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yI First Quartet'Groundwater Monitoring Report March 2003 Boyett Petroleum,419 S.Main,Manteca,CA Page 5 TABLE 4 Laboratory Analytical Results (March 21, 2003) Oxygenates/Additives B T E X TP Other Oxygenates/Additives Detection 0.5 0.5 0.5 1.0 0. 0.5-5.0 Limits: g� 4tg/1- lig/L µ� m�r5B8 ll� Analytical Method: 8260B 8260B 82608 8260B 90 8260B Sample LD. 3761-MW1-3/21/03 <2.0 <2.0 <2.0 <4.0 <0.05 2,800 5.9 TAME 3761-MW2-3/21/03 <0.5 <0.5 <0.5 <1.0 <0.05 <0.5 <0.5-5.0 3761-MW3-3/21/03 <0.5 <0.5 <0.5 <1.0 <0.05 <0.5 <0.5-5.0 3761-MW6-3/21/03 <0.5 <0.5 <0.5 <1.0 <0.05 <0.5 <0.5-5.0 3761-MW7-3/21/03 <2.0 <2.0 <2.0 <4.0 <0.05 6,400 33 TAME 3761-MW8-3/21/03 <0.5 <0.5 <0.5 <1.0 <0.05 <0.5 <0.5-5.0 3761-MW9-3/21/03 <0.5 <0.5 <0.5 <1.0 <0.05 2.5 <0.5-5.0 Unit Conversions: Analytical gg/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 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 FUTURE WORK/RECOMMENDATIONS Condor recommends the following: ➢ Continue quarterly groundwater monitoring at the site. ➢ Redevelop monitor wells MW-1, MW-2, MW-3, MW-6, MW-7, MW-8, and MW-9. The monitor wells contain a high percentage of sediment and require redevelopment. Y Properly destroy damaged monitor wells MW-4 and MW-5. ➢ Replace monitor well MW-4 with a new monitor well screened from 10 to 25 feet below ground surface. ➢ Increase the groundwater monitoring frequency. Water levels in monitor wells MW-1 through MW- 3 and MW-6 through MW-9 should be measured on a monthly basis and groundwater samples should be collected for MTBE laboratory analysis for a period of six consecutive months. The objective of this increase in monitoring frequency is to garner additional information pertaining to the site's historically highly-variable groundwater gradient, which may help explain the fluctuations in the MTBE levels recorded in the groundwater samples collected in the site monitor wells. ➢ Prepare a problem assessment work plan(PAWP) to further investigate the lateral and vertical extent of groundwater contamination at the site. The proposed locations of shallow and deep borings are shown in Figure 8, attached. The purpose of the shallow borings is to collect groundwater grab . samples to evaluate the lateral extent of groundwater contamination in the apparent downgradient +a1� GONOOR