This study evaluated the occurrence and temporal variability of chlorate, perchlorate, and bromate in 26 low-strength onsite-generated (OSG) hypochlorite systems and three high-strength systems. None of the samples from the systems tested would have contributed more than 1 mu g/L perchlorate to the finished water, even at a 10-mg/L chlorine dose; similarly, none of the samples exceeded the NSF International specific product allowable concentration (SPAC) for bromate of 0.5 mu g/mg free chlorine. Of the samples collected, however, 10 of the 29 unique OSG systems would have exceeded the US Environmental Protection Agency (USEPA) 210-mu g/L health reference level (HRL) for chlorate at a dose of only 5 mg/L chlorine, and 21 of the 29 would have exceeded 210 mu g/L chlorate at the 10-mg/L maximum use level. No apparent correlation was found between chlorate production and OSG brand, age, or capacity nor was any correlation observed between chlorate production and pH, transition metals, chloride, conductivity, or temperature.
