CANONSBURG, Pa. – A study completed by international environmental engineering and consulting firm Tetra Tech, Inc., revealed that natural gas development was only a minor contributor to elevated levels of Total Dissolved Solids (TDS) in the Monongahela River last fall.
Tetra Tech found that the primary TDS load in the Monongahela River came from abandoned mine discharge, which was realized in high sulfate concentrations. Drilling activity accounted for approximately seven percent of the total TDS concentrations detected in the Monongahela River in October 2008 and decreased to less than one percent by December 2008. Increases in river flow rates and reductions in discharges from abandoned mines appear to be the most significant factors that contributed to the reductions in TDS concentrations between October and December 2008. Changes in TDS levels associated with restricting the discharges of drilling wastewater at municipal wastewater treatment plants along the Monongahela River were negligible compared to these other factors.
“The results of the Tetra Tech study clearly indicate that natural gas drilling activity contributed only minimally to the total TDS concentrations in the Monongahela River,” said Lou D’Amico, executive director of the Independent Oil and Gas Association of Pennsylvania and member of the Marcellus Shale Coalition(MSC) executive committee. “Natural gas development does create some wastewater in the form of salt water and the industry has a long-term plan to address treatment and disposal approaches in conjunction with the Pennsylvania Department of Environmental Protection.”
According to the U.S. Environmental Protection Agency, TDS in drinking water can be traced to a number of potential sources, including naturally occurring minerals in water, sewage, urban run-off, industrial wastewater, and chemicals used in the water treatment process, as well as the piping used to convey the water. TDS minerals are actually added to distilled drinking water in some commercial water operations for quality assurance and to enhance the taste.
In late summer/early fall 2008, PADEP began to detect unusually high levels of TDS at points along approximately 70 river miles of the Monongahela River, beginning at the West Virginia border to the confluence with the Youghiogheny River. During its investigation, PADEP suggested a number of possible sources, including the natural gas industry. In October 2008, PADEP directed municipal sewage treatment plants to reduce the amount of natural gas flowback and produced water received for treatment.
Tetra Tech reviewed a variety of flow and water quality data, including the U.S. Geological Survey Monongahela River gauges and PADEP’s comprehensive water quality data set, as part of its study. Tetra Tech found the daily and monthly average flow rates in October 2008 were much lower than historic flow rates. The DEP issued a drought watch in November 2008 and the U.S. Army Corps of Engineers minimized releases of water from reservoirs in the watershed per their drought release schedules in the same time period. PADEP’s water quality data showed that TDS concentrations were as high as 900 parts per million (ppm) in October 2008 and decreased to approximately 200 ppm in December 2008.
“The report concluded controlled drilling discharges to the river could occur without exceeding water quality limits during most of the year when low-flow conditions do not occur,” said Steve Rhoads, president of the Pennsylvania Oil and Gas Association and Marcellus Shale Coalition executive committee member. “This is supports the belief that Pennsylvania has ample drilling wastewater capacity for many years, while the industry develops and perfects other long-term solutions.”
The TDS found in the Monongahela posed no threats to health or safety, but did cause some inconveniences for residential and industrial water customers. A long-term statistical trend analysis indicated that there has been no statistically significant difference in the mass loadings of TDS in the Monongahela River over the past seven years.