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U.S. Department of the Interior
U.S. Geological Survey

Water Resources of Sweetwater County, Wyoming

Scientific Investigations Report 2004-5214

By Jon P. Mason and Kirk A. Miller

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Abstract

Sweetwater County is located in the southwestern part of Wyoming and is the largest county in the State. A study to quantify the availability and describe the chemical quality of surface-water and ground-water resources in Sweetwater County was conducted by the U.S. Geological Survey in cooperation with the Wyoming State Engineer’s Office. Most of the county has an arid climate. For this reason a large amount of the flow in perennial streams within the county is derived from outside the county. Likewise, much of the ground-water recharge to aquifers within the county is from flows into the county, and occurs slowly. Surface-water data were not collected as part of the study. Evaluations of streamflow and stream-water quality were limited to analyses of historical data and descriptions of previous investigations. Forty-six new ground-water-quality samples were collected as part of the study and the results from an additional 782 historical ground-water-quality samples were reviewed. Available hydrogeologic characteristics for various aquifers throughout the county also are described.

Flow characteristics of streams in Sweetwater County vary substantially depending on regional and local basin characteristics and anthropogenic factors. Because precipitation amounts in the county are small, most streams in the county are ephemeral, flowing only as a result of regional or local rainfall or snowmelt runoff. Flows in perennial streams in the county generally are a result of snowmelt runoff in the mountainous headwater areas to the north, west, and south of the county. Flow characteristics of most perennial streams are altered substantially by diversions and regulation.
Water-quality characteristics of selected streams in and near Sweetwater County during water years 1974 through 1983 were variable. Concentrations of dissolved constituents, suspended sediment, and bacteria generally were smallest at sites on the Green River because of resistant geologic units, increased vegetative cover, large diluting streamflows, and large reservoirs. Concentrations of dissolved constituents, suspended sediment, and bacteria generally were largest at sites in the Big Sandy River and Bitter Creek Basins. Some nutrient concentrations and bacteria counts exceeded various State and Federal water-quality criteria. Historical and recent anthropogenic activities contributed to natural sources of many dissolved constituents and suspended sediment.

Both water-table and artesian conditions occur in aquifers within the county. Shallow ground water is available throughout the county, although much of it is only marginally suitable or is unsuitable for domestic and irrigation uses mainly because of high total dissolved solids (TDS) concentrations. Suitable ground water for livestock use can be found in most areas of the county. Ground-water quality tends to deteriorate with increasing distance from recharge areas and with increasing depth below land surface. Ground water from depths of greater than a few thousand feet tends to have TDS concentrations that make it moderately saline to briny. In some areas even shallow ground water has moderately saline TDS concentrations. Specific constituents in parts of some aquifers in the county occur in relatively high concentrations when compared to U.S. Environmental Protection Agency drinking-water standards. Relatively high concentrations of sulfate, fluoride, boron, iron, and manganese were found in several aquifers. Many ground-water samples from the Battle Spring aquifer in the Great Divide Structural Basin had high radionuclide concentrations.

The estimated mean daily water use in Sweetwater County in 2000 was 170.73 million gallons per day. Irrigation was the largest single use of water in the county with an estimated mean use of more than 92 million gallons per day. Surface water irrigation accounted for nearly 90 percent of the total irrigation water used in 2000. Although ground water is used to a much lesser extent than surface water, in many areas of the county it is the only source of water available.


Contents

Abstract

Introduction

Purpose and Scope

Previous Invesigations

Acknowledgments

Description of Study Area

Physiography

Climate

Geology

Surface Water

Streamflow

Annual and Monthly Flows

Peak Flows

Low Flows

Flow Duration

Water Quality

Temperature

Dissolved Solids

Specific Conductance

Major Ions

Nutrients

Nitrogen

Phosphorus

Suspended Sediment

Bacteria

Ground Water

Ground-Water Recharge

Ground-Water Discharge

Ground-Water-Quality and other Hydrogeologic Characteristics

Quaternary Hydrogeologic Units

Alluvium and colluvium deposits

Gravel, pediment, and fan deposits

Landslide deposits

Dune sand and loess deposits

Playa lake and other lacustrine deposits

Alkalic extrusive and intrusive igneous rocks

Terrace gravels

Tertiary Hydrogeologic Units

Upper Tertiary hydrogeologic units

Browns Park Formation

Split Rock Formation and undifferentiated Miocene rocks

Lower Tertiary hydrogeologic units

Bishop Conglomerate

White River Formation

Ice Point Conglomerate

Washakie Formation

Bridger Formation

Crooks Gap Conglomerate

Green River Formation

Laney Member of the Green River Formation

Godiva Rim Member of the Green River Formation

Wilkins Peak Member of the Green River Formation

Tipton Shale Member of the Green River Formation

Farson Sandstone Member of the Green River Formation

Luman Tongue of the Green River Formation

Wasatch Formation

Cathedral Bluffs Tongue of the Wasatch Formation

Niland Tongue of the Wasatch Formation

Main body of the Wasatch Formation

Battle Spring Formation

Fort Union Formation

Mesozoic Hydrogeologic Units

Mesaverde aquifer

Baxter-Mowry confining unit

Cloverly aquifer

Morrison confining unit and Morrison aquifer

Sundance confining unit

Sundance aquifer

Gypsum Spring confining unit

Nugget aquifer

Chugwater-Dinwoody confining unit

Paleozoic Hydrogeologic Units

Upper Paleozoic aquifers

Upper Paleozoic confining units

Madison aquifer and Darby confining unit

Gallatin aquifer and Gros Ventre confining unit

Flathead aquifer

Basal confining unit

Water Use

Summary

References

Appendix 1.—Annual- and monthly-streamflow characteristics, selected sites in and near Sweetwater County, Wyoming

Appendix 2.—Peak-flow characteristics, selected sites in and near Sweetwater County, Wyoming

Appendix 3.—Low-flow characteristics, selected sites in and near Sweetwater County, Wyoming

Appendix 4.—Streamflow duration statistics, selected sites in and near Sweetwater County, Wyoming

Appendix 5.—Graphs showing statistical summaries of major ion concentrations in analyses of water-quality samples, selected sites in and near Sweetwater County, Wyoming, water years 1974-83

Appendix 6—Ground-water quality data

Appendix 7—Piper diagrams showing relative ionic compostitions of ground-water quality samples

Plates

1. Maps showing bedrock geology, physiographic and structural features, and stratigraphic chart of Sweetwater County, Wyoming

2. Map showing locations of sampled wells and springs in Sweetwater County, Wyoming

Figures

1-3. Maps showing:

1. Location of study area, Sweetwater County, Wyoming.

2. Drainage basins in southwestern Wyoming and surrounding States.

3. General climate classifications for Sweetwater County, Wyoming.

4. Modified Walter-Lieth diagram showing monthly means for 1971-2000 of precipitation and mean daily minimum, maximum, and mean temperatures for Green River, Wyoming.

5. Map showing mean annual precipitation, 1961-90, Sweetwater County, Wyoming.

6. Graph showing annual precipitation totals for Green River and Rock Springs, Wyoming.

7-8. Maps showing:

7. Structural configuration of Precambrian basement rocks in Sweetwater County, Wyoming.

8. Location of active (2002) and discontinued streamflow-gaging stations, active (2002) and discontinued surface-water-quality stations, and peak-flow-gaging stations in and around Sweetwater County, Wyoming.

9-12. Graphs showing:

9. Ratio of 7-day, 10-year low flow (7Q10) and annual mean streamflow to basin drainage area for selected sites in and near Sweetwater County, Wyoming.

10. Streamflow duration curves for selected sites in the Big Sandy River Basin in or near Sweetwater County, Wyoming, water years 1955-71, and streamflow duration curves for selected sites on the Green River Basin in or near Sweetwater County, Wyoming, water years 1965-2002.

11. Statistics of total dissolved-solids concentrations, nitrite plus nitrate concentrations, total phosphorus concentrations, and suspended-sediment concentrations for selected sites in or near Sweetwater County, Wyoming, water years 1974-83.

12. Relations between total phosphorus and suspended-sediment concentrations for selected stream sites, Bitter Creek Basin, Sweetwater County, Wyoming, water years 1974-83.

13-18. Maps showing:

13. Estimated distribution of ground-water recharge, in inches per year, in the Green River Structural Basin.
14. Potential for recharge by direct infiltration of precipitation to the aquifers in Mesozoic hydrogeologic units.

15. Potentiometric surface and inferred flow paths for the Wasatch zone of the Wasatch-Fort Union aquifer, Sweetwater County and surrounding area, 1986.

16. Generalized potentiometric surface, recharge and discharge areas, and inferred flow paths in the Mesaverde aquifer in part of Wyoming, Colorado, and Utah.

17. Potentiometric surface of the Tensleep aquifer in parts of Wyoming, Colorado, and Utah

18. Potentiometric surface of the Madison aquifer in parts of Wyoming, Colorado, and Utah.

19-21. Graphs showing:

19. Characteristics of selected dissolved constituents and sodium-adsorption ratios in ground-water samples from Quaternary hydrogeologic units in Sweetwater County, Wyoming.

20. Characteristics of selected dissolved constituents and sodium-adsorption ratios in ground-water samples from aquifers in Tertiary hydrogeologic units, Sweetwater County, Wyoming.

21. Total dissolved-solids concentrations in relation to sampling depths for produced-water samples from the Wasatch Formation, Sweetwater County, Wyoming.

22. Diagram showing west-east stratigraphic correlation of Eocene rocks across the Greater Green River Basin.

23-24. Graphs showing:

23. Characteristics of selected dissolved constituents and sodium-adsorption ratios in water from the Mesaverde aquifer in Sweetwater County, Wyoming.

24. Characteristics of total-dissolved solids in Mesozoic hydrogeologic units from produced-water samples collected in Sweetwater County, Wyoming.

25-26. Maps showing:

25. Dissolved-solids concentrations in the Mesaverde aquifer.

26. Dissolved-solids concentration of water in the Nugget aquifer.

Tables

1. Characteristics of selected streamflow, peak-flow, and water-quality sites in and near Sweetwater County, Wyoming.

2. Equations for estimating peak-flow characteristics, High Desert Region, Wyoming 19

3. Daily water-quality data periods of record, selected surface water sites in or near Sweetwater County, Wyoming.

4. Median concentrations of constituents in water-quality samples, selected surface water sites in or near Sweetwater County, Wyoming, water years 1974-83.

5. Estimated steady-state ground-water budget for Tertiary hydrogeologic units in the Green River Structural Basin.

6. Hydrogeologic units of Mesozoic age in southwestern Wyoming.

7. Hydrogeologic units of Paleozoic age in the Wyoming part of the Upper Colorado River Basin.

8. Estimated water use in 2000 in Sweetwater County, Wyoming.


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