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 loca tions 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 tem perature 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.

A numerical modeling approach has been developed for predicting temperatures in municipal solid waste landfills. Model formulation and details of boundary conditions are described. Model performance was evaluated using field data from a landfill in Michigan, USA. The numerical approach was based on finite element analysis incorporating transient conductive heat transfer. Heat generation functions representing decomposition of wastes were empirically developed and incorporated to the formulation. Thermal properties of materials were determined using experimental testing, field observations, and data reported in literature. The boundary conditions consisted of seasonal temperature cycles at the ground surface and constant temperatures at the far-field boundary. Heat generation functions were developed sequentially using varying degrees of conceptual complexity in modeling. First a step-function was developed to represent initial (aerobic) and residual (anaerobic) conditions. Second, an exponential growth-decay function was established. Third, the function was scaled for temperature dependency. Finally, an energy-expended function was developed to simulate heat generation with waste age as a function of temperature. Results are presented and compared to field data for the temperature-dependent growth-decay functions. The formulations developed can be used for prediction of temperatures within various components of landfill systems (liner, waste mass, cover, and surrounding subgrade), determination of frost depths, and determination of heat gain due to decomposition of wastes.

Cover temperature variations were determined at four municipal solid waste landfills located in different climatic regions in North America: Michigan, New Mexico, Alaska, and British Columbia. Cover temperatures varied seasonally similarly to air temperatures and demonstrated amplitude decrement and phase lag with depth. Elevated temperatures in the underlying wastes resulted in warmer temperatures and low frost penetration in the covers compared to surrounding subgrade soils. The ranges of measured temperatures decreased and average temperatures generally increased ͑approximately 2°C / m͒ with depth. The ranges of measured temperatures ͑T max − T min ͒ were 18-30°C and 13-21°C and the average temperatures were 13-18°C and 14-23°C at 1 and 2 m depths, respectively. For soil and geosynthetic barrier materials around 1 m depth, the maximum and minimum temperatures were 22-25°C and 3-4°C, respectively. Frost depths were determined to be approximately 50% of those for soils at ambient conditions. The main direction of heat flow in the covers was upward ͑negative gradients͒. The cover gradients varied between −18 and 14°C / m, with averages of −7 to 1°C/ m. The gradients for soil and geosynthetic barrier materials around 1 m depth varied between −11 and 9°C / m with an average of −2°C/ m. Cover thawing n-factors ranged between 1.0 and 1.4 and the cover freezing n-factor was 0.6. Design charts and guidelines are provided for cover thermal analyses for variable climatic conditions.