The effects of placement practices on decomposition of wastes were investigated at Anchorage Regional Landfill (Anchorage, Alaska) since 2002. Temperatures and gas concentrations of wastes placed at various seasons were monitored. Wastes were placed at sub-freezing temperatures during cold seasons. Waste temperatures generally increased upon placement. High variation was observed in waste temperatures near the surface whereas steady temperatures were obtained at depth. High maximum stable temperatures resulted from warm placement conditions. Steady temperatures between approximately –1 to +35°C were observed. The central portion of a frozen waste band (with a total initial thickness of 7 m at placement, currently between depths of approximately 8 m to 15 m) remains frozen 2 years after placement. Both the top and bottom regions of the frozen waste band have thawed. Heat Content (HC) varied between -8.2 (for 2-year-old waste at a depth of 11.9 m in frozen wastes) to +25.9°C-day/day (for 13-year-old waste at a depth of 32 m for waste placed in summer). The measured frost depths in waste ranged from 0.7 to 1.3 m and were less than that for native soil at the landfill site. Instantaneous thermal gradients ranged from -73 to +60°C/m. Gas concentrations were similar to air at the time of waste placement. Anaerobic decomposition conditions and onset of landfill gas production started within 3 to 4 years of placement for wastes placed during warm seasons. Virtually no decomposition or gas generation were observed in the frozen wastes. A 1-D numerical model was used to investigate distribution of temperatures for placement at varying temperatures and for varying lift thicknesses. It is recommended to minimize frozen lift thicknesses to obtain higher temperatures.


Civil and Environmental Engineering

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URL: http://digitalcommons.calpoly.edu/cenv_fac/132