(Inside Science) -- Hydraulic fracturing, better known as fracking, propels fluids deep into the Earth to break up rock and release natural gas. It's an impressive feat of engineering that collects a relatively clean-burning fuel, but it has issues. Scientists have linked the process to mild seismic activity. It also uses lots of water and many toxic chemicals.
Scientists haven't solved every potential problem with fracking. But they are working to replace many of the chemicals in the fluid, which contain sand, biocides, mineral-dissolving acids and more.
Last month, representatives from the natural gas industry, chemical companies and nonprofits came together in Bethesda, Maryland, at a session of the American Chemical Society Green Chemistry and Engineering Conference, to discuss ways to use fewer and safer chemicals in fracking. Though not yet widely adopted, these strategies are not only good for the environment, but are less risky for their employees and can even save money, said session chair Danny Durham, the manager of Global Upstream Chemicals of the Houston-based Apache Corporation.
"Some people will tell you that to use green chemistry it costs more, but really, that’s not the case," said Durham. "You have to be knowledgeable of what to select. You can have your cake and eat it too in terms of sustainability, cost and performance."
Fracking forces millions of gallons of water, laced with a variety of chemicals, into the ground through a well. Because most fracking occurs between 6,000 and 10,000 feet below the surface -- far below the depth of drinking-water reservoirs -- there is little evidence that gas or fluids rise through thousands of feet of rock to contaminate freshwater reserves.
The toxic chemicals are primarily a problem when there are accidents: spills at the surface of the well, escaped wastewater, trucking accidents, or breaks in the steel pipes that line the hole.
What goes in the well?
Natural gas companies stress that fracking fluids are 90 percent water and 9.5 percent "proppant," such as sand, which helps wedge cracks open. The remaining 0.5 percent of the fluids is a hodgepodge of ingredients: acids to dissolve minerals and start cracks in the rock, gelling agents to keep the sand suspended in the solution, chemical "breakers" to disperse the gel when it is no longer needed, friction reducers to keep the fluids moving, biocides to kill off bacteria that corrode the pipes, and other chemicals that stabilize, winterize or neutralize the well.
"When you look at the tens of millions of gallons of [fluids] used, the absolute amount of chemicals begin to add up," said Richard Liroff, the founder and executive director of the Investor Environmental Health Network, a nonprofit based in Falls Church, Virginia, which works to reduce toxic chemical use in the industry.
Traditionally, fracking fluids contained highly toxic ingredients such as methanol, petroleum distillates and diesel fuel, which can contain a group of compounds abbreviated as BTEX -- benzene, toluene, ethylbenzene and xylene -- organic molecules that can damage the human nervous system.
Some of the formulations look like a "toxic waste dump," according to chemical engineer and consultant Brian Penttila of iWatchChems in Seattle, Washington. Penttila was not associated with the conference session.
In collaboration with Clean Production Action, a company that assists government and industry in using safer chemicals, Penttila analyzed the toxicity of hundreds of chemicals disclosed by oil and gas companies on the website FracFocus. Some companies, such as Apache, attempt to reveal all of the chemicals they use, while others disclose as much information as is required by a patchwork of state laws. Many companies link to incorrect chemical identification numbers, or to products containing patented mixtures, which they are not always required to reveal.
"Sadly, about two-thirds of those are chemicals we don’t know much about," said Penttila.
Searching for cleaner fluids
Halliburton, a prominent producer of fracking fluids, presented a product called CleanStim at the conference. The product has several components that can be mixed with water and pumped down the well, replacing traditional fluids. CleanStim contains chemicals approved for use in the food industry, such as an enzyme found in soybean paste and partially hydrogenated vegetable oil. But the natural gas industry has not widely adopted the product, according to Liroff.
Dunham said Apache Corporation's goal is to use only chemicals that are approved by the Environmental Protection Agency's Design for the Environment program, which evaluates consumer products such as laundry detergents and window cleaners. If a spill results, biodegradable chemicals are easier to clean up, and have a smaller ecological impact than more toxic ones.
Biocides have been the hardest additive to replace, since they are designed to be toxic to the bacteria that can build up in wells. But some companies have tried alternative methods to keep bacteria in check, such as adding ozone to the production waters or using ultraviolet light to kill off microorganisms.
There are many ways to make fracking greener. Apache is replacing liquid chemicals with powdered ones, which cut down on the use of toxic solvents, and also shipping expenses.
Other issues still plague the natural gas industry, from increased local traffic noise, to an increase in earthquakes, but smarter chemical use is a step in the right direction.
"When you are able to substitute a less hazardous chemical for a more hazardous chemical, that’s concrete progress in my opinion," said Liroff.
With continued efforts on the part of the industries and their watchdogs, natural gas might one day be the cleaner fuel that so many hope it can be.
Patricia Waldron (@patriciawaldron) is a news intern at Inside Science.