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Water Quality Testing - Disinfection By-Products & Unregulated Contaminants
Disinfection by-products are substances that form when chlorine interacts with impurities in ground water. Chlorine is added to treat water for the control of microorganisms such as viruses and bacteria. Samples are collected from representative sample locations within the distribution system and tested for four trihalomethanes and 5 haloacetic acids. This testing occurs annually during the summer months when concentrations are expected to be highest. Since the levels of organic matter in the source water are low and the utility introduces relatively small amounts of chlorine, disinfection by-product levels are also very low in Madison drinking water.
State and federal regulations require that some water utilities monitor for specified unregulated contaminants, substances for which the EPA has not set a maximum contaminant level goal (MCLG) or maximum contaminant level (MCL). Monitoring for these substances helps the EPA determine where certain contaminants occur and whether it needs to regulate those contaminants. Between 2008 and 2010, water utilities around the country will be monitoring for a group of 25 contaminants, including the breakdown products of herbicides and pesticides from the synthetic organic compound class. Alachlor ESA, which has been detected at very low levels at some Madison wells, is one chemical on the unregulated contaminant list. None of the 25 potential contaminants were detected at any well or distribution location during the two sampling periods. All locations were sampled in August 2008. The majority of locations were sampled again in February 2009 with seasonal wells tested when they were brought back on-line in early spring and summer. More information on the regulation (UCMR2) and the contaminants tested can be found on the EPA website.