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Ge0bglci[TechAws Inc Page 19 Site Conceptual Model Report(2006 Revision) Valentine(Castle Motors) . Project No 723 2 June 16,2006 ' The plume bound has been defined b the advancement of the CPT borings The ' P �'S' Y g down gradient extent of the plume probably attenuates to non-detect levels within 50 feet of the CPT locations • The detections of THP-G in the northern two Shell Stations wells (MW-1 & MW-2) ' suggest that a co-mingled plume may be present ' 5.0 RECOMMENDATIONS Our recommendations are based on our knowledge of site conditions, and on the state and ' limitations of subsurface investigative technology Based on the conclusions outlined above, Geological Technics Inc recommends the following ' • Maintain the current groundwater monitoring schedule • We have recommended that interim remediation be considered before this plume migrates any further and the cost for cleanup continues to increase A work plan for ' interim remedial action utilizing high vacuum dual phase extraction, air stripping and carbon filtration of extracted groundwater technologies was sent to SJC/EHD for approval SJC/EHD approved the work plan and the permitting for the extraction and treatment system procurement, installation, and operation is underway We have received building and sewer discharge permits from the City of Stockton PG&E has identified high pressure gas service at the adjacent residential property and we had to ' obtain permission from this property owner to extend a line to the Castle Motors site We were successful in obtaining this permission, and have had to re-apply to the City of Stockton Building Department for an amended permit for the new gas/electrical ' service GTI will continue to follow up on this issue and we hope to have the system installed and operational by early September of 2006 ' 6.0 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 and evaluation of environmental conditions is an inexact science and that the state or practice ' of environmental geology/hydrology is changing and evolving and that standards existing at the present time may change as knowledge increases and the state of the practice continues to improve Further, that differing subsurface soil characteristics can be experienced within a ' small distance and therefore cannot be known in an absolute sense All conclusions and recommendations are based on the available data and information. The tasks proposed and completed during this protect were reviewed and approved by the local regulatory agency for compliance with the law No warranty, expressed or implied, is made