Tuesday, 27 October 2015

Elevated organic compounds in Pennsylvania drinking water from hydraulic fracturing surface operations, not gas wells


In the largest study of its kind, a Yale-led investigation found no evidence that trace contamination of organic compounds in drinking water wells near the Marcellus Shale in northeastern Pennsylvania came from deep hydraulic fracturing shale horizons, underground storage tanks, well casing failures, or surface waste containment ponds.
 
The presence of organic compounds in groundwater aquifers overlying the Marcellus Shale is likely the result of surface releases from hydraulic fracturing operations and not migration from gas wells or deep shale layers, according to researchers in the lab of Desiree L. Plata, assistant professor of chemical and environmental engineering at Yale. The results of the study were published in the journal Proceedings of the National Academy of Sciences. Brian Drollette, a Ph.D. student in Plata’s lab, is the lead author.

Due to its vast reserves of natural gas, the Marcellus Shale has become an active site for hydraulic fracturing. During a period of rapid natural gas well expansion, the researchers regularly visited the northeastern region of Pennsylvania, covering about 7,400 square kilometers, over three years and obtained 64 samples from the drinking water wells of residential properties.

Using a suite of chemical analyses, the researchers found that a subset of the groundwater samples contained low levels of organic compounds in areas close to natural gas wells. The analyses also indicated that these compounds most likely entered the groundwater supply from gas extraction operations above the ground surface — and not subsurface migration.

“These tests showed that there is some separation, both in space and time, of the materials that they’re injecting into the deep horizons and the groundwater sources,” Plata said.

A compound-specific analysis also revealed the presence of a hydraulic fracturing fluid additive in the affected water samples. Chemicals found in the water did not exceed any state or federal limits, and many were detected only because the researchers were using sophisticated and very sensitive instruments. None of the contaminants were derived from the shale itself.

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