A recent study (Drollette et al) on groundwater contamination in fracking regions of Pennsylvania has detected traces of fracking chemicals in groundwater. However, the authors believe that these chemicals, including the fracking substance bis(2-ethylhexyl)phthalate, aromatic hydrocarbons, and diesel range organic compounds, are from surface spills, rather than upwards seepage from the deep rocks where fracking occurs. They deduced this by looking at the salts in the water, and the quantities and isotope ratios of noble gases present in the water.
The presence of the chemicals was also correlated with distance from known surface spills. None of the chemicals, which were typically at ?g/kg (parts per billion) levels, were above the official safety limits.
However, the authors of the study point out that just because groundwater contamination from the underground fracking process was not identified, there is still a possibility it may occur in the future, since the fracking process weakens rocks, and may allow new fissures to occur.
The authors note that bis(2-ethylhexyl)phthalate is found in many plastic products, but since it was not in blank field samples, they believe that it originated from surface leakage of fracking chemicals, rather than from any other source. Although the arguments in the paper are persuasive, some of the trace pollutants involved might have other potential sources, such as leaks from diesel tanks unconnected with fracking, so it cannot be conclusively proved that all the contamination was solely due to spills of fracking chemicals.
The leakage of methane gas into surface water is another concern. This was brought to public attention in the US when a house in Bainbridge Township, Ohio was wrecked by a methane explosion back in 2007. The local fracking company accepted responsibility. It seems that faulty cement casing had allowed methane to reach groundwater wells. Such incidents are rare.
The study in Pennsylvania (Drollette et al) does not seem to mention methane levels. Studies on methane are complicated by the fact that methane naturally occurs in groundwater some fracking areas.
A 2014 study (Sang et al) looked at how flowback fluid, the fluid that comes back out of fracking wells, could affect colloids in the soil, by examining colloid removal in the laboratory. The authors found that flowback fluid released colloidal particles from sand to a much greater degree than water alone (32-36% colloid removal with the fluid, compared to less than 5% colloid removal with distilled water). These results suggest that the fluid may contaminate groundwater by removing existing colloidal pollutants from contaminated soil. Further field work is needed to confirm that this effect actually occurs outside of the laboratory.
The Department of Energy and Climate Change has published guidance on fracking in the UK. The department takes the view that the risks of groundwater contamination and other pollution can be managed effectively provided best practice is implemented.
The government refers to the report ?Shale Gas Extraction in the UK?, prepared by the Royal Society and the Royal Academy of Engineering, which recommended that fracking should be permitted, provided proper Environmental Risk Assessments (ERAs) are carried out, and independent experts check the design of each well.
It is believed that appropriate standards can largely avoid the problems with ground contamination and groundwater pollution seen in some parts of the USA. However, many will feel that a wider consideration of the threat posed by global warming would suggest that we should be leaving the gas in the ground, even if it can be extracted without undue pollution. The fracking debate is set to continue for many years.
Drollette, B.D. et al, ?Elevated levels of diesel range organic compounds in groundwater near Marcellus gas operations are derived from surface activities?, Proceedings of the National Academy of Sciences, (2015), vol. 112(43), pp.13184-13189. http://www.pnas.org/content/112/43/13184.abstract
Post, J. ?Study drills out truth on fracking?, Yale Daily News (1st Dec. 2015). http://yaledailynews.com/blog/2015/12/01/study-drills-out-truth-on-fracking/
Sang, W. et al, ?Effect of hydrofracking fluid on colloid transport in the unsaturated zone?, Environmental Science and Technology, (2014), vol. 48, pp.8266-8274. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4102097/
Ryder, D. ?Bainbridge drilling case has national consequences?, The News Herald (26th May 2009). http://www.news-herald.com/general-news/20090526/bainbridge-drilling-case-has-national-consequences
Department of Energy and Climate Change ?Guidance on fracking: developing shale oil and gas in the UK.? https://www.gov.uk/government/publications/about-shale-gas-and-hydraulic-fracturing-fracking/developing-shale-oil-and-gas-in-the-uk
The Royal Society and the Royal Academy of Engineering, ?Final report - Shale gas extraction in the UK?, (2012). https://royalsociety.org/topics-policy/projects/shale-gas-extraction/report/