WATER QUALITY MANAGEMENT OF A WATER SUPPLY RESERVOIR

Aurora Reservoir in Colorado is the City of Aurora's 30,000 acre-feet terminal water supply reservoir for the Wemlinger Water Treatment Plant. Oxygen loss during thermal stratification results in significant internal phosphorus loading and contributes to phytoplankton productivity and the accumulation of anaerobic respiration products, which periodically cause water treatment problems. To mitigate the loss of oxygen, six in-reservoir aeration and oxygenation alternatives were evaluated. The alternatives involved using compressed air or pure oxygen, via a submerged downflow contact oxygen system (Speece Cone), to increase the soluble dissolved oxygen concentration in the hypolimnion and in the mid-layer, which is that part of the water column just below the thermocline. The water quality simulation model, CE-QUAL-W2, was used to evaluate the performance of the alternatives. The computer program, Criterium Decision Plus, was used to numerically rank the alternatives based on selected ranking criteria. Water quality benefits; effect on open space values, in terms of wildlife habitat, fishing and water sports; and operation and maintenance were considered to be the most important criteria.