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Executive Summary The fate and transport model VLEACH(Version 2 2 0 2) was used to predict future groundwater impacts from MTBE+impacted soils previously detected beneath the subject site Cambria used site specific data to calibrate the model Site specific parameters that are most sensitive to the model output include MTBE concentrations,area, depth to groundwater,fraction organic carbon, soil texture,and soil water content Published data were used for MTBE chemical parameters The VLEACH model was run using maximum soil MTBE concentrations that were detected in soil samples collected during August 1996 A fine-grained silt loam soil was used as the representative soil profile covering an estimated area of 176 feet2 The VLEACH model output predicts that the highest MTBE groundwater concentrations will occur after 1 year and concentrations will be reduced by over 50% after 10 years After 57 years, the model predicts that MTBE concentrations will fall below state and federal regulatory levels for drmkuig water These findings agree reasonably well with the actual groundwater analytical data collected from • well MW-1, located closest to the MTBE source, where the highest MTBE concentrations were ' at observed 2 to 3 years following soil sample collection The actual data also indicate that MTBE' 7 groundwater concentrations fell below regulatory Ievels in the first quarter 2004 or approximately 8 years following soil sample collection. These findings are significantly less than the predicted timeframe of 57 years because the initial conditions used in the model overestimate the actual MTBE mass between the depths of 9 and 14 fbg Consequently, the modeled MTBE concentrations require a longer period of time to leach from the soil profile and attenuate in groundwater The site characteristics and modeling results supporting this conclusion are discussed in detail below Site Characteristics Soil Types: Soils beneath the subject site are classified primarily as fine-grained soils (silt and clay) with lesser amounts of coarse-grained sediments (sands) to the total explored depth of 45 fbg Soil samples collected from well boring MW-1 were classified as sandy silt(AM)from the near surface to a depth of approximately 10 fbg The ML contained approximately 10% clay, 70% silt, and 20% fine sand Soils beneath 10 fbg and extending to a depth of approximately 23 S fbg contained approximately 25% clay, 65% silt, and 10% fine to medium sand and were classified as clayey silt (MH) Below the clayey silt layer, sandy silt and silty sands (SM) were . encountered to the total depth of 32 fbg r