Sorting Through PFAS – An Update on Standards and Guidance
In B&L’s last blog post on per- and poly-fluorinated alkyl substances (PFAS), we commented that what is “emerging” about PFAS contamination is their regulation. Regulatory proposals continue to emerge. Prominently, the USEPA has recently proposed new National Primary Drinking Water Regulations (NPDWRs) for several PFAS compounds. NPDWRs are legally enforceable primary standards that apply to public drinking water systems. Municipal and private suppliers of drinking water sources will be required to meet these new standards.
A handful of states (CA, MA, MI, MN, NH, NJ, NY, PA, RI, VT, and WA) have already promulgated drinking water standards for various PFAS compounds. But if approved, the federal standards would be lower than any of the state-promulgated values. For example, EPA proposes to set Maximum Contaminant Levels (MCLs) for PFOA and PFOS, the most commonly regulated PFAS compounds, at 4 nanograms/liter (ng/L or ppt). This compares to ranges of 8-20 ng/L for PFOA MCLs and 10-40 ng/L for PFOS MCLs set by the several states.
A more significant tightening of PFAS regulation (compared to the state-promulgated standards) is the proposed NPDWRs for four additional PFAS compounds – GenX, PFBS, PFNA, and PFHxS. Rather than set specific MCLs for each compound, EPA considers the concentrations of these four compounds in aggregate. Specifically, a water supplier has to calculate a Hazard Quotient (HQ) comprising the ratio of the measured concentration to the individual compound health-based values (HBVs). Then a Hazard Index (HI) is calculated as the sum of the HQs. Water suppliers must maintain a HI below 1.0 to meet the NPDWR for these compounds. In practice, this means that all four compounds can be below their HBVs, but still exceed the NPDWR.
While the HI approach represents a de facto lowering of the effective standards (compared to the HBVs) for these four compounds (if more than one are present), the HBVs are in some cases even lower than MCLs promulgated by various states (only a subset of the states listed above have promulgated MCLs for these four compounds), as shown in the following table:
At first impression, the slightly lower proposed federal MCLs and HBVs compared to promulgated state standards would not appear to be significant. For example, treatment technologies for water exceeding a 4 ng/L PFOA MCL would be the same as for treating water exceeding a 20 ng/L PFOA MCL. Activated carbon, a typical treatment technology for water supply treatment, removes all PFAS to zero ng/L until breakthrough. However, this masks the fact that some water suppliers who previously would not have to treat for PFAS under state regulations may now have to add treatment.
For example, the supporting documentation for the promulgation of the New York PFOA and PFOS MCLs (which are 10 ng/L each), the state provided data for PFOA and PFOS concentrations in 278 sampled water suppliers. These data indicated that with MCLs of 10 ng/L, 9% to 12% of the suppliers would have to add treatment due to PFOS and/or PFOA, respectively. However, if the MCL is lowered to 4 ng/L, then the portions of these 278 New York systems needing treatment jumps to 46% (based on PFOA) and/or 36% (based on PFOS). While this dataset is limited in number and evaluates just two PFAS compounds, it points to an expected large increase in the number of systems requiring new treatment systems, despite a relatively minor lowering of the MCL values.