Laboratory simulations have helped resolve several problems concerning the role of bacteria in producing acidic drainage from active and abandoned coal mines. It is well established that the bacteriumThiobacillus ferrooxidansoxidizes pyrite in synthetic liquid media and in flooded or agitated experimental simulations of coal mine environments. However, many geologists remain skeptical regarding the role ofT. ferrooxidansin producing acidity below a near‐surface belt of soil water. We have demonstrated thatT. ferrooxidansis capable of colonizing and acidifying a near‐neutralpH environment of crushed coal or overburden, without prior establishment of apH‐dependent succession of bacteria. We have suggested thatT. ferrooxidansmay accomplish this by direct oxidation of pyrite. We have also shown thatT. ferrooxidanscatalyzes pyrite oxidation in the intermediate belt of the zone of aeration, although only for a limited period of time after rainfall infiltration.T. ferrooxidanswas not found to be significant in the simulated zone of groundwater saturation.