Long-term spatial and temporal variations in temperatures have been investigated in covers, wastes, and liners at four municipal solid waste landfills located in different climatic regions: Alaska, British Columbia, Michigan, and New Mexico. Temperatures were measured in wastes with a broad range of ages from newly placed to old (up to 40 years). The characteristic shape of waste temperature versus depth relationships consisted of a convex temperature profile with maximum temperatures observed at central locations within the middle third fraction of the depth of the waste mass. Lower temperatures were observed above and below this central zone, with seasonal fluctuations occurring near the surface and steady and elevated values (above mean annual earth temperature) near the base of the landfills. Heat gain and long-term temperatures were directly affected by placement temperatures. Sustained concave temperature profiles were observed for winter waste placement. The highest heat gain and resulting high temperatures were observed in Michigan followed by British Columbia, New Mexico, and Alaska. The high heat gain in Michigan was attributed to coupled precipitation/moisture content and waste density. The time-averaged waste temperature ranges were 0.9–33.0, 14.4–49.2, 14.8–55.6, and 20.5–33.6°C in Alaska, British Columbia, Michigan, and New Mexico, respectively. Temperature increases occurred rapidly (over multiple years) in British Columbia and then dissipated for tens of years. Longer periods of temperature increase were observed at the other sites. Temperatures, temperature increases, and heat gain were higher during anaerobic decomposition of wastes than aerobic decomposition. A parametric study indicated that use of insulating materials over covers decreased temperature variations compared to uninsulated conditions for prevention of frost penetration or desiccation and for optimum methane oxidation. Overall, thermal regime of landfills is controlled by climatic and operational conditions.
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