Per- and Polyfluoroalkyl Substances (PFAS) Initial Monitoring

Summary of PFAS Initial Monitoring Requirements

In April 2024, the U.S. Environmental Protection Agency (EPA) announced the final National Primary Drinking Water Regulation (NPDWR) for six per- and polyfluoroalkyl substances (PFAS) for public water systems. Maximum Contaminant Levels (MCLs) were set for PFOS and PFOA (both set at 4.0 parts per trillion or ppt), HFPO-DA or GenX chemicals (10 ppt), PFNA (10 ppt), and PFHxS (10 ppt). The final rule additionally regulates HFPO-DA, PFNA, PFHxS and PFBS through a Hazard Index calculation. An MCL of 1 was set for the Hazard Index.

The PFAS NPDWR requires that community water systems (CWS) and non-transient, non-community water systems (NTNCWS) complete initial monitoring (40 CFR 141.902(b)(1)). Systems must take all samples during normal operating conditions at all entry points to the distribution system (EPTDS) (40 CFR 141.902(a)(1)). The results of initial monitoring will be used to determine the compliance monitoring schedule for each EPTDS (40 CFR 141.902(b)(2)).

The minimum required frequency for initial monitoring is determined by system type, as described below: 

  • Groundwater systems serving greater than 10,000 persons, all surface water systems, and all groundwater under the direct influence of surface water (GWUDI) systems must take four consecutive samples 2 to 4 months apart within a 12-month period (quarterly samples) for each regulated PFAS.
  • All groundwater systems serving 10,000 or fewer persons must take two samples five to seven months apart within a 12-month period (semi-annual samples) for each regulated PFAS.
  • For systems that use both surface water and groundwater: 
    • If the EPTDS provides surface water, the requirements for a surface water system apply. 
    • If the EPTDS provides groundwater, the requirements for a groundwater system apply, based on system size.
    • If an EPTDS provides a blend of surface water and groundwater, the requirements for a surface water system apply. 
    • For systems that change the source water type at an EPTDS during the initial monitoring period (i.e., one part of the year it is surface water and the remaining part of the year it is groundwater), the sampling requirements for a surface water system apply.
  • Systems must ensure that all required quarterly or semi-annual sampling periods are represented, with sample calendar months appropriately spaced. Supplemental data can be collected in one calendar year such that, when coupled with the previous monitoring, it meets the timing requirements of this rule (40 CFR 141.902(b)(1)(viii)).

EPA's Quick Reference Guide

How to Submit Initial Monitoring Data

To satisfy the initial monitoring requirements set by the PFAS NPDWR, you must ensure that your laboratory uploads sample results to the Compliance Monitoring Data Portal (CMDP) as soon as possible but no later than April 26, 2027. Please note the following: 

  • For small systems that serve a population of 10,000 or fewer, available sample results from the fifth Unregulated Contaminant Monitoring Rule (UCMR 5) for PFAS included in the NPDWR will be uploaded to our database to satisfy the initial monitoring requirements set by the rule. However, if your water system has more recent data from samples collected outside of UCMR 5, you must ensure that your laboratory uploads these results to CMDP as soon as possible but no later than April 26, 2027.
  • For large systems that serve a population of greater than 10,000, available sample results from UCMR 5 for PFAS included in the NPDWR can be uploaded to our database to satisfy initial monitoring requirements. To submit UCMR 5 data for initial monitoring, water systems should contact their laboratory to request that the data be reprocessed and uploaded to CMDP. Reprocessing is necessary because UCMR 5 results will not indicate whether concentrations are below the trigger level, which is a requirement for sample analyses occurring on or after June 25, 2024 (40 CFR 141.901(b)(2)(iii)). Analyses that occurred before June 25, 2024, can be used to meet initial monitoring requirements but could not be used to set a reduced monitoring schedule at the start of the compliance monitoring period unless the data is reprocessed.
  • If multiple years of data are available for a given water system, the most recent data must be used to satisfy initial monitoring requirements (40 CFR 141.902(b)(1)(vii)).
  • Previously acquired data can be used to satisfy initial monitoring requirements if samples were collected starting on or after January 1, 2019, and otherwise meet the analytical method and timing requirements specified in the federal rule (40 CFR 141.902(b)(1)(vi)).
  • For previously acquired data analyzed before June 25, 2024, results with reporting limits above the MCLs do not meet initial monitoring requirements (40 CFR 141.902(b)(1)(vi)).
  • Sample analyses for regulated PFAS must only be conducted by certified laboratories, beginning on June 25, 2024 (40 CFR 141.900(b)(1)). Access the list of NC certified laboratories. 
  • Samples must be analyzed using either EPA Method 533 or 537.1 with no modifications (40 CFR 141.901(b)(1)). Versions 1 and 2 of Method 537.1 are both allowable for initial monitoring (90 FR 4658). Only version 2 of Method 537.1 is allowable for compliance monitoring, beginning on April 26, 2027.
  • To confirm that results have been reported to the State, check Drinking Water Watch after you receive results from your lab.
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