This study demonstrates that containment of municipal and hazardous waste in arid and semiarid environments can be accomplished effectively without traditional, synthetic materials and complex, multi-layer systems. This research demonstrates that closure covers combining layers of natural soil, native plant species, and climatic conditions to form a sustainable, functioning ecosystem will meet the technical equivalency criteria prescribed by the U. S. Environmental Protection Agency.In this study, percolation through a natural analogue and an engineered cover is simulated using the one-dimensional, numerical code UNSAT-H. UNSAT-H is a Richards' equation-based model that simulates soil water infiltration, unsaturated flow, redistribution, evaporation, plant transpiration, and deep percolation. This study incorporates conservative, site-specific soil hydraulic and vegetation parameters. Historical meteorological data are used to simulate percolation through the natural analogue and an engineered cover, with and without vegetation.This study indicates that a 3-foot (ft) cover in arid and semiarid environments is the minimum design thickness necessary to meet the U. S. Environmental Protection Agency-prescribed technical equivalency criteria of 31.5 millimeters/year and 1 x 10 -7 centimeters/second for net annual percolation and average flux, respectively. Increasing cover thickness to 4 or 5 ft results in limited additional improvement in cover performance. 4This page intentionally left blank 5
A vegetation study was conducted in Technical Area 3 at Sandia National Laboratories, Albuquerque, New Mexico in 2003 to assist in the design and optimization of vegetative soil covers for hazardous, radioactive, and mixed waste landfills at Sandia National Laboratories/New Mexico and Kirtland Air Force Base. The objective of the study was to obtain site-specific, vegetative input parameters for the one-dimensional code UNSAT-H and to identify suitable, diverse native plant species for use on vegetative soil covers that will persist indefinitely as a climax ecological community with little or no maintenance.The identification and selection of appropriate native plant species is critical to the proper design and long-term performance of vegetative soil covers. Major emphasis was placed on the acquisition of representative, site-specific vegetation data. Vegetative input parameters measured in the field during this study include root depth, root length density, and percent bare area. Sitespecific leaf area index was not obtained in the area because there was no suitable platform to measure leaf area during the 2003 growing season due to severe drought that has persisted in New Mexico since 1999. Regional LAI data was obtained from two unique desert biomes in New Mexico, Sevilletta Wildlife Refuge and Jornada Research Station. structure; soft, very friable; many very fine and fine roots and interstitial pores; moderately alkaline; abrupt smooth boundaries. B Horizon10 to 33 cm: Brown sandy clay loam (in the general description of the B Horizon, the Madurez Series can also be heavy sandy loam, light clay loam, heavy fine sandy loam, or light sandy clay loam); weak, coarse, sub-angular blocky structure; hard, friable, sticky and plastic; many very fine and fine roots and interstitial pores; moderately alkaline; clear, smooth boundaries.33 to 53 cm: Light brown heavy fine sandy loam (in the general description of the B Horizon, the Madurez Series can also be heavy sandy loam, light clay loam, heavy fine sandy loam, or light sandy clay loam); weak, coarse, sub-angular blocky structure; hard, friable, sticky and plastic; common very fine and fine roots and interstitial pores; moderately calcareous; moderately alkaline; clear, smooth boundary. C Horizon53 to 89 cm: Pink heavy sandy loam (in the general description of the C Horizon, the Madurez Series can also be sandy clay loam, light clay loam, heavy fine sandy loam or light sandy clay loam); massive; hard, friable, sticky and plastic; few very fine roots and interstitial pores; moderately calcareous; moderately alkaline; clear smooth boundary.89 to 130 cm: Pinkish gray sandy loam (in the general description of the C Horizon, the Madurez Series can also be sandy clay loam, light clay loam, heavy fine sandy loam or light sandy clay loam); massive; hard, friable, slightly sticky and slightly plastic; strongly calcareous; moderately alkaline; gradual smooth boundaries.130 to 152 cm: Light brown sandy loam (in the general description of the C Horizon, the Madurez Series can ...
An alternative cover design consisting of a monolithic layer of native soil is proposed as the closure path for the Mixed Waste Landfill at Sandia National Laboratories, New Mexico. The proposed design would rely upon soil thickness and evapotranspiration to provide long-term performance and stability, and would be inexpensive to build and maintain. The proposed design is a 3-ft-thick, vegetated soil cover. The alternative cover meets the intent of RCRA Subtitle C regulations in that a) water migration through the cover is minimized; b) maintenance is minimized by using a monolithic soil layer; c) cover erosion is minimized by using erosion control measures; d) subsidence is accommodated by using a "soft" design; and e) the permeability of the cover is less than or equal to that of natural subsurface soil present.Performance of the proposed cover is integrated with natural site conditions, producing a "system performance" that will ensure that the cover is protective of human health and the environment. Natural site conditions that will produce a system performance include a) extremely low precipitation and high potential evapotranspiration; b) negligible recharge to groundwater; c) an extensive vadose zone; d) groundwater approximately 500 ft below the surface; and e) a versatile, native flora that will persist indefinitely as a climax ecological community with little or no maintenance. The Mixed Waste Landfill (MWL) is located 4 miles south of SNL/NM's central facilities and 5 miles southeast of Albuquerque International Sunport. The landfill is a fenced, 2.6-acre compound in the north-central portion of Technical Area (TA)-3. The MWL was established in 1959 as a disposal area for low-level radioactive and mixed waste generated by SNL/NM research facilities. The landfill accepted low-level radioactive and minor amounts of mixed waste from March 1959 through December 1988. Approximately 100,000 cubic feet (ft) of lowlevel radioactive and mixed waste containing approximately 6,300 curies of activity were disposed of in the landfill.The MWL consists of two distinct disposal areas. The classified area occupies 0.6 acres and the unclassified area occupies 2.0 acres. Low-level radioactive and mixed waste was disposed of in each of these areas. Classified wastes were buried in unlined, cylindrical pits in the classified area. Unclassified wastes were buried in shallow, unlined trenches in the unclassified area.A Phase 1 Resource Conservation and Recovery Act (RCRA) Facility Investigation (RFI) was conducted in 1989 and 1990 to determine if a release of RCRA contaminants had occurred at the MWL. The Phase 1 RFI indicated that tritium had been released to the environment. A Phase 2 RFI was conducted from 1992 to 1995 to determine the contaminant source, define the nature and extent of contamination, identify potential contaminant transport pathways, evaluate potential risks posed by the levels of contamination identified, and provide remedial action alternatives for the landfill.The Phase 2 RFI confirmed that...
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