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Report:Groundwater-qualihi Monitoring—January 20, 2003: 7500 West Eleventh Street, Tracy, CA. Page 14 t 3.0 RECOMMENDATIONS } SIC has the following recommendations for the ongoing environmental management of G ; the subject site. 3.1 Close Wells Penetrating Protective Aquitards As was detailed in SJC's report for the October 25, 2002 round of groundwater-quality monitoring, when the well-head box that protects the top of the casing of Monitoring Well MW-12 was opened on that date, it was found to be filled with contaminated water. The depth of water in the well-head box was sufficient to have submerged the casing cap. i-: Although clear, the water had a chemical odor reminiscent of some types of solvents and ? its surface was affected by a slight sheen (The San Joaquin Company Inc. 2002a). Fortunately, the seal on the well-casing cap had prevented the contaminated liquid from flowing into the well and there was no evidence in the analyses performed on the samples recovered on October 25 that any of that fluid had affected the groundwater beneath the site. nitoring Well MW-12 is located on the 7500 West Eleventh As is shown on Figure 2, Mo Street property to the east of the truck service bay situated behind the Casa Mendoza = restaurant. On October 25, 2002, the service bay was being used to repair and maintain very large, truck-mounted, concrete pumping equipment. 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 in the unconfined, near-surface aquifer (see Figure 3 for the hydrostratigraphy). If a similar spillage to that which was observed on October 25, 2002 occurs close to Well MW-12A and contaminated water were to gain entry to the deep aquifers beneath the site i via the well casing, the quality of the groundwater in that deeper aquifer will be compromised. As was the case for Monitoring Wells MW-3A and MW-3B, which also penetrate through aquitards that protect the deeper water-bearing zones beneath site, Monitoring Well MW-12A was installed at a location, to the total depth and with the screened interval specifically directed by the SCEHD. Due to the risks to which such wells expose the deeper, uncontaminated, confined aquifers, SJC's California Registered Geotechnical Engineer who is the Professional Engineer of Record for the characterization and remediation of the 7500 West Eleventh Street site strongly recommended that such installations should not be made. However, despite the engineer's objections, they were installed at the insistence of unlicensed SCEHD staff. Four consecutive rounds of groundwater-quality have verified, as could have been readily concluded and was so stated by SJC, two years ago based on the results of the previously reported stratigraphic and geochemical studies that were undertaken at the site when it was first characterized in 2000 (The San Joaquin Company Inc. 2001d), water in the deeper aquifers that lie at depth of less than 50 ft. BGS, but beneath the unconfined, near- surface aquifer at the 7500 West Eleventh Street site, are free of any contaminants. As we sic