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PFAS are a large class of man-made synthetic chemicals that were created in the 1930s and 1940s for use in many industrial and manufacturing applications. PFAS have been widely used for their unique properties that make products repel water, grease and stains, reduce friction and resist heat. Because of their unique chemical structure, PFAS readily dissolve in water and are mobile, are highly persistent in the environment and bioaccumulate in living organisms over time. PFAS are referred to as “forever chemicals,” because they do not readily break down when exposed to air, water, or sunlight. The primary means of distribution of PFAS throughout the environment has been though the air, water, biosolids, food, landfill leachate and fire-fighting activities. Exposure to these chemicals are known to cause a number of adverse health effects in laboratory animals and in humans. Exposure can occur when fish caught in waters contaminated with PFAS are eaten, foods packaged in PFAS coated materials are consumed, soil and dust polluted with PFAS are unintentionally ingested, or products made with PFAS chemicals are handled. For more information on actions under other DEP program areas, please visit: DEP Involvement.

The PFAS MCL Rule was published in the Pennsylvania Bulletin on January 14, 2023. This rule establishes maximum contaminant levels (MCLs) and maximum contaminant level goals (MCLGs) for 2 PFAS –: perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) –, which are two of the more common and persistent PFAS chemicals detected in the human body in published toxicological studies as of 2022. The MCLs and MCLGs set by this rule, in nanograms per liter (ng/L) or parts per trillion (ppt), are:

 MCLG (ng/L or ppt)MCL (ng/L or ppt)

Although the rule applies to all public water systems (PWSs) in the Commonwealth; , monitoring requirements under the rule are applicable to community water systems (CWSs), nontransient noncommunity water systems (NTNCWS), and bottled, vended, retail, and bulk systems (BVRBs). Initial monitoring is required quarterly for 4 four consecutive calendar quarters at each entry point (EP) to the distribution system (EP), beginning January 1, 2024 for PWSs serving more than 350 persons and for BVRBs, and January 1, 2025 for CWS and NTNCWS serving 350 or fewer persons. Repeat monitoring is quarterly, annual, or triennial, based on whether analytical results are detected and at what level. Compliance with the MCLs is determined based on a running annual average (RAA) at each EP; if any quarterly result causes the RAA to exceed the an MCL, a violation is incurred for that quarter.

In addition to the monitoring and reporting requirements, the PFAS MCL Rule also establishes MCL violations as a Tier 2 violation requiring issuance of Tier 2 public notice (PN) and requires community water systems to report results in their annual Consumer Confidence Report (CCR). The rule also establishes analytical requirements (including approved methods for analysis and minimum reporting limits) and approved treatment technologies (including granular activated carbon (GAC), ion exchange, and reverse osmosis), with the option of other treatment technologies that may be approved by the Department if the technology is demonstrated to provide an adequate and reliable quantity and quality of water.


The final PFAS MCL Rule, which amended DEP’s safe drinking water regulations at 25 Pa. Code Chapter 109, was published in the Pennsylvania Bulletin on January 14, 2023. The following documents supported the PFAS MCL rulemaking: Final-form rulemaking for the PFAS MCL Rule: Safe Drinking Water Amendments (25 Pa Code, Chapter 109).

Resources and Related Documents:


Rule Training for PWS Operators and Staff: DEP held classroom training on the PFAS MCL rule in the fall of 2023. The following is a 5-part virtual recording of the training course and the associated workbook:

Webinar: PFAS MCL Rule and UCMR 5: Monitoring Overlap Implications