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' Fourth Quarter,2002 Quarterly Groundwater Monitoring Report Boyett Petroleum,419 S.Main,Manteca,CA Page 4 (TBA), di-isopropyl ether (DIPE), ethyl-tent butyl ether (ETBE), tert-amyl methyl ether (TAME), 1,2- dichloroethane (1,2-DCA), and 1,2-dibromoethane (EDB). Laboratory analytical results for the groundwater samples collected at the site on December 27, 2002, indicate that BTEX constituents and TPH-G were not detected in the groundwater samples collected from MW-1, MW-2, MW-3, MW-6, MW-7, MW-8, and MW-9. The selected gasoline oxygenates/additives ' were not detected at or above the laboratory reported detection limits in the groundwater samples collected from MW-6. MTBE was detected in the groundwater samples collected from MW-1, MW-2, MW-3, MW-7, MW-8, and MW-9. TAME was detected in the groundwater samples collected from MW- 1 and MW-7. In addition, TBA was detected in the groundwater sample collected from MW-l. The laboratory analytical results for the December 2002 monitoring event relative to the previous sampling event conducted in September 2002 indicate a decrease in the concentration of MTBE detected in samples collected from MW-2 and MW-7, and an increase in the concentration of MTBE detected in MW-1,MW- 3, MW-8, and MW-9. The laboratory analytical results for MW-6 are consistent with historical data. The laboratory analytical results for the fourth quarter 2002 quarterly groundwater monitoring event are ' presented in Table 4,below. A map representing MTBE isoconcentration contours in shallow groundwater is included as Figure 4 in Attachment A. A graph showing MTBE concentrations versus time in monitor wells MW-1, MW-7, and MW-8 is presented as Figure 5, Attachment A. Historical groundwater 1 monitoring data are presented in Attachment D. Laboratory certificates of analyses and chain of custody record are included in Attachment E. ' TABLE 4 • Laboratory Analytical Results (December 27,2002) ' Oxygenates/Additives B T E X TPH-G MTBE Other Oxygenates/Additives Detection 0.5 0.5 0.5 1.0 0.05 0.5 0.5-5.0 Limits: µg/L µBIL µg/L µg/L mg/L µg/L µg/L Analytical Method: 826013 8260B 8260B 8260B 8015M 826013 8260B Sample I.D. ' 3 761-M W 1-12127102J<O5 <2.0 <2.0 <4.0 <0.05 23,000 63 TSA;75 TAME 3761-MW2-12/27/02 <0.5 <0.5 <1.0 <0.05 11 <0.5—5.0 ' 3761-MW3-12127102 <0.5 <0.5 <1.0 <0.05 12 <0.5—5.0 3761-MW6-12/27/02 <0.5 I <0.5 <0.5 <L0 <0.05 <0.5 <0.5—5.0 ' 3761-MW7-12/27/02 <2.0 <2.0 <2.0 <4.0 <0.05 3,500 18 TAME 376 1-MW8-12/27/02 <0.5 <0.5 <0.5 <1.0 <0.05 93 <0.5--5.0 ' 3761-MW9-12/27/02 <0.5 <0.5 <0.5 <1.0 <0.05 2.1 <0.5—5.0 Unit Conversions: Analytical µg/L:parts per billion(ppb) BTEX=benzene,toluene,ethyl benzene,and total xylenes. mg/L:parts per million(ppm) TPH-G=total petroleum hydrocarbons,quantified as gasoline. MTBE=methyl tertiary-butyl ether EtOH=ethanol AdIIL TBA=tertiary-butanol DIPE=di-isopropyl ether ETBE=ethyl tertiary-butyl ether TAME=tertiary-amyl methyl ether 1,2-DCA= 1,2-dichloroethane ' EDB=1,2-Dibromoethane CONDOR