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d,4' ;S w �o CPT -2, and CPT -3). The analytical data for soil are included in Table 1 / uThe analytical data for groundwater are included in Table 2. i, The CPT investigation indicated that the lateral extent of impacted groundwater was largely contained within the Earthgrains property boundaries. PSC reported the results of this investigation in the May 1999 Subsurface Investigation and r Groundwater Monitoring Report. Air Sparging/Soil Vapor Extraction (2000 through 2002) L Vapor extraction well VW -1 was installed and an additional AS/SVE pilot test was performed in June 2000. The pilot test results indicated that the combined use of these technologies would be an effective method of remediating petroleum hydrocarbons at the site. Operation of a full- scale AS/SVE remediation system was initiated on April 25, 2001. PSC installed a new air sparging well (SP -A) on March 14, 2002, upon determining that air injection at well SP -1 was not adequately remediating the petroleum hydrocarbon impact in groundwater. In December 2002, the remediation system was disengaged, since its effectiveness to remove contaminants had become limited. Post -remediation monitoring was perfonned to evaluate the concentrations of petroleum hydrocarbons in groundwater and the stability of the plume. The �. 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 v 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. The February 20, 2004 Subsurface Investigation Work Plan was submitted to and approved by SJCEHD. 4 L_ Subsurface Investigation (2004) In June 2004, PSC performed an additional subsurface investigation. Continuous soil lithology, from ground surface to a depth of 100 feet bgs was evaluated at boring CPT -A using CPT technology. Seven CPT borings 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 (RIPE), ethyl tertiary butyl ether (ETBE), and tertiary amyl methyl ether (TAME)], and 7