Investigating the effects of micropores on subsurface contaminant transport with microscopic and macroscopic approaches

The field of contaminant transport and remediation has advanced greatly in recent years. However, practice has shown that remediation efforts are often plagued by extremely long breakthrough curve tails, an indication of almost infinite time requirements for the remediation efforts to bring the level of contaminants below the regulatory standards. One hypothesis is that these long tails are the manifestation of very slow diffusive processes in soil micropore zones (Wood, 1996). The research subject of this dissertation is to develop a method to forecast the effects of micropores on contaminant transport at both macroscopic and microscopic levels and to establish a link between macroscopic and microscopic approaches for validation and calibration purposes.; Following a macroscopic approach, transport in the micropore zone and its interplay with the mobile and immobile zones is simulated semi-analytically using the Laplace transform technique. Applying Laplace transforms a set of three coupled partial differential equations (one for each zone) is transformed to a set of coupled ordinary differential equations that are solved analytically. The solutions obtained are transformed back to real space with the help of the Stehfest inversion algorithm and under different flow patterns and boundary conditions.; The microscopic approach is based on two separate steps, namely flow generation and the Random Walk Particle Transport (RWPT) method. To generate different flow schemes, a numerical code is used to solve the Navier-Stokes equations at the pore scale. This approach does not rely on averaging the flow processes but instead solves explicitly at the pore scale for the velocity and vorticity field. Using the results obtained from the solution of the Navier-Stokes equations, contaminant transport simulations using the RWPT method are conducted.; A link between the macroscopic and microscopic models of contaminant transport is established through comparisons and testing of the two models. The link helps forecast the effects of micropore zone transport processes in the subsurface and thus develop a tool that could contribute towards more efficient remediation designs.