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M <br /> PRE-TANK REPLACEMENT Site Assessment Work Ptan <br /> 420 WEST KETTLEMAN LANE,L001, CA. <br /> Aegis Project No. 89-013 <br /> Page 8 <br /> 2.7 Site GeolOqY <br /> Surface geologic units in the vicinity of the site are depicted on the <br /> "Geologic Map of California" as Quaternary basin alluvium consisting <br /> of unconsolidated poorly sorted basin deposits from clay to boulder <br /> size. The deposits are considered to be of Holocene age (10,000 years <br /> ago to present) . Underlying the Holocene Alluvium is the Pleistocene <br /> Victor Formation which consists of unconsolidated sands, silts (with <br /> varying degrees of cementation) , clays and gravels along old stream <br /> channels which vary from 0-100 feet thick. <br /> 2.8 site HydragBolo <br /> Alluvial deposits in the Lodi area contain horizons of gravel, sand, <br /> silt, and clay. Horizons of gravels and sand deposits act as important <br /> recharge areas And yield large amounts of water to wells while <br /> horizons of silt and clay are low in permeability, and do not yield <br /> significant amounts of water to wells. The water bearing formation <br /> immediately beneath the site is the Victor Formation. Well logs from <br /> mater and monitoring wells in the area of the site indicate that <br /> ground water beneath the site is between 55 and 65 feet below grade. <br /> The local hydraulic gradient is anticipated to be toward the southeast <br /> (DWR 1967) . <br /> 2.9 Regional Geology <br /> The site lies within the northern section of the San Joaquin Valley, <br /> which is located in the southern portion of the Great valley Province. <br /> The San Joaquin Valley is a structural trough extending south from the <br /> Sacramento-San Joaquin Delta to the Tehachapi Mountains. The San <br /> Joaquin Valley is bounded by the Sierra Nevada in the east and the <br /> Coast Ranges in the west. <br /> Cretaceous sandstones and shales overlay pre-Cretaceous ultra basic <br /> igneous rocks, granitic rocks, and metamorphosed sedimentary and <br /> volcanic rocks. Sediments originating from the Sierra Nevada and the <br /> Coast Ranges were deposited in a marine environment during the <br /> Cretaceous and the Pleistocene periods. Interruptions in the pre- <br /> Pleistocene sedimentary depositional cycle occurred several times as <br /> volcanic activity, uplift, faulting and/or folding altered the region. <br /> From the Pleistocene to the Present, deposition has been alluvial-. <br /> The subject site is situated near the axis of the San Joaquin trough. <br /> Recent Alluvium and the Victor Formation overlay the Laguna Formation. <br /> The Laguna Formation consists of clay and sand units and unconformably <br /> -.--over I ays-the--ande E;itic-_sediments--af-the--Mehr-ten-Format i on—From--the------ <br /> Pleistocene: to the present, the depositional environment has been <br /> alluvial. Several thousand Biet of unconsolidated silty, sandy and <br /> gravelly sediments lie within the basin (DWR 1967) . <br /> a <br />