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1 Site History
<br /> Boyett Petroleum(419 S.Main St.,Manteca)
<br />' Page 9 of 9
<br /> • described in Condor's Additional Groundwater Investigation, Monitor Well Destruction and Installation,
<br /> and Interim Remediation Pump Test Report, dated January 30, 2004.
<br /> On November 26, 2003, a Condor representative was on site to measure water levels and collect
<br /> groundwater samples for MTBE laboratory analysis from monitor wells MW-2, MW-3, MW-4R, MW-6
<br /> through MW-11, and EW-1. Monitor well MW-6 was dry, and MW-2 and MW-7 contained an
<br /> insufficient water column for sampling. Due to an error by the field technician, MW-8 was not measured
<br /> or sampled during the November 2003 monitoring event. Laboratory analytical results indicated that
<br /> 1 MTBE was detected in the groundwater samples collected from MW-4R, MW-9, MW-10, MW-11, and
<br /> EW-1. The laboratory analytical results indicated a slight increase in the concentration of MTBE detected
<br /> in the groundwater sample collected from MW-9 relative to the previous sampling event conducted in
<br /> October 2003. Depth to water measurements indicated that the average groundwater elevation was 12.44
<br /> feet on November 26, 2003. The extremely low groundwater levels in the monitor wells prompted
<br /> concerns regarding the reliability of water level measurements; the water level in MW-2 and MW-7 may
<br /> have been residual groundwater ponded in the cap at the base of the well casing. An estimated
<br />' groundwater gradient of 0.0315 ft/ft towards the southwest was calculated using water level data from
<br /> monitor wells MW-3, MW-4R, and MW-10.
<br /> 1 On December 31, 2003, a Condor representative was on site to measure water levels and collect
<br /> groundwater samples from monitor wells MW-2, MW-3, MW-4R, MW-6 through MW-11, and EW-1.
<br /> Laboratory analytical results indicated that MTBE was detected in the groundwater samples collected
<br /> from MW-4R, MW-7, MW-9, MW-10, MW-11, and EW-1. TAME was detected in the groundwater
<br /> samples collected from MW-7, MW-10, and MW-11. The concentration of MTBE in the groundwater
<br /> samples collected from MW-4R and MW-10 increased relative to the previous sampling event conducted
<br /> on November 26, 2003. The concentration of MTBE in the groundwater samples collected from MW-9,
<br /> MW-11, and EW-1 decreased relative to the previous sampling event. Groundwater elevations increased
<br /> by 1.70 feet relative to the previous monthly monitoring event (November 2003). Static water level
<br /> ' measurements generally indicated a groundwater flow direction to the north. An estimated groundwater
<br /> gradient of 0.0057 ft/ft towards the north was calculated using Water level data from monitor wells MW-
<br /> 2, MW-6, and MW-8.
<br /> On March 4, 2004, a Condor representative was on site to measure water levels and collect groundwater
<br /> samples from monitor wells MW-2, MW-3, MW-4R, MW-6 through MW-11, and EW-1. Laboratory
<br /> analytical results indicated that BTEX constituents, gasoline oxygenates/additives other than MTBE and
<br /> TAME, and TPH-G were not detected at or above the laboratory reported detection limits in the
<br /> groundwater samples collected from the monitor wells. MTBE was detected in the groundwater samples
<br /> collected from MW-3, MW-4R, MW-7 through MW-11, and EW-1. TAME was detected in the
<br /> groundwater sample collected from MW-10. The concentration of MTBE in the groundwater samples
<br /> collected from MW-3, MW-4R, MW-8, MW-10, and EW-1 increased relative to the previous sampling
<br /> event conducted on December 31, 2003. The concentration of MTBE in the groundwater samples
<br /> collected from MW-7, MW-9, and MW-11 decreased relative to the previous sampling event.
<br /> Groundwater elevations increased by 1.56 feet relative to the previous monitoring event (December
<br /> 2003). An estimated groundwater gradient of 0.0048 ft/ft towards the northeast was calculated using
<br /> water level data from monitor wells MW-2, MW-6, and MW-8.
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