Exercise 14
Part 1: A pumping well has a known efficiency of 90 percent at a pump rate of 500 m3/d. Would the measured drawdown in the well be greater than the expected drawdown or less than the expected drawdown?
Part 2: At a pumping rate of 600 m3/d, would you expect the efficiency to be higher—that is, greater than 90 percent—or lower—that is, less than 90 percent? Justify your answer.
Part 3: A pumping well is installed in a confined aquifer with a known transmissivity (0.0003 m2/s) and storativity (0.0004). The diameter of the borehole used to install the well is 0.30 m.
- Using the radius of the borehole (0.15 m) as [latex]r[/latex], calculate the drawdown in the well after 24 hours of pumping at 500 m3/d.
- The well is pumped for 24 hours, and the measured drawdown in the well is 17 meters. Calculate the well efficiency for that pumping rate and determine the amount of well loss.
Part 4: An aquifer test is performed in a pumping well with no observation wells (i.e., a single‑well aquifer test). The resulting transmissivity is 1,000 ft2/d. If we assume that the well has an efficiency of 75 percent, which of the following three statements is the most appropriate? Circle one and justify your answer.
- The test provides a good estimate of the actual formation transmissivity.
- The test results overestimate the actual formation transmissivity.
- The test results underestimate the formation transmissivity.