Reconnaissance Investigation of Water Quality, Sediment, and Biota Associated with Irrigation and Drainage

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1 RECONNAISSANCE INVESTIGATION OF WATER QUALITY, BOTTOM SEDIMENT, AND BIOTA ASSOCIATED WITH IRRIGATION DRAINAGE IN THE MIDDLE ARKANSAS RIVER BASIN, COLORADO AND KANSAS, 1988 -89 David K. Mueller, Lawrence R. DeWeese, A. Jack Garner, and Timothy B. Spruill ABSTRACT During the last several years, concern by the U.S. Department of the Interior has been increasing about the potential effects of irrigation drain- age on the health of humans, fish, and wildlife. During 1988, a reconnais- sance investigation was made of irrigation - drainage quality in the middle Arkansas River basin in southeastern Colorado and southwestern Kansas. This area was selected because high concentrations of selenium previously had been detected at several sites on the Arkansas River and its tributaries. This investigation was part of a program initiated in 1985 by the U.S. Department of the Interior to evaluate the effects of irrigation drainage on water quality, bottom sediment, and biota in the Western United States. Water, bottom- sediment, and biota samples were collected at 14 surface - water sites - -7 sites on the Arkansas River, 2 sites on tributary streams, and 5 sites on reservoirs. Ground -water samples were collected from five municipal wells completed in the Arkansas River valley alluvial aquifer. Drainage from irrigated land underlain by marine shale affects the Arkansas River between La Junta, Colo., and Deerfield, Kans.; two tributary streams in the vicinity of Pueblo, Colo.; and several off - channel reservoirs. Selenium was the only trace constituent associated with irrigation drainage that was detected at elevated concentrations in water, bottom sediment, and biota. Selenium concentrations in surface water ranged from 1 microgram per liter, in Pueblo Reservoir near the upstream end of the study area in Colorado, to 52 micrograms per liter in the St. Charles River near Vineland, Colo. The maximum concentration detected in alluvial ground water was 29 micrograms per liter at Las Animas, Colo. State drinking -water standards and the . U.S. Environmental Protection Agency maximum contaminant level for selenium (10 micrograms per liter) were exceeded at three streams sites and three ground -water sites. State aquatic -life standards and the U.S. Environmental Protection Agency criterion for acute exposure to selenium were not exceeded at any sites on the Arkansas River or in any reservoirs. However, the Colorado standard for chronic exposure and the U.S. Environmental Protection Agency criterion for chronic and acute exposure were exceeded in two tributary streams. The U.S. Environmental Protection Agency criterion for chronic exposure was exceeded at four sites on the Arkansas River and in three reservoirs. 1