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SIR 07-5068: Application of a Ground-Water Transport Model

Simulations of Ground-Water Flow, Transport, Age, and Particle Tracking near York, Nebraska, for a Study of Transport of Anthropogenic and Natural Contaminants (TANC) to Public-Supply Wells

By Brian R. Clark, Matthew K. Landon, Leon J. Kauffman, and George Z. Hornberger


Contamination of public-supply wells has resulted in public-health threats and negative economic effects for communities that must treat contaminated water or find alternative water supplies. To investigate factors controlling vulnerability of public-supply wells (PSW) to anthropogenic and natural contaminants using consistent and systematic data collected in a variety of principal aquifer settings in the United States, a study of Transport of Anthropogenic and Natural Contaminants (TANC) to PSW was begun in 2001 as part of the U.S. Geological Survey (USGS) National Water-Quality Assessment (NAWQA) Program. Results presented in this report are from a TANC study area near York, Nebraska (fig. 1), within the High Plains Ground Water (HPGW) study unit of the NAWQA program.
Ground-water flow is simulated for a 60-year period from September 1, 1944, to August 31, 2004. Steady-state conditions are simulated prior to September 1, 1944, and represent conditions before use of ground water for irrigation. Irrigation, municipal, and industrial wells were simulated using the Multi-Node Well package of the modular three-dimensional ground-water flow model, MODFLOW-2000, which allows simulation of flow and solutes through wells that are simulated in multiple nodes or layers. Ground-water flow, age, and transport of selected tracers were simulated using the Ground-Water Transport (GWT) process for MODFLOW-2000.
     In addition to transport simulations under transient conditions with multi-node pumping wells (hereafter referred to as the calibrated model), three alternative models were constructed to examine the effects of alternative conceptualizations of the physical system on simulation results. The first of the three models was identical to the calibrated model except that all registered abandoned wells and test holes were excluded from the simulation to test the sensitivity of the simulations to multilayer leakage in these inactive well bores. The second of these models used the conventional Well Package of MODFLOW-2000, which does not simulate flow between model layers through well bores, in place of the Multi-Node Well Package. The third model was identical to the calibrated model except that it was constructed as a steady-state simulation representing 1997-2001 conditions to examine the differences and importance of simulating transient conditions. The alternative model simulations indicate that simulation results are highly sensitive to the distribution of multilayer well bores where leakage can occur. The calibrated model resulted in smaller differences than the alternative models between simulated and interpreted ages and tracer concentrations in most, but not all wells.
     The results of the calibrated model and the first and third alternative models are shown in animations on the compact disk. All animations represent chlorofluorocarbon-11 (CFC-11) concentrations in picomoles per kilogram in model layer 11, or the middle portion of the upper confined aquifer. The calibrated and first alternative model animations cover the model simulation period of 60 years from September 1, 1944, to August 31, 2004. The third alternative model represents a steady-state time period from 1997 to 2001.

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NAWQA Transport of Anthropogenic and Natural Contaminants to Supply Wells

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Last modified: Thursday, 01-Dec-2016 20:01:49 EST