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y <br /> ✓J 3017 Kilgore Road,Suite 100 <br /> `^ Rancho Cordova,CA 95670 <br /> 916-861-0400 TEL <br /> 916-861-0430 FAX <br /> StanteC <br /> May 20, 2010 d 0 <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, 2010 Revised Site Progress and <br /> Second Quarter Report Extension Request <br /> ConocoPhillips Site No. 5449 <br /> Former Thrifty Oil Company Station No. 172 <br /> 7647 Pacific Avenue <br /> Stockton, California 95207 <br /> Dear Mr. Infurna: <br /> On April 5, 2010, the ConocoPhillips Company (ConocoPhillips) received a letter from the <br /> San Joaquin County Environmental Health Department (SJCEHD) requesting that a <br /> groundwater sampling event be performed at ConocoPhillips Site No. 5449 (Former Thrifty <br /> Oil Company Station No. 172), 7647 Pacific Avenue, Stockton within 30 days, and that the <br /> remediation system be inspected, repaired, and rebound testing initiated during April 2010. <br /> As has been informally communicated to the SJCEHD through telephone calls and emails, <br /> documented in our letter dated May 12, 2010, and is further documented through more <br /> formal written communication (this letter), although groundwater sampling was completed <br /> within April 2010, the system was unable to be restarted during the month of April 2010 due <br /> to extensive damage and theft of vital components. <br /> Groundwater monitoring completed on April 16, 2010 indicates the plume status has <br /> changed. Groundwater levels have risen since well installation such that some of the <br /> groundwater monitoring well screens are submerged, and we suspect that some of the <br /> vapor well screens may be partially submerged. The following is our proposed path forward <br /> for the next 30 to 45 days: <br /> • Restart the SVE by 6/30/10 <br /> • Restart the GWE as an interim plume control measure by 6/30/10 <br /> • Collect groundwater samples from vapor wells currently containing groundwater, if <br /> present in these wells, to help provide characterization of shallowest groundwater <br /> (currently planned for June 3, 2010) <br /> • Conduct repairs at MW-7 <br /> • Collect rebound testing data <br /> • Evaluate implementation of air sparging as a groundwater remediation method in <br /> addition to or as a substitute to ongoing GWE. <br /> Recommendations for next steps in the process for completing groundwater remediation <br /> will be included in the quarterly report for the second quarter 2010. <br />