In the early 2000’s, the Environmental Protection Agency (EPA) set out to assess the potential for the hydraulic fracturing process to effect drinking water in the United States.
How Can Water Become Contaminated Due to Fracking?
In its 2016 report, the EPA found that “These activities can impact drinking water resources under some circumstances. Impacts can range in frequency and severity, depending on the combination of hydraulic fracturing water cycle activities and local- or regional-scale factors... Cases of impacts were identified for all stages of the hydraulic fracturing water cycle. Identified impacts generally occurred near hydraulically fractured oil and gas production wells and ranged in severity, from temporary changes in water quality to contamination that made private drinking water wells unusable.” -- epa.gov
Above ground causes
Several studies have documented above ground spills of fracking fluid are primarily caused by equipment failure or human error. Spills have been reported to reach surface water bodies like creeks or streams and highly permeable soils or fractured rock can allow spilled liquids to move quickly into and through the subsurface.
Below ground causes
Casing, cement, and other well components need to be able to withstand changes in pressure and temperature, so the fracking fluids can flow to the targeted rock formation without leaking.
In the EPA’s study, “one percent of the fractures, creating through the hydrofracturing process, had a height greater than 1,148 feet (350 meters) and the maximum fracture height among all of the data reported was 1,929 feet (588 meters). These reported fracture heights suggest that some fractures can grow out of the targeted rock formation and into an overlying formation... A well with insufficient mechanical integrity can allow unintended fluid movement, either from the inside to the outside of the well or vertically along the outside of the well. The existence of one or more of these pathways can result in impacts on drinking water resources if hydraulic fracturing fluids reach groundwater resources.”
Older wells face changes in mechanical integrity over time and may also be hydraulically fractured at shallower depths, where cement around the casing may be inadequate or missing. Abandoned wells near a well undergoing hydraulic fracturing can provide a pathway for vertical fluid movement to drinking water resources if those wells were not properly plugged or if the plugs and cement have degraded over time.
Public Herald (Pennsylvania)
Scientific American (Wyoming)
Pennsylvania Grand Jury investigation 2020 Results