The goal of radioactive and hazardous waste disposal in shallow landfills is to reduce risk to human health and to the environment by isolating contaminants until they no longer pose a hazard. To achieve this for a semiarid region, we studied a landfill cover containing a gravel layer, an evapotranspiration (ET) cover, in the field for 7 yr. We measured total water balance at 6-h intervals for this landfill cover design in four 1.0- by 10.0-m plots with downhill slopes of 5, 10, 15, and 25%. During the 7 yr of the field study, runoff accounted for 1.4 to 3.8% of the precipitation losses on these unvegetated landfill cover designs, whereas similar values for evaporation ranged from 88 to 95%. Evaporation usually increased with increases in slope in our field plots; for example, the ET Cover at slopes of 5 and 15% displayed 274 and 296 cm of evaporation, respectively. Interflow and seepage usually decreased with increasing slope; for example, as slope increased from 10 to 25%, interflow decreased from 18.4 to 8.8 cm. Seepage consisted of up to 1.7% of the precipitation on the ET cover, showing a maximum value of 5.3 cm on the ET cover with the slope of 5%.

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