Accurate modeling of contaminant transport and sorption processes in the soil and landfill liners is a prerequisite for realistic model simulations of contaminant fate and transport in the environment. These studies are also important for the remediation of soil and groundwater contamination. Modeling of contaminant transport through soils and landfill liners consists of either solving the direct/forward problem or the inverse problem. In this thesis, an automated time-stepping implicit procedure is developed from the convergence and error studies of explicit and implicit finite-difference solutions for the advection-dispersion transport of contaminants through soil with different sorption mechanisms. This study is further extended for transient through-diffusion (TTD) transport of contaminant in landfills by considering linear sorption mechanism. To validate the numerical solution and also to study the behavior of finite-difference numerical solutions for TTD transport problem, closed-form analytical solution is derived. Further, a new interface condition is proposed based on the finite-volume procedure for stratified soil or landfill liner system. Solvers are developed for the parameter estimation of inverse problem by integrating the developed procedures for the above forward problem with different optimization procedures. Solvers based on Simulated Annealing (SA) and Genetic Algorithm (GA) are developed for TTD transport in the landfill liners and verified with the existing methods of parameter estimation. Novel swarm intelligence based solver is developed for the first time for parameter estimation in contaminant transport inverse problem to overcome some of the limitations of the classical optimization methods and evolutionary methods such as GA. Additionally, the proposed swarm intelligence based algorithms and a new variant is applied to solve ill-posed problem of contaminant source characterization. The presented work in this dissertation can be unswervingly applied for modeling the contaminant transport in laboratory through-diffusion tests and contaminant transport through landfill liners where the transport is usually considered to be one-dimensional and also diffusion-dominated. Similarly, the advection-dispersion transport through laboratory soil columns can also be modeled with the developed, fast, automated, implicit numerical procedure with very good accuracy. The present study can be applied further for contaminant transport through stratified soil/liner system using fast converging numerical algorithms. Finally, the problems of design parameter estimation and source characterization can be handled accurately by the use of developed automated nature-inspired solvers.

Eutrophication is one of the key environmental problems of today, both in terms of complexity and magnitude. For the Baltic Sea (BS), eutrophication is an acute problem, leading to hypoxic conditions at the bottom; a situation that is sustained and amplified, when phosphorus is released from hypoxic sediments. Reducing nutrient loading is a top political priority but the present situation is believed to require active measures within the catchments and recipients to reduce both loading and adverse effects. Implementation of effective and cost-efficient abatement methods requires understanding of natural processes in watersheds, streams and recipients as well as technological expertise in order to compare the effects of measures of different kinds and locations. This thesis tries to combine process understanding of catchment transport behaviour, especially in coastal zones, and feasibility of certain technologies for reducing nutrient loading and effects of eutrophication in-situ. The over-arching theme is the fate of the individual contaminant, from injection to removal. Transport and dispersion in catchments are investigated, combining physically-based, distributed, numerical groundwater models with Lagrangian stochastic advective reactive solute (LaSAR) transport modelling. The approach is powerful in the sense that it incorporates catchment structural, geomorphological dispersion in the numerical model with hydrodynamic and sub-scale dispersion as well as uncertainty in the LaSAR framework. The study exemplifies the complex nature of transport time distributions in catchments in general and when varying source size and location, importance of dispersion parameters and retention due to molecular diffusion. It is shown that geomorphological control on dispersion is present even for relatively heterogeneous systems and that neither the mean residence time nor a statistical distribution may provide accurate representations of hydrological systems. To combat internal loading of P from sediments in-situ, large-scale aeration of deep waters, halocline ventilation, has been suggested. This study further investigates the feasibility of wave-powered devices to meet the energy demands for such an operation. It is shown that the required amount of oxygen needed to keep the sediments at oxic conditions could be provided, cheaply and efficiently, through the use of wave power. / QC 20120511