Contaminant Fate and Reactive Transport in Groundwater

Understanding the complex, interacting processes that determine the fate and transport of contaminants in groundwater is a major challenge for evaluating and predicting risks to clean water, human and ecological receptors and for designing effective remediation plans. Different physical and biogeochemical processes including advection, hydrodynamic dispersion, dissolution, sorption and biodegradation affect the migration of contaminants in saturated porous media like a groundwater system. In this chapter an overview of these processes is presented together with the basic theory on contaminant transport modeling, which represents an essential tool for a quantitative description of contaminant migration in the subsurface. Numerical simulations of typical contamination scenarios are presented, with the main goal of identifying the influence of different parameters on contaminant fate and transport such as transverse dispersivity, thickness and strength of the contamination source, recharge, biodegradation rates and mixing enhancement through flow focusing in high permeability zones. These numerical simulations are complemented by two examples, i.e. the reactive transport of toluene from a LNAPL source and a field study, where ammonium is continuously released from a leaking landfill to the underlying aquifer. The principal processes at the landfill site have been quantitatively integrated into the framework of a two-dimensional reactive transport model.