According to a recent Gallup poll, opinions on the process of hydraulic fracturing, or “fracking”, are divided largely along party lines, with Democrats opposed and Republicans in favor. Opposition is growing, however, and opposition groups frequently cite concerns about groundwater contamination.

On May 18-19, 2015, representatives from industry, government, and academia gathered to discuss the ongoing challenges of hydraulic fracturing at a workshop titled “Chemistry and Engineering of Shale Gas and Tight Oil Resource Development” hosted at the National Academy of Sciences.

Over the two days of discussion, industrial representatives made it clear that newer well drilling techniques and improved concrete standards should prevent water contamination issues that are occasionally seen in older wells. But a bigger problem has flown under the public’s radar: industrial wastewater formed during fracking, referred to as flowback water. During fracking, water is pushed underground under extremely high pressure to split open rock containing oil and gas. The resulting waste fluid extracted from the well is a mixture of oil, natural gas, and water.

Dr. Avner Vengosh, a Professor of Earth and Ocean Sciences at Duke University, discussed the properties and composition of the flowback water which returns to the surface with the oil and gas. Surprisingly, only a small percentage of injected water actually makes it back to the surface, with as much as 70% of the water unaccounted for. What happens to that 70% is a mystery.

In the water that does return to the surface, signature compounds of the rock below appear, including high concentrations of salts and naturally occurring radioactive compounds like strontium. The high salinity of flowback water renders most analytical chemistry techniques useless, making it difficult to know exactly what compounds are in the wastewater.

Oil and gas companies have little to no incentive to treat the water. As engineering professor at Texas Tech University Dr. Danny Rieble discussed, most wastewater decisions are driven by regulatory and economic considerations. For instance, in the Marseilles shale region around Pennsylvania, the cost of water disposal is what drove companies to pursue wastewater recycling.

If oil and gas companies did choose to purify wastewater to a drinkable quality, many regulations prevent reselling this water back to municipalities. Much of the wastewater is stored on site, leading to potential spills and leaks. Some of the radioactive wastewater is sent to the landfill, especially in areas that allow radioactive materials to be dumped.

Until regulations specify how this wastewater should be disposed, the economics of water purification and disposal will continue to drive industrial practice.