Abstract
Landfill waste cells are capped with a final cover of vegetated topsoil. The impact of extreme climatic events on percolation of water from landfill final covers is currently not considered in landfill cover design. Covers designed to meet descriptive specifications or designed to prevent percolation from mean climatic events may be overwhelmed by extreme events. This dissertation improves an existing model so that it may be used to estimate the cover percolation that results from infrequent periods of low potential evapotranspiration and high precipitation. The cover stores and transpires infiltrated rainwater to the atmosphere. The cover attenuates percolation by accumulating water in storage during wet periods and transpiring it to the atmosphere during dry periods. When the water storage capacity of the cover is full and water infiltration exceeds the evapotranspiration demands of the vegetation, water will percolate from the cover to the waste cells. The percolation quantity and time of occurrence are estimated by the Climatic Water Balance model. The model is a water continuity equation. Climatic input variables to the model are precipitation and potential evapotranspiration. Cover design input variables to the model are water storage capacity and runoff coefficient. With these variables a site and design specific cover may be modeled for percolation. Synthetic extreme event scenarios for a design year are constructed from frequency analyses of actual or estimated precipitation and potential evapotranspiration data. Percolation is calculated under various arrangements (scenarios) of extreme events to determine the sensitivity of percolation to each of the climatic variables. Design inputs are varied to determine the optimum cover design in attenuating percolation for the site specific climate described by the scenarios. Errors in estimating recurrence percolation caused by dependence between the climatic variables are resolved by using data from actual extreme years to estimate recurrence percolation. The scenarios may be calibrated from the actual data and applied elsewhere within the same climate. Percolation curves generated from ranging climatic variable scenarios by recurrence interval and the storage variable by capacity, exhibited asymptotic behavior. Increases in storage capacity become ineffective in moderating percolation as the events become more extreme.
Rust, Richard Reynolds (1986). Estimation of percolation from landfill final covers based on extreme climatic events. Texas A&M University. Texas A&M University. Libraries. Available electronically from
https : / /hdl .handle .net /1969 .1 /DISSERTATIONS -440230.