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3.3 Checking the Piezometer Performance
If a rough check of the piezometer performance is needed, the following procedure is
recommended:
1)
Lower the piezometer to a point near the bottom of a water filled borehole, or below the
surface of a body of water.
2)
Allow 15-20 minutes for the piezometer to come to thermal equilibrium.
3)
Using a readout box, record the reading at the current depth.
4)
Raise the piezometer by a measured increment.
5)
Record the reading on the readout box at the new depth.
6)
Using the factory calibration factor, calculate the change in water depth.
7)
Compare the calculated change in depth with the measured depth increment. The two values
should be roughly the same.
Alternative Method using a dip meter:
1)
Lower the piezometer tip to a measured depth below the water surface.
2)
Allow 15-20 minutes for the piezometer to come to thermal equilibrium.
3)
Using a readout box, record the reading at that level.
4)
Calculate the elevation of the water surface using the given calibration factor.
5)
Compare the calculated elevation to the elevation measured using the dip meter.
There are a couple of things that can affect this checking procedure:
If the density of the water is not 1gm/cc.
If the water is saline or turbid.
The water level inside the borehole may vary during the test. This is due to the
displacement of water caused by the cable as it is raised and lowered in the borehole. The
smaller the borehole is, the greater the displacement will be. For example, a 4500S-50kPa
piezometer lowered 50 feet below the water column in a one inch (.875 inch ID)
standpipe will displace the water level by more than four feet.
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