Simulation of field test on temperature variation induced by single-well leachate pumping in landfills

Leachate pumping has been widely adopted in landfill engineering. The removal of leachate from the waste mass modifies the internal moisture content and generates convective flow, which unavoidably leads to variations in waste temperature. These temperature changes subsequently influence the degradation behaviour of the original waste. In this study, based on the previously completed leachate pumping test, the associated fluctuations in leachate level and waste temperature evolution during the pumping process were simulated. An axisymmetric saturated-unsaturated seepage model was established for high-level landfills, incorporating depth-dependent variations in permeability and porosity. Additionally, an axisymmetric heat convection-conduction model was developed, taking into account both the impact of seepage on temperature distribution and the influence of moisture content on waste degradation. The governing models were solved using numerical calculation methods. Comparisons between the calculated results and test data indicated that the proposed models and solution approach accurately captured the trends in leachate level variation and waste temperature changes induced by leachate pumping. The results suggest that, under single-well pumping conditions, the degradation duration of newly placed waste and the specific heat capacity exerted a relatively pronounced effect on temperature distribution. Waste permeability exhibited a negligible influence on temperature gradients outside the zone of influence; however, it played a decisive role in determining the magnitude of temperature variation within the affected area. The models developed in this study provide a theoretical basis for evaluating temperature distributions under leachate pumping conditions and offer important guidance for landfill operation, expansion and closure.