Disinfection By-Products & Unregulated Contaminants
Disinfection by-products are substances that form when chlorine interacts with impurities in ground water. Chlorine is added to control microorganisms such as bacteria and viruses that may be present in source water. Samples are collected from locations within the distribution system that have high water age, usually large reservoirs and water towers, and are expected to have the highest levels of four trihalomethanes and five haloacetic acids. Since the levels of organic matter in the source water are low and the utility adds relatively small amounts of chlorine, disinfection by-product levels are also very low in Madison drinking water.
Results of testing for Disinfection By-Products
Federal regulations require that some water utilities test drinking water for specific unregulated contaminants, substances for which the EPA has not set a maximum contaminant level (MCL) or MCL Goal. Monitoring for these substances typically occurs once every five years. Results of the testing helps the US EPA determine where certain contaminants occur and whether the agency needs to regulate these contaminants to protect public health.
UCMR4 (2018 – 2020)
In 2018 & 2019, Madison Water Utility tested twenty-two wells for 20 unregulated contaminants. These chemicals included two metals (germanium and manganese), pesticides and their by-products, semi-volatile chemicals, alcohols, by-products of disinfection in the brominated haloacetic acid (HAA) group, and two chemical indicators (bromide and total organic carbon [TOC]). In 2018, two chemicals were each found in one well – 2-methoxyethanol (Well 26) and 1-butanol (Well 28). Later tests did not find either chemical at any well. We commonly found manganese, bromide and the HAAs in Madison drinking water.
UCMR 3 (2013 – 2015)
Water utilities around the country previously monitored a group of 30 contaminants including hormones, volatile organic compounds, perfluorinated compounds (including PFOA and PFOS), metals, chromium-6, and 1,4-dioxane. All Madison wells were tested twice for these chemical contaminants. Some samples were also collected from our water distribution system.