7.2.2

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;

Pressure transducers;

Acoustic well probes;

Electric sensors; and

Air lines.

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

level elevations:

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

November 1992

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