This past Saturday, New York Governor David Paterson vetoed a bill outlawing all new hydraulic fracturing and instead signed an executive order banning any new permits for "high-volume, horizontal hydraulic fracturing" until we are assured of the practice's environmental safety. Meaning, until July 1, 2011.

But what exactly is high-volume, horizontal hydraulic fracturing? The latter part of the phrase -- also known as "fracking" -- refers to a technique used in natural gas drilling, whereby a rock formation like those found in the gigantic Marcellus Shale is "fractured" by a mixture of injected water, sand and chemicals to release the gas within. There are two very distinct ways of doing this, though, and that distinction is what Gov. Paterson's moratorium aims to address. To find out the real difference between "horizontal" and "vertical" wells, I spoke with fracking expert Anthony Ingraffea, a professor of civil and environmental engineering at Cornell University.

"Part of the imbroglio surrounding this moratorium has to do with people in the industry, in the government, in environmental groups, playing too loose with words," he told me. "When one says vertical wells in New York state, they don’t just mean vertical wells, they mean traditional, conventional wells." It turns out vertical doesn't really mean vertical, first of all: a conventional well can deviate from the vertical quite a bit, and can even have short horizontal components. They don't, however, have long lateral, or horizontal components. A "horizontal" well, meanwhile, can stretch laterally along a shale formation for as much as two miles.

The key difference, though, and what really defines the moratorium, is the amount of fracking fluid that is used in the fracturing process. The fluid, made of water along with mixes of chemicals that have been at the center of environmental concerns about contaminated drinking water and the like, is injected through a six-inch diameter pipe toward the rock formation that needs to be fractured. In a conventional -- vertical, for these purposes -- well, the maximum amount used is 80,000 gallons.

This sounds like a lot, but a horizontal, or high-volume well, can use 100 times as much. Ingraffea said that the average well in Pennsylvania, where no such moratorium is in place, uses between five and six million gallons of fracking fluid.

And using such huge amounts changes the entire gas drilling equation. "With such high volumes, you have to go to much higher pressures," Ingraffea said. The fluid is pumped into the well bore very quickly -- less than an hour for each individual segment of a horizontal well, of which there could be up to 20 or so -- and the attendant pressure of millions of gallons on a six-inch pipe carries a drastically increased risk of failure. Anything from valves, pipes, regulators, tanks, and other equipment (even cement casing, which probably should sound somewhat familiar) could fail and let out toxic fluid into the environment.

To be sure, there are still risks associated with vertical, conventional fracking, and banning the horizontal version may not solve all related problems. But, with such huge risks associated with the high-volume, horizontal drilling, the moratorium has to be a good thing, right?

"It’s a good step. It’s not enough, its just a step," said Ingraffea. The moratorium, lasting less than a year in its current form, will allow for the New York Department of Environmental Conservation, as well as the EPA and other bodies, to continue research into high-volume fracking's danger to drinking water, as well as any other potential harm. Ingraffea seemed optimistic, for the moment. "Hopefully, that science will lead to a correct set of decisions."

(Photo via Ruhrfisch/Wikimedia Commons)