TECHNICAL PAPER ## 61
L. C. Diaz
1600 Wilson Boulevard, Suite 500
Arlington, Virginia 22209 USA
Tel: 703/276-1800 . Fax:
Understanding Low-Cost Well Drilling
[C]1990, Volunteers in Technical Assistance
UNDERSTANDING LOW-COST WELL DRILLING
VITA Volunteer Stephen Greenwood
Safe drinking water is a basic human need.
For a small community,
no single project is more important to long-term social and
economic well-being, health, and comfort than a safe
Ground water is a very common source of drinking water.
to build a well to tap and use ground water, people must
first decide between hand-dug and drilled wells.
can be deeper, safer, and more durable than hand-dug wells,
their construction is more expensive and technically
Fortunately, most of the equipment for drilling a small well
be manufactured locally.
In addition, simple and relatively
inexpensive machinery for drilling wells has now been
that can be used if money or expertise is available.
THE PLANNING STAGE
Care in planning the design and location of a water well
extra effort, but improves the likelihood of building a
well. In the early
planning stages, these items must be taken
into account: the
specific needs of the community regarding well
location and required amounts of water; the collection of
geological data; site inspection to avoid contamination; and
ground water exploration, if there are no other wells in the
In selecting the site, avoid areas of possible
Checking local maps and the closest water wells to the
site can give valuable information on the amount of water
can be expected from the well.
Samples of water from existing
wells can be sent to a laboratory to determine the mineral
Contamination from surface sources must be avoided in
the site. The well
should be constructed at least 50 meters (m)
from the nearest potential source of surface
sources include latrines, animal stalls or barns, polluted
creeks, cemeteries, agricultural fields (pollution from
and roads (petrol and oil).
The next steps are to identify the best drilling method
geological factors and local experience; determine such
as the material and size of the casing, approximate depth
of casing and well screen, and labor requirements; and agree
the persons who will be responsible for record keeping,
and maintenance of the well.
A number of items influence well performance
and design. These
formations penetrated by the well, ground
water recharge or rate of replenishment,
amount of water needed, and type of soil in
the aquifer (water-bearing formation below
the surface of the ground).
A complete or
"engineering" analysis of these factors is
beyond the scope of low-cost, manually
Nevertheless, decisions must
be made on the location, well diameter,
length and type of well casing and well
screen, grouting, and type of pump if
necessary (Fig. 1).
(This paper does not
describe pumps; the VITA Technical Paper on
"Understanding Water Wells" and other
references contain pump information.)
The well casing prevents the collapse of
the bore hole and protects the pumping
major cost items, it ranks
after the pump. A
costs only a little more and lasts longer.
For steel casing, use "standard wall"
(schedule 40 steel) or thicker.
Plastic well casing is most widely used,
especially for shallower wells, because of
its low cost, good handling properties,
high corrosion resistance, and likelihood
of local manufacture.
A 15-cm diameter
polyvinyl chloride (PVC) casing should have
a minimum wall thickness of 0.6 cm.
diameter polystyrene (ABS) pipe should have
a minimum wall thickness of 0.5 to 0 6 cm.
Determining the depth at which the casing
should stop and the well-screen should
start requires careful observation by the
well driller. The
casing usually ends 2 to
3 m below the top of the aquifer.
The Well Screen
Well-screen design is a critical element in planning the
The screen permits water to flow into the well and keeps
gravel out. It must
be strong enough to prevent the collapse of
the bore hole, but should not excessively restrict water
features of a well screen are as follows:
high proportion of open area, close spacing of the slots,
strength to prevent collapse, single-metal construction
(including screws, if possible) to prevent corrosion, and
fittings for installation.
The four common types of well screen are continuous slot,
pipe, low-level sawn slot, and perforated pipe (Fig. 2).
The continuous-slot screen that is commercially available
more intake area per square meter (sq m) than any other type
screen, but can be expensive.
However, its use in economical when
the aquifer is not thick and is high yielding.
But if a low flow
rate within the aquifer is causing a slow recharge, a
number of openings will not increase it.
Louvre-slotted and perforated pipes can be easily and
made in most locations.
It is often best to select them even
though they are less efficient than some other types.
plastic pipes are being used more often in small diameter
because they are light in weight, noncorroding, and
The slots can be made at the construction site with a sharp
The length of the screen depends upon the thickness of the
pumping rates, aquifer particle size, and the type of
the exact dimensions requires experience.
small-diameter wells, doubling the length of the screen will
double the amount of water from the well.
Placing the screen at
the bottom of the aquifer will decrease the chance of a dry
during a period when the water table is low.
If it is not possible
to put the screen there, the top of the screen should
generally be at least 2 m below the top of the aquifer.
Selecting the Size of the Screen Openings
The choice of hole and slot size will depend on the particle
size of the sand and gravel in the aquifer.
In order to maintain
the strength of the pipe, the holes should not be too
spaced. Most locally
made pipes have a small open area but are
adequate for general use.
During final stages of drilling, a soil sample should be
from the formation where the screen will be placed.
screen size opening can best be selected by using a
selector field kit (Fig. 3).
Although the kit is not absolutely
necessary to well construction, it is described here to aid
understanding the relation of screen size to soil particle
The device is a box with removable square screens.
lines are drawn along the inside of the box.
Wire mesh screens
with openings of five different sizes are placed inside the
with the largest opening at the top of the box.
A dry sample from the soil in the aquifer is placed in the
compartment and thoroughly shaken.
The box is then placed on its
side and the side door is opened.
Using the drawn lines, the
height of each fraction of the sample between screens is
If the total amount of sample is known, the percentage of
the sample that passed each screen can be calculated.
that lets about 40 percent of the sample pass through should
selected to represent the screen-opening size that should be
used. The slots will
seldom be more than 3 millimeters (mm) wide.
SANITARY PROTECTION DURING CONSTRUCTION
Contamination of the well during construction can spoil the
site and make the well unusable for a while.
Here are the steps
to be taken while the well is being built to protect it f
o The well should always be covered when work is not in
o The well casing should extend at least 0.5 m above the
known flood level.
o The ground around the well should be sloped to drain water
from the well.
Building a concrete slab around the well
reduce the amount
of mud during construction.
o The casing joints should be tight so that no water seeps
o The space between the bore hole and the well casing should
concrete grout to at least 3 m below the ground.
Well construction consists of six basic operations:
casing installation, screen installation, gravel packing,
There are two drilling methods, percussion
and rotation. The
well driller must know the advantages and
limitations of each method to determine which is best suited
the geological formation and local experience.
For example, both
types of drilling methods may be used for the same
well. If there
is soft sandstone above a hard "rock" (compacted
a rotation method can be used to drill through the sandstone
a percussion method used in the hard formation.
Percussion methods raise and drop a heavy drill bit to break
the soil. The
material can then be removed f rom the hole by
several means, including a cable-driven bailing bucket and a
bucket. In soft
formations, the cut material is merely pushed
into the sides of the well.
The drill bit may be raised either manually or with a
methods of manually raising the drill bit are shown in Fig.
The drill bit should be raised about half a meter before it
dropped. A bouncing
action is preferred; as the cable stretches
and springs back from the impact of the drill tool, lifting
action is applied to keep it bouncing.
Experience develops this
skill. When the
reverse-circulation technique is used, flowing
water assists the percussion drilling process.
The drill bit can be mechanically lifted by the use of a
(capstan) attached to a jeep, truck motor, or other power
(Fig. 5). The
cathead consists of a metal spool, welded together
from a scrap section of metal pipe and two steel disks, one
which is drilled and bolted to the vehicle (Fig. 6).
should be parked 4 to 6 m from the well, the rear end
placing rocks under the axle for support.
The rear wheel is
removed and a cathead is attached to the wheel hub.
The rope or
cable supporting the drill bit is wrapped around the
Alternately tightening and loosening the rope will allow the
rotating cathead to raise and drop the drill bit.
ropes and cathead are very dangerous, they should be covered
to protect the operator from accidental injury.
The drill bit is turned to create the hole.
wood rod handles or chain tongs clamped to the drill rod as
in Fig. 7. Examples
are the bored (augered) well and the jetted
well. Jetting uses
water to assist the action of the drill.
Common Materials and Methods
The items required for well construction can include:
pipe, well screen, pipe couplings, concrete mix, tripod,
ropes, drill bit, bailer, "fishing" tools,
metal files, pipe wrenches, screwdrivers, shovels, measuring
tape, plumb bob, chain tongs, pipe-joint sealing material,
saw, wire, cold chisel, pipe dies, rod dies, first-aid kit,
hard hats. Some
items exist in several types according to the
methods of well construction.
The tripod is the most widely used and locally
type of drilling-support structure.
Tripods can be made of bamboo,
wood, or pipe (Fig. 8).
The height of a tripod is limited
by the strength of the legs.
Generally, the tripod should be at
least 4 m high.
Bailing--raising water, sand, and clay to the surface for
removal--is a common procedure during drilling and afterward
during the process of development.
Bailing involves lowering the
bailer (a bucket device) to the bottom of the well and
to the surface for disposal.
When drilling reaches the desired depth, the well screen is
installed and the well is grouted, developed, and
This section briefly describes the most commonly used
drilling or boring wells.
For each method, essential equipment
and basic procedures are given.
Essential equipment can usually
be made locally.
Driven Wells (Percussion)
A hammer of at least
20 kilograms (kg) is
on the well casing.
This method works
best when the water
table is less than
10 m below the
surface and there
are no rocks. A
well screen with a
drive shoe should be
used. The main kinds
of hammer are shown
in Figs. 9 and 10.
one or two people
can perform the
weight, drive head to
protect the casing,
tripod, ropes and
pulleys, well drive-point
Standardweight pipe is
usually not strong
enough; stronger drive
pipe and couplings are
Procedure: Dig a
vertical starter hole
about half a meter deep
and slightly larger
than the diameter of
the well. Erect the
tripod. Assemble the
drive head, casing, and
well point. Insert
well point into the
starter hole. Start
driving the well point
into the ground by the
method. When the top
the casing is near the
ground, remove the drive head.
Add a section of well casing and
install the drive head on the top of the casing.
and adding sections until the desired depth is reached.
Cable-Tool Drilled Wells (Percussion)
Cable-tool drilling is one of the most versatile methods
it can penetrate almost any type of geologic formation,
compacted soil. But
drilling is slow and casing must be
installed as drilling proceeds if the formation is
chisel-faced bit (Figs. 11 and 12) is repeatedly raised and
dropped, thus breaking and pulverizing the soil.
can be used to raise and drop the drill bit, as previously
described. Water is
added during the process to make a slurry.
This will make bailing more efficient.
The fall of the drill bit
will be slowed when too much slurry has accumulated.
must then be bailed out of the well.
The drill bit is lifted from
the hole and the slurry is removed with a bailer
is then added to replace the lost slurry.
If the bit is lifted manually, at least six persons are
mechanical lifting the work crew can be reduced to
three or four.
Percussion bit sized to fit inside the casing, bailer
to fit the casing, tripod and pulley, ropes, casing, and
Procedure: Dig a
vertical starter hole about half a meter deep
and slightly larger than the diameter of the well.
tripod. Secure one
end of the rope to the percussion bit and
guide the rope over the pulley.
Raise and drop the drill bit in
short rapid strokes of about half a meter with a bouncing
Add some water to the bore hole so that the cuttings will
When the cuttings become so thick that the bit speed is
slowed, bail the well.
First, remove the drill bit and lay
it on the ground.
Attach the bailer to the rope and lower it into
the well. Allow the
bailer to strike the bottom of the well a
number of times to suspend and pick up cuttings.
Raise the bailer
out of the well and drop the contents at the side of the
Repeat the process until the bailer is no longer picking up
material. Remove the
bailer and attach the drill bit.
drilling and bailing, until the desired depth is reached.
Install the casing as the drilling proceeds.
If a caving formation
is encountered, drive the casing down more frequently.
Dry-Bucket Drilled Wells (Percussion)
A cylindrical dry bucket is repeatedly dropped to the bottom
the hole and lifted (Fig. 13).
The impact forces the soil or
other material into the bucket.
When penetration decreases, the
bucket is lifted to the surface and the soil is removed by
the side of the bucket with a heavy object.
When the soil no
longer adheres to the bucket, a casing can be installed and
auger or bailer used to drill the hole below the water
This simple method of drilling is limited to depths of 20 m
diameters of 10 to 15 cm.
It works well in most clays and silts,
but not in heavy clay or loose sand.
The formation should be free
of rocks and fairly dry.
Dry-bucket drill bit to fit inside the casing, ropes
and pulley, tripod.
Procedure: Dig a
vertical starter hole
about half a meter
deep and slightly
larger than the
diameter of the well.
Erect the tripod.
Attach rope to the dry
bucket. Insert the
bucket into the hole
and begin repeatedly
lifting and dropping it
about half a meter.
When penetration slows
or stops, remove the
dry bucket drill bit.
Remove the dirt from
the bucket. Install
casing as required.
Continue operating the
bucket until the
desired depth in
Reverse Circulation Wells (Percussion)
This commonly used method of drilling (also termed
"hydraulic percussion" method) involves repeatedly
raising the hollow drill bit, which is equipped with a
check valve (Fig. 14).
The bore hole is kept filled with water
from a settling pond.
Cuttings in the well are removed through
the hollow drill stem as the drill is raised and
dropped. If the
drill bit lacks a check valve, a drilling assistant can
stop the discharge on the up stroke by placing a hand over
stem and releasing the stem on the down stroke.
The water and
cuttings flow to the settling pond, where the cuttings
The method is good for wells having an average depth of 20
with a maximum depth of 80 m.
It does not work well in hard
formations or gravel, but is suitable for sand, clay, and
Drilling can be done very rapidly by an experienced drilling
bit, preferably with one-way valve; hollow
drill stem; tripod; ropes and pulleys.
Procedure: Dig a
starter hole about half a
meter deepand slightly
larger than the diameter of
the well. Erect a
Dig a settling pond nearby
at least one meter square
and one meter deep.
the drill bit, drill stem,
and ropes. Fill the
hole with water.
raise and drop the drill bit
a distance of half a meter
If a one-way valve is unavailable,
assistant should substitute
his hand as described above.
Attach additional hollow
drill stem sections and, if
the walls of the hole are
unstable, sink casing as the
well deepens. When
desired depth is reached,
remove the drill.
Bored (Augered) Wells (Rotation)
This is one of the oldest and simplest drilling
methods. A hole
is drilled by manually rotating a drill bit or auger.
must be periodically lifted to the surface and emptied.
is rapid for the first five meters, but becomes slow at
depths because the drill rod must be uncoupled as the auger
lifted to the surface.
Drilling with an auger is suitable for sand, clay, silt, and
some gravels, but not for rocks or thick gravel.
Depths of 25 m
are obtainable. A
four- to six-person crew is required.
One type of auger is used for such cohesive solids as
different type of auger is used for loose solids such as
gravel. Augers of
more advanced design often have many teeth
mounted on rotating cones; these require machine operation
level of expertise beyond the scope of this paper.
drill rod, auger, handles for turning the
drill rod and auger.
Procedure: Dig a
starter hole about half a
meter deep and slightly
larger than the diameter of
the well. Erect a
Attach the auger to the
Plumb the drill stem by
adjusting the location of
the support tripod.
drill stem with a rod handle,
until the auger fills or
Lift the auger from the hole
and remove the soil.
additional drill stem sections
as the well gets
deeper. They may
have to be
removed as the auger is
raised to the surface.
raised platform can be
constructed to provide
additional support for them
as they are lifted to the
surface. When the
depth is reached, remove the
auger and drill stem.
the casing and screen.
Jetted Wells (Rotation)
A water jet cuts
through the soil or
other formation along
with the action of a
drill bit. Water
through the hollow drill
rod forces the sand,
silt, and clay to the
surface, where the
mixture is drained to a
settling pond. Water
from the settling pond
is pumped back to the
drill rod bit. The
casing fitted with a
drive shoe is sunk as
Several types of drill
bit suit different
(Fig. 18). The
bit is used for clays.
The side bit is used to
slip inside a casing and
expand below its lower
end so that the new hole
will be big enough for
the next section of casing.
This method is excellent
for drilling through
sandstone and soft rock.
Equipment: Motorized or
manual pump, tripod with
rope and pulley, drill
rod with couplings,
drill bit, a water
source, well casing and
screen. This method
equipment that may not
be easily available.
Procedure: Dig a vertical
starter hole about
half a meter deep and
slightly larger than
the diameter of the
well. Erect a
Dig a settling pond
nearby at least one
meter square and one
meter deep. Install
drill bit, drilling
rod, ropes, and pulley.
Connect hoses from the
settling pond to the
pump and drilling rod.
Start the pump.
the drill rod to enhance
erosion by the
casing when the desired
depth is reached.
WELL ALIGNMENT AND PLUMBNESS
A well may become crooked if the drill bit is deflected by
stones. A crooked
well can strain the shafts and bearings of some
types of pumps, or may result in damage to the casing by the
shaft. The driller
should check the alignment of the well several
times during drilling of a deep well.
In this way faulty construction
is avoided or promptly corrected.
Wells 30 to 60 m a deep are
often usable even if they are
a little crooked. If
is serious, it is usually
cheaper to start a new well
than to correct the fault.
Vertical alignment can be
checked by suspending a plumb
ring from a tripod and lowering
it to various depths (Fig. 19).
The diameter of the ring
must be less than the diameter
of the casing. An
method is to lower to the
bottom a dummy casing with a
diameter one centimeter (cm)
less than that of the regular
casing. If the dummy
freely to the bottom of the
well, a pump will operate
Grouting seals the space between the well casing and the
hole. It is required
to prevent contaminated surface water from
entering the well.
In addition, grouting extends the life of the
Grouting is performed after installation of the casing and
screen, and before well development.
The best method is to pump
the grout through a pipe to the lowest desired elevation,
the pipe as the grout is placed.
Because a grout pump is very
expensive, an easier but less reliable method is used: pour
cement grout into the space, upon a bed of gravel.
is made by mixing 20 liters (L) of water with 45 kg of
there is a large volume to fill, sand and gravel can be
with the cement.
Procedure: Pour fine ("pea") gravel into the space
casing to slightly above the water table, but at least 3 m
the ground surface.
Mix the cement grout and pour it to fill the
rest of that space.
After well-screen installation and grouting, the well must
developed to ensure maximum water flow rates.
of causing rapid reversals of water flow (called
through the screen and the surrounding aquifier.
It washes away
very fine sand, silt, and clay that may have remained in the
aquifer around the screen.
These fine particles restrict the flow
of water. In
addition, drilling may compact the soil next to the
bore hole; development returns the soil to a loose
In development, the rapid outflow
of water through the well screen
dislodges fine particles from the
flow of water allows the fine
particles to enter the well.
These are removed with a bailer
or by pumping. The
coarse material with good flow
characteristics around the
screen. (Fig. 20)
The mechanical surging of the
well can be done with a locally
made surge plunger (Fig. 21) or a
more expensive valved plunger.
The valved plunger has a lighter-surging
action and may be converted
to a solid plunger by
plugging its hole if necessary.
light surging action is recommended
to start the process.
Placing a heavy pipe above the
surge plunger is recommended for
increased weight if needed.
any sand in the well by bailing or pumping.
Lower the surge plunger until it is 2 to 3 m below the water
surface and above the screen.
Raise the surge plunger 2 to 3 m
and then drop it.
Repeat the action slowly; then increase the
rate. After several
minutes, pull the surge plunger to the top
of the well and remove the sand by bailing or pumping.
how much sand is in the water.
Repeat the operation of the surge
plunger until little or no sand can be removed.
the plunger through the screen to the bottom of the hole to
further clean the screen.
Well and pump maintenance are critical to the longevity and
performance of a water-well system.
Records of the well construction, water levels, and
history are important for maintenance decisions.
records of well construction and soil samples should be
driller's name and address; a soil log,
formations that were encountered during
drilling and the
depths of the transitions; well drilling
method; type and
size of well casing; bore-hole
total drilled depth; screen specifications;
level; any pumping records, indicating
pumping rate and
the descent of the water table;
used; and pump specifications. The
include a location map of the well
distance to sources of contamination,
Such information as types and depths of geological
can be easily forgotten.
It can be critically needed if the well
stops producing water.
Such records also are useful in planning
new wells in the area.
The data should be recorded as the drilling takes place or
soon as they become available.
Pumping rates of a well may decrease after a period of
causing a serious problem.
Before any repairs are attempted, the
operator should try to determine the cause of the
original depth to the water table should be compared to the
current depth. The
pump can be removed for inspection. If
the water and the well pump are good, then the problem may
the well screen.
Some common problems and solutions are given below:
Lowered water table
Drill the well deeper
(usually not possible)
Repair or replace pump
Encrusted well screen
Acid-treat or chlorinate
Encrustation, the accumulation of precipitated material on
well screen, can be removed by acidifying the well.
hydrochloric (muriatic) acid or sulfuric acid is used.
Although hydrochloric acid is available in three grades,
the strongest grade (28%) should be used.
The volume of acid
used should be about twice the volume of the water in the
section. The well
should be agitated for two hours with a surge
plunger immediately after the acid is added.
the well should be bailed out until the water is clean.
useful to chlorinate the well after acid treatment.
and discard the water until the acidity disappears.
Built-up bacterial growth on a well screen can be removed by
adding concentrated chlorine solutions to the well
a chlorine concentration of 300 milligrams (mg) per L in the
chlorination, the well should be agitated by means
of a surge plunger and then bailed out until the water is
By its nature, well drilling can cause contamination of the
Disinfection of the newly completed well is required
to ensure the sanitation of the ground water.
chlorine solution is added to the well to produce at least
100 mg/L of chlorine.
This solution should stand for 24 hours.
Most types of chlorine compounds can be used to make the
To make a solution with calcium hypochlorite (chlorinated
add a small quantity of water to the solid chemical and stir
until there are no lumps.
Add several liters of water and allow
the solids to settle.
The clear liquid should be used to disinfect
the well and the remaining material discarded.
To make stock solutions with other chlorine compounds,
add the compound to about 4 L of water, in the amount needed
the required chlorine concentration.
Procedure: After the well is drilled, clean and wipe the
thoroughly as possible of grease, oil, and dirt.
Pour the chlorine
solution into the well.
Mixing is aided with a hose or pipe.
Ensure that all surfaces of the well casing are exposed to
chlorine stock solution.
Lower the pump and its drop pipe into
the well, washing their exterior surfaces with chlorine solution
as they are lowered.
Operate the pump, discarding the water,
until a distinct chlorine odor can be detected.
Allow the chlorine
solution to remain in the well for 24 hours.
Then pump the
well until the chlorine odor disappears; discard the water.
If a well is abandoned because it does not produce water or
because it is contaminated, it should be sealed to prevent
surface water from entering it and mixing with the
ground water. The
common method of sealing a well by inserting a
short wooden log into the top of the well casing is
and should not be used.
Fill the well with clay to within one
meter of the top of the casing; then fill it to the top with
A well can also be sealed by injecting cement, concrete
clay into the well.
The cement should be introduced at the bottom
of the well first and placed progressively upwards to the
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International, P.O. Box 1126, Arcadia, California
91006 USA. Telephone
818/443-1787. Makes and sells a
drilling machine, designed for use in developing countries,
water wells up to 30 m deep.