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7.2 Man-made Receptors An updated Environmental Sensitive Receptors map (Appendix A, Figure 2), renamed to Water Well Receptor Map, has been prepared to reflect both the visual reconnaissance and a well construction record's request from the California State Department of Water Resources (DWR) in Sacramento, California for the Site vicinity. The revised map accurately reflects the 56 active wells identified within a half-mile of the site. This well inventory does not include the monitoring wells associated with the Site or wells that have been destroyed. Well Completion Reports for map ID wells #53, #54, and #55 are T- 2 presented in Appendix A. Well #56, noted below, was visually identified during the site reconnaissance, however was not listed in the DWR report. A well summary is present below: Map ID#53 Ma ID#54 Map ID#55 Map ID#56 Legal 407580 55296 44095 VISUAL observation Lat-Long 02N 06E 26P 02N 06E 26 2N 06E-35099 VISUAL observation Total De th ft—b s 240 204 264 VISUAL observation Screen Interval ft 200-240 156-204 199-264 VISUAL observation Diameter ID 6 10 14 VISUAL observation Use Domestic irrigation Municipal Municipal < r„ Year 1993 1 1960 1970 VISUAL observation 8.0 MASS EVALUATION 8.1 Contaminant Mass In-Place The majority of the contaminant mass is represented by adsorbed-phase petroleum compounds, specifically TPHd. Mass estimates were derived using adsorbed Site contaminate concentrations from H borings and samples collected during the 1997 UST closure activity (Refer to Table 3 which depicts a summary of soil analytical data). Dissolved-phase contaminant mss estimates were derived from the limited number and trace concentrations detected in the three monitoring wells and from groundwater collected during the completion of Site soil borings (Refer to Table 3, which depicts a summary of groundwater analytical data). A detailed summary of the Site contaminant volume and mass calculations are provided in Appendix B. A summary of the estimated contaminant mass is provided below. They represent the estimated contaminant mass remaining at the Site. The soil mass summary table is highlighted by TPHd, which represents the vast majority of adsorbed phase contaminant mass, likely beneath the former UST basin and the existing USTs. Soil: ln- lace Groundwater: In-place Analyte Mass lbs Analyte Mass Ibs j BTEX 0.035 BTEX 0.0028 TPHg 0.156 TPHg 0.0977 r•" TPHd 9.51 TPHd 0.0777,,t L MTBE 0.076 MTBE 0.0043 TBA 0.213 TBA 0.00 1,2-DCA 0.00 1,2-DCA 0.0026 r Workplan to Conduct Subsurface Soil Vapor Intrusion Study �Tc ATC Project 54.26874.0001 Page 5 r