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Statistical summary and evaluation of the quality of surface water in the Colorado River basin, 1973-82 water years

Water-Resources Investigations Report 85-4181

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Abstract

Significant upward trends in dissolved-solids concentrations were detected with the Seasonal Kendall Test for trends at three stations in the upper basin during the study period. The increases exceeded 270 milligrams per liter per year at two stations and 165 milligrams per liter per year at the third station.

The composition of dissolved constituents in the Colorado River basin changes from predominantly sodium and chloride ions in the upper basin to predominantly calcium and bicarbonate ions in the lower basin. The U.S. Environmental Protection Agency secondary drinking-water regulations of 500 milligrams per liter for total dissolved solids was exceeded 95 percent of the time at each station on the main stem of the Colorado River in the upper basin. In the middle Colorado River basin, the Environmental Protection Agency secondary drinking-water regulations for total dissolved solids was exceeded approximately 95 percent of the time at most stations.

Nutrient concentrations in the Colorado River basin generally were low. Only one sample exceeded the level set for nitrate nitrogen, and no other nutrient species exceeded Environmental Protection Agency levels. A general upward trend was detected in organic nitrogen and total nitrogen, but concentrations still remained low.

Densities of fecal-col iform and fecal-streptococcal bacteria ranged from less than 1 colony per 100 milliliters to 26,000 colonies per 100 milliliters and 1 colony per 100 milliliters to 50,000 colonies per 100 milliliters, respectively. Fecal-coliform densities exceeded Environmental Protection Agency criteria for public water supply (2,000 colonies per 100 milliliters) at several stations during the study.

Biochemical oxygen demand concentrations ranged from 0.00 to 34 milligrams per liter. Only one mean biochemical oxygen demand concentration exceeded 8 milligrams per liter, the upper range of concentration common in moderately contaminated streams.

Trace elements and pesticides were detected in many samples throughout the basin. The concentrations generally were low, and maximum contaminant levels rarely were exceeded.

Study Area

Additional publication details

Publication type:
Report
Publication Subtype:
USGS Numbered Series
Title:
Statistical summary and evaluation of the quality of surface water in the Colorado River basin, 1973-82 water years
Series title:
Water-Resources Investigations Report
Series number:
85-4181
Year Published:
1986
Language:
English
Publisher:
U.S. Geological Survey
Publisher location:
Austin, TX
Contributing office(s):
Texas Water Science Center
Description:
Report: vi, 97 p.; Plate: 21.78 x 10.92 inches
Country:
United States
State:
Texas
Other Geospatial:
Colorado River Basin
Online Only (Y/N):
N
Additional Online Files (Y/N):
N