Coal ash, which contains many of the world's worst carcinogens, is what's left over when coal is burnt for electricity. An estimated 113 million tons of coal ash are produced annually in the US, and stored in almost every state — some of it literally in people's backyards. With very little government oversight and few safeguards in place, toxic chemicals have been known to leak from these storage sites and into nearby communities, contaminating drinking water and making residents sick.

On February 2, 2014, up to 39,000 tons of coal ash and 27 million gallons of contaminated water spilled out into the Dan River in North Carolina after a pipe broke underneath a coal ash pond at a Duke Energy power plant. The environmental disaster thrust Duke Energy, the country's largest electricity company, into the spotlight, revealing a history of violations and inadequate oversight of ponds at all of its plants across the state.