The hydrologic evaluation of four cover designs for hazardous waste landfills at hill air force base

Results are presented here of a field study to evaluate the relative hydrologic performance of various landfill cover technologies installed at Hill Air Force Base, Utah. Four cover designs (two capillary barrier designs, one modified EPA RCRA design, and one control cover) were installed in large lysimeters instrumented to monitor the fate of natural precipitation between January 1, 1990 and September 20, 1993. After 45 months of study, results showed that the cover designs containing barrier layers were effective in reducing deep percolation as compared to the control cover. The RCRA cover, incorporating a clay hydraulic barrier, was the most effective of all cover designs in controlling deep percolation but was not 100-percent effective. The two capillary barriers were successful in reducing deep percolation, but significant amounts were still produced. Over 90 percent of all percolation through the covers and lateral flow within the covers occurred during the months of February through May of each year, primarily as a result of snowmelt, early spring rains, and low evapotranspiration. Gravel mulch surface treatments (70- to 80-percent ground cover) were effective in reducing runoff and erosion. The two plots receiving the gravel mulch treatments exhibited equal but enhanced amounts of evapotranspiration, despite the fact that one plot was planted with additional shrubs.

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