MODELING OF EVAPOTRANSPIRATION (ET) LANDFILL COVERS IN SUB-HUMID ENVIRONMENTS

An effort that is currently under research and has involved limited field application is a final cover system that is termed an evapotranspiration (ET) cover. An ET cover employs the ability of vegetation to hold and transpire the majority, if not all, precipitation that would migrate into and through the landfill. Use of ET covers to augment conventional leachate management methods has significantly increased.In order to effectively implement ET cover systems, computer modeling is used to enhance concept visualization, fast-track possible scenarios, and aid in optimization of plant species used to control water migration into the landfill.Predicting water movement through landfill covers is extremely important in leachate management design. A water balance is generally performed using the Hydrologic Evaluation of Landfill Performance (HELP) model, which is currently the standard in sanitary landfill modeling.In sub-humid to arid environments, water loss due to evaporation and transpiration through plants is greater than accumulated precipitation, causing an upward flux of soil moisture. Numerical models, Soil-Plant-Atmosphere-Water (SPAW) and Erosion Productivity Impact Calculator (EPIC), have been developed which account for the upward flow of water due to plant transpiration and evaporation. These models differ from the HELP model because HELP does not accurately account for upward water movement due to plant transpiration and evaporation. These inaccuracies are partially due to unsaturated conditions that exist in the subsurface of sub-humid to arid climates. The inability of HELP to assimilate full vegetative processes also provides inaccuracy when modeling.These models were used to evaluate water losses in landfill cover systems in South Dakota using various climatic (sub-humid to arid) and vegetative conditions. Limiting parameters and concerns that would be faced in an actual field environment were analyzed. This allowed for comparison and conclusions of how each model simulated a typical ET cover system. Results showed that the HELP model has limitations pertaining to vegetative processes and that HELP may not be the best suited model to use in landfill design in all climates.