the gallery is justified by a reduction in the amount
of chemicals needed to coagulate the water, the
elimination of the necessity of frequently
backwashing the filter, and the higher quality of
GROUND WATER DEVELOPMENT
Moisture is held beneath the surface of the
earth in three zones: (1) the zone of soil moisture,
where water is temporarily held in pore spaces by
capillary action or other soil conditions; (2) the
zone of aeration or zone of percolation beneath
the soil layer, where both water and air are pre-
sent in the pore spaces; and (3) the zone of satura-
tion, where all spaces are filled with water.
Ground water is the term customarily used for the
underground water in the saturated zone.
One possible objection to an underground
water supply is that the water may be excessively
hard. This condition may occur because of the
percolation of the water through mineral deposits
from which water-hardening constituents are
leached or extracted. On the other hand, an
underground supply generally has the advantage
of requiring less treatment because of the natural
removal of impurities as the water passes through
various underground soil formations. However,
these conditions are general; some mineral
deposits do not contribute to hardness, and some
underground formations may not be of the type
that effectively removes objectionable material.
Many times it is advantageous to use shallow
ground water sources or percolated waters adja-
cent to a turbid surface water. Well points are
issued in 2-inch diameters and 54-inch lengths. A
drive cap is placed over the thread and the well
point is driven into the ground with a sledge. Suc-
cessive sections of pipe, each 5 feet long, are added
and driven until the screen is well within the water-
bearing media. Several well points may be con-
nected in parallel to supply sufficient water to the
raw water pump. In developing drive point
sources, it must be remembered that the practical
limit of suction lift of the pumps issued with field
equipment is 22 to 25 feet at sea level. Suction-
lift pumps can be used, therefore, only where the
pumping level in the well will be within the limit
of suction llift, or 22 to 25 feet below the position
of the pump. At 5,000 feet above sea level, the
practical limit of suction lift is only 20 feet. It
should be noted that since a suction-lift pump
must create a partial vacuum in the suction line,
it is necessary that the line be absolutely airtight
if the pump is to function properly.
Springs yielding 20 gallons per minute or more
of water can be used as a source of field water
supply if properly developed. Springs may be
developed by enlarging the outlet of the spring
and by damming and conducting water to storage.
To reduce possible pollution, springs should be
cleared of all debris, undergrowth, top soil, loose
rocks, and sand.
Water that flows from rocks under the force
of gravity and collects in depressions can be col-
lected in boxes or basins of wood, tile, or con-
crete. The collecting box should be large enough
to impound most of the flow. It should be placed
below the ground level so only the top is slightly
above the surface. The box should be covered
tightly to prevent contamination and lessen
evaporation. The inlet should be designed to
exclude surface drainage and prevent pollution.
This requires fencing off the area and providing
proper drainage. Figure 9-10 shows a spring
inlet protected in this manner. The screen on the
overflow pipe prevents the entrance of insects and
small animals. Another screen on the intake pipe
prevents large suspended particles being ingested
by the pump used to distribute the springwater.
This prevents mechanical failure or reduces it to
The flow of water from a spring located on
a steep slope of loose earth can be obtained by
the following two methods.
. Constructing deep, narrow ditches leading
from the spring to the point of collection.
. Constructing pipeline tunnels from the
spring to the collecting points. Pipe of large
diameter is more suitable for this purpose. The
water from the tunnels can be trapped by con-
structing a dam at the point of collection.
Digging is a more positive and more economi-
cal method of developing a spring than blasting.
You must proceed with great caution if you use
exposives to develop the yield from springs.
Blasting in unconsolidated rocks may shift the
sand or gravel in such a way as to divert the spring
to a different point.
The method used for the development of
springs as a water source will depend upon the
extent and characteristics of the flow. Thermal
(hot) springs should not be developed since their
waters are likely to be highly mineralized.
Regardless of the type of construction, all
springs must be covered. Surplus water should be
piped from the structure so surface water cannot