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<br />on2353 <br /> <br />day. The drainage ditch into the lake at site 6 probably receives water from <br />the GF lateral (fig. 8), which is a lateral from the East Canal, and water at <br />site 6 may be surface runoff and shallow drainage from nearby fields. There <br />was no flow at site 6 during the January and March sampling visits. <br /> <br />Selenium concentrations in the three samples collected in March 1988 from <br />Sweitzer Lake (site 7 in table 16) exceeded the Colorado State water-quality <br />standard of 20 ~g/L for Sweitzer Lake (table 11). However, the selenium <br />concentrations in all samples collected from the lake exceeded the u.S. <br />Environmental Protection Agency's chronic criterion for protection of aquatic <br />life (5 ~g/L). Selenium concentrations in the samples collected from the lake <br />in March also exceeded the acute criterion for protection of aquatic life <br />(20 ~g/L). The State of Colorado does not apply water-quality standards to <br />irrigation canals; therefore, there are no State standards for selenium for <br />sites 5, 6, and 8. However, selenium concentrations in all samples collected <br />at those sites were greater than 5 ~g/L; selenium concentrations in all <br />samples collected at site 5 were greater than 20 ~g/L. Mercury was detected <br />in the samples collected in July 1988 (table 16) from Sweitzer Lake and in the <br />samples collected from both inflow sites (sites 5 and 6) and from the outflow <br />site (site 8). <br /> <br />In Sweitzer Lake, specific-conductance profiles indicated little change <br />in specific conductance from the surface to about the 20-ft depth, and <br />dissolved-solids concentrations in samples collected at the 1 and near 20-ft <br />depths were about equal during each of the four sampling surveys. The lake <br />was not thermally stratified at the time of sample collection in November, <br />January, and March. The lake was thermally stratified in July, and the <br />dissolved-oxygen concentration at the 20-ft depth was 0.2 mg/L. <br /> <br />A sample was collected from Sweitzer Lake near the dam (sample collected <br />March 30 at site 7 at a depth of 27 ft in table 16) from an anaerobic water <br />layer. Dissolved-solids, major-ion, nitrite plus nitrate, selenium, boron, and <br />uranium concentrations were considerably larger in this sample than in the <br />samples collected on the same day at the 1- and 19-ft depths (table 16). <br />Comparison of concentrations of constituents in the sample from the anaerobic <br />layer to the average concentrations for the same constituents in water samples <br />from the Garnet Canal (samples collected from November to March at site 5) <br />indicates that most of the water at the lake bottom was canal water or <br />irrigation-drainage water. The lake was not thermally stratified on March 30; <br />therefore, a chemocline may have formed in the lake during the winter. If <br />water that was sampled during November, January, and March in the diversion <br />ditch from the Garnet Canal (site 5) is assumed to be irrigation-drainage <br />water, then the irrigation-drainage water had much larger dissolved-solids <br />concentrations than the lake water. Therefore, the denser irrigation-drainage <br />water would sink to the lake bottom and would accumulate during the winter. <br />On May 10, specific-conductance and dissolved-oxygen were measured in the <br />deepest part of the lake near the dam. The dissolved-oxygen concentration <br />near the lake bottom was 5 mg/L, and specific conductance near the lake sur- <br />face and near the bottom was about 2,900 ~S/cm. These measurements indicate <br />that the anaerobic layer and the chemocline were not present, implying that <br />the lake had mixed sometime in April or early May. <br /> <br />45 <br />