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�� �cir6' " .a a'a �f �� 3 3S�tm ,`���' ,n,F��. ���s� .�.� � �•�'-�,s�,c:s�.�_r ' -�- "�'a.�e,��--�� .�:--� �£ .,.s?�` �; . <br /> 1 <br /> F� • <br /> r�+1 <br /> x. <br /> CHAPTER 3 <br /> E HYDROGEOLOGY <br /> To evaluate the potential impact of groundwater quality in the <br /> vicinity of ARCO Service Station 434 on the City of Lodi (Lodi) <br /> groundwater supply, this section presents the regional and site- <br /> ' pecific hydrogeology. <br /> �" Re Tonal Gea.lo Y <br /> Lodi is underlain by three major geological units. in descending <br /> stratigraphic order they are: (1) unconsolidated alluvial sediments, <br /> (2) consolidated nonmarine and marine sedimentary rocks, and (3) <br /> metamorphic and igneous basement rocks. The regional geology w 9Y was <br /> determined from the Department of dater Resources Bulletin 118-6 and <br /> f ; the State Geological Map, Sacramento Quadrangle. <br /> Alluvial deposits of Quaternary age immediately <br /> These Formations, underlie Lodi, <br /> which may be up to 500 feet in thickness, are made <br /> # *J up of layers of sand, silt, and clay, with interfingered ancient <br /> stream channel deposits of sand and gravel. Permeability is variable <br /> except in the ancient buried stream channels where it is 9enerall <br /> high. These unconsolidated deposits contain fresh water, y <br /> Underlying these formations are hate Eocene through Pliocene- <br /> , � Pleistocene age, alluvial, and lacustrine deposits up to 2,620 feel <br /> �. in thickness. With the exception of the Eocene age formations, these <br /> formations are generally freshwater-bearing. <br /> f <br /> Underlying the nonmarine sequence are consolidated marine rocks <br /> of Cretaceous and Early Tertiary age, These rocks generally do not <br /> contain fresh water. <br /> Beneath the marine rocks are. metamorphic and igneous basement <br /> rocks. These rocks contain small localized quantities of saline <br /> water. <br /> Regional Groun,3water Flow <br /> - -- -The -Qua ter age ar, <br /> Y g d Plio-Pleistocene age sedimentary deposits <br /> supply groundwater for the Lodi area, Recharge to the regional <br /> groundwater system occurs by deep percolation of rainEalZ :and applied : <br /> irrigation water, by percolation of the .Mokelumne . <br /> `+ subsurface inflow fRiver, and by <br /> rom the east. Regional <br /> generally thought to be to the west and south groundwater movement is .. <br /> q <br />