2
For the Model 4500MLP, the filter stone shown in Figure 1 is replaced by a tube leading to a
much larger, curved, and porous filter stone, which is forced against the walls of the borehole by
a spring mechanism. The spring mechanism can be actuated remotely after the piezometer has
been lowered in its closed configuration to its desired location. This is shown schematically in
Figure 2 and Figure 3.
With the filter stones pressed against the wall of the borehole in this manner, the borehole can be
filled completely with bentonite cement grout without running the risk of getting the filter stone
plugged with bentonite, or having substantial amounts of the impervious bentonite interposed
between the piezometer diaphragm and the ground water in the surrounding soil.
Figure 3 - 4500MLP System
Figure 2 - Close up of 4500MLP
