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Simulation of Watershed-Scale Nitrate Transport in Fractured Till Using Upscaled Parameters Obtained from Till Core
YEAR: 2017
INVESTIGATORS: Nathan Young, William Simpkins, Robert Horton

Nitrate contamination from agriculture is a major water-quality problem in Iowa and a contributor to hypoxia in the Gulf of Mexico. In Iowa’s till-dominated watersheds, previous studies on nitrate transport in groundwater have relied on black box or unfractured porous media models, despite studies showing fracture control of nitrate transport. To investigate the role of fracture flow on watershed-scale nitrate transport, I will utilize a 3-D, fully-coupled, distributed-parameter, fracture-flow hydrologic model with a sophisticated, equivalent porous media (EPM) approach. Fracture flow parameters will be derived from X-ray computed tomography (CT) and laboratory column experiments conducted on 6.4- to 15-cm-diameter till core sampled from both drill core and 6-m-deep trenches associated with the recent installation of the Dakota Access Pipeline in central Iowa. Industry-developed fracture analysis programs and discrete fracture network (DFN) models will be used to compute the properties of the EPM. Results will be compared to existing nitrate-transport models for a watershed in central Iowa.