Chemists 'clear' fracking of water pollution

Researchers from five US universities studied samples taken from drinking water wells across the Marcellus and Barnett shales, and concluded that the data ruled out “gas contamination by upward migration from depth through overlying geological strata triggered by horizontal drilling or hydraulic fracturing”.

The study revealing their conclusions and published in the Proceedings of the National Academy of Sciences of the United States instead blames the incidences of contamination that were discovered on poorly constructed wells.

“Our data clearly show that the contamination stems from well-integrity problems such as poor casing and cementing,” said Thomas H. Darrah, assistant professor of earth science at Ohio State, who led the study between 2012 and 2013 while he was a research scientist at Duke University.

Scientists from Duke, Ohio State, Stanford, Dartmouth and the University of Rochester used noble gas and hydrocarbon tracers to identify and distinguish between the signatures of naturally occurring methane and stray gas contamination from shale gas drill sites.

Analysis of 133 samples identified eight discrete clusters of “fugitive” methane contamination, seven in Pennsylvania and one in Texas, which showed increased contamination through time.

In four of the affected clusters, the team’s noble gas analysis shows that methane from drill sites escaped into drinking water wells from shallower depths through faulty or insufficient rings of cement surrounding a gas well’s shaft. In three clusters, the tests suggest the methane leaked through faulty well casings. In one cluster, it was linked to an underground well failure.

“These results appear to rule out the possibility that methane has migrated up into drinking water aquifers because of horizontal drilling or hydraulic fracturing, as some people feared,” said Avner Vengosh, professor of geochemistry and water quality at Duke.

Likewise, Darrah, who is continuing the analysis in his laboratory at Ohio State, added: “This is the first study to provide a comprehensive analysis of noble gases and their isotopes in groundwater near shale gas wells.

“Using these tracers, combined with the isotopic and chemical fingerprints of hydrocarbons in the water and its salt content, we can pinpoint the sources and pathways of methane contamination, and determine if it is natural or not.”

This research follows a call from chemists at Rice University, US to investigate new techniques to treat and reuse fracking water and clear it of potentially toxic chemicals.