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February 2003 groundwater sample from well MW -1 indicated an increase in petroleum hydrocarbon concentrations. However, petroleum hydrocarbon concentrations remained relatively stable in groundwater samples collected from other groundwater monitoring wells at the Site. PSC submitted the April 14, 2003 Remedial Action Completion Report to the San Joaquin County Environmental Health Department (SJCEHD). The report presented a Site Conceptual Model, which characterized the release, subsurface conditions, and associated risks to potential receptors. PSC determined that potential routes of exposure were improbable or incomplete and requested that SJCEHD consider granting closure of the environmental case. SJCEHD requested that additional site investigation be performed in their January 9, 2004 response letter. PSC submitted the February 20, 2004 Subsurface Investigation Work Plan to SJCEHD and the work plan was approved. f\PV ip J) Subsurface Investigation(2004) W ��fUfrr��erOO�Q 1 In June 2004, PSC performed an ad ' ional subsurface investigation. Continuous soil lithology, from ground surface :to a depth 100 feet BGS was evaluated at boring CPT -A using CPT technology. Seven CPT borings (A through G) were drilled in the vicinity of the former 10,000 -gallon diesel UST and former fuel pump island. Soil samples were collected from the borings at depths ranging from 10 to 35 feet BGS. Groundwater samples were collected from three of the borings (CPT -A, CPT -C, and CPT -F) at depths ranging from 60 to 100 feet BGS. TPH-g, BTEX, fuel!' oxygenates [tertiary butyl alcohol (TBA), methyl tertiary butyl ether (MTBE), di -isopropyl ether (DIPE), ethyl tertiary butyl ether (ETBE), and tertiary amyl methyl ether (TAME)], and fuel additives [1,2-dibromoethane (1,2 -DBA) and 1,2-dichloroethane (1,2 - DCA)] were not detected in any of the soil samples. Grab groundwater samples collected from the borings contained TPH-g, BTEX, DIPE, and 1,2 -DCA. TPH-g was detected at concentrations up to' 8,400 micrograms -per -liter (µg/L) at 60 feet BG PSC reported the results from the investigation in the June 2004 Site Investigation Report. n &,r - L I At the time of the 2004 subsurface investigation, groundwater samples were also collected from all onsite monitoring wells and two nearby private wells. This monitoring event indicated that the lateral extent of impacted groundwater was largely contained within the Earthgrains property boundaries. Based on the findings of this investigation, PSC recommended performing one more groundwater monitoring event, and then preparing a report which would propose either site closure or additional remedial work. SJCEHD approved the recommendations in a letter dated September 24, 2004. Subsurface Investigation (2006) r ETIC conducted a soil and groundwater quality investigation at the Site in November 2006. SL_AIR SCM and RI WP 8