Open File Report 1966-05

Open File Report 1966-05

OFR 1966-05

Exploration and Testing of an Unconfined Aquifer Near Cadogan, Alberta

This report contains the results of an aquifer exploration and testing program for an unconfined aquifer about 10 miles southwest of Cadogan. Four test holes were drilled and a 5-day constant-rate pump test and a step-drawdown test conducted. Two observation wells, at distances of 111 and 389 feet from the pumped well, were utilized during the constant-rate test.

The pumped well was especially designed and constructed for the purpose, using information gained during test drilling concerning size characteristics of the aquifer materials. The test-hole site at which the maximum saturated thickness of aquifer was observed was considered the most favorable one for the pumping test. The size characteristics of the aquifer material, which is also an important factor in choosing a pumping-test site, showed only minor variations at the four test-hole locations so that saturated thickness became the important criterion in site selection.

On the basis of the constant-rate and step-drawdown test results, it is predicted that the maximum 20-year safe yield for a single production well pumping continuously and completed at the base of the aquifer is about 42 imperial gallons per minute (igpm). This estimate is subject to the following limitations:

a. available drawdown and aquifer size characteristics at any production well site must be the same as those at the test site

b. construction and development of any production well must be the same as those for the test well

c. it has not been possible to take into account either the limited extent of the aquifer or recharge of the aquifer by precipitation.

It is nevertheless believed that the 42 igpm figure is a reasonable working value on which to base initial estimates of well-field production. Some estimates are provided in this report for pairs of wells separated by specified distances. It is important to note that maximum 20-year safe yields for the calculated examples range from 56 to 75 igpm (36 to 83 per cent production increases) for separations ranging from 1000 to 6000 feet. As the number of wells is increased, the effects of interference between wells will become even more serious.

The well pumped during the test was sold to the contractors. Development of this well, although adequate for testing purposes, was inadequate for its use on a steady production basis. This was evident from the gradual entry of appreciable amounts of sand into the well during testing period. Before the well is used as a producer this sand should be removed and further development carried out.