ARCHIVED REPORTS_QUARTERLY GROUNDWATER MONITORING AND REMEDIATION STATUS REPORT AND UPDATED SITE CONCEPTUAL MODEL 2009

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i Mr. James L. Barton April 8, 2009 Page 6 ' During the first quarter 2009, the SVE system operated for approximately 1,650 hours and extracted an estimated 188 pounds of hydrocarbons between the end of Fourth Quarter 2008 and the end of First Quarter 2009. ' Air Sparge System Status The AS system operated continuously between O&M visits during the first quarter 2009. The AS system ' was shut down for the quarterly groundwater sampling event, and consistent with the SVE system operation, a shut down may have been required during O&M visits. During the first quarter 2009 (January 2, 2009 through March 23, 2009), the AS system operated for approximately 1,653 hours. A summary of the air sparge system operating period is included in Table 1. Discussion ' The upgraded remediation system, which was restarted on July 30, 2008, was designed to address the regions beneath the Site with elevated concentrations of TPHg and benzene. The operational and groundwater monitoring data demonstrate that these regions are effectively being addressed with regard to groundwater remediation. Decreasing trends of dissolved concentrations in the Site's monitoring wells, particularly benzene concentrations in MW-8D and both TPHg and benzene in MW-4, MW-6, and MW-11 ' are leading indicators of the effectiveness of the upgraded remediation system. Although slight increases in dissolved contaminant concentrations were observed in the monitoring results for MW-3 and MW-25D for first quarter 2009, when compared to the fourth quarter 2008 results, the concentrations are consistent with those observed historically and generally are an order of magnitude lower than the highest concentrations observed for the respective monitoring well. AECOM expects the concentration trends to continue downward in the second quarter 2009. ' Future Work Quarterly monitoring events for the Site will continue to be performed by G-R. AECOM will submit the ' status of remediation activities pursuant to requirements of the CAO, the groundwater monitoring and sampling report prepared by G-R, and the updated SCM. On August 21, 2008, ENSR Corporation (now AECOM) received a voice-mail message from the CVWB ' requesting updates on the status of the remediation systems at the Site. On January 22, 2009, in an email from the CVWB, the request was modified to ask for providing notification only if there was a discovery of a problem with the system that required system shut down, and directed that such a notification shall be ' within 24 hours of the discovery. The email update AECOM provided to the CVWB during the first quarter 2009 and the CVWB response on January 22, 2009 are provided in Attachment H. ' Remarks/Signatures The interpretations in this report represent AECOM's professional opinions and are based, in part, on ' information supplied by the client pertaining to monitoring and remedial activities that occurred prior to AECOM's involvement with the Site, which began in 2003. These opinions are based on currently available information and are arrived at in accordance with currently accepted hydrogeologic and engineering practices at this time and location. Other than this, no warranty is implied or intended. ' AECOM AECOM Environment