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5470, and after 57 years the MTBE concentration decreases to below 5 micrograms per liter (ugR-) Summary: The model results demonstrate that the highest MTBE concentrations are observed after first year This observation corresponds reasonably well with the actual groundwater analytical data collected from well MW-1 Historical groundwater analytical data indicate that this well,which was sampled for the fust time during April 1998 containedug/L MTBE, and n 9 t; maximum concentrations were detected in October 1998 (1,800 ug/L) and October 1999 (1,640 ug/L) This tuneframe is approximately 2 to 3 years following soil sample collection Since October 1999, MTBE concentrations in well MW-1 have decreased to non-detect Ievels, winch suggests that the MTBE mass in soils near this well are no Ionger present The modelled MTBE concentrations do not agree well with actual MTBE concentrations detected in well MW-1 because the initial conditions used in the model overestimate the actual MTBE mass between the depths of 9 and 14 fbg This is also why the modeled MTBE concentrations require a longer period of time to leach from the soil profile and attenuate in groundwater A i The decline in groundwater elevations over the last several years can not be accounted for in the model However, based on MTBE's high solubility and low adsorption to soil, and the model 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, appear to have leached to groundwater as demonstrated by the VLEACH model and supported by the groundwater analytical data i 0323 4