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PFAS Safe Drinking Water Act Maximum Contaminant Levels Set

Over the next five years, U.S. EPA hopes its new national drinking water standard will reduce per- and polyfluoroalkyl substances (“PFAS”) compounds in drinking water to almost zero as a way to prevent potential health risks associated with the chemicals.  On April 10, 2024, EPA finalized Primary Drinking Water Standards that it estimates will require public water systems to spend $14.4 billion to achieve the new maximum contaminant levels (“MCLs”) for six PFAS chemicals. (See April 8, 2024 Pre-Publication PFAS National Primary Drinking Water Regulation Preamble (“Preamble”).) Just days prior, on April 5, 2024, California’s Office of Environmental Health Hazard Assessment (“OEHHA”) adopted public health goals for two PFAS chemicals:  perfluorooctanoic acid (“PFOA”) and perfluorooctane sulfonic acid (“PFOS”).  These public health goals will lead to lower MCLs in California for PFOA and PFOS.

These are three questions that the new federal MCLs raise:

  1. Do the new MCL requirements affect the majority of public water systems nationwide?   The scope of the new MCLs require public water systems to monitor, report, and by 2029 remediate PFAS in drinking water. The affected entities are every public water system that serves “an average of at least twenty-five individuals daily at least 60 days out of the year.”  (Preamble, § I.B’ 40 C.F.R. § 141.2.)
  2. Will the new federal MCLs affect other non-drinking water regulatory programs?   The new federal MCLs will influence and potentially drive other standards such as effluent limits that wastewater treatment plants must meet to comply with permits issued under the National Pollutant Discharge Elimination System (“NPDES”) regulations and remediation clean-up levels for ground or surface waters.
  3. What are the true costs of compliance to achieve the federal MCLs? For the drinking water regulatory programs alone, the costs of compliance to achieve the federal MCLs are significant and range from EPA’s estimate of $14.4 billion to $47.3 billion, a reported estimate from American Water Works, the largest publicly traded water and wastewater utility company.

The impact of the new MCLs is important because although PFOA and PFOS largely have been phased out of production since the 1940s, the chemicals are still present in the environment.  (Preamble § II.B.) PFAS are synthetic “forever” chemicals that breakdown slowly and are commonly used in fast-food boxes and non-stick cookware as well as for other purposes (e.g., stain- and water-repellant clothing and carpets, some fire-fighting foams, and various industrial and manufacturing processes.)  (See e.g., July 2023 U.S. Geological Survey Study.) In California, monitoring data EPA reviewed found that 35.8 percent of California public water systems detected PFOA and 39 percent detected PFOS, with reported concentrations of PFOA ranging from 0.9 to 190 ppt and reported concentrations of PFOS ranging from 0.4 to 250 ppt.  (Preamble, § VI.)

  1. Federal MCL Requirements

EPA estimates that about 6% to 10% of the 66,000 public drinking water systems nationwide will need to reduce PFAS to meet the following new MCLs and unenforceable MCL Goals (“MCLGs”):

  MCLGs MCL
Perfluorooctanoic acid (“PFOA”) Perfluorooctane sulfonic acid (“PFOS”) Zero 4 ppt
GenX Chemicals Perfluorohexane sulfonic acid (“PFHxS”) Perfluorononanoic acid (“PFNA”) Hexafluoropropylene oxide dimer acid (“HFPO-DA”) 10 ppt 10 ppt
Mixtures containing two or more GenX or perfluorobutane sulfonic acid (“PFBS”) 1 (unitless)* 1 (unitless)

* There is no unit for this this Hazard Index MCL because it is a sum of fractions.  EPA is currently developing an online calculator that will add up each fraction that represents average PFAS ratios (e.g., PFHxS/10 ppt + PFNA level/10 ppt) and see if the annual average is greater than the MCL of 1. (
EPA Hazard Index Fact Sheet.)


At this time, these federal MCLs are for the most part slightly lower than the notification and response levels that California established in 2020 under the California Safe Water Drinking Act.  (See State Water Resources Control Board PFAS Webpage [setting forth 5.1 and 6.5 ppt notification levels for PFOA and PFOS, respectively, and 10 and 40 ppt response levels for PFOA and PFOS, respectively].) In California, however, public water systems will also be required to comply with California MCLs, which will be based on the new OEHHA public health goals (“PHGs”):

California Public Health Goal  
PFOA 0.007 ppt
PFOS 1 ppt


(OEHHA’s April 5, 2024 notice.) A PHG is the level of a drinking water contaminant at which adverse health effects are not expected to occur from a lifetime of exposure. Health & Safety Code §116365(a) requires a contaminant’s MCL to be as close to its PHG as is technologically and economically feasible. Some key takeaways from the final rule are as follows:

  • Monitoring. Public water systems have three years to complete initial monitoring (by 2027). Water systems must calculate the running annual average (using all samples and no composite samples). The overall annual average must be below the MCLs, and samples with results below 2 ppt are averaged as zeros. (Preamble, § VIII.B.3.) According to Section V of the Preamble, most laboratories (89%) can analyze levels accurately to as low as 2 ppt.
  • Public Notice. Beginning in 2027, public water systems must provide information to the public about PFAS levels, and, beginning in 2029, public water systems must provide notification to the public of any MCL violation. In California, Health and Safety section 116455 already requires timely notification by drinking water systems whenever a notification level is exceeded.
  • Compliance Deadline. By 2029, public water systems must reduce PFAS levels that exceed the MCLs. EPA has concluded that PFAS can be reduced or eliminated using granular activated carbon (“GAC”), anion exchange resins (“AIX”), and high-pressure membranes (nanofiltration (“NF”) and reverse osmosis (“RO”)). (Preamble, § X.)

EPA’s health-related evaluations concluded that the PFAS at issue are linked to many health effects ranging from liver and kidney cancers and low birth weight infants to high blood pressure and high cholesterol. (See id., §§ II.B, XII.F; Table 44; EPA Frequently Asked Questions (“FAQ”).)  One key finding throughout EPA’s rulemaking is that “[p]regnant and lactating women, as well as infants and children, may be more sensitive to the harmful effects of certain PFAS,” including the co-occurrence of the GenX Chemicals. (See e.g., Preamble, § II.)   Nearly half of the tap water nationwide contains at least one type of PFAS, according to a July 2023 U.S. Geological Survey Study.  EPA’s PFAS webpage recommends that households use certain certified water filters to reduce PFAS but the “current certification standards for PFAS filters (as of April 2024) do not yet indicate that a filter will remove PFAS down to the levels EPA has now set for a drinking water standard.  EPA also recommends nursing mothers ask pediatricians about potential PFAS exposures while nursing or giving infants formula, according to the EPA FAQ.

The Executive Summary of the rulemaking concludes that “the quantifiable annual [health] benefits of the final rule will be $1,549.40 million per year” based on the monetized benefits associated with 29,858 fewer illnesses and 9,614 fewer deaths.  EPA further found that “the quantifiable costs of the rule will be $1,548.64 million per year.”  This analysis supports EPA’s Executive Summary conclusion that the costs of the rule are justified by the benefits.  EPA did receive comments that it over-estimated health benefits (see e.g., id., § XII.A.1) and underestimated compliance costs (see e.g., id., at § XII.A.2).

  1. Non-Drinking Water Impacts

What EPA opted not to address in the MCL rulemaking is that the MCLs will affect non-drinking water environmental programs.  The MCLs set up a reference point that other state and federal agencies undoubtedly will use to evaluate allowable PFAS levels in wastewater discharges and at remediation sites.  For example:

  • NPDES Permits – A Regional Water Quality Control Board uses MCLs to determine allowable pollutant levels in discharges of water. Most, if not all, Water Quality Control Plans (called Basin Plans) throughout the state include a Chemical Constituents objective that requires compliance with MCLs for discharges to waters designated for municipal supply. For example, the Los Angeles Region Basin Plan states in Chapter 3: “Water designated for use as Domestic or Municipal Supply (MUN) shall not contain concentrations of chemical constituents in excess of the limits specified [Title 22 State MCLs] . . .”  Thus, the numeric levels in state MCLs (once adopted based on the PHGs) will be automatically incorporated into limits applicable under Basin Plans.  Additionally, under 40 C.F.R. § 122.44(d), if a point source discharge has reasonable potential to cause or contribute to an exceedance of a water quality standard, historically a Regional Water Board will impose a water-quality-based effluent limitation.
  • Clean-ups The Comprehensive Environmental Response, Compensation, and Liability Act (“CERCLA”) or similar state laws often seek that MCLs be attained in remediation actions, including CERCLA removal actions. EPA has stated that “typically MCLs should be attained to the extent practicable during the removal action[.]” (EPA Removal Management Level User Guide.)
  • POTWs The EPA has provided guidance for pretreatment and wastewater disposal to manage PFAS that enter the sanitary sewer system and must be managed by publicly owned treatment works (“POTWs”). (See e.g., USEPA, Addressing PFAS Discharges In EPA-Issued NPDES Permits And Expectations Where EPA is the Pretreatment Control Authority (April 28, 2022); USEPA, Addressing PFAS Discharges in NPDES Permits and Through The Pretreatment Program and Monitoring Programs (December 5, 2022)). EPA has stated that “[s]ite-specific technology-based effluent limits (TBELs) for PFAS discharges developed on a best professional judgment (BPJ) basis may be appropriate for facilities for which there are no applicable effluent guidelines (see 40 CFR 122.44(a), 125.3).”  (Dec. 2022 EPA Guidance.)
  • Hazardous Waste EPA’s MCL rulemaking concludes that potential hazardous waste disposal requirements may increase treatment costs but only marginally up to 12 percent. (Preamble, §§ V, X.C.) EPA’s conclusion may underestimate these costs because EPA has not yet updated its 2020 PFAS Destruction and Disposal guidance.  (§ X.C.2.)

EPA’s failure to consider non-drinking water costs was intentional because it asserts that under the Safe Drinking Water Act, EPA must “exclude ‘costs resulting from compliance with other proposed or promulgated regulations’” and is required only to include “costs that ‘are likely to occur solely as a result of compliance with the [MCL].’”  (Id., § V.)

  1. Costs of Compliance

The compliance costs that public water systems will incur to achieve the federal MCLs appear uncertain and range considerably.  EPA estimates that the initial capital costs to comply with the MCLs will be approximately $14.4 billion nationwide and “reasonably anticipates” that federal funding of $11.7 billion in Drinking Water State Revolving Fund and an additional $5 billion for emerging contaminants, should “be able support a substantial portion of the initial capital costs of the final rule.”  (Preamble, §XII.A.2.)

In late November 2023, American Water, the largest publicly traded water and wastewater utility company, estimated about “$47 billion in infrastructure investments across the U.S. to treat for PFAS at four parts per trillion.”  (See CNBC Nov. 30, 2023 “U.S. tap water has a $47 billion forever chemical problem.”)  Though the $47.3 billion American Water estimate is not mentioned in the Preamble, Section XII.A.2.a and Table 24 of the Preamble dispute a study conducted by Black & Veatch on behalf of the American Water Works Association in detail, specifying, for example, that granulated activated carbon (“GAC”) treatment should cost $300,000 per unit (to treat 1 million gallons a day) not $900,000 and that the new MCLs will affect 5,136 total public water systems, not 7,449 systems as Black & Veatch estimated.

The $14.4-billion EPA estimate also is at odds with estimates by California water districts.  In 2020, a total of eleven water districts in Orange County, California, including the Orange County Water District, estimated $1 billion in PFAS clean-up costs, according to a lawsuit filed by these water districts against DuPont, 3M, Chemours and Corteva.  (See CMBG3 Law Dec. 3, 2020 Newsletterhttps://www.cmbg3.com/california-water-district-pfas-lawsuit-1-billion-at-stake.)  If $1 billion is an accurate estimated for 11 California water districts, this would result in approximately $90.9 million per water district, not $2.8 million per public water system based on EPA’s estimate (i.e., $14.4 billion/5,136 public water systems.)

Whatever compliance costs will be, public water systems will need funds over the next five years to pay for treatment systems. For small or disadvantaged communities, the federal Emerging Contaminant (“EC”) fund can be used for eligible projects.  State funds are also available through the State Water Resources Control Board, which under the California Budget Act of 2021 was most recently appropriated $20 million from the General Fund for technical and financial assistance for the 2023-2024 fiscal year.  (See SWRCB PFAS Funding Webpage and California Supplemental Intended Use Plan.)