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<br />other irrigated areas in the lower Gunnison River
<br />Basin. The BaR (1982, 1984) estimated that about
<br />360,000 tons/yr of salt from irrigation-induced
<br />sources in the Uncompahgre Project is conveyed to
<br />the Uncompahgre and Gunnison Rivers, and the salt
<br />ultimately is discharged to the Colorado River. The
<br />salt loading is attributed to conveyance-system losses,
<br />on-farm seepage, and deep percolation of irrigation
<br />water into weathered and fractured shale of the
<br />Mancos Shale and into alluvium derived from shale.
<br />As this irrigation-induced ground water flows through
<br />the shale, salt is picked up and eventually is
<br />discharged to drains and rivers and, thus, into the
<br />Colorado River system.
<br />The Winter Water Replacement Program of the
<br />Lower Gunnison Basin Unit (Bureau of Reclamation,
<br />1987) provides a replacement winter-water supply for
<br />livestock operators who depended on Uncompahgre
<br />Project canals and laterals for their livestock watering
<br />needs during the winter. Winter canal flows were
<br />terminated, and replacement water supplies were
<br />provided by expanding the existing rural domestic-
<br />water systems. The replacement program was
<br />expected to decrease salt loading to the Colorado
<br />River by 74,000 tons/yr. As of October 1994, the
<br />replacement program was 95 percent complete.
<br />The East Side Lateral Program of the Lower
<br />Gunnison Basin Unit is planned to replace about
<br />195 mi of earthen irrigation laterals and about 7 mi
<br />of small canals east of the Uncompahgre River with
<br />underground pipeline. That program is planned to
<br />decrease salt loading from the Uncompahgre Project
<br />to the Colorado River by about 65,000 tons/yr.
<br />Implementation of the program was scheduled to
<br />begin in fiscal year 1995; however, as of early 1996,
<br />this project has not been started.
<br />The Grand Valley Unit is a salinity-control
<br />project that consists of the Colorado River Valley
<br />between Palisade and the Colorado-Utah State line.
<br />The Grand Valley Unit contributes an estimated
<br />580,000 tons/yr of salt to the Colorado River through
<br />deep percolation of waler from canals, laterals, and
<br />on-farm irrigation (Bureau of Reclamation, 1983,
<br />1985). Between 1980 and 1982, the BaR lined 7 mi
<br />of canal and placed 34 mi of earthen laterals in
<br />underground pipeline in the Reed Wash Basin (fig. 3)
<br />for a test program known as Stage One (Bureau of
<br />Reclamation, ] 978). Post-construction monitoring
<br />indicated that Stage One improvements decreased the
<br />
<br />annual salt loading to the Colorado River by
<br />21,900 tons. The Stage 1\vo program of the Grand
<br />Valley Unit presently (1996) is under construction
<br />and completion is scheduled in 1998 (Bureau of
<br />Reclamation, 1985, 1986b). Stage 1\vo is planned
<br />to replace about 320 mi of laterals with underground
<br />pipeline and to line about 40 mi of canals, decreasing
<br />the salt loading to the Colorado River by an estimated
<br />15 I ,000 tons/yr.
<br />The Natural Resources Conservation Service
<br />(NRCS), formerly the Soil Conservation Service of
<br />the U.S. Department of Agriculture, is conducting
<br />the on-farm parts of the salinity-control program in
<br />the Lower Gunnison Basin Unit and in the Grand
<br />Valley Unit. The total irrigated area in the Lower
<br />Gunnison Basin Unit that was studied by NRCS
<br />was 171,000 acres, which includes the Uncompahgre
<br />Project. The estimated total salt loading from irriga-
<br />tion sources in the Lower Gunnison Basin Unit (the
<br />17 I ,000 irrigated acres) was about 640,000 tons/yr
<br />(Bureau of Reclamation, 1984). The NRCS is
<br />improving the private on-farm irrigation water
<br />delivery and application systems through a volunteer
<br />cost-share program. Those improvements include
<br />leveling of irrigation land, underground and gated
<br />pipelines, sprinkler and drip-application systems,
<br />concrete-lined ditches, and associated irrigation water-
<br />management practices. The NRCS estimates that the
<br />total salt decrease attributed to on-farm improvements
<br />to be about 166,000 tons/yr in the Lower Gunnison
<br />Basin Unit and about 132,000 tons/yr in the Grand
<br />Valley Unit (Hedlund, 1994).
<br />
<br />Previous Studies
<br />
<br />Much of the water-quality data collected in the
<br />study area were for salinity studies. As a result, trace-
<br />constituent data often were not collected; however, a
<br />few studies provide selenium concentrations in water,
<br />soil, plants, and biota in the Uncompahgre Project
<br />area and the Grand Valley. Selenium data were
<br />collected as early as 1934-36 in the Uncompahgre
<br />Project area and in the Grand Valley (Anderson and
<br />others, 1961). These data were for the Gunnison and
<br />Colorado Rivers in the Grand Junction area, for the
<br />Uncompahgre River, for a few drains in irrigated
<br />areas of the Uncompahgre Valley and Grand Valley,
<br />and for soil and saIl-crust samples. Anderson and
<br />others (1961) reported a selenium concentration of
<br />
<br />14 Detailed Study of Selenium and Other Constituents In Water, Bottom Sediment, Soli. Alfalf., and Biota A880clated with
<br />Irrigation Drainage In the Uncompahgre Project Area and In the Grand Valley, We8toCentral Colorado,l991-93
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