Methane Contamination of Drinking Water Accompanying Gas-Well Drilling and Hydraulic Fracturing

By Alex Frumkin

Directional drilling and hydraulic-fracturing technologies are dramatically increasing natural-gas extraction across the United States. Hydraulic fracturing remains largely unregulated at the Federal level regardless of the growing concerns about contamination of drinking water. However, the potential contamination risks in shallow drinking-water systems are still not fully understood, and a topic of study for many scientists. There are four main reasons why scientists and public health officials are concerned about methane contamination in the ground water: that the chemicals use in fracturing fluid can leak into the ground water, that the water can become explosive if methane levels are high enough, that the methane could be released into the environment, and that the untested and unregulated shallow ground water in rural areas near drilling sites could be ingested during household or agricultural use. Scientists have continued to study whether water wells are being contaminated in any of these ways by hydraulic fracturing and drilling.

This paper analyzed the aquifers overlying the Marcellus and Utica shale formations of northeastern Pennsylvania and Upstate New York and whether there is evidence for methane contamination of drinking water associated with shale-gas extraction. Gibson et al (2011) studied the presence of dissolved salts, water isotopes, and isotopes of dissolved carbon, boron, and radium in ground water from 68 private water wells ranging in depth from 36- to 190-m deep. In addition, 60 of these 68 wells were also analyzed for dissolved-gas concentrations of methane. Methane concentrations were detected in 51 of 60 drinking-water wells, but concentrations were substantially higher closer to natural-gas wells. Methane concentrations were 17-times higher on average in shallow wells from active drilling and extraction areas (areas with multiple drilling and extraction areas within 1 km of each other) than in wells from non-active areas. The average concentrations found near the drilling sites fell within the defined action level for hazard mitigation.

In order to understand the origin of the methane found in the water it must be determined whether the methane is coming from shallow biogenic or deeper thermogenic contamination. The presence of ethane and propane indicates that the methane is a result of deeper thermogenic contamination. Ethane was found in only 3 of the 35 water wells from non-active drilling sites, whereas it was detected in 21 of 26 water wells in active drilling sites. This indicates that the high methane concentrations observed are most likely due to thermogenic gas. There are multiple explanations for why methane concentrations may be increased near gas wells, but these results suggest the need for long-term sampling and monitoring of the hydraulic fracturing and drilling industry and private water wells. In addition, these results support the need for regulation of the hydraulic fracturing at the Federal level.

Stephen G. Osborn, Avner Vengosh, Nathaniel R. Warner, and Robert B. Jackson, 2011. Methane contamination of drinking water accompanying gas-well drilling and hydraulic fracturing. PNAS  108 (20) 8172-8176; published ahead of print May 9, 2011, doi:10.1073/pnas.1100682108

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