HR: 14:25h
AN: H52B-04    [PDF]
TI: Field Evidence for Abundant Fracture Connectivity in Sedimentary Rocks
AU: * Parker, B L
EM: blparker@uwaterloo.ca
AF: Department of Earth Sciences University of Waterloo, 200 University Avenue West, Waterloo, ON N2L 3G1 Canada
AB: The behavior of contaminants in fractured rock is strongly dependent on the degree of fracture connection in the fracture network. Although many fracture connectivity studies have been done by cross-hole testing, little is known about fracture connectivity at the scale of contaminant plumes. Field evidence for abundant fracture connectivity obtained from chemical analysis of rock core samples is presented from sites contaminated with chlorinated solvents, such as trichloroethene (TCE), in sedimentary rocks. These analyses determine the contaminant mass in the low-permeability rock matrix. This mass occurs in the matrix due to diffusion-driven mass transfer from the fractures, where all or nearly all the advective transport occurs. The contaminant mass in the rock matrix blocks between fractures represents an imprint of the contaminant migration pattern formed over many years of plume evolution. Vertical core holes were drilled through zones of chlorinated solvent contamination in the depth range of 10 to 300 m bgs at several sites. The chemical analyses were done at close spacing along each core to provide detailed information about concentration versus depth. Also, hydraulic head and other types of borehole information were determined in some of the core holes. The concentration profiles show that the plumes have contaminant mass originating from contaminant transport in numerous fractures rather than just a few fractures with apparent, large, local aperture indicated by borehole hydraulic and geophysical tests. The abundant contaminant migration pathways perceived from the rock core analyses are consistent with simulations of plume behavior using a 2-D model (Fractran) with statistically generated fracture networks of othrogonal fractures with variable apertures and lengths and strong connectivity. Without the constraints on the simulations imposed by the rock core chemical data, the perceptions of the nature of contaminant plumes would be much different.
DE: 1800 HYDROLOGY
DE: 1803 Anthropogenic effects
DE: 1829 Groundwater hydrology
DE: 1831 Groundwater quality
DE: 1832 Groundwater transport
SC: Hydrology [H]
MN: 2003 Fall Meeting