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Massachusetts Adopts Summing Approach in Final Drinking Water Standards for PFAS


The Massachusetts Department of Environmental Protection (MassDEP) is preparing to publish final Maximum Contaminant Levels (MCL) for the sum of six per- and polyfluoroalkyl substances (PFAS). The final rule, set to publish Oct. 2, 2020, will apply to all public water systems and require sampling, reporting, and corrective action when sampling detects PFAS exceedances.

The MCL is 20 parts per trillion (ppt) for the sum of six PFAS compounds: 

  • perfluorooctanesulfonic acid (PFOS)
  • perfluorooctanoic acid (PFOA)
  • perfluorohexane sulfonic acid (PFHxS)
  • perfluorononanoic acid (PFNA)
  • perfluoroheptanoic acid (PFHpA)
  • perfluorodecanoic acid (PFDA)

MassDEP initiated the rulemaking process to develop a state drinking water standard in January 2019. On Dec. 27, 2019, Massachusetts published revisions to the drinking water regulations in the Massachusetts Register and accepted comments on the proposal.  The proposed regulation, like the final regulation, contained a drinking water standard of 20 ppt for the sum of six specific PFAS. 

Notably, Massachusetts’ MCL – 20 ppt for the sum of six individual PFAS compounds – differs significantly from U.S. EPA’s Lifetime Drinking Water Health Advisory level of 70 ppt for PFOS and PFOA combined. MassDEP received public comments questioning the scientific justification for the departure from U.S. EPA’s Health Advisory Levels. MassDEP also received public comments questioning the scientific justification for using a “summing approach” for regulating the six individual PFAS compounds, which treats the toxicity or human health impacts of the six different PFAS compounds as if they were interchangeable. Despite the concerns raised in public comments, MassDEP finalized the 20 ppt MCL, as proposed.

The new rules will require large public water suppliers, serving greater than 50,000 individuals, to begin initial monitoring by Jan. 1, 2021. Medium public water suppliers, serving between 10,000 and 50,000 individuals, must begin initial monitoring by April 1, 2021. Small public water suppliers and non-transient, non-community public water suppliers serving fewer than 10,000 individuals must begin initial sampling by Oct. 1, 2021. Transient, non-community public water systems are not subject to MassDEP’s MCL requirements, but they will be required to collect one sample for the six PFAS compounds by Sept. 30, 2022.

The regulations also detail the responsive actions that public water suppliers must take when MCLs are exceeded, which include public notice, increased monitoring frequency, and corrective action. Corrective action may entail submission of a corrective action plan detailing the specific interim and long-term action measures the public water supplier intends to take to reduce contaminant concentrations to safe levels. 


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