Groundwater Quality and Fracking: Current Understanding and Science Needs
A consensus view developed from two NGWA workshops held in 2014 and 2017 identified two primary risks to shallow aquifers from fracking: 1) stray gas associated with shale wells, and 2) groundwater contamination from surface spills of frack chemicals and produced fluids. Induced seismicity from the disposal of fracking wastewater down underground injection control (UIC) wells is an additional risk, but does not directly affect shallow groundwater. A lack of data on the true environmental risks of fracking is driving unsupported arguments on both sides of the issue.
Several field studies have provided evidence that gas or frack fluid do not migrate upward from hydraulic fractures into overlying aquifers. Groundwater and surface water contamination is typically caused by surface spills and leaks of frack chemicals and produced fluids, both at production sites and UIC wells. Stray gas in groundwater has been statistically linked to shale gas wellbore integrity problems, although the specific causes of wellbore integrity failures have not been identified.
Data gaps and science needs include a lack of pre-drilling baseline data, ongoing challenges gaining access to field sites and data from industry, uncertainties about the origins and migration pathways of stray gas, and the introduction of new frack chemicals with unknown degradation pathways and breakdown products. Non-standardized sampling and analytical methods make comparison of results from different studies challenging. A consensus recommendation from the workshops was to improve data-sharing, and develop standardized methodologies.