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KLEINFELDER In June 1995 PSC proceeded with the installation of air-s ar ing wells SP-2 through . p P 9 ' SP-6 However, implementation of the sparge and vent remediation was postponed due to naturally occurring petroleum-hydrocarbon concentration reductions that were observed at the time In May 1999, PSC performed a subsurface investigation using cone-penetrometer- testing (CPT) technology Soil and groundwater samples were submitted for analysis from three CPT borings (CPT-1 through CPT-3) The CPT investigation indicated that the lateral extent of impacted groundwater was largely contained within the Earthgrain's property boundaries PSC reported the results of this investigation in the May 1999 Subsurface Investigation and Groundwater Monitoring Report An additional air-sparging and soil-venting pilot test was performed in June 2000 using VW-1 as the vent well The test was performed in accordance with the May 15, 2000 Pilot Testing Work Plan The pilot test results indicated that this technology would be an effective method of treating petroleum-hydrocarbon impact at the site Operation of a full-scale air-sparging and soil-venting remediation system was initiated on April 25, 2001 PSC installed a new air-sparging well (SP-A) on March 14, 2002 upon indication that the air infection at SP-1 was not resulting an adequate decrease of petroleum ' impact in the groundwater In December 2002, the remediation system was disengaged, since its effectiveness to remove contaminants became limited This allowed time to evaluate whether the petroleum concentrations in groundwater would remain stable The February 2003 ' groundwater sample from MWA indicated an increase in petroleum concentrations However, concentrations remained relatively stable in samples collected from other wells in the area of impact ' PSC submitted the April 14, 2003 Remedial Action Completion Report to SJCEHD The report presented a Site Conceptual Model, which characterized the release, subsurface conditions, and associated risks to potential receptors PSC determined that potential routes of exposure were improbable or incomplete and requested that SJCEHD consider granting closure SJCEHD directed additional site investigation be performed in their January 9, 2004 response letter The February 20, 2004 Subsurface Investigation Work Plan, which proposed details of site work, was submitted to and approved by SJCEHD C23-484517-BOOISAC5R609 Page 3 of 12 September 14, 2005 Copyright 2005 Kleinfelder Inc