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5 SUMMARY AND RECOMMENDATIONS Groundwater monitoring has been conducted at this facility since 1987 to evaluate groundwater quality A summary of the current site conditions and a recommendation for subsequent work are as follows • During this event, the depths to groundwater among the wells average at about 48 68' (-32 01 MSL) The groundwater flow was generally easterly to southeasterly at a gradient of about 2 94 x 10-3 feet per linear foot ' • The total depth measurements indicated that at air sparging wells SP-1, SP-5, and SP-6 an appreciable amount of fill material has entered the wells In y&5 order to conduct further sampling or remediation activities at these locations, J rpt the air sparge points will need to be developed qJJ • The benzene concentrations appear to be increasing in down-gradient wells Concentrations in the suspected source area appear to be increasing as well This may be strongly influenced by the variations in groundwater elevations • The current BTEX concentrations were evaluated against the California Drinking Water Maximum Contaminant Levels (MCL)s Based on the current groundwater monitoring data, the MCL for benzene has been exceeded in wells MW-1, MW-7, MW-11, MW-12, SP-1, SP-4, SP-6, PZ-1, �� 1 and PZ-2 The MCL for Toluene has been exceeded in well SP-i 4 X4 IX'-- ' t ,t rn � • The TPH-G concentrations appear to be increasing in wells MW-11, MW-12, SP-1, SP-4, and PZ-1 The remaining wells remained stable or decreased in concentration 11 • The analyte 1,2-DCA was detected in wells MW-5, MW-8, MW-10 SP-31— and SP-5 PSC was unable to discern a pattern for where this analyte was detected relevant to the former UST's 1,2-DCA is not a component of any product previously stored in the former USTs • The Contaminant Mass estimation indicated that a total mass for TPH-G was at 70 7 Kg and the total mass for benzene was at 1 8 Kg In comparison to the previous estimation, it appears that the contaminant mass has decreased significantly • The groundwater fate and transport model for benzene indicated that the associated C,concentrations decrease rapidly at a conservative distance of 30 feet from the source to be within the associated MCL The model for TPH-G indicated that the concentrations decrease rapidly at a conservative distance of 24 feet from the source to be within the goal of 50 mg/L 34 Quarterly Groundwater Monitoring Report October 2004 The Earthgrains Company Facility 2651 South Airport Way-Stockton,California Prepared for SARA LEE BAKERY GROUP Prepared by Philip Services Corp H\ENV\62400132\121382EQSiocktun Airport WayUnvesugatton and Quarterly ReporWQuarterly Report 10_2004 doc December 09,2004