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an effective disinfectant and residual concentrations can be maintained to guard against biological contamination in the water distribution system. Coliform bacteria are indicator organisms that are ubiquitous in nature. They are a useful tool because of the ease in monitoring and analysis. The City collects weekly samples for total coliforms at various locations in the distribution system and monthly at each well. If coliform bacteria are detected in the drinking water sample, it indicates a potential problem that needs to be investigated and followed up with additional sampling. It is not unusual for a system to have an occasional positive sample. Although USEPA set the MCLG for total coliforms at 0 percent positive, there is no commercially available technology that will guarantee 0 percent positive every single month; therefore, the cost of achieving the PHG cannot be estimated. The City will continue several programs that are in place to prevent contamination of the water supply with microorganisms. These include: Disinfection using chlorine or chloramines and maintenance of a chlorine residual at every point in the distribution system Monitoring throughout the distribution system to verify the absence of total coliform and the presence of a protective chlorine residual • Flushing program in which water pipelines known to have little use are flushed to remove stagnant water and bring in fresh water with residual disinfectant • Cross -connection control program that prevents the accidental entry of non - disinfected water into the drinking water system. Gross Alpha, Gross Beta, and Uranium — The only BAT for the removal of gross alpha in water for large water systems is reverse osmosis, which can also remove gross beta, and uranium, if detected. Gross alpha was detected above the MCLG in the local groundwater and in the surface water supplied by MWDSC. Gross beta was detected above the MCLG in the surface water supplied by MWDSC. Uranium was detected above the PHG in the local groundwater (Wells 16, 18, 20, 21, 24, 27, 28, 29, 30, 33, City of Santa Ana 7 2019 PHGs Report 75C-10