2 research outputs found
Natural Gas Residual Fluids: Sources, Endpoints, and Organic Chemical Composition after Centralized Waste Treatment in Pennsylvania
Volumes of natural gas extraction-derived
wastewaters have increased
sharply over the past decade, but the ultimate fate of those waste
streams is poorly characterized. Here, we sought to (a) quantify natural
gas residual fluid sources and endpoints to bound the scope of potential
waste stream impacts and (b) describe the organic pollutants discharged
to surface waters following treatment, a route of likely ecological
exposure. Our findings indicate that centralized waste treatment facilities
(CWTF) received 9.5% (8.5 Ă— 10<sup>8</sup> L) of natural gas
residual fluids in 2013, with some facilities discharging all effluent
to surface waters. In dry months, discharged water volumes were on
the order of the receiving body flows for some plants, indicating
that surface waters can become waste-dominated in summer. As disclosed
organic compounds used in high volume hydraulic fracturing (HVHF)
vary greatly in physicochemical properties, we deployed a suite of
analytical techniques to characterize CWTF effluents, covering 90.5%
of disclosed compounds. Results revealed that, of nearly 1000 disclosed
organic compounds used in HVHF, only petroleum distillates and alcohol
polyethoxylates were present. Few analytes targeted by regulatory
agencies (e.g., benzene or toluene) were observed, highlighting the
need for expanded and improved monitoring efforts at CWTFs
Indications of Transformation Products from Hydraulic Fracturing Additives in Shale-Gas Wastewater
Unconventional natural
gas development (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. This study investigated six Fayetteville Shale wastewater
samples for organic composition using 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 azobisÂ(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. Our study highlights the possibility that UNGD
operations generate transformation products and underscores the value
of disclosing additives injected into the subsurface