HR: 1340h
AN: H33H-1719    [Abstracts]
TI: Evaluation of Negatively Correlated Porosity and Permeability on Chemical Migration Through Glacial Outwash Deposits
AU: Morin, R H
EM: rhmorin@usgs.gov
AF: U. S. Geological Survey, Denver Federal Center, Denver, CO 80225, United States
AU: * Wellman, T P
EM: twellman@usgs.gov
AF: U. S. Geological Survey, 3215 Marine Street, Boulder, CO 80303, United States
AB: Near surface geophysical logs and hydraulic measurements recorded at decimeter-scale increments along vertical well bores in the glacial outwash deposits of Cape Cod, Massachusetts reveal a negative relation between total porosity and saturated hydraulic conductivity. This finding is somewhat unexpected since many empirical relations predict a positive relation between these parameters for well-sorted sand and gravel deposits with less than one percent fines. To explain the observed negative correlation, we propose a physically-based paradigm that considers the heterogeneity of effective pathways controlling fluid movement. When pathways are conceptualized as idealized conduits with Poiseuille flow the hydraulic conductivity is proportional to the fourth power of their cross-sectional radius while porosity scales to the second power. This disparity in scaling implies that a region may exhibit both lower porosity and greater hydraulic conductivity than at other locations if some or all of its pathways have sufficiently larger effective radii as to offset the conductance loss due to less pore space. The significance of this finding on solute migration is examined using a suite of groundwater models constrained by measurements of hydraulic conductivity and porosity, and observed bedding geometries reported by the U.S. Geological Survey. It is our hypothesis that the negative correlation between hydraulic conductivity and porosity causes localized effects within individual cross beds that eventually diminish at larger length scales, thereby explaining observed tracer behavior. For each model, the relation between porosity and hydraulic conductivity is evaluated as being negatively correlated, positively correlated, and uncorrelated with constant and variable porosity. The range in predicted transport behavior is shown to reflect the variability that could result from assuming alternate parameter relations, as well as the implications of the observed negative correlation.
DE: 1829 Groundwater hydrology
DE: 1832 Groundwater transport
DE: 1835 Hydrogeophysics
DE: 1847 Modeling
DE: 1895 Instruments and techniques: monitoring
SC: Hydrology [H]
MN: 2007 Fall Meeting