2014 GSA Annual Meeting in Vancouver, British Columbia (19–22 October 2014)

Paper No. 295-7
Presentation Time: 10:30 AM

SPATIAL ANALYSIS OF POTENTIAL BRINE CONTAMINATION TO AQUATIC RESOURCES IN THE GLACIAL DEPOSITS OF THE WILLISTON BASIN


PRESTON, Todd, Northern Rocky Mountain Science Center, U.S. Geological Survey, 2327 University Way, Suite 2, Bozeman, MT 59715, CHESLEY-PRESTON, Tara, Institute of the Environment, Montana State University, 2327 University Way, Suite 2, Bozeman, MT 59715, POST VAN DER BURG, Max, U.S. Geological Survey, Northern Prairie Wildlife Research Center, 8711 37th Street SE, Jamestown, ND 58401-7317, SMITH, Bruce D., U.S. Geological Survey, Crustal Geophysics and Geochemistry Science Center, Denver Federal Center, Bld 20, ms964, Lakewood, CO 80225 and TANGEN, Brian, U.S. Geological Survey, Northern Prairie Wildlife Research Center, Jamestown, ND 58401

Co-produced water (brine) from oil production in the Williston Basin is among the most saline in the nation. Much of the Williston Basin is mantled by glacial deposits and brine contamination to aquatic resources has been documented within these deposits. The Montana Bureau of Mines and Geology developed a Contamination Index (CI) to delineate the presence and magnitude of brine contamination to aquatic resources within Sheridan County, Montana, which lies in the glacial deposits of the Williston Basin.

Recently, the U.S. Geological Survey conducted a GIS-based vulnerability assessment of brine contamination to aquatic resources in Sheridan County, Montana. This assessment produced a score for each Public Land Survey System section based on two oilfield (age and density of oil wells) and three hydrogeological (percent of wetland and glacial outwash cover and stream reach) variables located in that section. The model, evaluated with surface and groundwater samples from 10 of the 780 modeled sections, showed these variables were successful in identifying sections with potential contamination.

The vulnerability assessment was modified and expanded to 54,979 sections mantled by glacial deposits in the Williston Basin. The model was validated by comparing CI values from the 37 surface and groundwater samples from the original assessment to the section scores for both the Williston Basin and Sheridan County assessments. Results were also compared to CI values from 123 surface water samples from 97 sections for a regional characterization of Williston Basin water quality. The Williston Basin assessment (R2 = 0.65) outperformed the Sheridan County assessment (R2 = 0.62) and performed better when compared to contaminated samples (R2 = 0.68) versus all samples (R2 = 0.48) from the regional characterization. Our results show improved success in identifying sections with potential contamination, but that not all aquatic resources in those sections are contaminated. The two sets of water samples only contain 20 groundwater samples and cover 104 sections, or less than 0.2% of the modeled area. Thus, additional water samples are necessary for further validation. These results can guide future sampling by identifying areas for 1) geophysical surveys to locate groundwater samples and 2) additional surface water samples.

Session No. 295

Environmental and Engineering Geology (Posters)
Wednesday, 22 October 2014: 9:00 AM-6:30 PM
Exhibition Hall C (Vancouver Convention Centre-West)
Geological Society of America Abstracts with Programs. Vol. 46, No. 6, p.715
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