There is no enforceable federal Maximum Contaminant Level (MCL) for PFAS; only a federal EPA lifetime health advisory for PFOA + PFOS that was set in 2016. Some States that have identified PFAS contamination have proactively developed drinking water standards and guidelines. While states use the same standardized risk assessment approach for developing acceptable drinking water concentrations, there are many points in the process where professional scientific judgement is needed. Different decisions in the risk assessment process can result in variations in drinking water standards and guidelines; each of which are scientifically defensible.
In addition, some states have set acceptable PFAS drinking water levels more recently than other states. Consideration of newer toxicological data about PFAS can result in differing acceptable levels.