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<br />.-4 <br />OJ <br />M <br />N <br />c. <br />C' <br /> <br />valley transition zone, and (3) the Virgin Valley zone. The aquifers <br />are Paleozoic carbonate rocks and Quaternary Littlefield Formation. <br />The spring locations and source are controlled by fault zones and <br />lithology in an environment that is arid to semiarid. The Littlefield <br />Springs have essentially constant discharge and quality of 65 ft3/s at <br />2,940 mg/L TDS. Tritium analysis of the springs and river water <br />indicates that there are at least two different sources of recharge to <br />the Littlefield Springs; one a minimum of 22 years old and the other <br />less than 22 years old. Analysis of the losing reach of the Virgin <br />River upstream from the springs indicates an average annual water loss <br />of 50 ft3/s having 2,130 mg/L and the same ionic ratio of dissolved <br />const ituents at the spri ngs. Local recharge to the spri ngs has been <br />estimated to be 11 ft3/s. Trudeau concluded that the most likely <br />sources of water to the Littlefield Springs are percolating Virgin <br />River water and local recharge from precipitation within the springs <br />basin. <br /> <br />Because of the way the springs are spread out along the river, <br />the investigation concentrated on the group of springs in the vicinity <br />of Littlefield. A group was chosen having an average combined flow of <br />5.7 ft3/s and an average salinity of 2,960 mg/L. Based on this, the <br />sa lt contributi on to the ri ver averages 16,700 tons per yea r. The <br />mineral salts in the spring discharges are chiefly carbonates, <br />sulfates, and chlorides of calcium and sodium. The springs are <br />unsatisfactory for domestic use, but they are used to irrigate salt <br />tolerant crops near Littlefield. <br /> <br />An interesting observation was that the springs caused the river <br />to be slightly "milky" for several miles downstream from Littlefield <br />during low flow. This was attributed to the formation of minute <br />particles of calcium carbonate precipitate from the spring water, <br />which is supersaturated with calcium carbonate. Another interesting <br />finding was that several fields of hay were irrigated entirely with <br />spring water having a salinity of about 3,000 mg/L. <br /> <br />12 <br />