Select the proper length of time and velocity for flushing a main.

The proper length of time and velocity for flushing a main is important to ensure that the system is thoroughly cleaned and any contaminants are properly removed. Flushing at a velocity of 2.5 feet per second is effective for scouring the pipes and ensuring that deposits and sediments are dislodged. The longer duration of 30 minutes allows for an ample amount of water to flow through the system, increasing the effectiveness of the cleaning process. This time frame also helps to ensure that the entire system is adequately flushed out, promoting better water quality and performance.

Moreover, in water systems maintenance, maintaining lower velocities for an extended period can help minimize disturbances in the sediment layers while ensuring that the water flow is sufficient to flush out particles. In this case, the combination of a 30-minute flushing duration with a velocity of 2.5 feet per second aligns with best practices for effective water system maintenance.