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<br />~ <br />~:, <br /> <br />". <br />... ~ <br />"1;< <br /> <br />and the weight of the overlying formations, a deeply buried layer of <br />salt (Paradox Member) has flowed upward into the faulted area to create <br />an elongated swell known as an anticline. As this has taken place, the <br />Dolores River has remained in its ancestral streambed and, in combination <br />with other erosional forces, has removed the collapsing upper materials <br />to form the valley. <br /> <br />Much of the salt load of the river is derived from the underlying form- <br /> <br /> <br />ations in the form of a saline groundwater inflow. As Figure 4 illus- <br /> <br /> <br />trates, this brine layer is generally overlain by a thin layer of fresh <br /> <br /> <br />water to the west of the river. However, the brine surfaces to intersect <br /> <br /> <br />the river channel in several places and is often higher than the streambed <br /> <br /> <br />to the east of the river. During a period of low riverflow, concentrations <br /> <br /> <br />as high as 240,000 mg/l were measured in several small pools discharging into <br /> <br /> <br />the river. <br /> <br />INVESTIGATION <br /> <br />Early estimates of the amount of salt entering the Dolores River in <br />Paradox Valley were based on spot measurements of the flow and quality <br />of stream as it enters and leaves the valley. Feasibility investigations <br />were initiat,~,l in Fiscal Year (FY) 1972, when stream gaging and water <br />quality stations were established at three sites: on the river at Bedrock <br />(as it enters the valley), on West Paradox Creek ( a tributary in the <br />valley), and on the river as it leaves the valley. Two years of continuous <br />flow measurements and weekly water quality samplings have verified the <br />preliminary estimate of 200,000 tons of salt pickup annually. The <br />average monthly salt pickup in tons/day is shown in ,Figure 5. During <br />this period, the salt concentration of the river has ranged from 140 mg/l <br />.to 3,700 mg/l at the-entrance to the valley and from 170 mg/l to 166,000 <br />mg/l at the exit. The latter reading occurred during a period of no <br />riverflow, when the water in the channel was composed entirely of surfacing <br />ground water and irrigation return flows. <br />flO~58R <br />In order to determine the depth and areal extent of the sali~e g~oun~ <br />water body, a resistivity survey was conducted along the river late in <br /> <br />7 <br />