CITIZEN POWER ALLIANCE

The risks and benefits of drilling for natural gas have been so widely discussed over the past year that even if you haven't been following gas drilling closely, you might now be familiar with the word "frack."

For those who aren't, the term is short for hydraulic fracturing, a practice where gas drillers shoot pressurized water mixed with sand and chemicals into a well to release natural gas from the earth. The practice has been around for decades, but it's gained new prominence in the past few years with the growth of horizontal drilling, where drillers mine the earth laterally deep underground. The technique has allowed the expansion of drilling into gas-bearing shales across the country, but it also requires large quantities of fracking fluids, sometimes millions of gallons per well. And it's this mix of water and chemicals that has generated the bulk of the controversy and a series of studies, orders and regulations in 2010 from the federal government and a number of states.

Of particular concern to regulators and public health advocates are the specific chemicals that go into that chemical mixture. The industry has fought disclosure for years and had largely been able to keep well-to-well specifics secret, but that began to change this year. Wyoming updated its oil and gas regulations and, in an effort to fend off potential federal oversight, started requiring drillers to list the name and concentration of each of the chemicals used in each well. In Pennsylvania, where drilling in the region's Marcellus Shale continues to expand, regulators have written similar rules that await final approval by the legislature. In both cases, however, drillers may be able to find exceptions.

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