the depth of the well.
Then compute the drawdown at various levels of
pumping, and arrive at the percent of drawdown by dividing the drawdown by
the original depth of water.
g. Finally, determine the recovery rate of the well. The ground does
not give up its water all at once to the pumped well.
The flow of water
into the well is held back by the resistance of the ground to the flow of
water through the pores. This resistance varies in every well. Thus, the
rate of flow, or time required to refill the well to the static level,
depends on the resistance to flow in the ground. The term used to describe
this is recovery. Recovery is expressed as a percent of the well's total
water. Wells that do not totally recover after four hours should be avoided
as they could be pumped dry and never recover. Determine the recovery rate
by dividing the total amount of water contained in the well originally by
the amount of water recovered after four hours. Recovery is expressed as a
percent of the total in a given period of time (four hours).
7. Pumping tests are made on wells to determine their capacity; The
measurements that should be made in testing wells include the following:
a. The depth of the well.
b. The volume of water pumped per minute or per hour.
c. The depth to the static water level before pumping is started.
d. The depth to the pumping level at one or more constant rates of
pumping.
e. The recovery of the water level after pumping is stopped.
f. The length of time the well is pumped at each rate during the
testing procedure.
8. Use the following
procedures
to
conduct
more
extensive
well
test
measurements:
a. The pump and generator used for testing a well should be capable of
continuous operation at a constant rate of pumping for several hours. Army
standard is the 15-kw generator set and a 50-GPM submersible pump for wells
at or less than a 600-foot depth and the 30-kw generator set and 50-GPM
submersible pump for wells between 600 and 1,200 feet.
To avoid an
undesirable forced shutdown in the middle of the test, it is important that
the equipment be in good condition for an
4-7
QM4912
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