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contained within the April 25, 1994 Groundwater Monitoring Well <br /> Installation Report and then again in PSC's August 31, 2000 Remedial <br /> Action Work Plan These tests identified naturally occurring microbes <br /> in the facility's soil that grew on and digested petroleum <br /> 1 hydrocarbons <br /> Groundwater samples were collected in December 1996 and analyzed <br /> for various parameters to indicate the occurrence of natural intrinsic <br /> biodegradation of the petroleum hydrocarbon impact Laboratory <br /> results were submitted within PSC's February 21, 1997 Quarterly <br /> 1 Groundwater Monitoring And Natural Biodegradation Assessment <br /> Report <br /> The tested parameters included alkalinity, dissolved oxygen (DO), <br /> oxidation-reduction (redox)potential, pH, specific conductivity, <br /> temperature, nitrate, sulfate, and ferrous iron PSC observed definite <br /> correlations between petroleum hydrocarbon concentrations and the <br /> location of samples within the plume using the DO, nitrate, sulfate and <br /> redox values These results and the observed decreases in petroleum <br /> concentrations over time (prior to active remediation) indicate that <br /> naturally active biodegradation is occurring in groundwater at this site <br /> 2.4 Estimate of Contaminant Mass <br /> PSC calculated residual TPH mass in groundwater for conditions that were <br /> present on October 18, 2000 (prior to active air sparging and soil venting <br /> remediation) and again on February 5, 2003 using current laboratory data As <br /> �.� shown in Table 7, the TPH mass in groundwater before remedial activities <br /> were initiated is estimated at almost 70 kg (154 pounds) In contrast, the TPH <br /> mass in groundwater on February 5, 2003 is estimated at 33 kg (73 pounds), <br /> which indicates the remediation system's effectiveness in treating impacted <br /> groundwater at the facility <br /> Boring soil sample analytical results suggest that residual petroleum <br /> hydrocarbon impact in the vadose zone is relatively negligible Based on this <br /> data, it appears that overexcavation in the vicinity of the gasoline USTs was <br /> successful in removing most of the mass of impacted soil However, the mass <br /> of contaminants calculated to have been removed from the site's soil vapor <br /> extraction system (over 1,000 pounds as discussed in Section 3) exceeds that <br /> estimated in groundwater prior to system start-up The additional mass <br /> removed, over that originally estimated, may be located within the vadose <br /> zone in areas not identified from boring soil samples <br /> 13 <br /> Remedial Action Completion Report <br /> The Earthgrams Company Facility <br /> 2651 South Airport Way <br /> Stockton California <br />' Prepared for -1 FIE EARTHCRAINS COMPANN Prepared by Ph111p SiF-vices Corp <br /> H%ENV}62400132U21382EG1Stockton%Stockton%RemedtalCompleoonReportdoc April 14 2003 <br />