Title: A Primer on Ground Water
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Permanent Link: http://ufdc.ufl.edu/WL00004543/00001
 Material Information
Title: A Primer on Ground Water
Physical Description: Book
Language: English
Publisher: US Dept. of the Interior, Geological Survey
 Subjects
Spatial Coverage: North America -- United States of America -- Florida
 Notes
Abstract: Jake Varn Collection - A Primer on Ground Water (JDV Box 91)
General Note: Box 23, Folder 1 ( Miscellaneous Water Papers, Studies, Reports, Newsletters, Booklets, Annual Reports, etc. - 1973 -1992 ), Item 46
Funding: Digitized by the Legal Technology Institute in the Levin College of Law at the University of Florida.
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Bibliographic ID: WL00004543
Volume ID: VID00001
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Full Text


A PRIMER

ON

GROUND

WATER



UNITED STATES
DEPARTMENT OF THE INTERIOR
GEOLOGICAL SURVEY








A PRIMER ON

GROUND WATER
Helene L. Baldwin -'/
C. L. McGuinness V '


U.S. GOVERNMENT PRINTING OFFICE, WASHINGTON : 1963

































UNITED STATES DEPARTMENT OF THE INTERIOR

STEWART L. UDALL, Secretary



GEOLOGICAL SURVEY

Thomas B. Nolan, Director










Reprinted
1964


For sale by the Superintendent of Documents, U.S. Government Printing Office
Washington, D.C., 20402 Price 25 cents (paper cover)


p 2



















The water seekers . . . .
The water wizards . ..........
What is ground water? . .........
How good is ground water? . .......
W hat about wells? . . . .
Managing our ground-water resources . ..


ILLUSTRATIONS


The Brownsville area .............. ..
Folded and displaced rocks..... . . .
The water table and movement of ground water . . .
Zone of aeration and zone of saturation ......... ....
How water occurs in the rocks .................
Artesian aquifer and recharge area . . .
Overdrawn ground-water reservoirs in Western States.. . ..
Ground-water areas in the conterminous United States capable ol
yielding 50 gpm or more to wells. ... ............
Quality of water in relation to use .. . ..........
Relation of fresh water to salt water in a coastal area .. .....
Artificial recharge . . . . . .
Old-fashioned lift pump .........
Cones of depression . . . . . .
Flood-season map of conterminous United States .........
Total use of ground water in the United States, 1960 ... .... .


CONTENTS


Page


3
5
. . 5
10
15
22


Figur
1.
2.
3.
4.
5.
6.
7.
8.


9.
10.
11.
12.
13.
14.
15.


Page
2
4
4
6
6
8
9


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e

















A PRIMER ON GROUND WATER



Helene L. Baldwin and C. L. McGuinness


THE WATER SEEKERS


Most of us don't have to look for water. We
grew up either in big cities where there was a
public water supply, or in small towns or on farms
where the water came from wells. But there are
some people to whom finding a new supply of
water is vitally important.
Take John Jones, for instance. He is on the
town council of Brownsville, and has just bought
a farm a little distance from town, in the same
pleasant valley where the town is situated. There
is only one small stream in the valley, and it flows
all the way across the valley only after heavy rains
(fig. 1).
The town needs more water for its municipal
system. The present supply comes from widely
spaced wells. Some of the councilmen want to
consult a dowser, or water witch. As you may
know, the dowser claims that he can locate under-
ground water by the use of a magic forked stick.
When he is over water, the stick will twist or bend
downward of its own accord. Even if you try
with all your might to hold the stick upright, it
will bend downward-if you have the magic gift
of being able to locate water under the ground.
At least, that's what people who believe in dows-
ing say. Others haven't made up their minds on
the subject, and still others don't believe in this
magic. Scientists who have studied the subject
carefully know that, whatever else a dowser can


do, he cannot locate water reliably, with or with-
out his rod.
Some twentieth-century water wizards don't
use a forked stick, but can tell you where to dig
or drill for water much more accurately than the
old-time dowser. They are the geologists, engi-
neers, and other scientists who have been trained
in hydrology. They are called hydrologists, or
students of the science of water. They can aid not
only in the search for water, but also in its devel-
opment once the source has been found.
John recommends that the townspeople hire a
professional consultant, but he suggests that before
they do so they might consult the U.S. Geological
Survey in Smith City, where the Survey has set
up a local office to manage the studies it is making
in cooperation with State agencies. Hydrologists
there should know something about ground water
in the county where Brownsville is located.
How did John happen to think of the Survey?
Many people are not acquainted with its opera-
tions, and do not realize that geologists and engi-
neers of the Survey are constantly working with
State officials all over the country, mapping and
measuring water resources on and below the
ground. One day several years ago, John had
met a young man who was measuring a well near
John's former home. They fell into conversation
and John learned that the young man was em-


_ I


MOW-














































FIGURE 1-The Brownsville area.


played by the Survey to record the yield and level
of water in the wells in the area. He had for-
gotten about this incident, but now it came back
to him. He felt sure that the Survey people could
tell the town where the best supplies of ground
water might be.
John also hopes the Survey can give him a tip
on where and how he might put down a well for
his new farm. A friend of his dug a well on a
site recommended by the local dowser. The well
did provide water-for a while. Then it dried up
completely, in the middle of summer, when he
needed water desperately for his family, crops,
and cattle. John doesn't want that to happen to
him. Since his living depends on water, hit-or-
miss well sinking won't do. Finding the right
location and putting down a well that produces


a good, steady supply of water, year in and year
out, is a problem for experts-first, hydrologists
who can tell John Jones what his prospects are,
and then a competent well driller to put the well
down.
John, chosen by the council to consult the
Survey, went to Smith City and had a long talk
with the hydrologists there. Armed with much
useful general information, he drove back to
Brownsville. As he was driving along, it occurred
to him that the assurance of a steady supply of
good-quality water might attract new industry to
the town. He persuaded the council to contact
several small companies, and eventually the Smith
Co., which makes electronic equipment, located
in Brownsville. The Smith Co. likewise called on
the Geological Survey for the available general


_


I _








information, then hired a private consultant to
make detailed plans for water development.
State agencies and universities, too, maintain
hydrologists on their staffs, and have information
on local ground-water conditions. Wherever
they are, competent authorities should be con-
sulted. Ground water is not just water under the
ground. It is water held in the rocks by certain
forces, replenished by nature according to the
climate and the local geology, and consequently
variable in both amount and quality. No magic
means are necessary to locate it, just scientific
knowledge and plain common sense.
Our purpose in this booklet is to tell you the
basic facts about ground water, and what is be-
hind the need for the studies which enabled the
Survey to be helpful to the water seekers.

THE WATER WIZARDS
How does the hydrologist know where a well
can be drilled with successful results? How does
he know where to find water, a good, steady sup-
ply of it? He doesn't use a forked stick, like the
dowser's. His methods are more complicated,
but at the same time much less mysterious. He
goes out into the "field" or into a big city-
wherever there is a need to know about ground
water-armed with his geologist's pick and com-
pass, a steel tape for measuring water levels, a
current meter for measuring flow of water, and
other equipment needed for water prospecting.
Most important, he takes his scientific experience
and native curiosity about the why's and where-
fore's of water. Before he starts out, he arms
himself with the best maps of the area he can
find-preferably one of the Geological Survey's
own topographic maps. He reads carefully all
the publications he can find that relate to the
geology and hydrology of his area. In this way
he can check his own work against previous work,
and will not waste time redoing what has already
been done.
Our hydrologist knows that there is no simple
way of locating ground water. But he knows
something else that most people don't appreci-
ate-locating water is really the least of his wor-
ries! There is some water under the earth's
surface almost everywhere. This simple fact is
behind the seeming success of so many dowsers.
The hydrologist knows that in nearly all humid
areas, and in most arid areas as well, there is at
least a little ground water in the rocks below the


surface of the earth. The question is: How
much? How free is it to come into a well? That
is, can it come in fast enough to be useful? The
hydrologist has learned from his own experience,
and from that of hundreds of others who have
studied ground water all over the world, what
kinds of rocks water can be found in and where
to look for them.
Certain clues are helpful in locating ground-
water supplies. For instance, ground water is
likely to occur in larger quantities under valleys
than under hills. In arid regions, certain types
of water-loving plants give the clue that there has
to be ground water at a shallow depth underneath
to feed them. Any area where water shows up
at the surface-in springs, seeps, swamps, or
lakes-has to have some ground water, though
not necessarily in large quantity, or of usable
quality.
But the most valuable clues are the rocks.
Hydrologists use the word rock to mean both
hard, consolidated formations, such as sandstone,
limestone, granite, or lava rocks, and loose, un-
consolidated sediments such as gravel, sand, and
clay. They use the word aquifer for a layer of
rock that carries a usable supply of water. Gravel,
sand, sandstone, and limestone are the best water
carriers, but they form only a fraction of the rocks
in the earth's outer crust, and not all of them
yield useful supplies of water. The bulk of the
rocks consist of clay, shale, and crystalline rocks-
the term used for the great variety of hard rocks
that form most of the earth's crust. Clay, shale,
and crystalline rocks are all poor water producers,
but they may yield enough water for domestic and
stock uses in areas where no better aquifers are
present.
The hydrologist first of all prepares a geologic
map and cross sections showing where the differ-
ent rocks come to the land surface and how they
are arranged beneath the surface. He will ob-
serve how the rocks have been affected by earth
pressures in the past. Perhaps they are cracked
and broken so as to form openings that will carry
water (fig. 5). Or they may be folded or dis-
placed, as shown in figure 2. The geologic map
and sections and the accompanying explanations
will show just which rocks are likely to carry
water, and where they are beneath the surface.
Next he will gather all the information he can
on existing wells-their location, depth, depth to
water, and amount of water pumped, and what

3


7








kind of rocks they penetrate. Much of what he
is interested in is below the depth of ordinary
excavations, and he cannot afford to drill a well
or test hole in every place where he needs infor-
mation. Records of wells where the driller has
carefully logged the depth and type of different
rock strata are helpful. A really useful well record
will include the following: samples of the rocks;
information on which strata yield water and how
freely; where the water level stood in the well as
each successively deeper stratum was penetrated;
and data -from a pumping or bailing test of each
water-bearing stratum showing how much water
was yielded and how much the water level low-
ered at the given rate of pumping or bailing.
The hydrologist will then make a contour map
of the water table. The water table is the top of
the zone of saturation-the zone in which all the
rocks are saturated with water (fig. 3). The
hydrologist measures the depth from the land
surface to the water table at wells. Next he de-
termines, either from a topographic map or by
surveying, how high the land is above sea level.
Finally, he draws lines to connect all the points
of equal elevation of the water table, so that the
map shows the shape of the water table, in the
same way that a topographic map shows the
shape of the land surface. The water-table map
is especially important because it gives a clue not
only to the depth below which ground water is
stored, but also to the direction in which the water
is moving. If there is any slope to the water table,
the water moves in the direction of the slope
(fig. 3).
Where there are no wells, or not enough infor-
mation on existing ones, the hydrologist may have


to put down some test holes. If only a shallow
hole has to be put down, a small power auger,
which will bore to a depth of about 100 feet, can


Wouo,,"- W
A.-SMALL STREAM WHERE IT FIRST HAS
WATER IN CHANNEL


FIGURE 2-Folded and displaced rocks.


B.-DRY ZONE LIFTED UP TO SHOW
SURFACE OF SATURATED ZONE

FIGURE 3-The water table and movement of
ground water.


I -








be used. If a deeper hole is to be drilled, a profes-
sional well driller may be hired to do the drilling.
The samples of earth material brought up by
drilling are examined and analyzed to determine
which strata are water bearing and how large
an area they underlie. Drilling test holes is an
expensive business, generally costing a dollar or
more and sometimes as much as $30 a foot. A
deep hole obviously runs into a lot of money, and
unnecessary drilling would be wasteful.
Both on these test wells and on some of the
existing wells, the hydrologist will make pumping
tests, or aquifer tests. These scientifically con-
trolled tests are not really tests of the well itself,
but are designed to give information on the
water-bearing properties of the aquifer tapped by
the well. The test enables the hydrologist to de-
termine the amount of water moving through
the aquifer, the volume of water in the aquifer
that can enter the well, and what the effect of
pumping will be on the water level in the pumped
well and in other wells in the area.
Because quality is just as important as quan-
tity, he will collect samples of water from certain
wells, and have them analyzed chemically. From
this he will know what kind of water can be ob-
tained from different aquifers, and if samples are
collected over several years, how the quality may
change when large quantities of water are taken
out.
Thus you can see that there is no magic about
the hydrologist's work. It is based on common
sense and scientific observation. He uses all the
clues he can get-what he can see of the rocks as
they are exposed at the land surface or in road-
cuts, quarries, tunnels, or mines, and what he can
learn from wells.
These ground-water studies vary in complete-
ness with the need for information. If the need
is mostly for domestic supplies, an area the size
of a county can be studied in a summer, and the
report and maps prepared the following winter.
The hydrologist's report and maps will show
where water can be obtained, what kind of water
it is chemically, and in a very general way how
much is available. If a very large supply is
needed or if there are problems with the present
supply, more detailed studies must be made, either
in the area where the large need exists or, in some
cases, where a future need is anticipated. What-
ever the scope of the study, the report is designed
to provide a sound basis for whatever may follow


it, whether it is nothing more than drilling home
and farm wells, or large-scale water projects for
a city, an industry, or an irrigation project.

WHAT IS GROUND WATER?
It is hard to picture underground water. Most
people have a fanciful notion of an underground
lake, or a murky stream moving along slowly in
dark underground channels scarcely high enough
to stand upright in. There are such underground
streams in cavernous limestone or lava rock, but
they are not common. Mostly, ground water is
just the water filling pores or cracks in the rocks
(fig.5).
But if ground water is not a river or lake as we
think of them on the surface, how is it carried in
the earth? Why doesn't it soak through the
earth? It does not because the rocks at great
depth lack openings-pores or cracks-through
which water can move, or if they have openings
they are too tightly packed to let water move
through freely.
Between the land surface and the water table
there is a space which the hydrologist calls the
zone of aeration (figs. 4, 5). In the zone of
aeration there is usually at least a little water,
mostly in the smaller openings; the larger open-
ings in the rocks contain air instead of water.
After a heavy rain this zone may be almost satu-
rated; in a long, dry spell it may become almost
dry. In the zone of aeration, water is held to the
soil and rocks by forces the hydrologists call
capillarity, and it will not come into a well.
These are the same forces that hold enough water
in a wet towel to make it feel damp after it has
stopped dripping.
When rain falls, the first water that enters the
soil is held by capillarity, to make up for the water
that has been evaporated or taken up by plants
during the preceding dry spell. Then after the
thirsty plants and soil have had enough, and if
the rain still continues to fall, the excess water
will reach the water table-the top of the zone in
which the openings in the rock are saturated.
Below the water table, all the openings-crevices,
crannies, pores-are completely full of water (fig.
5). The raindrops have become ground water,
and this water is free to come into a well.
The reason the water below the water table will
come into a well, and the water above will not,
is a bit technical, but not too hard to understand.
The water above the water table, as in the damp




















FIGURE 4-Zone of aeration and zone of saturation.

towel, is sucked in and held against the pull of
gravity. The pressure in the water is less than
the pressure of the atmosphere, so it is forced by
atmospheric pressure to stay where it is. Below
the water table, all the water is under a pressure
greater than atmospheric. This pressure is suffi-
cient to force the water to move from one pore
into a larger one when the larger one is emptied.
A well is nothing but an extra-large pore into
which the pressure forces the water to move to
replace water drawn out by the pump.


% %, %
% %
%I


Thus, any well that extends below the water
table will fill with water up to the level of the
water table. If the well is pumped dry, it will
fill up again. The important thing is, will the
water come in fast enough to make the well useful
for a continuing water supply? A tight rock such
as clay or granite, with tiny pores or only a few
hairline cracks, may give up its water so slowly
that several days would be required for a well to
fill up to the level of the water table. Obviously,
such a rock would not be a useful water bearer.
On the other hand, the openings in the rock may
be large enough to let water through freely, so
that it can be taken out in useful amounts. The
amounts yielded to a well that justify calling a
rock water bearing range from a few hundred gal-
lons a day, where only a domestic supply is needed,
to as much as several million gallons a day.
The word aquifer comes from two Latin words:
aqua, or water, and ferre, to bring. The aquifer
literally brings water (underground, of course).
The aquifer may be a layer of gravel or sand, a
layer of sandstone or of cavernous limestone, or


Detail of water in zone
of aeration


,iRings" of capillary waters
(not ground water) surround
contacts of rock particles
as above


Approximate
level of the water table


All openings below water
table full of water-
ground water


Creviced rock


Gravel


FIGURE 5-How water occurs in the rocks.


I








even a large body of nonlayered rock that has
sizable openings.
An aquifer may be only a few feet thick, or
tens or hundreds of feet. It may be just below the
surface, or hundreds of feet below. It may un-
derlie a few acres or many square miles. The
Dakota Sandstone in the West carries water over
great distances, across several States. Many
aquifers, however, are only local in extent.
Underneath the water-bearing rocks everywhere,
at some depth, are rocks that are watertight.
This depth may be a few hundred feet, or tens of
thousands of feet.
The amount of water that a given rock can
contain depends on the porosity of the rock-the
spaces between the grains or the cracks that can
fill with water. If the grains are all about the
same size, or well sorted, as the geologists say, the
spaces between them account for a large propor-
tion of the whole volume. This is true of gravel
and sand. However, if the grains are poorly
sorted, that is, not all the same size, the spaces
between the larger grains will fill with small grains
instead of water. Poorly sorted rocks do not hold
as much water as well-sorted rocks. The gravel
in figure 5 is moderately well sorted.
If water is to move through the rock, the pores
must be connected one to another. If the rock
has a great many connected pore spaces, of which
a large part are sizable so that water can move
freely through them, we say that the rock is
permeable. Large amounts of water are avail-
able to a well from saturated permeable rocks.
But if the pores or cracks are small, poorly con-
nected, or nearly lacking, the aquifer can yield
only a small amount of water to a well. The
porosity of different kinds of rock varies widely.
In some the porosity is less than 1 percent; in
others, mostly unconsolidated rock such as sand
and gravel, it may be as high as 30 or 40 percent.
A rock that will be a good source of water must
contain either many pore spaces, or many cracks,
or both. A compact rock such as granite, almost
without pore spaces, may be permeable if it con-
tains enough sizable fractures. Nearly all con-
solidated rock formations are broken by cracks,
called joints by geologists (fig. 5). These joints
are caused by the same kind of stresses in the
earth's crust that cause earthquakes. At first they
are just hairline cracks, but they tend to open
through the day-to-day action of rain, sun, and
frost. The ice crystals formed by water that


freezes in rock crevices will cause the rocks to split
open. Heating by the sun and cooling at night
cause expansion and contraction that produce the
same result. Water will enter the joints and grad-
ually dissolve away the rock, enlarging the open-
ings.
If the joints intersect each other, water can
move from one to another, much as it flows
through the water pipes in a municipal water sys-
tem. Granite and slate are less porous than
sandstone. When water circulates in them, it
does so through joint cracks. The water yield of/
wells drilled in these rocks depends on how many
joints are intersected by the well, and how wide
they are.
Water will move faster in certain kinds of rocks.
A clayey silt having only very tiny pores will not
carry water very readily, but a coarse gravel will
carry water freely and rapidly. Sandstone is a
rock having natural pore spaces through which
water will move more easily than it will through
tighter rock, such as granite. Some rocks are what
we call cavernous; they have hollowed-out open-
ings in them. Some limestone is like this, and
water often flows through limestone at a faster
rate than through other formations. Gravel has
numerous open spaces. Water may travel'
through it at rates of tens or hundreds of feet per
day. In silt or fine sand it may move only a few
inches a day. Flow of streams is measured in feet
per second; movement of ground water is usually
measured in feet per year.
Ground water moves through permeable rocks,
and around and in between impermeable ones.
Just like surface water, it takes the path of least
resistance. Although it moves so slowly, it may
travel for miles before it emerges as a spring, or
seeps unseen into a stream, or is tapped by a well.
Fifty miles is not uncommon. In the Dakota
Sandstone beneath the northern Great Plains,
water travels hundreds of miles underground.
There isn't necessarily a relation between the
water-bearing capacity of rocks and the depth at
which they are found. A very dense granite may
be found at the earth's surface, as in New Eng-
land, while a porous sandstone may lie several
thousand feet below the surface, as in the Great
Plains. However, on the average, porosity and
permeability grow less as depth increases. Rocks
that yield fresh water have been found at depths
of more than 6,000 feet (and salty water has
come from oil wells at depths of more than 20,000








feet), but most wells drilled deeper than 2,000
feet find little water. The pores and cracks in
the rocks at great depths are closed up because of
the weight of overlying rocks.
The flow of ground water from rocks onto the
land surface, or discharge, takes place in several
ways. Water may seep into a stream through the
bed and banks, it may emerge as a spring, or it
may seep out to the surface in a swampy area.
The area where the aquifer is recharged with
water is higher than the area of discharge, so that
water moves through the aquifer by the force of
gravity (fig. 6). The recharge area is usually
where a layer of permeable material is close to the
land surface. The average amount of recharge
is an important consideration in the use of ground
water. There are areas in the Western States
where pumpage greatly exceeds natural replenish-
ment (fig. 7).
When rain falls, water enters the ground and
the water table rises; in times of drought, the
water table declines because of drainage to the
natural outlets. Because of this fluctuation, a
well that is not drilled very far below the current
water table may intermittently "go dry" when
the water table falls.
The words aquifer and ground-water reservoir
are sometimes used interchangeably, but generally
a ground-water reservoir is understood to mean


the whole "zone of saturation" from the water
table to the depth where openings in the rocks dis-
appear. Ground-water reservoirs provide water
for wells and springs and also supply water to
streams in rainless periods. We do not know
exactly how much these ground-water reservoirs
hold throughout the United States, but it is un-
doubtedly several times as much as all our lakes
and surface reservoirs put together.
Though similar in function, a ground-water
reservoir is obviously not quite the same thing as
a surface-water reservoir. For one thing, the
surface reservoir is used to regulate the flow of
streams. Water in the ground-water reservoir,
on the other hand, is not so easily regulated.
However, the rate of movement is so slow, com-
pared to that of streams, that for all practical
purposes these ground-water reservoirs may be
considered long-term media of water storage.
Ground-water reservoirs have certain practical
advantages over surface reservoirs: they do not
lose great quantities of water through evapora-
tion, nor do they fill up with sediment.
Besides moving horizontally and downhill,
ground water can move upward when it is con-
fined under pressure between two tight layers of
impermeable rock such as clay or shale. You
know that if the water is turned on and you acci-
dentally puncture the garden hose, water will


\ /Recharg area Water rises in
"~: i well to this


\ ezometric sur
/\CI C"N,
\\N,

%~
'EIclrock'

\ \\\%


Water flows from this well, and piezometric
surface is drawn down as shown
: ---sloping toward discharge area






Slpermeabled ..
NN'
"N ,"N


N- ,


FIGURE 6-Artesian aquifer and recharge area.


_____I-


/ i i i i~ii
I
B








GROUND-WATER RESERVOIRS WITH PERENNIAL OVERDRAFT


Santa Clara


Carpinteria
Valley


Storage progressively depleted
Areas of encroachment of inferior water
Remedial measures undertaken to balance draft and replenishment
? Insufficient data to be certain that overdraft exists
FIGURE 7-Overdrawn ground-water reservoirs in Western States.
(From ground water data by H. E. Thomas, The Conservation of Ground Water: New York, McGraw Hill Co.)


gush from the puncture hole. The water in the
hose has been confined under pressure and is
released by the accidental puncture. In the same
way, if an aquifer confined under pressure be-
tween layers of impermeable rock is pierced by a
well, water will rise above the top of the aquifer
and may even flow from the well spontaneously
(fig. 6). Water confined in this way is said to be
under artesian pressure, and the aquifer is called
an artesian aquifer.
The word artesian comes from the town of
Artois in France, the old Roman city of Artesium.
It was at Artois that the best known flowing
artesian wells were drilled in the Middle Ages.
Deep wells bored into rock to intersect the
water table and reach far below it are often called
artesian wells in ordinary conversation, but this


is an incorrect use of the term. Such deep wells
are just like ordinary wells. The word artesian
can be properly used only when the water is un-
der pressure, and the aquifer is confined between
layers of impermeable rock.
When ground water is not confined under
pressure, we describe it as occurring under water-
table conditions. For practical reasons hydrolo-
gists need to know whether they are dealing with
water under artesian or water-table conditions.
Generally, we can assume that artesian water is
continuous for some distance under the confining
layer of rock, and that it is replenished some dis-
tance away. Under water-table conditions,
ground water is recharged locally and is more
immediately responsive to precipitation. In gen-
eral, an artesian supply is less reliable for long,


I


t








continued long, use than an unconfined supply,
which is recharged more locally and easily.
Many people wonder what causes springs.
From what we have said about rising and falling
water tables, it is obvious that occasionally the
water table must rise high enough to intersect low
places on the land. A spring is a place where
there is natural discharge at the land surface of
water from a ground-water reservoir that is filled
to overflowing. There are different kinds of
springs. They may be classified according to the
type of geologic formation from which they come,
such as limestone springs or lava-rock springs.
Or they may be classified according to the amount
of water they discharge (large or small), or ac-
cording to the temperature of the water (hot,
warm, or cold), or by the forces causing the
springs (gravity or artesian flow).
Thermal springs are the same as ordinary
springs except that the water is warm, or, in some
places, actually hot. Many occur in volcanic
regions, and are fed by ground water that is
heated by contact with still-cooling rocks far
below the surface. There are many of these ther-
mal springs in Yellowstone National Park. Even
where there has been no recent volcanic action,
the rocks become warmer with increasing depth.
In some such areas, water may descend slowly
to considerable depth, getting warmer as it de-
scends. If it then reaches a large crevice in which
it can rise more quickly than it descended, it
will not have time to cool off completely before
it emerges, and we have another kind of thermal
spring. The famous Warm Springs of Georgia
and Hot Springs, Ark., are of this type.
Geysers are thermal springs which erupt inter-
mittently. Some spout only a few feet, others a
hundred feet or more. They may erupt at in-
tervals of a few seconds, minutes, hours, days, or
even weeks. Some erupt at intervals of years.
These eruptions may occur at more or less regu-
lar intervals or quite irregularly. A few geysers
erupt into pools of their own making, which are
beautifully adorned by deposits of silica. The
most famous geyser of them all, Old Faithful at
Yellowstone National Park, used to erupt about
every 66 minutes to a height of 110 to 160 feet.
But, since the earthquake in Yellowstone Park,
in 1959, its eruptions have become more
irregular.
Ground water slowly dissolves rocks and min-
erals, most conspicuously in limestone, dolomite,


and marble. Water percolating through these
rocks gradually dissolves them and forms caverns.
Some of these, such as Carlsbad Caverns in New
Mexico or Mammoth Cave in Kentucky, are
spectacularly large. The underground streams
that people so often picture in connection with
ground water occur only in such caverns. Else-
where ground water percolates slowly through
the rocks.
You may have wondered how the strangely
dramatic stalagmites and stalactites were formed
in these great caverns. Dripping water in the
caves deposits minerals. Where drops fall from
the roof of the cave, part of the water evaporates
and the deposits left behind form long mineral
"icicles." Those that grow downward are called
stalactites; those formed where the drops splash
on the cave floor and grow upward are called
stalagmites. Sometimes two of the formations
will grow together and form a column.
Where is ground water found in the United
States? It occurs nearly everywhere, but the ac-
companying map (fig. 8) shows areas where aqui-
fers typically will yield more than 50 gallons of
water per minute to a well. Three general types
of ground-water areas are shown: (1) a peren-
nial stream with the adjoining and underlying
water-saturated deposits, shown in solid color;
(2) loose sandy and gravelly water-bearing ma-
terials, including the productive aquifers of the
Coastal Plain, the High Plains, and western val-
leys, shown dotted; (3) consolidated water-bear-
ing rock, of which limestone, basalt, and sand-
stone are the most important, shown by diagonal
lines. The blank areas on the map are of course
not completely empty of ground water. Amounts
adequate for domestic use can be obtained in
most of them, though not all.

HOW GOOD IS GROUND WATER?
Ideal water, for most people, is spring water-
clear, cold, pure, and tasty. Ground water, on
the whole, is cleaner and purer than most surface
water. The soil and rocks through which it per-
colates screen out bacteria. But this does not
really mean that the water is completely pure.
Appearance isn't everything; the unseen qualities
are more important. We cannot see them with
the naked eye, but the delicious spring water may
contain many minerals, which give it the tangy
taste we like so much. Without the minerals,
it would taste flat and insipid. Some spring and


I r








well water, however, may contain so much dis-
solved matter that it is not fit to drink.
Water is a solvent. From the time rain falls
to the ground and begins to run off or pass into
and through soil and rocks, it dissolves the rocks
and thus picks up from them various mineral
constituents.
Because ground water is in contact with rocks
and soil longer than surface water, it usually has
more dissolved minerals in it. We call these dis-
solved minerals salts, and if there is a very high
concentration of them we call the water saline.
Such salts include, most commonly, sodium, cal-
cium, magnesium, and potassium, plus the chlo-
ride, sulfate, and bicarbonate needed to make
complete compounds. If the dissolved solids ex-
ceed 1,000 ppm (parts per million-that is, 1,000
pounds of salt for each million pounds of water)
the water is classed as saline. Water containing
more than 500 ppm of dissolved solids is not con-
sidered desirable for domestic supplies, though
more highly mineralized water is commonly used
where better water is not available.
Water that contains a lot of calcium and mag-
nesium salts is said to be hard. The hardness of
water can be measured according to the follow-
ing table, in terms of the amount of calcium
carbonate (the principal constituent of limestone)
or its equivalent that would be formed if the water
were evaporated:
Parts per million
0-60--------------_- ----- Soft
61-120 ----------------------- Moderately hard
121-180-_--------- ---------_ Hard
More than 180---------------------Very hard
Very hard water is not good for domestic sup-
plies because soap will not lather easily in it.
This is less a problem now than it was before syn-
thetic detergents were introduced, but detergents
have introduced problems of their own, as we
shall see. Hard water leaves a scaly deposit on
the inside of pipes, boilers, and tanks, and this
property reduces its suitability for both home and
some industrial uses. However, hard water can
be made soft at fairly reasonable cost. It is not
always desirable to remove all the minerals that
make water hard. Really soft water is likely to
corrode machines and boilers, and is suitable only
for laundering, dishwashing, and bathing.
Water for a municipal supply must strike a reason-
able balance between hardness and softness.


Another quality which must be considered in
water, whether from ground or surface sources, is
the balance between alkalies and acids. This
balance is known as the pH. A pH of 7 indi-
cates neutral water. Above a pH of 7, the water
is alkaline; below 7, it is acid. Alkaline water
will tend to form scale; acid water is corrosive.
Good water should be nearly neutral, neither too
alkaline nor too acid.
Excessive iron often occurs in ground water,
especially water that is a little on the acid side,
and it can be very annoying. It causes reddish
stains on fixtures and clothing. Like hardness,
an excessive iron content can be reduced rather
easily in a waterworks. All that is necessary is
to spray the water into the air so that it is exposed
to plenty of oxygen. The iron precipitates and
can be removed by settling or filtration. Some
home water softeners also remove iron.
In high concentrations, certain salts can cause
special troubles. Too much sodium chloride
(table salt) in the water can be harmful to peo-
ple who have heart trouble. Boron is a mineral
that is good for plants in small amounts, but is
poisonous in only slightly larger quantities.
All these and many other salts are present in
ground water to a greater or lesser degree. In
man's activities it is important to know the chem-
ical content and proportion of salts in the water
supply. For this purpose, chemical analyses are
made routinely and regularly on municipal and
industrial water supplies, whether from ground
or surface sources.
Mineral salts are natural ingredients of ground
water. However, disposal of industrial wastes
into ground and surface water is adding to the
accumulation of salts in our water. Industries
have always found it convenient to dispose of their
wastes in the nearest river, although in recent
years community action and legislation have some-
what restrained this practice. When stream
water is polluted by industrial wastes, the pollu-
tion can affect the water in adjacent aquifers.
This is because some ground-water reservoirs are
recharged by seepage from streams. For ex-
ample, the discharge of phenol wastes into the
Caloosahatchie River has made it necessary to
abandon some wells near Fort Myers, Fla. Oil-
well wastes have been dumped into the Canadian
and Arkansas Rivers in Oklahoma, and they have
contaminated some nearby wells. Chromium-
bearing wastes contaminated certain industrial






















'I


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1-*


/


I A
*'i A


/0


'9


I


EXPLANATION
Any pattern shows an area underlain by ar. saa.' r
generally capable of yielding to individual wells ju
gpm or more of water containing not more than
2000 ppm of dissolved solids (includes areas where
more highly mineralized water is actually used)

Watercourses in which ground water can be replen-
ished by perennial streams

SBuried valleys not now occupied by perennial streams

Unconsolidated and semiconsolidated aquifers (mostly
sand and gravel)

SConsolidated-rock aquifers (mostly limestone, sand-
stone, or volcanic rocks)

Both unconsolidated-and consolidated-rock aquifers

Not known to be underlain by aquifer that will gen-
erally yield as much as 50 gpm to wells


- -^ _--
S.A..
A. .


N'



K


S..3 N \


Note: Some productive ground-water area, mapped
recently are not shown. Information on them can
be obtained from offices of the U.S. Geological
Survey or of State geological and water-resources
agencies in the individual States.


FIGURE 8-Ground-water areas in the conterminous United Statt


I'


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/ E x A


. ., /


I

------~c ~c;










(













I N N E -1 rr X'I p

LqC 0 N S I




__ I





















M
AR NS I /
%-A OLU4A


r -d I
Li

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F1015 100 200 M ILES4
E




G r u d w t e a a b y H T h m s h e C n e v t i n o r o n a e r e o r M ~ a w H I C ,
ted tate capble f yildin 50 pm o mar to ells


I







wells at Waterbury, Conn., and also on Long
Island, during World War II.
Chemical fertilizers and pest controls also are
contaminating some water supplies. Their use
is increasing rapidly. No doubt they are enter-
ing fresh-water aquifers from fields and farms,
and we simply do not know what the long-term
effects of this form of contamination will be.
Synthetic detergents are proving to be another
threat to the quality of ground as well as surface
water. In some places detergent-bearing water
is dumped into streams that'are sources of re-
charge for ground-water reservoirs, or it seeps
from septic tanks into the ground-water reservoir.
Research is being done to determine at what con-
centration detergents become toxic, to overcome
their interference in conventional water-treatment
practices and to develop new materials that are
less resistant to natural decomposition than the
present ones.
Most people think of water pollution in terms
of bacterial pollution from human wastes. This
is certainly an important problem. The wide-
spread installation of modern sewer systems has
cleaned up the streets of our cities but has had
a marked adverse effect on rivers and in some
places even on ground-water supplies. Ground
water is naturally somewhat protected from the
effects of waste disposal by its mere inaccessibility
and the filtering action of soil and rocks. How-
ever, seepage from sewers and septic tanks can
contaminate an aquifer. Or floodwaters may
seep into ground-water reservoirs, carrying bac-
terial contamination along with them. Since it
takes an aquifer a long time to purify itself, it is
important to keep wells from being contaminated
by dirt or sewage. Wells should not be built near
privies or barnyards.
On the whole, ground water is of better sani-
tary quality than surface water. Even where
there are sources of contamination, the bacteria
tend to be filtered as the water passes through
the soil and rocks.
Water of different quality is needed for differ-
ent purposes (fig. 9). Water for drinking must
be free of harmful bacteria, and it must not con-
tain too many minerals, or it will be unpleasant
to taste, and may even make people ill. Water
used for irrigation should not have too many
minerals in it, either, and especially not too much
boron or too high a proportion of sodium. In-
dustry requires different kinds of water quality


for different processes. Water used to make syn-
thetic fabrics cannot contain too much iron, for it
will stain the fabrics. Water used for canning
peas and beans and other vegetables cannot be
too hard, or the vegetables will be tough. For
some processes, such as industrial cooling, cold
water of consistent temperature is necessary. For
many purposes, ground water if available is pref-
erable to surface water, because of its constant
temperature and bacteriological purity. Also, its
chemical content tends to remain more stable
than that of surface water, even if somewhat
higher, and this simplifies any treatment that may
be considered necessary for a particular use.
Where permeable rocks are in contact with
sea water, wells near the sea may become very
salty, if they are pumped excessively. Fresh
water is lighter than sea water, and literally floats
on the heavier sea water. Pumping upsets the
delicate balance between the fresh water and the
salt. The salt water then mixes into or en-
croaches upon the fresh water (fig. 10). If the
pumping is reduced, the excess salts may eventu-
ally be flushed out by fresh water recharging the
aquifer, but it may take many many years for
flushing to be complete. When the salt en-
croachment is severe, the reservoir may be spoiled
for future use. In many places, the local econ-
omy is dependent on pumping from these wells
and a reduction in pumping is not easy to ac-
complish.
Artificial recharge (figs. 10, 11) is being tried
as a remedy for salt-water encroachment. One
important example is in the Los Angeles area,
where it is vitally necessary to protect the fresh
water inland. By artificial recharge we mean that
fresh water is injected into an aquifer-in this
case, into specially dug wells along the shoreline.
The theory is that the fresh water will enter the
aquifer and set up a reverse gradient which will
force the salt water back (fig. 10).
Radioactive industrial wastes are a potential
hazard because wastes from nuclear-energy in-
dustries, if not carefully controlled, would con-
taminate water supplies. Civilian power reactors
are being built or are already in use in a dozen
States and in Puerto Rico, and others are
planned.
Water is the universal solvent, capable of dis-
solving more different substances than any other
liquid. Thus, if radioactive materials were re-
leased they could be transported in solution.








Water could be contaminated also by radioactive
materials buried in the ground. Earth materials
tend to attract adsorbrb") certain radioactive
substances, and thus can act as filters for these
substances so long as their adsorptive capacity is
not exceeded. Other radioactive substances,
however, may move freely through the ground
with the water. These are some of the reasons
why, though the nuclear-energy industry is small,
considerable effort is being expended in studies
of waste control in relation to water supplies to
assure the safety of our future supplies.
In the foreseeable future (A.D. 2000), many
areas of the United States will require complete
use of all their water resources. Water supply is
already scarce in some areas where nuclear facili-
ties are installed or are likely to be installed. We
cannot risk losing important sources of water by
radioactive contamination.

WHAT ABOUT WELLS?

Many people today have never seen a well
except in pictures. The wells pictured in books
are often the old-fashioned kind with a little
cupola over a bucket that comes up when the
crank is wound. Such wells were generally dug
by hand and were not very deep. However, even
a well dug by hand must be lined, or "curbed," to
keep the sides from falling in. A properly con-
structed dug well that taps a permeable aquifier
can have a large yield, but most dug wells for
home supplies are capable of yielding only 1 or 2
gallons per minute, when pumped steadily.
A well is drilled by means of a cable-tool drill-
ing rig which churns a bit up and down in the
hole, or it may be bored with a rotary drill. It is
lined with a long metal or plastic pipe called a
casing, which supports the walls so that rocks or
dirt won't fall in, and which also might serve to
seal off a zone containing poor-quality water.
The pump pipe hangs down inside the casing
below the water level. Most wells nowadays use
pumps to lift the water instead of only a bucket
on a rope. The old-fashioned pitcher or lift
pump can still be seen on farms or in villages
(fig. 12). Its raucous sound is familiar music to
many city dwellers who come from homes in the
country. It has a long iron handle; raising and
lowering this handle forces air out of the pump.
Water enters to fill the empty space left by the


air, and comes out in spurts. Most modern
pumps are driven by electric motors.
To test a well, you measure the water level;
then pump the well at a steady rate. The water
level will drop very fast at first and then more
slowly, as the rate at which water is flowing into
the well approaches the pumping rate. The dif-
ference between the original water level and the
water level after a period of pumping is called
the drawdown. The discharge rate is deter-
mined by a measuring device attached to the
discharge pipe. The ratio between the discharge
rate and the drawdown will provide the well's
specific capacity. For instance, if the drawdown
is 10 feet and the discharge rate is 100 gpm (gal-
lons per minute), the specific capacity of the well
will be 10 gpm per ft of drawdown. The hydrol-
ogist can take the results of carefully controlled
pumping tests and use them in formulas which
enable him to predict what will happen to water
levels in the future.
Pumping water from a well lowers the water
table around the well and creates a cone of de-
pression (fig. 13). Around small-yield wells in
productive aquifiers the cone of depression is
quite small and shallow. Wells pumped for irri-
gation or industry, however, may withdraw so
much water that the water table is lowered and
the cone of depression may extend for miles.
Locating wells too close together causes more
lowering of the water table than spacing them
far apart. This process is called interference.
Such interference may draw water levels so low
that pumping costs will be greatly increased.
There is a widespread popular notion that
there has been a progressive lowering of the water
table all over the Nation. It is true that in many
places water levels in wells are lower than they
used to be. This may indicate only that more
water is being withdrawn, not necessarily that it
is being withdrawn too rapidly. The water sit-
uation which is grave in a local area is not neces-
sarily symptomatic of trouble throughout the
country. For the Nation as a whole there is
neither a pronounced downtrend nor an uptrend.
Water levels rise in wet periods and decline in dry
periods, and in areas that are not heavily pumped
they average about the same as they did in the
past.
On the other hand, there are sizable areas
where ground water is being taken out faster than
it is replenished, and the water levels are lower-


U-















QUALITY OF WATER USED

PARTS PER MILLION
0 100 200 300


DISSOLVED SOLIDS
I HARDNESS


RAYON

ACETATE FIBER

PULP AND PAPER

GASOLINE

COPPER MINING

CARBON BLACK


FIGURE 9a-Quality of water in relation to use.














QUALITY DETERMINES USABILITY
tiwnr


PRINCIPAL PROPERTIES IMPORTANT TO USE


DOMESTIC INDUSTRIAL IR

FIGURE 9b-Quality of water in relation to use.


RIGATION







Land surface
tr table
-~eMasao,


NATURAL CONDITIONS


Pumped well

" e table


SALT INTRUSION


Pumped well
w I .a


A REMEDY
FIGURE 10-Relation of fresh water to salt water in
a coastal area.


ing persistently. Unfortunately, many of these
areas are in the dry Southwest, just where water
is scarcest (fig. 7).
Where the water table lowers persistently, it
means that more water is being taken out of the
ground-water reservoir than is being returned to
it from precipitation or streamflow. In some
places ground water is removed so much faster
than it is replenished that the process can be
called water mining. Obviously, the rates of
pumping and of precipitation are both important
in this connection. If there are many wells in
one area, all pumping at a very high rate, and
the rainfall is scanty or nonexistent over long
periods of time, then the water table will be low-
ered. Climate too is important. In many wells,
water levels decline when the weather is dry and
rise when it is wet. Another factor is the rate of
movement through the aquifer. If the rate of
movement is slow because the rocks are not per-
meable, not much water will come into the well
very quickly-even though a great quantity of it
may be available.
Aquifers are recharged by rain percolating
downward from the surface or by seepage from a
lake or a stream. The relation of a lake to ground
water is like that of a leaky dish or sieve set into
a sponge. In most cases, the aquifer will be
recharged where the permeable formation is near
the land surface. The area of recharge, where
rainwater or seepage actually enters the aquifer,
may be miles from the wells themselves, and
water moves very slowly underground. Or, even
if recharge occurs locally, it may occur at a very
low rate. Natural refilling of ground-water reser-
voirs thus may be a very slow process. It has
been estimated that if the ground-water reservoir
of the High Plains of Texas and New Mexico
were emptied, it would take many centuries to
refill at the present estimated rate of recharge.
Recharge generally occurs according to the
seasons. At different times, because of unusually
heavy rainfall combined with reduced evapora-
tion, or of snowmelt, there is enough water to sat-
urate the soil and reach the water table. In a
large part of the country, this usually happens in
the spring, at the same time that enough water is
available to cause floods in the streams (fig. 14).








In the summer, plants and trees use up most of
the rainfall, by transpiration through their leaves.
Only very heavy rainstorms are likely to recharge
ground-water reservoirs during the growing sea-
son; thus the water table usually declines during
that season. If there are heavy rains in the fall,
the water table will rise again, although not usu-
ally as high as in the spring. The water table
gradually sinks during the winter, and reaches a
low point in the spring just before the snow and
ice thaw and the spring rains begin. The pattern
is somewhat similar in the humid Southeast and
South, except that there is no snowmelt, and re-
charge must depend on rainfall. Floods and re-
charge thus may occur ip the winter. In arid
areas of the United States, ground-water re-
charge from rainfall is similar except that it may
be very low or even nonexistent. Western aqui-
fers depend largely on recharge from streams that


carry rainwater and snowmelt from the moun-
tains.
Gound-water reservoirs can be recharged arti-
ficially (figs. 10, 11). This technique, first used
in Denver in 1889, has been adopted in some other
parts of the country, especially in California. In
the Long Island area of New York City, consid-
erable ground water used for air conditioning is
returned to the ground through wells. Some
attempts to recharge a ground-water reservoir by
artificial means have failed. There is still a lot to
be learned about this technique and how or why
it succeeds or fails.
There are two chief ways of artificially re-
charging ground-water reservoirs. One is by
spreading water over the land through a spread-
ing ground or through pits, furrows, or ditches.
This method is used in the Central Valley of Cali-
fornia and in Peoria, Ill., among other areas.


7 Storm clouds
C -
.1 ,'* -"


'- S 'S Bedrock-,* s ,,- S s S *

FIGURE 1 -Artificial recharge.


1


r













x r


I
5-t?


FIGURE 12-Old-fashioned lift pump.


The other way is by pouring or injecting fresh
water directly into wells built for the purpose, as
in Long Island. This is a more expensive
method, and is justified only where the spreading
method is not feasible.
You may wonder why anyone would pour
water into a well only to haul it up again. Why
not keep the water on the surface to begin with,
if you have it to spare? But this is not a true
picture of what really happens.


Water used for recharge purposes is always
surplus water-water that has already been used
for some purpose, or water from high-flow pe-
riods of a river, which is not needed for use at
exactly that season. Such water, if not stored in
surface or ground-water reservoirs, would just
run down to the sea and be lost for beneficial use
by man. The purpose of recharging an aquifer
is not only to restore the water table to normal
levels, but to store surplus water for times when






A B
r' ;-'.-';^-: **''*'. '*';^<\;;.: ^^ '^ '*^*** *^ .^ ^ **'.^'* Int alw t r table











-- I / i i ~" .. i -'. ... ''-,, ". -. 1 _' .n a.


FIGURE 13-Cones of depression.


FIGURE 14-Flood-season map of conterminous United States.
(Flood data by W. G. Hoyt and W. B. Langbein, 1955, Floods: Princeton Univ. Press.)


if-


1


t








it will be needed. Storage of surplus water
underground has several advantages. The res-
ervoir is already built, though some cost is in-
volved in preparing it for recharge. And, the
water is protected to a considerable degree from
contamination and loss by evaporation.
Some aquifers are recharged as a byproduct
of irrigation. When water is evaporated from
growing plants, the dissolved salts are left behind
in the soil. If they accumulate, the soil will be-
come unfit for cultivation. For this reason, it is
necessary to apply more water than is actually
needed for growing plants. The excess irriga-
tion water seeps down and adds to the ground-
water supply. In the Shoshone Irrigation Project
in Wyoming, a normally dry rock formation be-
came saturated and turned into a ground-water
reservoir. The town of Powell, Wyo., has been
provided a municipal ground-water supply as a
result of this unplanned artificial recharge. In
the Snake River Plain of Idaho, seepage from
irrigation of the land has increased the water
stored in the ground by several million acre-feet
(3 acre-feet makes a million gallons). Seepage
from irrigation may cause the water table to rise
too high, however. If adequate drainage is not
also provided, the land may become waterlogged
and unusable for farming. The drainage may
be achieved by ditches or even by pumping from
wells.
Surface reservoirs may add water to the under-
ground reservoirs, in the same way that some
natural lakes do. The addition may be acci-
dental, if the reservoir bottom is leaky. But seep-
age through a permeable bottom may also be
deliberate, as in the case of the Santa Clara Val-
ley Water Conservation District in California.
As we have said, there are complications in
the artificial-recharge process. A recharge well
may become clogged by sediment, chemical pre-
cipitates, or growth of bacteria or algae. If a
well becomes clogged it must be cleaned or
pumped periodically, or the water treated before
it is injected. Geologic complications may pre-
vent recharge by water spreading and make it
necessary to sink wells for recharging.
Water for artificial recharge of wells or aquifers
must be of good quality. If sewage is used it
must be thoroughly treated, because once an
underground aquifer is contaminated by organic
or chemical pollution it may require years before
the aquifer can be purified by nature. The more


permeable the rocks in the aquifer, the faster the
contamination will spread. In very permeable
rocks, such as some limestone or basalt, it may
move miles in a few days or weeks. In sand or
sandstone it will move more slowly. If recharge
is done by spreading the water over the land, the
soil will act as a filter. The deeper the water
table, and the farther the water has to percolate,
the freer it will be of bacteria. Chemicals, in-
cluding synthetic detergents, are not screened out
in this way, however.
The increasing use of ground water, especially
in the West, has caused ground-water levels to
decline in some areas to the point where the water
is actually being mined; that is, more water is
being removed from the ground-water reservoir
than is being put back in by nature. To reduce
the amount of water pumped would in many
cases seriously dislocate the economy. Artificial
recharge-where it is economically feasible-will
be attempted more and more as a remedy for
declining water levels. To accomplish artificial
recharge successfully, certain data must be
known: the source of natural recharge, the nat-
ural direction and rate of movement of the
ground water, and the topography and geology
of the area. The main difficulty is that each
recharge procedure is a separate problem, and
must be tailormade to each situation.

MANAGING OUR GROUND-WATER
RESOURCES
There is water, more or less of it, more or less
accessible, almost everywhere under the earth.
As uses of water increase, this ground-water re-
source is becoming very important. We are
using more water than we used to, partly because
the population is constantly increasing. But this
is not the only reason. Increased uses by indus-
try, for irrigation, and for automatic washing
machines, dishwashers, garbage disposers, and
swimming pools are all placing an extra burden
on the country's water resources. The supply of
surface water is so variable that people have
tended to use ground water as a more reliable
source, where it has been available in needed
quantities. But now ground water is being in-
creasingly exploited as a principal source of
supply.
Ground-water reservoirs in 1960 supplied a
little less than a fifth of the Nation's water with-


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drawals. Figure 15 is a map which shows the
total use of ground water in 1960 by States.
Arid and semiarid areas in the West which used
to depend on ground water only during times of
drought now use more and more of it for irriga-
tion. In fact, irrigation is the largest single use
of ground water. During the 1950's the number
of irrigation wells in Nebraska, for instance, in-
creased about 25 percent each year. In 1960
there were more than 23,000 irrigation wells in
the State, and several billion gallons a day was
pumped during the irrigation season.
Even in the East people are now using more
ground water than they once did, taking advan-
tage of ground water's special properties. The
absence of sediment and bacteria and the con-
stancy of its temperature make ground water
more desirable than surface water for many uses.
Industrial use of ground water is growing all over
the country, but especially in the South and West.


Overall ground-water use more than doubled
from 1945 to 1960.
The use of ground water for public supplies
amounted to 6.3 billion gallons a day in 1960.
It was greatest in California, Texas, and Florida.
In 1960 there were 10 States each of which
pumped a billion gallons a day or more for all
uses. California, Texas, and Arizona used far
more than a billion a day (11.0; 9.1, and 3.2 bgd,
respectively).
In the past, this heavy ground-water develop-
ment has taken place with relatively little public
regulation. Water development was felt to be
necessary for economic benefits, and in any case,
water rights in States that followed the common
law inhibited legal restriction of development.
According to common law, rights to ground
water are based on ownership of the land. How-
ever, in the arid States where water is in short
supply, there has been increasing recognition of


SNote: Area of circle indicates water use.
HAWAII
a 25 million gallons per day
LASKA 150 million gallons
Sw per day
0 0o 150 MILES 1,000 million gallons
S- per day
FIGURE 15-Total use of ground water in the United States, 1960.








the doctrine of "prior appropriation" long used
for surface water. Under that doctrine, the first
user of water acquires priority to continue that
use, whether or not he owns the land from under
which the water drains to his wells. Western
States that wish to enact legislation to control
ground-water development have declared the
ground water to be public property. The few
Eastern States that have enacted laws so far have
tended to depend on the police power to regulate
water use in the public interest, under the
common law.
The use of so much ground water has created
new water problems. Under natural conditions
the hydrologic cycle tends to be in balance, but
man's use of the water upsets this balance. Use
of water without knowledge of the effects of use
or in disregard of them might be called exploita-
tion. In contrast, management of water re-
sources is use with knowledge of the probable
effects and with planning to minimize adverse
effects.
Early development in the High Plains of
Texas offers a good example of exploitation of
ground water. Largely as a result of heavy
pumping in the High Plains, Texas is second
only to California in its use of ground water; in
Texas it is the sole source of supply for nearly 600
towns and cities in the State, and is the principal
source used for irrigation. In 1960 Texas with-
drew about a fifth of all the ground water used
in the United States. Use of ground water is
heaviest in the southern High Plains, where it has
been stimulated by a long drought. In 1958 more
than 1,000 wells were added to the tens of thou-
sands already in existence, and water levels have
been declining for years. In this area, the water
reserve is gradually being mined.
The principal aquifer in the southern High
Plains of Texas, the Ogallala Formation, origi-
nally stored nearly 250 million acre-feet of water,
a very large quantity. Unfortunately, because
of the semiarid climate and flat surface (which
encourage evaporation at the expense of runoff
and ground-water recharge), the rate of replen-
ishment of the ground water is very low. At the
end of 1961 nearly 50 million acre-feet had al-
ready been pumped, and the current rate of
pumping is more than 50 times the estimated
recharge rate. Actually, the rate of withdrawal
will decrease gradually as water levels deepen.
Because of the cost of the pumping lift, a balance


will be struck long before the aquifer is depleted.
Surplus surface water to recharge the ground-
water reservoir artificially is not available. Arti-
ficial recharge through wells, using rainwater that
accumulates in depressions is being tried. How-
ever, this can help the situation only locally and
temporarily. Conservation measures to reduce
water waste are being used on an increasing
scale.
Strict regulation to limit the amount of pump-
ing would alleviate the situation, of course, but it
would effect a complete change in the economy
of the area. It is true that reversion to dry farm-
ing and grazing would reduce the water demand
drastically. Conversion of irrigated land to other
uses, principally housing, is already marked in a
few areas in Arizona and California, but so far
not in Texas. The economy of the High Plains
area is firmly based on ground-water mining.
Just leaving the water in the aquifer is less bene-
ficial than mining it. It is the rate of depletion
which causes concern.
What will happen when irrigation pumping
decreases greatly, as it inevitably will, is not cer-
tain. Under the laws of Texas, underground
water conservation districts have been formed in
the High Plains and are promoting conservation
measures to increase recharge, take advantage of
storm runoff for irrigation and artificial re-
charge, and reduce waste. Minimum well
spacing is required, to spread the pumping and
reduce the rate of water-table decline. The
problem is very much on the minds of the people
of Texas, and more and more thought is being
given to the future economic adjustments that
will have to be made. Thus the term exploitation,
as it implies development without knowledge of
the consequences, no longer applies. It is still
too early to use the term water management,
however.
On the Snake River Plain in Idaho, something
opposite to ground-water mining has happened.
The Plain is underlain by a very large body of
ground water. It also is an area of little precipi-
tation. But here rainfall and snowmelt in the
mountains feed the rivers, and much surface
water is used for irrigation. Excess irrigation
water has filtered into the ground and joined the
original ground-water body, increasing the rate
of discharge of ground water into the Snake
River by nearly 50 percent. In this area as a
whole, to date, water has not been mined; it has


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been put in the bank. A tremendous ground-
water reserve has been building up and could be
managed to great advantage.
For an example of good water management,
consider Louisville, Ky. During World War II,
pumping from closely placed industrial wells in-
creased greatly. From 37 million gallons a day,
use rose to 75 mgd, and the water levels in some
wells declined nearly to bedrock. The city offi-
cials and the War Production Board called on
the U.S. Geological Survey for advice. Survey
hydrologists in cooperation with local and State
agencies mapped the aquifer and studied its rate
of natural recharge. It became clear that Louis-
ville was living beyond its means, so far as ground
water was concerned. The adjacent Ohio River
was available, but substitution of its water for
that from wells would have been difficult or im-
possible, in view of shortages of critical materials
such as pumps and pipe. Conservation meas-
ures were adopted as rapidly as possible to re-
duce the ground-water draft, and filtered city
water from the river was injected into wells at
two plants where conditions were most critical.
The water was injected during the winter, when
it was cold, and thus made the wells even more
effective for their principal use, for cooling, when
the water was repumped the next summer. The
ground-water draft is now stable and water levels
have recovered to previous stages throughout
most of the area.
Good management of ground-water resources
depends upon knowledge of basic water facts.
We need more detailed studies of ground water
in local areas, and more basic research on replen-
ishment and movement of ground water. We
need to know more about ground-water chem-
istry also. We must continue to improve our
methods of storing surplus water in underground
reservoirs.
The ground water that seeps into streams pro-
vides the base flow of the streams-the low flow
that is sustained through the driest part of the
year. If water levels decline because of heavy
pumping, the base flow of streams will be re-
duced. Ground and surface waters are inex-
tricably connected and should be studied to-
gether. In plans for river-basin development
ground water has commonly been neglected, yet
plans for river basins may vitally affect the
ground-water reservoir, and vice versa. The
rate of natural replenishment need not limit the


use of ground water if floodwaters can be used
to increase recharge artificially. River-basin de-
velopment might include a coordinated program
of flood control and artificial recharge.
However, even the hydrologic facts on ground
water are not enough. We must know also what
the demand is for water in a given area, what the
economic trends are, what the future demand
may be. What will be the effects of withdrawal
and use of water upon the ground-water reser-
voir? In our water-resources bank the book-
keeping still is not adequate.
The Geological Survey has collected a great
deal of information on ground-water resources,
much of this work having been done in coopera-
tion with the States, and some States are making
studies on their own. Much remains to be done,
however, and there are few areas in which the
scale of the program is yet adequate to meet the
growing needs.
Are there any ways of saving ground water,
or making it go further in areas where it is des-
perately needed? Ground-water problems are
most critical in the Western States. The popu-
lation of these States is expected to increase faster
than the national average. Availability of ground
water for agriculture, public supplies, and in-
dustry is therefore especially important in the
West. There are several measures which, if un-
dertaken on a large scale, would conserve the
supply of ground water. Some crops require a
good deal of water. Other crops using less water
perhaps could be substituted in some areas. Nat-
ural replenishment can be increased in many
places by increasing the rate of infiltration into the
soil or streambeds. Certain nonuseful plants and
shrubs, such as saltcedar, consume great quan-
tities of water. Research to discover feasible
methods of controlling their growth or eradicat-
ing them completely is now active. Reduction
of evaporation from reservoirs, and even of tran-
spiration by certain methods of soil treatment,
holds some promise. Gradual conversion from
irrigation to uses that extract more dollars from
a given volume of water is bound to be a prin-
cipal method, but economic disruptions must be
minimized.
Where feasible, water of inferior quality in-
stead of first-quality water could be used for cer-
tain industrial processes. For cooling and certain
other purposes, the same water can be used sev-








eral times. The process of desalination of brack-
ish water is being refined and improved, and it is
hoped it will eventually become more economical.
Irrigation, municipal, and industrial use could
all be regulated by the States to maintain economy
of use and prevent waste. Surplus surface water
could be stored in underground reservoirs. None
of these measures is easy or inexpensive, but some
or all of them will become necessary as time goes
on.
In the past, the problem used to be to locate
ground-water supplies. Now, with years of ex-
perience behind them, geologists and well drillers
can find water very quickly and easily. The real
problem is not to find water but to evaluate the
ground-water resource and to manage it prudent-
ly, once we have found it.
Ground water is our principal reserve source
of fresh water. You may not have a well on
your property. You, as an individual, may use


little or no ground water. Yet your city, the in-
dustry where you are employed, or the farm that
produces some of your food may depend on
ground water for supply or for emergency re-
serve. If a nuclear war should contaminate
surface water supplies, ground-water reservoirs
may be the principal or even the only uncon-
taminated sources of water.,
Thus, every individual has a stake in our
ground-water resource, whether he is a well owner
or not. Groups of individuals in a community
will have to make decisions regarding water sup-
ply and disposal--decisions which may affect the
ground-water resource, or be affected by it. The
citizen can make a sounder decision if he has
some understanding of the principles of ground-
water occurrence. Even the simple facts con-
tained in this primer can help people make wiser
judgments about the use of our ground-water
resource.


* U.S. GOVERNMENT PRINTING OFFICE: 1964-0-741-747

















































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