HR: 1340h
AN: H13G-1676    [Abstracts]
TI: Electron Donor Potential of Eastern North Dakota Shale Formations
AU: * Salinas Klapperich, R J
EM: ryan.klapperich@und.edu
AF: University of North Dakota, Department of Geology and Geological Engineering 81 Cornell Stop 8358, Grand Forks, ND 58267, United States
AU: Korom, S F
EM: scottkorom@mail.und.nodak.edu
AF: University of North Dakota, Department of Geology and Geological Engineering 81 Cornell Stop 8358, Grand Forks, ND 58267, United States
AB: We have a network of 16 in situ mesocosms (ISMs) used to study aquifer denitrification at 9 sites in North Dakota and Minnesota. The site in the Elk Valley aquifer in northeastern North Dakota has the highest denitrification rates and the greatest concentration of electron donors (organic carbon ~0.4%, pyrite as S ~0.4%, and ferrous iron ~0.3%) in the sediments. In contrast, denitrification rates at our other ISM sites are lower (or even below detection), as are the electron donor concentrations in the sediments. Knowing that the sediments at all of our ISM sites were placed as outwash during the last Wisconsinan glaciation (~12ka), we wonder what caused the variation in electron donor supplies in our aquifers. It has been suggested that variations is the electron donor concentrations in the various Late Cretaceous shale strata exposed during glaciation may help explain the variation in electron donor concentrations in overlying aquifers formed nearby. The purpose of this study is to evaluate the amount of electron donors available in these bedrock units. Bedrock samples (n = 39) from 20 sites in eastern North Dakota were obtained by drilling during the summer of 2006 in conjunction with the North Dakota State Water Commission. Samples were frozen before analysis for bulk mineralogical content by X-ray diffraction, organic carbon, pyrite as inorganic S, and ferrous iron contents. It was hypothesized that the Pierre Shale would have the highest donor concentration, but it appears that other formations, such as the Carlile and Greenhorn contain higher concentrations of electron donors. Organic carbon concentrations in the Pierre (< 0.01% to 1.0%) are relatively low while concentrations in the Carlile (3.5% – 6.5%) and Greenhorn (~8.5%) are significantly higher. Pyrite as inorganic S concentrations in the Pierre (< 0.01% to 0.2%), Carlile (0.3% – 0.5%), and Greenhorn (~0.5%) are similarly distributed. In the future, it may be possible to create a qualitative index (low, med, high) of aquifer denitrification capacity based on the probable source of the parent material. This index could then be used to focus, in a cost-effective fashion, more extensive and expensive geochemical analysis on specific aquifers or sites.
DE: 1830 Groundwater/surface water interaction
DE: 1858 Rocks: chemical properties
DE: 1862 Sediment transport (4558)
SC: Hydrology [H]
MN: 2007 Fall Meeting