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<br /> Site History
<br /> Boyett Petroleum(419 S.Main St., Manteca)
<br /> Page 10 of 10
<br /> collected from the monitoring wells. MTBE was detected in the groundwater samples collected from
<br /> 1\4W-7, MW-10, and MW-11. The concentration of MTBE in the groundwater samples collected from
<br /> MW-7, MW-10, and MW-11 decreased relative to the previous sampling event conducted on March 4,
<br /> 2004. MTBE was not detected at or above the laboratory reported detection limit of 0.5 �ig/L in the
<br /> groundwater samples collected from MW-3, MW-4R, MW-8, MW-9, and EW-1, which indicated a
<br /> decrease from the concentrations detected in the groundwater samples collected from these wells during
<br /> the previous sampling event. Groundwater elevations decreased by 2,28 feet relative to the previous
<br /> monitoring event (March 2004). An estimated groundwater gradient of 0.0217 ft/ft towards the south was
<br /> calculated using water level data from monitoring wells MW-2, MW-6, and MW-8.
<br /> On September 28, 2004, a Condor representative measured the depth to water at monitoring wells MW-2,
<br /> MW-3, MW-4R, MW-6 through MW-11, and EW-1, and collected groundwater samples from monitoring
<br /> wells MW-3, MW-4R, MW-8, MW-9, MW-11, and EW-1. Monitoring wells MW-2, MW-6, and MW-7
<br /> were dry. MW-10 purged dry and did not recover, so a groundwater sample was not collected from the
<br /> well. Laboratory analytical results indicated that BTEX constituents, gasoline oxygenates/additives other
<br /> than MTBE, and TPH-G were not detected at or above the laboratory reported detection limits in the
<br /> groundwater samples collected from the monitoring wells. MTBE was detected in the groundwater
<br /> samples collected from MW-9, MW-11, and EW-1. The concentration of MTBE in the groundwater
<br /> samples collected from MW-9; MW-11, and EW-1 increased relative to the previous sampling event
<br /> conducted on June 24, 2004. MTBE was not detected at or above the laboratory reported detection limit
<br /> of 0.5 µ.g/L in the groundwater samples collected from MW-3, MW-4R, and MW-8. A groundwater
<br /> gradient was not calculated for the third quarter monitoring event. Only four shallow wells had sufficient
<br /> water for depth to water measurements. Three of the wells(MW-3, MW-4R, and MW-8) are aligned in a
<br /> nearly straight line. MW-10 purged dry and did not recover. It is likely, therefore, that the water in the
<br /> well was perched water and the depth to water measurement may not have accurately reflected the
<br /> groundwater elevation in the vicinity of MW-10.
<br /> On December 29, 2004, a Condor representative was on site to measure water levels and collect
<br /> groundwater samples from monitoring wells MW-2, MW-3, MW-4R, MW-6 through MW-11, and EW-1.
<br /> Laboratory analytical results indicated that BTEX constituents, gasoline oxygenates/additives other than
<br /> MTBE, and TPH-G were not detected at or above the laboratory reported detection limits in the
<br /> groundwater samples collected from the monitoring wells. MTBE was detected in the groundwater
<br /> samples collected from MW-4R, MW-7, MW-9, MW-10, MW-11, and EW-1. MTBE was not detected at
<br /> or above the laboratory reported detection limit of 0.5 pg/L in the groundwater samples collected from
<br /> MW-2, MW-3, MW-6, and MW-8. Groundwater elevations increased by 3.28 feet relative to the previous
<br /> monitoring event (September 2004). An estimated groundwater gradient of 0.0036 ft/ft towards the north
<br /> was calculated using water level data from monitoring wells MW-2,MW-6, and MW-8.
<br /> P:13000_pd\3761 Boyett Manteca1376IC Boyett Manteca Groundwater Monitoring\Reports11Q051Boyett Manteca Site History.doc
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