Fracking Flowback Could Pollute Groundwater with Heavy Metals Press Release by Cornell University, June 25, 2014, Newswise
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The chemical makeup of wastewater generated by “hydrofracking” could cause the release of tiny particles in soils that often strongly bind heavy metals and pollutants, exacerbating the environmental risks during accidental spills, Cornell University researchers have found.
Previous research has shown 10 to 40 percent of the water and chemical solution mixture injected at high pressure into deep rock strata, surges back to the surface during well development. Scientists at the College of Agriculture and Life Sciences studying the environmental impacts of this “flowback fluid” found that the same properties that make it so effective at extracting natural gas from shale can also displace tiny particles that are naturally bound to soil, causing associated pollutants such as heavy metals to leach out.
They described the mechanisms of this release and transport in a paper published in the American Chemical Society journal Environmental Science & Technology.
The particles they studied are colloids – larger than the size of a molecule but smaller than what can be seen with the naked eye – which cling to sand and soil due to their electric charge.
In experiments, glass columns were filled with sand and synthetic polystyrene colloids. They then flushed the column with different fluids – deionized water as a control, and flowback fluid collected from a Marcellus Shale drilling site – at different rates of flow and measured the amount of colloids that were mobilized.
On a bright field microscope, the polystyrene colloids were visible as red spheres between light-grey sand grains, which made their movement easy to track. The researchers also collected and analyzed the water flowing out of the column to quantify the colloid concentration leaching out.
They found that fewer than five percent of colloids were released when they flushed the columns with deionized water. That figure jumped to 32 to 36 percent when flushed with flowback fluid. Increasing the flow rate of the flowback fluid mobilized an additional 36 percent of colloids.
They believe this is because the chemical composition of the flowback fluid reduced the strength of the forces that allow colloids to remain bound to the sand, causing the colloids to actually be repelled from the sand.
“This is a first step into discovering the effects of flowback fluid on colloid transport in soils,” said postdoctoral associate Cathelijne Stoof, a co-author on the paper.
The authors hope to conduct further experiments using naturally occurring colloids in more complex field soil systems, as well as different formulations of flowback fluid collected from other drilling sites.
Stoof said awareness of the phenomenon and an understanding of the mechanisms behind it can help identify risks and inform mitigation strategies. “Sustainable development of any resource requires facts about its potential impacts, so legislators can make informed decisions about whether and where it can and cannot be allowed, and to develop guidelines in case it goes wrong,” Stoof said. “In the case of spills, you want to know what happens when the fluid moves through the soil.”
This research was supported by the Cornell University Agricultural Experiment Station’s USDA Hatch funds, as well as the U.S. National Science Foundation and the National Natural Science Foundation of China. Cornell University has television, ISDN and dedicated Skype/Google+ Hangout studios available for media interviews.
Another concern arises over groundwater contamination from fracking accidents by American Chemical Society, June 25, 2014, ScienceNewsLine
The oil and gas extraction method known as hydraulic fracturing, or fracking, could potentially contribute more pollutants to groundwater than past research has suggested, according to a new study in ACS’ journal Environmental Science & Technology. Scientists are reporting that when spilled or deliberately applied to land, waste fluids from fracking are likely picking up tiny particles in the soil that attract heavy metals and other chemicals with possible health implications for people and animals.
Tammo S. Steenhuis and colleagues note that fracking, which involves injecting huge volumes of fluids underground to release gas and oil, has led to an energy boom in the U.S. But it has also ignited controversy for many reasons. One in particular involves flowback, which refers to fluids that surge back out of the fracked wells during the process. It contains water, lubricants, solvents and other substances from the original fracking fluid or extracted from the shale formation. High-profile spills and in some places, legal application of these liquids to land, have raised alarms. Research has linked fracking to groundwater contamination that could have major health effects. But another factor that no one has really addressed could play a role: colloids. These tiny pieces of minerals, clay and other particles are a concern because they attract heavy metals and other environmental toxins, and have been linked to groundwater contamination. Steenhuis’ team set out to take a closer look.
To simulate what would happen to colloids in soil after a fracking spill, the researchers flushed flowback fluids through sand with a known amount of colloids. They found that the fluids dislodged about a third of the colloids, far more than deionized water alone. When they increased the flow rate, the fluids picked up an additional 36 percent. “This indicates that infiltration of flowback fluid could turn soils into an additional source of groundwater contaminants such as heavy metals, radionuclides and microbial pathogens,” the scientists conclude. More research with real soils is planned.
Effect of Hydrofracking Fluid on Colloid Transport in the Unsaturated Zone