conductivity, storativity, and transmissivity may be impossible. However, an aquifer test can

provide information on the presence of conduits, on storage characteristics, and on the

percentage of Darcian flow. McGlew and Thomas (1984) provide a more detailed discussion

of the appropriate use of aquifer tests in fractured bedrock, and the suitable interpretation of

test data. Dye tracing also is used to determine the rate and direction of ground water flow in

karst settings (Section 5.2.4).

Several additional factors should be considered when planning an aquifer test:

Owners and operators should provide for the proper storage and disposal of

potentially contaminated ground water pumped from the well system;

Owners and operators should consider the potential effects of pumping on

existing plumes of contaminated ground water;

In designing aquifer tests and interpreting aquifer test data, owners/operators

should account and correct for seasonal, temporal, and anthropogenic effects on

the potentiometric surface or water table. This is usually done by installing

piezometers outside the influence of the stressed aquifer. These piezometers

should be continuously monitored during the aquifer test. It may be necessary

to correct for anomalies when evaluating the aquifer test data. A qualified

ground water scientist could recommend several methods for this, many of

which are presented by Kruseman and deRidder (1989); and

EPA recommends the use of a step drawdown test to provide a basis for

selecting discharge rates prior to conducting a full scale pumping test. This

will ensure that the pumping rate chosen for the subsequent pump test(s) can

be sustained without exceeding the available drawdown of the pumped wells,

and will produce a measurable drawdown in the observation wells.

Certain flowmeters have recently been recognized for their ability to provide accurate

and vertically discrete measurements of hydraulic conductivity. One of these, the impeller

flowmeter, is currently available commercially; more sensitive types of flowmeters (i.e., the

heat pulse flowmeter and electromagnetic flowmeters) should be available in the near future.

Use of the impeller flowmeter requires running a caliper log to measure the uniformity of the

diameter of the well screen. The well is then pumped with a small pump operated at a

constant flow rate. The flowmeter is lowered into the well and the discharge rate is measured

every few feet by raising the flowmeter in the well. Hydraulic conductivity values can be

calculated from the recorded data using the Cooper Jacob (1946) formula for horizontal flow

to a well. Use of the impeller flowmeter is limited at sites where the presence of low

permeability materials does not allow pumping of the wells at rates sufficient to operate the

flowmeter. The applications of flowmeters in the measure of hydraulic conductivity is

described by Molz et al. (1990) and Molz et al. (1989).

November 1992

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