Operating Well Pumps. Pump wells carefully and keep pumping rates
within the specified design range. Continuous operation is generally preferable to
frequent starting and stopping, but varying water demand and storage capacity usually
require some combination of on and off time. Both over-pumping and frequent starting
and stopping can damage the aquifer, resulting in reduced yield. In coastal areas,
over-pumping may also cause saltwater intrusion. Frequent start/stop operation also
shortens equipment life and consumes more energy. It is usually preferable to limit
pump starts to less than once per hour. Additional information on well pump
information is included in pars. 2.2.14 and 2.2.31.
Measuring Water Levels and Drawdown. Well tests are necessary to
evaluate the performance of a well. These tests include measuring the static water
level, the pumping rate, the pumping levels at various times after pumping has started,
and the increasing water levels after pumping has stopped. Measure the static level,
pumping level, and drawdown on each well as often as practical. If a daily
measurement cannot be made owing to a large number of wells or difficulty in taking
the measurements, measure the level in each well at least twice a month at as near the
same time as possible. A sample calculation for static level, pumping level, and
drawdown is included in Appendix A.
Orifices, meters, and pitot tubes used to measure flow rates are
described in pars. 2.1.2 and 2.1.4.
Measure water levels using the air line method, electric sounders,
wetted tape, or electrical depth gages. The most common method of depth
measurement is the air line method, which is explained below and depicted on Figure
Place an air line of known length in a well (unless one has
been permanently attached) to a depth below the expected pumping level. Connect the
surface end of the line to an air pump and connect a pressure gage to the line so that
air pressure in the line can be read. Make all joints airtight.
With the well pump shut down, apply air pressure through
the air pump until the gage needle no longer registers any increase in pressure. The
gage reading then shows the amount of pressure that was necessary to force the
standing water out of the air line. This is directly proportional to the height of the water
standing in the well above the bottom of the air line. Multiply the gage pressure in psi
by 2.31 to determine the height in feet; multiply kiloPascals (kPa) by 10.1973 to obtain
centimeter (cm) of water.