TECHNICAL PAPER # 68
UNDERSTANDING
WATER WELLS
By William Ashe
Technical Reviewers
Douglas Denatale
Joseph Gitta
William Lorah
Robert Moran
P. Alen Pashkevich
Don Wells
Published By
VITA
1600
Wilson Boulevard, Suite 500
Arlington, Virginia 22209 USA
Tel: 703/276-1800 * Fax:
703243-1865
Internet: pr-info@vita.org
Understanding Water Wells
ISBN: 086619-307-3
[C] 1990,
Volunteers in Technical Assistance
PREFACE
This paper is one of a series published by Volunteers in
Technical
Assistance to provide an introduction to specific
state-of-the-art
technologies of intrest to people in developing countries.
The papers are intended to be used as guidelines to help
people chooe technologies that are suitable to their
situations.
They are not intended to provide construction or
implementation
details. People are
urged to contact VITA or a similar organization
for further information and technical assistance if they
find that a particular technology seems to meet their needs.
The papers in the series were written, reviewed, and
illustrated
almost entirely by VITA Volunteer technical experts on a
purely
voluntary basis.
Some 500 volunteers were involved in the production
of the first 100 titles issued, contributing approximately
5,000 hours of their time.
VITA staff included Patrice Matthews
handling typesetting and layout, and Margaret Crouch as
project
manager.
The author of the paper William Ashe, is the Director of
Lifewater
International. Mr.
Ashe has experience in drip irrigation,
wind mills and jet pumps. He has travelled in Haiti,
Dominican
Republic and Kenya.
The six reviewers who are all VITA Volunteers were, Douglas
Denatale who is employed by Whitman & Howard, Inc. and
is experienced
in geology, Joseph Gitta, self-employed in Beekeeping,
William Lorah, a civil engineer with Wright Water Engineers,
Robert Moran, a consultant in geology, P. Alan Pashkevich an
engineer in Georgia Tech Research Institute, and Don C.
Wells,
an engineer for the city of Portland.
VITA is a private, nonprofit organization that supports
people
working on technical problems in developing countries.
VITA
offers information and assistance aimed at helping
individuals
and groups to select and implement technologies appropriate
to
their situations.
VITA maintains an international Inquiry Service,
a specialized documentation center, and a computerized
roster of volunteer technical consultants; manages long-term
field projects; and published a variety of technical manuals
and
papers.
UNDERSTANDING WATER WELLS
By
VITA Volunteer William A. Ashe
BACKGROUND
Safe drinking water is a basic human need.
Yet, according to the
World Bank, water-borne diseases are the leading cause of
infant
mortality worldwide.
These diseases are among the most serious
found in the developing world.
There is no single community
project for development of long-term social and economic
well-being,
health, and comfort of a small community that is more
important than a safe drinking-water supply.
Wells provide access to ground water, which is almost always
safer and cleaner than surface water from lakes and rivers.
Digging a well appears simple, and inexperienced and
unskilled
people have made wells of many types, shapes, and sizes,
with a
variety of tools.
Such wells are usually not the best and often
prove dangerous during construction or after continued
use. Those
used to supply drinking water for humans are often
improperly
sealed at the surface and thus allow contaminated surface
water
to drain back into the well.
Contaminated water makes people
sick. Since the
microorganisms (bacteria and viruses) that cause
the diseases are too small to be seen, some people find it
hard
to believe that they are present.
They often do not trace the
source of their sickness to contaminated water.
This paper tells how to dig a well that provides safe
drinking
water for human consumption.
Wells for animals and irrigation
can be constructed to a much lower standard.
The paper intends to help people decide what type of well is
best
for them and whether hand-dug wells or drilled wells are
within
their means. Drilled
wells can be deeper, safer, and more durable
than hand-dug wells but their construction is more expensive
and
in many rural areas, the equipment or funds for drilling may
not
be available. Fortunately, simple machinery has been
developed
that can be used if money or expertise is not too scarce.
Although
this brings drilled wells within reach of some communities,
they remain too costly for others. In these cases, hand-dug
wells provide an alternative for producing safe drinking
water.
Many good "how-to" books are available that
describe in detail
the construction of different types of water wells.
A few are
listed in the Bibliography.
PRINCIPLES
Ground Water
When it rains, some of the water soaks into the ground and
is
trapped in porous soils.
Other water flows into and through
layers of loose or porous rock.
This is ground water.
Water
saturated layers of rock and soil that can yield a supply of
water sufficient for wells or springs are called
aquifers. The
level of the top of the saturated layers is called the water
table (Figure A).
The water table may be fairly close to the
38p02.gif (600x600)
surface or deep below ground. During rainy weather the water
table may be higher than normal and during dry seasons it
may be
lower.
How Wells Work
A water well is a hole that is dug, driven, or drilled
through
the earth, into the aquifier, to remove ground water for
human
use. The sides of
the hole can be left without support, but are
often supported by brick, stone, concrete, steel pipe, or
other
materials. Water is
removed from the well by a variety of
methods, of which the simplest is lowering and raising a
bucket
or other container.
A variety of pumps can also be used; these
may be hand operated or powered by petrol, electricity,
wind, or
other means.
Most hand-dug wells are less than 30 meters deep, but deeper
wells have been successfully constructed under special
conditions
(Figure B).
Machine-drilled wells have been drilled several
38p03.gif (600x600)
hundred meters deep.
When a hole, or well, is drilled or
dug into an aquifer, a pool develops
at the bottom of the hole.
If undisturbed,
the well will fill to the
level if the water table.
When the
well is finished and in use by drawing
water out, new water flows in to
refill the well; this process is
called recovery. The
rate of recovery
depends on the coarseness of the soil
and the amount of gravel in the aquifer.
In sand and gravel aquifers,
recovery is very fast.
In fine-grained
sand it is slower.
There are basically three sections to a well:
o
The sanitary seal at the top,
o
the well casing or well support in the
middle, and
o
the well intake or well screen at the
bottom.
The top section must be finished so that it stands higher
than
the ground and is sealed on the outside from surface water
that
would otherwise drain into the well.
Clay or concrete can be used
to seal the well for a distance of at least five meters away
from
the casing. The
middle section should be straight and well supported
with a strong wall or casing to keep the surrounding soil
from caving in.
The lowest, or water-bearing, section should extend as
deeply
into the aquifer as possible.
The well screen or well intake of the
lowest section must allow the water to
flow into the well but not admit fine
soil particles (Figure C).
For the
38p04.gif (600x600)
water to enter the well, it is important
that the well casing have many
small holes. If only
the bottom of
the casing is open to the aquifer,
only a small amount of water can be
pumped. If the casing in the aquifer
has many small holes (slots in steel
or plastic pipe, or drilled holes in
concrete) more water will be available
to the well and the water is likely to
be cleaner. This is
true because the
presence of many holes will lower the
entrance velocity of the water, which
thus will carry fewer particles.
Some wells are made without a casing.
In sandy soil, prefabricated concrete
rings, stones, or bricks can stabilize
the walls. But often
a concrete well
casing must be made in place.
Concrete
for well casings should be made from a
mixture of one part cement, two to
three parts sand, and four to five
parts gravel. To
make the more porous
concrete for the water bearing portion
of the casing, use one part cement,
one part sand, and four parts gravel.
Mix in the normal way with about five
gallons of water per 50 kg bag of
cement.
WHERE AND WHEN TO DIG THE WELL
Avoid areas of poor water quality.
Checking local maps and the closest
water wells to the proposed new site
can give valuable information on the quality of water that
can be
expected f rom the new well.
Samples of water f rom existing wells
can be sent to a laboratory to determine the mineral and
bacterial
content.
Contamination from surface sources must be avoided in
selecting
the proposed well site.
For example, avoid latrines, animal
stalls or barns, creeks, cemeteries, agricultural fields
(pollution
from pesticides, herbicides, etc.), and roads (fuels and
coolants). The well
should be constructed 50 to 100 meters from
the nearest potential source of surface contamination.
The water level in a well often changes from season to
season and
from year to year.
In dry seasons the water level will often be
low. wells that have penetrated the aquifer deeply are less
likely to go dry.
For this reason it is best to dig the well
during the dry season.
Some wells penetrate more than one aquifer
and are therefore more dependable for a permanent supply of
water. Moreover, water from deeper aquifers is less likely
to
be contaminated.
HEALTH AND SAFETY DURING CONSTRUCTION
Health Measures
During well construction, precautions must be taken to clean
any
tools that have been used in other projects because they may
be a
source of contamination.
The well should be covered after each
day's work to protect it from falling debris. Sanitary
toilets
should be provided for the construction workers, who should
be
warned against using the area near the well for this
purpose.
Defecating or urinating in the well during or after
construction
should be strictly prohibited.
Safety Measures
Many risks are associated with a hand dug well, especially
if the
open type is decided upon.
Understanding these risks and strictly
obeying simple safety procedures will minimize the chance of
an accident. The
biggest risk is a massive cave-in that traps
the diggers. Other
dangers arise from objects falling from the
surface on top of the diggers and misunderstood instructions
from
the diggers below to the workers above.
Without necessary vertical
supports and casing rings that stand above ground level, a
worker may accidentally fall into the well.
The rope and pulley
assembly used to lower objects into the well can fail or the
bucket can be allowed to descend too rapidly.
Heavy tools may
cause blows to the foot or hand.
Conditions inside a well are often hot and humid, and hard
labor
under these conditions can cause fatigue and fainting.
Fresh air
sometimes becomes displaced by other gases or it may become
very
scarce.
Petrol-engine exhaust and natural explosive gases from
within the earth are particularly deadly. Hence, a
ventilation
system is a must when working below 10 meters.
Pipes or hoses to
carry fresh air from the surface to the diggers must be
used. A
hand operated fan or bellows can be the responsibility of
one
person at the surface who ensures that the ventilation
system is
operating continuously while the diggers are working in a
well
deeper than 10 meters.
A further hazard arises when continuing to remove the soil
after
the water table is reached.
To dig the well deeper, the water
must be removed as it flows in from the surrounding aquifer,
either by pumping or with buckets.
The inflow carries soil with
it, thus undermining the part of the well hole below the
water
table. Eventually,
as the soil is brought out with the water that
is removed, a doughnut-shaped cavern will form around the
well
hole. This greatly
increases the danger of cave-in.
To minimize the danger, build a caisson
having the same diameter as the
well hole and lower it to the bottom
(Figure D). It can
be made of 200-liter
38p06.gif (600x600)
oil drums by cutting down one
side and splicing together as many as
are needed to reach the needed diameter.
If metal drums are not available,
wood or bamboo slats overlaid with
plastic sheet will do.
In this way,
the migration of silt and sand into
the hole will be prevented or greatly
reduced, while the water is being
removed to permit further digging.
The
caisson should be loose enough to
settle down as the hole is deepened.
If necessary, a second caisson can be
built and placed on top of the first
one.
V. WELL-DIGGING
METHODS
Whether hand or machine methods are used, digging is easiest
in
areas of loam, sand, or gravel and where small stones are
present
(Table 1). Digging a
well is very difficult in highly compacted
soils, fissured (cracked) rock, and rocky terrain.
It is important
to select the equipment most appropriate for the soil type
and terrain.
TABLE I
TYPES OF WELLS AND SOIL CONDITIONS
GENERAL GUIDE OF SIZES AND CONDITIONS
FOR EACH TYPE OF DRILLING SYSTEM
MACHINE DRILLED
HAND
HAND PERCUSSIONAUGERROTARYAIR
DUGDRILLED
HAMMER
Diameters
1-20m 10-20cm
15-50cm
15-50m 15-50m
15-50m
Depths
2-40m 10-50m
20-500m 20-500m
20-500m
20-500m
SOIL TYPES
FOR DRILLING
Top Soil
yes yes
yes
yes yes
yes
Sandy loam
yes yes
yes
yes yes
yes
Clay
yes yes
yes
yes
yes
yes
Silt
yes yes
yes
yes yes
yes
Sand
yes yes
yes
yes yes
yes
Sand stone
slow no
yes
no yes
yes
Lime stone
yes no
yes
no yes
yes
Gravel
yes yes
yes
yes yes
yes
Cobble stones
yes no
no
no no
no
Boulders
? no
no
no no
yes
Dense rock
no no
no
no no
yes
Hand-Dug Wells
Unsupported wells.
Open wells typically have diameters of 1 to 3
meters though wells larger than 4 meters in diameter are
sometimes
dug. The wells may
be 10 meters deep or less, without a
supporting wall and surface supports or frame.
Supported wells.
Hand-dug wells are generally built by one of two
methods. In the
first method, temporary forms are used to prevent
the walls of the well from caving in as digging goes
on. After
digging is completed, the temporary forms are removed and
the
wall is then reinforced with steel, plastic, bricks, rocks
or
cement casing. (Wood
or nondurable materials should be used only
for the temporary forms and not for permanent well
casing). This
method is faster and less expensive than the second type,
but is
more likely to cave in.
It is appropriate if the well is relatively
shallow and large in diameter and the soil is very compact.
The second type of hand-dug well is constructed by
reinforcing
the vertical walls as the well is dug so that when the water
table is reached, the reinforcement casing materials of the
first
and second sections are already in place.
The last portion of
the well to be completed (the water-bearing section) is dug
and
cased as deeply into the aquifer as possible.
Deep penetration
of the aquifer can be achieved if water is pumped from the
well
during construction (Figure E).
38p08.gif (600x600)
Concrete-Cased Wells
Wells can also be classified according
to the methods for making and installing
the concrete casing sections.
"Dig and Finish" wells vary in diameter
from one to three meters.
They are
constructed by completely digging the
first section followed by digging the
second section a meter at a time.
At
each meter of depth cement is poured
to finish the casing before digging is
resumed. This
sequence is repeated
until the aquifer in reached.
The
water-bearing section of the well is
then completed by lowering surface-constructed
casing sections to the
bottom and allowing then to sink into
the aquifer.
"Dig Complete and Finish Complete" is
a method used with wells that are
usually no deeper than 20 meters.
The
soil must be firm and temporarily
supported to reduce the risk of cave-in.
This kind of well is dug
without interruption until the aquifer is reached and then
is
finished by lowering the casing (made at the surface) into
the
well from the top.
A third method is "Pour and Form."
In this method forms made of
metal or strong plywood are placed at the bottom of the
completed
well. Concrete is
poured, and the forms are moved up about a
meter at a time until the well casing is complete.
Another type
of form is used at the surface, where its casing can be
constructed
without the restricted working conditions within the
well. After the
casing has cured, the forms are removed.
Reinforcement
rods are installed and locating rings can be formed
easily by the molds.
A major disadvantage of this and the
Dig-and-Finish types is the need for a heavy framework with
a
strong rope and pulley assembly to safely lower the heavy
concrete
casing into the well.
Hand-Drilled Wells
To drill a well 5 to 20 meters deep in soft soils, an auger
is
rotated at the surface by one or several workers using handles
attached to it. The
auger should be withdrawn from the hole at
every meter or so and cleaned at the surface.
When drilling is
completed, a plastic or steel casing should be lowered to
the
bottom. Usually,
hand pumps are then installed at the surface.
A percussion device can be used to drill a well 20 to 60
meters
deep through more compact soils.
A tripod or framework is supported
vertically with a rope and pulley (Figure F).
38p10a.gif (600x600)
The rope is attached to the drilling tool and in a bouncing
motion should be repeatedly pulled and dropped.
This will penetrate
the earth deeper and deeper as the weight of drilling tool
causes loosening of the soils.
Sometimes tools are constructed to
trap the earth inside, much like an auger, and are brought
to the
surface and cleaned each step of the way (Figure G).
Other tools
38p10b.gif (600x600)
are designed to loosen the soils, with a long narrow bailing
bucket to lower into the well.
Water is poured into the well to
form mud. The soil can then be removed with the bucket.
Machine-Drilled Wells
Small Machines.
Small well drilling machines with engines are
available to bore a hole in the earth.
These machines are efficient,
of moderate cost, and require only a few days to sink a
well. Water is
pumped down through the center of the drill pipe
to lubricate the bit in the bottom of the well.
As the drill rotates,
it cuts the soil, which is flushed back to the surface
with the returning water.
The water-mid slurry is then be pumped
back down the drill stem.
When the drill pipe penetrates all of
the aquifer, the well is completed as described below
(Figure H).
38p11a.gif (600x600)
Wells can also be driven into the earth with drive points
using
specially designed hammers or tripod driving tools (Figure
I).
38p11b.gif (600x600)
Large machines.
Larger wells (10 to 50 cm in diameter) can be
drilled quite efficiently with a truck-mounted machines
quite
efficiently using an auger, or a percussion, rotary, or air
hammer.
Steel or plastic casings are lowered when the drilling is
complete.
Several kinds of earth augers (Figure J) are used in well
drilling.
38p12.gif (600x600)
Each is suitable for a particular soil condition.
Another
method involves using an engine driven pump and water power
to
"jet" the well into the earth.
In this method, water is forced
down an inner pipe and through a cutting bit.
The water returns
to the surface through a larger pipe.
Both pipes are moved back
and forth to allow the cutting edge at the bottom to force
the
drilled and loosened soil to come up to the surf ace with
the
pumped water to the surface.
The pipes slowly sink into the
ground. The success of this method depends on soil
conditions.
Rocks or pebbles usually stop the process.
VI. WELL PUMPS
Suction and Down-Hole Pumps
An important decision is whether the water can be pumped by
suction or whether a "down-hole" pump must be
used. Suction pumps
can be used in
shallow" wells--those where the water tables less
than 8 meters below the surface.
A well with a water lifting
requirement greater than 8 meters is considered a
"deep" well
(Figure K). Atmospheric
pressure can force water up pipes to a
38p13.gif (600x600)
theoretical maximum of 10 meters. At greater depths,
operation
of a suction pump is
not possible. Down-hole pumps
can be used
at any depth.
The machinery or "action" (including the piston,
diaphragm, and
so on) of a suction pump is at the surface.
The action of down-hole
pumps is below the water table.
Positive-Displacement and Centrifugal Pumps
The two commonly used types of waterwell pumps for the wells
described here are positive displacement (or piston) and
centrifugal.
Each has its limitations and advantages.
Centrifugal pumps run at higher speeds
than can be obtained with hand operation.
They are usually powered by
petrol or diesel engines, or by electric
motors. Positive
displacement
pumps are used for hand-pumped wells.
Their cylinders can be mounted at the
surface and the water can be dispensed
from the well through a single pipe.
In deep wells, the cylinders can be
installed at the bottom of the well,
from where they push the water to the
surface. They can be
hand driven,
powered by a submersible motor at the
bottom, or driven by a shaft linked to
an electric motor at the surface.
Singlestage centrifugal pumps can be
used at the surface to draw the water
from shallow wells, but in deep wells,
several stages of centrifugal pumping
may be needed.
A jet pump (Figure L) is another type
38p14a.gif (600x600)
of centrifugal pump used at the surface
for pumping water from deep
wells. It circulates
water down one
pipe through a high-pressure nozzle
and returns it to the surface through
a second pipe when a small portion is
drawn off for use.
This system is
efficient only at depths less than 15
meters.
Power for Pumps
If hand pumps are not used, windmills may be a good choice
for
lifting water from shallow or deep water wells in rural
communities,
where conventional power supplies or fuel costs are very
expensive (Figure M).
The initial cost of windmills is high, but
38p14b.gif (600x600)
they are dependable machines and last many years.
When a single
well is to be used as a community project, a windmill can be
an
excellent investment.
Modern technology has produced solar cells that convert
sunlight
directly into electricity. one of the most important
applications
for solar cells, in rural areas all over the world, is water
pumping. Large
companies are competing to produce solar cells
cheaply, at a cost affordable in the United States and
developing
nations.
VII. CARE OF THE
WELL AFTER COMPLETION
Water in untapped aquifers is sealed from microorganisms and
is
therefore uncontaminated. Once well digging begins, the
aquifer
is exposed to then and other particles in the air.
For this
reason, after the well has been constructed, the water in it
must
be returned to a safe condition.
First, the completed well should be thoroughly disinfected
with
chlorine before anyone drinks the water.
Ordinary liquid household
bleach (containing 5.2 percent chlorine) is commonly used.
The procedure is as follows:
(1) Mix two liters of chlorine
bleach into 40 liters of clean water (see Table 2).
(2) Pour it
into the well. If a
hand pump has been installed at the surface,
pump the water through it and directly back into the well
for a
few minutes. (3)
Allow the well to stand idle overnight:
or at
least eight hours.
(4) Pump the treated water from the well until
no chemical odor is noticeable.
Verify your procedure with a local doctor or health care
worker
in advance. If
possible, a sample of water from the well (after
disinfection) should be sent to a laboratory to test its
safety
as drinking water.
TABLE II
AMOUNTS
OF CHEMICALS REQUIRED FOR A
STRONG
CHLORINE SOLUTION CAPABLE OF
DISINFECTING
WELLS AFTER THEIR CONSTRUCTION(*)
Water
Bleaching Powder High
Strength
Liquid Bleach
([m.sup.3])
(25-354) (g) Calcium
Hypochlorite (5% Sodium
(70%) (g)
Hypochlorite) (ml)
0.1
10
4.3
60
0.12
12
5.2
72
0.15
15
6.5
90
0.2
20
8.6
120
0.25
25
11
150
0.3
30
13
180
0.4
40
17
240
0.5
50
22
300
0.6
60
26
360
0.7
70
30 420
0.8
80
34
480
1
100
43
600
1.2
120
52
720
1.5
150
65
900
2
200
86
1 200
2.5
250
110
1 500
3
300
130
1 800
4
400
170
2 400
5
500
220
3 000
6
600
260
3 600
7
700
300
4 200
8
800
340
4 800
10
1 000
430
6 000
12
1 200
520
7 200
15
1 500
650
9 000
20
2 000
860
12 000
30
3 000
1 300
18 000
40
4 000
1 700
24 000
50
5 000
2 200
30 000
60
6 000
2 600
70
7 000
3 000
80
8 000
3 400
100
10 000
4 300
120
12 000
5 200
150
15 000
6 500
200
20 000
8 600
250
25 000
11 000
300
30 000
13 000
400
40 000
17 000
500
50 000
22 000
(*) This produces a chlorine concentration of approximately
30 mg/l
(ppm).
This water should not be drunk by people or
animals.
The community should be informed on how to keep the water
safe to
drink. Users should
be trained in simple health procedures and
general rules for proper water use.
Boiling or chlorinating
(Table 3) the water at home is often needed, in addition to
basic
well sanitation.
Washing or cooking should not be permitted in
the immediate area of the well.
Animals should be restricted from
the immediate area of the well and kept at a safe
distance. Only
repair and maintenance workers should enter the well.
Before the
well is put back into service after a repair, it should be
disinfected using the same method as when the well was first
put
into service. No
pools or stagnant water should be allowed to
collect around the well surface.
These pools can be breeding
areas for insects as well as for microorganisms, and can
spread
diseases that can be acquired by simply walking through
them.
No bucket or ropes with surface dirt should be allowed to
enter
the well. Ropes and
buckets used to draw water from the well can
transfer contamination from hands to rope and then to the
well
water. In this way,
any person later drawing water from the well
can take home enough microorganisms to make the family ill
when
they drink it.
VII. MANAGEMENT
CONSIDERATIONS
The need for a safe drinking water supply as expressed by
the
people of the community should be analyzed by workers who
are
responsible for deciding whether to construct the well.
Successful
projects require good leadership, planning, and execution,
but community initiative, planning, ownership, and support
are
essential from the start to ensure that the well is built
where
users want it, that the users understand how it will be paid
for,
that the well does not adversely affect the social structure
of
the community, that it is used, that the well and pump are
maintained,
and that water is clean when drawn and kept under sanitary
conditions by its users.
The first consideration should be for good water
quality. Other
considerations include cost and maintenance of the
system. What
is the total amount of money needed?
Where will the construction
money come from? Who will be responsible for repairing and
maintaining the well and the pump through the years?
If the
project is for several wells in a community, a number of
issues
must be carefully resolved to arrive at the proper
decision. For
example:
o
the local requirements for water
o
the kind of wells
o
the workers and their pay
o
the type of equipment to use
o
the costs and materials required for
construction
o
the availability of the materials
TABLE III
AMOUNTS OF CHEMICALS NEEDED TO
DISINFECT A KNOWN QUANTITY OF
WATER FOR DRINKING(*)
Water Bleaching Powder
High Strength Liquid Bleach
([m.sup.3]) (25-35%) (g)
Calcium Hypochlorite (5%
Sodium
(70%)
(g) Hypochlorite) (ml)
1
2.3
1
14
1.2
3
1.2
17
1.5
3.5
1.5
21
2
5
2
28
2.5
6
2.5
35
3
7
3
42
4
9
4
56
5
12
5
70
6
14
6
84
7
16
7
98
8
19
8
110
10
23
10
140
12
28
12
170
15
35
15
210
20
50
20
280
30
70
30
420
40
90
40 560
50
120
50
700
60
140
60
840
70
160
70
980
80
190
80
1 100
100
230
100
1 400
120
280
120
1 700
150
350
150
2 100
200
470
200
2 800
250
580
250
3 500
300
700
300
4 200
400
940
400
5 600
500
1 170
500
7 000
(*) Approximate dose = 0.7 mg of applied chlorine per litre
of water.
o
permits and advance approvals by local
authorities
o
financing of continued
operation/repairs/maintenance
The local availability of construction materials and water
lifting
devices should be a major factor in the selection of the
type
of well to be considered (Table 4).
Imported items will raise
the cost considerably.
Sometimes hand pumps or machine operated
pumps will be part of the project.
Their selection and maintenance
will require people with more advanced skills.
Local authorities must be consulted on laws and regulations
that
will apply to the new well project.
Someone must be assigned to
keep records so that details of the project can be
reviewed. The
records can often be used to resolve disputes or
misunderstandings.
TABLE IV
ADVANTAGES AND DISADVANTAGES
OF
VARIOUS TYPES OF WELLS AND PUMPS
WELL TYPE
ADVANTAGES DISAVTAGES
Hand
Inexpensive Unable
to dig deep into
Dug
water-bearing areas
Easy to do
Dangerous to construct
Easy to maintain
Contaminates easily
Machine Gets
deep in Cost more to drill
Dug
Water-bearing areas
Safety in drilling Site
must be accessible
Easy to seal Needs
expensive casing
Good for hand pumps
Requires skilled people
Usually safer water
Cylinder
Slow speed Small
volumes pumped
Pumps
Low
Cost
Easily repaired
Locally available
Simple equipment to
install
Centrifugal
Efficient High
cost
Pumps
Quiet operation
Usually an import item
More costly to
maintain
More skilled to repair
Needs high speed
driver
Large equipment to
install
Not adaptable to
windmills
BIBLIOGRAPHY
Brush, Richard E. "Wells Construction." Peace
Corps Information
Collection Exchange, 806 Connecticut Avenue NW, Washington,
D.C.
20525. Action
Pamphlet 4200.35, 1979.
Davis, S.N. and DeWiest, R.J.M.Hydrogeology.
John Wiley and
Sons, New York, New York, 1966.
DHV Consulting Engineers.Shallow Wells.P.O. Box 85,
Amerfsoort, The Netherlands, 1979
Driscoll, F.G. Groundwater and Wells, ed.2, Johnson
Division,
St. Paul, Minnesota, 1986.
Gibson, Ulric P. and Singer, Rexford D. Small Wells Manual.
Agency for International Development, Washington, DC 20523
USA,
1969.
Koegel, R.G. Self-Help Wells.Food and Agriculture
Organization
of the United Nations, Rome, Italy, 1977.
Peace Corps Volunteers.Construction and Maintenance of Water
Wells. Volunteers
for International Technical Assistance Inc.,
Schenectady, New York, 1969.
Village Technology Handbook.Volunteers in Technical Assistance,
1815 North Lynn Street, Suite 200, Arlington, Virginia
22209-8438
USA. 1988.
Watt, S.B. and Wood, W.E. Hand Dug Wells and Their
Construction.
Intermediate Technology Publications, London, England, 1979.
GLOSSARY
Apron - A slightly sloped concrete pad that surrounds the
well
and helps prevent contaminated surface water from finding
its way
back into the well.
Aquifier - A water-bearing layer (stratum) of permeable
rock,
sand, or gravel.
Bit - The cutting piece at the bottom end of the tool string
that
loosens the soil or rock to deepen the hole.
Bottom Section - That part of-the well that extends beneath
the
water table.
Casing - The vertical support inside the well.
Cement cylinders,
plastic, or steel pipe. Sometimes called caissons, lining.
Curb - A part of the well lining that extends out from the
place
and prevents it from sliding down.
Cutting Ring - A sharp-edged ring used on the bottom of a
lining
that is being sunk into place to make sinking easier.
Drop Pipe - That section of pipe in a deep well pump
assembly
that extends between the pump cylinder from flowing back
into
the well.
Foot Valve - A valve at the bottom of the suction pipe that
prevents
the water pulled up into it by the cylinder from flowing
back into the well.
Ground Water - Water contained in the part of the gorund
that is
completely saturated.
Ground water accumulates in quantity in
aquifiers, from which it can be drawn out of the ground
through
wells.
Hydrologic Cycle - Continual natural cycle through which
water
moves from oceans to clouds to ground and ultimately back to
the
oceans.
Intake Section - That part of the bottom section through
which
water enters the well.
Level (adjective) - Perfectly horizontal.
Level (noun) - A device used to establish a perfectly
horizontal
line.
Middle Section - That part of the well between the ground
surface
and the water table.
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