Monitoring Wells and Piezometers
In
environmental site assessments we use wells to monitor the conditions
of the groundwater. Here is a diagram of the construction of a
groundwater monitoring well:
This
is a 100-foot deep 4” diameter well (not to scale) with the bottom 30
feet screened. The blank section is a Schedule 40 PVC pipe. The screen
is the same pipe but with slots to enable entry of the groundwater. In
this case, groundwater is at 80 feet below the surface and the well
screen is designed so that 20 feet will be under and 10 feet above the
water table.
Erroneously, groundwater monitoring wells are some times called piezometers.
In Greek, piezein means to press, therefore piezo has come to mean pressure. Piezometers are wells designed to measure pressure of the groundwater.
Groundwater develops pressure when it flows through or being retained by confined aquifers.
The
above diagram illustrates a confined aquifer underlying a non-confined
aquifer. The water in the confined aquifer is under pressure. When a
well is inserted, the water will rise in the well. The degree of rise of
the water is an indication of the pressure in the aquifer. When we
measure the rise, we know the pressure.
Piezometer is a non-pumping well, generally of small diameter for measuring the elevation of a water table. Unlike monitoring wells, the piezometer has no screen, it is open only at the top and bottom of the casing.
The diagram below depicts three “nested” piezometers arranged to measure the pressure in the aquifer at different depths.
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