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Canepa's Car Wash 6230 Pacific Avenue,Stockton,CA Second Quarter Groundwater Monitoring Report,May 2006 • Page 7 of$ concentrations of benzene and total xylenes (236 1ig/L and 143 6 µg/1., respectively) in MW-11 were generally elevated compared to historic levels for that well In addition, 1,2-DCA was detected for the first time in MW-2 and MW-1 l (at concentrations of 480 pg/L and 7 9 µg/L, respectively) None of the contaminants of concern were detected at or above the laboratory reported detection limits in monitoring wells MW-4, MW-9, and MW-12D All other measurements and laboratory data for were generally consistent with previous quarters and trends The system operated approximately 1,427 hours between January 31, 2006 and May 18, 2006, which is 56% of the time The system has been in operation for a total of 7,690 hours since it began operating (November 1, 2004) through May 18, 2006 The groundwater treatment system removed petroleum hydrocarbons from approximately 376,792 gallons of groundwater during the second quarter of 2006, and a total of approximately 1,912,290 gallons have been treated by the system as of May 18, 2006 The average groundwater pumping rate between January 31, 2006 and May 18, 2006 was approximately 4 4 gallons per minute Condor estimates that approximately 65 41 pounds of gasoline have been removed from the groundwater during the second quarter of 2006 and approximately 372 5 pounds of gasoline since the pump and treat system was placed in operation on November 1, 2004 The soil vapor extraction system removed approximately 108 8 pounds of gasoline from the soil during the second quarter of 2006 and approximately 10,637 4 pounds of petroleum hydrocarbons since the SVE system was placed in service on November 1, 2004 FUTURE WORK Annual groundwater monitoring of wells MW-5, MW-6, MW-7, and MW-10 is currently conducted during the third quarter It is anticipated that a new monitoring well in the vicinity of MW-8 (which was destroyed on April 11,2003)and an additional down-gradient well will be installed within the next year The next quarterly groundwater monitoring event is scheduled for July 2006 and,as the annual event, will include sampling of monitoring wells MW-1 through MW-7 and MW-9 through MW-12D, and soil vapor extraction well SV-4 As monitoring wells MW-1 and MW-11 are dedicated groundwater extraction wells,they may also be sampled separately to meet the Groundwater Discharge Permit requirements The SVE and groundwater pump and treat system will be kept in operation and periodically maintained The soil vapor portion of the system is monitored weekly with a PID and monthly with laboratory analyses The groundwater portion of the system is monitored monthly and water samples are collected from the first and second carbon tanks The sample collected from the outlet of the second carbon tank will be held by the laboratory and not analyzed unless detectable concentrations are confirmed from the sample collected from the outlet of the first carbon tank Samples will be analyzed for BTEX, EtOH, EDB, MTBE, DIPE, ETBE, TAME,and TBA by the laboratory using EPA Method 8260B Condor proposed reducing quarterly sampling of MW-9 and MW-12D to an annual basis in the First Quarter Groundwater Monitoring Report and Treatment System Status Update dated April 26, 2006 This change would be conditional upon the receipt of an authorization letter from Mr Jeffrey Wong of the SJCEHD LIMITATIONS AND SIGNATURE This report was prepared under the direct supervision of a Certified Hydrogeologist in the State of California The standard of care for all services performed or furnished by Condor is commensurate with the care and skill ordinarily used by a member of the environmental profession practicing under similar conditions at the same time in the same locality Condor is not responsible for the accuracy and completeness of information collected and developed by others CONDOR