Bilott hunted through his files for other references to PFOA, which he learned was short for perfluorooctanoic acid. But there was nothing. He asked DuPont to share all documentation related to the substance; DuPont refused. In the fall of 2000, Bilott requested a court order to force them. Against DuPont’s protests, the order was granted. Dozens of boxes containing thousands of unorganized documents began to arrive at Taft’s headquarters: private internal correspondence, medical and health reports and confidential studies conducted by DuPont scientists. There were more than 110,000 pages in all, some half a century old. Bilott spent the next few months on the floor of his office, poring over the documents and arranging them in chronological order. He stopped answering his office phone. When people called his secretary, she explained that he was in the office but had not been able to reach the phone in time, because he was trapped on all sides by boxes.

‘‘I started seeing a story,’’ Bilott said. ‘‘I may have been the first one to actually go through them all. It became apparent what was going on: They had known for a long time that this stuff was bad.’’

Bilott is given to understatement. (‘‘To say that Rob Bilott is understated,’’ his colleague Edison Hill says, ‘‘is an understatement.’’) The story that Bilott began to see, cross-legged on his office floor, was astounding in its breadth, specificity and sheer brazenness. ‘‘I was shocked,’’ he said. That was another understatement. Bilott could not believe the scale of incriminating material that DuPont had sent him. The company appeared not to realize what it had handed over. ‘‘It was one of those things where you can’t believe you’re reading what you’re reading,’’ he said. ‘‘That it’s actually been put in writing. It was the kind of stuff you always heard about happening but you never thought you’d see written down.’’

The story began in 1951, when DuPont started purchasing PFOA (which the company refers to as C8) from 3M for use in the manufacturing of Teflon. 3M invented PFOA just four years earlier; it was used to keep coatings like Teflon from clumping during production. Though PFOA was not classified by the government as a hazardous substance, 3M sent DuPont recommendations on how to dispose of it. It was to be incinerated or sent to chemical-waste facilities. DuPont’s own instructions specified that it was not to be flushed into surface water or sewers. But over the decades that followed, DuPont pumped hundreds of thousands of pounds of PFOA powder through the outfall pipes of the Parkersburg facility into the Ohio River. The company dumped 7,100 tons of PFOA-laced sludge into ‘‘digestion ponds’’: open, unlined pits on the Washington Works property, from which the chemical could seep straight into the ground. PFOA entered the local water table, which supplied drinking water to the communities of Parkersburg, Vienna, Little Hocking and Lubeck — more than 100,000 people in all.

Bilott learned from the documents that 3M and DuPont had been conducting secret medical studies on PFOA for more than four decades. In 1961, DuPont researchers found that the chemical could increase the size of the liver in rats and rabbits. A year later, they replicated these results in studies with dogs. PFOA’s peculiar chemical structure made it uncannily resistant to degradation. It also bound to plasma proteins in the blood, circulating through each organ in the body. In the 1970s, DuPont discovered that there were high concentrations of PFOA in the blood of factory workers at Washington Works. They did not tell the E.P.A. at the time. In 1981, 3M — which continued to serve as the supplier of PFOA to DuPont and other corporations — found that ingestion of the substance caused birth defects in rats. After 3M shared this information, DuPont tested the children of pregnant employees in their Teflon division. Of seven births, two had eye defects. DuPont did not make this information public.

In 1984, DuPont became aware that dust vented from factory chimneys settled well beyond the property line and, more disturbing, that PFOA was present in the local water supply. DuPont declined to disclose this finding. In 1991, DuPont scientists determined an internal safety limit for PFOA concentration in drinking water: one part per billion. The same year, DuPont found that water in one local district contained PFOA levels at three times that figure. Despite internal debate, it declined to make the information public.

(In a statement, DuPont claimed that it did volunteer health information about PFOA to the E.P.A. during those decades. When asked for evidence, it forwarded two letters written to West Virginian government agencies from 1982 and 1992, both of which cited internal studies that called into question links between PFOA exposure and human health problems.)