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b <br /> S <br /> 15 <br /> MD <br /> Opar.flnjv, r <br /> REGIONAL NYDROGEOLOM C SETTING <br /> 5toc4ton is located in the -addle cf the Central Valley on the <br /> northern sdGe e` the [an Joaquin galley, lust south of theo <br /> structural <br /> uMljey, ;Ere Central Volley is a broad north 'st-trending <br /> trough bounded on the east by the Sierra Nevada and on the west by <br /> the northern Coast Ranges. fhe valley basement complex is composed <br /> of Paleozoic and 1•lerozoic metasediments and vcicanlcs as well t <br /> Jurassic end Cretaceous granitic rocks. Overlying the ba-set-lent <br /> complex is a thick sequence (up to }5,000 feet in the project area? <br /> ents c£ Jurassic to <br /> of „edimentery racks and unconsolidated edim <br /> Recent age. <br /> The unconsolidated sediments are of Pliocene to Recent aye and extend <br /> to depths of up to 5,000 feet in the Stockton area. These sediments <br /> csnsist chiefly of alluvium but in some areae include lacustrine and <br /> marsh or ..stuarine deposits- <br /> The unconsolidated sediments are the primary fresh-uater-bearing <br /> units in the Central Valley. Ground water occurs in both confined <br /> and unconfined conditions within these sediments, aecause both <br /> confined and unconfined water-bearing zones in much of the valley are <br /> considered°hydrologically interconnected, occurrence and rrnvement of <br /> ground u.zter within them are generally not difrerentiated. <br /> !}bile much of the regional water Supply comes from surface-water <br /> sources, a subelantial volume is also drawn from the ground-tiaier <br /> table by large irrigation and municipal wells- Proximity to these <br /> wells can often determine the local or regional direction of <br /> ,;: aund-cater flew. <br /> S:::me depression of the greund•uater table has occurred in the <br /> vicinity of the site. fl visual survey was conducted within 1/Z-nils <br /> of the site to identify nearby uells. The locations of identified <br /> wells are presented on Figure I. No information on construction or <br /> precise usage has yet been obtained for these wells. Itouever, <br /> conver5&tion5 with area residents indicate that most private wells in <br /> the re—cion are drilled to depths of 100 to 200 feet and tap the first <br /> encountered water-bearing zone. Therefore, the local direction of <br /> ground-uater flow is difficult to estimate but is presumed to <br /> parallel regional flow toward the northwest. <br /> kOO-1}:O! <br />