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i <br /> If� <br /> 3330 Cameron Park Drive, Ste 550 <br /> Cameron Park, Callfornla 95682 <br /> (530)676-6004-Fax:(S30)676-6005 <br /> March 23,2009 <br /> I <br /> I <br /> Mr. Rusty Benkoskey <br /> Stantec Consulting Corporation <br /> 3017 Kilgore Road, Suite 100 <br /> Rancho Cordova,California 95670 <br /> Re: Well Installation Data Package,Former Arco Service Station No.443, <br /> 2478 East Oak Street, Stockton, California(field activities performed <br /> between August 6, 2008, and February 27,2009). <br /> This data package has been prepared as a record of the site assessment activities carried <br /> out as requested in Stantec's Interim Remedial Action Plan, dated July 10, 2008, and <br /> revised in the Addendum to Remedial Action Plan, dated September 10, 2008, and the <br /> Addendum to Remedial Action Plan, dated October 17, 2008. The scope of work <br /> proposed in these documents consisted of installing two on-site monitoring wells (MW-5 <br /> and MW-8), and two off-site monitoring wells (MW-6 and MW-7). Access has not yet <br /> been received for installation of the off-site wells. Monitoring well MW-5 was to be a 2- <br /> inch diameter well, installed to approximately 65 feet below ground surface (bgs) with 8- <br /> inch diameter hollow-stem augers. Monitoring well MW-8 was to be a 4-inch diameter <br /> well installed to approximately 120 feet bgs, inside a steel conductor casing installed to <br /> 95 feet bgs. Well MW-8 was to be drilled with 18-inch hollow-stem augers to install the <br /> conductor casing, then with 10-inch hollow-stem augers through the conductor casing to <br /> drill the final length of the borehole. In addition, the plan of work regarding well MW-8 <br /> called for continuous soil sampling starting at 75 feet bgs. <br /> During the drilling of well MW-8, the original plan of work was modified, as necessitated <br /> by many issues: <br /> • The driller was not confident that 8-inch augers would make a sufficient pilot <br /> hole for the 18-inch augers needed for well MW-8, so 10-inch augers were <br /> used. <br /> • Nearby well MW-ID (installed in June 2007 by Stratus) had heaving sands <br /> present during drilling from approximately 65 to 80 feet bgs, and so boring <br /> MW-8 was only sampled every five feet to minimize complications from <br /> those conditions. Heaving sands were encountered in this interval. <br /> • During the grouting of the conductor casing for MW-8, the driller kept the <br /> 18-inch augers turning as the grout was pumped. The on-site San Joaquin <br /> County Environmental Health Department (SJCEHD) regulator (Mr. Mike <br /> Infurna) expressed concern that auger rotation would impact the integrity of <br /> K:\BP-ARCO Execute\443\2009 Data packages\Arco_443—Well Installation Data Package.doc <br /> f <br />