SDWA Specific Provisions

The USEPA also creates unenforceable maximum contaminant level goals (MCLGs) set at levels that present no known or anticipated health effects and include a margin of safety, regardless of technological feasibility or cost. The USEPA is also required (under SDWA) to periodically review the actual MCLs to determine whether they can be brought closer to the desired MCLGs. 

If monitoring the contaminant level in drinking water is not economically or technically feasible, the USEPA must specify a treatment technique that will effectively remove the contaminant from the water supply or reduce its concentration. The MCLs currently cover a number of volatile organic chemicals, organic chemicals, inorganic chemicals, and radionuclides, as well as microbes and turbidity (cloudiness or muddiness). The MCLs are based on an assumed human consumption of 2 liters (roughly 2 quarts) of water per day. 

For non-carcinogens, MCLGs are determined by a three-step process. The first step is calculating the reference dose (RfD) for each specific confaminanf. The RfD is an estimate of the amount of a chemical that a person can be exposed to on a daily basis that is not anticipated to cause adverse systemic health effects over the person s lifetime. A different assessment system is used for chemicals that are potential carcinogens. If toxicological evidence leads to the classification of the contaminant as a human or probable human carcinogen, the MCLG is set at zero (Boyce, 1997). 

Selected Primary Standard MCLs and MCLGs for Organic Chemicals 

Benzene Possible cancer risk 0.005-0 Industrial chemicals, paints, plasEcs, pesEcides 

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