Water-Quality Characteristics, Including Sodium-Adsorption Ratios, for Four Sites in the Powder River Drainage Basin, Wyoming and Montana,Water Years 2001-2004

View or download the PDF
(1.71 mb)

Abstract

The U.S. Geological Survey, in cooperation with the Wyoming Department of Environmental Quality, monitors streams throughout the Powder River structural basin in Wyoming and parts of Montana for potential effects of coalbed natural gas development. Specific conductance and sodium-adsorption ratios may be larger in coalbed waters than in stream waters that may receive the discharge waters. Therefore, continuous water-quality instruments for specific conductance were installed and discrete water-quality samples were collected to characterize water quality during water years 2001-2004 at four sites in the Powder River drainage basin: Powder River at Sussex, Wyoming; Crazy Woman Creek near Arvada, Wyoming; Clear Creek near Arvada, Wyoming; and Powder River at Moorhead, Montana.

During water years 2001-2004, the median specific conductance of 2,270 microsiemens per centimeter at 25 degrees Celsius (µS/cm) in discrete samples from the Powder River at Sussex, Wyoming, was larger than the median specific conductance of 1,930 µS/cm in discrete samples collected downstream from the Powder River at Moorhead, Montana. The median specific conductance was smallest in discrete samples from Clear Creek (1,180 µS/cm), which has a dilution effect on the specific conductance for the Powder River at Moorhead, Montana. The daily mean specific conductance from continuous water-quality instruments during the irrigation season showed the same spatial pattern as specific conductance values for the discrete samples.

Dissolved sodium, sodium-adsorption ratios, and dissolved solids generally showed the same spatial pattern as specific conductance. The largest median sodium concentration (274 milligrams per liter) and the largest range of sodium-adsorption ratios (3.7 to 21) were measured in discrete samples from the Powder River at Sussex, Wyoming. Median concentrations of sodium and sodium-adsorption ratios were substantially smaller in Crazy Woman Creek and Clear Creek, which tend to decrease sodium concentrations and sodium-adsorption ratios at the Powder River at Moorhead, Montana. Dissolved-solids concentrations in discrete samples were closely correlated with specific conductance values; Pearson’s correlation coefficients were 0.98 or greater for all four sites.

Regression equations for discrete values of specific conductance and sodium-adsorption ratios were statistically significant (p-values <0.001) at all four sites. The strongest relation (R²=0.92) was at the Powder River at Sussex, Wyoming. Relations on Crazy Woman Creek (R²=0.91) and Clear Creek (R²=0.83) also were strong. The relation between specific conductance and sodium-adsorption ratios was weakest (R²=0.65) at the Powder River at Moorhead, Montana; however, the relation was still significant. These data indicate that values of specific conductance are useful for estimating sodium-adsorption ratios.

A regression model called LOADEST was used to estimate dissolved-solids loads for the four sites. The average daily mean dissolved-solids loads varied among the sites during water year 2004. The largest average daily mean dissolved-solids load was calculated for the Powder River at Moorhead, Montana. Although the smallest concentrations of dissolved solids were in samples from Clear Creek, the smallest average daily mean dissolved-solids load was calculated for Crazy Woman Creek. The largest loads occurred during spring runoff, and the smallest loads occurred in late summer, when streamflows typically were smallest. Dissolved-solids loads may be smaller than average during water years 2001-2004 because of smaller than average streamflow as a result of drought conditions.

Contents

Abstract
Introduction

Purpose and Scope

Study Area Description

Acknowledgments

Methods

Data Collection

Data Analysis

Water-Quality Characteristics

Streamflow and Specific Conductance from Continuous Data

Specific Conductance, Major Ions, and Sodium-Adsorption Ratios from Discrete Samples

Regression Equations for Estimating Sodium-Adsorption Ratios

Estimates for Dissolved-Solids Loads

Summary

References

Figures

1. Map showing location of continuous water-quality sampling sites in the Powder River drainage basin, Wyoming and Montana, water years 2001-2004.

2–4. Graphs showing:

2. Daily mean streamflow and specific conductance for sites in the Powder River drainage basin, Wyoming and Montana, water years 2001-2004.

3. Specific conductance values; concentrations of dissolved calcium, dissolved magnesium, and dissolved sodium; sodium-adsorption ratios; and dissolved-solids concentrations in water-quality samples collected from sites in the Powder River drainage basin, Wyoming and Montana, water years 2001-2004.

4. Dissolved-solids concentrations in relation to specific conductance in water-quality samples collected from sites in the Powder River drainage basin, Wyoming and Montana, water years 2001-2004.

5. Diagram showing specific conductance and sodium-adsorption ratio and potential for reduction in rate of infiltration for water-quality samples collected from sites in the Powder River drainage basin, Wyoming and Montana, water years 2001-2004.

6–8. Graphs showing:

6. Sodium-adsorption ratios in relation to specific conductance in water-quality samples collected from sites in the Powder River drainage basin, Wyoming and Montana, water years 2001-2004.

7. Estimated and calculated sodium-adsorption ratios for sites in the Powder River drainage basin, Wyoming and Montana, water years 2001-2004.

8. Estimated and calculated dissolved-solids loads for sites in the Powder River drainage basin, Wyoming and Montana, water years 2001-2004.

Tables

1. Selected streamflow characteristics for water-quality monitoring sites in the Powder River drainage basin, Wyoming and Montana.

2. Period of record for discrete water-quality sample collection for sites in the Powder River drainage basin, Wyoming and Montana, water years 2001-2004.

3. Period of record for continuous data collection for sites in the Powder River drainage basin, Wyoming and Montana, water years 2001-2004.

4. Regression equations for estimates of sodium-adsorption ratios for sites in the Powder River drainage basin, Wyoming and Montana, water years 2001-2004.

5. Summary statistics of LOADEST regression models used to estimate daily mean dissolved-solids loads for sites in the Powder River drainage basin, Wyoming and Montana, water years 2001-2004.

6. Estimated dissolved-solids annual loads and runoff-weighted loads for sites in the Powder River drainage basin, Wyoming and Montana, water years 2001-2004.

For more information concerning the research in this report, contact:
Director, Wyoming Water Science Center
U.S. Geological Survey
2617 E. Lincolnway, Suite B
Cheyenne, Wyoming 82001-5662
(307) 778-2931
http://wy.water.usgs.gov/