When it is impossible to keep the trench or water main pipe dry during instal- lation, treat the pipe and any water in the trench with a chlorine material to destroy bacteria. Thoroughly flush the system upon completion of the installation.
Repairing Damaged Water Lines. Damaged water mains have a high potential for becoming contaminated. For instance, if digging or excavating in the area caused the damage, there also may be ruptured sewer lines, allowing untreated sewage to enter the trench during repairs. Under these conditions, treat water in the trench with a chlorine solution to destroy bacteria before beginning repair work. Hypochlorite tablets work best because they dissolve slowly and continue to release hypochlorite while pumping water from the excavation. After completing the repairs, flush the system to remove contaminants and particulate matter. Always perform a biological test for bacterial contamination before using water from the repaired system.
METHODS FOR DISINFECTING WATER LINES
Chlorine compounds are the acceptable pesticides used for disinfecting potable water systems. The three methods used for applying chlorine compounds include tablet or granule, continuous feed, and slug.
Tablet or Granule Method
The tablet or granule method requires that you keep the pipes dry until you complete the water main construction. The AWWA warns against using calcium hypochlorite granules on solvent-welded plastic pipe or screw-joint steel pipes be- cause of the danger of fire or explosion from the reaction of joint compounds with the calcium hypochlorite.
Following the AWWA standards, state and local codes, and the pesticide label, place the tablets or granules into pipe sections as you connect them. Once you have completed the water main, slowly fill it with water and eliminate any air pockets. Fol- low label or AWWA standards for the rate of filling. Label instructions will help you determine how long the solution must remain in the system before flushing. Cooler water temperatures usually require a longer holding time. Until properly flushed, do not allow anyone to use any water in the pipes and be sure this water cannot flow into other parts of the system.
Calcium Hypochlorite Granules. During construction, place granules at the upstream end of the first section of pipe, at the upstream end of each branch main, and at 500-foot intervals along the entire mainline system. Refer to the pesticide label for the quantity of granules to use. The diameter of the pipe and length of the water main determine the total amount to use.
Calcium Hypochlorite Tablets. During construction, place the prescribed number of tablets in each section of pipe and in each hydrant, hydrant branch, and in other branches of the mainline. Refer to the pesticide label for the number of tablets to use, based on the diameter of the pipe. Secure tablets to the pipe using an approved adhesive. Glue these to the top inside surface of each pipe; refer to the pesticide label and AWWA standards for the method of adhering tablets to the pipe and for the recommended type of adhesive to use.
Continuous Feed Chlorination
The process of continuous feed chlorination involves adding a liquid chlorine solution to water in the main over time to achieve prescribed concentration. This