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16 1 3 REMEDIAL ACTIVITIES On April 25, 2001, PSC initiated operation of an air sparging and soil venting 1 remediation system to address subsurface petroleum hydrocarbon impact Air sparging was initially performed in well SP-1 However, PSC suspected that air sparging at the SP-1 location was not resulting in an adequate decrease of petroleum ' impact in groundwater Therefore, new sparging well SP-A was drilled and completed on March 14, 2002 New sparging well SP-A was placed within the area of highest groundwater impact, about 10 feet southwest of well MW-1 Air sparging into ' SP-A was performed by supplying an approximate volume of 5 standard cubic feet per minute (scfm) Due to the malfunction of the original air sparging compressor, PSC installed a new air sparging compressor on September 5, 2002 ' Venting was performed by withdrawing an approximate volume of 25 to 35 scfm of soil gas from well VW-1 Soil gas was treated through a 1,000 pound granular activated carbon (GAC) adsorber and then through a 160 pound GAC adsorber Permits to operate the remediation system and emit treated air have been obtained from the SJAPCD Emission reports were routinely submitted to the SJAPCD The system was monitored weekly to ensure efficient operation and permit compliance A summary of system operation, vapor concentrations and total pounds of removed contaminant is included in Table 8 Vapor concentrations of influent and effluent streams are reported in Table 8 columns labeled C(>nf) and C(eff), respectively 1 Vapor extraction flow rates are labeled Q(mf) and Q(ef#) Pounds of contaminant removed by the soil vapor extraction system are tabulated under the PE columns Based on vapor sample concentrations, total mass of contaminants removed is calculated to be over 1,000 pounds As shown in Table 8 and the associated graph of influent air sample results, currently recovered vapors are reaching lower levels compared to those at the onset of remedial activities When first initiated, influent gas was recovered at a typical rate of at least 20 pounds per week or more Currently, influent gas is recovered at a typical rate of ' less than 2 pounds per week PSC considered that the remedial system's effectiveness to treat subsurface impact was nearing its end Therefore, the system was disengaged in December 2002 to evaluate whether petroleum concentrations in groundwater ' samples would remain stable The groundwater samples collected in February 2003 were the first obtained since the remediation system was disengaged As described in Section 2 3 1, petroleum hydrocarbon concentrations were somewhat higher in the February 2003 sample from MW-1 than those measured from samples collected during the three previous quarters However, petroleum concentrations in recent samples from SP-1, SP-2, PZ-1 and PZ-2 appear to be relatively stable 14 ' Remedial Action Completion Report The Earthgrams Company Facility 2651 South Airport Way Stockton California Prepared for Tilt EARTHGRAINS COMPANY Prepared by Philip Services Corp H TN V\62400132\121382EG1StockionSStocktonVRcmedlm&CompleuonRepo"doc April 14 2003