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<br />The State standard for selenium for the lower Uncompahgre River of <br />35 ~g/L (table 11) is much greater than selenium criteria for protection of <br />aquatic life suggested by the u.s. Environmental Protection Agency (1987) and <br />by Lemly and Smith (1987). The u.s. Environmental Protection Agency (1987) <br />chronic criterion is a 4-day average selenium concentration that should not <br />exceed 5 ~g/L more than once every 3 years and the acute criterion is a I-hour <br />average selenium concentration that should not exceed 20 ~g/L more than once <br />every 3 years. Lemly and Smith (1987) reported that selenium concentrations <br />in water greater than 2 to 5 ~g/L might cause reproductive failure or <br />mortality in fish and waterfowl because of food-chain bioaccumulation. <br /> <br />The Statewide standard for uranium (for domestic water supplies) is <br />40 pCi/L (about 59 ~g/L) (Colorado Department of Health, 1988). There are <br />standards for a few of the pesticides in water; for protection of aquatic <br />life, the standard is 0.10 ~g/L of malathion, 0.04 ~g/L of parathion; for <br />domestic water supplies, standards are 100 ~g/L for 2,4-D and 10 ~g/L for <br />2,4,5-T (Colorado Department of Health, 1988). <br /> <br />Gunnison River <br /> <br />Concentrations of dissolved solids (fig. 10), sodium, sulfate, selenium <br />(fig. 11), boron, and uranium (fig. 12) in the Gunnison River generally were <br />greater at site 3 (at Delta) than at site 2 (below the Gunnison Tunnel) and <br />concentrations also were greater at site 11 (upstream from Escalante Creek) <br />than at site 3. Increases in constituent concentrations between sites 2 and <br />3 can be attributed to numerous sources and include inflow from the Smith <br />Fork, inflow from the North Fork, inflow from areas north of the Gunnison <br />River between the North Fork confluence and Delta that are drained by streams <br />such as Tongue Creek, and irrigation drainage from the Uncompahgre Project. <br />Irrigation drainage from the Uncompahgre Project into the Gunnison River <br />between sites 2 and 3 occurs in the stream reach between Peach Valley Arroyo <br />(fig. 2) and site 3. This reconnaissance investigation did not separate the <br />effects of irrigation drainage from the Uncompahgre Project on water quality <br />of the Gunnison River between sites 2 and 3 from the effects of upstream tri- <br />butaries. The Smith Fork, North Fork, and Tongue Creek drain irrigated areas <br />outside the Uncompahgre Project area. There also are other potential sources <br />of trace elements, such as coal mines, in the North Fork basin. <br /> <br />Most increases of constituent concentrations in the Gunnison River <br />between sites 3 and 11 can be attributed to water discharging from the <br />Uncompahgre River and Roubideau Creek (fig. 2). Much of the irrigation <br />drainage from the Uncompahgre Project discharges into the Uncompahgre River. <br />Constituent loads for the four sets of samples collected from the Gunnison <br />and Uncompahgre Rivers were examined to approximate the constituent loading <br />of the Uncompahgre River to the Gunnison River. The difference (gain) in <br />constituent loads between sites 3 and 11 was compared to the constituent loads <br />at site 9 (Uncompahgre River at Delta). Generally, at least 50 percent of the <br />increase of dissolved-solids, sodium, sulfate, chloride, boron, selenium, and <br />uranium loads between sites 3 and 11 was accounted for in the Uncompahgre <br />River at site 9. <br /> <br />38 <br />