Well Development, Testing, and Disinfection
Domain 4 tests whether a new or repaired well is cleaned, tested, and made safe before it is put into service.
Development
Development removes drilling fines and loose formation material and improves yield. Methods include surging, bailing, jetting, air lift, and controlled overpumping. Development continues until the water is clear and sand content is acceptable.
Testing
A pump test measures stabilized yield, drawdown, and specific capacity in gallons per minute per foot of drawdown. Water quality sampling covers bacteria, nitrate, and site-specific contaminants such as arsenic or lead. Samples must be collected after disinfection and flushing, using clean technique.
Disinfection
Chlorine is added to the well, typically to a concentration of about 50–100 ppm, held for at least 24 hours, then flushed. The well is retested for coliform bacteria before use.
Worked example
A new well produces 20 gpm but is turbid. The driller surges and air-lifts until the water clears, disinfects with chlorinated water, waits 24 hours, flushes, and collects a bacteria sample. Reversing the order-disinfecting first-traps fines and gives a false sense of cleanliness.
Traps
Do not sample immediately after chlorination; residual chlorine can mask or alter results. Do not skip development because the yield looks adequate. Inadequate contact time and flushing are common causes of failed disinfection.