Experimental and computational investigations of subsurface heterogeneity and contaminant distributions in complex geologic media

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The subsurface is heterogeneous at multiple scales and this is the rule rather than the exception. Information about spatial variability of flow and transport parameters is most commonly obtained through geostatistical analysis of small-scale measurements. Despite its common use, it is unclear whether the geostatistical approach can preserve geological features, their connectivity and morphology which can have large impacts on fluid flow and more importantly, contaminant transport. We have recently made significant strides in mapping hydraulic conductivity (K) and specific storage (Ss) heterogeneity using hydraulic tomography. Hydraulic tomography involves the sequential pumping of water from packed-off intervals and the corresponding monitoring of head change information in straddle-packer systems in nearby boreholes. Pumping and collection of head change data in a tomographic manner allows one to obtain information on the propagation of pressure changes through the aquifer from various directions. This information is then used in a stochastic inverse model that computes K and Ss tomograms. Hydraulic tomography experiments performed in the laboratory by our group show that it can image the distributions of K and Ss as well as their connectivity considerably better than kriging. The approach has been recently extended to include partitioning tracer transport information to image the locations of Dense Nonaqueous Phase Liquid (DNAPL) saturations in 3-D. Preliminary results show that DNAPL saturations and their pools can be imaged accurately. Accurate imaging of DNAPL saturations in source zones will considerably improve our abilities to remediate thousands of sites in Canada and beyond. The proposed research focuses on conducting complementary experimental and computational investigations that should significantly advance our capabilities to map subsurface heterogeneity and contaminant source zones in complex geologic media. Development of these capabilities will also allow us to significantly advance our fundamental understanding of flow and transport processes in such media.