Hydraulic fracturing is a widely-used technology that enhances oil and gas extraction from unconventional shale. The fluids used in hydraulic fracturing operations contain water, proppant, and a complex mixture of chemicals. Since hydraulic fracturing frequently occurs in the vicinity of agricultural lands, improper storage and handling of hydraulic fracturing fluids may lead to soil and water contamination. In case of a spill, the frac fluid chemicals may substantially impact each other’s fate and transport: For instance, the presence of biocides may decrease the potential for biodegradation, while viscosity-enhancing compounds may alter the mobility of co-contaminants. Thus, this study aims to elucidate the environmental fate as well as the interactions among commonly used hydraulic fracturing chemicals in agricultural topsoil. Aerobic batch experiments focusing on the friction reducer polyacrylamide (PAM), polyethylene glycol surfactants (PEG), and the two biocides glutaraldehyde (GA) and didecyldimethyl ammonium chloride (DDAC) were set up to determine their transformation kinetics in the presence and absence of co-contaminants. Uncontaminated soil cores for this study were collected from an agricultural field in Weld County, Colorado. Transformation of PAM was only observed in biologically active soils. However, PEG concentrations decreased over time in both active and sterilized topsoil, but at higher rates in biologically active soil, indicating that PEG removal from the aqueous phase is due to both sorption and biodegradation. While DDAC underwent almost immediate sorption to soil, GA slowed the initial rate of PEG and PAM biodegradation in the aqueous phase. After one week, however, GA was completely eliminated from the aqueous phase due to sorption. These results clearly indicate that risk assessment of hydraulic fracturing fluids or flowback water must include an evaluation of potential compound interactions to accurately assess transport and persistence of spilled frac chemicals.

Fate of hydraulic fracturing chemicals in agricultural topsoil

249th National Meeting (2015)

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