It's an old fertilizer manufacturing facility. To make fertilizer, you mine phosphorus from the ground and combine it with sulfuric acid and other stuff. At one time 40 percent of the world's fertilizer was manufactured in Central Florida, but it's a nasty business and with increased environmental regulations much of the manufacturing moved to China. They can have it.
The leak now is a "pond" that is dammed by gypsum stacks, whch are the byproducts from phosphate mining. Gypsum is mildly radioactive, so when you read that the wastewater is the acidity of coffee, you are not getting the whole story. If the dam fails there will be a large flood that ultimately will wind up in Tampa Bay, likely fueling a huge algae bloom that will kill millions of fish and other sea creatures. Eventually the algae dies and rots, making everything stink (the dead fish don't help either).
I was bankruptcy counsel to put Piney Point, and other fertilizer manufacturing plants, back in the early 1990s, when we put them through Chapter 11. I got to know quite a bit about the fertilizer business.