A horizontal drill rig capable of drilling one to two miles vertically or horizontally.
The current boom in U.S. natural gas production from glassy shale rock formations is poised to usher in an era of energy independence and could bridge the gap between today's fossil-fuel age and a clean-energy future. But that future may be swamped in a legacy of wastewater, a new study suggests.
Natural gas production is soaring thanks to hydraulic fracturing, or fracking, a technique that shoots several million gallons of water laced with chemicals and sand deep underground to break apart chunks of the glassy rock, freeing trapped gas to escape through cracks and fissures into wells.
An average of 10 percent of this water flows back to the surface within a few weeks of the frack job. The rest is absorbed by the surrounding rock and mixes with briny groundwater, explained Radisav Vidic, a civil and environmental engineer at the University of Pittsburgh.
"What happens to that water is a very good question," he told NBC News. "We would like to know how much of it stays in the shale, and for how long, and is there a potential for migration away from the well."
Vidic led a review study of the scientific literature looking into these questions, which is published in Thursday's issue of the journal Science.
He said there is a small risk that some of this water could find its way into a crack that leads up to drinking-water aquifers. Most, though, follows the path of least resistance back to the well and flows out at the rate of around 30 to 50 gallons per day. "And what comes back out is much, much worse than anything you put in there, so the real concern is, what do you do with the water that comes back out? Because that's where the potential for major environmental impact occurs," he said.
This wastewater, he noted, is 10 times saltier than seawater and contains naturally occurring radioactive material released from the shale.
For now, this wastewater is either injected into wells where, in theory, it will stay indefinitely; or it is cleaned up and reused for subsequent frack jobs.
Recycling has become particularly common in Pennsylvania's Marcellus Shale region, where the geology limits disposal in injection wells. "I applaud the industry in Pennsylvania for coming up with that [recycling process], but it only works as long as you have more wells to inject into," Vidic said.
Eventually — and no one knows for sure when — more wastewater will be produced than there are new wells being drilled. The technology exists to treat the wastewater, but it is expensive and will leave behind mountains of salt and other solids that will need a proper home.
"The thing is, the industry is simply not addressing it right now," Vidic said. This oversight, he added, has potential be the source of panic and environmental woe when drilling slows.
The natural-gas industry downplays the issue. The concern is "a hypothetical situation that doesn't actually reflect what is really going on," Steve Everley, a spokesman for Energy-in-Depth, an industry trade group, told NBC News.
A sudden deluge of wastewater, he noted, is "highly unlikely." But if it were to happen, he said, "companies would still be treating and finding a way to do something with the wastewater in a responsible fashion."
That wait-and-see approach worries Kate Sinding, who directs the community fracking defense project for the National Resources Defense Council, an environmental group. She pointed out that wastewater cannot be reused indefinitely.
"I think they are all counting on shipping it off somewhere else to be dealt with," she told NBC News. "In the Marcellus that would be Ohio, but not surprisingly, Ohio doesn't want all of the stuff from these other states, so we think it is a big problem and one that has to be taken much more seriously."
Frack fluid discolosures
According to Vidic, the wastewater problem is more serious than the nondisclosure of what exactly is in the fluid injected into the well, which has generated concerns about drinking water contamination.
"There have been more than 1 million hydraulically fractured treatments done, and there is one case where we have seen the contamination of groundwater by the hydraulic fracturing fluids," he said. That one case occurred, he added, because the drilling took place in a region where there were abandoned wells, which served as conduits to the groundwater.
He and his colleagues note that understanding the exact composition of the injection fluid is important for water quality. It's also important to find out exactly where Pennsylvania's estimated 100,000 abandoned wells are located.
The dearth of this and other data, Vidic noted, means more research is needed to fully understand the impact of natural gas development on water quality, but added that to date the scientific literature provides "no evidence of severe environmental pollution."
"This is an industry," he noted. "And any industry has a footprint … We all want cheap energy and we want more of it. So, OK, you can dig out more coal and burn coal, but I would take natural gas any day of the week over coal."
More about fracking:
- Disputes over fracking's effect cloud its future
- Agreement reached on fracking standards
- Fracking provides energy, jobs ... and quakes?
In addition to Vidic, the authors of "Impact of Shale Gas Development on Regional Water Quality" include S.L. Brantley, J.M Vandenbossche, D. Yoxtheimer, J.D. Abad.
John Roach is a contributing writer for NBC News. To learn more about him, visit his website.