Fracking-A Bubba
Here is a New York Times article on the fracking process for natural gas extraction.  This article details how some drillers used diesel fuel as part of the "cocktail" that is shot into wells to loosen natural gas:

The diesel fuel was used by drillers as part of a contentious process known as hydraulic fracturing, or fracking, which involves the high-pressure injection of a mixture of water, sand and chemical additives — including diesel fuel — into rock formations deep underground. The process, which has opened up vast new deposits of natural gas to drilling, creates and props open fissures in the rock to ease the release of oil and gas.

But concerns have been growing over the potential for fracking chemicals — particularly those found in diesel fuel — to contaminate underground sources of drinking water.

Here is more information:

Two years later, when Congress amended the Safe Water Drinking Act to exclude regulation of hydraulic fracturing, it made an express exception that allowed regulation of diesel fuel used in fracking.

The Congressional investigators sent letters to 14 companies requesting details on the type and volume of fracking chemicals they used. Although many companies said they had eliminated or were cutting back on use of diesel, 12 companies reported having used 32.2 million gallons of diesel fuel, or fluids containing diesel fuel, in their fracking processes from 2005 to 2009.

The diesel-laced fluids were used in a total of 19 states. Approximately half the total volume was deployed in Texas, but at least a million gallons of diesel-containing fluids were also used in Oklahoma (3.3 million gallons); North Dakota (3.1 million); Louisiana (2.9 million); Wyoming (2.9 million); and Colorado (1.3 million).

Where this leaves the companies in relation to federal law is unclear. 

This "fracking" issue is going to be big as allegations of contaminated groundwater grow.