The waste from burning coal — coal combustion products, or CCPs, like coal ash and boiler slag — contains toxic heavy metals like mercury and cadmium. But don’t worry, the coal industry says that the concentrations aren’t high enough to do anyone harm. Taking the coal industry’s word for it, the U.S. EPA decided in 1993 and again in 2000 not to regulate CCPs as hazardous waste.

As a consequence, the coal industry isn’t all that careful with CCPs. Using a composite liner under CCP landfills can reduce the seepage of heavy metals into the water table, but eh, it’s kind of expensive, so why bother? Most don’t (sub rqd.):

EPA’s own assessment of the nation’s 600 coal combustion waste sites in 2000 found that 43 percent of landfills and 74 percent of surface impoundments were unlined.

Now, however, a draft EPA report (PDF) says that, oops, CCPs are dangerous after all:

People exposed to arsenic groundwater contamination from unlined coal ash landfills face a cancer risk 50 times greater than is considered safe under federal rules, the report said.

The report has been opened to public comment; the EPA is trying to figure out whether and how to regulate CCPs.

Special bonus fact: the cleaner coal’s air emissions are, the more ash it produces. Sweet.