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The site is situated in the southern part of the city of <br /> Stockton, a short distance west of Highway 99, and just to the <br /> south of Mariposa Road. The area is used primarily for <br /> industrial & light manufacturing purposes; there are some <br /> residences to the west of the property. <br /> E• <br /> The site is located in the southern part of the Sacramento <br /> Valley, which is the northern subprovince of what is referred to <br /> as the Great Valley of California. It consists of in excess of <br /> 20, 000 feet of sediments of Cretaceous & younger age generated by <br /> uplift & erosion of the Sierra Nevada Batholith to the east . The <br /> topography is very flat, with surface drainage to the west at <br /> about 5 ' /mile. Duck Creek is a short distance to the south, and <br /> Mormon Slough is about 1 mile to the north. <br /> DEPTH TO GROUNDWATER: <br /> According. to San Joaquin County Flood District maps, groundwater <br /> was as high as 47 ' bgl in the Spring of 1986 . Monitoring activi- <br /> ties since April, 1992 have recorded an average water table depth <br /> of .about 72 ' bgl . The last sampling event in November, 1996, <br /> found the static water level at an average of 67 . 72 ' bgl . <br /> PRIOR USE OF UST' S: <br /> Two, 5, 000 gallon UST' s which had been used for storing diesel <br /> fuel were removed from the property in March, 1987 . There are no <br /> records available concerning amounts of fuel used during the time <br /> the tanks were in use'. Refer to prior reports for more details . <br /> SUMMARY OF -PRIOR.-WORK <br /> March, 1987 - two, 5, 000 gallon diesel UST' s removed from site by <br /> Thorpe' Oil Co. Soil samples taken from beneath the tank revealed <br /> the presence of benzene, xylene, TVPH, & TEPH. Disposition of <br /> removed spoil not known. <br /> March, 1988 - Thorpe Oil Co. reexcavated the site, and soil <br /> samples were taken at 28 ' & 29 ' below grade . Laboratory results <br /> revealed the presence of xylene & TVPH in both samples . The <br /> excavation was filled with clean material . <br /> April 3 , 6, & 7, 1992 - Three (3) monitoring wells placed on site <br /> to depths of 841 , 861 , & 89 ' bgl . Casing size on MW-1 was 4" OD, <br /> MW-2 & MW-3 was 2" OD. Details of work included in report titled <br /> "GROUNDWATER INVESTIGATION REPORT" dated May, 1992 . <br /> V./ <br /> 2 <br />