Water samples taken downstream of facilities authorized to treat wastewater from natural gas wells in the Marcellus Shale had elevated concentrations of chloride but not total suspended solids (TSS), although the obverse was true in samples collected downstream of watersheds with shale gas wells drilled on them, according to a report published in the Proceedings of National Academies of Sciences (PNAS).
The researchers for the nonprofit group Resources for the Future -- Sheila Olmstead, Lucija Muehlenbachs, Jhih-Shyang Shih, Ziyan Chu and Alan Krupnick -- said additional study was necessary, but indicated that the risk of surface water contamination from a wastewater spill was unlikely.
"Although groundwater concerns may have primarily to do with contamination directly from well bores or shale formations, surface water concerns may have primarily to do with off-site waste treatment and above ground land management," the researchers said. They added that their six-page report, released Monday, takes an "econometric approach [that] cannot identify or rule out individual instances of water quality contamination."
In a separate statement, Olmstead added that "while much of the public concern and controversy around shale gas development has focused on its impacts on groundwater, our findings indicate that there are risks to rivers and streams."
The researchers analyzed 8,364 chloride concentration samples taken from 860 water quality monitors in Pennsylvania from January 2000 to December 2011, and 11,919 TSS concentration samples taken from 644 monitors during the same time frame. They also studied 4,908 natural gas wells drilled in the Marcellus through December 2011, and 74 facilities that at the time were permitted by the state Department of Environmental Protection (DEP) to accept and treat wastewater from shale gas wells.
According to the researchers, one facility that treats wastewater from shale gas wells causes downstream concentrations of chloride to increase by about 7%. They said if an additional 1.5 facilities were brought online, chloride concentrations would increase 10% to 11% downstream.
"Results for chloride suggest that the presence of shale gas wells upstream in a monitor's watershed does not raise observed concentrations, but that the treatment and release of wastewater from shale gas wells by permitted facilities upstream in a monitor's watershed does," the researchers said. "These results are not consistent with the presence of significant flows of high-chloride shale gas waste through accidental releases directly into surface water from well sites. However, surface water disposal of treated waste from shale gas wells represents a potentially important water quality burden."
The researchers found that TSS concentrations were elevated when downstream of a watershed with a shale gas well. They also found TSS concentrations were about 5% higher when downstream of an additional 18 well pads.
"In the case of TSS, the primary water quality burden may be associated with the process of clearing land for infrastructure," the researchers said. "However, given that we do not detect an increase in TSS impacts of well pads during precipitation events, or an increase associated with well pads in construction, the particular mechanisms through which shale gas infrastructure may increase TSS in local water bodies are unclear.
"Further analysis using data on pipeline and new road construction would be helpful in this regard. The observed increase in TSS concentrations could potentially be associated with spills or other emissions at well sites, rather than construction, but the inability of our models to detect increases in chloride from well sites...is not consistent with this possibility."
In 2011 the DEP, at the direction of Gov. Tom Corbett, ordered operators in the state to stop delivering wastewater to treatment facilities in the state (see Shale Daily, May 26, 2011; May 20, 2011; April 20, 2011). The DEP cited new regulations governing total dissolved solids (TDS) for the change.
TSS includes silt, decaying organic matter, industrial wastes and sewage that can be trapped by a fine filter. In surface water, TSS can harm animals and plants by reducing available sunlight, raising water temperature and decreasing dissolved oxygen and clarity. Meanwhile, removing TDS from wastewater also removes nontoxic bromides, but these become pollutants called trihalomethanes (THM) when combined with chlorine, which is used at water treatment facilities to disinfect drinking water.
The Ohio Environmental Protection Agency (OEPA) has also cracked down on the treatment of wastewater from shale gas wells, citing TDS concerns (see Shale Daily, March 21, 2012).