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� AMBRIA Model Settings: As shown in Appendix A, Profile 1 presents the Model Settings, Profile Structure, Chemical, and graphical representation of the model output for MTBE. The Model Settings are shown in the Case Settings and Initial Conditions tables. For the Case Settings table the simulation timestep or model recalculation interval was set at 0.1 years, and the simulation length was set at 100 years. The cell number was set at 30, which equals the depth to groundwater. We used 30 fbg as the depth to groundwater because this was the approximate ' :"--.,,,depth of the groundwater sample collected from CPT-1. The representative area is not shown in the model settings (but is part of setup) and is 2,400 feee. The surface water recharge rate is 0.17 feet per year. This value is approximately 10% of the annual rainfall for the area and assumes that this is the rate of water entering a paved surface and moving through the unsaturated zone. The output timestep was set at 1 year and allows the user to view model output results on a yearly interval between zero and 100 years. For the Initial Conditions table we selected the MTBE concentrations between depths of approximately 20 and 29 fbg,which ranged from 1.3 to 27 mg/Kg in boring CPT-1. The starting MTBE concentration was 1.3 mg/Kg and concentrations were assumed to increase by 1.4 mg/Kg each foot below 20 fbg ending at 25 fbg. Below 25 fbg,concentrations were assumed to increase by 5 mg/Kg ending at a final concentration of 27 mg/Kg at 29 fbg. For the soil profile, a 30-foot thick layer of sand was selected as the soil texture because this appears to be the most representative soil based on the CPT log. The input parameters for bulk density, effective porosity (total porosity in this model), water content, and fraction organic carbon value were based on research values. The chemical parameters used for MTBE were published values. Model Results: The VLEACH model output predicts that the highest MTBE groundwater concentrations will occur after 2 years and concentrations will continue to decrease thereafter with a reduction of over 85% after 10 years. After 30 years, the model predicts that MTBE concentrations will fall below state and federal regulatory levels for drinking water. The modeling, however, does not consider MTBE mass removal by remedial activities, which were performed between 2000 and 2001, and consequently the model predictions after 2 years are not applicable to this site. Additionally,the model does show remaining MTBE mass in soils below a depth of approximately 21 fbg,however,as discussed below,SVE testing demonstrated that the remaining Mi BE mass was augligib1c. 0324 3