After the applicable retention period, heavily chlorinated water should not remain in prolonged contact with pipes. To prevent damage to the pipe lining or cor- rosion damage to the pipe itself, you must flush the heavily chlorinated water from the main until the chlorine concentration in the water leaving the main is no higher than that generally prevailing in the system or is acceptable for domestic use. Be sure to read the “Hazards” section below for special precautions needed for disposing of high-chlorine residue water.
A very important step in disinfecting water mains is bacteriological testing to detect contamination and to verify adequate disinfecting procedures. After final flushing and before the water main is placed into service, collect one or more samples from the new or repaired main and from each branch in the water line. In extremely long mains, collect samples every 200 feet along the length of the line as well as at its end. Place sampled water into sterile bottles treated with sodium hyposulfite using methods prescribed by state or local standards. According to these standards, have the water samples tested for bacteriological quality by a certified laboratory. The samples must be free of coliform organisms.
If trench water has entered the main during construction or repair, allow water to sit in the treated main for at least 16 hours after final flushing before taking samples. Under these conditions, take samples at intervals of approximately 200 feet along the length of the main. Label the samples by their location.
When bacteriological testing indicates the presence of coliform organisms, the system must be retreated by one of the methods described above. A water main system cannot be used until bacteriological testing shows it is safe. However, before retreat- ing, test the water entering the system to be sure it is not the source of contamination.
AVOIDING HAZARDS AND POTENTIAL PROBLEMS
Using chlorine compounds for disinfecting water mains has several associated hazards and potential problems that you must recognize.
Chlorine compounds may cause serious skin and eye injuries and may dam- age your respiratory tract if you inhale chlorine vapors. Wear protective clothing to prevent skin contact with chlorine solutions or gas. The type of protective clothing required is dictated by the pesticide label and the conditions of use. For example, when working in a trench that contains water treated with chlorine, wear waterproof boots, chemical-resistant gloves, and chemical-resistant outer clothing; also wear protective goggles. In addition, be sure to wear protective eyewear and chemical-resistant gloves when taking samples of water from the system.
Keep chlorine pesticides stored in dry locations. Make sure storage areas are locked to prevent unauthorized entry.
Follow label instructions and state and local regulations for disposal of empty containers and unused pesticide residue.