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Mr. Alan Buehler, P.G., RWQCB May 16, 2017 Work Plan for Additional Site Investigation Project No. 2092-2057-01 2057 South El Dorado Street, Stockton, CA Page 2 additional 372 cubic yards of impacted soil was excavated from this former UST area. This soil (about 639 tons) was hauled offsite to Forward Landfill for proper disposal. Assessment of subsurface conditions was initiated in March 2004, with the advancement of exploratory soil borings and groundwater monitoring wells. To date, approximately 24 exploratory soil borings (B1 through B8, CPT-1, CPT-2, MW-1 through MW-8, EW-1, EW-2, and VW-1 through VW-4) have been completed at the Site, with 14 of these borings converted to groundwater monitoring or remediation wells. The locations of the borings and wells are depicted on Figure 2, and Table 1 presents a summary of well construction information. In 2004, a groundwater monitoring and sampling program was initiated at the Site. Groundwater levels beneath the property have generally increased during the 13 year monitoring period, from approximately 32 feet below ground surface (bgs) in 2004 to a maximum of approximately 20 feet bgs in 2011 and 2013. An east groundwater flow direction, with variations to the southeast and northeast, has predominately been observed. Gasoline range organics (GRO), diesel range organics (DRO), benzene, toluene, ethylbenzene, and total xylenes (collectively BTEX), methyl tertiary butyl ether (MTBE), tertiary butyl alcohol (TBA), tertiary amyl methyl ether (TAME), di-isopropyl ether (DIPE), and 1,2-dichloroethane (1,2-DCA) have been detected in samples collected beneath the Site. In general, high levels of fuel contaminants are present in shallow groundwater onsite. Figures 4 through 7 illustrate concentrations and the approximate extent of GRO, benzene, MTBE, and TBA in shallow groundwater using data collected during the first quarter 2017. The lateral extent of impact to shallow groundwater is not fully defined east of the Site. In May 2013, two CPT boring clusters were advanced onsite in order to conduct soil type profiling and to collect depth discrete groundwater samples. Fuel contaminant impact was detected in samples extending up to 120 feet bgs, the maximum depth explored. Soil vapor extraction (SVE) was completed at the Site for approximately 1.5 years, from April 14, 2011 until October 1, 2012. During this time, approximately 155 pounds of GRO was removed from the subsurface in the vapor phase. The SVE system was shut down due to low contaminant mass extraction rates. In our opinion, further remediation of the vadose zone does not appear necessary, due to the combination of SVE and excavation remediation work. Increases in groundwater levels beneath the property in recent years have likely resulted in decreased ability to remove fuel contaminants in the vapor phase by SVE. 10Quick N Save #2 \ Work Plans \Q-N-5#2 work plan 2017.doc STRATUS