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Site History Boyett Petroleum(419 S.Main St.,Manteca) Page 10 of 10 collected from the monitoring wells. MTBE was detected in the groundwater samples collected from MW-7, MW-10, and MW-11. The concentration of MTBE in the groundwater samples collected from MW-7, MW-10, and MW-11 decreased relative to the previous sampling event conducted on March 4, 2004. MTBE was not detected at or above the laboratory reported detection limit of 0.5 µg/L in the groundwater samples collected from MW-3, MW-4R, MW-8, MW-9, and EW-1, which indicated a decrease from the concentrations detected in the groundwater samples collected from these wells during the previous sampling event. Groundwater elevations decreased by 2.28 feet relative to the previous monitoring event (March 2004). An estimated groundwater gradient of 0.0217 ft/ft towards the south was calculated using water level data from monitoring wells MW-2, MW-6, and MW-8. On September 28, 2004, a Condor representative measured the depth to water at monitoring wells MW-2, MW-3, MW-4R, MW-6 through MW-11, and EW-1, and collected groundwater samples from monitoring wells MW-3, MW-4R, MW-8, MW-9, MW-11, and EW-1. Monitoring wells MW-2, MW-6, and MW-7 were dry. MW-10 purged dry and did not recover, so a groundwater sample was not collected from the well. Laboratory analytical results indicated that BTEX constituents, gasoline oxygenates/additives other than MTBE, and TPH-G were not detected at or above the laboratory reported detection limits in the groundwater samples collected from the monitoring wells. MTBE was detected in the groundwater samples collected from MW-9, MW-11, and EW-1. The concentration of MTBE in the groundwater samples collected from MW-9, MW-11, and EW-1 increased relative to the previous sampling event conducted on June 24, 2004. MTBE was not detected at or above the laboratory reported detection limit of 0.5 µglL in the groundwater samples collected from MW-3, MW-4R, and MW-8. A groundwater gradient was not calculated for the third quarter monitoring event. Only four shallow wells had sufficient water for depth to water measurements. Three of the wells (MW-3, MW-4R, and MW-8) are aligned in a nearly straight line. MW-10 purged dry and did not recover. It is likely, therefore, that the water in the . well was perched water and the depth to water measurement may not have accurately reflected the groundwater elevation in the vicinity of MW-10. P:13000_pd\3761 Boyett Manteca13761C Boyett Manteca Groundwater Monitoring\Reports14Q041Boyett Manteca Site History.doc