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� • i <br /> ' conclusions <br /> The results of the source investigation reveal that no <br /> ' hydrocarbon contamination is emanating from the Tesoro prop- <br /> erty. Based on the results of the water level data, product <br /> thickness measurements, and chemical analyses, it can be con- <br /> cluded that the source of the hydrocarbon contamination is north <br /> and west of the Tesoro site. Finding floating hydrocarbon <br /> product in the test holes on the north and west boundaries of the <br /> Tesoro site and finding that the predominant direction of ground- <br /> water flow is east and southeast demonstrates that the hydro- <br /> carbon contamination is migrating onto the Tesoro property from <br /> the Time Oil property and Southern Pacific pipeline right-of-way. <br /> Work Plan for Further Site Assessment <br /> The following plan outlines the activities Tesoro will <br /> ' undertake to monitor the new source of hydrocarbon contamination <br /> migrating onto the Stockton facility. <br /> Tesoro has addressed most requirements for further site <br /> assessment. The contamination source has been demonstrated to be <br /> originating north or northwest of Tesoro property. Tesoro <br /> 1 already has undertaken measurements to prove that their piping <br /> systems and storage tanks are tight . <br /> A groundwater monitoring network has been established that <br /> is located strategically to track the migration of contaminants <br /> onto Tesoro property. Tesoro personnel will continue monitoring <br /> hydrocarbon thickness and water level elevations at all test <br /> ' - 20 - <br />