The General Assembly recently considered lifting the ban on deep-well injection of waste fluids, but wastewater from shale oil and gas operations in North Carolina must not be disposed of in underground injection wells.
Recent experiences around the country have proved that the treatment and recycling of wastewater is more economical and friendlier to the environment.
A feature of shale gas operations is that even if fresh water is used in fracturing fluid, the water that returns is saltier. This flowback water will also have some remnants of chemicals from the original hydraulic fracturing fluid mix. The water also could have some radioactive elements naturally occurring in the earth. All of these characteristics make untreated flowback water unsuited to surface discharge.
There are only two responsible ways to dispose of these wastes. One is to treat it for a specified purpose, such as re-using it in shale gas operations or for drinking water. The other is to use deep underground injection wells, a process that can be conducted only under the strict guidelines of the EPA Underground Injection Control program for Class II wells.
Deep injection wells are believed to have caused earthquakes up to a magnitude of 4.5 on the Richter scale, but very few of the 170,000 deep injection wells have been implicated. Such occurrences are possible when the injection wells are close to active seismic faults of significant length. Were the Mining and Energy Commission to permit this option in North Carolina, we would likely be compelled to write a complex set of rules that minimized the risk. This would not be a good expenditure of state resources.
The geology in the vicinity of potential shale gas operations in North Carolina is not suited for disposal wells. The closest suitable area is near the coast, and feasible sites may be difficult to find even in that locale. Were suitable geologic formations found, they would have to be deep, in part because shallow saline aquifers are being used as a source of potable water after desalination.
Moreover, these prospective disposal sites would require over 150 miles in road travel from the gas wells. Such significant distance adds enormous transportation costs, increased potential for spills during the transport and disposal process and greater road damage attributable to long-haul traffic.
The simplest alternative, then, is to treat wastewater for re-use in shale gas operations. Recent advances in technology permit ever higher salinity water to be tolerated in hydraulic fracturing fluid. In fact, fresh water is not required even to begin fracturing operations in the state. Recent industry experience shows that treating the water for re-use is cost-effective compared with hauling it over long distances for deep discharge. Furthermore, the re-use reduces the burden on new fresh water.
When re-use is no longer required or feasible, the wastewater can be treated for discharge or for agricultural use. This could be on site or facility built for that purpose. If destined for a municipal water facility, some pre-treatment would be necessary.
Proposed rules will be reviewed by the Water and Waste Management Committee of the Mining and Energy Commission on Thursday. The committee will prescribe treatment for re-use, possibly followed by treatment for some other purpose, as the only acceptable method for oil and gas companies in their operations. Deep well injection should not be a disposal option in this state.
Vikram Rao is the executive director of the Research Triangle Energy Consortium and a member of the Mining and Energy Commission and chairs the Water and Waste Management Committee.