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<br />1:'- <br />0") <br />tv, <br />N <br />c' <br />{~ <br /> <br />Q = <br /> <br />dh <br />KA -, where <br />d1 <br /> <br />Q = Ground-water underflow. <br /> <br />K = Hydraulic conductivity. <br /> <br />A = Cross sectional area perpendicular to ground- <br />water flow direction. <br /> <br />dh <br />dl <br /> <br />= <br /> <br />Change in Head <br />Change in Length <br /> <br />= <br /> <br />Slope of water table. <br /> <br />The hydraulic conductivity was determined to be 0.037 feet per <br />second (ft/s) by dividing the average transmissivity from the aquifer <br />test (3.14 ft2/s) by the saturated thickness (86 feet). The cross <br />sectional area through which ground-water flows was determined to be <br />69,500 square feet (ft2) by planimetering the previously shown cross <br />section. The slope of the water table was assumed to be 0.006 the <br />same slope as the riverbed. The estimated underflow at the barrier <br />site is 15.5 ft3/s. <br /> <br />Ground-Water Quality <br />Ground-water quality data were gathered on six existing wells in <br />the Lower Virgin River area during the summer of 1979. Three of these <br />existing wells were developed in the stream alluvium. Additionally 10 <br />shallow observation wells 10 feet deep were installed in the vicinity <br />of the barrier axis for monitoring ground-water level and qual ity. <br />Well VID-102 was washed away in a flood during the spring of 1979. <br /> <br />The schematic cross section on Figure 3 shows the nature of the <br />quality of the underflow at the barrier axis. All availcble ground- <br />watel' quality information indicates the underflow in the stream <br />alluvium is not as saline as anticipated. A total of 125 tons of salt <br />per day is transported in the underflow at the barrier axis, basea on <br />an estimated average of 3,000 mg/L TDS. <br /> <br />17 <br />