Contaminant Migration Through Fractured Till Into An Underlying Aquifer

This paper examines the potential impact on groundwater quality of contaminant migration from a landfill site, through a fractured till, and into an underlying aquifer. The paper describes a simple, semi-analytic technique for modelling contaminant transport through the fractured till, including consideration of diffusion of contaminants from the fractures into the till matrix, sorption, and radioactive decay. The model also considers the finite mass of contaminant and dilution due to the flow of groundwater in the aquifer. The model can be readily implemented on a microcomputer. The model allows examination of variations in fracture spacing, fracture opening size, thickness of the fractured zone, diffusion coefficient, dispersivity, effective porosity of the matrix, radioactive decay, Darcy velocity, thickness of the aquifer, distribution coefficient, and mass of contaminant. The paper describes the results of a limited parametric study that, inter alia, examines the effects of uncertainty in fracture spacing, the thickness of the fractured till, and the effective porosity of the till matrix. Some of the practical implications are discussed. Key words: contaminant migration, fractures, till, groundwater, pollution, landfill, waste disposal.