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streamflow is at its minimum, the predominant ions are sodium and sulfate. The predominant ions are calcium and bicarbonate during the high streamflow months, April-July. Annual monotonic-trend analysis for 1951-83 indicated a significant increase in median annual streamflow of 6,440 acre-ft/yr and a marginally significant increase in median annual dissolved-solids load of 1,310 tons/yr (table 8). During the 33 years of record, these increases represent a 71-percent change in median annual streamflow and a 50-percent change in median annual load. Green River near Jensen, Utah (site 41) Streamflow at site 41 (table 3, pl. 1) is a mixture of water released from Flaming Gorge Reservoir and water from the Yampa River. The decreased seasonal variability and enhanced low flows since 1962 are shown in figure 18D, but the figure also shows the substantial input from the (Yampa River during the snowmelt-runoff season. Mean annual streamflow averages about 3.2 million acre-ft, and mean annual flow-weighted dissolved-solids concentration is 341 mg/L (table 7). The Yampa River dilutes the dissolved- solids concentration of the Green River by about 150 mg/L. Calcium, bicarbonate, and sulfate are the predominant ions during the high-flow season. Calcium, sodium, and sulfate predominate during the low-flow season. The period of record (1962-83) for dissolved solids coincides with the period following completion of Flaming Gorge Reservoir. No statistically significant trends were detected for this postintervention period. Duchesne River at Duchesne, Utah (site 42) Site 42 (table 3, pl. 1) is upstream from most of the irrigated land in the Duchesne River basin. Streamflow is depleted by the Duchesne Tunnel and by the diversions to Starvation Reservoir, which was completed in 1970, a few months before water-quality sampling was discontinued at the site. Mean annual flow-weighted dissolved-solids con- centrations were not large, averaging 189 mg/L during water years 1962-69 (table 7). Calcium and bicarbonate are the predominant ions throughout the year. Streamflow at site 42 probably has decreased since 1970, because of offstream storage in Starvation Reservoir. Duchesne River near Randlett, Utah (site 43) Streamflow at site 43 (table 3, pl. 1) near the mouth of the Duchesne River is greatly depleted by transbasin ex- ports and by consumptive use for irrigation. A considerable part of the base flow comes from agricultural return flows (fig. 18E). Mean annual streamflow is about 43 percent greater than at site 42, but mean annual dissolved-solids load increases fivefold, averaging 351,000 tons during 1957-83 (table 7). Streamflow is lowest and dissolved-solids concen- tration is highest during August through October. The mean annual flow-weighted dissolved-solids concentration at site 43 is 650 mg/L (table 7). Sodium and sulfate are the predomi- nant ions most of the year; calcium and bicarbonate also become predominant during the high flow months (May- July). Most of the dissolved-solids load, especially dissolved sodium and sulfate, may be from irrigation-return flow through the Tertiary Uinta and Duchesne River Formations, which contain gypsum and other evaporites (Mundorff, 1977). Excess salinity in poorly drained agricultural soils has been increasing in magnitude in the basin. The dissolved- solids load at site 43 is the largest source of dissolved solids in the Green region. Furthermore, a large but unquantified dissolved-solids load from the lower Duchesne River basin enters the Green River by means other than the Duchesne River (Mundorff, 1977). Because the enlarged part of Strawberry Reservoir had not been filled by 1983, annual step-trend analyses did not indicate any statistically significant trends. Annual monotonic-trend analyses for the entire period of record (1957-83) also did not indicate any statistically significant trends. White Subregion The White subregion includes a drainage area of about 5,000 mil. The headwaters of the White River are in the White River uplift, which is composed primarily of relatively insoluble Pennsylvanian and Permian rocks. The lower parts of the White subregion have abundant outcrops of relatively soluble Cretaceous and Tertiary sedimentary rocks, but dissolved-solids load is not large because little runoff is generated. About 33,000 acres is irrigated, including large tracts near the river upstream from Meeker, Colo., that are underlain by Mancos Shale. No transbasin exports occur from the White subregion, and no large reservoirs exist in the subregion. Many drilling operations for oil and gas have occurred throughout the subregion. A major point source of dissolved solids existed in the Meeker Dome area, just north of the White River upstream from Meeker, Colo. Highly saline water from deep aquifers was seeping upward through aban- doned and improperly plugged oil exploration wells drilled during the 1920's. Water from the Pennsylvanian and Per- mian Weber Formation was postulated to be rising through the deeper wells and discharging through the relatively shallow Meeker well (U.S. Bureau of Reclamation, 1983). Flow of about 3.2 ft3/s that had a dissolved-solids concen- tration of 19,200 mg/L was measured at the Meeker well. The dissolved-solids load was 57,000 tons/yr, mostly as dissolved sodium and chloride (U. S. Department of the Interior, 1985). The well was plugged in October 1968. The next year, seepage again occurred in the area and had an estimated dissolved-solids load of 27,000 tons/yr. In 1980 and 1981, three more abandoned wells were plugged. Water levels in observation wells declined, and the resulting decrease in dissolved-solids load was estimated to be 18,000 tons/yr. White Subregion 43