ARCHIVED REPORTS_XR0006919- CASE 2

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. 2$ April 2005 AGE-NC Project No 97-0351 Page 2 of 11 Division of Mines and Geology, 1977) Rocks composing the basement complex of the GVGP have not been completely defined, but are believed to be metamorphic and igneous in origin The Modesto, Riverbank, and Turlock Lake Formations and overlying Recent alluvium are the principal sources of domestic ground water in the 13,500-square mile San Joaquin Valley Ground Water Basin (Basin 5-22) The estimated depth to ground water at this property is approximately 20 feet below surface grade(bsg),based on information from Lines of Equal Depth of Water Wells, Fall 1995 published by the San Joaquin County Flood Control District and Water Conservation District However, San Joaquin County Environmental Health Department(EHD)records indicate that the highest ground water was observed at the site in 1986 at 10 feet bsg During previous site investigations,ground water was encountered at a depth of 12 feet bsg The prevailing ground water flow direction in this portion of western Stockton is generally toward the northeast, while localized ground water flow may vary during winter/summer cycles 2 2 UNDERGROUND STORAGE TANK REMOVAL In May 1986, one 550-gallon gasoline UST (West UST Area) was removed from the City of Stockton right-of-way in San Jose Street Total volatile hydrocarbons(TVH)and volatile aromatics benzene, toluene, ethylbenzene, and xylenes (BTEX) were detected at concentrations as high as 2,000 milligrams per kilogram(mg/kg)in a single soil sample collected from the UST excavation One 4,000-gallon gasoline UST(East UST Area)was removed from the site on 13 November 1997 The UST was Iocated in Lindsay Street, between the northern and southern blocks of on-site buildings Upon removal, holes were noted at the western end and in the bottom of the UST Hydrocarbon odors were not observed in soil above 11 feet bsg Approximately 5 cubic yards of hydrocarbon-impacted soil were removed and stockpiled during the UST excavation Soil samples were collected 2 feet below the UST, at depths of 12 feet bsg The overburden soil was used to backfill the lowest portion of the excavation Analytical results of soil samples collected from the UST excavation indicated that an unauthorized release of hydrocarbons had occurred at the western edge of the UST Total petroleum hydrocarbons quantified as gasoline(TPH-g)were detected in sample TI-W at 690 mg/kg TPH-g was not detected in the soil sample collected from the eastern end of the UST 23 PREVIOUS SITE INVESTIGATIONS On 14 November 1996 and 16 January 1997, a total of fifteen soil probe borings (P 1 through P 15) were advanced at the site under the supervision of the EHD Soil probe borings were advanced in Advanced Geoi✓nvironmental,Inc.