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Reclamation, 1982). Ground water moving through the shale or shale-derived soils dissolves salts. The ground water discharges to drainage ditches or natural drainages that ultimately discharge to the Gunnison River and then to the Colorado River. Selenium concerns in the Colorado River Basin are more recent than the concerns raised about salinity in the 1970's. Since 1985, a multiagency program within the Department of the Interior, the National Irri- gation Water Quality Program (NIWQP), has done investigations at various irrigation projects in the Western United States to determine if irrigation drainage was having adverse effects on water quality, Whitewater 38°57'30",G f ? 38°42`30" / 38°12'30"4 Ridgway Ridgwa? Reseruoir 1 Figure 1. Location of the lower Gunnison River Basin and study area. fish, and wildlife. Beginning in 1988, NIWQP studies have been done in the Uncompahgre Valley and Grand Valley in west-central Colorado. High levels of sele- nium were reported in some water, sediment, and biota samples in both valleys (Butler and others, 1996). Because selenium concentrations in some fish- and bird-tissue samples were at levels of concern, in late 1994 the NIWQP initiated the planning phase (phase IV) for remediation. One of the objectives of the NIWQP planning phase was to determine what, if any, remediation methods could be used to reduce selenium loading from irrigation sources to the Uncompahgre and Gunnison Rivers (fig. 1). 39°12'30" ?•? 107°47.30/ 108°02'30" ./?.•?. \108'27'30" ?''`?•.?•, Lower Gunnison River Basin Sweitzer Delta Lake ?pitr Riuer 107°22'30" JJJ .j c 07 /_4 38°2730" •Ne - \ Montrose Arroyo 10 15 20 25 MILES 0 5 10 15 20 25 KILOMETERS 2 Effects of Piping Irrigation Laterals on Selenium and Salt Loads, Montrose Arroyo Basin, Western Colorado LOCATION MAP