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�.. <br /> Mr. Frank Girardi <br /> December 3, 2007 <br /> CONESTOGA-ROVERS <br /> &ASSOCIATES <br /> 2315 North El Dorado Street. The SJCHED requested that Shell prepare a model of the dissolved <br /> plumes showing migration pathways and probable areas of distinct and commingled plumes. As <br /> discussed with and agreed upon by Mr. Frank Girardi of SJCEHD, additional onsite assessment data is <br /> needed to properly evaluate possible plume migration pathways and areas of probable distinct and <br /> commingled plumes. Therefore and as approved of by SJCEHD, Shell will provide an evaluation of the <br /> dissolved plumes (previously due December 3, 2007)following completion of proposed site investigation <br /> activities as discussed below. <br /> Site Conceptual Model (SCM): As discussed with and approved of by SJCEHD staff, an updated SCM <br /> will be submitted following completion of the proposed site investigation. <br /> Source of Tetrachoroethene (PCE) and Tricholoroethene (TCE): Cambria Environment Technology, <br /> Inc. (Cambria) performed a file review during 2006 to determine the location of the site's former waste <br /> oil 11ST. a possible PCE and TCE source area. The location of the former waste oil UST was not <br /> identified durine Cambria's file review. CRA intends to review Shell's historical files in hopes of <br /> identifying the location of the former waste oil UST. Any information obtained regarding the location of <br /> the former waste oil UST will be presented to the SJCEHD. <br /> Blaine Tech Services, Inc. (Blaine) will instruct the laboratory to report all identified peaks for <br /> groundwater samples collected during the first and second quarter 2008 monitoring events. <br /> Ethylene dibromide (EDB) and 1,2-dicholoroethene (1,2 DCA): The quarterly groundwater monitoring <br /> program has been revised to include the analysis of 1,2-DCA and EDB in groundwater samples collected <br /> from all site wells. Blaine intends to update their "Well Concentrations" table to include historical and <br /> future 1,2-DCA, EDB,PCE,and TICE analytical results. <br /> SITE INVESTIGATION WORK PLAN <br /> Based on a review of soil and groundwater monitoring data, the SJCEHD requested that the Shell <br /> perform additional vertical and horizontal assessment. Shell's proposed scope of work is presented <br /> below. <br /> Technical Rationale for Proposed Scope of Work <br /> • Soil and groundwater beneath the site have been impacted by gasoline constituents. <br /> 1641 2 <br /> �� Worldwide Engineering, Environmental,Construction,and IT Services <br />