BIOREMEDIATION OF THE SWEETWATER PIT LAKE

The Sweetwater Pit Lake, an oligotropic lake located in Sweetwater County, Wyoming was formed by the flooding of the Sweetwater open pit uranium mine following cessation of dewatering activities in April 1983. The lake exhibited levels of dissolved selenium (0.46 ppm) above reclamation standards (0.05 ppm) and dissolved uranium (8.1 ppm) above livestock standards (5.0 ppm). The lake, containing approximately 1.2 billion gallons of water, was treated by Kennecott Uranium Company with 548.7 tons of sugars, fats, proteins, alcohols, phosphates and nitrates from 10/19 to 12/22/99. Average concentrations of dissolved selenium and uranium in the pit lake dropped to 0.010 ppm and 4.33 ppm respectively, on 10/24/01.

The pit lake treatment process accelerated and enhanced the natural processes occurring in the pit lake prior to treatment, which had been slowly precipitating metals in the sediments. The addition of nutrients dramatically accelerated biological activity in the pit lake, which in turn accelerated the ongoing natural process of biologic concentration of metals in the pit lake sediments.