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Well design as a factor contributing to loss of water from the Floridan aquifer, eastern Clay County, Florida ( FGS: Inf...
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 Material Information
Title: Well design as a factor contributing to loss of water from the Floridan aquifer, eastern Clay County, Florida ( FGS: Information circular 35 )
Series Title: ( FGS: Information circular 35 )
Physical Description: iii, 10 p. : illus., maps ; 23 cm.
Language: English
Creator: Foster, J. B ( James B )
Geological Survey (U.S.)
Publisher: s.n.
Place of Publication: Tallahassee
Publication Date: 1962
 Subjects
Subjects / Keywords: Artesian wells -- Florida   ( lcsh )
Groundwater -- Florida -- Clay County   ( lcsh )
Genre: non-fiction   ( marcgt )
 Notes
Funding: Digitized as a collaborative project with the Florida Geological Survey, Florida Department of Environmental Protection.
 Record Information
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management:
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: aleph - 001692733
oclc - 01746281
notis - AJA4807
System ID: UF00001095:00001

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Table of Contents
    Title Page
        Page i
        Page ii
    Table of Contents
        Page iii
        Page iv
    Abstract
        Page 1
    Introduction
        Page 2
        Page 3
        Page 4
        Page 5
    Drilling and casing procedures
        Page 6
        Page 7
    Loss of water
        Page 7
        Page 8
    Discussion and conclusions
        Page 8
        Page 9
        Page 10
        Page 11
        Copyright
            Main
Full Text






STATE OF FLORIDA
STATE BOARD OF CONSERVATION
DIVISION OF GEOLOGY

FLORIDA GEOLOGICAL SURVEY
Robert 0. Vernon, Director





INFORMATION CIRCULAR NO. 35




WELL DESIGN AS A FACTOR CONTRIBUTING TO LOSS OF WATER

FROM THE FLORIDAN AQUIFER,

EASTERN CLAY COUNTY, FLORIDA




By
James B. Foster
U. S. Geological Survey





Prepared by the
UNITED STATES GEOLOGICAL SURVEY
in cooperation with the
FLORIDA GEOLOGICAL SURVEY



TALLAHASSEE
1962










AGRI.
CULTURAL
LIBRARY



































Completed manuscript received
September, 1961
Printed by the Florida Geological Survey
Tallahassee


i.














TABLE OF CONTENTS


Page

Abstract ............................................ 1

Introduction ...... ...... .. ... ...... ..... ....... 2
Drilling methods .......................... .... ..... ..... 6
Variations in casing procedures .................... ....... 6

Loss of water ........................................ 7
Loss of artesian head ................................... 8

Discussion and conclusions ............................... 8






ILLUSTRATIONS


Figure
1 Florida Peninsula showing the location of Clay County ...... 3

2 Clay County showing the area where wells tapping the Floridan
aquifer will flow ............. ... ................... 4

3 Diagrams showing four types of well-casing procedures used in the
construction of wells ..................................... 5
4 Clay County showing the decline of the piezometric surface in
eastern Clay County from June 1934 to June 1960.. ..... .. .. 10










































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WELL DESIGN AS A FACTOR CONTRIBUTING TO LOSS
OF WATER FROM THE FLORIDAN AQUIFER,
EASTERN CLAY COUNTY, FLORIDA


By
James B. Foster



ABSTRACT

A number of wells, penetrating the Floridan aquifer in eastern
Clay County wereifoQund to be losing water to permeable zones above
this aquifer.- A-differential in artesian pressure was observed in closely
spaced wells ofI similar depth. Further investigation revealed that
the .pressure differential in. the wells was due to the design of.the
wells, of which there were four principal types.

A comparison ofthe four types of wells in relationto the subsurface
geology showed that three types of wells were open to the permeable
zones above the Floridan aquifer. In such wells water of relatively
high head from the Floridan aquifer moves up through the well bore
and out into zones of relatively low head.

The estimated water loss from poorly designed wells ranged
from 32 to 180 gpm (gallons per minute). The artesian head loss in
leaky wells ranged from 3 to; 15 feet. A total loss of water of 39 mgd
(million gallons per day) was estimated from all the leaky wells in
the area.

A significant decline of the piezometric surface of. the Floridan
aquifer was observed in eastern Clay County. Some of this decline can
be attributed to the loss of water from the Floridan- aquifer through
these poorly designed wells.





FLORIDA GEOLOGICAL SURVEY


INTRODUCTION

Clay County is in the northeastern part of the Florida Peninsula.
(fig. 1). This report is concerned with the area in the eastern section
of the county that lies in the St. Johns River valley.

This area, which is shown by the crosshatched pattern on figure 2,.
is the part of Clay County in which wells tapping the Floridan aquifer
will flow. Most of the wells producing water from the Floridan aquifer
in Clay County have been drilled in this area. Although a few wells
have been drilled to obtain water for municipal and industrial use,
most wells have been drilled to obtain water for irrigation of truck
forms and pastures, and for domestic purposes. The population has
grown considerably in recent years in the area bounded by Orange Park,
Green Cove Springs, and Middleburg, and this growth has resulted in
an increase in the number of domestic wells .

An investigation of the water resources of Alachua, Bradford,
Clay, and Union counties is currently being conducted by the U. S.
Geological Survey in cooperation with the Florida Geological Survey.
During this investigation the artesian heads in a number of flowing
wells in eastern Clay County were measured and differential in artesian
pressure was observed between nearby wells of comparable depth, which
indicated that water was being- discharged from the Floridan aquifer
to other aquifers rather than to surface flow. This stimulated an interest
in the design of wells in the area, particularly in the casing procedures
used in the construction of flowing artesian wells. It appeared that
certain types of wells permitted water to be lost from the Floridan
aquifer to the zones above the aquifer.

A generalized geologic column for eastern Clay County is shown
in figure 3. Beds of sand and clayey sand are found at the surface
in a zone that is 5 to 20 feet thick. Below these surficial materials
usually are found beds of clay, shelly clay, clay containing shells
and phosphorite, and thin limestone. These beds form a zone that ranges
in thickness from 75 to 125 feet and overlies a thick sequence of alternate
hard and soft beds. The hard beds range in thickness from 5 to 25 feet
and are composed of one of the following: limestone, doloinite dolomitic
limestone, crystalline dolomitic limestone, or chert. Commonly the hard
beds grade downward from chert to crystalline dolomiticlimestone, to
dolomitic limestone, to limestone. The soft beds range in thickness





INFORMATION CIRCULAR NO. 35 3


Figure 1. Florida Peninsula showing the location of Clay County.






FLORIDA GEOLOGICAL SURVEY


, d as,' dW 35' 81 3d


i i t I I I I I I I I I I I 30'6


DUVAL COUNTY I
LCOUCNTY ORANGE







MIDDLECUT
















~_, 2 ^EXPLANATION

SFloridan aquifer will flow 5
0r < .- 55"







_


Area where wells topping theI I I I I I I I I45
Floridan aquifer will flow
0 2 3 4 5_6 7.5 9 I0m



Tr


82C05 82o00 565 5s 4 40' 35
Figure 2. Clay County showing the area where wells tapping the
aquifer will flow.


0


Floridon


from 10 to 30 feet and are composed of unconsolidated sand, clayey sand,
sandy clay, and clay; each bed contains phosphorite in varying amounts.
The total thickness of the succession containing alternate hard and soft
beds ranges from 175 to 250 feet. Beneath these beds are the water-
producing limestones of the Floridan aquifer. The Floridan aquifer (or
as it is known in Georgia, the principal artesian aquifer) underlies all
of Florida and southern Georgia and includes several hundred feet of
permeable limestone beds in eastern Clay County. Wells in the area
generally penetrate the Floridan aquifer as much as 100 to 350 feet but


.odf


mAk






INFORMATION CIRCULAR NO. 35


usually they do not exceed a total depth of 600 feet below the land
surface.

The piezometric surface of an artesian aquifer, such as the
Floridan aquifer, is an imaginary surface representing the pressure head
of the water confined in the aquifer. In eastern Clay County, in the area
outlined in figure 2, the piezometric surface of water in the Floridan
aquifer is above the land surface, and wells tapping the aquifer in this
area will flow.

Water in the Floridan aquifer is under a higher head than the water
in either the secondary artesian aquifers or the water-table aquifer both
of which are above the Floridan aquifer. Thus any open connection
between the Floridan aquifer and these other aquifers will permit water
to move upward from the Floridan aquifer and into these overlying
aquifers.


Figure 3. Diagrams showing four types of well-casing procedures used in the
construction of wells.






FLORIDA GEOLOGICAL SURVEY


DRILLING METHODS

Most of the wells drilled in the area are constructed by either
the letting or the cable-tool method. The usual procedure is to drive
a 20-foot length of casing, with a drive shoe attached to the bottom,
into the unconsolidated surface materials. The material in the casing
is then drilled out and an open hole is drilled below the casing. The
next step is to add a second length of casing to the top of the first
length and to drive it down to the bottom of the drilled hole. Because
the bit is operated through the casing, the diameter of the open hole
is somewhat smaller than the outside diameter of the drive shoe, and
the drive shoe must shear off a thin rim of rock around the hole as the
casing is driven. In this manner the drilling proceeds until one of the
hard beds of chert, dolomitic limestone, or dolomite is reached. It is
often impossible to drive the casing through these hard beds, thus an
alternate method of completing the well must be followed. Such a
situation has resulted in a variety of well-casing procedures.


VARIATIONS IN CASING PROCEDURES

There are four general types of well-casing procedures used to
overcome the situation where the casing is stopped by a hard bed.

One type of well in the area is shown by figure 3A. This type
is constructed by seating the casing on a hard rock and then drilling an
open hole to the top of the Floridan aquifer. A liner of pipe of smaller
diameter is lowered into the well and seated near the top of the Floridan
aquifer. The liner is sealed to the casing at the land surface to prevent
the flow of water through the opening between the casing and the liner.
Then an open hole is drilled into the aquifer to complete the well. This
type of well represents one of the most satisfactory methods of casing
and lining wells under the existing geologic conditions in the area.

A second type of well is shown by figure 3B; it is constructed
similarly, except that, instead of running the liner to the land surface
and sealing it to the casing, the liner is left a little below the top of
the casing and is not sealed. As a result, water moves up the well,
down between the casing and the liner, and into the permeable zones
below the casing and above the Floridan aquifer. (See the direction of L
movement shown by arrows.) Wells of this type could easily be changed






INFORMATION CIRCULAR NO. 35


to eliminate the loss of water, by sealing the liner to the casing with a
packer.

A third type of well is shown by figure 3C and is the most common
type in the area. Such a well is cased only to the first hard rock,
which in this area ranges in depth from 40 to 180 feet below the land
surface, and then an open hole is drilled from the casing into the Floridan
aquifer. In the beds below the casing and above the Floridan aquifer
there are permeable zones which absorb water from the well.

A fourth type of well is shown by figure 3D. This type of well
is cased to the first hard rock, and then an open hole is drilled to the
top of the Floridan aquifer. A short liner is set in the open hole to
prevent sand in the section above the Floridan aquifer from caving
into the well. After the liner is set in the well, an open hole is drilled
below the liner into the Floridan aquifer. In this type of well there
are permeable zones left uncased between the top of the liner and the
bottom of the casing which absorb water from the well.



LOSS OF WATER

Wells B, C, and D in figure 3 illustrate the situation where water
under the higher head in the Floridan aquifer is moving into the permeable
zones of lower head which are above the Floridan aquifer. At the present
time it is not feasible to measure the volume of water flowing from the
Floridan aquifer into the permeable zones through these wells. However,
it is possible to make some estimates of the losses from the Floridan
aquifer. The specific capacity (gallons per minute per foot of drawdown)
times the estimated loss of artesian head in the leaky wells is the
estimated loss of water from the Floridan aquifer. Specific capacities
of wells developed in the Floridan aquifer in this area range from 3 to
26 gprm per foot of drawdown. The estimated water loss in poorly
designed wells ranges from 32 to 180 gpm. Of the 69 wells inventoried,
14 were found to be leaking, and the total estimated loss of water from
the leaky wells amounts to about:1,000 gpm. It is assumed that 5 percent
of the existing wells were inventoried and it seems probable that the
same percentage of leaky wells would be found among all the wells in
in the area. If these assumptions are reasonably correct, the total
water loss would be about 20,000 gpm, or about 30 mgd.






INFORMATION CIRCULAR NO. 35


to eliminate the loss of water, by sealing the liner to the casing with a
packer.

A third type of well is shown by figure 3C and is the most common
type in the area. Such a well is cased only to the first hard rock,
which in this area ranges in depth from 40 to 180 feet below the land
surface, and then an open hole is drilled from the casing into the Floridan
aquifer. In the beds below the casing and above the Floridan aquifer
there are permeable zones which absorb water from the well.

A fourth type of well is shown by figure 3D. This type of well
is cased to the first hard rock, and then an open hole is drilled to the
top of the Floridan aquifer. A short liner is set in the open hole to
prevent sand in the section above the Floridan aquifer from caving
into the well. After the liner is set in the well, an open hole is drilled
below the liner into the Floridan aquifer. In this type of well there
are permeable zones left uncased between the top of the liner and the
bottom of the casing which absorb water from the well.



LOSS OF WATER

Wells B, C, and D in figure 3 illustrate the situation where water
under the higher head in the Floridan aquifer is moving into the permeable
zones of lower head which are above the Floridan aquifer. At the present
time it is not feasible to measure the volume of water flowing from the
Floridan aquifer into the permeable zones through these wells. However,
it is possible to make some estimates of the losses from the Floridan
aquifer. The specific capacity (gallons per minute per foot of drawdown)
times the estimated loss of artesian head in the leaky wells is the
estimated loss of water from the Floridan aquifer. Specific capacities
of wells developed in the Floridan aquifer in this area range from 3 to
26 gprm per foot of drawdown. The estimated water loss in poorly
designed wells ranges from 32 to 180 gpm. Of the 69 wells inventoried,
14 were found to be leaking, and the total estimated loss of water from
the leaky wells amounts to about:1,000 gpm. It is assumed that 5 percent
of the existing wells were inventoried and it seems probable that the
same percentage of leaky wells would be found among all the wells in
in the area. If these assumptions are reasonably correct, the total
water loss would be about 20,000 gpm, or about 30 mgd.






8 FLORIDA GEOLOGICAL SURVEY

When a poorly designed well is opened and allowed to flow freely,
most of the water that would be lost to zones of lower head will be
discharged at the surface. However, there are wells through permeable
zones that are not under artesian pressure, and these zones will continue
to absorb water from the well even when the well is opened and allowed
to flow. This condition is present in some of the wells in eastern Clay
County, where it was found that the well flow was considerably less
than the estimated volume of water being lost to the permeable zones.

In a sense, the water that is lost through these leaky wells is
not actually lost, because it recharges the permeable zones above the
Floridan aquifer. However, from the standpoint of recovery, the water
is lost because these low-pressure permeable zones are not used in
this area. The construction of a well in the low-pressure zones is
expensive, owing to the cost of screening that is required to keep the
sand out of the well.


LOSS OF ARTESIAN HEAD

When water is lost from a well by the movement of water from a
zone of higher head to a zone of lower head there is a resultant loss
of artesian head at the well. In a properly designed well there should
be no head loss due to leakage into the permeable zones above the
Floridan aquifer. If it can be assumed that wells of similar depth near
each other should have comparable artesian pressures, then the 14 wells
losing water had an accompanying loss of pressure head that ranged
from 3 to 15 feet.


DISCUSSION AND CONCLUSIONS.

From the available data it is not possible to determine the amount
of decline of the piezometric surface due to loss of water from the
Floridan aquifer. A map showing the decline of the piezometric surface
in eastern Clay County during the period from June 1934 to June 1960
shows a significant drop in head (fig. 4). The large increase in pumping
in the vicinity of Jacksonville, just northeast of this area, could account
for the major part of the decline in the piezometric surface, but certainly
a part of the decline must be the result of the estimated loss of 30 mg'd
of water from wells that were improperly designed. This would be;
enough water to supply a population of 150,000 to 200,000.






8 FLORIDA GEOLOGICAL SURVEY

When a poorly designed well is opened and allowed to flow freely,
most of the water that would be lost to zones of lower head will be
discharged at the surface. However, there are wells through permeable
zones that are not under artesian pressure, and these zones will continue
to absorb water from the well even when the well is opened and allowed
to flow. This condition is present in some of the wells in eastern Clay
County, where it was found that the well flow was considerably less
than the estimated volume of water being lost to the permeable zones.

In a sense, the water that is lost through these leaky wells is
not actually lost, because it recharges the permeable zones above the
Floridan aquifer. However, from the standpoint of recovery, the water
is lost because these low-pressure permeable zones are not used in
this area. The construction of a well in the low-pressure zones is
expensive, owing to the cost of screening that is required to keep the
sand out of the well.


LOSS OF ARTESIAN HEAD

When water is lost from a well by the movement of water from a
zone of higher head to a zone of lower head there is a resultant loss
of artesian head at the well. In a properly designed well there should
be no head loss due to leakage into the permeable zones above the
Floridan aquifer. If it can be assumed that wells of similar depth near
each other should have comparable artesian pressures, then the 14 wells
losing water had an accompanying loss of pressure head that ranged
from 3 to 15 feet.


DISCUSSION AND CONCLUSIONS.

From the available data it is not possible to determine the amount
of decline of the piezometric surface due to loss of water from the
Floridan aquifer. A map showing the decline of the piezometric surface
in eastern Clay County during the period from June 1934 to June 1960
shows a significant drop in head (fig. 4). The large increase in pumping
in the vicinity of Jacksonville, just northeast of this area, could account
for the major part of the decline in the piezometric surface, but certainly
a part of the decline must be the result of the estimated loss of 30 mg'd
of water from wells that were improperly designed. This would be;
enough water to supply a population of 150,000 to 200,000.






INFORMATION CIRCULAR NO. 35 9

The water loss and the resulting head loss from a poorly designed
well can seriously affect its usefulness to the owner. In some cases
the head loss makes the difference between using the natural pressure
of the well to supply water or having to install a booster pump with
the additional costs of power and maintenance.

As more information is obtained it will be possible to determine
more accurately the effect that water loss will have on water levels
in areas of the State where poorly designed wells permit the loss of
water from the Floridan aquifer. In the future, well design should be
an important consideration in the conservation of the ground-water
resources of Florida.







FLORIDA GEOLOGICAL SURVEY


UNITED STATES DEPARTMENT OF
GEOLOGICAL SURVEY


THE INTERIOR
50' 45'


Figure 4. Clay County showing the decline of the piezometric surface in eastern
Clay County from June 1934 to June 1960.


























































































































































































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FLRD GEOLOSk ( IC SUfRiW


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