TECHNICAL PAPER ## 61
 
                        UNDERSTANDING LOW-COST
                             WELL DRILLING
 
                                  By
                           Stephen Greenwood
 
                          Technical Reviewers
                             William Ashe
                              L. C. Diaz
                           Joseph Karakowski
                            Richard Koegel
                              Paul Maners
 
                             Published by
 
                                 VITA
                   1600 Wilson Boulevard, Suite 500
                     Arlington, Virginia 22209 USA
                Tel:  703/276-1800 . Fax:   703/243-1865
                      Internet: pr-info@vita.org
 
                 Understanding Low-Cost Well Drilling
                          ISBN: 0-86619-280-8
              [C]1990, Volunteers in Technical Assistance
 
                 UNDERSTANDING LOW-COST WELL DRILLING
 
                  By VITA Volunteer Stephen Greenwood
 
INTRODUCTION
 
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
drinking-water supply.
 
Ground water is a very common source of drinking water.   In planning
to build a well to tap and use ground water, people must
first decide between hand-dug and drilled wells.   Drilled wells
can be deeper, safer, and more durable than hand-dug wells, but
their construction is more expensive and technically demanding.
Fortunately, most of the equipment for drilling a small well can
be manufactured locally.  In addition, simple and relatively
inexpensive machinery for drilling wells has now been developed
that can be used if money or expertise is available.
 
THE PLANNING STAGE
 
Care in planning the design and location of a water well requires
extra effort, but improves the likelihood of building a successful
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 available
geological data; site inspection to avoid contamination; and
ground water exploration, if there are no other wells in the
area.
 
In selecting the site, avoid areas of possible contamination.
Checking local maps and the closest water wells to the proposed
site can give valuable information on the amount of water that
can be expected from the well.   Samples of water from 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 site.  The well should be constructed at least 50 meters (m)
from the nearest potential source of surface contamination.  Such
sources include latrines, animal stalls or barns, polluted
creeks, cemeteries, agricultural fields (pollution from chemicals),
and roads (petrol and oil).
 
The next steps are to identify the best drilling method based on
geological factors and local experience; determine such specifications
as the material and size of the casing, approximate depth
of casing and well screen, and labor requirements; and agree on
the persons who will be responsible for record keeping, operation,
and maintenance of the well.
 
WELL DESIGN
 
A number of items influence well performance
and design.  These include geological
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
drilled wells.  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

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describe pumps; the VITA Technical Paper on
"Understanding Water Wells" and other
references contain pump information.)
 
Well Casing
 
The well casing prevents the collapse of
the bore hole and protects the pumping
equipment.  Among major cost items, it ranks
after the pump.  A thicker-walled casing
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.   A 10-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 well.
The screen permits water to flow into the well and keeps sand and
gravel out.  It must be strong enough to prevent the collapse of
the bore hole, but should not excessively restrict water flow
rates.  Recommended features of a well screen are as follows:  a
high proportion of open area, close spacing of the slots, sufficient
strength to prevent collapse, single-metal construction
(including screws, if possible) to prevent corrosion, and end
fittings for installation.
 
The four common types of well screen are continuous slot, louvre-slotted
pipe, low-level sawn slot, and perforated pipe (Fig. 2).

ulw2x3.gif (600x600)


 
The continuous-slot screen that is commercially available has
more intake area per square meter (sq m) than any other type of
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 greater
number of openings will not increase it.
 
Louvre-slotted and perforated pipes can be easily and cheaply
made in most locations.  It is often best to select them even
though they are less efficient than some other types.   Slotted
plastic pipes are being used more often in small diameter wells
because they are light in weight, noncorroding, and inexpensive.
The slots can be made at the construction site with a sharp saw.
The length of the screen depends upon the thickness of the aguifer,
pumping rates, aquifer particle size, and the type of
screen.  Selecting the exact dimensions requires experience.  For
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 well
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 closely
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 taken
from the formation where the screen will be placed.   The proper
screen size opening can best be selected by using a well-screen
selector field kit (Fig. 3).   Although the kit is not absolutely

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necessary to well construction, it is described here to aid in
understanding the relation of screen size to soil particle size.
The device is a box with removable square screens.   Equally spaced
lines are drawn along the inside of the box.   Wire mesh screens
with openings of five different sizes are placed inside the box
with the largest opening at the top of the box.
 
A dry sample from the soil in the aquifer is placed in the upper
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 measured.
If the total amount of sample is known, the percentage of
the sample that passed each screen can be calculated.   The screen
that lets about 40 percent of the sample pass through should be
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 well
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 rom
contamination:
 
o The well should always be covered when work is not in progress.
 
o The well casing should extend at least 0.5 m above the highest
  known flood level.
 
o The ground around the well should be sloped to drain water away
  from the well.   Building a concrete slab around the well will
  reduce the amount of mud during construction.
 
o The casing joints should be tight so that no water seeps
  through.
 
o The space between the bore hole and the well casing should be
  sealed with concrete grout to at least 3 m below the ground.
 
WELL CONSTRUCTION:  GENERAL METHODS
 
Well construction consists of six basic operations:   drilling,
casing installation, screen installation, gravel packing, development,
and disinfection.  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 to
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 soil) formation,
a rotation method can be used to drill through the sandstone and
a percussion method used in the hard formation.
 
Percussion Drilling
 
Percussion methods raise and drop a heavy drill bit to break up
the soil.  The material can then be removed f rom the hole by
several means, including a cable-driven bailing bucket and a dry
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 motor.  Two
methods of manually raising the drill bit are shown in Fig. 4.

ulw4x6.gif (600x600)


The drill bit should be raised about half a meter before it is
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 cathead
(capstan) attached to a jeep, truck motor, or other power source
(Fig. 5).  The cathead consists of a metal spool, welded together

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from a scrap section of metal pipe and two steel disks, one of
which is drilled and bolted to the vehicle (Fig. 6).   The vehicle

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should be parked 4 to 6 m from the well, the rear end elevated by
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 cathead.
Alternately tightening and loosening the rope will allow the
rotating cathead to raise and drop the drill bit.   Since unprotected
ropes and cathead are very dangerous, they should be covered
to protect the operator from accidental injury.
 
Rotation Methods
 
The drill bit is turned to create the hole.   Turning requires
wood rod handles or chain tongs clamped to the drill rod as shown
in Fig. 7.  Examples are the bored (augered) well and the jetted

ulw7x7.gif (600x600)


well.  Jetting uses water to assist the action of the drill.
 
Common Materials and Methods
 
The items required for well construction can include:   casing
pipe, well screen, pipe couplings, concrete mix, tripod, pulley,
ropes, drill bit, bailer, "fishing" tools, hammers, hacksaw,
metal files, pipe wrenches, screwdrivers, shovels, measuring
tape, plumb bob, chain tongs, pipe-joint sealing material, wood
saw, wire, cold chisel, pipe dies, rod dies, first-aid kit, and
hard hats.  Some items exist in several types according to the
methods of well construction.
 
The tripod is the most widely used and locally manufacturable
type of drilling-support structure.   Tripods can be made of bamboo,
wood, or pipe (Fig. 8).  The height of a tripod is limited

ulw8x7.gif (600x600)


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 lifting it
to the surface for disposal.
 
When drilling reaches the desired depth, the well screen is
installed and the well is grouted, developed, and disinfected.
 
WELL CONSTRUCTION:  SPECIFIC METHODS
 
This section briefly describes the most commonly used methods of
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
repeatedly dropped
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
special pointed
drive shoe should be
used.  The main kinds
of hammer are shown
in Figs. 9 and 10.

ulw9x80.gif (600x600)


one or two people
can perform the
drilling.
 
Equipment:  Sliding
weight, drive head to
protect the casing,
tripod, ropes and
pulleys, well drive-point
and casing.
Standardweight pipe is
usually not strong
enough; stronger drive
pipe and couplings are
usually needed.
 
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 the
well point into the
starter hole.  Start
driving the well point
into the ground by the
selected hammering
method.  When the top of
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.   Continue driving
and adding sections until the desired depth is reached.
 
 
Cable-Tool Drilled Wells (Percussion)
 
Cable-tool drilling is one of the most versatile methods because
it can penetrate almost any type of geologic formation, including
compacted soil.  But drilling is slow and casing must be
installed as drilling proceeds if the formation is unstable.  A
chisel-faced bit (Figs. 11 and 12) is repeatedly raised and

ulw11x10.gif (600x600)


dropped, thus breaking and pulverizing the soil.   Various methods
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.   The slurry
must then be bailed out of the well.   The drill bit is lifted from
the hole and the slurry is removed with a bailer bucket.  Water
is then added to replace the lost slurry.
 
If the bit is lifted manually, at least six persons are usually
needed.  With mechanical lifting the work crew can be reduced to
three or four.
 
Equipment:  Percussion bit sized to fit inside the casing, bailer
to fit the casing, tripod and pulley, ropes, casing, and screen.
 
Procedure:  Dig a vertical starter hole about half a meter deep
and slightly larger than the diameter of the well.   Erect the
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 motion.
Add some water to the bore hole so that the cuttings will form a
slurry.
 
When the cuttings become so thick that the bit speed is significantly
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 well.
Repeat the process until the bailer is no longer picking up
material.  Remove the bailer and attach the drill bit.  Continue
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 of
the hole and lifted (Fig. 13).   The impact forces the soil or

ulw13x11.gif (600x600)


other material into the bucket.   When penetration decreases, the
bucket is lifted to the surface and the soil is removed by hitting
the side of the bucket with a heavy object.   When the soil no
longer adheres to the bucket, a casing can be installed and an
auger or bailer used to drill the hole below the water table.
 
This simple method of drilling is limited to depths of 20 m and
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.
 
Equipment:  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
reached.
 
Reverse Circulation Wells (Percussion)
 
This commonly used method of drilling (also termed "sludger" or
"hydraulic percussion" method) involves repeatedly dropping and
raising the hollow drill bit, which is equipped with a one-way
check valve (Fig. 14).  The bore hole is kept filled with water

ulw14x12.gif (600x600)


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 simply
stop the discharge on the up stroke by placing a hand over the
stem and releasing the stem on the down stroke.   The water and
cuttings flow to the settling pond, where the cuttings settle
out.
 
The method is good for wells having an average depth of 20 m,
with a maximum depth of 80 m.   It does not work well in hard
formations or gravel, but is suitable for sand, clay, and silt.
Drilling can be done very rapidly by an experienced drilling
crew.
 
Equipment:  Drill bit, preferably with one-way valve; hollow
drill stem; tripod; ropes and pulleys.
 
Procedure:  Dig a vertical
starter hole about half a
meter deepand slightly
larger than the diameter of
the well.  Erect a tripod.
Dig a settling pond nearby
at least one meter square
and one meter deep.  Attach
the drill bit, drill stem,
and ropes.  Fill the starter
hole with water.  Repeatedly
raise and drop the drill bit
a distance of half a meter
If a one-way valve is unavailable,
the drilling
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 the
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.   The auger
must be periodically lifted to the surface and emptied.   Drilling
is rapid for the first five meters, but becomes slow at greater
depths because the drill rod must be uncoupled as the auger is
lifted to the surface.  (Fig. 15)

fg15p13.gif (600x600)


 
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 clay.  A
different type of auger is used for loose solids such as sand and
gravel.  Augers of more advanced design often have many teeth
mounted on rotating cones; these require machine operation and a
level of expertise beyond the scope of this paper.   (Fig. 16)

ulw16x14.gif (600x600)


 
Equipment:  Tripod, drill rod, auger, handles for turning the
drill rod and auger.
 
Procedure:  Dig a vertical
starter hole about half a
meter deep and slightly
larger than the diameter of
the well.  Erect a tripod.
Attach the auger to the
drill stem.
 
Plumb the drill stem by
adjusting the location of
the support tripod.  Turn the
drill stem with a rod handle,
until the auger fills or
progress slows.
 
Lift the auger from the hole
and remove the soil.  Attach
additional drill stem sections
as the well gets
deeper.  They may have to be
removed as the auger is
raised to the surface.  A
raised platform can be
constructed to provide
additional support for them
as they are lifted to the
surface.  When the desired
depth is reached, remove the
auger and drill stem.  Install
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 pumped
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 well
casing fitted with a
drive shoe is sunk as
drilling proceeds.  (Fig. 17)

ulw17x14.gif (600x600)


 
Several types of drill
bit suit different
geological formations
(Fig. 18).  The straight

ulw18x15.gif (600x600)


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 uses
specially designed
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 tripod.
Dig a settling pond
nearby at least one
meter square and one
meter deep.  Install the
drill bit, drilling
rod, ropes, and pulley.
Connect hoses from the
settling pond to the
pump and drilling rod.
Start the pump.  Rotate
the drill rod to enhance
erosion by the
water.  Install screen
casing when the desired
depth is reached.
 
WELL ALIGNMENT AND PLUMBNESS
 
A well may become crooked if the drill bit is deflected by large
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 pump
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 the fault
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).

ulw19x16.gif (600x600)


The diameter of the ring
must be less than the diameter
of the casing.  An alternative
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 moves
freely to the bottom of the
well, a pump will operate
satisfactorily.
 
GROUTING
 
Grouting seals the space between the well casing and the bore
hole.  It is required to prevent contaminated surface water from
entering the well.  In addition, grouting extends the life of the
casing.
 
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, raising
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.   Cement grout
is made by mixing 20 liters (L) of water with 45 kg of cement.  If
there is a large volume to fill, sand and gravel can be mixed
with the cement.
Procedure: Pour fine ("pea") gravel into the space around the
casing to slightly above the water table, but at least 3 m from
the ground surface.  Mix the cement grout and pour it to fill the
rest of that space.
 
WELL DEVELOPMENT
 
After well-screen installation and grouting, the well must be
developed to ensure maximum water flow rates.   Development consists
of causing rapid reversals of water flow (called "surging")
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 condition.
 
In development, the rapid outflow
of water through the well screen
dislodges fine particles from the
surrounding layer.  The inward
flow of water allows the fine
particles to enter the well.
These are removed with a bailer
or by pumping.  The process leaves
coarse material with good flow
characteristics around the
screen.  (Fig. 20)

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The mechanical surging of the
well can be done with a locally
made surge plunger (Fig. 21) or a

ulw21x17.gif (486x486)


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.   A
light surging action is recommended
to start the process.
Placing a heavy pipe above the
surge plunger is recommended for
increased weight if needed.
 
Procedure:  Remove 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.   Notice
how much sand is in the water.   Repeat the operation of the surge
plunger until little or no sand can be removed.   Finally, lower
the plunger through the screen to the bottom of the hole to
further clean the screen.
 
 
WELL MAINTENANCE
 
Well and pump maintenance are critical to the longevity and
performance of a water-well system.
 
Records of the well construction, water levels, and performance
history are important for maintenance decisions.   The following
records of well construction and soil samples should be kept:
 
    Owner's name; driller's name and address; a soil log,
    recording the formations that were encountered during
    drilling and the depths of the transitions; well drilling
    method; type and size of well casing; bore-hole
    diameter and total drilled depth; screen specifications;
    static water level; any pumping records, indicating
    pumping rate and the descent of the water table;
    grouting material used; and pump specifications.  The
    records should include a location map of the well
    showing the distance to sources of contamination,
    lakes, and rivers.
 
Such information as types and depths of geological formations
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 as
soon as they become available.
 
Pumping rates of a well may decrease after a period of operation,
causing a serious problem.  Before any repairs are attempted, the
operator should try to determine the cause of the problem.  The
original depth to the water table should be compared to the
current depth.  The pump can be removed for inspection.  If both
the water and the well pump are good, then the problem may be at
the well screen.
 
Some common problems and solutions are given below:
 
    PROBLEM                    SOLUTION
 
Lowered water table      Drill the well deeper
                         (usually not possible)
 
Worn pump                Repair or replace pump
 
Encrusted well screen    Acid-treat or chlorinate
                         well
 
Encrustation, the accumulation of precipitated material on the
well screen, can be removed by acidifying the well.   Usually
hydrochloric (muriatic) acid or sulfuric acid is used.
 
Although hydrochloric acid is available in three grades, only
the strongest grade (28%) should be used.   The volume of acid
used should be about twice the volume of the water in the screen
section.  The well should be agitated for two hours with a surge
plunger immediately after the acid is added.   After agitation,
the well should be bailed out until the water is clean.   It is
useful to chlorinate the well after acid treatment.   Then pump
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 sufficient for
a chlorine concentration of 300 milligrams (mg) per L in the well
water.  After chlorination, the well should be agitated by means
of a surge plunger and then bailed out until the water is clear.
 
DISINFECTION
 
By its nature, well drilling can cause contamination of the
ground water.  Disinfection of the newly completed well is required
to ensure the sanitation of the ground water.   A concentrated
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 solution.
 
To make a solution with calcium hypochlorite (chlorinated lime),
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, simply
add the compound to about 4 L of water, in the amount needed for
the required chlorine concentration.
 
Procedure: After the well is drilled, clean and wipe the area as
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 the
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.
 
WELL ABANDONMENT
 
If a well is abandoned because it does not produce water or
because it is contaminated, it should be sealed to prevent contaminated
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 ineffective
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
concrete.
 
A well can also be sealed by injecting cement, concrete and/or
clay into the well.  The cement should be introduced at the bottom
of the well first and placed progressively upwards to the top of
the well.
 
                            REFERENCES
 
Ashe, William, Understanding Water Wells.   VITA Technical' Paper.
Arlington, Virginia: Volunteers in Technical Assistance, 1989.
 
Driscoll, Fletcher G., Groundwater and Wells, 2nd ed. New
Brighton, Maine: SES Johnson Division, 1986.
 
Gibson, Ulric P.; Rexford D. Singer, Small Wells Manual: A Manual
of Location, Design, Construction, Use, and Maintenance (in
English and in Spanish). Washington, D.C.: U.S. Agency for International
Development, 1969.
 
Institute for Rural Water; National Environmental Health Association;
U.S. Agency for International Development, Constructing
Cable Tool Wells (in Spanish and English).   Water for the World;
Rural Water Supply Tech.  Note No. RWS 2.C.5. Washington, D.C.:
U.S. Agency for International Development, 1982.
 
Institute for Rural Water; National Environmental Health Association;
U.S. Agency for International Development, Designing
Cable Tool Wells.  Water for the World; Rural Water Supply Tech.
Note No. RWS 2.D.5, Washington, D.C.: U.S. Agency for International
Development, 1982.
 
Koegel, R.G., Self-help Wells.   FAO Irrigation and Drainage Paper
No. 30. Rome: UN Food and Agriculture Organization, 1977.
 
Volunteers in Technical Assistance, Village Technology Handbook,
3rd ed. Arlington, Virginia: Volunteers in Technical Assistance,
1988.
 
COMMERCIAL SOURCE
 
    Lifewater International, P.O. Box 1126, Arcadia, California
91006 USA.  Telephone 818/443-1787.  Makes and sells a portable
drilling machine, designed for use in developing countries, for
water wells up to 30 m deep.
 
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