WSP06331

• File Number: 8170
• Description: Arkansas Basin Water Quality Issues
• State: CO
• Basin: Arkansas
• Water Division: 2
• Date: 1/1/1991
• Author: USGS
• Title: Reconnaissance Investigation of Water Quality - Bottom Sediment - and Biota Associated with Irrigation Drainage in the Middle Arkansas River Basin - Colorado and Kansas - 1988-89
• Water Supply Pro - Doc Type: Report/Study

PREVIOUS STUDIES

Miles (1977) published the first report relating irrigation and water-
quality in the study area. Based on data' collected by the U.S. Bureau of
Reclamation and the U.S. Geological Survey, he concluded that irrigation
return flows accounted for 14 percent of the salinity (dissolved-solids)
loading to the Arkansas River in Colorado. He attributed most of this loading
to dissolution of gypsum (calcium sulfate) from irrigated soils. Gypsum is a
common mineral in soils that are derived from marine shales. Cain (1985)
investigated irrigation return flows between Pueblo and the Colorado-Kansas
State line during the 1976 and 1977 irrigation seasons. He reported that
return flows may comprise much of the Arkansas River flow downstream from
La Junta during the early and late parts of the irrigation season. Neither of
these reports included information about selenium or other trace constituents;
however, dissolved-selenium concentrations have been analyzed in water samples
from the Arkansas River near Coolidge since 1975. The median concentration of
51 samples collected through water year 1987 was 19 ~g/L. Historical total-
selenium concentrations at other locations in the study area are listed in
table 1.

Table 1.--Median concentrations of total selenium from historical data
collected at water-quality monitoring sites in the study areal

[~g/L, micrograms per liter]

U.S. Geological
Survey station
number

U.S. Geological
Survey station
name

Number
of
samples

07099200

Arkansas River near
Pueblo, Colo.
Fountain Creek near
Pinon, Colo.
Fountain Creek at Pueblo, Colo.
St. Charles River near
Pueblo, Colo. (two sites)

4

07106300

44

07106500
381130104341600
381202104324700

25
8

381556104273300

St. Charles River at mouth
near Vineland, Colo.
Arkansas River near
Avondale, Colo.
Arkansas River near
Nepesta, Colo.
Arkansas River below John
Martin Reservoir, Colo.

4

07109500

4

07117000

4

07130500

8

Median
concen-
tration
(~g/L)

4.0

4.0

18
30

23.5

8.5

11.5

6

Period
of
record

1976-79

1976-83

1976-83
1979-80

1976-79

1976-79

1976-79

1980-81

lData from Cain and Edelmann (1980) and U.S. Geological Survey (1982-84).

18