Chemicals commonly used for shale drilling were discovered in the tap water of three Pennsylvania homes, according to a new analysis.

This wouldn't be the first time that fracking - which involves drilling into the earth and injecting a high-pressure water and chemical mixture to release natural gas - has been associated with contaminated water. Previous research has suggested that the flowback fluid from this process can leach out of the soil and into groundwater.

Now, researchers have applied a new analytical technique to drinking water and found traces of a chemical compound, 2-BE, as well as an unidentified complex mixture of organic contaminants - both which are seen in flowback water from Marcellus shale activity.

"These findings are important because we show that chemicals traveled from shale gas wells more than two kilometers in the subsurface to drinking water wells," co-author Susan Brantley from Penn State said in a statement. "The chemical that we identified either came from fracking fluids or from drilling additives and it moved with natural gas through natural fractures in the rock. In addition, for the first time, all of the data are released so that anyone can study the problem."

Some scientists say that the chemical composition of flowback fluid weakens the bind between microscopic particles called colloids and the soil. This makes groundwater susceptible to contamination when these particles leach out of the soil, bringing bound pollutants and heavy metals with it.

However, this kind of contamination from shale gas wells in shallow potable water sources has never been fully documented before, researchers say. That's because they didn't rely on routine testing, but rather what is referred to as GC-GC-TOFMS - a form of gas chromatography coupled with mass spectrometry. The new technique could be a valuable tool in evaluating alleged causes of unconventional gas drilling impacts to groundwater.

"More studies such as ours need to be disseminated to the general public to promote transparency and to help guide environmental policies for improving unconventional gas development," said Garth Llewellyn, the study's lead author.

The affected homes included in this research are located near a reported well-pad leak at a Marcellus shale site. Scientists believe stray natural gas and wastewater were driven one to three kilometers (0.6 to 1.8 miles) across along shallow to intermediate depth fractures to the source of the homes' well water.

Although state environmental regulators previously found high levels of natural gas in the drinking water, they did not discover flowback water contamination above regulatory limits.

"This work demonstrates that these events are possible, but that more sophisticated analytical work may be necessary to uncover the details of the impact," added co-author Frank Dorman, associate professor of biochemistry and molecular biology at Penn State.

However, while some blame fracking, others say leaky gas wells are the root of the groundwater pollution problem. Regardless, more research is needed to better understand how to keep our groundwater clean and prevent further water contamination.

Researchers note that the affected homes were sold to the gas company as part of a legal settlement in 2012, but scientists received samples before the transfer.

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