It was the dead cows on Wilbur Tennant’s farm that shaped most of Rob Bilott’s professional life. Tennant’s farm was located in Parkersburg, W. Va.; Bilott was—and remains—an environmental lawyer at the firm of Taft Stettinius & Hollister in Cincinnati. All had been well for Tennant until 1998, when half of his herd of 300 cows began to languish and die. … Currently, there are more than 15,000 claims that have been filed nationwide against DuPont—and its spinoffs Chemours and Corteva—along with 3M, the major manufacturers of PFAS in the U.S. … So far, DuPont, Chemours, Corteva, and 3M have paid a total of nearly $11.5 billion in damages for PFAS contamination. But that number could grow considerably, even exceeding the more than $200 billion paid by Big Tobacco in the 1990s. … Short for per- and polyfluoroalkyl substances, PFAS are also known as “forever chemicals”—because that’s pretty much how long they linger in the environment.