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' Raymond Greer An Individual y ( ) 15634 Steinegul Road, Escalon, California June 7, 1997 Phase II-Site Assessment, Report of Findings Page: 4 ' 4.0 Local Geology ' Escalon hes in the Central Valley Physiographic Province of California The Valley is about 40 miles wide in this area It is bounded to the west by the foothills of the Coast Ranges, and to the east by the foothills of the Sierra Nevada Range The Escalon area is ' nearly devoid of structural geologic features The Valley is floored by unconsolidated Quaternary sediments to depths of at least 400 or ' more feet in the Escalon area All of these units can be considered sods in the engineering sense, because they are unconsolidated Quaternary sediments in the Central Valley were deposited as a series of coalescing alluvial fans The fans originated where valleys of the wmajor streams which drained the Sierra Nevada Range emptied into the broad expanses of the valley The coarser sediments which comprise the fans are mainly arkosic in ' composition and were derived from erosion associated with glacial stages in the mountains The finer grained sediments are predominantly composed of rock flour washed out of the former extensive glaciers in the Sierras, (Arkley, 1964) The axis of the Central Valley Trough was a marshy, wet area throughout much of the Pleistocene Epoch Lacustrine, flood plain and marshy depositional environments predominated along the axial portions of the trough, in the toe areas of the fans, throughout much of this time period Coarser grained sediments of the upper portions of the fans occasionally prograded over the axial area of the trough in response to mayor climatic changes in the Sierras This has resulted in a predominance of fine grained silts and clays in the subsurface of the area 5.0 Soil Conditions ' The lithology at this site is characterized as thinly bedded silty sands, well-graded sands, silts and clays ILaboratory analysis of soil samples detected Benzene, Toluene, E-Benzenes, Xylene (BTEX) and Gasoline contamination in the soils above and at the water table in bonngs B- 1 Contaminants ranged from 1,400 mg/kg to 5 7 mg/kg of Gasoline, Benzene from 23,000 ug/kg to 950 ug/kg, Toluene from 200,000 ug/kg to 40,000 ug/kg, Ethyl Benzene from 53,000 ug/kg to 9,200 ug/kg and total Xylenes from 410,000 ug/kg to 80,000 ug/kg No MTBE was found in any sample (Table 1 & Appendix A) I