After a major repair to a potable water system following a main break, what disinfection procedure is recommended before returning the system to service?

• Disinfect with a 10 ppm chlorine solution for 1 hour.
• Boil all water from the system for 10 minutes.
• Disinfect with a 50 ppm chlorine solution for 24 hours.
• Flush with clean water for 1 hour.