Sources of High Total Dissolved Solids to Drinking Water Supply in Southwestern Pennsylvania

Abstract

Fossil fuel extraction activities generate wastewaters that are often high in total dissolved solids (TDS) and specific constituents that can affect drinking water, if these wastewaters enter surface waters. Control of TDS in source waters is difficult without identification of the potential sources of high TDS wastewater associated with fossil fuel activities. Characteristics of natural waters, oil and gas-produced waters, and coal-related wastewaters were analyzed to extract information about constituent concentrations and anion ratios. Statistical analysis of the anion ratios indicates that the SO4/Cl ratio is higher in coal-related wastewaters than in oil and gas-produced waters, suggesting that wastewaters can be distinguished based on this ratio. An approach that compared the SO4/Cl ratio with bromide concentration for the wastewaters can serve to separate oil and gas-produced waters from brine treatment plant discharges, and from the various coal-related wastewaters. This method was applied to surface water quality data collected from two tributaries in Southwestern Pennsylvania from September 2009 to September 2012. Results show that this constituent and ratio method, combined with mixing curve calculations, can be used to identify water quality changes in these two tributaries. Similar mixing models, when applied to regionally relevant high TDS wastewater data, may be used in other areas experiencing water quality changes resulting from fossil fuel extraction activities.