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Tuesday, July 10, 2012

New Duke study: fluids can migrate upwards from deep underground to contact aquifers

A new Duke University study concludes that Northeastern Pennsylvania’s complex geology contains networks of “natural pathways” that allow gases and brines from the Marcellus shale formation to migrate upward into shallow groundwater aquifers.  As a result, some drinking water supplies in northeastern Pennsylvania could be at increased risk for contamination, especially from methane leaks from poorly-constructed shale gas wells.

Last year, the same team of Duke researchers published a study that found elevated levels of methane contamination in drinking water wells located within a kilometer of hydraulically fractured shale gas wells, but found no evidence of contamination from fracturing fluids or brines.

The new study found elevated levels of salinity with similar geochemistry to deep Marcellus brine in drinking water samples from three groundwater aquifers that underlie six northeastern Pennsylvania counties.  The elevated salinity was not linked to hydraulic fracturing, according to the study, for two reasons.  First, the locations of the samples containing brine don’t match up with the locations of shale-gas wells. In addition, results from the new study are similar to water-quality tests conducted in the same aquifers in the 1980s, decades before shale-gas development began. 

The study did not reach conclusions as to how long it took the brines to migrate upward.  For that reason, because the brines could have come from deeper than the Marcellus formation, and because the act of drilling could actually preempt saline water from rising by reducing pressure in the Marcellus formation, the study immediately drew sharp criticism from both the oil and gas industry and a scientist on the National Academy of Science's peer review panel.

This essential truth does not appear to be in dispute, and should not be lost in any debate: fluids – in addition to gases - can migrate from deep underground upwards to come in contact with groundwater sources. How long it takes is to me somewhat irrelevant; the specific geology is very relevant.  The risks to water supplies from surface spills at gas drilling sites are already abundantly clear. The potential for contamination from upward migration of fluids (and gases) must be taken extremely seriously.

A modeling study by another researcher that was published in May suggested that frack fluids themselves could migrate upwards toward aquifers – and in a matter of decades, much more quickly than has been previously assumed. That study contradicted a UK study that found that the risk of groundwater contamination from hydraulic fracturing is very low, and that it can be virtually eliminated if fracking is stopped a minimum of 600 meters from aquifers.  

More research is clearly needed.

Avner Vengosh, professor of geochemistry and water quality at Duke's Nicholas School of the Environment, summed up the latest study – and its global implications - in a university news release:

"As shale gas exploration is becoming global -- including in Poland, China, Australia and New Zealand -- the take-home message of this study is that pre-drilling water quality monitoring is important for evaluating water-quality baselines that can be used to detect future changes in water quality, and for evaluating possible hydraulic 'short cuts' and pathways between fluids and gases in deep shale gas formations and shallow aquifers. Such geochemical reconnaissance would provide a better risk assessment for water contamination in newly developed shale gas exploration areas."

I would go further.

All of these studies underscore the need for additional research; for the gas industry to perform at the highest possible level - every well, every time - and with more environmentally benign methods; for vigorous enforcement of existing rules (Pennsylvania adopted enhanced gas well construction standards in February, 2011 after a two-year design) and constant review of their adequacy; and for requirements for much more detailed, up-front geological and groundwater testing, site characterization, and study by drillers before shale gas wells are drilled.  That is the path to minimizing risks to water supplies from shale gas exploration, and it should not be controversial at all.

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