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George's Service <br /> Remedial Action Work Plan <br /> Project No.425.2 <br /> June 30,2011 <br /> On August 20, 2002, GTI prepared and submitted the work plan Additional Soil and <br /> Groundwater Investigation. In a letter dated October 21, 2002, Nuel C. Henderson,Jr., R.G., <br /> San Joaquin County Environmental Health Department (SJCEHD), found the work proposed <br /> to be adequate and necessary with some conditions. The Additional Site Characterization <br /> and P Quarter 2004 groundwater monitoring report prepared by GTI dated March 22, 2004 <br /> documents the work performed in accordance to the October 2002 work plan including the <br /> installation of four additional groundwater-monitoring wells at the Site during September and <br /> October of 2003. <br /> GTI prepared and submitted the Interim Remediation Action Plan β€” In Situ Remedial Pilot <br /> Test (RAP) dated March 21, 2005. SJCEHD reviewed the RAP and did not approve the <br /> implementation in a letter dated May 24, 2005. SJCEHD discussed the reasons for not <br /> approving the RAP and requested a feasibility work plan. <br /> GTI prepared and submitted the Feasibility Work Plan β€” In Situ Remediation Pilot Test <br /> (FWP) on June 14, 2005. SJCEHD approved the FWP in a letter dated September 16, 2005, <br /> with revisions to well locations and sample constituents. GTI then prepared and submitted <br /> the Feasibility Work Plan β€”In Situ Remediation Pilot Test Addendum (Addendum FWP) on <br /> November 17, 2005. SJCEHD approved the Addendum FWP in a letter dated December 1, <br /> 2005. <br /> SJCEHD requested additional testing of selected monitoring,observation and domestic wells <br /> based on concerns that the Site may have naturally occurring hexavalent chromium. In <br /> December 2006 and January 2007 samples were collected and analyzed. In the Additional <br /> Groundwater Investigation Report prepared by GTI, dated January 22, 2007, it was <br /> determined that hexavalent chromium is naturally occurring in the groundwater below the <br /> Site. Hexavalent chromium was reported to be present in the observation wells at the same <br /> level prior to the pilot test as they were reported in January 2007. <br /> GTI submitted a remedial action plan on November 29, 2007 followed by 3 addenda dated <br /> February 5, 25 and March 19, 2008 to mitigate the residual groundwater contamination using <br /> air sparging, vapor extraction and Oxygen Releasing Compound (ORC) technology in situ <br /> (in place). SJCEHD approved the air sparging and vapor extraction portion of the remedial <br /> action plan subject to positive results from a limited 2-week pilot test in their correspondence <br /> dated April 30, 2008, and directed further Site investigation to clarify the horizontal and <br /> vertical extent of the plume toward northern portion of the Site(under Durham Ferry Road). <br /> In a letter dated October 16, 2008, SJCEHD approved of the short term pilot test in efforts of <br /> obtaining data to design the air treatment portion of the soil vapor extraction system and <br /> recommended that PID readings be taken hourly during each test. GTI prepared and <br /> submitted the Soil Vapor Extraction Pilot Test Report on August 6,2009. <br /> Geological Technics Inc. 3 <br /> 4252 RAP.docx <br />