HR: 14:25h
AN: H13G-04    [Abstracts]
TI: Analysis of spatial moments from a nonreactive tracer using electrical resistivity tomography
AU: * Singha, K
EM: ksingha@pangea.stanford.edu
AF: Stanford University, Building 320, Geology Corner, Stanford, CA 94305-2115 United States
AU: Gorelick, S M
EM: gorelick@pangea.stanford.edu
AF: Stanford University, Building 320, Geology Corner, Stanford, CA 94305-2115 United States
AB: The use of geophysical data for hydrogeologic characterization has traditionally been qualitative. In this study, we use modified moment analysis of the 3D electrical resistivity tomograms through time to estimate the mass, center of mass, and spatial variance of a 2.2 g/L sodium-chloride tracer injected over 9 hours into saturated sands and gravels at the Massachusetts Military Reservation in Cape Cod, Massachusetts. Sixty ERT data sets were collected over 20 days, and each data set was inverted to produce a 3D map that images the plume. The inverted tomograms provide valuable insights into field-scale tracer migration behavior, but standard tomographic inversion and application of Archie's Law to convert bulk electrical conductivities to solute concentration results in underestimation of tracer mass and greater temporal spreading than observed in field data of concentration breakthrough at the pumping well. The ERT inversions also display greater apparent dispersion than tracer plumes estimated by 3D advective-dispersive simulation. This behavior is attributed to 1) reduced measurement sensitivity to electrical resistivity values with distance from the electrodes and, 2) differential smoothing from tomographic inversion. Despite these issues, the center of mass calculated from the ERT inversions coincides with that estimated by migration of the simulated tracer plume.
DE: 5109 Magnetic and electrical properties
DE: 1829 Groundwater hydrology
DE: 1832 Groundwater transport
DE: 1894 Instruments and techniques
DE: 0925 Magnetic and electrical methods
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting