Determining the appropriate criteria and designs for hazardous waste landfill covers has spawned much discussion within the environmental remediation arena. Ve y little reliable comparison of various technologies exists. Researchers at Los Alamos National Laboratory studied the relative hydrologic performance of four landfill cover designstwo capillary barrier designs, one modified EPA RCRA design, and one control cover. Monitoring the fate of natural precipitation for nearly four years showed that the covers with barrier layers more effectively reduced deeppercolation than the control cover. Although none entirely eliminated deeppercolation, the RCRA cover, incorporating a clay hydraulic barrier, most effectively controlled it. The two capilla y barriers reduced deep percolation, but significant amounts were stillproduced. Over POpercent of allpercolation through the covers, and lateralflow within the covers, occurred during Februa y through May each year, primarily as a result of snowmelt, early spring rains, and low evapotranspiration. The study also showed that gravel mulch su$ace treatments (70-to 80-percentground cover) reduced runoff and erosion. Despite additional shrubsplanted on one, the two plots receiving thegravel mulch treatmentsexhibited equally enhanced amounts of evapotranspiration.Landfilling, the oldest method of waste disposal practiced by humans (Hagerty, 19731, enjoys widespread use for hazardous waste disposal. Today, satisfactory landfill technology must prevent leaching of contaminants to surrounding soil or underlying groundwater. Remediating previously contaminated sites often relies on containment; it is cost-effective, generates little by-product waste, and can be designed to meet regulatory requirements. Successfully containing wastes in landfills or contaminated sites depends almost entirely on the landfill cover.Most containment failures result from interactions of water with the landfill covers, as documented by operating experience at major low-level radioactive waste disposal sites since the early 1940s (Duguid, 1977;Jacobs et al., 1980;Hakonson et al., 1982;Herzog et al., 1982). Landfill covers seem particularly susceptible to failure during snowmelt periods when large inputs of water occur and when evapotranspiration is low (Nyhan et al., ). Choosing the best cover design for a particular site becomes a critical decision in the overall landfill design or remediation strategy.Unfortunately, few field studies have evaluated the relative performance of cover design alternatives and whether they meet EPA's performance requirements. Previous work generally examined individual processes affecting cover performance, for example: erosion (Hakonson et al.). While each of these processes are important, data are needed to evaluate them acting together under field conditions.Although directly measuring water balance could best evaluate the performance of cover designs, few studies have attempted to do so (Healy et al., 1989;Nyhan et al., 1990;Campbell et al., 1991;Limbach et al., 1994...

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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Perched groundwater percolating through radionuclide contamination in the E Tunnel Complex on the Nevada National Security Site, formerly the Nevada Test Site, emerges and is stored in a series of ponds making it available to wildlife, including bats. Since many bat species using the ponds are considered sensitive or protected/regulated and little information is available on dose to bats from radioactive water sources, bats were sampled to determine if the dose they were receiving exceeded the United States Department of Energy dose limit of 1.0E-3 Gy/day. Radionuclide concentrations in water, sediment, and flying insects were also measured as input parameters to the dose rate model and to examine trophic level relationships. The RESRAD-Biota model was used to calculate dose rates to bats using different screening levels. Efficacy of RESRAD-Biota and suggested improvements are discussed. Dose to bats foraging and drinking at these ponds is well below the dose limit set to protect terrestrial biota populations.