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L_ r- <br /> . 1r <br /> AR.011ed 000SystemS 43255 Mission Blvd. Suite B Fremont,CA 94539 (415)651-1906 <br /> February 11, 1987 <br /> 0211jmcc <br /> 8691-4 <br /> Mr. Jim McCutchen <br /> Beacon Oil Company <br /> 525 West Third Street <br /> Hanford, California 93230 <br /> Subject: Letter report No. 8691-4 regarding drilling of <br /> monitoring well MW-4 at Beacon station #1-502, 35 N. <br /> Cherokee Lane, Lodi, California <br /> Dear Mr. McCutchen: <br /> This letter report summarizes the drilling of soil boring B-4 and <br /> installation of monitoring well MW-4 at the above-referenced <br /> site. The purpose of the well was to investigate whether or not <br /> the source of the ground water contamination found in previous <br /> wells on site was leakage which occurred within the tank cavity <br /> on site, or was due to offsite contamination. <br /> The results of our previous work have been presented in reports <br /> for Beacon Oil dated October 28, 1986, and November 7, 1986. The <br /> data presented in these reports indicated that soil immediately <br /> below the tank cavity was contaminated, and that the ground water <br /> in that area was contaminated. Soil outside of the tank cavity, <br /> sampled during soil boring operations, showed very low to <br /> nondetectable levels of hydrocarbons. The source of the ground <br /> water contamination could not be confidently evaluated on the <br /> basis of the data available at that time, and may have been due <br /> to leakage on site or at a service station located immediately to <br /> the north of the site. <br /> A geologist arrived at the station on November 19, 1986 to <br /> supervise drilling operations and log the boring. Drilling was <br /> done with a Mobile B-61 drilling rig equipped with 7 . 5 inch <br /> diameter hollow-stem augers and operated by Datum Exploration, <br /> Inc. , of Pittsburg, California. The augers were steam-cleaned <br /> prior to use in order to minimize the possibility of down hole <br /> contamination. Total depth of the boring was 60. 5 feet. <br />