WSP02811

• File Number: 8200.766
• Description: Gunnison River General
• State: CO
• Basin: Gunnison
• Water Division: 4
• Date: 1/1/1991
• Author: USGS
• Title: Reconnaissance Investigation of Water Quality-Bottom Sediment-and Biota Associated with Irrigation Drainage - Gunnison and Uncompahgre River Basins and Sweitzer Lake - West Central Colorado
• Water Supply Pro - Doc Type: Report/Study

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SITE NAME AND NUMBER

Figure 12.--Concentralions of dissolved uranium in the Gunnison and
Uncompahgre Rivers, November 1987 and January, March, and July 1988.

The sulfate concentration at site 3 exceeded the drinking-water standard
of 250 mgfL in July. The sulfate concentrations at site II exceeded the
standard in November and July. The only trace-element concentrations in the
Gunnison River exceeding State standards were the mercury concentration of
0.6 ~g/L in the sample collected in July at site 2 and the lead concentration
of 35 ~g/L in the sample collected in November at site 3. The standard for
mercury is 0.05 ~g/L (table II), but because the analytical reporting limit
was 0.1 ~g/L. mercury concentrations reported as less than 0.1 ~g/L (table 16)
could have exceeded the standard. A selenium concentration of 13 ~g/L was
reported for the sample collected at site 3 in November, which would exceed
the State standard for selenium for that reach of the Gunnison River.
However, that selenium result seemed to be questionable after an analysis of
selenium loads, other constituent concentrations, and the selenium concentra-
tions in November at site II and at gaging station 09152500. Therefore, the
selenium analysis for the sample collected at site 3 in November was not used.
The maximum selenium concentration in the Gunnison River was 10 ~g/L in the
sample collected at site II in July 1988.

Although selenium concentrations in the Gunnison River did not exceed
State standards, the concentrations in samples collected in July 1988 at
site 3 (8 ~g/L) and site 11 (10 ~g/L) exceeded the U.S. Environmental
Protection Agency's criterion of 5 ~g/L for chronic exposure. The selenium
concentrations in samples collected in November 1987 and January 1988 at
site II were equal to 5 ~g/L.

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