. >> reporter: emily bernhardt is a professor of biogeochemistry at duke university.'s been researching the decapitation of mountains for seven years, trying to understand how it affects the rivers and streams below. >> the problem is that for every, about a meter of coal, you have about 99 meters of rock that you have to put somewhere during this process. and, when you're in a landscape like appalachia, the place that most of that rock ends up being put is in river valleys. >> reporter: when the rock is pulverized in the mining process, toxic chemicals and minerals locked inside for millennia are released, and exposed to the air, creating two areas of concern. >> one, that the water coming out of these mines is salty, it's full of rock-derived salts, and that by itself is stressful to many freshwater organisms. and the sort of subsidiary problem is that, that salt contains lots of elevated levels of trace metals, which have known toxicity to organisms. >> reporter: but the mining industry believes that concern is overstated. >> this is a good example of a ditch that