ARCHIVED REPORTS_SEMI ANNUAL GROUNDWATER MONITORING OCTOBER 2010

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A=COM Mr. James L. L. Barton Regional Water Quality Control Board -Central Valley October 27, 2010 Page 5 Remediation System Update Residual dissolved concentrations of petroleum hydrocarbons beneath the Site have been volatilized, extracted, and treated through the operation of a combined air sparge (AS)and soil vapor extraction (SVE) remediation system. Vapors from the SVE system are vented through two 1,000-pound granulated activated carbon (GAC) vessels prior to discharging to the atmosphere in accordance with the San Joaquin Valley Air Pollution Control District(SJVAPCD) permit to operate number N-5879-1-1. Figure 12 depicts the location of the remediation compound and a plan layout of the remediation well network. AECOM submitted a Proposed Remediation System Rebound Testing Schedule (Rebound Test) dated August 31, 2009, to the CVWB, requesting the shut-down of the AS/SVE system for rebound testing. The CVWB approved the Rebound Test in a letter dated September 8, 2009, and AECOM turned off the AS/SVE system on September 15, 2009. After a shutdown period of six weeks, AECOM collected groundwater samples on October 29, 2009, from four key wells (MW-2, MW-3, MW-8D, and MW-11)to evaluate rebound. Based on results from this first rebound evaluation sampling event (October 2009), AECOM re-started the AS/SVE system on November 16, 2009,for a six-week period of operation. The system was subsequently shut down on December 28, 2009, in preparation for a second rebound evaluation sampling event. On February 19, 2010, approximately 7.5 weeks following system shut-down, the semi-annual monitoring event(which served as the second rebound event)was conducted. As noted in the Semi-Annual Groundwater Monitoring and Remediation Status Report for the First Quarter of 2010, AECOM recommended keeping the remediation system turned OFF until the completion of the first soil vapor investigation sampling event, in order to evaluate the soil vapor risks without interference of the induced air movement in the subsurface by the AS and/or SVE systems. AECOM installed three soil vapor wells on May 13, 2010, and conducted the first soil vapor investigation sampling event on May 20, 2010. Based on the February 2010 groundwater monitoring analytical results (TPHg >2,000 pg/L in MW-3), and the criteria agreed to during the January 21, 2010, meeting with the CVWB (see "Discussion" below), AECOM re-started the AS system (only)on June 3, 2010. The AS system operated continuously throughout the remainder of the second quarter 2010. On July 9, 2010, AECOM observed that, although the AS system was operating, the AS system was not delivering air to the subsurface in the intended manner, and corrected its functionality the same day. In preparation for the third quarter semi-annual groundwater monitoring event(i.e.,third rebound evaluation sampling event), the AS system was shut down on August 13, 2010. On August 27, 2010, the third quarter semi-annual monitoring event was conducted. A summary of the rebound sampling results are presented in the next section of this report. Rebound Sampling Analytical Results AECOM evaluated the analytical results from groundwater samples from the following monitoring wells: