Well Development, Disinfection, Pumping Equipment, and Abandonment
This domain tests what happens after the hole is drilled: removing drilling fluids and fines, disinfecting the well, selecting and setting the pump, and sealing a well that is no longer used. The exam wants sequence and verification, not just a list of tools.
Development
Development removes mud cake, silt, and fine sand so the aquifer feeds the well efficiently. Common methods are surging, bailing, air-lift pumping, and jetting. Continue until the water is clear and sand-free, and record yield and drawdown.
Disinfection
New and repaired wells are disinfected with a chlorine solution of at least 100 mg/L (ppm), kept in contact with the casing, screen, and pump for about 24 hours, then flushed. Collect the bacteriological sample only after the chlorine has been flushed out; sampling too soon gives a false positive.
Pumps and abandonment
Submersible pumps suit deep wells, jet pumps shallow suction lifts, and turbine pumps high-capacity applications. Set the pump above the screen and size it to the tested yield. Abandonment requires removing obstructions, filling the borehole with approved grout from bottom to top, sealing the casing, and filing the required report.
Worked example
A new 200-foot well yields 20 gpm but stays turbid. Surging and bailing remove fines until the water clears, then the well is chlorinated at 100 ppm for 24 hours, flushed, and sampled for coliform bacteria. The pump is set at 140 feet, above the screen. If the sample is positive, rechlorinate and resample before putting the well into service.
Traps that cost marks
Sampling while chlorine is still present; abandoning a well by filling it with sand or gravel; setting the pump in the screen; and skipping development because the yield looks adequate.