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tEckert Cold Storage Company P 1' 7S7 Moffat Blvd, Manteca, California May 5, 1995 Underground Tank Investigation, Phase I Report of Findings Page: 5 from a Teflon bailer into clean glass vials with Teflon-lined screw caps and half gallon plastic containers provided by the laboratory Care was taken to ensure that no air space existed in the vials by inverting to check for bubbles and re-sampling if necessary The samples were analyzed or extracted within fourteen days according to their EPA methods Water samples collected for analysis were analyzed by EPA method 602 for ' BTX&E, method GCFID (5030) for TPH Gasoline and GCFID (3510) for TEPH Analyses were conducted by California Laboratory Services, Inc, a State-certified ' laboratory in Rancho Cordova, California. 4.0 Local Geology Manteca lies in the Central Valley Physiographic Province of California The Valley is about 40 mules 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 Manteca area is nearly devoid of structural geologic features The Valley is floored by anconsolidated Quaternary sediments to depths of at least 400 or more feet in the Manteca area All of these units can be considered soils 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 ' major streams which drained the Sierra Nevada Range emptied into the broad expanses of the valley The coarser sediments which comprise the fans are mainly arkosmc in composition and were derived from erosion associated with glacial stages in. the mountains The finer grained sedanents are predommnantly 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 Lacustnne, 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 major 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 hthology at thins site is characterized as thinly bedded silty sands, well-graded sands, silts and clays(Figures 4 & 5) Saturated sands below the water table became very fluid ("heaved", "flowed", "caved") and made well installation very difficult 1