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' 01 June 2006 • AGE-NC Project No 02-0977 ' Page 4 of 5 ' March 2006,MTBE increases were generally reported from wells MW-1 through MW-3 and MW-5 A trend analysis of the increasing dissolved MTBE concentrations for selected monitoring wells is depicted In Appendix E The steady and significant rise in dissolved ' MTBE concentrations at well MW-2 potentially indicates a possible liquid phase or high soil vapor concentration migration from the soil into the shallow ground water table • A significant spike in MTBE concentrations was evident at wells MW-1 through MW-3 and ' MW-5 between the December 2005 and the March 2006 ground water monitoring events The spike in ground water concentrations observed in the above wells may be related to the increasing ground water elevation and desorption of MTBE-impacted soil ' 0 The fuel additive TAME was detected in samples from wells MW-1 through MW-3 and MW-5 at maximum concentrations of 400 µg11 (MW-2) ' DIPE was detected from MW-2 at a concentration of 9 3 [tg/l 4 ' 5.0. RECOMMENDATIONS '• Based upon data collected during the first quarter 2006, AGE recommends • Continued utilization of wells MW-1 through MW-8 for quarterly ground water monitoring ' and sampling, the 2"d quarter 2006 ground water monitoring event has tentatively been scheduled for 07 June 2006 ' • Based on the findings of SVE pilot test conducted at site in April 2006(Soil Vapor Extraction Pilot Test Report -April 2006, dated 17 May 2006), AGE recommends preparation of an Interim remediation work plan proposing SVE as the remediation technology to be used to ' mitigate the TPH-g, BTEX and MTBE-adsorbed soil at the site • An interim ground water remediation program should immediately be implemented at the site ' to establish sufficient hydraulic controls and inhibit the documented off-site migration of the MTBE-ground water plume AGE had previously proposed installation of a ground water extraction wells in the November 2004 Site Assessment Work Plan At a minimum, AGE ' recommends the installation of two ground water extraction well near wells MW-2 and MW-3 with the implementation of interim ground water extraction (pump-and-trat) remediation system utilizing carbon-based treatment with discharge into the City of Lodi sewer system ' The State Water Resource Control Board document Guidelines For Investigation and Cleanup of MTBE and Other Ether-Based Oxygenates, dated 27 March 2000, recommends that "Removing MTBE from the subsurface at high concentrations is much more cost ' effective than extracting ground water or vapor with low concentrations" Further more, the documents states " aggressive interim remediation in the source area can help to diminish ' Advaneed GeoEnvironmental,Inc