Measurement of Static Water Level Elevation
The QAPjP should include procedures for measuring the static water level elevation in
each well prior to each sampling event, as required in 264.97(f). The QAPjP also should
include procedures for measuring the depth of each well prior to each sampling event.
Measuring water level elevations on a regular basis is important for determining whether
horizontal and vertical components of the hydraulic gradient have changed since initial site
characterization. A change in ground water flow direction may necessitate modifying the
design of the ground water monitoring system.
Water level elevations typically have been measured using a number of devices and
methods, including the following:
Steel tape coated with carpenter's chalk (wetted tape method);
Float type devices;
Acoustic well probes;
Electric sensors; and
These devices and methods are described in more detail in Aller et al. (1989), USEPA
(1987a), and Dalton et al. (1991). Dalton et al. (1991) provide the water level measurement
accuracy of each of these devices. The QAPjP should specify the device to be used for water
level measurements, as well as the procedure for measuring water levels.
Regardless of the method or device chosen to measure the water level elevation in a
monitoring well or piezometer, the following criteria should be met when determining water
Prior to measurement, water levels in piezometers and wells should be allowed
to recover for a minimum of 24 hours after well construction, well
development, or well purging. In low yield aquifers, recovery may take longer
than 24 hours. If necessary, several water level measurements should be made
over a period of several days to ensure that recovery has occurred.
Water levels should be measured with a precision of 0.01 foot. Water levels
should be measured from the surveyed datum on the top of the inner well