Susan Brantley

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.

Salty wastewater
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. 

Jim Lo Scalzo / EPA

This file photo shows a hydraulic fracturing drill rig at dusk near Tunkhannock, Penn.

A new water desalination technology may prove a savior for the oil and natural gas industries confronting growing concerns about the wastewater that flows to the surface in the months and years after a well is fracked.

In fracking, or hydraulic fracturing, operations 3 million to 5 million gallons of water are injected deep underground, along with sand and a chemical cocktail, to fracture shale rock and extract the embedded natural gas. 

Some of that water returns to the surface immediately after the fracturing. The rest comes back over the course of months and years, which a recent study indicates could overwhelm the wastewater treatment infrastructure in the Marcellus Shale formation, which stretches from New York to Virginia.

The new desalination technology is not aimed at the large volumes of water that flow back just after a frack, but could work unattended by a human for months as it treats the really salty water to drinking-water quality, according to engineers working on the system.

The technique "is very much like an engineered version of what nature does in the rain cycle where seawater vaporizes, forms clouds in the atmosphere which condense and come down as rain," John Lienhard, a mechanical engineer at the Massachusetts Institute of Technology, told NBC News.

"But what we’ve got is clearly a system that’s been designed to optimize performance and to minimize the amount of energy that is required to do the vaporization."

David Castro-Olmedo / MIT

Water from actual natural gas wells, sent to MIT by the companies that operate them, was run through the system, producing clean, potable water.

The system is a variation of the standard desalination process where salty water is vaporized and then condenses on a cold surface. The salt is separated out in the vaporization. 

Lienhard and colleagues use what’s called a carrier gas process where water is sprayed onto warm air to vaporize it. This warm moist air, which carries pure water vapor, is bubbled through cool water where the vapor condenses. 

While other researchers have developed so-called humidification dehumidification desalination systems, Lienhard and colleagues maintain that theirs is more energy efficient and comes with the advantages of having simple hardware, low maintenance, and is optimized to process between 1,200 and 2,400 liters a day.

That makes the technology well-suited for desalination in rural coastal villages in developing countries, which the researchers said was the inspiration for their research.

"And it turns out that those are very similar to the requirements that you have in dealing with water that is coming up in the oil and gas wells," Lienhard said.

Hundreds of natural gas wells are distributed across landscapes such as the Marcellus Shale, the Bakken formation in North Dakota and the Permian Basin of West Texas. 

Lienhard said he envisions the desalination plants at each individual well pad, processing hundreds to a few thousand liters of produced water per day at a cost of about "a couple of dollars" per barrel.

The team has filed for patents on the technology and launched a company to commercialize it. 

"We hope to have a pilot plant running at a natural gas site within 12 months," Lienhard said. "If the pilot works, then we could immediately scale it up."

John Roach is a contributing writer for NBC News. To learn more about him, visit his website. 

Mladen Antonov / AFP - Getty Images

In this file photo, a fracking fluid pit sits next to a drill site near Waynesburg, Pa.

The practice of hydraulic fracturing, or fracking, produces a relatively small amount of wastewater, given all the gas the technique recovers, according to a new analysis of operations in Pennsylvania. Nevertheless, the number of fracking operations has grown so rapidly that the wastewater being produced threatens to overwhelm the region’s capacity to properly treat it.

In fracking operations, 3 million to 5 million gallons of water are injected deep underground, along with sand and a chemical cocktail, to fracture shale rock and extract the embedded natural gas. Some of that water returns to the surface immediately after the fracturing. The rest comes back over the course of months and years. The result is that each well brings up hundreds of thousands to millions of gallons of wastewater.

Pennsylvania has invested very little in the infrastructure needed to deal with wastewater, even though the region was where the U.S. oil and gas industry got its start more than 150 years ago, Brian Lutz, a biogeochemist at Kent State University, told NBC News.

What’s more, the geology of the region limits the ability to dispose of the massive quantities of wastewater generated during fracking operations by injecting it deep underground, as is done in other regions of the country.

"That’s critical," Lutz said, "because that means we’re generating large wastewater streams in a new geography of the country where we don’t necessarily have a pre-existing capacity and, perhaps, we don’t have the necessary physical capacity to handle these wastes that we have in other regions."

Conventional vs. fracking
He and colleagues analyzed data from 2,189 active Marcellus Shale wells in Pennsylvania, and compared gas production and wastewater volumes to conventional well data. They found that shale gas wells typically produced 10 times the amount of wastewater as conventional wells, but they also produced about 30 times more natural gas. 

Lutz noted that the study is the first to put shale gas production into the perspective of conventional production in order to benchmark the amount of wastewater being produced per unit of gas recovered from shale gas wells.

The findings make the point that "as we expand domestic natural gas production, even if the expansion were driven by conventional production, our wastewater challenge would be no less and perhaps much worse," Lutz said.

Despite the greater efficiency in getting the gas out with fracking, however, the region has seen 570 percent growth in the amount of wastewater generated since 2004, due to the boom in natural gas production. 

In 2011, the last year data were analyzed, more than 830 million gallons of wastewater were generated in Pennsylvania's Marcellus Shale formation, Lutz and colleagues report in their study, which was published Wednesday in the journal Water Resources Research. 

Natural-gas boom
Over the past decade, the Marcellus Shale, which stretches from New York to Virginia, has gone from producing 2 percent of the nation’s natural gas output to about 10 percent. And the rush may have only just begun. Hydraulic fracturing was pioneered by the U.S. Department of Energy and its industry partners, and is largely responsible for a boom in natural gas production that some forecasts indicate will help make the country energy independent by 2035.

But independence comes at a price. As the fracking boom has accelerated, so too have concerns about the wastewater it generates and groundwater contamination from the chemicals injected into the wells.

Surprisingly, Lutz and colleagues note, only about a third of the wastewater from the Marcellus Shale wells was classified as flowback — the wastewater that comes back to the surface within a few days of a frack. The rest is brine, water that is generated in the wells over a much longer time.

"What surprised us about this, and what’s certain, is that waste was definitely being documented as being generated at the well and taken to treatment facilities two, three, four years out after the well began producing and substantial quantities of waste," Lutz said. 

Much of the controversy surrounding fracking has focused on the chemicals in the flowback, many of which are unknown to outside researchers because the drilling companies consider them proprietary. But the brine often contains a much higher pollution load than the flowback, Lutz noted. What’s more, the finding suggests that truck traffic on back roads will have to continue long after the few weeks required for the initial fracturing operation, in order to haul the wastewater off to treatment zones.

Water issues overblown?
John Krohn is a spokesman for Energy in Depth, a gas industry trade group. He said the study highlights the water efficiencies that have come with the technological advancements used to access oil and gas in shale rock formations.

Those findings, coupled with increasing water recycling rates in the natural gas industry show that wastewater issues surrounding hydraulic fracturing "are at the very least overblown and discredited, potentially, by this study," he told NBC News.

Krohn noted that wastewater recycling rates in Pennsylvania were 70 percent in 2012, and some companies have reported rates of 100 percent. Recycling for the industry means using one of many technologies to clean the flowback and brine sufficiently to be used for subsequent fracturing operations.

"In a lot of areas, natural gas producers are able to use this fracturing fluid in excess of 20 to 25 times," he said. "And so what that does is it lessens the water footprint of the entire industry."

Lutz acknowledges that the industry has made strides in wastewater recycling, but he's concerned about a future when new wells aren't being drilled rapidly enough to handle the recycled waste. 

"As soon as your well population starts to stabilize or decline, then you are left with a large volume of wastewater, and there currently is no method than can recycle that water for an alternative use — municipal or agricultural or something like that," he said.

Krohn said he doubted that such a slowdown in well drilling would occur. If it does, other options such as injection wells will offer viable alternatives, he said.

Given the unlikelihood of a slowdown, Lutz hopes the wastewater issue stays in the discussion.

"Wastewater from the Marcellus Shale is really a central challenge to future development," he said. "It is not an ancillary problem that is perhaps going to solve itself, but something that really needs to lead the discussion, at least from the environmental side of things, as we think about future development."

John Roach is a contributing writer for NBC News. To learn more about him, check out his website.