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Extended site Characterization Report: 7500 West Eleventh street, Tracy, CA. Page 14 5.3.4 Groundwater_Quality at Apparent Source of Secondary Plume Monitoring Wells MW-12 and MW-12A form a cluster that was installed to investigate the condition of soil and groundwater at the apparent source of a secondary plume of affected groundwater that has been identified beneath the property. They are located, as shown on Figure 2, on the southern boundary of the site near a structure that serves as a truck service bay. That location, which is also as shown on Figure 3, is at the southern end of Pipe Trench No. 2, from which piping of unknown function was exhumed when - the underground storage tanks were removed from the site in 1998. -E Well MW-12 has a total depth of 35.5 ft. and its screened interval is between 30 and 35 ft. BGS. Well MW-12B has a total depth of 50.5 ft. and its screened interval is between ' 45 and 50 ft. BGS. The logs and construction details for both wells are included in Appendix A 5.4 Summary of Groundwater-quality Monitoring Wells Following is a summary of all of the groundwater monitoring wells SJC had installed by the time the extended site characterization program was complete. Well Total Screened Purpose No. Depth Interval MW- 1 22 ft. 7 to 22 ft. Investigate up-gradient extent of affected groundwater. MW-2 22 ft. 7 to 22 ft. Investigate western lateral extent of affected groundwater. --- MW-3 22 ft. 7 to 22 ft. Investigate concentrations of analytes of concern in area where the principal release of hydrocarbon fuels occurred. MW-3A 36 ft. 30 to 35 ft. Investigate vertical extent of affected groundwater in area where principal release of fuel hydrocarbons occurred. MW-313 51 ft. 45 to 50 ft. Investigate vertical extent of affected groundwater in area where principal release of fuel hydrocarbons occurred MW- 4 22 ft. 7 to 22 ft. Investigate groundwater quality near former - , sites of underground tanks. sic