Municipal treatment plants located downstream
Levels of contamination were just as high in wastewater coming from conventional oil and gas wells as from hydraulically fractured shale gas wells.
"This discovery raises new concerns about the environmental and human health impacts of oil and gas wastewater in areas where it is discharged or leaked directly into the environment," said Avner Vengosh, professor of geochemistry and water quality at Dukeís Nicholas School of the Environment.
"Our data clearly show that the current brine treatment practice in Pennsylvania is not sufficient to remove these contaminants," Vengosh said.
When dissolved in water, ammonium can convert into ammonia, which is highly toxic to aquatic life. The scientists detected ammonium levels of up to 100 milligrams per liter in oil and gas effluents they collected at the wastewater discharge sites. Those levels are more than 50 times higher than the EPA water-quality threshold for protecting freshwater organisms.
Elevated iodide in surface water can promote the formation of highly toxic byproducts in drinking water when the iodide mixes with the chlorine used to disinfect the water at municipal treatment plants located downstream from oil and gas operations. Such disinfection byproducts are not monitored by state or federal agencies.
The peer-reviewed study, appearing this week in the journal Environmental Science & Technology, is the first to document the presence of high levels of ammonium and iodide in oil and gas wastewater.