Numerical Modeling of Contaminant Tailing in Physically and Chemically Heterogeneous Formations
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The groundwater contamination is a serious worldwide problem and billions of dollars are spent annually in cleaning the contaminated sites. The cleanup technologies used to recover contaminants from subsurface were often not successful in removing the entire contaminant mass. The contaminant tailing, or presence of a small fraction of contaminants for long time periods, is a relevant practical problem and the topic of this dissertation. The presence of tailing is attributed to several factors including the heterogeneity of the subsurface formations. The main objective of this research is to increase general understanding of impacts of heterogeneity on tailing. This dissertation investigates the impacts of subsurface heterogeneities on reactive solute transport, with emphasis on tailing, on two scales: single heterogeneity scale and porous formation scale. The impact of a single heterogeneity (i.e. a geological lens) on tailing is quantified first. The single heterogeneity is shaped as a 3D ellipsoid located in a homogeneous background of different properties. The impact of shape and material properties of the heterogeneity, as well as plume history, is quantified by running a large number of numerical simulations in a systematic fashion. The transport results increase the general understanding about the role of advection, diffusion, and sorption on tailing. The formation scale investigations are based on novel geostatistical descriptions of materials found at a sand quarry located approximately 2km north-west of the classic Stanford-Waterloo site at the Canadian Force Base Borden, Ontario, Canada, and on few theoretical investigations of effective (average) formation properties. Two large-scale 3D heterogeneity models were developed and used to identify the impacts of different conceptual models on tailing and to investigate the sensitivity of tailing on geometric and material properties of geologic materials.