Straight-line methods

Cooper-Jacob on one well, Theis recovery after pumping stops, and well losses from a step-drawdown test.

The Tools menu has the classic straight-line methods. They open in one window with a tab for each.

Cooper-Jacob

Tools > Cooper-Jacob... fits a straight line to drawdown against the logarithm of time at one well. Transmissivity comes from the slope per log cycle and storativity from where the line crosses zero drawdown. The straight line holds only once u = r squared S / (4 T t) is small, so with Line starts at empty PumpPilot starts the line on the later half of the record and moves the start later until u is at most 0.05 at every point used. Give a start time to choose it yourself.

At the pumping well the slope still gives T, but S depends on the effective well radius and on well losses; take S from an observation well.

Theis recovery

Tools > Theis recovery... uses the readings after pumping stops. Residual drawdown plotted against the logarithm of t / t', the time since pumping started over the time since it stopped, is a straight line whose slope gives T. The schedule must have a step at rate 0 where pumping stopped; see Entering a test.

Step-drawdown

Tools > Step-drawdown... fits Jacob's s = BQ + CQ squared to the drawdown in the pumping well at the end of each step of equal length. B is the aquifer loss and C the well loss; the efficiency at each rate is the share of the drawdown due to the aquifer, BQ / (BQ + CQ squared). When the schedule has two or more steps and the pumping well has readings, the table is filled from them.

The fit minimises the error in drawdown, which is what was measured, rather than the textbook line through s / Q against Q, which gives the low-rate steps more weight.