Chlorination of HPC washed from water mains

The installation of new mains into water distribution systems, or the repai r of existing mains following breaks, often necessitates the disinfection o f the system which had been repaired. This is generally accomplished (at le ast in the US) by chlorination. The basis for existing criteria for the dis infection in such cases has not been placed on a firm technical footing. Fu rthermore, pressures for cost reduction (and thus reduction in chemical use ) are providing incentives for reexamination of current practice. in this w ork, we present results of studies on the inactivation of heterotrophic pla te count organisms washed from actual pipe sections by chlorine under condi tions used for main disinfection. Sodium and calcium hypochlorite, as well as dissolved chlorine, are used as germicidal agents. It is concluded that current practices can achieve high levels of reduction of these indigenous organisms.