On December 7, 2021, the Illinois Environmental Protection Agency (IEPA) filed proposed amendments to Illinois’ groundwater quality standards with the Illinois Pollution Control Board (Board). The proposal includes Class I and Class II groundwater quality standards for six per- and polyfuoroalkyl substances (PFAS), including perfluorooctanoic acid (PFOA), perfluorooctanesulfonic acid (PFOS), perfluorononanoic acid (PFNA), perfluorohexanesulfonic acid (PFHxS), perfluorobutanesulfonic acid (PFBS), and hexafluoropropylene oxide dimer acid (HFPO-DA).  Illinois follows several states that are choosing to regulate PFAS constituents while federal regulation of the constituents is pending. Ubiquitous, PFAS can be found in a variety of consumer products, industrial processes, and fire-fighting foams, and can come to be located throughout the environment.