*TM 5-813-1/AFM-88-10, Vol. 1
clogging the openings. A second cause is corrosion of
rock formations. However it may be difficult to tell in
the screen which is a chemical reaction of the metal.
advance if the shooting operation will produce the
This action results in the screen being dissolved and
enlarging the openings, allowing caving to occur.
(b) Acidizing can be used in wells in
Records of pump performance and pumping levels are
very important in a good maintenance program.
Incrustation. The effect of incrustation is
opened up in the aquifer surrounding the well hole by the
usually decreased capacity due to clogging of the screen
(c) Sand fracking is the action of
openings. For incrustation due to calcium deposits or
forcing high pressure water containing sand or plastic
beads in to the fractures surround a well. This serves to
treatment with an acid solution will dissolve the deposits
force the crevices open.
and open up the screen. For bacterial growths and slime
Disinfection of completed well.
deposits, a strong chlorine solution has been found
disinfection of the completed well shall conform to
effective. In some instances, explosives may be used to
break up incrustation from wells in consolidated rock
Bacteriological samples must be collected and examined
Corrosion. The best method to prevent
in accordance with Standard Methods for the
Examination of Water and Wastewater.
corrosion is to use a metal which is resistant to the
Disinfection of flowing artesian wells.
attack. Once a screen has deteriorated, the only method
Flowing artesian wells often require no disinfection, but if
of rehabilitation may be to remove it and install a new
a bacteriological test, following completion of the well,
screen. The design of the initial installation should allow
for removal of the screen in the future. Corrosion is also
be accomplished as follows. The flow from the well will
a problem in pumps. The use of pumps constructed of
be controlled either by a cap or a standpipe. If a cap is
special non-corrosive materials will help. Care should be
required, it should be equipped with a one-inch valve and
taken to use pumps with single metal types. Chemical
a drop-pipe extending to a point near the bottom of the
inhibitors can be injected into wells to prevent corrosion,
well. With the cap valve closed, stock chlorine solution
but this is costly.
Downhole Inspections. Special television
will be injected, under pressure, into the well through the
drop-pipe in an amount such that when the chlorine
equipment has been developed to permit a visual
solution is dispersed throughout all the water in the well,
inspection of a well. Special lighting will permit high
the resultant chlorine concentration will be between 50
resolution pictures even under water. Wells as deep as
and 100 mg/l. After injection of the required amount of
3000 feet, in casings as small as 4 inches diameter can
stock chlorine solution, compressed air will be injected
be inspected. The entire inspection can be videotaped
through the drop-pipe, while simultaneously partially
for later review.
Well cleaning. Where incrustation is a
opening the cap valve. This will permit the chlorine
solution to be mixed with the water in the well. As soon
problem, periodic well cleaning (also called "well
as chlorine is detected in the water discharged through
stimulation" or "well rehabilitation") may be practiced. An
the cap valve, the air injection will be stopped, the cap
effective cleaning procedure should be developed and
valve closed and the chlorinated water allowed to remain
applied annually or more often if necessary.
in the well for 12 hours. The well will then be allowed to
Maintenance procedures are given in Ground Water and
flow to waste until tests show the absence of residual
Wells, and Water Well Technology.
chlorine. Finally, samples for bacteriological examination
will be collected in accordance with Standard Methods
5-9. Abandonment of wells and test holes.
for the Examination of Water and Wastewater. If the
It is essential that wells, test wells, and test holes have
well flow can be controlled by means of a standpipe,
served their purpose and are to be abandoned, be
disinfection can be accomplished as described for a
effectively sealed for safety and to prevent pollution of
water table well.
the ground water resources in the area.
abandonment of wells shall follow the guidance of
5-8. Renovation of Existing Wells
Well yield can be maintained by proper operating
procedures. The most common cause of dedining
capacity in a well is incrustation which results from
material being deposited on the well screen and thereby