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<br />..-l <br />co <br />c" <br />N <br /> <br />r. <br />-- <br /> <br />o <br /> <br />Sll!I~I!al'L-,I~1i_~.o!lcl ~15i (1.!IS <br />The Virqin Rivet" originates in the lIIollllldins III sOlltherll lItdh dlld <br />flows past the towns of St. George, Utah and Mesquite, Nevada before <br />discharging into Lake Mead, a mainstream Colorado River reservoir. <br />The Lower Virgin River extends from the downstream end of the Virgin <br />Ri ver Gorge, a deep gorge downstream from St. George, to Lake Mead. <br />It contains numerous saline springs averaging 2,900 mg/L. About <br />3,500 acres of irrigated agriculture are served with water from the <br />river. The flow in the Lower Virgin River varies greatly during the <br />yea r, from hi gh flows up to 35,200 cubi c feet per second (ft3 / s) <br />duri ng the wi nter and spri ng to a low of between 40 and 60 ft3/ s <br />during the late summer, when flow through the narrows ceases entirely <br />and the springs provide the only flow in the lower reach, <br /> <br />The investigation proceeded through three sequential phases. It <br />began in 1972 as the Littlefield Springs Unit of the CRWQIP. The <br />initial approach was to study the saline Littlefield Springs, with a <br />view to diverting them from the river's edge and treating them or <br />disposing of them in some way. However, such a project was <br />strenuously opposed locally because the springs form the only reliable <br />water supply for downstream irrigation during the summer when surface <br />flows cease in the river. <br /> <br />Consequently, this approach was abandoned and beginning in 1977 <br />the possibility of extracting saline underflow from the riverbed <br />downstream from the irrigated areas was studied. Available <br />information on flows and salinity indicated that less salt was leaving <br />the reach in surface flow than was entering it, and it was postulated <br />that unaccounted for salt was leaving the reach as underflow in the <br />alluvial bed of the river. Preliminary calculations indicated that <br />the underflow would contain water with as much as 32,000 mg/L of <br />dissolved salts. An exploration program was conducted which involved <br />installing a line of observation wells across the alluvial valley <br />fill. However, the results showed that the average water quality was <br />only about 3,000 mg/L, far less saline than needed to support a <br />project for its extraction and treatment or disposal. <br /> <br />3 <br />