What is the chlorine dosage required for a brand new water main?

The correct choice is based on the standard practice for disinfecting newly installed water mains. A dosage of 50 parts per million (ppm) is typically required for effective chlorination. This concentration is sufficient to ensure that the entire system is thoroughly disinfected, which is crucial for eliminating any pathogens that may have been introduced during the installation process.

Using this dosage helps to create a residual level of chlorine, which not only disinfects but also protects against future contamination. It's important to note that the specific requirements can vary based on local regulations and the guidelines of organizations such as the American Water Works Association (AWWA).

Lower dosages may not provide adequate disinfection, while higher dosages could lead to excessive chlorine levels, which can be harmful or lead to unpleasant tastes and odors in the water. Therefore, the selected dosage of 50 ppm strikes a balance between effective disinfection and water quality.