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Pipe material's influence on chlorine residuals in a municipal drinking water distribution system

Kroeger, Ryan

Drinking water must be treated chemically in order to eliminate pathogenic microbes. Fully treated water is legally required to contain a certain concentration of disinfectant to prevent recontamination in the distribution system. This additional disinfectant is called disinfectant residual. The U.S. Environmental Protection Agency (EPA) regulation mandates that municipalities monitor residual concentrations throughout the distribution system to ensure that safe water is delivered to consumers. An Oklahoma municipality detected multiple sites throughout their distribution system with substandard residual concentrations during routine monitoring. The Oklahoma State Environmental Science Graduate program sampled 119 sites throughout the distribution system with a HACH SL 1000 portable analyzer. The HACH unit was used to measure free chlorine, total chlorine, monochloramine, free and total ammonia, total alkalinity, nitrite, and ph. Laboratory research generally supports the idea that pipe material can influence residual concentrations. Data were analyzed to determine if there were any significant differences in water quality between 4 different pipe materials that are used in the city’s distribution system (asbestos-cement, cast-iron pipe, ductile-iron pipe, and PVC). Results do not indicate that pipe material influences total chlorine, monochloramine, free ammonia, total ammonia, total alkalinity, nitrite, and pH. Increased distance from the treatment facility was found to result in lower residual concentrations. Increased residual concentration resulted in decreased bacterial presence as measured by heterotrophic plate counts.