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jf <br /> Delta Area I <br /> , i f <br /> s The Delta within San Joaquin County generally <br /> Plil <br /> contains ground water of undesirable mineral quality <br /> throughout its entire surface area and from Just below pi <br /> ' ground surface to the depth of unconsolidated sediments <br /> (see Figure 15) . The few exceptions are local lenses of <br /> + fresh water which <br /> are <br /> probably supplied from seepage from <br /> 3 <br /> ' the Delta channels , and areas in the northwest portion of <br /> n <br /> the County, where surplus surface water and ground water <br /> ' from the Mokelumne River system have probably flushed out <br /> I <br /> or diluted poor quality ground waters . iI <br /> The origin of the inferior quality ground waters it <br /> ' in the Delta is still a matter of speculation. There are <br /> i. <br /> ' several possible reasons for the poor quality waters under- <br /> lying the Delta. Among these, the following seem more likely ; <br /> however, there is no agreement on which source , or combination <br /> x I <br /> of sources , is most probable : <br /> 1. Poor quality water may have accumulated in the <br /> trough of the valley and then moved northward <br /> to be squeezed out of the trough by higher water <br /> levels or pressure from the south. <br /> 2 . A source of the inferior water in the Delta <br /> could be rising connates . These connates , <br /> deposited with the Deltaic sediments , are <br /> subject to pressure from surrounding areas and <br /> consequent upward movement in the Delta. The <br /> comparison of ratios of Delta ground water <br /> constituents with those of saline connates , II. <br /> indicates that this could be a possibility . <br /> i <br /> i <br /> I� <br /> 1. -103- L. <br /> I. <br />