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104 Chapter 3 Water Sources: Groundwater
Domestic systems commonly employ one of the following pumps:

1. For lifts under 25 ft (7.62 m), a small reciprocating or piston pump
2. For lifts up to 125 ft (38.10 m), a centrifugal pump to which water is lifted by
recirculating part of the discharge to a jet or ejector
3. For lifts that cannot be managed by jet pumps, a cylinder pump installed in the well
and driven by pump rods through a jack mounted at the well head
Systems of choice normally incorporate pressure tanks for smooth pressure-switch
operation. The well itself may provide enough storage to care for differences between
demand rates in the house and flow rates from the aquifer. This is why domestic wells
are seldom made less than 100 ft (30 m) deep even though the water table may lie only a
few feet below the ground surface. Deep wells and pump settings maintain the supply
when groundwater levels sink during severe droughts or when nearby wells are drawn
down steeply.
Large-capacity systems are normally equipped with centrifugal or turbine pumps
driven by electric motors. A sufficient number of pump bowls are mounted one above
the other to provide the pressure necessary to overcome static and dynamic heads at the
lowest water levels. For moderate quantities and lifts, submersible motors and pumps,
assembled into a single unit, are lowered into the well. The water being pumped cools
the compact motors normally employed. Large-capacity wells should be equipped with
suitable measuring devices. Continuous records of water levels and rates of withdrawal
permit the operator to check the condition of the equipment and the behavior of the
source of supply. This is essential information in the study and management of the
groundwater resource.

3.17.7 Development
Steps taken to open up or enlarge flow passages in the formation in the vicinity of the well
are called development. Thorough development of the completed well is essential regard-
less of the method of construction used to obtain higher specific capacities, to increase ef-
fective well radius, and to promote efficient operation over a longer period of time. This
can be achieved in several ways. The method selected depends on the drilling method
used and on the formation in which the well is located. The most common method em-
ployed is overpumping, that is, pumping the well at a higher capacity than the design
yield. Temporary equipment can provide the required pumping rates. Pumping is contin-
ued until no sand enters the well. Other methods used include flushing, surging, high-
velocity jetting, and backwashing. Various chemical treatments and explosives are used in
special circumstances.

3.17.8 Testing
After a well is completed, it should be tested to determine its characteristics and
productivity. Constant-rate and step-drawdown pumping tests are used for this pur-
pose. The test should be of sufficient duration; the specific capacity of a well based on
a 1-hour test may be substantially higher than that based on a 1-day test. Longer dura-
tion is also required to detect the effect of hydraulic boundaries, if any. The extent to
which the specific yield would decrease depends on the nature and the effectiveness of
the boundaries.