Oxygen may be the key to containing coal ash contamination, according to a new study. Scientists have found that this gas could help deal with the problem of aging coal ash disposal facilities.
"The tests that the Environmental Protection Agency relies on consider variables like the pH of the water, but they don't look at whether the system is aerobic or anaerobic," said Heileen Hsu-Kim, one of the researchers involved in the study. "We wanted to demonstrate that oxygenation actually matters a lot, especially for arsenic and selenium."
In 2014, there was a coal ash spill into North Carolina's Dan River from a ruptured Duke Energy drainage pipe. This, in particular, raised the question of what to do with aging coal ash retention ponds and also with future waste being generated.
The current goal for Duke Energy is to dig up 24 of its 36 ponds. However, the 12 remaining ponds hold more than 70 percent of the 108 million tons of ash currently being held in the ponds.
"Some of these ponds did not have bottom liners when they were originally constructed, so they'll be susceptible to leaking to groundwater even if they are covered on top," Hsu-Kim said. "When you cap a site, you're separating it from air. And if the buried waste goes anaerobic, it could enhance the leaching of some elements, leading to more contaminations than expected."
In this latest study, Hsu-Kim and other researchers at the Duke's Nicholas School of the Environment set up a series of microcosms, which are small-scale laboratory versions of an environment. They then looked at how much arsenic and selenium leached out of the system both with and without oxygen.
So, what did they find? When there was oxygen in the system, the levels of selenium leaching were much higher than that of arsenic. When there wasn't much oxygen in the system, there was an increase in the leaching of arsenic and a decrease for selenium.
"I'm trying to figure out if anyone is thinking about the fact that they're changing the oxygen conditions within the ash site by covering it," Hsu-Kim said. "This research suggests that some of the proposed methods for ash ponds closure in North Carolina may not be a slam dunk solution to the problem."
The findings were published in the April 2016 edition of the journal Applied Geochemistry.
