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AMBRIA 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 drinking 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 observed 2 to 3 years following soil sample collection The actual data also indicate that MTBE groundwater concentrations fell below regulatory levels 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 approximately 9 and 14 fbg As a result, the modeled MTBE concentrations require a longer period of time to leach from the soil profile and attenuate in groundwater Current MTBE concentrations in well MW-1 have decreased to levels near or below the method reporting limit, which suggests that the MTBE mass in soils near this well are no longer present The decline in groundwater elevations over the last several years can not be accounted for in the model However, based on MTBE's higli solubility and low adsorption to soil, and the model r prediction that most of the MTBE would reach groundwater in 1 year, it is unlikely that the decrease in groundwater elevation would allow for MTBE mass accumulation in soils located between depths of 15 and 25 fbg {past and present depths to groundwater, respectively} Consequently, it is our technical opinion that the majority of the MTBE mass previously identified in soils near well MW-1, appears to have leached to groundwater as demonstrated by the VLEACH model and supported by the groundwater analytical data An estimate of the projected maximum plume extent resulting from the modeled addihional impacts of groundwater. As discussed above, the model predicts, and empirical data have shown, that the maximum concentrations of MTBE have occurred in groundwater at this site and have subsequently declined to levels at or near the method reporting lirrut It appears that the plume had reached its maximum size in the past and has attenuated to levels at or near the method reporting hunt Based on these findings there is no expectation that the plume will increase in size in the future - 0323 7