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Creofogual Team"Inv. Page 6 ' 3ro Quarter 2005 Groundwater Monitoring Report Project No 507 2 October 31,2005 from its source and suggests that contaminant migration may be occurring primarily by diffusion with a slight influence by advection ' 3.0 CONCLUSIONS AND RECOMAMNDATIONS Conclusions ' 1 Elevated concentrations of BTEX, TPH-G and MTBE are present in a laterally limited (less then 100 ft radius) groundwater plume that is centered on MW-9 2 The MTBE and previously monitored 1,2-DCA plumes are insignificant in comparison to ' the BTEX and TPH-G plumes 3 The lateral extent of the TPH-G plume is defined to the southeast, northeast and east by wells MW-1, MW-2 and MW-3 respectively 4 The lateral extent of the TPH-G plume is defined to the southwest and northwest by wells MW-7 and MW-10 respectively 5 The BTEX/TPH-G groundwater contamination plume is defined vertically by MW-109, ' which is screened 40 feet below MW-9 This suggests that the vertical gradient has not moved the contaminants very deep into the subsurface 6 The groundwater gradient flows to the northeast or east with relatively flat slopes, which appear not to significantly influence contaminant migration 7 The groundwater contaminant concentrations have increased in the core of the plume (well MW-9) after a temporary decrease (after the injection pilot test started on March 19, ' 2004) in the first quarter 2004 8 The center of the plume has not migrated beyond the source area providing evidence that the plume is not migrating laterally or vertically by advective flow ' 9 The data shows that the plume is stable and is not being degraded by natural biodegradation causes Recommendations • Maintain the modified quarterly monitoring schedule Lower the sampling frequency of ' historically low concentration and non-detect wells to an annual basis to achieve cost savings (MW-1, MW-2,MW-3, MW-7, MW-10 and MW-109) • GTI submitted our June 10, 2003 "In-Situ Remediation Pilot Test" work plan for an in ' situ hydrogen peroxide injection pilot project The SJC PHS/EHD issued approval of the work plan in their September 10, 2003 letter and the work was completed by July 2004 A report on the pilot test was submitted to SJC PHS/EHD for review They have since ' commented on the field work and requested that a site conceptual model (SCM) be submitted • Perform the continuous core boreholes in the core contaminant area There is uncertainty ' regarding the interbedded nature of the fine grained silts/clays with the coarser grained sand units in the vertical profile of the soil at the site The purpose of the borings is to provide detailed understanding of the thinner geologic units at this site GTI developed our March 7, 2005 "Site Characterization Work Plan" that includes continuous core 1