Perfluorononanoic acid, or PFNA, the chemical that led to a do not drink order on tap water in the Chautauqua County Village of Mayville late last week, was detected more than a year ago in regular sampling of two of the three wells that serve the village, county and state officials said. This is not a new change to the water, Mayville Mayor Ken Shearer said during an online forum Friday. This is a little different from some other emergencies. Nothing spilled into our water program yesterday. This is a new test, something that has not been tested for before.