Backstory
Hydraulic fracturing – the injection of water, sand and chemicals into the ground to extract oil and natural gas – has sparked fears of groundwater contamination in rural communities like Pavillion, Wyo. ("Hydrofracked: One man's quest for answers about natural gas drilling," HCN, 6/27/11). Diesel is one of the more controversial ingredients used in some fracking fluids because it contains known carcinogens. Though the Environmental Protection Agency has had the power to regulate diesel in fracking fluid since 2005, it hadn't done so, unable to settle on exactly what "diesel" meant.

Followup
In 2011, a congressional investigation found that 14 companies had used 32 million gallons of diesel in fracking since 2005, though most said they'd phased it out. This February, the EPA finally defined five categories of diesel, and drillers will now need a permit to use them. But critics say the guidelines won't have much input, since only a tiny fraction of frackers still use diesel, and the guidelines lack the power to prohibit its use.