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o0lrgieal nechma I" Page 6 <br /> 2"d Quarter 2003 Groundwater Monitoring Report <br /> Project No 507 2 <br /> September 24,2003 <br /> 3.0 CONCLUSIONS AND RECOMMENDATIONS <br /> ' Conclusions <br /> 1 Elevated concentrations of BTEX, TPH-G and MTBE are present in a laterally limited <br /> groundwater plume that is centered on MW-9 <br /> ' 2 The MTBE and previously monitored 1,2-DCA plumes are insignificant in comparison <br /> to the BTEX and TPH-G plumes <br /> ' 3 The lateral extent of the contamination plume is defined to the east, northeast and <br /> southeast by wells MW-3, MW-2 and MW-i respectively <br /> 4 The TPH-G plume is defined to the northwest and southwest by wells MW-10 and MW- <br /> 7 respectively <br /> 5 The BTEX/TPH-G groundwater contamination plume is defined by MW-109 in the <br /> vertical plane, which is screened 40 feet below MW-9 This suggests that the vertical <br /> gradient is not moving the contaminants to any degree <br /> 6 The groundwater gradient generally flows to the northeast or east with relatively flat <br /> slopes, which appears not to significantly influence contaminant migration <br /> 7 The site exhibits a predominantly downward component of vertical groundwater flow, <br /> which is approximately the same slope as the horizontal gradient These components of <br /> groundwater flow appear not to cause preferential contaminant migration <br /> 8 The groundwater contaminant concentrations are on the rise, which correlates with a <br /> decrease of groundwater levels The center of the plume has not migrated beyond the <br /> source area giving evidence that the plume is not migrating laterally or vertically by <br /> ' advective flow <br /> ' Recommendations <br /> • Maintain the modified quarterly monitoring schedule <br /> • Monitor the site wells for indicators of remediation by natural attenuation <br /> ' • A work plan for "In Situ Remediation Feasibility Study" dated September 20, 2002 and <br /> an addendum to this report was submitted on December 20, 2002 San Joaquin County <br /> approved the study in their March 20, 2003 letter and requested a detailed work plan for <br /> evaluation GTI submitted our June 10, 2003 "1n-Situ Remediation Pilot Test" work <br /> plan for an in-situ remediation pilot project and we are currently awaiting regulatory <br /> approval — - <br />' 4.0 LIMITATIONS <br /> This report was prepared in accordance with the generally accepted standard of care and <br />' practice in effect at the time Services were rendered It should be recognized that definition <br /> and evaluation of environmental conditions is an inexact science and that the state or <br /> practice of environmental geology/hydrology is changing and evolving and that standards <br /> existing at the present time may change as knowledge increases and the state of the practice <br /> 1 <br />