Wastewater from oil and gas wells that is spread on unpaved roads to control dust contains high levels of the carcinogenic element radium, inorganic salts, and oil and gas hydrocarbons. A new study shows that these harmful components are likely leaching off roads into surrounding soils and water (Environ. Sci. Technol. 2018, DOI: 10.1021/acs.est.8b00716).
At least a dozen U.S. states allow the spreading of wastewater produced from rock formations during the recovery of oil and gas to reduce the dust kicked up on unpaved surfaces, or for other purposes such as deicing. Unchecked, such dust can promote respiratory and cardiovascular disease. The high levels of calcium salts in the wastewater bind clays to the road, suppressing dust. Since oil and gas companies freely provide the waste to municipalities, it’s a much cheaper solution than other dust suppressants, such as chloride salts.
William D. Burgos of Pennsylvania State University and his colleagues wanted to investigate the environmental impacts of spreading such wastewater on roads after learning that this was an approved option in Pennsylvania for disposing of wastewater from conventional oil and gas development. “It’s not what you’d expect as a practice for wastewater treatment,” Burgos says. (Pennsylvania and four other states have banned road spreading of wastewater from hydraulically fractured wells.)
To get a handle on the environmental and health impacts of spreading the waste on roads, Burgos’s team started by sampling 14 tanks in which oil and gas companies deposit wastewater for use by road managers in the state and then chemically characterizing these fluids. Radium in the samples produced a median radioactivity of 1,230 picocuries per liter, much higher than the 5 pCi/L federal drinking water standard and the 60 pCi/L limit for discharge from treatment plants processing industrial wastewater. Total dissolved solids, which include inorganic salts and organic matter, also far exceeded the 500 mg/L standard for drinking water with a median concentration of 293,000 mg/L. Hydrocarbons derived from oil and gas, including diesel-range and lighter gas-range organics, were also abundant in the samples.
The researchers also simulated the effect of rainfall on wastewater-treated roads by treating the road aggregate first with the wastewater, then drying it and treating it with artificial rainwater. Afterwards, they analyzed how much of the wastewater components leached off. About half of the radium leached off, along with a quarter of the diesel-range organics and most of the inorganic salts. The researchers also carried out repeated tests to judge the effect of roads being treated multiple times per season; they found that after four repetitions of the leaching experiment, the road aggregate became saturated with radium and nearly all of it leached out.
In Pennsylvania, records show that more than 130 million liters of oil and gas wastewater on average were spread on roads each year from 2008 to 2014. Based on the findings of the current study, the researchers estimate that in the state, this application released four times as much radium to the environment as treatment facilities that process oil and gas wastewater, and 200 times as much radium as spills of the wastewater.
Brian W. Stewart, a geochemist at the University of Pittsburgh, says the study is important in identifying that road spreading is a potentially bigger problem than some other issues environmental scientists have been concerned about, like spills. “This is effectively large-scale spilling on purpose,” he says.
Stewart says that the study shows there is clearly potential for environmental contamination from this road spreading—“maybe enough to consider halting the practice.” Burgos says wastewater should at least be pretreated to reduce levels of radium and hydrocarbons to those required for treatment plants, and ideally, managers should pursue a more environmentally friendly solution. However, municipalities using wastewater for this purpose often can’t afford alternative brine solutions, he says.
As of May, the Pennsylvania Department of Environmental Protection has halted road spreading of oil and gas wastewater in the state while it clarifies procedures for road application, in response to a lawsuit by a state resident.