Frequent Questions

What are the constituents of the total trihalomethanes (TTHMs) group and what is the maximum contaminant level (MCL) and maximum contaminant level goal (MCLG) for this contaminant group?

The four constituents of the TTHM group are chloroform, bromodichloromethane, dibromochloromethane, and bromoform. TTHMs are regulated as a group with one MCL of 0.080 mg/L (40 CFR 141.64). Although there is no collective MCLG for this contaminant group, three of the four constituents, bromodichloromethane, dibromochloromethane, and bromoform, have individual MCLGs of zero, 0.06 mg/L, and zero, respectively (40 CFR 141.53).

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