U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2015–5008

Prepared in cooperation with the U.S. Forest Service

Water-Quality Trends for Selected Sites in the Boulder River 

and Tenmile Creek Watersheds, Montana, Based on Data 

Collected During Water Years 1997–2013
Cover photograph: Looking upstream from seepage from the Bullion Mine adit, 

Jefferson County, Montana, May 23, 2013. Photograph by Craig L. Bowers, 

U.S. Geological Survey.
Water-Quality Trends for Selected Sites 

in the Boulder River and Tenmile Creek 

Watersheds, Montana, Based on Data 

Collected During Water Years 1997–2013

By Steven K. Sando, Melanie L. Clark, Thomas E. Cleasby, and Elliott P. Barnhart 

Prepared in cooperation with the U.S. Forest Service

Scientific Investigations Report 2015–5008

U.S. Department of the Interior

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

SALLY JEWELL, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2015

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

U.S. Government.

Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials 

as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner.

Suggested citation:

Sando, S.K., Clark, M.L., Cleasby, T.E., and Barnhart, E.P., 2015, Water-quality trends for selected sites in the 

Boulder River and Tenmile Creek watersheds, Montana, based on data collected during water years 1997–2013: 

U.S. Geological Survey Scientific Investigations Report 2015–5008, 46 p., http://dx.doi.org/10.3133/sir20155008.

ISSN: 2328-0328 (online)
iii

Acknowledgments

The authors would like to recognize the U.S. Geological Survey hydrologists and hydrologic technicians involved in the collection of the water-quality and streamflow data for their dedicated 

efforts. Also, the authors would like to recognize the valuable contributions to this report from 

the insightful technical reviews by Skip Vecchia and Dave Naftz of the U.S. Geological Survey.

Special thanks are given to Nancy Rusho and Robert Wintergerst of the U.S. Forest Service for 

their support of this study. 
iv

Contents

Acknowledgments........................................................................................................................................iii

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

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

Purpose and Scope ..............................................................................................................................2

Description of Study Area ...................................................................................................................2

Hydrographic and Hydrologic Characteristics .......................................................................2

Boulder River Watershed ..................................................................................................5

Tenmile Creek Watershed .................................................................................................6

Physiographic, Climatic, and Geologic Characteristics........................................................6

Overview of Mining and Remediation Activities ....................................................................7

Data Collection and Analytical Methods ...................................................................................................9

Quality Assurance........................................................................................................................................10

Overview of Water-Quality Characteristics for Selected Sites in the Boulder River and 

Tenmile Creek Watersheds...........................................................................................................11

Adit Sites in the Boulder River Watershed.....................................................................................14

Stream Sites in the Boulder River Watershed...............................................................................14

Stream Sites in the Tenmile Creek Watershed ..............................................................................19

Trend-Analysis Methods ............................................................................................................................20

Factors that Affect Trend Analysis and Interpretation..........................................................................22

Data-Collection Factors.....................................................................................................................22

Potential Effects of Diel Cycling of Trace Elements ......................................................................23

Statistical and Other Factors ............................................................................................................23

Water-Quality Trends for Selected Sites in the Boulder River and Tenmile Creek Watersheds....24

Adit Sites in the Boulder River Watershed.....................................................................................24

Bullion Mine Adit (site 2) ..........................................................................................................24

Crystal Mine Adit (site 6) ..........................................................................................................24

Summary of Trend Results for the Adit Sites in the Boulder River Watershed ...............26

Stream Sites in the Boulder River Watershed...............................................................................26

Boulder River Above Kleinsmith Gulch (site 1) .....................................................................27

Bullion Mine Tributary at Mouth (site 3).................................................................................27

Jack Creek at Mouth (site 4)....................................................................................................27

Basin Creek at Basin (site 5)....................................................................................................34

Cataract Creek Above Uncle Sam Gulch (site 7)..................................................................34

Cataract Creek at Basin (site 8)...............................................................................................34

High Ore Creek Near Basin (site 9).........................................................................................35

Boulder River Below Little Galena Gulch (site 10) ...............................................................35

Summary of Trend Results for the Stream Sites in the Boulder River Watershed .........35

Stream Sites in the Tenmile Creek Watershed ..............................................................................36

Tenmile Creek Above City Diversion (site 11)........................................................................36

Minnehaha Creek Near Rimini (site 12) .................................................................................36

Tenmile Creek Near Rimini (site 13)........................................................................................36

Summary of Trend Results for the Stream Sites in the Tenmile Creek Watershed.........37

Water-Quality Monitoring Considerations with Respect to Trend Analysis .............................37
v

Summary and Conclusions.........................................................................................................................38

References....................................................................................................................................................39

Appendixes 1–3............................................................................................................................................43

Appendix 1. Summary Information Relating to Quality-Control And Water-Quality Data ......44

Appendix 2. Summary of Multiple Linear Regression as Applied in this Study........................44

Appendix 3. Trend-Analysis Results ................................................................................................46

Figures

1. Map showing location of selected sites in the Boulder River and Tenmile Creek 

watersheds, Montana..................................................................................................................3

2. Diagram showing simplified hydrographic flow diagram for the study area in the 

Boulder River watershed, Montana ..........................................................................................5

3. Diagram showing simplified hydrographic flow diagram for the study area in the 

Tenmile Creek watershed, Montana .........................................................................................7

4. Graph showing temporal characteristics of water-quality sample collection for 

sites in the Boulder River and Tenmile Creek watersheds, Montana..................................9

5. Graphs showing statistical distributions of selected constituents for the adit sites 

in the Boulder River watershed, Montana, based on data collected during water 

years 2009–2013 ..........................................................................................................................12

6. Graphs showing statistical distributions of selected constituents for the stream 

sites in the Boulder River and Tenmile Creek watersheds, Montana, based on data 

collected during water years 2009–2013 ................................................................................13

7. Graphs showing selected streamflow and constituent concentration information 

for Basin Creek at Basin (site 5, fig. 1, table 1), based on data collected during water 

years 1997–2013 ..........................................................................................................................21

8. Graphs showing water-quality trends (not flow adjusted) for June 2003 through 

September 2013 for the adit sites in the Boulder River watershed, Montana..................25

9. Graphs showing flow-adjusted water-quality trends for water years 2000–13 for

 the stream sites in the Boulder River and Tenmile Creek watersheds, Montana ..........28

3–1. Graphs showing flow-adjusted fitted trends for selected water-quality constituents 

and properties for Boulder River above Kleinsmith Gulch (site 1, fig. 1, table 1), 

based on analysis of data collected during water years 1997–2013..................................46

3–2. Graphs showing fitted trends (not flow adjusted) for selected water-quality 

constituents and properties for Bullion Mine adit (site 2, fig. 1, table 1), based on 

analysis of data collected during water years 1999–2013 ...................................................46

3–3. Graphs showing flow-adjusted fitted trends for selected water-quality constituents 

and properties for Bullion Mine tributary at mouth (site 3, fig. 1, table 1), based on 

analysis of data collected during water years 1997–2013 ...................................................46

3–4. Graphs showing flow-adjusted fitted trends for selected water-quality constituents 

and properties for Jack Creek at mouth (site 4, fig. 1, table 1), based on analysis of 

data collected during water years 2000–13 ...........................................................................46

3–5. Graphs showing flow-adjusted fitted trends for selected water-quality constituents 

and propertiesfor Basin Creek at Basin (site 5, fig. 1, table 1), based on analysis of 

data collected during water years 1997–2013 .......................................................................46

3–6. Graphs showing fitted trends (not flow adjusted) for selected water-quality constituents and properties for Crystal Mine adit (site 6, fig. 1, table 1), based on analysis of 

data collected during water years 2003–13 ...........................................................................46
vi

3–7. Graphs showing flow-adjusted fitted trends for selected water-quality constituents 

and properties for Cataract Creek above Uncle Sam Gulch (site 7, fig. 1, table 1), 

based on analysis of data collected during water years 1997–2013..................................46

3–8. Graphs showing flow-adjusted fitted trends for selected water-quality constituents 

and properties for Cataract Creek at Basin (site 8, fig. 1, table 1), based on analysis 

of data collected during water years 1997–2013...................................................................46

3–9. Graphs showing flow-adjusted fitted trends for selected water-quality constituents 

and properties for High Ore Creek near Basin (site 9, fig. 1, table 1), based on 

analysis of data collected during water years 1997–2013 ...................................................46

3–10. Graphs showing flow-adjusted fitted trends for selected water-quality constituents 

and properties for Boulder River below Little Galena Gulch (site 10, fig. 1, table 1), 

based on analysis of data collected during water years 1997–2013..................................46

3–11. Graphs showing flow-adjusted fitted trends for selected water-quality constituents 

and properties for Tenmile Creek above City Diversion (site 11, fig. 1, table 1), based 

on analysis of data collected during water years 1999–2013..............................................46

3–12. Graphs showing flow-adjusted fitted trends for selected water-quality constituents 

and properties for Minnehaha Creek near Rimini (site 12, fig. 1, table 1), based on 

analysis of data collected during water years 1997–2013 ...................................................46

3–13. Graphs showing flow-adjusted fitted trends for selected water-quality constituents 

and properties for Tenmile Creek near Rimini (site 13, fig. 1, table 1), based on 

analysis of data collected during water years 2005–13 .......................................................46

Tables

1. Information for selected sampling sites in the Boulder River and Tenmile Creek 

watersheds, Montana..................................................................................................................4

2. Property and constituents included in the trend analysis and information relating 

to laboratory reporting levels ...................................................................................................10

3. Ranks of median values of properties and constituents among all stream sites in 

the Boulder River and Tenmile Creek watersheds, Montana, based on data 

collected during water years 2009–13 ....................................................................................15

4. Percent of samples with unadjusted unfiltered-recoverable concentrations 

exceeding water-quality standards for sites in the Boulder River and Tenmile 

Creek watersheds, Montana, water years 2009–13..............................................................16

5. Summary of water-quality trends (not flow adjusted) for June 2003 through 

September 2013 for the adit sites in the Boulder River watershed, Montana..................26

6. Summary of flow-adjusted water-quality trends for water years 2000–13 for the stream 

sites in the Boulder River and Tenmile Creek watersheds, Montana................................30

1–1. Summary information relating to quality-control samples (equipment blank and 

replicate samples) collected at sites in the Boulder River and Tenmile Creek 

watersheds, Montana, based on data collected during water years 1997–2013 ............44

1–2. Summary information relating to water-quality constituents and properties in 

samples collected at sites in the Boulder River and Tenmile Creek watersheds, 

Montana, based on data collected during water years 2009–13........................................44

1–3. Aquatic life standards (based on median hardness for water years 2009–13) for 

selected sites in the Boulder River and Tenmile Creek watersheds, based on data 

collected during water years 2009–13 ....................................................................................44
vii

3–1. Detailed water-quality trend results (not flow adjusted) for the adit sites in the 

Boulder River watershed, Montana, based on analysis of data collected during 

water years 1999–2013...............................................................................................................46

 3–2. Detailed flow-adjusted water-quality trend results for the stream sites in the 

Boulder River and Tenmile Creek watersheds, Montana, based on analysis of data 

collected during water years 1997–2013 ................................................................................46
viii

Conversion Factors

Inch/Pound to International System of Units

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

yard (yd) 0.9144 meter (m)

Area

acre 4,047 square meter (m2

)

acre 0.4047 hectare (ha)

acre 0.004047 square kilometer (km2

)

square mile (mi2

) 259.0 hectare (ha)

square mile (mi2

) 2.590 square kilometer (km2) 

Volume

ounce, fluid (fl. oz) 0.02957 liter (L) 

pint (pt) 0.4732 liter (L) 

quart (qt) 0.9464 liter (L) 

gallon (gal) 3.785 liter (L) 

cubic foot (ft3

) 28.32 cubic decimeter (dm3) 

cubic foot (ft3

) 0.02832 cubic meter (m3) 

cubic yard (yd3

) 0.7646 cubic meter (m3) 

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

)

acre-foot (acre-ft) 0.001233 cubic hectometer (hm3

) 

Flow rate

cubic foot per second (ft3

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

Mass

ounce, avoirdupois (oz) 28.35 gram (g) 

pound, avoirdupois (lb) 0.4536 kilogram (kg) 

ton, short (2,000 lb) 0.9072 megagram (Mg) 

ton per day (ton/d) 0.9072 metric ton per day

ton per day (ton/d) 0.9072 megagram per day (Mg/d)

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

°F=(1.8×°C)+32

Datum

Vertical coordinate information is referenced to the National Geodetic Vertical Datum of 1988 

(NGVD 88).

Horizontal coordinate information is referenced to North American Datum of 1983 (NAD 83).

Altitude, as used in this report, refers to distance above the vertical datum.
ix

Supplemental Information

Specific conductance is given in microsiemens per centimeter at 25 degrees Celsius 

(μS/cm at 25 °C).

Concentrations of chemical constituents in water are given either in micrograms per liter 

(μg/L) or milligrams per liter (mg/L).

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 2010 is the period from October 1, 2009, through September 30, 2010.
x

Abbreviations

EPA U.S. Environmental Protection Agency

FAC flow-adjusted concentration

log logarithm (base 10)

LRL laboratory reporting level

NGVD 88 National Geodetic Vertical Datum of 1988

NWQL National Water Quality Laboratory

MLR multiple linear regression 

p-value statistical probability level

Q daily mean streamflow, in cubic feet per second

RPD relative percent difference

SEE standard error of estimate

USFS U.S. Forest Service

USGS U.S. Geological Survey
Abstract

In the Boulder River and Tenmile Creek watersheds in 

southwestern Montana, there was intensive mining during a 

40-year period after the discovery of gold in the early 1860s. 

Potential effects from the historic mining activities include 

acid-mine drainage and elevated concentrations of potentially 

toxic trace elements from mining remnants such as waste rock 

and tailing piles. In support of remediation efforts, water-quality monitoring by the U.S. Geological Survey began in 1997 

in the Boulder River and Tenmile Creek watersheds and has 

continued to present (2014). The U.S. Geological Survey, in 

cooperation with the U.S. Forest Service, investigated temporal trends in water quality at 13 sites, including 2 adit (or 

mine entrance) sites and 11 stream sites. The primary purpose 

of this report is to present results of trend analysis of specific 

conductance, selected trace-elements (cadmium, copper, lead, 

zinc, and arsenic), and suspended sediment for the 13 sites. 

For the stream sites, multiple linear regression of constituent concentrations on time, streamflow, and season was 

used for flow-adjusted trend analysis. For the adit sites, relations between constituent concentrations and streamflow were 

much weaker than for the stream sites. Thus, streamflow was 

not included in multiple linear regression trend models for the 

adit sites, and the trend results represent temporal changes in 

unadjusted concentrations. 

The datasets for the sites in the Boulder River and 

Tenmile Creek watersheds were not specifically designed for 

trend analysis. All of the study sites have variability in withinyear sampling frequency. However, the within-year sampling 

frequency was similar among most sites in individual years. 

Although the study datasets are not ideally suited for precise 

definition of temporal trends, generally strong similarity in 

sample-collection characteristics of the datasets among most 

sites provides a reasonable basis for relative comparisons of 

trend results among sites. 

Trend results for the adit sites in the Boulder River 

watershed (Bullion Mine adit [site 2] and Crystal Mine adit 

[site 6]) do not provide clear evidence of substantial trending during June 2003 through September 2013. Water quality 

of the adit sites probably is affected by complex processes 

that are not well defined in the study datasets. As such, the 

trend-analysis structure of the study might not be suitable for 

accurate description of temporal trends in water quality at the 

two adit sites.

Trend results for most stream sites in the Boulder 

River watershed for water years 2000–13 (water year is the 

12-month period from October 1 through September 30 and 

is designated by the year in which it ends) indicate decreasing 

trends in flow-adjusted specific conductance, in flow-adjusted 

concentrations (FACs) for most filtered and unfiltered-recoverable trace elements, and in suspended sediment. Overall, 

magnitudes of the decreasing trends in FACs of metallic 

contaminants are largest for Bullion Mine tributary at mouth 

(site 3), Jack Creek at mouth (site 4), and Cataract Creek at 

Basin (site 8). For sites 3, 4, and 8, magnitudes of decreasing 

trends generally ranged from about -5 to -10 percent per year. 

Notably, the watersheds upstream from sites 3, 4, and 8 have 

been targeted by substantial remediation activities.

Overall, magnitudes of decreasing trends in FACs of 

metallic contaminants are considered intermediate for Basin 

Creek at Basin (site 5), High Ore Creek near Basin (site 9), 

and Boulder River below Little Galena Gulch (site 10). For 

sites 5, 9, and 10, the magnitudes of the decreasing trends 

generally ranged from about -2 to -5 percent per year. 

Decreasing trends in FACs of metallic contaminants for 

Boulder River above Kleinsmith Gulch (site 1) and Cataract 

Creek above Uncle Sam Gulch (site 7) generally are minor to 

small (ranging from about -1 to -2 percent per year) and for 

most metallic contaminants the changes are within fairly small 

ranges at generally low FACs. The watershed of site 1 has 

smaller mining effects than most other study sites. The watersheds of site 1 and 7 have not been targeted by substantial 

remediation activities. Consideration of trend patterns among 

all stream sites in the Boulder River watershed provides strong 

evidence that remediation activities are the primary cause of 

decreasing trends in metallic contaminants.

Trend results for sites in the Tenmile Creek watershed 

generally are more variable and difficult to interpret than 

for sites in the Boulder River watershed. Trend results for 

Tenmile Creek above City Diversion (site 11) and Minnehaha 

Creek near Rimini (site 12) for water years 2000–13 indicate 

decreasing trends in FACs of cadmium, copper, and zinc. 

The magnitudes of the decreasing trends in FACs of copper 

Water-Quality Trends for Selected Sites in the Boulder 

River and Tenmile Creek Watersheds, Montana, Based on 

Data Collected During Water Years 1997–2013

By Steven K. Sando, Melanie L. Clark, Thomas E. Cleasby, and Elliott P. Barnhart 
2 Water-Quality Trends for Selected Sites in the Boulder River and Tenmile Creek Watersheds, Montana

generally are moderate and statistically significant for sites 

11 and 12. The magnitudes of the decreasing trends in FACs 

of cadmium and zinc for site 11 are minor to small and not 

statistically significant; however, the magnitudes for site 12 

are moderate and statistically significant. In general, patterns 

in FACs for Tenmile Creek near Rimini (site 13) are not well 

represented by fitted trends within the short data collection 

period, which might indicate that the trend-analysis structure 

of the study is not appropriate for describing trends in FACs 

for site 13. The large decreasing trend in FACs of suspended 

sediment is the strongest indication of change in water quality 

during the short period of record for site 13; however, this 

trend is not statistically significant.

Introduction

In the Boulder River and Tenmile Creek watersheds in 

southwestern Montana, there was intensive mining during a 

40-year period after the discovery of gold in the early 1860s. 

Although most of the mining involved small operations, the 

cumulative environmental effect was large because of the 

hundreds of sites where mine wastes and mill tailings were 

discarded with little regard for potential lasting effect on rivers 

or streams. Potential effects from the historic mining activities include acid-mine drainage and elevated concentrations 

of potentially toxic trace elements from mining remnants such 

as waste rock and tailing piles. Remediation of these mining 

remnants in both watersheds has been ongoing since about 

1998 (Nimick and others, 2004). 

Much of the study area is located on public land, including State land, U.S. Forest Service (USFS) land, and Bureau 

of Land Management land. As such, remediation of environmental effects of the mine wastes has involved coordinated 

efforts by multiple State and Federal agencies to assess 

the extent of contamination and to develop and implement 

remediation strategies. In support of the coordinated remediation efforts, water-quality monitoring by the U.S. Geological 

Survey (USGS) began in water year 1997 (water year is the 

12-month period from October 1 through September 30 and is 

designated by the year in which it ends) in the Boulder River 

and Tenmile Creek watersheds and has continued to present 

(2014). 

Data in the USGS monitoring program span a sufficient 

number of years to allow statistical testing for temporal trends 

in water-quality constituents and properties. Thus, the USGS, 

in cooperation with the USFS, investigated temporal trends in 

water quality at 13 sampling sites (fig. 1, table 1). 

Purpose and Scope

The primary purpose of this report is to present results of 

trend analysis of specific conductance, selected trace-elements 

(cadmium, copper, lead, zinc, and arsenic), and suspended 

sediment for 13 selected sampling sites in the Boulder River 

and Tenmile Creek watersheds based on data collected during 

water years 1997–2013. The 13 sites include 2 adit (or mine 

entrance) sites and 11 stream sites. The report also presents 

background information on mining and remediation activities in the Boulder River and Tenmile Creek watersheds, 

trend-analysis methods, and factors that affect trend analysis 

and interpretation. The information is presented to assist in 

evaluating trend results. 

The datasets of the 13 sites are variable with respect to 

data-collection periods; within-year frequency of data collection; and thus, the amount of data available for trend analysis. 

Variability in the datasets complicates consistent statistical 

analysis among the sites. A primary objective of this report is 

to generally describe relative variability in trend patterns as 

consistently as possible among site and constituent combinations, given the available data. In cases where the structure 

of the datasets might affect confidence in the trend-analysis 

results and the capability to compare results among sites, 

factors that contribute to greater uncertainty in results are 

acknowledged and discussed. 

Description of Study Area

The study area consists of the Boulder River watershed 

upstream from Boulder River below Little Galena Gulch near 

Boulder, Mont (site 10, fig. 1, table 1) and the Tenmile Creek 

watershed upstream from Tenmile Creek near Rimini (site 13, 

fig. 1, table 1). Boulder River and Tenmile Creek originate in 

the Boulder Mountains (not shown on fig. 1) in southwestern 

Montana. The Boulder River flows generally southeast about 

75 miles (mi) from the headwaters to the confluence with the 

Jefferson River near Cardwell (fig. 1). Tenmile Creek flows 

generally northeast about 30 mi from the headwaters to the 

confluence with Prickly Pear Creek (not shown on fig. 1). 

Hydrographic and Hydrologic Characteristics

In this section of the report, the hydrography (stream 

lengths and drainage areas) and hydrology (mean annual 

streamflow) of the study area are described to facilitate 

understanding fluvial transport characteristics for trace elements within the study area. Hydrographic characteristics 

were determined by geographic information system analysis 

of the USGS National Hydrography Dataset (U.S. Geological 

Survey, 2014a). 

For the Boulder River watershed, none of the study 

sampling sites have associated streamflow-gaging stations. 

Mean annual streamflows of the sampling sites were estimated by synthesizing daily mean streamflows for water years 

1997–2013 based on analyses of at-site streamflows at times 

of sampling (measured by using methods described in Rantz 

and others, 1982) in conjunction with daily mean streamflows 

for USGS streamflow gaging station 06033000 (Boulder River 

near Boulder, Mont.; U.S. Geological Survey, 2014b), which 

is located outside of the study area (and not shown on fig. 1) 
Introduction 3

CONTINENTAL DIVIDE

46°30'

46°15'

112°25' 112°20' 112°15'

112°10'

5 8

9

10

1

1

7

6

2

3

4

13

12

11

Boulder

12

15

JEFFERSON

COUNTY

LEWIS AND CLARK

COUNTY

POWELL

COUNTY

Boulder River

Bison

Bullion

Mine

tributary

Tenmile

Tenmile Cr

Tenmile

Creek

Creek

Cr

Minnehaha

Cr

Boulder River

Boulder

Little Boulder R

River

High

Jack Cr

Basin Creek

Ore

Creek

Jefferson R

Cataract Creek

Uncle Sam

Gulch

Cardwell

Helena

Rimini

Boulder Basin

Site 13

Site 10

Site 12

Site 11

Site 1

Site 5

Site 4

Site 3 Site 7

Site 9

Site 8

Basin Cr

Study area

BULLION

MINE

CRYSTAL

MINE

RED WATER MINE

ARMSTRONG MINE

UPPER VALLEY FORGE

MINE

BEATRICE MINE

JUSTICE MINE

SUSIE MINE

LEE MOUNTAIN MINE

TENMILE MINE

BUNKER HILL

MINE

LITTLE LILLIE MINE

MORNING GLORY MINE

RED MOUNTAIN 

MINE

LITTLE SAMPSON MINE

COMET MINE

Figure 1. 

0 2 4 MILES

0 2 4 KILOMETERS

Base from U.S. Census Bureau TIGER, 1990, 1:100,000; Montana State Library, 2003, 1:24,000 

Montana Department of Transportation, 2003,1:24,000 

Lambert Conformal Conic projection 

Standard parallels 45°00’and 49°00’; Central meridian 109°30’ 

North American Datum 1983 (NAD 83)

EXPLANATION

Watershed boundary (table 1)—Sites 2 

and 6 are adit sites with minor surface 

drainage areas (not shown on figure)

Sampling site location and identifier (table 1)

Luttrell Repository

Abandoned mine location

Notable abandoned mine location

Major

Sampling site

MONTANA

Helena

Study area

Rocky Mountains

R

o

c

k

y

M o u n t a i n s

R

o

c

k

y

M o u n t a i n s

Figure 1. Location of selected sites in the Boulder River and Tenmile Creek watersheds, Montana.
Table 1. Information for selected sampling sites in the Boulder River and Tenmile Creek watersheds, Montana. [Water year is the 12-month period from October 1 through September 30 and is designated by the year in which it ends. NA, not applicable] Site number (fig. 1) Site identification Site name Abbreviated site name Site group Drainage area, square miles Abandoned mine density, mines per square mile Period of wa

quality dat

collection du

water yea

1997–2013 

1 06031450 Boulder River above Kleinsmith Gulch, near Basin, Mont. Boulder River above Kleinsmith Gulch Stream (Boulder River watershed) 217.7 0.3 1997–2003, 2012–13 2 462120112173701 Bullion Mine Adit near Basin, Mont. Bullion Mine adit Adit (Boulder River watershed) NA NA 1999–2013 3 462153112181701 Bullion Mine tributary at mouth, near Basin, Mont. Bullion Mine tributary at mouth Stream (Boulder River watershed) 3.6 2.2 1997–2013 4 462047112201901 Jack Creek at mouth, near Basin, Mont. Jack Creek at mouth Stream (Boulder River watershed) 8.5 1.9 2000–13 5 06031600 Basin Creek at Basin, Mont. Basin Creek at Basin Stream (Boulder River watershed) 41.6 1.5 1997–2013 6 462053112153601 Crystal Mine Adit near Basin, Mont. Crystal Mine adit Adit (Boulder River watershed) NA NA 2003–13 7 461905112144201 Cataract Creek ab Uncle Sam Gulch near Basin, Mont. Cataract Creek above Uncle Sam Gulch Stream (Boulder River watershed) 23.0 2.3 1997–2003, 2005–07, 2011–13 

8 06031960 Cataract Creek at Basin, Mont. Cataract Creek at Basin Stream (Boulder River watershed) 33.5 2.7 1997–2013 9 06032300 High Ore Creek near Basin, Mont. High Ore Creek near Basin Stream (Boulder River watershed) 8.8 1.5 1997–2002, 2011–13 

10 06032400 Boulder River below Little Galena Gulch near Boulder, Mont. Boulder River below Little Galena Gulch Stream (Boulder River watershed) 322.8 0.8 1997–2013 

11 462853112144101 Tenmile Creek above City Diversion, near Rimini, Mont. Tenmile Creek above City Diversion Stream (Tenmile Creek watershed) 15.2 3.0 1997–2013 

12 463023112153701 Minnehaha Creek above City 

Diversion near Rimini, Mont.

Minnehaha Creek near 

Rimini

Stream (Tenmile 

Creek watershed)

5.4 1.3 1997–2013 

13 06062500 Tenmile Creek near Rimini, 

Mont.

Tenmile Creek near 

Rimini

Stream (Tenmile 

Creek watershed)

33.0 2.1 2005–13 
Introduction 5

about 6.5 miles downstream from Boulder River below Little 

Galena Gulch (site 10). Estimated daily mean streamflows 

were synthesized by using the MOVE 1 procedure (Hirsch, 

1982) in the USGS Streamflow Record Extension Facilitator 

software described by Granato (2009). For the Tenmile 

Creek watershed, Tenmile Creek near Rimini (site 13, fig. 1, 

table 1) has an associated streamflow-gaging station; thus, 

mean annual streamflow was determined from the recorded 

data. However, for the other sites in the Tenmile Creek 

watershed (Tenmile Creek above City Diversion [site 11, 

fig. 1, table 1] and Minnehaha Creek near Rimini [site 12], 

fig. 1, table 1), at-site streamflows at times of sampling were 

not sufficiently correlated with daily mean streamflows of 

nearby streamflow-gaging stations to allow synthesis of daily 

mean streamflows; thus, estimated mean annual streamflows 

are not reported for sites 11 and 12.

Boulder River Watershed

To facilitate discussion of the hydrography of the study 

area in the Boulder River watershed, a simplified hydrographic 

flow diagram is presented in figure 2. Upstream from Boulder 

River above Kleinsmith Gulch (site 1, fig. 1, table 1), the 

geology of the Boulder River watershed largely is unmineralized with little historic mining, as evidenced by a low density 

of abandoned mines for site 1 (0.3 mines per square mile 

(mi2

); table 1). The drainage area of site 1 is 217.7 mi2, which 

accounts for about 67 percent of the drainage area of Boulder 

River below Little Galena Gulch (site 10, fig. 1, table 1) at the 

downstream end of the study area in the Boulder River watershed. The estimated mean annual streamflow for site 1 is about 

23 cubic feet per second (ft3/s), which accounts for about 

61 percent of the estimated mean annual streamflow for 

site 10 (about 38 ft3/s). 

From site 1, the Boulder River flows about 1 mi to the 

confluence with Basin Creek. Basin Creek at Basin (site 5, 

fig. 1, table 1), which is about 1 mi upstream from the 

confluence with the Boulder River, has a drainage area of 

41.6 mi2 (about 13 percent of the drainage area of site 10) and 

an estimated mean annual streamflow of about 6.4 ft3/s (about 

17 percent of the mean annual streamflow of site 10). Jack 

Creek enters Basin Creek about 7.5 mi downstream from the 

Basin Creek headwaters. Jack Creek at mouth (site 4, fig. 1, 

table 1), which is about 0.1 mi upstream from the confluence 

Figure 2. Simplified hydrographic flow diagram for the study area in the Boulder River watershed, Montana.

 7.5 miles

7.5 miles

2 miles

2 miles

About 8.5 miles

 3.5 miles

 6.5 miles

21 miles

2.5 miles

About 2.5 miles

2.5 miles

7

4 2

3

6

1

5

8

9

10

Boulder River 

headwaters

Basin Creek

headwaters

Jack Creek

headwaters

Bullion Mine

tributary

headwaters

Confluence of 

Jack Creek and 

Bullion Mine tributary

Confluence of 

Basin Creek and 

Jack Creek

Cataract Creek

headwaters

High Ore Creek

headwaters

Confluence of 

Boulder River

and Basin Creek

Confluence of

Boulder River

and Cataract Creek

Confluence of

Boulder River

and High Ore Creek

Confluence of 

Cataract Creek and 

Uncle Sam Gulch

Uncle Sam Gulch

headwaters

BULLION 

MINE

CRYSTAL

MINE

COMET MINE

MORNING GLORY MINE

EXPLANATION

Hydrographic flow line

Sampling site location and identifier (table 1)

Hydrographic node—Important hydrographic feature, such 

as the confluence of two streams. Notation on flow line 

indicates approximate distance between nodes

Notable abandoned mine location

1
6 Water-Quality Trends for Selected Sites in the Boulder River and Tenmile Creek Watersheds, Montana

with Basin Creek, has a drainage area of about 8.5 mi2

 and an 

estimated mean annual streamflow of about 2.1 ft3/s. Bullion 

Mine tributary enters Jack Creek about 2.0 mi downstream 

from the Jack Creek headwaters. Bullion Mine tributary 

at mouth (site 3, fig. 1, table 1), which is about 20 feet (ft) 

upstream from the confluence with Jack Creek, has a drainage 

area of about 3.6 mi2 and an estimated mean annual streamflow of about 0.26 ft3

/s. Bullion Mine adit (site 2, fig. 1, 

table 1) is located about 1.6 mi upstream from the mouth of 

Bullion Mine tributary.

From the mouth of Basin Creek, the Boulder River flows 

about 1.0 mi to the confluence with Cataract Creek. Cataract 

Creek at Basin (site 8, fig. 1, table 1), which is about 250 ft 

upstream from the confluence with the Boulder River, has a 

drainage area of 33.5 mi2 (about 10 percent of the drainage 

area of site 10) and an estimated mean annual streamflow of 

about 5.1 ft3/s (about 13 percent of the mean annual streamflow of site 10). Cataract Creek above Uncle Sam Gulch 

(site 7, fig. 1, table 1), which is located about 8.5 mi downstream from the Cataract Creek headwaters and about 50 ft 

upstream from Uncle Sam Gulch, has a drainage area of 

23.0 mi2 and an estimated mean annual streamflow of 4.5 ft3/s. 

Uncle Sam Gulch flows about 2.5 mi from the headwaters to 

the confluence with Cataract Creek. Crystal Mine adit (site 

6, fig. 1, table 1) is located at the headwaters of Uncle Sam 

Gulch. Cataract Creek at Basin (site 8, fig. 1, table 1) is about 

3.5 mi downstream from Uncle Sam Gulch.

From the mouth of Cataract Creek, the Boulder River 

flows about 2.5 mi to the confluence with High Ore Creek. 

High Ore Creek near Basin (site 9, fig. 1, table 1), which is 

about 0.1 mi upstream from the confluence with the Boulder 

River, has a drainage area of 8.8 mi2 (about 3 percent of the 

drainage area of site 10) and an estimated mean annual streamflow of about 0.74 ft3

/s (about 2 percent of the mean annual 

streamflow of site 10). From the mouth of High Ore Creek, the 

Boulder River flows about 2 mi to Boulder River below Little 

Galena Gulch (site 10, fig. 1, table 1). 

Tenmile Creek Watershed

To facilitate discussion of the hydrography of the study 

area in the Tenmile Creek watershed, a simplified hydrographic flow diagram is presented in figure 3. Tenmile Creek 

flows about 7 mi from the headwaters to Tenmile Creek above 

City Diversion (site 11, fig. 1, table 1). Site 11 has a drainage 

area of 15.2 mi2

,

which accounts for about 46 percent of the 

drainage area of Tenmile Creek near Rimini (33.0 mi2) at the 

downstream end of the study area in the Tenmile Creek watershed. In the watershed of site 11, there is transbasin diversion 

of tributary streamflows to provide municipal water supply to 

the city of Helena. The principle municipal supply diversion 

is directly from Tenmile Creek about 200 ft downstream from 

site 11.

From site 11, Tenmile Creek flows about 2 mi to the confluence with Minnehaha Creek. Minnehaha Creek near Rimini 

(site 12, fig. 1, table 1), which is about 150 ft upstream from 

the confluence with Tenmile Creek, has a drainage area of 

5.4 mi2 (about 16 percent of the drainage area of site 13). 

From the confluence with Minnehaha Creek, Tenmile Creek 

flows about 1.5 mi to Tenmile Creek near Rimini (site 13, 

fig. 1, table 1). In the intervening watershed between sites 11 

and 13, there are multiple transbasin diversions of tributary 

streamflows (including Minnehaha Creek) to provide municipal water supply to the city of Helena. 

Physiographic, Climatic, and Geologic 

Characteristics

The study area lies within the Middle Rockies Ecoregion (not shown on fig. 1; Woods and others, 2002), which 

is characterized by forested mountains and intermontane 

valleys. Altitudes in the Boulder River watershed upstream 

from Boulder River below Little Galena Gulch (site 10, fig. 1, 

table 1) range from about 5,480 to 8,750 ft above the National 

Geodetic Vertical Datum of 1988 (NGVD 88). Altitudes in 

the Tenmile Creek watershed upstream from Tenmile Creek 

near Rimini (site 13, fig. 1, table 1) range from about 4,860 

to 8,230 ft above NGVD 88. In the study area, vegetation is 

predominantly subalpine fir, Douglas fir, and ponderosa pine 

conifer forests in the high-altitude mountainous areas; mixed 

conifers, shrubs, and grasses in the mid-altitude foothills; and 

grasses in the low-altitude valley areas (Woods and others, 

2002). In the mountainous areas, the predominant land uses 

are recreation, timber harvest, and mining; and in the valleys, the predominant land uses are livestock grazing and hay 

production.

Areally-weighted mean annual precipitation (1981–2010 

30-year normal; PRISM Climate Group, 2014) in the study 

area is about 20 inches. Based on climatic data for Boulder, 

Mont., at an altitude of about 4,900 ft (Western Regional Climate Center, 2014), mean annual precipitation for low-altitude 

parts of the study area is about 11 inches, with about 50 percent of mean annual precipitation falling primarily as rain during May–July. December is the coldest month (mean monthly 

temperature of 4.6 degrees Celsius), and July is the warmest 

month (mean monthly temperature of 18.4 degrees Celsius). 

Based on climatic data for the Basin Creek SNOTEL station at 

an altitude of 7,180 ft (Natural Resources Conservation 

Service, 2014), mean annual precipitation for high-altitude 

parts of the study area is about 25 inches, with about 

35 percent of mean annual precipitation falling primarily as 

rain during May–July. Fall and winter precipitation falling 

primarily as snow accounts for a larger part of annual precipitation in high-altitude areas than in low-altitude areas. 

Most of the study area is underlain by the Cretaceous 

granitic rocks of the Boulder Batholith bedrock unit (Church 

and others, 2004). Other bedrock units in the study area 

(particularly in parts of the Tenmile Creek watershed) include 

Cretaceous metamorphosed sandstone and siltstone, Cretaceous andesitic volcanic rocks of the Elkhorn Mountains 

Volcanics, and Tertiary volcanic rocks composed of rhyolite 
Introduction 7

and tuff (Cleasby and Nimick, 2002). The ore bodies in the 

study area that have been the target of extensive mining 

activities are variable in composition and resulted from late 

Cretaceous and late Tertiary periods of mineralization (Church 

and others, 2004; Knopf, 1913). The geology of the study area 

is described in detail by Nimick and others (2004), in Cleasby 

and Nimick (2002), and in numerous citations in those reports.

Overview of Mining and Remediation Activities

In the Boulder River and Tenmile Creek watersheds in 

southwestern Montana, there was intensive mining during a 

40-year period after the discovery of gold in the early 1860s. 

Most of the mining involved small operations, which generally accessed ore deposits less than 50 ft wide (U.S. Geological Survey, 2004). Although these operations generally were 

small, the cumulative environmental effect was large because 

of the numerous sites where mine wastes and mill tailings 

were discarded with little regard for environmental effects. 

Densities of abandoned mines (table 1) in the study samplingsite watersheds provide general relative information on extent 

of mining activities among the watersheds. However, the 

abandoned mine densities do not always provide an accurate 

indication of mining effects on stream systems between the 

watersheds. For an individual mine, mining effects are related 

to the size of the mine operation, the amount of waste generated, and the handling of the waste; these factors are highly 

variable among individual mines. 

In addition to the numerous small mining operations in 

the study area, there were several notable large mines that 

remained in operation longer, generated more waste than most 

small operations, or both. Notable abandoned mines in the 

7 miles

3 miles

2 miles

1.5 miles

Confluence of 

Tenmile Creek and 

Minnehaha Creek

City diversion

Tenmile Creek

headwaters

Minnehaha Creek

headwaters

13

12

11

EXPLANATION

Hydrographic flow line

Sampling site location and identifier (table 1)

Hydrographic node—Important hydrographic feature, such 

as the confluence of two streams. Notation on flow line 

indicates approximate distance between nodes

Notable abandoned mine location

11

Transbasin

diversion

Transbasin

diversion

Transbasin 

diversion

from tributary

RED WATER MINE

LITTLE LILLIE MINE

RED MOUNTAIN MINE

TENMILE MINE

LITTLE SAMPSON MINE

BUNKER HILL MINE

UPPER VALLEY FORGE MINE

SUSIE MINE

LEE MOUNTAIN MINE

BEATRICE MINE

ARMSTRONG MINE

JUSTICE MINE

Figure 3. Simplified hydrographic flow diagram for the study area in the Tenmile Creek watershed, 

Montana.
8 Water-Quality Trends for Selected Sites in the Boulder River and Tenmile Creek Watersheds, Montana

Boulder River watershed include the Bullion, Crystal, Morning Glory, and Comet Mines (fig. 1). The Bullion Mine in the 

Basin Creek watershed periodically operated during 1897–

1984, was most productive during 1901–48 (U.S. Environmental Protection Agency, 2014a), and produced about 30,000 

tons of ore during 1905–55 (CH2MHILL, 2013a). The Crystal 

Mine in the Cataract Creek watershed periodically operated 

during 1885–1983 and produced about 61,000 tons of ore 

during the operation period (CH2MHILL, 2013b). The Morning Glory Mine in the Cataract Creek watershed operated 

from the late 1890s through the 1960s and produced about 

20,000 tons of ore during 1920–57 (Montana Department 

of Environmental Quality, 2009). The Morning Glory Mine 

produced less ore than the other notable mines in the Boulder 

River watershed, but was considered notable because of the 

close proximity to the Cataract Creek channel. The Comet 

Mine in the High Ore Creek watershed periodically operated 

during 1880–1941 and produced about 496,000 tons of ore 

after 1902 (Montana State University, 2014). In the study area, 

stream channels downstream from the Bullion, Crystal, and 

Comet Mines were among the most contaminated by mining 

wastes (Finger and others, 2004). Further, based on analysis of 

data collected during 2001–05, the Bullion and Crystal Mine 

adits were the primary sources of metals in the Basin Creek 

and Cataract Creek watersheds, respectively, and lead isotopic data indicated that the Crystal Mine was the major source 

of some metals in streambed sediment in the Boulder River 

(Unruh and others, 2009). 

In the Tenmile Creek watershed, individual mines generally had shorter longevity and smaller total ore production 

than the Bullion, Crystal, and Comet Mines in the Boulder 

River watershed. Active mining in the Tenmile Creek watershed was from the 1870s through the 1930s, with sporadic 

mining through 1953 (U.S. Environmental Protection Agency, 

2008). Notable abandoned mines in the Tenmile Creek watershed include the Armstrong, Beatrice, Bunker Hill, Justice, 

Lee Mountain, Little Lillie, Little Sampson, Red Mountain, 

Red Water Mines, Susie, Tenmile, and Upper Valley Forge 

Mines (fig. 1). Several mines have been noted as major 

contributors to trace-element loads to Tenmile Creek, including the Lee Mountain, Little Sampson, Red Water, and Susie 

Mines (fig. 1; U.S. Environmental Protection Agency, 2008). 

The Armstrong, Beatrice, and Justice Mines (fig. 1) operated 

within the Minnehaha Creek watershed.

Unremediated surface contamination from historic mining can potentially affect many aspects of a watershed for 

many centuries (Gray, 1997; Leblanc and others, 2000). In the 

Boulder River watershed, early remediation focused on the 

Comet Mine in the High Ore Creek watershed. In the 1980s, 

a diversion channel was constructed to route High Ore Creek 

around the tailings deposited in the valley bottom near the 

Comet Mine (Church and others, 2004), and then in 1997–99, 

mill tailings and tailings flood-plain deposits were removed 

by the Montana Department of Environmental Quality and the 

Bureau of Land Management (Finger and others, 2004). The 

Basin Creek, Cataract Creek, and Tenmile Creek watersheds 

were designated as Superfund sites on the National Priorities List in 1999. During 2001–02, remediation activities by 

the USFS and U.S. Environmental Protection Agency (EPA) 

began in the Basin Creek and Cataract Creek watersheds 

and focused primarily on wastes associated with the Bullion 

and Crystal Mines. U.S. Environmental Protection Agency 

(2014a) reported that during 2001–02, about 27,000 cubic 

yards of waste associated with the Bullion Mine operations 

in the Basin Creek watershed were removed, uncontaminated 

limed soils were installed, and vegetation was re-established. 

Unruh and others (2009) reported that 40,900 cubic yards of 

mine and mill wastes were removed during 2000–02. After 

2002, various additional remediation activities were done 

in the Basin Creek watershed, including waste removal and 

revegetation near some smaller mines in headwaters areas of 

Jack Creek (Browne, 2009). During 2000-02 in the Cataract 

Creek watershed, some wastes associated with the Crystal 

Mine operations were removed and a surface mine trench was 

lined and backfilled (U.S. Environmental Protection Agency, 

2014b). After 2002, various additional remediation activities 

were done in the Cataract Creek watershed, including waste 

removal and revegetation near some smaller mines and also 

at the Morning Glory Mine near the confluence of Uncle Sam 

Gulch and Cataract Creek (Robert Wintergerst, U.S. Forest 

Service, written commun., September 2014).

In the Tenmile Creek watershed, groundwater, streams, 

and soils have been affected by historic mining activities. 

Primary constituents of concern are arsenic, cadmium, copper, lead, and zinc (U.S. Environmental Protection Agency, 

2014c). The USFS has the lead role in remediation activities 

of Federal lands in the Tenmile Creek watershed. Remediation 

activities where there is a mix of Federal and private land have 

been done cooperatively by the EPA, USFS, and the State of 

Montana. Remediation in the Tenmile Creek watershed began 

in 1999, when the EPA removed waste from the Bunker Hill, 

Tenmile, Red Mountain, and Susie Mines. During 2000–01, 

additional waste removal was done at the Bunker Hill, Tenmile, Red Mountain, Susie, Beatrice, Justice, and Upper Valley 

Forge Mines (U.S. Environmental Protection Agency, 2008). 

Other high-priority mine waste was removed in the upper 

watershed including at the Lee Mountain Mine. Contaminated 

soils have been removed from some residential properties near 

Rimini, Mont., and road base was applied to Rimini Road to 

eliminate contaminated dust (U.S. Environmental Protection 

Agency, 2014d). During 2012–13, about 20,000 cubic yards of 

mine waste was excavated from Lee Mountain and Little Lillie 

Mine areas. Mine wastes have been transported to the Luttrell Repository (fig. 1). Excavated areas were backfilled with 

uncontaminated material and vegetation was re-established. 

Total volume of material excavated from the upper Tenmile 

Creek watershed was about 354,000 cubic yards (U.S. Environmental Protection Agency, 2014d). 
Data Collection and Analytical Methods 9

Data Collection and Analytical 

Methods

Water-quality sample collection (fig. 4) by the USGS 

began in water year 1997 at seven sites in the Boulder River 

watershed (sites 1, 3, 5, 7, 8, 9, and 10; fig. 1, table 1) and 

two sites in the Tenmile Creek watershed site (sites 11 and 12, 

fig. 1, table 1). During water years 1999–2000, the monitoring program was expanded by the addition of two sites in the 

Boulder River watershed (sites 2 and 4, fig. 1, table 1). The 

monitoring program also was expanded during 2003–05 by the 

addition of one site in the Boulder River watershed (site 6, 

fig. 1, table 1) and one site in the Tenmile Creek watershed 

(site 13, fig. 1, table 1). Thus, there have been 13 sites in the 

monitoring program with variable periods of record (fig. 4, 

table 1). Sites 1, 7, and 9 (fig. 1, table 1) have periods (ranging 

from 1 to 8 years) when data collection was suspended.

The within-year frequency of data collection was somewhat inconsistent for the monitoring program, with the number of samples collected at an individual site ranging from 

1 to 12 samples per year. However, all sites have median 

within-year sampling frequencies of 4 samples per year during years of data collection. Interannual variability in the 

operation of the monitoring program resulted from variability 

in available funding and program objectives. 

During the study period, water samples for the 11 stream 

sites (table 1) were collected from vertical transits throughout 

the entire stream depth at multiple locations across the stream 

by using standard USGS methods (U.S. Geological Survey, 

variously dated). Those methods provide a width-and-depth 

integrated composite that is intended to be representative of 

the entire flow passing through the cross section of a stream. 

Isokinetic samplers were used when water depth was sufficient 

and grab sampling was used when water depth was insufficient. For the two adit sites (table 1), grab sampling was used 

for all samples because of insufficient water depth.

Specific conductance was measured onsite in subsamples 

from the composite water samples. Subsamples of the composite water samples also were analyzed at the USGS National 

Water Quality Laboratory (NWQL) in Denver, Colo. for 

filtered (0.45-micrometer pore size filtration completed in the 

field) and unfiltered-recoverable concentrations of the trace 

elements included in the trend analysis (table 2). The methods 

of analysis used by NWQL for filtered and unfiltered-recoverable trace elements are described by Fishman (1993), Garbarino and Struzeski (1998), Garbarino and others (2006), and 

Hoffman and others (1996). Water samples also were analyzed 

Water year 

(October–September)

1995 2000 2005 2010 2013 Adit sites in the Boulder River watershed Stream sites in the Tenmile Creek watershed Stream sites in the Boulder River watershed

1

10

11

12

13

3

2

6

4

5

7

8

9

Site number (fig.1, table 1)

Sample collection

Winter sample

Spring sample

Summer sample

Fall sample

[Water year is defined as the 

12-month period from October 1 

through September 30 and is 

designated by the year in 

which it ends]

EXPLANATION

Figure 4. Temporal characteristics of water-quality sample collection for sites in the Boulder River and Tenmile Creek watersheds, 

Montana.
10 Water-Quality Trends for Selected Sites in the Boulder River and Tenmile Creek Watersheds, Montana

for suspended-sediment concentrations by the U.S. Geological Survey laboratory in Helena, Mont., using procedures 

described by Dodge and Lambing (2006).

Consistent field-collection and laboratory-analytical 

methods are important in trend analysis to be confident that 

observed trends represent real environmental changes and 

not methodology changes. Therefore, any changes made in 

field-collection and laboratory-analytical methods during the 

study period could be an issue of concern. Consistent field and 

laboratory methods were generally applied during the study 

period. However, a change was made in about water year 2000 

by NWQL in the analytical method for most metallic trace 

elements from graphite furnace atomic absorption spectrophotometry (Fishman, 1993) to inductively coupled plasma-mass 

spectrometry (Garbarino and Struzeski, 1998; Garbarino and 

others, 2006). Potential effects of this issue on trend analysis 

were investigated by Sando and others (2014) and determined 

to be minor. 

Quality Assurance

Analytical results for individual environmental samples 

were carefully reviewed based on (1) comparisons with associated quality-assurance sample results, (2) comparisons with 

results for previously collected samples at the site, 

(3) relations between filtered and unfiltered-recoverable 

concentrations, (4) relations between unfiltered-recoverable 

concentrations and suspended-sediment concentrations, and 

(5) relations between concentrations and streamflow conditions. When one or more of the review criteria indicated 

problematic results for a given trace-element constituent, 

laboratory re-analysis was performed. If the re-analysis did 

not resolve the problematic results, the analytical results were 

excluded from the trend analysis. For the study period, exclusion of analytical results based on quality-assurance reviews 

affected a small percentage of the study datasets (less than 

1 percent of all trace-element analyses). Excluded sample 

results generally were sporadic and limited to short periods, 

and are considered to have negligible effects on trend analysis.

Analytical results for field quality-assurance samples 

(including field blank and replicate samples) that were collected during water years 1997–2013 were compiled and statistically summarized (table 1–1 in appendix 1 at the back of 

this report). The data in appendix 1 provide information on the 

consistency and environmental representativeness of data collection. Analysis of analytical results for field blank samples 

provides information on potential effects of contamination 

during the sampling process on trend-analysis results. For 

field blank samples, the frequency of detection at concentrations greater than the laboratory reporting level at the time of 

analysis was less than about 10 percent for all trace elements 

(except copper and zinc). Filtered and unfiltered-recoverable 

copper had detection frequencies in blank samples of 27 and 

10 percent, respectively. Filtered and unfiltered-recoverable 

zinc had detection frequencies in blank samples of 43 and 

20 percent, respectively. The high frequency of detection in 

blank samples for these constituents might indicate the difficulties in representative sampling in the monitoring program, 

where some sites have extremely high concentrations and 

there is large potential for cross-contamination of sampling 

equipment between sites. However, for filtered and unfilteredrecoverable copper, the maximum detected concentrations 

in blank samples did not exceed the minimum detected 

concentrations in environmental samples of any of the sites 

except site 1. For filtered and unfiltered-recoverable zinc, the 

maximum detected concentrations in blank samples did not 

exceed the minimum detected concentrations in environmental 

samples of any of the sites except site 1 (fig. 1, table 1). For 

filtered and unfiltered-recoverable zinc, the maximum detected 

concentrations in blank samples exceeded the median detected 

concentrations in environmental samples for site 1 (fig. 1, 

table 1); as a result, reported results for zinc for site 1 should 

be used with caution and conclusions from these trend results 

are qualified as having larger uncertainty than other site and 

constituent combinations.

Table 2. Property and constituents included in the trend analysis 

and information relating to laboratory reporting levels.

[Water year is the 12-month period from October 1 through September 30 and 

is designated by the year in which it ends. NWQL, U.S. Geological Survey 

National Water Quality Laboratory; μS/cm at 25 °C, microsiemens per centimeter at 25 degrees Celsius; μg/L, micrograms per liter; mg/L, milligrams per 

liter]

Property 

or 

constituent

Units of 

measurement

Number of 

NWQL 

laboratory 

reporting

levels during 

water years 

1997–2010

Range in 

NWQL 

laboratory 

reporting 

levels

Specific conductance μS/cm at 

25 °C

NA NA

Cadmium, filtered μg/L 4 0.016–0.14

Cadmium, 

unfilteredrecoverable

μg/L 7 0.014–0.11

Copper, filtered μg/L 6 0.2–1

Copper, 

unfilteredrecoverable

μg/L 5 0.6–1.2

Lead, filtered μg/L 4 0.015–0.12

Lead, unfilteredrecoverableμg/L 4 0.036–1

Zinc, filtered μg/L 4 0.6–1.8

Zinc, unfilteredrecoverableμg/L 4 1–3

Arsenic, filtered μg/L 8 0.022–0.26

Arsenic, unfilteredrecoverableμg/L 8 0.09–2.6

Suspended sediment mg/L NA NA
Overview of Water-Quality Characteristics for Selected Sites in the Boulder River and Tenmile Creek Watersheds 11

Relative percent differences (RPDs) for field replicate 

samples typically were within plus or minus 15 percent 

(table 1–1), generally indicating acceptable precision of analytical results. However, for suspended sediment, 10th percentile and 90th percentile RPDs indicated strong deviation from 

zero. Several factors probably contribute to lower precision for 

suspended-sediment analyses. The study sites generally have 

low suspended-sediment concentrations, with median concentrations typically less than 4 milligrams per liter (mg/L). The 

reporting limit for suspended-sediment analysis is 1 mg/L; 

and at concentrations less than 4 mg/L, the resolution of 

suspended-sediment analyses is poor, because concentrations 

are reported to the nearest whole number (Dodge and Lambing, 2006). Thus, for low concentration ranges, small absolute 

differences in concentrations between primary and replicate 

samples can result in large RPDs. Further, some of the study 

sites are located near areas of mine drainage and are affected 

by dynamic processes as the mine drainage equilibrates with 

surface waters. In some cases, colloidal material is produced 

and is incorporated in the suspended-sediment analysis. 

Dynamic instream processes near areas of mine drainage also 

might contribute to large ranges in precision for suspendedsediment analyses.

Based on analysis of quality-assurance data, the quality of the study datasets were determined to be suitable for 

trend analysis. However, based on field blank concentrations 

in excess of median concentrations for site 1, reported results 

for zinc for site 1 should be used with caution and conclusions 

from these trend results are qualified as having larger uncertainty than other site and constituent combinations. 

Overview of Water-Quality 

Characteristics for Selected Sites in 

the Boulder River and Tenmile Creek 

Watersheds

In parts of the study area that generally are free from 

human disturbance, water quality of streams is governed 

by runoff of dilute atmospheric water deposited on generally steeply sloped watersheds with rock and soil materials 

derived from erosion resistant granitic rocks. Concentrations 

of dissolved solids typically are low and pH values typically 

are near to slightly above neutral. In general, mining activities in the Boulder River and Tenmile Creek watersheds can 

affect water-quality characteristics by lowering pH, increasing 

specific conductance, and contributing filtered and unfilteredrecoverable concentrations of trace elements (Nimick and 

others, 2004; Cleasby and Nimick, 2002). 

Statistically summarizing water-quality characteristics of 

the sites is useful for generally describing water quality of the 

study sites and for providing comparative information relevant 

for interpretation of trend results. Statistical summaries of 

water-quality data for sites in the Boulder River and Tenmile 

Creek watersheds are presented in table 1–2 in appendix 1 

(at the back of this report). For trace elements, in addition 

to statistical summaries of raw concentrations, ratios of 

median filtered to median unfiltered-recoverable concentrations, expressed as a percentage, also are presented in 

table 1–2 to provide general information on the predominant 

phase (that is, dissolved or particulate) of transport. Data are 

summarized for water years 2009–13; this period was selected 

as the summary period because all sites have available data, a 

somewhat large range in streamflow conditions is represented, 

and recent water-quality conditions are represented. Waterquality characteristics of the study sites are illustrated by using 

boxplots of the trend-analysis constituents presented in 

figure 5 (for the adit sites in the Boulder River watershed) and 

figure 6 (for the stream sites in the Boulder River and Tenmile 

Creek watersheds). Distributions of constituents for adit sites 

and stream sites are separated into two figures because of difficulties in appropriately displaying the distributions given the 

large differences in concentration ranges between the adit sites 

and stream sites. 

In figure 6 (showing data for the stream sites), aquatic 

life standards for all metallic contaminant trace elements 

(cadmium, copper, lead, and zinc; hereinafter referred to as 

metallic contaminants) are plotted in relation to the statistical 

distributions of concentrations. However, in figure 5 (showing data for the adit sites), only the aquatic life standard for 

lead is plotted in relation to the statistical distributions of lead 

concentrations; for cadmium, copper and zinc, the aquatic 

life standards are less than the plotted scales. In figures 5 and 

6, the aquatic life standards for metallic contaminants were 

calculated based on median hardness for water years 2009–13. 

In figures 5 and 6, the human health standard for arsenic is 

plotted in relation to the statistical distributions of arsenic 

concentrations.

Distributions of filtered and unfiltered-recoverable 

concentrations of trace elements are shown in figures 5 and 6 

to provide general information on the predominant phase of 

transport. The predominant phase of transport varied between 

sites; however, cadmium, copper, and zinc generally had similar filtered and unfiltered phases compared to lead and arsenic, 

where the unfiltered phase was commonly the dominant phase 

of transport.

In this section of the report, water-quality characteristics 

are briefly discussed by site; first for the adit sites in the Boulder River watershed, then for the stream sites in the Boulder 

River watershed, and then for the stream sites in the Tenmile 

Creek watershed. Although information concerning relations 

between filtered and unfiltered-recoverable concentrations of 

trace elements is presented in table 1–2 and figures 5 and 6, 

the relations primarily are presented for informational purposes and are not routinely discussed. Emphasis is placed on 

describing spatial differences in water quality among the sites 

and factors that affect those differences. 

In the text discussion on water-quality characteristics of 

the stream sites, property and constituent values for a given 

site are compared with those for the other stream sites. To 
12 Water-Quality Trends for Selected Sites in the Boulder River and Tenmile Creek Watersheds, Montana

2 6

Bullion Mine adit Crystal Mine adit

Site number (fig.1, table 1)

Bullion Mine adit Crystal Mine adit

Site number (fig.1, table 1)

2 6

No data collected. Graph included as a placeholder to assist in comparison

with figure 4.

C. Filtered and unfiltered-recoverable cadmium (micrograms per liter)

E. Filtered and unfiltered-recoverable lead (micrograms per liter)

D. Filtered and unfiltered-recoverable copper (micrograms per liter)

F. Filtered and unfiltered-recoverable zinc (micrograms per liter)

G. Filtered and unfiltered-recoverable arsenic (micrograms per liter)

A. Specific conductance (microsiemens per centimeter at 25 degrees Celsius) B. Suspended sediment (milligrams per liter)

FIGURE 5

100

1,000

10,000

1

10

100

100

10

100

100

1,000

1,000

10,000

100,000

1,000

10,000

100,000

10,000

10

100

1,000

10,000

1

10

100

1,000

Unadjusted (not flow adjusted) constituent or property values, in indicated units of measurement

Unadjusted (not flow adjusted) constituent or property values, in indicated units of measurement

Denotes filtered concentrations for cadmium, copper, lead, zinc, and arsenic

Denotes unfiltered-recoverable concentrations for cadmium, copper, lead, zinc, and arsenic

Aquatic life standards for lead based on median hardness for given site for 

water years 2009–13 (Montana Department of Environmental Quality, 2012a)

 Acute

 Chronic

Human health standard for arsenic (Montana Department of Environmental 

Quality, 2012a)

[Water year is defined as the 12-month period from October 1 through September 30 and is designated by the year in which it ends]

Interquartile

range

EXPLANATION

75th percentile

Median

25th percentile

Data value less than or equal to 

1.5 times the interquartile range 

outside the quartile

Data value greater than 1.5 times 

the interquartile range outside 

the quartile

Figure 5. Statistical distributions of selected constituents for the adit sites in the Boulder River watershed, Montana, based on data 

collected during water years 2009–2013.
Overview of Water-Quality Characteristics for Selected Sites in the Boulder River and Tenmile Creek Watersheds 13

Figure 6. Statistical distributions of selected constituents for the stream sites in the Boulder River and Tenmile Creek watersheds, 

Montana, based on data collected during water years 2009–2013.

Tenmile Creek

Boulder River watershed watershed

Tenmile Creek

Boulder River watershed watershed

1 3 4 5 7 8 9 10 11 12 13

1 3 4 5 7 8 9 10 11 12 13

Site number (fig.1, table 1)

Site number (fig.1, table 1)

Jack Creek at mouth

Basin Creek at Basin

Boulder River above Kleinsmith Gulch

Bullion Mine tributary at mouth

Cataract Creek at Basin

Cataract Creek above Uncle Sam Gulch

High Ore Creek near Basin

Tenmile Creek near Rimini

Tenmile Creek above City Diversion

Boulder River below 

Little Galena Gulch

Minnehaha Creek near Rimini

Jack Creek at mouth

Basin Creek at Basin

Boulder River above Kleinsmith Gulch

Bullion Mine tributary at mouth

Cataract Creek at Basin

Cataract Creek above Uncle Sam Gulch

High Ore Creek near Basin

Tenmile Creek near Rimini

Tenmile Creek above City Diversion

Boulder River below Little Galena Gulch

Minnehaha Creek near Rimini

10

100

1,000

1

10

100

1

10

100

1

10

100

1,000

0.1

1

10

100

1,000

1,000

10,000

0.1

0.1

1

10

100

0.01

0.1

1

10

100

0.01

Unadjusted (not flow adjusted) constituent or property values, in indicated units of measurement

Unadjusted (not flow adjusted) constituent or property values, in indicated units of measurement

FIGURE 6

Interquartile

range

75th percentile

Median

25th percentile

Data value less than or equal to 

1.5 times the interquartile range 

outside the quartile

Data value greater than 1.5 times 

the interquartile range outside 

the quartile

Denotes filtered concentrations for cadmium, copper, lead, zinc, and arsenic

Denotes unfiltered-recoverable concentrations for cadmium, copper, lead, zinc, and arsenic

Aquatic life standards for cadmiun, copper, lead, and zinc based on median hardness for 

given site for water years 2009–13 (Montana Department of Environmental Quality, 2012a)

 Acute (for lead at site 9, equal to 117 micrograms per liter)

 Chronic (for zinc, identical to acute)

Human health standard for arsenic (Montana Department of Environmental Quality, 2012a)

[Water year is defined as the 12-month period from October 1 through September 30 and is designated by the year in which it ends]

EXPLANATION

C. Filtered and unfiltered-recoverable cadmium 

(micrograms per liter)

E. Filtered and unfiltered-recoverable lead 

(micrograms per liter)

D. Filtered and unfiltered-recoverable copper 

(micrograms per liter)

F. Filtered and unfiltered-recoverable zinc 

(micrograms per liter)

G. Filtered and unfiltered-recoverable arsenic (micrograms per liter)

A. Specific conductance 

(microsiemens per centimeter at 25 degrees Celsius)

B. Suspended sediment 

(milligrams per liter)
14 Water-Quality Trends for Selected Sites in the Boulder River and Tenmile Creek Watersheds, Montana

facilitate this discussion, the ranks of median values of properties and constituents among the stream sites are presented 

in table 3. The ranks of medians are ordered from largest to 

smallest. For example, Bullion Mine tributary at mouth 

(site 3, fig. 1, table 1) has the highest median concentration of 

filtered copper (52.8 micrograms per liter [μg/L]; table 1–2) 

of the 11 stream sites in this study; thus, the rank for the 

median concentration of filtered copper for site 3 is 1. Conversely, Boulder River above Kleinsmith Gulch (site 1, fig. 1, 

table 1) has the lowest median concentration of filtered copper 

(1.90 μg/L; table 1–2); thus, the rank for the median concentration of filtered copper for site 1 is 11. For the trace-element 

constituents, lower ranks of median values denote higher concentrations and represent greater effects from mining activities. However, the measurement units for pH are such that 

the reverse condition is true. Mining activities generally tend 

to acidify stream waters resulting in lower pH. Thus, higher 

ranks of median pH values generally represent greater effects 

from mining activities.

For each site, the percent of samples exceeding waterquality standards during water years 2009–13 is presented 

in table 4. For the hardness-based aquatic life standards for 

cadmium, copper, lead, and zinc, the percent exceedances 

presented in table 4 were based on comparison of traceelement concentrations of each individual sample with the 

aquatic life standards that were calculated using the hardness 

for each individual sample. In contrast, the statistical distributions of trace-element concentrations for water years 2009–13 

shown in figures 5 and 6 are plotted in relation to aquatic life 

standards calculated using median hardness for water years 

2009–13. Thus, in some cases, there are generally small 

discrepancies between the frequency of samples exceeding 

standards shown in figures 5 and 6 and the percent exceedances presented in table 4. The percent exceedances presented 

in table 4 and discussed in the text more accurately represent 

regulatory compliance.

Adit Sites in the Boulder River Watershed

The adit sites (sites 2 and 6) have water-quality characteristics that are substantially different from the stream sites. 

Bullion Mine adit (site 2, fig. 1, table 1) is a primary source 

of metallic contaminants in the Basin Creek watershed, and 

Crystal Mine adit (site 6, fig. 1, table 1) is a primary source 

of metallic contaminants in the Cataract Creek watershed 

(Nimick and others, 2004). Basin Creek and Cataract Creeks 

are tributary to the Boulder River (fig. 1). Medians of streamflow at time of sampling (0.01 and 0.05 ft3

/s for sites 2 and 6, 

respectively; table 1–2) are low and represent seepage of mine 

drainage from the adits. Medians of pH (3.0 and 4.7 units for 

sites 2 and 6, respectively) are lower than for any stream site 

and reflect the acidic nature of the mine seepage. Medians of 

specific conductance (1,580 and 695 microsiemens per centimeter at 25 degrees Celsius (μS/cm at 25 °C) for sites 2 and 6, 

respectively; fig. 5, table 1–2) are higher than for any stream 

site and reflect interaction of acidic mine water with rock and 

soil materials. Relative rankings of median concentrations of 

trace elements between the adit sites reflect differences in 

the characteristics of the ore bodies. Site 2 has median concentrations of unfiltered-recoverable lead and arsenic (384 and 

1,530 μg/L, respectively) that are higher than site 6 median 

concentrations (81.3 and 372 μg/L, respectively). Site 6 has 

median concentrations of unfiltered-recoverable cadmium, 

copper, and zinc (521; 7,370; and 41,500 μg/L, respectively) 

that are higher than site 2 median concentrations (314; 5,020; 

and 31,800 μg/L, respectively). For both adit sites, all samples 

collected during water years 2009–13 exceeded all waterquality standards, except for the acute aquatic life standard for 

lead (exceeded in 89 and 28 percent of samples for sites 2 and 

6, respectively; table 4). 

Stream Sites in the Boulder River Watershed

Boulder River above Kleinsmith Gulch (site 1, fig. 1, 

table 1) is upstream from Basin Creek and Cataract Creek. 

The water quality at the site has relatively small effects from 

mining operations, which is evidenced by an abandoned mine 

density of 0.3 mines per mi2 (substantially lower than for any 

other sampling site; table 1). Median streamflow at time of 

sampling (23 ft3/s; table 1–2) and pH (7.6 units) for site 1 are 

higher than for most other stream sites. Median specific conductance (141 μS/cm at 25 o

C; fig. 6, table 1–2) for site 1 also 

is higher than for most other sites, probably because of a larger 

drainage area than for most other sites, with greater opportunity for the stream water to interact with soil and rock materials. Median concentrations of unfiltered-recoverable cadmium 

(0.019 μg/L), copper (1.80 μg/L), lead (0.15 μg/L), and zinc 

(3.20 μg/L) for site 1 are lower than for any other stream site. 

The median concentration of unfiltered-recoverable arsenic 

(3.5 μg/L) for site 1 is lower than for most other stream sites. 

The median suspended sediment (3 mg/L) for site 1 is higher 

than for most other stream sites. For site 1, there were few 

exceedances of water-quality standards for any samples collected during water years 2009–13 (table 4). Water-quality 

standards exceedances include (1) the copper acute and 

chronic aquatic life standards (exceeded in 14 percent of samples) and (2) the lead chronic aquatic life standard (exceeded 

in 29 percent of samples). Water-quality characteristics of site 

1 generally are representative of a background index site with 

small effects from mining operations.

Bullion Mine tributary at mouth (site 3, fig. 1, table 1) is 

about 1 mi downstream from Bullion Mine adit (site 2, fig. 1, 

table 1), which is a primary source of metallic contaminants 

to Basin Creek (Nimick and others, 2004) and strongly affects 

water quality at site 3. Site 3 is about 20 ft upstream from the 

confluence of the Bullion Mine tributary with Jack Creek. 

Median streamflow at time of sampling (0.61 ft3

/s; table 1–2) 

for site 3 is lower than for any other stream site, reflecting the 

small drainage area (3.6 mi2). Median pH (6.8 units) for site 

3 also is lower than for any other stream site. Median specific 

conductance (115 μS/cm at 25 o

C; fig. 6, table 1–2) for site 3 is 

higher than for most other stream sites. Median concentrations 
Table 3. Ranks of median values of properties and constituents among all stream sites in the Boulder River and Tenmile Creek watersheds, Montanaduring water years 2009–13.[Water year is the 12-month period from October 1 through September 30 and is designated by the year in which it ends]

Site name and number 

(fig. 1, table 1)

Rank1 of median value (largest to smallest) among all stream sites for indicated property 

Abandoned mine 

density Streamflow pH Specific conductance Hardness Calcium, filtered Magnesium, filtered 

Boulder River above Kleinsmith Gulch (site 1) 11 2 4 2 2 2 2 

Bullion Mine tributary at mouth (site 3) 4 11 11 4 6 6 4 

Jack Creek at mouth (site 4) 6 8 7 8 8 8 8 

Basin Creek at Basin (site 5) 7 3 4 9 9 9 9 

Cataract Creek above Uncle Sam Gulch (site 7) 3 7 6 6 5 5 6 

Cataract Creek at Basin (site 8) 2 4 3 5 4 3 5 

High Ore Creek near Basin (site 9) 7 10 1 1 1 1 1 

Boulder River below Little Galena Gulch (site 10) 10 1 2 3 3 4 3 

Tenmile Creek above City Diversion (site 11) 1 6 10 11 11 11 11 

Minnehaha Creek near Rimini (site 12) 9 9 8 10 10 10 10 

Tenmile Creek near Rimini (site 13) 5 5 8 7 7 7 7 

Copper, 

filtered

Copper, 

unfilteredrecoverable Lead, filtered Lead, unfiltered- recoverable Zinc, filtered Zinc, unfiltered- recoverable Arsenic, filtered Arsenic, unfiltered- recoverable 

Boulder River above Kleinsmith Gulch (site 1) 11 11 11 11 11 11 9 9 

Bullion Mine tributary at mouth (site 3) 1 1 3 2 1 1 8 3 

Jack Creek at mouth (site 4) 2 2 5 7 5 4 6 4 

Basin Creek at Basin (site 5) 6 4 7 9 8 8 4 6 

Cataract Creek above Uncle Sam Gulch (site 7) 8 8 10 10 9 10 11 11 

Cataract Creek at Basin (site 8) 3 3 6 5 7 7 7 8 

High Ore Creek near Basin (site 9) 10 10 4 1 2 2 1 1 

Boulder River below Little Galena Gulch (site 10) 4 6 9 8 10 9 3 5 

Tenmile Creek above City Diversion (site 11) 9 9 2 4 4 5 5 6 

Minnehaha Creek near Rimini (site 12) 5 5 8 6 6 6 10 10 

Tenmile Creek near Rimini (site 13) 7 7 1 3 3 3 2 2 

1Ranks are shaded as follows:

Rank of 1Rank of 2–3Rank of 4–5Rank of 6Rank of 7–8Rank of 9–10Rank of 11
Table 4. Percent of samples with unadjusted unfiltered-recoverable concentrations exceeding water-quality standards for sites in the BoTenmile Creek watersheds, Montana, water years 2009–13. [Water year is the 12-month period from October 1 through September 30 and is designated by the year in which it ends] Site number (fig. 1, table 1) Site name (fig. 1, table 1) Percent of samples exceeding indicated standard1 Aquatic life standards 

Cadmium Copper Lead Zinc Acute Chronic Acute Chronic Acute Chronic Acute a

chroni

1 Boulder River above Kleinsmith Gulch 0 0 14 14 0 29 0 2 Bullion Mine adit 100 100 100 100 89 100 100 3 Bullion Mine tributary at mouth 100 100 100 100 10 100 100 4 Jack Creek at mouth 100 100 100 100 5 65 100 5 Basin Creek at Basin 30 100 63 79 15 45 75 6 Crystal Mine adit 100 100 100 100 28 100 100 7 Cataract Creek above Uncle Sam Gulch 8 75 33 42 8 33 25 8 Cataract Creek at Basin 75 100 65 85 5 50 100 9 High Ore Creek near Basin 17 100 17 17 17 67 100 

10 Boulder River below Little Galena Gulch 10 100 45 80 5 40 25 

11 Tenmile Creek above City Diversion 100 100 61 78 17 100 100 

12 Minnehaha Creek near Rimini 100 100 89 100 17 72 100 13 Tenmile Creek near Rimini 94 100 65 76 18 82 100 

1Aquatic life standards used in determining exceedances for an individual sample were calculated based on the hardness of that sample according to methods des

Department of Environmental Quality (2012).
Overview of Water-Quality Characteristics for Selected Sites in the Boulder River and Tenmile Creek Watersheds 17

of filtered and unfiltered-recoverable cadmium (13.9 and 

15.0 μg/L, respectively), copper (52.8 and 122 μg/L, respectively), and zinc (1,690 and 1,840 μg/L, respectively) for site 3 

are higher than for any other stream site; and median concentrations of filtered and unfiltered-recoverable lead (0.70 and 

5.16 μg/L, respectively) are higher than for most other stream 

sites. Although the median filtered arsenic concentration 

(3.5 μg/L) for site 3 is lower than for most other stream sites, 

the median unfiltered-recoverable arsenic concentration 

(19.1 μg/L) for site 3 is higher than for most other stream sites. 

This pattern probably relates to dynamic instream processes as 

the mine drainage from Bullion Mine adit equilibrates with the 

tributary flow, and most of the arsenic (and likewise copper 

and lead) drops out of solution in association with colloidal 

material. Production of colloidal material in the short reach 

between sites 2 and 3 also is evidenced by ratios of median 

filtered to unfiltered-recoverable concentrations of arsenic, 

copper, and lead that are lower for site 3 than for any other 

stream site (table 1–2). Median suspended-sediment concentration (7 mg/L) for site 3 is higher than for any other stream 

site except High Ore Creek near Basin (site 9, fig. 1, table 1), 

which probably relates to production of colloidal material. 

For site 3, all samples collected during water years 2009–13 

exceeded all water-quality standards except for the lead acute 

aquatic life standard (exceeded in 10 percent of samples) and 

the arsenic human health standard (exceeded in 85 percent of 

samples; table 4).

Jack Creek at Mouth (site 4, fig. 1, table 1) is about 2 mi 

downstream from Bullion Mine tributary at mouth (site 3, 

fig. 1, table 1). Median streamflow at time of sampling 

(5.2 ft3

/s; table 1–2) for site 4 is lower than for most other 

stream sites and reflects about a 7.5-fold increase from the 

median for site 3. Changes in water quality between sites 3 

and 4 primarily reflect dilution of the relatively small inflow 

from the Bullion Mine tributary by surface-water and groundwater inflows from areas with less mining effects. Median pH 

(7.4 units) for site 4 represents an increase of 0.6 unit from 

the median for site 3. Median specific conductance (78 μS/cm 

at 25 oC; fig. 6, table 1–2) for site 4 is about 32 percent lower 

than the median for site 3 and also is lower than for most other 

stream sites. In association with the relatively low specific 

conductance, hardness also is lower than for most other stream 

sites, which contributes to relatively higher toxicity of metallic 

contaminants for site 4. Median concentrations of filtered and 

unfiltered-recoverable cadmium (1.27 and 1.43 μg/L, respectively), copper (11.6 and 17.4 μg/L, respectively), lead (0.29 

and 0.99 μg/L, respectively), and zinc (169 and 198 μg/L, 

respectively) for site 4 are higher than for most other stream 

sites. However, the median concentrations of the metallic contaminants for site 4 typically are about 80–90 percent lower 

than median concentrations for site 3. The median filtered 

arsenic concentration (4.2 μg/L) for site 4 is about 20 percent 

higher from the median concentration for site 3; however, the 

median unfiltered-recoverable arsenic concentration 

(7.9 μg/L) is about 60 percent lower than the median concentration for site 3. This pattern might indicate that mixing of 

inflow from the Bullion Mine tributary with other Jack Creek 

inflows results in dissolution of some colloidal arsenic from 

the Bullion Mine tributary but overall dilution of unfilteredrecoverable arsenic. Median suspended-sediment concentration (1 mg/L) for site 4 is lower than for any other stream site 

except Cataract Creek above Uncle Sam Gulch (site 7, fig. 1, 

table 1), which might provide evidence that colloidal material contributed from the Bullion Mine tributary is altered or 

deposited in the 2 mi reach between site 3 and site 4. For 

site 4, all samples collected during water years 2009–13 

exceeded all water-quality standards except for the following: 

(1) the lead acute and chronic aquatic life standards (exceeded 

in 5 and 65 percent of samples, respectively) and (2) the 

arsenic human health standard (exceeded in 30 percent of 

samples).

Basin Creek at Basin (site 5, fig. 1, table 1) is about 

7 mi downstream from Jack Creek at mouth (site 4, fig. 1, 

table 1). Median streamflow at time of sampling (18 ft3

/s; 

table 1–2) for site 5 is higher than for most other stream sites 

and reflects about a 2.5-fold increase from the median for site 

4. Changes in water quality between site 4 and site 5 primarily reflect dilution of the Jack Creek inflows by surface-water 

and groundwater inflows from areas with less mining effects. 

Median pH (7.6 units) for site 5 represents an increase of 

0.2 unit from the median for site 4. Median specific conductance (76 μS/cm at 25 o

C; fig. 6, table 1–2) for site 5 is similar 

to the median specific conductance for site 4 and also is lower 

than for most other stream sites. In association with the relatively low specific conductance, hardness also is lower than 

for most other stream sites, which contributes to relatively 

higher toxicity of metallic contaminants for site 5. Median 

concentrations of filtered and unfiltered-recoverable cadmium 

(0.245 and 0.302 μg/L, respectively), copper (5.50 and 

7.60 μg/L, respectively), lead (0.27 and 0.65 μg/L, respectively), and zinc (41.9 and 48.9 μg/L, respectively) for site 5 

generally are about 60–80 percent lower than median concentrations for site 4. The median filtered arsenic concentration 

(4.7 μg/L) for site 5 is about 10 percent higher than the 

median concentration for site 4; however, the median unfiltered-recoverable arsenic concentration (6.3 μg/L) is about 

20 percent lower than the median concentration for site 4. 

Median suspended-sediment concentration (2 mg/L) for site 

5 is lower than for most other stream sites and only slightly 

higher than the median concentration for site 4 (1 mg/L). 

For site 5, all samples collected during water years 2009–13 

exceeded at least one water-quality standard. Water-quality 

standards exceedances (table 4) include (1) the cadmium 

acute and chronic aquatic life standards (exceeded in 30 and 

100 percent of samples, respectively), (2) the copper acute and 

chronic aquatic life standards (exceeded in 63 and 79 percent of samples, respectively), (3) the lead acute and chronic 

aquatic life standards (exceeded in 15 and 45 percent of 

samples, respectively), (4) the zinc acute and chronic aquatic 

life standard (exceeded in 75 percent of samples), and 

(5) the arsenic human health standard (exceeded in 15 percent 

of samples).
18 Water-Quality Trends for Selected Sites in the Boulder River and Tenmile Creek Watersheds, Montana

Cataract Creek above Uncle Sam Gulch (site 7, fig. 1, 

table 1) is about 50 ft upstream from Uncle Sam Gulch, which 

receives seepage from the Crystal Mine adit (a primary source 

of metallic contaminants to Cataract Creek). Although site 7 is 

upstream from the Crystal Mine adit, site 7 drains a watershed 

with a somewhat high density of abandoned mines (2.3 per 

mi2

; table 1) with potential for mining effects on water quality. 

Median streamflow at time of sampling for site 7 is 5.9 ft3/s, 

median pH is 7.6 units, and median specific conductance is 

101 μS/cm at 25 oC (fig. 6, table 1–2). Median concentrations 

of filtered and unfiltered-recoverable cadmium (0.147 and 

0.171 μg/L, respectively), copper (3.55 and 3.90 μg/L, respectively), lead (0.14 and 0.46 μg/L, respectively), and zinc (37.2 

and 38.8 μg/L, respectively) for site 7 generally are lower than 

for most other stream sites except Boulder River above Kleinsmith Gulch (site 1, fig. 1, table 1). Median concentrations of 

filtered and unfiltered-recoverable arsenic (2.5 and 2.8 μg/L, 

respectively) for site 7 are lower than for any other stream site. 

Median suspended-sediment concentration (1 mg/L) for 

site 7 is lower than for any other stream site except Jack Creek 

at mouth (site 4, fig. 1, table 1). For site 7, exceedances of 

water-quality standards in samples collected during water 

years 2009–13 were fewer than for any other stream site 

except site 1. Water-quality standards exceedances include 

(1) the cadmium acute and chronic aquatic life standards 

(exceeded in 8 and 75 percent of samples, respectively), 

(2) the copper acute and chronic aquatic life standards 

(exceeded in 33 and 42 percent of samples, respectively), 

(3) the lead acute and chronic aquatic life standards (exceeded 

in 8 and 33 percent of samples, respectively), and (4) the zinc 

acute and chronic aquatic life standard (exceeded in 25 percent 

of samples).

Cataract Creek at Basin (site 8, fig. 1, table 1) is about 

4 mi downstream from Cataract Creek above Uncle Sam 

Gulch (site 7, fig. 1, table 1). Median streamflow at time of 

sampling (15 ft3

/s; table 1–2) for site 8 is higher than for most 

other stream sites and reflects about a 1.5-fold increase from 

the median for site 7. Changes in water quality between sites 7 

and 8 are affected by a combination of (1) inflows from Uncle 

Sam Gulch, which receives seepage from the Crystal Mine 

adit (a primary source of metallic contaminants to Cataract 

Creek; Nimick and others, 2004) and (2) surface-water and 

groundwater inflows from areas with less mining effects 

than Uncle Sam Gulch. Median concentrations of unfilteredrecoverable cadmium (1.04 μg/L), copper (10.6 μg/L), lead 

(1.38 μg/L), and zinc (103 μg/L) for site 8 generally are higher 

than for most other stream sites and typically are about 1.5- to 

5-fold higher than median concentrations for site 7 (fig. 6, 

table 1–2). The median unfiltered-recoverable arsenic concentration (6.1 μg/L) for site 8 is about 120 percent higher than 

the median for site 7. For site 8, all samples collected during 

water years 2009–13 exceeded at least one water-quality standard. Water-quality standards exceedances (table 4) include 

(1) the cadmium acute and chronic aquatic life standards 

(exceeded in 75 and 100 percent of samples, respectively), 

(2) the copper acute and chronic aquatic life standards 

(exceeded in 65 and 85 percent of samples, respectively), 

(3) the lead acute and chronic aquatic life standards (exceeded 

in 5 and 50 percent of samples, respectively), (4) the zinc 

acute and chronic aquatic life standard (exceeded in 

100 percent of samples), and (5) the arsenic human health 

standard (exceeded in 30 percent of samples).

High Ore Creek near Basin (site 9, fig. 1, table 1) receives 

seepage from the Comet Mine, a major source of metallic 

contaminants to the Boulder River (Nimick and others, 

2004). Median streamflow at time of sampling for site 9 is 

1.6 ft3

/s. The median pH (8.1 units; fig. 6, table 1–2) and 

median specific conductance (277 μS/cm at 25 oC; fig. 6, 

table 1–2) for site 9 are higher than for any other stream 

site. The relatively high specific conductance is associated 

with high hardness, which also is highest compared to any 

other site. The increased hardness decreases the toxicity of 

metallic contaminants and results in values for aquatic life 

standards that are higher than values for any other stream site 

(table 1–3). Median concentrations of unfiltered-recoverable 

cadmium (1.96 μg/L) and zinc (462 μg/L) for site 9 are higher 

than for most other stream sites. The median unfiltered-recoverable concentration of lead (6.77 μg/L) for site 9 is higher 

than for any other stream site. However, the median concentration of unfiltered-recoverable copper (3.50 μg/L) for site 9 

is lower than for any other stream site except Boulder River 

above Kleinsmith Gulch (site 1, fig. 1, table 1). The 

median concentrations of unfiltered-recoverable arsenic 

(30.0 μg/L) and suspended sediment (8 mg/L) for site 9 are 

higher than for any other stream site. Mine wastes, mill tailings, and fluvial deposits appear to be the source of arsenic 

in High Ore Creek (Nimick and others, 2004). In contrast to 

the high metal concentrations, aquatic life standards exceedances generally were lower at site 9 compared to most other 

stream sites; however, at least one water-quality standard 

was exceeded in all samples collected at site 9. Water-quality 

standards exceedances include (1) the cadmium acute and 

chronic aquatic life standards (exceeded in 17 and 100 percent 

of samples, respectively), (2) the copper acute and chronic 

aquatic life standards (exceeded in 17 percent of samples), 

(3) the lead acute and chronic aquatic life standards (exceeded 

in 17 and 67 percent of samples, respectively), (4) the 

zinc acute and chronic aquatic life standard (exceeded in 

100 percent of samples), and (5) the arsenic human health 

standard (exceeded in 100 percent of samples). For site 9, the 

high hardness contributes to the low percentage of samples 

with aquatic life standards exceedances for cadmium and 

copper.

Boulder River below Little Galena Gulch (site 10, fig. 1, 

table 1) is about 7 mi downstream from Boulder River above 

Kleinsmith Gulch (site 1, fig. 1, table 1) and about 6, 5, and 

2 mi downstream from the mouths of Basin Creek, Cataract 

Creek, and High Ore Creeks, respectively. Median streamflow 

at time of sampling (101 ft3/s; table 1–2) for site 10 is higher 

than for any other stream site and reflects about a 3.4-fold 

increase from the median for site 1. Changes in water quality between site 1 and site 10 are affected by a combination 
Overview of Water-Quality Characteristics for Selected Sites in the Boulder River and Tenmile Creek Watersheds 19

of (1) inflows from Basin Creek, Cataract Creek, and High 

Ore Creek (the primary sources of metallic contaminants to 

the Boulder River; Nimick and others, 2004) and (2) surfacewater and groundwater inflows from areas with less mining 

effects than Basin Creek, Cataract Creek, and High Ore Creek. 

Median pH (8.0 units) for site 10 represents an increase of 

0.4 unit from the median for site 1. Median specific conductance (124 μS/cm at 25 o

C; fig. 6, table 1–2) for site 10 

is about 12 percent lower than the median for site 1 but is 

higher than for most other stream sites. Median concentrations of unfiltered-recoverable cadmium (0.281 μg/L), copper 

(6.95 μg/L), lead (0.89 μg/L), and zinc (41.6 μg/L) for site 10 

are about 3–5-fold (copper and lead) to greater than 10-fold 

(cadmium and zinc) higher than median concentrations for site 

1 but generally are lower than for most other stream sites. The 

median unfiltered-recoverable arsenic concentration (6.4 μg/L) 

for site 10 is about 83 percent higher than the median for site 1 

and is higher than for most other stream sites. Median suspended-sediment concentration (3 mg/L) for site 10 is identical to the median concentration for site 1 and is higher than for 

most other stream sites. For site 10, all samples collected during water years 2009–13 exceeded at least one water-quality 

standard. Water-quality standards exceedances include (1) the 

cadmium acute and chronic aquatic life standards (exceeded 

in 10 and 100 percent of samples, respectively), (2) the copper 

acute and chronic aquatic life standards (exceeded in 45 and 

80 percent of samples, respectively), (3) the lead acute and 

chronic aquatic life standards (exceeded in 5 and 40 percent 

of samples, respectively), (4) the zinc acute and chronic 

aquatic life standard (exceeded in 25 percent of samples), and 

(5) the arsenic human health standard (exceeded in 15 percent 

of samples).

Stream Sites in the Tenmile Creek Watershed

Tenmile Creek above City Diversion (site 11, fig. 1, 

table 1) drains a watershed with high density of abandoned 

mines (3.0 mines per mi2; table 1) and with potential for mining effects on water quality. However, the watershed does 

not contain mine point sources of metallic contaminants 

of similar magnitude to the Bullion, Crystal, and Comet Mines 

in the Boulder River watershed. Median streamflow at time 

of sampling for site 11 is 6.6 ft3

/s. Median pH (7.2 units; 

table 1–2) for site 11 is lower than for any other stream site 

except Bullion Mine tributary at mouth (site 3, fig. 1, 

table 1). Median specific conductance (55 μS/cm at 25 oC; 

fig. 6, table 1–2) for site 11 is lower than for any other 

stream site. In association with the relatively low specific 

conductance, hardness also is lower than for any other site 

(table 1–3). Median concentrations of filtered and unfilteredrecoverable cadmium (0.682 and 0.754 μg/L, respectively) and 

copper (3.25 and 3.65 μg/L, respectively) for site 11 generally 

are lower than for most other stream sites, but median 

concentrations of filtered and unfiltered-recoverable lead 

(0.80 and 1.75 μg/L, respectively) and zinc (179 and 

167 μg/L, respectively) for site 11 generally are higher than 

for most other stream sites. Median concentrations of filtered 

and unfiltered-recoverable arsenic (4.4 and 6.3 μg/L, respectively) and median suspended-sediment concentration (3 

mg/L) for site 11 also generally are higher than for most other 

stream sites. For site 11, all samples collected during water 

years 2009–13 exceeded at least one water-quality standard. 

Water-quality standards exceedances include (1) the cadmium 

acute and chronic aquatic life standards (exceeded in 100 percent of samples), (2) the copper acute and chronic aquatic life 

standards (exceeded in 61 and 78 percent of samples, respectively), (3) the lead acute and chronic aquatic life standards 

(exceeded in 17 and 100 percent of samples, respectively), 

(4) the zinc acute and chronic aquatic life standard (exceeded 

in 100 percent of samples), and (5) the arsenic human health 

standard (exceeded in 17 percent of samples). For site 11, 

the low hardness contributes to the high toxicity of metallic 

contaminants as indicated by the high percentage of samples 

with aquatic life standards exceedances for cadmium, copper, 

and zinc.

Minnehaha Creek near Rimini (site 12, fig. 1, table 1) 

drains a watershed with moderate density of abandoned mines 

(1.3 mines per mi2

; table 1) and with potential for mining 

effects on water quality. However, the watershed does not 

contain mine point sources of metallic contaminants of similar 

magnitude to the Bullion, Crystal, and Comet Mines in the 

Boulder River watershed. Median streamflow at time of sampling for site 12 is 2.8 ft3

/s. Median pH (7.3 units; table 1–2) 

and specific conductance (62 μS/cm at 25 oC; fig. 6, table 1–2) 

for site 12 are lower than for most other stream sites. In association with the relatively low specific conductance, hardness 

also is lower than for most other sites, which contributes to 

relatively higher toxicity of metallic contaminants for site 12 

(table 1–3). Median concentrations of filtered and unfilteredrecoverable cadmium (0.824 and 0.927 μg/L, respectively), 

copper (5.70 and 7.25 μg/L, respectively), lead (0.252 and 

1.04 μg/L, respectively), and zinc (145 and 148 μg/L, respectively) for site 12 generally are higher than for most other 

stream sites. Median concentrations of filtered and unfilteredrecoverable arsenic (3.1 and 4.0 μg/L, respectively) are lower 

than for any other stream site except Cataract Creek above 

Uncle Sam Gulch (site 7, fig. 1, table 1). Median suspendedsediment concentration (4 mg/L) for site 12 is higher than for 

most other stream sites. For site 12, all samples collected during water years 2009–13 exceeded at least one water-quality 

standard. Water-quality standards exceedances include (1) the 

cadmium acute and chronic aquatic life standards (exceeded 

in 100 percent of samples), (2) the copper acute and chronic 

aquatic life standards (exceeded in 89 and 100 percent of 

samples, respectively), (3) the lead acute and chronic aquatic 

life standards (exceeded in 17 and 72 percent of samples, 

respectively), (4) the zinc acute and chronic aquatic life standard (exceeded in 100 percent of samples), and (5) the arsenic 

human health standard (exceeded in 6 percent of samples). For 

site 12, the low hardness contributes to the high toxicity of 

metallic contaminants as indicated by the high percentage of 
20 Water-Quality Trends for Selected Sites in the Boulder River and Tenmile Creek Watersheds, Montana

samples with aquatic life standards exceedances for cadmium, 

copper, and zinc.

Tenmile Creek near Rimini (site 13, fig. 1, table 1) is 

about 3.5 mi downstream from Tenmile Creek above City 

diversion (site 11, fig. 1, table 1) and about 1.5 mi downstream from Minnehaha Creek near Rimini (site 12, fig. 1, 

table 1) and the mouth of Minnehaha Creek. About 0.5 mi 

downstream from site 11, part of the streamflow of Tenmile 

Creek is diverted into a canal that feeds Chessman Reservoir 

(not shown on fig. 1) and supplies drinking water to the city 

of Helena, Mont. (Parrett and Kendy, 2001). Site 13 drains a 

watershed with a somewhat high density of abandoned mines 

(2.1 mines per mi2

; table 1) and with potential for mining 

effects on water quality. However, the watershed does not 

contain mine point sources of metallic contaminants of similar 

magnitude to the Bullion, Crystal, and Comet Mines in the 

Boulder River watershed. Further, the highest density of abandoned mines in the site 13 watershed is upstream from site 11 

and part of the streamflow at site 11 is transferred outside of 

the watershed by the city diversion. Thus, changes in water 

quality between sites 11 and 13 are affected by a combination 

of the following: (1) undiverted inflows from site 11, 

(2) inflows from Minnehaha Creek, and (3) surface-water and 

groundwater inflows from areas that generally have less mining effects than site 11 and Minnehaha Creek. Median streamflow at time of sampling (14 ft3

/s; table 1–2) for site 13 is 

about 114 percent higher than the median for site 11. Median 

pH (7.3 units; table 1–2) for site 13 is lower than for most 

other stream sites. Median specific conductance (88 μS/cm at 

25 oC; fig. 6, table 1–2) for site 13 is about 60 and 42 percent 

higher than the medians for sites 11 and 12, respectively. 

Median concentration of unfiltered-recoverable cadmium 

(1.32 μg/L) for site 13 is about 74 and 42 percent higher than 

the medians for sites 11 and 12, respectively. Median concentration of unfiltered-recoverable copper (6.05 μg/L) for site 

13 is about 66 percent higher than the median for site 11 but 

about 17 percent lower than the median for site 12. Median 

concentration of unfiltered-recoverable lead (2.04 μg/L) is 

about 17 and 97 percent higher than the medians for sites 

11 and 12, respectively. Median concentration of unfilteredrecoverable zinc (234 μg/L) for site 13 is about 40 and 

58 percent higher than the medians for sites 11 and 12, 

respectively. Median concentration of unfiltered-recoverable 

arsenic (22.6 μg/L) is about 2.6- and 6.3-fold higher than the 

medians for sites 11 and 12, respectively. Site 13 has higher 

median concentrations of most metallic contaminants and 

arsenic than sites 11 and 12; however, the intervening drainage 

area between the upstream sites (11 and 12) and site 13 has a 

relatively low density of abandoned mines and few substantial point sources of metallic contaminants and arsenic. This 

circumstance might suggest that (1) contaminants are mobilized from channel and flood-plain deposits in the intervening 

drainage area or (2) groundwater inflows downstream from 

site 11 have high concentrations of metallic contaminants 

and arsenic. For site 13, all samples collected during water 

years 2009–13 exceeded at least one water-quality standard. 

Water-quality standards exceedances include (1) the cadmium 

acute and chronic aquatic life standards (exceeded in 94 and 

100 percent of samples, respectively), (2) the copper acute and 

chronic aquatic life standards (exceeded in 65 and 76 percent of samples, respectively), (3) the lead acute and chronic 

aquatic life standards (exceeded in 18 and 82 percent of 

samples, respectively), (4) the zinc acute and chronic aquatic 

life standard (exceeded in 100 percent of samples), and (5) 

the arsenic human health standard (exceeded in 82 percent of 

samples). Investigation of the effects of diversions for municipal water use and small amounts of irrigation in the upper part 

of the Tenmile Creek watershed (Parrett and Kendy, 2001; 

U.S. Environmental Protection Agency, 2002) on water quality 

of Tenmile Creek was beyond the scope of this study. 

Trend-Analysis Methods 

For the stream sites, multiple linear regression (MLR) 

of constituent concentrations on time, streamflow, and season 

(Helsel and Hirsch, 2002) was used for trend analysis of 

selected constituents (table 2). The constituents selected for 

trend analysis were considered most relevant to evaluating 

effects of remediation of mining activities. The water-quality 

property pH is relevant to mining activities but was not 

included in the trend analysis. The log-based units of measurement for pH result in transformational complexities within the 

trend-analysis approach of this study and would have required 

an analytical approach distinctly different from all other 

trend-analysis constituents. Application of a special analytical 

approach for trend analysis for pH was beyond the scope of 

the study. 

Inclusion of streamflow in the MLR trend analysis provides for definition of flow-adjusted trends. Flow adjustment 

is necessary because concentrations of many water-quality 

constituents are dependent on streamflow conditions that 

primarily are affected by climatic variability. The intent of 

flow adjustment is to identify and remove streamflow-related 

variability in concentration and thereby enhance capability to 

detect trends independent from effects of climatic variability.

The importance of flow adjustment is illustrated in 

figure 7 by using streamflow and constituent concentration 

data that were collected at Basin Creek (site 5, fig. 1, table1) 

during water years 1997–2013. Daily mean streamflow is 

shown in figure 7, with an associated locally weighted scatter plot smooth (LOWESS; Cleveland, 1985; Cleveland and 

McGill, 1984) line illustrating central tendency of the data. 

Unadjusted (that is, measured) concentrations of unfilteredrecoverable copper, unfiltered-recoverable arsenic, and 

suspended sediment also are shown in figure 7, with associated LOWESS smooth lines. LOWESS smooth lines for the 

constituents have similar patterns to the LOWESS smooth line 

for streamflow, with the relations being most pronounced for 

copper and suspended sediment. The similarity in LOWESS 

smooth lines among unadjusted concentrations and streamflow 
Trend-Analysis Methods 21

Figure 7. Selected streamflow and constituent concentration information for Basin Creek at Basin (site 5, fig. 1, table 1), based on data

collected during water years 1997–2013.

Water year (October–September)

19952000200520102013

A. Streamflow 

B. Unfiltered-recoverable copper

C. Unfiltered-recoverable arsenic

D. Suspended sediment

FIGURE 7

1

100

10

1

100

10

1

100

10

1

10

100

Unfiltered-recoverable

arsenic concentration,

in micrograms per liter

Unfiltered-recoverable 

copper concentration,

in micrograms per liter

Suspended-sediment concentration,

in milligrams per liter

Streamflow, 

in cubic feet per second

Daily mean streamflow

Geometric mean streamflow 

for water years 1997–2013

Locally weighted scatter 

plot smooth (LOWESS; 

Cleveland, 1985; Cleveland 

and McGill, 1984) line for 

daily mean streamflow

Unadjusted (not flow adjusted) 

concentration

LOWESS line for unadjusted 

concentration

Flow-adjusted concentration

Flow-adjusted fitted trend

[Water year is defined as the 

12-month period from October 1 

through September 30 and is 

designated by the year in which it 

ends]

EXPLANATION
22 Water-Quality Trends for Selected Sites in the Boulder River and Tenmile Creek Watersheds, Montana

indicates that temporal variability in unadjusted concentrations is strongly affected by temporal variability in streamflow. 

Flow-adjusted concentrations (FACs) for the constituents 

also are shown in figure 7, with associated MLR fitted trends. 

The FACs and fitted trends indicate general decreases that are 

independent from the temporal variability in streamflow. The 

dissimilar patterns among unadjusted concentrations and FACs 

indicate the importance of flow-adjusted trend analysis for 

identifying actual patterns in constituent concentrations independent from variability in streamflow conditions, which typically result from changes in land use or other human activities.

For the stream sites, a consistent MLR model was used 

to provide general application for the many (128) site and 

constituent combinations. In general, log-transformed (base10 logarithm) constituent concentrations were regressed on 

log-transformed streamflow, decimal time, and periodic functions used to represent seasonal variability in concentration 

and streamflow relations. Regression models were developed 

by using least squares regression if the concentration data 

contained no censored observations or by using adjusted 

maximum-likelihood estimation (Cohn, 2005) if censored 

observations were present. Specific information that concerns 

the suitability of the MLR application to the study datasets and 

the procedures that determine the statistical significance and 

magnitude of trends are presented in appendix 2.

For the adit sites, relations between constituent concentrations and streamflow were much weaker than for the stream 

sites. Streamflow for the adit sites represented groundwater 

seepage from the adits that typically was less than 0.07 ft3

/s 

and had small variability among sampling dates. Thus, streamflow was not included in MLR trend models for the adit sites 

and the trend results represent temporal changes in unadjusted 

concentrations. 

For MLR, fitted trends are straight-line monotonic trends 

determined for defined trend-analysis periods. Definition of 

trend-analysis periods is affected by several factors, including the timing of data collection, temporal patterns in FACs 

(or unadjusted concentrations for the adit sites), and the study 

objectives.

For the adit sites (Bullion Mine adit [site 2, fig. 1, 

table 1] and Crystal Mine adit [site 6, fig. 1, table 1]) trendanalysis periods were assigned consistently even though the 

data-collection periods somewhat differed between the sites. 

Data collection for site 2 during water years 1999–2002 had 

within-year sampling frequency that was particularly variable and two water years had only one sample each. During 

water years 2003–13, data-collection activities were consistent 

among the adit sites. Thus, for the adit sites, trends were analyzed for June 2003 through September 2013. This definition 

of trend-analysis periods provides for consistent comparison 

of trends between the adit sites.

For each stream site, the trend-analysis period was from 

the start of data collection to the end of water year 2013. 

Examination of time-series plots of FACs for the stream sites 

indicated that temporal patterns in FACs for most site and 

constituent combinations could reasonably be represented by 

single trend-analysis periods. Variability in the start of data 

collection among the stream sites generally was small. Start 

times ranged from water years 1997–2000 for all stream sites 

except Tenmile Creek near Rimini (site 13, fig. 1, table 1), 

which had a start time of water year 2005. Thus, for all stream 

sites except site 13, the definition of trend-analysis periods 

provides for generally consistent comparison of trends among 

the sites. However, for several stream sites sample-collection 

characteristics differ from most other stream sites and affect 

the comparability of trend results. This issue is discussed in 

the following section of this report “Factors that Affect Trend 

Analysis and Interpretation.”

Factors that Affect Trend Analysis and 

Interpretation

Ideally, water-quality trend analysis is done on data that 

were consistently and systematically collected within a monitoring network specifically designed for the purpose of trend 

analysis. The datasets for the sites in the Boulder River and 

Tenmile Creek watersheds do not represent ideal cases. However, the datasets were considered sufficient in longevity, data 

density, and quality for trend analysis to generally describe 

relative differences in temporal patterns in FACs. For site and 

constituent combinations where there are large uncertainties in 

trend results, conclusions concerning the results are qualified.

Data-Collection Factors

All of the study sites have variability in within-year sampling frequency among years. However, the within-year sampling frequency was similar in individual years among most 

sites. A notable characteristic of the study datasets is relatively 

poor representation of samples collected in the fall and winter. 

Overall, about 80 percent of all samples were collected during 

the spring or summer and about 20 percent were collected 

during the fall or winter. However, the seasonal distribution of 

samples generally was similar among sites. 

Although the study datasets are not ideally suited for 

precise definition of temporal trends, generally strong similarity in sample-collection characteristics of the datasets among 

most sites provides a reasonable basis for relative comparisons 

of trend results among sites. The adit sites (Bullion Mine adit 

[site 2, fig. 1, table 1] and Crystal Mine adit [site 6, fig. 1, 

table 1]) have nearly identical sample-collection characteristics during the trend-analysis periods for the adit sites, providing a basis for comparison of results between the adit sites.

Stream sites in the Boulder River watershed that have 

similar sample-collection characteristics (fig. 4) are Bullion 

Mine tributary at mouth (site 3, fig. 1, table 1), Basin Creek at 

Basin (site 5, fig. 1, table 1), Cataract Creek at Basin (site 8, 

fig. 1, table 1), and Boulder River below Little Galena Gulch 

(site 10, fig. 1, table 1). Sample collection for Jack Creek at 
Factors that Affect Trend Analysis and Interpretation 23

mouth (site 4, fig. 1, table 1) started later (in water year 2000) 

than for sites 3, 5, 8, and 10; however, during water years 

2000–13, sample collection for site 4 was similar to sites 3, 5, 

8, and 10. Trend results for site 4 are considered comparable 

to results for sites 3, 5, 8, and 10. Stream sites in the Boulder 

River watershed that have multi-year gaps in data collection 

are Boulder River above Kleinsmith Gulch (site 1, fig. 1, 

table 1), Cataract Creek above Uncle Sam Gulch (site 7, fig. 1, 

table 1), and High Ore Creek near Basin (site 9, fig. 1, table 1). 

The larger dissimilarity between the datasets for sites 1, 7, and 

9 and the datasets for most other stream sites results in larger 

uncertainties in directly comparing trend results for sites 1, 7, 

and 9 with trend results for most other stream sites. 

Stream sites in the Tenmile Creek watershed that have 

similar sample-collection characteristics (fig. 4) are Tenmile 

Creek above City Diversion (site 11, fig. 1, table 1) and Minnehaha Creek near Rimini (site 12, fig. 1, table 1). Samplecollection characteristics for sites 11 and 12 in the Tenmile 

Creek watershed also generally are similar to sample-collection characteristics for sites 3, 4, 5, 8, and 10 in the Boulder 

River watershed. Similarities in the datasets for sites 3, 4, 5, 8, 

10, 11, and 12 provide a basis for comparison of trend results 

among the sites. Tenmile Creek near Rimini (site 13, fig. 1, 

table 1) has a much shorter sample collection period (water 

years 2005–13) than any other stream site; therefore, there 

might be large uncertainties in comparing trend results for 

site 13 than with trend results for other stream sites. 

Potential Effects of Diel Cycling of Trace 

Elements

An important consideration in trend analysis for trace 

elements is potential effects of diel cycling in trace-element 

concentrations. Complex biogeochemical processes affected 

by the daily solar photocycle produce regular and dynamic 

changes in many physical and chemical characteristics of 

streams (Nimick and others, 2011). In some streams (including 

some of the sampling sites in this study), the biogeochemical 

processes can result in large diel variability in trace-element 

concentrations (Nimick and others, 2003). 

Diel cycling in trace element concentrations has potential to affect trend results if (1) there is strong diel cycling 

for a given site and constituent combination and (2) there is 

a systematic temporal bias in the dataset with respect to time 

of day of sampling. For most sites, sampling times during 

the data-collection periods generally were within a narrow 

range (with the interquartile ranges of sampling times generally between 10 a.m. and 2 p.m.). During exploratory data 

analysis, time-series plots of sampling time were qualitatively 

examined for systematic temporal bias, and such bias was not 

clearly indicated. Also during exploratory analysis, potential 

effects of diel cycling on the trend results were quantitatively 

evaluated by including decimal day (time of sampling) as an 

explanatory variable in the trend models. The decimal day 

variable indicates the strength of diel cycling for a given site 

and constituent combination and also allows evaluation of the 

effect of temporal variability in time of sampling on the trend 

results. Although several site and constituent combinations 

had strong and statistically significant diel cycling, in no case 

did the inclusion of the decimal day variable in trend models 

provide substantially different trend results from the reported 

results. Thus, potential effects on trend results of diel cycling 

of trace elements were determined to be minor.

Statistical and Other Factors

An important consideration in interpreting trend results 

relates to the MLR method incorporating log transformation of 

constituent concentrations and streamflow. Thus, the methods 

evaluate changes in geometric mean concentrations (generally 

similar to untransformed median concentrations) in reference 

to log-transformed streamflow. Log transformation results in 

datasets that are approximately normally distributed and allow 

analysis using rigorous parametric procedures. However, log 

transformation decreases variability in the data relative to the 

original untransformed units representative of actual environmental variability. This factor is important in interpreting trend 

results with respect to regulatory issues, including compliance with human health or aquatic life standards. The trends 

in FACs provide general information on overall temporal 

changes (in terms of directions and relative magnitudes) in 

concentrations. However, the trends in FACs lack the specificity to indicate compliance or noncompliance with regulatory 

standards. In presentation of trend results, trend magnitudes 

and directions for trace elements are shown in conjunction 

with water-quality standards to provide general information on temporal changes in water quality in relation to the 

standards (determined based on median hardness values during water years 2009–13). Providing specific information on 

actual compliance with standards is not intended and relations 

between the reported trends and water-quality standards are 

not discussed in this report.

Trend-magnitude and fitted trend values are considered 

semiquantitative estimates determined by statistical analysis. Throughout this report, trend-magnitude and fitted trend 

values frequently are referred to (reported to two significant 

figures) in discussion of temporal and spatial changes in water 

quality. Reference to specific trend-magnitude and fitted trend 

values is intended to facilitate discussion of relative spatial 

and temporal differences among values; however, reference 

to the values is not intended to represent absolute accuracy 

at two significant figures. The text discussion on trend results 

focuses on the trend-magnitude and fitted trend values. The 

p-values (statistical probability levels) and levels of significance associated with the trend results are indicated in the 

tables and figures that present trend results. However, the 

p-values and levels of significance are not emphasized in 

the discussion of trend results. In this study, trend analysis 

using MLR is considered to be a useful tool for simplifying the environmental complexity in the Boulder River and 
24 Water-Quality Trends for Selected Sites in the Boulder River and Tenmile Creek Watersheds, Montana

Tenmile Creek watersheds to provide a large-scale evaluation 

of general temporal changes in FACs. Thus, the best-fit trend 

lines are considered to provide important information beyond 

the strict statistical characteristics of the trend results (in terms 

of p-values and levels of significance) because the trend lines 

aid in comparing and summarizing large-scale patterns among 

sites. 

Water-Quality Trends for Selected 

Sites in the Boulder River and Tenmile 

Creek Watersheds

Trend results for all sites are presented in summary 

figures (figs. 8 and 9) and tables (tables 5 and 6). Detailed 

results for each site are presented in appendix 3 in figures 

(figs. 3–1 through 3–13, http://pubs.usgs.gov/sir/2015-5008/

downloads/sir20155008_Appendix03_figures.pdf) and tables 

(tables 3–1 and 3–2). In the tables and text figures, trend 

results are presented for all constituents analyzed for trends 

(table 2). However, in the figures presented in appendix 3, presentation of results is restricted to specific conductance, copper, zinc, arsenic, and suspended sediment. Further, in the text 

discussion, emphasis is placed on specific conductance, copper, zinc, arsenic, and suspended sediment. Specific conductance is an index of ionic strength and provides information 

on extent of water contact with geologic materials and types 

of geologic materials present in the sampling-site watersheds. 

Mining activities can increase specific conductance by interaction of acidic mine water with rock and soil materials. Copper, 

zinc, and arsenic are constituents of concern with respect to 

potential toxicity issues. Copper and zinc provide examples 

of geochemical characteristics of metallic contaminants, and 

arsenic is a metalloid element with substantially different 

geochemical characteristics than most metallic elements. Suspended sediment is presented because it provides information 

on transport of particulate materials, which is a factor that can 

strongly affect transport of metallic contaminants. 

Temporal trends are discussed by site groups (table 1; 

adit sites in the Boulder River watershed, stream sites in the 

Boulder River watershed, and stream sites in the Tenmile 

Creek watershed) and by site within each group. To allow 

various comparisons, trend magnitudes are presented as total 

percent change during indicated multi-year periods and also as 

percent change per year. 

In the text discussion, qualitative observations on trend 

magnitudes are made. Trend magnitudes are considered to be 

(1) large, if the deviation from zero of the trend magnitude 

was larger than about 5 percent per year; (2) moderate, if 

the deviation from zero of the trend magnitude was about 

3–5 percent per year; (3) small, if the deviation from zero of 

the trend magnitude was about 1.5–3 percent per year; and 

(4) minor, if the deviation from zero of the trend magnitude 

was about 0–1.5 percent per year. In some cases, where trending is in a small range at low concentrations, relatively large 

trend magnitudes (on a percent basis) also are considered to be 

minor. The qualitative descriptions were subjectively defined 

and are intended to facilitate relative comparison of trend 

patterns among site and constituent combinations. In the text 

discussion, the terms “significant” or “significantly” refer to 

statistical significance (p-value < 0.01) unless otherwise noted.

Factors affecting temporal variability in water quality in 

the Boulder River and Tenmile Creek watersheds are complex. 

Much information on observed changes in water quality is 

presented in this report. However, to provide detailed explanations for all of the observed changes or to link specific trends 

with specific remediation activities is beyond the scope of this 

report. The primary focus is on describing general temporal 

changes in water quality within the Boulder River and Tenmile 

Creek watersheds.

Adit Sites in the Boulder River Watershed

For the adit sites, trends were analyzed for June 2003 

through September 2013. Trend results for specific conductance and filtered trace elements for the adit sites in the Boulder River watershed (Bullion Mine adit [site 2, fig. 1, table 1] 

and Crystal Mine adit [site 6, fig. 1, table 1]) are summarized 

in figure 8 and table 5. Data are incomplete for unfilteredrecoverable trace elements before water year 2009, and trend 

results for unfiltered-recoverable trace elements are not 

included in figure 8 and table 5 and are not discussed. Detailed 

trend results for all constituents are presented in figures 3–2

and 3–6 and in table 3–1 (http://pubs.usgs.gov/sir/2015-5008/

downloads/sir20155008_Appendix03_tables.pdf). 

Bullion Mine Adit (site 2)

Trend results for Bullion Mine adit (site 2, fig. 1, table 1) 

for June 2003 through September 2013 indicate minor to small 

decreasing trends in specific conductance and concentrations 

of most filtered trace elements (cadmium, lead, and zinc), a 

moderate decreasing trend in copper, and a moderate increasing trend in arsenic (figs. 8 and 3–2, tables 5 and 3–1). None 

of the trends for site 2 are statistically significant. 

Crystal Mine Adit (site 6)

Trend results for Crystal Mine adit (site 6, fig. 1, table 1) 

for June 2003 through September 2013 indicate minor to small 

decreasing trends in specific conductance and concentrations 

of most filtered trace elements (cadmium, copper, zinc, and 

arsenic) but also indicate a large increasing trend in lead 

(figs. 8 and 3–6, tables 5 and 3–1). The small decreasing 

trends for specific conductance and filtered cadmium and the 

large increasing trend for filtered lead are statistically significant (tables 5 and 3–1). 
Water-Quality Trends for Selected Sites in the Boulder River and Tenmile Creek Watersheds 25

2 6 2 6

Site number (fig.1, table 1)

Bullion Mine adit Crystal Mine adit

Site number (fig.1, table 1)

Bullion Mine adit Crystal Mine adit

FIGURE 8

10,000

1,000

10,000

100,000

1,000,000

1,000

-15

-10

-5

0

10

5

-15

-10

-5

0

10

5

-15

-10

-5

0

10

5

100

100

10,000

1,000

100,000

10

100

10,000

1,000

-15

-10

-5

0

10

5

10

100

10,000

1,000

-15

-10

-5

0

10

5

10

100

10,000

1,000

-15

-10

-5

0

10

5

Percent change per year 

in flow-adjusted 

concentration 

Percent change per year 

in flow-adjusted 

concentration 

Percent change per year 

in flow-adjusted 

concentration 

Fitted trend values, 

in indicated 

units of measurement

Fitted trend values, 

in indicated 

units of measurement

Fitted trend values, 

in indicated 

units of measurement

E. Filtered zinc (micrograms per liter)

B. Filtered cadmium (micrograms per liter)

C. Filtered copper (micrograms per liter) D. Filtered lead (micrograms per liter)

A. Specific conductance (microsiemens per centimeter 

at 25 degrees Celsius)

F. Filtered arsenic (micrograms per liter)

7.8 micrograms 

per liter

Fitted trend value June 2003

Fitted trend value at end of water year 2013—Solid arrowhead 

denotes statistical significance (p-value less than 0.01)

Qualitative trend

magnitude description for

comparison purposes

Large increasing

Moderate increasing

Small increasing

Small decreasing

Moderate decreasing

Large decreasing

Minor

Acute

Chronic

Human health standard for arsenic (Montana Department of 

Environmental Quality, 2012a)

Aquatic life standards for lead based on median 

hardness for given site for water years 2009–13

(Montana Department of Environmental Quality, 2012a)

[Water year is defined as the 12-month period from October 1 through September 30 and is designated by the year in which it ends;

p-value, statistical probability level]

EXPLANATION

Figure 8. Water-quality trends (not flow adjusted) for June 2003 through September 2013 for the adit sites in the Boulder River 

watershed, Montana.
26 Water-Quality Trends for Selected Sites in the Boulder River and Tenmile Creek Watersheds, Montana

Summary of Trend Results for the Adit Sites in 

the Boulder River Watershed

Trend results for the adit sites in the Boulder River watershed (Bullion Mine adit [site 2, fig. 1, table 1] and Crystal 

Mine adit [site 6, fig. 1, table 1]) do not provide clear evidence 

of substantial trending during June 2003 through September 

2013. For some trace elements, temporal variability in concentrations is somewhat inconsistent, with sporadic increases and 

decreases. Although apparent for several trace elements, this 

pattern is well evidenced by filtered arsenic for site 2 (fig. 3–2) 

and unfiltered-recoverable arsenic for site 6 (fig. 3–6). The 

statistically significant large increasing trend for filtered lead 

for site 6 was affected by a sharp increase in concentrations 

within a short time frame near the end of the trend-analysis 

period (from water year 2010 to water years 2011–12). Water 

quality of the adit sites probably is affected by complex processes that are not well defined in the study datasets. As such, 

the trend-analysis structure of the study might not be suitable 

for accurate description of temporal trends in water quality for 

the adit sites.

Stream Sites in the Boulder River Watershed

Stream sites in the Boulder River watershed include 

Boulder River above Kleinsmith Gulch (site 1, fig. 1, table 1), 

Bullion Mine tributary at mouth (site 3, fig. 1, table 1), Jack 

Creek at mouth (site 4, fig. 1, table 1), Basin Creek at Basin 

(site 5, fig. 1, table 1), Cataract Creek above Uncle Sam Gulch 

(site 7, fig. 1, table 1), Cataract Creek at Basin (site 8, fig. 1, 

table 1), High Ore Creek near Basin (site 9, fig. 1, table 1), and 

Boulder River below Little Galena Gulch (site 10, fig. 1, table 

1). For each stream site in the Boulder River watershed, 

trends were analyzed for the period from the start of data collection through September 2013. The detailed trend 

results based on the entire periods of record are presented in 

figure 3–1, figures 3–3 through 3–5, figures 3–7 through 3–10, 

and table 3–2. Because of the small differences in the starts 

of data collection among sites, a 14-year comparison period 

(water years 2000–13) was defined to allow for summaries and 

comparisons of trend magnitudes among sites. Trend results 

for water years 2000–13 for the stream sites in the Boulder 

River watershed are summarized in figure 9 and table 6.

Table 5. Summary of water-quality trends (not flow adjusted) for June 2003 through September 2013 for the adit sites in the Boulder 

River watershed, Montana.

[Water year is the 12-month period from October 1 through September 30 and is designated by the year in which it ends. Gray shading indicates statistically 

significant trend (p-value less than 0.01). p-value, statistical probability level; μS/cm at 25 °C, microsiemens per centimeter at 25 degrees Celsius; μg/L, micrograms per liter]

Constituent or 

property, 

flow-adjusted 

units of measurement

Fitted trend values Trend magnitudes1

Fitted trend value 

June 2003

Fitted trend value at 

end of water year 

2013

Percent change 

per year 

Total percent 

change from June 2003 

to end of water year 

2013

Bullion Mine adit (site 2, fig. 1, table 1)

Specific conductance, 

μS/cm at 25 °C

1,900 1,600 -1.6 -16

Cadmium, filtered, μg/L 400 340 -1.6 -15

Copper, filtered, μg/L 7,200 4,900 -3.9 -33

Lead, filtered, μg/L 380 300 -2.1 -20

Zinc, filtered, μg/L 43,000 37,000 -1.4 -14

Arsenic, filtered, μg/L 1,500 2,000 3.1 36

Crystal Mine adit (site 6, fig. 1, table 1)

Specific conductance, 

μS/cm at 25 °C

800 620 -2.5 -23

Cadmium, filtered, μg/L 540 410 -2.8 -25

Copper, filtered, μg/L 5,300 6,300 1.7 19

Lead, filtered, μg/L 37 78 7.7 114

Zinc, filtered, μg/L 46,000 39,000 -1.6 -16

Arsenic, filtered, μg/L 110 120 1.1 12

1

Small discrepancies between trend magnitudes expressed as percent change per year and trend magnitudes expressed as total percent change are the result 

of rounding artifacts.
Water-Quality Trends for Selected Sites in the Boulder River and Tenmile Creek Watersheds 27

In figure 9, trend magnitudes and directions for trace elements are shown in conjunction with water-quality standards 

to provide general information on temporal changes in water 

quality in relation to the standards. Providing specific information on actual compliance with standards is not intended. 

Subjectively-based qualitative descriptions of trend magnitudes are indicated in figure 9 and are intended to facilitate 

relative comparison of trend patterns among site and constituent combinations. 

Boulder River Above Kleinsmith Gulch (site 1)

Trend results for Boulder River above Kleinsmith Gulch 

(site 1, fig. 1, table 1) for water years 2000–13 generally indicate minor to small decreasing trends in flow-adjusted specific 

conductance, in FACs of filtered and unfiltered-recoverable 

trace elements, and in FACs of suspended sediment (figs. 9

and 3–1, tables 6 and 3–2). However, moderate decreasing 

trends were determined for unfiltered-recoverable copper and 

zinc, but the trends were within fairly small ranges at generally low FACs. No statistically significant trends are indicated. 

Overall, the magnitudes of the decreasing trends generally 

are within the range of about -1 to -2 percent per year, and 

for most trace elements these changes are within fairly small 

ranges at generally low FACs. Notably, the dataset for 

site 1 is largely dissimilar from datasets for most other sites, 

which results in larger uncertainties in directly comparing 

trend results for site 1 with those for most other stream sites. 

However, site 1 has a low density of abandoned mines and is 

generally representative of a background index site with small 

effects from mining operations; thus, small trending in FACs 

of trace elements is intuitively reasonable.

Bullion Mine Tributary at Mouth (site 3)

Trend results for Bullion Mine tributary at mouth 

(site 3, fig. 1, table 1) for water years 2000–13 indicate moderate to large decreasing trends in flow-adjusted specific conductance, in FACs of all filtered and unfiltered-recoverable trace 

elements (except filtered arsenic), and in FACs of suspended 

sediment (figs. 9 and 3–1, tables 6 and 3–2). The decreasing 

trends in FACs for all constituents (except filtered lead and 

arsenic) are statistically significant (tables 6 and 3–2). 

Overall, the magnitudes of the decreasing trends in FACs of 

trace elements generally are within the range of about -8 to 

-10 percent per year. The magnitudes of the decreasing trends 

in flow-adjusted specific conductance and in FACs of all 

metallic contaminants and unfiltered-recoverable arsenic for 

site 3 are larger than for any other stream site. 

Decreasing trends for Bullion Mine tributary at mouth 

(site 3) are consistent with remediation efforts in the watershed. The EPA, in partnership with the USFS, began remediation of mining wastes at the Bullion Mine during 2000 

(CH2MHILL, 2013a). About 40,900 cubic yards of mine and 

mill waste was removed and disposed at the Luttrell Repository (Unruh and others, 2009). The surface was graded and 

soils were amended and reseeded with native vegetation. 

Removal of wastes was completed in 2002. Minor to small 

decreasing trends for some metals also were determined for 

the Bullion Mine adit (site 2), which might also have contributed to the decreasing trends for site 3. Factors that contribute 

to the trends for site 2 were not determined; however, the magnitude of the trends for site 3 was larger than the magnitude 

of the trends for site 2, suggesting remediation downstream 

from site 2 probably is the major cause of the trends for site 3. 

Although FACs are decreasing for site 3, measured concentrations during water years 2009–13 exceeded all aquatic life 

standards except the lead acute aquatic life standard (table 4). 

The Bullion Mine adit discharges have been identified as the 

primary source of trace elements in the Basin Creek watershed 

(Nimick and others, 2004). A feasibility study was prepared 

for the Bullion Mine to identify potential remediation alternatives for the mine area (CH2MHILL, 2013c). 

Jack Creek at Mouth (site 4)

Trend results for Jack Creek at mouth (site 4, fig. 1, 

table 1) for water years 2000–13 indicate a minor decreasing 

trend in flow-adjusted specific conductance, moderate to large 

decreasing trends in FACs of all filtered and unfiltered-recoverable trace elements (except filtered lead and arsenic), and a 

large decreasing trend in FACs of suspended sediment (figs. 9

and 3–4, tables 6 and 3–2). The decreasing trends in FACs for 

all trace elements (except filtered lead and arsenic) and suspended sediment are statistically significant (tables 6 and 3–2). 

Overall, the magnitudes of the decreasing trends in FACs of 

trace elements generally are within the range of about -5 to 

-8 percent per year. The magnitudes of the decreasing trends 

in FACS of all metallic trace elements and unfiltered-recoverable arsenic for site 4 generally are larger than for the 

other stream sites except Bullion Mine tributary at mouth 

(site 3, fig. 1, table 1) and (for some constituents) Cataract 

Creek at Basin (site 8, fig. 1, table 1). The magnitude of the 

decreasing trend in FACs of suspended sediment for site 4 

was larger than for any other stream site in the Boulder River 

watershed.

The pattern of decreasing trends in FACs of all filtered 

and unfiltered-recoverable trace elements for Jack Creek at 

mouth (site 4) is similar to the pattern of trends for site 3, 

which indicates that remediation efforts in the Bullion Mine 

tributary watershed probably are a major cause of the trends 

for site 4. Additional removal of smelter waste and mine waste 

from the flood plain and tailings ponds in the Jack Creek 

drainage during 2003–05 (Unruh and others, 2009) also likely 

contributed to the decreasing trends. The magnitude of the 

trends for site 4 are smaller than the magnitude of the trends 

for site 3, which is a result of dilution of trace element concentrations by surface-water and groundwater inflows from areas 

with less mining effects. 
28 Water-Quality Trends for Selected Sites in the Boulder River and Tenmile Creek Watersheds, Montana

Tenmile Creek

Boulder River watershed watershed

Tenmile Creek

Boulder River watershed watershed

1

10

100

1,000

-15

-10

-5

0

10

5

-15

-10

-5

0

10

5

-15

-10

-5

0

10

5

0

100

200

300

350

0

10

5

15

0.1

1

10

100

-15

-10

-5

0

10

5

1 3 4 5 7 8 9 10 11 12 13 1 3 4 5 7 8 9 10 11 12 13

Site number (fig.1, table 1)

FIGURE 9A Percent change per year, in flow-adjusted concentration Fitted trend values for comparison period, in indicated units of measurement

Not determined (excessive censoring) Not determined (excessive censoring)

Fitted trend value at start of comparison period 

(October 1, 1999, for all sites except site 13 [March 1, 2005])

Fitted trend value at end of water year 2013 (September 30, 2013)—

Solid arrowhead denotes statistical significance

(p-value less than 0.01)

Qualitative trend

magnitude description for

comparison purposes

Large increasing

Moderate increasing

Small increasing

Small decreasing

Moderate decreasing

Large decreasing

Minor

[Water year is defined as the 12-month period from October 1 through September 30 and is designated by the year in which it ends; p-value, statistical probability level]

EXPLANATION

Denotes filtered concentrations for cadmium, copper, lead, zinc, and arsenic

Denotes unfiltered-recoverable concentrations for cadmium, copper, lead, 

zinc, and arsenic

Aquatic life standards for cadmium, copper, lead, and zinc based on median 

hardness for given site for water years 2009–13 

(Montana Department of Environmental Quality, 2012a)

Human health standard for arsenic (Montana Department of Environmental 

Quality, 2012a)

 Chronic (for zinc, identical to acute)

 Acute

Percent change per year

 in flow-adjusted concentration 

Fitted trend values for 

comparison period, 

in indicated units 

of measurement

Site number (fig.1, table 1)

Boulder River above

Jack Creek at mouth

Basin Creek at Basin

Kleinsmith Gulch

Bullion Mine tributary at mouth

Cataract Creek at Basin

Cataract Creek above Uncle Sam Gulch

High Ore Creek near Basin

Tenmile Creek near Rimini

Tenmile Creek above City Diversion

Boulder River below

Little Galena Gulch

Minnehaha Creek near Rimini

Boulder River above

Jack Creek at mouth

Basin Creek at Basin

Kleinsmith Gulch

Bullion Mine tributary at mouth

Cataract Creek at Basin

Cataract Creek above Uncle Sam Gulch

High Ore Creek near Basin

Tenmile Creek near Rimini

Tenmile Creek above City Diversion

Boulder River below 

Little Galena Gulch

Minnehaha Creek near Rimini

D. Copper (micrograms per liter)

A. Specific conductance 

(microsiemens per centimeter 

at 25 degrees Celsius)

B. Suspended sediment (milligrams per liter)

C. Cadmium (micrograms per liter)

Figure 9. Flow-adjusted water-quality trends for water years 2000–13 for the stream sites in the Boulder River and Tenmile Creek 

watersheds, Montana.
Water-Quality Trends for Selected Sites in the Boulder River and Tenmile Creek Watersheds 29

120 micrograms per liter

F. Zinc (micrograms per liter)

G. Arsenic (micrograms per liter)

13 percent

1

10

100

10,000

1,000

-15

-10

-5

0

10

5

1

10

100

1,000

-15

-10

-5

0

10

5

-15

-10

-5

0

10

5

0.1

1

10

100

1 3 4 5 7 8 9 10 11 12 13

1 3 4 5 7 8 9 10 11 12 13

Site number (fig.1, table 1)

FIGURE 9B

Percent change per year 

in flow-adjusted concentration 

Fitted trend values for 

comparison period, in indicated 

units of measurement

Percent change per year,

in flow-adjusted concentration 

Fitted trend values for 

comparison period, 

in indicated units 

of measurement

E. Lead (micrograms per liter) Not determined (excessive censoring) Not determined (excessive censoring)

Fitted trend value at start of comparison period 

(October 1, 1999, for all sites except site 13 [March 1, 2005])

Fitted trend value at end of water year 2013 (September 30, 2013)—

Solid arrowhead denotes statistical significance

(p-value less than 0.01)

Qualitative trend

magnitude description for

comparison purposes

Large increasing

Moderate increasing

Small increasing

Small decreasing

Moderate decreasing

Large decreasing

Minor

[Water year is defined as the 12-month period from October 1 through September 30 

and is designated by the year in which it ends; p-value, statistical probability level]

EXPLANATION

Denotes filtered concentrations for cadmium, copper, lead, zinc, and arsenic

Denotes unfiltered-recoverable concentrations for cadmium, copper, lead, 

zinc, and arsenic

Aquatic life standards for cadmium, copper, lead, and zinc based on median 

hardness for given site for water years 2009–13 

(Montana Department of Environmental Quality, 2012a)

Human health standard for arsenic (Montana Department of Environmental 

Quality, 2012a)

 Chronic (for zinc, identical to acute)

 Acute

Boulder River watershed

Tenmile Creek

watershed Boulder River watershed

Tenmile Creek

watershed

Site number (fig.1, table 1)

Boulder River above

Jack Creek at mouth

Basin Creek at Basin

Kleinsmith Gulch

Bullion Mine tributary at mouth

Cataract Creek at Basin

Cataract Creek above Uncle Sam Gulch

High Ore Creek near Basin

Tenmile Creek near Rimini

Tenmile Creek above City Diversion

Boulder River below

Little Galena Gulch

Minnehaha Creek near Rimini

Boulder River above

Jack Creek at mouth

Basin Creek at Basin

Kleinsmith Gulch

Bullion Mine tributary at mouth

Cataract Creek at Basin

Cataract Creek above Uncle Sam Gulch

High Ore Creek near Basin

Tenmile Creek near Rimini

Tenmile Creek above City Diversion

Boulder River below

Little Galena Gulch

Minnehaha Creek near Rimini

Figure 9. Flow-adjusted water-quality trends for water years 2000–13 for the stream sites in the Boulder River and Tenmile Creek 

watersheds, Montana.—Continued
30 Water-Quality Trends for Selected Sites in the Boulder River and Tenmile Creek Watersheds, Montana

Table 6. Summary of flow-adjusted water-quality trends for water years 2000–13 for the stream sites in the Boulder River and Tenmile 

Creek watersheds, Montana.

[Water year is the 12-month period from October 1 through September 30 and is designated by the year in which it ends. Gray shading indicates statistically 

significant (p-value less than 0.01) trend. p-value, statistical probability level; μS/cm at 25 °C, microsiemens per centimeter at 25 degrees Celsius; μg/L, micrograms per liter; mg/L, milligrams per liter; ND, not determined]

Constituent or property, 

flow-adjusted units 

of measurement

Fitted trend values Trend magnitudes1

Fitted trend value at 

start of comparison 

period 

(October 1, 1999, for 

all sites except site 13 

[March 1, 2005])

Fitted trend value 

at end of water year 

2013

Percent change 

per year 

Total percent change 

from start of comparison 

period to end of water year 

2013

Boulder River above Kleinsmith Gulch (site 1, fig. 1, table 1)

Specific conductance, μS/cm at 25 °C 109 90 -1.3 -17

Cadmium, filtered, μg/L ND2 ND2 ND2 ND2

Cadmium, unfiltered-recoverable, μg/L ND2 ND2 ND2 ND2

Copper, filtered, μg/L 2.3 1.6 -2.3 -30

Copper, unfiltered-recoverable, μg/L 3.0 1.9 -3.2 -37

Lead, filtered, μg/L ND2 ND2 ND2 ND2

Lead, unfiltered-recoverable, μg/L ND2 ND2 ND2 ND2

Zinc, filtered, μg/L 2.8 2.4 -1.1 -14

Zinc, unfiltered-recoverable, μg/L 11 6.7 -3.4 -39

Arsenic, filtered, μg/L 3.2 2.8 -1.1 -13

Arsenic, unfiltered-recoverable, μg/L 4.2 3.1 -2.0 -26

Suspended sediment, mg/L 9.4 7.5 -1.6 -20

Bullion Mine tributary at mouth (site 3, fig. 1, table 1)

Specific conductance, μS/cm at 25 °C 167 108 -2.9 -35

Cadmium, filtered, μg/L 26 7.2 -8.1 -72

Cadmium, unfiltered-recoverable, μg/L 27 7.5 -8.0 -72

Copper, filtered, μg/L 270 63 -9.1 -77

Copper, unfiltered-recoverable, μg/L 390 110 -8.2 -72

Lead, filtered, μg/L 1.8 0.82 -5.1 -54

Lead, unfiltered-recoverable, μg/L 15 2.9 -9.9 -81

Zinc, filtered, μg/L 3,100 970 -7.3 -69

Zinc, unfiltered-recoverable, μg/L 3,300 980 -7.6 -70

Arsenic, filtered, μg/L 1.4 2.2 3.5 57

Arsenic, unfiltered-recoverable, μg/L 43 11 -8.5 -74

Suspended sediment, mg/L 13 5.0 -6.3 -62

Jack Creek at mouth (site 4, fig. 1, table 1)

Specific conductance, μS/cm at 25 °C 79 76 -0.3 -3.8

Cadmium, filtered, μg/L 2.6 1.1 -6.2 -58

Cadmium, unfiltered-recoverable, μg/L 3.1 1.2 -6.8 -61

Copper, filtered, μg/L 26 11 -6.1 -58

Copper, unfiltered-recoverable, μg/L 44 16 -6.9 -64

Lead, filtered, μg/L 0.30 0.29 -0.2 -3.3

Lead, unfiltered-recoverable, μg/L 2.6 0.93 -7.3 -64

Zinc, filtered, μg/L 310 170 -4.5 -45

Zinc, unfiltered-recoverable, μg/L 350 170 -5.3 -51
Water-Quality Trends for Selected Sites in the Boulder River and Tenmile Creek Watersheds 31

Constituent or property, 

flow-adjusted units 

of measurement

Fitted trend values Trend magnitudes1

Fitted trend value at 

start of comparison 

period 

(October 1, 1999, for 

all sites except site 13 

[March 1, 2005])

Fitted trend value 

at end of water year 

2013

Percent change 

per year 

Total percent change 

from start of comparison 

period to end of water year 

2013

Jack Creek at mouth (site 4, fig. 1, table 1)—Continued

Arsenic, filtered, μg/L 4.1 3.8 -0.5 -7.3

Arsenic, unfiltered-recoverable, μg/L 13 6.7 -4.8 -48

Suspended sediment, mg/L 5.6 1.9 -7.4 -66

Basin Creek at Basin (site 5, fig. 1, table 1)

Specific conductance, μS/cm at 25 °C 73 70 -0.3 -4.1

Cadmium, filtered, μg/L 0.37 0.21 -3.8 -43

Cadmium, unfiltered-recoverable, μg/L 0.60 0.37 -3.3 -38

Copper, filtered, μg/L 5.9 4.2 -2.3 -29

Copper, unfiltered-recoverable, μg/L 7.4 5.1 -2.5 -31

Lead, filtered, μg/L 0.40 0.41 0.1 2.5

Lead, unfiltered-recoverable, μg/L 1.6 1.1 -2.7 -31

Zinc, filtered, μg/L 61 40 -2.8 -34

Zinc, unfiltered-recoverable, μg/L 69 42 -3.4 -39

Arsenic, filtered, μg/L 5.2 4.0 -1.8 -23

Arsenic, unfiltered-recoverable, μg/L 9.3 5.8 -3.2 -38

Suspended sediment, mg/L 4.6 3.1 -2.6 -33

Cataract Creek above Uncle Sam Gulch (site 7, fig. 1, table 1)

Specific conductance, μS/cm at 25 °C 85 79 -0.5 -7.1

Cadmium, filtered, μg/L 0.24 0.19 -1.7 -21

Cadmium, unfiltered-recoverable, μg/L 0.39 0.33 -1.2 -15

Copper, filtered, μg/L 5.4 3.9 -2.2 -28

Copper, unfiltered-recoverable, μg/L 6.1 4.5 -2.1 -26

Lead, filtered, μg/L 0.35 0.32 -0.6 -9

Lead, unfiltered-recoverable, μg/L 0.97 0.80 -1.3 -18

Zinc, filtered, μg/L 49 42 -1.0 -14

Zinc, unfiltered-recoverable, μg/L 52 41 -1.6 -21

Arsenic, filtered, μg/L 2.4 2.4 -0.0 0.0

Arsenic, unfiltered-recoverable, μg/L 2.9 3.0 0.1 3.4

Suspended sediment, mg/L 2.7 2.0 -2.1 -26

Cataract Creek at Basin (site 8, fig. 1, table 1)

Specific conductance, μS/cm at 25 °C 95 95 -0.0 0.0

Cadmium, filtered, μg/L 2.3 0.75 -7.1 -67

Cadmium, unfiltered-recoverable, μg/L 2.7 0.89 -7.1 -67

Copper, filtered, μg/L 23 6.7 -7.8 -71

Copper, unfiltered-recoverable, μg/L 30 8.6 -8.0 -71

Table 6. Summary of flow-adjusted water-quality trends for water years 2000–13 for the stream sites in the Boulder River and Tenmile 

Creek watersheds, Montana.—Continued

[Water year is the 12-month period from October 1 through September 30 and is designated by the year in which it ends. Gray shading indicates statistically 

significant (p-value less than 0.01) trend. p-value, statistical probability level; μS/cm at 25 °C, microsiemens per centimeter at 25 degrees Celsius; μg/L, micrograms per liter; mg/L, milligrams per liter; ND, not determined]
32 Water-Quality Trends for Selected Sites in the Boulder River and Tenmile Creek Watersheds, Montana

Constituent or property, 

flow-adjusted units 

of measurement

Fitted trend values Trend magnitudes1

Fitted trend value at 

start of comparison 

period 

(October 1, 1999, for 

all sites except site 13 

[March 1, 2005])

Fitted trend value 

at end of water year 

2013

Percent change 

per year 

Total percent change 

from start of comparison 

period to end of water year 

2013

Cataract Creek at Basin (site 8, fig. 1, table 1)—Continued

Lead, filtered, μg/L 0.49 0.55 0.8 12

Lead, unfiltered-recoverable, μg/L 2.0 1.9 -0.3 -5.0

Zinc, filtered, μg/L 220 96 -5.5 -56

Zinc, unfiltered-recoverable, μg/L 270 100 -6.1 -63

Arsenic, filtered, μg/L 3.2 3.9 1.4 22

Arsenic, unfiltered-recoverable, μg/L 7.2 5.6 -1.7 -22

Suspended sediment, mg/L 4.1 2.4 -3.7 -41

High Ore Creek near Basin (site 9, fig. 1, table 1)

Specific conductance, μS/cm at 25 °C 280 233 -1.3

-4.9

-3.6

-4.5

-17

Cadmium, filtered, μg/L 3.1 1.5 -52

Cadmium, unfiltered-recoverable, μg/L 3.9 2.3 -41

Copper, filtered, μg/L 4.3 2.2 -49

Copper, unfiltered-recoverable, μg/L 8.8 5.7 -3.0 -35

Lead, filtered, μg/L 1.3 1.1 -1.2 -15

Lead, unfiltered-recoverable, μg/L 21 14 -2.6 -33

Zinc, filtered, μg/L 820 420 -4.4 -49

Zinc, unfiltered-recoverable, μg/L 1,000 560 -3.9 -44

Arsenic, filtered, μg/L 17 23 2.1 35

Arsenic, unfiltered-recoverable, μg/L 45 41 -0.7 -9

Suspended sediment, mg/L 15 12 -1.2 -20

Boulder River below Little Galena Gulch (site 10, fig. 1, table 1)

Specific conductance, μS/cm at 25 °C 111 110 -0.1 -0.9

Cadmium, filtered, μg/L 0.45 0.20 -5.2 -56

Cadmium, unfiltered-recoverable, μg/L 0.82 0.43 -4.3 -48

Copper, filtered, μg/L 9.6 5.6 -3.6 -42

Copper, unfiltered-recoverable, μg/L 14 8.4 -3.3 -40

Lead, filtered, μg/L 0.31 0.41 2.1 32

Lead, unfiltered-recoverable, μg/L 1.7 1.5 -1.0 -12

Zinc, filtered, μg/L 68 34 -4.6 -50

Zinc, unfiltered-recoverable, μg/L 91 47 -4.3 -48

Arsenic, filtered, μg/L 4.6 4.8 0.4 4.3

Arsenic, unfiltered-recoverable, μg/L 7.7 6.5 -1.2 -16

Suspended sediment, mg/L 10 6.6 -3.0 -34

Table 6. Summary of flow-adjusted water-quality trends for water years 2000–13 for the stream sites in the Boulder River and Tenmile 

Creek watersheds, Montana.—Continued

[Water year is the 12-month period from October 1 through September 30 and is designated by the year in which it ends. Gray shading indicates statistically 

significant (p-value less than 0.01) trend. p-value, statistical probability level; μS/cm at 25 °C, microsiemens per centimeter at 25 degrees Celsius; μg/L, micrograms per liter; mg/L, milligrams per liter; ND, not determined]
Water-Quality Trends for Selected Sites in the Boulder River and Tenmile Creek Watersheds 33

Constituent or property, 

flow-adjusted units 

of measurement

Fitted trend values Trend magnitudes1

Fitted trend value at 

start of comparison 

period 

(October 1, 1999, for 

all sites except site 13 

[March 1, 2005])

Fitted trend value 

at end of water year 

2013

Percent change 

per year 

Total percent change 

from start of comparison 

period to end of water year 

2013

Tenmile Creek above City Diversion (site 11, fig. 1, table 1)

Specific conductance, μS/cm at 25 °C 52 53 0.1 1.9

Cadmium, filtered, μg/L 0.94 0.73 -1.8 -22

Cadmium, unfiltered-recoverable, μg/L 1.0 0.83 -1.6 -17

Copper, filtered, μg/L 4.8 2.9 -3.6 -40

Copper, unfiltered-recoverable, μg/L 5.8 3.4 -3.7 -41

Lead, filtered, μg/L 0.80 0.90 0.8 13

Lead, unfiltered-recoverable, μg/L 3.4 2.0 -3.5 -41

Zinc, filtered, μg/L 160 160 -0.2 0.0

Zinc, unfiltered-recoverable, μg/L 180 160 -0.8 -11

Arsenic, filtered, μg/L 3.4 4.7 2.3 38

Arsenic, unfiltered-recoverable, μg/L 6.1 6.2 0.1 1.6

Suspended sediment, mg/L 4.8 3.4 -2.4 -29

Minnehaha Creek near Rimini (site 12, fig. 1, table 1)

Specific conductance, μS/cm at 25 °C 63 58 -0.6 -8

Cadmium, filtered, μg/L 1.4 0.70 -4.5 -50

Cadmium, unfiltered-recoverable, μg/L 1.6 0.89 -4.0 -44

Copper, filtered, μg/L 7.2 5.1 -2.4 -28

Copper, unfiltered-recoverable, μg/L 9.4 5.7 -3.4 -39

Lead, filtered, μg/L 0.24 0.47 5.4 96

Lead, unfiltered-recoverable, μg/L 1.0 1.2 1.1 20

Zinc, filtered, μg/L 250 140 -3.9 -44

Zinc, unfiltered-recoverable, μg/L 270 140 -4.3 -48

Arsenic, filtered, μg/L 2.7 2.6 -0.2 -3.7

Arsenic, unfiltered-recoverable, μg/L 3.2 3.3 0.1 3.1

Suspended sediment, mg/L 3.5 3.1 -0.9 -11

Tenmile Creek near Rimini (site 13, fig. 1, table 1)

Specific conductance, μS/cm at 25 °C 96 96 0.0 0.0

Cadmium, filtered, μg/L 0.68 1.1 6.7 62

Cadmium, unfiltered-recoverable, μg/L 0.87 1.3 5.7 49

Copper, filtered, μg/L 3.6 4.2 2.1 19

Copper, unfiltered-recoverable, μg/L 5.1 5.9 1.9 16

Lead, filtered, μg/L 0.17 0.42 13 147

Lead, unfiltered-recoverable, μg/L 1.1 1.8 7.1 64

Zinc, filtered, μg/L 170 290 7.3 71

Zinc, unfiltered-recoverable, μg/L 180 290 6.1 61

Table 6. Summary of flow-adjusted water-quality trends for water years 2000–13 for the stream sites in the Boulder River and Tenmile 

Creek watersheds, Montana.—Continued

[Water year is the 12-month period from October 1 through September 30 and is designated by the year in which it ends. Gray shading indicates statistically 

significant (p-value less than 0.01) trend. p-value, statistical probability level; μS/cm at 25 °C, microsiemens per centimeter at 25 degrees Celsius; μg/L, micrograms per liter; mg/L, milligrams per liter; ND, not determined]
34 Water-Quality Trends for Selected Sites in the Boulder River and Tenmile Creek Watersheds, Montana

Basin Creek at Basin (site 5)

Trend results for Basin Creek at Basin (site 5, fig. 1, 

table 1) for water years 2000–13 indicate a minor decreasing 

trend in flow-adjusted specific conductance, small to moderate decreasing trends in FACs of all filtered and unfilteredrecoverable trace elements (except filtered lead), and a small 

decreasing trend in FACs of suspended sediment (figs. 9 and 

3–5, tables 6 and 3–2). The decreasing trends in FACs of 

all trace elements (except lead) are statistically significant 

(tables 6 and 3–2). Overall, the magnitudes of the decreasing trends in FACs of trace elements generally are within the 

range of about -2 to -4 percent per year. 

The pattern of decreasing trends in FACs of filtered and 

unfiltered-recoverable trace elements (except for unfiltered 

lead and filtered arsenic) for Basin Creek at Basin (site 5) is 

similar to the pattern of trends for Jack Creek at mouth 

(site 4) and Bullion Mine tributary at mouth (site 3), suggesting that remediation activities in the upper Basin Creek 

watershed have an effect in the lower Basin Creek watershed. 

The magnitudes of the trends for Basin Creek at Basin (site 5) 

again are smaller than trends observed for Jack Creek at mouth 

(site 4) and Bullion Mine tributary at mouth (site 3) as a result 

of further dilution with increased drainage area. 

Cataract Creek Above Uncle Sam Gulch (site 7)

Trend results for Cataract Creek above Uncle Sam Gulch 

(site 7, fig. 1, table 1) for water years 2000–13 indicate minor 

to small decreasing trends in flow-adjusted specific conductance, in FACs of all filtered and unfiltered-recoverable trace 

elements (except arsenic), and in FACs of suspended sediment 

(figs. 9 and 3–7, tables 6 and 3–2). The small decreasing 

trends for filtered and unfiltered-recoverable copper 

and unfiltered-recoverable zinc are statistically significant 

(tables 6 and 3–2). Overall, the magnitudes of the decreasing 

trends generally are within the range of about -0.5 to 

-2 percent per year, and for most trace elements these changes 

are within fairly small ranges at generally low FACs. The dataset for site 7 is somewhat dissimilar (with 2 data gaps of one 

or more years) from datasets for most other sites, which results 

in larger uncertainties in directly comparing trend results for 

site 7 with those for most other stream sites. However, trend 

results suggest that trending in trace elements and suspended 

sediment for site 7 is smaller than for most other sites.

Cataract Creek at Basin (site 8)

Trend results for Cataract Creek at Basin (site 8, fig. 1, 

table 1) for water years 2000–13 indicate a minor decreasing trend in flow-adjusted specific conductance, moderate to 

large decreasing trends in FACs of all filtered and unfilteredrecoverable trace elements (except lead and arsenic), and a 

moderate decreasing trend in FACs of suspended sediment 

(figs. 9 and 3–8, tables 6 and 3–2). The decreasing trends in 

FACs of all trace elements (except lead and arsenic) are statistically significant. Overall, the magnitudes of the decreasing 

trends in FACs of most trace elements generally are within the 

range of about -6 to -8 percent per year. The magnitudes of 

the decreasing trends in FACS of all metallic trace elements 

and suspended sediment for site 8 generally are larger than for 

most other stream sites except Bullion Mine tributary at mouth 

(site 3, fig. 1, table 1) and (for some constituents) Jack Creek 

at mouth (site 4, fig. 1, table 1). 

Table 6. Summary of flow-adjusted water-quality trends for water years 2000–13 for the stream sites in the Boulder River and Tenmile 

Creek watersheds, Montana.—Continued

[Water year is the 12-month period from October 1 through September 30 and is designated by the year in which it ends. Gray shading indicates statistically 

significant (p-value less than 0.01) trend. p-value, statistical probability level; μS/cm at 25 °C, microsiemens per centimeter at 25 degrees Celsius; μg/L, micrograms per liter; mg/L, milligrams per liter; ND, not determined]

Constituent or property, 

flow-adjusted units 

of measurement

Fitted trend values Trend magnitudes1

Fitted trend value at 

start of comparison 

period 

(October 1, 1999, for 

all sites except site 13 

[March 1, 2005])

Fitted trend value 

at end of water year 

2013

Percent change 

per year 

Total percent change 

from start of comparison 

period to end of water year 

2013

Tenmile Creek near Rimini (site 13, fig. 1, table 1)—Continued

Arsenic, filtered, μg/L 15 17 1.3 13

Arsenic, unfiltered-recoverable, μg/L 22 21 -0.3 -4.5

Suspended sediment, mg/L 5.2 1.6 -13 -69

1

Small discrepancies between trend magnitudes expressed as percent change per year and trend magnitudes expressed as total percent change are the result 

of rounding artifacts.

2

Not determined because of an excessive number of censored values (that is, greater than 50 percent of values were reported as less than the laboratory 

reporting level).
Water-Quality Trends for Selected Sites in the Boulder River and Tenmile Creek Watersheds 35

High Ore Creek Near Basin (site 9)

Trend results for High Ore Creek near Basin (site 9, 

fig. 1, table 1) for water years 2000–13 indicate a minor 

decreasing trend in flow-adjusted specific conductance, moderate decreasing trends in FACs of all filtered and unfilteredrecoverable trace elements (except lead and arsenic), and a 

small decreasing trend in FACs of suspended sediment (figs. 

9 and 3–9, tables 6 and 3–2). The decreasing trends in flowadjusted specific conductance and in FACs of filtered and 

unfiltered-recoverable cadmium, filtered copper, and filtered 

and unfiltered-recoverable zinc are statistically significant. 

Overall, the magnitudes of the decreasing trends in FACs of 

most metallic trace elements generally are within the range of 

about -3 to -5 percent per year. The dataset for site 9 is somewhat dissimilar (with a multi-year data gap) from datasets 

for most other sites, which results in larger uncertainties in 

directly comparing trend results for site 9 with those for most 

other stream sites. However, trend results suggest that trending in some trace elements and suspended sediment for site 9 

generally is intermediate with respect to most other sites.

Boulder River Below Little Galena Gulch (site 10)

Trend results for Boulder River below Little Galena 

Gulch (site 10, fig. 1, table 1) for water years 2000–13 indicate 

a minor decreasing trend in flow-adjusted specific conductance, generally moderate decreasing trends in FACs of all 

filtered and unfiltered-recoverable trace elements (except 

lead and arsenic), and a small decreasing trend in FACs of 

suspended sediment (figs. 9 and 3–10, tables 6 and 3–2). The 

trends in FACs for filtered and unfiltered-recoverable cadmium, copper, and zinc are statistically significant. Overall, 

the magnitudes of the decreasing trends in FACs of most 

metallic trace elements generally are within the range of about 

-4 to -5 percent per year. 

Summary of Trend Results for the Stream Sites in 

the Boulder River Watershed

Trend results for most stream sites in the Boulder River 

watershed for water years 2000–13 indicate decreasing trends 

in flow-adjusted specific conductance, in FACs of most filtered 

and unfiltered-recoverable trace elements, and in FACs of suspended sediment (fig. 9, table 6). Overall, magnitudes of the 

decreasing trends in FACs of metallic contaminants are largest 

for Bullion Mine tributary at mouth (site 3, fig.1, table 1), Jack 

Creek at mouth (site 4, fig. 1, table 1), and Cataract Creek 

at Basin (site 8, fig. 1, table 1). For sites 3, 4, and 8, magnitudes of decreasing trends generally ranged from about -5 to 

-10 percent per year. Notably, the watersheds upstream from 

sites 3, 4, and 8 have been targeted by substantial remediation 

activities (U.S. Environmental Protection Agency, 2014a and 

2014b).

Overall, magnitudes of decreasing trends in FACs of 

metallic contaminants are considered intermediate for Basin 

Creek at Basin (site 5, fig. 1, table 1), High Ore Creek near 

Basin (site 9, fig. 1, table 1), and Boulder River below Little 

Galena Gulch (site 10, fig. 1, table 1). For sites 5, 9, and 10, 

the magnitudes of the decreasing trends generally ranged from 

about -2 to -5 percent per year. 

Decreasing trends in FACs of metallic contaminants 

for Boulder River above Kleinsmith Gulch (site 1, fig. 1, 

table 1) and Cataract Creek above Uncle Sam Gulch (site 7, 

fig. 1, table 1) generally are minor to small (ranging from 

about -1 to -2 percent per year) and for most metallic contaminants the changes are within fairly small ranges at generally 

low FACs. The watershed of site 1 has smaller mining effects 

than most other study sites. The watersheds of site 1 and 7 

have not been targeted by substantial remediation activities.

In the Basin Creek watershed, the magnitudes of the 

decreasing trends in FACs of unfiltered-recoverable zinc 

for sites 3, 4, and 5 are -7.6, -5.3, and -3.4 percent per year, 

respectively (table 3–2). The pattern in decreasing trends in 

FACs of unfiltered-recoverable zinc among sites 3, 4, and 

5 suggests that a major cause of the trending is remediation 

activities in the watershed upstream from site 3, with dilutional reduction (that is, effects of contributions from areas 

with smaller mining effects) in trend magnitudes between the 

sites. In the Cataract Creek watershed, the magnitudes of the 

decreasing trends in FACs of unfiltered-recoverable zinc for 

sites 7 and 8 are -1.6 and -6.1 percent per year, respectively; 

the large difference between the trend magnitudes for these 

sites probably represent effects of remediation activities in or 

near Uncle Sam Gulch. Consideration of trend patterns among 

all stream sites in the Boulder River watershed provides strong 

evidence that remediation activities are the major cause of 

decreasing trends in metallic contaminants.

For most individual sites in the Boulder River watershed, 

decreasing trend magnitudes generally are similar among the 

FACs of cadmium, copper, and zinc. For most sites, trending in FACs of lead and arsenic is somewhat different from 

trending in FACs of cadmium, copper, and zinc. For most sites 

(except site 3) trending in filtered lead is minor and within 

fairly small ranges at generally low FACs (tables 6 and 3–2). 

This pattern suggests that for most stream sites in the Boulder 

River watershed, lead is so strongly adsorbed to colloidal and 

particulate materials that there is relatively small variability 

in filtered lead FACs, even in association with relatively large 

variability in FACs of other trace elements. For most sites 

(except sites 3 and 4), the magnitudes of the decreasing trends 

in FACs of unfiltered-recoverable lead are minor to small and 

less than trend magnitudes for cadmium, copper and zinc. For 

sites 3 and 4, the magnitudes of the decreasing trends in FACs 

of unfiltered-recoverable lead are large and might represent 

effects of remediation activities in the upstream watersheds.

Trend results for most sites (sites 1, 7, 8, 9, and 10; 

fig. 1, table 1) indicate minor to small increasing or decreasing 

trends in FACs of unfiltered-recoverable arsenic. Trend results 

for three sites in the Basin Creek watershed (Bullion Mine 
36 Water-Quality Trends for Selected Sites in the Boulder River and Tenmile Creek Watersheds, Montana

tributary at mouth [site 3, fig. 1, table 1], Jack Creek at mouth 

[site 4, fig. 1, table 1], and Basin Creek at Basin [site 5, fig. 1, 

table 1]) indicate moderate to large decreasing trends in FACs 

of unfiltered-recoverable arsenic. Site 3 has higher unfilteredrecoverable arsenic concentrations than any other stream site 

(except High Ore Creek near Basin [site 9, fig. 1, table 1]; 

fig. 6), probably affected by ore body characteristics of the 

Bullion Mine. The magnitudes of the decreasing trends in 

FACs of unfiltered-recoverable arsenic for sites 3, 4, and 5 are 

-8.5, -4.8, and -3.2 percent per year, respectively. The pattern 

in decreasing trends in unfiltered-recoverable arsenic among 

sites 3, 4, and 5 suggests that the major cause of the trending 

is remediation activities in the watershed upstream from site 

3, with dilutional reduction in trend magnitudes between the 

sites. Site 5 is the only site for which a statistically significant 

decreasing trend (small magnitude; -1.8 percent per year) in 

FACs of filtered arsenic is indicated. For most other sites in 

the Boulder River watershed, trends in FACs of filtered arsenic 

are either minor increasing or decreasing trends (sites 1, 4, 7, 

8, and 10) or small to moderate increasing trends (sites 3 and 

9). For site 3, the moderate increasing trend in FACs of filtered 

arsenic was within a fairly small range at generally low FACs. 

In the Boulder River watershed, site 9 has the highest arsenic 

concentrations (probably affected by the ore body characteristics of the Comet Mine and other mines in the High Ore Creek 

watershed) and also the highest pH values. For site 9, the 

small (2.1 percent per year) statistically significant increasing 

trend in FACs of filtered arsenic might be related to pH effects 

on arsenic solubility and temporal changes in pH.

Trend results for all sites in the Boulder River watershed 

indicate decreasing trends in FACs of suspended sediment. 

Trend results for two sites in the Boulder River watershed 

(Bullion Mine tributary at mouth [site 3, fig. 1, table 1] and 

Jack Creek at mouth [site 4, fig. 1, table 1])] indicate statistically significant large decreasing trends in FACs of suspended 

sediment. The decreasing trends in FACs of suspended 

sediment for sites 3 and 4 (large magnitudes of -6.3 and 

-7.4 percent per year, respectively) might represent effects of 

remediation activities in the watershed upstream from site 3. 

Stream Sites in the Tenmile Creek Watershed

Stream sites in the Tenmile Creek watershed include Tenmile Creek above City Diversion (site 11, fig. 1, table 1), Minnehaha Creek near Rimini (site 12, fig. 1, table 1), and Tenmile 

Creek near Rimini (site 13, fig. 1, table 1). For each stream 

site in the Tenmile Creek watershed, trends were analyzed for 

the period from the start of data collection through September 

2013. The detailed trend results based on the entire periods of 

record are presented in figures 3–11 through 3–13. Temporal 

characteristics of water-quality sample collection for sites 11 

and 12 generally are similar to characteristics for most sites 

in the Boulder River watershed; thus, the 14-year comparison 

period (water years 2000–13; fig. 9, table 6) used for sites in 

the Boulder River watershed also applies to sites 11 and 12 

for summaries and comparisons of trend magnitudes among 

sites. Site 13 has a much shorter data collection period (water 

years 2005–13) than any other stream site in the Boulder River 

and Tenmile Creek watersheds. Trend results for site 13 are 

presented for informational purposes in figure 9 and table 6. 

However, in figure 9 and table 6 the difference in the comparison period for site 13 and all other stream sites is specifically noted; there are large uncertainties in directly comparing 

results for site 13 with results for other sites.

Tenmile Creek Above City Diversion (site 11)

Trend results for Tenmile Creek above City Diversion 

(site 11, fig. 1, table 1) for water years 2000–13 indicate a 

minor increasing trend in flow-adjusted specific conductance, 

generally small to moderate decreasing trends in FACs of 

filtered and unfiltered-recoverable trace elements (except 

filtered lead and filtered and unfiltered-recoverable zinc and 

arsenic), and a small decreasing trend in FACs of suspended 

sediment (figs. 9 and 3–11, tables 6 and 3–2). Trend results 

for filtered lead and for filtered and unfiltered-recoverable 

zinc and arsenic indicate minor to small increasing or decreasing trends in FACs. The moderate decreasing trends in FACs 

for filtered and unfiltered-recoverable copper and the small 

increasing trend for filtered arsenic are statistically significant. 

Overall, the magnitudes of the decreasing trends in FACs of 

filtered and unfiltered-recoverable cadmium and copper and in 

unfiltered-recoverable lead generally are in the range of about 

-2 to -4 percent per year. 

Minnehaha Creek Near Rimini (site 12)

Trend results for Minnehaha Creek near Rimini 

(site 12, fig. 1, table 1) for water years 2000–13 indicate a 

minor decreasing trend in flow-adjusted specific conductance, 

small to moderate decreasing trends in FACs of most filtered 

and unfiltered-recoverable trace elements (except lead and 

arsenic), and a minor decreasing trend in FACs of suspended 

sediment (figs. 9 and 3–12, tables 6 and 3–2). The decreasing trends in flow-adjusted specific conductance and in FACs 

of filtered and unfiltered-recoverable cadmium, copper, and 

zinc are statistically significant. Overall, the magnitudes of 

the decreasing trends in FACs of most metallic trace elements 

(except lead) are in the range of about -3 to -4 percent per 

year.

Tenmile Creek Near Rimini (site 13)

Trend results for Tenmile Creek near Rimini (site 13, 

fig. 1, table 1) for water years 2005–13 indicate no trend in 

flow-adjusted specific conductance, minor to large increasing trends in FACs of most filtered and unfiltered-recoverable 

trace elements (except unfiltered-recoverable arsenic), and a 

large decreasing trend in FACs of suspended sediment (figs. 9
Water-Quality Trends for Selected Sites in the Boulder River and Tenmile Creek Watersheds 37

and 3–12, tables 6 and 3–2). The increasing trend in FACs of 

filtered lead is statistically significant; however, the indicated 

change is within a fairly small range at low FACs. In general, 

patterns in FACs for site 13 are not well represented by fitted trends within the short data collection period (fig. 3–13), 

which might indicate that the trend-analysis structure of the 

study is not appropriate for describing trends in FACs for 

site 13. The large decreasing trend in FACs of suspended 

sediment is the strongest indication of change in water quality 

during the short period of record for site 13 (figs. 9 and 3–13); 

however, this trend is not statistically significant.

Summary of Trend Results for the Stream Sites in 

the Tenmile Creek Watershed

Trend results for sites in the Tenmile Creek watershed 

generally are more variable and difficult to interpret than 

for sites in the Boulder River watershed. Trend results for 

Tenmile Creek above City Diversion (site 11, fig. 1, table 1) 

and Minnehaha Creek near Rimini (site 12, fig. 1, table 1) for 

water years 2000–13 indicate decreasing trends in FACs of 

cadmium, copper, and zinc. The magnitudes of the decreasing 

trends in FACs of copper generally are moderate and statistically significant for sites 11 and 12. The magnitudes of 

the decreasing trends in FACs of cadmium and zinc for 

site 11 are minor to small and not statistically significant; 

however, the magnitudes for site 12 are moderate and statistically significant. 

For site 11, trend results indicate a minor nonsignificant increasing trend in FACs of filtered lead and a moderate 

significant decreasing trend in FACs of unfiltered-recoverable 

lead. For site 12, trend results indicate a large significant 

increasing trend in filtered lead (but within a small range at 

low FACs) and a minor nonsignificant increasing trend in 

unfiltered-recoverable lead.

For site 11, trend results indicate a small significant 

increasing trend in FACs of filtered arsenic and a minor nonsignificant decreasing trend in FACs of unfiltered-recoverable 

arsenic. For site 12, trend results indicate minor nonsignificant 

increasing or decreasing trends in filtered and unfiltered-recoverable arsenic.

For site 11, trend results indicate a small nonsignificant 

decreasing trend in FACs of suspended sediment. For site 12, 

trend results indicate a minor nonsignificant decreasing trend 

in FACs of suspended sediment.

In general, patterns in FACs for site 13 are not well 

represented by fitted trends within the short data collection 

period (fig. 3–13), which might indicate that the trend-analysis 

structure of the study is not appropriate for describing trends 

in FACs for site 13. The large decreasing trend in FACs of suspended sediment is the strongest indication of change in water 

quality during the short period of record for site 13 (figs. 9 and 

3–13); however, this trend is not statistically significant.

Water-Quality Monitoring Considerations with 

Respect to Trend Analysis

Water-quality trend analysis for sites in the Boulder River 

and Tenmile Creek watersheds is limited by the available data. 

The datasets of the sites in the Boulder River and Tenmile 

Creek watersheds are not specifically structured for precise 

detection and quantification of water-quality trends. Several 

factors that contribute to the non-ideal and inconsistent data 

collection include the variability in funding, the priority of 

trend analysis with respect to other monitoring objectives, and 

the difficulties in site access during the fall and winter. 

To improve the capability of trend analysis in the future, 

consideration might be given to more consistent and systematic design of the program for the purpose of trend analysis. 

Specific considerations might be (1) prioritizing the program 

objectives to clarify the importance of trend analysis relative 

to other monitoring objectives, (2) prioritizing each sampling 

site with respect to overall trend analysis for the monitoring 

program, and (3) making concerted effort to provide representation of fall and winter periods in the sampling design.

Overall objectives of the monitoring program might 

include (1) evaluating compliance with water-quality standards, (2) evaluating short-term effects of specific remediation activities, (3) evaluating annual transport (loads) of 

contaminants, and (4) analyzing for long-term water-quality 

trends. Each of these objectives has different optimal sampling 

designs. For example, evaluating annual transport of contaminants would focus sampling during high-streamflow periods 

when there might be large variability in concentrations, but 

most of the annual load is transported. However, for long-term 

trend analysis, it might be appropriate to focus more sampling 

(than has been done in the past) on moderate- and low-flow 

periods when there is less variability in concentrations. During 

moderate- and low-flow periods, concentration and streamflow 

relations are representative of a substantial part of the annual 

period. Thus, the priority of long-term water-quality trend 

analysis with respect to other program objectives needs to be 

clarified to allow appropriate sampling design.

If determined that trend analysis is an important objective, consideration might be given to prioritizing each sampling site within the framework of long-term water-quality 

trend analysis for the overall monitoring program. In the Boulder River watershed, sites 3, 5, 8, and 10 (fig. 1, table 1) represent key locations for evaluation of remediation efforts and 

have the densest and most consistent datasets. For sites 3, 5, 8, 

and 10, consideration might be given to establishing a minimum within-year sampling frequency (for example, quarterly 

sampling) that has priority on an annual basis over sampling 

at other monitoring sites. Consideration also might be given 

to placing higher priority on data collection for site 1 (fig. 1, 

table 1) than was done in the past. Site 1 is an important background site that might serve as a benchmark for evaluating 

trend magnitudes of other sites. Currently (2014), dissimilarity 

between the dataset for site 1 and the datasets for most other 
38 Water-Quality Trends for Selected Sites in the Boulder River and Tenmile Creek Watersheds, Montana

sites somewhat compromises the capability of using site 1 as 

a benchmark. Further, if evaluating characteristics of annual 

transport (loads) of contaminants is an important monitoring 

objective, site 1 is a critical site. Annual load characteristics 

for site 1 are necessary as a comparison to background conditions to evaluate changes in annual load characteristics for the 

primary source areas of contaminants. 

Consideration might also be given to placing higher 

priority on sampling during the fall and winter than was done 

in the past. Constituent transport during the fall and winter 

generally accounts for relatively small parts of annual loads. 

However, for flow-adjusted trend analysis, adequate representation of the fall and winter is important to better define 

concentration and flow relations throughout the annual period. 

Site access during the fall and winter might present challenges. Therefore, consideration might be given to deployment 

of MiniSipper samplers (Chapin and Todd, 2012) specifically 

designed for unattended collection of water samples in remote 

high-elevation streams affected by mining activities.

Summary and Conclusions

In the Boulder River and Tenmile Creek watersheds in 

southwestern Montana, there was intensive mining during a 

40-year period after the discovery of gold in the early 1860s. 

Potential effects from the historic mining activities include 

acid-mine drainage and elevated concentrations of potentially 

toxic trace elements from mining remnants such as waste rock 

and tailing piles. Remediation of environmental effects of the 

mine wastes has involved coordinated efforts by multiple State 

and Federal agencies to assess the extent of contamination and 

to develop and implement remediation strategies. In support 

of the coordinated remediation efforts, water-quality monitoring by the U.S. Geological Survey (USGS) began in 1997 

in the Boulder River and Tenmile Creek watersheds and has 

continued to present (2014). The USGS, in cooperation with 

the U.S. Forest Service, investigated temporal trends in water 

quality at 13 sites, including 2 adit (or mine entrance) sites and 

11 stream sites. The primary purpose of this report is to present results of trend analysis of specific conductance, selected 

trace-elements (cadmium, copper, lead, zinc, and arsenic), and 

suspended sediment for the 13 sites. The report also presents 

background information on mining and remediation activities 

in the Boulder River and Tenmile Creek watersheds, trendanalysis methods, and factors that affect trend analysis and 

interpretation. 

For the stream sites, multiple linear regression (MLR) 

of constituent concentrations on time, streamflow, and season 

was used for trend analysis. Inclusion of streamflow in the 

MLR trend analysis provides for definition of flow-adjusted 

trends for the stream sites. For the adit sites, relations between 

constituent concentrations and streamflow were much weaker 

than for the stream sites. Thus, streamflow was not included 

in MLR trend models for the adit sites and the trend results 

represent temporal changes in unadjusted concentrations. 

For MLR, fitted trends are straight-line monotonic trends 

determined for defined trend-analysis periods. Definition of 

trend-analysis periods is affected by several factors, including the timing of data collection, temporal patterns in FACs 

(or unadjusted concentrations for the adit sites), and the study 

objectives. For the adit sites (Bullion Mine adit and Crystal Mine adit) trends were analyzed for June 2003 through 

September 2013. For each stream site, the trend-analysis 

period was from the start of data collection to the end of water 

year 2013. Variability in the start of data collection among 

the stream sites generally was small. Start times ranged from 

water years 1997–2000 for all stream sites except Tenmile 

Creek near Rimini (site 13), which had a start time of water 

year 2005. Thus, for all stream sites except site 13, the definition of trend-analysis periods provides for generally consistent 

comparison of trends among the sites. 

Ideally, water-quality analysis is done on data that was 

consistently and systematically collected within a monitoring 

network specifically designed for the purpose of trend analysis. However, the datasets for the sites in the Boulder River 

and Tenmile Creek watersheds do not represent ideal cases. 

All of the study sites have variability in within-year sampling frequency. However, among most sites the within-year 

sampling frequency was similar in individual years. Although 

the study datasets are not ideally suited for precise definition 

of temporal trends, generally strong similarity in samplecollection characteristics of the datasets among most sites 

provides a reasonable basis for relative comparisons of trend 

results among sites. Stream sites in the Boulder River watershed that have multi-year gaps in data collection are Boulder 

River above Kleinsmith Gulch (site 1), Cataract Creek above 

Uncle Sam Gulch (site 7), and High Ore Creek near Basin 

(site 9). The larger dissimilarity between the datasets for sites 

1, 7, and 9 and the datasets for most other stream sites results 

in larger uncertainties in directly comparing trend results for 

sites 1, 7, and 9 with trend results for most other stream sites. 

Also, Tenmile Creek near Rimini (site 13) has a much shorter 

sample collection period (water years 2005–13) than any other 

stream site; therefore; there might be large uncertainties in 

comparing trend results for site 13 with trend results for other 

stream sites. 

Trend results for the adit sites in the Boulder River 

watershed (Bullion Mine adit [site 2]) and Crystal Mine adit 

[site 6])) do not provide clear evidence of substantial trending during June 2003 through September 2013. Water quality 

of the adit sites probably is affected by complex processes 

that are not well defined in the study datasets. As such, the 

trend-analysis structure of the study might not be suitable for 

accurate description of temporal trends in water quality.

Trend results for most stream sites in the Boulder River 

watershed for water years 2000–13 indicate decreasing trends 

in flow-adjusted specific conductance, in flow-adjusted 

concentrations (FACs) for most filtered and unfiltered-recoverable trace elements, and in suspended sediment. Overall, 
References 39

magnitudes of the decreasing trends in FACs of metallic 

contaminants are largest for Bullion Mine tributary at mouth 

(site 3), Jack Creek at mouth (site 4), and Cataract Creek at 

Basin (site 8). For sites 3, 4, and 8, magnitudes of decreasing 

trends generally ranged from about -5 to -10 percent per year. 

Notably, the watersheds upstream from sites 3, 4, and 8 have 

been targeted by substantial remediation activities.

Overall, magnitudes of decreasing trends in FACs of 

metallic contaminants are considered intermediate for Basin 

Creek at Basin (site 5), High Ore Creek near Basin (site 9), 

and Boulder River below Little Galena Gulch (site 10). For 

sites 5, 9, and 10, the magnitudes of the decreasing trends 

generally ranged from about -2 to -5 percent per year. 

Decreasing trends in FACs of metallic contaminants for 

Boulder River above Kleinsmith Gulch (site 1) and Cataract 

Creek above Uncle Sam Gulch (site 7) generally are minor 

to small (ranging from about -1 to -2 percent per year) and 

for most metallic contaminants the changes are within fairly 

small ranges at generally low FACs. The watershed of site 1 

has smaller mining effects than most other study sites. The 

watersheds of site 1 and 7 have not been targeted by substantial remediation activities.

In the Basin Creek watershed, the magnitudes of the 

decreasing trends in FACs of unfiltered-recoverable zinc 

for sites 3, 4, and 5 are -7.6, -5.3, and -3.4 percent per year, 

respectively. The pattern in decreasing trends in FACs of unfiltered-recoverable zinc among sites 3, 4, and 5 might suggest 

that the major cause of the trending is remediation activities 

in the watershed upstream from site 3, with dilutional reduction (that is, effects of contributions from areas with smaller 

mining effects) in trend magnitudes between the sites. In the 

Cataract Creek watershed, the magnitudes of the decreasing 

trends in FACs of unfiltered-recoverable zinc for sites 7 and 8 

are -1.6 and -6.1 percent per year, respectively. The large difference between the trend magnitudes for sites 7 and 8 might 

represent effects of remediation activities in and near Uncle 

Sam Gulch. Consideration of trend patterns among all stream 

sites in the Boulder River watershed provides strong evidence 

that remediation activities are the major cause of decreasing 

trends in metallic contaminants.

For most individual sites in the Boulder River watershed, 

decreasing trend magnitudes generally are similar among the 

FACs of cadmium, copper, and zinc. For most sites, trending in FACs of lead and arsenic is somewhat different from 

trending in FACs of cadmium, copper, and zinc. For most sites 

(except site 3) trending in filtered lead is minor and within 

fairly small ranges at generally low FACs. This pattern suggests that for most stream sites in the Boulder River watershed, lead is so strongly adsorbed to colloidal and particulate 

materials that there is relatively small variability in filtered 

lead FACs, even in association with relatively large variability 

in FACs of other trace elements. For most sites (except sites 

3 and 4), the magnitudes of the decreasing trends in FACs of 

unfiltered-recoverable lead are minor to small and less than 

trend magnitudes for cadmium, copper, and zinc. For sites 

3 and 4, the magnitudes of the decreasing trends in FACs 

of unfiltered-recoverable lead are large and might represent 

effects of remediation activities in the watershed upstream 

from site 3. Trend results for most sites (sites 1, 7, 8, 9, and 

10) indicate minor to small increasing or decreasing trends in 

FACs of unfiltered-recoverable arsenic. Trend results for three 

sites in the Basin Creek watershed (Bullion Mine tributary at 

mouth [site 3]), Jack Creek at mouth [site 4]), and Basin Creek 

at Basin [site 5])) indicate moderate to large decreasing trends 

in FACs of unfiltered-recoverable arsenic. Trend results for all 

sites in the Boulder River watershed indicate decreasing trends 

in FACs of suspended sediment. 

Trend results for sites in the Tenmile Creek watershed 

generally are more variable and difficult to interpret than 

for sites in the Boulder River watershed. Trend results for 

Tenmile Creek above City Diversion (site 11) and Minnehaha 

Creek near Rimini (site 12) for water years 2000–13 indicate 

decreasing trends in FACs of cadmium, copper, and zinc. 

The magnitudes of the decreasing trends in FACs of copper 

generally are moderate and statistically significant for sites 

11 and 12. The magnitudes of the decreasing trends in FACs 

of cadmium and zinc for site 11 are minor to small and not 

statistically significant; however, the magnitudes for site 12 

are moderate and statistically significant. 

In general, patterns in FACs for site 13 are not well represented by fitted trends within the short data collection period, 

which might indicate that the trend-analysis structure of the 

study is not appropriate for describing trends in FACs for site 

13. The large decreasing trend in FACs of suspended sediment 

is the strongest indication of change in water quality during 

the short period of record for site 13; however, this trend is not 

statistically significant.

References

Browne, Mike, 2009, Vindicator, Morning, and North Ada 

mine sites removal project—Final report: U.S. Forest 

Service, Beaverhead-Deer Lodge National Forest, Dillon, 

Mont., 18 p.

CH2MHILL, 2013a, Focused remedial investigation, Bullion 

Mine, OU6, Jefferson County, Montana: Report prepared 

for U.S. Environmental Protection Agency, Region 8, Helena, Mont., 815 p.

CH2MHILL, 2013b, Focused remedial investigation, Crystal 

Mine, OU5, Jefferson County, Montana: Report prepared 

for U.S. Environmental Protection Agency, Region 8, Helena, Mont., 1612 p.

CH2MHILL, 2013c, Focused Feasibility Study, Bullion Mine, 

OU6, Jefferson County, Montana: Report prepared for U.S. 

Environmental Protection Agency, Region 8, Helena, Mont., 

227 p. 
40 Water-Quality Trends for Selected Sites in the Boulder River and Tenmile Creek Watersheds, Montana

Chapin, T.P., and Todd, A.S., 2012, MiniSipper—A new in situ 

water sampler for high-resolution, long-duration acid mine 

drainage monitoring: Science of the Total Environment, 

v. 439, p. 343–353.

Church, S.E., Nimick, D.A., Finger, S.E., and O’Neill, J.M., 

2004, The Boulder River Watershed Study, Jefferson 

County, Montana, chap. B in Nimick, D.A., Church, S.E., 

and Finger, S.E., eds., Integrated investigations of environmental effects of historical mining in the Basin and Boulder Mining Districts, Boulder River watershed, Jefferson 

County, Montana: U.S. Geological Survey Professional 

Paper 1652–B, chap. B, p. 13–28.

Cleasby, T.E., and Nimick, D.A., 2002, Streamflow, water 

quality, and quantification of metal loading in the upper 

Tenmile Creek watershed, Lewis and Clark County, westcentral Montana, September 1998: U.S. Geological Survey 

Water-Resources Investigations Report 02–4072, 64 p.

Cleveland, W.S., 1985, The elements of graphing data: Monterey, Calif., Wadsworth Books, 323 p.

Cleveland, W.S., and McGill, R., 1984, The many faces of a 

scatterplot: Journal of the American Statistical Association, 

v. 79, p. 807–822. 

Cohn, T.A., 1988, Adjusted maximum likelihood estimation of 

the moments of lognormal populations from type 1 censored 

samples: U.S. Geological Survey Open-File Report 88-350, 

34 p.

Cohn, T.A., 2005, Estimating contaminant loads in rivers–

an application of adjusted maximum likelihood to type I 

censored data: Water Resources Research, v. 41, 13 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]. 

Finger, S.E., Church, S.E., and Nimick, D.A., 2004, Evaluating the success of remediation in the Boulder River watershed, chap. F in Nimick, D.A., Church, S.E., and Finger, 

S.E., eds., Integrated investigations of environmental effects 

of historical mining in the Basin and Boulder mining districts, Boulder River watershed, Jefferson County, Montana: 

U.S. Geological Survey Professional Paper 1652–F, chap. F, 

p. 13–28.

Fishman, M.J., 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. 

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 whole-water 

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.

Gray, N.F., 1997, Environmental impact and remediation of 

acid mine drainage: a management problem: Environmental 

Geology, v. 30, no. 1-2, p. 62–71.

Granato, G.E., 2009, Computer programs for obtaining and 

analyzing daily mean streamflow data from the U.S. Geological Survey National Water Information System Web 

Site: U.S. Geological Survey Open-File Report 2008–1362, 

123 p.

Helsel, D.R., and Hirsch, R.M., 2002, Statistical methods in 

water resources: U.S. Geological Survey Techniques of 

Water-Resources Investigations, book 4, chap. A3, 522 p.

Hirsch, R.M., 1982, A comparison of four streamflow record 

extension techniques: Water Resources Research, v. 18, 

p. 1081–1088.

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 digestion of wholewater samples: U.S. Geological Survey Open-File Report 

96–225, 28 p.

Knopf, Adolph, 1913, Ore deposits of the Helena mining 

region, Montana: U.S. Geological Survey Bulletin 527, 

143 p.

Leblanc, M., Morales, J.A., Borrego, J., and Elbaz-Poulichet, 

F., 2000, 4,500-year old mining pollution in southwestern 

Spain—Long-term implications for modern mining polltion: 

Economic Geology, v. 95, no. 3, p. 655–662.

Montana Department of Environmental Quality, 2009, Montana abandoned mine lands: accessed at January 20, 2015 at 

http://www.deq.mt.gov/abandonedmines/linkdocs/210tech.

mcpx.

Montana Department of Environmental Quality, 2012, 

DEQ—7 Montana numeric water quality standards: Helena, 

Montana, Water Quality Planning Bureau, Water Quality 

Standards Section, 76 p.
References 41

Montana State University, 2014, Ecosystem Restoration–

Comet Mine Reclamation Project, Phase I: accessed 

July 22, 2014, at http://www.ecorestoration.montana.edu/

mineland/histories/metal/comet/default.htm.

Natural Resources Conservation Service, 2014, SNOTEL data: 

accessed July 22, 2014, at http://www.wcc.nrcs.usda.gov/

nwcc/rgrpt?report=precip_accum_hist&state=MT.

Nimick, D.A., Gammons, C.H., Cleasby, T.E., Madison, J.P., 

Skaar, Don, and Brick, C.M., 2003, Diel cycles in dissolved 

metal concentrations in streams—occurrence and possible 

causes: Water Resources Research, v. 39, 17 p.

Nimick, D.A., Church, S.E., and Finger, S.E., eds., 2004, Integrated investigations of environmental effects of historical 

mining in the Basin and Boulder mining districts, Boulder 

River watershed, Jefferson County, Montana: U.S. Geological Survey Professional Paper 1652, 503 p.

Nimick, D.A., Gammons, C.H., and Parker, S.R., 2011, Diel 

biogeochemical processes and their effect on the aqueous 

chemistry of streams—a review: Chemical Geology, v. 283, 

p. 3–17.

Parrett, Charles, and Kendy, Eloise, 2001, Streamflow and 

water quality of the Lower Tenmile Creek watershed, Lewis 

and Clark County, west-central Montana, 1997 and 1998: 

U.S. Geological Survey Water-Resources Investigations 

Report 01–4120, 35 p.

PRISM Climate Group, 2014, PRISM Products Matrix: 

accessed July 22, 2014, at http://www.prism.oregonstate.

edu/products/matrix.phtml?vartype=ppt&view=data.

Sando, S.K., Vecchia, A.V., Lorenz, D.L., and Barnhart, E.P., 

2014, Water-quality trends for selected sampling sits in the 

upper Clark Fork Basin, Montana, water years 1996–2010: 

U.S. Geological Survey Scientific Investigations Report 

2013–5217, 162 p.

Unruh, D.M., Church, S.E., Nimick, D.A., and Fey, D.L., 

2009, Metal contamination and post-remediation recovery 

in the Boulder River watershed, Jefferson County, Montana: 

Geochemistry: Exploration, Environment, Analysis, v. 9, 

no. 2, p. 179–199.

U.S. Environmental Protection Agency, 2002, Upper Tenmile Creek Mining Area, Record of Decision, EPA ID 

MTSFN7578012, 361 p.

U.S. Environmental Protection Agency, 2008, First five-year 

review report for upper Tenmile Creek NPL site, Lewis and 

Clark County, Montana: U.S. Environmental Protection 

Agency, Region 8, Helena, Mont., 61 p.

U.S. Environmental Protection Agency, 2014a, Bullion Mine 

Operable Unit 6—Proposed Plan: accessed July 31, 2014, 

at http://www2.epa.gov/sites/production/files/2014-03/

documents/basin-mining-area-bullion-mine-proposedplan-3-4-2014.pdf.

U.S. Environmental Protection Agency, 2014b, Crystal Mine 

Operable Unit 5—Proposed Plan: accessed July 31, 2014, 

at http://www2.epa.gov/sites/production/files/2014-03/

documents/basin-mining-area-crystal-mine-proposedplan-3-4-2014.pdf.

U.S. Environmental Protection Agency, 2014c, Upper Tenmile 

Creek Mining Area: accessed July 31, 2014, at http://www2.

epa.gov/region8/upper-tenmile-creek-mining-area.

U.S. Environmental Protection Agency, 2014d, Upper Tenmile 

Creek Mining Area: accessed July 31, 2014, at http://www.

epa.gov/superfund/accomp/factsheets04/up10.htm.

U.S. Geological Survey, 2004, Summary and conclusions from 

investigation of the effects of historical mining in the Boulder River watershed, Jefferson County, Montana, in Nimick, 

D.A., Church, S.E., and Finger, S.E., eds., Integrated investigations of environmental effects of historical mining in the 

Basin and Boulder mining districts, Boulder River watershed, Jefferson County, Montana: U.S. Geological Survey 

Professional Paper 1652-E2, chap. E2, p. 13–28.

U.S. Geological Survey, 2014a, National Hydrography Dataset: accessed July 22, 2014, at http://nhd.usgs.gov/.

U.S. Geological Survey, 2014b, USGS surface-water data for 

Montana: accessed July 22, 2014, at http://nwis.waterdata.

usgs.gov/mt/nwis/sw.

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

manual for the collection of water-quality data (ver. 2.0): 

U.S. Geological Survey Techniques of Water-Resources 

Investigations, book 9, chaps. A1–A9, [variously paged]. 

(Also available at http://pubs.water.usgs.gov/twri9A). Chapters originally were published from 1997–1999; updates and 

revisions are ongoing and are summarized at http://water.

usgs.gov/owq/FieldManual/mastererrata.html).

Woods, A.J., Omernik, J.M., Nesser, J.A., Shelden, James, 

Comstock, J.A., Azevedo, S.H., 2002, Ecoregions of 

Montana, (2d ed.): U.S. Environmental Protection Agency, 

Western Ecology Division, accessed July 22, 2014, at http://

www.epa.gov/wed/pages/ecoregions/mt_eco.htm.

Western Regional Climate Center, 2014, Montana Climate 

Summaries, Boulder, Mont., accessed July 22, 2014, at 

http://www.wrcc.dri.edu/cgi-bin/cliMAIN.pl?mt1008.

Appendixes 1–3
44 Water-Quality Trends for Selected Sites in the Boulder River and Tenmile Creek Watersheds, Montana

Appendix 1. Summary Information 

Relating to Quality-Control And WaterQuality Data 

Summary information is presented relating to quality-control 

and water-quality data. Results for quality-control equipment blank and replicate samples collected during water 

years 1997–2013 are summarized in table 1–1. Statistical 

summaries of water-quality data collected during water 

years 2009–13 are presented in table 1–2. Aquatic life standards (based on median hardness for water years 2009–13) 

are presented in table 1–3.

Appendix 1 tables can be located here: http://pubs.usgs.gov/

sir/2015/5008/downloads/sir20155008_Appendix01_tables.

pdf

Table 1–1. Summary information relating to quality-control 

samples (equipment blank and replicate samples) collected 

at sites in the Boulder River and Tenmile Creek watersheds, 

Montana, based on data collected during water years 1997–2013.

Table 1–2. Summary information relating to water-quality 

constituents and properties in samples collected at sites in the 

Boulder River and Tenmile Creek watersheds, Montana, based on 

data collected during water years 2009–13.

Table 1–3. Aquatic life standards (based on median hardness for 

water years 2009–13) for selected sites in the Boulder River and 

Tenmile Creek watersheds, based on data collected during water 

years 2009–13.

Appendix 2. Summary of Multiple 

Linear Regression as Applied in this 

Study

For the stream sites, multiple linear regression (MLR) of 

water-quality constituents on time, streamflow, and season was 

applied in this study following guidelines presented in Helsel 

and Hirsch (2002). The regression model used is represented 

by the equation:

log(Ct) = b0 + b1Tt + b2log(Qt) + b3 sin(2πTt) + b3 cosin(2πTt) + Et  

(1)

where

log denotes the base-10 logarithm;

Ct is the value of the water-quality constituent 

or property, in indicated units of 

measurement, at time t;

b0 is the intercept;

b1–b4 are the estimated slope coefficients associated 

with the various explanatory variables;

Tt is decimal time at time t;

Qt is instantaneous streamflow at the time of 

sampling, in cubic feet per second;

sin(2πTt) and cosin(2πTt) are periodic functions that describe 

seasonal variability; and

Et is an approximately normally distributed 

random error.

Use of MLR for trend analysis involves regression of 

constituent concentration (log(Ct), eq. (1)) on streamflow 

(log(Qt), eq. (1)), which inherently provides for flow adjustment and quantifies concentration and streamflow relations. 

The residuals from the regression of concentration on streamflow represent flow-adjusted concentrations (FACs; Helsel and 

Hirsch, 2002). Inclusion of periodic functions that describe 

seasonal variability sin(2πTt) and cosin(2πTt) (eq. [1]) account 

for the effect of repetitive and persistent seasonal variability 

on concentration and streamflow relations. The residuals from 

the regression of concentration on streamflow and the periodic 

functions represent changes in concentration and streamflow 

relations through the trend-analysis period. The inclusion of 

decimal time (Tt

, eq. [1]) in the model provides quantification of the change in concentration and streamflow relations 

through time and describes the temporal trend in FACs for 

the specified trend-analysis period. The slope coefficient for 

decimal time (b1, eq. [1]) is used to determine the significance 

and magnitude of the trend, in percent change in the geometric 

mean FAC per year. The null hypothesis in the test for trend 

significance is that there is no trend (that is, b1 = 0). If the twotailed p-value for b1

 is less than the selected alpha level (0.01 

in this report), the null hypothesis is rejected and the trend is 

determined to be significant. Determination of a nonsignificant 

trend (that is, a p-value > 0.01) does not imply that the null 

hypothesis is accepted (that is, that there is no trend). However, the determination of a nonsignificant trend does indicate 

that within the statistical framework of the analysis, a significant trend was not detected. The trend magnitude is calculated 

by

%∆FAC = 100(10b2 –1), (2)

where

%∆FAC is the percent change per year in the 

geometric mean of the flow adjusted 

concentration.

Application of linear regression for flow-adjusted trend 

analysis assumes that the residuals of the trend models are 

approximately normally distributed and that relations between 

the response variable (a given water-quality constituent) and 

the combined explanatory variables (time, streamflow, and 

periodic functions that describe seasonal variability) can be 

appropriately represented by a linear fit. Data for many waterquality constituents typically do not conform to a normal distribution because of positive skew (Helsel and Hirsch, 2002). 

To approximate normality, constituent concentrations and 

streamflow were transformed to logarithm (base 10) units. 
Appendix 2. Summary of Multiple Linear Regression as Applied in this Study 45

For the stream sites, streamflow was included as an 

explanatory variable in the MLR models for all site and 

constituent combinations. Ordinary least squares regressions 

of constituent concentrations on streamflow were statistically 

significant (p-value less than 0.05) for all site and constituent 

combinations except one. However, in the MLR trend models the streamflow coefficient was not statistically significant 

(p-value less than 0.05) for about 20 percent of site and constituent combinations. Concerns in including nonsignificant 

explanatory variables in regression analysis are over fitting 

the regression model, unrepresentatively decreasing the error 

of the analysis, and possibly incorrectly defining a given trend 

as significant (type I error). In all cases where the streamflow coefficient was nonsignificant, trend models that did not 

include streamflow were examined and found to have minor 

effects on the errors; in no case was a type I error indicated. 

Thus, including streamflow in models when the streamflow 

coefficient was nonsignificant had minor effect on the trend 

results.

For the adit sites, relations between constituent concentrations and streamflow were much weaker than for the stream 

sites. Streamflow for the adit sites represented groundwater 

seepage from the adits that typically was less than 0.07 cubic 

foot per second (ft3

/s) and had small variability among sampling dates. Few site and constituent combinations (less than 

about 20 percent) had concentrations that were significantly 

correlated with streamflow. The streamflow coefficient generally was not significant when streamflow was included in the 

MLR trend models during exploratory analysis. Thus, streamflow was not included in MLR trend models for the adit sites. 

The regression models for the adit sites are represented by eq. 

1 with the exclusion of the b2Qt, term.

In accounting for seasonal variability, 2π sine and cosine 

terms were included in the regression models for all site and 

constituent combinations. At least one of the periodic-function 

coefficients was statistically significant in regression models 

for most (about 70 percent) of the site and constituent combinations. During exploratory analysis, representation of seasonality was investigated by considering models that included no 

periodic functions and also models that used different multiples of π. The various models were evaluated for effects on 

the trend results. Use of the 2π terms was determined to provide the best representation of most of the datasets. Inclusion 

of periodic functions when they were not significant in the 

regression model for some site and constituent combinations 

probably had small effect on the trend-analysis results.

The effect of serial correlation on MLR results was evaluated for each site and constituent combination. Significant 

serial correlation was determined if Spearman’s correlation 

coefficient on the lag-one residuals produced a p-value less 

than 0.05 (Helsel and Hirsch, 2002). Significant serial correlation was infrequent (about 15 percent of all trend models), 

with the exception of filtered lead. For site and constituent 

combinations with significant serial correlation, trend results 

were evaluated for potential type I errors and determined to be 

unaffected by serial correlation. 

The regression model results for each site and constituent combination were evaluated by examining distributions 

of standardized residuals, standard error of estimates (SEEs), 

influence and leverage statistics, and homoscedasticity of 

residuals. For the adit sites in the Boulder River watershed, 

SEEs for trend models for filtered and unfiltered-recoverable 

metallic trace elements ranged from 13–88 percent (mean of 

40 percent), and the SEEs for trend models for filtered and 

unfiltered-recoverable arsenic ranged from 56–114 percent 

(mean of 85 percent). The SEEs for trend models for filtered 

and unfiltered-recoverable arsenic for the adit sites were larger 

than for most other site and constituent combinations, and 

conclusions based on the trend results are qualified as having 

large uncertainty. 

Statistical summaries of SEEs for the regression models 

for the stream sites in the Boulder River and Tenmile Creek 

watersheds are presented in table 2–1 (http://pubs.usgs.gov/

sir/2015/5008/downloads/sir20155008_Appendix02.table.pdf). 

The SEEs for trend models for most trace elements (cadmium, copper, zinc, and arsenic) ranged from 14–81 percent 

(mean of 33 percent). The SEEs for trend models for filtered 

and unfiltered lead ranged from 29–250 percent (mean of 

66 percent). The SEEs for trend models for filtered and 

unfiltered-recoverable lead were highly variable among the 

stream sites; conclusions based on the trend results for site and 

constituent combinations with unusually large SEEs are qualified on a case-by-case basis. The SEEs for trend models for 

suspended sediment ranged from 51–120 percent (mean of 

84 percent). The SEEs for trend models for suspended sediment were larger than for most other site and constituent 

combinations, and conclusions based on the trend results are 

qualified as having large uncertainty. 

Because of the application of a consistent regression 

model to the large number of site and constituent combinations and of practical considerations to keep the trend periods 

comparable among sites and constituents, some small deviations of the residuals from model assumptions were tolerated. 

However, the reported regression model results were judged 

to provide acceptable fits representative of linearity through 

nearly all of the ranges in FACs. For each site and constituent 

combination, the fit of the regression model can be assessed 

by examination of the fitted trends in relation to the FACs that 

are shown in figures 3–1 through 3–13. For plotting purposes, 

the FACs were determined by adding the residuals from the 

regression of concentration on streamflow to the geometric 

mean concentration for the trend-analysis period. The distribution of the FACs about the fitted trend lines indicates the 

extent to which the regression model results were affected by 

factors such as residual heteroscedasticity and curvature.

In some cases, the fitted trends within a defined trendanalysis time period do not precisely follow the patterns in 

FACs and there are short-term (typically about 2–3 years) 

trend patterns in the FACs that are unresolved in the fitted 

trends. In those cases, better temporal resolution might have 

been attained by defining two or more trend-analysis periods 

within the single defined trend-analysis period for each site. 
46 Water-Quality Trends for Selected Sites in the Boulder River and Tenmile Creek Watersheds, Montana

This approach was avoided because it would have required 

detailed case-by-case trend analysis for the large number of 

site and constituent combinations. An important consideration 

in the design of the trend-analysis structure of this study was 

the capability to make general comparisons among the sites 

and constituents with respect to evaluating potential effects 

of mining and remediation activities on a large-scale basis 

throughout consistent time periods. In some cases, when unresolved trending was apparent, more complicated trend models 

(with additional trend-analysis periods) were tested and the 

more complicated models did not change the general findings 

and conclusions of this report; that is, the overall fitted trends 

during the affected trend-analysis periods were consistent with 

overall patterns in FACs during the periods. However, examination of time-series plots of concentrations for both adit sites 

indicated somewhat inconsistent temporal patterns, with sporadic increases and decreases. Water quality of the adit sites 

probably is affected by complex processes that are not well 

defined in the study datasets. As such, the trend-analysis structure of the study might not be suitable for accurate description 

of temporal trends in water quality.

Appendix 3. Trend-Analysis Results

Appendix 3 tables can be located here: http://pubs.usgs.gov/

sir/2015/5008/downloads/sir20155008_Appendix03_tables.

pdf

Appendix 3 figures can be located here: http://pubs.usgs.gov/

sir/2015/5008/downloads/sir20155008_Appendix03_figures.

pdf

Table 3–1. Detailed water-quality trend results (not flow

adjusted) for the adit sites in the Boulder River watershed, 

Montana, based on analysis of data collected during water years 

1999–2013.

Table 3–2. Detailed flow-adjusted water-quality trend results 

for the stream sites in the Boulder River and Tenmile Creek 

watersheds, Montana, based on analysis of data collected during 

water years 1997–2013.

Figure 3–1. Flow-adjusted fitted trends for selected waterquality constituents and properties for Boulder River above 

Kleinsmith Gulch (site 1, fig. 1, table 1), based on analysis of data 

collected during water years 1997–2013.

Figure 3–2. Fitted trends (not flow adjusted) for selected waterquality constituents and properties for Bullion Mine adit (site 2, fig. 

1, table 1), based on analysis of data collected during water years 

1999–2013.

Figure 3–3. Flow-adjusted fitted trends for selected waterquality constituents and properties for Bullion Mine tributary at 

mouth (site 3, fig. 1, table 1), based on analysis of data collected 

during water years 1997–2013.

Figure 3–4. Flow-adjusted fitted trends for selected waterquality constituents and properties for Jack Creek at mouth (site 

4, fig. 1, table 1), based on analysis of data collected during water 

years 2000–13.

Figure 3–5. Flow-adjusted fitted trends for selected waterquality constituents and properties for Basin Creek at Basin (site 

5, fig. 1, table 1), based on analysis of data collected during water 

years 1997–2013.

Figure 3–6. Fitted trends (not flow adjusted) for selected waterquality constituents and properties for Crystal Mine adit (site 6, fig. 

1, table 1), based on analysis of data collected during water years 

2003–13.

Figure 3–7. Flow-adjusted fitted trends for selected waterquality constituents and properties for Cataract Creek above 

Uncle Sam Gulch (site 7, fig. 1, table 1), based on analysis of data 

collected during water years 1997–2013.

Figure 3–8. Flow-adjusted fitted trends for selected waterquality constituents and properties for Cataract Creek at Basin 

(site 8, fig. 1, table 1), based on analysis of data collected during 

water years 1997–2013.

Figure 3–9. Flow-adjusted fitted trends for selected waterquality constituents and properties for High Ore Creek near Basin 

(site 9, fig. 1, table 1), based on analysis of data collected during 

water years 1997–2013.

Figure 3–10. Flow-adjusted fitted trends for selected waterquality constituents and properties for Boulder River below Little 

Galena Gulch (site 10, fig. 1, table 1), based on analysis of data 

collected during water years 1997–2013.

Figure 3–11. Flow-adjusted fitted trends for selected waterquality constituents and properties for Tenmile Creek above 

City Diversion (site 11, fig. 1, table 1), based on analysis of data 

collected during water years 1999–2013.

Figure 3–12. Flow-adjusted fitted trends for selected waterquality constituents and properties for Minnehaha Creek near 

Rimini (site 12, fig. 1, table 1), based on analysis of data collected 

during water years 1997–2013.

Figure 3–13. Flow-adjusted fitted trends for selected waterquality constituents and properties for Tenmile Creek near Rimini 

(site 13, fig. 1, table 1), based on analysis of data collected during 

water years 2005–13.
Publishing support provided by:

Rolla Publishing Service Center

For more information concerning this publication, contact: 

Director, Wyoming-Montana Water Science Center 

U.S. Geological Survey 

3162 Bozeman Ave 

Helena, MT 59601 

(406) 457–5900

Or visit the Wyoming-Montana Water Science Center Web site at: 

http://wy-mt.water.usgs.gov/


ISSN: 2328-0328 (online)

http://dx.doi.org/10.3133/sir20155008

Sando and others—Water-Quality Trends for Selected Sites in the Boulder River and Tenmile Creek Watersheds, Montana—Scientific Investigations Report 2015–5008