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i• <br /> Fourth Quarter 2005 Groundwater Monitoring Report <br /> Boyett Petroleum,419 S.Main,Manteca,CA <br /> Page 4 <br /> • collected from MW-9 and MW-10,and above the MCL in the groundwater samples collected from MW- <br /> 11 and EW-1. MTBE was not detected at or above the laboratory reported detection limit in the <br /> groundwater samples collected from the other monitoring wells at the site. <br /> Concentrations of MTBE in groundwater at the site have decreased significantly during the last three <br /> years, as shown on the graph in Figure 5, attached. There has also been a corresponding reduction in the <br /> estimated size of the MTBE plume during the same time period. The decrease in concentrations and the <br /> reduction in the estimated size of the plume suggest that intrinsic bioremediation has been taking place <br /> within the MTBE plume at the site. The concentrations of dissolved oxygen decreased in all of the site <br /> monitor wells since the September 2005 monitoring event. The increase in MTBE concentrations in MW- <br /> 10, MW-11, and EW-1 suggest that intrinsic bioremediation may be limited by the amount of dissolved <br /> oxygen available in the aquifer. <br /> BTEX and TPH-G have not been detected in any of the site monitor wells since December 2001. Condor <br /> recommends that all groundwater samples be analyzed for gasoline oxygenates/additives only. <br /> MTBE has not been detected in the groundwater samples collected from monitor wells MW-2 and MW-6 <br /> for more than two years. The last time MTBE was detected in a water sample collected from monitor well <br /> MW-8 was in March 2004. Since contaminants have not been detected in these three wells for seven or <br /> more quarters, Condor recommends that the sampling frequency for MW-2, MW-6, and MW-8 be <br /> reduced to once a year. <br /> LIMITATIONS <br /> This report was prepared under the direct supervision of a Professional Geologist in the State of <br /> • California. The standard of care for all services performed or furnished by Condor is commensurate with <br /> the care and skill ordinarily used by a member of the environmental profession practicing under similar <br /> conditions at the same time in the same locality. Condor is not responsible for the accuracy and <br /> completeness of information collected and developed by others. <br /> 4 <br /> �/� CONDOR <br />