Abstract
The widespread application of directional drilling and hydraulic fracturing technologies expanded oil and gas (OG) development to previously inaccessible resources. A single OG well can generate millions of liters of wastewater, which is a mixture of brine produced from the fractured formations and injected hydraulic fracturing fluids (HFFs). With thousands of wells completed each year, safe management of OG wastewaters has become a major challenge to the industry and regulators. OG wastewaters are commonly disposed of by underground injection, and previous research showed that surface activities at an Underground Injection Control (UIC) facility in West Virginia affected stream biogeochemistry and sediment microbial communities immediately downstream from the facility. Because microbially driven processes can control the fate and transport of organic and inorganic components of OG wastewater, we designed a series of aerobic microcosm experiments to assess the influence of high total dissolved solids (TDS) and two common HFF additives—the biocide 2,2-dibromo-3-nitrilopropionamide (DBNPA) and ethylene glycol (an anti-scaling additive)—on microbial community structure and function. Microcosms were constructed with sediment collected upstream (background) or downstream (impacted) from the UIC facility in West Virginia. Exposure to elevated TDS resulted in a significant decrease in aerobic respiration, and microbial community analysis following incubation indicated that elevated TDS could be linked to the majority of change in community structure. Over the course of the incubation, the sediment layer in the microcosms became anoxic, and addition of DBNPA was observed to inhibit iron reduction. In general, disruptions to microbial community structure and function were more pronounced in upstream and background sediment microcosms than in impacted sediment microcosms. These results suggest that the microbial community in impacted sediments had adapted following exposure to OG wastewater releases from the site. Our findings demonstrate the potential for releases from an OG wastewater disposal facility to alter microbial communities and biogeochemical processes. We anticipate that these studies will aid in the development of useful models for the potential impact of UIC disposal facilities on adjoining surface water and shallow groundwater.
Highlights
Wastewaters co-produced during shale gas development become of particular concern in the event of an environmental release, potentially affecting surface and shallow subsurface waters and the biological communities that depend on them
Oil and gas wastewaters are complex mixtures that reflect the high salinity of the formation and the chemicals used for HF, and releases of these fluids have the potential for adverse effects on the environment
Downstream surface water was elevated in Cl, Na, Sr, and organic constituents that were consistent with signatures of oil and gas (OG) wastewaters
Summary
Wastewaters co-produced during shale gas development become of particular concern in the event of an environmental release, potentially affecting surface and shallow subsurface waters and the biological communities that depend on them. Studies suggest that the high salinity of shale gas wastewaters can inhibit aerobic biodegradation (Kekacs et al, 2015; McLaughlin et al, 2016; Hanson et al, 2019) While these studies indicate that some organic compounds present in HFF are utilized as carbon sources by indigenous microbes, the potential effect of adding this carbon to the stream environments is less clear. Lozano et al (2019) observed shifts in microbial soil communities exposed to different synthetic HFF compositions Another commonly used biocide in hydraulic fracturing is 2,2dibromo-3-nitrilopropionamide (DBNPA), which has a short half-life of 4 hours at neutral pH (United States Environmental Protection Agency [U.S EPA], 1994). This work provides information on the community-level effects of HFF components in the environment and the potential for microbial activity to be altered in the event of OG wastewater releases into streams
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