USGS Groundwater Information: Branch of Geophysics
by Kamini Singha, F. D. Day-Lewis, and J. W. Lane, Jr.
Non-Fickian solute-transport behavior has been observed at research and aquifer remediation sites in diverse geologic settings. Anomalous behavior such as concentration rebound, long breakthrough tailing, and poor pump-and-treat efficiency have been explained by rate-limited mass transfer, where the pore space is treated as a bicontinuum comprising (1) the mobile domain, which consists of well connected pores and fractures, and (2) the immobile domain, which consists of poorly connected pores and dead-end fractures. Despite recognition of the importance of non-Fickian transport, verification of its occurrence and inference of controlling parameters remain problematic. Conventional geochemical measurements preferentially sample from the mobile domain and thus provide only indirect information for the immobile domain and exchange between domains. Here, we present a petrophysical framework, experimental methodology, and analytical expressions that can be used to infer mass-transfer parameters from co-located breakthrough curves of mobile concentration and bulk conductivity from geoelectrical measurements. We present (1) field-experimental geoelectrical data from an aquifer-storage recovery site showing evidence of mass transfer, and (2) results of numerical column experiments demonstrating an approach to estimate heterogeneous mass-transfer rate coefficients and mobile-immobile porosity ratios based on the temporal moments of bulk electrical conductivity measurements and mobile-domain concentration. Our results indicate that geoelectrical measurements can provide valuable, practical insights into heterogeneous mass-transfer parameters.
Final copy as submitted to American Society of Civil Engineers for publication as: Singha, Kamini, Day-Lewis, F.D., and Lane, J.W., Jr., 2008, Monitoring and quantifying rate-limited mass transfer using geoelectrical measurements [abs.], in World Environmental and Water Resources Congress, May 13-16, 2008, Honolulu, Hawaii, Proceedings: Reston, Virginia, Environmental and Water Resources Institute of American Society of Civil Engineers.