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' Mr. Nuel Henderson Page 4 of 5 VAPOR EXTRACTION SYSTEM ACTIVITIES ' Vapor Extraction System Operation The faulty thermal oxidizer burner was replaced and the system was started on February 10, 2005 to collect samples as per San Joaquin Valley Air Pollution Control District permit requirements. Vapor samples were collected on February 10, 2005 and submitted to state-certified Air Toxics Laboratories for the analysis of TPHg, BTEX and MTBE by EPA Method TO-3. The system ' was then shut down pending the laboratory results. Field notes are included in Attachment D. Analytical data are summarized in Table 4. Laboratory reports and chain of custody documentation are included in Attachment E. ' Additional repairs are necessary before the system can be placed back in operation. ' RECOMMENDATIONS ' Groundwater Monitoring and Sampling Reduce the sampling frequency for wells that are monitoring the plume of contamination ' originating from the onsite release to an annual schedule. Given the massive quantity of historical groundwater data at this site, continued quarterly sampling is not warranted. We ' also recommend that sampling responsibility for the wells that are affected by the offsite release(s) be transferred to the appropriate responsible parties. ' Vapor Extraction System Operation The vapor extraction system is currently undergoing repair. We will conduct a period of ' testing as soon as the repairs have been completed. Site Conceptual Model and Meeting I ' As requested by EHD, a Site Conceptual Model report is in preparation and will be submitted to your office in the near future. Following your review of the report we recommend that a ' meeting be scheduled to consider alternative approaches to future corrective action at the subject site and adjacent contamination sites. 1 ' G:\GROLNDZE\RoFK\QMRUOOS\lqni2oo5.doe