WSP07583

• File Number: 8270.200
• Description: Selenium
• State: CO
• Basin: Gunnison
• Water Division: 4
• Date: 1/1/1996
• Author: USGS
• Title: Detailed Study of Selenium and Other Constituents in Water-Bottom Sediment-Soil-Alfalfa and Biota Associated with Irrigation Drainage - Uncompahgre Project Area and in the Grand Valley - 1991-93
• Water Supply Pro - Doc Type: Report/Study

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Specific objectives of this report are to:

\. Describe concentrations and distribution of
selenium and other trace constituents in soil and
in alfalfa in irrigated areas of the Uncompahgre
Project.
2. Describe the concentrations and distribution of
selenium and other trace constituents in ground
water in the Uncompahgre Project area and in
the Grand Valley and the hydrochemical
processes affecting selenium release and
mobilization in ground water in irrigated areas
on Mancos Shale terrain.
3. Discuss selenium concentrations and loads in the
Gunnison and Colorado Rivers.
4. Describe distribution and variability of selenium
concentrations in surface water and in bottom
sediment in irrigated areas in the Uncompahgre
Project area and in the Grand Valley.
5. Discuss selenium loads in streams, washes, and
drains in the Uncompahgre Project area and in
the Grand Valley and identify areas that are
major sources of selenium to the Gunnison,
Uncompahgre, and Colorado Rivers.
6. Describe concentrations and distribution of
dissolved solids, major constituents, and
selected trace constituents in surface water in
the Uncompahgre Project area and in the Grand
Valley and the relations of selenium to
dissolved solids and selected constituents.
7. Describe concentrations and distribution of
selenium and other trace constituents in fish,
aquatic plants, and aquatic invertebrates in
tributarY streams and washes draining the
Uncompahgre Project area and the Grand
Valley.
8. Describe concentrations and distribution of
selenium and other trace constituents in fish
from the Gunnison, Uncompahgre, and
Colorado Rivers and the potential effects of
selenium on threatened and endangered fish.
9. Describe concentrations and distribution of
selenium and other trace constituents in
waterfowl and their effects on waterfowl
reproduction in the Uncompahgre Project
area and in the Grand Valley.
10. Discuss food-<:hain bioaccumulation of selenium.
II. Discuss implications of selenium concentrations
to human health.

Soil, alfalfa, ground-water, mineralogic,
surface-water, bottom-sediment, and biota samples
were collected from March 1991 to August 1992 in the
Uncompahgre Project area and in the Grand Valley.
Selenium was the trace constituent of primary
concern. Some water, bottom-sediment, and aquifer-
sediment samples were analyzed for selenate and
selenite selenium. Other trace elements were analyzed
in water and biota samples collected in 199\. Also,
streams and reservoirs outside the irrigated land
served by the Uncompahgre Project (fig. l) were
sampled to detennine if selenium and other trace-
constituent concentrations were of concern in other
irrigated areas in the lower Gunnison River Basin.
Soil and alfalfa samples were collected in
irrigated areas of the Uncompahgre Project in
June 1991. Soil samples were analyzed for total and
extractable selenium, and trace constituents and alfalfa
samples were analyzed for total selenium. Ground-
water samples were collected in February and
March 1992 to define ground-water quality during the
nonirrigation season. Some ground-water samples
were analyzed for hydrogen, oxygen, and sulfur
isotopes. Samples of bedrock core, shale residuum,
alluvium, and ground-water filtrate were collected for
semiquantitative analyses of clay and bulk mineralogy.
Reconnaissance-level sampling of streams was
done in 1991 in the Uncompahgre Project area and in
the Grand Valley. Detailed synoptic sampling of
streams, washes, and ditches draining irrigated areas
in the Uncompahgre Project and in the Grand Valley
was done during January through March 1992.
Constituents analyzed in synoptic samples were
selenium, boron, nitrite plus nitrate, dissolved solids,
and major constituents. Selenium data were collected
at selected surface-water sites in 1993 and were used
for analyses of selenium distribution and loads in the
study area. Bottom-sediment samples were collected
from selected streams and ponds in 1992.
Biota samples collected in 1991 included
aquatic plants and invertebrates, fish, birds, and
bird eggs. Sample collection from March to
September 1991 was designed to detennine if other
trace constituents or pesticides were of concern in
the Uncompahgre Project and in the Grand Valley.
Fish samples were collected from the Gunnison,
Uncompahgre, and Colorado Rivers during March and
April 1992 for selenium and selected trace-constituent
analyses. Wetland sites were monitored for bird usage
and nesting from April through July 1992. Birds and

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