A community water system (CWS), using chlorine dioxide as a disinfectant, draws routine daily monitoring samples for chlorite at the entrance to the distribution system. If a CWS exceeds the MCL for chlorite, what additional monitoring must the system con
On each day following a routine sample monitoring result that exceeds the chlorite MCL at the entrance to the distribution system, the system is required to take three chlorite distribution system samples at the following locations: as close to the first customer as possible, in a location representative of average residence time, and as close to the end of the distribution system as possible. This follow-up monitoring is in addition to the daily sample required at the entrance to the distribution system (40 CFR 141.132(b)(2)).
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