Modelling of two-dimensional contaminant migration in a layered and fractured zone beneath landfills

A new two-dimensional finite layer formulation that allows consideration of both vertical and horizontal contaminant migration in systems that may consist of both fractured and unfractured layers is described. Consideration is given to contaminant migration from typical municipal and nonhazardous waste disposal sites. The migration of concentrated dense nonaqueous phase contaminant, which involves additional transport mechanisms, is not considered in this paper. The use of the theory is illustrated with respect to a number of hypothetical cases. The results indicate that even relatively widely spaced small fractures can have a significant effect on potential impact on groundwater quality in an underlying aquifer. It is also shown that when dealing with relatively impermeable tills, impact on an underlying aquifer may not occur until after the landfill leachate is at a low strength; however, the impact may be quite significant and may last for hundreds of years. Consideration is given to the implication of regulatory policies that specify the maximum impact that can ever be permitted and those that simply specify that there be no impact for a specified (e.g., 100 year) period. It is shown that landfills that meet the requirements of no impact within the first 100 years may subsequently have a significant (unacceptable) impact on groundwater quality. Key words: clay, fractures, contaminant impact, analysis, design, diffusion.