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GeologualTechmaW Page 6 1"Quarter 2003 Groundwater Momtonng Report Project No 507 2 May 15,2003 ' 3.0 CONCLUSIONS AND RECOMMENDATIONS ' 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 east, northeast and southeast by wells MW-3, MW-2 and MW-1 respectively 4 The TPH-G plume is defined to the northwest and southwest by wells MW-10 and MW- ' 7 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 are on the rise, which correlates with a decrease of groundwater levels 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 ' Recommendations 0 Maintain the modified quarterly monitoring schedule • Monitor the site wells for indicators of remediation by natural attenuation ' • Use the geologic cross sections showing Isoconcentration contours of petroleum contaminants in the soil and groundwater as the basis for performing contaminant mass estimate calculations ' • A work plan for "In Situ Remediation Feasibihty Study" dated September 20, 2002 and an addendum to this report was submitted on December 20, 2002 San Joaquin County _ ' approved the study in their March 20, 2003 letter and requested a detailed work plan for evaluation This work plan for an in-situ remediation pilot project is in development and will be submitted in May 2003 4.0 LIMITATIONS This report was prepared in accordance with the generally accepted standard of care and practice in effect at the time Services were rendered It should be recognized that definition