U.S. Department of the Interior

U.S. Geological Survey

Open-File Report 2013-1017

Prepared in cooperation with the U.S. Environmental Protection Agency

Water-Quality, Bed-Sediment, and Biological Data 

(October 2010 through September 2011) and Statistical 

Summaries of Data for Streams in the Clark Fork Basin, 

Montana
Banner: Metal salts on the surface of tailings deposit near Silver Bow at Opportunity (12323600) gage (photograph by 

Kent A. Dodge, U.S. Geological Survey, taken May 2012).

Cover: Looking upstream at the confluence of Silver Bow Creek and Warm Springs Creek, which form the Clark Fork 

near Warm Springs, Montana (photograph by Kent A. Dodge, U.S. Geological Survey, taken May 2012).
Water-Quality, Bed-Sediment, and 

Biological Data (October 2010 through 

September 2011) and Statistical Summaries 

of Data for Streams in the Clark Fork Basin, 

Montana

By Kent A. Dodge, Michelle I. Hornberger, and Jessica L. Dyke

Prepared in cooperation with the U.S. Environmental Protection Agency

Open-File Report 2013-1017

U.S. Department of the Interior

U.S. Geological Survey
ISBN 978-1-4113-3570-7

U.S. Department of the Interior

SALLY JEWELL, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2013

For more information on the USGS—the Federal source for science about the Earth, its natural and living 

resources, natural hazards, and the environment, visit http://www.usgs.gov or call 1–888–ASK–USGS.

For an overview of USGS information products, including maps, imagery, and publications, 

visit http://www.usgs.gov/pubprod

To order this and other USGS information products, visit http://store.usgs.gov

Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the 

U.S. Government.

Although this report is in the public domain, permission must be secured from the individual copyright owners to 

reproduce any copyrighted materials contained within this report.

Suggested citation:

Dodge, K.A., Hornberger, M.I., and Dyke, J.L., 2013, Water-quality, bed-sediment, and biological data (October 

2010 through September 2011) and statistical summaries of data for streams in the Clark Fork basin, Montana: 

U.S. Geological Survey Open-File Report 2013–1017, 132 p.
iii

Contents

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

Introduction.....................................................................................................................................................1

Sampling Locations and Types of Data......................................................................................................2

Water-Quality Data........................................................................................................................................2

Methods..................................................................................................................................................2

Results ....................................................................................................................................................7

Quality Assurance.................................................................................................................................7

Bed-Sediment Data .....................................................................................................................................10

Methods................................................................................................................................................10

Results ..................................................................................................................................................11

Quality Assurance...............................................................................................................................11

Biological Data.............................................................................................................................................12

Methods................................................................................................................................................12

Results ..................................................................................................................................................12

Quality Assurance...............................................................................................................................13

Statistical Summaries of Data ...................................................................................................................13

References Cited..........................................................................................................................................14

Data ...............................................................................................................................................................17

Figure

1. Map showing location of study area in the Clark Fork basin, Montana..............................3

Tables

1. Type and period of data collection at sampling sites in the Clark Fork 

basin, Montana .............................................................................................................................4

2. Properties and constituents measured onsite or analyzed in water, 

bed-sediment, and biota samples from the Clark Fork basin, Montana..............................6

3. Data-quality objectives for analyses of water samples collected in the 

Clark Fork basin, Montana ..........................................................................................................6

4. Water-quality data for the Clark Fork basin, Montana, October 2010 

through September 2011............................................................................................................19

5. Daily mean streamflow and suspended-sediment data for Clark Fork 

at Deer Lodge, Montana, October 2010 through September 2011......................................46

6. Daily mean streamflow and suspended-sediment data for Clark Fork 

at Turah Bridge, near Bonner, Montana, October 2010 through 

September 2011...........................................................................................................................50

7. Daily mean streamflow and suspended-sediment data for Blackfoot 

River near Bonner, Montana, October 2010 through September 2011 ..............................54
iv

8. Daily mean streamflow and suspended-sediment data for Clark Fork 

above Missoula, Montana, October 2010 through September 2011 ..................................58

9. Seasonal daily maximum, minimum, and mean turbidity, with monthly 

summary statistics at Mill Creek near Anaconda, Montana, April 

through September 2011............................................................................................................62

10. Seasonal daily maximum, minimum, and mean turbidity, with monthly 

summary statistics at Willow Creek near Anaconda, Montana, May 

through September 2011............................................................................................................64

11. Seasonal daily maximum, minimum, and mean turbidity, with monthly 

summary statistics at Warm Springs Creek near Anaconda, Montana, 

April through September 2011 ..................................................................................................66

12. Seasonal daily maximum, minimum, and mean turbidity, with monthly 

summary statistics at Lost Creek near Anaconda, Montana, April 

through September 2011............................................................................................................68

13. Analyses of field replicates for water samples, Clark Fork basin, Montana....................70

14. Precision of analyses of field replicates for water samples, Clark Fork 

basin, Montana ...........................................................................................................................76

15. Precision of analyses of laboratory replicates for water samples, 

Clark Fork basin, Montana ........................................................................................................76

16. Recovery efficiency for analyses of laboratory-spiked deionized-water 

blank samples..............................................................................................................................77

17. Recovery efficiency for analyses of laboratory-spiked stream samples, 

Clark Fork basin, Montana ........................................................................................................77

18. Analyses of field blanks for water samples ...........................................................................78

19. Bed-sediment data for the Clark Fork basin, Montana, August 2011 ................................79

20. Recovery efficiency for analyses of standard reference materials for 

bed-sediment samples...............................................................................................................80

21. Analyses of procedural blanks for bed-sediment samples.................................................81

22. Biological data for the Clark Fork basin, Montana, August 2011........................................82

23. Recovery efficiency for analyses of standard reference material for 

biota samples ..............................................................................................................................84

24. Analyses of procedural blanks for biota samples.................................................................85

25. Statistical summary of long-term water-quality data for the Clark Fork 

basin, Montana, March 1985 through September 2011........................................................86

26. Statistical summary of long-term bed-sediment data for the Clark Fork 

basin, Montana, August 1986 through August 2011............................................................106

27. Statistical summary of long-term biological data for the Clark Fork 

basin, Montana, August 1986 through August 2011...........................................................111
v

Conversion Factors, Datum, Abbreviated Water-Quality Units, 

and Acronyms

Multiply By To obtain

acre-foot (acre-ft) 1,233 cubic meter (m3

)

cubic foot per second (ft3

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

gallon (gal) 3.785 liter (L)

gallon (gal) 3,785 milliliter (mL)

inch (in.) 25.4 millimeter (mm)

inch (in.) 25,400 micrometer (μm)

mile (mi) 1.609 kilometer (km)

ounce (oz) 28.35 gram (g)

part per million (ppm) 1 microgram per gram (μg/g)

square mile (mi2

) 2.59 square kilometer (km2)

ton 907.2 kilogram

ton per day (ton/d) 907.2 kilogram per day (kg/d)

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

°F = (1.8 x °C) + 32

Horizontal coordinate information is referenced to the North American Datum of 1927 (NAD 27).

Water-year definition:

Water year is the 12-month period from October 1 through September 30 of the following 

calendar year. The water year is designated by the calendar year in which it ends. For example, 

water year 2011 is the period from October 1, 2010, through September 30, 2011.
vi

Abbreviated water-quality units used in this report:

μg/g microgram per gram

μg/L microgram per liter

μg/mL microgram per milliliter

μm micrometer

μS/cm microsiemens per centimeter at 25 degrees Celsius

mg/L milligrams per liter

mm millimeter

ppm part per million

Acronyms used in the report:

FNU formazin nephelometric units

ICP–AES inductively coupled plasma–atomic emission spectrometry

ICP–MS inductively coupled plasma–mass spectrometry

LRL laboratory reporting level

LT–MDL long-term method detection level

MRL minimum reporting level

NTRU nephelometric turbidity ratio unit

NWQL USGS National Water Quality Laboratory, Denver, Colo.

PTFE polytetrafluoroethylene

RSD relative standard deviation

spp. species

SRM standard reference material

USGS U.S. Geological Survey

YSI Yellow Springs Instruments Company
 

Water-Quality, Bed-Sediment, and Biological Data 

(October 2010 through September 2011) and Statistical 

Summaries of Data for Streams in the Clark Fork Basin, 

Montana

By Kent A. Dodge, Michelle I. Hornberger, and Jessica L. Dyke

Abstract

Water, bed sediment, and biota were sampled in streams 

from Butte to near Missoula, Montana, as part of a monitoring 

program in the upper Clark Fork basin of western Montana; 

additional water samples were collected from near Galen 

to near Missoula at select sites as part of a supplemental 

sampling program. The sampling program was conducted 

by the U.S. Geological Survey in cooperation with the U.S. 

Environmental Protection Agency to characterize aquatic 

resources in the Clark Fork basin, with emphasis on trace 

elements associated with historic mining and smelting 

activities. Sampling sites were located on the Clark Fork and 

selected tributaries. Water samples were collected periodically 

at 20 sites from October 2010 through September 2011. Bedsediment and biota samples were collected once at 14 sites 

during August 2011. 

This report presents the analytical results and qualityassurance data for water-quality, bed-sediment, and biota 

samples collected at sites from October 2010 through 

September 2011. Water-quality data include concentrations of 

selected major ions, trace elements, and suspended sediment. 

Turbidity was analyzed for water samples collected at the 

four sites where seasonal daily values of turbidity were being 

determined. Daily values of suspended-sediment concentration 

and suspended-sediment discharge were determined for four 

sites. Bed-sediment data include trace-element concentrations 

in the fine-grained fraction. Biological data include traceelement concentrations in whole-body tissue of aquatic 

benthic insects. Statistical summaries of water-quality, bedsediment, and biological data for sites in the upper Clark Fork 

basin are provided for the period of record since 1985.

Introduction

The Clark Fork originates near the town of Warm Springs 

in western Montana at the confluence of Silver Bow and 

Warm Springs Creeks (fig. 1). Along the 148-mile (mi) reach 

of stream from Silver Bow Creek in Butte to the Clark Fork 

near Missoula, six major tributaries enter: Blacktail Creek, 

Warm Springs Creek, Little Blackfoot River, Flint Creek, 

Rock Creek, and Blackfoot River. Principal surface-water 

uses in the 6,000-square-mile (mi2) upper Clark Fork basin 

above Missoula include irrigation, stock watering, smallscale industry, and habitat for trout fisheries. Primary current 

land uses are cattle production, logging, mining, residential 

development, and recreation. Large-scale mining and smelting 

were prevalent land uses in the upper basin for more than 100 

years but are now either discontinued or substantially reduced 

in scale.

Deposits of copper, gold, silver, and lead ores were extensively mined, milled, and smelted in the drainages of Silver 

Bow and Warm Springs Creeks from about the 1860s to the 

1980s (U.S. Environmental Protection Agency, 2004). Moderate- and small-scale mining also occurred in the basins of 

most of the major tributaries to the upper Clark Fork. Tailings 

produced during past mineral processing commonly contain 

large quantities of trace elements such as arsenic, cadmium, 

copper, lead, and zinc. Eroded tailings mix with stream 

sediment and get deposited further downstream in stream 

channels, on flood plains, in the Warm Springs Ponds, and at 

the location of the former Milltown Reservoir (Milltown Dam 

was removed on March 28, 2008) (Andrews, 1987), especially 

during times of increased flow. The occurrence of elevated 

trace-element concentrations in water and bed sediment can 

pose a potential risk to aquatic biota and human health (U.S. 

Environmental Protection Agency, 2004).

Concern about the potential toxicity of trace elements 

to aquatic biota and human health has resulted in a 

comprehensive effort by State, Federal, Tribal, and private 

entities to characterize the aquatic resources in the upper Clark 

Fork basin in order to guide and monitor remedial cleanup 

activities. A long-term database was considered necessary to 

detect trends over time in order to evaluate the effectiveness 

of remediation. Water-quality data have been collected by the 

U.S. Geological Survey (USGS) at selected sites in the upper 
2 Water-Quality, Bed-Sediment, and Biological Data, and Statistical Summaries of Data, Clark Fork Basin, Montana

Clark Fork basin since 1985 (Lambing, 1987 through 1991; 

Lambing and others, 1994, 1995; Dodge and others, 1996 

through 2010, 2012). Trace-element data for bed sediment and 

biota (aquatic benthic insects) have been collected intermittently at selected sites since 1986 as part of studies on the 

contamination of bed-sediment quality and bioaccumulation 

of metals conducted by the USGS National Research Program 

(Axtmann and Luoma, 1991; Cain and others, 1992, 1995; 

Axtmann and others, 1997; Hornberger and others, 1997). In 

March 1993, an expanded monitoring program for water, bed 

sediment, and biota in the upper basin was implemented by the 

USGS in cooperation with the U.S. Environmental Protection 

Agency to systematically quantify the seasonal and annual 

variability in selected constituents. 

The purpose of this report is to present water-quality 

data from samples collected at 20 sites and bed-sediment 

and biological data from samples collected at 14 sites in the 

Clark Fork basin from October 2010 through September 

2011. Quality-assurance data are presented for water-quality, 

bed-sediment, and biota samples collected during the same 

time period. Statistical summaries also are provided for waterquality, bed-sediment, and biological data collected at the sites 

since 1985.

Sampling Locations and Types of Data

Sampling sites for the monitoring program in the upper 

Clark Fork basin from Butte to near Missoula (fig. 1) are 

located on the Clark Fork main stem (including Silver Bow 

Creek), three major tributaries (Blacktail Creek, Warm Springs 

Creek, and Blackfoot River), and three smaller tributaries 

(Mill Creek, Willow Creek, and Lost Creek). The sites, types 

of data collected, and period of record for each type of data 

are listed in table 1. Main-stem sampling sites were selected to 

divide the upper Clark Fork into reaches of relatively uniform 

length, with each reach encompassing either a major tributary 

or depositional environment (Warm Springs Ponds and the 

former Milltown Reservoir). Major tributaries were sampled to 

describe water-quality, bed-sediment, and biological characteristics of important hydrologic sources in the upper basin 

and to provide reference comparisons to the main stem. The 

three smaller tributaries were sampled to gain better spatial 

resolution on sources of metals entering the Clark Fork in an 

area of historical metal-processing activities near Anaconda, 

Mont. Water-quality samples were collected periodically at 

20 sites. Daily suspended-sediment samples were collected at 

4 sites, and daily turbidity values were computed using data 

collected by continuous turbidity monitors at 4 sites. Bedsediment and biological samples were collected once annually 

at 14 sites. Continuous streamflow data were collected at 

19 sites.

Properties measured onsite and constituents for which 

water, bed-sediment, and biota samples were analyzed are 

listed in table 2. Data-quality objectives for analyses of water 

samples are listed in table 3. Results of onsite measurements 

of stream properties; laboratory analyses of water-quality, 

bed-sediment, and biota samples; and quality-assurance data 

for water year 2011 are listed in tables 4 through 24 at the 

back of the report. Statistical summaries of water-quality, bedsediment, and biological data collected between March 1985 

and September 2011 are listed in tables 25 through 27 at the 

back of the report.

Quality assurance of data was maintained through 

the use of documented procedures designed to provide 

environmentally representative data. Acceptable performance 

of the procedures was verified with quality-control samples 

that were collected systematically to provide a measure of the 

accuracy, precision, and bias of the environmental data, and 

to identify problems associated with sampling, processing, 

or analysis.

Water-Quality Data

Water-quality data consist of onsite measurements of 

selected stream properties and concentrations of chemical 

and physical constituents analyzed in periodically collected 

stream samples. Routine water samples for the monitoring 

program were collected at 20 sites in the upper Clark Fork 

basin 6–8 times per year on a schedule designed to describe 

seasonal and hydrologic variability. Supplemental water 

samples were collected 4 additional times at 7 sites. At the 4 

daily suspended-sediment sites, suspended-sediment samples 

were collected by an observer 1–11 times per week, depending 

on season and flow conditions. Continuous turbidity monitors 

operated seasonally (April or May to September 2011) at 

4 sites near Anaconda collected turbidity values every 15 

minutes that were used to compute daily turbidity values 

(table 1).

Methods

Water samples were collected and composited from 

vertical transits throughout the entire stream depth at multiple 

locations across the stream by using depth- and widthintegration methods described by Ward and Harr (1990), 

Edwards and Glysson (1999), and the U.S. Geological 

Survey (variously dated). These methods provide a vertically 

and laterally discharge-weighted composite sample that 

is intended to be representative of the entire flow passing 

through the cross section of a stream. Samplers consisted 

of depth-integrating water-quality samplers (Davis, 

2005) that were constructed of plastic or coated with a 

nonmetallic rubber-coating paint and equipped with nylon or 

polytetrafluoroethylene (PTFE) nozzles.

Instantaneous streamflow was determined at the time 

of water sampling either by direct measurement or from 

stage-discharge rating tables (Rantz and others, 1982). Daily 

mean streamflow values during ice periods were estimated 
Water-Quality Data 3

Mill

Willow

Creek

Cr Silver

Bow

Opportunity

Missoula

Butte

Anaconda

Opportunity

Galen

Warm Springs

Deer Lodge

Garrison

Goldcreek

Drummond

Bonner

Turah

Clinton Bitterroot

River

Blackfoot

River

Fork

Rock

Little

River

DIVIDE

Fork

Cr

Silver

Bow

CONTINENTAL

Base modified from 

U.S. Geological Survey, 

State base map,

1:1,000,000, 1966.

North American Datum of 

1927 (NAD 27) 

0 10 20 MILES

0 10 20 KILOMETERS

12340500

12340000

12334550

12331800

12324680

12324200

12323800

12323770 12323750

12323600

12323250

Streamflow site type

 Continuous record

 Periodic measurement

Water-quality, bed-sediment, and

biota site type

 Periodic water quality

 Daily suspended sediment

 Daily turbidity

 Once-annual bed-sediment

 Once-annual biota

EXPLANATION

Site number

461903112440701 Miscellaneous site number

12324200

12323700

12323720

Lost Cr 12323850

46o

114o

113o

12323230

Racetrack

12323840

12323670

Mill

12323760

461903112440701

461559112443301

461415112450801

Helena

M O N T A N A

Study area

Milltown

Reservoir

former

Dempsey

Creek

Blackfoot

Flint

Creek

Willow

Creek

Warm Springs

Warm Springs

 Ponds

Clark

Blacktail

Creek

Creek

Creek

Cr

12324400

Clark

Creek

12323710

Figure 1. Location of study area in the Clark Fork basin, Montana.
Table 1. Type and period of data collection at sampling sites in the Clark Fork basin, Montana. [Abbreviations: P, present; D, discontinued. Symbol: --, no data] Station number (fig. 1) Station name Continuous- record streamflow Periodic water quality1 Daily suspended sediment Daily turbidity (seasonal) Fine-grained bed sediment2 Bulk 

sedim

12323230 Blacktail Creek at Harrison Avenue, at Butte -- 03/93–08/95, 12/96–08/03, 12/04–P -- -- -- 

12323250 Silver Bow Creek below Blacktail Creek, at Butte 10/83–P 03/93–08/95, 12/96–P -- -- -- 

12323600 Silver Bow Creek at Opportunity 07/88–P 03/93–08/95, 12/96–P 03/93–09/95, D -- 07/92–P 08/93–

08/97–

12323670 Mill Creek near Anaconda 10/04–P 12/04–P -- 06/06–P -- 12323700 Mill Creek at Opportunity 04/03–P 03/03–P -- -- -- 

12323710 Willow Creek near Anaconda 03/05–P 12/04–P -- 06/06–P -- 

12323720 Willow Creek at Opportunity 04/03–P 03/03–P -- -- -- 

12323750 Silver Bow Creek at Warm Springs 03/72–09/79, 04/93–P 03/93–P 04/93–09/95, D -- 07/92–P 08/93, 

08/0

12323760 Warm Springs Creek near Anaconda 10/97–P 10/05–P -- 05/06–P -- 12323770 Warm Springs Creek at Warm Springs 10/83–P 03/93–P -- -- 08/95, 08/97, 08/99, 08/02, 08/05, 08/08, 08/11 08/95

08/99, 

12323800 Clark Fork near Galen 07/88–P 07/88–P -- -- 08/87, 08/91–P 08/93–12323840 Lost Creek near Anaconda 10/04–P 12/04–P -- 05/06–P -- 

12323850 Lost Creek near Galen 04/03–P 03/03–P -- -- -- 

461415112450801 Clark Fork below Lost Creek, near Galen -- -- -- -- 08/96–P 08/96–

461559112443301 Clark Fork at county bridge, near Racetrack -- -- -- -- 08/96–P 08/96–

461903112440701 Clark Fork at Dempsey Creek diversion, near Racetrack -- -- -- -- 08/96–P 08/96–
Table 1. Type and period of data collection at sampling sites in the Clark Fork basin, Montana.—Continued[Abbreviations: P, present; D, discontinued. Symbol: --, no data].

Station number 

(fig. 1) Station name

Continuousrecord 

streamflow

Periodic 

water quality1

Daily suspended 

sediment

Daily turbidity 

(seasonal)

Fine-grained 

bed sediment2

Bul

sedi

12324200 Clark Fork at Deer Lodge 10/78–P 03/85–P 03/85–08/86, 

04/87–03/03, 

08/03–P

-- 08/86–08/87, 

08/90–P

08/93–

12324400 Clark Fork above Little 

Blackfoot River, near Garrison

02/09–P 03/09–P -- -- 08/09–P 

12324680 Clark Fork at Goldcreek 10/77–P 03/93–P -- -- 07/92–P 08/93–

12331800 Clark Fork near Drummond 04/93–P 03/93–P -- -- 08/86, 08/87, 

08/91–P

08/93–

12334550 Clark Fork at Turah Bridge, 

near Bonner

03/85–P 03/85–P 03/85–03/03, 

08/03–P

-- 08/86, 08/91–P 08/93–

12340000 Blackfoot River near Bonner 10/39–P 03/85–P 07/86–04/87, 

06/88–09/95,

10/05–P

-- 08/86–08/87, 

08/91, 

08/93–08/96, 

08/98-08/01, 

09/03,

08/06–P

08/93

08/9

09/0

12340500 Clark Fork above Missoula 03/29–P 07/86–P4 07/86–04/87, 

06/88–01/96, 03/96–03/03, 

08/03–P

04/07–09/07 08/97–P 08/97–

1Onsite measurements of physical properties and laboratory analyses for selected major ions, trace elements, and suspended sediment. Prior to March 1993, laboratory analys

and suspended sediment.

2Laboratory analyses for trace elements.3Bulk bed-sediment sampling was discontinued in 2005.4Prior to October 1989, water-quality data for Clark Fork above Missoula included only suspended-sediment data.
6 Water-Quality, Bed-Sediment, and Biological Data, and Statistical Summaries of Data, Clark Fork Basin, Montana

Water Bed sediment Biota

Property Constituent Constituent Constituent

Streamflow Hardness (calculated) Arsenic Arsenic

pH Calcium Cadmium Cadmium

Specific conductance Magnesium Chromium Chromium

Temperature Arsenic Copper Copper

Turbidity Cadmium Iron Iron

Copper Lead Lead

Iron Manganese Manganese

Lead Nickel Nickel

Manganese Zinc Zinc

Zinc

Suspended sediment

Table 2. Properties and constituents measured onsite or analyzed in water, bed-sediment, and biota samples from the Clark Fork 

basin, Montana.

Constituent

Data-quality objectives

Detectability Precision Bias

Laboratory reporting 

level

Maximum relative standard 

deviation of replicate analyses 

(percent)

Maximum deviation of spike 

recovery (percent)

Calcium, filtered 0.02 mg/L 20 --

Magnesium, filtered .008 mg/L 20 --

Arsenic, filtered .02 μg/L 20 25

Arsenic, unfiltered recoverable .09 μg/L 20 25

Cadmium, filtered .02 μg/L 20 25

Cadmium, unfiltered recoverable .05 μg/L 20 25

Copper, filtered .50 μg/L 20 25

Copper, unfiltered recoverable .70 μg/L 20 25

Iron, filtered 3 μg/L 20 25

Iron, unfiltered recoverable 5 μg/L 20 25

Lead, filtered .01 μg/L 20 25

Lead, unfiltered recoverable .04 μg/L 20 25

Manganese, filtered .1 μg/L 20 25

Manganese, unfiltered recoverable .4 μg/L 20 25

Zinc, filtered 1.4 μg/L 20 25

Zinc, unfiltered recoverable 2.4 μg/L 20 25

Sediment, suspended, percent finer 

than 0.062 mm 1 percent 20 --

Sediment, suspended 1 mg/L 20 --

Table 3. Data-quality objectives for analyses of water samples collected in the Clark Fork basin, Montana.

[Abbreviations: μg/L, micrograms per liter; mg/L, milligrams per liter; mm, millimeter. Symbol: --, not determined]
Water-Quality Data 7

because backwater affected the stage-discharge relation. 

Onsite measurements of pH, specific conductance, and water 

temperature were made during collection of periodic water 

samples. Onsite sample processing, including filtration 

and preservation, was performed according to procedures 

described by Ward and Harr (1990), Horowitz and others 

(1994), and the U.S. Geological Survey (variously dated).

Composite water samples were analyzed for the 

constituents listed in table 2. The terms “filtered” and 

“unfiltered recoverable” replace the terms “dissolved” and 

“total recoverable,” respectively, which were used in past 

reports from this project. Filtered [0.45-micrometer (μm) 

pore size] and unfiltered recoverable concentrations of 

the trace elements (arsenic, cadmium, copper, iron, lead, 

manganese, and zinc) and filtered concentrations of calcium 

and magnesium were measured by the USGS National 

Water Quality Laboratory (NWQL) in Denver, Colo. 

Concentrations of calcium and magnesium were used in the 

calculation of water hardness. 

Filtered concentrations of arsenic, cadmium, copper, 

lead, manganese, and zinc were measured using inductively 

coupled plasma-mass spectrometry (ICP–MS) (Faires, 

1993; Garbarino and others, 2006). Filtered concentrations 

of calcium, magnesium, and iron were measured using 

inductively coupled plasma-atomic emission spectrometry 

(ICP–AES) (Fishman, 1993). Unfiltered recoverable concentrations of trace elements were measured in unfiltered samples that were first digested with dilute hydrochloric acid 

(Hoffman and others, 1996). For cadmium, iron, lead, and 

manganese, the digested samples were analyzed by ICP–MS 

as described by Garbarino and Struzeski (1998). For arsenic, 

copper, and zinc, the digested samples were analyzed by 

ICP–MS as described by Garbarino and others (2006). 

Water samples for analysis of suspended-sediment also 

were collected from multiple vertical transits when periodic 

water samples were collected. These samples were analyzed 

for suspended-sediment concentration and the percentage of 

suspended-sediment mass finer than 0.062-millimeter (mm) 

diameter (silt size and smaller) by the USGS Montana Water 

Science Center sediment laboratory (hereinafter referred 

to as the Montana Sediment Laboratory) in Helena, Mont., 

according to methods described by Guy (1969) and Dodge 

and Lambing (2006).

Suspended-sediment samples for the four daily 

suspended-sediment sites (table 1) were collected by local 

contract observers using the depth-integration method at 

a single vertical transit near midstream. The samples were 

analyzed for suspended-sediment concentration and used 

to calculate daily mean suspended-sediment concentrations 

according to methods described by Porterfield (1972).

Suspended-sediment discharge is determined according 

to the following equation (Porterfield, 1972):

 , (1)

where

Qs is suspended-sediment discharge, in tons 

per day;

Qw is streamflow, in cubic feet per second;

Cs is suspended-sediment concentration, in 

milligrams per liter; and

 k is a units-conversion constant (0.0027) 

to convert instantaneous suspendedsediment discharge to an equivalent 

daily suspended-sediment discharge.

Turbidity data were measured using continuous turbidity 

monitors [Yellow Springs Instruments Company (YSI) 6136 

turbidity sensor] at four tributary sites in the upper Clark Fork 

basin near Anaconda (table 1). The monitors were installed 

in May–June 2006 to provide supporting information on 

runoff conditions in an area where remediation activities are 

being conducted. They are operated seasonally, generally 

from early spring (after ice breakup) to early fall (before 

stream freeze-up). Turbidity values are recorded at 15-minute 

intervals and can be viewed in real-time on the Web at http://

waterdata.usgs.gov/mt/nwis/current?type=quality. Continuous 

recordings enable the determination of the minimum and 

maximum values for each day as well as a daily mean 

turbidity, which is based on the average of all values in a 

24-hour period. Procedures for the operation of continuous 

turbidity monitors and for daily record computations are 

described by Wagner and others (2006).

Results

Water-quality data from samples collected periodically 

during water year 2011 are listed in table 4. Daily mean 

streamflow, daily mean suspended-sediment concentration, 

and daily suspended-sediment discharge for water year 

2011 at the four daily suspended-sediment sites are listed in 

tables 5 through 8 along with monthly summary statistics 

and annual totals for streamflow and suspended-sediment 

discharge. Daily maximum, minimum, and mean turbidity at 

four sites are listed in tables 9 through 12 along with monthly 

summary statistics.

Quality Assurance

Quality-assurance procedures used for the collection 

and field processing of water samples are described by Ward 

and Harr (1990), Horowitz and others (1994), Edwards and 

Glysson (1999), Lambing (2006), and the U.S. Geological 

Survey (variously dated). Standard procedures used by the 

NWQL for internal sample handling and quality assurance are 

described by Friedman and Erdmann (1982), Jones (1987), 

and Pritt and Raese (1995). Quality-assurance procedures 

Q Q s w = × Cs ×k used by the Montana Sediment Laboratory are described by 
8 Water-Quality, Bed-Sediment, and Biological Data, and Statistical Summaries of Data, Clark Fork Basin, Montana

Dodge and Lambing (2006). Standard procedures used for the 

calibration, measurement, and quality assurance of turbidity 

monitors are described by Anderson (2005).

The quality of analytical results reported for water 

samples was evaluated using quality-control samples that 

were submitted from the field and analyzed concurrently in the 

laboratory with routine samples. These quality-control samples 

consisted of replicates, spikes, and blanks that provided quantitative information on the precision and bias of the overall 

field and laboratory process. Each type of quality-control 

sample was submitted at a proportion equivalent to about 

5 percent of the total number of water samples. Therefore, 

the total number of quality-control samples represented about 

15 percent of the total number of water samples.

In addition to the use of quality-control samples 

submitted from the field, internal quality-assurance practices 

are performed systematically by the NWQL to provide 

quality control of analytical procedures (D.L. Stevenson, U.S. 

Geological Survey, written commun., 2012). These internal 

practices include analyses of quality-control samples such 

as calibration standard samples, standard reference water 

samples, replicate samples, deionized-water blank samples, or 

spiked samples at a proportion equivalent to at least 10 percent 

of the sample load. The NWQL participates in a blind-sample 

program in which standard reference water samples prepared 

by the USGS Branch of Quality Systems are routinely 

inserted into the sample line for each analytical method at a 

frequency proportional to the sample load (http://bqs.usgs.

gov). The laboratory also participates in external evaluation 

studies and audits with the National Environmental Laboratory 

Accreditation Program, the U.S. Environmental Protection 

Agency, Environment Canada, and the USGS Branch of 

Quality Systems, to assess analytical performance.

Replicate data can be collected in different ways to 

provide an assessment of precision (reproducibility) of 

analytical results. Replicate samples are two or more samples 

considered to be essentially identical in composition. 

Replicate samples can be collected in the field (field replicate) 

either by repeating the collection process to obtain two 

or more independent composite samples or by splitting a 

single composite sample into two or more subsamples. The 

individual replicate samples are then analyzed separately. 

Likewise, a single sample can be analyzed two or more times 

in the laboratory to obtain a measure of analytical precision 

(laboratory replicate).

Precision of analytical results for field replicates can be 

affected by numerous sources of variability within the field 

and laboratory environments, including sample collection, 

processing, and analysis. To provide data on overall 

precision for samples exposed to both field and laboratory 

sources of variability, replicate stream samples for chemical 

analysis were obtained in the field by splitting a composite 

stream sample. Replicate stream samples for suspendedsediment analysis were obtained in the field by collecting 

two independent cross-sectional samples. Analyses of field 

replicate samples indicate the reproducibility of environmental 

data that are affected by the combined potential variability 

introduced by field and laboratory processes.

Precision of analytical results for laboratory replicates, 

which exclude field sources of variability, was determined 

using two independent chemical analyses of aliquots from a 

single sample selected from the group of samples constituting 

each analytical run. A separate analysis of the sample was 

made at the beginning and end of each analytical run to 

provide information on the reproducibility of laboratory 

analytical results independent of possible variability caused by 

field sample collection and processing. Laboratory replicates 

are not obtainable for suspended-sediment samples because 

the samples are consumed during the analysis.

Spiked samples are used to evaluate bias, which measures 

the ability of an analytical method to accurately quantify 

a known amount of analyte added to a sample. Because 

some constituents in stream water can potentially interfere 

with the analysis of a sample for a targeted analyte, it is 

important to determine whether such effects are causing biased 

(consistently high or low) results. Deionized-water blank 

samples and aliquots of stream samples were spiked in the 

laboratory with known amounts of the same trace elements for 

which water samples were being analyzed. Analyses of spiked 

blanks indicate if the spiking procedure and analytical method 

are within control for a water matrix that is presumably free of 

chemical interference. Analyses of spiked aliquots of stream 

samples indicate if the chemical matrix of the stream water 

interferes with the analytical measurement and whether these 

interferences could contribute substantial bias to reported 

trace-element concentrations for stream samples.

Deionized-water blank samples were submitted for every 

field trip and analyzed to identify the presence and magnitude 

of contamination that could potentially bias analytical results. 

The type of blank sample routinely tested was a field blank. 

Field blanks are aliquots of deionized water that are certified 

as trace-element free and are processed in the field through 

the sampling equipment used to collect stream samples. These 

blanks then are subjected to the same processing (sample 

splitting, filtration, preservation, transportation, and laboratory 

handling) as stream samples. Blank samples are analyzed for 

the same constituents as stream samples in order to identify 

whether any detectable concentrations exist.

All water samples were handled in accordance with 

chain-of-custody procedures that provide documentation of 

sample identity, shipment, receipt, and laboratory handling. 

All routine and quality-control samples submitted from a 

sampling episode were stored in a secure area of the NWQL 

and analyzed as a discrete sample group, independent of other 

samples submitted to the NWQL. Therefore, the qualitycontrol data apply solely to the analytical results for stream 

samples reported herein and provide a direct measure of data 

quality for this monitoring program.

Data-quality objectives (table 3) were established 

for water-quality data as part of the study plan for the 

expanded long-term monitoring program initiated in 1993. 

The objectives identify the analytical requirements of 
Water-Quality Data 9

detectability and serve as a guide for identifying questionable 

data by establishing acceptable limits for precision and bias 

of laboratory results. Comparisons of quality-control data 

to data-quality objectives were used to evaluate whether 

sampling and analytical procedures produced environmentally 

representative data in a consistent manner. Data that did 

not meet the objectives were evaluated for acceptability. If 

necessary, additional quality-control samples were submitted 

and corrective action was taken.

The NWQL uses a statistically-based convention for 

establishing minimum laboratory reporting levels (LRLs) 

for analytical results and for reporting low-concentration 

data (Childress and others, 1999). Quality-control data are 

collected by the NWQL on a continuing basis to determine 

long-term method detection levels (LT–MDLs) and LRLs. 

These values are reevaluated each year and, consequently, 

can change from year to year. The methods used to determine 

the LRLs are designed to limit the likelihood of a possible 

occurrence of a false positive or false negative error to 1 

percent or less. Accordingly, concentrations are reported as 

less than the LRL for samples in which the analyte was either 

not detected or did not pass identification criteria. Analytes 

that are detected at concentrations between the LT–MDL and 

the LRL and that pass identification criteria are reported as 

estimated concentrations. Estimated concentrations are noted 

with a remark code of “E.” These data need to be used with 

the understanding that their uncertainty is greater than that of 

data reported without the “E” remark code.

The precision of analytical results for a constituent can 

be determined by estimating a standard deviation of the differences in concentrations between replicate analyses for several 

sets of samples. These replicate analyses may consist either 

of individual analyses of a pair of samples considered to be 

essentially identical (field replicates) or of multiple analyses of 

an individual sample (laboratory replicates). The differences 

in concentration between replicate analyses can be used to 

estimate a standard deviation according to the following 

equation (Taylor, 1987):

 S

d

k =

2

2

 , (2)

where

S is the standard deviation of the difference in 

concentration between replicate analyses;

d is the difference in concentration between 

each pair of replicate analyses; and

k is the number of pairs of replicate analyses.

Precision also can be expressed as a relative standard 

deviation (RSD), in percent, which is computed from the 

standard deviation and the mean concentration for all the 

replicate analyses. Expressing precision relative to a mean 

concentration standardizes the comparison of precision among 

individual constituents. The RSD is calculated according to the 

following equation (Taylor, 1987):

 , (3)

where

RSD is the relative standard deviation;

S is the standard deviation; and

 is the mean concentration for all replicate 

analyses.

Paired analyses of field replicates are listed in table 13. 

The overall precision for each constituent estimated from 

analyses of field replicates, which include both field and 

laboratory sources of variability, is listed in table 14. The 

data-quality objective used to indicate acceptable precision of 

results for field replicates was a maximum RSD of 20 percent 

(table 3). Precision estimates for the analytical results of 

field replicates were within the 20-percent RSD limit for all 

constituents (table 14). 

The precision for each constituent estimated from 

laboratory replicate analyses, which include only laboratory 

sources of variability, is listed in table 15. Statistics for the 

precision of analytical results for laboratory replicates are 

calculated by using unrounded values stored in laboratory data 

files. The data-quality objective used to indicate acceptable 

precision of results for laboratory replicates was a maximum 

RSD of 20 percent (table 3). Precision estimates for the 

laboratory replicates were within the 20-percent RSD limit 

for all constituents (table 15). No adjustments were made to 

analytical data on the basis of replicate analyses precision.

Recovery efficiency for analyses of constituents 

is determined by comparison of a sample and a spiked 

aliquot of the same sample. The data-quality objective for 

acceptable spike recovery of trace elements in water samples 

was a maximum deviation of 25 percent from a theoretical 

100-percent recovery of added constituent (table 3). At the 

laboratory, a spiked deionized-water blank sample and a 

spiked aliquot of a stream sample were prepared and analyzed 

along with the original unspiked sample. The differences 

between the spiked and unspiked sample concentrations 

were determined and used to compute recovery, in percent, 

according to equation 4:

 , (4)

where

R is the spike recovery, in percent;

D is the difference between the spiked and 

unspiked sample concentrations; and

C is the concentration of material used to spike 

the sample.

If the spike recovery of a trace element was outside a 

range of 75 to 125 percent, the instrument was recalibrated 

and the entire sample set and all spiked samples were 

reanalyzed for that particular trace element until recoveries 

were improved to the extent possible. Recovery efficiency 

RSD

S

x

= ×100

x

_

R

D

C

= ×100
10 Water-Quality, Bed-Sediment, and Biological Data, and Statistical Summaries of Data, Clark Fork Basin, Montana

for individual trace elements in laboratory-spiked deionizedwater blank samples and in laboratory-spiked stream samples 

is listed in tables 16 and 17, respectively. The mean spike 

recovery for deionized-water blank samples spiked with trace 

elements (table 16) ranged from 93.9 to 111 percent. The 

95-percent confidence intervals (Taylor, 1987) for the mean 

spike recovery for each constituent for which deionized-water 

blank samples were analyzed (table 16) did not exceed a 

25-percent deviation from an expected 100-percent recovery, 

except for filtered iron (89.3–132 percent), which was caused 

by one sample with a 138 percent recovery. When the data 

from this one sample is removed from the data set, filtered 

iron falls within the data-quality objective limit (88.9–119 

percent) for the 95-percent confidence interval. The mean 

spike recovery for spiked stream samples (table 17) ranged 

from 86.7 to 108 percent. The 95-percent confidence intervals 

for the mean spike recovery for each constituent for which 

stream water samples were analyzed (table 17) did not exceed 

a 25-percent deviation from an expected 100-percent recovery. 

No adjustments were made to analytical data on the basis of 

the mean spike recovery.

High or low bias is indicated if the 95-percent confidence 

interval does not include 100-percent recovery, thereby 

indicating a consistent deviation or bias, either high or low. 

Confidence intervals for percent recovery include 100 percent 

for all laboratory-spiked deionized-water blank samples 

(table 16) except for filtered arsenic (102–109 percent), 

unfiltered arsenic (90.2–99.3 percent), unfiltered cadmium 

(92.4–99.0 percent), and unfiltered copper (91.6–96.2 percent). 

Confidence intervals for percent recovery include 100 percent 

for all laboratory-spiked stream samples (table 17) except for 

filter arsenic (101–111 percent), unfiltered arsenic (90.5–99.0 

percent), unfiltered cadmium (91.5–96.3 percent), unfiltered 

copper (85.4–91.2 percent), unfiltered lead (94.5–98.4 

percent), unfiltered manganese (88.3–94.2 percent), and 

unfiltered zinc (80.7–92.7). Because the mean spike recoveries 

for all constituents of laboratory-spiked stream samples met 

data-quality objectives (less than a 25-percent deviation from 

100-percent recovery), no adjustments were made to analytical 

results for stream samples on the basis of spike recoveries.

Analytical results for field blanks are listed in table 18. 

A field blank with constituent concentrations equal to or less 

than the LRL for the analytical method indicates that the entire 

process of sample collection, field processing, and laboratory 

analysis is presumably free of contamination. If detectable 

concentrations of trace elements in field blanks were equal 

to or greater than twice the LRL, the concentrations were 

noted during data review. Analytical results from the field 

blank collected as part of the subsequent sample set were 

evaluated for evidence of a consistent trend that could indicate 

systematic contamination. Sporadic, infrequent exceedances 

of twice the LRL probably represented random contamination 

or instrument calibration error that was not persistent in the 

process and was not likely to cause positive bias in a longterm record of analytical results. However, if concentrations 

for a particular constituent exceeded twice the LRL in field 

blanks from two consecutive field trips, additional blank 

samples were collected from individual components of the 

processing sequence and were submitted for analysis to 

identify the source of contamination.

Trace-element concentrations in field blanks (table 18) 

were almost always less than the LRL. Two concentrations of 

filtered calcium [0.03 and 0.02 milligrams per liter (mg/L)] 

were equal to or exceeded the LRL of 0.02 mg/L; one concentration of filtered cadmium [0.06 micrograms per liter (μg/L)] 

exceeded the LRL of 0.02 μg/L; one concentration of filtered 

copper (0.61 μg/L) exceeded the LRL of 0.50 μg/L; two concentrations of filtered lead (both 0.02 μg/L) exceeded the LRL 

of 0.01 μg/L; one concentration of unfiltered lead (0.05 μg/L) 

exceeded the LRL of 0.04 μg/L; two concentrations of filtered 

manganese (both 0.3 μg/L) exceeded the LRL of 0.1 μg/L; and 

two concentrations of filtered zinc (1.9 and 1.6 μg/L) exceeded 

the LRL of 1.4 μg/L. Because no trends were indicated in subsequent sampling trips or follow-up office equipment blanks, 

no adjustments were made to water-quality sample results on 

the basis of these detections.

Bed-Sediment Data

Bed-sediment data for the long-term monitoring program 

in the Clark Fork basin consist of trace-element concentrations 

in the fine-grained (less than 0.063 mm) fraction of bedsediment samples. Collection of bulk bed sediment (finegrained plus coarse-grained fractions) was discontinued in 

2005; therefore, no bulk bed-sediment analytical results or 

statistical summaries are presented in this report. Bed-sediment samples are collected once annually at 14 sites (fig. 1 

and table 1) during low, stable flow conditions at about the 

same time of year as previous samples (typically August), to 

facilitate data comparisons among years. Warm Springs Creek 

at Warm Springs is sampled once every 3 years rather than 

once annually.

Methods

Fine-grained bed-sediment samples were collected in 

August 2011 using protocols described by Axtmann and 

Luoma (1991). Samples were collected from the surfaces of 

streambed deposits in areas near the edge of the stream using 

an acid-washed polypropylene scoop. Whenever possible, 

samples were collected from both sides of the stream. 

Individual samples of bed sediment were collected by 

scooping material from the surfaces of three to five randomly 

selected deposits along pools or low-velocity areas. The three 

to five individual samples were combined to form a single 

composite sample. This collection process was repeated three 

times to obtain three composite samples. Each composite 

sample was wet-sieved onsite through a 0.063-mm polyestermesh sieve using ambient stream water. The fraction of bed 

sediment in each composite sample that was finer than 0.063 
Bed-Sediment Data 11

mm was collected in an acid-washed 500-milliliter (mL) 

polyethylene bottle and transported to the laboratory on ice.

Bed-sediment samples were processed and analyzed 

at the USGS National Research Program Ecology and 

Contaminants Project laboratory in Menlo Park, Calif. Bedsediment samples were oven-dried at 60°C and ground into 

smaller particle sizes using an acid-washed, ceramic mortar 

and pestle. Single aliquots of approximately 0.5–0.6 grams (g) 

of sediment from each of the three composite bed-sediment 

samples were digested using a hot, concentrated, nitric acid 

reflux according to methods described by Luoma and Bryan 

(1981). Lab replicates were analyzed by taking an aliquot 

from one of the three sieved replicate samples at each station. 

After a 2-week digestion period, the aliquots were evaporated 

to dryness on a hot plate. The dry residue was reconstituted in 

10 mL of 0.6N (normal) hydrochloric acid. The reconstituted 

aliquots were then filtered through a 0.45-μm pore-size filter 

by using a syringe and in-line disposable filter cartridge. 

The filtrate was diluted to a 1:10 ratio with 0.6N hydrochloric acid. These final solutions were analyzed for arsenic, 

cadmium, chromium, copper, iron, lead, manganese, nickel, 

and zinc by using inductively coupled plasma-atomic emission 

spectrometry (ICP–AES). The smallest concentration of a 

constituent that can be reliably reported for analyses of bed 

sediment is termed the minimum reporting level (MRL).

Results

Concentrations of trace elements measured in samples of 

fine-grained bed sediment collected during August 2011 are 

listed in table 19. Liquid-phase concentrations, in micrograms 

per milliliter (μg/mL) (which is equivalent to parts per 

million; ppm), that were analyzed in the reconstituted aliquots 

of digested bed sediment were converted to solid-phase 

concentrations, in micrograms per gram (μg/g), by using the 

following equation: 

 . (5)

The reported solid-phase concentrations (table 19) are 

the means of all analyses for replicate aliquots from each 

composite bed-sediment sample collected at the site. Because 

the conversion from liquid-phase to solid-phase concentration 

is dependent on both the dilution ratio and the dry weight of 

the sample, MRLs for some trace elements might differ among 

stations and among years.

Quality Assurance

The USGS protocols for field collection and 

processing of bed-sediment samples are designed to prevent 

contamination from metal sources. Non-metallic sampling 

and processing equipment (white plastic scoop, funnel-frame 

apparatus, and 500-mL sample bottles) were acid-washed 

and rinsed with deionized water prior to the collection of 

the first sample. Polyester-mesh sieves were washed in 

laboratory-grade detergent and rinsed with deionized water. 

All equipment received a final rinse onsite with native 

stream water. Sampling equipment used at more than one 

site was rinsed thoroughly between sites with native stream 

water. Separate sieves were used at each site and, therefore, 

did not require between-site cleaning. Bed-sediment samples were collected sequentially at sites along an increasing 

concentration gradient to minimize effects from potential siteto-site carryover contamination.

Quality assurance of analytical results for bed-sediment 

samples included laboratory instrument calibration with 

standard solutions and analysis of quality-control samples 

designed to identify the presence and magnitude of bias 

(EllenV. Axtmann, U.S. Geological Survey, written commun., 

1994). Quality-control samples consisted of standard reference 

materials (SRMs) and procedural blanks. Sixteen procedural 

blanks, a set of ten low-concentration SRMs, and a set of ten 

high-concentration SRMs were analyzed.

Standard reference materials are commercially prepared 

materials that have certified concentrations of trace elements. 

Analyses of SRMs are used to indicate the ability of the 

method to accurately measure a known quantity of a constituent. Multiple analyses of SRMs are made to derive a mean 

and 95-percent confidence interval for recovery. Recovery 

efficiency for trace-element analyses of SRMs for bed 

sediment is listed in table 20. Two SRMs consisting of 

agricultural soils representing low and high concentrations 

of trace elements were analyzed to test recovery efficiency 

for a range of concentrations similar to those occurring in the 

bed sediment in streams in the upper Clark Fork basin. The 

digestion process used to analyze bed-sediment samples is 

not a “total” digestion (does not liberate elements associated 

with crystalline lattices); therefore, 100-percent recovery may 

not be achieved for elements strongly bound to the sediment. 

The percent recovery of trace elements for SRM analyses that 

use less than a total digestion is useful to indicate which trace 

elements display strong sediment-binding characteristics in the 

SRM and whether analytical recovery is consistent between 

multiple sets of analyses.

Although data-quality objectives have not been established for bed sediment, percent recoveries for individual 

trace elements (table 20) illustrate analytical performance. 

For copper, iron, manganese, nickel, and zinc, mean 

SRM recoveries for the low concentration standard (SRM 

2709a) ranged from 85.7 to 98.1 percent of the certified 

concentrations. Mean recoveries for cadmium and chromium 

were 70.7 and 77.8 percent, respectively; and for arsenic and 

lead 54.0 and 54.4 percent, respectively. The small range of 

variation (less than 9 percent) in the 95-percent confidence 

interval indicates good reproducibility of multiple analyses 

of SRM 2709a. For arsenic, cadmium, copper, iron, lead, 

manganese, nickel, and zinc, mean SRM recoveries for the 

high concentration standard (SRM 2711a) ranged from 82.6 to 

μ

dry weight of sample, in grams = (μ g/mL volume of digested sample, in mL ) ( )

( ) ( ) g/g

dilution ratio
12 Water-Quality, Bed-Sediment, and Biological Data, and Statistical Summaries of Data, Clark Fork Basin, Montana

104 percent of the certified concentrations. Mean recovery for 

chromium is 75.3 percent for SRM 2711a. The small range of 

variation (less than 10 percent) for the 95-percent confidence 

interval indicates good reproducibility of multiple analyses 

of SRM 2711a. No adjustments were made to trace-element 

concentrations in bed-sediment samples on the basis of 

recovery efficiencies.

Procedural blanks for bed-sediment samples consisted 

of the same reagents used for sample digestion and 

reconstitution. Concentrated nitric acid used for sample 

digestion was heated and evaporated to dryness. After 

evaporation, 0.6N hydrochloric acid was added to reconstitute 

the dry residue. Procedural blanks, therefore, represent the 

same chemical matrix and exposure to analytical materials 

and handling as the reagents used to digest and reconstitute 

bed-sediment samples. Analytical results of procedural blanks 

for bed sediment (table 21) are reported as a liquid-phase 

concentration, in micrograms per milliliter. A procedural 

blank was prepared and analyzed concurrently with bedsediment samples for each site. Concentrations of trace 

elements in all procedural blanks were less than the MRL 

indicating no contamination bias, so no adjustments to the data 

were necessary.

Biological Data

Biological data for the long-term monitoring program in 

the Clark Fork basin consist of analyses of trace-element concentrations in the whole-body tissue of aquatic benthic insects. 

Insect samples are collected once annually at the same 14 sites 

and on the same dates as bed-sediment samples (fig. 1 and 

table 1), allowing for a direct comparison of biological data 

with bed-sediment data among the years. Warm Springs Creek 

at Warm Springs is sampled once every 3 years rather than 

once annually.

Methods

Insect samples were collected using protocols described 

in Hornberger and others (1997). Benthic insects at immature 

stages were collected with a large nylon-mesh kick net. 

A single riffle at each site was sampled repeatedly until 

an adequate number of individual insects were collected 

to provide sufficient mass for analysis. Targeted taxa for 

collection were the order Trichoptera (caddisflies) and the 

order Plecoptera (stoneflies).

Two caddisfly species of the genus Hydropsyche

(Hydropsyche cockerelli and Hydropsyche occidentalis) were 

targeted for collection in this study because of their occurrence 

at most sites. Hydropsyche species (spp.) that could not 

be positively identified were categorized as Hydropsyche

spp. or Hydropsyche morosa group (in previous reports). 

When Hydropsyche could not be found, another caddisfly, 

Rhyacophila spp., was collected (specifically, at Clark Fork 

below Lost Creek, near Galen). The caddisfly Arctopsyche 

grandis and the stoneflies Claassenia sabulosa and

Hesperoperla spp. were collected where available to represent 

additional insect taxa that are commonly distributed in the 

Clark Fork basin. In addition, specimens from the caddisfly 

group Brachycentrus spp. were collected in previous years 

when targeted taxa were not available.

Samples of each taxon were sorted by genus in the field 

and placed in acid-washed plastic containers. Samples were 

frozen in a small amount of ambient stream water on dry ice 

within 30 minutes of collection. Between 1986 and 1998, 

macroinvertebrate containers were kept on ice to allow the 

insects to evacuate their gut contents (depurate) for a period 

of 6 to 8 hours. Excess water was drained and insects were 

frozen for transport to the laboratory. Since 1999, samples 

were immediately frozen on dry ice in the field to reduce 

the possibility of metal loss through intracellular breakdown 

during depuration. A comparison of immediately frozen 

to depurated samples showed that although no substantial 

difference occurred for most metals, concentrations of copper 

were about 20 percent lower in the depurated samples than in 

the samples that were immediately frozen. The data were not 

adjusted for this difference.

Insect samples were processed and analyzed at the 

USGS National Research Program Ecology and Contaminants 

Project laboratory in Menlo Park, Calif. Insects were 

thawed and rinsed with ultrapure deionized water to remove 

particulate matter and then sorted to their lowest possible taxonomic level. If large numbers of specimens were 

collected at a site, similar-sized individuals were composited 

into replicate subsamples. Subsamples were placed in tared 

scintillation vials and oven-dried at 70°C. Subsamples were 

weighed to obtain a final dry weight and digested by reflux 

using concentrated nitric acid (Cain and others, 1992). After 

digestion, insect samples were evaporated to dryness on a hot 

plate. The dry residue was reconstituted in 0.6N hydrochloric 

acid, filtered through a 0.45-μm pore-size filter, and analyzed 

undiluted by ICP–AES for arsenic, cadmium, chromium, 

copper, iron, lead, manganese, nickel, and zinc. The smallest 

concentration of a constituent that can be reliably reported for 

analyses of biota is termed the MRL.

Results

Concentrations of trace elements in whole-body tissue 

of aquatic insects collected during August 2011 are listed in 

table 22. The variability in the number of composite samples 

among species and among sites reflects differences in insect 

abundance, with the number of composite samples increasing 

with the relative abundance of insects. Liquid-phase 

concentrations, in μg/mL, analyzed in the reconstituted 

samples were converted to solid-phase concentrations, in 

μg/g, by using equation 5. All tissue samples were analyzed 

undiluted (dilution ratio 1:1). As with MRLs for trace elements 
Statistical Summaries of Data 13

in bed sediment, MRLs for trace elements in insects may 

differ among sites as a result of varied sample weights. In 

general, the smaller the biological-sample weight (primarily a 

function of insect abundance), the higher the MRL. Therefore, 

higher MRLs do not necessarily imply a higher trace-element 

concentration in tissue.

Quality Assurance

The protocols for field collection and processing of biota 

samples are designed to prevent contamination from metal 

sources. Nonmetallic nets, sampling equipment, and processing equipment were used in all sample collection. Equipment 

was acid-washed and rinsed in ultrapure deionized water 

prior to the first sample collection. Nets and equipment were 

thoroughly rinsed in ambient stream water at each main-stem 

site. New nets were used for all tributary sites. Biota samples were collected sequentially at sites along an increasing 

concentration gradient to minimize effects from potential siteto-site carryover contamination (Hornberger and others, 1997).

Quality assurance of analytical results for biota samples 

included laboratory-instrument calibration with standard solutions and analyses of quality-control samples designed to 

quantify precision and to identify the presence and magnitude 

of bias. Quality-control samples consisted of 12 replicates of 

the tissue SRM (lobster hepatopancreas) and 14 procedural 

blanks (one at each site). Quality-control samples were 

analyzed in a proportion equivalent to about 20 percent of the 

total number of biota samples.

Recovery efficiency for trace-element analyses of the 

SRM for biota is listed in table 23. Data-quality objectives 

have not been established for analytical recovery in biota, but 

percent recoveries are shown to illustrate analytical performance. Mean SRM recoveries ranged from 71.6 to 129 

percent for all constituents. The small range of variation (less 

than 7 percent) for the 95-percent confidence interval indicates 

good reproducibility of multiple analyses of TORT-2 for 

arsenic, cadmium, copper, iron, manganese, nickel, and zinc. 

However, chromium and lead had a slightly higher variation 

(13 percent or less). The mean SRM recovery and small range 

of variation for the 95-percent confidence interval represent a 

reasonable range of recoveries. No adjustments were made to 

trace-element concentrations in biota samples on the basis of 

recovery efficiencies. 

Procedural blanks for biota consisted of undiluted 

aliquots of the same reagents used to digest and reconstitute 

tissue of aquatic insects. Analytical results of procedural 

blanks for biota (table 24) are reported as a liquid-phase 

concentration, in μg/mL. A procedural blank was prepared 

and analyzed concurrently with biota samples for each site. 

Concentrations of trace elements in all procedural blanks 

were less than the MRL; therefore, no adjustments to the data 

were necessary.

Statistical Summaries of Data

Statistical summaries of long-term water-quality, bedsediment, and biological data for the Clark Fork basin are 

listed in tables 25 through 27 for the period of record at each 

site since 1985. The summaries include the period of record; 

number of samples; and maximum, minimum, mean, and 

median concentrations.

Statistical summaries of water-quality data (table 25) 

are based on results of cross-section samples collected 

periodically by the USGS for the long-term monitoring 

program in the Clark Fork basin during the period of 

record for each site. The summaries do not include data for 

supplemental samples collected at selected sites that targeted 

high-flow conditions or maintenance drawdowns of Milltown 

Reservoir, which might disproportionately skew the long-term 

statistics relative to the other sites in the network. Statistical 

summaries of bed-sediment (table 26) and biological data 

(table 27) are based on results of samples collected once 

annually during the indicated years. Because not all sites 

were sampled for bed sediment and biota every year, the 

data for some sites do not represent a consecutive annual 

record. Sampling of bulk bed sediment has been discontinued; 

therefore, a statistical summary is not presented. Statistical 

summaries are not presented for discontinued sites.

Statistics for bed-sediment data (table 26) are based on 

the mean trace-element concentrations determined for each 

year from the mean of the analyses of composite samples. 

Therefore, the number of samples for bed sediment represents 

the number of years that the constituent was analyzed. In 

contrast, statistics for biological data (table 27) are based on 

individual analyses for each composite sample collected rather 

than on a single mean concentration for each year. Also, the 

number of samples for arsenic for both bed sediment and biota 

is smaller than the number for other trace elements because 

sampling for arsenic began in September 2003. In addition, 

the number of samples analyzed for silver in bed sediment is 

smaller because analysis for this constituent was discontinued 

in 2004.

Differences in the number of composited biota samples 

among species reflect differences in species abundance, 

both within and between sites and among years. As a result, 

the statistics for biota describe a wider range of variation in 

trace-element concentrations than would be evident if results 

from individual composite samples were averaged. The 

abundance of aquatic insects at a particular site in a given year 

limits the biomass of the sample, which in turn may result in 

varied MRLs. When MRLs vary among years, differences in 

concentration with time are difficult to determine, especially 

when a large percentage of the samples have concentrations 

less than MRLs.

The presence or absence of insect species at a given 

site can vary among years and may result in different taxa 

being analyzed in the long-term period of record. Because 

Hydropsyche insects were not sorted to the species level 
14 Water-Quality, Bed-Sediment, and Biological Data, and Statistical Summaries of Data, Clark Fork Basin, Montana

during 1986–89, statistics for stations sampled during those 

years are based on the results of all Hydropsyche species 

combined. At some sites, statistics for the Hydropsyche 

morosa group are based on the combined results for two or 

more species because these samples could not be clearly 

identified to the species level, but the individual insects had 

morosa characteristics.

References Cited

Anderson, C.W., 2005, Turbidity (version 2.0): U.S. 

Geological Survey Techniques of Water-Resources 

Investigations, book 9, chap. A6, section 6.7, 64 p. (Also 

available at http://pubs.water.usgs.gov/twri9A6/.)

Andrews, E.D., 1987, Longitudinal dispersion of trace metals 

in the Clark Fork River, Montana, in Averett, R.C., and 

McKnight, D.M., eds., Chemical quality of water and 

the hydrologic cycle: Chelsea, Mich., Lewis Publishers, 

p. 179–191.

Axtmann, E.V., Cain, D.J., and Luoma, S.N., 1997, Effect 

of tributary inflows on the distribution of trace metals in 

fine-grained sediment and benthic insects of the Clark Fork 

River, Montana: Environmental Science and Technology, 

v. 31, no. 3, p. 750–758.

Axtmann, E.V., and Luoma, S.N., 1991, Large scale 

distribution of metal contamination in the fine-grained 

sediment of the Clark Fork River, Montana: Applied 

Geochemistry, v. 6, no. 6, p. 75–88.

Cain, D.J., Luoma, S.N., and Axtmann, E.V., 1995, Influence 

of gut content in immature aquatic insects on assessments 

of environmental metal contamination: Canadian Journal of 

Fisheries and Aquatic Sciences, v. 52, no. 12, p. 2736–2746.

Cain, D.J., Luoma, S.N., Carter, J.L., and Ferd, S.V., 

1992, Aquatic insects as bioindicators of trace element 

contamination in cobble-bottom rivers and streams: 

Canadian Journal of Fisheries and Aquatic Sciences, v. 49, 

no. 10, p. 2141–2154.

Childress, C.T., Foreman, W.T., Connor, B.F., and Maloney, 

T.J., 1999, New reporting procedures based on long-term 

method detection levels and some considerations for 

interpretations of water-quality data provided by the U.S. 

Geological Survey National Water Quality Laboratory: 

U.S. Geological Survey Open-File Report 99–193, 19 p.

Davis, B.E., 2005, A guide to the proper selection and use of 

federally approved sediment and water-quality samplers: 

U.S. Geological Survey Open-File Report 2005–1087, 20 p. 

(Also available at http://pubs.usgs.gov/of/2005/1087.)

Dodge, K.A., Hornberger, M.I., and Axtmann, E.V., 1996, 

Water-quality, bed-sediment, and biological data (October 

1994 through September 1995) and statistical summaries 

of data for streams in the upper Clark Fork basin, Montana: 

U.S. Geological Survey Open-File Report 96–432, 109 p.

Dodge, K.A., Hornberger, M.I., and Axtmann, E.V., 1997, 

Water-quality, bed-sediment, and biological data (October 

1995 through September 1996) and statistical summaries 

of data for streams in the upper Clark Fork basin, Montana: 

U.S. Geological Survey Open-File Report 97–552, 91 p.

Dodge, K.A., Hornberger, M.I., and Axtmann, E.V., 1998, 

Water-quality, bed-sediment, and biological data (October 

1996 through September 1997) and statistical summaries 

of data for streams in the upper Clark Fork basin, Montana: 

U.S. Geological Survey Open-File Report 98–407, 102 p.

Dodge, K.A., Hornberger, M.I., and Bouse, R.M., 1999, 

Water-quality, bed-sediment, and biological data (October 

1997 through September 1998) and statistical summaries 

of data for streams in the upper Clark Fork basin, Montana: 

U.S. Geological Survey Open-File Report 99–251, 102 p.

Dodge, K.A., Hornberger, M.I., and David, C.P.C., 2000, 

Water-quality, bed-sediment, and biological data (October 

1998 through September 1999) and statistical summaries 

of data for streams in the upper Clark Fork basin, Montana: 

U.S. Geological Survey Open-File Report 00–370, 102 p.

Dodge, K.A., Hornberger, M.I., and David, C.P.C., 2001, 

Water-quality, bed-sediment, and biological data (October 

1999 through September 2000) and statistical summaries 

of data for streams in the upper Clark Fork basin, Montana: 

U.S. Geological Survey Open-File Report 01–379, 95 p.

Dodge, K.A., Hornberger, M.I., and David, C.P.C., 2002, 

Water-quality, bed-sediment, and biological data (October 

2000 through September 2001) and statistical summaries 

of data for streams in the upper Clark Fork basin, Montana: 

U.S. Geological Survey Open-File Report 02–358, 94 p.

Dodge, K.A., Hornberger, M.I., and Dyke, J.L., 2005, 

Water-quality, bed-sediment, and biological data (October 

2003 through September 2004) and statistical summaries 

of data for streams in the upper Clark Fork basin, 

Montana: U.S. Geological Survey Open-File Report 

2005–1356, 124 p. (Also available at http://pubs.usgs.gov/

of/2005/1356.)

Dodge, K.A., Hornberger, M.I., and Dyke, J.L., 2006, 

Water-quality, bed-sediment, and biological data (October 

2004 through September 2005) and statistical summaries 

of data for streams in the upper Clark Fork basin, 

Montana: U.S. Geological Survey Open-File Report 

2006–1266, 109 p. (Also available at http://pubs.usgs.gov/

of/2006/1266.)
References Cited 15

Dodge, K.A., Hornberger, M.I., and Dyke, J.L., 2007, 

Water-quality, bed-sediment, and biological data (October 

2005 through September 2006) and statistical summaries 

of long-term data for streams in the Clark Fork basin, 

Montana: U.S. Geological Survey Open-File Report 

2007–1301, 124 p. (Also available at http://pubs.usgs.gov/

of/2007/1301.)

Dodge, K.A., Hornberger, M.I., and Dyke, J.L., 2008, 

Water-quality, bed-sediment, and biological data (October 

2006 through September 2007) and statistical summaries 

of long-term data for streams in the Clark Fork basin, 

Montana: U.S. Geological Survey Open-File Report 

2008–1318, 132 p. (Also available at http://pubs.usgs.gov/

of/2008/1318.)

Dodge, K.A., Hornberger, M.I., and Dyke, J.L., 2009, 

Water-quality, bed-sediment, and biological data (October 

2007 through September 2008) and statistical summaries 

of long-term data for streams in the Clark Fork basin, 

Montana: U.S. Geological Survey Open-File Report 

2009–1178, 139 p. (Also available at http://pubs.usgs.gov/

of/2009/1178.)

Dodge, K.A., Hornberger, M.I., and Dyke, J.L., 2010, 

Water-quality, bed-sediment, and biological data (October 

2008 through September 2009) and statistical summaries 

of long-term data for streams in the Clark Fork basin, 

Montana: U.S. Geological Survey Open-File Report 

2010–1267, 137 p. (Also available at http://pubs.usgs.gov/

of/2010/1267.)

Dodge, K.A., Hornberger, M.I., and Dyke, J.L., 2012, 

Water-quality, bed-sediment, and biological data (October 

2009 through September 2010) and statistical summaries 

of data for streams in the Clark Fork basin, Montana: U.S. 

Geological Survey Open-File Report 2011–1314, 120 p. 

(Also available at http://pubs.usgs.gov/of/2011/1314.)

Dodge, K.A., Hornberger, M.I., and Lavigne, I.R., 2003, 

Water-quality, bed-sediment, and biological data (October 

2001 through September 2002) and statistical summaries 

of data for streams in the upper Clark Fork basin, Montana: 

U.S. Geological Survey Open-File Report 03–356, 95 p.

Dodge, K.A., Hornberger, M.I., and Lavigne, I.R., 2004, 

Water-quality, bed-sediment, and biological data (October 

2002 through September 2003) and statistical summaries 

of data for streams in the upper Clark Fork basin, Montana: 

U.S. Geological Survey Open-File Report 2004–1340, 

107 p.

Dodge, K.A., and Lambing, J.H., 2006, Quality-assurance 

plan for the analysis of suspended sediment by the U.S. 

Geological Survey in Montana: U.S. Geological Survey 

Open-File Report 2006–1242, 25 p. (Also available at 

http://pubs.usgs.gov/of/2006/1242.)

Edwards, T.K., and Glysson, G.D., 1999, Field methods for 

measurement of fluvial sediment: U.S. Geological Survey 

Techniques of Water-Resources Investigations, book 3, 

chap. C2, 89 p. (Also available at http://pubs.usgs.gov/twri/

twri3-c2/.)

Faires, L.M., 1993, Methods of analysis by the U.S. Geological Survey National Water Quality Laboratory—

Determination of metals in water by inductively coupled 

plasma-mass spectrometry: U.S. Geological Survey 

Open-File Report 92–634, 28 p.

Fishman, M.J., ed., 1993, Methods of analysis by the U.S. 

Geological Survey National Water Quality Laboratory—

Determination of inorganic and organic constituents in 

water and fluvial sediments: U.S. Geological Survey 

Open-File Report 93–125, 217 p.

Friedman, L.C., and Erdmann, D.E., 1982, Quality assurance 

practices for the chemical and biological analyses of water 

and fluvial sediments: U.S. Geological Survey Techniques 

of Water-Resources Investigations, book 5, chap. A6, 181 p. 

(Also available at http://pubs.usgs.gov/twri/twri5a6/.)

Garbarino, J.R., and Struzeski, T.M., 1998, Methods of 

analysis by the U.S. Geological Survey National Water 

Quality Laboratory—Determination of elements in wholewater digests using inductively coupled plasma-optical 

emission spectrometry and inductively coupled 

plasma-mass spectrometry: U.S. Geological Survey 

Open-File Report 98–165, 101 p.

Garbarino, J.R., Kanagy, L.K., and Cree, M.E., 2006, 

Determination of elements in natural-water, biota, sediment, 

and soil samples using collision/reaction cell inductively 

coupled plasma-mass spectrometry: U.S. Geological Survey 

Techniques and Methods, book 5, sec. B, chap. 1, 88 p.

Guy, H.P., 1969, Laboratory theory and methods for sediment 

analysis: U.S. Geological Survey Techniques of WaterResources Investigations, book 5, chap. C1, 58 p. (Also 

available at http://pubs.usgs.gov/twri/twri5c1/.)

Helsel, D.R., and Cohn, T.A., 1988, Estimation of descriptive 

statistics for multiply censored water quality data: Water 

Resources Research, v. 24, no. 12, p. 1997–2004.

Hoffman, G.L., Fishman, M.J., and Garbarino, J.R., 1996, 

Methods of analysis by the U.S. Geological Survey National 

Water Quality Laboratory—In-bottle acid digestion of 

whole-water samples: U.S. Geological Survey Open-File 

Report 96–225, 28 p.

Hornberger, M.I., Lambing, J.H., Luoma, S.N., and Axtmann, 

E.V., 1997, Spatial and temporal trends of trace metals in 

surface water, bed sediment, and biota of the upper Clark 

Fork basin, Montana, 1985–95: U.S. Geological Survey 

Open-File Report 97–669, 84 p.
16 Water-Quality, Bed-Sediment, and Biological Data, and Statistical Summaries of Data, Clark Fork Basin, Montana

Horowitz, A.J., Demas, C.R., Fitzgerald, K.K., Miller, T.L., 

and Rickert, D.A., 1994, U.S. Geological Survey protocol 

for the collection and processing of surface-water samples 

for the subsequent determination of inorganic constituents 

in filtered water: U.S. Geological Survey Open-File Report 

94–539, 57 p.

Jones, B.E., 1987, Quality control manual of the U.S. 

Geological Survey’s National Water Quality Laboratory: 

U.S. Geological Survey Open-File Report 87–457, 17 p.

Lambing, J.H., 1987, Water-quality data for the Clark Fork 

and selected tributaries from Deer Lodge to Milltown, 

Montana, March 1985 through June 1986: U.S. Geological 

Survey Open-File Report 87–110, 48 p.

Lambing, J.H., 1988, Water-quality data (July 1986 through 

September 1987) and statistical summaries (March 1985 

through September 1987) for the Clark Fork and selected 

tributaries from Deer Lodge to Missoula, Montana: 

U.S. Geological Survey Open-File Report 88–308, 55 p.

Lambing, J.H., 1989, Water-quality data (October 1987 

through September 1988) and statistical summaries (March 

1985 through September 1988) for the Clark Fork and 

selected tributaries from Galen to Missoula, Montana: 

U.S. Geological Survey Open-File Report 89–229, 51 p.

Lambing, J.H., 1990, Water-quality data (October 1988 

through September 1989) and statistical summaries (March 

1985 through September 1989) for the Clark Fork and 

selected tributaries from Galen to Missoula, Montana: 

U.S. Geological Survey Open-File Report 90–168, 68 p.

Lambing, J.H., 1991, Water-quality and transport 

characteristics of suspended sediment and trace elements 

in streamflow of the upper Clark Fork basin from Galen 

to Missoula, Montana, 1985–90: U.S. Geological Survey 

Water-Resources Investigations Report 91–4139, 73 p.

Lambing, J.H., comp., 2006, Quality-assurance plan for 

water-quality activities of the U.S. Geological Survey 

Montana Water Science Center: U.S. Geological Survey 

Open-File Report 2006–1275, 39 p. (Available online only 

at http://pubs.usgs.gov/of/2006/1275/.)

Lambing, J.H., Hornberger, M.I., Axtmann, E.V., and Dodge, 

K.A., 1995, Water-quality, bed-sediment, and biological 

data (October 1993 through September 1994) and statistical 

summaries of data for streams in the upper Clark Fork 

basin, Montana: U.S. Geological Survey Open-File 

Report 95–429, 104 p.

Lambing, J.H., Hornberger, M.I., Axtmann, E.V., and Pope, 

D.A., 1994, Water-quality, bed-sediment, and biological 

data (October 1992 through September 1993) and statistical 

summaries of water-quality data (March 1985 through 

September 1993) for streams in the upper Clark Fork 

basin, Montana: U.S. Geological Survey Open-File Report 

94–375, 85 p.

Luoma, S.N., and Bryan, G.W., 1981, A statistical assessment 

of the form of trace metals in oxidized estuarine sediments 

employing chemical extractants: Science of the Total 

Environment, v. 17, no. 17, p. 167–196.

Porterfield, George, 1972, Computation of fluvial-sediment 

discharge: U.S. Geological Survey Techniques of 

Water-Resources Investigations, book 3, chap. C3, 66 p. 

(Also available at http://pubs.usgs.gov/twri/twri3-c3/.)

Pritt, J.W., and Raese, J.W., eds., 1995, Quality assurance/

quality control manual—National Water Quality 

Laboratory: U.S. Geological Survey Open-File Report 

95–443, 35 p.

Rantz, S.E., and others, 1982, Measurement and computation 

of streamflow: U.S. Geological Survey Water-Supply Paper 

2175, v.2, 631 p.

Taylor, J.K., 1987, Quality assurance of chemical 

measurements: Chelsea, Mich., Lewis Publishers, 328 p.

U.S. Environmental Protection Agency, 2004, Milltown 

Reservoir Sediments Operational Unit of the Milltown 

Reservoir/Clark Fork River Superfund Site—Record of 

decision, part 2— Decision Summary: U.S. Environmental 

Protection Agency, 141 p. (Also available at http://www.epa.

gov/region8/superfund/mt/milltown/mrsrod.html.)

U.S. Geological Survey, variously dated, National field manual 

for the collection of water-quality data: U.S. Geological 

Survey Techniques of Water-Resources Investigations, book 

9, chaps. A1–A9. (Also available at http://pubs.usgs.gov/

twri/.)

Wagner, R.J., Boulger, R.W., Oblinger, C.J., and Smith, B.A., 

2006, Guidelines and standard procedures for continuous 

water-quality monitors—Station operation, record 

computation, and data reporting: U.S. Geological Survey 

Techniques and Methods 1–D3, 51 p., 8 attachments. (Also 

available at http://pubs.usgs.gov/tm/2006/tm1D3/.)

Ward, J.R., and Harr, C.A., eds., 1990, Methods for collection 

and processing of surface-water and bed-material samples 

for physical and chemical analyses: U.S. Geological Survey 

Open-File Report 90–140, 71 p.
Data

Data 19

Table 4. Water-quality data for the Clark Fork basin, Montana, October 2010 through September 2011.

[Abbreviations: CaCO3, calcium carbonate; ft3/s, cubic feet per second; °C, degrees Celsius; E, estimated; lab, laboratory; μg/L, micrograms per liter; μS/cm, 

microsiemens per centimeter at 25°C; mg/L, milligrams per liter; mm, millimeters; NTRU, nephelometric turbidity ratio unit; ton/d, tons per day. Symbols: <, 

less than laboratory reporting level; --, no data]

12323230--Blacktail Creek at Harrison Avenue, at Butte

Date Time

Streamflow, 

instantaneous 

(ft3

/s)

pH, onsite 

(standard 

units)

Specific 

conductance, onsite 

(μS/cm)

Temperature, 

water 

(°C)

Hardness, 

filtered 

(mg/L as 

CaCO3

)

Calcium, 

filtered 

(mg/L)

Magnesium, 

filtered 

(mg/L)

11/15/2010 0840 16 7.6 261 2.0 106 28.8 8.28

03/14/2011 0920 15 7.3 276 1.0 104 28.0 8.39

04/11/2011 0925 24 7.7 250 3.5 98.4 27.6 7.16

05/16/2011 0915 55 7.5 181 7.5 75.2 21.3 5.34

05/31/2011 0845 E80 7.6 168 5.0 66.2 18.4 4.91

06/13/2011 0900 E150 7.5 156 10.0 63.2 17.9 4.49

07/12/2011 0845 21 7.6 240 12.5 99.9 28.5 7.00

08/15/2011 0840 10 7.6 291 12.0 115 32.3 8.27

Date

Arsenic, 

filtered 

(μg/L)

Arsenic, 

unfiltered 

recoverable 

(μg/L)

Cadmium, 

filtered 

(μg/L)

Cadmium, 

unfiltered 

recoverable 

(μg/L)

Copper, 

filtered 

(μg/L)

Copper, 

unfiltered 

recoverable 

(μg/L)

Iron, 

filtered 

(μg/L)

Iron, 

unfiltered 

recoverable 

(μg/L)

11/15/2010 2.4 3.3 0.04 <0.05 2.2 4.9 171 611

03/14/2011 3.6 4.9 .05 .05 4.0 4.9 294 640

04/11/2011 3.9 5.1 .02 <.05 2.6 4.1 372 793

05/16/2011 6.3 8.3 .03 .07 5.9 11.0 319 1,190

05/31/2011 6.6 7.9 .03 <.05 5.6 8.8 219 695

06/13/2011 12.3 13.7 .03 <.05 7.0 11.1 296 835

07/12/2011 8.9 11.9 .03 <.05 2.6 4.9 528 1,310

08/15/2011 5.4 6.9 .04 <.05 1.8 2.5 236 713

Date

Lead, 

filtered 

(μg/L)

Lead, 

unfiltered 

recoverable 

(μg/L)

Manganese, 

filtered 

(μg/L)

Manganese, 

unfiltered 

recoverable 

(μg/L)

Zinc, 

filtered 

(μg/L)

Zinc, 

unfiltered 

recoverable 

(μg/L)

Sediment, 

suspended 

(percent finer 

than 0.062 

mm)

Sediment, 

suspended 

(mg/L)

Sediment 

discharge, 

suspended 

(ton/d)

11/15/2010 0.07 1.15 43.6 57.9 4.0 8.8 92 10 0.43

03/14/2011 .16 .50 109 119 4.9 5.5 69 8 .32

04/11/2011 .15 .61 60.1 79.0 <1.4 4.2 74 5 .32

05/16/2011 .29 1.76 35.7 69.9 2.1 6.6 66 25 3.7

05/31/2011 .19 .86 21.5 38.9 3.6 5.1 70 12 E2.6

06/13/2011 .29 1.21 27.1 46.6 4.0 7.3 62 17 E6.9

07/12/2011 .20 .95 74.8 136 2.1 4.4 89 11 .62

08/15/2011 .11 .42 58.6 74.0 1.8 2.6 90 6 .16
20 Water-Quality, Bed-Sediment, and Biological Data, and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 4. Water-quality data for the Clark Fork basin, Montana, October 2010 through September 2011.—Continued

[Abbreviations: CaCO3, calcium carbonate; ft3/s, cubic feet per second; °C, degrees Celsius; E, estimated; lab, laboratory; μg/L, micrograms per liter; μS/cm, 

microsiemens per centimeter at 25°C; mg/L, milligrams per liter; mm, millimeters; NTRU, nephelometric turbidity ratio unit; ton/d, tons per day. Symbols: <, 

less than laboratory reporting level; --, no data]

12323250--Silver Bow Creek below Blacktail Creek, at Butte

Date Time

Streamflow, 

instantaneous 

(ft3

/s)

pH, onsite 

(standard 

units)

Specific 

conductance, onsite 

(μS/cm)

Temperature, 

water 

(°C)

Hardness, 

filtered 

(mg/L as 

CaCO3

)

Calcium, 

filtered 

(mg/L)

Magnesium, 

filtered 

(mg/L)

11/15/2010 1025 32 7.6 452 4.0 150 42.3 10.8

03/14/2011 1115 29 7.5 430 7.0 139 39.0 10.0

04/11/2011 1050 38 7.7 405 4.5 138 38.7 10.0

05/16/2011 1025 65 7.6 262 9.0 93.0 26.4 6.58

05/31/2011 1030 114 7.6 234 6.5 85.2 23.8 6.23

06/13/2011 0945 202 7.6 209 11.0 78.1 22.2 5.52

07/12/2011 1030 37 8.2 358 14.5 139 39.4 9.81

08/15/2011 1030 32 7.7 465 14.0 153 43.0 11.1

Date

Arsenic, 

filtered 

(μg/L)

Arsenic, 

unfiltered 

recoverable 

(μg/L)

Cadmium, 

filtered 

(μg/L)

Cadmium, 

unfiltered 

recoverable 

(μg/L)

Copper, 

filtered 

(μg/L)

Copper, 

unfiltered 

recoverable 

(μg/L)

Iron, 

filtered 

(μg/L)

Iron, 

unfiltered 

recoverable 

(μg/L)

11/15/2010 3.1 4.0 0.07 0.13 3.4 9.4 61 335

03/14/2011 3.9 5.2 .08 .13 5.3 9.2 171 418

04/11/2011 4.1 5.1 .05 .10 5.7 8.9 198 546

05/16/2011 6.0 8.8 .05 .13 6.3 17.8 212 1,040

05/31/2011 6.9 8.7 .04 .09 6.3 15.3 177 713

06/13/2011 13.4 14.8 .06 .10 8.4 15.1 216 597

07/12/2011 8.0 11.8 .04 .14 3.8 10.7 292 1,140

08/15/2011 5.3 9.6 .07 .24 3.2 19.6 47 1,390

Date

Lead, 

filtered 

(μg/L)

Lead, 

unfiltered 

recoverable 

(μg/L)

Manganese, 

filtered 

(μg/L)

Manganese, 

unfiltered 

recoverable 

(μg/L)

Zinc, 

filtered 

(μg/L)

Zinc, 

unfiltered 

recoverable 

(μg/L)

Sediment, 

suspended 

(percent finer 

than 0.062 

mm)

Sediment, 

suspended 

(mg/L)

Sediment 

discharge, 

suspended 

(ton/d)

11/15/2010 0.15 1.47 68.7 87.9 43.6 48.9 82 6 0.52

03/14/2011 .25 1.24 107 122 32.7 38.4 84 5 .39

04/11/2011 .16 1.27 86.3 103 23.0 32.2 81 5 .51

05/16/2011 .32 3.74 47.9 97.6 10.9 28.3 84 21 3.7

05/31/2011 .29 2.73 32.8 73.0 12.1 22.6 64 15 4.6

06/13/2011 .44 2.17 29.8 50.9 20.0 31.5 44 13 7.1

07/12/2011 .24 3.28 68.2 134 5.3 21.2 90 14 1.4

08/15/2011 .11 6.21 69.5 289 19.1 58.8 85 25 2.2
Data 21

Table 4. Water-quality data for the Clark Fork basin, Montana, October 2010 through September 2011.—Continued

[Abbreviations: CaCO3, calcium carbonate; ft3/s, cubic feet per second; °C, degrees Celsius; E, estimated; lab, laboratory; μg/L, micrograms per liter; μS/cm, 

microsiemens per centimeter at 25°C; mg/L, milligrams per liter; mm, millimeters; NTRU, nephelometric turbidity ratio unit; ton/d, tons per day. Symbols: <, 

less than laboratory reporting level; --, no data]

12323600--Silver Bow Creek at Opportunity

Date Time

Streamflow, 

instantaneous 

(ft3/s)

pH, onsite 

(standard 

units)

Specific 

conductance, onsite 

(μS/cm)

Temperature, 

water 

(°C)

Hardness, 

filtered 

(mg/L as 

CaCO3)

Calcium, 

filtered 

(mg/L)

Magnesium, 

filtered 

(mg/L)

11/15/2010 1610 51 8.3 453 3.5 160 47.3 10.2

03/15/2011 0820 E45 8.1 431 1.0 152 44.1 10.2

04/12/2011 1050 71 8.0 439 5.0 154 44.3 10.5

05/17/2011 0800 241 7.9 237 7.0 88.3 25.8 5.79

*05/25/2011 1030 505 7.8 260 8.5 99.7 29.6 6.26

06/01/2011 0805 329 7.8 231 7.0 88.2 26.3 5.46

*06/08/2011 1010 546 7.8 233 9.0 86.6 25.9 5.32

06/13/2011 1550 648 7.9 224 11.0 83.7 25.0 5.16

*06/24/2011 0900 352 8.0 233 9.0 90.6 27.1 5.58

*06/29/2011 1000 239 8.2 249 12.0 97.5 29.1 6.02

07/13/2011 0810 99 8.0 324 11.5 125 37.3 7.83

08/15/2011 1635 39 8.8 435 20.0 153 44.3 10.2

Date

Arsenic, 

filtered 

(μg/L)

Arsenic, 

unfiltered 

recoverable 

(μg/L)

Cadmium, 

filtered 

(μg/L)

Cadmium, 

unfiltered 

recoverable 

(μg/L)

Copper, 

filtered 

(μg/L)

Copper, 

unfiltered 

recoverable 

(μg/L)

Iron, 

filtered 

(μg/L)

Iron, 

unfiltered 

recoverable 

(μg/L)

11/15/2010 6.5 9.3 0.34 0.77 15.1 54.8 27 733

03/15/2011 9.1 12.0 .56 .78 27.6 51.5 96 910

04/12/2011 6.8 11.1 .47 .79 19.5 52.4 47 1,010

05/17/2011 12.4 29.1 .21 1.27 23.2 150 194 5,650

*05/25/2011 14.9 46.7 .74 2.29 68.9 310 182 7,220

06/01/2011 10.4 15.8 .24 .55 19.3 58.7 146 1,600

*06/08/2011 14.2 40.9 .52 1.57 57.2 228 104 5,780

06/13/2011 16.4 38.7 .39 1.19 48.7 190 159 4,330

*06/24/2011 12.9 18.2 .28 .58 22.2 61.9 126 1,890

*06/29/2011 11.2 15.6 .26 .50 17.1 54.1 146 1,520

07/13/2011 10.2 12.6 .31 .48 16.5 37.5 44 625

08/15/2011 13.1 13.7 .23 .34 16.6 26.9 25 253
22 Water-Quality, Bed-Sediment, and Biological Data, and Statistical Summaries of Data, Clark Fork Basin, Montana

12323600--Silver Bow Creek at Opportunity

Date

Lead, 

filtered 

(μg/L)

Lead, 

unfiltered 

recoverable 

(μg/L)

Manganese, 

filtered 

(μg/L)

Manganese, 

unfiltered 

recoverable 

(μg/L)

Zinc, 

filtered 

(μg/L)

Zinc, 

unfiltered 

recoverable 

(μg/L)

Sediment, 

suspended 

(percent finer 

than 0.062 

mm)

Sediment, 

suspended 

(mg/L)

Sediment 

discharge, 

suspended 

(ton/d)

11/15/2010 0.46 15.2 76.8 140 90.1 156 75 25 3.4

03/15/2011 .60 9.41 165 224 129 169 47 51 E6.2

04/12/2011 .27 12.0 211 310 120 192 65 40 7.7

05/17/2011 1.26 48.8 73.0 404 44.4 260 49 206 134

*05/25/2011 1.47 101 158 519 148 463 57 347 473

06/01/2011 .73 15.7 43.4 131 57.2 114 50 69 61

*06/08/2011 1.08 76.0 100 358 106 337 56 268 395

06/13/2011 1.21 60.7 72.2 332 75.0 259 51 187 327

*06/24/2011 .84 18.9 72.8 152 61.6 113 54 71 67

*06/29/2011 .76 14.6 66.6 135 43.3 97.3 61 53 34

07/13/2011 .46 8.22 83.4 124 57.0 97.8 54 28 7.5

08/15/2011 .28 3.27 45.0 69.8 19.2 52.5 90 5 .53

Table 4. Water-quality data for the Clark Fork basin, Montana, October 2010 through September 2011.—Continued

[Abbreviations: CaCO3, calcium carbonate; ft3/s, cubic feet per second; °C, degrees Celsius; E, estimated; lab, laboratory; μg/L, micrograms per liter; μS/cm, 

microsiemens per centimeter at 25°C; mg/L, milligrams per liter; mm, millimeters; NTRU, nephelometric turbidity ratio unit; ton/d, tons per day. Symbols: <, 

less than laboratory reporting level; --, no data]
Data 23

Table 4. Water-quality data for the Clark Fork basin, Montana, October 2010 through September 2011.—Continued

[Abbreviations: CaCO3, calcium carbonate; ft3/s, cubic feet per second; °C, degrees Celsius; E, estimated; lab, laboratory; μg/L, micrograms per liter; μS/cm, 

microsiemens per centimeter at 25°C; mg/L, milligrams per liter; mm, millimeters; NTRU, nephelometric turbidity ratio unit; ton/d, tons per day. Symbols: <, 

less than laboratory reporting level; --, no data]

12323670--Mill Creek near Anaconda

Date Time

Streamflow, 

instantaneous 

(ft3

/s)

Turbidity, 

unfiltered, 

lab 

(NTRU)

pH, onsite 

(standard 

units)

Specific 

conductance, onsite 

(μS/cm)

Temperature, 

water 

(°C)

Hardness, 

filtered 

(mg/L as 

CaCO3

)

Calcium, 

filtered 

(mg/L)

Magnesium, 

filtered 

(mg/L)

11/15/2010 1255 14 <2.0 8.0 171 4.0 74.9 20.7 5.66

03/14/2011 1340 11 <2.0 7.7 193 3.5 89.5 24.4 6.93

04/11/2011 1400 15 <2.0 7.9 185 7.5 77.2 20.8 6.16

05/16/2011 1300 124 E8.0 7.8 88 6.0 34.7 9.85 2.46

05/31/2011 1315 137 E4.1 7.7 96 8.0 39.6 11.2 2.81

06/13/2011 1250 309 E4.9 7.7 74 7.0 30.0 8.65 2.04

07/12/2011 1500 169 E2.8 7.5 69 11.0 29.3 8.49 1.96

08/15/2011 1255 33 <2.0 7.9 136 13.0 56.0 15.3 4.29

Date

Arsenic, 

filtered 

(μg/L)

Arsenic, 

unfiltered 

recoverable 

(μg/L)

Cadmium, 

filtered 

(μg/L)

Cadmium, 

unfiltered 

recoverable 

(μg/L)

Copper, 

filtered 

(μg/L)

Copper, 

unfiltered 

recoverable 

(μg/L)

Iron, 

filtered 

(μg/L)

Iron, 

unfiltered 

recoverable 

(μg/L)

11/15/2010 12.7 13.0 0.06 0.08 1.1 1.6 38 86

03/14/2011 13.2 14.1 .05 .08 1.2 1.6 29 90

04/11/2011 28.2 27.3 .04 .07 1.9 2.9 32 133

05/16/2011 24.2 27.6 .05 .15 4.3 9.3 46 511

05/31/2011 32.3 32.1 .06 .09 4.0 6.7 64 261

06/13/2011 26.0 27.5 .04 .11 3.2 7.3 49 309

07/12/2011 10.5 12.4 .02 .09 1.6 4.5 25 530

08/15/2011 14.3 15.4 .03 .05 1.2 2.4 42 140

Date

Lead, 

filtered 

(μg/L)

Lead, 

unfiltered 

recoverable 

(μg/L)

Manganese, 

filtered 

(μg/L)

Manganese, 

unfiltered 

recoverable 

(μg/L)

Zinc, 

filtered 

(μg/L)

Zinc, 

unfiltered 

recoverable 

(μg/L)

Sediment, 

suspended 

(percent finer 

than 0.062 

mm)

Sediment, 

suspended 

(mg/L)

Sediment 

discharge, 

suspended 

(ton/d)

11/15/2010 0.07 0.22 5.2 7.8 1.9 2.6 55 1 0.04

03/14/2011 .05 .28 7.0 9.1 1.8 <2.4 80 1 .03

04/11/2011 .14 .42 4.9 8.6 <1.4 <2.4 83 1 .04

05/16/2011 .17 2.39 5.6 22.1 1.8 7.0 60 21 7.0

05/31/2011 .20 1.08 4.0 10.9 2.8 4.9 56 9 3.3

06/13/2011 .15 1.77 3.1 13.1 2.1 5.2 32 15 13

07/12/2011 .07 1.23 4.4 20.4 <1.4 6.2 35 26 12

08/15/2011 .10 .65 9.7 15.3 <1.4 <2.4 61 4 .36
24 Water-Quality, Bed-Sediment, and Biological Data, and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 4. Water-quality data for the Clark Fork basin, Montana, October 2010 through September 2011.—Continued

[Abbreviations: CaCO3, calcium carbonate; ft3/s, cubic feet per second; °C, degrees Celsius; E, estimated; lab, laboratory; μg/L, micrograms per liter; μS/cm, 

microsiemens per centimeter at 25°C; mg/L, milligrams per liter; mm, millimeters; NTRU, nephelometric turbidity ratio unit; ton/d, tons per day. Symbols: <, 

less than laboratory reporting level; --, no data]

12323700--Mill Creek at Opportunity

Date Time

Streamflow, 

instantaneous 

(ft3

/s)

pH, onsite 

(standard 

units)

Specific 

conductance, onsite 

(μS/cm)

Temperature, 

water 

(°C)

Hardness, 

filtered 

(mg/L as 

CaCO3

)

Calcium, 

filtered 

(mg/L)

Magnesium, 

filtered 

(mg/L)

11/15/2010 1505 9.3 7.9 196 3.5 85.8 24.0 6.31

03/14/2011 1600 7.1 7.8 222 3.0 99.4 27.7 7.36

04/12/2011 0820 11 7.9 205 2.5 87.6 23.9 6.81

05/16/2011 1520 87 7.7 97 9.0 38.5 11.0 2.70

05/31/2011 1620 113 7.9 104 10.0 41.2 11.6 2.95

06/13/2011 1425 210 7.7 80 7.5 32.6 9.35 2.25

07/12/2011 1855 159 7.5 78 11.0 32.5 9.37 2.20

08/15/2011 1520 13 8.0 155 15.0 64.5 17.8 4.85

Date

Arsenic, 

filtered 

(μg/L)

Arsenic, 

unfiltered 

recoverable 

(μg/L)

Cadmium, 

filtered 

(μg/L)

Cadmium, 

unfiltered 

recoverable 

(μg/L)

Copper, 

filtered 

(μg/L)

Copper, 

unfiltered 

recoverable 

(μg/L)

Iron, 

filtered 

(μg/L)

Iron, 

unfiltered 

recoverable 

(μg/L)

11/15/2010 17.8 17.3 0.09 0.10 1.5 2.0 38 74

03/14/2011 17.0 18.1 .06 .08 1.7 2.1 19 59

04/12/2011 21.9 24.8 .06 .09 2.2 3.3 23 107

05/16/2011 29.3 36.1 .07 .30 5.8 16.4 90 930

05/31/2011 33.9 35.8 .07 .16 4.5 10.0 60 477

06/13/2011 30.5 34.1 .06 .18 4.1 12.9 49 1,100

07/12/2011 15.3 17.8 .04 .12 2.3 7.2 28 595

08/15/2011 19.3 19.8 .05 .06 1.6 2.3 38 106

Date

Lead, 

filtered 

(μg/L)

Lead, 

unfiltered 

recoverable 

(μg/L)

Manganese, 

filtered 

(μg/L)

Manganese, 

unfiltered 

recoverable 

(μg/L)

Zinc, 

filtered 

(μg/L)

Zinc, 

unfiltered 

recoverable 

(μg/L)

Sediment, 

suspended 

(percent finer 

than 0.062 

mm)

Sediment, 

suspended 

(mg/L)

Sediment 

discharge, 

suspended 

(ton/d)

11/15/2010 0.11 0.17 2.8 4.0 4.5 4.9 67 1 0.03

03/14/2011 .06 .20 2.4 3.2 3.1 3.2 88 1 .02

04/12/2011 .07 .39 2.1 4.9 2.9 4.4 87 2 .06

05/16/2011 .35 5.77 4.8 39.3 3.1 14.6 53 40 9.4

05/31/2011 .22 2.16 4.1 17.4 2.8 8.1 55 18 5.5

06/13/2011 .19 3.97 2.8 26.0 3.0 12.4 31 56 32

07/12/2011 .11 2.04 4.5 21.6 2.0 6.3 45 38 16

08/15/2011 .11 .32 7.5 11.0 <1.4 <2.4 80 2 .07
Data 25

Table 4. Water-quality data for the Clark Fork basin, Montana, October 2010 through September 2011.—Continued

[Abbreviations: CaCO3, calcium carbonate; ft3/s, cubic feet per second; °C, degrees Celsius; E, estimated; lab, laboratory; μg/L, micrograms per liter; μS/cm, 

microsiemens per centimeter at 25°C; mg/L, milligrams per liter; mm, millimeters; NTRU, nephelometric turbidity ratio unit; ton/d, tons per day. Symbols: <, 

less than laboratory reporting level; --, no data]

12323710--Willow Creek near Anaconda

Date Time

Streamflow, 

instantaneous 

(ft3

/s)

Turbidity, 

unfiltered, 

lab 

(NTRU)

pH, onsite 

(standard 

units)

Specific 

conductance, onsite 

(μS/cm)

Temperature, 

water 

(°C)

Hardness, 

filtered 

(mg/L as 

CaCO3

)

Calcium, 

filtered 

(mg/L)

Magnesium, 

filtered 

(mg/L)

11/15/2010 1200 1.6 <2.0 7.7 133 1.5 50.4 16.5 2.21

04/11/2011 1245 4.0 E4.0 7.7 151 5.0 56.3 18.3 2.60

05/16/2011 1145 55 20 7.6 83 5.0 30.0 10.0 1.22

05/31/2011 1205 78 E11 7.6 81 5.0 30.5 10.1 1.29

06/13/2011 1150 114 E16 7.7 72 6.0 27.0 8.91 1.14

07/12/2011 1355 15 E2.1 7.7 109 12.0 42.7 14.1 1.83

08/15/2011 1200 4.1 E2.1 7.7 129 11.0 45.3 14.8 2.06

Date

Arsenic, 

filtered 

(μg/L)

Arsenic, 

unfiltered 

recoverable 

(μg/L)

Cadmium, 

filtered 

(μg/L)

Cadmium, 

unfiltered 

recoverable 

(μg/L)

Copper, 

filtered 

(μg/L)

Copper, 

unfiltered 

recoverable 

(μg/L)

Iron, 

filtered 

(μg/L)

Iron, 

unfiltered 

recoverable 

(μg/L)

11/15/2010 11.8 11.7 0.04 <0.05 1.3 1.7 55 119

04/11/2011 16.7 16.5 .02 .05 2.0 2.5 86 307

05/16/2011 23.5 26.1 .04 .15 4.2 7.7 136 1,050

05/31/2011 19.1 21.1 .05 .12 3.5 7.4 124 879

06/13/2011 19.5 23.7 .04 .22 3.3 10.8 267 2,210

07/12/2011 20.4 20.8 .03 .05 2.4 3.4 56 174

08/15/2011 23.8 23.9 .03 .05 2.4 3.4 82 203

Date

Lead, 

filtered 

(μg/L)

Lead, 

unfiltered 

recoverable 

(μg/L)

Manganese, 

filtered 

(μg/L)

Manganese, 

unfiltered 

recoverable 

(μg/L)

Zinc, 

filtered 

(μg/L)

Zinc, 

unfiltered 

recoverable 

(μg/L)

Sediment, 

suspended 

(percent finer 

than 0.062 

mm)

Sediment, 

suspended 

(mg/L)

Sediment 

discharge, 

suspended 

(ton/d)

11/15/2010 0.10 0.19 19.9 24.2 1.6 <2.4 80 2 0.01

04/11/2011 .25 .50 17.8 27.4 <1.4 <2.4 93 3 .03

05/16/2011 .36 2.72 9.1 42.5 2.6 8.3 64 41 6.1

05/31/2011 .26 2.45 7.6 40.2 2.7 6.8 46 39 8.2

06/13/2011 .26 5.72 8.8 72.1 2.2 14.0 30 161 50

07/12/2011 .14 .48 24.4 30.0 1.6 <2.4 58 8 .32

08/15/2011 .18 .49 28.2 34.7 <1.4 6.2 79 5 .06
26 Water-Quality, Bed-Sediment, and Biological Data, and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 4. Water-quality data for the Clark Fork basin, Montana, October 2010 through September 2011.—Continued

[Abbreviations: CaCO3, calcium carbonate; ft3/s, cubic feet per second; °C, degrees Celsius; E, estimated; lab, laboratory; μg/L, micrograms per liter; μS/cm, 

microsiemens per centimeter at 25°C; mg/L, milligrams per liter; mm, millimeters; NTRU, nephelometric turbidity ratio unit; ton/d, tons per day. Symbols: <, 

less than laboratory reporting level; --, no data]

12323720--Willow Creek at Opportunity

Date Time

Streamflow, 

instantaneous 

(ft3

/s)

pH, onsite 

(standard 

units)

Specific 

conductance, onsite 

(μS/cm)

Temperature, 

water 

(°C)

Hardness, 

filtered 

(mg/L as 

CaCO3

)

Calcium, 

filtered 

(mg/L)

Magnesium, 

filtered 

(mg/L)

11/15/2010 1550 8.0 8.0 302 5.5 128 37.6 8.38

03/14/2011 1700 6.8 8.1 285 5.5 124 36.3 7.99

04/12/2011 0935 8.7 7.9 287 3.5 123 35.8 8.12

05/16/2011 1550 40 7.7 146 11.0 58.5 18.1 3.24

05/31/2011 1650 62 7.7 156 11.0 62.7 19.1 3.62

06/13/2011 1505 116 7.7 167 10.0 67.8 20.5 4.03

07/12/2011 1930 17 7.8 219 14.5 91.9 27.4 5.73

08/15/2011 1555 6.5 8.1 285 16.0 117 33.2 8.25

Date

Arsenic, 

filtered 

(μg/L)

Arsenic, 

unfiltered 

recoverable 

(μg/L)

Cadmium, 

filtered 

(μg/L)

Cadmium, 

unfiltered 

recoverable 

(μg/L)

Copper, 

filtered 

(μg/L)

Copper, 

unfiltered 

recoverable 

(μg/L)

Iron, 

filtered 

(μg/L)

Iron, 

unfiltered 

recoverable 

(μg/L)

11/15/2010 19.3 23.0 0.03 0.06 1.8 6.1 25 228

03/14/2011 15.9 19.2 .03 .08 2.0 5.6 46 283

04/12/2011 16.9 21.1 .03 .06 2.3 5.8 54 284

05/16/2011 38.9 49.4 .04 .45 9.5 43.4 127 1,670

05/31/2011 47.5 49.2 .05 .16 9.1 21.1 111 594

06/13/2011 73.7 70.6 .07 .14 11.3 20.4 100 387

07/12/2011 46.6 55.1 .05 .17 3.4 8.8 274 796

08/15/2011 20.9 21.7 .03 <.05 2.3 3.4 17 139

Date

Lead, 

filtered 

(μg/L)

Lead, 

unfiltered 

recoverable 

(μg/L)

Manganese, 

filtered 

(μg/L)

Manganese, 

unfiltered 

recoverable 

(μg/L)

Zinc, 

filtered 

(μg/L)

Zinc, 

unfiltered 

recoverable 

(μg/L)

Sediment, 

suspended 

(percent finer 

than 0.062 

mm)

Sediment, 

suspended 

(mg/L)

Sediment 

discharge, 

suspended 

(ton/d)

11/15/2010 0.16 1.74 25.6 33.1 2.3 9.4 81 12 0.26

03/14/2011 .17 2.03 53.5 68.8 3.4 8.7 72 9 .17

04/12/2011 .13 1.51 57.5 70.5 4.1 9.6 80 6 .14

05/16/2011 .61 14.4 50.3 114 5.4 54.9 73 87 9.4

05/31/2011 .37 4.49 15.4 37.1 8.3 23.4 54 33 5.5

06/13/2011 .33 2.88 13.6 25.7 10.2 19.1 57 18 5.6

07/12/2011 .89 2.74 50.6 84.4 5.7 10.5 97 13 .60

08/15/2011 .11 .68 10.3 15.5 <1.4 2.9 94 3 .05
Data 27

Table 4. Water-quality data for the Clark Fork basin, Montana, October 2010 through September 2011.—Continued

[Abbreviations: CaCO3, calcium carbonate; ft3/s, cubic feet per second; °C, degrees Celsius; E, estimated; lab, laboratory; μg/L, micrograms per liter; μS/cm, 

microsiemens per centimeter at 25°C; mg/L, milligrams per liter; mm, millimeters; NTRU, nephelometric turbidity ratio unit; ton/d, tons per day. Symbols: <, 

less than laboratory reporting level; --, no data]

12323750--Silver Bow Creek at Warm Springs

Date Time

Streamflow, 

instantaneous 

(ft3

/s)

pH, onsite 

(standard 

units)

Specific 

conductance, onsite 

(μS/cm)

Temperature, 

water 

(°C)

Hardness, 

filtered 

(mg/L as 

CaCO3

)

Calcium, 

filtered 

(mg/L)

Magnesium, 

filtered 

(mg/L)

11/16/2010 0830 72 8.5 527 2.0 226 65.7 15.0

03/15/2011 0925 95 9.0 525 2.0 217 62.4 14.9

04/12/2011 1300 87 8.5 495 7.0 204 59.1 13.7

05/17/2011 0905 299 8.8 366 8.5 150 44.4 9.40

06/01/2011 0935 486 9.3 319 9.0 136 43.0 6.92

06/14/2011 0825 1,030 9.0 283 10.0 113 35.6 5.86

07/13/2011 1010 216 8.7 182 12.0 74.9 22.5 4.52

08/16/2011 0800 89 9.3 370 15.5 154 45.6 9.86

Date

Arsenic, 

filtered 

(μg/L)

Arsenic, 

unfiltered 

recoverable 

(μg/L)

Cadmium, 

filtered 

(μg/L)

Cadmium, 

unfiltered 

recoverable 

(μg/L)

Copper, 

filtered 

(μg/L)

Copper, 

unfiltered 

recoverable 

(μg/L)

Iron, 

filtered 

(μg/L)

Iron, 

unfiltered 

recoverable 

(μg/L)

11/16/2010 17.5 19.6 0.05 0.08 3.0 5.5 8 187

03/15/2011 11.3 13.6 .07 .11 4.5 6.6 8 168

04/12/2011 12.3 17.3 .03 .23 2.3 15.9 15 422

05/17/2011 24.4 26.7 .05 .13 5.3 11.3 39 331

06/01/2011 31.7 32.4 .10 .19 12.4 22.1 42 313

06/14/2011 34.2 34.7 .09 .22 21.4 35.2 57 437

07/13/2011 21.4 24.1 .03 .09 3.7 7.4 45 272

08/16/2011 38.0 37.9 .04 .05 3.7 5.6 14 89

Date

Lead, 

filtered 

(μg/L)

Lead, 

unfiltered 

recoverable 

(μg/L)

Manganese, 

filtered 

(μg/L)

Manganese, 

unfiltered 

recoverable 

(μg/L)

Zinc, 

filtered 

(μg/L)

Zinc, 

unfiltered 

recoverable 

(μg/L)

Sediment, 

suspended 

(percent finer 

than 0.062 

mm)

Sediment, 

suspended 

(mg/L)

Sediment 

discharge, 

suspended 

(ton/d)

11/16/2010 0.05 0.85 87.6 138 3.0 9.7 88 4 0.78

03/15/2011 .06 1.18 67.4 106 4.3 11.8 85 3 .77

04/12/2011 .10 4.13 133 205 2.3 29.0 98 9 2.1

05/17/2011 .19 1.98 60.6 98.9 2.6 14.1 87 9 7.3

06/01/2011 .33 2.68 31.5 64.9 4.3 26.2 93 5 6.6

06/14/2011 .57 4.92 38.5 77.3 6.1 34.4 86 9 25

07/13/2011 .18 1.27 34.3 62.8 2.1 7.1 91 7 4.1

08/16/2011 .08 .55 42.3 60.3 <1.4 4.0 60 2 .48
28 Water-Quality, Bed-Sediment, and Biological Data, and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 4. Water-quality data for the Clark Fork basin, Montana, October 2010 through September 2011.—Continued

[Abbreviations: CaCO3, calcium carbonate; ft3/s, cubic feet per second; °C, degrees Celsius; E, estimated; lab, laboratory; μg/L, micrograms per liter; μS/cm, 

microsiemens per centimeter at 25°C; mg/L, milligrams per liter; mm, millimeters; NTRU, nephelometric turbidity ratio unit; ton/d, tons per day. Symbols: <, 

less than laboratory reporting level; --, no data]

12323760--Warm Springs Creek near Anaconda

Date Time

Streamflow, 

instantaneous 

(ft3

/s)

Turbidity, 

unfiltered, 

lab 

(NTRU)

pH, onsite 

(standard 

units)

Specific 

conductance, onsite 

(μS/cm)

Temperature, 

water 

(°C)

Hardness, 

filtered 

(mg/L as 

CaCO3

)

Calcium, 

filtered 

(mg/L)

Magnesium, 

filtered 

(mg/L)

11/15/2010 1425 85 <2.0 8.4 253 4.0 124 37.0 7.79

04/11/2011 1640 64 <2.0 8.8 268 9.0 134 38.8 9.07

05/16/2011 1415 153 E5.1 8.4 202 8.0 105 32.0 6.18

05/31/2011 1515 221 <2.0 8.2 213 9.0 98.7 29.9 5.86

07/12/2011 1720 495 E2.2 7.8 147 11.0 68.5 21.1 3.87

08/15/2011 1415 186 <2.0 8.6 220 11.0 102 30.3 6.41

Date

Arsenic, 

filtered 

(μg/L)

Arsenic, 

unfiltered 

recoverable 

(μg/L)

Cadmium, 

filtered 

(μg/L)

Cadmium, 

unfiltered 

recoverable 

(μg/L)

Copper, 

filtered 

(μg/L)

Copper, 

unfiltered 

recoverable 

(μg/L)

Iron, 

filtered 

(μg/L)

Iron, 

unfiltered 

recoverable 

(μg/L)

11/15/2010 2.0 2.1 0.02 <.05 0.58 1.1 4 27

04/11/2011 2.6 3.0 <.02 <.05 .56 1.3 6 36

05/16/2011 2.5 3.7 .02 .06 2.0 7.7 22 366

05/31/2011 3.5 4.3 .02 <.05 1.5 3.5 11 140

07/12/2011 3.9 4.5 .05 .06 6.4 10.3 8 109

08/15/2011 3.1 3.2 .03 <.05 .85 2.5 4 80

Date

Lead, 

filtered 

(μg/L)

Lead, 

unfiltered 

recoverable 

(μg/L)

Manganese, 

filtered 

(μg/L)

Manganese, 

unfiltered 

recoverable 

(μg/L)

Zinc, 

filtered 

(μg/L)

Zinc, 

unfiltered 

recoverable 

(μg/L)

Sediment, 

suspended 

(percent finer 

than 0.062 

mm)

Sediment, 

suspended 

(mg/L)

Sediment 

discharge, 

suspended 

(ton/d)

11/15/2010 <.01 0.07 0.5 1.3 <1.4 <2.4 69 1 0.23

04/11/2011 <.01 .12 <.1 2.0 <1.4 <2.4 42 17 2.9

05/16/2011 .04 1.00 2.0 14.9 <1.4 6.9 66 19 7.8

05/31/2011 .03 .38 1.4 6.0 <1.4 3.1 61 7 4.2

07/12/2011 .03 .42 2.3 7.3 5.6 7.5 65 6 8.0

08/15/2011 .02 .20 1.5 4.2 <1.4 <2.4 67 3 1.5
Data 29

Table 4. Water-quality data for the Clark Fork basin, Montana, October 2010 through September 2011.—Continued

[Abbreviations: CaCO3, calcium carbonate; ft3/s, cubic feet per second; °C, degrees Celsius; E, estimated; lab, laboratory; μg/L, micrograms per liter; μS/cm, 

microsiemens per centimeter at 25°C; mg/L, milligrams per liter; mm, millimeters; NTRU, nephelometric turbidity ratio unit; ton/d, tons per day. Symbols: <, 

less than laboratory reporting level; --, no data]

12323770--Warm Springs Creek at Warm Springs

Date Time

Streamflow, 

instantaneous 

(ft3

/s)

pH, onsite 

(standard 

units)

Specific 

conductance, onsite 

(μS/cm)

Temperature, 

water 

(°C)

Hardness, 

filtered 

(mg/L as 

CaCO3

)

Calcium, 

filtered 

(mg/L)

Magnesium, 

filtered 

(mg/L)

11/16/2010 0805 76 8.2 299 3.0 145 43.8 8.66

04/12/2011 1205 56 8.3 328 5.0 165 48.6 10.5

05/17/2011 0830 145 8.1 234 5.0 114 34.8 6.59

06/01/2011 0845 193 8.1 227 6.0 111 33.6 6.51

07/13/2011 0915 414 7.9 172 10.0 79.0 24.3 4.43

08/16/2011 0735 134 8.0 255 9.0 117 34.9 7.16

Date

Arsenic, 

filtered 

(μg/L)

Arsenic, 

unfiltered 

recoverable 

(μg/L)

Cadmium, 

filtered 

(μg/L)

Cadmium, 

unfiltered 

recoverable 

(μg/L)

Copper, 

filtered 

(μg/L)

Copper, 

unfiltered 

recoverable 

(μg/L)

Iron, 

filtered 

(μg/L)

Iron, 

unfiltered 

recoverable 

(μg/L)

11/16/2010 2.8 3.5 0.04 <.05 1.2 6.0 9 119

04/12/2011 3.0 3.7 .03 <.05 1.3 4.1 9 67

05/17/2011 3.3 6.0 .03 .10 2.6 23.8 20 562

06/01/2011 3.8 6.1 .03 .05 2.4 13.2 13 259

07/13/2011 10.8 13.1 .05 .09 6.6 22.0 14 453

08/16/2011 4.7 5.8 .04 .06 1.9 13.7 10 219

Date

Lead, 

filtered 

(μg/L)

Lead, 

unfiltered 

recoverable 

(μg/L)

Manganese, 

filtered 

(μg/L)

Manganese, 

unfiltered 

recoverable 

(μg/L)

Zinc, 

filtered 

(μg/L)

Zinc, 

unfiltered 

recoverable 

(μg/L)

Sediment, 

suspended 

(percent finer 

than 0.062 

mm)

Sediment, 

suspended 

(mg/L)

Sediment 

discharge, 

suspended 

(ton/d)

11/16/2010 0.03 0.56 57.1 76.8 1.6 3.4 63 6 1.2

04/12/2011 .02 .32 64.7 78.2 <1.4 <2.4 63 2 .30

05/17/2011 .05 2.60 25.8 88.3 <1.4 11.9 55 34 13

06/01/2011 .03 1.29 18.8 39.2 <1.4 5.9 59 14 7.3

07/13/2011 .05 1.61 23.3 42.4 4.5 9.8 70 22 25

08/16/2011 .03 1.01 42.5 58.6 1.5 5.8 60 14 5.1
30 Water-Quality, Bed-Sediment, and Biological Data, and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 4. Water-quality data for the Clark Fork basin, Montana, October 2010 through September 2011.—Continued

[Abbreviations: CaCO3, calcium carbonate; ft3/s, cubic feet per second; °C, degrees Celsius; E, estimated; lab, laboratory; μg/L, micrograms per liter; μS/cm, 

microsiemens per centimeter at 25°C; mg/L, milligrams per liter; mm, millimeters; NTRU, nephelometric turbidity ratio unit; ton/d, tons per day. Symbols: <, 

less than laboratory reporting level; --, no data]

12323800--Clark Fork near Galen

Date Time

Streamflow, 

instantaneous 

(ft3

/s)

pH, onsite 

(standard 

units)

Specific 

conductance, onsite 

(μS/cm)

Temperature, 

water 

(°C)

Hardness, 

filtered 

(mg/L as 

CaCO3

)

Calcium, 

filtered 

(mg/L)

Magnesium, 

filtered 

(mg/L)

11/16/2010 1000 162 8.3 417 2.5 190 56.3 12.0

03/15/2011 1110 172 8.7 452 2.5 197 57.7 13.0

04/12/2011 1450 155 8.6 435 8.0 198 58.2 12.8

05/17/2011 1045 445 8.6 323 9.5 143 42.7 8.82

*05/25/2011 1230 873 8.9 300 10.5 133 40.1 7.92

06/01/2011 1105 664 9.1 294 10.0 129 40.5 6.87

*06/08/2011 1145 1,110 8.8 249 9.0 106 32.6 5.83

06/14/2011 1020 1,380 8.7 278 10.5 115 36.0 6.19

*06/24/2011 1030 1,210 8.9 227 10.0 99.3 30.8 5.44

*06/29/2011 1100 1,130 8.9 228 13.5 103 32.1 5.52

07/13/2011 1240 628 8.2 182 12.0 76.4 23.2 4.44

08/16/2011 0935 215 8.7 305 12.0 136 40.5 8.49

Date

Arsenic, 

filtered 

(μg/L)

Arsenic, 

unfiltered 

recoverable 

(μg/L)

Cadmium, 

filtered 

(μg/L)

Cadmium, 

unfiltered 

recoverable 

(μg/L)

Copper, 

filtered 

(μg/L)

Copper, 

unfiltered 

recoverable 

(μg/L)

Iron, 

filtered 

(μg/L)

Iron, 

unfiltered 

recoverable 

(μg/L)

11/16/2010 9.8 11.1 0.04 0.08 2.5 6.4 10 153

03/15/2011 8.2 10.8 .05 .11 3.7 10.4 8 210

04/12/2011 8.7 12.6 .03 .16 2.5 15.3 9 330

05/17/2011 18.1 23.5 .05 .23 5.1 33.6 28 728

*05/25/2011 29.5 39.0 .08 .36 11.2 75.2 60 1,480

06/01/2011 23.8 26.8 .07 .20 9.7 32.0 29 493

*06/08/2011 28.2 36.1 .13 .38 20.7 82.1 47 1,120

06/14/2011 27.5 31.5 .11 .29 19.8 51.6 41 629

*06/24/2011 26.6 27.7 .10 .21 18.0 40.0 38 576

*06/29/2011 24.7 25.5 .09 .20 12.9 32.2 33 461

07/13/2011 14.9 17.8 .04 .10 5.9 21.9 22 415

08/16/2011 18.2 18.9 .04 .07 3.6 11.2 11 160
Data 31

12323800--Clark Fork near Galen

Date

Lead, 

filtered 

(μg/L)

Lead, 

unfiltered 

recoverable 

(μg/L)

Manganese, 

filtered 

(μg/L)

Manganese, 

unfiltered 

recoverable 

(μg/L)

Zinc, 

filtered 

(μg/L)

Zinc, 

unfiltered 

recoverable 

(μg/L)

Sediment, 

suspended 

(percent finer 

than 0.062 

mm)

Sediment, 

suspended 

(mg/L)

Sediment 

discharge, 

suspended 

(ton/d)

11/16/2010 0.04 0.79 60.9 93.5 2.5 7.1 35 11 4.8

03/15/2011 .04 1.45 55.8 99.8 3.2 11.9 75 9 4.2

04/12/2011 .07 3.01 86.3 150 2.6 20.3 87 8 3.3

05/17/2011 .13 4.56 42.0 123 1.9 27.9 53 37 44

*05/25/2011 .36 10.3 47.6 173 11.0 55.8 55 74 174

06/01/2011 .23 3.92 26.5 85.8 3.1 29.6 51 19 34

*06/08/2011 .30 9.10 31.9 121 13.7 60.9 48 59 177

06/14/2011 .39 6.33 30.7 81.2 9.4 45.1 32 40 149

*06/24/2011 .33 4.00 31.1 74.2 10.4 30.5 69 24 78

*06/29/2011 .25 3.23 29.8 64.9 5.8 25.6 66 19 58

07/13/2011 .10 2.09 27.7 60.5 2.6 12.6 67 20 34

08/16/2011 .06 1.11 39.8 59.4 <1.4 7.9 76 6 3.5

Table 4. Water-quality data for the Clark Fork basin, Montana, October 2010 through September 2011.—Continued

[Abbreviations: CaCO3, calcium carbonate; ft3/s, cubic feet per second; °C, degrees Celsius; E, estimated; lab, laboratory; μg/L, micrograms per liter; μS/cm, 

microsiemens per centimeter at 25°C; mg/L, milligrams per liter; mm, millimeters; NTRU, nephelometric turbidity ratio unit; ton/d, tons per day. Symbols: <, 

less than laboratory reporting level; --, no data]
32 Water-Quality, Bed-Sediment, and Biological Data, and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 4. Water-quality data for the Clark Fork basin, Montana, October 2010 through September 2011.—Continued

[Abbreviations: CaCO3, calcium carbonate; ft3/s, cubic feet per second; °C, degrees Celsius; E, estimated; lab, laboratory; μg/L, micrograms per liter; μS/cm, 

microsiemens per centimeter at 25°C; mg/L, milligrams per liter; mm, millimeters; NTRU, nephelometric turbidity ratio unit; ton/d, tons per day. Symbols: <, 

less than laboratory reporting level; --, no data]

12323840--Lost Creek near Anaconda

Date Time

Streamflow, 

instantaneous 

(ft3

/s)

Turbidity, 

unfiltered, 

lab 

(NTRU)

pH, onsite 

(standard 

units)

Specific 

conductance, onsite 

(μS/cm)

Temperature, 

water 

(°C)

Hardness, 

filtered 

(mg/L as 

CaCO3

)

Calcium, 

filtered 

(mg/L)

Magnesium, 

filtered 

(mg/L)

11/15/2010 1335 8.0 <2.0 8.2 214 3.0 105 31.5 6.29

03/14/2011 1450 6.4 E3.5 7.8 223 4.0 109 32.6 6.77

04/11/2011 1510 6.9 <2.0 8.3 226 7.0 111 32.6 7.09

05/16/2011 1345 26 E7.0 7.9 153 7.5 78.2 24.0 4.42

05/31/2011 1400 31 E3.5 8.1 170 7.0 82.2 25.3 4.61

06/13/2011 1330 73 E7.1 7.8 133 6.0 63.8 19.8 3.46

07/12/2011 1600 46 E3.4 8.0 160 11.0 71.4 22.0 4.01

08/15/2011 1330 25 <2.0 8.1 210 10.0 96.4 28.9 5.87

Date

Arsenic, 

filtered 

(μg/L)

Arsenic, 

unfiltered 

recoverable 

(μg/L)

Cadmium, 

filtered 

(μg/L)

Cadmium, 

unfiltered 

recoverable 

(μg/L)

Copper, 

filtered 

(μg/L)

Copper, 

unfiltered 

recoverable 

(μg/L)

Iron, 

filtered 

(μg/L)

Iron, 

unfiltered 

recoverable 

(μg/L)

11/15/2010 2.1 2.3 0.02 <0.05 0.80 1.3 6 28

03/14/2011 3.1 4.8 .03 .06 2.5 8.2 7 205

04/11/2011 2.6 3.3 .02 <.05 1.4 4.6 7 115

05/16/2011 3.6 5.9 .02 .11 2.9 22.8 27 772

05/31/2011 2.9 4.6 .02 .05 1.7 8.7 12 434

06/13/2011 4.3 6.0 .02 .08 2.2 12.8 23 637

07/12/2011 4.0 5.3 <.02 .05 1.5 9.3 11 466

08/15/2011 2.8 2.9 .02 <.05 .86 2.6 10 116

Date

Lead, 

filtered 

(μg/L)

Lead, 

unfiltered 

recoverable 

(μg/L)

Manganese, 

filtered 

(μg/L)

Manganese, 

unfiltered 

recoverable 

(μg/L)

Zinc, 

filtered 

(μg/L)

Zinc, 

unfiltered 

recoverable 

(μg/L)

Sediment, 

suspended 

(percent finer 

than 0.062 

mm)

Sediment, 

suspended 

(mg/L)

Sediment 

discharge, 

suspended 

(ton/d)

11/15/2010 0.02 0.08 0.5 1.2 <1.4 <2.4 50 1 0.02

03/14/2011 .03 .86 .8 5.9 <1.4 3.2 86 9 .16

04/11/2011 .02 .48 .8 3.9 <1.4 <2.4 80 6 .11

05/16/2011 .08 3.10 1.8 22.2 1.5 11.3 51 47 3.3

05/31/2011 .04 2.12 1.4 14.2 <1.4 5.5 24 33 2.8

06/13/2011 .06 2.42 1.8 17.3 <1.4 7.0 39 45 8.9

07/12/2011 .03 1.71 2.2 13.0 <1.4 5.1 40 26 3.2

08/15/2011 .02 .36 2.1 5.4 -- -- 49 7 .47
Data 33

Table 4. Water-quality data for the Clark Fork basin, Montana, October 2010 through September 2011.—Continued

[Abbreviations: CaCO3, calcium carbonate; ft3/s, cubic feet per second; °C, degrees Celsius; E, estimated; lab, laboratory; μg/L, micrograms per liter; μS/cm, 

microsiemens per centimeter at 25°C; mg/L, milligrams per liter; mm, millimeters; NTRU, nephelometric turbidity ratio unit; ton/d, tons per day. Symbols: <, 

less than laboratory reporting level; --, no data]

12323850--Lost Creek near Galen

Date Time

Streamflow, 

instantaneous 

(ft3

/s)

pH, onsite 

(standard 

units)

Specific 

conductance, onsite 

(μS/cm)

Temperature, 

water 

(°C)

Hardness, 

filtered 

(mg/L as 

CaCO3

)

Calcium, 

filtered 

(mg/L)

Magnesium, 

filtered 

(mg/L)

11/16/2010 0925 46 8.2 626 3.5 304 89.0 19.8

03/15/2011 1030 48 8.2 574 2.0 289 84.6 18.9

04/12/2011 1405 52 8.3 598 8.0 294 85.3 19.8

05/17/2011 1005 18 8.2 677 8.0 362 106 23.6

06/01/2011 1030 34 8.3 556 9.0 272 79.0 18.2

06/14/2011 0925 59 8.1 645 9.0 311 88.9 21.6

07/13/2011 1135 18 8.3 652 15.5 306 87.7 21.0

08/16/2011 0910 8.9 8.0 632 11.0 299 85.3 20.8

Date

Arsenic, 

filtered 

(μg/L)

Arsenic, 

unfiltered 

recoverable 

(μg/L)

Cadmium, 

filtered 

(μg/L)

Cadmium, 

unfiltered 

recoverable 

(μg/L)

Copper, 

filtered 

(μg/L)

Copper, 

unfiltered 

recoverable 

(μg/L)

Iron, 

filtered 

(μg/L)

Iron, 

unfiltered 

recoverable 

(μg/L)

11/16/2010 11.9 12.9 0.02 <0.05 1.3 2.8 7 67

03/15/2011 10.1 12.3 .02 .05 1.4 4.3 10 138

04/12/2011 10.5 13.1 .02 <.05 1.3 5.5 8 159

05/17/2011 11.1 12.6 .02 <.05 1.1 3.7 10 119

06/01/2011 12.7 14.4 .02 <.05 1.4 4.1 12 99

06/14/2011 30.8 30.2 .03 <.05 2.9 5.7 25 89

07/13/2011 23.1 25.3 .02 <.05 2.0 4.1 15 80

08/16/2011 19.0 18.8 .03 <.05 1.7 3.2 7 49

Date

Lead, 

filtered 

(μg/L)

Lead, 

unfiltered 

recoverable 

(μg/L)

Manganese, 

filtered 

(μg/L)

Manganese, 

unfiltered 

recoverable 

(μg/L)

Zinc, 

filtered 

(μg/L)

Zinc, 

unfiltered 

recoverable 

(μg/L)

Sediment, 

suspended 

(percent finer 

than 0.062 

mm)

Sediment, 

suspended 

(mg/L)

Sediment 

discharge, 

suspended 

(ton/d)

11/16/2010 0.03 0.24 5.7 8.9 2.0 3.2 44 25 3.1

03/15/2011 .05 .57 16.4 23.1 2.6 3.8 75 19 2.5

04/12/2011 .03 .66 16.1 27.1 <1.4 3.8 70 9 1.3

05/17/2011 .03 .41 24.1 34.1 <1.4 2.6 51 14 .68

06/01/2011 .03 .36 14.2 20.3 <1.4 2.5 81 8 .73

06/14/2011 .05 .31 17.1 21.4 2.1 2.9 80 3 .48

07/13/2011 .02 .22 11.0 17.9 <1.4 <2.4 75 17 .83

08/16/2011 .02 .15 8.5 10.7 <1.4 <2.4 41 23 .55
34 Water-Quality, Bed-Sediment, and Biological Data, and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 4. Water-quality data for the Clark Fork basin, Montana, October 2010 through September 2011.—Continued

[Abbreviations: CaCO3, calcium carbonate; ft3/s, cubic feet per second; °C, degrees Celsius; E, estimated; lab, laboratory; μg/L, micrograms per liter; μS/cm, 

microsiemens per centimeter at 25°C; mg/L, milligrams per liter; mm, millimeters; NTRU, nephelometric turbidity ratio unit; ton/d, tons per day. Symbols: <, 

less than laboratory reporting level; --, no data]

12324200--Clark Fork at Deer Lodge

Date Time

Streamflow, 

instantaneous 

(ft3

/s)

pH, onsite 

(standard 

units)

Specific 

conductance, onsite 

(μS/cm)

Temperature, 

water 

(°C)

Hardness, 

filtered 

(mg/L as 

CaCO3

)

Calcium, 

filtered 

(mg/L)

Magnesium, 

filtered 

(mg/L)

11/16/2010 1110 316 8.2 461 3.0 205 60.7 13.0

03/15/2011 1335 282 8.4 462 4.0 211 61.9 13.6

04/13/2011 0835 286 8.1 470 6.0 208 60.9 13.6

05/17/2011 1225 619 8.1 331 12.0 138 41.1 8.53

*05/25/2011 1430 1,290 8.1 330 11.0 142 42.2 8.80

06/01/2011 1250 907 8.5 327 10.0 141 43.1 8.09

*06/08/2011 1330 1,480 7.9 299 10.0 126 37.8 7.55

06/14/2011 1235 2,000 7.9 357 10.0 145 43.6 8.88

*06/24/2011 1130 1,570 8.2 269 12.0 115 34.9 6.69

*06/29/2011 1245 1,500 8.2 261 15.0 115 35.3 6.55

07/13/2011 1600 1,020 7.9 228 15.0 97.1 29.1 5.92

08/16/2011 1135 250 8.1 373 10.0 159 47.1 10.1

Date

Arsenic, 

filtered 

(μg/L)

Arsenic, 

unfiltered 

recoverable 

(μg/L)

Cadmium, 

filtered 

(μg/L)

Cadmium, 

unfiltered 

recoverable 

(μg/L)

Copper, 

filtered 

(μg/L)

Copper, 

unfiltered 

recoverable 

(μg/L)

Iron, 

filtered 

(μg/L)

Iron, 

unfiltered 

recoverable 

(μg/L)

11/16/2010 8.7 10.8 0.05 0.10 4.4 15.2 7 294

03/15/2011 8.8 13.4 .07 .17 6.2 32.2 8 555

04/13/2011 9.3 15.0 .07 .20 5.2 36.5 13 600

05/17/2011 16.8 35.6 .07 .62 10.2 136 27 2,620

*05/25/2011 25.7 73.2 .14 1.28 29.2 377 56 5,780

06/01/2011 23.4 34.7 .09 .39 14.7 97.6 27 1,440

*06/08/2011 25.8 51.6 .21 .88 44.1 232 67 3,340

06/14/2011 36.6 46.6 .28 .50 45.9 120 46 1,220

*06/24/2011 32.9 37.8 .22 .36 35.6 87.6 36 976

*06/29/2011 29.3 33.7 .18 .31 25.4 70.9 58 920

07/13/2011 19.4 33.3 .10 .36 14.4 103 34 1,780

08/16/2011 18.7 20.0 .09 .12 7.4 21.0 9 244
Data 35

Table 4. Water-quality data for the Clark Fork basin, Montana, October 2010 through September 2011.—Continued

[Abbreviations: CaCO3, calcium carbonate; ft3/s, cubic feet per second; °C, degrees Celsius; E, estimated; lab, laboratory; μg/L, micrograms per liter; μS/cm, 

microsiemens per centimeter at 25°C; mg/L, milligrams per liter; mm, millimeters; NTRU, nephelometric turbidity ratio unit; ton/d, tons per day. Symbols: <, 

less than laboratory reporting level; --, no data]

12324200--Clark Fork at Deer Lodge

Date

Lead, 

filtered 

(μg/L)

Lead, 

unfiltered 

recoverable 

(μg/L)

Manganese, 

filtered 

(μg/L)

Manganese, 

unfiltered 

recoverable 

(μg/L)

Zinc, 

filtered 

(μg/L)

Zinc, 

unfiltered 

recoverable 

(μg/L)

Sediment, 

suspended 

(percent finer 

than 0.062 

mm)

Sediment, 

suspended 

(mg/L)

Sediment 

discharge, 

suspended 

(ton/d)

11/16/2010 0.04 2.60 25.6 57.9 6.6 17.7 80 10 8.5

03/15/2011 .06 4.88 36.2 82.6 5.5 27.2 75 25 19

04/13/2011 .08 5.40 38.5 111 7.4 34.2 81 23 18

05/17/2011 .23 20.0 22.8 263 5.7 107 49 162 271

*05/25/2011 .55 54.1 63.0 430 16.6 254 42 440 1,530

06/01/2011 .25 12.5 21.9 146 5.5 70.3 39 92 225

*06/08/2011 .41 30.5 65.4 266 36.6 183 52 186 743

06/14/2011 .37 12.4 39.1 107 50.6 107 62 53 286

*06/24/2011 .40 8.98 54.9 102 36.3 71.1 36 70 297

*06/29/2011 .47 7.51 49.6 95.2 20.2 54.5 53 51 207

07/13/2011 .23 13.7 46.1 141 8.7 66.6 70 77 212

08/16/2011 .08 1.95 31.1 59.1 6.6 17.8 84 9 6.1
36 Water-Quality, Bed-Sediment, and Biological Data, and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 4. Water-quality data for the Clark Fork basin, Montana, October 2010 through September 2011.—Continued

[Abbreviations: CaCO3, calcium carbonate; ft3/s, cubic feet per second; °C, degrees Celsius; E, estimated; lab, laboratory; μg/L, micrograms per liter; μS/cm, 

microsiemens per centimeter at 25°C; mg/L, milligrams per liter; mm, millimeters; NTRU, nephelometric turbidity ratio unit; ton/d, tons per day. Symbols: <, 

less than laboratory reporting level; --, no data]

12324400--Clark Fork above Little Blackfoot River, near Garrison

Date Time

Streamflow, 

instantaneous 

(ft3

/s)

pH, onsite 

(standard 

units)

Specific 

conductance, onsite 

(μS/cm)

Temperature, 

water 

(°C)

Hardness, 

filtered 

(mg/L as 

CaCO3

)

Calcium, 

filtered 

(mg/L)

Magnesium, 

filtered 

(mg/L)

11/16/2010 1240 353 8.3 459 3.0 210 61.9 13.5

03/15/2011 1500 322 8.8 455 4.0 206 60.5 13.2

04/13/2011 1010 315 8.2 471 6.5 202 58.8 13.5

05/17/2011 1435 726 8.1 320 12.0 135 40.1 8.54

*05/25/2011 1600 1,400 8.1 312 10.0 136 40.5 8.59

06/01/2011 1440 973 8.4 331 11.0 141 42.7 8.26

*06/08/2011 1515 2,110 7.8 276 9.0 114 33.7 7.34

06/14/2011 1430 2,310 7.9 361 14.5 148 43.5 9.47

*06/24/2011 1330 1,930 8.1 279 14.5 119 35.4 7.37

*06/29/2011 1450 1,710 8.1 272 14.0 118 35.8 7.00

07/13/2011 1815 1,130 8.0 249 16.0 107 31.9 6.65

08/16/2011 1345 284 8.3 386 17.5 160 46.9 10.4

Date

Arsenic, 

filtered 

(μg/L)

Arsenic, 

unfiltered 

recoverable 

(μg/L)

Cadmium, 

filtered 

(μg/L)

Cadmium, 

unfiltered 

recoverable 

(μg/L)

Copper, 

filtered 

(μg/L)

Copper, 

unfiltered 

recoverable 

(μg/L)

Iron, 

filtered 

(μg/L)

Iron, 

unfiltered 

recoverable 

(μg/L)

11/16/2010 9.2 11.7 0.04 0.22 4.2 24.3 5 414

03/15/2011 9.3 13.3 .06 .17 6.8 31.9 6 586

04/13/2011 9.3 15.8 .07 .23 6.1 46.2 11 731

05/17/2011 16.9 39.5 .08 .73 11.5 187 28 3,200

*05/25/2011 24.1 78.9 .15 1.51 29.4 448 49 6,360

06/01/2011 23.1 37.8 .10 .52 16.4 129 26 1,990

*06/08/2011 24.8 52.6 .17 .86 38.8 227 210 4,770

06/14/2011 36.7 46.0 .23 .45 40.6 103 43 1,330

*06/24/2011 34.4 50.9 .20 .39 36.2 103 46 1,400

*06/29/2011 30.6 38.7 .19 .42 27.7 94.2 38 1,230

07/13/2011 20.4 30.8 .12 .34 14.8 83.5 30 1,310

08/16/2011 19.4 20.7 .10 .14 9.1 21.8 8 241
Data 37

12324400--Clark Fork above Little Blackfoot River, near Garrison

Date

Lead, 

filtered 

(μg/L)

Lead, 

unfiltered 

recoverable 

(μg/L)

Manganese, 

filtered 

(μg/L)

Manganese, 

unfiltered 

recoverable 

(μg/L)

Zinc, 

filtered 

(μg/L)

Zinc, 

unfiltered 

recoverable 

(μg/L)

Sediment, 

suspended 

(percent finer 

than 0.062 

mm)

Sediment, 

suspended 

(mg/L)

Sediment 

discharge, 

suspended 

(ton/d)

11/16/2010 0.05 3.03 22.6 82.3 5.8 26.7 80 17 16

03/15/2011 .07 4.16 35.3 81.5 3.7 28.8 74 30 26

04/13/2011 .08 6.42 35.6 117 6.7 41.2 85 30 26

05/17/2011 .28 26.7 21.0 298 7.0 148 72 152 298

*05/25/2011 .58 63.0 49.4 458 20.1 311 60 365 1,380

06/01/2011 .30 17.9 18.5 191 7.1 99.5 46 108 284

*06/08/2011 1.19 33.7 46.0 310 24.9 198 49 244 1,390

06/14/2011 .34 10.8 28.1 99.0 37.1 93.9 55 65 405

*06/24/2011 .40 10.8 51.5 120 28.0 78.6 51 74 386

*06/29/2011 .35 10.8 49.9 126 20.6 77.1 57 59 272

07/13/2011 .27 10.7 45.4 129 9.6 63.7 67 56 171

08/16/2011 .07 1.90 29.6 66.6 5.4 18.2 75 10 7.7

Table 4. Water-quality data for the Clark Fork basin, Montana, October 2010 through September 2011.—Continued

[Abbreviations: CaCO3, calcium carbonate; ft3/s, cubic feet per second; °C, degrees Celsius; E, estimated; lab, laboratory; μg/L, micrograms per liter; μS/cm, 

microsiemens per centimeter at 25°C; mg/L, milligrams per liter; mm, millimeters; NTRU, nephelometric turbidity ratio unit; ton/d, tons per day. Symbols: <, 

less than laboratory reporting level; --, no data]
38 Water-Quality, Bed-Sediment, and Biological Data, and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 4. Water-quality data for the Clark Fork basin, Montana, October 2010 through September 2011.—Continued

[Abbreviations: CaCO3, calcium carbonate; ft3/s, cubic feet per second; °C, degrees Celsius; E, estimated; lab, laboratory; μg/L, micrograms per liter; μS/cm, 

microsiemens per centimeter at 25°C; mg/L, milligrams per liter; mm, millimeters; NTRU, nephelometric turbidity ratio unit; ton/d, tons per day. Symbols: <, 

less than laboratory reporting level; --, no data]

12324680--Clark Fork at Goldcreek

Date Time

Streamflow, 

instantaneous 

(ft3

/s)

pH, onsite 

(standard 

units)

Specific 

conductance, onsite 

(μS/cm)

Temperature, 

water 

(°C)

Hardness, 

filtered 

(mg/L as 

CaCO3

)

Calcium, 

filtered 

(mg/L)

Magnesium, 

filtered 

(mg/L)

11/16/2010 1345 549 8.4 410 3.0 185 55.1 11.4

03/16/2011 0840 723 8.1 379 2.5 166 49.4 10.4

04/13/2011 1110 622 8.3 392 6.0 176 51.6 11.5

05/17/2011 1610 2,240 8.0 224 10.5 104 30.6 6.62

06/01/2011 1550 2,400 8.1 250 12.0 106 31.9 6.53

06/14/2011 1545 4,450 7.9 285 13.0 121 35.7 7.66

07/14/2011 0810 1,890 7.9 253 14.0 110 32.8 6.77

08/16/2011 1450 464 8.3 366 12.5 153 45.3 9.71

Date

Arsenic, 

filtered 

(μg/L)

Arsenic, 

unfiltered 

recoverable 

(μg/L)

Cadmium, 

filtered 

(μg/L)

Cadmium, 

unfiltered 

recoverable 

(μg/L)

Copper, 

filtered 

(μg/L)

Copper, 

unfiltered 

recoverable 

(μg/L)

Iron, 

filtered 

(μg/L)

Iron, 

unfiltered 

recoverable 

(μg/L)

11/16/2010 7.2 8.9 0.03 0.14 3.0 15.2 4 273

03/16/2011 7.1 14.0 .06 .28 7.1 53.2 17 1,290

04/13/2011 6.9 10.8 .04 .14 4.6 28.2 17 594

05/17/2011 8.9 22.9 .04 .38 6.8 78.6 94 2,850

06/01/2011 12.7 20.2 .06 .45 9.8 78.9 52 1,400

06/14/2011 22.5 28.4 .12 .32 23.3 64.8 62 1,620

07/14/2011 16.1 26.8 .10 .33 14.1 79.9 33 1,490

08/16/2011 14.0 14.5 .07 .09 6.4 13.2 <3 160

Date

Lead, 

filtered 

(μg/L)

Lead, 

unfiltered 

recoverable 

(μg/L)

Manganese, 

filtered 

(μg/L)

Manganese, 

unfiltered 

recoverable 

(μg/L)

Zinc, 

filtered 

(μg/L)

Zinc, 

unfiltered 

recoverable 

(μg/L)

Sediment, 

suspended 

(percent finer 

than 0.062 

mm)

Sediment, 

suspended 

(mg/L)

Sediment 

discharge, 

suspended 

(ton/d)

11/16/2010 0.03 1.89 12.6 58.9 3.5 17.0 85 11 16

03/16/2011 .08 7.70 32.8 127 7.3 54.1 74 77 150

04/13/2011 .07 3.93 19.3 82.2 3.8 26.5 77 26 44

05/17/2011 .40 15.0 14.0 197 4.9 79.0 59 162 980

06/01/2011 .27 8.26 16.3 149 6.0 66.5 63 69 447

06/14/2011 .30 8.81 24.0 121 17.7 69.0 63 84 1,010

07/14/2011 .20 10.5 35.1 134 10.2 63.0 56 80 408

08/16/2011 .04 1.08 17.3 45.3 3.7 11.1 83 8 10
Data 39

Table 4. Water-quality data for the Clark Fork basin, Montana, October 2010 through September 2011.—Continued

[Abbreviations: CaCO3, calcium carbonate; ft3/s, cubic feet per second; °C, degrees Celsius; E, estimated; lab, laboratory; μg/L, micrograms per liter; μS/cm, 

microsiemens per centimeter at 25°C; mg/L, milligrams per liter; mm, millimeters; NTRU, nephelometric turbidity ratio unit; ton/d, tons per day. Symbols: <, 

less than laboratory reporting level; --, no data]

12331800--Clark Fork near Drummond

Date Time

Streamflow, 

instantaneous 

(ft3

/s)

pH, onsite 

(standard 

units)

Specific 

conductance, onsite 

(μS/cm)

Temperature, 

water 

(°C)

Hardness, 

filtered 

(mg/L as 

CaCO3

)

Calcium, 

filtered 

(mg/L)

Magnesium, 

filtered 

(mg/L)

11/17/2010 0940 799 8.2 419 2.0 189 54.4 13.0

03/16/2011 1020 887 8.2 419 4.5 193 56.3 12.8

04/13/2011 1250 951 8.3 415 8.0 192 55.1 13.3

05/18/2011 0830 2,540 8.0 244 9.5 112 32.8 7.41

06/02/2011 0825 2,830 8.0 276 11.0 121 35.6 7.85

06/15/2011 0820 5,540 8.0 299 11.5 129 37.9 8.34

07/14/2011 1015 2,350 8.0 280 14.0 124 36.4 8.05

08/17/2011 0800 633 8.1 436 15.0 190 54.2 13.3

Date

Arsenic, 

filtered 

(μg/L)

Arsenic, 

unfiltered 

recoverable 

(μg/L)

Cadmium, 

filtered 

(μg/L)

Cadmium, 

unfiltered 

recoverable 

(μg/L)

Copper, 

filtered 

(μg/L)

Copper, 

unfiltered 

recoverable 

(μg/L)

Iron, 

filtered 

(μg/L)

Iron, 

unfiltered 

recoverable 

(μg/L)

11/17/2010 6.7 8.8 0.04 0.10 2.5 13.6 4 318

03/16/2011 7.8 13.1 .06 .23 6.0 35.0 10 938

04/13/2011 7.2 10.9 .04 .13 4.4 23.1 8 527

05/18/2011 9.8 23.4 .06 .54 9.0 107 89 3,170

06/02/2011 12.4 21.5 .08 .38 10.2 77.9 50 1,930

06/15/2011 23.9 30.7 .10 .36 19.8 72.0 58 1,790

07/14/2011 15.7 24.7 .08 .34 9.6 63.0 23 1,360

08/17/2011 14.0 14.2 .07 .08 5.4 10.2 6 141

Date

Lead, 

filtered 

(μg/L)

Lead, 

unfiltered 

recoverable 

(μg/L)

Manganese, 

filtered 

(μg/L)

Manganese, 

unfiltered 

recoverable 

(μg/L)

Zinc, 

filtered 

(μg/L)

Zinc, 

unfiltered 

recoverable 

(μg/L)

Sediment, 

suspended 

(percent finer 

than 0.062 

mm)

Sediment, 

suspended 

(mg/L)

Sediment 

discharge, 

suspended 

(ton/d)

11/17/2010 0.05 2.45 8.8 69.2 4.2 18.6 86 15 32

03/16/2011 .08 6.11 21.8 107 6.2 45.3 64 58 139

04/13/2011 .07 3.79 15.0 74.5 3.1 27.4 70 29 74

05/18/2011 .59 19.1 10.7 294 7.9 134 55 216 1,480

06/02/2011 .30 11.3 20.0 184 8.4 85.9 58 111 848

06/15/2011 .43 9.52 27.2 153 13.2 86.1 75 99 1,480

07/14/2011 .20 9.60 36.8 186 6.7 64.9 63 80 508

08/17/2011 .05 1.08 17.8 49.8 5.3 11.8 86 7 12
40 Water-Quality, Bed-Sediment, and Biological Data, and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 4. Water-quality data for the Clark Fork basin, Montana, October 2010 through September 2011.—Continued

[Abbreviations: CaCO3, calcium carbonate; ft3/s, cubic feet per second; °C, degrees Celsius; E, estimated; lab, laboratory; μg/L, micrograms per liter; μS/cm, 

microsiemens per centimeter at 25°C; mg/L, milligrams per liter; mm, millimeters; NTRU, nephelometric turbidity ratio unit; ton/d, tons per day. Symbols: <, 

less than laboratory reporting level; --, no data]

12334550--Clark Fork at Turah Bridge, near Bonner

Date Time

Streamflow, 

instantaneous 

(ft3

/s)

pH, onsite 

(standard 

units)

Specific 

conductance, onsite 

(μS/cm)

Temperature, 

water 

(°C)

Hardness, 

filtered 

(mg/L as 

CaCO3

)

Calcium, 

filtered 

(mg/L)

Magnesium, 

filtered 

(mg/L)

11/17/2010 1130 1,100 8.3 357 2.5 159 45.4 11.0

03/16/2011 1230 1,200 8.4 351 4.5 157 44.9 10.9

04/14/2011 0755 1,590 8.1 330 5.5 150 42.1 10.9

*05/13/2011 1030 4,300 7.9 178 10.0 79.3 22.4 5.69

05/18/2011 1010 5,710 7.8 170 9.0 78.5 22.3 5.55

*05/26/2011 0845 8,750 7.8 149 9.5 68.3 19.4 4.79

06/02/2011 1035 7,200 8.0 188 10.0 81.0 23.0 5.71

*06/09/2011 1000 11,100 7.7 158 7.5 70.3 20.1 4.88

06/15/2011 1025 10,600 7.9 213 11.0 90.5 26.0 6.18

*06/30/2011 1100 8,440 8.1 191 12.0 86.1 24.8 5.89

07/14/2011 1235 4,420 8.0 227 14.5 98.1 28.0 6.82

08/17/2011 0945 1,110 8.1 321 14.0 139 38.8 10.3

Date

Arsenic, 

filtered 

(μg/L)

Arsenic, 

unfiltered 

recoverable 

(μg/L)

Cadmium, 

filtered 

(μg/L)

Cadmium, 

unfiltered 

recoverable 

(μg/L)

Copper, 

filtered 

(μg/L)

Copper, 

unfiltered 

recoverable 

(μg/L)

Iron, 

filtered 

(μg/L)

Iron, 

unfiltered 

recoverable 

(μg/L)

11/17/2010 5.0 6.2 0.03 0.08 2.5 9.0 <3 206

03/16/2011 5.6 8.1 .05 .12 4.5 16.0 7 411

04/14/2011 4.9 7.6 .03 .11 3.4 19.1 13 496

*05/13/2011 5.4 12.4 .03 .32 5.3 54.1 94 2,130

05/18/2011 5.8 12.5 .05 .31 6.3 56.0 81 2,010

*05/26/2011 8.0 16.5 .05 .49 9.4 77.0 106 3,060

06/02/2011 7.1 12.8 .06 .29 6.5 53.9 54 2,140

*06/09/2011 11.6 27.6 .07 1.03 11.2 147 63 5,970

06/15/2011 14.2 21.0 .07 .40 11.9 61.9 63 2,450

*06/30/2011 12.3 14.3 .08 .18 9.1 30.5 41 956

07/14/2011 10.4 13.8 .06 .18 6.3 30.8 20 665

08/17/2011 8.7 8.7 .05 <.05 3.4 6.0 3 92
Data 41

12334550--Clark Fork at Turah Bridge, near Bonner

Date

Lead, 

filtered 

(μg/L)

Lead, 

unfiltered 

recoverable 

(μg/L)

Manganese, 

filtered 

(μg/L)

Manganese, 

unfiltered 

recoverable 

(μg/L)

Zinc, 

filtered 

(μg/L)

Zinc, 

unfiltered 

recoverable 

(μg/L)

Sediment, 

suspended 

(percent finer 

than 0.062 

mm)

Sediment, 

suspended 

(mg/L)

Sediment 

discharge, 

suspended 

(ton/d)

11/17/2010 0.05 1.55 3.0 48.1 3.3 13.4 89 10 30

03/16/2011 .06 2.59 8.9 50.7 3.9 21.8 78 22 71

04/14/2011 .06 3.14 8.6 64.2 3.7 26.2 81 24 103

*05/13/2011 .37 11.5 13.2 192 5.0 79.7 62 152 1,760

05/18/2011 .40 10.4 9.0 166 5.7 78.0 59 118 1,820

*05/26/2011 .41 14.2 17.2 245 9.0 117 55 245 5,790

06/02/2011 .22 8.39 13.6 148 6.4 70.0 44 186 3,620

*06/09/2011 .33 27.1 32.0 525 13.2 258 63 404 12,100

06/15/2011 .29 11.9 24.5 212 9.4 109 56 182 5,210

*06/30/2011 .19 4.23 31.7 102 7.7 41.1 62 71 1,620

07/14/2011 .13 3.89 22.5 95.9 4.9 34.5 60 40 477

08/17/2011 .03 .51 9.2 26.1 3.8 7.5 73 5 15

Table 4. Water-quality data for the Clark Fork basin, Montana, October 2010 through September 2011.—Continued

[Abbreviations: CaCO3, calcium carbonate; ft3/s, cubic feet per second; °C, degrees Celsius; E, estimated; lab, laboratory; μg/L, micrograms per liter; μS/cm, 

microsiemens per centimeter at 25°C; mg/L, milligrams per liter; mm, millimeters; NTRU, nephelometric turbidity ratio unit; ton/d, tons per day. Symbols: <, 

less than laboratory reporting level; --, no data]
42 Water-Quality, Bed-Sediment, and Biological Data, and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 4. Water-quality data for the Clark Fork basin, Montana, October 2010 through September 2011.—Continued

[Abbreviations: CaCO3, calcium carbonate; ft3/s, cubic feet per second; °C, degrees Celsius; E, estimated; lab, laboratory; μg/L, micrograms per liter; μS/cm, 

microsiemens per centimeter at 25°C; mg/L, milligrams per liter; mm, millimeters; NTRU, nephelometric turbidity ratio unit; ton/d, tons per day. Symbols: <, 

less than laboratory reporting level; --, no data]

12340000--Blackfoot River near Bonner

Date Time

Streamflow, 

instantaneous 

(ft3

/s)

pH, onsite 

(standard 

units)

Specific 

conductance, onsite 

(μS/cm)

Temperature, 

water 

(°C)

Hardness, 

filtered 

(mg/L as 

CaCO3

)

Calcium, 

filtered 

(mg/L)

Magnesium, 

filtered 

(mg/L)

11/17/2010 1345 654 8.4 249 2.0 126 32.4 10.9

04/14/2011 1015 2,460 8.2 200 5.0 96.6 24.6 8.53

*05/13/2011 1200 8,060 7.8 150 9.0 74.5 19.6 6.20

05/18/2011 1410 11,300 8.0 156 8.5 81.8 21.2 7.01

*05/26/2011 1200 13,400 8.1 158 8.3 81.7 21.1 7.02

06/02/2011 1240 8,880 8.1 171 9.0 84.6 21.9 7.27

*06/09/2011 1230 17,000 8.0 157 8.0 80.1 21.0 6.72

06/15/2011 1225 13,100 8.0 168 9.5 81.4 21.4 6.81

*06/30/2011 0945 10,100 8.2 158 11.0 79.0 20.5 6.76

07/14/2011 1450 5,340 8.3 187 14.0 91.5 23.5 7.94

08/17/2011 1150 1,210 8.4 255 15.5 122 30.1 11.4

Date

Arsenic, 

filtered 

(μg/L)

Arsenic, 

unfiltered 

recoverable 

(μg/L)

Cadmium, 

filtered 

(μg/L)

Cadmium, 

unfiltered 

recoverable 

(μg/L)

Copper, 

filtered 

(μg/L)

Copper, 

unfiltered 

recoverable 

(μg/L)

Iron, 

filtered 

(μg/L)

Iron, 

unfiltered 

recoverable 

(μg/L)

11/17/2010 0.88 1.1 <0.02 <0.05 0.90 1.6 5 54

04/14/2011 .88 1.3 <.02 <.05 1.1 2.2 55 265

*05/13/2011 .90 1.9 <.02 <.05 1.1 4.2 32 1,140

05/18/2011 .89 1.7 <.02 <.05 1.1 3.9 50 915

*05/26/2011 1.0 2.1 <.02 <.05 .88 3.6 44 1,240

06/02/2011 .87 1.7 <.02 <.05 1.6 6.2 27 604

*06/09/2011 1.1 2.8 <.02 <.05 1.0 6.5 26 2,120

06/15/2011 1.1 2.1 <.02 <.05 .78 3.6 36 1,180

*06/30/2011 1.1 1.5 <.02 <.05 .61 2.5 35 685

07/14/2011 1.1 1.5 <.02 <.05 .55 1.3 15 280

08/17/2011 1.4 1.4 <.02 <.05 .51 .70 <3 41
Data 43

Table 4. Water-quality data for the Clark Fork basin, Montana, October 2010 through September 2011.—Continued

[Abbreviations: CaCO3, calcium carbonate; ft3/s, cubic feet per second; °C, degrees Celsius; E, estimated; lab, laboratory; μg/L, micrograms per liter; μS/cm, 

microsiemens per centimeter at 25°C; mg/L, milligrams per liter; mm, millimeters; NTRU, nephelometric turbidity ratio unit; ton/d, tons per day. Symbols: <, 

less than laboratory reporting level; --, no data]

12340000--Blackfoot River near Bonner

Date

Lead, 

filtered 

(μg/L)

Lead, 

unfiltered 

recoverable 

(μg/L)

Manganese, 

filtered 

(μg/L)

Manganese, 

unfiltered 

recoverable 

(μg/L)

Zinc, 

filtered 

(μg/L)

Zinc, 

unfiltered 

recoverable 

(μg/L)

Sediment, 

suspended 

(percent finer 

than 0.062 

mm)

Sediment, 

suspended 

(mg/L)

Sediment 

discharge, 

suspended 

(ton/d)

11/17/2010 0.02 0.08 1.2 5.2 <1.4 <2.4 78 4 7.1

04/14/2011 .06 .33 2.8 19.9 <1.4 <2.4 86 11 73

*05/13/2011 .04 1.65 3.8 85.0 1.4 6.7 77 103 2,240

05/18/2011 .06 1.23 3.8 56.1 <1.4 4.9 72 83 2,530

*05/26/2011 .05 1.50 4.0 71.1 <1.4 5.2 73 124 4,490

06/02/2011 .04 .78 2.9 36.2 <1.4 3.9 71 56 1,340

*06/09/2011 .03 2.68 3.3 116 1.6 10 68 239 11,000

06/15/2011 .04 1.28 3.7 57.9 <1.4 4.6 72 108 3,820

*06/30/2011 .05 .83 5.1 45.1 <1.4 3.1 69 74 2,020

07/14/2011 .02 .36 2.9 22.1 <1.4 <2.4 81 21 303

08/17/2011 <.01 .06 1.4 6.5 <1.4 <2.4 81 3 9.8
44 Water-Quality, Bed-Sediment, and Biological Data, and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 4. Water-quality data for the Clark Fork basin, Montana, October 2010 through September 2011.—Continued

[Abbreviations: CaCO3, calcium carbonate; ft3/s, cubic feet per second; °C, degrees Celsius; E, estimated; lab, laboratory; μg/L, micrograms per liter; μS/cm, 

microsiemens per centimeter at 25°C; mg/L, milligrams per liter; mm, millimeters; NTRU, nephelometric turbidity ratio unit; ton/d, tons per day. Symbols: <, 

less than laboratory reporting level; --, no data]

12340500--Clark Fork above Missoula

Date Time

Streamflow, 

instantaneous 

(ft3

/s)

pH, onsite 

(standard 

units)

Specific 

conductance, onsite 

(μS/cm)

Temperature, 

water 

(°C)

Hardness, 

filtered 

(mg/L as 

CaCO3

)

Calcium, 

filtered 

(mg/L)

Magnesium, 

filtered 

(mg/L)

11/17/2010 1600 1,690 8.4 314 2.5 146 40.6 10.8

03/16/2011 1635 2,160 8.7 301 5.0 138 38.1 10.4

04/14/2011 1330 4,270 8.3 247 6.0 113 30.3 9.08

*05/13/2011 1345 11,900 7.9 159 9.5 76.2 20.6 6.01

05/18/2011 1230 17,200 8.0 162 9.5 80.2 21.3 6.54

*05/26/2011 1415 22,200 8.1 155 9.2 75.2 20.3 5.95

06/02/2011 1435 15,500 8.1 177 9.0 83.4 22.6 6.57

*06/09/2011 1400 28,200 7.9 149 7.5 75.4 20.6 5.85

06/15/2011 1350 22,900 8.0 189 10.5 85.8 23.5 6.56

*06/30/2011 0754 17,400 7.9 173 13.0 82.2 22.4 6.41

07/14/2011 1720 9,510 8.2 208 15.0 96.5 26.1 7.61

08/17/2011 1430 2,410 8.3 283 16.0 128 33.6 10.8

Date

Arsenic, 

filtered 

(μg/L)

Arsenic, 

unfiltered 

recoverable 

(μg/L)

Cadmium, 

filtered 

(μg/L)

Cadmium, 

unfiltered 

recoverable 

(μg/L)

Copper, 

filtered 

(μg/L)

Copper, 

unfiltered 

recoverable 

(μg/L)

Iron, 

filtered 

(μg/L)

Iron, 

unfiltered 

recoverable 

(μg/L)

11/17/2010 3.6 4.9 0.03 0.09 1.6 9.3 22 275

03/16/2011 3.8 5.3 .03 .08 3.2 10.1 22 347

04/14/2011 2.5 3.9 .02 <.05 2.1 8.4 41 343

*05/13/2011 2.7 7.4 .02 .20 3.5 33.1 72 1,860

05/18/2011 2.8 6.4 .03 .24 4.0 49.9 60 1,640

*05/26/2011 4.4 14.6 .06 .53 8.4 90.6 47 2,840

06/02/2011 3.5 6.7 .03 .17 3.5 29.5 42 1,270

*06/09/2011 6.3 23.1 .06 .83 10.2 145 43 4,960

06/15/2011 7.1 13.2 .05 .35 7.0 53.1 54 2,030

*06/30/2011 6.0 8.0 .04 .14 4.6 24.1 32 1,030

07/14/2011 5.6 7.1 .03 .08 3.6 14.2 18 466

08/17/2011 4.8 4.9 .03 <.05 2.0 3.7 4 70
Data 45

12340500--Clark Fork above Missoula

Date

Lead, 

filtered 

(μg/L)

Lead, 

unfiltered 

recoverable 

(μg/L)

Manganese, 

filtered 

(μg/L)

Manganese, 

unfiltered 

recoverable 

(μg/L)

Zinc, 

filtered 

(μg/L)

Zinc, 

unfiltered 

recoverable 

(μg/L)

Sediment, 

suspended 

(percent finer 

than 0.062 

mm)

Sediment, 

suspended 

(mg/L)

Sediment 

discharge, 

suspended 

(ton/d)

11/17/2010 0.03 1.60 6.6 38.7 2.7 17.1 71 17 78

03/16/2011 .06 1.64 12.5 40.8 2.4 13.9 82 17 99

04/14/2011 .08 1.46 8.4 36.7 <1.4 11.1 74 18 208

*05/13/2011 .19 6.96 11.8 141 3.4 47.7 50 206 6,620

05/18/2011 .21 7.48 9.1 109 3.4 46.3 64 128 5,940

*05/26/2011 .21 14.6 18.3 190 14.1 131 57 270 16,200

06/02/2011 .12 4.31 10.4 87.8 3.6 38.8 61 108 4,520

*06/09/2011 .22 23.0 26.9 349 11.9 210 60 427 32,500

06/15/2011 .21 8.04 20.0 155 5.5 84.4 62 176 10,900

*06/30/2011 .10 3.52 18.4 88.5 3.6 32.0 58 102 4,790

07/14/2011 .08 2.02 15.8 52.5 2.4 16.0 65 33 847

08/17/2011 .03 .30 9.2 20.7 1.5 4.1 85 4 26

Table 4. Water-quality data for the Clark Fork basin, Montana, October 2010 through September 2011.—Continued

[Abbreviations: CaCO3, calcium carbonate; ft3/s, cubic feet per second; °C, degrees Celsius; E, estimated; lab, laboratory; μg/L, micrograms per liter; μS/cm, 

microsiemens per centimeter at 25°C; mg/L, milligrams per liter; mm, millimeters; NTRU, nephelometric turbidity ratio unit; ton/d, tons per day. Symbols: <, 

less than laboratory reporting level; --, no data]

*

Sample collected as part of a supplemental sampling program.
46 Water-Quality, Bed-Sediment, and Biological Data, and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 5. Daily mean streamflow and suspended-sediment data for Clark Fork at Deer Lodge, Montana, October 2010 through 

September 2011.

[Abbreviations: acre-ft, acre-feet; ft3/s, cubic feet per second; e, estimated; max, maximum; mg/L, milligrams per liter; min, minimum; ton/d, tons per day. 

Symbol: --, no data or value not computed]

Day

Mean 

streamflow 

(ft3

/s)

Suspended sediment Mean 

streamflow 

(ft3/s)

Suspended sediment Mean 

streamflow 

(ft3/s)

Suspended sediment

Mean concentration 

(mg/L)

Discharge 

(ton/d)

Mean concentration 

(mg/L)

Discharge 

(ton/d)

Mean concentration 

(mg/L)

Discharge 

(ton/d)

OCTOBER NOVEMBER DECEMBER

1 228 7 4.3 277 21 16 268 36 26

2 227 7 4.3 277 23 17 286 39 30

3 229 6 3.7 269 25 18 288 29 23

4 227 5 3.1 270 25 18 e270 20 15

5 270 8 5.8 275 25 19 e250 17 11

6 274 10 7.4 279 24 18 e250 18 12

7 258 9 6.3 279 23 17 e260 20 14

8 256 10 6.9 290 24 19 e270 22 16

9 256 10 6.9 303 24 20 275 25 19

10 256 10 6.9 285 16 12 276 21 16

11 278 11 8.3 281 12 9.1 e270 17 12

12 302 13 11 282 13 9.9 276 16 12

13 294 7 5.6 283 13 9.9 315 18 15

14 294 7 5.6 286 15 12 324 19 17

15 290 8 6.3 297 25 20 293 22 17

16 283 8 6.1 319 11 9.5 262 28 20

17 281 8 6.1 324 12 10 e240 32 21

18 277 8 6.0 334 14 13 e210 32 18

19 276 8 6.0 321 16 14 e230 31 19

20 277 8 6.0 315 19 16 257 30 21

21 278 8 6.0 282 21 16 271 28 20

22 280 8 6.0 e250 25 17 262 25 18

23 288 9 7.0 e200 27 15 263 20 14

24 292 9 7.1 e150 20 8.1 263 17 12

25 298 10 8.0 e160 12 5.2 238 15 9.6

26 297 11 8.8 e180 13 6.3 219 15 8.9

27 290 12 9.4 206 16 8.9 220 16 9.5

28 288 13 10 228 20 12 213 26 15

29 288 14 11 e240 25 16 e200 35 19

30 289 16 12 e260 31 22 e190 37 19

31 276 18 13 -- -- -- e180 36 17

TOTAL 8,497 -- 220.9 8,002 -- 423.9 7,889 -- 516

MEAN 274 10 7.1 267 20 14 254 25 17

MAX 302 18 13 334 31 22 324 39 30

MIN 227 5 3.1 150 11 5.2 180 15 8.9
Data 47

Day

Mean 

streamflow 

(ft3

/s)

Suspended sediment Mean 

streamflow 

(ft3/s)

Suspended sediment Mean 

streamflow 

(ft3/s)

Suspended sediment

Mean concentration 

(mg/L)

Discharge 

(ton/d)

Mean concentration 

(mg/L)

Discharge 

(ton/d)

Mean concentration 

(mg/L)

Discharge 

(ton/d)

JANUARY FEBRUARY MARCH

1 e180 36 17 e150 28 11 190 40 21

2 e190 37 19 e150 28 11 195 32 17

3 e200 39 21 e160 30 13 228 33 20

4 214 42 24 e170 48 22 233 35 22

5 224 44 27 217 73 43 235 36 23

6 243 40 26 e210 56 32 243 40 26

7 256 42 29 e200 49 26 248 35 23

8 242 41 27 e190 48 25 248 30 20

9 e220 45 27 194 49 26 249 30 20

10 e210 44 25 236 49 31 263 31 22

11 e200 40 22 219 50 30 288 30 23

12 e220 36 21 215 51 30 268 28 20

13 238 35 22 227 50 31 277 27 20

14 243 35 23 232 48 30 285 23 18

15 251 35 24 241 47 31 290 36 28

16 254 37 25 248 45 30 339 35 32

17 386 65 68 225 45 27 333 23 21

18 306 40 33 224 45 27 304 29 24

19 253 37 25 220 44 26 297 24 19

20 222 36 22 221 43 26 286 21 16

21 246 40 27 239 34 22 286 25 19

22 249 45 30 260 24 17 294 22 17

23 232 37 23 236 20 13 291 21 16

24 228 30 18 e200 18 9.7 288 21 16

25 231 28 17 e150 19 7.7 288 22 17

26 223 28 17 e160 21 9.1 286 23 18

27 220 28 17 179 28 14 290 20 16

28 221 28 17 192 49 25 301 21 17

29 224 28 17 -- -- -- 296 32 26

30 218 28 16 -- -- -- 284 27 21

31 e180 28 14 -- -- -- 296 23 18

TOTAL 7,224 -- 740 5,765 -- 645.5 8,499 -- 636

MEAN 233 37 24 206 41 23 274 28 21

MAX 386 65 68 260 73 43 339 40 32

MIN 180 28 14 150 18 7.7 190 20 16

Table 5. Daily mean streamflow and suspended-sediment data for Clark Fork at Deer Lodge, Montana, October 2010 through 

September 2011.—Continued

[Abbreviations: acre-ft, acre-feet; ft3/s, cubic feet per second; e, estimated; max, maximum; mg/L, milligrams per liter; min, minimum; ton/d, tons per day. 

Symbol: --, no data or value not computed]
48 Water-Quality, Bed-Sediment, and Biological Data, and Statistical Summaries of Data, Clark Fork Basin, Montana

Day

Mean 

streamflow 

(ft3

/s)

Suspended sediment Mean 

streamflow 

(ft3/s)

Suspended sediment Mean 

streamflow 

(ft3/s)

Suspended sediment

Mean concentration 

(mg/L)

Discharge 

(ton/d)

Mean concentration 

(mg/L)

Discharge 

(ton/d)

Mean concentration 

(mg/L)

Discharge 

(ton/d)

APRIL MAY JUNE

1 318 22 19 299 26 21 878 148 351

2 312 21 18 289 27 21 924 226 564

3 311 25 21 289 24 19 963 294 764

4 313 30 25 291 21 16 879 240 570

5 321 29 25 295 19 15 819 177 391

6 326 28 25 313 19 16 856 133 307

7 317 24 21 319 23 20 1,120 126 381

8 304 20 16 342 47 43 1,470 97 385

9 302 18 15 398 63 68 1,760 96 456

10 302 19 15 448 170 206 1,920 138 715

11 297 19 15 410 157 174 1,910 102 526

12 293 24 19 397 176 189 1,900 95 487

13 294 23 18 420 185 210 1,920 55 285

14 318 22 19 516 153 213 1,960 23 122

15 298 22 18 573 109 169 1,870 11 56

16 300 25 20 608 81 133 1,800 9 44

17 306 25 21 614 136 225 1,680 9 41

18 307 25 21 601 112 182 1,580 10 43

19 313 32 27 564 239 364 1,510 6 24

20 307 38 31 546 432 637 1,500 6 24

21 328 29 26 586 281 445 1,490 5 20

22 360 22 21 580 236 370 1,470 5 20

23 341 23 21 660 166 296 1,510 9 37

24 327 23 20 894 117 282 1,580 61 260

25 317 30 26 1,210 204 666 1,680 51 231

26 329 24 21 1,220 114 376 1,690 51 233

27 327 60 53 1,190 121 389 1,600 43 186

28 318 77 66 1,100 103 306 1,490 45 181

29 311 68 57 1,020 88 242 1,510 51 208

30 304 35 29 1,010 85 232 1,630 48 211

31 -- -- -- 981 132 350 -- -- --

TOTAL 9,421 -- 749 18,983 -- 6,895 44,869 -- 8,123

MEAN 314 29 25 612 125 222 1,496 79 271

MAX 360 77 66 1,220 432 666 1,960 294 764

MIN 293 18 15 289 19 15 819 5 20

Table 5. Daily mean streamflow and suspended-sediment data for Clark Fork at Deer Lodge, Montana, October 2010 through 

September 2011.—Continued

[Abbreviations: acre-ft, acre-feet; ft3/s, cubic feet per second; e, estimated; max, maximum; mg/L, milligrams per liter; min, minimum; ton/d, tons per day. 

Symbol: --, no data or value not computed]
Data 49

Day

Mean 

streamflow 

(ft3

/s)

Suspended sediment Mean 

streamflow 

(ft3/s)

Suspended sediment Mean 

streamflow 

(ft3/s)

Suspended sediment

Mean concentration 

(mg/L)

Discharge 

(ton/d)

Mean concentration 

(mg/L)

Discharge 

(ton/d)

Mean concentration 

(mg/L)

Discharge 

(ton/d)

JULY AUGUST SEPTEMBER

1 1,720 59 274 347 44 41 217 8 4.7

2 1,720 62 288 372 46 46 215 7 4.1

3 1,630 48 211 336 38 34 208 7 3.9

4 1,560 40 168 328 36 32 211 6 3.4

5 1,590 50 215 331 34 30 207 5 2.8

6 1,590 50 215 343 31 29 206 5 2.8

7 1,560 43 181 351 29 27 201 4 2.2

8 1,490 40 161 328 28 25 201 4 2.2

9 1,360 41 151 300 27 22 205 4 2.2

10 1,230 36 120 277 26 19 204 4 2.2

11 1,120 32 97 298 25 20 202 4 2.2

12 1,030 31 86 285 24 18 201 5 2.7

13 1,030 50 139 274 21 16 205 5 2.8

14 1,240 43 144 269 17 12 205 4 2.2

15 1,320 29 103 243 13 8.5 208 4 2.2

16 1,150 28 87 249 8 5.4 220 4 2.4

17 1,060 27 77 236 4 2.5 221 4 2.4

18 968 28 73 229 5 3.1 216 3 1.7

19 863 30 70 223 5 3.0 214 3 1.7

20 804 33 72 208 6 3.4 213 4 2.3

21 711 35 67 197 5 2.7 214 4 2.3

22 627 36 61 193 5 2.6 216 4 2.3

23 560 37 56 181 4 2.0 210 4 2.3

24 501 38 51 177 4 1.9 204 4 2.2

25 465 37 46 181 5 2.4 199 4 2.1

26 441 41 49 195 5 2.6 193 4 2.1

27 415 51 57 193 4 2.1 195 4 2.1

28 385 65 68 186 4 2.0 192 5 2.6

29 356 89 86 192 4 2.1 192 5 2.6

30 326 63 55 196 4 2.1 193 5 2.6

31 307 41 34 204 6 3.3 -- -- --

TOTAL 31,129 -- 3,562 7,922 -- 422.7 6,188 -- 76.3

MEAN 1,004 43 115 256 17 14 206 5 2.5

MAX 1,720 89 288 372 46 46 221 8 4.7

MIN 307 27 34 177 4 1.9 192 3 1.7

Total for water year 2011 (unrounded sum of daily values): streamflow–164,388 ft3/s (annual runoff–326,100 acre-ft); suspended-sediment 

discharge–23,010.3 tons.

Table 5. Daily mean streamflow and suspended-sediment data for Clark Fork at Deer Lodge, Montana, October 2010 through 

September 2011.—Continued

[Abbreviations: acre-ft, acre-feet; ft3/s, cubic feet per second; e, estimated; max, maximum; mg/L, milligrams per liter; min, minimum; ton/d, tons per day. 

Symbol: --, no data or value not computed]
50 Water-Quality, Bed-Sediment, and Biological Data, and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 6. Daily mean streamflow and suspended-sediment data for Clark Fork at Turah Bridge, near Bonner, Montana, October 2010 

through September 2011.

[Abbreviations: acre-ft, acre-feet; ft3/s, cubic feet per second; e, estimated; max, maximum; mg/L, milligrams per liter; min, minimum; ton/d, tons per day. 

Symbol: --, no data or value not computed]

Day

Mean 

streamflow 

(ft3

/s)

Suspended sediment Mean 

streamflow 

(ft3/s)

Suspended sediment Mean 

streamflow 

(ft3/s)

Suspended sediment

Mean concentration 

(mg/L)

Discharge 

(ton/d)

Mean concentration 

(mg/L)

Discharge 

(ton/d)

Mean concentration 

(mg/L)

Discharge 

(ton/d)

OCTOBER NOVEMBER DECEMBER

1 910 4 9.8 1,010 6 16 871 5 12

2 909 4 9.8 1,000 7 19 e985 5 13

3 905 5 12 1,000 7 19 1,000 5 14

4 916 5 12 1,000 7 19 962 6 16

5 964 10 26 1,000 7 19 903 6 15

6 1,060 17 49 1,000 7 19 945 7 18

7 1,070 16 46 1,020 7 19 983 8 21

8 1,030 12 33 1,030 8 22 898 10 24

9 1,040 12 34 1,050 8 23 1,010 11 30

10 1,050 12 34 1,040 7 20 1,060 10 29

11 1,060 12 34 1,010 6 16 980 9 24

12 1,090 11 32 1,010 6 16 956 9 23

13 1,090 10 29 1,000 5 14 995 8 21

14 1,070 10 29 1,010 6 16 1,080 7 20

15 1,060 9 26 1,010 6 16 1,090 6 18

16 1,050 9 26 1,080 8 23 1,010 5 14

17 1,040 8 22 1,110 10 30 971 4 10

18 1,030 8 22 1,080 9 26 e920 3 7.5

19 1,030 7 19 1,070 8 23 e920 4 9.9

20 1,030 7 19 1,020 7 19 e880 4 9.5

21 1,020 7 19 1,000 6 16 e820 5 11

22 1,020 8 22 870 4 9.4 e840 4 9.1

23 1,020 9 25 803 4 8.7 e800 4 8.6

24 1,020 9 25 578 4 6.2 e820 3 6.6

25 1,040 10 28 655 4 7.1 e880 4 9.5

26 1,060 10 29 647 5 8.7 e840 5 11

27 1,050 8 23 773 6 13 e830 5 11

28 1,030 7 19 917 6 15 e880 6 14

29 1,020 7 19 924 6 15 e910 6 15

30 1,010 7 19 915 7 17 e915 6 15

31 1,010 6 16 -- -- -- e820 5 11

TOTAL 31,704 -- 767.6 28,632 -- 510.1 28,774 -- 470.7

MEAN 1,023 9 25 954 6 17 928 6 15

MAX 1,090 17 49 1,110 10 30 1,090 11 30

MIN 905 4 9.8 578 4 6.2 800 3 6.6
Data 51

Day

Mean 

streamflow 

(ft3

/s)

Suspended sediment Mean 

streamflow 

(ft3/s)

Suspended sediment Mean 

streamflow 

(ft3/s)

Suspended sediment

Mean concentration 

(mg/L)

Discharge 

(ton/d)

Mean concentration 

(mg/L)

Discharge 

(ton/d)

Mean concentration 

(mg/L)

Discharge 

(ton/d)

JANUARY FEBRUARY MARCH

1 e635 5 8.6 766 25 52 863 10 23

2 e755 6 12 710 24 46 879 9 21

3 e790 6 13 790 24 51 916 10 25

4 e820 7 15 809 25 55 941 10 25

5 e850 7 16 984 39 104 962 12 31

6 e810 8 17 963 34 88 959 11 28

7 943 11 28 963 27 70 975 9 24

8 974 14 37 928 20 50 992 10 27

9 937 13 33 843 14 32 990 11 29

10 874 10 24 781 11 23 1,010 12 33

11 856 8 18 827 11 25 1,160 46 144

12 969 7 18 940 16 41 1,120 42 127

13 956 8 21 1,070 32 92 1,090 27 79

14 894 8 19 1,250 45 152 1,160 27 85

15 1,060 10 29 1,240 42 141 1,200 27 87

16 1,130 23 70 1,500 59 239 1,250 31 105

17 1,580 115 491 1,300 52 183 1,410 52 198

18 2,130 137 788 1,110 39 117 1,280 34 118

19 1,820 86 423 1,030 26 72 1,200 22 71

20 1,300 43 151 943 18 46 1,150 18 56

21 1,140 18 55 782 15 32 1,110 17 51

22 1,190 14 45 865 16 37 1,150 19 59

23 1,170 15 47 961 24 62 1,150 17 53

24 1,090 15 44 896 20 48 1,120 17 51

25 1,070 16 46 717 15 29 1,140 17 52

26 1,080 20 58 705 14 27 1,160 17 53

27 1,050 24 68 763 15 31 1,140 18 55

28 1,040 28 79 789 13 28 1,150 17 53

29 1,030 31 86 -- -- -- 1,140 18 55

30 1,040 33 93 -- -- -- 1,160 20 63

31 919 30 74 -- -- -- 1,250 29 98

TOTAL 32,902 -- 2,926.6 26,225 -- 1,973 34,177 -- 1,979

MEAN 1,061 25 94 937 26 70 1,102 21 64

MAX 2,130 137 788 1,500 59 239 1,410 52 198

MIN 635 5 8.6 705 11 23 863 9 21

Table 6. Daily mean streamflow and suspended-sediment data for Clark Fork at Turah Bridge, near Bonner, Montana, October 2010 

through September 2011.—Continued

[Abbreviations: acre-ft, acre-feet; ft3/s, cubic feet per second; e, estimated; max, maximum; mg/L, milligrams per liter; min, minimum; ton/d, tons per day. 

Symbol: --, no data or value not computed]
52 Water-Quality, Bed-Sediment, and Biological Data, and Statistical Summaries of Data, Clark Fork Basin, Montana

Day

Mean 

streamflow 

(ft3

/s)

Suspended sediment Mean 

streamflow 

(ft3/s)

Suspended sediment Mean 

streamflow 

(ft3/s)

Suspended sediment

Mean concentration 

(mg/L)

Discharge 

(ton/d)

Mean concentration 

(mg/L)

Discharge 

(ton/d)

Mean concentration 

(mg/L)

Discharge 

(ton/d)

APRIL MAY JUNE

1 1,810 131 640 1,620 19 83 6,830 142 2,620

2 2,110 132 752 1,610 20 87 7,320 190 3,760

3 2,110 86 490 1,660 24 108 8,890 215 5,160

4 1,890 55 281 1,730 28 131 8,930 191 4,610

5 1,750 42 198 1,770 29 139 8,760 154 3,640

6 1,710 36 166 1,940 40 210 8,870 159 3,810

7 1,640 31 137 2,180 64 377 9,340 224 5,650

8 1,560 28 118 2,490 99 666 10,500 372 10,500

9 1,500 26 105 3,020 155 1,260 11,600 386 12,100

10 1,470 23 91 3,550 198 1,900 12,100 304 9,930

11 1,460 23 91 3,820 174 1,790 12,700 301 10,300

12 1,480 23 92 4,000 179 1,930 12,400 234 7,830

13 1,510 24 98 4,380 186 2,200 12,300 196 6,510

14 1,590 26 112 5,190 286 4,010 11,900 194 6,230

15 1,600 26 112 5,860 281 4,450 10,800 184 5,370

16 1,560 27 114 6,040 212 3,460 10,400 164 4,610

17 1,620 27 118 6,040 164 2,670 9,720 145 3,810

18 1,730 33 154 5,720 116 1,790 9,240 138 3,440

19 1,720 30 139 5,460 89 1,310 8,740 128 3,020

20 1,670 24 108 5,470 77 1,140 8,710 117 2,750

21 1,620 22 96 5,640 75 1,140 8,510 101 2,320

22 1,630 19 84 5,940 89 1,430 8,700 92 2,160

23 1,600 18 78 6,420 109 1,890 8,930 111 2,680

24 1,570 20 85 7,300 172 3,390 9,860 130 3,460

25 1,600 23 99 8,770 297 7,030 9,580 133 3,440

26 1,660 23 103 8,730 224 5,280 9,280 87 2,180

27 1,670 25 113 8,580 172 3,980 8,690 77 1,810

28 1,680 26 118 7,820 121 2,550 8,160 72 1,590

29 1,700 23 106 7,380 113 2,250 8,310 76 1,710

30 1,650 17 76 7,190 161 3,130 8,500 76 1,740

31 -- -- -- 7,250 155 3,030 -- -- --

TOTAL 49,870 -- 5,074 154,570 -- 64,811 288,570 -- 138,740

MEAN 1,662 36 169 4,986 133 2,090 9,619 170 4,620

MAX 2,110 132 752 8,770 297 7,030 12,700 386 12,100

MIN 1,460 17 76 1,610 19 83 6,830 72 1,590

Table 6. Daily mean streamflow and suspended-sediment data for Clark Fork at Turah Bridge, near Bonner, Montana, October 2010 

through September 2011.—Continued

[Abbreviations: acre-ft, acre-feet; ft3/s, cubic feet per second; e, estimated; max, maximum; mg/L, milligrams per liter; min, minimum; ton/d, tons per day. 

Symbol: --, no data or value not computed]
Data 53

Day

Mean 

streamflow 

(ft3

/s)

Suspended sediment Mean 

streamflow 

(ft3/s)

Suspended sediment Mean 

streamflow 

(ft3/s)

Suspended sediment

Mean concentration 

(mg/L)

Discharge 

(ton/d)

Mean concentration 

(mg/L)

Discharge 

(ton/d)

Mean concentration 

(mg/L)

Discharge 

(ton/d)

JULY AUGUST SEPTEMBER

1 8,380 65 1,470 1,730 14 65 894 6 14

2 7,840 58 1,230 1,760 13 62 896 6 15

3 7,430 57 1,140 1,740 12 56 893 5 12

4 7,090 56 1,070 1,680 11 50 885 5 12

5 6,800 53 973 1,660 11 49 890 5 12

6 6,440 53 922 1,620 11 48 867 5 12

7 6,090 51 839 1,570 11 47 851 4 9.2

8 5,940 50 802 1,520 11 45 849 4 9.2

9 5,630 49 745 1,440 10 39 848 5 11

10 5,050 49 668 1,350 9 33 844 5 11

11 4,570 47 580 1,330 9 32 835 5 11

12 4,220 39 444 1,300 8 28 839 5 11

13 4,200 37 420 1,260 9 31 827 5 11

14 4,370 40 472 1,210 8 26 821 6 13

15 4,630 51 638 1,180 7 22 827 6 13

16 4,390 43 510 1,120 7 21 863 7 16

17 4,140 37 414 1,100 5 15 903 7 17

18 3,720 34 341 1,060 5 14 924 8 20

19 3,400 31 285 1,030 5 14 928 8 20

20 3,210 28 243 986 5 13 941 9 23

21 3,050 25 206 967 5 13 948 9 23

22 2,920 23 181 943 5 13 938 9 23

23 2,780 22 165 913 5 12 922 8 20

24 2,580 20 139 876 5 12 906 8 20

25 2,410 18 117 863 5 12 885 8 19

26 2,290 19 117 862 5 12 880 7 17

27 2,170 19 111 861 5 12 864 7 16

28 2,080 17 95 851 5 11 846 6 14

29 1,980 15 80 856 5 12 832 7 16

30 1,860 14 70 849 5 11 838 7 16

31 1,770 13 62 862 6 14 -- -- --

TOTAL 133,430 -- 15,549 37,349 -- 844 26,284 -- 456.4

MEAN 4,304 37 502 1,205 8 27 876 6 15

MAX 8,380 65 1,470 1,760 14 65 948 9 23

MIN 1,770 13 62 849 5 11 821 4 9.2

Total for water year 2011 (unrounded sum of daily values): streamflow–872,487 ft3/s (annual runoff–1,731,000 acre-ft); suspended-sediment 

discharge–234,101.4 tons.

Table 6. Daily mean streamflow and suspended-sediment data for Clark Fork at Turah Bridge, near Bonner, Montana, October 2010 

through September 2011.—Continued

[Abbreviations: acre-ft, acre-feet; ft3/s, cubic feet per second; e, estimated; max, maximum; mg/L, milligrams per liter; min, minimum; ton/d, tons per day. 

Symbol: --, no data or value not computed]
54 Water-Quality, Bed-Sediment, and Biological Data, and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 7. Daily mean streamflow and suspended-sediment data for Blackfoot River near Bonner, Montana, October 2010 through 

September 2011.

[Abbreviations: acre-ft, acre-feet; ft3/s, cubic feet per second; e, estimated; max, maximum; mg/L, milligrams per liter; min, minimum; ton/d, tons per day. 

Symbol: --, no data or value not computed]

Day

Mean 

streamflow 

(ft3

/s)

Suspended sediment Mean 

streamflow 

(ft3/s)

Suspended sediment Mean 

streamflow 

(ft3/s)

Suspended sediment

Mean concentration 

(mg/L)

Discharge 

(ton/d)

Mean concentration 

(mg/L)

Discharge 

(ton/d)

Mean concentration 

(mg/L)

Discharge 

(ton/d)

OCTOBER NOVEMBER DECEMBER

1 547 4 5.9 e550 3 4.5 733 1 2.0

2 545 5 7.4 e550 3 4.5 699 2 3.8

3 541 5 7.3 e540 3 4.4 688 2 3.7

4 546 4 5.9 e540 3 4.4 697 2 3.8

5 555 5 7.5 540 3 4.4 e600 2 3.2

6 559 5 7.5 541 3 4.4 e500 1 1.4

7 575 5 7.8 541 3 4.4 e530 1 1.4

8 579 5 7.8 541 2 2.9 e675 2 3.6

9 584 5 7.9 541 2 2.9 e640 2 3.5

10 582 5 7.9 540 3 4.4 e620 2 3.3

11 586 5 7.9 537 3 4.3 e585 3 4.7

12 581 4 6.3 533 3 4.3 e590 3 4.8

13 582 4 6.3 536 3 4.3 e648 3 5.2

14 583 3 4.7 542 2 2.9 e700 3 5.7

15 582 3 4.7 548 2 3 e710 3 5.8

16 574 3 4.6 629 3 5.1 e605 4 6.5

17 571 3 4.6 665 6 11 e450 4 4.9

18 565 3 4.6 634 3 5.1 e435 3 3.5

19 561 2 3.0 590 3 4.8 e430 2 2.3

20 553 2 3.0 575 3 4.7 e475 1 1.3

21 552 2 3.0 538 3 4.4 e500 2 2.7

22 547 2 3.0 476 3 3.9 e470 2 2.5

23 542 2 2.9 434 1 1.2 e500 2 2.7

24 551 2 3.0 333 1 0.9 e500 2 2.7

25 553 3 4.5 419 1 1.1 e510 2 2.8

26 564 3 4.6 557 1 1.5 e530 1 1.4

27 560 2 3.0 628 1 1.7 e485 1 1.3

28 554 2 3.0 672 5 9.1 e495 1 1.3

29 554 3 4.5 627 1 1.7 e480 1 1.3

30 554 3 4.5 688 1 1.9 e475 1 1.3

31 549 3 4.4 -- -- -- e430 1 1.2

TOTAL 17,431 -- 163 16,585 -- 118.1 17,385 -- 95.6

MEAN 562 3 5.3 553 3 3.9 561 2 3.1

MAX 586 5 7.9 688 6 11 733 4 6.5

MIN 541 2 2.9 333 1 .9 430 1 1.2
Data 55

Table 7. Daily mean streamflow and suspended-sediment data for Blackfoot River near Bonner, Montana, October 2010 through 

September 2011.—Continued

[Abbreviations: acre-ft, acre-feet; ft3/s, cubic feet per second; e, estimated; max, maximum; mg/L, milligrams per liter; min, minimum; ton/d, tons per day. 

Symbol: --, no data or value not computed]

Day

Mean 

streamflow 

(ft3

/s)

Suspended sediment Mean 

streamflow 

(ft3/s)

Suspended sediment Mean 

streamflow 

(ft3/s)

Suspended sediment

Mean concentration 

(mg/L)

Discharge 

(ton/d)

Mean concentration 

(mg/L)

Discharge 

(ton/d)

Mean concentration 

(mg/L)

Discharge 

(ton/d)

JANUARY FEBRUARY MARCH

1 e345 1 0.93 521 16 23 691 3 5.6

2 e395 1 1.1 529 9 13 681 3 5.5

3 e430 1 1.2 629 6 10 670 5 9.0

4 e465 1 1.3 745 6 12 654 6 11

5 e480 2 2.6 807 6 13 638 9 16

6 e500 2 2.7 789 6 13 634 10 17

7 e450 2 2.4 792 6 13 624 9 15

8 e500 2 2.7 749 6 12 621 5 8.4

9 e490 2 2.6 666 5 9.0 620 3 5.0

10 e480 2 2.6 755 5 10 621 5 8.4

11 e455 2 2.5 740 6 12 649 6 11

12 e450 2 2.4 742 7 14 648 5 8.7

13 e490 2 2.6 775 7 15 667 5 9.0

14 e500 3 4.0 781 7 15 730 8 16

15 e890 6 14 785 7 15 788 12 26

16 e965 12 31 854 12 28 835 13 29

17 1,340 28 101 862 16 37 868 14 33

18 1,280 20 69 846 9 21 894 15 36

19 1,290 18 63 776 7 15 887 14 34

20 1,110 10 30 717 5 9.7 852 10 23

21 1,060 6 17 660 4 7.1 816 8 18

22 1,050 6 17 721 5 9.7 824 6 13

23 1,010 6 16 738 6 12 839 6 14

24 953 5 13 643 5 8.7 863 9 21

25 944 5 13 538 4 5.8 921 10 25

26 921 5 12 516 4 5.6 953 15 39

27 887 5 12 639 4 6.9 972 18 47

28 862 5 12 688 4 7.4 1,000 16 43

29 857 14 32 -- -- -- 1,030 15 42

30 855 20 46 -- -- -- 1,110 16 48

31 660 10 18 -- -- -- 1,550 33 138

TOTAL 23,364 -- 547.63 20,003 -- 372.9 25,150 -- 774.6

MEAN 754 7 18 714 7 13 811 10 25

MAX 1,340 28 101 862 16 37 1,550 33 138

MIN 345 1 .93 516 4 5.6 620 3 5.0
56 Water-Quality, Bed-Sediment, and Biological Data, and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 7. Daily mean streamflow and suspended-sediment data for Blackfoot River near Bonner, Montana, October 2010 through 

September 2011.—Continued

[Abbreviations: acre-ft, acre-feet; ft3/s, cubic feet per second; e, estimated; max, maximum; mg/L, milligrams per liter; min, minimum; ton/d, tons per day. 

Symbol: --, no data or value not computed]

Day

Mean 

streamflow 

(ft3

/s)

Suspended sediment Mean 

streamflow 

(ft3/s)

Suspended sediment Mean 

streamflow 

(ft3/s)

Suspended sediment

Mean concentration 

(mg/L)

Discharge 

(ton/d)

Mean concentration 

(mg/L)

Discharge 

(ton/d)

Mean concentration 

(mg/L)

Discharge 

(ton/d)

APRIL MAY JUNE

1 2,740 88 651 2,480 12 80 8,000 46 994

2 3,100 79 661 2,430 9 59 8,940 56 1,350

3 3,270 47 415 2,480 12 80 10,900 90 2,650

4 3,150 31 264 2,620 14 99 10,700 85 2,460

5 3,070 23 191 2,800 16 121 10,600 79 2,260

6 2,960 21 168 3,110 23 193 11,200 88 2,660

7 2,790 18 136 3,600 32 311 14,100 208 7,920

8 2,600 15 105 4,310 48 559 16,600 323 14,500

9 2,420 12 78 4,960 62 830 17,000 277 12,700

10 2,290 12 74 5,520 68 1,010 16,100 276 12,000

11 2,230 12 72 6,060 92 1,510 15,100 208 8,480

12 2,230 11 66 7,010 94 1,780 14,400 165 6,420

13 2,250 10 61 7,950 103 2,210 13,900 149 5,590

14 2,430 11 72 9,560 126 3,250 13,300 126 4,520

15 2,490 12 81 10,900 161 4,740 12,900 113 3,940

16 2,460 12 80 11,900 154 4,950 12,200 106 3,490

17 2,540 11 75 12,100 131 4,280 11,200 80 2,420

18 2,620 12 85 11,300 90 2,750 10,200 65 1,790

19 2,630 15 107 10,600 77 2,200 9,660 62 1,620

20 2,560 9 62 10,300 68 1,890 9,310 54 1,360

21 2,480 9 60 10,200 64 1,760 9,270 54 1,350

22 2,390 7 45 10,500 78 2,210 9,700 64 1,680

23 2,310 10 62 11,700 118 3,730 10,600 84 2,400

24 2,250 8 49 12,800 148 5,110 11,800 125 3,980

25 2,290 9 56 13,300 155 5,570 11,600 121 3,790

26 2,410 9 59 13,400 133 4,810 10,200 77 2,120

27 2,480 12 80 13,400 135 4,880 9,100 56 1,380

28 2,550 11 76 12,100 109 3,560 8,580 49 1,140

29 2,590 11 77 10,500 93 2,640 9,190 61 1,510

30 2,550 10 69 9,360 60 1,520 10,100 78 2,130

31 -- -- -- 8,350 46 1,040 -- -- --

TOTAL 77,130 -- 4,137 257,600 -- 69,732 346,450 -- 120,604

MEAN 2,571 19 138 8,310 82 2,250 11,550 114 4,020

MAX 3,270 88 661 13,400 161 5,570 17,000 323 14,500

MIN 2,230 7 45 2,430 9 59 8,000 46 994
Data 57

Table 7. Daily mean streamflow and suspended-sediment data for Blackfoot River near Bonner, Montana, October 2010 through 

September 2011.—Continued

[Abbreviations: acre-ft, acre-feet; ft3/s, cubic feet per second; e, estimated; max, maximum; mg/L, milligrams per liter; min, minimum; ton/d, tons per day. 

Symbol: --, no data or value not computed]

Day

Mean 

streamflow 

(ft3

/s)

Suspended sediment Mean 

streamflow 

(ft3/s)

Suspended sediment Mean 

streamflow 

(ft3/s)

Suspended sediment

Mean concentration 

(mg/L)

Discharge 

(ton/d)

Mean concentration 

(mg/L)

Discharge 

(ton/d)

Mean concentration 

(mg/L)

Discharge 

(ton/d)

JULY AUGUST SEPTEMBER

1 9,850 67 1,780 1,830 5 25 934 4 10

2 8,890 49 1,180 1,790 5 24 943 3 7.6

3 8,210 43 953 1,770 4 19 919 3 7.4

4 8,020 43 931 1,710 4 18 905 2 4.9

5 7,800 39 821 1,650 4 18 888 2 4.8

6 7,430 37 742 1,610 5 22 869 2 4.7

7 7,080 34 650 1,580 5 21 844 2 4.6

8 6,780 30 549 1,520 4 16 836 3 6.8

9 6,380 27 465 1,460 4 16 836 3 6.8

10 5,800 26 407 1,410 4 15 829 3 6.7

11 5,300 26 372 1,380 3 11 809 3 6.6

12 5,080 24 329 1,370 3 11 794 3 6.4

13 5,240 25 354 1,320 3 11 792 3 6.4

14 5,270 21 299 1,290 3 10 781 3 6.3

15 4,960 19 254 1,260 4 14 771 2 4.2

16 4,560 16 197 1,230 4 13 786 2 4.2

17 4,310 14 163 1,200 3 9.7 787 2 4.2

18 4,040 13 142 1,150 3 9.3 785 2 4.2

19 3,800 11 113 1,130 3 9.2 797 3 6.5

20 3,630 10 98 1,110 3 9 814 3 6.6

21 3,440 8 74 1,110 3 9 804 3 6.5

22 3,200 8 69 1,090 3 8.8 785 3 6.4

23 3,030 8 65 1,070 3 8.7 760 3 6.2

24 2,800 7 53 1,030 3 8.3 734 3 5.9

25 2,630 7 50 998 3 8.1 720 3 5.8

26 2,490 7 47 976 3 7.9 711 3 5.8

27 2,360 8 51 951 3 7.7 704 4 7.6

28 2,240 7 42 938 4 10 697 4 7.5

29 2,130 6 35 932 3 7.5 686 3 5.6

30 2,020 6 33 926 3 7.5 685 3 5.5

31 1,940 5 26 929 3 7.5 -- -- --

TOTAL 150,710 -- 11,344 39,720 -- 392.2 24,005 -- 182.7

MEAN 4,862 21 366 1,281 4 13 800 3 6.1

MAX 9,850 67 1,780 1,830 5 25 943 4 10

MIN 1,940 5 26 926 3 7.5 685 2 4.2

Total for water year 2011 (unrounded sum of daily values): streamflow–1,015,533 ft3/s (annual runoff–2,014,000 acre-ft); suspended-sediment 

discharge–208,463.7 tons.
58 Water-Quality, Bed-Sediment, and Biological Data, and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 8. Daily mean streamflow and suspended-sediment data for Clark Fork above Missoula, Montana, October 2010 through 

September 2011.

[Abbreviations: acre-ft, acre-feet; ft3/s, cubic feet per second; e, estimated; max, maximum; mg/L, milligrams per liter; min, minimum; ton/d, tons per day. 

Symbol: --, no data or value not computed]

Day

Mean 

streamflow 

(ft3

/s)

Suspended sediment Mean 

streamflow 

(ft3/s)

Suspended sediment Mean 

streamflow 

(ft3/s)

Suspended sediment

Mean concentration 

(mg/L)

Discharge 

(ton/d)

Mean concentration 

(mg/L)

Discharge 

(ton/d)

Mean concentration 

(mg/L)

Discharge 

(ton/d)

OCTOBER NOVEMBER DECEMBER

1 1,470 8 32 1,470 13 52 1,470 22 87

2 1,460 9 35 1,470 13 52 1,560 17 72

3 1,440 9 35 1,460 12 47 1,560 12 51

4 1,440 9 35 1,450 11 43 1,460 11 43

5 1,480 9 36 1,460 11 43 1,360 11 40

6 1,580 11 47 1,450 10 39 1,310 11 39

7 1,610 11 48 1,480 12 48 1,400 12 45

8 1,570 10 42 1,490 16 64 1,560 13 55

9 1,580 10 43 1,510 20 82 1,630 14 62

10 1,580 11 47 1,510 24 98 1,680 12 54

11 1,580 11 47 1,470 18 71 1,560 10 42

12 1,610 10 43 1,460 13 51 1,540 9 37

13 1,610 9 39 1,460 9 35 1,650 9 40

14 1,590 8 34 1,470 7 28 1,820 15 74

15 1,580 8 34 1,490 8 32 1,870 15 76

16 1,550 7 29 1,630 13 57 1,730 146 682

17 1,540 7 29 1,700 17 78 1,540 63 262

18 1,520 7 29 1,650 16 71 1,430 7 27

19 1,500 6 24 1,620 15 66 e1,400 9 34

20 1,500 6 24 1,490 15 60 e1,400 10 38

21 1,480 6 24 1,390 14 53 e1,350 7 26

22 1,480 6 24 1,150 21 65 e1,350 10 36

23 1,480 7 28 1,030 23 64 e1,350 15 55

24 1,480 7 28 758 20 41 e1,350 9 33

25 1,500 9 36 808 20 44 e1,400 4 15

26 1,540 20 83 1,060 25 72 e1,400 13 49

27 1,520 21 86 1,350 21 77 e1,350 28 102

28 1,500 21 85 1,620 22 96 e1,400 26 98

29 1,490 20 80 1,580 13 55 e1,400 16 60

30 1,480 17 68 1,450 9 35 e1,400 26 98

31 1,480 15 60 -- -- -- e1,300 73 256

TOTAL 47,220 -- 1,334 42,386 -- 1,719 45,980 -- 2,688

MEAN 1,523 10 43 1,413 15 57 1,483 21 87

MAX 1,610 21 86 1,700 25 98 1,870 146 682

MIN 1,440 6 24 758 7 28 1,300 4 15
Data 59

Day

Mean 

streamflow 

(ft3

/s)

Suspended sediment Mean 

streamflow 

(ft3/s)

Suspended sediment Mean 

streamflow 

(ft3/s)

Suspended sediment

Mean concentration 

(mg/L)

Discharge 

(ton/d)

Mean concentration 

(mg/L)

Discharge 

(ton/d)

Mean concentration 

(mg/L)

Discharge 

(ton/d)

JANUARY FEBRUARY MARCH

1 e1,100 161 478 1,290 16 56 1,570 7 30

2 e1,200 179 580 1,270 22 75 1,580 7 30

3 e1,300 111 390 1,400 40 151 1,630 8 35

4 e1,350 53 193 1,640 74 328 1,620 8 35

5 e1,400 25 95 1,900 98 503 1,630 7 31

6 e1,400 41 155 1,850 83 415 1,620 7 31

7 e1,450 80 313 1,880 67 340 1,620 6 26

8 e1,500 113 458 1,740 52 244 1,640 6 27

9 e1,500 132 535 1,540 36 150 1,620 6 26

10 e1,450 134 525 1,610 20 87 1,640 12 53

11 e1,400 128 484 1,620 9 39 1,820 25 123

12 e1,450 189 740 1,780 13 62 1,810 19 93

13 e1,500 221 895 1,950 16 84 1,780 16 77

14 e1,600 118 510 2,190 23 136 1,910 18 93

15 e2,000 48 259 2,180 26 153 2,040 19 105

16 e2,100 54 306 2,560 49 339 2,130 18 104

17 2,980 116 933 2,410 44 286 2,370 32 205

18 3,850 132 1,370 2,130 27 155 2,270 25 153

19 3,630 85 833 1,970 18 96 2,160 19 111

20 2,730 38 280 1,760 12 57 2,080 15 84

21 2,420 15 98 1,490 11 44 1,980 12 64

22 2,440 13 86 1,640 15 66 2,020 13 71

23 2,380 11 71 1,790 20 97 2,030 13 71

24 2,220 10 60 1,580 12 51 2,020 13 71

25 2,190 9 53 1,230 3 10 2,100 15 85

26 2,170 11 64 1,130 3 9.2 2,160 17 99

27 2,090 13 73 1,350 8 29 2,150 16 93

28 2,040 15 83 1,500 6 24 2,180 17 100

29 2,030 17 93 -- -- -- 2,210 18 107

30 2,050 21 116 -- -- -- 2,300 26 161

31 1,690 17 78 -- -- -- 2,800 73 552

TOTAL 60,610 -- 11,207 48,380 -- 4,086.2 60,490 -- 2,946

MEAN 1,955 75 362 1,728 29 146 1,951 17 95

MAX 3,850 221 1,370 2,560 98 503 2,800 73 552

MIN 1,100 9 53 1,130 3 9.2 1,570 6 26

Table 8. Daily mean streamflow and suspended-sediment data for Clark Fork above Missoula, Montana, October 2010 through 

September 2011.—Continued

[Abbreviations: acre-ft, acre-feet; ft3/s, cubic feet per second; e, estimated; max, maximum; mg/L, milligrams per liter; min, minimum; ton/d, tons per day. 

Symbol: --, no data or value not computed]
60 Water-Quality, Bed-Sediment, and Biological Data, and Statistical Summaries of Data, Clark Fork Basin, Montana

Day

Mean 

streamflow 

(ft3

/s)

Suspended sediment Mean 

streamflow 

(ft3/s)

Suspended sediment Mean 

streamflow 

(ft3/s)

Suspended sediment

Mean concentration 

(mg/L)

Discharge 

(ton/d)

Mean concentration 

(mg/L)

Discharge 

(ton/d)

Mean concentration 

(mg/L)

Discharge 

(ton/d)

APRIL MAY JUNE

1 4,610 166 2,070 4,310 14 163 14,100 84 3,200

2 5,290 146 2,090 4,250 15 172 15,200 108 4,430

3 5,510 99 1,470 4,320 17 198 18,600 160 8,040

4 5,210 60 844 4,520 19 232 18,400 139 6,910

5 5,000 41 554 4,700 24 305 18,000 117 5,690

6 4,860 33 433 5,080 36 494 18,600 120 6,030

7 4,650 28 352 5,700 58 893 21,800 224 13,200

8 4,420 23 274 6,530 97 1,710 25,900 399 27,900

9 4,180 18 203 7,470 137 2,760 28,000 478 36,100

10 4,010 18 195 8,480 151 3,460 28,100 385 29,200

11 3,910 18 190 9,380 155 3,930 27,300 358 26,400

12 3,910 18 190 10,400 151 4,240 25,900 287 20,100

13 3,980 22 236 11,700 187 5,910 24,800 266 17,800

14 4,200 19 215 13,900 283 10,600 23,700 225 14,400

15 4,290 19 220 16,100 264 11,500 22,900 187 11,600

16 4,240 19 218 17,500 225 10,600 21,800 167 9,830

17 4,340 19 223 18,100 186 9,090 20,300 145 7,950

18 4,520 20 244 17,100 129 5,960 18,700 134 6,770

19 4,550 19 233 16,000 103 4,450 17,700 125 5,970

20 4,440 15 180 15,500 90 3,770 17,300 119 5,560

21 4,310 14 163 15,400 83 3,450 17,100 108 4,990

22 4,250 12 138 15,900 94 4,040 17,400 110 5,170

23 4,130 12 134 17,300 129 6,030 18,300 131 6,470

24 4,050 12 131 19,100 209 10,800 19,900 167 8,970

25 4,110 13 144 21,300 358 20,600 20,000 153 8,260

26 4,280 14 162 22,300 295 17,800 18,300 121 5,980

27 4,360 17 200 22,300 236 14,200 16,800 100 4,540

28 4,430 18 215 20,400 164 9,030 15,800 87 3,710

29 4,490 16 194 18,200 124 6,090 16,300 96 4,220

30 4,420 13 155 16,300 107 4,710 17,600 111 5,270

31 -- -- -- 15,000 90 3,640 -- -- --

TOTAL 132,950 -- 12,270 404,540 -- 180,827 604,600 -- 324,660

MEAN 4,432 32 409 13,050 136 5,853 20,150 180 10,800

MAX 5,510 166 2,090 22,300 358 20,600 28,100 478 36,100

MIN 3,910 12 131 4,250 14 163 14,100 84 3,200

Table 8. Daily mean streamflow and suspended-sediment data for Clark Fork above Missoula, Montana, October 2010 through 

September 2011.—Continued

[Abbreviations: acre-ft, acre-feet; ft3/s, cubic feet per second; e, estimated; max, maximum; mg/L, milligrams per liter; min, minimum; ton/d, tons per day. 

Symbol: --, no data or value not computed]
Data 61

Day

Mean 

streamflow 

(ft3

/s)

Suspended sediment Mean 

streamflow 

(ft3/s)

Suspended sediment Mean 

streamflow 

(ft3/s)

Suspended sediment

Mean concentration 

(mg/L)

Discharge 

(ton/d)

Mean concentration 

(mg/L)

Discharge 

(ton/d)

Mean concentration 

(mg/L)

Discharge 

(ton/d)

JULY AUGUST SEPTEMBER

1 17,300 95 4,440 3,650 8 79 1,960 4 21

2 15,900 80 3,430 3,630 8 78 1,970 4 21

3 14,800 70 2,800 3,590 8 78 1,950 3 16

4 14,300 67 2,590 3,490 7 66 1,930 3 16

5 13,900 66 2,480 3,400 7 64 1,910 3 15

6 13,300 58 2,080 3,300 7 62 1,880 3 15

7 12,700 54 1,850 3,220 7 61 1,840 3 15

8 12,200 49 1,610 3,120 6 51 1,830 3 15

9 11,600 44 1,380 2,990 6 48 1,830 3 15

10 10,600 42 1,200 2,870 6 46 1,820 3 15

11 9,670 40 1,040 2,810 5 38 1,790 4 19

12 9,140 39 962 2,770 5 37 1,780 4 19

13 9,250 38 949 2,680 5 36 1,760 4 19

14 9,430 35 891 2,610 5 35 1,750 4 19

15 9,400 45 1,140 2,550 4 28 1,740 5 23

16 8,910 38 914 2,480 4 27 1,780 5 24

17 8,480 31 710 2,420 4 26 1,820 5 25

18 7,890 27 575 2,340 4 25 1,840 5 25

19 7,370 24 478 2,280 4 25 1,860 5 25

20 7,050 21 400 2,230 4 24 1,890 5 26

21 6,720 18 327 2,210 4 24 1,890 5 26

22 6,340 15 257 2,170 4 23 1,860 5 25

23 6,020 13 211 2,120 4 23 1,820 5 25

24 5,540 12 179 2,050 4 22 1,770 5 24

25 5,170 12 168 2,000 4 22 1,740 5 23

26 4,880 11 145 1,970 4 21 1,720 6 28

27 4,640 10 125 1,950 4 21 1,700 6 28

28 4,410 9 107 1,930 4 21 1,680 7 32

29 4,200 8 91 1,930 4 21 1,660 7 31

30 3,980 8 86 1,920 4 21 1,660 7 31

31 3,800 9 92 1,930 4 21 -- -- --

TOTAL 278,890 -- 33,707 80,610 -- 1,174 54,430 -- 661

MEAN 8,996 35 1,090 2,600 5 38 1,814 5 22

MAX 17,300 95 4,440 3,650 8 79 1,970 7 32

MIN 3,800 8 86 1,920 4 21 1,660 3 15

Total for water year 2011 (unrounded sum of daily values): streamflow–1,861,086 ft3/s (annual runoff–3,691,000acre-ft); suspended-sediment 

discharge–577,279.2 tons.

Table 8. Daily mean streamflow and suspended-sediment data for Clark Fork above Missoula, Montana, October 2010 through 

September 2011.—Continued

[Abbreviations: acre-ft, acre-feet; ft3/s, cubic feet per second; e, estimated; max, maximum; mg/L, milligrams per liter; min, minimum; ton/d, tons per day. 

Symbol: --, no data or value not computed]
62 Water-Quality, Bed-Sediment, and Biological Data, and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 9. Seasonal daily maximum, minimum, and mean turbidity, with monthly summary statistics at Mill Creek near Anaconda, 

Montana, April through September 2011.

[Turbidity values are based on near-infrared monochrome light emitted at wavelengths of 780 to 900 nanometers with a detection angle of 90 +/- 2.5 degrees to 

incident beam, reported in formazin nephelometric units (FNU). Symbol: --, no data]

Day

Maximum Minimum Mean Maximum Minimum Mean Maximum Minimum Mean

APRIL MAY JUNE

1 -- -- -- 5.5 3.5 4.0 7.5 6.0 6.5

2 -- -- -- 6.5 3.5 4.5 8.5 6.0 7.0

3 -- -- -- 7.0 4.0 5.5 7.5 5.5 6.0

4 -- -- -- 9.0 4.5 6.0 6.5 5.0 5.5

5 -- -- -- 13 5.0 7.5 9.0 4.5 5.5

6 -- -- -- 13 6.0 8.5 12 6.0 7.0

7 -- -- -- 25 7.5 13 28 7.5 20

8 -- -- -- 30 14 20 26 13 16

9 -- -- -- 29 18 21 23 10 14

10 -- -- -- 20 16 18 13 8.0 9.0

11 3.5 2.5 3.0 23 16 18 9.0 7.0 8.0

12 4.5 2.5 3.0 29 18 23 9.5 6.5 7.5

13 5.0 3.0 3.5 26 17 20 8.0 5.5 6.5

14 4.0 3.0 3.5 29 12 16 7.5 5.0 6.0

15 4.0 3.0 3.5 15 10 12 7.0 5.0 5.5

16 5.5 2.5 3.5 15 10 12 7.0 5.0 5.5

17 7.5 4.0 4.5 12 8.5 9.5 6.5 4.5 5.0

18 7.5 4.5 5.5 10 7.5 8.5 5.5 4.0 4.5

19 6.5 4.0 4.5 9.0 7.0 8.0 5.0 3.5 4.5

20 6.5 4.0 4.5 12 7.5 8.0 6.0 3.5 4.5

21 4.5 3.5 4.0 10 6.5 8.0 8.0 3.5 5.0

22 4.5 3.5 3.5 23 7.0 10 14 4.5 7.0

23 5.0 3.0 3.5 25 9.5 14 60 8.5 18

24 4.5 3.0 3.5 30 25 27 67 30 44

25 5.0 3.0 4.0 29 18 22 38 15 21

26 5.5 3.5 4.0 21 13 16 20 11 14

27 5.5 3.5 4.0 15 10 12 20 9.5 12

28 6.5 4.0 4.5 13 8.5 9.5 31 8.5 15

29 5.0 4.0 4.5 9.5 7.0 8.0 45 18 29

30 5.0 3.5 4.0 12 7.0 7.5 40 14 23

31 -- -- -- 8.0 6.5 7.0 -- -- --

MONTH1 7.5 2.5 3.9 30 3.5 12 67 3.5 11
Data 63

Day

Maximum Minimum Mean Maximum Minimum Mean Maximum Minimum Mean

JULY AUGUST SEPTEMBER

1 17 9.0 12 5.0 1.5 2.5 -- -- --

2 12 7.0 8.5 3.5 1.5 2.0 2.5 0.5 1.5

3 21 6.5 9.5 3.5 1.5 2.0 3.0 .5 1.5

4 26 8.0 13 3.5 1.5 2.0 3.0 .5 1.0

5 14 8.0 11 3.0 1.5 2.0 2.0 .5 1.0

6 14 7.0 10 3.0 1.0 2.0 2.0 .5 1.0

7 13 6.0 7.5 3.0 1.0 2.0 2.5 .5 1.5

8 12 6.0 7.5 3.5 1.0 2.0 2.0 .5 1.0

9 11 7.0 9.0 3.5 1.0 2.0 2.0 .5 1.0

10 7.5 5.5 6.5 3.5 1.0 2.0 2.5 .5 1.0

11 8.5 4.5 6.0 4.0 1.0 2.0 2.0 .5 1.0

12 9.5 4.5 6.0 3.0 1.0 2.0 2.0 .5 1.0

13 16 4.5 7.5 3.5 1.0 1.5 2.5 .5 1.0

14 16 6.0 10 3.0 1.0 2.0 2.5 .5 1.5

15 7.0 4.5 5.5 3.0 1.0 2.0 2.0 .5 1.0

16 6.0 4.0 4.5 3.5 1.0 2.0 3.0 1.0 1.5

17 5.5 4.0 4.5 3.0 1.0 2.0 2.0 .5 1.5

18 6.0 3.5 4.5 3.5 1.0 2.0 2.0 .5 1.0

19 6.0 3.0 4.0 3.5 1.0 2.0 2.0 .5 1.0

20 5.0 3.0 4.0 3.0 1.0 2.0 3.5 .5 1.5

21 5.5 3.0 4.0 3.5 1.0 1.5 2.5 .5 1.5

22 5.5 2.5 3.5 3.5 .5 1.5 3.0 .5 1.5

23 5.0 2.5 3.5 3.5 .5 1.5 2.5 .5 1.5

24 5.0 2.5 3.5 3.0 .5 1.5 2.5 .5 1.5

25 4.5 2.0 3.0 2.5 1.0 1.5 2.5 .5 1.0

26 4.0 2.0 3.0 2.5 .5 1.5 2.0 .5 1.0

27 4.0 2.0 2.5 2.5 .5 1.0 2.5 .5 1.0

28 4.0 2.0 2.5 2.0 .5 1.0 3.0 1.0 1.5

29 3.5 1.5 2.5 2.0 1.0 1.5 -- -- --

30 3.5 1.5 2.5 2.5 .5 1.0 -- -- --

31 3.5 1.5 2.5 3.0 .5 1.5 -- -- --

MONTH1 26 1.5 5.9 5.0 .5 1.8 3.5 .5 1.2

1

For months with missing daily values, the means are calculated using available values.

Table 9. Seasonal daily maximum, minimum, and mean turbidity, with monthly summary statistics at Mill Creek near Anaconda, 

Montana, April through September 2011.—Continued

[Turbidity values are based on near-infrared monochrome light emitted at wavelengths of 780 to 900 nanometers with a detection angle of 90 +/- 2.5 degrees to 

incident beam, reported in formazin nephelometric units (FNU). Symbol: --, no data]
64 Water-Quality, Bed-Sediment, and Biological Data, and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 10. Seasonal daily maximum, minimum, and mean turbidity, with monthly summary statistics at Willow Creek near Anaconda, 

Montana, May through September 2011.

[Turbidity values are based on near-infrared monochrome light emitted at wavelengths of 780 to 900 nanometers with a detection angle of 90 +/- 2.5 degrees to 

incident beam, reported in formazin nephelometric units (FNU). Symbols: --, no data]

Day

Maximum Minimum Mean Maximum Minimum Mean Maximum Minimum Mean

MAY JUNE JULY

1 -- -- -- 30 14 17 8.0 5.0 6.0

2 -- -- -- 29 20 22 8.0 5.0 6.0

3 -- -- -- 26 18 21 8.0 5.0 6.0

4 -- -- -- 29 16 20 7.0 4.5 5.5

5 -- -- -- -- -- -- 7.5 4.5 5.5

6 28 17 21 110 8.0 46 7.0 4.5 5.5

7 44 18 26 120 32 67 7.5 4.5 5.5

8 64 22 31 45 18 26 7.0 4.0 5.0

9 64 28 35 42 30 37 6.5 4.0 4.5

10 38 25 30 110 9.0 40 6.0 4.0 4.5

11 48 21 27 110 18 48 7.5 3.5 5.0

12 56 27 38 39 23 31 7.5 3.5 4.5

13 90 35 49 36 23 28 -- -- --

14 67 33 48 37 21 25 -- -- --

15 37 26 30 41 17 22 -- -- --

16 33 24 27 23 14 17 -- -- --

17 32 18 21 20 13 15 -- -- --

18 19 16 17 17 11 13 -- -- --

19 17 15 16 23 11 13 -- -- --

20 19 14 15 13 9.5 11 8.0 5.5 6.0

21 16 14 15 13 9.5 10 10 5.0 6.5

22 57 14 18 10 8.0 9.0 11 5.0 6.5

23 62 29 42 11 8.0 8.5 8.0 5.0 6.0

24 290 62 150 9.5 7.0 8.0 32 6.0 9.0

25 300 62 170 10 7.0 8.0 14 5.5 7.0

26 87 33 65 9.5 7.0 7.5 11 5.5 7.0

27 59 27 38 8.5 6.5 7.5 14 5.0 7.0

28 35 22 27 8.5 6.0 7.0 9.5 5.0 6.5

29 46 17 26 8.5 5.5 6.5 11 4.5 6.5

30 25 16 19 8.5 5.5 6.0 11 4.5 6.0

31 20 15 16 -- -- -- 10 4.5 6.5

MONTH1 300 14 39 120 5.5 21 32 3.5 6.0
Data 65

Table 10. Seasonal daily maximum, minimum, and mean turbidity, with monthly summary statistics at Willow Creek near Anaconda, 

Montana, May through September 2011.—Continued

[Turbidity values are based on near-infrared monochrome light emitted at wavelengths of 780 to 900 nanometers with a detection angle of 90 +/- 2.5 degrees to 

incident beam, reported in formazin nephelometric units (FNU). Symbols: --, no data]

Day

Maximum Minimum Mean Maximum Minimum Mean

AUGUST SEPTEMBER

1 10 4.0 6.0 8.0 3.5 4.5

2 9.5 4.0 6.0 7.5 3.5 4.5

3 10 4.0 6.0 8.0 3.0 4.5

4 9.5 4.0 5.5 7.0 3.0 4.5

5 9.5 4.0 6.0 7.0 3.5 5.0

6 7.5 4.0 5.0 6.5 3.0 4.5

7 8.5 4.0 5.0 7.0 3.5 5.0

8 8.5 4.0 5.0 7.0 3.5 4.5

9 8.5 3.5 5.0 7.5 3.0 4.5

10 9.5 3.5 5.0 7.5 3.0 4.5

11 8.5 3.5 5.0 6.5 3.0 4.0

12 8.5 3.5 5.0 8.5 3.0 4.5

13 8.5 3.5 5.0 8.5 2.5 4.0

14 7.0 3.0 4.5 6.5 2.5 4.0

15 9.0 3.0 4.5 13 3.5 5.5

16 8.0 3.0 4.5 17 3.5 6.0

17 9.5 3.0 5.5 11 4.0 6.0

18 9.0 4.0 5.5 13 5.0 8.5

19 9.0 4.0 5.5 22 7.0 13

20 9.0 4.5 6.0 -- -- --

21 10 4.0 5.5 -- -- --

22 10 4.0 6.0 -- -- --

23 8.0 4.0 5.0 -- -- --

24 11 4.0 5.5 -- -- --

25 9.0 4.5 6.5 -- -- --

26 6.0 4.0 5.0 -- -- --

27 8.5 4.0 5.5 -- -- --

28 8.5 3.5 5.0 -- -- --

29 7.0 3.5 4.5 -- -- --

30 8.0 3.5 5.0 -- -- --

31 9.5 3.5 5.0 -- -- --

MONTH1 11 3.0 5.3 22 2.5 5.3

1

For months with missing daily values, the means are calculated using available values.
66 Water-Quality, Bed-Sediment, and Biological Data, and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 11. Seasonal daily maximum, minimum, and mean turbidity, with monthly summary statistics at Warm Springs Creek near 

Anaconda, Montana, April through September 2011.

[Turbidity values are based on near-infrared monochrome light emitted at wavelengths of 780 to 900 nanometers with a detection angle of 90 +/- 2.5 degrees to 

incident beam, reported in formazin nephelometric units (FNU). Symbols: --, no data]

Day

Maximum Minimum Mean Maximum Minimum Mean Maximum Minimum Mean

APRIL MAY JUNE

1 -- -- -- 5.0 2.5 3.0 5.0 3.5 4.5

2 -- -- -- 3.5 3.0 3.0 26 4.0 6.0

3 -- -- -- 4.0 2.5 3.0 5.0 3.5 4.0

4 -- -- -- 4.0 2.5 3.0 4.5 3.0 4.0

5 -- -- -- 6.5 2.5 3.5 5.0 3.5 4.0

6 -- -- -- 5.0 3.0 3.5 8.0 4.5 5.5

7 -- -- -- 5.5 3.0 4.0 54 8.0 29

8 -- -- -- 10 3.5 5.0 54 18 30

9 -- -- -- 20 5.5 8.5 20 11 15

10 -- -- -- 14 4.0 5.5 16 9.0 11

11 4.0 2.5 3.0 7.5 4.0 5.0 16 8.0 9.5

12 3.5 2.5 3.0 6.5 4.0 5.0 9.5 6.0 7.0

13 32 3.0 4.0 16 5.0 7.0 7.5 5.0 6.0

14 5.0 3.0 3.0 18 7.0 11 6.5 5.0 6.0

15 3.5 2.5 3.0 18 6.5 10 9.0 5.5 6.5

16 4.5 2.5 3.0 21 5.5 12 6.5 4.5 5.5

17 4.5 3.0 3.0 11 5.5 7.0 5.5 4.5 5.0

18 3.5 3.0 3.0 6.0 4.5 5.0 6.0 4.0 4.5

19 4.0 2.5 3.0 6.0 4.0 5.0 5.5 4.0 4.5

20 8.0 2.5 3.5 6.5 4.5 5.5 6.5 4.0 5.0

21 6.0 3.0 3.5 7.0 4.5 5.5 8.5 5.0 6.0

22 4.0 2.5 3.0 10 5.5 6.5 15 8.0 10

23 5.0 2.5 3.0 -- -- -- 30 11 17

24 4.0 2.5 3.0 -- -- -- 39 16 28

25 4.0 2.5 3.0 -- -- -- 19 9.5 14

26 5.0 2.5 3.0 -- -- -- 12 6.5 8.5

27 5.5 2.5 3.0 10 6.5 7.5 9.5 5.5 6.5

28 3.5 3.0 3.0 8.0 5.0 6.0 16 5.5 7.0

29 3.5 3.0 3.0 9.0 4.5 5.0 18 9.5 13

30 3.5 2.5 3.0 26 4.5 6.0 14 9.5 12

31 -- -- -- 5.5 4.0 4.5 -- -- --

MONTH1 32 2.5 3.1 26 2.5 5.8 54 3.0 9.8
Data 67

Table 11. Seasonal daily maximum, minimum, and mean turbidity, with monthly summary statistics at Warm Springs Creek near 

Anaconda, Montana, April through September 2011.—Continued

[Turbidity values are based on near-infrared monochrome light emitted at wavelengths of 780 to 900 nanometers with a detection angle of 90 +/- 2.5 degrees to 

incident beam, reported in formazin nephelometric units (FNU). Symbols: --, no data]

Day

Maximum Minimum Mean Maximum Minimum Mean Maximum Minimum Mean

JULY AUGUST SEPTEMBER

1 12 7.0 9.5 3.0 2.5 2.5 4.0 2.5 2.5

2 12 6.5 7.5 2.5 2.0 2.5 4.0 2.5 2.5

3 10 5.5 7.5 4.0 2.0 2.5 4.5 2.5 2.5

4 13 6.5 9.0 3.0 2.0 2.5 3.5 2.5 2.5

5 16 5.5 8.5 3.0 2.0 2.5 5.0 2.0 2.5

6 24 5.0 8.0 4.0 2.0 2.5 3.0 2.0 2.5

7 8.0 5.0 6.0 3.0 2.0 2.5 3.5 2.0 2.5

8 7.0 4.5 5.5 3.0 2.0 2.5 4.5 2.5 2.5

9 8.5 5.0 6.0 3.0 2.0 2.5 3.0 2.0 2.5

10 11 4.5 5.5 3.0 2.0 2.5 4.0 2.5 2.5

11 9.5 3.5 4.5 3.0 2.5 2.5 3.0 2.5 3.0

12 6.0 3.5 4.5 3.0 2.0 2.5 3.5 2.5 2.5

13 7.0 4.0 4.5 3.0 2.0 2.5 3.5 2.0 2.5

14 6.5 4.0 5.0 3.0 2.0 2.5 3.0 2.0 2.5

15 5.0 3.5 4.0 3.0 2.0 2.5 4.5 2.0 2.5

16 4.5 3.0 3.5 3.0 2.0 2.5 3.5 2.5 3.0

17 5.0 3.0 3.5 3.0 2.5 2.5 3.5 2.5 2.5

18 4.0 3.0 3.5 -- -- -- 3.0 2.0 2.5

19 5.0 3.0 3.5 3.5 2.5 2.5 3.0 2.5 2.5

20 4.5 3.0 3.0 3.5 2.5 3.0 3.0 2.0 2.5

21 4.0 3.0 3.0 3.0 2.5 2.5 3.0 2.0 2.5

22 4.0 2.5 3.0 3.5 2.5 3.0 3.0 2.0 2.5

23 4.0 2.5 3.0 4.0 2.5 2.5 3.5 2.0 2.5

24 4.5 2.5 3.0 4.0 2.5 2.5 3.0 2.0 2.5

25 3.5 2.5 3.0 4.5 2.5 3.0 3.0 2.0 2.5

26 3.5 2.5 3.0 3.5 2.5 3.0 3.0 2.0 2.5

27 4.0 2.5 2.5 3.5 2.5 3.0 3.0 2.0 2.5

28 3.5 2.5 2.5 3.5 2.5 3.0 3.0 2.0 2.5

29 3.5 2.5 3.0 81 2.5 7.0 3.0 2.0 2.5

30 3.5 2.5 2.5 3.5 2.5 3.0 2.5 2.0 2.5

31 5.0 2.5 2.5 3.5 2.5 3.0 -- -- --

MONTH1 24 2.5 4.6 81 2.0 2.8 5.0 2.0 2.5

1

For months with missing daily values, the means are calculated using available values.
68 Water-Quality, Bed-Sediment, and Biological Data, and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 12. Seasonal daily maximum, minimum, and mean turbidity, with monthly summary statistics at Lost Creek near Anaconda, 

Montana, April through September 2011.

[Turbidity values are based on near-infrared monochrome light emitted at wavelengths of 780 to 900 nanometers with a detection angle of 90 +/- 2.5 degrees to 

incident beam, reported in formazin nephelometric units (FNU). Symbols: <, less than; --, no data]

Day Maximum Minimum Mean Maximum Minimum Mean Maximum Minimum Mean

APRIL MAY JUNE

1 -- -- -- 4.5 2.5 3.0 14 4.5 6.5

2 -- -- -- 6.0 2.5 3.0 13 5.0 8.0

3 -- -- -- 6.0 3.0 3.5 8.0 4.5 6.0

4 -- -- -- 6.0 2.5 3.5 19 5.0 7.0

5 -- -- -- 6.0 3.0 3.5 15 5.5 8.5

6 -- -- -- 7.5 3.0 4.5 27 8.5 14

7 -- -- -- 8.5 3.5 4.5 87 26 48

8 -- -- -- 18 5.0 8.5 86 31 46

9 -- -- -- 33 9.5 15 57 25 33

10 -- -- -- 15 6.5 9.5 95 19 30

11 7.0 3.0 4.5 13 7.5 10 25 16 19

12 4.5 2.0 3.0 20 9.0 13 25 13 16

13 5.5 2.0 3.0 40 17 23 18 11 14

14 4.0 2.0 2.5 44 20 30 18 9.5 12

15 5.0 2.0 2.5 58 12 21 18 9.5 12

16 4.5 2.0 2.5 96 13 21 13 9.0 10

17 6.0 2.0 3.0 18 9.5 13 19 8.0 9.5

18 5.5 2.0 3.0 15 7.0 9.0 12 7.5 9.0

19 3.5 2.0 2.5 15 6.5 8.0 13 7.0 9.0

20 7.5 2.0 3.5 11 6.0 7.5 15 6.5 9.0

21 5.5 2.0 3.0 23 6.0 7.5 20 7.5 11

22 6.0 2.0 2.5 20 5.5 8.5 38 9.5 16

23 5.0 2.0 2.5 33 15 20 41 18 27

24 7.0 2.0 3.5 80 33 56 73 27 43

25 7.0 2.5 3.5 56 22 36 41 21 26

26 5.5 2.5 3.5 28 15 21 24 16 19

27 6.0 2.5 3.0 20 12 15 19 14 16

28 5.0 2.5 3.0 16 8.5 11 30 11 15

29 6.5 2.5 3.5 14 7.0 9.0 28 13 18

30 4.5 2.5 3.0 14 5.5 8.0 22 14 17

31 -- -- -- 9.5 6.0 7.5 -- -- --

MONTH1 7.5 2.0 3.0 96 2.5 13 95 4.5 18
Data 69

Table 12. Seasonal daily maximum, minimum, and mean turbidity, with monthly summary statistics at Lost Creek near Anaconda, 

Montana, April through September 2011.—Continued

[Turbidity values are based on near-infrared monochrome light emitted at wavelengths of 780 to 900 nanometers with a detection angle of 90 +/- 2.5 degrees to 

incident beam, reported in formazin nephelometric units (FNU). Symbols: <, less than; --, no data]

Day

Maximum Minimum Mean Maximum Minimum Mean Maximum Minimum Mean

JULY AUGUST SEPTEMBER

1 20 12 15 5.5 2.5 3.5 5.0 1.5 2.0

2 16 9.5 12 6.5 3.0 3.5 3.0 1.5 2.0

3 16 8.5 11 14 3.0 5.0 2.5 1.5 2.0

4 15 8.0 10 10 3.5 5.5 2.0 1.5 1.5

5 12 7.0 9.0 6.5 3.0 4.0 2.0 1.5 1.5

6 12 7.0 8.5 7.0 3.0 4.0 2.0 1.5 1.5

7 16 7.0 9.0 8.5 3.0 4.0 2.0 1.5 1.5

8 17 7.0 9.0 6.5 2.0 3.5 2.0 1.5 1.5

9 11 6.5 8.5 6.5 2.5 4.0 2.0 1.5 1.5

10 23 6.0 8.5 6.5 2.0 3.5 2.0 1.5 1.5

11 10 6.0 7.5 6.5 2.0 3.5 2.0 1.5 1.5

12 14 5.5 7.0 6.5 2.0 3.0 2.0 1.5 1.5

13 150 5.0 13 7.5 2.0 3.0 2.5 1.5 1.5

14 15 5.0 7.0 5.0 2.5 3.5 2.0 1.5 1.5

15 7.5 4.5 5.5 4.5 2.5 3.5 2.0 1.5 1.5

16 8.0 4.5 5.5 5.5 2.5 3.0 2.0 1.5 1.5

17 9.5 4.0 5.5 4.5 2.5 3.0 2.0 1.5 1.5

18 15 4.0 5.5 4.5 2.0 3.0 1.5 1.5 1.5

19 17 4.5 7.0 6.0 2.5 3.5 2.0 1.5 1.5

20 6.5 4.0 5.0 13 2.5 4.5 2.0 1.5 1.5

21 8.0 3.5 5.0 8.0 2.5 3.5 2.0 1.5 1.5

22 9.0 3.5 5.0 5.5 2.0 2.5 2.0 1.5 1.5

23 8.0 3.5 4.5 5.5 1.5 2.5 2.0 1.0 1.5

24 12 3.5 5.5 5.0 2.0 2.5 2.0 1.0 1.5

25 8.0 4.0 5.5 4.5 2.0 2.5 1.5 1.0 1.5

26 11 4.0 6.0 4.0 2.0 2.5 2.0 1.0 1.5

27 7.0 3.5 5.0 3.0 1.5 2.0 2.5 1.0 2.0

28 11 3.5 6.0 3.0 1.5 2.0 2.5 1.0 1.5

29 9.0 3.0 5.0 2.5 1.5 2.0 4.0 1.5 1.5

30 7.5 3.0 4.0 4.0 1.5 2.0 4.5 1.5 1.5

31 6.5 2.5 3.5 7.5 1.5 2.0 -- -- --

MONTH1 150 2.5 7.2 14 1.5 3.2 5.0 1.0 1.6

1

For months with missing daily values, the means are calculated using available values.
Table 13. Analyses of field replicates for water samples, Clark Fork basin, Montana. [Abbreviations: CaCO3, calcium carbonate; μg/L, micrograms per liter; mg/L, milligrams per liter; mm, millimeter. Symbol: <, less than laboratory reporting level] Site number (fig. 1) Site name Date Time Hardness, filtered (mg/L as CaCO3) Calcium, filtered (mg/L) Magnesium filtered (mg/L) Arsenic, filtered (μg/L) Ar

unf

reco

(μ

12323600 Silver Bow Creek at Opportunity 05/25/2011 1030 99.7 29.6 6.26 14.9 46

05/25/2011 1040 98.1 29.1 6.16 14.5 47

12323700 Mill Creek at Opportunity 08/15/2011 1520 64.5 17.8 4.85 19.3 19

08/15/2011 1525 66.3 18.3 5.00 19.6 19

12323750 Silver Bow Creek at Warm Springs 07/13/2011 1010 74.9 22.5 4.52 21.4 24

07/13/2011 1015 76.7 23.1 4.65 22.4 24

12323800 Clark Fork near Galen 06/08/2011 1145 106 32.6 5.83 28.2 36

06/08/2011 1155 106 32.9 5.85 28.2 35

12323840 Lost Creek near Anaconda 04/11/2011 1510 111 32.6 7.09 2.6 3

04/11/2011 1515 115 33.8 7.32 2.3 3

12324200 Clark Fork at Deer Lodge 05/17/2011 1225 138 41.1 8.53 16.8 35

05/17/2011 1230 146 43.1 9.37 16.9 35

06/24/2011 1130 115 34.9 6.69 32.9 37

06/24/2011 1135 115 35.1 6.73 32.4 37

12324400 Clark Fork above Little Blackfoot, near Garrison 03/15/2011 1500 206 60.5 13.2 9.3 13

03/15/2011 1505 213 62.4 13.9 9.3 13
Site number 

(fig. 1) Site name Date Time

Cadmium, 

unfiltered 

recoverable 

(μg/L)

Copper, 

filtered 

(μg/L)

Copper, 

unfiltered 

recoverable 

(μg/L)

Iron, 

filtered 

(μg/L)

Iron, 

unfiltered 

recoverable 

(μg/L)

12323600 Silver Bow Creek at Opportunity 05/25/2011 1030 2.29 68.9 310 182 7,220 

05/25/2011 1040 2.23 65.9 346 201 7,410 

12323700 Mill Creek at Opportunity 08/15/2011 1520 .06 1.6 2.3 38 106 

08/15/2011 1525 .06 1.6 2.3 40 105 

12323750 Silver Bow Creek at Warm Springs 07/13/2011 1010 .09 3.7 7.4 45 272 

07/13/2011 1015 .09 3.8 7.5 48 279 

12323800 Clark Fork near Galen 06/08/2011 1145 .38 20.7 82.1 47 1,120 

06/08/2011 1155 .37 20.1 79.0 44 1,100 

12323840 Lost Creek near Anaconda 04/11/2011 1510 <.05 1.4 4.6 7 115 

04/11/2011 1515 <.05 1.5 4.8 6 119 

12324200 Clark Fork at Deer Lodge 05/17/2011 1225 .62 10.2 136 27 2,620 

05/17/2011 1230 .56 10.4 143 31 2,640 

06/24/2011 1130 .36 35.6 87.6 36 976 06/24/2011 1135 .38 35.4 82.1 43 920 

12324400 Clark Fork above Little Blackfoot, 

near Garrison

03/15/2011 1500 .17 6.8 31.9 6 586 

03/15/2011 1505 .19 7.0 35.2 8 587 

Table 13. Analyses of field replicates for water samples, Clark Fork basin, Montana.—Continued[Abbreviations: CaCO3, calcium carbonate; μg/L, micrograms per liter; mg/L, milligrams per liter; mm, millimeter. Symbol: <, less than laboratory reporting level]
Table 13. Analyses of field replicates for water samples, Clark Fork basin, Montana.—Continued [Abbreviations: CaCO3, calcium carbonate; μg/L, micrograms per liter; mg/L, milligrams per liter; mm, millimeter. Symbol: <, less than laboratory reporting level] Site number (fig. 1) Site name Date Time Manganese, filtered (μg/L) Manganese, unfiltered recoverable (μg/L) Zinc, filtered (μg/L) Zinc, unfiltered recoverable (μg/L) Sedi

 susp

(percent 

0.062 

12323600 Silver Bow Creek at Opportunity 05/25/2011 1030 158 519 148 463 5

05/25/2011 1040 156 544 145 461 5

12323700 Mill Creek at Opportunity 08/15/2011 1520 7.5 11.0 <1.4 <2.4 8

08/15/2011 1525 7.6 10.9 <1.4 <2.4 8

12323750 Silver Bow Creek at Warm Springs 07/13/2011 1010 34.3 62.8 2.1 7.1 9

07/13/2011 1015 36.3 64.2 2.1 7.1 9

12323800 Clark Fork near Galen 06/08/2011 1145 31.9 121 13.7 60.9 4

06/08/2011 1155 31.9 118 12.8 60.7 5

12323840 Lost Creek near Anaconda 04/11/2011 1510 .80 3.9 <1.4 <2.4 8

04/11/2011 1515 .80 3.9 <1.4 <2.4 7

12324200 Clark Fork at Deer Lodge 05/17/2011 1225 22.8 263 5.7 107 4

05/17/2011 1230 23.6 250 5.8 105 5

06/24/2011 1130 54.9 102 36.3 71.1 3

06/24/2011 1135 55.5 117 34.5 69.4 2

12324400 Clark Fork above Little Blackfoot, near Garrison 03/15/2011 1500 35.3 81.5 3.7 28.8 7

03/15/2011 1505 36.2 84.4 4.5 29.1 7
Table 13. Analyses of field replicates for water samples, Clark Fork basin, Montana.—Continued[Abbreviations: CaCO3, calcium carbonate; μg/L, micrograms per liter; mg/L, milligrams per liter; mm, millimeter. Symbol: <, less than laboratory reporting level]

Site number 

(fig. 1) Site name Date Time

Hardness, 

filtered 

(mg/L as CaCO3)

Calcium, 

filtered 

(mg/L)

Magnesium 

filtered 

(mg/L)

Arsenic, 

filtered 

(μg/L)

Ar

unf

reco

(μ

12324680 Clark Fork at Goldcreek 11/16/2010 1345 185 55.1 11.4 7.2 8

11/16/2010 1350 186 55.2 11.7 7.2 9

12334550 Clark Fork at Turah Bridge, near 

Bonner

06/02/2011 1035 81.0 23.0 5.71 7.1 12

12334550 1040 1040 81.5 23.2 5.69 7

06/30/2011 1100 86.1 24.8 5.89 12.3 14

06/30/2011 1110 84.3 24.2 5.81 12.6 14

12340000 Blackfoot River near Bonner 05/26/2011 1200 81.7 21.1 7.02 1.0 2

05/26/2011 1210 81.6 21.0 7.07 1.0 2

12340500 Clark Fork above Missoula 06/09/2011 1400 75.4 20.6 5.85 6.3 23

06/09/2011 1410 75.4 20.6 5.85 6.3 23

06/15/2011 1350 85.8 23.5 6.56 7.1 13

06/15/2011 1355 87.6 24.1 6.68 7.2 13
Site number (fig. 1) Site name Date Time Cadmium, unfiltered recoverable (μg/L) Copper, filtered (μg/L) Copper, unfiltered recoverable (μg/L) Iron, filtered (μg/L) Iron, unfiltered recoverable (μg/L) 

12324680 Clark Fork at Goldcreek 11/16/2010 1345 0.14 3.0 15.2 4 273 

11/16/2010 1350 .12 3.0 15.3 5 270 

12334550 Clark Fork at Turah Bridge, near Bonner 06/02/2011 1035 .29 6.5 53.9 54 2,140 

12334550 1040 .28 7.2 48.4 58 2,070 

06/30/2011 1100 .18 9.1 30.5 41 956 06/30/2011 1110 .17 9.2 28.4 39 801 

12340000 Blackfoot River near Bonner 05/26/2011 1200 <.05 .88 3.6 44 1,240 

05/26/2011 1210 <.05 .87 3.6 49 1,240 

12340500 Clark Fork above Missoula 06/09/2011 1400 .83 10.2 145 43 4,960 

06/09/2011 1410 .84 10.0 148 39 5,020 

06/15/2011 1350 .35 7.0 53.1 54 2,030 

06/15/2011 1355 .32 7.0 52.8 53 1,990 

Table 13. Analyses of field replicates for water samples, Clark Fork basin, Montana.—Continued [Abbreviations: CaCO3, calcium carbonate; μg/L, micrograms per liter; mg/L, milligrams per liter; mm, millimeter. Symbol: <, less than laboratory reporting level]
Table 13. Analyses of field replicates for water samples, Clark Fork basin, Montana.—Continued[Abbreviations: CaCO3, calcium carbonate; μg/L, micrograms per liter; mg/L, milligrams per liter; mm, millimeter. Symbol: <, less than laboratory reporting level]

Site number 

(fig. 1) Site name Date Time

Manganese, 

filtered 

(μg/L)

Manganese, 

unfiltered 

recoverable 

(μg/L)

Zinc, 

filtered 

(μg/L)

Zinc, 

unfiltered 

recoverable 

(μg/L)

Sedi

 susp

(percent 

0.062 

12324680 Clark Fork at Goldcreek 11/16/2010 1345 12.6 58.9 3.5 17.0 8

11/16/2010 1350 12.6 59.8 3.5 16.4 8

12334550 Clark Fork at Turah Bridge, near 

Bonner

06/02/2011 1035 13.6 148 6.4 70.0 4

12334550 1040 14.2 133 6.6 64.7 4

06/30/2011 1100 31.7 102 7.7 41.1 606/30/2011 1110 31.7 93.9 8.0 34.7 6

12340000 Blackfoot River near Bonner 05/26/2011 1200 4.0 71.1 <1.4 5.2 7

05/26/2011 1210 4.6 71.9 <1.4 5.4 7

12340500 Clark Fork above Missoula 06/09/2011 1400 26.9 349 11.9 210 6

06/09/2011 1410 26.5 347 9.3 215 606/15/2011 1350 20.0 155 5.5 84.4 6

06/15/2011 1355 20.3 151 5.8 84.0 6
76 Water-Quality, Bed-Sediment, and Biological Data, and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 14. Precision of analyses of field replicates for water samples, Clark Fork basin, Montana.

[Abbreviations: μg/L, micrograms per liter; mg/L, milligrams per liter; mm, millimeter]

Constituent and reporting unit Number of 

replicate pairs

Standard 

deviation1

 (listed units)

Relative standard 

deviation 

(percent)

Within limits2

of data-quality 

objective

Calcium, filtered, mg/L 14 0.62 2.0 Yes

Magnesium, filtered, mg/L 14 .22 3.1 Yes

Arsenic, filtered, μg/L 14 .26 1.9 Yes

Arsenic, unfiltered recoverable, μg/L 14 .28 1.4 Yes

Cadmium, filtered, μg/L 14 .00 4.0 Yes

Cadmium, unfiltered recoverable, μg/L 14 .02 4.6 Yes

Copper, filtered, μg/L 14 .60 4.5 Yes

Copper, unfiltered recoverable, μg/L 14 7.2 10 Yes

Iron, filtered, μg/L 14 4.3 9.3 Yes

Iron, unfiltered recoverable, μg/L 14 51 2.9 Yes

Lead, filtered, μg/L 14 .03 9.7 Yes

Lead, unfiltered recoverable, μg/L 14 1.0 7.4 Yes

Manganese, filtered, μg/L 14 .62 1.9 Yes

Manganese, unfiltered recoverable, μg/L 14 6.9 4.7 Yes

Zinc, filtered, μg/L 14 .86 4.9 Yes

Zinc, unfiltered recoverable, μg/L 14 1.9 2.3 Yes

Sediment, suspended, percent finer than 0.062 mm 14 2.6 4.1 Yes

Sediment, suspended, mg/L 14 14 12 Yes

1

Standard deviation is calculated using one-half the laboratory reporting level for censored values (less than the laboratory reporting level).

2

Data-quality objective for an acceptable level of precision is a maximum relative standard deviation of 20 percent for field replicate analyses (table 3).

Table 15. Precision of analyses of laboratory replicates for water samples, Clark Fork basin, Montana.

[Abbreviations: μg/L, micrograms per liter; mg/L, milligrams per liter]

Constituent and reporting unit Number of 

replicate pairs

Standard deviation1

, 

in listed units

Relative standard 

deviation, 

in percent

Within limits2

of data-quality 

objective

Calcium, filtered, mg/L 8 0.48 1.3 Yes

Magnesium, filtered, mg/L 8 .09 1.2 Yes

Arsenic, filtered, μg/L 8 .06 .50 Yes

Arsenic, unfiltered recoverable, μg/L 8 .32 1.9 Yes

Cadmium, filtered, μg/L 8 .00 9.0 Yes

Cadmium, unfiltered recoverable, μg/L 8 .00 2.4 Yes

Copper, filtered, μg/L 8 .02 .48 Yes

Copper, unfiltered recoverable, μg/L 8 1.6 4.2 Yes

Iron, filtered, μg/L 8 .90 2.9 Yes

Iron, unfiltered recoverable, μg/L 8 16 1.6 Yes

Lead, filtered, μg/L 8 .00 3.1 Yes

Lead, unfiltered recoverable, μg/L 8 .08 1.4 Yes

Manganese, filtered, μg/L 8 .09 .48 Yes

Manganese, unfiltered recoverable, μg/L 8 1.0 1.1 Yes

Zinc, filtered, μg/L 8 .46 12 Yes

Zinc, unfiltered recoverable, μg/L 8 1.2 3.2 Yes

1

Standard deviation is calculated using laboratory reporting level for censored values.

2

Data-quality objective for an acceptable level of precision is a maximum relative standard deviation of 20 percent for laboratory replicate analyses (table 3).
Data 77

Table 16. Recovery efficiency for analyses of laboratory-spiked deionized-water blank samples.

[Abbreviation: μg/L, micrograms per liter]

Constituent and reporting unit Number of 

samples

95-percent confidence 

interval for spike recovery, 

in percent

Mean spike recovery, 

in percent

Within limits1

of data-quality 

objective

Arsenic, filtered, μg/L 5 102–109 105 Yes

Arsenic, unfiltered recoverable, μg/L 5 90.2–99.3 94.7 Yes

Cadmium, filtered, μg/L 5 97.9–111 105 Yes

Cadmium, unfiltered recoverable, μg/L 5 92.4–99.0 95.7 Yes

Copper, filtered, μg/L 5 89.4–103 96.2 Yes

Copper, unfiltered recoverable, μg/L 5 91.6–96.2 93.9 Yes

Iron, filtered, μg/L 5 89.3–132 111 No2

Iron, unfiltered recoverable, μg/L 5 98.2–117 107 Yes

Lead, filtered, μg/L 5 98.8–113 106 Yes

Lead, unfiltered recoverable, μg/L 5 98.4–101 99.8 Yes

Manganese, filtered, μg/L 5 97.0–104 101 Yes

Manganese, unfiltered recoverable, μg/L 5 97.8–100 98.9 Yes

Zinc, filtered, μg/L 5 94.3–122 108 Yes

Zinc, unfiltered recoverable, μg/L 5 92.2–100 96.1 Yes

1

Data-quality objective for acceptable bias is a maximum deviation of 25 percent from a theoretical 100-percent recovery (table 3).

2

Exceedance of data-quality objective resulted from one sample having a recovery of 138 percent. When data from this one spiked-sample set are removed 

from the 95-percent confidence interval calculation, filtered iron meets the data-quality objective limit (88.9–119 percent).

Table 17. Recovery efficiency for analyses of laboratory-spiked stream samples, Clark Fork basin, Montana.

[Abbreviation: μg/L, micrograms per liter]

Constituent and reporting unit Number of 

samples

95-percent confidence 

interval for spike recovery, 

in percent

Mean spike recovery, 

in percent

Within limits1

of data-quality 

objective

Arsenic, filtered, μg/L 5 101–111 106 Yes

Arsenic, unfiltered recoverable, μg/L 5 90.5–99.0 94.7 Yes

Cadmium, filtered, μg/L 5 99.2–109 104 Yes

Cadmium, unfiltered recoverable, μg/L 5 91.5–96.3 93.9 Yes

Copper, filtered, μg/L 5 79.9–113 96.6 Yes

Copper, unfiltered recoverable, μg/L 5 85.4–91.2 88.3 Yes

Iron, filtered, μg/L 5 92.0–124 108 Yes

Iron, unfiltered recoverable, μg/L 5 85.2–117 101 Yes

Lead, filtered, μg/L 5 98.8–110 104 Yes

Lead, unfiltered recoverable, μg/L 5 94.5–98.4 96.5 Yes

Manganese, filtered, μg/L 5 92.2–104 98.2 Yes

Manganese, unfiltered recoverable, μg/L 5 88.3–94.2 91.3 Yes

Zinc, filtered, μg/L 5 90.2–114 102 Yes

Zinc, unfiltered recoverable, μg/L 5 80.7–92.7 86.7 Yes

1

Data-quality objective for acceptable bias is a maximum deviation of 25 percent from a theoretical 100-percent recovery (table 3).
Table 18. Analyses of field blanks for water samples.[Abbreviations: μg/L, micrograms per liter; μS/cm, microsiemens per centimeter at 25 degrees Celsius; mg/L, milligrams per liter. Symbol: <, less than laboratory reporting lev

Date Time pH, onsite (standard units) Specific conductance, onsite (μS/cm) Calcium, filtered (mg/L) Magnesium, filtered (mg/L) Arsenic, filtered (μg/L) Arsenic, unfiltered recoverable (μg/L) Cadmium, filtered (μg/L) C

u

re

11/15/2010 1155 4.9 2 <0.02 <0.008 <0.02 <0.09 <0.02 

*03/07/2011 0800 5.6 2 .03 <.008 <.02 <.09 .06 04/14/2011 1255 5.3 2 <.02 <.008 <.02 <.09 <.02 *05/12/2011 0900 5.3 2 <.02 <.008 <.02 <.09 <.02 05/13/2011 0930 5.9 1 <.02 <.008 <.02 <.09 <.02 05/16/2011 1340 5.2 2 <.02 <.008 <.02 <.09 <.02 06/01/2011 1245 5.4 1 <.02 <.008 <.02 <.09 <.02 06/15/2011 0755 5.5 1 <.02 <.008 <.02 <.09 <.02 06/29/2011 1420 7.1 2 <.02 <.008 <.02 <.09 <.02 

07/13/2011 1245 5.6 <1 .02 <.008 <.02 <.09 <.02 08/16/2011 0755 5.5 2 <.02 <.008 <.02 <.09 <.02 

Date Copper, filtered (μg/L) Copper, unfil- tered recover- able (μg/L) Iron, filtered (μg/L) Iron, unfiltered recoverable (μg/L) Lead, filtered (μg/L) Lead, unfiltered recoverable (μg/L) Manganese, filtered (μg/L) Manganese, unfiltered recoverable (μg/L) 

11/15/2010 <0.50 <0.70 <3 <5 <0.01 <0.04 <0.1 <0.4 

*03/07/2011 .61 <.70 <3 <5 <.01 <.04 <.1 <.4 

04/14/2011 <.50 <.70 <3 <5 <.01 <.04 <.1 <.4 

*05/12/2011 <.50 <.70 <3 <5 .02 .05 <.1 <.4 

05/13/2011 <.50 <.70 <3 <5 .02 <.04 .3 <.4 

05/16/2011 <.50 <.70 <3 <5 <.01 <.04 <.1 <.4 

06/01/2011 <.50 <.70 <3 <5 <.01 <.04 <.1 <.4 

06/15/2011 <.50 <.70 <3 <5 <.01 <.04 <.1 <.4 

06/29/2011 <.50 <.70 <3 <5 <.01 <.04 .3 <.4 

07/13/2011 <.50 <.70 <3 <5 <.01 <.04 <.1 <.4 

08/16/2011 <.50 <.70 <3 <5 <.01 <.04 <.1 <.4 

* Annual office equipment blank collected before any equipment was used in the field.
Table 19. Bed-sediment data for the Clark Fork basin, Montana, August 2011.[Trace-element concentrations in bed sediment were determined for the fine-grained fraction (material less than 0.063 millimeter in diameter). Reported concentrations are the maliquots from each composite sample. Abbreviation: μg/g, micrograms per gram of dry sample weight]

Site number 

(fig. 1) Site name

Number of composite 

samples

Concentration (μg/g)

Arsenic Cadmium Chromium Copper Iron Lead Mang

12323600 Silver Bow Creek at Opportunity 3 73 7.9 42.6 1,080 34,300 279 1,7

12323750 Silver Bow Creek at Warm Springs 3 68 4.9 33.9 296 23,800 61 2,4

12323770 Warm Springs Creek near Warm Springs 3 34 1.2 33.2 496 19,600 42 5

12323800 Clark Fork near Galen 3 95 3.8 38.8 1,110 26,700 110 1,5

461415112450801 Clark Fork below Lost Creek, near Galen 3 126 4.8 38.5 1,500 28,700 153 1,4

461559112443301 Clark Fork at county bridge, near 

Racetrack 

3 132 5.4 39.2 1,490 29,000 149 1,6

461903112440701 Clark Fork at Dempsey Creek diversion, 

near Racetrack 

3 90 4.1 38.0 1,190 30,100 141 1,2

12324200 Clark Fork at Deer Lodge 3 95 3.9 45.8 1,200 31,500 142 1,2

12324400 Clark Fork above Little Blackfoot River, 

near Garrison

3 91 4.2 46.4 1,260 29,100 144 1,

12324680 Clark Fork at Goldcreek 3 62 3.0 46.5 843 27,300 118 9

12331800 Clark Fork near Drummond 3 41 1.7 36.0 405 36,800 75 

12334550 Clark Fork at Turah Bridge, near Bonner 3 35 2.0 37.4 405 24,100 69 1,0

12340000 Blackfoot River near Bonner 3 4 .05 23.7 21 18,300 12 5

12340500 Clark Fork above Missoula 3 30 1.2 29.5 281 20,400 43 7
80 Water-Quality, Bed-Sediment, and Biological Data, and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 20. Recovery efficiency for analyses of standard reference materials for bed-sediment samples.

[Dilution ratio is the proportion of initial volume of concentrated nitric acid used as a digesting reagent to final volume of solution after 

addition of 0.6N (normal) hydrochloric acid used for reconstituting dried residue. Abbreviations: μg/g, micrograms per gram of dry 

sample weight; SRM, standard reference material (agricultural soils)]

Constituent Number of 

analyses

Dilution 

ratio

Certified 

concentration 

(μg/g)

Mean SRM 

recovery

(percent)

95-percent 

confidence interval 

for SRM recovery 

(percent)

SRM sample 2709a

Arsenic 10 1:10 10.5 54.0 51.4–56.5

Cadmium 10 1:10 .371 70.7 67.4–74.1

Chromium 10 1:10 130 77.8 73.9–81.7

Copper 10 1:10 33.9 85.7 81.2–90.1

Iron 10 1:10 33,600 95.1 90.8–99.4

Lead 10 1:10 17.3 54.4 52.1–56.8

Manganese 10 1:10 529 93.4 89.2–97.6

Nickel 10 1:10 85 86.6 83.6–89.7

Zinc 10 1:10 103 98.1 94.9–101

SRM sample 2711a

Arsenic 10 1:10 107 84.6 82.1–87.1

Cadmium 10 1:10 54.1 96.5 93.5–99.6

Chromium 10 1:10 52 75.3 70.9–79.8

Copper 10 1:10 1,410 104 99.0–109

Iron 10 1:10 28,200 88.5 84.4–92.7

Lead 10 1:10 1,400 88.5 86.1–90.8

Manganese 10 1:10 675 82.6 78.9–86.3

Nickel 10 1:10 21.7 86.0 83.5–88.5

Zinc 10 1:10 414 98.8 95.4–102
Table 21. Analyses of procedural blanks for bed-sediment samples.[Dilution ratio is the proportion of initial volume of concentrated nitric acid used as a digesting reagent to final volume of solution after addition of 0.6N (normal) hydrochloric aresidue. Abbreviation: μg/mL, micrograms per milliliter. Symbol: <, less than minimum reporting level for liquid-phase concentration, in μg/mL]

Site number 

(fig. 1) Site name Dilution ratio Trace-element concentration (μg/mL) Arsenic Cadmium Chromium Copper Iron Lead Mangane

12323600 Silver Bow Creek at 

Opportunity 

1:10 <0.004 <0.0002 <0.003 <0.003 <0.03 <0.003 <0.001 

12323750 Silver Bow Creek at Warm 

Springs

1:10 <.004 <.0002 <.003 <.003 <.03 <.003 <.001 

12323770 Warm Springs Creek at 

Warm Springs

1:10 <.004 <.0002 <.003 <.003 <.03 <.003 <.001 

12323800 Clark Fork near Galen 1:10 <.004 <.0002 <.003 <.003 <.03 <.003 <.001 

461415112450801 Clark Fork below Lost 

Creek, near Galen 

1:10 <.004 <.0002 <.003 <.003 <.03 <.003 <.001 

461559112443301 Clark Fork at county bridge, 

near Racetrack 

1:10 <.004 <.0002 <.003 <.003 <.03 <.003 <.001 

461903112440701 Clark Fork at Dempsey 

Creek diversion, near Racetrack 

1:10 <.004 <.0002 <.003 <.003 <.03 <.003 <.001 

12324200 Clark Fork at Deer Lodge 1:10 <.004 <.0002 <.003 <.003 <.03 <.003 <.001 

12324400 Clark Fork above Little 

Blackfoot River, near Garrison

1:10 <.004 <.0002 <.003 <.003 <.03 <.003 <.001 

12324680 Clark Fork at Goldcreek 1:10 <.004 <.0002 <.003 <.003 <.03 <.003 <.001 

12331800 Clark Fork near Drummond 1:10 <.004 <.0002 <.003 <.003 <.03 <.003 <.001 

12334550 Clark Fork at Turah Bridge, 

near Bonner 

1:10 <.004 <.0002 <.003 <.003 <.03 <.003 <.001 

12340000 Blackfoot River near Bonner 1:10 <.004 <.0002 <.003 <.003 <.03 <.003 <.001 

12340500 Clark Fork above Missoula 1:10 <.004 <.0002 <.003 <.003 <.03 <.003 <.001 
82 Water-Quality, Bed-Sediment, and Biological Data, and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 22. Biological data for the Clark Fork basin, Montana, August 2011.

[Analyses are for the whole-body tissue of aquatic insects. Composite samples were made by combining similar-sized insects of the same species into a sample 

of sufficient mass for analysis. Concentrations for biota samples composed of two or more composite samples are the means of all analyses. Abbreviations: 

μg/g, micrograms per gram of dry sample weight; spp., species. Symbol: <, less than minimum reporting level for solid-phase concentration, in μg/g]

Taxon

Number of 

composite 

samples

Concentration (μg/g)

Arsenic Cadmium Chromium Copper Iron Lead ManganeseNickel Zinc

12323600--Silver Bow Creek at Opportunity

Hydropsyche cockerelli 1 21.4 9.3 25.5 522 6,150 74.3 1,500 3.6 1,470

Hydropsyche spp. 2 9.0 2.7 3.8 214 2,910 27.7 697 1.4 571

12323750--Silver Bow Creek at Warm Springs

Hydropsyche cockerelli 1 16.7 0.9 2.2 45.3 1,650 6.0 1,010 1.4 169

Hydropsyche occidentalis 1 14.3 .9 2.2 46.9 1,610 5.6 996 1.3 170

12323770--Warm Springs Creek at Warm Springs

Arctopsyche grandis 1 7.9 0.4 4.2 53.2 897 4.9 738 1.1 192

Hesperoperla spp. 1 1.2 1.0 2.0 64.9 456 1.9 202 .6 573

12323800--Clark Fork near Galen

Hydropsyche cockerelli 1 16.9 2.0 9.6 119 1,580 17.1 3,360 3.3 363

Hydropsyche occidentalis 3 11.2 1.2 3.0 131 2,310 9.4 705 2.2 212

461415112450801--Clark Fork below Lost Creek, near Galen

Rhyacophila spp. 2 4.3 4.1 1.1 83.4 335 5.4 256 0.3 356

461559112443301--Clark Fork at county bridge, near Racetrack

Hydropsyche occidentalis 3 10.2 1.0 2.0 122 1,500 9.8 709 1.3 199

461903112440701--Clark Fork at Dempsey Creek diversion, near Racetrack

Hydropsyche occidentalis 3 18.9 1.4 3.2 257 3,100 17.5 904 2.0 249

12324200--Clark Fork at Deer Lodge

Hydropsyche occidentalis 3 18.7 1.3 3.4 199 2,930 18.2 777 2.0 271

12324400--Clark Fork above Little Blackfoot River, near Garrison

Arctopsyche grandis 1 16.6 3.2 4.6 209 2,580 18.0 972 2.2 378

Hydropsyche occidentalis 2 13.0 1.5 3.5 165 2,370 15.5 1,080 1.7 275

Hydropsyche spp. 1 13.6 1.7 4.3 187 2,570 18.5 919 1.8 296

12324680--Clark Fork at Goldcreek

Arctopsyche grandis 3 14.1 2.6 4.9 201 2,850 15.2 1,020 2.7 299

Claassenia sabulosa 2 2.0 1.4 1.3 74.5 532 2.3 132 .3 275

Hydropsyche occidentalis 2 11.4 1.1 3.6 159 2,380 13.1 734 1.7 216
Data 83

Table 22. Biological data for the Clark Fork basin, Montana, August 2011.—Continued

[Analyses are for the whole-body tissue of aquatic insects. Composite samples were made by combining similar-sized insects of the same species into a sample 

of sufficient mass for analysis. Concentrations for biota samples composed of two or more composite samples are the means of all analyses. Abbreviations: 

μg/g, micrograms per gram of dry sample weight; spp., species. Symbol: <, less than minimum reporting level for solid-phase concentration, in μg/g]

Taxon

Number of 

composite 

samples

Concentration (μg/g)

Arsenic Cadmium Chromium Copper Iron Lead ManganeseNickel Zinc

12331800--Clark Fork near Drummond

Arctopsyche grandis 2 8.0 3.4 3.8 102 1,710 11.6 1,010 1.5 307

Claassenia sabulosa 2 1.8 2.0 1.0 74.2 438 1.9 143 .3 345

Hydropsyche occidentalis 2 7.5 1.0 2.6 92.9 1,670 10.6 890 1.2 218

12334550--Clark Fork at Turah Bridge, near Bonner

Arctopsyche grandis 2 6.6 2.6 3.8 80.2 1,990 9.6 813 1.6 271

Claassenia sabulosa 2 .9 1.6 1.1 63.8 279 1.2 178 .2 250

Hydropsyche cockerelli 1 9.8 2.2 14.2 126 3,180 19.7 848 2.7 332

Hydropsyche occidentalis 2 7.1 1.4 3.7 89.0 2,320 10.1 934 1.8 236

12340000--Blackfoot River near Bonner

Arctopsyche grandis 1 1.9 0.5 5.6 18.0 1,880 1.9 624 2.4 152

Claassenia sabulosa 2 <.12 .2 .8 49.5 237 .1 77 .3 232

Hydropsyche occidentalis 3 1.5 .3 2.3 17.9 1,800 1.4 435 1.5 124

12340500--Clark Fork above Missoula

Arctopsyche grandis 1 4.9 1.6 3.4 60.5 2,050 5.9 751 1.6 215

Claassenia sabulosa 2 1.1 .6 .8 51.8 247 .7 129 .2 225

Hydropsyche occidentalis 2 5.2 .9 3.3 66.2 2,200 6.3 769 1.6 195
84 Water-Quality, Bed-Sediment, and Biological Data, and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 23. Recovery efficiency for analyses of standard reference material for biota 

samples.

[Abbreviations: μg/g, micrograms per gram of dry sample weight; SRM, standard reference material (lobster 

hepatopancreas)]

Constituent Number of 

analyses

Certified 

concentration 

(μg/g)

Mean 

SRM recovery

(percent)

95-percent confidence 

interval for SRM recovery

(percent)

SRM sample TORT-2

Arsenic 12 21.6 95.5 94.5–96.6

Cadmium 12 26.7 77.4 74.2–80.6

Chromium 12 .77 129 123–136

Copper 12 106 92.7 90.6–94.8

Iron 12 105 90.0 86.9–92.6

Lead 12 .35 78.1 72.0–84.2

Manganese 12 13.6 89.8 86.9–92.8

Nickel 12 2.5 71.6 69.1–74.1

Zinc 12 180 91.4 88.1–94.8
Table 24. Analyses of procedural blanks for biota samples.[Procedural blanks were not diluted prior to analyses. Abbreviation: μg/mL, micrograms per milliliter. Symbol: <, less than minimum reporting level for liquid-phase concent

Site number 

(fig. 1) Site name Dilution ratio Trace-element concentration (μg/mL) Arsenic Cadmium Chromium Copper Iron Lead Manganes

12323600 Silver Bow Creek at Opportunity 1:1 <0.0013 <0.0002 <0.0009 <0.0014 <0.01 <0.002 <0.0012 

12323750 Silver Bow Creek at Warm 

Springs

1:1 <.0013 <.0002 <.0009 <.0014 <.01 <.002 <.0012 

12323770 Warm Springs Creek at Warm 

Springs

1:1 <.0013 <.0002 <.0009 <.0014 <.01 <.002 <.0012 

12323800 Clark Fork near Galen 1:1 <.0013 <.0002 <.0009 <.0014 <.01 <.002 <.0012 

461415112450801 Clark Fork below Lost Creek, 

near Galen

1:1 <.0013 <.0002 <.0009 <.0014 <.01 <.002 <.0012 

461559112443301 Clark Fork at county bridge, near 

Racetrack

1:1 <.0013 <.0002 <.0009 <.0014 <.01 <.002 <.0012 

461903112440701 Clark Fork at Dempsey Creek 

diversion, near Racetrack

1:1 <.0013 <.0002 <.0009 <.0014 <.01 <.002 <.0012 

12324200 Clark Fork at Deer Lodge 1:1 <.0013 <.0002 <.0009 <.0014 <.01 <.002 <.0012 

12324400 Clark Fork above Little 

Blackfoot River, near Garrison

1:1 <.0013 <.0002 <.0009 <.0014 <.01 <.002 <.0012 

12324680 Clark Fork at Goldcreek 1:1 <.0013 <.0002 <.0009 <.0014 <.01 <.002 <.0012 

12331800 Clark Fork near Drummond 1:1 <.0013 <.0002 <.0009 <.0014 <.01 <.002 <.0012 

12334550 Clark Fork at Turah Bridge, near 

Bonner

1:1 <.0013 <.0002 <.0009 <.0014 <.01 <.002 <.0012 

12340000 Blackfoot River near Bonner 1:1 <.0013 <.0002 <.0009 <.0014 <.01 <.002 <.0012 

12340500 Clark Fork above Missoula 1:1 <.0013 <.0002 <.0009 <.0014 <.01 <.002 <.0012 
86 Water-Quality, Bed-Sediment, and Biological Data, and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 25. Statistical summary of long-term water-quality data for the Clark Fork basin, Montana, March 1985 through 

September 2011.

[Abbreviations: CaCO3, calcium carbonate; ft3/s, cubic feet per second; °C, degrees Celsius; μg/L, micrograms per liter; μS/cm, microsiemens per 

centimeter at 25°C; mg/L, milligrams per liter; mm, millimeter; ton/d, tons per day. Symbols: <, less than laboratory reporting level1]

Property or constituent and reporting unit Number of 

samples Maximum Minimum Mean Median

12323230--Blacktail Creek at Harrison Avenue, at Butte

Period of record for water-quality data: March 1993–August 1995, December 1996–August 2003, December 2004–September 2011

Streamflow, instantaneous (ft3

/s) 139 156 1.9 16 9.2

pH, onsite (standard units) 139 8.4 7.3 7.8 7.7

Specific conductance, onsite (μS/cm) 139 412 116 261 259

Temperature, water (°C) 139 17.5 1.0 8.1 8.5

Hardness, filtered (mg/L as CaCO3

) 139 146 37.7 103 104

Calcium, filtered (mg/L) 139 41.8 10.6 29.4 29.8

Magnesium, filtered (mg/L) 139 11.0 2.71 7.14 7.16

Arsenic, filtered (μg/L) 138 13.0 1.0 4.2 3.6

Arsenic, unfiltered recoverable (μg/L) 139 18.0 1.0 2

5.6 4.9

Cadmium, filtered (μg/L) 137 .50 <.04 2

.05 .02

Cadmium, unfiltered recoverable (μg/L) 139 .11 <.01 2

.04 <1

Copper, filtered (μg/L) 138 10.0 <1.0 2

3.7 3.2

Copper, unfiltered recoverable (μg/L) 139 52.0 1.5 6.7 5.2

Iron, filtered (μg/L) 139 640 15 188 171

Iron, unfiltered recoverable (μg/L) 139 4,220 139 674 590

Lead, filtered (μg/L) 139 2.80 <.08 2

.20 <1.00

Lead, unfiltered recoverable (μg/L) 139 47.0 <1.00 2

1.78 .72

Manganese, filtered (μg/L) 139 144 14.2 42.1 37.5

Manganese, unfiltered recoverable (μg/L) 139 240 23.5 59.5 51.3

Zinc, filtered (μg/L) 137 11 <1.0 2

3.5 2.8

Zinc, unfiltered recoverable (μg/L) 139 130 <10 2

8.5 4.0

Sediment, suspended (percent finer than 0.062 mm) 139 97 50 82 83

Sediment, suspended concentration (mg/L) 139 139 1 12 7

Sediment, suspended discharge (ton/d) 139 59 .01 1.1 .18
Data 87

Property or constituent and reporting unit Number of 

samples Maximum Minimum Mean Median

12323250--Silver Bow Creek below Blacktail Creek, at Butte

Period of record for water-quality data: March 1993–August 1995, December 1996–August 2003, December 2004–September 2011

Streamflow, instantaneous (ft3

/s) 147 202 13 31 25

pH, onsite (standard units) 147 8.2 7.2 7.6 7.6

Specific conductance, onsite (μS/cm) 147 691 209 458 468

Temperature, water (°C) 147 20.0 1.0 10.3 9.5

Hardness, filtered (mg/L as CaCO3

) 147 217 66.0 146 150

Calcium, filtered (mg/L) 147 62.7 19.0 41.7 42.4

Magnesium, filtered (mg/L) 147 14.6 4.51 10.3 10.5

Arsenic, filtered (μg/L) 147 13.4 2.3 6.3 6.0

Arsenic, unfiltered recoverable (μg/L) 147 45.0 3.0 10.3 9.0

Cadmium, filtered (μg/L) 147 6.2 .04 .95 .50

Cadmium, unfiltered recoverable (μg/L) 147 6.0 .09 1.29 .90

Copper, filtered (μg/L) 147 303 3.2 32.3 13.2

Copper, unfiltered recoverable (μg/L) 147 550 8.9 74.5 27.1

Iron, filtered (μg/L) 147 292 10 94.5 76.0

Iron, unfiltered recoverable (μg/L) 147 7,400 85 842 570

Lead, filtered (μg/L) 147 2.4 <.5 2.44 .24

Lead, unfiltered recoverable (μg/L) 147 250 .64 11.5 3.00

Manganese, filtered (μg/L) 147 1,700 21.4 317 236

Manganese, unfiltered recoverable (μg/L) 147 1,600 25.9 360 289

Zinc, filtered (μg/L) 147 2,200 5.3 311 182

Zinc, unfiltered recoverable (μg/L) 147 2,200 21.2 377 230

Sediment, suspended (percent finer than 0.062 mm) 146 98 42 84 85

Sediment, suspended concentration (mg/L) 146 405 2 21 10

Sediment, suspended discharge (ton/d) 146 70 .08 2.5 .68

Table 25. Statistical summary of long-term water-quality data for the Clark Fork basin, Montana, March 1985 through 

September 2011.—Continued

[Abbreviations: CaCO3, calcium carbonate; ft3/s, cubic feet per second; °C, degrees Celsius; μg/L, micrograms per liter; μS/cm, microsiemens per 

centimeter at 25°C; mg/L, milligrams per liter; mm, millimeter; ton/d, tons per day. Symbols: <, less than laboratory reporting level1]
88 Water-Quality, Bed-Sediment, and Biological Data, and Statistical Summaries of Data, Clark Fork Basin, Montana

Property or constituent and reporting unit Number of 

samples Maximum Minimum Mean Median

12323600--Silver Bow Creek at Opportunity

Period of record for water-quality data: March 1993–August 1995, December 1996–September 2011

Streamflow, instantaneous (ft3

/s) 149 648 13 81 52

pH, onsite (standard units) 149 9.5 7.2 8.4 8.3

Specific conductance, onsite (μS/cm) 149 633 202 410 400

Temperature, water (°C) 149 22.5 0.0 9.4 9.5

Hardness, filtered (mg/L as CaCO3

) 149 240 60.2 147 143

Calcium, filtered (mg/L) 149 71.6 18.5 43.5 43.0

Magnesium, filtered (mg/L) 149 15.0 3.42 9.31 9.01

Arsenic, filtered (μg/L) 149 34.0 1.0 10.9 10.3

Arsenic, unfiltered recoverable (μg/L) 149 235 9.1 24.6 17.0

Cadmium, filtered (μg/L) 148 41.0 <.1 2

1.05 .58

Cadmium, unfiltered recoverable (μg/L) 149 49.0 .34 2

1.90 1.18

Copper, filtered (μg/L) 147 450 12.0 43.0 32.7

Copper, unfiltered recoverable (μg/L) 149 3,900 26.9 188 100

Iron, filtered (μg/L) 149 307 <3 2

49 27

Iron, unfiltered recoverable (μg/L) 148 24,100 240 1,540 780

Lead, filtered (μg/L) 149 5.1 <.5 2

.70 .33

Lead, unfiltered recoverable (μg/L) 149 650 3.27 35.4 14.9

Manganese, filtered (μg/L) 149 9,300 30.3 394 302

Manganese, unfiltered recoverable (μg/L) 149 10,000 69.8 512 404

Zinc, filtered (μg/L) 148 13,000 11.2 271 137

Zinc, unfiltered recoverable (μg/L) 149 15,000 52.5 478 260

Sediment, suspended (percent finer than 0.062 mm) 150 95 37 78 82

Sediment, suspended concentration (mg/L) 150 801 5 50 20

Sediment, suspended discharge (ton/d) 149 781 .18 23 2.7

Table 25. Statistical summary of long-term water-quality data for the Clark Fork basin, Montana, March 1985 through 

September 2011.—Continued

[Abbreviations: CaCO3, calcium carbonate; ft3/s, cubic feet per second; °C, degrees Celsius; μg/L, micrograms per liter; μS/cm, microsiemens per 

centimeter at 25°C; mg/L, milligrams per liter; mm, millimeter; ton/d, tons per day. Symbols: <, less than laboratory reporting level1]
Data 89

Property or constituent and reporting unit Number of 

samples Maximum Minimum Mean Median

12323670--Mill Creek near Anaconda

Period of record for water-quality data: December 2004–September 2011

Streamflow, instantaneous (ft3

/s) 56 309 7.4 65 30

pH, onsite (standard units) 56 8.6 7.5 8.0 8.0

Specific conductance, onsite (μS/cm) 56 213 56 131 132

Temperature, water (°C) 56 17.0 0.0 8.3 8.0

Hardness, filtered (mg/L as CaCO3

) 56 97.5 23.7 56.6 57.1

Calcium, filtered (mg/L) 56 25.9 7.00 15.7 16.0

Magnesium, filtered (mg/L) 56 8.01 1.45 4.24 4.18

Arsenic, filtered (μg/L) 56 32.9 7.3 16.9 15.3

Arsenic, unfiltered recoverable (μg/L) 56 34.8 8.6 18.4 16.9

Cadmium, filtered (μg/L) 55 .11 .02 2

.04 .04

Cadmium, unfiltered recoverable (μg/L) 56 .19 .03 .08 .07

Copper, filtered (μg/L) 56 5.1 .72 2.3 2.1

Copper, unfiltered recoverable (μg/L) 56 10.6 1.3 4.0 3.5

Iron, filtered (μg/L) 56 125 21 46 40

Iron, unfiltered recoverable (μg/L) 56 619 78 201 162

Lead, filtered (μg/L) 56 .24 <.08 2

.12 .11

Lead, unfiltered recoverable (μg/L) 56 3.12 .15 .79 .59

Manganese, filtered (μg/L) 56 11.9 3.1 5.8 5.6

Manganese, unfiltered recoverable (μg/L) 56 36.6 7.4 14.1 12.6

Zinc, filtered (μg/L) 56 4.0 <1.4 2

1.6 1.3

Zinc, unfiltered recoverable (μg/L) 56 9.2 1.0 2

3.1 2.6

Sediment, suspended (percent finer than 0.062 mm) 56 83 28 63 66

Sediment, suspended concentration (mg/L) 56 29 1 7 4

Sediment, suspended discharge (ton/d) 56 13 .02 2.1 .28

Table 25. Statistical summary of long-term water-quality data for the Clark Fork basin, Montana, March 1985 through 

September 2011.—Continued

[Abbreviations: CaCO3, calcium carbonate; ft3/s, cubic feet per second; °C, degrees Celsius; μg/L, micrograms per liter; μS/cm, microsiemens per 

centimeter at 25°C; mg/L, milligrams per liter; mm, millimeter; ton/d, tons per day. Symbols: <, less than laboratory reporting level1]
90 Water-Quality, Bed-Sediment, and Biological Data, and Statistical Summaries of Data, Clark Fork Basin, Montana

Property or constituent and reporting unit Number of 

samples Maximum Minimum Mean Median

12323700--Mill Creek at Opportunity

Period of record for water-quality data: March 2003–September 2011

Streamflow, instantaneous (ft3

/s) 72 261 0.43 39 12

pH, onsite (standard units) 72 8.2 7.5 8.0 8.0

Specific conductance, onsite (μS/cm) 72 230 59 147 152

Temperature, water (°C) 72 20.0 0.0 9.2 9.0

Hardness, filtered (mg/L as CaCO3

) 72 102 24.0 62.5 65.0

Calcium, filtered (mg/L) 72 28.0 7.01 17.5 18.2

Magnesium, filtered (mg/L) 72 7.83 1.56 4.54 4.67

Arsenic, filtered (μg/L) 72 55.1 9.0 22.4 20.6

Arsenic, unfiltered recoverable (μg/L) 72 53.5 10.0 25.7 24.5

Cadmium, filtered (μg/L) 72 .13 .02 .06 .06

Cadmium, unfiltered recoverable (μg/L) 72 .85 .04 .14 .10

Copper, filtered (μg/L) 72 6.1 1.0 3.0 2.6

Copper, unfiltered recoverable (μg/L) 72 38.8 1.5 6.8 4.4

Iron, filtered (μg/L) 72 94 16 47 42

Iron, unfiltered recoverable (μg/L) 72 1,960 44 314 145

Lead, filtered (μg/L) 72 .35 <.08 2

.14 .13

Lead, unfiltered recoverable (μg/L) 72 12.7 .07 1.54 .44

Manganese, filtered (μg/L) 72 32.8 2.1 7.3 5.5

Manganese, unfiltered recoverable (μg/L) 72 113 3.2 19.4 13.0

Zinc, filtered (μg/L) 71 7.7 1.3 3.0 2.8

Zinc, unfiltered recoverable (μg/L) 72 41 1.7 6.8 5.0

Sediment, suspended (percent finer than 0.062 mm) 72 90 26 68 72

Sediment, suspended concentration (mg/L) 72 107 1 13 2

Sediment, suspended discharge (ton/d) 72 55 <.01 2

3.8 .06

Table 25. Statistical summary of long-term water-quality data for the Clark Fork basin, Montana, March 1985 through 

September 2011.—Continued

[Abbreviations: CaCO3, calcium carbonate; ft3/s, cubic feet per second; °C, degrees Celsius; μg/L, micrograms per liter; μS/cm, microsiemens per 

centimeter at 25°C; mg/L, milligrams per liter; mm, millimeter; ton/d, tons per day. Symbols: <, less than laboratory reporting level1]
Data 91

Property or constituent and reporting unit Number of 

samples Maximum Minimum Mean Median

12323710--Willow Creek near Anaconda

Period of record for water-quality data: December 2004–September 2011

Streamflow, instantaneous (ft3

/s) 51 114 1.0 17 7.7

pH, onsite (standard units) 51 8.2 7.5 7.7 7.7

Specific conductance, onsite (μS/cm) 51 151 66 103 108

Temperature, water (°C) 51 15.5 .5 7.0 6.5

Hardness, filtered (mg/L as CaCO3

) 51 56.3 22.1 37.4 38.5

Calcium, filtered (mg/L) 51 18.3 7.56 12.5 13.0

Magnesium, filtered (mg/L) 51 2.60 .78 1.48 1.44

Arsenic, filtered (μg/L) 51 24.9 9.9 15.8 14.7

Arsenic, unfiltered recoverable (μg/L) 51 27.0 9.8 16.9 15.6

Cadmium, filtered (μg/L) 49 .05 <.04 2

.03 .03

Cadmium, unfiltered recoverable (μg/L) 51 .33 <.04 2

.07 .05

Copper, filtered (μg/L) 51 4.2 .90 2.1 2.0

Copper, unfiltered recoverable (μg/L) 51 16.8 1.0 4.0 3.2

Iron, filtered (μg/L) 51 277 28 84 66

Iron, unfiltered recoverable (μg/L) 51 2,380 86 392 226

Lead, filtered (μg/L) 51 .37 .03 2

.15 .14

Lead, unfiltered recoverable (μg/L) 51 7.96 .10 1.00 .49

Manganese, filtered (μg/L) 51 34.5 6.0 14.6 13.2

Manganese, unfiltered recoverable (μg/L) 51 99.9 14.0 28.1 24.2

Zinc, filtered (μg/L) 51 3.3 .65 2

1.7 1.6

Zinc, unfiltered recoverable (μg/L) 51 17.8 <2.0 2

3.5 2.2

Sediment, suspended (percent finer than 0.062 mm) 51 94 25 72 78

Sediment, suspended concentration (mg/L) 51 195 1 19 6

Sediment, suspended discharge (ton/d) 51 50 <.01 2

2.8 .14

Table 25. Statistical summary of long-term water-quality data for the Clark Fork basin, Montana, March 1985 through 

September 2011.—Continued

[Abbreviations: CaCO3, calcium carbonate; ft3/s, cubic feet per second; °C, degrees Celsius; μg/L, micrograms per liter; μS/cm, microsiemens per 

centimeter at 25°C; mg/L, milligrams per liter; mm, millimeter; ton/d, tons per day. Symbols: <, less than laboratory reporting level1]
92 Water-Quality, Bed-Sediment, and Biological Data, and Statistical Summaries of Data, Clark Fork Basin, Montana

Property or constituent and reporting unit Number of 

samples Maximum Minimum Mean Median

12323720--Willow Creek at Opportunity

Period of record for water-quality data: March 2003–September 2011

Streamflow, instantaneous (ft3

/s) 72 116 4.5 18 9.1

pH, onsite (standard units) 72 9.0 7.7 8.1 8.1

Specific conductance, onsite (μS/cm) 72 371 116 271 291

Temperature, water (°C) 72 20.5 1.5 11.2 11.2

Hardness, filtered (mg/L as CaCO3

) 72 169 58.5 117 126

Calcium, filtered (mg/L) 72 47.4 18.1 34.1 36.4

Magnesium, filtered (mg/L) 72 12.3 3.24 7.78 8.24

Arsenic, filtered (μg/L) 72 164 10.9 41.1 32.0

Arsenic, unfiltered recoverable (μg/L) 72 164 12.0 44.0 33.2

Cadmium, filtered (μg/L) 72 .12 <.04 2

.04 .04

Cadmium, unfiltered recoverable (μg/L) 72 .52 .02 .11 .07

Copper, filtered (μg/L) 72 21.4 1.1 5.5 3.4

Copper, unfiltered recoverable (μg/L) 72 48.8 2.8 11.9 8.0

Iron, filtered (μg/L) 72 274 7.0 50 42

Iron, unfiltered recoverable (μg/L) 72 1,670 27 303 216

Lead, filtered (μg/L) 72 .89 .04 2

.23 .18

Lead, unfiltered recoverable (μg/L) 72 14.4 .27 2.45 1.62

Manganese, filtered (μg/L) 72 200 3.3 32.1 24.0

Manganese, unfiltered recoverable (μg/L) 72 228 4.7 46.0 36.4

Zinc, filtered (μg/L) 72 19.8 <1.4 2

5.2 4.0

Zinc, unfiltered recoverable (μg/L) 72 68 1.1 13.2 9.8

Sediment, suspended (percent finer than 0.062 mm) 72 97 54 84 86

Sediment, suspended concentration (mg/L) 72 87 1 12 6

Sediment, suspended discharge (ton/d) 72 11 .02 1.1 .16

Table 25. Statistical summary of long-term water-quality data for the Clark Fork basin, Montana, March 1985 through 

September 2011.—Continued

[Abbreviations: CaCO3, calcium carbonate; ft3/s, cubic feet per second; °C, degrees Celsius; μg/L, micrograms per liter; μS/cm, microsiemens per 

centimeter at 25°C; mg/L, milligrams per liter; mm, millimeter; ton/d, tons per day. Symbols: <, less than laboratory reporting level1]
Data 93

Property or constituent and reporting unit Number of 

samples Maximum Minimum Mean Median

12323750--Silver Bow Creek at Warm Springs

Period of record for water-quality data: March 1993–September 2011

Streamflow, instantaneous (ft3

/s) 156 1,030 16 145 88

pH, onsite (standard units) 154 9.6 8.0 8.8 8.8

Specific conductance, onsite (μS/cm) 154 783 182 464 476

Temperature, water (°C) 155 25.0 .5 10.6 10.5

Hardness, filtered (mg/L as CaCO3

) 154 314 74.9 192 196

Calcium, filtered (mg/L) 154 90.4 22.5 56.1 57.3

Magnesium, filtered (mg/L) 154 21.4 4.52 12.7 13.0

Arsenic, filtered (μg/L) 154 60.0 6.8 23.1 23.4

Arsenic, unfiltered recoverable (μg/L) 154 94.0 10.0 26.9 26.4

Cadmium, filtered (μg/L) 154 .31 <.04 2

.06 .03

Cadmium, unfiltered recoverable (μg/L) 154 .56 <.1 2

.12 .06

Copper, filtered (μg/L) 154 40.0 1.7 7.9 5.8

Copper, unfiltered recoverable (μg/L) 154 96.8 2.4 15.8 11.3

Iron, filtered (μg/L) 154 93 <5 2

18 15

Iron, unfiltered recoverable (μg/L) 154 3,000 36 321 247

Lead, filtered (μg/L) 154 1.0 <.08 2

.12 <1.0

Lead, unfiltered recoverable (μg/L) 154 41.8 <1 2

2.30 1.24

Manganese, filtered (μg/L) 154 875 11.8 118 78.6

Manganese, unfiltered recoverable (μg/L) 154 899 24.0 178 140

Zinc, filtered (μg/L) 154 73 <1.0 2

7.4 4.0

Zinc, unfiltered recoverable (μg/L) 154 180 2.0 2

30.2 18.0

Sediment, suspended (percent finer than 0.062 mm) 155 98 43 82 85

Sediment, suspended concentration (mg/L) 156 229 1 10 6

Sediment, suspended discharge (ton/d) 156 279 .07 6.4 1.4

Table 25. Statistical summary of long-term water-quality data for the Clark Fork basin, Montana, March 1985 through 

September 2011.—Continued

[Abbreviations: CaCO3, calcium carbonate; ft3/s, cubic feet per second; °C, degrees Celsius; μg/L, micrograms per liter; μS/cm, microsiemens per 

centimeter at 25°C; mg/L, milligrams per liter; mm, millimeter; ton/d, tons per day. Symbols: <, less than laboratory reporting level1]
94 Water-Quality, Bed-Sediment, and Biological Data, and Statistical Summaries of Data, Clark Fork Basin, Montana

Property or constituent and reporting unit Number of 

samples Maximum Minimum Mean Median

12323760--Warm Springs Creek near Anaconda

Period of record for water-quality data: October 2005–September 2011

Streamflow, instantaneous (ft3

/s) 36 573 41 148 88

pH, onsite (standard units) 36 8.8 7.8 8.5 8.5

Specific conductance, onsite (μS/cm) 36 271 125 217 230

Temperature, water (°C) 36 16.0 4.0 8.9 8.5

Hardness, filtered (mg/L as CaCO3

) 36 134 58.5 105 110

Calcium, filtered (mg/L) 36 39.2 18.5 31.6 33.2

Magnesium, filtered (mg/L) 36 9.07 2.96 6.39 6.72

Arsenic, filtered (μg/L) 36 3.9 1.8 2.3 2.2

Arsenic, unfiltered recoverable (μg/L) 36 5.6 2.0 2.8 2.6

Cadmium, filtered (μg/L) 36 .05 <.02 2

.02 .02

Cadmium, unfiltered recoverable (μg/L) 36 .14 <.04 2

.04 .03

Copper, filtered (μg/L) 36 6.4 <1.0 2

1.2 .88

Copper, unfiltered recoverable (μg/L) 36 28.0 1.1 2

3.9 2.1

Iron, filtered (μg/L) 36 22 <6 2

8 6

Iron, unfiltered recoverable (μg/L) 36 1,000 27 141 76

Lead, filtered (μg/L) 36 .11 <.01 2

.03 <.12

Lead, unfiltered recoverable (μg/L) 36 3.51 .07 .50 .26

Manganese, filtered (μg/L) 36 2.9 <.1 2

1.2 1.0

Manganese, unfiltered recoverable (μg/L) 36 45.2 1.2 6.7 4.2

Zinc, filtered (μg/L) 36 5.6 <1.4 21.1 <2.8

Zinc, unfiltered recoverable (μg/L) 36 20.1 <2 2

3.6 2.0

Sediment, suspended (percent finer than 0.062 mm) 36 83 32 64 66

Sediment, suspended concentration (mg/L) 36 65 1 9 4

Sediment, suspended discharge (ton/d) 36 68 .13 5.3 1.3

Table 25. Statistical summary of long-term water-quality data for the Clark Fork basin, Montana, March 1985 through 

September 2011.—Continued

[Abbreviations: CaCO3, calcium carbonate; ft3/s, cubic feet per second; °C, degrees Celsius; μg/L, micrograms per liter; μS/cm, microsiemens per 

centimeter at 25°C; mg/L, milligrams per liter; mm, millimeter; ton/d, tons per day. Symbols: <, less than laboratory reporting level1]
Data 95

Property or constituent and reporting unit Number of 

samples Maximum Minimum Mean Median

12323770--Warm Springs Creek at Warm Springs

Period of record for water-quality data: March 1993–September 2011

Streamflow, instantaneous (ft3

/s) 115 420 2.8 99 57

pH, onsite (standard units) 114 8.7 7.4 8.3 8.2

Specific conductance, onsite (μS/cm) 114 795 139 291 296

Temperature, water (°C) 115 20.0 0.0 8.5 8.0

Hardness, filtered (mg/L as CaCO3

) 114 415 39.8 141 144

Calcium, filtered (mg/L) 114 130 10.5 43.1 43.7

Magnesium, filtered (mg/L) 114 22.0 3.29 8.13 8.06

Arsenic, filtered (μg/L) 114 14.0 2.0 5.0 4.4

Arsenic, unfiltered recoverable (μg/L) 114 27.0 3.0 7.4 6.0

Cadmium, filtered (μg/L) 114 .1 <.04 2

.04 <.1

Cadmium, unfiltered recoverable (μg/L) 114 .41 <.05 2

.08 .03

Copper, filtered (μg/L) 114 16.0 1.0 3.3 2.9

Copper, unfiltered recoverable (μg/L) 114 147 2.3 19.6 9.0

Iron, filtered (μg/L) 114 30 <5 2

11 10

Iron, unfiltered recoverable (μg/L) 114 2,110 39 311 121

Lead, filtered (μg/L) 114 1.8 <.08 2

.08 <.6

Lead, unfiltered recoverable (μg/L) 114 14.0 <1.00 2

1.92 .56

Manganese, filtered (μg/L) 114 570 18.8 116 85.6

Manganese, unfiltered recoverable (μg/L) 114 1,400 37.0 202 158

Zinc, filtered (μg/L) 113 10 <1.0 2

2.1 1.4

Zinc, unfiltered recoverable (μg/L) 114 60 <2.4 2

9.2 3.0

Sediment, suspended (percent finer than 0.062 mm) 115 88 43 70 71

Sediment, suspended concentration (mg/L) 115 127 1 18 8

Sediment, suspended discharge (ton/d) 115 87 .05 8.5 1.1

Table 25. Statistical summary of long-term water-quality data for the Clark Fork basin, Montana, March 1985 through 

September 2011.—Continued

[Abbreviations: CaCO3, calcium carbonate; ft3/s, cubic feet per second; °C, degrees Celsius; μg/L, micrograms per liter; μS/cm, microsiemens per 

centimeter at 25°C; mg/L, milligrams per liter; mm, millimeter; ton/d, tons per day. Symbols: <, less than laboratory reporting level1]
96 Water-Quality, Bed-Sediment, and Biological Data, and Statistical Summaries of Data, Clark Fork Basin, Montana

Property or constituent and reporting unit Number of 

samples Maximum Minimum Mean Median

12323800--Clark Fork near Galen

Period of record for water-quality data: July 1988–September 2011

Streamflow, instantaneous (ft3

/s) 197 1,380 14 226 136

pH, onsite (standard units) 184 9.2 7.5 8.5 8.6

Specific conductance, onsite (μS/cm) 185 720 182 413 420

Temperature, water (°C) 196 23.5 0.0 9.8 10.0

Hardness, filtered (mg/L as CaCO3

) 183 365 76.4 180 188

Calcium, filtered (mg/L) 183 110 23.2 53.4 55.3

Magnesium, filtered (mg/L) 183 22.0 4.44 11.4 11.8

Arsenic, filtered (μg/L) 183 53.0 4.0 15.2 14.8

Arsenic, unfiltered recoverable (μg/L) 183 78.0 3.0 19.5 17.0

Cadmium, filtered (μg/L) 183 1.0 <.04 2

.06 <1

Cadmium, unfiltered recoverable (μg/L) 183 3.0 <.1 2

.19 .05

Copper, filtered (μg/L) 183 50.0 1.7 7.8 6.0

Copper, unfiltered recoverable (μg/L) 182 240 4.1 27.5 15.5

Iron, filtered (μg/L) 183 110 <3 2

16 11

Iron, unfiltered recoverable (μg/L) 183 9,200 56 477 270

Lead, filtered (μg/L) 183 3.00 <.08 2

.15 <1.00

Lead, unfiltered recoverable (μg/L) 183 31.0 <1.00 2

3.42 1.86

Manganese, filtered (μg/L) 183 460 24.0 105 76.0

Manganese, unfiltered recoverable (μg/L) 183 1,400 47.3 221 170

Zinc, filtered (μg/L) 183 110 <1.0 2

8.9 4.4

Zinc, unfiltered recoverable (μg/L) 183 360 <10.0 2

36.4 20.0

Sediment, suspended (percent finer than 0.062 mm) 196 97 32 76 77

Sediment, suspended concentration (mg/L) 197 338 1 18 8

Sediment, suspended discharge (ton/d) 197 459 .12 21 2.8

Table 25. Statistical summary of long-term water-quality data for the Clark Fork basin, Montana, March 1985 through 

September 2011.—Continued

[Abbreviations: CaCO3, calcium carbonate; ft3/s, cubic feet per second; °C, degrees Celsius; μg/L, micrograms per liter; μS/cm, microsiemens per 

centimeter at 25°C; mg/L, milligrams per liter; mm, millimeter; ton/d, tons per day. Symbols: <, less than laboratory reporting level1]
Data 97

Property or constituent and reporting unit Number of 

samples Maximum Minimum Mean Median

12323840--Lost Creek near Anaconda

Period of record for water-quality data: December 2004–September 2011

Streamflow, instantaneous (ft3

/s) 55 73 0.37 13 8.2

pH, onsite (standard units) 55 8.6 7.4 8.2 8.2

Specific conductance, onsite (μS/cm) 55 253 121 197 210

Temperature, water (°C) 55 17.0 1.0 8.0 8.0

Hardness, filtered (mg/L as CaCO3

) 55 122 50.4 93.3 98.6

Calcium, filtered (mg/L) 55 37.1 15.7 28.3 29.3

Magnesium, filtered (mg/L) 55 7.22 2.71 5.47 5.78

Arsenic, filtered (μg/L) 55 156 1.8 7.2 3.2

Arsenic, unfiltered recoverable (μg/L) 55 3,860 2.0 75.2 3.8

Cadmium, filtered (μg/L) 54 .90 <.02 2

.04 .02

Cadmium, unfiltered recoverable (μg/L) 55 147 .01 2

2.7 .04

Copper, filtered (μg/L) 55 90.5 .80 3.6 1.7

Copper, unfiltered recoverable (μg/L) 55 29,100 1.3 536 4.5

Iron, filtered (μg/L) 55 27 <6 2

10 9

Iron, unfiltered recoverable (μg/L) 55 99,700 22 2,020 110

Lead, filtered (μg/L) 55 .18 <.03 2

.04 .02

Lead, unfiltered recoverable (μg/L) 55 1,290 .08 24.4 .46

Manganese, filtered (μg/L) 55 42.4 <.2 2

2.0 1.1

Manganese, unfiltered recoverable (μg/L) 55 8,830 1.2 168 4.6

Zinc, filtered (μg/L) 54 30.0 <1.4 2

1.8 1.0

Zinc, unfiltered recoverable (μg/L) 54 7,780 <2 2

148 2.5

Sediment, suspended (percent finer than 0.062 mm) 55 97 22 58 59

Sediment, suspended concentration (mg/L) 55 58,900 1 1,080 6

Sediment, suspended discharge (ton/d) 55 1,320 <.01 2

25 .11

Table 25. Statistical summary of long-term water-quality data for the Clark Fork basin, Montana, March 1985 through 

September 2011.—Continued

[Abbreviations: CaCO3, calcium carbonate; ft3/s, cubic feet per second; °C, degrees Celsius; μg/L, micrograms per liter; μS/cm, microsiemens per 

centimeter at 25°C; mg/L, milligrams per liter; mm, millimeter; ton/d, tons per day. Symbols: <, less than laboratory reporting level1]
98 Water-Quality, Bed-Sediment, and Biological Data, and Statistical Summaries of Data, Clark Fork Basin, Montana

Property or constituent and reporting unit Number of 

samples Maximum Minimum Mean Median

12323850--Lost Creek near Galen

Period of record for water-quality data: March 2003–September 2011

Streamflow, instantaneous (ft3

/s) 72 71 1.3 23 16

pH, onsite (standard units) 72 8.7 8.0 8.3 8.3

Specific conductance, onsite (μS/cm) 72 934 540 645 630

Temperature, water (°C) 72 26.5 0.0 10.5 9.8

Hardness, filtered (mg/L as CaCO3

) 72 451 203 301 299

Calcium, filtered (mg/L) 72 122 48.5 85.1 85.3

Magnesium, filtered (mg/L) 72 35.7 17.3 21.6 20.8

Arsenic, filtered (μg/L) 72 41.8 6.0 14.4 12.6

Arsenic, unfiltered recoverable (μg/L) 72 43.0 6.0 15.2 14.0

Cadmium, filtered (μg/L) 71 .05 <.04 2

.03 .02

Cadmium, unfiltered recoverable (μg/L) 72 .11 .01 2

.04 .04

Copper, filtered (μg/L) 72 6.7 .99 2.3 2.2

Copper, unfiltered recoverable (μg/L) 72 22.5 1.6 5.4 4.4

Iron, filtered (μg/L) 72 61 <6 2

13 10

Iron, unfiltered recoverable (μg/L) 72 293 14 99 78

Lead, filtered (μg/L) 71 .33 <.06 2

.05 <.02

Lead, unfiltered recoverable (μg/L) 72 1.30 .04 .35 .26

Manganese, filtered (μg/L) 72 54.0 1.9 15.3 13.6

Manganese, unfiltered recoverable (μg/L) 72 56.5 2.2 20.5 18.4

Zinc, filtered (μg/L) 71 3.8 <1.0 2

1.5 1.3

Zinc, unfiltered recoverable (μg/L) 72 9.0 <2 2

2.8 2.0

Sediment, suspended (percent finer than 0.062 mm) 72 86 18 58 60

Sediment, suspended concentration (mg/L) 72 79 2 16 15

Sediment, suspended discharge (ton/d) 72 4.2 .01 1.0 .52

Table 25. Statistical summary of long-term water-quality data for the Clark Fork basin, Montana, March 1985 through 

September 2011.—Continued

[Abbreviations: CaCO3, calcium carbonate; ft3/s, cubic feet per second; °C, degrees Celsius; μg/L, micrograms per liter; μS/cm, microsiemens per 

centimeter at 25°C; mg/L, milligrams per liter; mm, millimeter; ton/d, tons per day. Symbols: <, less than laboratory reporting level1]
Data 99

Table 25. Statistical summary of long-term water-quality data for the Clark Fork basin, Montana, March 1985 through 

September 2011.—Continued

[Abbreviations: CaCO3, calcium carbonate; ft3/s, cubic feet per second; °C, degrees Celsius; μg/L, micrograms per liter; μS/cm, microsiemens per 

centimeter at 25°C; mg/L, milligrams per liter; mm, millimeter; ton/d, tons per day. Symbols: <, less than laboratory reporting level1]

Property or constituent and reporting unit Number of 

samples Maximum Minimum Mean Median

12324200--Clark Fork at Deer Lodge

Period of record for water-quality data: March 1985–September 2011

Streamflow, instantaneous (ft3

/s) 249 2,000 23 310 227

pH, onsite (standard units) 197 8.9 7.4 8.3 8.3

Specific conductance, onsite (μS/cm) 232 642 228 471 498

Temperature, water (°C) 248 23.0 0.0 9.9 10.0

Hardness, filtered (mg/L as CaCO3

) 189 282 94.9 199 208

Calcium, filtered (mg/L) 189 82.0 28.2 58.8 61.0

Magnesium, filtered (mg/L) 189 18.7 5.53 12.6 13.2

Arsenic, filtered (μg/L) 199 39.0 6.0 14.6 13.7

Arsenic, unfiltered recoverable (μg/L) 198 215 4.8 24.0 18.0

Cadmium, filtered (μg/L) 198 2.0 <.10 2

.08 <1.0

Cadmium, unfiltered recoverable (μg/L) 198 5.0 <.10 2

.40 .10

Copper, filtered (μg/L) 199 120 3.2 10.9 8.0

Copper, unfiltered recoverable (μg/L) 197 1,500 8.2 80.2 37.0

Iron, filtered (μg/L) 199 190 <3 2

15 9

Iron, unfiltered recoverable (μg/L) 199 29,000 27 1,450 520

Lead, filtered (μg/L) 199 6.00 <.08 2

.31 <1.00

Lead, unfiltered recoverable (μg/L) 199 200 .33 2

10.6 4.70

Manganese, filtered (μg/L) 199 400 1.0 41.3 33.4

Manganese, unfiltered recoverable (μg/L) 199 4,600 11.9 231 132

Zinc, filtered (μg/L) 199 230 <10.0 2

11.7 8.0

Zinc, unfiltered recoverable (μg/L) 197 1,700 4 84.2 40.0

Sediment, suspended (percent finer than 0.062 mm) 240 99 31 71 72

Sediment, suspended concentration (mg/L) 249 2,250 1 69 22

Sediment, suspended discharge (ton/d) 249 8,690 .18 145 12
100 Water-Quality, Bed-Sediment, and Biological Data, and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 25. Statistical summary of long-term water-quality data for the Clark Fork basin, Montana, March 1985 through 

September 2011.—Continued

[Abbreviations: CaCO3, calcium carbonate; ft3/s, cubic feet per second; °C, degrees Celsius; μg/L, micrograms per liter; μS/cm, microsiemens per 

centimeter at 25°C; mg/L, milligrams per liter; mm, millimeter; ton/d, tons per day. Symbols: <, less than laboratory reporting level1]

Property or constituent and reporting unit Number of 

samples Maximum Minimum Mean Median

12324400--Clark Fork above Little Blackfoot River, near Garrison

Period of record for water-quality data: March 2009–September 2011

Streamflow, instantaneous (ft3

/s) 23 2,310 186 626 353

pH, onsite (standard units) 23 8.8 7.9 8.3 8.3

Specific conductance, onsite (μS/cm) 23 494 249 390 386

Temperature, water (°C) 23 19.0 3.0 10.7 12.0

Hardness, filtered (mg/L as CaCO3

) 23 221 104 169 160

Calcium, filtered (mg/L) 23 64.0 31.8 49.8 46.9

Magnesium, filtered (mg/L) 23 14.8 5.93 10.8 10.4

Arsenic, filtered (μg/L) 23 36.7 9.2 16.3 16.4

Arsenic, unfiltered recoverable (μg/L) 23 46.0 11.7 24.8 20.7

Cadmium, filtered (μg/L) 23 .23 .04 .08 .08

Cadmium, unfiltered recoverable (μg/L) 23 .75 .08 .34 .25

Copper, filtered (μg/L) 23 40.6 4.2 11.4 9.1

Copper, unfiltered recoverable (μg/L) 23 197 12.4 76.3 59.4

Iron, filtered (μg/L) 23 43 5 16 11

Iron, unfiltered recoverable (μg/L) 23 3,200 119 1,140 731

Lead, filtered (μg/L) 23 .39 .04 .15 .11

Lead, unfiltered recoverable (μg/L) 23 29.4 .90 10.2 7.75

Manganese, filtered (μg/L) 23 45.4 15.6 27.3 23.6

Manganese, unfiltered recoverable (μg/L) 23 309 40.5 144 129

Zinc, filtered (μg/L) 23 37.1 2.9 7.6 6.0

Zinc, unfiltered recoverable (μg/L) 23 152 10.1 62.9 41.2

Sediment, suspended (percent finer than 0.062 mm) 23 85 42 66 66

Sediment, suspended concentration (mg/L) 23 179 5 59 30

Sediment, suspended discharge (ton/d) 23 428 2.5 131 42
Data 101

Table 25. Statistical summary of long-term water-quality data for the Clark Fork basin, Montana, March 1985 through 

September 2011.—Continued

[Abbreviations: CaCO3, calcium carbonate; ft3/s, cubic feet per second; °C, degrees Celsius; μg/L, micrograms per liter; μS/cm, microsiemens per 

centimeter at 25°C; mg/L, milligrams per liter; mm, millimeter; ton/d, tons per day. Symbols: <, less than laboratory reporting level1]

Property or constituent and reporting unit Number of 

samples Maximum Minimum Mean Median

12324680--Clark Fork at Goldcreek

Period of record for water-quality data: March 1993–September 2011

Streamflow, instantaneous (ft3

/s) 155 4,450 87 799 529

pH, onsite (standard units) 154 8.9 7.9 8.4 8.3

Specific conductance, onsite (μS/cm) 154 510 206 367 380

Temperature, water (°C) 155 23.0 0.0 10.0 10.5

Hardness, filtered (mg/L as CaCO3

) 154 232 85.8 161 169

Calcium, filtered (mg/L) 154 68.0 25.9 47.5 49.7

Magnesium, filtered (mg/L) 154 15.0 5.15 10.3 10.6

Arsenic, filtered (μg/L) 154 22.5 5.8 10.2 10.0

Arsenic, unfiltered recoverable (μg/L) 154 75.0 7.0 15.0 12.6

Cadmium, filtered (μg/L) 154 .2 <.04 2

.04 <.10

Cadmium, unfiltered recoverable (μg/L) 154 2 <.10 2

.18 .06

Copper, filtered (μg/L) 153 36.0 2.1 6.8 5.4

Copper, unfiltered recoverable (μg/L) 153 440 5.2 40.4 24.5

Iron, filtered (μg/L) 154 100 <3 2

19 12

Iron, unfiltered recoverable (μg/L) 154 12,000 27 868 433

Lead, filtered (μg/L) 152 .6 <.08 2

.11 <.6

Lead, unfiltered recoverable (μg/L) 153 73.0 .14 2

5.64 3.00

Manganese, filtered (μg/L) 154 57.3 4.0 18.9 17.0

Manganese, unfiltered recoverable (μg/L) 154 1,100 10.5 120 87.7

Zinc, filtered (μg/L) 154 26 <1.0 2

5.6 4.0

Zinc, unfiltered recoverable (μg/L) 154 510 2 43.7 30.0

Sediment, suspended (percent finer than 0.062 mm) 155 94 43 74 77

Sediment, suspended concentration (mg/L) 155 752 1 49 22

Sediment, suspended discharge (ton/d) 155 7,960 .55 215 33
102 Water-Quality, Bed-Sediment, and Biological Data, and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 25. Statistical summary of long-term water-quality data for the Clark Fork basin, Montana, March 1985 through 

September 2011.—Continued

[Abbreviations: CaCO3, calcium carbonate; ft3/s, cubic feet per second; °C, degrees Celsius; μg/L, micrograms per liter; μS/cm, microsiemens per 

centimeter at 25°C; mg/L, milligrams per liter; mm, millimeter; ton/d, tons per day. Symbols: <, less than laboratory reporting level1]

Property or constituent and reporting unit Number of 

samples Maximum Minimum Mean Median

12331800--Clark Fork near Drummond

Period of record for water-quality data: March 1993–September 2011

Streamflow, instantaneous (ft3

/s) 155 5,540 149 1,100 799

pH, onsite (standard units) 154 8.7 7.8 8.3 8.3

Specific conductance, onsite (μS/cm) 154 630 189 405 417

Temperature, water (°C) 155 22.5 .5 10.9 11.0

Hardness, filtered (mg/L as CaCO3

) 154 298 73.9 182 189

Calcium, filtered (mg/L) 154 83.0 21.0 52.2 54.3

Magnesium, filtered (mg/L) 154 22.0 5.2 12.5 12.8

Arsenic, filtered (μg/L) 154 23.9 3.2 10.6 10.0

Arsenic, unfiltered recoverable (μg/L) 154 62 8 16.3 13.0

Cadmium, filtered (μg/L) 153 .30 <.04 2

.05 .02

Cadmium, unfiltered recoverable (μg/L) 154 2.0 <.10 2

.24 .08

Copper, filtered (μg/L) 151 21.0 1.0 6.6 5.0

Copper, unfiltered recoverable (μg/L) 152 360 4.6 43.3 23.0

Iron, filtered (μg/L) 154 150 <3 2

19 9

Iron, unfiltered recoverable (μg/L) 153 8,800 20 1,010 490

Lead, filtered (μg/L) 150 1.2 <.08 2

.17 <1.0

Lead, unfiltered recoverable (μg/L) 150 56.0 <1.00 2

7.76 3.61

Manganese, filtered (μg/L) 153 60.7 3.3 16.5 14.4

Manganese, unfiltered recoverable (μg/L) 154 880 8.0 146 96.0

Zinc, filtered (μg/L) 154 21.0 <3 2

6.0 4.4

Zinc, unfiltered recoverable (μg/L) 154 490 2.9 60.0 31.9

Sediment, suspended (percent finer than 0.062 mm) 155 92 38 73 74

Sediment, suspended concentration (mg/L) 155 530 2 64 27

Sediment, suspended discharge (ton/d) 155 4,720 1.7 333 53
Data 103

Table 25. Statistical summary of long-term water-quality data for the Clark Fork basin, Montana, March 1985 through 

September 2011.—Continued

[Abbreviations: CaCO3, calcium carbonate; ft3/s, cubic feet per second; °C, degrees Celsius; μg/L, micrograms per liter; μS/cm, microsiemens per 

centimeter at 25°C; mg/L, milligrams per liter; mm, millimeter; ton/d, tons per day. Symbols: <, less than laboratory reporting level1]

Property or constituent and reporting unit Number of 

samples Maximum Minimum Mean Median

12334550--Clark Fork at Turah Bridge, near Bonner

Period of record for water-quality data: March 1985–September 2011

Streamflow, instantaneous (ft3

/s) 252 10,600 296 1,980 1,160

pH, onsite (standard units) 198 8.8 7.4 8.2 8.2

Specific conductance, onsite (μS/cm) 227 483 139 299 313

Temperature, water (°C) 251 22.0 0.0 9.5 10.0

Hardness, filtered (mg/L as CaCO3

) 188 205 53.6 130 132

Calcium, filtered (mg/L) 188 59.0 14.9 36.8 37.2

Magnesium, filtered (mg/L) 188 14.0 3.94 9.36 9.39

Arsenic, filtered (μg/L) 197 17.0 2.7 6.1 5.6

Arsenic, unfiltered recoverable (μg/L) 197 110 3.0 9.8 7.0

Cadmium, filtered (μg/L) 196 .10 <.04 2

.04 <.1

Cadmium, unfiltered recoverable (μg/L) 197 4.00 <.01 2

.25 <1.00

Copper, filtered (μg/L) 196 25.0 1.1 4.8 3.9

Copper, unfiltered recoverable (μg/L) 195 500 2.7 33.8 16.0

Iron, filtered (μg/L) 197 190 <3 2

24 13

Iron, unfiltered recoverable (μg/L) 197 19,000 33 1,000 389

Lead, filtered (μg/L) 193 7.00 <.08 2

.28 <1.00

Lead, unfiltered recoverable (μg/L) 193 100 <1.00 2

6.87 3.00

Manganese, filtered (μg/L) 197 37.4 <1.0 2

8.4 7.0

Manganese, unfiltered recoverable (μg/L) 197 2,000 8.9 120 62.8

Zinc, filtered (μg/L) 195 39 <3.0 2

5.9 4.0

Zinc, unfiltered recoverable (μg/L) 197 1,100 <10.0 2

57.2 29.0

Sediment, suspended (percent finer than 0.062 mm) 241 98 27 73 75

Sediment, suspended concentration (mg/L) 252 1,370 2 56 18

Sediment, suspended discharge (ton/d) 252 34,700 3.0 640 61
104 Water-Quality, Bed-Sediment, and Biological Data, and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 25. Statistical summary of long-term water-quality data for the Clark Fork basin, Montana, March 1985 through 

September 2011.—Continued

[Abbreviations: CaCO3, calcium carbonate; ft3/s, cubic feet per second; °C, degrees Celsius; μg/L, micrograms per liter; μS/cm, microsiemens per 

centimeter at 25°C; mg/L, milligrams per liter; mm, millimeter; ton/d, tons per day. Symbols: <, less than laboratory reporting level1]

Property or constituent and reporting unit Number of 

samples Maximum Minimum Mean Median

12340000--Blackfoot River near Bonner

Period of record for water-quality data: March 1985–September 2011

Streamflow, instantaneous (ft3

/s) 184 13,400 344 2,790 1,340

pH, onsite (standard units) 144 8.7 7.5 8.3 8.3

Specific conductance, onsite (μS/cm) 161 294 131 208 204

Temperature, water (°C) 184 22.5 0.0 9.5 9.5

Hardness, filtered (mg/L as CaCO3

) 136 146 55.1 104 98.4

Calcium, filtered (mg/L) 136 37.7 14.0 26.4 25.2

Magnesium, filtered (mg/L) 136 13.2 4.90 9.12 8.66

Arsenic, filtered (μg/L) 143 2.0 <1.0 2

.97 .96

Arsenic, unfiltered recoverable (μg/L) 144 4.0 <1.0 2

1.3 1.0

Cadmium, filtered (μg/L) 142 1.00 <.02 2

.02 <.10

Cadmium, unfiltered recoverable (μg/L) 144 2.00 <.01 2

.09 <1.00

Copper, filtered (μg/L) 140 7.0 <1.0 2

1.3 .8

Copper, unfiltered recoverable (μg/L) 141 34.0 <1.0 2

4.6 2.0

Iron, filtered (μg/L) 143 100 <3 2

17 10

Iron, unfiltered recoverable (μg/L) 144 3,600 14 420 195

Lead, filtered (μg/L) 138 8.00 <.01 2

.33 <.60

Lead, unfiltered recoverable (μg/L) 140 25.0 <.60 2

2.21 .08

Manganese, filtered (μg/L) 143 11.0 <1.0 2

2.4 2.0

Manganese, unfiltered recoverable (μg/L) 144 180 <10.0 2

28.9 18.6

Zinc, filtered (μg/L) 142 15.0 <.60 2

2.0 <10.0

Zinc, unfiltered recoverable (μg/L) 144 60.0 <1.0 2

5.3 <10.0

Sediment, suspended (percent finer than 0.062 mm) 182 98 42 80 82

Sediment, suspended concentration (mg/L) 184 271 1 29 8

Sediment, suspended discharge (ton/d) 184 7,670 1.1 533 31
Data 105

Table 25. Statistical summary of long-term water-quality data for the Clark Fork basin, Montana, March 1985 through 

September 2011.—Continued

[Abbreviations: CaCO3, calcium carbonate; ft3/s, cubic feet per second; °C, degrees Celsius; μg/L, micrograms per liter; μS/cm, microsiemens per 

centimeter at 25°C; mg/L, milligrams per liter; mm, millimeter; ton/d, tons per day. Symbols: <, less than laboratory reporting level1]

Property or constituent and reporting unit Number of 

samples Maximum Minimum Mean Median

12340500--Clark Fork above Missoula

Period of record for water-quality data: July 1986–September 2011

Streamflow, instantaneous (ft3

/s) 218 22,900 720 4,630 2,430

pH, onsite (standard units) 175 8.8 7.9 8.3 8.3

Specific conductance, onsite (μS/cm) 195 399 142 253 261

Temperature, water (°C) 215 22.0 0.0 9.6 9.5

Hardness, filtered (mg/L as CaCO3

) 175 168 60.5 116 118

Calcium, filtered (mg/L) 175 46.0 14.0 31.4 31.7

Magnesium, filtered (mg/L) 175 13.4 5.28 9.19 9.20

Arsenic, filtered (μg/L) 175 9.0 1.0 3.5 3.2

Arsenic, unfiltered recoverable (μg/L) 175 69.0 1.0 5.5 4.0

Cadmium, filtered (μg/L) 174 .20 <.04 2

.03 <.10

Cadmium, unfiltered recoverable (μg/L) 175 5.0 <.01 2

.16 <1.0

Copper, filtered (μg/L) 174 12.6 .7 2.9 2.2

Copper, unfiltered recoverable (μg/L) 173 400 2.0 20.1 8.8

Iron, filtered (μg/L) 175 200 <3 2

22 15

Iron, unfiltered recoverable (μg/L) 175 13,000 43 647 260

Lead, filtered (μg/L) 168 1.20 <.08 2

.15 <1.00

Lead, unfiltered recoverable (μg/L) 170 78.0 <1.00 2

3.57 1.64

Manganese, filtered (μg/L) 175 230 5.9 16.2 13.8

Manganese, unfiltered recoverable (μg/L) 175 1,100 10.0 66.9 40.0

Zinc, filtered (μg/L) 174 16.0 <1.0 2

3.6 2.4

Zinc, unfiltered recoverable (μg/L) 175 1,100 <10.0 2

34.4 15

Sediment, suspended (percent finer than 0.062 mm) 213 99 14 83 88

Sediment, suspended concentration (mg/L) 218 950 2 45 12

Sediment, suspended discharge (ton/d) 218 21,900 5.8 1,140 91

1

Differing less-than (<) values for an individual constituent are the result of changes in the laboratory reporting level during the period of record.

2

Value for the mean is estimated by using a log-probability regression to predict the values of data less than the laboratory reporting level (Helsel 

and Cohn, 1988). Minimum values that are not censored when the mean indicates that a censored value was used in the mean calculation, are a result 

of changes in the laboratory reporting level during the period of record.
106 Water-Quality, Bed-Sediment, and Biological Data, and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 26. Statistical summary of long-term bed-sediment data for the Clark Fork basin, Montana, August 1986 through 

August 2011.

[Reported concentrations are in micrograms per gram dry weight (μg/g). Number of samples represents the number of years that the constituent was analyzed, 

with each year represented by a single mean concentration of composite samples. Arsenic was not analyzed until 2003; therefore, the number of samples is 

smaller than that for the other trace elements. Values are reported using U.S. Geological Survey rounding standards. Symbols: <, less than the minimum reporting level; --, indicates insufficient data (less than three samples) to compute statistic]

Constituent Number of samples Maximum Minimum Mean Median

12323600--Silver Bow Creek at Opportunity

Period of record for bed-sediment data: 1992–2011

Arsenic 9 186 34 120 123

Cadmium 20 43.9 6.8 28.6 28.2

Chromium 18 50.7 16.8 29.5 26.7

Copper 20 9,020 837 4,030 4,360

Iron 20 45,300 28,200 35,500 34,300

Lead 20 1,030 181 616 572

Manganese 20 9,220 1,160 3,270 2,680

Nickel 19 21.4 12.0 14.8 14.5

Silver 12 20.0 8.3 15.5 15.8

Zinc 20 13,400 1,610 6,980 6,940

12323750--Silver Bow Creek at Warm Springs

Period of record for bed-sediment data: 1992–2011

Arsenic 9 177 67 112 103

Cadmium 20 12.2 4.2 7.1 6.5

Chromium 18 46.8 <15.7 1

23.9 123.2

Copper 20 769 169 349 295

Iron 20 32,500 15,400 23,400 22,100

Lead 20 100 49 71 72

Manganese 20 17,700 1,470 7,660 7,690

Nickel 19 20.0 9.2 15.0 14.7

Silver 12 4.4 .3 1

1.9 11.8

Zinc 20 2,220 554 929 727

12323770--Warm Springs Creek at Warm Springs

Period of record for bed-sediment data: 1995, 1997, 1999, 2002, 2005, 2008, 2011

Arsenic 3 66 34 51 52

Cadmium 7 5.8 1.2 3.2 3.3

Chromium 7 39.3 27.5 32.1 31.5

Copper 7 1,060 496 849 881

Iron 7 26,600 16,800 21,400 21,900

Lead 7 86 42 75 82

Manganese 7 12,100 555 6,890 7,780

Nickel 7 25.5 14.5 19.4 19.2

Silver 4 5.1 3.1 3.8 3.5

Zinc 7 453 237 381 396
Data 107

Constituent Number of samples Maximum Minimum Mean Median

12323800--Clark Fork near Galen

Period of record for bed-sediment data: 1987, 1991–2011

Arsenic 9 119 73 99 95

Cadmium 22 20.1 3.8 8.2 7.3

Chromium 18 44.6 19.1 29.4 28.3

Copper 22 2,300 838 1,190 1,110

Iron 22 39,800 22,600 27,700 26,900

Lead 22 235 92 132 128

Manganese 22 17,300 1,530 9,160 9,780

Nickel 19 23.2 13.9 18.6 18.3

Silver 14 7.3 <3.2 1

4.4 14.5

Zinc 22 3,560 721 1,420 1,140

461415112450801--Clark Fork below Lost Creek, near Galen

Period of record for bed-sediment data: 1996–2011

Arsenic 9 204 92 119 109

Cadmium 16 10.0 4.8 6.9 6.7

Chromium 15 42.4 20.5 30.4 31.8

Copper 16 2,050 1,150 1,500 1,440

Iron 16 32,800 24,400 29,300 29,900

Lead 16 218 127 165 168

Manganese 16 9,820 1,430 5,470 5,660

Nickel 16 19.9 11.7 16.1 16.4

Silver 8 7.8 4.2 6.5 6.7

Zinc 16 1,680 930 1,300 1,290

461559112443301--Clark Fork at county bridge, near Racetrack

Period of record for bed-sediment data: 1996–2011

Arsenic 9 132 56 91 90

Cadmium 16 8.7 5.0 6.6 6.4

Chromium 15 45.2 19.0 29.2 29.2

Copper 16 1,810 933 1,290 1,320

Iron 16 31,700 21,200 27,500 28,400

Lead 16 186 103 145 143

Manganese 16 6,310 1,600 3,280 3,020

Nickel 16 18.4 10.3 14.5 15.2

Silver 8 6.1 <3.3 1

5.0 15.4

Zinc 16 1,550 999 1,200 1,180

Table 26. Statistical summary of long-term bed-sediment data for the Clark Fork basin, Montana, August 1986 through 

August 2011.—Continued

[Reported concentrations are in micrograms per gram dry weight (μg/g). Number of samples represents the number of years that the constituent was analyzed, 

with each year represented by a single mean concentration of composite samples. Arsenic was not analyzed until 2003; therefore, the number of samples is 

smaller than that for the other trace elements. Values are reported using U.S. Geological Survey rounding standards. Symbols: <, less than the minimum reporting level; --, indicates insufficient data (less than three samples) to compute statistic]
108 Water-Quality, Bed-Sediment, and Biological Data, and Statistical Summaries of Data, Clark Fork Basin, Montana

Constituent Number of samples Maximum Minimum Mean Median

461903112440701--Clark Fork at Dempsey Creek diversion, near Racetrack

Period of record for bed-sediment data: 1996–2011

Arsenic 9 100 58 79 80

Cadmium 16 10.3 4.1 6.2 5.8

Chromium 15 39.2 16.0 27.7 26.4

Copper 16 1,580 721 1,110 1,100

Iron 16 33,700 20,600 27,000 26,600

Lead 16 155 92 131 134

Manganese 16 8,370 1,200 3,850 3,210

Nickel 16 16.9 8.7 13.0 12.7

Silver 8 6.2 2.7 4.9 5.0

Zinc 16 1,570 900 1,130 1,080

12324200--Clark Fork at Deer Lodge

Period of record for bed-sediment data: 1986–87, 1990–2011

Arsenic 9 102 49 73 70

Cadmium 24 10.0 3.5 6.0 5.3

Chromium 18 50.7 19.5 32.3 30.4

Copper 24 4,180 683 1,260 1,070

Iron 24 35,300 21,100 27,400 26,300

Lead 24 242 103 145 142

Manganese 24 6,020 1,070 2,640 2,450

Nickel 19 21.1 11.5 14.9 14.3

Silver 16 7.9 2.4 4.7 4.5

Zinc 24 1,730 844 1,190 1,140

12324400--Clark Fork above Little Blackfoot River, near Garrison

Period of record for bed-sediment data: 2009-2011

Arsenic 3 91 81 85 83

Cadmium 3 5.5 4.2 4.8 4.8

Chromium 3 52.8 45.5 48.3 46.4

Copper 3 1,290 1,260 1,270 1,270

Iron 3 32,400 27,300 29,600 29,100

Lead 3 145 140 143 144

Manganese 3 2,950 1,150 1,890 1,560

Nickel 3 17.2 13.9 15.3 14.9

Silver 0 -- -- -- --

Zinc 3 1,240 1,100 1,150 1,100

Table 26. Statistical summary of long-term bed-sediment data for the Clark Fork basin, Montana, August 1986 through 

August 2011.—Continued

[Reported concentrations are in micrograms per gram dry weight (μg/g). Number of samples represents the number of years that the constituent was analyzed, 

with each year represented by a single mean concentration of composite samples. Arsenic was not analyzed until 2003; therefore, the number of samples is 

smaller than that for the other trace elements. Values are reported using U.S. Geological Survey rounding standards. Symbols: <, less than the minimum reporting level; --, indicates insufficient data (less than three samples) to compute statistic]
Data 109

Constituent Number of samples Maximum Minimum Mean Median

12324680--Clark Fork at Goldcreek

Period of record for bed-sediment data: 1992–2011

Arsenic 9 62 23 43 39

Cadmium 20 8.1 2.6 4.6 4.1

Chromium 18 55.3 21.3 34.1 32.6

Copper 20 1,080 338 698 738

Iron 20 32,100 15,500 24,000 24,400

Lead 20 152 52 97 99

Manganese 20 2,610 977 1,800 1,810

Nickel 19 18.6 9.0 14.3 14.4

Silver 12 4.8 2.3 3.3 3.2

Zinc 20 1,320 584 929 944

12331800--Clark Fork near Drummond

Period of record for bed-sediment data: 1986–87, 1991–2011

Arsenic 9 66 31 41 34

Cadmium 23 7.7 1.7 4.3 4.3

Chromium 18 41.9 17.0 29.8 31.4

Copper 23 747 303 481 469

Iron 23 43,700 16,500 24,900 23,200

Lead 23 135 59 88 85

Manganese 23 4,820 832 2,080 1,890

Nickel 19 16.8 9.3 13.4 13.7

Silver 15 4.7 <3.2 1

3.0 12.9

Zinc 23 1,230 637 946 948

12334550--Clark Fork at Turah Bridge, near Bonner

Period of record for bed-sediment data: 1986, 1991–2011

Arsenic 9 43 19 29 30

Cadmium 22 7.3 1.9 3.5 3.5

Chromium 18 42.5 15.3 27.2 28.4

Copper 22 635 211 357 334

Iron 22 25,900 12,600 19,500 17,400

Lead 22 115 47 68 66

Manganese 22 2,340 671 1,310 1,250

Nickel 19 19.1 6.9 12.6 11.6

Silver 14 3.9 <1.9 1

2.1 11.9

Zinc 22 1,160 584 808 786

Table 26. Statistical summary of long-term bed-sediment data for the Clark Fork basin, Montana, August 1986 through 

August 2011.—Continued

[Reported concentrations are in micrograms per gram dry weight (μg/g). Number of samples represents the number of years that the constituent was analyzed, 

with each year represented by a single mean concentration of composite samples. Arsenic was not analyzed until 2003; therefore, the number of samples is 

smaller than that for the other trace elements. Values are reported using U.S. Geological Survey rounding standards. Symbols: <, less than the minimum reporting level; --, indicates insufficient data (less than three samples) to compute statistic]
110 Water-Quality, Bed-Sediment, and Biological Data, and Statistical Summaries of Data, Clark Fork Basin, Montana

Constituent Number of samples Maximum Minimum Mean Median

12340000--Blackfoot River near Bonner

Period of record for bed-sediment data: 1986–87, 1991, 1993–96, 1998–2001, 2003, 2006–11

Arsenic 7 6 <0.2 1

3 13

Cadmium 18 2.0 .05 1

.5 1.3

Chromium 14 35.2 15.1 23.0 23.7

Copper 18 27 11 20 21

Iron 18 23,000 12,400 17,700 18,100

Lead 18 20 <13 1

13 112

Manganese 18 746 298 530 543

Nickel 15 14.3 6.0 11.3 11.7

Silver 12 <1.9 <.3 1

.5 1<.6

Zinc 18 82 35 61 62

12340500--Clark Fork above Missoula

Period of record for bed-sediment data: 1997–2011

Arsenic 9 54 17 34 30

Cadmium 15 5.8 1.2 3.1 2.8

Chromium 14 40.7 19.0 27.7 29.0

Copper 15 551 166 369 353

Iron 15 27,000 18,100 21,100 20,500

Lead 15 78 37 56 57

Manganese 15 2,250 477 1,080 1,020

Nickel 15 15.8 7.6 12.8 13.0

Silver 7 2.9 .8 1

2.0 12.1

Zinc 15 1,090 438 740 716

1

Value determined by substituting one-half of the minimum reporting level for censored (<) values when both uncensored and censored values were used to 

determine the mean and (or) median.

Table 26. Statistical summary of long-term bed-sediment data for the Clark Fork basin, Montana, August 1986 through 

August 2011.—Continued

[Reported concentrations are in micrograms per gram dry weight (μg/g). Number of samples represents the number of years that the constituent was analyzed, 

with each year represented by a single mean concentration of composite samples. Arsenic was not analyzed until 2003; therefore, the number of samples is 

smaller than that for the other trace elements. Values are reported using U.S. Geological Survey rounding standards. Symbols: <, less than the minimum reporting level; --, indicates insufficient data (less than three samples) to compute statistic]
Data 111

Table 27. Statistical summary of long-term biological data for the Clark Fork basin, Montana, August 1986 through 

August 2011.

[Concentrations are in micrograms per gram dry weight (μg/g). Number of composite samples represents the total of all individual composite samples collected 

for every year that the constituent was analyzed. Values for a single sample are arbitrarily listed in the “Mean” column. Because Hydropsyche insects were not 

sorted to the species level during 1986–89, Hydropsyche species statistics for stations sampled during those years are based on the results of all Hydropsyche

species combined. At some sites, statistics of Hydropsyche morosa group are based on the combined results of two or more species. Insects collected during 

1986–98 were depurated prior to analysis; depuration was discontinued in 1999. Arsenic was not analyzed until 2003; therefore, the number of samples may be 

small or zero for some taxa. Values are reported using U.S. Geological Survey rounding standards. Abbreviation: spp., one or more similar species. Symbols: 

<, less than minimum reporting level; --, indicates either too few samples (less than three) or insufficient data to compute statistic, or element not analyzed]

Constituent Number of 

composite samples Maximum Minimum Mean Median

12323600--Silver Bow Creek at Opportunity

Period of record for biological data: 1992, 1994–95, 1997–2011

Brachycentrus spp.

Arsenic 0 -- -- -- --

Cadmium 5 12.5 5.8 10.1 11.6

Chromium 5 5.9 .7 2.1 .9

Copper 5 846 235 587 592

Iron 5 1,190 335 617 469

Lead 5 21.5 7.4 13.7 13.8

Manganese 5 817 231 515 503

Nickel 5 2.1 <.1 1

1.3 11.6

Zinc 5 995 629 803 815

Hydropsyche cockerelli

Arsenic 14 33.3 9.5 15.7 13.6

Cadmium 20 9.7 3.1 5.8 5.4

Chromium 20 25.5 1.0 4.4 3.1

Copper 20 1,090 232 426 378

Iron 20 6,150 689 2,650 2,110

Lead 20 74.3 19.0 40.3 39.8

Manganese 20 3,030 180 1,050 1,120

Nickel 20 3.6 .7 2.4 2.5

Zinc 20 1,590 619 920 835

Hydropsyche spp.

Arsenic 13 23.1 6.1 12.6 10.7

Cadmium 18 11.0 2.0 5.5 5.1

Chromium 18 4.7 .6 2.5 2.9

Copper 18 930 80.7 443 385

Iron 18 3,250 1,050 2,180 2,170

Lead 18 237 19.3 46.5 36.5

Manganese 18 1,340 612 1,000 1,040

Nickel 18 2.7 .7 2.0 2.3

Zinc 18 1,290 388 879 893

Hydropsyche tana

Arsenic 0 -- -- -- --

Cadmium 6 9.2 4.8 6.8 6.9

Chromium 6 11.5 .9 4.5 1.8

Copper 6 456 10.5 236 298

Iron 6 1,520 875 1,100 1,050

Lead 6 21.0 15.6 18.6 18.3

Manganese 6 969 307 634 675

Nickel 6 1.8 .7 1.4 1.6

Zinc 6 1,070 760 961 1,020
112 Water-Quality, Bed-Sediment, and Biological Data, and Statistical Summaries of Data, Clark Fork Basin, Montana

Constituent Number of 

composite samples Maximum Minimum Mean Median

12323750--Silver Bow Creek at Warm Springs

Period of record for biological data: 1992–2011

Claassenia sabulosa

Arsenic 1 -- -- 1.8 --

Cadmium 1 -- -- 1.1 --

Chromium 1 -- -- 2.8 --

Copper 1 -- -- 47.6 --

Iron 1 -- -- 151 --

Lead 1 -- -- .6 --

Manganese 1 -- -- 98.1 --

Nickel 1 -- -- .5 --

Zinc 1 -- -- 400 --

Hydropsyche cockerelli

Arsenic 15 23.6 7.9 12.9 10.4

Cadmium 41 2.1 .2 .6 .5

Chromium 41 4.3 .4 1.1 .8

Copper 41 97.0 16.7 36.9 29.9

Iron 41 1,650 351 809 762

Lead 41 6.0 .3 3.1 2.9

Manganese 41 3,890 491 1,270 1,010

Nickel 41 1.8 .3 .9 .8

Zinc 41 276 115 175 168

Hydropsyche occidentalis

Arsenic 8 31.0 10.5 19.1 16.8

Cadmium 23 1.6 .2 .6 .4

Chromium 23 6.8 .3 1.7 1.0

Copper 23 48.9 11.0 33.4 32.8

Iron 23 2,960 372 1,230 998

Lead 23 8.2 <1.7 1

4.1 13.8

Manganese 23 6,940 996 2,420 1,940

Nickel 23 2.7 .7 1.5 1.4

Zinc 23 220 140 180 181

Hydropsyche spp.

Arsenic 1 -- -- 14.0 --

Cadmium 5 2.3 0.4 1.0 0.6

Chromium 5 2.5 .5 1.4 1.3

Copper 5 47.6 34.9 39.9 40.4

Iron 5 1,100 561 763 767

Lead 5 5.1 1.9 4.0 4.5

Manganese 5 1,190 443 817 804

Nickel 5 1.9 <.4 1

1.0 1.8

Zinc 5 284 141 188 162

Table 27. Statistical summary of long-term biological data for the Clark Fork basin, Montana, August 1986 through 

August 2011.—Continued

[Concentrations are in micrograms per gram dry weight (μg/g). Number of composite samples represents the total of all individual composite samples collected 

for every year that the constituent was analyzed. Values for a single sample are arbitrarily listed in the “Mean” column. Because Hydropsyche insects were not 

sorted to the species level during 1986–89, Hydropsyche species statistics for stations sampled during those years are based on the results of all Hydropsyche

species combined. At some sites, statistics of Hydropsyche morosa group are based on the combined results of two or more species. Insects collected during 

1986–98 were depurated prior to analysis; depuration was discontinued in 1999. Arsenic was not analyzed until 2003; therefore, the number of samples may be 

small or zero for some taxa. Values are reported using U.S. Geological Survey rounding standards. Abbreviation: spp., one or more similar species. Symbols: 

<, less than minimum reporting level; --, indicates either too few samples (less than three) or insufficient data to compute statistic, or element not analyzed]
Data 113

Constituent Number of 

composite samples Maximum Minimum Mean Median

12323770--Warm Springs Creek at Warm Springs

Period of record for biological data: 1995, 1997, 1999, 2002, 2005, 2008, 2011

Arctopsyche grandis

Arsenic 4 9.8 7.9 9.2 9.5

Cadmium 8 3.6 .4 2.5 2.7

Chromium 8 4.2 .8 2.3 2.4

Copper 8 133 53.2 102 100

Iron 8 1,350 684 970 969

Lead 8 7.2 3.0 1

5.2 15.2

Manganese 8 3,560 738 2,320 2,380

Nickel 8 3.5 1.1 1

2.3 12.3

Zinc 8 267 181 205 196

Hesperoperla spp.

Arsenic 1 -- -- 1.2 --

Cadmium 1 -- -- 1.0 --

Chromium 1 -- -- 2.0 --

Copper 1 -- -- 64.9 --

Iron 1 -- -- 456 --

Lead 1 -- -- 1.9 --

Manganese 1 -- -- 202 --

Nickel 1 -- -- .6 --

Zinc 1 -- -- 573 --

Hydropsyche occidentalis

Arsenic 3 13.6 12.7 13.2 13.3

Cadmium 5 1.3 .7 1.0 1.2

Chromium 5 8.6 .3 3.8 3.2

Copper 5 183 125 158 165

Iron 5 2,360 1,590 1,940 1,950

Lead 5 12.6 6.7 8.5 7.7

Manganese 5 3,190 2,400 2,800 2,880

Nickel 5 4.5 2.0 3.0 3.0

Zinc 5 204 148 169 166

Hydropsyche spp.

Arsenic 0 -- -- -- --

Cadmium 2 1.1 0.6 0.8 --

Chromium 2 1.6 1.4 1.5 --

Copper 2 95.9 94.8 95.4 --

Iron 2 1,220 1,150 1,180 --

Lead 2 5.9 5.2 5.6 --

Manganese 2 3,390 956 2,170 --

Nickel 2 2.0 1.8 1.9 --

Zinc 2 129 125 127 --

Table 27. Statistical summary of long-term biological data for the Clark Fork basin, Montana, August 1986 through 

August 2011.—Continued

[Concentrations are in micrograms per gram dry weight (μg/g). Number of composite samples represents the total of all individual composite samples collected 

for every year that the constituent was analyzed. Values for a single sample are arbitrarily listed in the “Mean” column. Because Hydropsyche insects were not 

sorted to the species level during 1986–89, Hydropsyche species statistics for stations sampled during those years are based on the results of all Hydropsyche

species combined. At some sites, statistics of Hydropsyche morosa group are based on the combined results of two or more species. Insects collected during 

1986–98 were depurated prior to analysis; depuration was discontinued in 1999. Arsenic was not analyzed until 2003; therefore, the number of samples may be 

small or zero for some taxa. Values are reported using U.S. Geological Survey rounding standards. Abbreviation: spp., one or more similar species. Symbols: 

<, less than minimum reporting level; --, indicates either too few samples (less than three) or insufficient data to compute statistic, or element not analyzed]
114 Water-Quality, Bed-Sediment, and Biological Data, and Statistical Summaries of Data, Clark Fork Basin, Montana

Constituent Number of 

composite samples Maximum Minimum Mean Median

12323800--Clark Fork near Galen

Period of record for biological data: 1987, 1991–2011

Claassenia sabulosa

Arsenic 1 -- -- 2.0 --

Cadmium 1 -- -- .2 --

Chromium 1 -- -- 1.5 --

Copper 1 -- -- 54.7 --

Iron 1 -- -- 242 --

Lead 1 -- -- 1.0 --

Manganese 1 -- -- 323 --

Nickel 1 -- -- .5 --

Zinc 1 -- -- 237 --

Hydropsyche cockerelli

Arsenic 9 16.9 13.2 14.4 14.0

Cadmium 34 2.7 .7 1.5 1.5

Chromium 34 9.6 .8 2.2 1.7

Copper 34 181 48.7 105 104

Iron 34 2,660 816 1,470 1,430

Lead 34 17.1 1.2 8.3 7.9

Manganese 34 3,620 1,070 2,290 2,250

Nickel 34 6.5 .9 1.8 1.6

Zinc 34 363 136 214 208

Hydropsyche morosa group

Arsenic 0 -- -- -- --

Cadmium 5 3.2 2.4 2.5 2.4

Chromium 5 4.6 1.8 2.6 2.2

Copper 5 185 156 173 175

Iron 5 1,890 1,360 1,510 1,430

Lead 5 12.4 7.1 8.5 7.9

Manganese 5 3,960 2,360 3,500 3,860

Nickel 5 3.6 1.9 2.3 2.1

Zinc 5 349 292 309 303

Table 27. Statistical summary of long-term biological data for the Clark Fork basin, Montana, August 1986 through 

August 2011.—Continued

[Concentrations are in micrograms per gram dry weight (μg/g). Number of composite samples represents the total of all individual composite samples collected 

for every year that the constituent was analyzed. Values for a single sample are arbitrarily listed in the “Mean” column. Because Hydropsyche insects were not 

sorted to the species level during 1986–89, Hydropsyche species statistics for stations sampled during those years are based on the results of all Hydropsyche

species combined. At some sites, statistics of Hydropsyche morosa group are based on the combined results of two or more species. Insects collected during 

1986–98 were depurated prior to analysis; depuration was discontinued in 1999. Arsenic was not analyzed until 2003; therefore, the number of samples may be 

small or zero for some taxa. Values are reported using U.S. Geological Survey rounding standards. Abbreviation: spp., one or more similar species. Symbols: 

<, less than minimum reporting level; --, indicates either too few samples (less than three) or insufficient data to compute statistic, or element not analyzed]
Data 115

Constituent Number of 

composite samples Maximum Minimum Mean Median

12323800--Clark Fork near Galen—Continued

Period of record for biological data: 1987, 1991–2011

Hydropsyche occidentalis

Arsenic 15 17.0 9.1 14.0 14.7

Cadmium 47 1.6 .6 1.1 1.2

Chromium 47 6.6 .4 2.1 1.7

Copper 47 151 49.2 90.2 84.3

Iron 47 2,590 642 1,450 1,390

Lead 47 13.5 1.6 7.7 7.5

Manganese 47 6,170 653 2,530 2,110

Nickel 47 3.5 .8 1.8 1.6

Zinc 47 286 168 204 198

Hydropsyche tana

Arsenic 0 -- -- -- --

Cadmium 1 -- -- 1.5 --

Chromium 1 -- -- 1.4 --

Copper 1 -- -- 92.9 --

Iron 1 -- -- 1,340 --

Lead 1 -- -- 9.0 --

Manganese 1 -- -- 2,160 --

Nickel 1 -- -- 2.1 --

Zinc 1 -- -- 206 --

Hydropsyche spp.

Arsenic 5 15.7 5.5 11.1 14.2

Cadmium 9 3.5 .7 1.8 1.3

Chromium 5 2.4 1.1 1.8 1.9

Copper 9 154 55.3 110 126

Iron 9 2,110 914 1,350 1,300

Lead 9 13.5 3.8 9.0 10.5

Manganese 5 4,760 668 2,410 1,520

Nickel 5 2.7 .9 1.6 1.5

Zinc 9 329 132 239 228

Table 27. Statistical summary of long-term biological data for the Clark Fork basin, Montana, August 1986 through 

August 2011.—Continued

[Concentrations are in micrograms per gram dry weight (μg/g). Number of composite samples represents the total of all individual composite samples collected 

for every year that the constituent was analyzed. Values for a single sample are arbitrarily listed in the “Mean” column. Because Hydropsyche insects were not 

sorted to the species level during 1986–89, Hydropsyche species statistics for stations sampled during those years are based on the results of all Hydropsyche

species combined. At some sites, statistics of Hydropsyche morosa group are based on the combined results of two or more species. Insects collected during 

1986–98 were depurated prior to analysis; depuration was discontinued in 1999. Arsenic was not analyzed until 2003; therefore, the number of samples may be 

small or zero for some taxa. Values are reported using U.S. Geological Survey rounding standards. Abbreviation: spp., one or more similar species. Symbols: 

<, less than minimum reporting level; --, indicates either too few samples (less than three) or insufficient data to compute statistic, or element not analyzed]
116 Water-Quality, Bed-Sediment, and Biological Data, and Statistical Summaries of Data, Clark Fork Basin, Montana

Constituent Number of 

composite samples Maximum Minimum Mean Median

461415112450801--Clark Fork below Lost Creek, near Galen

Period of record for biological data: 1996–2011

Claassenia sabulosa

Arsenic 1 -- -- 1.5 --

Cadmium 2 0.4 0.3 .4 --

Chromium 2 1.9 .4 1.2 --

Copper 2 70.1 67.1 68.6 --

Iron 2 209 189 199 --

Lead 2 1.2 .7 1.0 --

Manganese 2 238 90.4 164 --

Nickel 2 .2 <.2 1

.2 --

Zinc 2 245 208 226 --

Hydropsyche cockerelli

Arsenic 11 27.8 8.8 14.3 11.6

Cadmium 22 2.8 1.1 1.8 1.6

Chromium 22 3.6 .8 2.0 2.0

Copper 22 338 48.8 134 113

Iron 22 4,080 691 1,530 1,180

Lead 22 28.6 4.5 11.6 9.0

Manganese 22 3,160 1,230 1,850 1,720

Nickel 22 2.8 .9 1.4 1.2

Zinc 22 339 151 228 223

Hydropsyche occidentalis

Arsenic 9 20.9 12.7 15.8 15.0

Cadmium 23 1.9 .9 1.4 1.4

Chromium 23 3.6 1.2 2.1 2.0

Copper 23 219 52.1 117 119

Iron 23 2,830 963 1,650 1,510

Lead 23 19.4 6.6 11.0 10.7

Manganese 23 4,150 1,220 2,540 2,190

Nickel 23 3.0 .9 1.6 1.5

Zinc 23 308 174 243 245

Table 27. Statistical summary of long-term biological data for the Clark Fork basin, Montana, August 1986 through 

August 2011.—Continued

[Concentrations are in micrograms per gram dry weight (μg/g). Number of composite samples represents the total of all individual composite samples collected 

for every year that the constituent was analyzed. Values for a single sample are arbitrarily listed in the “Mean” column. Because Hydropsyche insects were not 

sorted to the species level during 1986–89, Hydropsyche species statistics for stations sampled during those years are based on the results of all Hydropsyche

species combined. At some sites, statistics of Hydropsyche morosa group are based on the combined results of two or more species. Insects collected during 

1986–98 were depurated prior to analysis; depuration was discontinued in 1999. Arsenic was not analyzed until 2003; therefore, the number of samples may be 

small or zero for some taxa. Values are reported using U.S. Geological Survey rounding standards. Abbreviation: spp., one or more similar species. Symbols: 

<, less than minimum reporting level; --, indicates either too few samples (less than three) or insufficient data to compute statistic, or element not analyzed]
Data 117

Constituent Number of 

composite samples Maximum Minimum Mean Median

461415112450801--Clark Fork below Lost Creek, near Galen—Continued

Period of record for biological data: 1996–2011

Hydropsyche spp.

Arsenic 4 14.5 7.0 10.2 9.7

Cadmium 8 1.8 1.0 1.3 1.3

Chromium 8 2.4 .9 1.4 1.2

Copper 8 153 45.1 96.4 93.0

Iron 8 1,810 533 1,160 1,130

Lead 8 20.5 4.1 9.5 8.0

Manganese 8 1,980 775 1,270 1,230

Nickel 8 2.8 .9 1.6 1.4

Zinc 8 228 143 182 173

Rhyacophila spp.

Arsenic 2 5.2 3.5 4.4 --

Cadmium 2 4.3 3.9 4.1 --

Chromium 2 1.1 1.0 1.0 --

Copper 2 93.1 73.7 83.4 --

Iron 2 346 324 335 --

Lead 2 5.9 4.8 5.4 --

Manganese 2 320 192 256 --

Nickel 2 .3 .3 .3 --

Zinc 2 411 301 356 --

Table 27. Statistical summary of long-term biological data for the Clark Fork basin, Montana, August 1986 through 

August 2011.—Continued

[Concentrations are in micrograms per gram dry weight (μg/g). Number of composite samples represents the total of all individual composite samples collected 

for every year that the constituent was analyzed. Values for a single sample are arbitrarily listed in the “Mean” column. Because Hydropsyche insects were not 

sorted to the species level during 1986–89, Hydropsyche species statistics for stations sampled during those years are based on the results of all Hydropsyche

species combined. At some sites, statistics of Hydropsyche morosa group are based on the combined results of two or more species. Insects collected during 

1986–98 were depurated prior to analysis; depuration was discontinued in 1999. Arsenic was not analyzed until 2003; therefore, the number of samples may be 

small or zero for some taxa. Values are reported using U.S. Geological Survey rounding standards. Abbreviation: spp., one or more similar species. Symbols: 

<, less than minimum reporting level; --, indicates either too few samples (less than three) or insufficient data to compute statistic, or element not analyzed]
118 Water-Quality, Bed-Sediment, and Biological Data, and Statistical Summaries of Data, Clark Fork Basin, Montana

Constituent Number of 

composite samples Maximum Minimum Mean Median

461559112443301--Clark Fork at county bridge, near Racetrack

Period of record for biological data: 1996–2011

Claassenia sabulosa

Arsenic 0 -- -- -- --

Cadmium 1 -- -- 0.4 --

Chromium 1 -- -- .3 --

Copper 1 -- -- 40.3 --

Iron 1 -- -- 113 --

Lead 1 -- -- .8 --

Manganese 1 -- -- 172 --

Nickel 1 -- -- .2 --

Zinc 1 -- -- 213 --

Hydropsyche cockerelli

Arsenic 10 20.2 11.1 14.1 13.1

Cadmium 21 2.0 .8 1.5 1.5

Chromium 21 2.8 .6 1.7 1.4

Copper 21 198 50.0 102 98.2

Iron 21 3,330 657 1,270 992

Lead 21 17.2 3.7 8.7 7.5

Manganese 21 2,360 646 1,630 1,900

Nickel 21 2.0 .7 1.2 1.0

Zinc 21 302 139 193 186

Hydropsyche occidentalis

Arsenic 12 16.8 9.2 13.3 14.0

Cadmium 25 2.3 .7 1.5 1.4

Chromium 25 3.7 1.1 2.2 2.0

Copper 25 164 59.5 118 129

Iron 25 3,690 1,030 1,700 1,600

Lead 25 15.7 4.3 10.9 10.7

Manganese 25 3,770 660 1,990 2,020

Nickel 25 2.3 1.1 1.5 1.3

Zinc 25 361 181 233 229

Hydropsyche spp.

Arsenic 5 12.8 6.5 10.3 11.9

Cadmium 7 2.4 1.0 1.5 1.5

Chromium 7 3.9 .7 1.7 1.1

Copper 7 144 74.0 101 85.2

Iron 7 1,880 847 1,280 1,200

Lead 7 15.0 5.7 9.1 7.4

Manganese 7 2,370 886 1,340 1,130

Nickel 7 2.0 .7 1.3 1.3

Zinc 7 228 151 188 181

Table 27. Statistical summary of long-term biological data for the Clark Fork basin, Montana, August 1986 through 

August 2011.—Continued

[Concentrations are in micrograms per gram dry weight (μg/g). Number of composite samples represents the total of all individual composite samples collected 

for every year that the constituent was analyzed. Values for a single sample are arbitrarily listed in the “Mean” column. Because Hydropsyche insects were not 

sorted to the species level during 1986–89, Hydropsyche species statistics for stations sampled during those years are based on the results of all Hydropsyche

species combined. At some sites, statistics of Hydropsyche morosa group are based on the combined results of two or more species. Insects collected during 

1986–98 were depurated prior to analysis; depuration was discontinued in 1999. Arsenic was not analyzed until 2003; therefore, the number of samples may be 

small or zero for some taxa. Values are reported using U.S. Geological Survey rounding standards. Abbreviation: spp., one or more similar species. Symbols: 

<, less than minimum reporting level; --, indicates either too few samples (less than three) or insufficient data to compute statistic, or element not analyzed]
Data 119

Constituent Number of 

composite samples Maximum Minimum Mean Median

461903112440701--Clark Fork at Dempsey Creek diversion, near Racetrack

Period of record for biological data: 1996–2011

Arctopsyche grandis

Arsenic 1 -- -- 11.8 --

Cadmium 2 7.1 1.7 4.4 --

Chromium 2 12.9 <2.4 1

7.0 --

Copper 2 151 30.8 90.9 --

Iron 2 1,500 340 920 --

Lead 2 12.4 <14.5 1

9.8 --

Manganese 2 1,190 510 850 --

Nickel 2 2.3 1.0 1.6 --

Zinc 2 489 86.8 288 --

Claassenia sabulosa

Arsenic 1 -- -- 3.1 --

Cadmium 1 -- -- 2.4 --

Chromium 1 -- -- 1.7 --

Copper 1 -- -- 73.4 --

Iron 1 -- -- 297 --

Lead 1 -- -- 1.9 --

Manganese 1 -- -- 115 --

Nickel 1 -- -- .4 --

Zinc 1 -- -- 330 --

Hydropsyche cockerelli

Arsenic 9 18.8 8.0 13.0 10.4

Cadmium 18 2.0 .7 1.3 1.3

Chromium 18 4.0 .5 1.6 1.3

Copper 18 247 60.7 113 90.2

Iron 18 3,010 552 1,200 923

Lead 18 21.9 3.5 8.7 7.3

Manganese 18 2,650 487 1,370 1,230

Nickel 18 2.5 .5 1.2 1.0

Zinc 18 279 162 208 190

Table 27. Statistical summary of long-term biological data for the Clark Fork basin, Montana, August 1986 through 

August 2011.—Continued

[Concentrations are in micrograms per gram dry weight (μg/g). Number of composite samples represents the total of all individual composite samples collected 

for every year that the constituent was analyzed. Values for a single sample are arbitrarily listed in the “Mean” column. Because Hydropsyche insects were not 

sorted to the species level during 1986–89, Hydropsyche species statistics for stations sampled during those years are based on the results of all Hydropsyche

species combined. At some sites, statistics of Hydropsyche morosa group are based on the combined results of two or more species. Insects collected during 

1986–98 were depurated prior to analysis; depuration was discontinued in 1999. Arsenic was not analyzed until 2003; therefore, the number of samples may be 

small or zero for some taxa. Values are reported using U.S. Geological Survey rounding standards. Abbreviation: spp., one or more similar species. Symbols: 

<, less than minimum reporting level; --, indicates either too few samples (less than three) or insufficient data to compute statistic, or element not analyzed]
120 Water-Quality, Bed-Sediment, and Biological Data, and Statistical Summaries of Data, Clark Fork Basin, Montana

Constituent Number of 

composite samples Maximum Minimum Mean Median

461903112440701--Clark Fork at Dempsey Creek diversion, near Racetrack—Continued

Period of record for biological data: 1996–2011

Hydropsyche occidentalis

Arsenic 15 24.0 10.2 15.6 15.9

Cadmium 32 2.4 .7 1.4 1.3

Chromium 32 6.2 .8 2.2 1.9

Copper 32 345 74.9 130 112

Iron 32 3,390 940 1,780 1,550

Lead 32 21.8 6.1 12.9 11.8

Manganese 32 4,460 826 2,410 2,290

Nickel 32 2.4 1.1 1.6 1.5

Zinc 32 386 211 266 245

Hydropsyche spp.

Arsenic 2 6.5 6.4 6.4 --

Cadmium 4 1.7 .9 1.3 1.3

Chromium 4 2.1 .8 1.4 1.2

Copper 4 140 65.5 94.1 85.4

Iron 4 1,610 875 1,120 987

Lead 4 13.2 7.3 9.7 9.1

Manganese 4 1,150 638 824 756

Nickel 4 1.6 .6 1.1 1.1

Zinc 4 212 162 184 180

Table 27. Statistical summary of long-term biological data for the Clark Fork basin, Montana, August 1986 through 

August 2011.—Continued

[Concentrations are in micrograms per gram dry weight (μg/g). Number of composite samples represents the total of all individual composite samples collected 

for every year that the constituent was analyzed. Values for a single sample are arbitrarily listed in the “Mean” column. Because Hydropsyche insects were not 

sorted to the species level during 1986–89, Hydropsyche species statistics for stations sampled during those years are based on the results of all Hydropsyche

species combined. At some sites, statistics of Hydropsyche morosa group are based on the combined results of two or more species. Insects collected during 

1986–98 were depurated prior to analysis; depuration was discontinued in 1999. Arsenic was not analyzed until 2003; therefore, the number of samples may be 

small or zero for some taxa. Values are reported using U.S. Geological Survey rounding standards. Abbreviation: spp., one or more similar species. Symbols: 

<, less than minimum reporting level; --, indicates either too few samples (less than three) or insufficient data to compute statistic, or element not analyzed]
Data 121

Constituent Number of 

composite samples Maximum Minimum Mean Median

12324200--Clark Fork at Deer Lodge

Period of record for biological data: 1986–87, 1990–2011

Arctopsyche grandis

Arsenic 2 8.3 5.8 7.0 --

Cadmium 4 4.7 <4.2 1

3.4 13.1

Chromium 4 4.7 1.0 1

2.8 12.8

Copper 4 90.5 34.9 68.0 73.2

Iron 4 1,090 537 788 760

Lead 4 11.2 3.8 1

8.2 1<9.5

Manganese 4 1,010 380 766 837

Nickel 4 1.2 <1.3 1

1.1 11.1

Zinc 4 369 140 250 246

Hydropsyche cockerelli

Arsenic 6 11.4 5.8 8.2 7.8

Cadmium 29 3.5 .6 1.4 1.3

Chromium 29 3.2 .4 1.6 1.7

Copper 29 180 54.7 98.2 98.2

Iron 29 3,340 490 1,120 1,040

Lead 29 18.1 3.8 9.5 8.9

Manganese 29 1,570 396 879 815

Nickel 29 2.4 .3 1.1 1.0

Zinc 29 391 132 190 185

Hydropsyche occidentalis

Arsenic 18 21.1 6.6 11.6 11.0

Cadmium 55 3.4 .6 1.4 1.3

Chromium 55 3.7 .6 2.0 1.9

Copper 55 222 49.4 124 118

Iron 55 3,240 558 1,510 1,480

Lead 55 20.1 3.5 11.9 11.7

Manganese 55 2,850 649 1,630 1,680

Nickel 55 12.9 1.0 1.7 1.4

Zinc 55 346 166 246 238

Hydropsyche spp.

Arsenic 1 -- -- 6.0 --

Cadmium 4 2.6 1.6 2.2 2.3

Chromium 1 -- -- .8 --

Copper 4 222 91 166 176

Iron 4 2,220 1,070 1,770 1,900

Lead 4 16.7 9.0 14.4 15.9

Manganese 1 -- -- 837 --

Nickel 1 -- -- .9 --

Zinc 4 298 196 242 237

Table 27. Statistical summary of long-term biological data for the Clark Fork basin, Montana, August 1986 through 

August 2011.—Continued

[Concentrations are in micrograms per gram dry weight (μg/g). Number of composite samples represents the total of all individual composite samples collected 

for every year that the constituent was analyzed. Values for a single sample are arbitrarily listed in the “Mean” column. Because Hydropsyche insects were not 

sorted to the species level during 1986–89, Hydropsyche species statistics for stations sampled during those years are based on the results of all Hydropsyche

species combined. At some sites, statistics of Hydropsyche morosa group are based on the combined results of two or more species. Insects collected during 

1986–98 were depurated prior to analysis; depuration was discontinued in 1999. Arsenic was not analyzed until 2003; therefore, the number of samples may be 

small or zero for some taxa. Values are reported using U.S. Geological Survey rounding standards. Abbreviation: spp., one or more similar species. Symbols: 

<, less than minimum reporting level; --, indicates either too few samples (less than three) or insufficient data to compute statistic, or element not analyzed]
122 Water-Quality, Bed-Sediment, and Biological Data, and Statistical Summaries of Data, Clark Fork Basin, Montana

Constituent Number of 

composite samples Maximum Minimum Mean Median

12324400--Clark Fork above Little Blackfoot River, near Garrison

Period of record for biological data: 2009-11

Arctopsyche grandis

Arsenic 3 16.6 5.5 9.4 6.0

Cadmium 3 4.9 3.2 3.8 3.2

Chromium 3 4.6 <2.2 1

3.2 3.2

Copper 3 209 65.7 120 83.6

Iron 3 2,580 694 1,370 826

Lead 3 18.0 6.6 10.9 8.1

Manganese 3 990 940 967 972

Nickel 3 2.2 .7 1.2 .8

Zinc 3 378 253 304 282

Hydropsyche cockerelli

Arsenic 1 -- -- 11.1 --

Cadmium 1 -- -- 4.0 --

Chromium 1 -- -- 3.4 --

Copper 1 -- -- 158 --

Iron 1 -- -- 2,150 --

Lead 1 -- -- 18.8 --

Manganese 1 -- -- 1,500 --

Nickel 1 -- -- 1.7 --

Zinc 1 -- -- 284 --

Hydropsyche occidentalis

Arsenic 6 14.7 7.9 11.3 11.7

Cadmium 6 2.5 1.3 2.1 2.4

Chromium 6 3.6 .7 2.2 2.1

Copper 6 182 98.2 135 141

Iron 6 2,390 1,290 1,870 1,940

Lead 6 17.9 11.1 14.8 15.5

Manganese 6 1,610 975 1,300 1,230

Nickel 6 1.9 1.0 1.4 1.6

Zinc 6 299 223 257 258

Hydropsyche spp.

Arsenic 1 -- -- 13.6 --

Cadmium 1 -- -- 1.7 --

Chromium 1 -- -- 4.3 --

Copper 1 -- -- 187 --

Iron 1 -- -- 2,570 --

Lead 1 -- -- 18.5 --

Manganese 1 -- -- 919 --

Nickel 1 -- -- 1.8 --

Zinc 1 -- -- 296 --

Table 27. Statistical summary of long-term biological data for the Clark Fork basin, Montana, August 1986 through 

August 2011.—Continued

[Concentrations are in micrograms per gram dry weight (μg/g). Number of composite samples represents the total of all individual composite samples collected 

for every year that the constituent was analyzed. Values for a single sample are arbitrarily listed in the “Mean” column. Because Hydropsyche insects were not 

sorted to the species level during 1986–89, Hydropsyche species statistics for stations sampled during those years are based on the results of all Hydropsyche

species combined. At some sites, statistics of Hydropsyche morosa group are based on the combined results of two or more species. Insects collected during 

1986–98 were depurated prior to analysis; depuration was discontinued in 1999. Arsenic was not analyzed until 2003; therefore, the number of samples may be 

small or zero for some taxa. Values are reported using U.S. Geological Survey rounding standards. Abbreviation: spp., one or more similar species. Symbols: 

<, less than minimum reporting level; --, indicates either too few samples (less than three) or insufficient data to compute statistic, or element not analyzed]
Data 123

Constituent Number of 

composite samples Maximum Minimum Mean Median

12324680--Clark Fork at Goldcreek

Period of record for biological data: 1992–2011

Arctopsyche grandis

Arsenic 31 17.0 1.8 5.1 4.7

Cadmium 60 6.6 .6 2.0 1.8

Chromium 60 5.3 .1 1.4 1.1

Copper 60 232 19.9 52.2 39.3

Iron 60 3,070 195 783 540

Lead 60 16.9 1.0 4.2 3.4

Manganese 60 1,580 436 870 870

Nickel 60 3.1 .2 .8 .7

Zinc 60 326 146 205 186

Claassenia sabulosa

Arsenic 23 2.5 0.4 1.5 1.5

Cadmium 43 3.5 .1 1.1 .7

Chromium 43 1.6 .2 .6 .5

Copper 43 84.9 33.0 59.3 58.3

Iron 43 640 63.0 201 171

Lead 43 2.8 .4 1.0 .8

Manganese 43 320 50.6 151 129

Nickel 43 .7 .1 .3 .3

Zinc 43 364 166 266 261

Hydropsyche cockerelli

Arsenic 16 9.8 4.1 5.9 5.6

Cadmium 35 4.2 .5 1.5 1.3

Chromium 35 4.7 .5 2.0 1.9

Copper 35 188 17.1 73.6 58.4

Iron 35 3,250 522 1,160 930

Lead 35 17.6 2.4 6.7 5.3

Manganese 35 1,710 538 1,000 963

Nickel 35 3.5 .3 1.2 1.0

Zinc 35 359 106 193 186

Table 27. Statistical summary of long-term biological data for the Clark Fork basin, Montana, August 1986 through 

August 2011.—Continued

[Concentrations are in micrograms per gram dry weight (μg/g). Number of composite samples represents the total of all individual composite samples collected 

for every year that the constituent was analyzed. Values for a single sample are arbitrarily listed in the “Mean” column. Because Hydropsyche insects were not 

sorted to the species level during 1986–89, Hydropsyche species statistics for stations sampled during those years are based on the results of all Hydropsyche

species combined. At some sites, statistics of Hydropsyche morosa group are based on the combined results of two or more species. Insects collected during 

1986–98 were depurated prior to analysis; depuration was discontinued in 1999. Arsenic was not analyzed until 2003; therefore, the number of samples may be 

small or zero for some taxa. Values are reported using U.S. Geological Survey rounding standards. Abbreviation: spp., one or more similar species. Symbols: 

<, less than minimum reporting level; --, indicates either too few samples (less than three) or insufficient data to compute statistic, or element not analyzed]
124 Water-Quality, Bed-Sediment, and Biological Data, and Statistical Summaries of Data, Clark Fork Basin, Montana

Constituent Number of 

composite samples Maximum Minimum Mean Median

12324680--Clark Fork at Goldcreek—Continued

Period of record for biological data: 1992–2011

Hydropsyche morosa group

Arsenic 0 -- -- -- --

Cadmium 4 1.7 1.1 1.4 1.4

Chromium 4 1.4 1.3 1.4 1.4

Copper 4 72.9 43.8 60.5 62.7

Iron 4 1,320 612 1,050 1,130

Lead 4 6.9 2.4 4.6 4.6

Manganese 4 1,030 538 804 822

Nickel 4 1.4 .9 1.2 1.2

Zinc 4 190 137 167 170

Hydropsyche occidentalis

Arsenic 12 11.5 4.7 7.0 6.3

Cadmium 27 2.3 .4 1.3 1.3

Chromium 27 3.9 .4 1.8 1.7

Copper 27 170 26.4 74.1 62.6

Iron 27 2,720 466 1,250 1,160

Lead 27 15.7 2.9 7.6 6.0

Manganese 27 2,210 530 1,220 1,140

Nickel 27 2.5 .8 1.2 1.1

Zinc 27 276 97.0 202 204

Hydropsyche spp.

Arsenic 2 5.9 5.7 5.8 --

Cadmium 2 1.8 1.7 1.8 --

Chromium 2 1.6 1.6 1.6 --

Copper 2 83.5 73.6 78.6 --

Iron 2 1,150 1,110 1,130 --

Lead 2 9.2 8.0 8.6 --

Manganese 2 1,180 1,130 1,160 --

Nickel 2 .8 .8 .8 --

Zinc 2 210 196 203 --

Table 27. Statistical summary of long-term biological data for the Clark Fork basin, Montana, August 1986 through 

August 2011.—Continued

[Concentrations are in micrograms per gram dry weight (μg/g). Number of composite samples represents the total of all individual composite samples collected 

for every year that the constituent was analyzed. Values for a single sample are arbitrarily listed in the “Mean” column. Because Hydropsyche insects were not 

sorted to the species level during 1986–89, Hydropsyche species statistics for stations sampled during those years are based on the results of all Hydropsyche

species combined. At some sites, statistics of Hydropsyche morosa group are based on the combined results of two or more species. Insects collected during 

1986–98 were depurated prior to analysis; depuration was discontinued in 1999. Arsenic was not analyzed until 2003; therefore, the number of samples may be 

small or zero for some taxa. Values are reported using U.S. Geological Survey rounding standards. Abbreviation: spp., one or more similar species. Symbols: 

<, less than minimum reporting level; --, indicates either too few samples (less than three) or insufficient data to compute statistic, or element not analyzed]
Data 125

Constituent Number of 

composite samples Maximum Minimum Mean Median

12331800--Clark Fork near Drummond

Period of record for biological data: 1986, 1991–2011

Arctopsyche grandis

Arsenic 23 8.2 2.3 4.1 3.9

Cadmium 55 3.8 .4 1.5 1.3

Chromium 55 4.2 .2 1.1 1.0

Copper 55 103 16.9 35.6 29.6

Iron 55 1,720 193 644 547

Lead 55 11.8 1.6 4.9 4.2

Manganese 55 2,010 456 850 775

Nickel 55 1.9 .2 .7 .6

Zinc 55 314 140 201 190

Claassenia sabulosa

Arsenic 19 1.9 0.7 1.3 1.2

Cadmium 55 2.8 .1 1.1 1.1

Chromium 55 3.3 .2 .7 .6

Copper 55 165 18.0 65.3 61.3

Iron 55 449 45.4 176 148

Lead 55 2.9 .2 1.0 .9

Manganese 55 748 33.1 186 150

Nickel 55 1.1 .1 1

.3 1.2

Zinc 55 567 103 276 265

Hydropsyche cockerelli

Arsenic 13 7.1 3.9 5.4 5.3

Cadmium 42 4.5 .3 1.2 1.0

Chromium 42 3.5 .4 1.6 1.5

Copper 42 156 30.0 59.5 52.6

Iron 42 2,500 506 1,190 987

Lead 42 15.0 4.7 8.5 7.7

Manganese 42 1,680 549 1,010 934

Nickel 42 2.0 .5 1.1 1.1

Zinc 42 322 134 197 190

Table 27. Statistical summary of long-term biological data for the Clark Fork basin, Montana, August 1986 through 

August 2011.—Continued

[Concentrations are in micrograms per gram dry weight (μg/g). Number of composite samples represents the total of all individual composite samples collected 

for every year that the constituent was analyzed. Values for a single sample are arbitrarily listed in the “Mean” column. Because Hydropsyche insects were not 

sorted to the species level during 1986–89, Hydropsyche species statistics for stations sampled during those years are based on the results of all Hydropsyche

species combined. At some sites, statistics of Hydropsyche morosa group are based on the combined results of two or more species. Insects collected during 

1986–98 were depurated prior to analysis; depuration was discontinued in 1999. Arsenic was not analyzed until 2003; therefore, the number of samples may be 

small or zero for some taxa. Values are reported using U.S. Geological Survey rounding standards. Abbreviation: spp., one or more similar species. Symbols: 

<, less than minimum reporting level; --, indicates either too few samples (less than three) or insufficient data to compute statistic, or element not analyzed]
126 Water-Quality, Bed-Sediment, and Biological Data, and Statistical Summaries of Data, Clark Fork Basin, Montana

Constituent Number of 

composite samples Maximum Minimum Mean Median

12331800--Clark Fork near Drummond—Continued

Period of record for biological data: 1986, 1991–2011

Hydropsyche morosa group

Arsenic 0 -- -- -- --

Cadmium 6 1.3 1.1 1.2 1.2

Chromium 6 2.8 1.9 2.3 2.2

Copper 6 57.4 50.2 55.2 55.8

Iron 6 1,730 1,370 1,570 1,600

Lead 6 10.8 7.0 8.9 9.0

Manganese 6 1,940 1,260 1,610 1,610

Nickel 6 1.7 1.3 1.5 1.5

Zinc 6 250 227 239 240

Hydropsyche occidentalis

Arsenic 15 7.7 4.3 5.6 5.4

Cadmium 31 2.0 .4 1.1 1.0

Chromium 31 8.1 .4 2.2 2.1

Copper 31 118 13.3 58.5 55.8

Iron 31 2,060 424 1,260 1,190

Lead 31 14.0 3.0 8.8 9.1

Manganese 31 2,920 619 1,430 1,220

Nickel 31 2.4 .5 1.3 1.2

Zinc 31 293 157 221 222

Hydropsyche spp.

Arsenic 0 -- -- -- --

Cadmium 1 -- -- 2.6 --

Chromium 0 -- -- -- --

Copper 1 -- -- 85.0 --

Iron 1 -- -- 913 --

Lead 1 -- -- 9.1 --

Manganese 0 -- -- -- --

Nickel 0 -- -- -- --

Zinc 1 -- -- 260 --

Table 27. Statistical summary of long-term biological data for the Clark Fork basin, Montana, August 1986 through 

August 2011.—Continued

[Concentrations are in micrograms per gram dry weight (μg/g). Number of composite samples represents the total of all individual composite samples collected 

for every year that the constituent was analyzed. Values for a single sample are arbitrarily listed in the “Mean” column. Because Hydropsyche insects were not 

sorted to the species level during 1986–89, Hydropsyche species statistics for stations sampled during those years are based on the results of all Hydropsyche

species combined. At some sites, statistics of Hydropsyche morosa group are based on the combined results of two or more species. Insects collected during 

1986–98 were depurated prior to analysis; depuration was discontinued in 1999. Arsenic was not analyzed until 2003; therefore, the number of samples may be 

small or zero for some taxa. Values are reported using U.S. Geological Survey rounding standards. Abbreviation: spp., one or more similar species. Symbols: 

<, less than minimum reporting level; --, indicates either too few samples (less than three) or insufficient data to compute statistic, or element not analyzed]
Data 127

Constituent Number of 

composite samples Maximum Minimum Mean Median

12334550--Clark Fork at Turah Bridge, near Bonner

Period of record for biological data: 1986, 1991–2011

Arctopsyche grandis

Arsenic 27 7.2 3.1 4.6 4.5

Cadmium 69 2.7 .4 1.2 1.0

Chromium 69 4.1 .5 1.6 1.5

Copper 69 125 20.1 38.4 32.2

Iron 69 2,870 372 942 793

Lead 69 13.2 1.6 4.4 3.7

Manganese 69 902 324 650 662

Nickel 69 2.6 .4 1.1 .9

Zinc 69 282 111 201 198

Claassenia sabulosa

Arsenic 19 1.9 0.5 1.1 1.1

Cadmium 45 2.5 .1 1.1 .8

Chromium 45 2.0 .2 .7 .6

Copper 45 95.1 37.5 60.3 60.2

Iron 45 378 58.6 134 114

Lead 45 1.6 .2 .7 .6

Manganese 45 229 37.2 102 90.2

Nickel 45 .6 .04 .2 .2

Zinc 45 342 144 230 235

Hydropsyche cockerelli

Arsenic 19 9.8 3.7 5.0 4.9

Cadmium 47 2.2 .3 .9 .7

Chromium 47 14.2 .2 2.2 1.7

Copper 47 126 26.4 50.5 44.4

Iron 47 3,180 566 1,260 1,160

Lead 47 19.7 2.2 5.7 5.2

Manganese 47 848 426 646 661

Nickel 47 2.7 .6 1.3 1.3

Zinc 47 332 119 190 195

Table 27. Statistical summary of long-term biological data for the Clark Fork basin, Montana, August 1986 through 

August 2011.—Continued

[Concentrations are in micrograms per gram dry weight (μg/g). Number of composite samples represents the total of all individual composite samples collected 

for every year that the constituent was analyzed. Values for a single sample are arbitrarily listed in the “Mean” column. Because Hydropsyche insects were not 

sorted to the species level during 1986–89, Hydropsyche species statistics for stations sampled during those years are based on the results of all Hydropsyche

species combined. At some sites, statistics of Hydropsyche morosa group are based on the combined results of two or more species. Insects collected during 

1986–98 were depurated prior to analysis; depuration was discontinued in 1999. Arsenic was not analyzed until 2003; therefore, the number of samples may be 

small or zero for some taxa. Values are reported using U.S. Geological Survey rounding standards. Abbreviation: spp., one or more similar species. Symbols: 

<, less than minimum reporting level; --, indicates either too few samples (less than three) or insufficient data to compute statistic, or element not analyzed]
128 Water-Quality, Bed-Sediment, and Biological Data, and Statistical Summaries of Data, Clark Fork Basin, Montana

Constituent Number of 

composite samples Maximum Minimum Mean Median

12334550--Clark Fork at Turah Bridge, near Bonner—Continued

Period of record for biological data: 1986, 1991–2011

Hydropsyche morosa group

Arsenic 0 -- -- -- --

Cadmium 2 1.3 1.1 1.2 --

Chromium 2 4.6 2.4 3.5 --

Copper 2 84.1 26.8 55.4 --

Iron 2 1,800 986 1,390 --

Lead 2 6.6 <7.8 1

5.2 --

Manganese 2 1,320 537 928 --

Nickel 2 1.7 1.3 1.5 --

Zinc 2 231 171 201 --

Hydropsyche occidentalis

Arsenic 16 7.3 3.6 4.8 4.3

Cadmium 36 1.8 .3 1.0 .9

Chromium 36 5.0 .6 2.0 1.7

Copper 36 102 27.4 50.5 45.8

Iron 36 2,590 472 1,290 1,170

Lead 36 14.2 3.0 6.6 5.7

Manganese 36 1,600 454 867 821

Nickel 36 3.2 .6 1.3 1.2

Zinc 36 416 145 214 222

Hydropsyche spp.

Arsenic 0 -- -- -- --

Cadmium 1 -- -- 1.3 --

Chromium 1 -- -- 2.4 --

Copper 1 -- -- 84.1 --

Iron 1 -- -- 1,800 --

Lead 1 -- -- <7.8 --

Manganese 1 -- -- 537 --

Nickel 1 -- -- 1.3 --

Zinc 1 -- -- 171 --

Table 27. Statistical summary of long-term biological data for the Clark Fork basin, Montana, August 1986 through 

August 2011.—Continued

[Concentrations are in micrograms per gram dry weight (μg/g). Number of composite samples represents the total of all individual composite samples collected 

for every year that the constituent was analyzed. Values for a single sample are arbitrarily listed in the “Mean” column. Because Hydropsyche insects were not 

sorted to the species level during 1986–89, Hydropsyche species statistics for stations sampled during those years are based on the results of all Hydropsyche

species combined. At some sites, statistics of Hydropsyche morosa group are based on the combined results of two or more species. Insects collected during 

1986–98 were depurated prior to analysis; depuration was discontinued in 1999. Arsenic was not analyzed until 2003; therefore, the number of samples may be 

small or zero for some taxa. Values are reported using U.S. Geological Survey rounding standards. Abbreviation: spp., one or more similar species. Symbols: 

<, less than minimum reporting level; --, indicates either too few samples (less than three) or insufficient data to compute statistic, or element not analyzed]
Data 129

Table 27. Statistical summary of long-term biological data for the Clark Fork basin, Montana, August 1986 through 

August 2011.—Continued

[Concentrations are in micrograms per gram dry weight (μg/g). Number of composite samples represents the total of all individual composite samples collected 

for every year that the constituent was analyzed. Values for a single sample are arbitrarily listed in the “Mean” column. Because Hydropsyche insects were not 

sorted to the species level during 1986–89, Hydropsyche species statistics for stations sampled during those years are based on the results of all Hydropsyche

species combined. At some sites, statistics of Hydropsyche morosa group are based on the combined results of two or more species. Insects collected during 

1986–98 were depurated prior to analysis; depuration was discontinued in 1999. Arsenic was not analyzed until 2003; therefore, the number of samples may be 

small or zero for some taxa. Values are reported using U.S. Geological Survey rounding standards. Abbreviation: spp., one or more similar species. Symbols: 

<, less than minimum reporting level; --, indicates either too few samples (less than three) or insufficient data to compute statistic, or element not analyzed]

Constituent Number of 

composite samples Maximum Minimum Mean Median

12340000--Blackfoot River near Bonner

Period of record for biological data: 1986–87, 1991, 1993, 1996, 1998, 2000, 2003, 2006–11

Arctopsyche grandis

Arsenic 7 4.6 1.6 2.8 2.2

Cadmium 17 .5 .1 .3 .2

Chromium 12 6.9 .5 2.4 1.3

Copper 17 18.0 9.9 13.1 12.5

Iron 17 1,880 108 740 759

Lead 17 2.3 .5 1.1 .9

Manganese 12 633 286 485 496

Nickel 12 3.7 .7 1.4 1.2

Zinc 17 156 123 141 139

Claassenia sabulosa

Arsenic 10 3.0 0.3 1.0 0.7

Cadmium 21 .2 .1 .1 .2

Chromium 16 5.2 .3 1.0 .7

Copper 21 88.5 19.0 43.8 44.0

Iron 21 317 46.2 147 138

Lead 21 .8 .1 .3 .2

Manganese 16 133 26.3 81.5 76.6

Nickel 16 1.1 .1 .3 .3

Zinc 21 328 117 222 205

Hydropsyche cockerelli

Arsenic 5 4.2 2.4 3.2 3.1

Cadmium 5 .6 <.1 1

.4 1.4

Chromium 5 3.8 2.4 3.2 3.6

Copper 5 16.2 5.6 13.3 14.8

Iron 5 2,390 1,550 1,910 1,970

Lead 5 2.3 1.9 2.1 2.1

Manganese 5 814 428 642 637

Nickel 5 4.6 1.8 2.7 2.2

Zinc 5 162 140 146 142
130 Water-Quality, Bed-Sediment, and Biological Data, and Statistical Summaries of Data, Clark Fork Basin, Montana

Constituent Number of 

composite samples Maximum Minimum Mean Median

12340000--Blackfoot River near Bonner—Continued

Period of record for biological data: 1986–87, 1991, 1993, 1996, 1998, 2000, 2003, 2006–11

Hydropsyche occidentalis

Arsenic 10 3.8 1.2 2.4 2.2

Cadmium 22 .5 .1 .2 .2

Chromium 22 5.8 .8 2.2 1.9

Copper 22 20.6 12.0 15.7 15.1

Iron 22 2,090 1,010 1,530 1,500

Lead 22 2.0 .8 1.5 1.6

Manganese 22 798 414 529 470

Nickel 22 4.9 .9 1.6 1.4

Zinc 22 163 116 138 142

Hydropsyche spp.

Arsenic 0 -- -- -- --

Cadmium 1 -- -- 0.6 --

Chromium 1 -- -- 1.6 --

Copper 1 -- -- 13.9 --

Iron 1 -- -- 1,140 --

Lead 1 -- -- 2.9 --

Manganese 1 -- -- 525 --

Nickel 1 -- -- 2.8 --

Zinc 1 -- -- 132 --

Table 27. Statistical summary of long-term biological data for the Clark Fork basin, Montana, August 1986 through 

August 2011.—Continued

[Concentrations are in micrograms per gram dry weight (μg/g). Number of composite samples represents the total of all individual composite samples collected 

for every year that the constituent was analyzed. Values for a single sample are arbitrarily listed in the “Mean” column. Because Hydropsyche insects were not 

sorted to the species level during 1986–89, Hydropsyche species statistics for stations sampled during those years are based on the results of all Hydropsyche

species combined. At some sites, statistics of Hydropsyche morosa group are based on the combined results of two or more species. Insects collected during 

1986–98 were depurated prior to analysis; depuration was discontinued in 1999. Arsenic was not analyzed until 2003; therefore, the number of samples may be 

small or zero for some taxa. Values are reported using U.S. Geological Survey rounding standards. Abbreviation: spp., one or more similar species. Symbols: 

<, less than minimum reporting level; --, indicates either too few samples (less than three) or insufficient data to compute statistic, or element not analyzed]
Data 131

Constituent Number of 

composite samples Maximum Minimum Mean Median

12340500--Clark Fork above Missoula

Period of record for biological data: 1997–2011

Arctopsyche grandis

Arsenic 23 7.2 2.1 4.1 4.1

Cadmium 42 2.3 .1 .9 .7

Chromium 42 4.2 .6 1.8 1.6

Copper 42 81.2 19.5 41.4 37.5

Iron 42 2,340 476 1,100 994

Lead 42 8.8 1.2 4.4 4.2

Manganese 42 1,410 476 910 891

Nickel 42 2.1 .5 1.2 1.1

Zinc 42 272 133 200 200

Claassenia sabulosa

Arsenic 15 1.9 0.5 1.3 1.4

Cadmium 24 2.0 .2 .8 .5

Chromium 24 1.4 .3 .8 .8

Copper 24 81.1 33.0 53.8 51.2

Iron 24 402 95.3 235 233

Lead 24 3.1 .4 1.0 1.0

Manganese 24 683 57.8 206 156

Nickel 24 .5 <.3 1

.4 1.4

Zinc 24 363 191 274 271

Hydropsyche cockerelli

Arsenic 16 8.9 3.7 6.5 6.6

Cadmium 25 2.0 .4 1.0 1.0

Chromium 25 6.0 1.8 3.1 3.3

Copper 25 99.7 29.9 68.5 75.9

Iron 25 3,590 1,400 2,170 2,160

Lead 25 12.1 4.2 8.1 7.6

Manganese 25 1,910 764 1,250 1,220

Nickel 25 2.4 1.4 1.9 1.9

Zinc 25 266 156 223 226

Table 27. Statistical summary of long-term biological data for the Clark Fork basin, Montana, August 1986 through 

August 2011.—Continued

[Concentrations are in micrograms per gram dry weight (μg/g). Number of composite samples represents the total of all individual composite samples collected 

for every year that the constituent was analyzed. Values for a single sample are arbitrarily listed in the “Mean” column. Because Hydropsyche insects were not 

sorted to the species level during 1986–89, Hydropsyche species statistics for stations sampled during those years are based on the results of all Hydropsyche

species combined. At some sites, statistics of Hydropsyche morosa group are based on the combined results of two or more species. Insects collected during 

1986–98 were depurated prior to analysis; depuration was discontinued in 1999. Arsenic was not analyzed until 2003; therefore, the number of samples may be 

small or zero for some taxa. Values are reported using U.S. Geological Survey rounding standards. Abbreviation: spp., one or more similar species. Symbols: 

<, less than minimum reporting level; --, indicates either too few samples (less than three) or insufficient data to compute statistic, or element not analyzed]
132 Water-Quality, Bed-Sediment, and Biological Data, and Statistical Summaries of Data, Clark Fork Basin, Montana

Constituent Number of 

composite samples Maximum Minimum Mean Median

12340500--Clark Fork above Missoula—Continued

Period of record for biological data: 1997–2011

Hydropsyche occidentalis

Arsenic 9 7.4 3.9 5.8 6.2

Cadmium 15 1.5 .4 .9 .8

Chromium 15 5.5 1.5 3.2 3.1

Copper 15 80.7 30.3 59.2 59.5

Iron 15 2,540 1,450 2,080 2,210

Lead 15 11.4 4.0 7.4 7.1

Manganese 15 2,470 718 1,620 1,600

Nickel 15 2.4 1.4 1.9 1.9

Zinc 15 278 192 233 230

1

Values determined by substituting one-half of the minimum reporting level for censored (<) values when both uncensored and censored values were used 

in determining the mean and median. When all data were less than the minimum reporting level, the median was determined by ranking the censored values in 

order of detection.

Table 27. Statistical summary of long-term biological data for the Clark Fork basin, Montana, August 1986 through 

August 2011.—Continued

[Concentrations are in micrograms per gram dry weight (μg/g). Number of composite samples represents the total of all individual composite samples collected 

for every year that the constituent was analyzed. Values for a single sample are arbitrarily listed in the “Mean” column. Because Hydropsyche insects were not 

sorted to the species level during 1986–89, Hydropsyche species statistics for stations sampled during those years are based on the results of all Hydropsyche

species combined. At some sites, statistics of Hydropsyche morosa group are based on the combined results of two or more species. Insects collected during 

1986–98 were depurated prior to analysis; depuration was discontinued in 1999. Arsenic was not analyzed until 2003; therefore, the number of samples may be 

small or zero for some taxa. Values are reported using U.S. Geological Survey rounding standards. Abbreviation: spp., one or more similar species. Symbols: 

<, less than minimum reporting level; --, indicates either too few samples (less than three) or insufficient data to compute statistic, or element not analyzed]
Publishing support provided by the: 

Denver Publishing Service Center

For more information concerning this publication, contact: 

Director, Montana Water Science Center 

U.S. Geological Survey 

3162 Bozeman Ave. 

Helena, MT 59601 

(406) 457–5900

Or visit the Montana Water Science Center Web site at: 

http://mt.water.usgs.gov/
Dodge and others—Water-Quality, Bed-Sediment, and Biological Data (October 2010 through September 2011) and Statistical Summaries of Data for Streams 

in the Clark Fork Basin, Montana—OFR 2013-1017