The results from several field experiments on methods to control soil erosion, biointrusion, and water infiltration were used to design and test an enhanced landfill cover that improves the ability of the disposal site to isolate buried wastes. The performance of the improved cover design in managing water and biota at the disposal site was compared for 3 yr with that obtained from a more conventional design that has been widely used in the industry. The conventional cover design consisted of 20 cm of sandy loam topsoil over 108 cm of a sandy silt backfill, whereas the improved design consists of 71 cm of topsoil over a minimum of 46 cm of gravel, 91 cm of river cobble, and 38 cm of sandy silt backfill. Each plot was lined with an impermeable liner to allow for mass balance calculation of water dynamics. Results over a 3-yr period, including 2 wet yr, demonstrated that the improved design reduced percolation of water through the landfill cover by a factor of >4 over the conventional design. This decrease in percolation was attributed to a combination of increased evapotranspiration from the plant cover and the effect of a capillary barrier embedded in the enhanced cover profile in diverting water laterally in the cover. The field data are finally discussed in terms of its usefulness for waste management decisions to be made in the future for both new and existing landfills at Los Alumos, NM, and at other semiarid waste disposal sites.

The distribution of Pu, 241Am, and water in Bandelier Tuff beneath a former liquid waste disposal site at Los Alamos was investigated. The waste use history of the site was described, as well as the previous field and laboratory studies of radionuclide migration performed at this site. One of the absorption beds studied had 20.5 m of water added to it in 1961 in an aggressive attempt to change the distribution of radionuclides in the tuff beneath the bed. Plutonium and 241Am were detected to sampling depths of 30 m in this bed, but only found to depths of 6.5 to 13.41 m in an adjacent absorption bed (bed 2) not receiving additional water in 1961. After 17 yr of migration of the slug of water added to bed 1, 0.3 to 5.1% of the Pu inventory and 3.0 to 49.6% of the 241Am inventory was mobilized within the 30‐m sampling depth, as less than one column volume of water moved through the tuff profile under the bed. The results of similar lab and field studies performed since 1953 were compared with our 1978 data and site hydrologic data was used as a time marker to estimate how fast radionuclide migration occurred in the tuff beneath absorption bed 1. Most of the radionuclide migration appeared to have occurred within 1 yr of the 20.5‐m water leaching in 1961. The implications of our research results to nuclear waste management were also discussed.

The Los Alamos National Laboratory and the USDA‐ARS examined soil erosion and water balance relationships for a trench cap used for the shallow land burial of low‐level radioactive wastes at Los Alamos, NM. Eight 3.05 by 10.7 m plots were installed with bare soil, tilled, and vegetated surface treatments on a 15 by 63 m trench cap constructed from soil and crushed tuff layers. A rotating boom rain simulator was used to estimate the soil erodibility and cover‐management factors of the Universal Soil Loss Equation (USLE) for this trench cap and for two undisturbed plots with natural vegetative cover. The implications of the results of this study are discussed relative to the management of infiltration and erosion processes at waste burial sites and compared with similar USDA research performed throughout the USA.

The results from several field experiments on methods to control soil erosion, biointrusion and water infiltration were used to design and test a burial site cover which improves the ability of the disposal site to isolate the wastes. The performance of the improved cover design in managing water and biota at the disposal site was compared for three years with that obtained from a more conventional design widely used in the industry. The conventional trench cover design consists of 15 cm of sandy loam topsoil over 75 cm of sandy silt backfill, whereas the improved trench cover design consists of 75 cm of topsoil over a minimum of 25 cm of gravel and 90 cm of river cobble. Each plot was lined with an impermeable liner to allow for mass balance calculation of water dynamics and contains hydrologic tracer ions (iodide and bromide) to demonstrate movement of water through the various zones of the trench cap. Cesium was emplaced beneath the trench cap to indicate root penetration through the trench cap, observed by sampling plant samples collected on the plots and assaying them for cesium. The field data are finally summarized and discussed in terms of its usefulness for waste management decisions to be made in the future for both new and existing landfills at Los Alamos and at other semiarid waste disposal sites. I.

Commercially available differential pressure transducers, tensiometers, and a data acquisition system were combined to evaluate soil water tension changes with time within two landfill cover designs used for the shallow land burial of waste materials. A typical error for the differential pressure transducers in the voltage‐pressure calibration curve was estimated to be 0.14 V at a transducer output of 4 V. Tensiometer data collected simultaneously using the data‐acquisition system and a hand‐held manual pressure‐transducer system agreed well (r2 = 0.994). The utility of the tensiometer data acquisition system to collect field data was demonstrated successfully using reference tensiometers with known hydraulic heads. Diurnal fluctuations in tensiometer data collected in the field are discussed relative to future experiments to be performed with the system. In addition, tensiometers with unknown and variable hydraulic heads were used to determine tensiometer response times of approximately 50 min.