Environmental Engineering Reference
In-Depth Information
attached to an electronic sounding device at the tip that emits an audio alarm when water
is encountered.
The depth to groundwater using the water level indicator should be measured from the
top of the monitoring well casing to the water table surface. Usually a reference mark is
placed at some common point on the top of the monitoring well casing, because accurate
measurements to within 3 mm (1/100 of a foot) are routinely required when measuring
the depth to groundwater. This mark should be consulted every time a water level mea-
surement reading is conducted to ensure consistency and accuracy because the top of the
monitoring well casing is not always level.
As explained in Chapter 3, the elevation at the top of the casing of the monitoring well
must also be measured accurately to determine the direction of groundwater flow. The
geographic position and elevation at the top of the casing of each monitoring well should
be measured by a licensed surveyor.
If the monitoring wells will be used for any length of time, usually more than 1 year,
consideration should be given to periodically checking the elevation of each monitor-
ing well to ensure the elevation of the casing has not changed. The elevation can change
from natural causes, such as frost heave, and from anthropogenic causes, such as damage
caused if snow removal or other equipment accidentally run into the monitoring well.
Figure 4.27 is a photograph of a Teflon bailer containing groundwater with relatively
high turbidity (cloudy appearance) extracted from the monitoring well located near the
bottom of the picture. Teflon bailers are routinely used for collecting groundwater sam-
ples. The bailer pictured in Figure 4.27 has a check valve at the bottom that allows water
to fill the bailer when groundwater is encountered as the bailer is slowly lowered into the
well. After the check valve is engaged upon lifting of the bailer, water is prevented from
escaping.
FIGURE 4.27
Teflon bailer containing groundwater. (Photo by Daniel T.
Rogers.)
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