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Scientific Investigations Report 2013–5163

Prepared in cooperation with Blaine County, City of Hailey, City of Ketchum, The Nature Conservancy, City of Sun Valley, Sun Valley Water and Sewer District, Blaine Soil Conservation District, and the City of Bellevue

Quality of Groundwater and Surface Water, Wood River Valley, South-Central Idaho, July and August 2012

By Candice B. Hopkins and James R. Bartolino

Thumbnail of and link to report PDF (1.8 MB)Abstract

Residents and resource managers of the Wood River Valley of south-central Idaho are concerned about the effects that population growth might have on the quality of groundwater and surface water. As part of a multi-phase assessment of the groundwater resources in the study area, the U.S. Geological Survey evaluated the quality of water at 45 groundwater and 5 surface-water sites throughout the Wood River Valley during July and August 2012. Water samples were analyzed for field parameters (temperature, pH, specific conductance, dissolved oxygen, and alkalinity), major ions, boron, iron, manganese, nutrients, and Escherichia coli (E.coli) and total coliform bacteria.

This study was conducted to determine baseline water quality throughout the Wood River Valley, with special emphasis on nutrient concentrations. Water quality in most samples collected did not exceed U.S. Environmental Protection Agency standards for drinking water. E. coli bacteria, used as indicators of water quality, were detected in all five surface-water samples and in two groundwater samples collected. Some analytes have aesthetic-based recommended drinking water standards; one groundwater sample exceeded recommended iron concentrations. Nitrate plus nitrite concentrations varied, but tended to be higher near population centers and in agricultural areas than in tributaries and less populated areas. These higher nitrate plus nitrite concentrations were not correlated with boron concentrations or the presence of bacteria, common indicators of sources of nutrients to water. None of the samples collected exceeded drinking-water standards for nitrate or nitrite.

The concentration of total dissolved solids varied considerably in the waters sampled; however a calcium-magnesium-bicarbonate water type was dominant (43 out of 50 samples) in both the groundwater and surface water. Three constituents that may be influenced by anthropogenic activity (chloride, boron, and nitrate plus nitrite) deviate from this pattern and show a wide distribution of concentrations in the unconfined aquifer, indicating possible anthropogenic influence.

Time-series plots of historical water-quality data indicated that nitrate does not seem to be increasing or decreasing in groundwater over time; however, time-series plots of chloride concentrations indicate that chloride may be increasing in some wells. The small amount of temporal variability in nitrate concentrations indicates a lack of major temporal changes to groundwater inputs.

First posted September 20, 2013

For additional information contact:
Director, Idaho Water Science Center
U.S. Geological Survey
230 Collins Road
Boise, Idaho 83702

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Suggested citation:

Hopkins, C.B., and Bartolino, J.R., 2013, Quality of groundwater and surface water, Wood River Valley, south-central Idaho, July and August 2012: U.S. Geological Survey Scientific Investigations Report 2013-5163, 32 p.,




Study Methods and Quality Assurance

Quality of Groundwater and Surface Water

Suggestions for Further Study

Summary and Conclusions


References Cited


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