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Eckert Cold Storage Company 7S7Moffat Blvd, Manteca, California November 26, 1997 • Underground Tank Investigation, Continued Phase I Report of Findings Page: S 1 which does not introduce air into the water column, or a Teflon bailer. The pH, ' temperature, and electrical conductivity of the water was monitored as the well was evacuated. These parameters were noted on a Field Log. Instruments calibrated to known standards were used to monitor these parameters. ' At least three well volumes were evacuated from each welland more if necessary, ' until the above parameters had stabilized. Wells that were de-watered before evacuation of three well volumes had been accomplished were sampled upon eighty percent recovery of the initial water level. The wells or other sampling points were ' sampled in order of the least to the most contaminated, as best known or estimated. The samples were pumped from a stainless steel bladder pump or carefully poured 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- Diesel. 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 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 Manteca 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 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 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, (Ackley, 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