Well Development
All monitoring wells should be developed to create an effective filter pack around the
well screen, to rectify damage to the formation caused by drilling, to remove fine particles
from the formation near the borehole, and to assist in restoring the natural water quality of
the aquifer in the vicinity of the well. Development stresses the formation around the screen,
as well as the filter pack, so that mobile fines, silts, and clays are pulled into the well and
removed. The process of developing a well creates a graded filter pack around the well
screen. Development is also used to remove any foreign materials (drilling water, muds, etc.)
that may have been introduced into the well borehole during drilling and well installation, and
to aid in the equilibration that will occur between the filter pack, well casing, and the
formation water.
The development of a well is extremely important to ensuring the collection of
representative ground water samples. If the well has been properly completed, then adequate
development should remove fines that may enter the well either from the filter pack or the
formation. This improves the yield, but more importantly it creates a monitoring well capable
of producing samples of acceptably low turbidity. Turbid samples from an improperly
constructed and developed well may interfere with subsequent analyses.
When development is initiated, a wide range of grain sizes of the natural material is
drawn into the well, and the well typically produces very turbid water. However, as pumping
continues and the natural materials are drawn into the filter pack, an effective filter will form
through a sorting process. Inducing movement of ground water into the well (i.e., in one
direction) generally results in bridging of the particles. A means of inducing flow reversal is
necessary to break down bridges and produce a stable filter.
The common methods for developing wells are described by Aller et al. (1989) and
Driscoll (1986) and include:
Pumping and overpumping;
Surging with a surge block;
Airlift pumping; and
Air surging.
November 1992
6 46






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