Pumps, Water Systems, and Disinfection
This domain tests the equipment side of the trade: selecting and setting a pump against a well's real drawdown behaviour, controlling cycling, and bringing a new or repaired well into service biologically clean.
Pump and system rules
- Submersible pumps dominate deep wells; jet pumps suit shallow settings and low yields.
- Set the pump below the worst-case pumping level with a margin, and well above the bottom so it does not pull sand.
- A check valve protects the pump from backspin and keeps the column primed; a torque arrestor limits starting shudder.
- The pressure tank is sized on drawdown, and its air precharge is about 2 psi below the cut-in pressure (for a 30/50 switch, about 28 psi).
- Specific capacity from a flow test tells you where the pumping level really sits at the design rate.
Disinfection
Shock chlorinate to roughly 100 mg/L free chlorine, hold 12–24 hours with taps opened to reach the lines, flush until chlorine is gone, then retest for total coliform and E. coli before the well goes into service.
Worked example
A 6-inch well holds a 120-ft water column. Volume = 0.196 ft² × 120 ft = 23.6 ft³ = 176 gallons. To reach 100 mg/L using 5.25% household bleach (about 52,500 mg/L): 176 gal × 100 ÷ 52,500 = 0.34 gallon, roughly 1.3 quarts. Note how far that is from the folklore "one gallon per hundred gallons," which yields about 500 mg/L.
Traps
Setting the pump above the pumping level so it breaks suction; ignoring precharge; under-dosing chlorine; skipping the retest; and treating a coliform hit as a water-quality nuisance instead of a construction or seal defect.