HR: 1340h
AN: H23G-1706    [Abstracts]
TI: Solute transport in a physically and chemically heterogeneous aquifer model
AU: * Frippiat, C C
EM: cfrippia@mines.edu
AF: Environmental Science and Engineering, Colorado School of Mines, 1500 Illinois Street, Golden, CO 80401, United States
AU: * Frippiat, C C
EM: cfrippia@mines.edu
AF: Dept. of Civil and Environmental Engineering, Univ. catholique de Louvain, Place du Levant, 1, Louvain-la-Neuve, B-1348, Belgium
AU: Benson, D A
EM: dbenson@mines.edu
AF: Geology and Geological Engineering, Colorado School of Mines, 1516 Illinois Street, Golden, CO 80401, United States
AU: Illangasekare, T H
EM: tissa@mines.edu
AF: Environmental Science and Engineering, Colorado School of Mines, 1500 Illinois Street, Golden, CO 80401, United States
AB: Solute transport in heterogeneous soil has been intensely studied for the past 30 years. Theories have shown the dependence of effective transport parameters on heterogeneity, and mathematical models have been developed to explain anomalous concentration observations. Yet, little experimental data are available to validate these theories and models under conditions of high heterogeneity and chemical interaction between soil and solute, which are most likely to occur in the field. In an attempt to address this lack of data, we performed a tracer test in a physically and chemically heterogeneous aquifer model set up in an intermediate-scale laboratory test bed. The hydraulic conductivity (K) field follows a three-facies Markov Chain transition probability model. It is highly anisotropic and is characterized by high permeability contrasts between facies (up to 1/7000), resulting in an overall variance of ln(K) close to 16. Steady-state flow is established by imposing a constant flux over the upstream boundary and by fixing the head at the downstream boundary. A numerical flow model developed using MODFLOW 2000 was calibrated based on total discharge and pressure data recorded at 19 locations within the test aquifer. The model allowed the estimation of material permeabilities and highlighted the high-velocity preferential pathways and zones of low velocity. Rhodamine WT (RWT) was injected as a tracer in the upstream inflow reservoir. RWT is known to be composed of two isomers present in equal weight proportion, but having different sorption properties. Concentrations were monitored at 17 locations and at the outlet boundary. Recorded breakthrough curves (BTC"s) are highly skewed, with early arrivals and heavy late-time tails. Numerical transport models are set up using MT3DMS and RT3D. Qualitative comparison of experimental BTC's with the numerical results highlights that the early breakthroughs are caused by (1) rapid advection in preferential pathways; and (2) the presence of an inert isomer. The heavy tails are caused by (1) slow advection and diffusion through low-permeability zones; (2) the presence of a sorbing isomer; and (3) nonlinear sorption. These results and findings are presented and discussed.
DE: 1829 Groundwater hydrology
DE: 1831 Groundwater quality
DE: 1832 Groundwater transport
DE: 1847 Modeling
SC: Hydrology [H]
MN: 2007 Fall Meeting