PPG Industries has operated a manufacturing facility at 559 Pittsburgh Road in Circleville for decades. Beneath that facility, and spreading west toward the Scioto River, sits a plume of 1,4-dioxane — a synthetic industrial chemical the EPA classifies as a probable human carcinogen. The plume has been there since at least August 1998. That is the earliest data in the monitoring records. Nobody knows how long it was there before anyone started lo…