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w Kristi Shelton Page 2 November 1,2007 The following remediation measures are currently being implemented. • Monitored natural attenuation(MNA). The naturally occurring nondestructive and destructive processes in the subsurface(1)limit the downgradient migration of hydrocarbon constituents in groundwater and(2)reduce the mass of residual hydrocarbon residuals in the vadose and groundwater zones,both in the former pipeline release"source area' and the areas downgradient of the source area. MNA was implemented with a 3-year pilot study that began in 2004 with shutdown of the active remediation systems(SVETS,GWETS). The pilot study concluded in 2007 with collection of the first quarter 2007 groundwater monitoring event. The aboveground portions of the SVETS and GWETS were removed from the site as approved by the RWQCB based on the positive results of the pilot study. The results of the pilot study are documented in the 3-Year Bioremediation Pilot Study Evaluation Report submitted to the RWQCB(CH2M HILL,2007a). • Phytoremediation. The maturing root system from the tree system planted in 2005 and 2006 in the"source area" will enhance the naturally occurring process described above. This will limit the downgradient migration of hydrocarbon constituents in groundwater and reduce the mass of hydrocarbon residuals in the vadose and groundwater zones. The phytoremediation system was constructed and is currently maintained as described in the Cleanup Plan Using Phytoremediation for the Source Area(CH2M HILL,2004). Construction of the phytoremediation system is documented in the following as-built reports submitted to the RWQCB: Phytoremediation As-Built Report(CH2M HILL,2005a) and Phytoremediation As-Built Report, Construction Season 2 (CH2M HILL,2007b). The recently submitted Second Semiannual and 2007 Annual Groundwater Monitoring Report documents current groundwater conditions at the Site(CH2M HILL,2007c). This report was submitted to the RWQCB on October 31,2007. Attached Figures 3,4,and 5 from this report present contour maps of the groundwater table elevation,total petroleum hydrocarbons,gasoline-range organics (TPH-g)concentrations,and benzene concentrations in groundwater for third quarter 2007 monitoring data,respectively. The current remediation activities(MNA,phytoremediation)and recommendations for future site management activities were discussed with the RWQCB at two meetings held on July 12,2007,and September 21,2007. As agreed at the September 21,2007,meeting,the RWQCB will provide a draft M&RP that will revise current M&RP No. R5-2004-0803 to incorporate the recommendations in the 3-Year Bioremediation Pilot Study Evaluation Report, after the RWQCB receives the Second Semiannual and 2007 Annual Groundwater Monitoring Report(CH2M HILL,2007c)and a work plan(this work plan)to destroy the select groundwater monitoring and extraction wells as recommended in the 3-Year Bioremediation Pilot Study Evaluation Report. As noted above,the Second Semiannual and 2007 Annual Groundwater Monitoring Report was submitted to the RWQCB on October 31,2007. ES102007015SCO/HOLT-WORK-PLAN-LETTER-WL369.DOC/073050005 COPYRIGHT 2007 BY CH2M HILL,INC.•COMPANY CONFIDENTIAL