Brine Contamination to Plains and Potholes Environments from Energy Development in the Williston Basin
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The Williston Basin, in north-central United States and south-central Canada, has been a leading source of domestic oil and gas production for more than 50 years. This region, which includes parts of Montana, North Dakota, South Dakota, Saskatchewan, and Manitoba, is currently in the midst of a modern energy boom driven by advances in oil and gas production technologies. The main energy-producing formations associated with the current boom are the Bakken and Three Forks.
A portion of the Williston Basin is overlain by the Prairie Pothole Region (PPR), which is known for its depressional wetlands that provide critical breeding and nesting habitats for a majority of North America’s migratory waterfowl as well as habitat for other wildlife. Most of the United States portion of the Williston Basin also is overlain by the Missouri River Watershed.
The U.S. Geological Survey (USGS) has placed a focused effort on providing a comprehensive understanding of the Nation’s energy and mineral resources and the possible environmental effects of their extraction. To address these topics in the Williston Basin, the USGS-led Science Team about Energy and Plains and Pothole Environments (STEPPE), has come together to:
The results of this research have been used to identify potential effects on the landscape and future environmental vulnerability associated with oil and gas production in the Williston Basin.
Brine contamination in shallow groundwater and surface water.
Geophysical and geochemical methods were used to determine the extent and magnitude of brine contamination in the shallow groundwater and surface water in the Williston Basin. The techniques were initially used on the Fort Peck Indian Reservation in Montana and in the western part of the Williston Basin, to indicate where brine water, originating from storage-tank facilities, oil wells, brine-injection wells, pipelines, and pits used during oil production in the area contributed to groundwater and surface water contamination. The shallow groundwater is the only available source of potable groundwater for about 3,000 residents in and near the East Poplar oil field. The same techniques were applied to determine that plumes of brine-contaminated groundwater from abandoned oil wells are affecting wetlands in the Prairie Pothole Region.
Water needs and availability for energy resource production.
The development of the Williston structural basin provides a critical opportunity to study the water-energy nexus within a groundwater availability context. Large volumes of water are currently needed for hydraulic fracturing in this basin. The regional glacial, lower Tertiary, and Upper Cretaceous aquifer systems contain the shallowest, most accessible, and in some cases, the only potable aquifers within the Williston Basin. This study area is part of the USGS Groundwater Resources Program to assess and quantify the availability of the Nation’s groundwater resources.
In 2013, water samples were collected from 30 randomly located domestic wells in the Upper Fort Union Formation of Montana and North Dakota to assess groundwater quality in the context of oil and gas development. Samples were analyzed for a broad suite of inorganic and organic chemical constituents as well as groundwater-age, gas, and isotopic tracers. Results from this study will provide detailed understanding of current groundwater-quality conditions in the Upper Fort Union Formation and provide a basis for comparison with future water-quality studies.
Assessing the ecological effects of oil and gas production.
Contamination associated with oil and gas production has been identified in the Williston Basin, but there is very little information regarding the actual ecological effects of contamination or oilfield operations. To address this information gap, various studies are being conducted to investigate potential effects of habitat fragmentation, the spread of invasive plant species, and the effects of elevated chloride concentrations on aquatic plants and invertebrates.
Predicting areas with high potential for produced-water contamination to aquatic resources.
Vulnerability of aquatic resources is based on oil field (age and density of oil wells) and hydrogeological (surficial geology, wetland area, and length of streams) characteristics. Scientists evaluated the performance of the vulnerability assessment at ten study sites in eastern Sheridan County, Montana using a Contamination Index (CI), which determines the presence and magnitude of brine contamination in a water sample. Nineteen of the forty water samples collected had CI values indicating contamination. Additionally, CI values generally increased with increasing vulnerability assessment score, with a stronger correlation for groundwater samples than surface water samples.