U.S. Department of the Interior

U.S. Geological Survey

Summary of Surface-Water-Quality Data Collected for the 

Northern Rockies Intermontane Basins National WaterQuality Assessment Program in the Clark Fork-Pend Oreille 

and Spokane River Basins, Montana, Idaho, and Washington,

Water Years 1999-2001

Open-File Report 02–472

National Water-Quality Assessment Program
Summary of Surface-Water-Quality Data 

Collected for the Northern Rockies Intermontane 

Basins National Water-Quality Assessment 

Program in the Clark Fork-Pend Oreille and 

Spokane River Basins, Montana, Idaho, and 

Washington, Water Years 1999–2001 

By Michael A. Beckwith 

Open-File Report 02–472 

Boise, Idaho 

2003 
U.S. DEPARTMENT OF THE INTERIOR 

Gale A. Norton, Secretary 

U.S. GEOLOGICAL SURVEY 

Charles G. Groat, Director 

The use of firm, trade, and brand names in this report is for identification purposes 

only and does not constitute endorsement by the U.S. Government. 

Additional information can be obtained from:

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230 Collins Road

Boise, ID 83702-4520

http://idaho.usgs.gov 

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e-mail: infoservices@usgs.gov
FOREWORD 

The U.S. Geological Survey (USGS) is committed to serve the Nation with accurate and timely scientific information that helps enhance and protect the overall quality of life, and facilitates effective management of water, biological, energy, and mineral resources. (http://www.usgs.gov/). Information on the 

quality of the Nation’s water resources is of critical interest to the USGS because it is so integrally linked 

to the long-term availability of water that is clean and safe for drinking and recreation and that is suitable 

for industry, irrigation, and habitat for fish and wildlife. Escalating population growth and increasing 

demands for the multiple water uses make water availability, now measured in terms of quantity and quality, even more critical to the long-term sustainability of our communities and ecosystems. 

The USGS implemented the National Water-Quality Assessment (NAWQA) Program to support 

national, regional, and local information needs and decisions related to water-quality management and policy. (http://water.usgs.gov/nawqa/). Shaped by and coordinated with ongoing efforts of other Federal, 

State, and local agencies, the NAWQA Program is designed to answer: What is the condition of our 

Nation’s streams and ground water? How are the conditions changing over time? How do natural features 

and human activities affect the quality of streams and ground water, and where are those effects most pronounced? By combining information on water chemistry, physical characteristics, stream habitat, and 

aquatic life, the NAWQA Program aims to provide science-based insights for current and emerging water 

issues and priorities. NAWQA results can contribute to informed decisions that result in practical and 

effective water-resource management and strategies that protect and restore water quality. 

Since 1991, the NAWQA Program has implemented interdisciplinary assessments in more than 50 of 

the Nation’s most important river basins and aquifers, referred to as Study Units. 

(http://water.usgs.gov/nawqa/nawqamap.html). Collectively, these Study Units account for more than 60 

percent of the overall water use and population served by public water supply, and are representative of the 

Nation’s major hydrologic landscapes, priority ecological resources, and agricultural, urban, and natural 

sources of contamination. 

Each assessment is guided by a nationally consistent study design and methods of sampling and analysis. The assessments thereby build local knowledge about water-quality issues and trends in a particular 

stream or aquifer while providing an understanding of how and why water quality varies regionally and 

nationally. The consistent, multi-scale approach helps to determine if certain types of water-quality issues 

are isolated or pervasive, and allows direct comparisons of how human activities and natural processes 

affect water quality and ecological health in the Nation’s diverse geographic and environmental settings. 

Comprehensive assessments on pesticides, nutrients, volatile organic compounds, trace metals, and aquatic 

ecology are developed at the national scale through comparative analysis of the Study-Unit findings. 

(http://water.usgs.gov/nawqa/natsyn.html). 

The USGS places high value on the communication and dissemination of credible, timely, and relevant science so that the most recent and available knowledge about water resources can be applied in management and policy decisions. We hope this NAWQA publication will provide you the needed insights and 

information to meet your needs, and thereby foster increased awareness and involvement in the protection 

and restoration of our Nation’s waters. 

The NAWQA Program recognizes that a national assessment by a single program cannot address all 

water-resource issues of interest. External coordination at all levels is critical for a fully integrated understanding of watersheds and for cost-effective management, regulation, and conservation of our Nation’s 

water resources. The Program, therefore, depends extensively on the advice, cooperation, and information 

from other Federal, State, interstate, Tribal, and local agencies, non-government organizations, industry, 

academia, and other stakeholder groups. The assistance and suggestions of all are greatly appreciated. 

Robert M. Hirsch


Associate Director for Water


Foreword iii 
CONTENTS 

Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii 


Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 


Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 


Purpose and scope. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 


Description of study area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 


Environmental history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 


Water-quality sampling and analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 


Streamflow and water-quality data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 


Summaries and graphical displays of data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 


Physical and chemical characteristics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 


Streamflow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 


Nutrients. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 


Organic carbon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 


Trace elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 


Comparison with other National Water-Quality Assessment Program studies . . . . . . . . . . . . . . . . . . . . . . . . . . 17 

References cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 

FIGURES 

1. Location of the Northern Rockies Intermontane Basins study area and surface-water-quality 

sampling sites in Montana, Idaho, and Washington . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

2–11. Graphs showing:

2.	 Selected streamflow statistics and water-quality sampling dates for the Clark Fork at 

Turah Bridge near Bonner, Montana (12334550) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 

3.	 Selected streamflow statistics and water-quality sampling dates for the Bitterroot River 

near Missoula, Montana (12352500) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 

4.	 Selected streamflow statistics and water-quality sampling dates for the Clark Fork at 

St. Regis, Montana (12354500) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 

5.	 Selected streamflow statistics and water-quality sampling dates for the Flathead River 

at Perma, Montana (12388700) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 

6.	 Daily streamflow and water-quality sampling dates for Lightning Creek at Clark Fork, 

Idaho (12392155). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 

7.	 Daily streamflow and water-quality sampling dates for the St. Joe River at Red Ives 

Ranger Station, Idaho (12413875) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 

8.	 Selected streamflow statistics and water-quality sampling dates for the North Fork 

Coeur d’Alene River at Enaville, Idaho (12413000) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 

9.	 Selected streamflow statistics and water-quality sampling dates for the South Fork 

Coeur d’Alene River near Pinehurst, Idaho (12413470) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 

10.	 Selected streamflow statistics and water-quality sampling dates for the Spokane River 

near Post Falls, Idaho (12419000) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 

11. Daily streamflow and water-quality sampling dates for the Spokane River at Seven Mile

Bridge near Spokane, Washington (12424500) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 

12–40. Boxplots showing:

12.	 Distribution of streamflow values for samples collected at surface-water-quality sampling 

sites in the Northern Rockies Intermontane Basins study area, water years 1999–2001 . . . . . . 33 

Contents v 
13.	 Distribution of specific conductance values for samples collected at surface-water-quality 

sampling sites in the Northern Rockies Intermontane Basins study area, water years 

1999–2001 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 

14.	 Distribution of onsite pH values for samples collected at surface-water-quality 

sampling sites in the Northern Rockies Intermontane Basins study area, water years 

1999–2001 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 

15.	 Distribution of water temperature values for samples collected at surface-water-quality 

sampling sites in the Northern Rockies Intermontane Basins study area, water years 

1999–2001 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 

16.	 Distribution of hardness values for samples collected at surface-water-quality sampling 

sites in the Northern Rockies Intermontane Basins study area, water years 1999–2001 . . . . . . 35 

17.	 Distribution of alkalinity values for samples collected at surface-water-quality sampling 

sites in the Northern Rockies Intermontane Basins study area, water years 1999–2001 . . . . . . 35 

18.	 Distribution of suspended sediment concentrations for samples collected at surfacewater-quality sampling sites in the Northern Rockies Intermontane Basins study area, 

water years 1999–2001 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 

19.	 Distribution of dissolved solids concentrations for samples collected at surface-waterquality sampling sites in the Northern Rockies Intermontane Basins study area, water 

years 1999–2001 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 

20.	 Distribution of total nitrogen concentrations for samples collected at surface-waterquality sampling sites in the Northern Rockies Intermontane Basins study area, water 

years 1999–2001 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 

21.	 Distribution of total phosphorus concentrations for samples collected at surface-waterquality sampling sites in the Northern Rockies Intermontane Basins study area, water 

years 1999–2001 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 

22.	 Distribution of dissolved arsenic concentrations for samples collected at surface-waterquality sampling sites in the Northern Rockies Intermontane Basins study area, water 

years 1999–2001 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 

23.	 Distribution of total recoverable arsenic concentrations for samples collected at surfacewater-quality sampling sites in the Northern Rockies Intermontane Basins study area, 

water years 1999–2001 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 

24.	 Distribution of dissolved cadmium concentrations for samples collected at surfacewater-quality sampling sites in the Northern Rockies Intermontane Basins study area, 

water years 1999–2001 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 

25.	 Distribution of total recoverable cadmium concentrations for samples collected at 

surface-water-quality sampling sites in the Northern Rockies Intermontane Basins 

study area, water years 1999–2001 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 

26.	 Distribution of dissolved copper concentrations for samples collected at surface-waterquality sampling sites in the Northern Rockies Intermontane Basins study area, water 

years 1999–2001 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 

27.	 Distribution of total recoverable copper concentrations for samples collected at surfacewater-quality sampling sites in the Northern Rockies Intermontane Basins study area, 

water years 1999–2001 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 

28.	 Distribution of dissolved lead concentrations for samples collected at surface-waterquality sampling sites in the Northern Rockies Intermontane Basins study area, water 

years 1999–2001 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 

29.	 Distribution of total recoverable lead concentrations for samples collected at surfacewater-quality sampling sites in the Northern Rockies Intermontane Basins study area, 

water years 1999–2001 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 

vi Surface-Water-Quality, Clark Fork-Pend Oreille and Spokane River Basins, 1999–2001 
30.	 Distribution of total recoverable mercury concentrations for samples collected at 

surface-water-quality sampling sites in the Northern Rockies Intermontane Basins 

study area, water years 1999–2001 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 

31.	 Distribution of dissolved zinc concentrations for samples collected at surface-waterquality sampling sites in the Northern Rockies Intermontane Basins study area, water 

years 1999–2001 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 

32.	 Distribution of total recoverable zinc concentrations for samples collected at surfacewater-quality sampling sites in the Northern Rockies Intermontane Basins study area, 

water years 1999–2001 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 

33.	 Distribution of dissolved arsenic concentrations for samples collected in surface water 

in National Water-Quality Assessment study areas in the Western United States 

affected by historical mining activities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 

34.	 Distribution of dissolved cadmium concentrations for samples collected in surface 

water in National Water-Quality Assessment study areas in the Western United States 

affected by historical mining activities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 

35.	 Distribution of dissolved copper concentrations for samples collected in surface water 

in National Water-Quality Assessment study areas in the Western United States 

affected by historical mining activities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 

36.	 Distribution of total recoverable copper concentrations for samples collected in 

surface water in National Water-Quality Assessment study areas in the Western 

United States affected by historical mining activities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 

37.	 Distribution of dissolved lead concentrations for samples collected in surface water 

in National Water-Quality Assessment study areas in the Western United States 

affected by historical mining activities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 

38.	 Distribution of total recoverable lead concentrations for samples collected in surface 

water in National Water-Quality Assessment study areas in the Western United States 

affected by historical mining activities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 

39.	 Distribution of dissolved zinc concentrations for samples collected in surface water 

in National Water-Quality Assessment study areas in the Western United States 

affected by historical mining activities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 

40.	 Distribution of total recoverable zinc concentrations for samples collected in surface 

water in National Water-Quality Assessment study areas in the Western United 

States affected by historical mining activities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 

TABLES 

1. Surface-water-quality sampling sites in the Northern Rockies Intermontane Basins study area . . . . . 3 

2. Land cover in the Northern Rockies Intermontane Basins study area. . . . . . . . . . . . . . . . . . . . . . . . . . 6 

3.	 Selected physical and chemical characteristics for samples collected at surface-water-quality 

sampling sites in the Northern Rockies Intermontane Basins study area, water years 

1999–2001. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 

4.	 Nutrient and organic carbon concentrations in samples collected at surface-water-quality 

sampling sites in the Northern Rockies Intermontane Basins study area, water years 

1999–2001, and comparative median concentrations in samples collected for the National 

Water-Quality Assessment Program and other national monitoring programs . . . . . . . . . . . . . . . . . . 12 

5.	 Selected trace-element data for samples collected at surface-water-quality sampling sites in 

the Northern Rockies Intermontane Basins study area, water years 1999–2001 . . . . . . . . . . . . . . . . . 15 

Contents vii 
CONVERSION FACTORS AND OTHER ABBREVIATED UNITS
 

Multiply By To obtain 

cubic foot per second (ft

3/s) 0.02832 cubic meter per second (m3/s) 

cubic mile (mi3) 4.168 cubic kilometer (km3) 

foot (ft) 0.3048 meter (m) 

inch (in.) 2.54 centimeter (cm) 

mile (mi) 1.609 kilometer (km) 

square mile (mi2) 2.590 square kilometer (km2) 

ton 0.9072 metric ton 

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows: 

°F=(1.8) (°C) + 32 

Other abbreviated units: 

microgram per liter (μg/L) 

milligram per liter (mg/L) 

viii Surface-Water-Quality, Clark Fork-Pend Oreille and Spokane River Basins, 1999–2001 
Summary of Surface-Water-Quality Data Collected 

for the Northern Rockies Intermontane Basins 

National Water-Quality Assessment Program in the 

Clark Fork-Pend Oreille and Spokane River Basins, 

Montana, Idaho, and Washington, Water Years 

1999–2001 

By Michael A. Beckwith 

Abstract 

Water-quality samples were collected at 10 

sites in the Clark Fork-Pend Oreille and Spokane 

River Basins in water years 1999 – 2001 as part of 

the Northern Rockies Intermontane Basins (NROK) 

National Water-Quality Assessment (NAWQA) 

Program. Sampling sites were located in varied 

environments ranging from small streams and rivers in forested, mountainous headwater areas to 

large rivers draining diverse landscapes. Two sampling sites were located immediately downstream 

from the large lakes; five sites were located downstream from large-scale historical mining and oreprocessing areas, which are now the two largest 

“Superfund” (environmental remediation) sites in 

the Nation. Samples were collected during a wide 

range of streamflow conditions, more frequently 

during increasing and high streamflow and less 

frequently during receding and base-flow conditions. Sample analyses emphasized major ions, 

nutrients, and selected trace elements. 

Streamflow during the study ranged from 

more than 130 percent of the long-term average in 

1999 at some sites to 40 percent of the long-term 

average in 2001. River and stream water in the 

study area exhibited small values for specific conductance, hardness, alkalinity, and dissolved solids. Dissolved oxygen concentrations in almost all 

samples were near saturation. Median total nitrogen and total phosphorus concentrations in samples from most sites were smaller than median 

concentrations reported for many national programs and other NAWQA Program study areas. 

The only exceptions were two sites downstream 

from large wastewater-treatment facilities, where 

median concentrations of total nitrogen exceeded 

the national median. Maximum concentrations of 

total phosphorus in samples from six sites exceeded 

the 0.1 milligram per liter threshold recommended 

for limiting nuisance aquatic growth. Concentrations of arsenic, cadmium, copper, lead, mercury, 

and zinc were largest in samples from sites downstream from historical mining and ore-processing 

areas in the upper Clark Fork in Montana and the 

South Fork Coeur d’Alene River in Idaho. Concentrations of dissolved lead in all 32 samples 

from the South Fork Coeur d’Alene River exceeded 

the Idaho chronic criterion for the protection of 

aquatic life at the median hardness level measured 

during the study. Concentrations of dissolved zinc 

in all samples collected at this site exceeded both 

the chronic and acute criteria at all hardness levels 

measured. 

When all data from all NROK sites were combined, median concentrations of dissolved arsenic, 

dissolved and total recoverable copper, total recoverable lead, and total recoverable zinc in the NROK 

study area appeared to be similar to or slightly 

smaller than median concentrations at sites in 

other NAWQA Program study areas in the Western 

United States affected by historical mining activiAbstract 1 
ties. Although the NROK median total recoverable 

lead concentration was the smallest among the 

three Western study areas compared, concentrations in several NROK samples were an order of 

magnitude larger than the maximum concentrations measured in the Upper Colorado River and 

Great Salt Lake Basins. Dissolved cadmium, dissolved lead, and total recoverable zinc concentrations at NROK sites were more variable than in the 

other study areas; concentrations ranged over 

almost three orders of magnitude between minimum and maximum values; the range of dissolved 

zinc concentrations in the NROK study area 

exceeded three orders of magnitude. 

INTRODUCTION 

The U.S. Geological Survey (USGS) National 

Water-Quality Assessment (NAWQA) Program began 

at full scale in 1991 (Hirsch and others, 1988). Goals of 

the NAWQA Program are to assess the quality of surface and ground water and aquatic biological conditions in the Nation’s major river basins and aquifer 

systems. Included in the assessments are attempts to 

characterize both the natural and human factors affecting environmental conditions, determine spatial patterns 

of variability, and identify trends over time. NAWQA 

Program studies employ consistent data-collection and 

analysis methods, thus allowing for aggregation of the 

information at the regional and national levels and for 

comparisons over a wide range of geographic and environmental settings. 

Typically, NAWQA Program studies consist of an 

initial phase of planning and review of existing information. A sampling strategy is designed to build upon 

previous information and to address water-quality 

issues of concern in the study area. An intensive datacollection, interpretation, and reporting phase follows 

for 3 to 4 years. Low-intensity data collection then is 

conducted for 5 to 6 years at a few key sites to maintain 

data continuity over time and to monitor trends and 

identify emerging water-quality issues. NAWQA studies are intended to repeat monitoring cycles at approximately 10-year intervals. However, several NAWQA 

studies will end after the first phase of intensive data 

collection and reporting because of program funding 

constraints. Among the studies to be discontinued is the 

subject of this report, the Northern Rockies Intermontane Basins (NROK). 

Purpose and Scope 

This report summarizes water-quality data collected at 10 sampling sites in the NROK study area 

during water years 1999–2001. Selected data also are 

compared with regulatory standards and guidelines and 

with data from other NAWQA Program studies. 

Description of Study Area 

The NROK study area includes the Clark ForkPend Oreille and Spokane River Basins in northwestern Montana, northern Idaho, and northeastern Washington (table 1, fig. 1). It also contains two extensive 

valley-fill aquifers designated by the U.S. Environmental Protection Agency as the sole source of water for 

Spokane, Washington; Missoula, Montana; and their 

surrounding suburban areas. 

The headwaters of the Clark Fork begin along the 

continental divide near Butte, Montana. At St. Regis, 

Montana, upstream from its confluence with the Flathead River, the Clark Fork has an annual mean discharge of 7,225 ft3/s (Shields and others, 2001). The 

three forks of the Flathead River drain much of Glacier 

National Park and surrounding wilderness areas and 

include Hungry Horse Reservoir, one of the largest 

hydroelectric reservoirs in the Columbia River system. 

The Flathead River flows into Flathead Lake, the largest freshwater lake in the Western United States, having 

a surface area of 192 mi2. Flowing out through a hydroelectric dam that regulates the level of Flathead Lake, 

the Flathead River joins the Clark Fork as its largest 

tributary with an annual mean discharge of 11,850 ft3/s 

(Shields and others, 2001). More than 350 mi downstream from its headwaters, the Clark Fork enters Pend 

Oreille Lake in Idaho (after passing through three relatively small hydroelectric reservoirs at Thompson Falls 

and Noxon, Montana, and Cabinet Gorge at the Montana-Idaho State boundary). With a depth of about 

1,170 ft and containing about 13 mi3 of water, Pend 

Oreille Lake is one of the deepest and largest lakes (in 

volume) in the Western United States. The Pend Oreille 

River flows out of Pend Oreille Lake through a hydroelectric dam, through northeastern Washington and two 

more hydroelectric reservoirs, and joins the Columbia 

River in British Columbia, Canada. At the international 

2 Surface-Water-Quality, Clark Fork-Pend Oreille and Spokane River Basins, 1999–2001 
Table 1. Surface-water-quality sampling sites in the Northern Rockies Intermontane Basins study area 

[No., number; USGS, U.S. Geological Survey; mi2, square miles; ft, feet; MT, Montana; ID, Idaho; WA, Washington; Stream order, U.S. Geological Survey 

(1999)] 

Site 

No. 

(fig. 1) Site name 

USGS 

gagingstation 

No. Latitude Longitude 

Drainage 

area 

(mi2

 upstream 

from 

gaging 

station) 

Elevation 

(ft above 

sea level) 

Stream 

order 

Clark Fork - Pend Oreille River Basin 

1 lark Fork at Turah Bridge near Bonner, MT . . . . . . . . . . . . . . 12334550 46ο49'34" 113ο48'48" 3,641 3,320 4 

2 itterroot River near Missoula, MT . . . . . . . . . . . . . . . . . . . . . . 12352500 46ο49'55" 114ο03'11" 2,814 3,110 4 

3 lark Fork at St. Regis, MT . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12354500 47ο18'07" 115ο05'11" 10,709 2,600 5 

4 Flathead River at Perma, MT . . . . . . . . . . . . . . . . . . . . . . . . . . . 12388700 47ο22'03" ο35'03" 8,795 2,469 5 

5 ightning Creek at Clark Fork, ID . . . . . . . . . . . . . . . . . . . . . . . 12392155 48ο09'04" ο10'56" 115 2,094 2 

Spokane River Basin 

6 St. Joe River at Red Ives Ranger Station, ID . . . . . . . . . . . . . . . 12413875 47ο03'22" ο21'08" 108 3,710 1 

7 orth Fork Coeur d’Alene River at Enaville, ID . . . . . . . . . . . . 12413000 47ο34'08" ο15'06" 895 2,180 3 

8 South Fork Coeur d’Alene River near Pinehurst, ID . . . . . . . . . 12413470 47ο33'06" ο14'13" 299 2,190 3 

9 Spokane River near Post Falls, ID . . . . . . . . . . . . . . . . . . . . . . . 12419000 47ο42'11" ο58'37" 3,840 2,003 5 

10 Spokane River at 7 Mile Bridge near Spokane, WA. . . . . . . . . . 12424500 47ο44 ' 25 " 117ο31'10" 5,020 1,624 5 

C 

B 

C 

114 

L 116 

115 

N 116 

116 

116 

boundary, the Pend Oreille River drains an area of 

about 25,200 mi2 (or about 79 percent of the study 

area) and has an annual mean discharge of 26,760 ft3/s 

(Kimbrough and others, 2001). 

The Spokane River Basin covers approximately 

6,600 mi2, or about 21 percent of the study area. The 

Spokane River begins at the outlet of Coeur d’Alene 

Lake in northern Idaho. Coeur d’Alene Lake covers 

about 50 mi2; its two primary inflows are the Coeur 

d’Alene and St. Joe Rivers, whose headwaters are in 

subranges of the Bitterroot Mountains west of the 

Idaho-Montana boundary. A hydroelectric dam on the 

Spokane River downstream from the lake outlet also 

regulates the Coeur d’Alene Lake level. After flowing 

through three more hydroelectric dams, the Spokane 

River near downtown Spokane, Washington, has an 

annual mean discharge of 6,765 ft3/s (Kimbrough and 

others, 2001). Downstream from the city is yet another 

small hydroelectric dam, and a large hydroelectric reservoir (Lake Spokane, also known as Long Lake) created in the early 1900s. The Spokane River then enters 

Lake Roosevelt, the reservoir on the Columbia River 

created by Grand Coulee Dam in eastern Washington. 

The study area has a complex geologic history 

involving multiple episodes of uplift, igneous activity, 

erosion, and sedimentation caused primarily by glacial 

and fluvial processes. The area consists mainly of 

coniferous forest-covered mountains and ridges interspersed with river valleys. Elevations range from more 

than 10,000 ft above sea level in the mountains of 

northwestern Montana and Glacier National Park to 

less than 1,500 ft at the confluence of the Spokane and 

Columbia Rivers. 

Both continental and maritime influences affect 

the climate of the study area. Most of the annual precipitation falls between late autumn and spring, much 

of it as snow. Precipitation ranges from approximately 

100 in. in the mountains of northwestern Montana and 

northern Idaho to less than 15 in. in the drier intermontane valleys in Montana and plateau areas near the confluence of the Spokane and Columbia Rivers in eastern 

Washington. Mountain snowmelt runoff from April 

through July dominates streamflow conditions. Typically, major floods are caused by weather systems from 

the Pacific Ocean bringing warm wind and rain that 

rapidly melt snowpack accumulated at low to middle 

elevations. 

Introduction 3 
117° 

4 Surface-Water-Quality, Clark Fork-Pend Oreille and Spokane River Basins, 1999–2001 

Bunker Hill 

Superfund Site 

SPOKANE 

RESERVATION 

KALISPELL 

INDIAN 

RESERVATION 

COEUR 

D'ALENE 

INDIAN 

RESERVATION 

Coeur 

d'Alene 

Lake 

Lake 

Spokane 

Priest 

Lake 

Pend 

Oreille 

Lake 

Hangman

Creek

Lightning

Creek

Rock

Creek

Priest 

River 

Pend 

Oreille 

River 

River 

Spokane

Little 

Spokane River 

Coeur d'Alene 

Bull 

River 

River 

Clark 

St 

River Joe 

Fork 

Fork 

South 

Fork 

North 

Spokane 

Post 

Falls Coeur d'Alene 

Sandpoint 

Priest 

River Clark 

Fork 

Pinehurst 

Enaville Kellogg 

St. 

Maries 

Noxon 

116° 

49° 

48° 

118° 

47° 

WASHINGTON

IDAHO 

CANADA 

UNITED STATES 

MONTANA

IDAHO 

6 

5 

8 

7 

10 9 

Base from U.S. Geological Survey digital data. 

Hydrologic unit maps, 1:100,000, 1994; 

and streams, 1:250,000, 1994; 

Area Projection. ° 00' , 

48° 30', and 115° 00', 45° 00' . 

or false northing 

WASHINGTON 

OREGON IDAHO

MONTANA 

ALBERTA

BRITISH

COLUMBIA 

Columbia 

River Northern 

Rocky 

Study Mtns

area 

Figure 1. Location of the Northern Rockies Intermontane Basins study area and surface-water-quality sampling sites in Montana, Idaho, and 

Washington. 

INDIAN 

rivers 

Albers EqualStandard parallels 46

No false easting 
114° 

CANADA 

EXPLANATION 

Clark 

Fork 

Superfund 

Site 

FLATHEAD 

INDIAN 

RESERVATION 

GLACIER 

NATIONAL 

PARK 

CONTINENTAL 

DIVIDE 

Flathead 

Lake 

Hungry 

Horse 

Reservoir 

Nevada Creek

Rock

Creek

Flint

Creek

Warm

Creek

Springs

Silver

Bow Creek

Fork 

B itterroot 

River 

Clark 

Flathead 

River 

Clark 

Fork 

River 

Little 

Blackfoot 

Riv

Blackfoot er

Fork 

South 

Fork 

North 

Fork 

Middle 

St. 

Regis 

Superior 

Perma 

Kalispell 

Columbia 

Falls 

West 

Glacier 

Bonner 

Missoula 

Frenchtown 

Hamilton 

Anaconda 

Butte 

115° 

46° 

113° 

UNITED STATES 

2 

4 

3 

1 

0 10 20 30 40 50 MILES 

0 0 20 30 40 50 KILOMETERS 

Superfund site 

Basin boundary 

Surface-water sampling site 

and number (site names 

listed in table below) 

4 

1 

2 

3 

4 

5 

Clark Fork at Turah Bridge near Bonner, Montana 

Bitterroot River near Missoula, Montana 

Clark Fork at St. Regis, Montana 

Flathead River at Perma, Montana 

Lightning Creek at Clark Fork, Idaho 

Clark Fork - Pend Oreille River Basin 

6 

7 

8 

9 

10 

St. Joe River at Red Ives Ranger Station, Idaho 

North Fork Coeur d'Alene River at Enaville, Idaho 

South Fork Coeur d'Alene River near Pinehurst, Idaho 

Spokane River near Post Falls, Idaho 

Spokane River at Seven Mile Bridge near Spokane, 

Washington 

Spokane River Basin 

1

Introduction 5

Table 2. Land cover in the Northern Rockies Intermontane Basins 

study area 

[mi2, square miles] 

Classification 

Area 

(mi2) Percent 

Forest . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23,534 74.8 

Rangeland . . . . . . . . . . . . . . . . . . . . . . . . . 3,364 10.7 

Agricultural (including orchards) . . . . . . . 2,626 8.4 

Bare land (including rock, mountain peaks 

above tree line, glaciers, snowfields, tundra) 821 2.6 

Water and wetlands . . . . . . . . . . . . . . . . . . 762 2.4 

Urban . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 356 1.1 

Total . . . . . . . . . . . . . . . . . . . . . . . . . . 31,463 100 

Approximately 56 percent of the land in the study 

area is publicly owned (primarily national and State 

forests, Glacier National Park, and designated wilderness areas). About 37 percent is privately owned and 

about 7 percent is within the Coeur d’Alene, Flathead, 

Kalispell, and Spokane Indian Reservations (Maret and 

Dutton, 1999). Almost 75 percent of the study area is 

covered by forest. Rangeland and agricultural land 

make up about 11 and 8 percent, respectively (table 2). 

Only slightly more than 1 percent of the study area is 

classified as urban (U.S. Geological Survey, 1996). 

The population of the NROK study area was about 

720,000 in the 2000 census: 250,000 in Montana, 

110,000 in Idaho, and 360,000 in Washington. Population in the study area increased by more than 20 percent between 1990 and 2000. Kootenai County in Idaho, 

containing the cities of Coeur d’Alene and Post Falls, 

grew by almost 56 percent. Ravalli County in Montana 

(covering much of the Bitterroot River drainage) increased almost 45 percent in population in the 1990s. 

Population in Stevens and Pend Oreille Counties (adjacent to the Spokane, Washington, metropolitan and 

suburban areas) grew about 30 percent (U.S. Census 

Bureau Website http://quickfacts.census.gov/qfd). Much of 

this low-density population growth occurred in suburban, undeveloped forest, agricultural, or rangeland 

areas. 

Environmental History 

About 1,600 active and abandoned hard-rock 

mines are known to exist in the NROK study area 

(Maret and Dutton, 1999). Placer gold deposits brought 

the first miners to the upper Clark Fork Basin in Montana in the 1860s and to north Idaho’s Coeur d’Alene 

mining district in the 1880s. By the early 1900s, the 

mines and smelters surrounding Butte, Montana, and 

the South Fork Coeur d’Alene River valley were 

among the largest mining and industrial areas in the 

Nation. In Montana, copper was the major product. 

However (in order of the quantity extracted between 

1880 and 1972), the area also produced zinc, manganese, lead, silver, cadmium, bismuth, selenium, tellurium, and gold (Shavers and others, 1991). In Idaho, 

silver was the primary product, as well as large amounts 

of lead and zinc. In both areas, large-scale ore processing and mining ended in the early 1980s; however, 

some mining continues on a much-reduced basis compared with historical levels. 

Mining and ore-processing activities generated 

large amounts of metal-enriched waste materials that 

entered the Clark Fork and the South Fork Coeur 

d’Alene River and their tributaries. An estimated 

100 million tons of mining and ore-processing wastes 

were produced and discharged to the headwaters of the 

Clark Fork and its tributaries during 1880 to 1982 

(Andrews, 1987). A similar amount was produced in 

Idaho, more than half of which is estimated to have 

entered the South Fork Coeur d’Alene River and its 

tributaries (Long, 1998). 

Elevated concentrations of trace elements (metals) 

in streams and rivers, channel and flood-plain sediments, and aquatic biota have been documented in the 

Clark Fork-Pend Oreille and Spokane River Basins 

downstream from historical mining and ore-processing 

areas (Johns and Moore, 1987; Moore and Luoma, 

1990; Lambing, 1991; Phillips and Lipton, 1995; 

Horowitz and others, 1993, 1995a, 1995b; Beckwith, 

1996; Beckwith and others, 1997; Hornberger and others, 1997; Woods and Beckwith, 1997; Maret and Dutton, 1999; Maret and Skinner, 2000; Grosbois and 

others, 2001; Beckwith, 2002). As a result, several 

operable units along Silver Bow Creek and the Clark 

Fork (including their flood plains) downstream from 

Butte, Montana, to Milltown Reservoir (a small hydroelectric reservoir at the confluence with the Blackfoot 

River) collectively make up the largest contiguous 

“Superfund” (U.S. Environmental Protection Agency 

environmental remediation) site in the Nation. Metalenriched sediments also appear to have been transported as far downstream as Priest River, Idaho, where 

Pend Oreille River bed sediments contain elevated concentrations of arsenic, cadmium, copper, lead, mercury, 

6 Surface-Water-Quality, Clark Fork-Pend Oreille and Spokane River Basins, 1999–2001 
and zinc, compared with background concentrations 

(Beckwith, 2002). 

A 21-mi2 area of the lower South Fork Coeur 

d’Alene River valley is the Nation’s next-largest Superfund site. Metal-enriched sediments have been transported downstream and deposited in the bed, banks, 

and extensive flood plain and wetlands of the Coeur 

d’Alene River, as well as on the bottom of Coeur 

d’Alene Lake (Horowitz and others, 1993, 1995a, 

1995b; Woods and Beckwith, 1997). Elevated concentrations of trace elements also have been reported in the 

bed and bank sediments of the Spokane River as far 

downstream as its confluence with the Columbia River 

in Washington (Bortleson and others, 1994; Grosbois 

and others, 2001; Beckwith, 2002). 

Mining activities also have affected ground-water 

quality, which has the potential to further affect surfacewater quality. For example, when large-scale mining 

ended in the Butte, Montana, area in the early 1980s, 

pumping to remove water from the vast complex of 

underground mine shafts and the mile-wide, 1,300-ftdeep open-pit mine ceased. Surface runoff and ground 

water continues filling these abandoned workings. 

Without intervention, highly acidic, metal-enriched 

water could overtop the pit, enter adjacent alluvial 

aquifers, and eventually reach the Clark Fork early in 

the 21st century (Moore and Luoma, 1990). In Idaho, 

ground water flowing under and through deposits of 

mine wastes and metal-enriched sediments is a continuing source of dissolved lead and zinc to the South 

Fork Coeur d’Alene River and its tributaries (Barton, 

2002). 

Extensive timber harvest also occurred throughout 

the forested mountains of the NROK study area. Early 

logging practices were highly disruptive and produced 

large-scale deforestation, erosion, sedimentation, and 

destabilized streambanks and channels (Rabe and Flaherty, 1974). For example, entire drainages were clearcut and “splash dams” were built, which formed temporary lakes that were periodically and suddenly 

breached (often with explosives), thereby releasing a 

torrent of cut logs, logging debris, and sediment downstream. Natural forest fires, combined with uncontrolled 

burning of logging debris, disturbed additional large 

areas of forest. Also, large areas surrounding the smelters in Idaho and Montana were devegetated by acidic 

precipitation and toxic fumes. Consequently, many 

watersheds in the NROK study area show the cumulative effects of deforestation, destabilization of stream 

channels and drainage systems, and altered flood and 

runoff patterns (Rabe and Flaherty, 1974). 

Early municipal and industrial sewer systems discharged directly to nearby rivers and streams with little 

or no treatment. In the Butte-Anaconda, Montana, area, 

settling ponds for controlling mine and smelter wastes 

were constructed in the early 1900s, and more advanced 

treatment such as liming/precipitation was initiated in 

the 1950s (Phillips and Lipton, 1995). Other than low, 

wooden dams constructed at various points across the 

South Fork Coeur d’Alene River valley, a system of 

settling ponds was not constructed in this mining district until the late 1960s, and some of these received 

municipal wastewater as well (Cornell, Howland, 

Hayes and Merryfield, Engineers and Planners, 1964). 

Although municipal and industrial dischargers 

now employ advanced wastewater-treatment processes, 

in late summer the wastewater discharges from Missoula, Montana; Coeur d’Alene and Post Falls, Idaho; 

and Spokane, Washington, contribute significant proportions of the streamflow and nutrient loads carried by 

the Clark Fork and Spokane Rivers. Interstate nutrientmanagement efforts have been underway in both the 

Clark Fork and Spokane River Basins since the 1980s. 

Nevertheless, in late summer thick mats of attached, 

filamentous, green algae grow in the Clark Fork (Land 

and Water Consulting, Inc., written commun., 1998), 

and Lake Spokane has a history of nuisance algae 

blooms, including toxic blue-green strains (Soltero and 

others, 1973, 1974; Raymond A. Soltero, Eastern 

Washington University, oral and written communs., 

1975–2001; Ken Merrill, Washington Department of 

Ecology, oral and written communs., 2001–2002). 

The effects of agriculture on water quality in the 

NROK study area are less pronounced than in many 

other NAWQA Program study areas. However, as in 

many other parts of the West, livestock grazing has 

altered riparian areas, stream channels, and flood plains. 

Large tracts of forest land were cleared for large-scale 

dryland agriculture in the extreme southwestern portion of the study area, beginning in the early 1900s. 

Soil-erosion rates from agricultural areas south and 

west of Coeur d’Alene Lake can be among the highest 

in the Nation (Rabe and Flaherty, 1974). 

Water-Quality Sampling and Analysis 

Water-quality samples were collected at 10 NAWQA 

sites throughout the Clark Fork-Pend Oreille and 

Introduction 7 
Spokane River Basins (fig. 1, table 1). These sites represent major subbasins and stream reaches or specific 

hydrologic and environmental areas of interest. For 

example, the sites at the Clark Fork at Turah Bridge 

near Bonner, Montana (site 1), and the South Fork 

Coeur d’Alene River near Pinehurst, Idaho (site 8), are 

located near the downstream boundaries of the Superfund sites and represent those areas in the respective 

river basins affected by large-scale, mining-associated 

contamination. Lightning Creek at Clark Fork, Idaho 

(site 5), represents a forested, mountainous basin 

where considerable logging and road-building activities have occurred. The sites on the Flathead River at 

Perma, Montana (site 4), and the Spokane River near 

Post Falls, Idaho (site 9), are downstream from large 

lakes. 

All but two NROK NAWQA sampling sites were 

located at USGS gaging stations where streamflow data 

were being collected. A new gaging station was established in water year 1999 at the St. Joe River at Red 

Ives Ranger Station, Idaho (site 6), to represent relatively undisturbed reference conditions in the forested, 

mountainous watersheds of the Northern Rocky Mountains. Another NROK NAWQA sampling site was 

established on the Spokane River at 7 Mile Bridge near 

Spokane, Washington (site 10), downstream from the 

wastewater-treatment facility and storm-sewer outfalls 

of the city and surrounding metropolitan area. Streamflow at this site was determined by adding the discharge values from the wastewater-treatment facility 

and from gaging stations on the Spokane River and 

near the mouth of Hangman Creek approximately 10 

mi upstream; little additional inflow occurs in this 

reach where the river is confined in a bedrock canyon. 

Water-quality samples were collected approximately 9 to 12 times per year at each site from late 

1998 to mid-2001 (water years 1999 – 2001). Samples 

were collected more frequently during periods of 

increasing and high streamflow (spring snowmelt runoff) and less frequently during receding or base-flow 

conditions. Considerable effort was made to collect 

approximately similar numbers of samples in each 

increment (deciles) of streamflow (figs. 2–11, back of 

report). 

Water samples for analysis of chemical constituents and suspended sediment were collected using 

standard USGS depth-integrating samplers and using 

isokinetic and cross-section integrating sampling methods (Edwards and Glysson, 1988; Ward and Harr, 

1990). Specific conductance, pH, water temperature, 

and alkalinity were determined in the field using standard instruments and methods as specified for the 

NAWQA Program (Shelton, 1994). Subsamples for 

chemical analysis were split and processed in the field 

in mobile laboratories. Documented protocols used 

consistently by all NAWQA Program studies included 

the use of a 10-port cone splitter constructed of Teflon 

(to produce representative subsamples of solid-phase 

constituents), specific procedures for positive-pressure 

filtration (using capsule filters with a nominal pore size 

of 0.45 micrometer), sample preservation (conducted 

in isolation chambers), and rigorous equipment cleaning to minimize contamination during sampling and 

sample processing (Shelton, 1994). 

Major ion and nutrient concentrations were analyzed by the USGS National Water Quality Laboratory 

according to methods described by Fishman and Friedman (1989) and Fishman (1993). Trace elements 

(except for mercury) were analyzed by inductively 

coupled plasma-mass spectrometry as described by 

Faires (1993) and Jones and Garbarino (1999). Organic 

carbon was analyzed according to the method of Brenton and Arnett (1993). Total recoverable mercury was 

analyzed by cold vapor atomic absorption by methods 

described by Fishman and Friedman (1989). 

STREAMFLOW AND WATER-QUALITY DATA 

Summaries and Graphical Displays of Data 

Boxplots are used throughout this report as a convenient means of graphically portraying the distribution of the data. In a boxplot, the middle line within the 

box represents the median, or 50th percentile, value. 

When arranged in ascending order, one-half of the values are greater than the median and one-half are less 

than the median. The top of the box represents the 75th 

percentile (75 percent of the values are less than this 

value). The bottom of the box represents the 25th percentile (25 percent of the values are less than this 

value). The difference between the 25th and 75th percentile values (and comprising half of the values) is the 

interquartile range. In the boxplots presented in this 

report, the lines (called whiskers) extending from the 

top of the box represent values that are as much as 1.5 

times the interquartile range greater than the 75th percentile value. Conversely, the whiskers extending from 

the bottom of the box represent values as much as 1.5 

times the interquartile range less than the 25th percen8 Surface-Water-Quality, Clark Fork-Pend Oreille and Spokane River Basins, 1999–2001 
EXPLANATION the mean daily values for the respective periods of 

for boxplots shown in record (figs. 2–5 and 8–11). At three sites—Lightning 

figures 12 through 40 Creek at Clark Fork, Idaho; St. Joe River at Red Ives 

Interquartile range 

27 Number of measurements Ranger Station, Idaho; and Spokane River at 7 Mile 

(IQR) 

or samples Bridge near Spokane, Washington—the hydrologic 

Far outlier data period of streamflow record was insufficient to 

Outlier compute long-term statistics. Therefore, only sampling 

dates are plotted on the study-period hydrograph for 

75th percentile plus 

1.5 times the IQR these sites for water years 1999 – 2001 in figures 6, 7, 

75th percentile	 and 11. In water year 2000, streamflow at sites in the 

Spokane River Basin was near or slightly greater than 

the long-term mean, but at Clark Fork sites, streamflow 

Median (50th percentile) was less than the long-term mean. Streamflow in water 

year 2001 was considerably less than the long-term 25th percentile mean at all sites, ranging from about 75 percent of the 

mean at the Clark Fork at Turah Bridge near Bonner, 25th percentile minus Montana, to about 40 percent at the North Fork Coeur 1.5 times the IQR 

Outlier d’Alene River at Enaville, Idaho. 

Far outlier 

NUTRIENTS 

Concentrations of dissolved ammonia, nitrite plus 

nitrate, ammonia plus total organic nitrogen, orthophos­ tile value. Values that lie outside the ranges indicated phorus, total phosphorus, suspended organic carbon, by the whiskers are shown as solid dots (outliers) and and dissolved organic carbon are summarized in table 

as circles (far outliers). These extreme values do not 4. Also included for comparison in table 4 are median imply a problem with the quality of the data, but indi- values from 85 relatively undisturbed watersheds across 

cate the rareness of such values within the overall data the Nation from NAWQA and other national program set. 	 studies (Clark and others, 2000). Nutrient data from the 

NROK NAWQA study include many censored or estimated values, not only because of the small concentra- Physical and Chemical Characteristics	 tions present in rivers and streams in the NROK 

NAWQA study area, but also because of changes in 

Common physical and chemical characteristics of analytical methodology and data reporting conventions 

rivers and streams at the 10 surface-water sampling at the USGS National Water Quality Laboratory that 

sites in the NROK NAWQA study area are statistically occurred during the study. Therefore, for the graphical 

summarized in table 3 and depicted in boxplots in fig- depiction (boxplots) of nutrient data provided in figures 

ures 12 –19 (back of report). In general, rivers and 20 and 21, censored data were assigned a value of onestreams in the study area contain small concentrations half the reported “less than” value, and estimated val­


of dissolved substances and exhibit small values for ues were used directly.
 

specific conductance, hardness, alkalinity, and dis- The median total nitrogen concentration at most 
 

solved solids. Dissolved oxygen concentrations gen- NROK sites was smaller than the median concentra­


erally were near saturation at all sites during the study tions reported by Clark and others (2000) at 85 rela­


and, therefore, were not included in the tables or fig- tively undisturbed sites from around the Nation. How­


ures. ever, the median total nitrogen concentration at the 
 

South Fork Coeur d’Alene River near Pinehurst, Idaho, 

STREAMFLOW was 106 percent of the national median, and the 

median concentration at the Spokane River at 7 Mile 

In water year 1999, streamflow at NROK sam- Bridge near Spokane, Washington, was more than doupling sites was greater than or near (96 – 131 percent) ble the national median. Both of these sites are downStreamflow and Water-Quality Data 9 
10 

Table 3. Selected physical and chemical characteristics for samples collected at surface-water-quality sampling sites in the Northern Rockies Intermontanyears 1999–2001 [No., number; ft3/s, cubic feet per second; μS/cm, microsiemens per centimeter at 25°C; °C, degrees Celsius; mg/L, milligrams per liter; CaCO3, calcium carbonate, μm, m

Idaho; WA, Washington] 

Surface-Water-Quality, Clark Fork-Pend Oreille and Spokane River Basins, 1999–2001 Site No. (fig. 1) Site name Streamflow (ft3/s) Specific conductance (μS/cm) pH, field (standard units) 

Water 

temperature (°C) 

Hardness 

(mg/L as 

CaCO3) 

Alkalinity, 

field 

(mg/L as 

CaCO3) 

Suspended 

sediment 

(mg/L) 

1 lark Fork at Turah Bridge near Bonner, MT 

No. of samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Minimum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Maximum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Median . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

27 

287 

5,280 

929 

27 

153 413 352 

27 

7.5 8.5 8.1 

27 

0 

19.0 

7.0 

27 64 

192 160 

27 46 

148 128 

26 

3 

131 

9 

2 itterroot River near Missoula, MT 

No. of samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Minimum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Maximum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Median . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

27 

482 

13,700 

1,415 

27 39 

177 117 

27 

7.1 8.6 7.8 

27 

2.0 

21.5 

9.5 

27 15 77 51 

27 14 86 48 

27 

1 

168 

6 

3 lark Fork at St. Regis, MT 

No. of samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Minimum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Maximum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Median . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

24 

1,660 

35,300 

4,160 

20 95 

277 224 

24 

7.5 8.5 8.1 

24 

0 

22.0 

6.8 

24 

106 124 

97 

24 41 

120 

97 

23 

1 

280 

6 

4 Flathead River at Perma, MT 

No. of samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Minimum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Maximum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Median . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

21 

4,090 

32,400 10,100 

20 

158 193 173 

21 

7.8 8.4 8.2 

21 

0 

23.0 

8.0 

21 81 94 89 

21 83 96 87 

20 

1 

13 

3 

5 Lightning Creek at Clark Fork, ID 

No. of samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Minimum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Maximum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Median . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

18 

6 

2,120 

162 

18 12 36 26 

18 

6.6 7.5 7.1 

18 

3.0 

25.0 

6.0 

18 

4 

15 10 

18 

4 

13 10 

18 

1 6 1 

C 

B 

C 
Table 3. Selected physical and chemical characteristics for samples collected at surface-water-quality sampling sites in the Northern Rockies Intermontan

years 1999–2001—Continued 

Site No. 

(fig. 1) Site name 

Streamflow 

(ft3/s) 

Specific 

conductance 

(μS/cm) 

pH, field 

(standard 

units) 

Water 

temperature 

(°C) 

Hardness 

(mg/L as 

CaCO3) 

Alkalinity, 

field 

(mg/L as 

CaCO3) 

Suspended 

sediment 

(mg/L) 

6 St. Joe River at Red Ives Ranger Station, ID 

No. of samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Minimum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Maximum. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Median . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

17 46 

2,190 

181 

17 26 51 41 

17 

6.7 8.0 7.5 

17 

0 

15.0 

6.0 

17 12 24 18 

17 12 25 19 

17 

1 9 1 

7 orth Fork Coeur d’Alene River at Enaville, ID 

No. of samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Minimum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Maximum. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Median . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

28 

144 

18,200 

1,465 

28 25 62 41 

28 

6.7 7.7 7.3 

28 

1.5 

15.5 

5.8 

28 10 23 19 

28 10 41 18 

28 

1 

207 

1 

8 South Fork Coeur d’Alene River near Pinehurst, ID 

No. of samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Minimum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Maximum. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Median . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

33 82 

4,890 

413 

33 46 

328 147 

33 

6.6 7.5 7.2 

33 

1.5 

18.0 

7.5 

33 18 

136 

56 

33 12 38 25 

32 

1 

302 

3 

9 Spokane River near Post Falls, ID 

No. of samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Minimum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Maximum. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Median . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

29 

242 

28,000 

4,510 

29 41 71 50 

29 

7.0 7.7 7.4 

29 

2.0 

25.0 

8.5 

29 16 23 20 

28 16 21 18 

29 

1 3 1 

10 Spokane River at 7 Mile Bridge near Spokane, WA 

No. of samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Minimum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Maximum. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Median . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

27 

680 

26,800 

5,940 

26 57 

303 

95 

27 

6.9 8.1 7.6 

27 

3.5 

16.0 

8.5 

27 23 

133 

39 

27 21 

115 

35 

27 

1 

116 

3 

N 

Streamflow and Water-Quality Data 11 
12 

Table 4. Nutrient and organic carbon concentrations in samples collected at surface-water-quality sampling sites in the Northern Rockies Intermontane years 1999–2001, and comparative median concentrations in samples collected for the National Water-Quality Assessment Program and other national m[No., number; mg/L, milligrams per liter; N, nitrogen; P, phosphorus; C, carbon; MT, Montana; ID, Idaho; 

WA, Washington; %, percent; e, estimated value; <, less than; >

available] 

Surface-Water-Quality, Clark Fork-Pend Oreille and Spokane River Basins, 1999–2001 Site No. (fig. 1) Site name Ammonia, dissolved (mg/L as N) Nitrite plus nitrate, dissolved (mg/L as N) Ammonia plus organic nitrogen, total (mg/L as N) 

Total nitrogen, 

nitrite + nitrate-N 

added to 

ammonia + organic-N 

(mg/L as N) 

Orthophosphorus, 

dissolved 

(mg/L as P) 

Total 

phosphorus 

(mg/L as P) 

1 Clark Fork at 

Turah Bridge near 

Bonner, MT 

No. of samples. . . . . . . . . . . . . . . . . . 

No. of censored or e values . . . . . . . . % censored or e values . . . . . . . . . . . Minimum . . . . . . . . . . . . . . . . . . . . . . Maximum . . . . . . . . . . . . . . . . . . . . . Median. . . . . . . . . . . . . . . . . . . . . . . . 

27 

9 

33.3 

<.002 

.011 .003 

27 

2 7.4 

<.005 

.20 .017 

27 

2 7.4 

e.08 

.86 

.23 0.247 

27 

7 

25.9 

<.001 

.023 .007 

27 

0 0 

.011 .172 .029 

2 itterroot River near Missoula, MT 

No. of samples. . . . . . . . . . . . . . . . . . No. of censored or e values . . . . . . . . % censored or e values . . . . . . . . . . . Minimum . . . . . . . . . . . . . . . . . . . . . . Maximum . . . . . . . . . . . . . . . . . . . . . Median. . . . . . . . . . . . . . . . . . . . . . . . 

27 

8 

29.6 

<.002 

.017 .004 

27 

5 

18.5 

<.005 

.102 .019 

27 

3 

11.1 

e.05 

.62 .17 .189 

27 

9 

33.3 

<.001 

.008 .002 

27 

1 3.7 

.004 .117 .02 

3 lark Fork at St. Regis, MT 

No. of samples. . . . . . . . . . . . . . . . . . No. of censored or e values . . . . . . . . % censored or e values . . . . . . . . . . . Minimum . . . . . . . . . . . . . . . . . . . . . . Maximum . . . . . . . . . . . . . . . . . . . . . Median. . . . . . . . . . . . . . . . . . . . . . . . 

24 

5 

20.8 

<.002 

.018 .0045 

24 

4 

16.7 

<.005 

.159 .0385 

24 

2 8.3 

e.06 

.66 .20 .2385 

24 

8 

33.3 

<.001 

.01 .002 

24 

3 

12.5 

.004 .183 .0185 

4 Flathead River at Perma, MT 

No. of samples. . . . . . . . . . . . . . . . . . 

No. of censored or e values . . . . . . . . 

% censored or e values . . . . . . . . . . . Minimum . . . . . . . . . . . . . . . . . . . . . . 

Maximum . . . . . . . . . . . . . . . . . . . . . Median. . . . . . . . . . . . . . . . . . . . . . . . 

21 

9 

42.9 

<.002 

.045 .002 

21 

2 9.5 

<.005 

.064 .022 

21 

7 

33.3 

e.07 

.30 .115 .137 

21 13 61.9 

<.001 

.007 .001 

21 13 61.9 

e.002 

.038 .0045 

5 ightning Creek at Clark Fork, ID 

No. of samples. . . . . . . . . . . . . . . . . . No. of censored or e values . . . . . . . . % censored or e values . . . . . . . . . . . Minimum . . . . . . . . . . . . . . . . . . . . . . Maximum . . . . . . . . . . . . . . . . . . . . . Median. . . . . . . . . . . . . . . . . . . . . . . . 

18 

8 

44.4 

<.002 

.024 .002 

18 

0 0 

.025 .247 .101 

18 16 88.9 

e.06 

.19 

e.07 e.171 

18 13 72.2 

<.001 

.003 .001 

18 16 88.9 

e.002 

.004 .0035 

B C L 
Table 4. Nutrient and organic carbon concentrations in samples collected at surface-water-quality sampling sites in the Northern Rockies Intermontane 

years 1999–2001, and comparative median concentrations in samples collected for the National Water-Quality Assessment Program and other national m

Continued 

Site 

No. 

(fig. 1) Site name 

Ammonia, 

dissolved 

(mg/L as N) 

Nitrite 

plus 

nitrate, 

dissolved 

(mg/L as N) 

Ammonia 

plus organic 

nitrogen, 

total 

(mg/L as N) 

Total nitrogen, 

nitrite + nitrate-N 

added to 

ammonia + organic-N 

(mg/L as N) 

Orthophosphorus, 

dissolved 

(mg/L as P) 

Total 

phosphorus 

(mg/L as P) 

6 St. Joe River at Red Ives Ranger Station, ID 

No. of samples . . . . . . . . . . . . . . . . . No. of censored or e values. . . . . . . . % censored or e values . . . . . . . . . . . Minimum . . . . . . . . . . . . . . . . . . . . . Maximum . . . . . . . . . . . . . . . . . . . . . Median . . . . . . . . . . . . . . . . . . . . . . . 

17 13 76.5 

<.002 

.011 

<.002 

17 

4 

23.5 

<.005 

.053 .009 

17 13 76.5 

e.05 

.16 .075 0.084 

17 

7 

41.2 

<.001 

.004 .0015 

17 

9 

52.9 

e.003 

.012 .005 

7 orth Fork Coeur d’Alene River at 

Enaville, ID 

No. of samples . . . . . . . . . . . . . . . . . No. of censored or e values. . . . . . . . % censored or e values . . . . . . . . . . . Minimum . . . . . . . . . . . . . . . . . . . . . Maximum . . . . . . . . . . . . . . . . . . . . . Median . . . . . . . . . . . . . . . . . . . . . . . 

28 12 42.9 

<.002 

.014 .002 

28 

5 

17.9 

<.005 

.048 .013 

28 21 75 

e.06 

.36 

e.08 e.21 

28 11 39.3 

<.001 

.008 .003 

28 13 46.4 

e.003 

.189 .006 

8 South Fork Coeur d’Alene River near 

Pinehurst, ID 

No. of samples . . . . . . . . . . . . . . . . . No. of censored or e values. . . . . . . . % censored or e values . . . . . . . . . . . 

Minimum . . . . . . . . . . . . . . . . . . . . . Maximum . . . . . . . . . . . . . . . . . . . . . Median . . . . . . . . . . . . . . . . . . . . . . . 

33 

0 0 

.006 .408 .07 

33 

0 0 

.025 .448 .128 

33 

7 

21.9 

e.06 

.62 .21 .338 

32 

1 3.1 

.002 .027 .009 

33 

0 0 

.012 .171 .032 

9 Spokane River near Post Falls, ID 

No. of samples . . . . . . . . . . . . . . . . . No. of censored or e values. . . . . . . . % censored or e values . . . . . . . . . . . Minimum . . . . . . . . . . . . . . . . . . . . . Maximum . . . . . . . . . . . . . . . . . . . . . Median . . . . . . . . . . . . . . . . . . . . . . . 

27 

6 

22.2 

<.002 

.052 .004 

27 

1 3.7 

<.005 

.257 .054 

27 

5 

18.5 

e.05 

.65 .13 .184 

27 10 37 

<.001 

.133 .0015 

27 

3 

11.1 

e.005 

.057 .011 

10 Spokane River at 7 Mile Bridge near 

Spokane, WA 

No. of samples . . . . . . . . . . . . . . . . . 

No. of censored or e values. . . . . . . . % censored or e values . . . . . . . . . . . Minimum . . . . . . . . . . . . . . . . . . . . . Maximum . . . . . . . . . . . . . . . . . . . . . Median . . . . . . . . . . . . . . . . . . . . . . . 

27 

8 

29.6 

<.002 

.067 .004 

27 

0 0 

.101 

2.86 

.591 

27 

5 

18.5 

e.06 

.31 .15 .741 

27 

4 

14.8 

<.001 

.108 .012 

27 

0 0 

.006 .118 .027 

National median for 85 undisturbed sites (Clark and 

others, 2000) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .020 .080 — .32 .010 .037 

N 

Streamflow and Water-Quality Data 13 
stream from wastewater-treatment facilities. Under 

conditions of low streamflow, treated wastewater from 

the city of Spokane composed as much as 9 to 11 percent of the discharge in the Spokane River at 7 Mile 

Bridge in the late summer and early autumn in water 

years 1999 – 2001 (fig. 11). 

The median total phosphorus concentration at all 

NROK sites was smaller (often by a considerable 

amount) than the median concentration at 85 undisturbed sites reported by Clark and others (2000). However, the maximum concentration of total phosphorus 

measured at six NROK NAWQA sites exceeded the 

0.1 mg/L threshold recommended for limiting nuisance 

aquatic algae and plant growth in rivers or streams 

(U.S. Environmental Protection Agency, 1986). These 

sites were the Clark Fork at Turah Bridge, Bitterroot 

River near Missoula, and Clark Fork at St. Regis, in 

Montana; the North Fork Coeur d’Alene River at 

Enaville and the South Fork Coeur d’Alene River near 

Pinehurst, in Idaho; and the Spokane River at 7 Mile 

Bridge near Spokane, in Washington. 

ORGANIC CARBON 

Dissolved and suspended organic carbon were 

sampled and analyzed at most NROK sites from late 

1998 to early 2000 (table 4). Analyses for carbon were 

discontinued in 2000, primarily because of the small 

concentrations routinely measured at NROK NAWQA 

sites and also because of methodological changes at the 

USGS National Water Quality Laboratory. 

TRACE ELEMENTS 

Concentrations of selected trace elements of environmental concern in the NROK study area are summarized in table 5. Methodological changes, varying 

analytical detection and data reporting (censoring) limits during the NROK NAWQA study made data analysis, interpretation, and reporting difficult. These varying 

reporting limits affected statistical treatment of censored values, resulting in intervals rather than discrete 

values for some medians (table 5). For the graphical 

depictions (boxplots) of selected trace-element data in 

figures 22 – 32 (back of report), censored data were 

assigned values of one-half the reported “less than” 

value, and estimated values were used directly. Nevertheless, some of the boxplots appear distorted. For 

example, at sites having a large proportion of censored 

values, the boxplots appear compressed, either because 

of limited variation in the values or because of analytical reporting limits that were too large to observe variation over much of the range of ambient concentrations. 

Dissolved arsenic concentrations were largest at 

the Clark Fork at Turah Bridge and at St. Regis, Montana, and the Spokane River at 7 Mile Bridge near Spokane, Washington (table 5, fig. 22). These sites are 

downstream from the historical Butte-Anaconda mining and ore-processing areas in Montana and the city of 

Spokane, Washington, metropolitan area. A similar pattern was apparent for total recoverable arsenic (fig. 23). 

In addition, several total recoverable arsenic concentrations (measured during high streamflow) at the South 

Fork Coeur d’Alene River near Pinehurst, Idaho, (downstream from the historical Coeur d’Alene mining and 

ore-processing district) exceeded the maximum concentration at the Clark Fork at Turah Bridge (table 5). 

Median dissolved and total recoverable cadmium 

concentrations were substantially larger at the South 

Fork Coeur d’Alene River near Pinehurst, Idaho, compared with other sites. Concentrations were moderately 

elevated, relative to concentrations at the remaining 

sites, at the Spokane River near Post Falls, Idaho, and 

at 7 Mile Bridge near Spokane, Washington (table 5, 

figs. 24 and 25). 

Dissolved copper concentrations were largest at 

the Clark Fork at Turah Bridge near Bonner and at St. 

Regis, Montana (table 5, fig. 26). Total recoverable 

copper concentrations also were largest at the Clark 

Fork at Turah Bridge (fig. 27). 

Dissolved lead concentrations were largest at the 

South Fork Coeur d’Alene River near Pinehurst, Idaho 

(fig. 28), and generally were less than 1 μg/L at the 

remaining sites. Total recoverable lead concentrations 

also were largest at the South Fork Coeur d’Alene 

River near Pinehurst and were one or more orders of 

magnitude larger than at the main-stem Clark Fork and 

Spokane River sites (fig. 29), which also are downstream from historical mining areas (fig. 1). 

At the minimum and median hardness levels measured throughout the NROK NAWQA study, dissolved 

lead concentrations in all 32 samples collected at the 

South Fork Coeur d’Alene River near Pinehurst, Idaho, 

exceeded the Idaho criterion for chronic toxicity designated for the protection of aquatic life; 75 percent of 

the dissolved lead concentrations exceeded the criterion at the maximum hardness level measured. The 

hardness-dependent chronic criterion is the 4-day average concentration not to be exceeded more than once 

every 3 years on average (Idaho Department of Envi14 Surface-Water-Quality, Clark Fork-Pend Oreille and Spokane River Basins, 1999–2001 
Table 5. Selected trace-element data for samples collected at surface-water-quality sampling sites in the Northern Rockies Intermontane Basins study a

[No., number; μg/L, micrograms per liter; MT, Montana; ID, Idaho; WA, Washington; e, estimated value; %, percent; <, less than] 

Site 

No. 

(fig. 1) Site name 

Arsenic, 

dissolved 

(μg/L as As) 

Arsenic, total 

recoverable 

(μg/L as As) 

Cadmium, 

dissolved 

(μg/L as 

Cd) 

Cadmium, 

total 

recoverable 

(μg/L as Cd) 

Copper, 

dissolved 

(μg/L as 

Cu) 

Copper, total 

recoverable 

(μg/L as Cu) 

Lead, 

dissolved 

(μg/L as 

Pb) 

Lead, 

total 

recoverable 

(μg/L as Pb) 

Mercu

total 

recovera

(μg/L as 

1 Clark Fork at Turah Bridge near 

Bonner, MT 

No. of samples . . . . . . . . . . . . . No. of censored or e values . . . % of censored or e values . . . . Minimum . . . . . . . . . . . . . . . . . Maximum . . . . . . . . . . . . . . . . Median . . . . . . . . . . . . . . . . . . . 

24 

0 0 3.1 7.9 5.5 

23 

0 0 3 

11 

6 

24 22 91.7 

e.02 

.04 

<1.0 

23 17 73.9 

.04 

<1.0 

<.11 

24 

0 0 1.9 6.5 2.65 

23 14 60.9 

3.5 

48.4 17.4 

24 21 87.5 

e.04 

.10 

<1.0 

23 

9 

39.1 

e.50 

10 

1.2 

16 15 93.8 

<.10 <.30 <.30 

2 Bitterroot River near Missoula, MT 

No. of samples . . . . . . . . . . . . . No. of censored or e values . . . % of censored or e values . . . . Minimum . . . . . . . . . . . . . . . . . Maximum . . . . . . . . . . . . . . . . Median . . . . . . . . . . . . . . . . . . . 

19 13 68.4 

.24 

<2.0 <1.0 

18 18 

100 

<1.0 <2.6 <1.9 

19 19 

100 

e.02 

<1.0 <1.0 

18 17 94.4 

<.04 

1.9 

<.11 

19 14 73.7 

.52 .86 

<1.0 

18 15 83.3 

e.52 

<20 <12 

19 19 

100 

<.08 

<1.0 <1.0 

18 18 

100 

<1.0 

e1.0 

<1.0 

13 13 

100 

<.10 <.30 <.30 

3 Clark Fork at St. Regis, MT 

No. of samples . . . . . . . . . . . . . No. of censored or e values . . . % of censored or e values . . . . Minimum . . . . . . . . . . . . . . . . . Maximum . . . . . . . . . . . . . . . . Median . . . . . . . . . . . . . . . . . . . 

22 

5 

22.7 

e.67 

2.4 

e1.6 

22 14 63.6 

<1.0 

3.1 2.2 

22 22 

100 

e.02 

<1.0 <1.0 

22 22 

100 

e.02 

<1.0 

<.11 

22 

5 

22.7 

<1.0 

2.4 1.2 

22 15 68.2 

1.0 

21 

<12 – e12 

22 21 95 

e.04 

.10 

<1.0 

22 19 

86.4 

e.62 

6.7 

<1.0 

16 16 

100 

<.10 <.30 <.30 

4 Flathead River at Perma, MT 

No. of samples . . . . . . . . . . . . . No. of censored or e values . . . % of censored or e values . . . . Minimum . . . . . . . . . . . . . . . . . Maximum . . . . . . . . . . . . . . . . Median . . . . . . . . . . . . . . . . . . . 

14 

8 

57.1 

.37 

<2.0 

.56 – <.9 

14 13 92.9 

<1.0 <2.6 <1.9 

14 14 

100 

e.02 

<1.0 <1.0 

14 13 92.9 

<.04 

<1.0 

.11 

14 

8 

57.1 

.4 

<1.0 <1.0 

14 12 85.7 

e.41 

<20.0 <12 

14 14 

100 

e.04 

<1.0 <1.0 

14 14 

100 

<1.0 <1.0 <1.0 

8 8 

100 

<.10 <.30 

<.10 – <.

5 Lightning Creek at Clark Fork, ID 

No. of samples . . . . . . . . . . . . . No. of censored or e values . . . % of censored or e values . . . . Minimum . . . . . . . . . . . . . . . . . Maximum . . . . . . . . . . . . . . . . Median . . . . . . . . . . . . . . . . . . . 

17 17 

100 

e.11 

<2.0 

<.90 

17 17 

100 

<1.9 <2.6 <2.6 

17 16 94.1 

e.02 

<1.0 <1.0 

17 17 

100 

<.04 <.11 <.11 

17 13 76.5 

e.16 

<1.0 <1.0 

17 17 

100 

e.41 

<20.0 <20.0 

17 11 64.7 

e.05 

<1.0 <1.0 

17 17 

100 

e.51 

<1.0 <1.0 

10 10 

100 

<.30 <.30 <.30 

Streamflow and Water-Quality Data 15 
16 

Table 5. Selected trace-element data for samples collected at surface-water-quality sampling sites in the Northern Rockies Intermontane Basins study a

Surface-Water-Quality, Clark Fork-Pend Oreille and Spokane River Basins, 1999–2001 

2001

—Continued 

Site 

No. 

(fig. 1) Site name 

Arsenic, 

dissolved 

(μg/L as As) 

Arsenic, total 

recoverable 

(μg/L as As) 

Cadmium, 

dissolved 

(μg/L as 

Cd) 

Cadmium, 

total 

recoverable 

(μg/L as Cd) 

Copper, 

dissolved 

(μg/L as 

Cu) 

Copper, total 

recoverable 

(μg/L as Cu) 

Lead, 

dissolved 

(μg/L as 

Pb) 

Lead, 

total 

recoverable 

(μg/L as Pb) 

Mercu

tota

recover

(μg/L as 

6 St. Joe River at Red Ives Ranger 

Station, ID 

No. of samples . . . . . . . . . . . . No. of censored or e values . . % of censored or e values. . . . Minimum . . . . . . . . . . . . . . . . Maximum . . . . . . . . . . . . . . . . Median . . . . . . . . . . . . . . . . . . 

16 15 93.8 

e.11 

<2.0 

<.90 

15 15 

100 

<1.0 <2.6 <1.9 

17 17 

100 

e.02 

<1.0 <1.0 

16 16 

100 

<.04 

<1.0 

<.11 

17 14 82.4 

e.16 

<1.0 <1.0 

16 16 

100 

e.31 

<20 <12 

16 15 93.8 

<.08 

<1.0 <1.0 

15 15 

100 

<1.0 <1.0 <1.0 

12 12 

100 

<.1<.3<.3

7 orth Fork Coeur d’Alene River at 

Enaville, ID 

No. of samples . . . . . . . . . . . . No. of censored or e values . . % of censored or e values. . . . Minimum . . . . . . . . . . . . . . . . Maximum . . . . . . . . . . . . . . . . Median . . . . . . . . . . . . . . . . . . 

21 20 95 

e.09 

<2.0 <1.0 

22 20 91 

<1.0 

3.0 

<1.9 

21 21 

100 

e.02 

<1.0 <1.0 

22 21 95 

e.02 

<1.0 

<.11 

21 17 81 

e.18 

<1.0 <1.0 

22 22 

100 

e.30 

<20 

e11 – <12 

21 20 95.2 

e.04 

<1.0 <1.0 

22 17 77.3 

<1.0 

24 

<1.0 

15 15 

100 

<.1<.3<.3

8 South Fork Coeur d’Alene River 

near Pinehurst, ID 

No. of samples . . . . . . . . . . . . No. of censored or e values . . % of censored or e values. . . . Minimum . . . . . . . . . . . . . . . . Maximum . . . . . . . . . . . . . . . . Median . . . . . . . . . . . . . . . . . . 

32 22 69 

.30 

<2.0 <1.0 

31 22 71 

<1.0 

13 

<2.6 

32 

0 0 1.5 

18 

6.55 

30 

0 0 2.6 

19 

6.4 

32 18 56 

.84 

<3.0 <1.0 

31 21 68 

1.2 

<20 

14 

32 

0 0 2.1 

12 

4.4 

31 

0 0 

13 

790 

20 

23 19 83 

<.1

.6

<.3

9 Spokane River near Post Falls, ID 

No. of samples . . . . . . . . . . . . No. of censored or e values . . % of censored or e values. . . . Minimum . . . . . . . . . . . . . . . . Maximum . . . . . . . . . . . . . . . . Median . . . . . . . . . . . . . . . . . . 

26 17 65 

<1.0 <2.0 

<.90 

26 25 96 

<1.0 <2.6 

<1.9 – <2.6 

26 17 65 

.08 

<1.0 

<.10 

26 

6 

23 

.10 

<1.0 

.23 

26 16 62 

.5 

1.5 

<10 

26 18 69 

e.58 

<20 <12 

26 17 65 

e.04 

1.6 

<.10 

26 

8 

31 

e.59 

7.8 1.15 

17 17 

100 

<.1<.3<.3

10 Spokane River at 7 Mile Bridge 

near Spokane, 

WA 

No. of samples . . . . . . . . . . . . No. of censored or e values . . % of censored or e values. . . . Minimum . . . . . . . . . . . . . . . . Maximum . . . . . . . . . . . . . . . . Median . . . . . . . . . . . . . . . . . . 

25 13 52 

e.51 

3.2 

<1.0 

24 23 95.8 

<1.0 

2.7 

1.9 – e2.0 

25 18 72 

.05 

<1.0 <1.0 

24 

7 

29.2 

e.08 

<1.0 

.185 

25 18 72 

.54 

<1.0 <1.0 

24 17 70.8 

.67 

1.3 

<12 – <20 

25 19 

76 

e.06 

1.4 

<1.0 

24 10 41.7 

e.88 

16 

1.5 

18 18 

100 

<.1<.3<.3

N 
ronmental Quality, 1999; U.S. Environmental Protection Agency, 2000). 

Although most total recoverable mercury concentrations were reported either as less than 0.10 or less 

than 0.30 μg/L (table 5), mercury was measured at 

detectable or estimated concentrations on one occasion 

at the Clark Fork at Turah Bridge and on four occasions 

at the South Fork Coeur d’Alene River near Pinehurst 

(fig. 30). The concentration reported for the Clark Fork 

at Turah Bridge was 0.12 μg/L from a sample collected 

during high streamflow. At the South Fork Coeur 

d’Alene River near Pinehurst, three concentrations 

ranging from 0.30 to 0.66 μg/L were measured in samples collected during high streamflow, and a concentration of 0.15 μg/L was measured in a sample collected 

during low streamflow. 

Dissolved zinc concentrations were substantially 

elevated at the South Fork Coeur d’Alene and Spokane 

River sites (table 5, fig. 31). These sites are downstream 

from historical mining areas (fig. 1); sites on the 

Spokane River are also downstream from Coeur 

d’Alene Lake. The elevated concentrations of zinc 

in the Spokane River indicate that a portion of the upstream zinc input passes through Coeur d’Alene Lake. 

A similar pattern also was evident for total recoverable 

zinc concentrations (fig. 32). At the South Fork Coeur 

d’Alene River near Pinehurst, Idaho, dissolved zinc 

concentrations in all 32 samples exceeded both the 

chronic and acute criteria for the protection of aquatic 

life at all hardness levels measured throughout the 

study (Idaho Department of Environmental Quality, 

1999; U.S. Environmental Protection Agency, 2000). 

The acute criterion is the 1-hour average concentration 

not to be exceeded more than once every 3 years on 

average. At the Spokane River near Post Falls, Idaho, 

22 of 26 (85 percent) dissolved zinc concentrations 

exceeded both the chronic and acute criteria. At the 

Spokane River at 7 Mile Bridge near Spokane, Washington, at the median hardness level, 9 of 24 (38 percent) dissolved zinc concentrations exceeded the chronic 

criterion, and 5 of 24 concentrations (21 percent) exceeded the acute criterion. 

COMPARISON WITH OTHER NATIONAL WATERQUALITY ASSESSMENT PROGRAM STUDIES 

Trace-element data from sites in other NAWQA 

Program study areas in the Western United States that 

have a history of mining activities were obtained for 

comparison with results from the NROK NAWQA 

study. These studies covered the following geographic 

areas: Upper Colorado River Basin (UCOL); Sacramento River Basin (SACR); Great Salt Lake Basins 

(GRSL); and Nevada Basins and Range (NVBR). Censored values were set to one-half the reporting value, 

and “estimated” values were used directly. Along with 

the NROK data, the distributions of these data are 

graphically depicted (boxplots) in figures 33 – 40 (back 

of report). 

Overall, median concentrations of dissolved 

arsenic, dissolved and total recoverable copper, total 

recoverable lead, and total recoverable zinc in the 

NROK study area appeared to be similar to or slightly 

smaller than those reported for other Western NAWQA 

study areas affected by historical mining activities 

(figs. 33, 35, 36, 38, and 40). Although the NROK 

median total recoverable lead concentration was the 

smallest among the three Western study areas compared (fig. 38), concentrations in several samples from 

the NROK study area were an order of magnitude 

larger than the maximum concentrations in samples 

from the UCOL or GRSL study areas. Dissolved cadmium, dissolved lead, and total recoverable zinc at 

NROK sites were more variable than in the other study 

areas; concentrations ranged over nearly three orders of 

magnitude between the minimum and maximum values. The largest range in concentration was measured 

for dissolved zinc, which exceeded three orders of 

magnitude in the NROK study area. 

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Figures 2 -40
Michael A. Beckwith / Surface-Water-Quality Data Collected for the Northern Rockies Intermontane Basins NAWQA Program in the Clark Fork-Pend Oreille and Spokane River Basins, 

Montana, Idaho, and Washington, Water Years 1999–2001 / OFR 02 – 472 

Printed on recycled paper