| Landfill final covers (caps) are regulated by federal and state regulations with the purpose of minimizing the amount of infiltration into the waste (percolation). Conventional cover designs typically consist of a compacted clay layer overlain by a geomembrane. While these covers restrict percolation to relatively small quantities, desiccation cracking of the clay barrier layer is a common long-term shortcoming. Hence, as an alternative, evapotranspirative (ET) covers have been routinely explored. While ET covers can decrease desiccation cracking potential, preferential flow is still a threat. Macropores formed by desiccation, roots, insects, and earthworms are present in almost all soil covers including ET covers.;In this study, preferential flow through an ET cover is evaluated using HYDRUS 1D and 2D (beta version) software which included single-permeability (capillary flow) and dual-permeability (capillary and preferential flow) modeling options. Simulation duration, presence of preferential flow, preferential flow depth, fracture hydraulic conductivity, the amount of fractures, the fraction of surface flow entering the fractures, hydraulic conductivity of the storage layer and waste layer, and waste layer thickness were varied to evaluate their effect on percolation. The key conclusion of this study is that preferential flow can significantly increase percolation through the cap and into the waste layer of a landfill. Ignoring preferential flow, whether it is currently present or will be in the future, can be detrimental when designing and evaluating landfill final covers. |
