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1 ENMS I • Mr James L Barton ' July 27, 2005 Page 6 Control District (SJVAPCD) permit to operate number N-5879 Refer to Figure 15 for a visual depiction of the remediation well network and general system layout Soil Vapor Extraction System Status ' EAI received approval to discontinue operation of the SVE system as a result of "a general downward concentration trend for all wells, including MW-11 and MW-12, with occasional ' spikes" as stated in the RWQCB letter dated October 23, 2003 Unocal retained ENSR to perform remediation and monitoring at this site as of December 2003 ' ENSR observed an increase in dissolved concentrations of TPI-Ig and benzene in the fourth quarter 2003 groundwater sampling results and the TPI-Ig and benzene plumes appeared to ' migrate outside of the site's well network The RWQCB directed ENSR to install four new groundwater monitoring wells to identify the new plume limits ENSR detailed the well drilling activities and provided information on the new plume limits in a report dated July 30, 2004 In the report, ENSR described efforts that were taken to cease plume migration, including preparing to restart the SVE system ENSR received Authority to Construct (ATC) No N-5879- 1-0 to restart the SVE system on August 25, 2004 The SJVAPCD allowed ENSR to operate the SVE system under the conditions of the ATC in lieu of receipt of the Permit to Operate The SVE system was restarted on September 24, 2004 On November 30, 2004, ENSR observed that a combustion chamber wall for the thermal oxidizer had failed On December 7, 2004, ENSR sent a letter to the RWQCB providing an assessment of the events resulting in the interruption of SVE system operation ENSR recommended replacing the vapor abatement porton of the SVE system with granulated activated carbon (GAC) ENSR received a new ATC from the SJVAPCD for operating the SVE ' system with GAC on February 11, 2005 ENSR installed two 1,000 pound activated carbon vessels and plumbed them into the SVE system on February 14th and 15P On February 17"' a SJVAPCD inspector visited the site and approved the system to operate under the conditions stipulated on the AT[: A rannrt siirnmar171nn the cvctam'c nnarntenn nmrometerg and camr%1= analytical results was submitted to the SJVAPCD on March 21, 2005 ENSR received the SJVAPCD permit to operate on June 15, 2005 Prior to the oxidizer failure, the influent concentrations were 900 micrograms per liter (pg/L) in September 2004 and 160 NgIL in October 2004 Since restarting the SVE system with GAC, the influent concentration was 34 pglL for February 2005 and 140 NgIL for March 2005 The April 2005 results were unexpectedly low at 1 3 pglL ENSR tried to verify that the vapor ' Celebrating 35 Years of Excellence in Environmental Services