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cgolaglul hchfucs lnr Page 9 Valentine(Castle Motors) Report—Additional Site Characterization Project No 723 2 January 21,2004 1 ' 5.0 CONCLUSIONS & RECOMMENDATIONS Conclusions ' • The soil contamination above the water table appears to be limited in lateral extent to the areas directly within 15 feet of the former dispenser island • The residual soil TPH-G contamination in the vadose zone and sorbed hydrocarbons below the water table continues to provide a source for dissolved hydrocarbon ' groundwater plume • The fluctuating groundwater table has contributed to a smear zone extending to the property boundaries ' • Mr Jeff Wong of the San Joaquin County Environmental Health Department (SJC/EHD) supplied GTI staff with a copy of groundwater monitoring report for the Shell Service Station facility across N El Dorado Street (see Appendix D) The data indicate that a gasoline release has occurred at the site Pending the results of the new well sampling, a co-mingled plume may be present Recommendations The following recommendations are made N I Incorporate the new MCT well in the quarterly monitoring schedule The new well chambers have been developed (January 3, 2004) but the field technician was unable to sound the chambers This was caused by the friction on the probe due to the twist in the MCT tubing GTI's subcontractor is working on a solution to the problem and the new wells will be included in the first quarter 2004 monitoring event 2 Perform mass balance for groundwater contamination after the new wells are sampled 3 Perform a dual phase extraction test to evaluate the feasibility of utilizing both soil vapor and groundwater extraction technologies to treat the gasoline plume at the site GTI's September S, 2003 work plan for this test has been approved by SJC/EHD in their November 15, 2003 letter The work is currently in the development and budgeting phase ' 4 Perform a file review of SJC/EHD records to gather additional information on the Shell Service Station site including boring logs, etc 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.