HR: 1340h
AN: H23D-1622    [Abstracts]
TI: Effects of concentration fluctuations and gradients on reactive mixing
AU: * Luo, J
EM: jianluo@ce.gatech.edu
AF: Georgia Institute of Technology, School of Civil & Environmental Engineering, Atlanta, GA 30339, United States
AU: Dentz, M
EM: marco.dentz@upc.es
AF: Technical University of Catalonia (UPC), Department of Geotechnical Engineering & Geosciences, Barcelona, 08034, Spain
AU: Carrera, J
EM: jcarrera@ija.csic.es
AF: Technical University of Catalonia (UPC), Department of Geotechnical Engineering & Geosciences, Barcelona, 08034, Spain
AU: Kitanidis, P
EM: peterk@stanford.edu
AF: Stanford University, Department of Civil & Environmental Engineering, Stanford, CA 94305, United States
AB: Sound understanding of mixing-controlled reactions in heterogeneous media is needed for the realistic modeling of contaminant transport in aquifers in the evaluation of natural attenuation processes, the design of nuclear waste disposal, and the engineered remediation of contaminated sites. Macroscopic formulations of reactive transport may not adequately describe mixing-controlled reactions because reaction rates are related to fine- grained concentration distributions. We use bimolecular dissolution-precipitation equilibrium reactions to demonstrate the segregation effects of reactants on the evaluation of effective reaction rates. The reaction rate predicted by macroscopic models is controlled by two competing effects: the large heterogeneity induced macrodispersion coefficient leads to an increase of reaction rate, while a more smoothed concentration gradient may lead to a decrease of the reaction rate. Under certain conditions, macroscopic models can give a good approximation at large times and away from the plume center of mass, due to the balanced variance budget, but should generally be viewed with skepticism. For example, they significantly underestimate reaction rate near the plume center due to the smoothed concentration gradient field.
DE: 1831 Groundwater quality
DE: 1832 Groundwater transport
DE: 1869 Stochastic hydrology
SC: Hydrology [H]
MN: 2007 Fall Meeting