After a new main is installed, which chlorine-related step is described as required prior to flushing?

• A. Flushed with clean water for 24 hours and put into service
• B. Filled with a solution of 25 ppm to 50 ppm of free chlorine for at least 24 hours prior to flushing
• C. Left unflushed and allowed to sit
• D. Photographed mapping

Answer: (B)

Disinfecting the new main with chlorine before flushing is required. After installation, the pipe must be filled with a free chlorine solution at about 25 to 50 mg/L and kept in contact for at least 24 hours. This ensures any bacteria or microorganisms introduced during construction are killed, protecting public health before the line is put into service. After this contact time, the line is flushed to remove the chlorine and any debris, and residual chlorine levels are checked before service begins. Flushing with clean water alone would not disinfect, leaving the line unflushed would risk contamination, and photographing mapping has no role in the disinfection process.