The Michigan Department of Environment, Great Lakes, and Energy (EGLE) developed Maximum Contaminant Levels (MCLs) for seven PFAS compounds in Michigan, which took effect in August 2020. These MCLs amend existing rules for public drinking water supplies under Michigan's Safe Drinking Water Act (SDWA), affecting approximately 2,700 public water supplies statewide.

Following the initial compliance monitoring period (August 2020 - February 2021), all supplies required to conduct ongoing compliance monitoring under the SDWA were assigned a sampling schedule based on their initial result.

For PFAS MCLs, the standard compliance monitoring schedule is quarterly - this applies to any supply which has a detection for one or more PFAS analytes with an MCL, above the method reporting limit. A supply may be reduced to an annual monitoring schedule if they demonstrate PFAS levels consistently and reliably below the MCLs.

Compliance with PFAS MCLs for a supply is determined based on a running annual average for each compound, calculated at each sampling point. A supply is not out of compliance until either 1) one full year of quarterly sampling is complete, or 2) fewer samples cause the running annual average to exceed one or more MCLs. If a supply is determined to be out of compliance with one or more PFAS MCLs, the supply is required to notify the public within 30 days.

Compliance Monitoring Results (since August 3, 2020)

The initial compliance monitoring period ran from the date of MCL promulgation (August 3, 2020) until February 3, 2021, and included two groups of supplies:

• Those supplies which had collected a sample during EGLE's statewide PFAS survey and returned a PFAS result with a detection greater than half of one of the proposed MCLs AND those supplies which had not previously collected a PFAS sample during EGLE's statewide PFAS survey, would sample during the first full quarter following promulgation (October 1, 2020 - December 31, 2020).
• All remaining supplies which had collected a sample during EGLE's statewide PFAS survey would sample during the first six months following promulgation (August 3, 2020 - February 3, 2021).

Quarterly sampling for PFAS MCL compliance monitoring began on January 1, 2021, and follows the following schedule each year:

• Quarter 1: January 1 – March 31
• Quarter 2: April 1 – June 30
• Quarter 3: July 1 – September 30
• Quarter 4: October 1 – December 31

Sampling for PFAS MCL compliance for those supplies on an annual schedule runs concurrently with quarterly sampling.