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1 16 1 4 SUMMARY OF FINDINGS AND RECOMMENDATIONS A summary of current groundwater conditions and PSC's recommendations are contained in the following sections 4.1 Groundwater Conditions PSC recommends continuation of routine groundwater monitoring to assess subsurface conditions and the plume of gasoline-impacted groundwater at the Earthgrains facility PSC's data from this current monitoring event and from previous assessments indicates that the plume of groundwater impacted with detectable hydrocarbons is approximately 100 feet wide, and some 550 feet long, elongated in the same east-northeast direction as groundwater flow The highest concentrations of petroleum hydrocarbon compounds are centered around the former gasoline USTs near wells MW-1, SP-1, and PZ-1 The lateral extent to the north, south, and west had been delineated by historic, non- detectable, petroleum concentrations measured in groundwater samples collected from wells in those directions To the east, a TPH-G concentration of 100 µg/1 was measured in a groundwater sample collected from CPT-3 during the May 1999 site investigation This CPT-3 sample did not contain benzene, and Acculabs characterized the TPH-G analysis as being uncharacteristic of a typical gasoline, suggesting that the impact was more characteristic of degraded petroleum The oxygenate compound DIPE has been detected in samples collected from wells in relatively close proximity to the source The oxygenate compound TBA, not observed this quarter, has only been detected sporadically PSC will continue to monitor oxygenate levels to assess site conditions 1 4.2 Remedial Recommendations Groundwater sample and air vapor analytical results suggest that the air sparging and soil venting remedial operations are beginning to prove successful in removing dissolved phase gasoline contaminants in groundwater However, it is PSC's opinion that the remediation system requires augmenting to improve and increase the rate of I contaminant removal Expected decreases in petroleum hydrocarbon concentrations, particularly in wells MW-1 and SP-1, have not yet been observed Therefore, PSC proposes to discontinue air sparging at SP-1, install a new sparge well (SP-A), and resume air infection at that point Sparge well SP-A will be located just to the west of MW-1 as shown in Figure 2 PSC has scheduled this new well to be installed during the week of March 11, 2002 11 January 2002 Groundwater Monitoring Report The Earthgralns Baking Company 2651 South Airport Way Stockton,Califorma Prepared for THE EARTHGRAINs BAKING COMPANY Prepared by Philip Services Corp H\ENV\62400132\121382EG1Stockton\Swckton10102mon d" February 15 2002