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Since 1985, the U.S. Department of the Interior has conducted a multiagency program named the National Irrigation Water Quality Program to assess effects of Federal irrigation projects on water quality and fish and wildlife in the Western United States. Field investigations have been done for the Uncompahgre Project Area and the Grand Valley in west-central Colorado. The data collected for a reconnaissance investigation in 1988-89 and for a detailed study in 1991-92 were published in previously released reports of the U.S. Geological Survey. Since 1992, considerable water, bottom-sediment, and biological data have been collected for additional studies and for remediation planning in the Uncompahgre Project area and in the Grand Valley. None of the post-1992 data have been published. This report contains all selenium data and other water-quality and chemical data for samples collected during water years 1993-97 in the two study areas. Also included in this report are chemical results for samples collected through March 1998 that have completed analyses. INTRODUCTION In 1985, the U.S. Department of the Interior (DOI) began a program to determine if irrigation drainage from DOI-constructed or managed projects was having adverse effects on water quality and on fish and wildlife in the Western United States. The program, named the National Irrigation Water Quality Program (NIWQP), had five phases (Deason, 1986): (1) Site identification, (2) reconnaissance investigations, (3) detailed studies, (4) planning, and (5) remediation. About 600 irrigation projects were initially screened for phase 1. Reconnaissance investigations and field screenings (phase 2) were done at 39 sites from 1986 to 1997 to determine whether irrigation drainage had caused or had the potential to cause harmful effects on human health or on fish and wildlife or could limit the beneficial use of water. Detailed studies (phase 3) were done at eight sites (through 1998) and were initiated if reconnaissance investigations indicated that potentially serious water-quality problems were related to irrigation drainage. The detailed studies were to provide the scientific information needed to develop alternatives to mitigate or resolve the problems. The purpose of remediation planning (phase 4) is to develop a plan of action for cleanup of sites, which involved the appropriate government agencies and private concerns. As of 1998, five study areas were involved in phase 4 remediation planning at various levels of activity. Phase 5 involves the implementation of corrective actions developed during the planning phase. As of 1998, one study area had begun remediation. A reconnaissance-level study was done of the Uncompahgre Project in west-central Colorado (fig. 1; pi. 1), which is a Bureau of Reclamation (BOR) irrigation project, and of Sweitzer Lake from late 1987 to 1989 (Butler and others, 1991). That study identified potentially adverse concentrations of selenium in some water, bottom sediment, and biota samples. All data collected in 1987-89 are listed in Butler and others (1991). On the basis of results of the reconnaissance investigation, a detailed study of the project area was started in 1991. The detailed study also included areas adjacent to and upstream from the irrigation project boundary (pi. 1) and was referred to as the

Physical, chemical, and biological data for the Uncompahgre Project area and the Grand Valley, west-central Colorado, 1993-98