SINGLE AND DUAL-DOMAIN MODELS TO ASSESS THE EFFECTS OF HETEROGENEITY ON THE SOLUTE TRANSPORT IN ALLUVIAL AQUIFERS

Groundwater contamination is a fundamental environmental concern, since aquifers are a major source of drinking water in many regions of the world. The effects of different sources of pollutants on water quality can be investigated through the modeling of water flow and solute transport in the aquifers. An important issue to be addressed in the development of such models is the heterogeneity of the aquifers, which can occur at different spatial scales. The fine scale heterogeneity significantly affects the transport of contaminants at the scales of interest for practical applications. The primary objective of this thesis is to implement some models to effectively describe non-reactive solute transport in heterogeneous alluvial aquifers, by considering the porous medium as either an equivalent homogeneous volume (single-domain model) or a superposition of two domains (dual-domain models). Specifically, the dual-porosity model assumes that water flows in only one of the two domains, which can exchange solute by diffusion. The dual-permeability models assume that water flows in both domains, which have different hydrodispersive parameters and can be coupled, i.e., they can exchange solute, or uncoupled. These models are applied for the interpretation of some numerical tracer tests performed in portions of aquifers with different degrees of heterogeneity and at different scales: from a laboratory test on a decimeter-scale sand column, to numerical transport experiments on meter- and decameter-scale blocks of sediments, to an hectometer-scale field tracer test performed at the Cape Cod site. The effective model parameters are linked to the heterogeneity pattern of the different tests and the ability of the different models to describe the effects of structured heterogeneity on the solute transport is compared. The uncoupled dual-permeability model is shown to be the best one for alluvial aquifers characterized by the presence of preferential flow paths, which are connected bands of high-permeability sediments.