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Report: Groundwater-quality Monitoring—Octo$er 25,2002: 7500 West Eleventh Street, Tracy, CA. Page 14 =_ As is shown on Figure 2, Monitoring Well-12 is located on the 7500 West Eleventh Street property to the east of the truck service bay that is situated behind the Casa Mendoza restaurant. The service bay is currently being used to repair and maintain very large, truck-mounted, concrete pumping equipment. . r Based on the data for the October 25, 2002 sampling round that is presented in Table 2, there is no apparent deterioration to groundwater quality in Monitoring Well MW-12 beyond that already present due the presence of components of fuel hydrocarbons. Apparently, the sealed casing cap prevented any of the contaminated material from passing down through the casing to the water table. Nevertheless, SJC considers the occurrence to be of a serious nature. t Monitoring Well MW-12 is located only a few feet from Monitoring Well MW-12A, which is 35 ft. deep and penetrates through the clay aquitard that protects a deeper sand aquifer from contamination by fuel hydrocarbons present at the depth of the water table and in the first shallow sand aquifer that lies beneath the site (see Figure 3 for hydrostratigraphy). If a similar spillage were to occur close to Well MW-12A and contaminated water were to gain entry to the deep aquifers beneath the site via the well .'{ casing, the quality of that deeper aquifer will be compromised. As was discussed in Section 2.4 of this report, an unknown compound was detected in the sample recovered from Monitoring Well MW-12A on October 25, 2002, but, because similar unidentified � i compounds were also recovered from Monitoring Wells MW-3A and MW-3B on that date, it appears unlikely that the analyte detected in the sample from MW-12A had its source at the site of the chemical spillage that obviously occurred in the area immediately around MW-12. SJC has strongly recommended that Well MW-12A and all similar deep wells on the site that penetrate through the clay aquitard that protects the deeper sand aquifers be closed on the earliest date possible. 'i - I { 'i i 1 sic j