Amna Nawaz:

Coal ash is an especially bad and dangerous byproduct of our dependence on coal and fossil fuels. Now over the years, a number of communities have dealt with coal ash spills that have turned into emergencies with real public health concerns over what's seeped into the water. In some places, utilities have been pushed to adopt tougher standards.

But as Miles O'Brien reports, some residents and activists say the power companies are fighting changes that could help protect public health. It's part of our regular segment on the "Leading Edge" of science and technology.