Geochemical and Biological Measures of Oil and Gas Wastewater Releases to Surface Waters

Liquid wastes from oil and gas (OG) resource development pose potential risks to the quality of the Nation's water resources and the health of organisms, from microbes to humans. Wastewaters that contain chemical additives or naturally occurring salts, metals or radioactive elements may enter the environment from accidental or intentional releases. In North Dakota from 2008-2015, for ex., more than 8,000 spills were recorded, releasing 20-Mgal of waste fluids, and impacting 13% of the streams in the state. USGS is conducting interdisciplinary studies at laboratory to site to regional scales to enable a national scale understanding of the environmental effects of OG wastewater releases. We are 1) characterizing the composition of OG wastes; 2) studying the geochemical alterations of water and sediments at OG wastewater-impacted sites; 3) targeting potentially harmful compounds to aquatic and human health and constituents that serve as useful tracers of wastes; 4) employing geophysical techniques to trace wastewater pathways and 5) conducting in-situ investigations of biological responses to spill conditions. Our approach includes studies at field sites across the United States where releases have occurred and characterization of reactive and potentially toxic components of OG wastewaters. To track materials from releases, we use newly developed analytical methods for trace levels of hydrocarbons, and stable and radioactive isotopes, and conduct bioassays and microbial community characterization as proxies for ecological disturbance. I will present an overview of our recent site-based studies including a large wastewater spill in North Dakota and legacy wastewater disposal activity in Montana. Our investigations at these sites identified a suite of analytes that can be used as OG-wastewater signatures. Elevated concentrations of Na, Cl, Ba, Sr, Li, and trace hydrocarbons, combined with Sr and Ra isotopic ratios, were key markers. In one recent study in North Dakota, the presence of OG-wastewater markers, alterations in microbial communities and in situ mortality of resident and caged-fish were observed six months after a large wastewater spill. These analyses, combined with hydrologic and geophysical investigations, have allowed us to identify contaminant discharges and track their impact over time.