Frequent Questions

Must a community water system (CWS) that intermittently uses chlorine dioxide monitor daily for chlorine dioxide and chlorite as specified in 40 CFR 141.132(b)(2) and (c)(2)?

According to the Final Implementation Guidance for the Stage 1 Disinfectants/Disinfection Byproducts Rule (EPA816-R-01-012, June 2001), a CWS that uses chlorine dioxide intermittently is not required to conduct the daily monitoring for chlorine dioxide and chlorite for days when the chlorine dioxide is not in use. In addition, a CWS is not required to conduct monthly monitoring for chlorite as specified in 141.132(b)(2)(I)(B) if the chlorine dioxide has not been used at all for the entire month. However, monthly monitoring for chlorite is required if chlorine dioxide is used at any time during the month.
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