HR: 1340h
AN: H33F-0543    [Abstracts]
TI: 18 Years Later: Revisiting a Groundwater Model of the Cambric Site at NTS
AU: * Considine, E J
EM: ejconsid@unr.edu
AF: Graduate Program of Hydrologic Sciences University of Nevada, MS 175 , Reno, NV 89557 United States
AU: Wheatcraft, S W
EM: wheatcraft@unr.edu
AF: Department of Geological Sciences University of Nevada, MS 172 , Reno, NV 89557 United States
AU: Meerschaert, M M
EM: mcubed@unr.edu
AF: Department of Physics University of Nevada, MS 220, Reno, NV 89557 United States
AB: Since its advent in 1974, the Radionuclide Migration Project at the Nevada Test Site has spawned several interesting groundwater modeling ventures. Of interest to this research is the Cambric detonation site, where a tracer test was conducted from 1975 to 1991. Burbey and Wheatcraft (1986) built a groundwater/transport model of the Cambric site and at the time of calibration had achieved a good match to the measured data. Since then the predicted concentrations have diverged from the measured concentrations, which exhibit classic heavy-tailed behavior. It has been hypothesized that the Fractional Advection Dispersion Equation (FADE) will better predict these late-time high concentrations; this research will apply the FADE to the Cambric problem and aims to reach a more complete understanding of the physical significance of the coefficients contained in the FADE. We first built a preliminary groundwater model, employing the traditional Advection Dispersion Equation, in the hopes of duplicating Burbey's predicted concentrations. Burbey used the Deep Well Disposal Model, whereas this investigation used MODFLOW and MT3D. While the new model has produced a breakthrough curve fitting the peak concentration, it too fails to produce the heavy tail seen in the measured data. Also of concern is the nonuniqueness of the new model's solution; the best-fit breakthrough curve can be produced by changing either one of at least two parameters. We believe that both of these shortcomings (under predicted late-time concentrations and non-uniqueness) may be resolved by using the FADE. Not only does fractional theory permit heavy tails, but also it effectively replaces aquifer heterogeneity with fractional derivatives, thereby reducing the probability of a nonunique solution. Future work includes modeling the Cambric problem with Tadjeran and Meerschaert's numerical, fractional, radial-flow transport code (2003) and evaluating the code's applicability to varied flow and transport conditions.
DE: 1832 Groundwater transport
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting