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Scientific Investigations Report 2013–5132

Prepared in cooperation with the Bureau of Land Management, White River Field Office

Chemistry and Age of Groundwater in Bedrock Aquifers of the Piceance and Yellow Creek Watersheds, Rio Blanco County, Colorado, 2010–12

By P.B. McMahon, J.C. Thomas, and A.G. Hunt

Thumbnail of and link to report PDF (25.5 MB)Abstract

Fourteen monitoring wells completed in the Uinta and Green River Formations in the Piceance Creek and Yellow Creek watersheds in Rio Blanco County, Colorado, were sampled for chemical, isotopic, and groundwater-age tracers to provide information on the overall groundwater quality, the occurrence and distribution of chemicals that could be related to the development of underlying natural-gas reservoirs, and to better understand groundwater residence times in the flow system. Methane concentrations in groundwater ranged from less than 0.0005 to 387 milligrams per liter. The methane was predominantly biogenic in origin, although the biogenic methane was mixed with thermogenic methane in water from seven wells. Three BTEX compounds (benzene, toluene, and ethylbenzene) were detected in water from six of the wells, but none of the concentrations exceeded Federal drinking-water standards. The presence of thermogenic methane in the aquifers indicates a connection and vulnerability to chemicals in deeper geologic units. Helium-4 data indicate that groundwater had ages ranging from less than 1,000 years to greater than 50,000 years. The presence of old groundwater in parts of the aquifers indicates that these aquifers may not be useful for large-scale water supply because of low recharge rates.

First posted September 24, 2013

For additional information contact:
Director, Colorado Water Science Center
U.S. Geological Survey
Box 25046, Mail Stop 415
Denver, CO 80225
http://co.water.usgs.gov

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Suggested citation:

McMahon, P.B., Thomas, J.C., and Hunt, A.G., 2013, Chemistry and age of groundwater in bedrock aquifers of the Piceance and Yellow Creek watersheds, Rio Blanco County, Colorado, 2010–12: U.S. Geological Survey Scientific Investigations Report 2013–5132, 89 p., http://pubs.usgs.gov/sir/2013/5132/.



Contents

Abstract

Introduction

Study Methods

Groundwater Levels

Sources of Groundwater

Redox Processes

Major-Ion Chemistry

Minor- and Trace-Element Chemistry

Hydrocarbon Chemistry

Hydrocarbon Migration

Groundwater Age

Study Limitations

Summary and Conclusions

Acknowledgments

References Cited

Appendixes


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