Effect of plant root intrusion on the water balance of landfill cover systems

Abstract

Landfill covers systems are designed to isolate contaminants from the environment for hundreds to thousands of years. In the long term, however, the landfill covers are susceptible to failure caused by physical, chemical and biological effects. Plant intrusion is a major concern of landfill sustainability; the roots of plants have been found to increase the soil hydraulic conductivity by two orders of magnitude. The objective of this thesis was to evaluate the effect of plant intrusion and the resulting increase in the saturated hydraulic conductivity on the water balance of landfill cover systems. The finite element software model HYDRUS-1D was used to simulate water flux and root water uptake processes. Plant growth effects on the Burrell, Pennsylvania, uranium mill tailings site were evaluated as a case study. Additionally, a comparison of the water balance and effects of plant growth for different landfill cover designs (RCRA Subtitle C, RCRA Subtitle D and evapotranspiration covers) was performed. For each of the cases, different precipitation events were used to simulate arid and humid conditions. The plant roots effectively reduced the water content in the landfill cover systems, and it was concluded that vegetation should not be eliminated once established.