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S E C 0 R '-- 3.3 Geology The site is in the Central Valley, which is a structural depression (approximately 400 miles long and 20 to 70 miles wide) extending from Redding to the Tehachapi Mountains. Water - producing deposits in the valley are primarily unconsolidated continental deposits (alluvium) of Pliocene age that extend to depths of up to 3,500 feet (USGS, 1998a). The Central Valley is divided into two distinct valleys, each drained by a major river. The northern one-third of the valley is called the Sacramento Valley and the southern two-thirds are called the San Joaquin Valley. The two valleys are separated by an area commonly called the Delta, where the Sacramento and San Joaquin Rivers meet and discharge through a natural outlet at Suisun Bay and into San Francisco Bay. Topographically, the Central Valley is relatively flat and of low altitude. Altitudes in the Valley are mostly less than 500 ft above MSL. Maximum altitudes of about 1,800 ft occur at the apexes of some alluvial fans and on the Sutter Buttes to the north. In general, the Central Valley is a long, northwest -trending, asymmetrical structural trough that is filled with sediments. Continental deposits of post -Eocene to Holocene age overlie marine sedimentary rocks. The continental deposits include some volcanic material but contain mostly fluvial deposits with lesser amounts of interbedded lacustrine deposits. The continental deposits consist predominantly of lenses of gravel, sand, silt, and clay. The numerous lenses of fine-grained deposits (clay, sandy clay, sandy silt, and silt) are distributed throughout the valley and constitute over half of the total thickness penetrated by wells. Most of the lenses are not widespread, although several major ones have been mapped in the Valley. Locally, the site is relatively flat and is situated approximately 43 ft above MSL. Soil in the vicinity of the site consists of Pliocene to Holocene continental rocks and deposits consisting of heterogeneous mix of generally poorly sorted clay, silt, sand, and gravel (R.W. Page, 1986). The nearest surface water is South Main Canal, located approximately 0.75 miles west of the site. Pixley Slough is located approximately 2.5 miles north of the subject site. 3.4 Hydrology The Central Valley aquifer within the area of the site is primarily composed of continental deposits. The thickness of the deposits average about 2,400 ft and increases from the north to south. These deposits constitute the primary groundwater reservoir in the Central Valley. 3.5 Stratigraphic Profile The stratigraphic profile at the site and vicinity consists of unconsolidated fluvial deposits that are post -Eocene in age. A review of the City of Lodi water supply well logs indicates that the deposits extended to over 500 ft bgs. 95775 NFAR REPORT Final.doc 6 SECOR lntemational Incorporated