What is the recommended contact time for chlorine in a well-disinfection procedure before flushing?

• A. 12-24 hours
• B. 1-2 hours
• C. 6-8 hours
• D. 24-48 hours

Answer: (A)

The key idea is that enough time must pass for the chlorine to stay in contact with all interior surfaces of the well and plumbing so it can inactivate microorganisms. In well disinfection, allowing the chlorine solution to remain in place for about 12 to 24 hours gives the disinfectant time to penetrate sediments, screens, and narrow passages and to achieve reliable microbial kill before flushing. Shorter times, like 1–2 hours, may not provide sufficient contact, especially in colder or more stagnant water. While 6–8 hours is closer, it often isn’t as robust as the 12–24 hour window. Extending to 24–48 hours isn’t typically necessary and can unnecessarily extend the process. After the contact period, flushing removes residual chlorine and any dislodged contaminants before use.