Management of spontaneous combustion in coal overburden spoil piles

Laboratory testing was undertaken to examine the spontaneous combustion propensity of some of the coal seams being mined at Leigh Creek. Tests indicated that while carbonaceous rocks retained a fuel load, in isolation, these did not have the capacity to reach thermal runaway. However, the potential existed for heat from another source, such as coal, to raise the temperature of these rocks to above the threshold for thermal runaway (>100 °C). The mine closure plan submitted to the regulator (Department of Premier and Cabinet, South Australia) incorporated a monitoring trial of the selected spontaneous combustion management rehabilitation strategy to demonstrate its effectiveness. The strategy included reducing batter slopes of waste spoil piles and the application of an inert cover. The trial was established in June 2017 in a location with active combustion immediately prior to rehabilitation treatment. Measurements of temperature and oxygen concentrations within the spoil pile over twelve months show that oxygen is consumed within 1 m of the outer surface of the waste, while maximum spoil pile temperatures have been decreasing, indicating a net heat loss from the trial spoil pile area. No spontaneous combustion outbreaks have occurred in the trial area since the trial commenced. Characteristics of the trial area materials, the management strategy, and outcomes from the field trial measurements are presented.