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Description
This thesis assesses the hydrogeologic factors necessary for the design of an anaerobic bioremediation project at a site contaminated by a leaking underground gasoline storage tank. The project intends to remediate contaminated soil and groundwater by circulating nitrate and nutrient rich water throughout the region of contamination by injecting treated water through an infiltration gallery positioned over the tank pit and extracting water down gradient. The hydrologic characteristics and pressure head relationships of both the unsaturated and saturated zones around the excavated tank pit were examined. The saturated zone was characterized by pump testing. The pump tests displayed unconfined aquifer characteristics and resulted in estimates of hydraulic conductivity at this site that vary locally from 1.0 to 50 ft/day. Simulations using the computer program RESSQ were used to estimate the rate and areal extent of flowlines generated from two different circulation systems under steady state conditions. The pore pressures and liquid transmission characteristics of the unsaturated zone were modeled with the computer program UNSAT2. Field and laboratory data for the UNSAT2 model were gathered using a Guelph permeameter and a pressure plate apparatus. The Guelph permeameter resulted in estimates of the in-situ hydraulic conductivity-pressure head relationship for the near surface deposits at depths of 2, 4, 6 and 11.5 feet below land surface. The pressure plate apparatus was used to estimate the soil suction-moisture content relationship of core samples from borings at the above depths. UNSAT2 simulations indicate that ponded water percolating through the infiltration gallery and native soil adjacent to the tank pit would reach the water table (30 feet below the land surface) within eight days. The circulation rate and coverage of the treated water are shown to be strongly controlled by the geology. The design of the circulation system must account for lithologic heterogeneities for the system to be effective.
