Source water changes and energy extraction activities in the Monongahela River, 2009-2012.

Fossil fuel wastewaters disposed of to surface waters used as sources for potable water supply have the potential to affect finished drinking water quality since these produced waters contain high concentrations of constituents that are of concern to drinking water providers (including dissolved solids, sulfate, chloride, and bromide). A 3-year field study in the Monongahela River was conducted to determine how constituent concentrations and associated loads changed in the river basin, and whether these changes were caused by surface discharges associated with shale gas extraction. Low flow during the dry summer of 2010 contributed to increases in bromide concentrations at drinking water intakes; however, similar low flow conditions in summer of 2012 did not, indicating bromide loads discharged to the river decreased from 2010 to 2012. Analysis of bromide to chloride ratios as an indicator of fossil fuel associated wastewaters showed significant increases in Br/Cl at drinking water intakes over the first year of the study (2009-2010). This indicator ratio declined in the final year of the study (2011-2012), likely associated with a voluntary decrease in the use of surface-discharging treatment plants for shale gas wastewater disposal. Predictions of future concentrations based on historical flow data are also presented.