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Site History Boyett Petroleum(419 S.Main St.,Manteca) Page 9 of 9 described in Condor's Additional Groundwater Investigation, Monitor Well Destruction and Installation, and Interim Remediation Pump Test Report, dated January 30, 2004, On November 26, 2003, a Condor representative was on site to measure water levels and collect groundwater samples for MTBE laboratory analysis from monitor wells MW-2, MW-3, MW-4R, MW-6 through MW-11, and EW-1. Monitor well MW-6 was dry, and MW-2 and MW-7 contained an insufficient water column for sampling. Due to an error by the field technician, MW-8 was not measured or sampled during the November 2003 monitoring event. Laboratory analytical results indicated that MTBE was detected in the groundwater samples collected from MW-4R, MW-9, MW-10, MW-11, and . EW-1. The laboratory analytical results indicated a slight increase in the concentration of MTBE detected in the groundwater sample collected from MW-9 relative to the previous sampling event conducted in October 2003. Depth to water measurements indicated that the average groundwater elevation was 12.44 feet on November 26, 2003. The extremely low groundwater levels in the monitor wells prompted concerns regarding the reliability of water level measurements; the water level in MW-2 and MW-7 may have been residual groundwater ponded in the cap at the base of the well casing. An estimated groundwater gradient of 0.0315 ft/ft towards the southwest was calculated using water level data from monitor wells MW-3, MW-4R, and MW-10. On December 31, 2003, a Condor representative was on site to measure water levels and collect groundwater samples from monitor wells MW-2, MW-3, MW-4R, MW-6 through MW-11, and EW-1. Laboratory analytical results indicated that MTBE was detected in the groundwater samples collected from MW-4R, MW-7, MW-9, MW-10, MW-11, and EW-1. TAME 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-4R and MW-10 increased relative to the previous sampling event conducted on November 26, 2003. The concentration of MTBE in the groundwater samples collected from MW-9, MW-11, and EW-1 decreased relative to the previous sampling event. Groundwater elevations increased by 1.70 feet relative to the previous monthly monitoring event (November 2003). Static water level measurements generally indicated a groundwater flow direction to the north. An estimated groundwater gradient of 0.0057 ft/ft towards the north was calculated using water level data from monitor wells MW- 2, MW-6, and MW-8. P 17l1l1l5 rri1T7F1 Rmivt+M-t-oa'17F1 4 An-tt W- PI.-R.CRC Ro+.nrt\RPnnrtslllTAR11 f1f1dM-m'tt M-t-Cita TJictn Anr -