Frequent Questions

Why did EPA establish maximum residual disinfectant level goals (MRDLGs) for disinfectants rather than maximum contaminant level goals (MCLGs)?

The MRDLG concept was introduced for disinfectants to reflect the fact that these substances have beneficial disinfection properties. As with MCLGs, MRDLGs are established at the level at which no known or anticipated adverse effects on the health of persons occur and which allows an adequate margin of safety. By using the term "residual disinfectant" in lieu of "contaminant", EPA intends to avoid situations in which treatment plant operators are reluctant to apply disinfectant dosages above the MRDLG during short periods of time to control for microbial risk (63 FR 69389, 69398; December 16, 1998).
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