal
movement of 2.7 feet per day through the shallow aquifer, water from the
landfill site would reach Old Tampa Bay in about 2 years.






BUREAU OF GEOLOGY


The site could be made hydrologically favorable for a sanitary landfill if
some precautions are taken. A perimeter canal could intercept water leaving the
site. Also, maintaining a monitoring system would allow early detection of
possible movement of contaminated water.

INTRODUCTION

The disposal of about 200 tons of solid waste each day constitutes a major
problem for the city of Clearwater. The disposal can lead to health, esthetic, and
environmental problems. The public recognizes that many problems are
associated with solid-waste disposal and their demands are increasing for
properly selected, engineered, and effectively and economically operated
solid-waste-disposal facilities.

The use of a sanitary landfill for solid-waste disposal overcomes some of
the serious health and esthetic problems that are associated with open-dump
disposal- However, unless the landfill site is selected and properly operated with
respect to the hydrologic environment, leachate from the land fill site may
contaminate the water resources of the area.

The sanitary landfill is defined by the American Society of Civil Engineers
(1959) as "A method of disposing of refuse on land without creating nuisances
or hazards to public health or safety, by utilizing the principles of engineering to
confine the refuse to the smallest practical area, to reduce it to the smallest
practical volume, and to cover it with a layer of dirt at the completion of each
day's operation or at such more frequent intervals as may be necessary."

The sanitary landfill method of disposal is primarily a containment and
compaction of material. It is a convenient disposal method by which all solid
waste, irrespective of size, moisture, or other characteristics, can be disposed,
and it consists of four basic operations:
1. The solid wastes are deposited in a controlled manner in a prepared
part of the site,
2. The solid wastes are spread and compacted in thin layers,
3. The solid wastes are covered daily or more frequently, if necessary,
with a layer of dirt,
4. The cover material is compacted daily.

PURPOSE AND SCOPE

The city of Clearwater is faced with a critical need to expand its sanitary
landfill facilities. The city officials, aware of environmental problems commonly
associated with sanitary landfills, entered into a cooperative agreement with the






REPORT OF INVESTIGATIONS NO. 68


U. S. Geological Survey to investigate a prospective landfill site. The purpose of
this investigation was to evaluate the hydrologic consequences of operating a
sanitary landfill northeast of the city of Clearwater. This report presents an
evaluation of the site based on hydrologic conditions.

ACKNOWLEDGMENTS

Cooperation of Merrett Stierheim, City Manager; Max Battle, City
Engineer; and N. J. Seher, Engineering Department, Clearwater, Florida, is
gratefully acknowledged. The helpful cooperation of the property owners who
permitted access to their land and wells in order to collect hydrologic data is
greatly appreciated.

GEOGRAPHY

The proposed sanitary landfill site is about 7 miles northeast of
Clearwater, just north of the intersection of State Roads 593 and 580 (fig. 1).
The site covers about 320 acres, or one-half square mile.

Land surface in the area of the proposed site ranges in elevation from sea
level at Old Tampa Bay to more than 80 feet above sea level at the crest of a
ridge west of the landfill site (fig. 2 and table 1). In the proposed landfill site
elevations of the land surface range from about 40 feet above sea level near the
eastern boundary to about 65 feet above sea level near the west boundary. The
western part slopes about 3 feet per 1,000 ft, and the eastern part about 10 feet
per 1,000 ft.

The proposed site is drained by two unnamed streams; one drains
northeastward into the Lake Tarpon outfall canal, and the other is a tributary of
Bishop Creek (fig. 1).

HYDROGEOLOGY

The proposed sanitary landfill site is underlain by three hydrogeologic
units. The uppermost unit consists of sand, sandy clay, and sandy limestone
called the shallow aquifer, the middle unit is a clay confining layer, and the
lower unit is the Floridan aquifer. Figure 3 shows the thickness of the
uppermost and middle units in the proposed sanitary landfill site.

SHALLOW AQUIFER

The upper part of the shallow aquifer is an unconsolidated, fine to very
fine, well sorted, yellowish-brown to dark-brown sand. The lower part of this

































82040'


Figure 1. Proposed landfill and data-collection sites.


28002'


2800'









27058'


































8248' 46' 44' 42'
Figure 2. Topographic map of the proposed sanitary landfill site and adjacent area.


28002'


2800'










27058'


82040'







Table 1, General information concerning test, observation and domestic wells in the proposed sanitary landfill area
(msl" feet above mean sea level)

SHALLOW AQUIFER

Elevation Depth to Water level elevations
Well Casing land Clay Floridan
Site Well Depth Depth surface thickness aquifer Date msl Date mal
number number (feet) (feet) (msl) (feet) (feet)
1 280127N0824232.1 17 15 57.80 13 4- 9-71 55.19 5-26-71 54,21
2 280127N0824232.2 15 13 57.80 13 4- 9-71 55.44 5-26-71 54,20
9A 280137N0824203.2 15 13 50.90 4- 9-71 45,80 5-26-71 45.35
11A 280159N0824204.2 15 13 35.94 4- 9-71 32.35 5-26-71 31.49
13A 280147N0824215.2 13 11 56.48 4- 9-71 54.06 5-26-71 52.62
14A 280200N0824212.2 15 12 45.30 4- 9-71 42.82 5-26-71 41.95
15 280142N0824214.,1 13 10 57.18 4- 9-71 54.07 5-26-71 53.14
16A 280137N0824214.2 15 13 55.55 4- 9-71 53.15 5-26-71 52.25
17 280153N0824214.1 13 11 54.66 4- 9-71 51.66 5-26-71 50,97
18 286153N0824208.1 14 12 49.67 4- 9-71 43.44 5-26-71 47.83
19 280147N0824208.1 14 12 54.10 4- 9-71 49.06 5-26-71 48.51
20 280142N0824208.1 15 13 54.17 4- 9-71 50.35 5-26-71 49.52
21 280140N0824224.1 12 10 56.86 4- 9-71 54.32 5-26-71 53.51
22 280147N0824227.2 19 17 56.86 4- 9-71 53.74 5-26-71 52.85
23A 280202N0824242.2 12 10 53.86 4- 9-71 50.56 5-26-71 49.45
24A 280202N0824234.2 14 12 54.58 4- 9-71 51.71 5-26-71 50.63
25A 280143N0824248.2 15 13 63.48 4- 9-71 60.98 5-26-71 59.95
27A 280112N0824247.2 15 13 63.59 4- 9-71 61.51 5-26-71 60.12
28A 280147N0824238.2 15 13 58.48 4- 9-71 55.51 5-26-71 54.50
29A 280137N0824234.2 13 11 57.36 -- 4- 9-71 55.11 5-26-71 53.87
30A 280123N0824234.2 20 18 59.50 4- 9-71 56.35 5-26-71 55.50
31A 280i37N0824258.2 20 17 79.68 4- 9-71 77.78 5-26-71 77.24
32 280105N0824232.1 15 13 49.53 4- 9-71 46.37 5-26-71 46.30
33 280146N0824154.1 15 13 37.46 4- 9-71 35.03 5-26-71 34.62
35 280227N0824235.1 10 8 37.10 4- 9-71 34.59 5-26-71 33.54
36 280117N0824217.1 13 11 56.56 -- 4- 9-71 54.06 5-26-71 54.30
37 280135N0824221.1 18 16 57.35 4- 9-71 53.36 5-26-71 52.50


(. '







SHALLOW AQUIFER continued


Elevation Depth to Water level elevations
Well Casing land Clay Floridan
Site Well Depth Depth surface thickness aquifer Date msl Date msl
number number (feet) (feet) (msl) (feet) (feet)
.71 275807N0824548.1 19.1 14.1 71.10 95 4-21-71 66.97 5-25-71 67.40
72 275914N.0824341.1 16.0 11 57 49 4-20-71 52.59 5-25-71 52.80
73 275922N0824520.1 19.0 14 62.2 61 4-20-71 55.40 5-25-71 55.85
74 275933N0824623.1 39.0 34 30.5 40 4-20-71 9.24 5-25-71 9.50
75 280059N0824649.1 34.0 29 35.56 70 4-20-71 14.42 5-25-71 15.46
76 280108N0824338.1 50 48 97.1 85 4-20-71 92.61 5-25-71 92.85
77 280107N0824449.1 18.8 14 71.4 60 4-20-71 67.73 5-25-71 67.94
78 280107N0824604.1 14 10 30.5 40 4-20-71 26.73 5-25-71 27.13
79 280254N082441'6.3 25 20 66.82 45 4-20-71 62.95 5-25-71 62.92
80 280251N0824530.1 19 14 25.2 30 4-20-71 5-21-70 17.00
FLORIDAN AQUIFER

9 280137N0824203.1 60 58 50.90 33 53 4- 9-71 7.85 5-26-71 8.30
11 280159N0824204.1 58 56 35.94 27 52 4- 9-71 7.14 5-26-71 6.89
13 280147N0824215.1 55 53 56.26 33 53 4- 9-71 5-26-71
16 280137N0824214.1 55 50 55.55 35 53 4- 9-71 5-26-71 7.21
23 280202N0824242.1 52 48 53.86 31 50 4- 9-71 11.10 5-26-71 10.88
24 280202N0824234.1 47 45 54.58 25 45 4- 9-71 5-26-71 -
25 280143N0824848.1 54 51 63.74 27 54 4- 9-71 5-26-71
26 280147N0824227.1 62 60 57.36 40 60 4- 9-71 9.25 5-26-71 9.28
27 280112N0824247.1 70 68 63.59 43 68 4- 9-71 9.48 5-26-71 9.53
28 280147N0824238.1 59 56 58.48 36 55 4- 9-71 8.42 5-26-71 8.29
29, 280137N0824234.1 70 67 57.36 43 64 4- 9-71 5-26-71
30 280123N0824234.1 64 61 59.50 40 60 4- 9-71 9.16 5-26-71 9.28
41 280018N0824229.1 129 69 45 49 79 6- -46 42 5-26-71
42 280137N0824132.1 27 25 20 15 25 8- 1-65 9.00 5-26-71
43 280111N0824236.1 100 54
44 280111N0824237.1 59
45 280112N0824242.1 100 50 63
46 280119N0824235.1 200 59 -
47 280131N0824204.1 120 50
48 280133N0824204.1 111 50


0











Ci
zo






FLORIDAN AQUIFER continued
Elevation Depth to Water level elevations
Well Cusing land Clay Floridan
Site Well Depth Depth surface thickness oqultbr Date msl Date msl
number number (feet) (feet) (msl) (feet) (feet)
49 280134N0824215,1 110 70 56
50 280137N0824256,1 140 70 75
51 280204N0824223.1 50
52 275815N0824404,1 299 81 33,64 4-21-71 9.53 5-24-71 8.43
53 275845N0824135.1 58 58 4,7 4-21-71 .67 5-24.71 1.20
54 275917N0824352.1 67,18 4-20-71 11,05 5-24-71 11,35
55 275945N0824545,1 51 4-20-71 4.50 5-24-71 4.70
56 280035N0824054.1 90 25 30 4-20-71 -3.73 5-24-71 -3,10
57 280111N0824535.1 175 76.5 59.27 4-20-71 5-25-71 2.85
58 280104N0824631.1 242 67 33.20 4-20-71 4.03 5-25-71 4.00
59 280116N0824712.1 250 12.86 4-20-71 1.18 5-25-71 .84
60 280138N08241 1.2 120 35 4-20-71 3.30 5-24-71 1.25
61 280158N0824417.1 70 50.85 4-20-71 7.55 5-25-71 8.05
62 280214N0824642.1 11.30 4-20-71 5.06 5-25-71 5.28
63 280230N0824550.1 4346 4-20-71 3.37 5-25-71 5.78
64 280254N0824416.2 405 390 65,53 4-20-71 8.53 5-25-71 8.74
65 280256N0824501.1 64 48 45.58 4-20-71 7.87 5-25-71 7.84
66 280254N0824635.1 6.79 4-20-71 -.61 5-25-71 4.81
TEST WELLS
2A 280127N0824232.3 33 57.80 1- 7-71 56.8
3 280131N0824227.1 80 56.95 50 73 1- 7-71 8.0
4 280135N0824221.2 19 57.35 1- 7-71 54.4
5 280134N0824232.1 22 58.05 1- 8-71 55.0
6 280153N0824234.1 19 56.51 1- 8-71 53.5
7 280153N0824239.1 19 57.88 1- 8-71 54.9
8 280136N0824247.1 .63 62.33 -. 1-11-71
10 280147N0824203.1 40 45.31 25
12 280142N0824203.1 40 50.42 15
14 280200N0824212.1 50 45.30 33 48
31 280137N0824258.1 80 79.68 47 77
34 280213N0824237.1 25 41.61 20 4- 7-71
40 280108N0824338.2 80 97.1






REPORT OF INVESTIGATIONS NO. 68


Figure 3. Diagram showing the thickness of shallow aquifer and confining layer
overlying the Floridan aquifer in the proposed sanitary landfill site.


aquifer is sandy clay. Within the sand and sandy clay unit is a gray to white,
sandy, phosphatic limestone. This sandy limestone underlies the central part of
the proposed site (fig. 3). In some places, the sandy limestone forms the base of
the shallow aquifer. The sand, sandy clay, and sandy limestone units range in
combined thickness from about 10 to 35 feet and average about 15 feet in
thickness.

The sand in the upper part of the shallow aquifer ranges in thickness from
less than 10 feet near the central part of the site to more than 20 feet along the
west boundary of the site. An organically rich, very fine sand occurs along the
west boundary. The median particle size of the sand is about 0.15 mm
(millimeter) diameter, and the sand is well sorted; 85 percent to 90 percent of
the particles range in diameter from 0.10 mm to 0.19 mm. The permeability of
the sand, as determined by an aquifer tet at a site west of the landfill site, was
about 250 gpd per sq ft (gallons per day per square foot). Because the sand is
well sorted, the horizontal permeability is probably no ihore than 10 times the






BUREAU OF GEOLOGY


vertical permeability. Therefore, the vertical permeability probably ranges from
25-100 gpd sq ft.

Figure 4 shows north and east geohydrologic sections through the sanitary
landfill site and adjacent area. This figure shows that the water level in the
shallow aquifer is near the land surface, the potentiometric surface of the
Floridan aquifer is above the top of the Floridan aquifer, and the water level of
the shallow aquifer is above the potentiometric surface of the Floridan aquifer.

The shallow aquifer is recharged from local rainfall, and it is not used
extensively as a source of water in the landfill area. Locally elsewhere, it is used
for irrigating lawns.

Figures 5 and 6 show regional and detailed water-level contours in the
shallow aquifer in the general area of the landfill site and infer the direction of
water movement in May 1971. The slope of the water surface is controlled by
the hydraulic and physical characteristics of water-bearing materials, and local
variations in recharge and discharge. Rises in water level are caused by recharge
from rainfall. Declines in water level are caused by seepage into streams, lakes,
and canals, by evapotranspiration, by pumpage from wells, and by leakage into
the underlying Floridan aquifer. Water moves downgradient and normal to the
contour lines. The water level in the shallow aquifer is highest, about 90 feet
above sea level, a mile west of the proposed landfill site. From this high, which
forms a ground-water divide, water moves westward to the Gulf of Mexico or
eastward to Old Tampa Bay.

The velocity at which water moves eastward through the shallow aquifer
material was calculated using the equation:
PI
V-
7.48S
where:
V = velocity of flow of water through the shallow aquifer, in fpd
(feet per day).
P = permeability of the shallow aquifer, in gpd per sq ft.
I = the average hydraulic gradient, in feet per foot.
S = the effective porosity, expressed as a fraction.

Based on a permeability of 250 gpd per sq ft, a hydraulic gradient of 0.02 foot
per foot (difference in elevation of 45-foot water-level contour and sea level and
the distance from 45-foot water-level contour to Old Tampa Bay (fig. 6) and an
effective porosity of 0.25, the velocity would be 2.7 feet per day. At this rate
water would take about 2 years to move through the shallow aquifer from the
landfill site to the bay.
























LEVEL


-SEA LEVEL


LEVEL

20'

40'


9 590 IPo FIT
VERTICAL EXAMSRATION AWPOXIMATIY XI

Figure 4. Geohydrologic sections through the proposed sanitary landfill site area.





















28000 -- Woer-lel ontour, Shaws elevtionJ1 S
DUNK













of water evel. Contour Interval f" Q
28002' ow l d tion o
sio M BAY



EXPLANATION







2048 46 44' 42' 8240
28000' w aisrt-lvel confou shows elevation
10 feet. Datum Is mean sea leve


Flow Ilne shows direction of
ground-water movement near
and within proposed landfill




2700 1 .
82048' 46' 44' 42' 82040'

Figure 5. Generalized water-level contours of the shallow aquifer in and near the proposed sanitary landfill site,
May 1971.





























Figure 6. Water-level contours in the shallow aquifer in the proposed landfill site, May 1971.


:e28o0


CN
00
z


I0






BUREAU OF GEOLOGY


The quantity of water moving horizontally from the landfill site in the
shallow aquifer in a day was calculated using Darcy's law:

Q = PIA
where:
Q = the quantity of water, in gpd, moving through the shallow aquifer.
P = the permeability of the shallow aquifer, in gpd per sq ft.
I = the hydraulic gradient of the shallow aquifer, in feet per foot.
A = the cross-sectional area of the shallow aquifer at the eastern
boundary, in sq ft.

Based on a permeability of 250 gpd per sq ft, a hydraulic gradient of 0.01 foot
per foot (gradient across the 45-foot water-level contour, fig. 6), and a
cross-sectional area of 49,500 sq ft (determined from the length, 3,300 feet, of
the 45-foot water level contour fig. 6), and an average saturated thickness of 15
feet; the water moving horizontally from the sanitary landfill site toward Old
Tampa Bay is about 124,000 gpd.

The theoretical velocity and quantity of water moving are based upon the
assumption that the water moves at a uniform rate throughout the thickness of
the aquifer.

A perimeter ditch could intercept water moving horizontally from the
landfill site and reduce ground-water mounding within the site by drainage away
from the site. The water could be treated if necessary.



CONFINING LAYER

Underlying the sand and sandy limestone of the shallow aquifer is a layer
of pale green, dense, sandy clay of the Hawthorn Formation (?) of middle
Miocene Age.

At the landfill site, this clay ranges in thickness from 30 to 50 feet and
averages 35 feet thick (fig. 4 and table 2). Tentative identification by X-ray
analysis indicates that the clay is a montmorillonite type.

The permeability values shown in table 2 indicate that some water would
move vertically through the clay layer. The coefficient of permeability of the
clay beneath the proposed site is as low as 4.9 x 10-4 gpd per sq ft. During
drilling, some of the clay samples recovered by a split spoon sampler were in part
dry indicating that locally the clay has an extremely low vertical permeability.









Table 2. Laboratory analyses and description of materials in


Coefficient of vertical Geohydrologic
th (feet) permeability (gpd per sq ft) Unit


.8-15.3 1.59 x 10-2 Confining layer


.5-22.0 9.07 x 10'1 Confining layer


I


Sample No.

3A-3


3A-4



3A.5



3A-6





3A-7



3A-8


3A-9


3Al 107.553 0iCofnn ae


the confining layer from test well 3.


Dep


14


21


3.28 x 10'2



4.17 x 10-3





3.19 x 10'3



1.64 x 10'3


4.90 x 10-4'


29.0-29.5



36.0-36.5





41.0-41.5



51.0-51.5


60.5-61.0


5.39 x 10'3 Confining layer


3A-10 71.0-71.5


Confining layer



Confining layer





Confining layer



Confining layer


Confining layer


Description


Cream-colored, sandy, calcareous clay.


Off white, noncalcareous clay. Sample appears
homogeneous.


Off white, noncalcareous. Silty clay; homogeneous.
Sample extruded. No stratification noticed.


Light gray, noncalcareous. Light-greenish clay,
interbedded with black clay sections. No apparent
structure. Some very hard cement sections in core.


Gray noncalcareous clay. Greenish-blue clay with
brown streaks. No structure noticed.


Greenish-gray clay; homogeneous. No visible structure.


Dark and light-gray clay. Small part of sample showed
carbonate.

Mixture of white and dark gray sandy clay.






BUREAU OF GEOLOGY


The quantity of water moving from the shallow aquifer vertically through
the clay layer to the Floridan aquifer was determined using the following form
of Darcy's law:

Q = (P' /m') AhA
where:
Q = leakage through confining bed, in gpd
P' = coefficient of vertical permeability of confining bed, in gpd per sq
ft.
m'= average thickness of confining bed through which leakage occurs,
in feet.
A = area of confining bed through which leakage occurs, in sq ft.
H = average difference between the potentiometric surface in the
Floridan aquifer and water level in the shallow aquifer in feet.

On the basis of an average coefficient of permeability of 0.002 gpd per sq ft, a
clay thickness of 35 feet, and area of 320 acres (about 13,940,000 sq ft) and a
40-foot difference in head between the shallow aquifer and the Floridan aquifer,
the amount of water moving vertically through the clay layer in the proposed
landfill site is about 32,000 gpd or about one fourth the amount moving through
the shallow aquifer to the bay.

Another important property of clay minerals other than the low
permeability is their ability to sorb certain ions and retain them in an
exchangeable state. Montmorillonite clays, in general, have a high ion-exchange
capacity which ranges from about 80 to 150 milliequivalents per 100 grams.
Many factors influence the cation exchange capacity, and this accounts for a
wide range in exchange capacity values (Grim, 1968).

FLORIDAN AQUIFER

The highly productive Floridan aquifer underlies the Middle Gulf area
(Cherry, Stewart, and Mann, 1971). This aquifer supplies virtually all
ground-water withdrawals and feeds some of the largest fresh-water springs in
the world. Regionally, the aquifer is composed of numerous thick and highly
permeable zones of limestone and dolomite. Zones of lesser productivity occur
within the aquifer. Some zones yield large volumes of water whereas others yield
little water.

The elevation of the top of the Floridan aquifer differs throughout the
proposed landfill area. The top of the aquifer is highest, about 10 feet above sea
level, just west of the proposed site and is lowest, about 30 feet below sea level,
in the east part near the coast (fig. 7).



































8240'


Figure 7. Structure contours on top of Florida aquifer in and near the proposed sanitary landfill site.


2802'


28800'










27058'










28002'









2800'









2758'


82048' 46' 44' 42'
Figure 8. Potentiometric surface of the Florida aquifer in and near the proposed sanitary landfill site, May 1971.


82040'







REPORT OF INVESTIGATIONS NO. 68


Figure 8 shows that the potentiometric surface of the Floridan aquifer in
the area of the landfill site is 6 to 10 feet above msl. Water movement in the
Floridan aquifer in the area of the proposed site is generally eastward, toward
Old Tampa Bay. The potentiometric surface is highest in the same general area as
the highest land elevation and the highest water level in the shallow aquifer.
(compare figs. 2 and 7). This potentiometric high forms a ground-water divide.

Water in the upper part of the Floridan aquifer generally contains less than
250 mg/1 (milligrams per liter) of chloride. Salt water occurs in the lower part of
the Floridan aquifer.

The city of Dunedin, about 4 miles west of the proposed sanitary landfill
site, receives all of its water, and Clearwater, about 7 miles southwest, receives
part of its water from the Floridan aquifer. A natural ground-water divide in the
potentiometric surface of the Floridan aquifer occurs between the well fields of
both cities and the proposed sanitary landfill site (fig. 8).

STREAMS
The unnamed tributary to the Lake Tarpon outfall canal is the principal
stream draining the area of the proposed landfill site. The headwaters for this
stream is a marsh near the center of the landfill site. The marsh is drained by a
canal that connects with the tributary. Near the north boundary of the site, the
stream has cut through the shallow sand and sandy limestone of the shallow
aquifer to the clay of the confining layer. Flow was observed, although not
measured, during the 1971 dry season.

The discharge from the shallow aquifer to the stream was calculated using
the equation:

Q = PIA
where:
Q = the quantity of water in gpd moving through the shallow aquifer to
the stream.
P = the permeability of the shallow aquifer, in gpd per sq ft.
I = the hydraulic gradient in the shallow aquifer, feet per foot.
A = the cross sectional area, in sq ft of the aquifer contributing water to
the stream.

Assuming the stream fully penetrates the shallow aquifer and has a depth
of 15 feet, a length of 2,500 feet that contributes water to the stream (a cross
sectional area of 37,500 sq ft), and the shallow aquifer has a hydraulic gradient
of 0.01 foot per foot and a permeability of 250 gpd per sq ft, the discharge from
the shallow aquifer to the stream is 190,000 gpd:






BUREAU OF GEOLOGY


EVALUATION OF THE PROPOSED LANDFILL SITE

According to Stewart and Hanan (1970), a sanitary landfill should be in an
area where the underlying deposits are relatively impermeable and where the
leachate from the refuse is contained or its movement from the site is retarded.
Sites underlain by highly permeable sand are generally unfavorable. Sites directly
underlain by fractured and cavernous limestone should be avoided because of
the unpredictability of the direction and rate of ground-water movement in such
materials. Other areas that should be avoided are swamps and marshes tributary
to streams and those that contain sinkholes.

On the basis of criteria by Stewart and Hanan (table 3) and other
hydrologic considerations, the proposed sanitary landfill site has both favorable
features and unfavorable features. The favorable features include:

1. The combined thickness of the sand, sandy limestone and clay units
which overlie the Floridan aquifer is about 50 feet.
2. The land surface ranges in elevation from 40 to 65 feet;parts of the
site can be drained.
3. The site is in an area of minimal urban development.
4. A clay layer separates the shallow aquifer from the Floridan aquifer.
The clay is a montmorillonite type which generally has a high
ion-exchange capacity, a selective sorbingg) capacity for organic
compounds and will tend to sorb materials from water passing
through it.
5. The clay layer will retard vertical flow from the shallow aquifer to
the Floridan aquifer. The amount of water moving through the
clayey material is probably less than 32,000 gpd.
6. The Floridan which is the principal aquifer, shows some evidence of
salt-water encroachment in the general area of the landfill site, and
thus is unlikely to be extensively developed in this area as a
municipal water supply.
7. The proposed sanitary landfill site is on the east slope of asurface-
and ground-water divide. All the municipal water-supply wells for
Clearwater and Dunedin are on the west slope of the divide.


The unfavorable hydrologic features are:

I The uppermost part of the deposits that underlie the site forms a
shallow aquifer.
2. Although the site is more than 40 feet above msl, part of the site is
not well drained.







Table 3. Evaluation of the proposed site according to Stewart and Hanan's criteria


Stewart and Hanan's Criteria


Proposed Site


1. Type of unconsolidated material.
Favorable: clay. silty clay, clayey silt, silt.
Unfavorable: sand.

2. Thickness of unconsolidated materials.
Favorable: at least 25 feet.
Unfavorable: less than 15 feet.


3.


Site topography.
Favorable: adequate drainage not subject to flooding.
Unfavorable: low swampy areas; areas subject to flood-
ing; sinkholes and areas near sinkholes; along stream
channel hydraulically connected with Floridan aquifer.


4. Ground-water levels.
Nonartesian aquifer.
Favorable: greater than 15 feet below land surface.
Unfavorable: less than 5 feet below land surface.

Artesian aquifer.
Favorable: Potentiometric surface at least 5 feet above
water table.
Unfavorable: Potentiometric surface near or below the
water table.

5. Character of limestone aquifer.
Favorable: dense, unfractured.
Unfavorable: fractured and cavernous.

6. Relation to public water supply wells.
Favorable: at least several miles down-gradient from
large primping withdrawals.
Unfavorable: Adjacent to or within the immediate
cone of, influence of large-scale pumping.


Favorable Upp6r material (shallow aquifer) is sandy and grades to a
clay with' depth. The permeability of sand is low. The
lower unconsolidated. material is clay and nearly
impermeable.

Favorable Unconsolidated material is greater than 50 feet thick.


Favorable Land surface elevation is greater than 40 feet above msl.
Although parts of the site are marshy,.it could be drained.



Unfavorable The water level of the shallow aquifer is about 3 to 4 feet
below the land surface. Therefore, a perimeter canal
around all parts of the landfill would be needed to lower
the water table in the working area and to intercept water
leaving the site.

Unfavorable The potentiometric surface is about 40 feet below the
water level of the shallow aquifer. However, a massive clay
layer of low permeability retards flow from the shallow
aquifer to the Floridan aquifer.

Unfavorable Floridan aquifer is probably fractured and cavernous.


Favorable Nearest public-supply wells are beyond the ground water
divide and at least 3 miles away.


Remarks


O











o
0I
.
'<11






BUREAU OF GEOLOGY


3. The water level of the shallow aquifer is above the potentiometric
surface of the Floridan aquifer. Therefore, water will move from the
shallow aquifer to the Floridan aquifer.
4. The Floridan aquifer underlying the area is probably fractured and
cavernous.
5. The proposed site is in an area where the water table is generally less
than 5 feet below land surface.
6. The leachate from the refuse will contaminate the shallow aquifer
within and downgradient from the landfill site.
7. This contamination will move by stream (190,000 gpd) and through
the shallow aquifer (124,000 gpd) toward Old Tampa Bay.

The foregoing unfavorable features indicate that at least the following
precautions are desirable before use of the site:

1. Installing a canal or ditch or series of shallow wells around the site to
intercept water leaving the site and lower the water level in the
working area. If necessary the water could be treated. This will
minimize or prevent contamination downgradient from the landfill
site.
2. Maintaining a monitoring system of wells at least in a downgradient
direction to determine the nature and extent of movement of
contaminants.
3. Checking the private water supplies in the general area of the
proposed site periodically to provide warning of incipient
contamination.
4. Providing an alternative source of water for domestic use in the
general area of the proposed landfill site in the event contamination
should occur.

SUMMARY

The proposed landfill site is on the east flank of a topographic ridge at an
elevation of 40-65 feet above sea level. The upper 15 feet of material at the
landfill site is chiefly sand. The material becomes more clayey with depth and
becomes a clay at about 20 feet. The sand of the shallow aquifer has an
estimated permeability of about 250 gpd per sq ft. About 124,000 gpd of water
moves laterally from the sanitary landfill site through shallow aquifer materials
toward Old Tampa Bay at a rate of about 2.7 feet per day.

The top of the clay layer underlying the shallow aquifer occurs at an
elevation of about 40 feet above sea level. This clay layer is about 35 feet thick.
The day is of a montmorillonite type and has an estimated average permeability






REPORT OF INVESTIGATIONS NO. 68 23

of 0.002 gpd per sq ft. Water moves vertically from the shallow aquifer on the
320-acre site through the thick clay layer at a rate of about 32,000 gpd.

Most of the water for domestic and municipal uses in this area and on the
peninsula is obtained from the Floridan aquifer. Water from deep
high-production wells generally contains some salt. Water from relatively shallow
domestic wells contains little salt.

Geohydrologic features of the site are both favorable and unfavorable with
respect to its use as a sanitary landfill. With proper precautions the unfavorable
features could be modified or partly controlled and the site made hydrologically
suitable.







24 BUREAU OF GEOLOGY







REPORT OF INVESTIGATIONS NO. 68


SELECTED REFERENCES

American Society of Civil Engineers,
Committee on Sanitary LandfillPractice
1959 Sanitary landfill: Am. Soc. Civil Engineers Manual Eng. Practice 39,
61 p.

Cherry, R.N., Stewart, J. W., and Mann, J. A.
1970 General hydrology of the Middle Gulf area, Florida: Florida Bur.
Geology Rept. Inv. 56, 96 p.

Cooke, C. W.
1945 Geology of Florida: Florida Geol. Survey Bull. 29, 339 p.

Denson, K. H., Shindala, Adrain, and Genn, C. D.
1968 Permeability of sand with dispersed clay particles: Water Resources
Research, v. 4, no. 6, p. 1275-1276.

Grim, R. E.
1968 Clay Mineralogy (2d ed): McGraw-Hill Book. Co., New York, 596 p.

Schneider, W. J.
1970 Hydrologic implications of solid-waste, disposal: U.S. Geol. Survey
Circ. 601-F, 10 p.

Sorg, T. J. and Hickman, H. L.
1968 Sanitary landfill facts: U.S. Public Health Service Pub. 1972, 30 p.

Stewart, J. W. and Hanan, R. V.
1970 Hydrologic factors affecting the utilization of land for sanitary land-
fills in northern Hillsborough County, Florida: Florida Bur. Geology
Map Ser. 39.

U.S. Department of Health, Education, and Welfare
1968 Land reclamation by accelerated stabilization: U.S. Public Health
Service Interim Rept. 127 p.