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

Abstract

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.

Impact of Landfill Closure Designs on Long-Term Natural Attenuation of Chlorinated Hydrocarbons

“…Capillary force causes the layer of fine soil overlying the coarser layer to hold more water than if there were no change in particle size between the layers (Hauser et al, 2001a). Hill AFB, Utah explored the potential to use capillary barrier covers to control the infiltration of natural precipitation (Warren et al, 1996a). The capillary-barrier designs investigated consisted of 150 centimeters (cm) of topsoil over 30 cm of gravel.…”

“…This conclusion is based on the fact that capillary barriers have been used primarily in experimental installations, and field experience shows that they may fail periodically (Nyhan et al, 1990;Warren et al, 1996a). Based on the research of Warren et al (1996b), even in semi-arid climates, the ability of capillary barriers to shed water laterally along the capillary break within covers is likely to be inadequate, particularly during months with frequent rainfall.…”

Calculation set for design and optimization of vegetative soil covers Sandia National Laboratories, Albuquerque, New Mexico.

“…The EPA (1989) notes that alternatives to clay hydraulic barriers should be considered for sites with a high risk for barrier desiccation. Warren et al (1997) performed a study on four cover designs at Hill Air Force Base 1.25 mile (mi) south of Ogden, Utah. A flexible membrane liner was not installed in a RCRA Subtitle C cap under the assumption that the liner had failed as EPA guidance (1989) specifies will occur after some unspecified time.…”

Distribution of Microorganisms and their Activities in Capillary Barriers: Implications for Modeling of Hydrologic Transport through Capillary Barriers

“…The long‐term performance of capillary and other surface barrier designs has not been fully evaluated (NRC, 2000). Field‐scale prototype capillary barriers have been constructed and their hydraulic performance predicted based on short‐term studies of soil physical properties and plant evapotranspiration (Dwyer, 1997; Gee and Ward, 1997; Porro, 2001; Warren et al, 1997). The effects of soil microorganisms on the hydraulic performance of capillary barriers have not been studied nor accounted for in hydrologic models.…”