A couple of recent reports about the effects of fracking on groundwater quality seem to be contradictory. A study published in the Proceedings of the National Academy of Science (Jackson, R.B., et al., 2013. Increased stray gas abundance in a subset of drinking water wells near Marcellus shale gas extraction) found that wells in northeastern Pennsylvania where the Marcellus Shale is being drilled for natural gas has high levels of gases (methane, ethane, propane) that they say are due to drilling practices. On the other hand, a paper published in the journal Groundwater (Molofsky, L.J., et al., 2013. Evaluation of Methane Sources in Groundwater in Northeastern Pennsylvania. Groundwater 51(3):333–349) suggests that methane is ubiquitous in groundwater in northeastern Pennsylvania, and is not the result of shale gas extraction.
Image from UConn Today
Jackson et al. analyzed 141 drinking water wells, measuring natural gas concentrations and isotopic signatures. They found that concentrations of methane and ethane were significantly higher in water wells near gas wells. They also found, using isotopic data and gas ratios, that the gases were characteristic of the Marcellus Formation being their source. The authors stress that the contamination is probably due to poor well construction, rather than hydraulic fracturing itself. If that is true, the problem is probably relatively simple to fix, i.e., drilling and regulations should emphasize well integrity.
Molofsky et al. tested 1701 water wells in the same region. Unlike Jackson et al., they found higher methane concentrations in valleys compared to upland areas. They also observed that concentrations were a function of the major ion chemistry, i.e., being higher in groundwater in which sodium was a dominant cation. Their results suggest that methane concentrations are best correlated to topographic and hydrogeologic features on a regional scale, rather than shale-gas extraction activities. In contrast to the Jackson study, their isotopic and molecular analyses suggest that gases present in the groundwater most likely originated from formations other than the Marcellus.
Methane is common in many aquifers in Illinois as well. Sometimes the source is thermal (petroleum), but most often, especially in glacial sand and gravel aquifers, the source is microbial. Methane is one of the byproducts of the decay of organic matter buried in the sediments.
It’s still unclear how widespread fracking will be in Illinois, especially for shale gas. Even if the Molofsky study is more “correct” than the Jackson study, it still seems prudent to me that groundwater monitoring should be part of any fracking operation. This is included in the Hydraulic Fracturing Regulatory Act recently signed by Governor Quinn.
