Geostatistical characterization of heterogeneity, simulation of advective transport, and evaluation of pump-and-treat systems in braided stream deposits

Difficulties in predicting plume migration rates and clean-up times during pump-and-treat remediations have been attributed, in part, to aquifer heterogeneities. To represent heterogeneity at the scale of a field site, three-dimensional braided stream deposits were generated using output from a geometrical simulation model (Webb, 1992) and reconstructed from field descriptions of facies at a field site (Aiken, 1993). The spatial distribution of hydraulic conductivity was specified in terms of different facies in order to represent the discrete internal geological structures that produce preferential flowpaths.; An investigation was conducted to examine whether multiple indicator geostatistics could reproduce the heterogeneity and facies continuity observed in braided stream deposits. The structure of the geologic deposits was analyzed using indicator variograms and these variogram parameters were used to generate stochastic representations. Comparison of breakthrough curves from transport simulations illustrated that under certain conditions the stochastic representations simulated the range of flow conditions and preferential flow pathways observed in the geologic deposits.; Groundwater flow and transport simulations examined the relative importance of different parameters and conditions as they relate to early arrival and tailing of contaminants. Increased connectedness of facies and increased contrast in hydraulic conductivity between facies (more heterogeneous) resulted in better development of preferential flow pathways, increased tailing, and longer clean-up times. In particular, the frequency and connectedness of the high conductivity facies were important in development of preferential flow pathways. Site characterization efforts should focus on identification and delineation of high conductivity units, even when they compose a small percentage of the entire aquifer.; Simulations also examined the efficiency of five different pumping well configurations under a variety of hydrogeologic conditions and parameters. Which well configuration performed best often varied over time, facies realization, degree of heterogeneity, contaminant plume distribution, and orientation of the regional hydraulic gradient. Though results suggest that optimal well arrangements are site-specific, under certain conditions a particular well design did perform better. Because reduction of pump-and-treat operation times can result in significant cost savings, further investigation into improved well design is warranted.