ESTIMATION OF DUAL-DOMAIN TRANSPORT PARAMETERS USING ELECTROMAGNETIC BOREHOLE FLOWMETER FIELD DATA

The dual-domain model (DDM) of solute transport has recently attracted considerable attention for field-scale applications involving heterogeneous unconsolidated sediments. This is due largely to successful application to the MADE-2 and NATS sites at Columbus Air Force Base, MS. In these cases, optimal DDM transport parameters were defined through calibration to tracer plume data (i.e. inverse modeling). Ideally, hydraulic conductivity (K) data would be used to define the mobile volume fraction and mass transfer coefficient, so that blind predictions of field-scale plume migration could be made. Achieving this result is a challenge, because the physical meaning of DDM parameters has not been rigorously established for unconsolidated sediment. In this communication we investigate the physical meaning of DDM parameters in a heterogeneous granular aquifer, and the degree to which appropriate values can be objectively estimated from field data. In particular, hydraulic conductivity characterization data obtained through electromagnetic borehole flowmeter testing at the U.S. Department of Energy Savannah River Site (SRS) are used to estimate site-specific mobile volume fraction and mass transfer coefficient. These estimates are then compared to optimal values determined through model calibration to plume monitoring data at the SRS. The site-specific study suggests that, while DDM parameters are scale-dependent in general, the mobile fraction might reasonably be estimated initially from borehole flowmeter data and/or known statistical properties of K for a sedimentary aquifer. However, it appears that only order of magnitude estimates can be made for mass transfer coefficient.