SITE INFORMATION AND CORRESPONDENCE

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Tracy Cold Storage Addendum to Case Closure Request Page: 2 • No additional construction data is available for the South Well. A video log of the South Well will not provide information regarding the placement or condition of the well seal.. Ground water analytical data collected over the past few years,-which indicate no detectable contaminants in the lower aquifers, provide the best evidence that the well seal for the South Well is intact and functioning properly. • During more than 40 years of facility operation substantial,volumes of water have been extracted with no demonstrated impact to ground water quality. The South Well served as the primary water well during this period. This includes the period of time that the maximum threat to ground water quality existed following the UST leak in the 1970's. Over the past five years multiple water samples have been collected from each well, both before and after the remedial excavation, with no detectable levels of gasoline or gasoline constituents detected in either the North Well or South Well. Table 1 below summarizes the analytical data for the two wells. The analytical data covers the period of time that the South Well was providing the bulk of the plant's water needs and coincides with the period of time which would have presented the greatest risk to ground water quality. TABLE 1 Summary of Ground Water Analytical Results, Water Supply Wells Analyte Sample Sample Benzene Toluene Ethyl Total TPH-Gas Location Date Benzene Xylenes (Fig/L) (ltg/L) (µg/L) (FLg/L) tmg/L) 12/21/95 ND ND ND ND ND North Well 09/30/98 ND ND ND ND ND 12/18/98 ND ND ND ND ND 06/22/99 ND ND ND ND ND 12/21/95 ND ND ND ND ND South Well 09/30/98 ND ND ND ND ND 12/18/98 ND ND ND ND ND 06/22/99 ND ND ND ND ND ND=Not detected above the laboratory detection limit. Future risk to the producing aquifer through the South Well is minimal for the following reasons: • Ground water contaminant levels have decreased dramatically at MW-IA, installed adjacent.to the former UST location. The levels are expected to continue to decline over time as natural attenuation processes operate. The degradation of residual contamination will also decrease the likelihood of contaminant migration. Thus, the potential risk to the South Well will continue to decline as the residual contaminants are naturally attenuated.