Analysis of Nitrate-Nitrogen Movement Near High-Capacity Irrigation Wells |
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| Authors: | Xunhong Chen Jerry F. Ayers David C. Gosselin |
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| Affiliation: | Xunhong Chen is a research hydrogeologist and an associate professor with the Conservation and Survey Division, Institute of Agriculture and Natural Resources, University of Nebraska-Lincoln (113 Nebraska Hall, Lincoln, NE 68588-0517). He received a B.S. in geology from Zhejiang University, China, an M.S. in geology from the California State University-Northridge, and a Ph.D. in hydro geology from the University of Wyoming. Before joining the University of Nebraska-Lincoln, he worked with an environmental consulting company. His current research projects relate to characterization of aquifer and aquitard hydraulic properties, numerical modeling of ground water flow, vapor flow, and chemical transport, and analysis of stream-aquifer interactions.;Jerry F. Ayers is a research hydrogeologist with the Conservative and Survey Division, Institute of Agriculture and Natural Resources, University of Nebraska-Lincoln (113 Nebraska Hall, Lincoln, NE 68588-0517). He earned a B.A. in geology from the California State University at Sacramento and an M.S. and PhD. from Washington State University, Pullman, Washington. His current research interests include the application of geophysics to hydrogeological and geotechnical investigations, characterizing contaminant pathways, hydrogeology of the western Sandhills region of Nebraska, and hydrogeology of saline wetlands.;David C. Gosselin is a research hydrogeologist and geochemist with the Conservation and Survey Division, Institute of Agriculture and Natural Resources, University of Nebraska-Lincoln (113 Nebraska Hall, Lincoln, NE 68588-0517). He received his B.A. in geology from the University of St. Thomas, St. Paul, Minnesota, and his Ph.D. in geology from the South Dakota School of Mines and Technology, Rapid City, South Dakota. Current research activities include hydrology and geochemistry of lakes and wetlands, applications of remote sensing to lake hydrology, and nonpoint source contamination. |
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| Abstract: | AGalerkin finite-element model coupled with a particle tracking routine was developed to analyze the flow and transport dynamics near a high-capacity irrigation well. The model was used to compute the head distribution around the pumping well, to determine the area of influence, and to define ground water flowlines during short-term pumping periods typical of those used to collect water quality samples from high-capacity wells. In addition to hypothetical example results, the model was used to qualitatively analyze data obtained from pump-and-sample experiments conducted in an unconfined alluvial aquifer within the Platte River valley of south-central Nebraska where nitrate-nitrogen (NO3-N) contamination is prevalent.
Simulation results of both the hypothetical and field cases suggest that short-term pumping events, impact a limited volume of aquifer. The area of influence and flowlines are affected by aquifer anisotropy, pumping rate, and well construction characteristics). Ground water above or below the screened intervals does not enter a partially penetrating well in anisotropic aquifers. In aquifers where NO3-N concentration varies vertically and horizontally, waler quality samples from an irrigation, or other high-capacity, well provide only limited information about ground water contamination. A numerical model is thus recommended for calculating the area of influence and determining flowlines around high-capacity wells so that information derived from water quality samples collected at the wellhead can be better interpreted. |
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