Which option best describes the complete process to disinfect a well using chlorine?

• A. Need 50 ppm chlorine in the system for 12–24 hours; add bleach based on pipe diameter (e.g., 1 gallon for a 16 inch pipe), let stand 30 minutes, surge pump, open farthest tap until chlorine odor is detected, wait 24 hours, pump well water to the ground until no chlorine odor, and test for coliform
• B. Add a small amount of chlorine and flush immediately
• C. Use heat disinfection by boiling the well water
• D. Disinfect using UV light only

Answer: (A)

Disinfecting a well with chlorine relies on getting enough chlorine into every part of the system and keeping it there long enough to inactivate microorganisms, then removing the residual and confirming the system is clean.

The best approach specifies dosing to produce about 50 ppm of chlorine in the entire system and maintaining a 12–24 hour contact time. Circulating or surging the chlorine through the well and distribution lines helps ensure the entire interior—the well itself, storage tanks, and all piping—is filled with the disinfectant. Opening the farthest tap until you detect the chlorine odor makes sure every component is reached. After the contact period, you flush the system by pumping water out until there is no chlorine odor, and you test to verify that disinfectant residual remains and that coliform is absent. This combination—adequate concentration, sufficient contact time, complete distribution, thorough flushing, and verification—provides reliable disinfection.

The other options don’t meet these requirements. Using only a small amount of chlorine with immediate flushing fails to achieve the necessary contact time and distribution. Heat disinfection by boiling the well water isn’t practical for disinfecting the entire well system and piping. UV disinfection alone does not leave a residual disinfectant in the distribution system and may be ineffective if water quality is not ideal, making it insufficient by itself for a well.