The Wall Street Journal reported in 2016 that mine waste dams are some of the largest man-made structures on Earth. The graphic below, which accompanied the article, illustrates the basic engineering of these facilities.
There are some regional variations in how coal impoundments are constructed. For example, coal impoundments on flatter landscapes—such as those in Wyoming—look more like large pits. But impoundments in the mountainous region of Appalachia mostly take the form depicted above.
As of 2013, there were 601 coal-related impoundments in the U.S., according to data provided by the Mine Safety and Health Administration.