UNGD generates large volumes of wastewater, the detailed composition of which must be known for adequate risk assessment and treatment. In particular, transformation products of geogenic compounds and disclosed additives have not been described.
The analytical method consisted in a suite of one- and two-dimensional gas chromatographic techniques to capture a broad distribution of chemical structures. Following the application of strict compound-identification-confidence criteria, we classified compounds according to their putative origin. Samples displayed distinct chemical distributions composed of typical geogenic substances (hydrocarbons and hopane biomarkers), disclosed UNGD additives (e.g., hydrocarbons, phthalates such as diisobutyl phthalate, and radical initiators such as azobis(isobutyronitrile)), and undisclosed compounds (e.g., halogenated hydrocarbons, such as 2-bromohexane or 4-bromoheptane). Undisclosed chloromethyl alkanoates (chloromethyl propanoate, pentanoate, and octanoate) were identified as potential delayed acids (i.e., those that release acidic moieties only after hydrolytic cleavage, the rate of which could be potentially controlled), suggesting they were deliberately introduced to react in the subsurface. In contrast, the identification of halogenated methanes and acetones suggested that those compounds were formed as unintended byproducts.
Kathrin Hoelzer, Andrew J. Sumner, Osman Karatum, Robert K. Nelson, Brian D. Drollette, Megan P. O’Connor, Emma L. D’Ambro, Gordon J. Getzinger, P. Lee Ferguson, Christopher M. Reddy, Martin Elsner, and Desiree L. Plata
Indications of Transformation Products from Hydraulic Fracturing Additives in Shale-Gas Wastewater
Environ. Sci. Technol., Article ASAP
Publication Date (Web): July 15, 2016