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41 Canepa's Car wash 6230 Pacific Avenue,Stockton,CA Second Quarter Groundwater Monitoring Report,April 2005 Page 8of10 and air-stripper, resulting in an overall destructive efficiency of approximately 98 5% A work sheet 40 showing the calculations for the current quarter is included in Attachment D SUMMARY The second quarter groundwater monitoring event field data and laboratory analytical results indicate that some change has occurred since the first quarter 2005 This change is probably related to the operation of the remediation system First, the cone of depression around MW-1 had a greater radius of influence than measured during the previous quarter The lateral extent of detectable concentrations of benzene has decreased in size principally on the eastern perimeter Concentrations of MTBE decreased in the pumping wells, MW-1 and MW-11, while the concentration increased in MW-3 All other measurements and laboratory data were generally consistent with previous quarters and trends The system was operating 744 hours between March 1, 2005 and June 1 2005, or 33% of the time The groundwater treatment system has removed petroleum hydrocarbons from 205,410 gallons of groundwater during the second quarter of 2005 The system was operational 2,174 hours between November 1, 2004 and June 1, 2005, or 38% of the time The groundwater treatment system has removed petroleum hydrocarbons from 504,626 gallons of groundwater The average groundwater pumping rate between March 1, 2005, and June 1, 2005, was approximately 4 gallons per minute Condor estimates that approximately 51 pounds of gasoline have been removed during the second quarter of 2005 and 126 pounds of gasoline have been removed from groundwater since the pump and treat system was placed in operation on November 1, 2004 The soil vapor extraction system has removed approximately 40 pounds of gasoline during the second quarter of 2005 and 9,760 pounds of petroleum hydrocarbons from the soil since the Soil Vapor Extraction system was returned to service on November 1, 2004 The data collected from the monitoring wells and soil vapor influent stream indicate that the winter/spring rise in groundwater elevation has resulted in a sharp reduction in the soil vapor removal rate The data collected from the groundwater extraction and treatment system indicate that the system continues remove hydrocarbons at a steady rate and from a radius of influence that is larger than reported during the first quarter 2005 FUTURE WORK The next quarterly groundwater monitoring event is scheduled for July 2005 and will include quarterly sampling of monitoring wells MW-1, MW-2, MW-3, MW-4, MW-9, MW-11, MW-12D and SVE well SV-4, and annual monitoring of wells MW-5, MW-6, MW-7, and MW-10 Monitoring wells MW-1 and MW-11 are dedicated groundwater extraction wells and may be sampled separately to meet the sanitary sewer district 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 will be monitored weekly with a PID, monthly with laboratory analyses, and the groundwater portion monitored monthly Water samples will be collected from the first and second carbon tanks on a monthly basis 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, MTBE, and TBA by the laboratory using EPA Method 8260B � i LIMITATIONS AND SIGNATURE -This report was prepared under the direct supervision of a Registered Geologist 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 i �� CONDOR