Each hydraulically fractured oil or gas well yields millions of gallons of wastewater over its production lifetime. Most of this wastewater is stored underground in what are known as Class II wells. The authors of a study in Environmental Health Perspectives show that in Ohio, Class II wells that receive fracking wastewater are disproportionately situated in lower-income and rural communities.At different stages, fracking wastewater may contain different proportions of residual fracturing fluids, potentially toxic agents that occur naturally in some rock formations, and sodium chloride. In Class II wells, wastewater is injected into underground rock formations through a protective steel and cement casing. The layers of rock act as a natural containment barrier for the waste, although some studies have pointed to multiple potential pathways by which wastewater can contaminate drinking-water sources.The U.S. EPA has identified several ways by which fracking wastewater can reach drinking-water sources. Among them are fluid movement 1) through a fault in the well’s casing, 2) through the space between the casing and the wellbore, 3) into the underground formations that were meant to contain the injection site, or 4) through abandoned or completed wells that have been not been properly plugged. Image: U.S. Government Accountability Office.
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