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Y DeBoer Family Trust 201 West Sth Street, Ripon, California June 20, 1995 Soil/Groundwater Workplan Page: 6 in MW-3 at 25.5 and 26 feet, respectively. Both of these beds (SM& MH) do not appear in MW-1 and may account for the migration of contaminants to 15 feet in MW-1. v Ripon 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, s and to the east by the foothills of the Siena Nevada Range. The Ripon 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 Ripon 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 r-' composition and were derived from erosion associated with glacial stages in. the mountains. The finer grained sediments are predominantly composed of rock. flour ,. s 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 major climatic changes in the Sierras. This has resulted in a predominance of fine grained silts and clays in the subsurface of the area. i 5.0 Hydrology Water samples taken 7/27/94 from the three developed monitoring wells all tested "ND", r non-detect. Water level readings taken 7/27/94 and surveyed well collar elevations were t used to calculate the groundwater elevation at each monitoring well. The groundwater gradient was calculated at 0.003 ft/ft, dipping N 4°E. r, California and the Federal Govennment have mandated that virtually all groundwater is beneficial for current or future use unless it can be demonstrated that no beneficial use is rknown. This aquifer is considered to be of beneficial use and as a result, must be protected from contamination. Those identified uses include agriculture and industrial, as well as potential use for animal or human consumption. r f