ARCHIVED REPORTS XR0001370 - Laserfiche WebLink

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I ' ADDITIONAL MONITORING WELL INSTALLATION • ' Between, 27 August and 10 October 2002, AGE prepared for and advanced seven soil bonngs for collection of soil samples and/or installation of monitoring wells (MW-4 through MW-9) Screen ' intervals were installed at the following intervals 20 to 40 feet bsg, 115 to 120 feet bsg, 141 to 146 feet bsg, and 165 to 170 feet bsg Monitoring wells MW-4 and MW-5 were constructed with a fifth screened interval from approximately 193 feet bsg to 198 feet bsg A total of 28 soil samples were analyzed The highest concentrations of petroleum hydrocarbon compounds were detected from soil samples collected at between 40 and 60 feet bsg, in HU-1 ' Middle Zone TPH-g was detected in soil samples collected from soil bonngs MW-4,MW-5 and B-2 at concentrations as high as 4,500 milligrams per kilogram (mg/kg) (MW4-58), 3,600 mg/kg (MW5-50) and 2,000 mg/kg (B2-50) The BTEX compound benzene was detected in soil samples collected from MW-4,MW-5 and B-2 at maximum concentrations of 33 mg/kg (MW4-58), 21 mg/kg (MW5-50) and 20 mg/kg(B2-50), E toluene was detected at maximum concentrations of 180 mg/kg (MW4-58), 100 mg/kg (MW5-50) and 54 mg/kg (B2-50), ethylbenzene was detected at maximum concentrations of 19 5 :mg/kg (MW4-58), 30 mg/kg (MW5-50) and 13 mg/kg (B2-50), and total xylenes were detected at maximum concentrations of 224 mg/kg (MW4-58), 182 mg/kg (MW5-50) and 77 mg/kg (B2-50) . Fuel additives including DIPE, ETBE,MTBE,TAME,TBA,EDB and 1,2-DCA were not detected Iin the soil samples collected and analyzed from the three soil bonngs Additional VOCs detected in the analyzed samples included isopropylbenzene, n-propylbenzene,1,3,5-tnmethylbenzene, 1,2,4- tnmethylbenzene p-isopropyI-toluene and naphthalene ' REGIONAL GEOLOGIC SETTING According to the Geologic Map of California, published in 1977 by the State of California Department of Mines and Geology,the site area is within the Great Valley Geomorphic Province of California, a large, elongate, northwest trending structural trough The Great Valley Province has been filled to its present elevation with thick sequences of sediment ranging in age from Jurassic to present day, creating a nearly flat lying alluvial plain extending from the Tehachapi Mountains in the south to the Klamath Mountains in the north The western and eastern boundaries of this province are comprised of the California Coast Range and the Sierra Nevada Mountains, respectively The Great Valley Province is subdivided into two mayor divisions designated the Sacramento and San Joaquin Valleys Based on the General Soil Map from the San Joaquin County Soil Survey,published by the United States Department of Agriculture Soil Conservation Service in 1992, the site area is within the Jacktone-Hollenbeck-Stockton (JHS) association The JHS soils are located within basins, and Igenerally consist of moderate to poorly drained fine textured soils The soils are generally derived . from both marine and non-marine sediment, and are generally formed in alluvium derived from mixed rock sources I