6.7

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;

Backwashing;

Surging with a surge block;

Bailing;

Jetting;

Airlift pumping; and

Air surging.

November 1992

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