TM 5-814-7
Figure 8-1. Monitoring well details.
method is 4 inches (2 inches if inserted into hollowstem
creased hydraulic conductivity around the sampling
augers). However, larger non-continuous auger drilling
interval and to prevent clogging. The filter pack consists
equipment can be used in primarily finegrained deposits
of gravel or sand placed in the borehole around the
to install shallow wells with casing diameters up to 12
sampling interval of the well (see figure 8-2).
inches.
Selection of the grain-size of a filter pack requires
(2) If well drilling methods are employed,
sampling and sieve analysis of the aquifer materials.
drilling fluids should be chosen to minimize
Proper installation of the filter pack is necessary to
contamination, and care should be taken to prevent entry
prevent separation of the fine and coarse particles and
of drilling fluids into aquifer flow zones. Generally, all
consequent bridging of the material, which could result in
additives or drilling fluids are disallowed at DA facilities
formation of void spaces. Use of a tremie pipe is
except clean water and/or bentonite clay.
When
recommended for installation of the filter pack; however
subsurface or contaminant conditions warrant, a
in shallow wells, slow pouring or shovelling may be
variance should be requested and justification submitted
acceptable. For wells drilled in soil, the minimum boring
to the Major Command for consideration.
diameter in the filter pack portion of the well should be at
(3) Filter packing is used to develop a
least 4 inches larger than the inner diame
zone of in-
8-3
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