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B-1, SB-3, SB-4, and UST closure samples S-4-FD1, S-3-FD2, S-19-E1n, and S-24-E1b 4.edS6 -`fir` (refer to Table 2 for a summary of the soil analytical results). Ole- ' Figure 4 through 14 depict the estimated aerial extent of hydrocarbon and fuel oxygenate -- impact using analytical data collected from shallow and deep soil sample intervals. The areas exhibiting greater contaminant concentrations were observed near the existing pump island (S-3-FD2), along the former product piping trench identified by soil boring SB-3 (SB3- 35'), and the northwest corner of the current UST basin (S-24-E1 b). 6.2 Groundwater The monitoring well network at the Site includes three groundwater monitoring wells, MW-1, MW-2, and MW-3. The monitoring wells were completed to approximately 65 feet bgs with groundwater monitoring activities ongoing since 2004. During that time, Site-specific chemicals of concern have been below their respective laboratory detection limit with the exception of the following: 0.58 pg/l of xylenes reported in MW2 and 0.68 pg/1 of MTBE reported in MW1 on January 19, 2007 (refer to Table 3 for a summary of the groundwater analytical results). �1 (�(!�� J-&�.& 2- Groundwater Groundwater samples were also collected during the completion of on-Site soil borings. Petroleum hydrocarbon and fuel oxygenates concentrations (TPHd, TPHg, benzene, MTBE, and 1,2-DCA) from groundwater collected from on-Site soil borings exceeded their respective Tier 1 ESL as published by the San Francisco Bay Regional Water Quality Control Board (SF RWQCB) in November 2007 and/or the California Primary and Secondary Maximum Contaminant Levels (MCL). TPHd and TPHg detected in SB-3 on May 22, 2003, exceeded their established Tier 1 ESL of 100 pg/l. Benzene, also detected in SB-3 on May 22, 2003, exceeded the established ESL and MCL of 1.0 pg/l. MTBE - detected in soil borings SB-3 and SB-4 exceeded the ESL and secondary MCL of 5 pg/l, .. was below the primary MCL of 13 pg/I. 1,2-DCA detected in SB-3 on May 22, 2003, exceeded the ESL and MCL of 0.5 pg/l. None of the remaining analytes of interest detected in the groundwater samples collected from the on-site soil borings exceeded their respective ESLs or MCLs (Refer to Figures 15 through 19, which depict dissolved isoconcentrations for selected compounds). 7.0 RECEPTOR SURVEY 7.1 Wetlands ATC reviewed the USFWS National Wetlands Inventory map for the USGS Stockton West Quadrangle map, which is maintained by the USDA in San Joaquin County, California. The review of the USFWS National Wetlands Inventory map indicated that there are ponds identified as designated wetlands on the large industrial property to the south-southwest. There are other wetlands beyond the radius of concern to the west and north. As requested by the EHD, ATC has included a copy of the USFWS National Wetlands Inventory map showing the Site location and the ponds identified as designated wetlands is included in Appendix A, Figure 1. Workplan to Conduct Subsurface Soil Vapor Intrusion Study ��// �� ATC Project 54.26874.0001 v Page 4