Relationship between total dissolved solids and electrical conductivity in Marcellus hydraulic fracturing fluids

The production of hydraulic fracturing fluids (HFF) in natural gas extraction and their subsequent management leads to waste streams highly variable in total dissolved solids (TDS). TDS is often estimated from electrical conductivity (EC) assuming dissolved solids are predominantly ionic species of low enough concentration to yield a linear TDS-EC relationship. The composition and TDS-EC relationship of several fluids from Marcellus gas wells in Pennsylvania were assessed as part of investigating vegetation, soil, and groundwater impacts from accidental releases of HFF. Below EC of 75,000 ?S/cm, TDS (mg/L) can be estimated with little error assuming a 0.7 constant of proportionality. For more concentrated HFF, a curvilinear relationship is needed, while for hypersaline HFF, the use of an EC/TDS meter underestimated TDS by as much as 50%. A single linear relationship is unreliable as a predictor of brine strength and, in turn, potential water quality and soil impacts from accidental releases or the suitability of HFF for industrial wastewater treatment.