Parkersburg, West Virginia
In 1984, DuPont began dispatching employees to secretly fill jugs of water at gas stations and general stores around the plant and bring them in for testing. Sure enough, the tests revealed C8 in the water supplies of two nearby towns—Lubeck, West Virginia, and Little Hocking, Ohio, just across the river from Washington Works. DuPont considered notifying the public, but ultimately chose not to.
The Wikipedia article on DuPont devotes several pages-worth of material to their environmental record and the various controversies they’ve become embroiled in. The HuffPost article I’ve linked to here is quite a good read, and makes you wonder what makes people think they’ll get away with covering this sort of thing up.