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It was assumed that the measured changes in
<br />selenium and salt loads during the period of this study
<br />were solely attributed to the lateral project. Housing
<br />and golf-course development were occurring in the
<br />study area during 1998-2000. The long-term effects of
<br />new development on selenium and salt loads, espe-
<br />cially the conversion of agricultural land to residential
<br />or commercial uses or development on previously
<br />nonirrigated land in shale areas, is unknown. In
<br />November 2000, the USGS began monthly sampling
<br />at two of the sampling sites on Montrose Arroyo to
<br />monitor long-term changes in selenium and salt loads.
<br />REFERENCES CITED
<br />Bureau of Reclamation, 1978, Stage One development,
<br />Grand Valley Unit, definite plan report-Appendix A,
<br />hydrosalinity, land resource, economics: Salt Lake
<br />City, Bureau of Reclamation, five numbered sections
<br />plus attachments.
<br />-1982, Lower Gunnison Basin Unit-Feasibility
<br />report-Appendix B, hydrosalinity: Salt Lake City,
<br />Utah, Bureau of Reclamation, 86 p.
<br />Butler, D.L., Wright, W.G., Stewart, K.C., Osmundson,
<br />B.C., Krueger; R.P., and Crabtree, D.W., 1996,
<br />Detailed study of selenium and other constituents in
<br />water, bottom sediment, soil, alfalfa, and biota associ-
<br />ated with irrigation drainage in the Uncompahgre
<br />Project area and in the Grand Valley, west-central
<br />Colorado, 1991-93: U.S. Geological Survey Water-
<br />Resources Investigations Report 96-4138, 136 p.
<br />Butler, D.L., and Osmundson, B.C., 2000, Physical, chem-
<br />ical, and biological data for the Uncompahgre Project
<br />area and the Grand Valley, west-central Colorado,
<br />1993-98: U.S. Geological Survey Open-File Report
<br />99-453, 216 p.
<br />Duke, H.R., Kruse, E.G., Olsen, S.R., Champion, D.F., and
<br />Kincaid, _D.C., 1976, Irrigation return flow water
<br />quality as affected by irrigation water management in
<br />the Grand Valley of Colorado: Fort Collins, Colo., U.S.
<br />Department of Agriculture, 123 p.
<br />Helsel, D.R., and Hirsch, R.M., 1992, Statistical methods in
<br />water resources: Amsterdam, Elsevier Science
<br />Publishers, 529 p.
<br />U.S. Department of the Interior, 1999, Quality of water-
<br />Colorado River Basin: Salt Lake City, Utah, Bureau of
<br />Reclamation, Upper Colorado Region, Progress report
<br />no. 19, 93 p. plus appendix.
<br />14 Effects of Piping Irrigation Laterals on Selenium and Salt Loads, Montrose Arroyo Basin, Western Colorado
<br />* U.S. GOVERNMENT PRINTING OFFICE: 2001 - 773-096 J 47089 Region No. 8
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