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1 CreolagccalTecls�ucslnc Page 6 2'd Quarter 2004 Groundwater Monitoring Report Project No 507 2 August 30,2004 3.0 CONCLUSIONS AND RECOMNMNDATIONS ' Conclusions 1 Elevated concentrations of BTEX, TPH-G and MTBE are present in a laterally limited 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 contamination plume is defined to the southeast, northeast and ' east by wells MW-1, MW-2 and MW-3 respectively 4 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 by MW-109 in the vertical plane, which is screened 40 feet below MW-9 This suggests that the vertical gradient is not moving the contaminants to any degree 6 The groundwater gradient flows to the northeast or east with relatively flat slopes, which appears not to significantly influence contaminant migration 7 The site exhibits a predominantly downward component of vertical groundwater flow, which is approximately the same slope as the horizontal gradient These components of groundwater flow appear not to cause preferential contaminant migration 8 The groundwater contaminant concentrations have decreased in the core plume (well MW-9) but this is indicative of the infection pilot test started on March 19, 2004 The center of the plume has not migrated beyond the source area giving 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 t • A work plan for "In Situ Remediation Feasibility Study" dated September 20, 2002 and an addendum to the plan were submitted to San Joaquin County Environmental Health Department(SIC EHD) SIC EHD approved the study in their March 20, 2003 letter and ' requested a detailed work plan for evaluation GTI submitted our June 10, 2003 "In-Situ Remediation Pilot Test" work plan for an in-situ hydrogen peroxide infection pilot project and SJC EHD issued approval of the work plan in their September 10, 2003 ' letter The installation of three, 3/4" diameter monitoring wells was completed on February 5, 2004 and the infections began in mid March 2004 A brief status update is ' included in the following section We recommend that monthly field measurements be made of the DO & ORP in MW-9 for the next three months to track the concentrations of these two factors after the pilot test was completed