A study has been undertaken by Duke University of methane levels in water from 68 private wells above the Marcellus and Utica shales in Pennsylvania and New York. The details have just been published in the Proceedings of the National Academy of Sciences http://www.pnas.org/content/early/2011/05/02/1100682108.full.pdf+html. Of these, around one third were in an "active extraction area", which by definition is within one kilometre of a gas well, the remainder being more distant.
The results of the study are striking: in all but one case, making 15 altogether, it is only within 800 metres of a gas-well that levels of methane are high enough (10 - 28 mg/L) to merit warning of the occupants and prudent remediation down to levels < 10 mg/L, according to the US Office of the Interior, or above 28 mg/L at which point "potentially explosive or flammable quantities of the gas are being liberated in the well and/or may be liberated in confined areas of the home," which requires immediate mitigation. http://arblast.osmre.gov/downloads/Mine%20Gases%20and%20Dust/FINAL-Methane.pdf
In this particular study, no evidence for fracking fluid finding its way into the groundwater was found nor for intrusion from deep saline brines into aquifers closer to the surface. According to an isotopic analysis, the excess methane is consistent as originating from deeper thermogenic sediments, rather than being produced biologically in near surface environments.
Although more work is clearly necessary to establish absolutely and ubiquitously that fracking contaminates near proximate drinking water by methane in dangerous amounts, it appears that there is a significant and urgent human safety issue to be addressed.
By. Professor Chris Rhodes
Professor Chris Rhodes is a writer and researcher. He studied chemistry at Sussex University, earning both a B.Sc and a Doctoral degree (D.Phil.); rising to become the youngest professor of physical chemistry in the U.K. at the age of 34.
A prolific author, Chris has published more than 400 research and popular science articles (some in national newspapers: The Independent and The Daily Telegraph)
He has recently published his first novel, "University Shambles" was published in April 2009 (Melrose Books). http://universityshambles.com