The McCook Reservoir is a planned flood storage reservoir for the city of Chicago, Illinois. Since the storm water which would fill the reservoir could contain domestic sewage, concerns were expressed with the development of anoxic conditions in the reservoir and the subsequent development of hydrogen sulfide gas. A one dimensional numerical model was modified to predict the development of anoxic conditions by the uptake of dissolved oxygen from biochemical oxygen demand (BOD). A routine was added to simulate the effects of thermal destratification using a pneumatic diffuser system. Simulations conducted with the model included water years with high rainfall, low rainfall, and average rainfall conditions. Two period of record storm events were also simulated. Results of the simulations indicated the model was most sensitive to inflow concentration of BOD. Destratification alone had little effect on prevention of anaerobic conditions in the reservoir. A pneumatic aeration system was designed using oxygenation requirements predicted by the numerical model.