Landfill cap models under simulated climate change precipitation: assessing long-term infiltration using the HELP model

The Hydrologic Evaluation of Landfill Performance (HELP) model (v 3.04) was used to assess the hydrological performance of two large-scale (similar to 80 x 80 x 90 cm) laboratory-based landfill cap models. Desiccation cracking under simulated climate change precipitation (CCP) events was modelled to predict the performance of landfill caps over a 50-year period in Cumbria England, UK. Cumulative infiltration values under different climate conditions were highly sensitive to macro-pore development in the clay liner which is represented by the changing hydraulic conductivity in HELP simulations. Simulation results of cap design 1 (a clay barrier layer only) show that cumulative annual infiltration under normal precipitation (NP) and CCP events, with the initial hydraulic conductivity, ranged between 1 and 2% of the annual precipitation; however, cumulative annual infiltration was 10 to 68% when maximum (degraded) hydraulic conductivity values were used in simulations. A geosynthetic clay liner (GCL) included in cap design 2 significantly reduce cumulative infiltration.