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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 mg/L/yr at two stations and 165 mg/L/yr 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. EPA secondary drinking water regulations of 500 mg/L for total dissolved solids was exceeded 95% 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 EPA secondary drinking water regulations for total dissolved solids was exceeded approximately 95% 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 EPA levels. A general upward trend was detected in organic nitrogen and total nitrogen, but concentrations still remained low. Densities of fecal coliform and fecal streptococcal bacteria ranged less than 1 colony/100 ml to 26,000 colonies/100 ml and 1 colony/100 ml to 50,000 colonies/100 ml, respectively. Fecal coliform densities exceeded EPA criteria for public water supply (2,000 colonies/100 ml) at several stations during the study. Biochemical oxygen demand concentrations ranged from 0.00 to 34 mg/L. Only one mean biochemical oxygen demand concentration exceeded 8 mg/L, 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. (Author 's abstract)

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
Edition:
-
Year Published:
1986
Language:
ENGLISH
Publisher:
U.S. Geological Survey,
Description:
vi, 97 p. :ill., map ;28 cm.