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<br />The recommended I imit for fluoride in drinking water (lJ. S. Publ ic <br />Health Service, 1962) Is a function of annual average maximum dai ly <br />air temperature. In the basin the recommended limit is about 1.3 <br />mg/l. It "S apparent that this I imit is exceeded in a large area. <br />The flouride concentration increases with depth and distance from <br />the basin periphery. Water from depths of about 800 feet (244 m) <br />or more generally contains higher amounts of flouride than does <br />water from shallower depths. <br /> <br />With few exceptions, the temperature of water in the confined <br />acquifer is directly related to depth. The average temperature <br />gradient is about 1.20 C (2.20 F) per 100 feet 00.5 m) of depth. <br />Comparison of this gradient with work by Van Orstrand (1935) <br />indicates this temperature gradient is not extreme. Working with <br />similar depths, Van Orstrand concluded that the range in temperature <br />gradients for nonvolcanic areas is 0.70 to 2.70C per 100 feet <br />(30.5 m). ' <br /> <br />( ,~, <br />v. <br /> <br />1..... <br />, \..' ".. <br /> <br />D-8 <br />