Field hydrology and water balance modeling of earthen final covers for waste containment

The water balance of three test sections simulating earthen landfill final covers has been evaluated. These test sections are located in the U.S. at landfills in humid (Live Oak, Atlanta, GA) and semi-arid climates (East Wenatchee, WA). In Atlanta, a traditional resistive barrier and in Wenatchee, resistive and capillary barriers are being evaluated. Climatic data and hydrologic data including overland flow, percolation, and soil water content have been collected for three years. The computer models HELP and UNSAT-H are used to predict the water balance of the test sections. Most of the climatic, soil, and vegetative input to the models is measured in the field or laboratory. The influence of climate, thicknesses and hydraulic properties of soil layers, and vegetation on water balance of capillary barriers is evaluated with the aid of computer simulations.; For both sites, evapotranspiration has been the most significant component of water balance, whereas percolation has been the least significant component. Total percolation from the resistive barrier in Atlanta has been 23 cm (6.1% of precipitation), whereas for the resistive barrier in Wenatchee it has been 3.1 cm (5.6% of precipitation). Whenever soil water storage reached its capacity, percolation occurred. Percolation from the capillary barrier at Wenatchee is one-sixth of percolation from the resistive barrier. Desiccation cracking and animal burrows degraded the performance of the resistive barrier.; Water balance predictions of the test sections by UNSAT-H were more accurate than HELP. Errors related to prediction of overland flow, freezing of ground surface, and snow-melt affected accuracy of both models.; Field data and water balance simulations indicate that percolation from earthen covers can be minimized by using adequate thicknesses of soil layers such that most of the infiltration during the period of higher precipitation and lower evapotranspiration can be stored, and then released to atmosphere when the evapotranspiration rate increases.