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Stantec Consulting Corporation <br /> 3017 Kilgore Road Suite 100 <br /> Rancho Cordova CA 95670 <br /> Tel:(916)861-0400 <br /> Fax:(916)861-0430 <br /> StantLK - --- - <br /> June 8, 2010 <br /> Mr. Mike Infurna <br /> San Joaquin County Environmental Health Department <br /> 600 East Main Street <br /> Stockton, CA 95202-3029 <br /> RE: Addendum to May 12 and May 20, 2010 Revised Site Progress and Second Quarter Report <br /> Extension Request <br /> ConocoPhillips Site No. 5449 <br /> Former Thrifty Oil Company Station No. 172 <br /> 7647 Pacific Avenue <br /> Stockton, CA 95207 <br /> Dear Mr. Infurna, <br /> The ConocoPhillips Company (ConocoPhillips) received a letter from the San Joaquin County Environmental <br /> Health Department (SJCEHD) dated May 27, 2010, requesting changes to the proposed schedule for <br /> rebound testing and work plan submission, and the performance of a Human Health Risk Assessment, for <br /> ConocoPhillips Site No. 5449 (Former Thrifty Oil Company Station No. 172), 7647 Pacific Avenue, Stockton. <br /> This letter serves as a response to those requests, and an addendum to our previous extension request <br /> dated May 20, 2010. <br /> Based on site conditions and the previously reported and new data, and in accordance with the SJCEHD <br /> request, Stantec will perform a 5-day rebound test. Because groundwater elevations have risen significantly <br /> since the initial release, we are also proposing at least a week of dewatering using components of the existing <br /> GWE system before and during the test. Assuming successful start of a mobile SVE system and re-start of <br /> the existing GWE system by June 30, 2010, preliminary rebound testing data will be reported by July 31, <br /> 2010. To allow incorporation of the April 2010 groundwater monitoring, June 2010 vapor well monitoring, and <br /> rebound testing into one report, we request permission to submit the second quarter 2010 report by this date. <br /> If rebound testing indicates the need for continued SVE/GWE operation, we will propose continued operation <br /> of the systems as an interim remedial action. The SVE system brought to the site for the rebound testing will <br /> be permitted for sustained operation and stored on or offsite pending planned property upgrades. The <br /> repaired GWE system will be capable of continued operation at the site until shut down is required as <br /> necessary to accommodate the upcoming rebuild, and can be resituated for continued operation thereafter. <br /> We propose that ConocoPhillips and Stantec meet with you in August 2010 to discuss the results presented <br /> in the July report. We have presented a preliminary schedule below; however, further site remediation <br /> activities and deadlines can be decided at this meeting as necessary based on these results. <br /> As approved by your agency, we will perform groundwater monitoring and sampling during both the third and <br /> fourth quarters of 2010. By October 15, 2010, we will have another quarter of monitoring data, as well as <br /> additional data regarding system performance; this will allow us to update our Site Conceptual Model, and <br /> provide a work plan for additional assessment and/or changes to the remediation systems. This date was <br /> also proposed for reporting efficiency to coincide with the third quarter report. <br /> Stantec will address the State Water Resources Control Board Clean UP Fund recommendation that a <br /> Human Health Risk Assessment (HHRA) be performed for this site. Because the observed concentrations of <br />