While the regulation and oversight of coal ash may be less stringent than some, like, say, a local river frog, might like, power plants and other areas of concern are at least well-enough documented to fill databases that power some very handy maps. Southeast Coal Ash Waste is a site that draws upon EPA data to show the location and hazard rating of power stations throughout the southeastern United States. The site does have other functions as well.
There is a page for the Dan River spill, with details like capacity and the height of the retaining dam. It's difficult to see in the aerial Google Maps view, but the primary pond is reportedly surrounded by a 60-foot wall. Such a measure makes sense in light of the EPA's designation of the pond as "high hazard," which means the failure of that wall would likely result in a loss of human life. Of course, the height of the wall makes it all the more ironic that they put the whole thing on top of a drain pipe leading directly to the nearby Dan River.
Viewed on a map, that proximity to the river may be the most alarming fact of all:
A similar closeness to the water, combined with a high hazard rating and Duke Energy's deteriorating reputation for responsible handling of coal ash waste is what has raised concerns for residents of Lake Wylie, North Carolina, and those who enjoy the Catawba River.
The G.G. Allen Power Station, is nine times larger than the Dan River plant and sits right at the river's edge, opposite marinas where small pleasure boats are moored.