EPA Sets MCLs for 6 PFAS Under the Safe Drinking Water Act

On April 10, the Environmental Protection Agency (EPA) announced enforceable maximum contaminant levels (MCLs) for six per- and polyfluoroalkyl substances (PFAS) in drinking water sources across the nation. This rule, which is a giant leap from EPA’s stringent but merely advisory limits issued at the onset of its war against PFAS, marks a considerable escalation of EPA’s responses. However, amidst the celebration of certain environmental groups, a myriad of legal challenges and practical implications are set to emerge, not only for government and public entities but also for many private actors.

While the rule regulates six PFAS, it sets individual MCLs for only five. For PFOS and PFOA, that level is 4 parts per trillion—a level that essentially requires full elimination. For PFHxS, PFNA, HFPO-DA (GenX) the limit is 10 parts per trillion. EPAs final rule also incorporates EPA’s hazard index approach for regulating mixtures of up to four PFAS (PFHxS, PFNA, HFPO-DA (GenX), and PFBS), meaning cumulative concentrations of those substances are limited under the rule as well. While this new rule has garnered much praise, even those that support regulation of PFAS in theory have criticized this rule for the technical difficulties and high costs currently associated with essentially eliminating PFAS from drinking water sources. Indeed, EPA itself estimates the costs to public water systems to be $1.5 billion per year to implement. 

EPA’s new rule has also been criticized for its novelty. The new rule is the first National Primary Drinking Water Regulation for any new contaminant in decades. As a result, it inevitably will invite legal scrutiny from state, local, and industry stakeholders, who have concerns regarding both legal and scientific aspects of the proposed rule. This rule also faces potential challenges relating to the looming Supreme Court review of Chevron deference, a doctrine which has provided regulatory agencies considerable discretion in interpreting statutes. 

In terms of this rule’s impact on private entities, there is much for private actors to be concerned about. First, if states, cities, and drinking water providers are required to incur extensive treatment costs, there can be little doubt such costs will further spur greater litigation against manufacturers and users of PFAS products. Such litigation has already resulted in such notable settlements as 3M’s over-$10 billion settlement with a class of public water suppliers. Moreover, the regulation's ramifications extend to liability under the Comprehensive Environmental Response, Compensation, and Liability Act (“CERCLA”). By establishing a nationwide MCL for certain PFAS, EPA has effectively dictated the groundwater cleanup standard for those substances. because MCLs become applicable or relevant and appropriate requirements (ARARs), to be considered in CERCLA remedy selection.

The EPA has taken certain measures to ease compliance concerns for water systems, however. The final rule extends the compliance window to five years from the proposed three—although it requires monitoring and reporting of exceedances after only three. Additionally, the federal government is to provide billions of dollars in funding to address drinking water quality. Estimating the impact this additional time and added resources will have is impossible at this point. What is certain, however, is that this new rule will face significant scrutiny in the courts. 

For more information on EPA’s new rule, see EPA’s discussion and FAQ at

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