When preparing to turn on a 12-inch water main within 12 hours, what is the required amount of chlorine?

For the process of disinfecting a newly installed or repaired water main, the recommended amount of chlorine is essential to ensure that any harmful bacteria or pathogens present in the system are effectively eliminated. A concentration of 200 parts per million (ppm) is the standard for this type of disinfection.

The high concentration of 200 ppm provides a sufficient level of chlorine to ensure the water main is effectively sanitized before it is placed back into service. This level of chlorination allows for adequate contact time with the water to kill any microorganisms that could pose a health risk to consumers. Following the required retention time and proper flushing procedures after chlorination will help ensure that the system is safe for use.

The other concentrations available in your question are either lower than the recommended standard or are less common for this specific purpose, making 200 ppm the correct choice.