ARCHIVED REPORTS_SEMI ANNUAL GROUNDWATER MONITORING OCTOBER 2010

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AXOM Mr. James L. L. Barton Regional Water Quality Control Board —Central Valley October 27, 2010 Page 7 Following the January 21 meeting, the CVW B issued a letter dated February 2, 2010, confirming the discussion at the meeting and stated the following: "...Staff concurred with AECOM's proposal as reasonable, and reserved final approval for stopping SVE/AS pending review of the February 2010 data..." "...if the February data shows slightly higher, equal to, or lower than proposed biosparging mode concentrations, the Responsible Parties may submit a no further action report with applicable additional rationale why case closure is appropriate, including an evaluation of risk from vapor intrusion to the current building occupants and future workers. Staff also suggested that AECOM might want to conduct limited quarterly monitoring to speed up the closure process..." The February 2010 data indicated that only one l wells with benzene cded slightly ll tr tl ons below µg/L. concentrations measured at 2,100 µg/L), but Based on these results, as well as the CVW B's February 2, 2010, concurrence with AECOM's proposed path forward, the remediation system remained OFF until completion of the first soil vapor investigation sampling event (—May 2010). B directed CEMC and Stone Bros. to"submit r workplan In a letter dated February 2, 2010, the CVW for soil vapor investigation for all potential areas of concern, such as the Macaroni Grill (former Wards) and the bank (former Unocal), and for a direct-push soil and groundwater investigation under Robinhood Drive."AECOM submitted the work plan for the proposed soil vapor investigation on April 2, 2010. In an email dated May 28, 2010, Geocon Consultants, Inc. (Geocon), on behalf of Stone Bros. and CEMC, requested that the CVWB withdraw its directive for the soil and groundwater investigation under Robinhood Drive, based on the February 2010 groundwater monitoring data indicating no significant concems regarding subsurface conditions in that area. In an email dated June 1, 2010, the CVWB agreed and rescinded the requirement to investigate soil and groundwater under Robinhood Drive. OM Consistent with AECOM's Work plan for S installed three soil vapor wells (SV-1, SV-2,oland SV l VaporI3 ) nsar�orrmer UST locationaon (dated April 1, nd former Cdispenser island locations on May 13, 2010. Initial sampling of these wells was conducted on May 20, 2010. A report documenting both the well installation and soil vapor sampling activities was submitted to the CVWB on July 15, 2010,which should be referred to for additional information. Future Work Based on the results of the initial soil vapor sampling, additional sampling of SV-1 was conducted on September 9, 2010, and a"seasonal"variation sampling event of all three wells was conducted on October 20, 2010. The results of these additional sampling events will be provided in a report to the CVWB by December 3, 2010. Consistent with the agreed-upon approach, TPHg groundwater concentrations from the first and third quarter semi-annual monitoring events (i.e., second and third rebound evaluation sampling events) were lower than proposed biosparging mode concentrations and accordingly, AECOM has not re-