Geochemical Signatures of Oil and Gas Wastewater from an Accidental Release Detected in Stream Sediment and Pore Waters Two Years Post Spill Completed

Rapid increases in the development of unconventional oil and gas resources using technologies such as directional drilling and hydraulic fracturing have met the growing need for fossil fuel use in the United States. However, during oil and gas extraction, wastewater containing chemicals used to enhance well production, in addition to chemicals from the hydrocarbon reservoir, are co-produced. Wastewaters can contain salts (often referred to as brine), hydrocarbons, metals, radioactive elements such as radium, and elements like arsenic and mercury.

U.S. Geological Survey (USGS) and collaborating researchers are studying the pathways of oil and gas wastewaters and the potential effects of accidental or intentional wastewater releases on the environment by providing an understanding of the persistence of the components of those wastewaters and their pathways in the environment.

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Previous USGS research in West Virginia demonstrated that co-produced wastewaters have the potential to reach streams in a variety of ways including accidental leaks or spills, which pose largely unknown risks to organisms in the environment. In a previous study in North Dakota, the presence of oil and gas-wastewater markers and in situ mortality of resident and caged fish were observed 6 months after an 11-million-liter wastewater spill was discovered in January 2015 in Blacktail Creek, North Dakota. During these studies, sodium, chloride, barium, strontium, lithium, and trace hydrocarbons, combined with strontium and radium isotopic ratios, were determined to be key markers of OG-wastewater releases.

The 2015 spill, directly adjacent to a creek, provided an opportunity to examine the processes controlling the response of a stream system to a large pulse-input of contaminants. Scientists built upon their previous studies in Blacktail Creek to further understand whether signatures of the oil and gas wastewater could be detected in water and sediment samples collected as many as 2.5 years after the spill. They used a combination of geochemical measurements and modeling, hydrologic analysis, and geophysical investigations to track contaminant persistence and movement to better assess future biological exposure and effects and to understand transport to downstream drinking water sources.

Data from the Blacktail Creek spill from February and June 2015 indicated that oil and gas wastewater comprised 0.1 to 0.3 percent of the stream-water compositions at downstream sites but could not be quantified during the more recent investigations in June 2016 and June 2017. In contrast, oil and gas-wastewater constituents from the spill were detected in streambed sediments and groundwater seeps into the stream for 2.5 years post spill and extended downstream at least 7.2 kilometers. Geophysical and hydrogeochemical investigations in June 2017 revealed subsurface groundwater pathways were contributing wastewater to the stream intermittently, indicating episodic exposure for organisms living in or near these channels. Radium was detected in shallow flood-plain sediments in June 2016, providing an additional potential animal and human exposure pathway outside the creek channel. These results indicate sediment movement and bank seepage of stored water provide potential conduits for exposure of organisms to OG-wastewater constituents. Potential health effects were indicated by fish bioassays during 2015, in which fish experienced mortality downstream from the spill.

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The scientists also developed a tool to extrapolate their results from the intensively studied Blacktail Creek to unmonitored watersheds with similar characteristics in the region with oil and gas development from the Bakken formation. They identified 41 watersheds across the North Dakota landscape that may be subject to similar episodic inputs from oil and gas-wastewater spills that could result in wildlife exposure.

This sustained and interdisciplinary research from USGS and collaborating scientists provides information to understand the short-term (1–3 years) persistence of oil and gas wastewater in streams arising from accidental spills and provides tools to extrapolate the results to identify current and future hazards for water resources with similar characteristics.

This project was funded by the USGS Ecosystems Mission Area through the Environmental Health Program (Contaminant Biology and Toxic Substances Hydrology), Energy Resources Program, and Fisheries Program.