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KLEINFELDER 5.2.1 Regional Geology The J-M Mfg. facility is located near the center of the Great Valle of California. The marine g Y Y sediments of the Great Valley were deposited approximately 35 to 150 million years ago. This sequence of marine clays, silts, and sands is approximately 6,000 feet thick under the site. Sediments derived from the eroding Sierra Nevada's in the east and the Coast Ranges in the west were deposited in the Great Valley by rivers and streams from about 35 million years ago to the present. In the vicinity of the J-M Mfg. facility, the marine sediments are generally overlain by unconsolidated Tertiary and Quaternary sediments of the Valley Springs, Mehrten, Laguna, and Victor Formations. Sediments of these formations were deposited by the activity of the major streams in this area (Calaveras and San Joaquin Rivers) which meandered across the valley floor. Additional information on the regional-and local geology of the Stockton area is presented in the SWAT proposal for the J-M Mfg. site (March 1, 1989). The most recent deposit in the Stockton area is the Victor Formation. The Victor Formation is typically heterogeneous and laterally and vertically discontinuous, indicative of a fluvial depositional environment. The Victor Formation is generally coarse grained, but is slightly clayey in the interfan sediment areas in the vicinity of Stockton. In the vicinity of the J-M Mfg. facility the Victor Formation is approximately 120 feet thick. 5.2.2 Site Geology Subsurface information exists for the J-M Mfg. site in the form of boring and monitoring well dogs from field activities performed in the summer of 1989. In addition, four soil borings were drilled at the facility by Kleinfelder in 1972. The information concerning site geology obtained during the 1972 investigation is discussed in the SWAT proposal. A fence diagram was prepared from information obtained when logging the monitoring wells and borings drilled during the SWAT investigation. The fence diagram is contained in the SWAT prepared by Kleinfelder dated June 27, 1990. The fence diagram indicates that a clay rich soil is encountered from the surface to a depth of approximately 10 to 15 feet followed by a fairly continuous silt layer to approximately 20 to 25 feet. The exceptions are that MW-1 does not have clay at the surface and MW-2 has a minor amount of sand at the surface underlain by clay. Below the silt layer continuous layers of clay underlain by sand are CR14-92-12 Page 15 of 39 24-220109-1709 Copyright 1992 Kleinfelder, Inc.