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WORK PLAN FOR GROUNDWATER EXTRACTION;REMEDIATION PROGRAM VALLEY MOTORS 800 East MainStreet Stockton,California 1.0 INTRODUCTION Investigation of soil and groundwater contamination at 800 East Main Street(Figure 1) began in 1994,when several borings were drilled to collect soil samples for laboratory analysis of petroleum-:range hydrocarbons. :Further drilling took place in 1995, and again. in 1996, 1998, 1999;and 2003. At the completion of that work, eight groundwater monitoring wells,one vapor extraction well, one air sparging well, and numerous soil borings and vapor probes had been installed(Figure 2). The results of the investigation were subsequently summarized in a Problem Assessment Report and.Soil Remediation .flan that was prepared in October 2003 and submitted to the San Joaquin County Environmental Health.Department(SJCEHD). A thermal oxidation vapor extraction system was.installed at the site:in mid'-2005, and _ soil remediation began in December of that year. The remediation system operated until November 2006,when it was shut down for reasons of cost effectiveness. If further soil remediation was deemed necessary by SJCEHD,Upgradient En.viroJunental. recommended removing the thermal vapor extraction unit and replacing it with a regenerative blower and granulated activated carbon canisters for vapor destruction. Upgradient also:recommended that a groundwater extraction test be conducted to determine whether signif cant reduction in groundwater contaminant levels could be attained. In subsequent correspondence, SJCEHD indicated that.it would consider a proposal to conduct a groundwater extraction test, but requested that multiple methods of groundwater extraction be evaluated. Two potential.methods.of groundwater treatment were submitted on.January 25;2008 in a report entitled Groundujate; Remediation Feasibility Study. In a response.dated February 8, SJCEHD directed Valley Motors to submit a Work Plan to.test the feasibility groundwater extraction The requested plan was submitted in,March 2008,revised in February 2009, and implemented in May 2009. The test was conducted over a period of several months,and concluded in December.2009. The results were reported in February 2010. SJCEHD responded in a comment letter dated.May 27,2010. SJCEHI)did not concur with.the main conclusions of the report, and.instead requested that Valley Motors either: 1)proceed with groundwater extraction.and.monitor for chlorinated hydrocarbon migration; 2)conduct additional assessment; f