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06 April 2012 AGE-NC Project No. 95-0184 Page 4 of 7 Remediation of impacted ground water should be conducted concurrently with soil remediation to prevent re-contamination of remediated soil. In-situ air sparging combined with soil vapor extraction appears to be a viable alternative for remediation of both soil and _ ground water in the vicinity of the former UST location. Combined with SVE,the IAS method"mechanically/physically"strips volatile hydrocarbons from ground water without the addition of any chemicals or microbe solution into the environment. IAS is a widely accepted method of volatilizing hydrocarbons. As IAS has few, if any, adverse environmental effects, it is likely to be more readily approved for implementation by regulatory agencies. Based upon these considerations and the presence of relatively_sandy soil at the site,AGE recommends installation of an IAS system ; r for remediation of round water in the former UST area. rJ� -19 G rl,ry r — A 12 month remediation period can be expected to be required to reduce volatile and light-end hydrocarbon concentrations by 70 % or 80% to near State of California drinking water standards (benzene). A sparging / extraction system may also have a secondary effect of bioventing impacted soil, increasing the oxygen concentrations available for biologic processes, thereby possibly increasing the natural degradation rate. Ground water in the former UST area may be more effectively addressed by IAS, while ground water outside the direct plume area may be more effectively addressed by attempting to stimulate bioremdiation through sparging to increase dissolved oxygen concentrations. P AGE recommends addressing ground water impacted primarily by long chain TT�PH by encouraging biodegradation by increasing dissolved oxygen concentrations. This can be accomplished by installation of sparge points for slow sparging. If a discharge permit can � be procured from the CVRWQCB, injection of additional bacterial inoculum and nutrients l would stimulate the process. 3.0. PROPOSED SCOPE OF WORK Previous feasibility pilot test work plans have beef submitted for the site. The Feasibility Pilot Test4 Work Plan, dated 09 September 2009 which included a scope for an air-sparge pilot test, has been completed and reported by ln-Siy Air Sparging& Soil Vapor Extraction Feasibility Pilot Test Report, dated 10 March 2010 . Air was injected into drowned vapor- well apor well VW-5C and soil vapor extraction was performed on wells EW-1,VW-2A,VW-3,VW-4, VW-5A and VW-5B through out the IAS pilot test. Advanced CeoEnAronmenml,Inc.