When most people think about oil and gas production, water probably isn't something that comes to mind. But maybe it should.
When a typical oil well starts producing, there are three main products pumped out: gas, oil, and water. The amount of water is significant. In Colorado, for every barrel of oil produced in 2013, there were 6 barrels of wastewater pumped from the ground. (A barrel is 42 gallons.)
How that water -- sometimes referred to as produced water -- is treated and disposed of has become a growing issue as oil and gas production has increased in Colorado and across the United States.
Mark Engle, a U.S. Geological Survey scientist, is working to pin down just how much of the wastewater is being produced nationwide.
"Since the big explosion in shale gas and tight oil production in the last four or five years, [there is almost no data on] how much the amount of produced water has changed in the U.S," Engle said.
Quantities of wastewater, which can be 10 times saltier than seawater and is often laced with hydrocarbons, have grown because of the shale boom, which requires continual drilling of new wells to be profitable.
"And so just to have stable production, you have to keep putting more and more and more wells in, and they are all producing water," said Engle.
Most of these wells, drilled in shale formations like the Niobrara in Northern Colorado, or the Bakken in North Dakota, are horizontal wells that are hydraulically fractured. To do this, millions of gallons of water, chemicals, and proppants, like sand, are pumped into the ground at high pressure, opening up tiny cracks in the shale.
The goal of this process is to free up trapped oil and gas. But trapped water flows back as well. Some of that water is what was used in the fracking process, but a lot of it is also ancient water from deep within the Earth.
That wastewater picks up a lot of chemicals because of where it comes from, said Ken Carlson, an engineering professor at Colorado State University who studies energy and water issues.
While many folks worry about what's in fracking fluid, Carlson is more concerned with the naturally occurring pollutants from deep below.
"Sometimes people think it is hazardous because of what we put down there," said Carlson. "And the truth is, the water that comes back has been in contact with oil and gas compounds for maybe millions of years."
Wastewater is almost always incredibly salty. It also often contains dissolved metals and compounds like benzene, a known carcinogen, said Carlson. In some places, like Pennsylvania's Marcellus Shale, that wastewater can also be radioactive, as it picks up naturally occurring elements like radium from deep inside the earth. (Waste from Northern Colorado has not been shown to be more radioactive than natural background levels.)
Because of this, such water is usually disposed of, said Greg Deranleau, the environmental manager of the Colorado Oil and Gas Conservation Commission.
"It is a waste product with some negative characteristics. So it does have to be handled carefully," said Deranleau.
When a well is producing, companies separate the products that make them money -- oil and gas -- from the water. In Colorado, that water is usually stored in on-site tanks or pits that fill up. Later, it gets trucked away.
There are a few main things that happen to the wastewater after that.
By far the most common way of dealing with wastewater is disposing of it deep underground, in injection wells. While some energy companies have their own wastewater disposal wells, an injection well industry has also cropped up to meet this need. In the U.S., there are around 30,000 injection wells used to dispose of fluids from oil and gas production.
Even though wastewater is disposed of deep underground, there are still risks. Recently, some injection wells have been linked to earthquakes. Spills are also an issue. Pipelines carrying wastewater can leak, as can holding pits, and trucks transporting waste can spill it.
In Colorado, the spill rate for wastewater is very low -- over the last 15 years, just 0.009 percent of all wastewater produced was spilled, according to COGCC data. The agency's oversight over spills has grown in recent years, and it recently made its spill reporting requirements more stringent, requiring spill reports for even one barrel, rather than five.
"All spills, regardless of their size, are required to be cleaned up by an operator," said Deranleau. The agency also has tighter restrictions around oil and gas operations that are near public water supply areas, he added.
"I would say an industry with a spill rate of a thousandth of a percent, they are working pretty hard to keep those numbers low," Deranleau added.
While overall, the state does have a very low spill rate, simply because so much wastewater is produced, the total spill quantities can still be high. From 2005 to 2013, spill amounts ranged from 10,000 to 72,000 barrels (420,000 to 3,024,000 gallons) per year.
In 2008, in Garfield County, a rancher took a drink of water from a tap in his cabin, and swallowed a toxic mix of oil and gas related compounds, landing him in the hospital. The polluted drinking water was contaminated from a produced water holding pit that leaked; the COGCC fined the energy company Williams $432,000.
Other pits containing produced water have also leaked; Oxy USA also received a COGCC fine for contaminating two springs with produced water from leaking pits.
Some companies have tried recycling wastewater, re-using it for hydraulic fracturing future wells. In states like Pennsylvania, where disposing of wastewater is expensive, and Texas, where water is scarce, recycling has grown in popularity. Some Colorado companies are also recycling wastewater.
There are some concerns about this approach. For one, treating the wastewater creates yet another waste stream -- the chemicals that were taken out of the water, and are now concentrated. Moving more water around can cause other problems, like increasing the potential for spills as the water is transported and handled.
Sometimes, wastewater is so dirty that cleaning it up to the standards they need for hydraulic fracturing just isn't worth the cost. The COGCC is working with some companies on recycling produced water to reuse, but "it takes a lot of work to clean up the water to a point even that they want to use it," said Deranleau.
For every new well drilled and the oil it produces, though, there will be wastewater to be dealt with. Getting a handle on that water -- whether it is injected or recycled, piped or trucked -- will continue to be a significant task.
This story has been updated to correct the spelling of Greg Deranleau's name.