WSP10284

• File Number: 8170
• Description: Arkansas Basin Water Quality Issues
• State: CO
• Basin: Arkansas
• Water Division: 2
• Date: 1/1/1998
• Author: USGS
• Title: Water-Quality Assessment of the Arkansas River Basin - Southeastern Colorado - 1990-93
• Water Supply Pro - Doc Type: Report/Study

elements generally were not exceeded at most
main-stem sites in the lower basin; however,
total-recoverable iron and selenium standards
were frequently exceeded. During storm events in
the lower basin, tributaries contributed substantial
amounts of trace elements to the Arkansas River.
Median concentrations of dissolved solids
in the Arkansas River increased from a minimum
of 62.5 milligrams per liter in the upper basin at
Granite to 3,825 milligrams per liter in the lower
basin near the State line. A transition from
igneous and metamorphic rock to sedimentary
rock, in addition to the concentrating effects of
the use and reuse of water for irrigation, caused
this downstream increase in dissolved-solids
concentrations.
Ammonia and nitrate concentrations
increased downstream but were low in compar-
ison to State and Federal standards. Median
ammonia concentrations in the Arkansas River
ranged from 0.0 I 0 to 0.145 milligram per liter;
median nitrate concentrations at main-stem sites
ranged from 0.020 to 2.4 milligrams per liter.
High concentrations of ammonia downstream
from John Martin Reservoir, particularly during
low-flow regimes, are indicative of anoxic condi-
tions in the reservoir. Median total-phosphorus
concentrations were relatively low in the upper
basin, but they exceeded the recommended
concentration for total-phosphorus in rivers
(0.10 milligram per liter) at three sites in the
lower basin.
Suspended-sediment concentrations in the
Arkansas River upstream from Pueblo Reservoir
were relatively low but increased downstream.
Suspended-sediment concentrations typically
were much larger during snowmelt runoff, owing
to tributary inflow and resuspension of fluvial
sediment. Suspended-sediment concentrations
increased substantially during periods of elevated
runoff; the largest measured concentration in the
upper basin occurred during stonn-runoff condi-
tions. In the lower basin, median concentrations
ranged from 19 milligrams per liter at Pueblo to
724 milligrams per liter at Catlin Dam.

INTRODUCTION

The Arkansas River drains about 25,400 mi2
and flows nearly 400 mi in Colorado before reaching
the Colorado-Kansas border (fig. I). Streamflow in the
Arkansas River Basin primarily is derived from snow-
melt in the mountains that border the upper region of
the basin and, to a lesser extent, from summer thunder-
storms that occur primarily on the eastern plains.
Water uses in the Arkansas River Basin include agri-
cultural, commercial, domestic, industrial, livestock,
mining, and power production. Although the primary
water use in the basin is agricultural, many municipal-
ities within and outside the Arkansas River Basin have
become increasingly dependent on the river as a water
supply. Thus, quality of water in the Arkansas River
Basin has become an important consideration to a
multitude of water users in Colorado.
In 1990, the U.S. Geological Survey (USGS),
in cooperation with the Colorado Springs Utilities,
Water Resources Department; Pueblo Board of Water
Works; Southeastern Colorado Water Conservancy
District; Pueblo County, Department of Planning and
Development; city of Aurora, Department of Utilities;
SI. Charles Mesa Water District; Upper Arkansas Area
Council of Governments; Upper Arkansas Water
Conservancy District; city of Pueblo, Department of
Utilities; Pueblo West Metropolitan District; Fremont
Sanitation District; cities of Rocky Ford, Las Animas,
and Lamar; and the Bureau of Reclamation, began a
study to assess existing water-quality conditions in the
Arkansas River Basin.

Purpose and Scope

This report describes the spatial and temporal
variations in water-quality conditions in the Arkansas
River Basin between April 1990 and March 1993. The
primary focus of this report is the water quality of the
Arkansas River; however tributary data, when appro-
priate, were used to assess water-quality effects on the
main stem of the river.
An extensive streamflow and water-quality
monitoring network was established in April 1990.
Water-quality data collected at ] 9 main-stem, 16 tribu-
tary, and 2 mine-drainage sites were used to describe
the spatial and temporal variations in water quality in
the Arkansas River Basin between April 1990 and
March 1993 (table I). The Leadville Mine Drainage

2 Water-Quality Assessment of tha Arkansas River Sasln.. Southaa.tern Colorado, 199~3