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performed on March 14, 2002 when it was indicated that air infection at SP-1 was not resulting in an adequate decrease of petroleum impact in groundwater The remediation system was disengaged in December 2002 when it had reached a point where its effectiveness in removing contaminants became limited and to evaluate whether petroleum concentrations in groundwater samples would remain stable An increase in petroleum concentrations were noted in the MW-1 groundwater sample collected in February 2003, however, concentrations remained relatively stable in samples collected from other wells in the area of impact PSC submitted the April 14, 2003 Remedial Action Completion Report to SJCEHD that presented a Site Conceptual Model for this facility, which is a characterization of the release, subsurface conditions and associated risks to potential receptors PSC found that potential routes of exposure were improbable e or incompleteand requested"that SJCEHer granD considting d i closure for this UST site SJCEHD responden_their 3anuary 9;2004-letter that directed additional site investigation be performed The February 20, 2004 Subsurface Investigation Work Plan, which proposed details of site work, was submitted to and approved by SJCEHD In June, 2004, PSC performed an additional subsurface investigation Continuous soil lithology, from ground surface to a depth of 100 feet was evaluated at the CPT-A boring location using an electronic cone penetrometer system Seven CPT borings (CPT-A, -B, -C, -D, -E, -F, and -G) were driven in the vicinity of the former gasoline USTs Soil samples were collected from ' the borings and were submitted for the analysis of TPH-G, BTEX, TBA, MTBE, ETBE, TAME, 1,2-DCA, and EDB Groundwater samples were collected at three of the boring locations and were submitted for the same analytical parameters This CPT soil investigation indicated that the residual petroleum hydrocarbon impact that remained after the 1987 excavation a sufficiently addressed by the soil vapor extraction sys em that op rated at the site andthat the mass of impact i❑ the vadose zone is negligible Tliis CPT groundwater investigation was used to assess the vertical extent of petroleum impact at the site Based on the data obtained, PSC conservatively estimates ✓ that the vertical extent is approximately 90 feet Although, the relatively higher petroleum concentrations appear to occur at depths shallower than 70' Results from this investigation were reported in PSC's June 2004 Site tInvestigation Report Additionally, groundwater samples were collected from all of the on-site monitoring wells and two nearby private wells This groundwater monitoring_event indicated that the lateral extent of impacted groundwater is largely contained within the Earthgrain's property boundaries In addition, historical and current decreases of petroleum impact to groundwater have been observed;which are likely due to natural degradation rand the use of air sparging s a remedial method Based on the findings of s 6-- �- Quarterly Groundwater Monitoring Report October 2004 The Earthgratns Company Facility 2651 South Airport Way-Stockton,California Prepared for SARA LEE BAKERY GROUP Prepared by Philip Services Corp H\ENIA62400132U21382EGLStockton Airport Wayllnvestigatron and Quarterly ReportslQuarterly Report 10_2004 doc December 09,2004