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4 SUMMARY OF FINDINGS AND RECOMMENDATIONS <br />' A summa of current groundwater conditions and PSC's recommendations summary g ons are <br /> contained in the following sections <br /> 4.1 Groundwater Conditions <br /> PSC's data from this current monitoring event and from previous assessments <br /> indicates that the highest concentrations of petroleum hydrocarbon compounds are <br /> centered around the former gasoline USTs near wells MW-1, SP-1, and PZ-1 Since <br /> the installation of new air sparging well SP-A, petroleum hydrocarbon concentrations <br /> in most monitoring well groundwater samples have decreased significantly, typically <br /> ' by a factor of 10 <br /> The plume of groundwater impacted with detectable hydrocarbons may be less than <br /> 100 feet wide and 550 feet long, elongated in the same east-northeast direction as <br /> groundwater flow The lateral extent to the north, south, and west has been delineated <br /> by historic, non-detectable, petroleum concentrations measured in groundwater <br /> samples collected from wells in those directions To the east, a TPH-G concentration <br /> of 100 µg11 was measured in a groundwater sample collected from CPT-3 during the <br /> May 1999 site investigation This CPT-3 sample did not contain benzene, and the <br /> laboratory characterized the TPH-G analysis as being uncharacteristic of a typical <br /> gasoline, suggesting that the impact was more characteristic of degraded petroleum <br /> Oxygenates concentrations have also displayed a reduction since the installation of <br /> sparging well SP-A The oxygenate compound DIPE has been detected in samples <br /> collected from wells in relatively close proximity to the source The oxygenate <br /> compound TBA, not observed this quarter, has only been detected sporadically <br /> PSC recommends continuation of routine groundwater monitoring to assess evolving <br /> subsurface conditions at the Earthgrains facility <br />' 4.2 Remedial Recommendations <br /> Groundwater sample and air vapor analytical results suggest that the air sparging and <br /> venting remedial operations are proving successful in removing dissolved phase <br /> gasoline contaminants in soil and groundwater PSC will continue remedial actions in <br /> an effort to ultimately achieve case closure for this site <br /> II <br /> Apri12002 <br /> r Groundwater Monitoring And <br /> Air Spargmg Well Installation Report <br /> The Earthgrams Baking Company <br /> 2651 South Airport Way <br /> Stockton,California <br /> Prepared for THE EARTHGRAINS BAKING C40MPANY Prepared by Philip Services Corp <br /> H\ENV5624001325121362EG\Swckwn\Smckion10402mon doc May 21,2002 <br />