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RELIEF WELLS REHABILITATION AT ALUM CREEK AND DILLON DAMS

Relief well networks were installed at the downstream toes of Alum Creek and Dillon Dams in Ohio to reduce excess hydrostatic pressures in pervious foundation materials. Decline in performance of the networks and the need for rehabilitation, were evident from historic flow measurements, microbial test results, and down-hole video observations. Rehabilitation of the wells was accomplished by first brushing and airlift surging and pumping to remove gross biomass, mineral scale, and sediment within screens and casings. Mechanical cleaning was followed by the application of a patented blended chemical heat treatment process designed to further and more thoroughly clean the wells, filter packs and surrounding formations. A low pH, heated chemical mixture consisting of native water, hydroxyacetic acid, sulfamic acid, a mud dispersant, and a wetting agent was injected using a jetting tool and allowed to act overnight. After two such phases, the wells were pumped, with rehabilitation water filtered, and neutralized as necessary before surface discharge in accordance with regulations. Airlift surging and pumping were again performed after chemical treatment to remove any remaining fragmented biomass and blocking materials from the wells. Effectiveness of the employed procedures for removing biological and mechanical blockages, and improving performance of the relief wells, is demonstrated through observations of reduced well screen coating by bacterial slime, and comparisons of pre- and post-rehabilitation flow rate, piezometric, and pump-test data. These hydrologic performance data were acquired during a five month period in which pool and tail water elevations remained essentially constant.