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Site History Boyett Petroleum(419 S.Main St.,Manteca) Page 4 of . location should be useful in evaluating whether the UST area is the likely source of the elevated levels of MTBE in groundwater in the northwestern portion of the site. On December 27, 2002, a Condor representative was onsite to measure water levels in and collect groundwater samples from all nine monitor wells as part of the fourth quarter 2002 quarterly groundwater monitoring event. Monitor well MW-5 was dry, and MW-4 contained significant sediment and was purged dry during sampling and did not recharge; thus, groundwater samples were not collected No floating product, sheen, or odors associated with petroleum hydrocarbons were observed in any of the wells sampled during the fourth quarter 2002 monitoring event. All of the groundwater monitor wells sampled contained a significant amount of suspended sediment. Laboratory analytical results for the groundwater samples collected at the site on December 27, 2002, indicated that BTEX and TPH-G were not detected at or above the laboratory reported detection limits in any of the groundwater samples collected from the monitor wells. Selected gasoline oxygenates/additives were not detected at or above the laboratory reported detection limits in the groundwater sample collected from MW-6. MTBE was detected in the groundwater samples collected from MW-1 through MW-3 and MW-7 through MW-9. TAME was detected in the groundwater samples collected from MW-I and MW-7. In addition, TBA was detected in the groundwater sample collected from MW-1. Static water level measurements collected on December 27, 2002, generally indicated a groundwater flow direction to the north/northeast, a reversal from that reported in the Groundwater Monitoring Report, Third Quarter 2002, dated January 16, 2003. In the Fourth Quarter Groundwater Monitoring Report, December 2002, Condor made the following recommendations: 1) quarterly monitoring of the site should continue; 2) all of the monitor wells contained a significant percentage of sediment and should be redeveloped, 3) a new monitor well should be installed south of MW-9 between the historically high MTBE concentrations in MW-1 and the . USTs/dispenser island; and 4) on a monthly basis, the water levels in the site's monitor wells should be measured and groundwater samples be collected for MTBE laboratory analyses for a six month period. The primary objective of this increase in monitoring frequency would be 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 for MW-2 and MW-8 and the historically elevated levels of MTBE in groundwater samples collected from MW-1 and MW-7. P:13761 Boyett Manteea\3761 Boyett MantecalQMRslMarch 20031Boyett Manteca Site I istory.doc