U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2015–5166

Prepared in cooperation with the Idaho Department of Lands and the Midas Gold Corporation

Occurrence and Transport of Selected Constituents in

Streams near the Stibnite Mining Area, Central Idaho, 2012–14
Cover: Photograph of Glory Hole near Stibnite, Idaho, June 13, 2012. 

Photograph by Alexandra Etheridge, U.S. Geological Survey. 
Occurrence and Transport of Selected 

Constituents in Streams near the Stibnite 

Mining Area, Central Idaho, 2012–14

By Alexandra B. Etheridge

Prepared in cooperation with the Idaho Department of Lands and the 

Midas Gold Corporation

Scientific Investigations Report 2015–5166

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

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Suggested citation:

Etheridge, A.B., 2015, Occurrence and transport of selected constituents in streams near the Stibnite mining area, 

central Idaho, 2012–14: U.S. Geological Survey Scientific Investigations Report 2015–5166, 47 p., http://dx.doi.

org/10.3133/20155166.

ISSN 2328-0328 (online)
iii

Contents

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

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

Purpose and Scope ..............................................................................................................................4

Description of Study Area ............................................................................................................................4

Study Methods ...............................................................................................................................................5

Hydrologic Monitoring .........................................................................................................................5

Continuous Water-Quality Monitoring...............................................................................................5

Water-Quality Sampling and Analysis...............................................................................................6

Data Quality Assurance and Quality Control....................................................................................7

Model Development .............................................................................................................................8

LOADEST Models for Estimating Constituent Loads..............................................................8

Surrogate Regression Models for Estimating Constituent Concentrations.......................9

Calculation of Streamflow-Weighted Concentrations using LOADEST Results ........................9

Statistical Analysis of Sample Results..............................................................................................9

Ambient Water-Quality Criteria .........................................................................................................9

Streamflow and Water-Quality Monitoring ............................................................................................10

Occurrence, Transport, and Deposition of Selected Constituents......................................................14

LOAD ESTimation (LOADEST) Model Results..........................................................................................31

Streamflow Variability and Hysteresis in Particulate Constituent Transport ...........................31

Surrogate Regression Modeling of Constituent Concentrations.........................................................35

Areas of Further Study................................................................................................................................37

Summary........................................................................................................................................................37

Acknowledgments.......................................................................................................................................38

References Cited..........................................................................................................................................38

Appendix A. Analysis of Quality-Assurance and Quality-Control Data from 

Field Samples in Streams in the Stibnite Mining Area, Central Idaho, and 

Laboratory Samples from the National Water-Quality Laboratory, 2012–14 ........................43

Appendix B. Statistical Summary of Constituent Concentrations in Water-Quality 

Samples Collected at Streamflow-Gaging Stations in the Stibnite Mining Area, 

Central Idaho, 2012–14...................................................................................................................47
iv

Figures

1. Map showing streamflow-gaging stations and water-quality monitoring sites

near the Stibnite mining area, central Idaho, 2012–14 ...........................................................2

2. Hydrograph showing streamflow duration (1928–2014) and measured

streamflow at East Fork of South Fork of the Salmon River at Stibnite, central

Idaho, 2012–14 ..............................................................................................................................6

3. Hydrographs showing 50th and 90th streamflow percentiles for the periods of

record, daily mean streamflow, and timing of water-quality sample collection at

East Fork of South Fork of the Salmon River at Stibnite, central Idaho, 2012–14.............10

4. Boxplot showing total mercury concentrations in five streamflow and

water-quality monitoring sites in the Stibnite mining area, central Idaho, 2012–14 .......12

5. Graphs showing temperature exceedance for five streamflow and water-quality

monitoring sites in the Stibnite mining area, central Idaho, 2012–14 ................................13

6. Graph showing correlation between streamflow and constituent concentrations

for trace elements and suspended sediment in streams in the Stibnite mining

area, central Idaho, 2012–14.....................................................................................................15

7. Pie diagrams showing streamflow and load contributions from discrete reaches

as a percentage of total estimated streamflow and loads attributable to streams

in the Stibnite mining area, central Idaho, 2012–14 ..............................................................16

8. Diagram showing estimated mean annual total arsenic loads in streams in the

Stibnite mining area, central Idaho, 2012–14 .........................................................................17

9. Diagram showing estimated mean annual total antimony loads in streams in the

Stibnite mining area, central Idaho, 2012–14 .........................................................................18

10. Diagram showing estimated mean annual dissolved manganese loads in

streams in the Stibnite mining area, central Idaho, 2012–14...............................................19

11. Graphs showing estimated mean annual streamflow-weighted concentrations

of arsenic, antimony, and manganese in streams in the Stibnite mining area,

central Idaho, 2012–14 ...............................................................................................................24

12. Map showing locations of substantial sources of arsenic and antimony

identified along Meadow Creek, Stibnite mining area, central Idaho, September

22, 2011 .........................................................................................................................................26

13. Diagram showing estimated mean annual suspended sediment loads at

monitoring sites in the Stibnite mining area, central Idaho, 2012–14 ................................27

14. Diagram showing estimated mean annual total aluminum loads at monitoring

sites in the Stibnite mining area, central Idaho, 2012–14.....................................................28

15. Diagram showing estimated mean annual dissolved aluminum loads at

monitoring sites in the Stibnite mining area, central Idaho, 2012–14 ................................29

16. Graphs showing estimated mean annual streamflow-weighted concentrations

of aluminum, lead, and suspended sediment at monitoring sites in the Stibnite

mining area, central Idaho, 2012–14........................................................................................30

17. Graph showing sampled streamflow and total mercury concentrations in Sugar

Creek near Stibnite, central Idaho, 2012–14 ..........................................................................34
v

Tables

1. Streamflow-gaging and water-quality monitoring stations near the Stibnite

mining area, central Idaho, 2012–14..........................................................................................3

2. Exceedances of water-quality criteria in samples collected from five streamflow

and water-quality monitoring sites in the Stibnite mining area, central Idaho,

2012–14 .........................................................................................................................................11

3. Ratio of dissolved to total mean streamflow-weighted concentrations for

selected constituents at five streamflow and water-quality monitoring sites in

the Stibnite mining area, central Idaho, 2012–14 ..................................................................15

4. Estimated annual loads of selected trace elements and suspended sediment at

five streamflow and water-quality monitoring sites in the Stibnite mining area,

central Idaho, 2012–14 ...............................................................................................................20

5. Estimated streamflow-weighted concentrations of selected constituents at five

streamflow and water-quality monitoring sites in the Stibnite mining area,

central Idaho, 2012–14 ...............................................................................................................22

6. Substantial sources of arsenic and antimony identified at selected sites along

Meadow Creek, Stibnite mining area, central Idaho, September 22, 2011 .......................25

7. Regression coefficients and coefficients of determination (R2) for models used

to estimate loads of selected constituents at monitoring sites in the Stibnite

mining area, central Idaho, 2012–14........................................................................................32

8. Regression coefficients and model diagnostics for surrogate models used to

estimate concentrations of selected constituents at monitoring sites in the

Stibnite mining area, central Idaho, 2012–14 .........................................................................36
vi

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)

Area

acre 4,047 square meter (m2

)

acre 0.004047 square kilometer (km2

)

square mile (mi2

) 2.590 square kilometer (km2) 

Volume

cubic yard (yd3

) 0.7646 cubic meter (m3)

Flow rate

cubic foot per second (ft3

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

Mass

pound per day (lb/d) 0.4536 kilogram per day (kg/d)

pound per year (lb/yr) 0.4536 kilogram per year (kg/yr)

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

ton per year (ton/yr) 0.9072 metric ton per year

International System of Units to Inch/Pound

Multiply By To obtain

Length

millimeter (mm) 0.03937 inch (in.)

meter (m) 3.281 foot (ft)

meter (m) 1.094 yard (yd)

Volume

milliliter (mL) 0.033814 ounce, fluid (fl. oz)

liter (L) 0.2642 gallon (gal)

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

°F=(1.8×°C)+32.

Concentrations of chemical constituents in water are given either in milligrams per liter (mg/L) 

or micrograms per liter (μg/L).
vii

Datums

Vertical coordinate information is referenced to the North American Vertical Datum of 1988 (NAVD 88).

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

Elevation, as used in this report, refers to feet above NAVD 88.

Abbreviations

AWQC ambient water-quality criteria 

BFI base-flow index

CVO Cascades Volcano Observatory

EFSFSR East Fork of South Fork of the Salmon River

EPA U.S. Environmental Protection Agency

FWC streamflow-weighted concentration

IDEQ Idaho Department of Environmental Quality 

IBSP Inorganic Blind Sample Project

IDEQ Idaho Department of Environmental Quality

LOADEST LOAD ESTimation program

LRL laboratory reporting level

LT-MDL long-term method detection level 

MDAT maximum daily average water temperature criterion for cold-water aquatic life

MDAT-SS maximum daily average water temperature criterion for salmonid spawning

MDMT maximum daily maximum water temperature (criterion for salmonid spawning)

MWMT maximum weekly maximum water temperature criterion for bull trout habitat

MGI Midas Gold, Inc.

MLE maximum likelihood estimation method 

NWIS National Water Information System

NWQL National Water Quality Laboratory

QA/QC quality-assurance/quality-control 

QC quality-control 

R2 coefficient of determination

RMSE root mean square error

RPD relative percent difference 

SVT streamflow variability term

USFS U.S. Forest Service

USGS U.S. Geological Survey

Occurrence and Transport of Selected Constituents in 

Streams near the Stibnite Mining Area, Central Idaho, 

2012–14

By Alexandra B. Etheridge

Abstract 

Mining of stibnite (antimony sulfide), tungsten, gold, 

silver, and mercury near the town of Stibnite in central Idaho 

has left a legacy of trace element contamination in local 

streams. Water-quality and streamflow monitoring data from 

a network of five streamflow-gaging stations were used to 

estimate trace-element and suspended-sediment loads and 

flow-weighted concentrations in the Stibnite mining area 

between 2012 and 2014. Measured concentrations of arsenic 

exceeded human health-based water-quality criteria at each 

streamflow-gaging station, except for Meadow Creek (site 2), 

which was selected to represent background conditions in the 

study area. Measured concentrations of antimony exceeded 

human health-based water-quality criteria at sites 3, 4, and 5.

Regression models developed using the U.S. Geological 

Survey LOAD ESTimation (LOADEST) program showed 

that concentrated sources of arsenic and antimony are present 

in specific reaches along Meadow Creek and the East Fork 

of South Fork of the Salmon River (EFSFSR) between the 

EFSFSR at Stibnite (site 3) and the EFSFSR above Sugar 

Creek (site 4). Eighty percent of the arsenic and antimony 

loads were attributable to discrete reaches that accounted 

for 25 percent of the total streamflow in the study area. 

Streamflow was negatively correlated with arsenic and 

antimony concentrations, indicating groundwater sources. 

Continuously monitored specific conductance, alone or 

combined with continuously computed streamflow, was more 

significant than streamflow alone as a surrogate measure of 

dissolved arsenic and antimony concentrations. Surrogate 

regression models (with coefficients of determination ranging 

from 0.96 to 0.65) can be used to estimate arsenic and 

antimony concentrations in real time at all five streamflowgaging stations. 

LOADEST model simulation results indicated hysteresis 

in transport of suspended sediment and sediment-associated 

constituents. Predictor variables that account for streamflow 

variability reduced model bias and root mean square error 

when included in regression models used to estimate 

concentrations and loads of suspended sediment, total 

aluminum, total lead, and total mercury. 

 Ninety-eight percent of the estimated total mercury load 

transported downstream of the study area is attributable to 

Sugar Creek. A maximum concentration of 26 micrograms 

per liter was measured in Sugar Creek during May 2013 

when snowmelt runoff occurred during a single peak in the 

hydrograph. Monitoring and modeling results indicate sediment 

and sediment-associated constituent concentrations and loads 

increase along Meadow Creek, likely because of the inflow of 

the East Fork of Meadow Creek, and decrease between sites 

3 and 4 because the Glory Hole is trapping sediments. Sugar 

Creek (site 5) accounted for most of the sediment and sedimentassociated constituent loading leaving the study area because 

loads from the East Fork of Meadow Creek remained trapped 

in the Glory Hole. Additionally, total mercury was detected 

at all five streamflow-gaging stations, and sampled mercury 

concentrations exceeded Idaho ambient water-quality criteria at 

all five streamflow-gaging stations.

Introduction

The Stibnite mining area (study area) is in the Boise and 

Payette National Forests along the East Fork of South Fork of 

the Salmon River (EFSFSR), 14 mi southeast of Yellow Pine, 

Idaho (fig. 1). Deposits of gold, silver, mercury, antimony, 

iron, arsenic, and tungsten occur in the study area. In 2009, 

Midas Gold, Inc. (MGI) began mineral exploration activities as 

part of the Golden Meadows Exploration Project to better define 

the potential of mineral deposits in the area. The exploration 

project defined a need to evaluate existing water‐quality 

conditions in the study area and to identify potential source 

areas to target further reclamation efforts to be completed 

prior to or incorporated into plans for renewed mining 

activity. In cooperation with the Idaho Department of Lands 

and MGI, the U.S. Geological Survey (USGS) maintains and 

collects water‐quality samples at five streamflow‐gaging 

and waterquality monitoring -stations (herein referred 

to as monitoring sites) in the study area (fig. 1, table 1). 

The monitoring site at the EFSFSR at Stibnite, (site 3, 

table 1) was installed in 1928 and operated intermittently. 
2 Occurrence and Transport of Selected Constituents in Streams near the Stibnite Mining Area, Central Idaho, 2012–14

tac15-0986_fig01

Sugar Creek

Sugar Creek

Cinnabar Creek

Cane Creek

Fiddle Creek

Midnight Creek

West End Creek

Garnet Creek

Glory

Hole

Glory Hole

Reach

East Fork South Fork Sa ml on River

BOISE

NATIONAL FOREST

PAYETTE

NATIONAL FOREST

Yellow

Pine Mine

West

End

Mine

Stibnite

2

1 3

4

5

Cinnabar

Mine

Meadow

Creek

Mine

Meadow Creek

Bradley Reach

Tailings Meadow

Creek Pond

Base map modified from U.S. Geological Survey National Map,

Hydrography data from the National Hydrography Dataset, medium resolution,

Transportation data from the National Transportation Dataset.

Universal Transverse Mercator, Zone 11, North American Datum of 1983.

East Fork South Fork Salmon River

Pyramid

Creek

Meadow Creek

Hennessey Creek

East Fork Meadow

Creek

115°20' 115°16'

45°

00'

44°

56'

44°

52'

0 0.5 1 1.5 2 MILES

0 0.5 1 1.5 2 KILOMETERS

IDAHO

Study

area

Yellow Pine

EXPLANATION

Study area boundary

National forest boundary

Streamflow-gaging station, 

continuous water-quality 

monitor, and water-quality 

monitoring site No.

Fire year

1

2000

2006

2007

2006 and 2007

Figure 1. Streamflow-gaging stations and water-quality monitoring sites near the Stibnite mining area, central Idaho, 2012–14.
Introduction 3

During October 2010 the site was reinstated on a continuous 

basis. The remaining monitoring sites were installed in 

September 2011 to support the analysis of trace element 

occurrence and transport in surface water. This report 

summarizes findings from hydrologic and water-quality 

monitoring in the network of five monitoring sites in the 

Stibnite mining area during water years1 2012–14. 

Gold, antimony, mercury, and tungsten have been mined 

and processed in the study area since the early 1900s. During 

World War II, the Stibnite mining area produced 98 percent of 

the antimony and 60 percent of the tungsten for the Allied war 

effort. Mining operations took place at Meadow Creek Mine in 

the Meadow Creek valley between 1919 and 1938; at Yellow 

Pine Mine in the area surrounding the Glory Hole (a pit lake) 

between 1937 and 1952; and at West End Mine in areas near 

1

A water year is the period from October 1 of any given year to September 

30 of the following year. Water year is used almost exclusively throughout 

this report. To reduce confusion between calendar years and water years, 

all reference to years and periods in this report is to water years unless 

specifically referred to as calendar year.

Table 1. Streamflow-gaging and water-quality monitoring stations near the Stibnite mining area, central Idaho, 2012–14.

Abbreviated 

site No.

Streamflow-gaging 

and water-quality 

monitoring station

Streamflow-gaging and water-quality 

monitoring station name Continuous parameters collected Number ofwaterquality samples

1 13310800 East Fork of South Fork Salmon River above 

Meadow Creek, near Stibnite, Idaho

Continuous stage-discharge; 

seasonally continuous 

water temperature, specific 

conductance, pH

20

2 13310850 Meadow Creek near Stibnite, Idaho Continuous stage-discharge; 

seasonally continuous 

water temperature, specific 

conductance, pH

20

3 13311000 East Fork of South Fork Salmon River at 

Stibnite, Idaho

Continuous stage-discharge; 

seasonally continuous 

water temperature, specific 

conductance, pH

24

4 13311250 East Fork of South Fork Salmon River above 

Sugar Creek, near Stibnite, Idaho

Continuous stage-discharge; 

seasonally continuous 

water temperature, specific 

conductance, pH

22

5 13311450 Sugar Creek near Stibnite, Idaho Continuous stage-discharge; 

seasonally continuous 

water temperature, specific 

conductance, pH

21

West End Creek and Garnet Creek between 1982 and 1999 

(fig. 1). Cinnabar Mine was operated intermittently between 

1902 and 1966 in the Cinnabar Creek drainage, which is a 

tributary to Sugar Creek (fig. 1). 

Historical mining-related activities altered stream 

configuration and habitat in the study area. Mill tailings, 

known as the Bradley tailings, were disposed in 

impoundments covering 100 acres of the Meadow Creek 

valley floor during active mining periods. The Meadow Creek 

stream channel was diverted around tailings and reconstructed 

several times to mitigate effects on water-quality from tailings. 

A dam constructed for mining operations in the East Fork 

of Meadow Creek failed in 1965, which resulted in tailings 

and debris deposits downstream. Waste rock dumps were 

generated upstream and downstream of the Glory Hole, and 

the EFSFSR was diverted around the Glory Hole as it was 

mined prior to 1955. After 1955, the Glory Hole was allowed 

to fill with water and remains part of the EFSFSR channel 

to date. An estimated 3,000 yd3

 of mercury-laden tailings 

deposited near the Cinnabar Mine on Cinnabar Creek act as a 

substantial source of mercury in Cinnabar and Sugar Creeks 

(Trainor, 2003).
4 Occurrence and Transport of Selected Constituents in Streams near the Stibnite Mining Area, Central Idaho, 2012–14

Mining-related activities also have affected surface-water 

quality in the study area. Water-quality monitoring efforts 

historically preceded periods of renewed mining exploration 

and followed the completion of various reclamation efforts. 

A water-quality trend study conducted from 1979 to 1985 

showed large increases in turbidity and concentrations of 

arsenic, antimony, and iron after a renewed period of mining 

activity in 1982 (Klahr, 1987). Prior investigations monitoring 

water quality report concentrations of arsenic, free cyanide, 

lead, mercury, silver, and zinc exceeding chronic freshwater 

ambient water-quality criteria (AWQC) established for the 

protection of aquatic organisms in the study area (Trainor, 

1993; URS Corporation, 2000). 

Federal agencies implemented remediation efforts 

in mining-affected areas in the late 1990s. The U.S. 

Environmental Protection Agency (EPA) oversaw a 

reconstruction of the upper Meadow Creek stream channel 

that was completed in 1998 (URS Corporation, 2000). The 

U.S. Forest Service (USFS) reconstructed 4,300 ft of the 

lower Meadow Creek channel in 2005. The USFS and the 

EPA capped or removed mercury-contaminated tailings in the 

Cinnabar Mine area in 2003, and the EPA has shown renewed 

interest in remediating the Cinnabar Mine area.

The Federal Water Pollution Control Act (the “Clean 

Water Act”, 33 U.S.C §§1251–1387; see http://www.epa.gov/

oecaagct/lcwa.html) requires states to evaluate surface-water 

quality and periodically update a list of water bodies where 

beneficial uses are impaired as a result of poor water quality 

(the 303[d] list). The Idaho Department of Environmental 

Quality (IDEQ) determined that beneficial uses in the EFSFSR 

and Sugar Creek included cold-water salmonid spawning 

and primary-contact recreation. Additional beneficial uses in 

the EFSFSR include drinking-water supply for the town of 

Yellow Pine, and “special-resource water,” a classification 

indicating the need for intensive protection to preserve 

unique characteristics (Idaho Department of Environmental 

Quality, 2002). Streams in the study area are critical habitat 

for Chinook salmon (Oncorhynchus tshawytscha), steelhead 

(Oncorhynchus mykiss), bull trout (Salvelinus confluentus), 

and westslope cutthroat trout (Oncorhynchus clarki lewisi), 

which are all threatened, endangered, or sensitive species 

(Idaho Department of Environmental Quality, 2002). The 

IDEQ listed the EFSFSR as impaired for contamination of 

metals and sediment in 1998, but removed the EFSFSR from 

the 303(d) list in 2002 (Idaho Department of Environmental 

Quality, 2002). In 2012, IDEQ listed the EFSFSR and Sugar 

Creek as water-quality impaired because of concentrations 

of arsenic and antimony that exceed human health criteria 

(Idaho Department of Environmental Quality, 2014). 

IDEQ also listed Sugar Creek as water-quality impaired 

because of concentrations of mercury that exceed the Idaho 

chronic AWQC.

Purpose and Scope

This report summarizes findings from a five-station 

water-quality and hydrologic monitoring network in the 

Stibnite mining area during 2012–14. Findings will provide a 

baseline understanding of surface-water-quality conditions and 

trace-metals transport in the study area prior to future mining 

activities. Water-quality models summarized in this report 

may be used to estimate constituent loads and concentrations 

with ongoing model validation using discrete samples. The 

monitoring network was designed to provide interpretable 

results that meet the following objectives: 

• Identify and quantify contributions and transport of 

selected trace elements in discrete reaches between 

monitoring sites in the Stibnite mining area;

• Estimate the spatial and temporal variation in 

trace-metals and suspended-sediment loading and 

streamflow‐weighted concentrations in the Stibnite 

mining area; and

• Evaluate continuous water-quality parameters and 

streamflow as surrogates to estimate concentrations of 

selected constituents. 

Description of Study Area

Trace elements and sediment occurrence and transport 

were evaluated in the EFSFSR from the headwaters to the 

confluence with Sugar Creek and in the Sugar Creek watershed 

(fig. 1). The study area includes 42.9 mi2 of steep mountain 

terrain ranging from 5,930 to 9,310 ft in elevation. Seventyone percent of the study area slopes at a gradient greater 

than 30 percent (U.S. Geological Survey, 2012), resulting 

in occasional mass wasting and substantial surface erosion 

during periods of rainfall and snowmelt runoff. Mean annual 

precipitation is 31 in., falling mostly as snow between October 

and April. Peak snowmelt and streamflow typically occur 

between May and July and low flows occur from September to 

January (Kuzis, 1997). Most of the study area is comprised of 

USFS public land in the Payette and Boise National Forests. 

Mining-related activity occurs on both private and public lands. 

Wildfires in 2000, 2006, and 2007 burned about 40 percent of 

the forested land in the MGI-proposed exploration area (fig. 1). 

Recent wildfires likely resulted in increased soil erosion and 

solar loading to surface-water bodies (U.S. Forest Service, 

2012). Streams in the study area are critical habitat for Chinook 

salmon, steelhead, bull trout, and westslope cutthroat trout, 

which are all either threatened, endangered, or sensitive species 

(Idaho Department of Environmental Quality, 2002).

Mineralization and mineral extraction influence 

hydrogeology and water quality in the study area. The 

granitic Idaho batholith intruded the region in the Cretaceous 
Study Methods 5

period, leaving a roof of Neoproterozoic to Cambrian age 

metasedimentary rocks known as a roof pendant in the east 

side of the study area (Mitchell, 2000). Eocene mineralization 

occurred in a series of faults that cut through granitic and 

metasedimentary rocks, and Pleistocene glaciation deposited 

as much as 60 ft of alluvium in valley floors (Larsen and 

Livingston, 1920). During low flow conditions, streams 

in the study area generally gain streamflow from shallow 

groundwater, which is present in seeps and springs at the 

surface and ranges to depths of about 20 ft below the alluvial 

surface (URS Corporation, 2000). Depth to groundwater 

is deeper where mining waste materials have been placed. 

Groundwater also is present to a limited extent in fractured 

bedrock (Mitchell, 2000). Naturally occurring mineralized 

zones and mine tailings in contact with the water table act as 

sources of trace elements to both groundwater and surface 

water (Kuzis, 1997). Concentrations of dissolved metals are 

typically higher in groundwater than in surface water (Trainor, 

1993; URS Corporation, 2000). 

Water-quality conditions generally deteriorate in 

a downstream direction in the EFSFSR. In particular, 

concentrations of arsenic and antimony increase downstream 

of the confluence with Meadow Creek and between 

the confluences with Meadow and Sugar Creeks (URS 

Corporation, 2000). As streamflow increases in the EFSFSR, 

concentrations of sediment and sediment-associated metals 

including aluminum, iron, and mercury also increase. 

Suspended-sediment concentrations and total concentrations 

of some trace elements decrease as the EFSFSR flows 

past the Glory Hole, which acts as a sediment trap (Idaho 

Department of Environmental Quality, 2002). In May 2014, 

the Glory Hole was surveyed with a water surface elevation 

of 6,037.5 ft and a maximum depth of 35.2 ft (K. Fend, Midas 

Gold, written commun., 2014). Most surface-water-quality 

samples show similar concentrations of total and dissolved 

arsenic or antimony, indicating a groundwater source 

(URS Corporation, 2000). An negative correlation between 

streamflow and concentrations of arsenic and antimony also 

implicates groundwater as a source of arsenic and antimony 

in the study area. Concentrations of suspended sediment and 

sediment-associated metals such as aluminum and mercury 

are lower in filtered samples and higher in unfiltered samples, 

suggesting surface runoff as the largest contributing source. A 

positive correlation between streamflow and concentrations of 

suspended sediment, total aluminum, and total mercury also 

implicates surface runoff as a source of sediment, aluminum, 

and mercury in the study area. Sugar Creek is also a known 

source of mercury (Trainor, 1993; URS Corporation, 2000).

Water-quality samples and streamflow data from the 

five monitoring sites provided information necessary to 

evaluate the spatial and temporal transport of trace elements 

and suspended sediment (fig. 1, table 1). The EFSFSR 

monitoring site upstream of the confluence with Meadow 

Creek (site 1) quantifies constituent loads in the EFSFSR 

absent any loading from Meadow Creek. The monitoring site 

on Meadow Creek (site 2), upstream of the Bradley tailings 

disposal area, provided data used to quantify background 

water‐quality conditions. Site 3 is on the EFSFSR about 

1,300 ft downstream of the confluence of Meadow Creek and 

the EFSFSR, and is used to quantify source contributions 

from the East Fork of Meadow Creek (also known as Blowout 

Creek) and the Bradley tailings disposal area. Site 4 is on 

the EFSFSR about 2,660 ft downstream of the Glory Hole 

and about 700 ft upstream of the confluence with Sugar 

Creek and is used to quantify loads from ungaged tributaries, 

groundwater exchange along this reach, and the Glory Hole. 

Site 5, near the mouth of Sugar Creek, quantifies constituent 

loading from the Sugar Creek watershed including Cinnabar 

Creek, a known source of mercury contamination. Combined, 

hydrologic and water-quality data from sites 4 and 5 provide 

information on trace elements transport to the EFSFSR from 

the entire study area.

Study Methods

In October 2010 and September 2011, five monitoring 

sites were established as a network to provide information 

about trace elements and the occurrence and transport of 

suspended sediments in the study area (fig. 1). Hydrologic 

and water-quality data from each monitoring site were 

used in regression models to estimate constituent loads and 

concentrations. Estimated loads were compared between 

stations to identify source areas for trace elements and to 

quantify constituent loading in discrete reaches. 

Hydrologic Monitoring

Streamflow at the five monitoring sites and water-quality 

sampling sites (fig. 1, table 1) was measured using standard 

USGS methods as described in Mueller and Wagner (2009) 

and Turnipseed and Sauer (2010). Continuous streamflow 

records were computed using methods described in Rantz and 

others (1982). Streamflow was computed using a continuous 

record of water stage calibrated to periodic streamflow 

measurements. Monitoring sites were operated year-round.

Continuous Water-Quality Monitoring

Water temperature, specific conductance, and pH 

were measured continuously at each of the monitoring 

sites. Continuous monitors were installed at sites 1–3 in 

September 2011 and at sites 4 and 5 in April 2012. Continuous 

monitors were operated and continuous water-quality data 

were reviewed in accordance with Wagner and others (2006). 

Continuous water-quality monitors were operated seasonally 

(April to late October) and removed during the winter because 

of limited access and to prevent damage during extreme 

cold conditions. 
6 Occurrence and Transport of Selected Constituents in Streams near the Stibnite Mining Area, Central Idaho, 2012–14

Water-Quality Sampling and Analysis

Discrete water-quality samples were routinely analyzed 

for total and dissolved concentrations of aluminum, antimony, 

arsenic, cadmium, chromium, copper, iron, lead, mercury, 

and zinc. Discrete water-quality samples were also routinely 

analyzed for acid neutralizing capacity (hardness) as calcium 

carbonate, and for major ions including dissolved calcium, 

magnesium, manganese, potassium, silica, sodium, chloride, 

fluoride, and sulfate. Water-quality constituents collected in the 

field included water temperature, specific conductance, and pH.

Although the number of samples collected at each site 

varied, the approach at each site was designed to allocate 

samples over the full range of the station hydrograph to 

develop a robust relation between constituent concentration 

and streamflow. For example, samples collected at site 3 are 

plotted on the streamflow duration hydrograph to summarize 

hydrologic conditions during the sampling periods (fig. 2). 

Figure 2. Streamflow duration (1928–2014) and measured streamflow at East Fork of South Fork of the Salmon 

River at Stibnite, central Idaho, 2012–14.

● ●

●

●

●

● ●

●

●

●

●

●

● ●

●

●

●

●

●

●

●

●

1

2

5

10

20

50

100

200

500

1,000

Streamflow, in cubic feet per second

0 10 20 30 40 50 60 70 80 90 100

Percentage of time streamflow is exceeded

Daily streamflow

Sampled streamflow

EXPLANATION
Study Methods 7

Although the magnitude of measured streamflow differed 

among sites, the timing of sample collection over the 

streamflow hydrograph was similar at each site.

Water-quality samples at all sites were collected using 

nonmetallic samplers and cross-sectional, depth-integrated 

sampling procedures (U.S. Geological Survey, various dates). 

Most samples were collected isokinetically and in equal-width 

increments. However, low-streamflow conditions with shallow, 

slow moving water occasionally precluded isokinetic sample 

collection. Prior to installation of bank-operated cableways 

in October 2013, samples collected during high streamflow at 

sites 3 and 4 were collected non-isokinetically using multiple 

vertical transects. Minor variations in sample collection 

methods are documented in sample metadata stored in the 

USGS National Water Information System (U.S. Geological 

Survey, 2015). Sampling equipment was cleaned and samples 

were collected according to trace-metal protocols described 

in the USGS National Field Manual (U.S. Geological 

Survey, various dates). Samples for laboratory analyses 

were composited and subsampled using a polyethylene 

churn splitting device. Samples for whole-water recoverable 

(total) analyses were withdrawn directly from the splitting 

device. Samples for dissolved (smaller than 0.45-micrometer 

[μm] diameter) analyses were withdrawn directly from the 

churn splitter and filtered through a pre‐rinsed, 0.45-μm 

pore size, disposable capsule filter. Samples to be analyzed 

for trace elements were preserved with 2 milliliters (mL) 

of Ultrex® nitric acid. Samples to be analyzed for mercury 

were preserved with 2 mL of Omni-Trace® hydrochloric acid. 

Samples were shipped in plastic coolers to the USGS National 

Water Quality Laboratory (NWQL) in Denver, Colorado. 

All water-quality samples (excluding suspended 

sediment) were analyzed at the NWQL using established 

analytical techniques. Trace-element concentrations were 

determined at NWQL by atomic absorption spectrometry 

in conjunction with a graphite furnace and inductively 

coupled plasma-mass spectrometry (Fishman and Friedman, 

1989; Fishman, 1993; Hoffman and others, 1996; Garbarino 

and Struzeski, 1998; Garbarino and others, 2005, 2006). 

Mercury concentrations were determined by atomic 

fluorescence spectrometry (Garbarino and Damrau, 2001). 

Suspended‐sediment samples were analyzed for concentration 

and the weight percentage of particles less than 0.0625 mm by 

the USGS Cascades Volcano Observatory (CVO) Sediment 

Laboratory using methods described in Guy (1969) and the 

American Society for Testing and Materials (2002) method 

D3977-97. Quality-assurance/quality-control (QA/QC) 

procedures used at the NWQL were documented by Pritt 

and Raese (1995). The CVO Sediment Laboratory QA/QC 

procedures are described in Knott and others (1993). All 

the data collected as part of this study are publicly available 

from the USGS National Water Information System (U.S 

Geological Survey, 2015).

Data Quality Assurance and Quality Control

Water-quality sample results were reviewed after 

receipt of the laboratory analysis. Data validation included 

use of a relative percent difference (RPD) to evaluate the 

relation between dissolved concentrations and whole-water 

concentrations. RPDs were calculated using the absolute value 

of the difference between the result pair, divided by the mean 

of the result pair, multiplied by 100. Expressing precision 

relative to a mean concentration standardizes comparison of 

precision among individual constituents. Laboratory analyses 

were rerun and (or) verified when the dissolved fraction 

exceeded the whole-water fraction with an RPD greater 

than 10 percent. Suspended-sediment results were reviewed 

for anomalies in comparison with historical results at the 

same location.

Analytical data also were validated using results from 

quality-control (QC) programs in use at the NWQL. The 

NWQL monitors and evaluates quality of inorganic analytical 

results through the use of double-blind QC samples as part of 

the Inorganic Blind Sample Project (IBSP). A “double‐blind 

sample” is a QC sample submitted for analysis for which 

the identity of the sample and the concentration of the 

individual constituents within the sample are not known 

to the analyst. The QC samples typically are not synthetic 

reference materials; rather, they are derived from snowmelt, 

surface-water, or groundwater sources (Woodworth and 

Connor, 2003). Analytical errors settle into two major 

categories: bias and variability. Bias is systematic error that 

causes consistently positive or negative deviation in the 

results relative to the median expected concentration in the 

reference sample. Variability is random error that affects 

the ability to reproduce results. Repeated measurements of 

the IBSP samples over time provide estimates of systematic 

bias and random variability in the analytical procedures at 

the laboratory.

Quality-control samples also were collected in the field 

to evaluate the quality of the analytical results, and were 

analyzed concurrently in the laboratory with routine samples. 

Split replicates were collected and submitted at a proportion 

equivalent to at least 10 percent of the total number of water 

samples, and one field blank sample was collected during 

every sampling event. 

Replicate data can be obtained in different ways to 

provide an assessment of precision (reproducibility) of 

analytical results. All replicate samples collected as part of 

this study were split replicates representing a single composite 

sample collected in the field and split into two subsamples 

for separate analysis. Analyses of split replicates indicate the 

reproducibility of environmental data that are affected by 

the combined variability potentially introduced by field and 

laboratory processes. The precision of the analytical results 

was determined using the RPD between the split replicates. 

An RPD of less than 20 percent for chemical analytes was 

considered acceptable.
8 Occurrence and Transport of Selected Constituents in Streams near the Stibnite Mining Area, Central Idaho, 2012–14

Blank samples identify the presence and magnitude 

of potential contamination that could bias analytical 

results. Field blanks are aliquots of deionized water that 

are certified as contaminant free and are processed through 

the sampling equipment used to collect stream samples. 

All blanks were collected as field blanks. Field blanks are 

subjected to the same processing (sample splitting, filtration, 

preservation, transportation, and laboratory handling) as 

environmental samples. Field blanks included all sources of 

contamination associated with source-solution blanks plus 

any contamination from ambient conditions at sample sites. 

Field blanks also included any contamination from shipping 

or delivering the blanks to the analytical laboratory and 

storing, processing, and analyzing the blanks at the laboratory. 

Blank samples were analyzed for the same constituents as the 

environmental samples.

Summarized quality-assurance data analysis (appendix A) 

shows that dissolved cadmium and lead results from this 

study should be used with caution. Both analytes commonly 

were not detected at concentrations greater than the long-term 

method detection level (LT-MDL). Less frequently, dissolved 

cadmium and lead were detected near the laboratory LT-MDL 

at concentrations that did not exceed hardness-based AWQC.

Model Development

Two types of regression models were developed to 

estimate trace-metal and suspended-sediment transport and 

occurrence. The USGS LOAD ESTimator (LOADEST) 

FORTRAN program (Runkel and others, 2004; Runkel, 2013) 

was used to estimate daily and monthly loads. Estimated 

annual loads and total annual streamflow were used to 

compute streamflow-weighted concentrations (FWCs) of 

selected water-quality constituents. Surrogate regression 

models were developed using continuously monitored 

water-quality parameters, and optionally, functions of time 

and streamflow to estimate 15-minute and daily trace metal 

concentrations and loads. 

LOADEST Models for Estimating Constituent 

Loads

For this study, loads were estimated for selected 

constituents using LOADEST. The LOADEST modeling 

program is based on a rating-curve method (Cohn and others, 

1989, 1992; Crawford, 1991) that uses regression to estimate 

constituent concentrations and loads in relation to several 

predictor variables related to streamflow and time. This type 

of model has been used to estimate constituent concentrations 

for periods when sample data were not available (Gilroy and 

others, 1990), and to estimate a basin flux of water-quality 

constituents (Goolsby and others, 1999). Additional predictor 

variables describing streamflow variability were tested for 

significance in LOADEST models according to methods 

described by Garrett (2012). 

Streamflow variability terms (SVTs) were defined in 

one of two ways. The first type of SVT was defined as the 

difference between mean streamflow (Q) on day i and the 

mean streamflow of the previous k days, given as:

dQk Qj

k j i k

i

=

= −

−

∑

1 ln (1)

This variability term (dQ) with a 1-day time step (dQ1) 

helps describe effects of hysteresis (Wang and Linker, 2008). 

Hysteresis occurs when the value of a physical property 

(constituent concentration) changes at a different rate than 

the effect assumed to be causing it (streamflow). Use of a 

streamflow variability term eliminates the need to develop a 

different regression between streamflow and load on the rising 

compared to the falling limb of the hydrograph. A term with a 

30-day step (dQ30) helps describe effects of sequential events 

or prolonged event peaks. In some instances, the absolute 

value of dQ1 ( dQ1) better describes loads in the regression 

model than dQ1, representing cases where the degree of 

flashiness of the event was the critical element, rather than 

hysteresis. In some instances, use of the untransformed 

streamflow also better describes loads in the regression model 

than the use of lnQ. 

The second type of SVT used the base-flow index (BFI) 

to explain streamflow variability. The BFI describes the 

amount of streamflow in a river derived from groundwater 

discharge using a simple ratio of estimated daily runoff to 

daily mean streamflow. Runoff was estimated using the 

local minimum method of hydrograph separation (Lim and 

others, 2005; Gustard and Demuth, 2009).

LOADEST was used for this study to develop regression 

models for estimating loads of arsenic, antimony, aluminum, 

manganese, lead, cadmium, zinc, mercury, and suspended 

sediment for each site. Because of the short duration of the 

study and to facilitate comparison among sites, predictor 

variables related to trends over time were not used. Data 

collected between September 2011 and October 2014 were 

used to calibrate the regression models, and constituent loads 

were estimated for 2012–14. The equation for the regression 

models is:

ln ln ln sin

cos T

L I a Q b Q c T

d e

= + ( ) + ( ) +  ( )  



+  ( )  

 + ( ) +

2 2

2

π

π ε SVT

(2)

where 

ln is the natural logarithm;

L is the constituent load, in pounds per day;

I is the regression intercept;

Q is the centered streamflow, in cubic feet per 

second;

T is the centered decimal time in years from the 

beginning of the calibration period;
Study Methods 9

sin (2πT) and

cos (2πT) are periodic time functions that describe 

seasonal variability;

SVT is the term describing streamflow variability 

(dQk, dQ k , or BFI);

a, b, c, d, e are regression coefficients that remain 

constant over time; and

	 ε	 is the unaccounted error associated with the 

regression model.

For each model, time and streamflow predictor variables 

in the regression equation were selected on the basis of Akaike 

Information Criterion (Akaike, 1981; Judge and others, 1985). 

The criterion is designed to achieve a good compromise 

between using as many predictor variables as possible to 

explain the variance in load while minimizing the standard 

error of the resulting estimates. The streamflow variability 

predictor variable was selected based on its significance 

level. Estimates of the daily constituent load for each site 

were computed using the selected model and daily mean 

streamflow. Bias introduced by conversion of the logarithm 

of load into estimates of actual load was corrected using the 

Bradu-Mundlak method (Bradu and Mundlak, 1970; Cohn and 

others, 1989; Crawford, 1991).

Surrogate Regression Models for Estimating 

Constituent Concentrations

Multiple linear regression models were developed using 

continuously monitored water-quality parameters (surrogates) 

to estimate concentrations of dissolved arsenic, dissolved 

antimony, and total mercury at selected sites. Functions of 

time and discharge also were used as predictor variables in 

surrogate regression models if determined to be significant. 

Surrogate models were developed using stepwise linear 

regression analysis as described in Wood and Etheridge (2011) 

using the U.S. Geological Survey R statistical programming 

package “GSqwsr” (DeCicco and Corsi, 2014). The functional 

form of the surrogate models is:

C I a SC b SC c Q d Q

e T f T

= + ( ) + ( ) + + ( )

+  ( )  

 +  ( )   +

ln ( ) ln

sin c 2 2 π π os g( ) BFI (3)

where 

C is the constituent concentration, in 

micrograms per liter;

I is the y-intercept; and

a,c,...g are regression coefficients.

Surrogate models were calibrated using 15-minute values 

of continuously monitored streamflow and water-quality 

parameters in conjunction with laboratory analytical results for 

environmental samples. 

Calculation of Streamflow-Weighted 

Concentrations using LOADEST Results

Interpretation of concentrations of trace elements in 

streams is improved by examining the mean FWC spanning 

a specified time period rather than individual concentrations 

or statistics based on a dataset of individual concentrations. 

An FWC is an estimate of the mean concentration in a total 

volume of water flowing past a site during a specific period, 

such as a year, or group of years. For this study, a mean 

FWC at each site was calculated using the LOADEST result 

for a constituent load during a given water year or wateryear span divided by the total streamflow during that water 

year or water-year span. Loads and FWCs were estimated 

for each water year (2012–14) and as a mean for the 3-year 

study period.

Statistical Analysis of Sample Results

Summary statistics are provided for concentrations of 

all analyzed constituents and are compared with applicable 

ambient water-quality criteria (AWQC). Concentrations 

of total and dissolved mercury, cadmium, lead, and zinc, 

as well as dissolved manganese, were commonly lower 

than applicable LT-MDLs and LOADEST (which requires 

7 detections to compute regression estimates); could not be 

used to estimate loads; and, thus, mean FWCs could not be 

determined for these constituents at all sites in the study area. 

The maximum likelihood estimation (MLE) method was used 

to estimate summary statistics on censored sample results. 

Logarithmic transformation was used with MLE as necessary 

to normalize the distribution of censored results (Helsel, 

2012). Summary statistics were calculated from the data when 

less than 25 percent of the results were censored (Helsel and 

Hirsch, 2002).

Ambient Water-Quality Criteria 

Streamflow-weighted concentrations and (or) summary 

statistics of constituent concentrations were compared 

to applicable AWQC. Comparisons of measured AWQC 

values for trace metals are complicated because criteria 

change as a function of water hardness. For this assessment, 

chronic freshwater AWQC concentrations were based on the 

applicable State of Idaho criteria for the protection of aquatic 

life (Idaho Department of Environmental Quality, various 

dates). Representative chronic criteria values were calculated 

using the minimum hardness value measured in samples 

collected from each site. The statewide cadmium criterion is 

from Mebane (2006) and the statewide zinc criterion is from 

U.S. Environmental Protection Agency (2002).
10 Occurrence and Transport of Selected Constituents in Streams near the Stibnite Mining Area, Central Idaho, 2012–14

Streamflow and Water-Quality 

Monitoring 

Monitoring sites in the study area were established in 

September 2011 except for site 3, operated from 1928–42, 

1983–97, and 2011–14. Statistics for the 50th and 90th 

percentiles of streamflow over 32 years of record at site 3 

show that peak snowmelt runoff occurred earlier in the water 

year during the study period (fig. 3). Sample-collection timing 

shown on the hydrograph for site 3 suggests that streamflows 

at all sites likely included the 90th percentile of streamflow 

(figs. 2 and 3). Concentrations of suspended sediment and 

sediment-associated constituents generally were highest in 

the samples collected during peak streamflows in May 2013, 

possibly because snowmelt runoff in 2013 occurred as a 

single peak with higher capacity to mobilize, transport, and 

concentrate sediment near the peak of snowmelt runoff. 

Samples were collected after relatively short-duration rainfall 

runoff events in October 2011 and August 2014, but were not 

collected on the rising limb of the hydrograph for any rainfall 

runoff event.

Figure 3. 50th and 90th streamflow percentiles for the periods of record, daily mean streamflow, and timing of waterquality sample collection at East Fork of South Fork of the Salmon River at Stibnite, central Idaho, 2012–14.

0 

50 

100 

150 

200 

250 

300 

Oct. 2011 

Jan. 2012 

Apr. 2012 

July 2012 

Oct. 2012 

Jan. 2013 

Apr. 2013 

July 2013 

Oct. 2013 

Jan. 2014 

Apr. 2014 

July 2014 

Oct. 2014 

Daily mean streamflow

50th Percentile (median)

90th Percentile

Sample 

Flow percentiles based on periods of 

record 1928–42, 1983–97, and 2011–14. 

EXPLANATION

Daily mean streamflow, in cubic feet per second
Streamflow and Water-Quality Monitoring 11

Table 2. Exceedances of water-quality criteria in samples collected from five streamflow and water-quality monitoring sites in the 

Stibnite mining area, central Idaho, 2012–14.

[Site names and locations are shown in table 1 and figure 1, respectively. Applicable criteria: Criteria shown are not hardness-dependent. MDAT, maximum 

daily average water-temperature criterion for coldwater aquatic life; MDAT-SS, maximum daily average water-temperature criterion for salmonid spawning; 

MDMT, maximum daily maximum water-temperature criterion for salmonid spawning; MWMT, maximum weekly maximum water-temperature criterion 

for bull trout habitat. Criterion type: HHB, human-health based criterion; CCC, criterion continuous concentration or “chronic” aquatic-life criterion; CMC, 

criterion maximum concentration or “acute” aquatic-life criterion; CW, coldwater; SS, salmonid spawning; BT, bull trout. Abbreviations: μg/L, microgram per 

liter; °C, degrees Celcius; <, less than; NA, not applicable]

Constituent Applicable criteria Criterion

type

Site 1 Site 2 Site 3 Site 4 Site 5

Frequency of exceedance, in percent

Dissolved arsenic Minimum: 10 μg/L HHB 45 0 100 100 48

Maximum: 150 μg/L CCC 0 0 0 0 0

Number of samples NA 20 21 24 22 21

Dissolved antimony Miniumum: 5.6 μg/L HHB 0 0 87 100 30

Maximum: NA NA NA NA NA NA NA

Number of samples NA 20 18 23 21 20

Total mercury Miniumum: 0.012 μg/L CCC 43 14 46 33 95

Maximum: 2.1 μg/L CMC 0 0 0 0 11

Number of samples NA 7 7 13 15 19

Water temperature1 MDAT: 19 oC CW 0 0 0 0 0

MDAT-SS: 9 oC SS 29 32 37 47 47

MDMT: 13 oC SS < 1 < 1 9 9 4

MWMT: 13 oC BT 0 0 0 1 11

Number of 15-minute values assessed NA 53,731 51,727 52,674 51,534 49,126

1

Water-temperature data collected seasonally (April–October) every 15 minutes from each site were assessed with applicable criteria. A 7-day average was 

computed from 15-minute values and used to assess the MWMT. A daily average was computed from 15-minute values and used to assess the MDAT and 

MDAT-SS. 

Except for arsenic, antimony, and mercury, 

concentrations of trace elements in streams in the EFSFSR 

(sites 1, 3, and 4), Meadow Creek (site 2), and Sugar Creek 

(site 5) did not exceed applicable AWQC or human-health 

criteria (appendix B, table 2). Arsenic concentrations 

exceeded the human-health-based criterion of 10 μg/L in 

all samples collected in the EFSFSR at stations 3 and 4 

downstream of the confluence with Meadow Creek. Antimony 

concentrations exceeded the human-health based criterion 

of 5.6 μg/L in 87 percent of the samples collected from 

site 3 and 100 percent of the samples collected from site 4. 

Every site had at least one exceedance of the 0.012-μg/L 

chronic AWQC for total mercury, and two samples from 

site 5 exceeded the 2.1-μg/L acute AWQC for total mercury 

(table 2, fig. 4, appendix A). Concentrations of regulated trace 

elements, including cadmium, copper, and zinc, were detected 

infrequently and did not exceed the AWQC. Water-quality 

sample results for chromium were not speciated, but dissolved 

and total chromium were not detected at concentrations higher 

than hardness-dependent AWQC for hexavalent chromium. 
12 Occurrence and Transport of Selected Constituents in Streams near the Stibnite Mining Area, Central Idaho, 2012–14

tac15-0986_fig04

Site1 Site 2 Site 3 Site 4 Site 5

1×10−3

1×10−2

1×10−1

1×100

1×101

1×102

7 7 13 15 19

EXPLANATION

Number of samples

90th percentile

75th percentile

50th percentile

(median)

25th percentile

10th percentile

 Censoring level

 Maximum or minimum

Acute exposure ambient water-quality criterion = 

2.1 micrograms per liter

Chronic exposure ambient water-quality 

criterion = 0.012 micrograms per liter

Total mercury concentration, in micrograms per liter

19

Figure 4. Total mercury concentrations in five streamflow and water-quality monitoring sites in the 

Stibnite mining area, central Idaho, 2012–14. Site names and locations are shown in table 1 and figure 1, 

respectively.

Continuous measurements of stream temperature and pH 

showed few exceedances of applicable State-of-Idaho general 

water-quality criteria (Idaho Department of Environmental 

Quality, various dates). pH was greater than the general 

minimum criterion of 6.5 and less than the general maximum 

criterion of 9.0 at all of the sites. 

Applicable salmonid spawning criteria in the South 

Fork of the Salmon River and its tributaries apply to seasonal 

periods between March 15 and July 1 for spring spawning 

salmonids (steelhead), and between August 15 and June 1 

of the following year for autumn-spawning salmonids 

(Chinook salmon) (Idaho Department of Environmental 

Quality, 2012). Therefore, seasonal salmonid spawning 

criteria apply during a substantial part of the year because of 

the presence of both spring and autumn salmonid spawners. 

Continuous water‐temperature data collected from late 

April to late October during 2012–14 showed that water 

temperature exceeded the 9 °C maximum daily average 

temperature criterion for salmonid spawning (MDAT-SS) at 

least 29 percent of the time at all sites (table 2, fig. 5). Water 

temperature at sites 3 and 4 in the EFSFSR and site 5 in 

Sugar Creek exceeded the 13 oC maximum daily maximum 

temperature (MDMT) criterion for salmonid spawning 

between 4 and 9 percent of the time (table 2, fig. 5). 
Streamflow and Water-Quality Monitoring 13

tac15-0986_fig05

MDAT

MDMT/MWMT

MDAT-SS

MDAT

MDMT/MWMT

MDAT-SS

MDAT

MDMT/MWMT

MDAT-SS

MDAT

MDMT/MWMT

MDAT-SS

MDAT

MDMT/MWMT

MDAT-SS

MDAT

MDMT

MWMT

MDAT-SS

EXPLANATION

15-minute temperature values (used to assess MDMT)

7-day moving average of 15-minute values (used to 

assess MWMT) 

Daily average temperature values recorded (used to 

assess MDAT and MDAT-SS) 

Criterion:

Maximum daily average water temperature (MDAT) for 

coldwater aquatic life = 19 oC

Maximum daily maximum water temperature (MDMT) for 

salmonid spawning = 13 oC

Maximum weekly maximum water temperature (MWMT) for 

bull trout habitat = 13 oC

Maximum daily average water temperature (MDAT-SS) for 

salmonid spawning = 9 oC

Site 1 exceedances: 

MDAT-SS: 29 percent

MDMT: <1 percent

 0

 2

 4

 6

 8

10

12

14

16

18

20

Water temperature, in degrees Celsius

 0

 2

 4

 6

 8

10

12

14

16

18

20

Water temperature, in degrees Celsius

 0

 2

 4

 6

 8

10

12

14

16

18

20

Water temperature, in degrees Celsius

 0

 2

 4

 6

 8

10

12

14

16

18

20

Water temperature, in degrees Celsius

 0

 2

 4

 6

 8

10

12

14

16

18

20

Water temperature, in degrees Celsius

C. Site 3

E. Site 5

A. Site 1

D. Site 4

B. Site 2

 0 20 40 60 80 100

Percentage of time water temperature is exceeded

 0 20 40 60 80 100

Percentage of time water temperature is exceeded

Site 2 exeedances:

MDAT-SS: 32 percent 

MDMT: <1 percent 

Site 3 exceedances:

MDAT-SS: 37 percent 

MDMT: 9 percent

Site 4 exceedances:

MDAT-SS: 47 percent 

MDMT: 9 percent

MWMT: 1 percent

Site 5 exceedances:

MDAT-SS: 47 percent 

MDMT: 4 percent

Figure 5. Temperature exceedance for five streamflow and water-quality monitoring sites in the Stibnite mining area, central 

Idaho, 2012–14. Site names and locations are shown in table 1 and figure 1, respectively.
14 Occurrence and Transport of Selected Constituents in Streams near the Stibnite Mining Area, Central Idaho, 2012–14

Occurrence, Transport, and Deposition 

of Selected Constituents

Occurrence and transport of trace elements and suspended 

sediment in the Stibnite mining area depend on constituent 

source. Groundwater sources seem to control concentrations 

and loading of dissolved and total arsenic, dissolved and total 

antimony, dissolved manganese, and dissolved iron, whereas 

erosion and overland runoff control concentrations and loading 

of suspended sediment and sediment-associated constituents 

including aluminum, lead, and mercury. Ratios of dissolved 

to total estimated FWCs of arsenic and antimony are close 

to 1 in the EFSFSR, indicating that they are primarily in the 

dissolved phase, and probably are derived from groundwater 

sources (table 3). Negative correlations between streamflow 

and concentrations of total and dissolved arsenic, total and 

dissolved antimony, dissolved manganese, and dissolved iron 

also suggest groundwater sources for these constituents in the 

Meadow Creek and (or) Glory Hole reaches (figs. 1 and 6). 

Ratios of dissolved to total estimated FWCs of lead and 

aluminum are relatively low, and concentrations of aluminum, 

lead, mercury, total iron, and suspended sediment are 

positively correlated with streamflow, indicating surface and 

stream channel erosion as sources (table 3, fig. 6). LOADEST 

models were not used to estimate annual loads or FWCs of 

cadmium, chromium, copper, and zinc because of a low rate of 

detection throughout the study area and the requirement of at 

least seven uncensored values to calibrate LOADEST models 

(appendix A). Laboratory analytical results for dissolved 

antimony often were slightly higher than for total antimony, 

resulting in ratios of greater than 1 for FWCs of dissolved to 

total antimony. When this occurred, ratios were rounded down 

to 1 in table 3. Total manganese was not analyzed in waterquality samples.

Estimated annual loads and FWCs for each site indicate 

that the Glory Hole reach between sites 3 and 4 (fig. 1) 

is the primary source of arsenic, antimony, and dissolved 

manganese in the study area (figs. 7–11, tables 4 and 5). On 

average, the Glory Hole reach contributed only 10 percent of 

the streamflow, but contributed 52 percent of total arsenic, 

53 percent of total antimony, and 42 percent of the dissolved 

manganese loads attributable to streams in the study area 

(fig. 7). The Meadow Creek reach was the second largest 

source of arsenic, antimony, and dissolved manganese. On 

average, the Meadow Creek reach contributed only 15 percent 

of the streamflow, but 28 percent of total arsenic, 37 percent 

of total antimony, and 44 percent of the dissolved manganese 

loads attributable to streams in the study area (fig. 7). Mean 

estimated FWCs exceed human-health criteria for arsenic 

at sites 3, 4 and 5 and antimony at sites 3 and 4. Based on 

incremental changes in the streamflow between sites and the 

loads of arsenic, antimony, and dissolved manganese between 

sites, a mean FWC of sources to the reach can be estimated. 

Estimated FWCs from the Glory Hole reach and the Meadow 

Creek reach indicate that those reaches have much higher 

concentrations compared to the monitoring sites immediately 

downstream (fig. 11). Water-quality samples were collected at 

numerous locations along the Meadow Creek reach between 

sites 2 and 3 on September 22, 2011, in an effort to identify 

sources of arsenic and antimony to Meadow Creek. Five 

samples collected at discrete sampling sites on September 22, 

2011 (as opposed to regularly collected samples from 

monitoring sites) showed substantially higher concentrations 

and loads of arsenic or antimony relative to concentrations 

and loads measured at the adjacent upstream location (table 6, 

fig. 12). Results from all samples collected along Meadow 

Creek on September 22, 2011, are available from the USGS 

National Water Information System (U.S. Geological 

Survey, 2015).

Estimated annual loads and FWCs of suspended 

sediment, total aluminum, and total lead generally increased 

between sites 1 and 3 and decreased between sites 3 and 4, 

with the Glory Hole acting as a sediment trap (figs. 7, 13, 14, 

and 16; tables 4 and 5; appendix B). Although not sampled as 

part of this study, the East Fork Meadow Creek (fig. 1) likely 

is the source of suspended sediment and total aluminum load 

entering the Meadow Creek reach. The East Fork Meadow 

Creek is the only surface-water tributary to Meadow Creek 

capable of carrying a sediment (and sediment-associated 

constituent) load. The Meadow Creek reach contributed more 

sediment than Sugar Creek (site 5), but most of the sediment 

load discharged from the Meadow Creek reach was deposited 

in the Glory Hole (figs. 7 and 13). The FWCs of suspended 

sediment at sites 1 and 2 were less than 10 mg/L. However, 

the incremental gain between sites 1 and 2 downstream to 

site 3 indicates that the sources of suspended sediment to the 

Meadow Creek reach had a mean FWC of 78 mg/L (fig. 16C). 

The mean FWC of suspended sediment for 2012–14 at site 

3 was nearly 4 times higher than the corresponding FWC of 

suspended sediment at site 4 (table 5). Load models show that 

about 90 percent of the coarse-grained sediment (>0.0625 mm 

in diameter) load at site 3 was deposited in the Glory Hole; 

however, about 82 percent of the fine-grained sediment 

(<0.0625 mm in diameter) load at site 3 was transported 

through the Glory Hole downstream to site 4 (table 4). 
Occurrence, Transport, and Deposition of Selected Constituents 15

Table 3. Ratio of dissolved to total mean streamflow-weighted 

concentrations for selected constituents at five streamflow and waterquality monitoring sites in the Stibnite mining area, central Idaho, 2012–14.

[Site names and locations are shown in table 1 and figure 1, respectively. Ratios are 

unitless. Abbreviations: FWC, streamflow-weighted concentration; NA, not applicable]

Constituent

Ratio of dissolved to total mean FWC 2012–14

Site 1 Site 2 Site 3 Site 4 Site 5

Arsenic 0.96 0.67 0.97 0.93 0.88

Antimony 1.00 1.00 0.97 1.00 1.00

Lead NA NA 0.11 0.30 0.20

Aluminum 0.23 0.12 0.08 0.13 0.08

Mercury, total 

Mercury, dissolved 

Iron, total 

Suspended sediment 

Aluminum, total 

Aluminum, dissolved 

Lead, total 

Lead, dissolved 

Site 1 

Site 2 

Site 3 

Site 4 

Site 5 

Arsenic, dissolved 

Arsenic, total 

Antimony, dissolved 

Antimony, total 

Manganese, dissolved 

Iron, dissolved 

No bar is shown for 

constituents not 

significantly correlated 

with streamflow. 

EXPLANATION 

-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 

Statistically significant (p < 0.01) Spearman's rho correlation coefficients between streamflow and concentration, dimensionless 

Figure 6. Correlation between streamflow and constituent concentrations for trace elements and suspended sediment in streams in 

the Stibnite mining area, central Idaho, 2012–14. Site names and locations are shown in table 1 and figure 1, respectively.
16 Occurrence and Transport of Selected Constituents in Streams near the Stibnite Mining Area, Central Idaho, 2012–14

tac15-0986_fig07

28% 

52% 

14% 

6% 

Total arsenic 

37% 

53% 

8% 

Total antimony 2% 

44% 

42% 

8% 6% 

Dissolved manganese 

13% 5% 

41% 

41% 

Dissolved aluminum 

30% 

-17% 35% 

18% 

Total aluminum 

33% 

-32% 

23% 

12% 

Suspended sediment 

38% 

-11% 

31% 

20% 

Fine sediment 

32% 

-37% 

19% 

10% 

Coarse sediment 

98% 

Total mercury 2% 

Sites 1 and 2 combined

Meadow Creek Reach

Glory Hole Reach

Glory Hole Reach (losses)

Sources upstream of Site 4

Site 5 (Sugar Creek) 

EXPLANATION 15% 

10% 

39% 

36% 

Streamflow 

Figure 7. Streamflow and load contributions from discrete reaches as a percentage of total estimated streamflow and 

loads attributable to streams in the Stibnite mining area, central Idaho, 2012–14.
Occurrence, Transport, and Deposition of Selected Constituents 17

tac15-0986_fig08

Glory 

Hole

Glory Hole Reach

Meadow Creek Reach

1,180

2,150

30.5

1,430

3,580

598 217

Relative location and site No. 

Less than 50 pounds per year

51 to 500 pounds per year

501 to 1,500 pounds per year

1,501 to 5,000 pounds per year

Stream

Mean annual total arsenic load, in pounds, for water years 2012–14

EFSFSR

Meadow Creek

Sugar Creek

Notes:

Purple circles represent estimated loads at each monitoring site. 

Orange circles indicate relative location of loads attributable to 

 discrete reaches between monitoring sites. 

Ungaged tributaries are not shown. 

EFSFSR, East Fork of South Fork of the Salmon River.

EFSFSR

General flow direction

EXPLANATION

1,430

1

5

4 3

2

1

Figure 8. Estimated mean annual total arsenic loads in streams in the Stibnite mining area, central Idaho, 2012–14. Site names 

and locations are shown in table 1 and figure 1, respectively.
18 Occurrence and Transport of Selected Constituents in Streams near the Stibnite Mining Area, Central Idaho, 2012–14

tac15-0986_fig09

Glory Hole Reach

Meadow Creek Reach

716

1,010

7.95 1,760

159

EXPLANATION

Relative location and site No. 

Less than 50 pounds per year

51 to 500 pounds per year

501 to 1,500 pounds per year

1,501 to 5,000 pounds per year

Stream

747 Mean annual total antimony load, in pounds, for water years 2012–14

1

5

4 3

2

EFSFSR

Meadow Creek

Sugar Creek

Notes:

Purple circles represent estimated loads at each monitoring site. 

Orange circles indicate relative location of loads attributable to 

 discrete reaches between monitoring sites. 

Ungaged tributaries are not shown. 

EFSFSR, East Fork of South Fork of the Salmon River.

1

Glory 

Hole 747 23.0

EFSFSR

General flow direction

Figure 9. Estimated mean annual total antimony loads in streams in the Stibnite mining area, central Idaho, 2012–14. Site names 

and locations are shown in table 1 and figure 1, respectively.
Occurrence, Transport, and Deposition of Selected Constituents 19

tac15-0986_fig10

2

Glory 

Hole

Glory Hole Reach

Meadow Creek Reach

647 617

46.9

733

1,350

108 39.4

EXPLANATION

Relative location and site No. 

Less than 50 pounds per year

51 to 500 pounds per year

501 to 1,500 pounds per year

1,501 to 5,000 pounds per year

Stream

733 Mean annual dissolved manganese load, in pounds, for water years 2012–14

1

5

4 3

EFSFSR

Meadow Creek

Sugar Creek

EFSFSR

General flow direction

Notes:

Purple circles represent estimated loads at each monitoring site. 

Orange circles indicate relative location of loads attributable to 

 discrete reaches between monitoring sites. 

Ungaged tributaries are not shown. 

EFSFSR, East Fork of South Fork of the Salmon River.

1

Figure 10. Estimated mean annual dissolved manganese loads in streams in the Stibnite mining area, central Idaho, 2012–14. Site 

names and locations are shown in table 1 and figure 1, respectively.
20 Occurrence and Transport of Selected Constituents in Streams near the Stibnite Mining Area, Central Idaho, 2012–14

Table 4. Estimated annual loads of selected trace elements and suspended sediment at five streamflow and water-quality monitoring 

sites in the Stibnite mining area, central Idaho, 2012–14.

[Site names and locations are shown in table 1 and figure 1, respectively. Abbreviations: L95, lower 95-percent confidence interval; U95, upper 95-percent 

confidence interval; lb/yr, pound per year; ton/yr, ton per year]

Constituent

Water year

2012 2013 2014 2012–14 mean

Annual 

load L95 U95 Annual load L95 U95 Annual load L95 U95 Annual load L95 U95

Site 1

Arsenic, dissolved (lb/yr) 223 208 238 197 183 211 206 193 220 209 195 223

Arsenic, total (lb/yr) 233 215 253 203 187 220 214 198 232 217 200 235

Antimony, dissolved (lb/yr) 26.1 23.3 29.1 22.9 20.3 25.8 23.4 20.8 26.2 24.1 21.5 27.0

Antimony, total (lb/yr) 24.7 21.8 27.9 21.7 19.0 24.7 22.6 19.9 25.6 23.0 20.2 26.1

Manganese, dissolved (lb/yr) 43.7 29.5 62.4 34.8 23.6 49.7 39.6 26.4 57.2 39.4 26.5 56.5

Lead, dissolved (lb/yr) no suitable LOADEST model

Lead, total (lb/yr) no suitable LOADEST model

Aluminum, dissolved (ton/yr) 0.36 0.27 0.46 0.27 0.20 0.35 0.32 0.24 0.42 0.32 0.24 0.41

Aluminum, total (ton/yr) 1.54 1.19 1.97 1.28 0.95 1.68 1.37 1.02 1.81 1.40 1.05 1.82

Suspended sediment (ton/yr) 103 76.6 136 87.6 61.8 121 87.0 62.9 117 92.6 67.1 125

Fine sediment (ton/yr) 35.2 26.1 46.4 30.2 21.1 41.9 29.0 21.3 38.5 31.5 22.9 42.3

Coarse sediment (ton/yr) 68.9 41.7 107 58.6 32.2 98.3 58.1 33.4 94.5 61.9 35.8 100

Site 2

Arsenic, dissolved (lb/yr) 21.2 20.3 22.2 18.2 17.4 19.0 21.9 21.0 23.0 20.5 19.6 21.4

Arsenic, total (lb/yr) 32.2 27.5 37.5 25.7 22.0 29.8 33.6 28.4 39.3 30.5 26.0 35.5

Antimony, dissolved (lb/yr) 8.69 7.78 9.68 7.28 6.45 8.18 8.96 8.00 10.0 8.31 7.41 9.29

Antimony, total (lb/yr) 8.46 7.11 9.98 6.74 5.71 7.90 8.65 7.28 10.21 7.95 6.70 9.36

Manganese, dissolved (lb/yr) 49.0 36.2 64.9 41.1 31.0 53.5 50.5 37.5 66.6 46.9 34.9 61.7

Lead, dissolved (lb/yr) no suitable LOADEST model

Lead, total (lb/yr) no suitable LOADEST model

Aluminum, dissolved (ton/yr) 0.32 0.27 0.39 0.25 0.21 0.30 0.33 0.27 0.39 0.30 0.25 0.36

Aluminum, total (ton/yr) 2.98 1.74 4.80 1.98 1.17 3.13 2.45 1.50 3.78 2.47 1.47 3.90

Suspended sediment (ton/yr) 162 84.0 285 83.1 49.7 131 120 65.2 204 122 66.3 206

Fine sediment (ton/yr) 75.1 32.1 150 37.3 19.4 65.3 54.0 24.0 105 55.5 25.2 107

Coarse sediment (ton/yr) 85.6 44.6 149 46.4 27.2 74.2 65.0 35.9 109 65.7 35.9 111

Site 3

Arsenic, dissolved (lb/yr) 1,460 1,300 1,640 1,270 1,120 1,430 1,400 1,250 1,560 1,380 1,220 1,540

Arsenic, total (lb/yr) 1,540 1,350 1,760 1,280 1,110 1,450 1,460 1,280 1,670 1,430 1,250 1,630

Antimony, dissolved (lb/yr) 784 618 981 673 517 862 720 566 902 726 567 915

Antimony, total (lb/yr) 815 641 1020 682 524 873 743 586 929 747 584 941

Manganese, dissolved (lb/yr) 763 669 867 701 619 790 735 647 832 733 645 830

Lead, dissolved (lb/yr) 2.44 1.79 3.25 1.73 1.29 2.26 2.26 1.65 3.01 2.14 1.58 2.84

Lead, total (lb/yr) 23.2 2.15 97.3 20.0 1.63 87.7 11.7 3.17 31.0 18.3 2.32 72.0

Aluminum, dissolved (ton/yr) 0.95 0.77 1.16 0.57 0.47 0.69 0.89 0.71 1.09 0.80 0.65 0.98

Aluminum, total (ton/yr) 12.8 5.26 26.2 9.97 3.45 22.8 7.75 4.17 13.2 10.2 4.29 20.8

Suspended sediment (ton/yr) 1,100 342 2,670 545 222 1,130 835 347 1,700 825 304 1,830

Fine sediment (ton/yr) 339 120 767 174 76 343 223 103 422 245 100 511

Coarse sediment (ton/yr) 657 257 1,400 349 135 745 568 216 1,230 525 203 1,120
Occurrence, Transport, and Deposition of Selected Constituents 21

Constituent

Water year

2012 2013 2014 2012–14 mean

Annual 

load L95 U95 Annual load L95 U95 Annual load L95 U95 Annual load L95 U95

Site 4

Arsenic, dissolved (lb/yr) 3,520 3,150 3,910 3,070 2,740 3,430 3,380 3,030 3,760 3,320 2,970 3,700

Arsenic, total (lb/yr) 3,800 3,340 4,310 3,280 2,870 3,740 3,650 3,200 4,140 3,580 3,140 4,060

Antimony, dissolved (lb/yr) 2,050 1,690 2,460 1,750 1,410 2,150 1,940 1,600 2,330 1,910 1,570 2,310

Antimony, total (lb/yr) 1,910 1,600 2,270 1,560 1,300 1,850 1,810 1,510 2,150 1,760 1,470 2,090

Manganese, dissolved (lb/yr) 1,410 1,260 1,570 1,280 1,140 1,430 1,370 1,220 1,520 1,350 1,210 1,510

Lead, dissolved (lb/yr) 3.11 2.11 4.44 2.25 1.55 3.15 2.89 1.96 4.12 2.75 1.87 3.90

Lead, total (lb/yr) 11.0 6.77 16.9 6.52 4.09 9.90 10.4 6.16 16.5 9.30 5.67 14.4

Aluminum, dissolved (ton/yr) 1.03 0.76 1.36 0.64 0.48 0.84 0.96 0.70 1.28 0.88 0.65 1.16

Aluminum, total (ton/yr) 7.75 3.93 13.8 4.70 2.44 8.21 7.22 3.56 13.1 6.55 3.31 11.7

Suspended sediment (ton/yr) 284 162 463 175 103 277 292 152 508 250 139 416

Fine sediment (ton/yr) 229 121 397 140 76 235 231 111 426 200 103 353

Coarse sediment (ton/yr) 61.9 32.9 106 36.0 21.7 56.4 58.5 33.1 96.0 52.1 29.2 86.2

Mercury, total (lb/yr) 0.85 0.59 1.19 0.51 0.36 0.70 0.87 0.58 1.25 0.74 0.51 1.05

Site 5

Arsenic, dissolved (lb/yr) 568 511 629 477 425 534 545 492 602 530 476 588

Arsenic, total (lb/yr) 597 469 753 552 481 630 644 564 732 598 505 705

Antimony, dissolved (lb/yr) 176 143 214 158 126 195 169 138 205 168 136 205

Antimony, total (lb/yr) 166 109 244 150 121 185 162 133 196 159 121 208

Manganese, dissolved (lb/yr) 112 69.8 171 88.5 56.0 133 123 69.3 202 108 65.0 169

Lead, dissolved (lb/yr) 2.30 1.84 2.84 1.68 1.34 2.09 2.25 1.77 2.82 2.08 1.65 2.58

Lead, total (lb/yr) 8.60 2.35 22.7 8.33 2.16 22.5 14.1 4.50 33.8 10.3 3.00 26.3

Aluminum, dissolved (ton/yr) 0.69 0.48 0.95 0.45 0.31 0.62 0.73 0.50 1.02 0.62 0.43 0.86

Aluminum, total (ton/yr) 7.47 2.88 16.0 4.61 1.51 10.9 10.3 3.12 25.5 7.46 2.50 17.5

Suspended sediment (ton/yr) 379 204 644 255 118 485 612 267 1208 415 197 779

Fine sediment (ton/yr) 92.0 43.6 174 129 49.6 277 168 84.6 299 129 59.2 250

Coarse sediment (ton/yr) 223 105 416 187 58 456 290 114 616 233 92 496

Mercury, total (lb/yr) 28.7 8.37 72.5 62.0 10.1 209 41.6 10.1 116 44.1 9.51 133

Table 4. Estimated annual loads of selected trace elements and suspended sediment at five streamflow and water-quality monitoring 

sites in the Stibnite mining area, central Idaho, 2012–14.—Continued

[Site names and locations are shown in table 1 and figure 1, respectively. Abbreviations: L95, lower 95 percent confidence interval; U95, upper 95 percent 

confidence interval; lb/yr, pound per year; ton/yr, ton per year]
22 Occurrence and Transport of Selected Constituents in Streams near the Stibnite Mining Area, Central Idaho, 2012–14

Table 5. Estimated streamflow-weighted concentrations of selected constituents at five streamflow and water-quality monitoring 

sites in the Stibnite mining area, central Idaho, 2012–14.

[Site names and locations are shown in table 1 and figure 1, respectively. Abbreviations: FWC, streamflow-weighted concentration; L95, lower 95-percent 

confidence interval; U95, upper 95-percent confidence interval; μg/L, microgram per liter; mg/L, milligram per liter]

Constituent

Water years

2012 2013 2014 2012–14 mean

FWC L95 U95 FWC L95 U95 FWC L95 U95 FWC L95 U95

Site 1

Arsenic, dissolved (μg/L) 8.11 7.58 8.66 8.59 8.01 9.20 8.25 7.71 8.83 8.32 7.77 8.90

Arsenic, total (μg/L) 8.48 7.82 9.19 8.82 8.12 9.57 8.58 7.90 9.29 8.63 7.95 9.35

Antimony, dissolved (μg/L) 0.95 0.85 1.06 1.00 0.88 1.12 0.94 0.83 1.05 0.96 0.85 1.08

Antimony, total (μg/L) 0.90 0.79 1.01 0.94 0.83 1.07 0.90 0.80 1.02 0.92 0.80 1.04

Manganese, dissolved (μg/L) 1.59 1.07 2.27 1.52 1.03 2.16 1.59 1.06 2.29 1.56 1.05 2.24

Lead, dissolved (μg/L) no suitable LOADEST model

Lead, total (μg/L) no suitable LOADEST model

Aluminum, dissolved (μg/L) 25.9 19.8 33.3 23.5 17.7 30.6 25.7 19.3 33.5 25.0 18.9 32.5

Aluminum, total (μg/L) 112 86.4 143 111 82.9 147 110 81.8 145 111 83.7 145

Suspended sediment (mg/L) 7.51 5.57 9.91 7.63 5.38 10.51 6.96 5.04 9.39 7.37 5.33 9.93

Fine sediment (mg/L) 2.56 1.90 3.37 2.63 1.84 3.65 2.32 1.70 3.08 2.50 1.81 3.37

Coarse sediment (mg/L) 5.01 3.03 7.80 5.10 2.80 8.56 4.65 2.67 7.56 4.92 2.83 7.97

Site 2

Arsenic, dissolved (μg/L) 0.92 0.88 0.96 0.96 0.92 1.00 0.92 0.88 0.96 0.93 0.89 0.97

Arsenic, total (μg/L) 1.39 1.19 1.62 1.35 1.16 1.57 1.41 1.20 1.65 1.38 1.18 1.61

Antimony, dissolved (μg/L) 0.38 0.34 0.42 0.38 0.34 0.43 0.38 0.34 0.42 0.38 0.34 0.42

Antimony, total (μg/L) 0.36 0.31 0.43 0.35 0.30 0.42 0.36 0.31 0.43 0.36 0.30 0.43

Manganese, dissolved (μg/L) 2.11 1.56 2.80 2.16 1.63 2.81 2.12 1.57 2.80 2.13 1.59 2.80

Lead, dissolved (μg/L) no suitable LOADEST model

Lead, total (μg/L) no suitable LOADEST model

Aluminum, dissolved (μg/L) 27.9 23.1 33.4 26.3 21.9 31.4 27.6 22.8 33.0 27.2 22.6 32.6

Aluminum, total (μg/L) 258 150 414 208 124 329 206 126 318 224 133 354

Suspended sediment (mg/L) 11.8 6.10 20.7 7.23 4.33 11.4 9.64 5.22 16.3 9.55 5.22 16.1

Fine sediment (mg/L) 5.45 2.34 10.91 3.25 1.69 5.68 4.32 1.92 8.43 4.34 1.98 8.34

Coarse sediment (mg/L) 6.22 3.24 10.86 4.04 2.37 6.46 5.20 2.87 8.69 5.15 2.83 8.67

Site 3

Arsenic, dissolved (μg/L) 21.0 18.7 23.4 23.7 20.9 26.9 21.4 19.1 24.0 22.1 19.6 24.8

Arsenic, total (μg/L) 22.1 19.3 25.3 23.9 20.9 27.2 22.4 19.6 25.6 22.8 19.9 26.0

Antimony, dissolved (μg/L) 11.2 8.85 14.1 12.6 9.68 16.1 11.0 8.68 13.8 11.6 9.07 14.7

Antimony, total (μg/L) 11.7 9.19 14.6 12.8 9.81 16.4 11.4 8.98 14.2 11.9 9.33 15.1

Manganese, dissolved (μg/L) 10.9 9.6 12.4 13.1 11.6 14.8 11.3 9.9 12.8 11.8 10.4 13.3

Lead, dissolved (μg/L) 0.03 0.03 0.05 0.03 0.02 0.04 0.03 0.03 0.05 0.03 0.03 0.05

Lead, total (μg/L) 0.33 0.03 1.39 0.38 0.03 1.64 0.18 0.05 0.48 0.30 0.04 1.17

Aluminum, dissolved (μg/L) 27.3 22.2 33.3 21.4 17.7 25.7 27.2 21.9 33.5 25.3 20.6 30.8

Aluminum, total (μg/L) 366 151 750 373 129 856 238 128 405 326 136 670

Suspended sediment (mg/L) 31.4 9.80 76.4 20.4 8.32 42.2 25.6 10.65 52.2 25.8 9.59 56.9

Fine sediment (mg/L) 9.72 3.44 22.0 6.50 2.83 12.9 6.83 3.17 13.0 7.69 3.15 15.9

Coarse sediment (mg/L) 18.8 7.37 39.9 13.1 5.06 27.9 17.4 6.62 37.7 16.4 6.35 35.2
Occurrence, Transport, and Deposition of Selected Constituents 23

Table 5. Estimated streamflow-weighted concentrations of selected constituents at five streamflow and water-quality monitoring 

sites in the Stibnite mining area, central Idaho, 2012–14.—Continued

[Site names and locations are shown in table 1 and figure 1, respectively. Abbreviations: FWC, streamflow-weighted concentration; L95, lower 95-percent 

confidence interval; U95, upper 95-percent confidence interval; μg/L, microgram per liter; mg/L, milligram per liter]

Constituent

Water years

2012 2013 2014 2012–14 mean

FWC L95 U95 FWC L95 U95 FWC L95 U95 FWC L95 U95

Site 4

Arsenic, dissolved (μg/L) 42.0 37.6 46.7 48.6 43.3 54.3 43.2 38.7 48.1 44.6 39.9 49.7

Arsenic, total (μg/L) 45.4 39.9 51.5 51.9 45.3 59.1 46.6 40.9 52.9 48.0 42.1 54.5

Antimony, dissolved (μg/L) 24.5 20.2 29.4 27.7 22.3 34.0 24.8 20.4 29.7 25.6 21.0 31.0

Antimony, total (μg/L) 22.8 19.1 27.1 24.6 20.6 29.3 23.1 19.3 27.4 23.5 19.7 27.9

Manganese, dissolved (μg/L) 16.8 15.1 18.7 20.3 18.1 22.7 17.5 15.6 19.5 18.2 16.3 20.3

Lead, dissolved (μg/L) 0.04 0.03 0.05 0.04 0.02 0.05 0.04 0.02 0.05 0.04 0.02 0.05

Lead, total (μg/L) 0.13 0.08 0.20 0.10 0.06 0.16 0.13 0.08 0.21 0.12 0.07 0.19

Aluminum, dissolved (μg/L) 24.6 18.1 32.6 20.4 15.3 26.6 24.4 17.8 32.7 23.1 17.1 30.6

Aluminum, total (μg/L) 185 93.8 329 149 77.4 260 184 90.9 335 173 87.4 308

Suspended sediment (mg/L) 6.78 3.86 11.1 5.53 3.27 8.77 7.45 3.89 13.0 6.59 3.67 10.9

Fine sediment (mg/L) 5.48 2.89 9.49 4.42 2.42 7.43 5.89 2.84 10.9 5.26 2.71 9.27

Coarse sediment (mg/L) 1.48 0.79 2.54 1.14 0.69 1.79 1.49 0.85 2.45 1.37 0.77 2.26

Mercury (total) (μg/L) 0.010 0.007 0.014 0.008 0.006 0.011 0.011 0.007 0.016 0.010 0.007 0.014

Site 5

Arsenic, dissolved (μg/L) 11.2 10.1 12.4 12.1 10.8 13.5 10.9 9.9 12.1 11.4 10.2 12.7

Arsenic, total (μg/L) 11.8 9.27 14.9 14.0 12.2 16.0 12.9 11.3 14.7 12.9 10.9 15.2

Antimony, dissolved (μg/L) 3.48 2.83 4.23 4.00 3.20 4.95 3.38 2.76 4.11 3.62 2.93 4.43

Antimony, total (μg/L) 3.27 2.16 4.82 3.80 3.05 4.68 3.26 2.67 3.94 3.45 2.63 4.48

Manganese, dissolved (μg/L) 2.21 1.38 3.37 2.24 1.42 3.37 2.47 1.39 4.06 2.31 1.40 3.60

Lead, dissolved (μg/L) 0.05 0.04 0.06 0.04 0.03 0.05 0.05 0.04 0.06 0.04 0.04 0.06

Lead, total (μg/L) 0.17 0.05 0.45 0.21 0.05 0.57 0.28 0.09 0.68 0.22 0.06 0.57

Aluminum, dissolved (μg/L) 16.5 11.6 22.7 14.2 9.91 19.7 18.6 12.8 26.1 16.4 11.4 22.8

Aluminum, total (μg/L) 179 68.7 383 146 47.8 346 263 79.7 651 196 65.4 460

Suspended sediment (mg/L) 15.0 8.07 25.4 12.9 5.98 24.6 24.6 10.7 48.5 17.5 8.26 32.8

Fine sediment (mg/L) 3.63 1.72 6.85 6.53 2.51 14.0 6.72 3.40 12.0 5.63 2.54 11.0

Coarse sediment (mg/L) 8.80 4.16 16.4 9.49 2.96 23.1 11.6 4.55 24.7 9.98 3.89 21.4

Mercury (total) (μg/L) 0.57 0.17 1.43 1.57 0.26 5.30 0.83 0.20 2.33 0.99 0.21 3.02
24 Occurrence and Transport of Selected Constituents in Streams near the Stibnite Mining Area, Central Idaho, 2012–14

tac15-0986_fig11

0.1 

1.0 

10.0 

100.0 

1,000.0 

Human health criterion = 10 μg/L 

A. Arsenic 

EXPLANATION 

Total Concentration

Dissolved Concentration 

0.1 

1.0 

10.0 

100.0 

Human health criterion = 5.6 μg/L 

B. Antimony 

0 

10 

20 

30 

40 

50 

60 

Site 1 Site 2 Meadow Creek

Reach 

Site 3 Glory Hole

Reach

Site 4 Site 5 

C. Manganese 

Estimated mean annual streamflow-weighted concentration, in micrograms per liter 

Figure 11. Estimated mean annual streamflow-weighted concentrations of (A) arsenic, (B) antimony, and (C) 

manganese in streams in the Stibnite mining area, central Idaho, 2012–14. Site names and locations are shown in 

table 1 and figure 1, respectively.
Occurrence, Transport, and Deposition of Selected Constituents 25

Table 6. Substantial sources of arsenic and antimony identified at selected sites along Meadow Creek, Stibnite mining area, central 

Idaho, September 22, 2011.

[Site locations are shown in figure 12. Blowout Creek is officially named East Fork Meadow Creek in figure 1. Abbreviations: μg/L, 

microgram per liter; lb/d, pound per day; m, meter]

Site No. Site name Streamflow

Dissolved antimony

Concentration 

(μg/L)

Instantaneous

load 

(lb/d)

Increase in load 

relative to 

 adjacent 

upstream site

(percent)

4453251152046 Meadow Creek inflow, 280 m upstream of bend in road 0.095 173 8.86E-2 390

4453261152043 Meadow Creek inflow, 240 m upstream of bend in road 0.142 26.1 2.00E-2 36

4453391152029 Meadow Creek inflow, below extent of cascading section 0.105 3.45 1.95E-3 2.4

4453441152021 Blowout Creek at Meadow Creek 1.94 1.30 1.36E-2 13

4453461152017 Meadow Creek inflow, near runway entrance 0.054 269 7.84E-2 57

Site No. Site name

Dissolved arsenic

Concentration 

(μg/L)

Instantaneous 

load 

(lb/d)

Increase in load 

relative to 

 adjacent 

upstream site

(percent)

4453251152046 Meadow Creek inflow, 280 m upstream of bend in road 1,340 6.87E-1 257

4453261152043 Meadow Creek inflow, 240 m upstream of bend in road 21.4 1.64E-2 2.7

4453391152029 Meadow Creek inflow, below extent of cascading section 526 2.98E-1 36

4453441152021 Blowout Creek at Meadow Creek 7.32 7.66E-2 7.0

4453461152017 Meadow Creek inflow, near runway entrance 1,300 3.79E-1 29
26 Occurrence and Transport of Selected Constituents in Streams near the Stibnite Mining Area, Central Idaho, 2012–14

tac15-0986_fig12

EXPLANATION

National forest boundary

Streamflow-gaging station, 

continuous water-quality 

monitor, and water-quality 

monitoring site and No.

Surface-water-quality sampling 

site and No.

1

0 0.1 0.2 0.3 0.4 MILE

0 0.1 0.2 0.3 0.4 KILOMETER

East Fork Meadow Creek

Fiddle Creek

Garnet Creek

South Fork Salmon River

East Fork

Meadow Creek

115°21' 115°20' 115°19'

44°

55'

44°

54'

44°

53'

4453461152017

4453441152021 4453391152029

4453261152043

4453251152046

4453251152046

Base map modified from U.S. Geological Survey National Map,

Hydrography data from the National Hydrography Dataset, medium resolution,

Transportation data from the National Transportation Dataset.

Universal Transverse Mercator, Zone 11, North American Datum of 1983.

BOISE

NATIONAL FOREST

PAYETTE

NATIONAL FOREST

Meadow Creek

Reach

Glory Hole

Reach

Meadow

Creek

Mine

Bradley

Tailings

2

1

3

Figure 12. Locations of substantial sources of arsenic and antimony identified along Meadow Creek, 

Stibnite mining area, central Idaho, September 22, 2011.
Occurrence, Transport, and Deposition of Selected Constituents 27

tac15-0986_fig13

Glory Hole Reach

Meadow Creek Reach

611

-575 (loss)

122

825

415 92.6

EXPLANATION

Relative location and site No. 

Less than 100 tons per year

100 to 250 tons per year

251 to 500 tons per year

More than 500 tons per year

Stream

825 Mean annual suspended-sediment load, in tons, for water years 2012–14

1

5

4 3

2

1

Sugar Creek

General flow direction

Notes:

Purple circles represent estimated loads at each monitoring site. 

Orange circles indicate relative location of loads attributable to 

 discrete reaches between monitoring sites. 

Ungaged tributaries are not shown.

EFSFSR, East Fork of South Fork of the Salmon River.

Glory 

Hole

250

EFSFSR

Meadow Creek EFSFSR

Figure 13. Estimated mean annual suspended sediment loads at monitoring sites in the Stibnite mining area, central Idaho, 

2012–14. Site names and locations are shown in table 1 and figure 1, respectively.
28 Occurrence and Transport of Selected Constituents in Streams near the Stibnite Mining Area, Central Idaho, 2012–14

Figure 14. Estimated mean annual total aluminum loads at monitoring sites in the Stibnite mining area, central Idaho, 2012–14. Site 

names and locations are shown in table 1 and figure 1, respectively.

tac15-0986_fig14

-3.61 (loss)

Glory 

Hole

Glory Hole Reach

Meadow Creek Reach

6.29

2.47

10.2

6.55

7.46 1.40

EXPLANATION

Relative location and site No. 

Less than 0.50 ton per year

0.51 to 5 tons per year

5.1 to 10 tons per year

More than 10 tons per year

Stream

10.2 Mean annual total aluminum load, in tons, for water years 2012–14

1

5

4 3

2

1

EFSFSR

Meadow Creek

Sugar Creek

EFSFSR

General flow direction

Notes:

Purple circles represent estimated loads at each monitoring site. 

Orange circles indicate relative location of loads attributable to 

 discrete reaches between monitoring sites. 

Ungaged tributaries are not shown. 

EFSFSR, East Fork of South Fork of the Salmon River.
Occurrence, Transport, and Deposition of Selected Constituents 29

tac15-0986_fig15

Glory Hole Reach

Meadow Creek Reach

0.19 0.07

0.30

0.80

0.88

0.62 0.32

EXPLANATION

Relative location and site number 

Less than 0.50 ton per year

0.51 to 5 tons per year

5.1 to 10 tons per year

More than 10 tons per year

Stream

0.80 Mean annual load, water years 2012–14, in tons

1

5

4 3

2

1

General flow direction

Notes:

Purple circles represent estimated

loads at each monitoring site. Orange circles indicate 

relative location of loads attributable to discrete

reaches between monitoring sites. 

Ungaged tributaries are not shown. [Abbreviation: 

EFSFSR, East Fork of South Fork of the Salmon River]

Glory 

Hole

EFSFSR

Meadow Creek

Sugar Creek

EFSFSR

Figure 15. Estimated mean annual dissolved aluminum loads at monitoring sites in the Stibnite mining area, central Idaho, 

2012–14. Site names and locations are shown in table 1 and figure 1, respectively.
30 Occurrence and Transport of Selected Constituents in Streams near the Stibnite Mining Area, Central Idaho, 2012–14

tac15-0986_fig16

0.00 

0.05 

0.10 

0.15 

0.20 

0.25 

0.30 

0.35 

Minimum hardness-based aquatic life

criterion based on chronic exposure =

0.27 microgram per liter for dissolved lead 

EXPLANATION 

EXPLANATION 

Total concentration

Dissolved concentration 

Total lead

concentrations

not shown due to

loss in reach. 

B. Lead 

0 

100 

200 

300 

400 

500 

600 

700 

800 

900 A. Aluminum 

Total aluminum

concentrations

not shown due to

loss in reach. 

Estimated mean streamflow-weighted concentration, in micrograms per liter 

0 

10 

20 

30 

40 

50 

60 

70 

80 

90 

Site 1 Site 2 Meadow Creek

Reach 

Site 3 Glory Hole

Reach 

Site 4 Site 5 

C. Suspended sediment 

Estimated mean streamflow-weighted

concentration, in milligrams per liter 

Sediment

concentrations

not shown due to

loss in reach. 

Suspended sediment

Fine sediment (<0.0625 millimeter) 

Figure 16. Estimated mean annual streamflow-weighted concentrations of (A) aluminum, (B) lead, and (C) 

suspended sediment at monitoring sites in the Stibnite mining area, central Idaho, 2012–14. Site names and 

locations are shown in table 1 and figure 1, respectively.
LOAD ESTimation (LOADEST) Model Results 31

Loading and transport of total aluminum and total 

lead were similar to the loading and transport of suspended 

sediment. On average, the estimated annual total aluminum 

load in Sugar Creek (site 5) was about 1 ton higher than the 

annual total aluminum load discharged from the Meadow 

Creek reach. As compared to the EFSFSR at site 4, Sugar 

Creek (site 5) accounted for a slightly larger amount of the 

total aluminum load transported downstream of the study area 

(fig. 14). The estimated mean annual FWC of total aluminum 

in sources to the Meadow Creek reach was 4 times as high 

as the mean annual FWC of total aluminum in Sugar Creek 

at site 5, suggesting that the East Fork Meadow Creek is a 

concentrated source of total aluminum (fig. 16). With the 

exception of the East Fork Meadow Creek, total aluminum 

was not measured in the inflows shown in table 6 during 

intensive sampling in the Meadow Creek reach on September 

22, 2011. However, the total aluminum concentration in 

the East Fork Meadow Creek was 53 μg/L, compared to an 

average concentration of 21 μg/L measured in Meadow Creek 

upstream of East Fork Meadow Creek on September 22, 

2011. The total aluminum load in Meadow Creek doubled as 

a result of the total aluminum source from East Fork Meadow 

Creek and did not substantially increase in any additional 

samples collected downstream of East Fork Meadow Creek on 

September 22, 2011. Results from all samples collected along 

Meadow Creek on September 22, 2011, are available from the 

USGS National Water Information System (U.S. Geological 

Survey, 2015). 

Because detections of total and dissolved lead were 

infrequent at sites 1 and 2, loads for lead upstream of site 3 

were not estimated. About one-half of the total lead and one 

third of the total aluminum loads at site 3 were deposited 

in the Glory Hole (table 4, fig. 14). FWCs of total lead and 

total aluminum at site 3 were twice as high as those at site 4 

because of losses of total lead and total aluminum loads in the 

Glory Hole (fig. 16). The mean annual load of total lead for 

2012–14 at site 4 was 9.30 lb/yr compared to 

10.3 lb/yr at site 5 (Sugar Creek), suggesting that Sugar Creek 

contributes more than one-half of the total lead transported 

downstream of the study area in the EFSFSR (table 4). 

Dissolved FWCs of lead and aluminum changed little from 

upstream to downstream, with the largest sources attributable 

to background loads at sites 1, 2, and 5 (tables 4 and 5; figs. 7, 

15, and 16). 

A limited number of samples and (or) detections of total 

mercury prevented the use of load models to estimate annual 

FWCs and loads of total mercury at sites 1–3. Total mercury 

load models for sites 4 and 5 indicate that 98 percent of the 

mercury load transported downstream of the study area is 

attributable to Sugar Creek (fig. 7, table 4). Estimated annual 

FWCs of total mercury were 0.010 μg/L at site 4 on the 

EFSFWR, which is close to the State of Idaho 0.012-μg/L 

chronic exposure AWQC. However, the mean annual FWC 

estimated for total mercury at site 5 on Sugar Creek was 

0.99 μg/L, nearly two orders of magnitude higher than the 

FWC at site 4 (table 5). 

LOAD ESTimation (LOADEST) Model 

Results

Significant correlations (p <0.01) between streamflow 

and concentrations of modeled constituents generally resulted 

in favorable LOADEST models (fig. 6, table 7). Ninety-five 

percent confidence intervals around estimated mean annual 

loads and FWCs quantify uncertainty around estimates and 

generally were larger for constituents with greater variability 

in measured loads (tables 4 and 5). Recent research has 

shown that LOADEST models can produce biased estimates 

of long-term average constituent loads (Stenback and others, 

2011; Garrett, 2012; Hirsch, 2014), and LOADEST has 

since been modified to facilitate residual analysis and bias 

identification (Runkel, 2013). Long-term bias in model 

estimates was less of a concern because the modeling period 

was only 3 years and predictor variables describing trends 

in time were not used. High model bias often indicated 

hysteresis in transport of sediment and sediment-associated 

constituents in the study area. Bias diagnostics described by 

Runkel (2013) were used as an indication that an additional 

predictor variable may be necessary to account for hysteresis 

in constituent transport. Use of a predictor variable describing 

variation in streamflow frequently resulted in large reductions 

in overall model bias where hysteresis in constituent transport 

was evident. 

Streamflow Variability and Hysteresis in 

Particulate Constituent Transport

Various stream basin characteristics may have affected 

the significance of a particular streamflow variability term 

at each site. Moving averages of the previous 1, 3, 7, and 

30 days were compared to daily mean streamflow and tested 

for significance as predictor variables describing particulate 

constituent transport. The ratio of estimated daily surface 

runoff in cubic feet per second to daily mean streamflow in 

cubic feet per second (the base flow index [BFI]) also was 

tested as a predictor variable to account for hysteresis. A 

streamflow variability term with a longer daily time-step helps 

describe the effects of sequential events or prolonged peaks, 

whereas absolute values of variability terms help describe the 

degree of flashiness of increased streamflow events (Wang 

and Linker, 2008). Snowmelt runoff controls particulate 

constituent transport in the study area, and most samples 

used to calibrate LOADEST models were collected during 

snowmelt runoff (fig. 3). 
32 Occurrence and Transport of Selected Constituents in Streams near the Stibnite Mining Area, Central Idaho, 2012–14

Table 7. Regression coefficients and coefficients of determination (R2) for models used to estimate loads of selected constituents at 

monitoring sites in the Stibnite mining area, central Idaho, 2012–14.

[Site names and locations are shown in table 1 and figure 1, respectively. Each regression model was calibrated using the available data collected at each station 

for water years 2012–14. The regression equation is lnL = I + a (lnQ) + b (lnQ2) + c [sin(2πT)] + d [cos(2πT)] + e (SVT) + ɛ, where ln is the natural logarithm; 

L is the constituent load, in pounds per day; I is the regression intercept; Q is the centered streamflow, in cubic feet per second; T is the centered decimal time 

in years from the beginning of the calibration period; sin (2πT) and cos (2πT) are periodic time functions that describe seasonal variability; SVT is the term 

describing streamflow variability; a, b, c, d, and e are regression coefficients that remain constant over time; and ɛ is the unaccounted error associated with the 

regression model. R2 (coefficient of determination) represents the amount of variance explained by the model. Abbreviations: RMSE, root mean square error; 

lb/d, pound per day; –, no regression coefficient]

Constituent

Regression coefficient

R2 RMSE 

(lb/d)

Load

bias

(percent)

Number

of samples I a b c d e

Site 1

Arsenic, dissolved 20 -0.140 0.696 – – – – 97 1.15 0.04

Arsenic, total 20 -0.091 0.788 – – – – 96 1.19 1.68

Antimony, dissolved 20 -2.132 0.748 -0.090 0.279 0.312 – 95 1.24 -1.08

Antimony, total 20 -2.357 0.752 – 0.253 0.135 – 94 1.28 -0.16

Manganese, dissolved 15 -2.084 1.356 – – – – 89 1.70 -2.31

Lead, dissolved 19 no suitable LOADEST model

Lead, total 20 no suitable LOADEST model

Aluminum, dissolved 20 0.642 1.855 -0.166 – – – 97 1.51 0.11

Aluminum, total 19 -3.789 1.842 – 0.521 0.136 1

0.018 98 1.40 -3.15

Suspended sediment 19 0.895 1.767 – 0.448 0.508 1

0.030 97 1.49 -1.00

Fine sediment 19 0.606 1.504 – 0.395 0.339 1

0.047 97 1.52 1.79

Coarse sediment 19 -0.104 1.943 – 0.484 0.710 1

0.024 95 1.82 2.03

Site 2

Arsenic, dissolved 21 -2.677 0.821 0.037 – – – 99 1.10 -0.40

Arsenic, total 21 -2.641 1.019 0.180 – – – 96 1.35 -8.20

Antimony, dissolved 18 -3.377 1.133 – 0.221 0.557 – 98 1.22 -0.18

Antimony, total 21 -3.749 1.112 – – – – 96 1.38 -2.61

Manganese, dissolved 16 -1.977 0.923 – – – – 88 1.60 -5.76

Lead, dissolved no suitable LOADEST model

Lead, total no suitable LOADEST model

Aluminum, dissolved 21 0.551 1.341 – 0.123 0.315 – 97 1.38 1.47

Aluminum, total 19 -2.587 1.742 – -0.048 0.546 2

0.043 95 1.81 -15.0

Suspended sediment 20 1.749 1.424 – – – 1

0.101 95 1.83 -8.23

Fine sediment 20 1.243 1.284 – – – 1

0.116 92 2.03 -15.6

Coarse sediment 20 0.929 1.540 – 0.333 0.290 1

0.082 95 1.88 -3.06

Site 3

Arsenic, dissolved 23 1.557 0.589 – 0.210 -0.150 – 94 1.26 -0.50

Arsenic, total 23 1.695 0.798 – – – – 91 1.35 0.07

Antimony, dissolved 22 1.327 0.874 -0.271 0.625 0.542 – 92 1.50 -4.71

Antimony, total 22 1.266 0.914 -0.188 0.603 0.550 – 92 1.50 -3.87

Manganese, dissolved 17 0.417 – – – – 3

0.338 87 1.27 -1.63

Lead, dissolved 20 -4.945 1.207 – – – – 80 1.66 3.10

Lead, total 23 -5.710 1.400 – – – 4

-4.512 71 3.36 15.5

Aluminum, dissolved 23 1.370 1.691 – – – – 97 1.39 -0.72

Aluminum, total 22 -0.939 1.772 – – – 4

-3.224 92 2.05 17.4

Suspended sediment 20 -0.620 2.245 – 0.433 1.201 5

0.0215 91 2.41 -5.93

Fine sediment 20 1.052 1.418 – 0.448 0.362 2

0.022 91 2.21 -1.45

Coarse sediment 20 7.424 2.506 – 0.421 1.411 – 90 2.63 -6.82
LOAD ESTimation (LOADEST) Model Results 33

Constituent

Regression coefficient

R2 RMSE 

(lb/d)

Load

bias

(percent)

Number

of samples I a b c d e

Site 4

Arsenic, dissolved 22 2.514 0.575 – – – – 89 1.27 0.49

Arsenic, total 22 2.587 0.614 – – – – 87 1.33 0.53

Antimony, dissolved 21 1.888 0.611 – 0.327 0.050 – 88 1.42 -0.93

Antimony, total 21 1.868 0.787 – – – – 87 1.45 -0.25

Manganese, dissolved 16 1.717 0.467 -0.133 – – – 88 1.24 0.61

Lead, dissolved 19 -4.762 1.126 – – – – 65 1.89 4.46

Lead, total 21 -3.541 2.000 – -0.545 0.620 – 88 1.94 -6.36

Aluminum, dissolved 22 1.473 1.578 – – – – 94 1.62 2.50

Aluminum, total 21 3.124 1.709 – – – – 84 2.44 6.45

Suspended sediment 20 6.370 1.358 0.522 – – – 84 2.14 3.78

Fine sediment 20 6.198 1.424 0.430 – – – 82 2.31 3.08

Coarse sediment 20 4.211 1.125 0.822 – – 6

0.020 89 1.90 5.49

Mercury, total 15 -6.777 1.521 0.411 – – – 90 1.64 3.06

Site 5

Arsenic, dissolved 21 0.862 0.796 – 0.021 0.367 – 95 1.23 0.26

Arsenic, total 20 -0.915 0.377 – – – 7

0.015 94 1.31 4.52

Antimony, dissolved 20 -0.358 0.587 – -0.031 0.579 – 72 1.38 1.72

Antimony, total 19 -2.288 0.483 – 0.004 0.561 7

0.007 84 1.37 -1.30

Manganese, dissolved 15 -1.710 0.928 0.455 – – – 76 1.95 -7.03

Lead, dissolved 20 -9.042 1.069 – – – 8

0.018 88 1.04 10.0

Lead, total 20 -11.347 1.776 – – – 7

0.019 84 2.60 10.0

Aluminum, dissolved 21 0.815 1.780 – 0.409 -0.030 – 96 1.68 3.86

Aluminum, total 21 2.146 2.339 0.333 – – – 89 2.81 9.77

Suspended sediment 20 6.140 1.979 0.724 – – – 92 2.12 -6.41

Fine sediment 19 4.841 1.226 0.439 – – 7

1.756 95 1.83 -3.95

Coarse sediment 20 4.802 1.860 0.827 – – 6

5.341 95 1.90 -3.51

Mercury, total 19 1.868 1.685 0.223 – – 4

-7.106 91 2.71 -0.79

1

Moving average of streamflow for the previous 3 days compared to each daily streamflow. 

2

Moving average of streamflow for the previous 7 days compared to each daily streamflow.

3

Absolute value of the moving average of streamflow for the previous 7 days compared to each daily streamflow.

4

Ratio of estimated daily mean runoff to daily mean streamflow in cubic feet per second (known as the base flow index [BFI]).

5

Moving average of streamflow for the previous 1 day compared to each daily streamflow.

6

Absolute value of the moving average of streamflow for the previous 1 day compared to each daily streamflow.

7

Absolute value of the moving average of streamflow for the previous 30 days compared to each daily streamflow.

8

Absolute value of the moving average of streamflow for the previous 7 days compared to each daily streamflow.

 

Table 7. Regression coefficients and coefficients of determination (R2) for models used to estimate loads of selected constituents at 

monitoring sites in the Stibnite mining area, central Idaho, 2012–14.—Continued

[Site names and locations are shown in table 1 and figure 1, respectively. Each regression model was calibrated using the available data collected at each station 

for water years 2012–14. The regression equation is lnL = I + a (lnQ) + b (lnQ2) + c [sin(2πT)] + d [cos(2πT)] + e (SVT) + ɛ, where ln is the natural logarithm; 

L is the constituent load, in pounds per day; I is the regression intercept; Q is the centered streamflow, in cubic feet per second; T is the centered decimal time 

in years from the beginning of the calibration period; sin (2πT) and cos (2πT) are periodic time functions that describe seasonal variability; SVT is the term 

describing streamflow variability; a, b, c, d, and e are regression coefficients that remain constant over time; and ɛ is the unaccounted error associated with the 

regression model. R2 (coefficient of determination) represents the amount of variance explained by the model. Abbreviations: RMSE, root mean square error; 

lb/d, pound per day; –, no regression coefficient]
34 Occurrence and Transport of Selected Constituents in Streams near the Stibnite Mining Area, Central Idaho, 2012–14

The shape of the hydrograph may affect the significance 

of streamflow terms in the LOADEST models. Sample results 

from Sugar Creek (site 5) show that the way the snowpack 

melts affects particulate constituent transport (fig. 3, fig. 17). 

Snowmelt runoff was similar in 2012 and 2014, with 

numerous spring increases in the hydrograph as the snowpack 

melted. In contrast, most of the snowpack melted in one 

event in 2013, which also produced the highest concentration 

of mercury in Sugar Creek (site 5) at 26 μg/L. Although a 

sample from Sugar Creek was collected at the peak-of-record 

streamflow in May 2014, the total mercury concentration 

was only 2.8 μg/L, likely because several smaller-magnitude 

snowmelt events prior to the 2014 peak had already 

transported much of the sediment that had accumulated during 

the winter months of 2013–14 (fig. 17). 

185; 26.0

193; 2.8

19; 4.1 

0.01 

0.1 

1 

10 

1 10 100

Total mercury concentration, in micrograms per liter 

Streamflow, in cubic feet per second 

30 

200

EXPLANATION 

Sample result

Sample result from summer rainfall 

event, August 2014

Sample result from peak of 

record streamflow, May 2014

Sample result from peak snowmelt 

runoff, May 2013

Best fit line

185; 26.0: Streamflow, in cubic feet 

per second; total mercury concentration, 

in micrograms per liter 

Figure 17. Sampled streamflow and total mercury concentrations in Sugar Creek near Stibnite, central Idaho, 2012–14.
Surrogate Regression Modeling of Constituent Concentrations 35

Runoff and interflow (lateral flow in the unsaturated 

zone) associated with the first flow-inducing event of the 

snowmelt season tend to pick up unconsolidated, fine 

sediment that has accumulated on or just below the land 

surface and in the stream channel of the watershed (Wang 

and others, 2010). Because snowpack and snowmelt runoff 

vary from year to year, simple linear or periodic time 

functions probably do not adequately characterize hysteresis 

in constituent transport. Changes in particle-size distribution 

during prolonged streamflow events also have contributed to 

hysteresis in sediment and sediment-associated constituent 

transport (Landers and Sturm, 2013). Changes in sediment 

source during snowmelt runoff may be affected by antecedent 

conditions, including air temperature, soil moisture, and 

ground temperature. Forest fires burned much of the study area 

in 2000, 2006, and 2007 (fig. 1), and sediment transport in the 

study area may change as areas become re-vegetated and the 

sediment sources vary. 

Rainfall runoff events occurred each autumn in the study 

area, and samples were collected during one late-summer 

rainfall event in August 2014 (fig. 3). Changes in sediment 

source during rainfall runoff events may be affected by 

antecedent conditions and also can result from localized mass 

wasting. The relation between total mercury concentration 

and streamflow in the sample collected from Sugar Creek 

in August 2014 was substantially different as compared to 

all the other samples collected from Sugar Creek (fig. 17), 

likely because of conditions preceding the August rainfall 

event. The suspended-sediment concentration in the August 

2014 sample was 13 mg/L and the streamflow was 19 ft3

/s. 

The suspended-sediment concentration in the August 2014 

sample was in the range of suspended-sediment concentrations 

from other samples collected at streamflows between 80 and 

133 ft3/s on the rising or falling limb of the hydrograph 

during periods of sustained snowmelt runoff. The relatively 

high sediment and mercury concentration associated with a 

relatively low flow in August 2014 shows that sediment (and 

mercury) transport during a rainfall event preceded by a dry 

period is greater relative to sediment and mercury transport 

during a period of sustained high flows.

In general, use of the untransformed streamflow (rather 

than lnQ) to generate the streamflow variability term in load 

models resulted in greater significance of SVT as a predictor 

variable. Except for site 3, a specific streamflow variability 

term typically was more significant than other streamflow 

variability terms tested for significance in load models 

at a given site (table 7). At sites 1 and 2, which represent 

the headwaters of EFSFSR and Meadow Creek, a moving 

average of the previous 3 days compared to the daily mean 

streamflow generally was most significant as a term to account 

for hysteresis in constituent transport (table 7). Streamflow 

variability terms generally were insignificant in load models 

developed for site 4 (downstream of the Glory Hole), likely 

because most sediment and sediment-associated constituents 

were captured in the Glory Hole. A moving average of the 

previous 30 days compared to the daily mean streamflow 

generally was most significant as a term to account for 

hysteresis in constituent transport at site 5 (table 7). Mean 

slope in the watershed upstream of each monitoring site was 

similar (37–38 percent) at sites 1–4, but was 50 percent at 

site 5 (U.S. Geological Survey, 2012). Each monitoring site, 

with the exception of site 5, also showed a diurnal variation in 

streamflow during snowmelt runoff periods. A more detailed 

analysis of watershed characteristics that control sediment 

sources and transport is beyond the scope of this study.

Surrogate Regression Modeling of 

Constituent Concentrations

Results of surrogate regression modeling indicate the 

value of continuously measured specific conductance for 

estimating constituent concentrations. Specific conductance 

was used as a predictor variable in surrogate models developed 

to estimate concentrations of dissolved arsenic and antimony 

at all five monitoring sites (table 8). Continuous specific 

conductance was a more significant predictor than streamflow 

in four of five surrogate regression models for dissolved 

arsenic concentrations, and two of five surrogate regression 

models for dissolved antimony concentrations (table 8). 

Streamflow and specific conductance were both significant in 

models of dissolved arsenic and antimony concentrations at 

the remaining sites. 

Unlike LOADEST regression models, which were used 

to estimate and evaluate constituent transport in the study 

area on annual time scales, surrogate regression models 

were developed for the purpose of using real-time data from 

monitoring sites to generate a 15-minute time-series record 

of estimated constituent concentrations. LOADEST models 

also output estimated daily concentrations in addition to loads, 

and estimated LOADEST concentrations were compared 

to estimated daily concentrations from surrogate regression 

models. Surrogate regression models generally explained more 

variability in measured arsenic and antimony concentrations 

than LOADEST models, but specific conductance was not 

used as a predictor variable in the LOADEST models (tables 7

and 8). Results of surrogate regression modeling show that 

continuous water-quality and streamflow data at each studyarea monitoring site can be used to estimate concentrations 

of dissolved arsenic and antimony in real time. Further, in 

conjunction with real-time streamflow data, the estimated 

concentrations can be used to calculate loads in real time. 
36 Occurrence and Transport of Selected Constituents in Streams near the Stibnite Mining Area, Central Idaho, 2012–14

Specific conductance was not a significant predictor for 

estimating real-time concentrations of total mercury (table 8). 

Surrogate regression model results show that streamflow 

and the BFI calculated from the local minimum method of 

hydrograph separation (Lim and others, 2005) can be used 

to estimate concentrations and loads of total mercury in real 

time at sites 4 and 5. Additional total mercury samples are 

necessary to develop regression estimates of total mercury 

concentrations and loads at the remaining study sites. Sample 

results for total mercury from site 5 (Sugar Creek) suggest that 

summer storms can generate high concentrations of mercury at 

moderate streamflow (fig. 17). Substantial variance in sample 

results for total mercury at site 5 resulted in a large root mean 

square error for the surrogate regression model estimating total 

mercury concentrations at site 5. Additional samples collected 

during summer storms would provide valuable information 

towards understanding how mercury is transported to streams 

in the Stibnite area and would help to calibrate models for 

estimating mercury concentration and loading. 

Table 8. Regression coefficients and model diagnostics for surrogate models used to estimate concentrations of selected constituents 

at monitoring sites in the Stibnite mining area, central Idaho, 2012–14.

[Site names and locations are shown in table 1 and figure 1, respectively. Each regression model was calibrated using the available data collected at each station 

for water years 2012–14. The regression equation is lnC = I + a (SC) + b (lnSC) + c (Q) + d (lnQ)) + e [sin(2πT)] + f [cos(2πT)] + g(BFI), where C is the 

constituent concentration, in micrograms per liter; I is the regression intercept; Q is the centered streamflow, in cubic feet per second; sin (2πT) and cos (2πT) are 

periodic time functions that describe seasonal variability; BFI is the term describing streamflow variability; ln is the natural logarithm transformation; and a, b, 

c, d, e, f, and g are regression coefficients that remain constant over time. R2

 (coefficient of determination), represents the amount of variance explained by the 

model in percent. Abbreviations: BCF, bias correction factor; RMSE, root mean square error; –, no regression coefficient]

Constituent

Regression coefficient

BCF RMSE

(percent)

Surrogate 

concentration

model R2

LOADEST 

concentration 

model R2

N I a b c d e f g

Site 1

Arsenic, dissolved 20 0.614 0.025 – – – 0.107 0.007 – 1.003 8.34 96 86

Antimony, dissolved 20 -5.359 – 1.313 – – 0.314 0.175 – 1.009 15.2 86 72

Site 2

Arsenic, dissolved 21 -0.758 0.014 – – – – – – 1.004 9.65 87 89

Antimony, dissolved 18 14.457 – 2.920 – 0.816 0.375 0.583 – 1.012 18.1 72 62

Site 3

Arsenic, dissolved 23 2.273 – 1.126 – – 0.127 -0.106 – 1.020 20.8 76 58

Antimony, dissolved 22 -9.525 – 2.377 – 0.503 0.532 0.303 – 1.055 37.3 65 54

Site 4

Arsenic, dissolved 21 -3.072 – 1.561 – – -0.044 -0.180 – 1.007 13.6 95 72

Antimony, dissolved 21 -11.776 – 2.888 – 0.615 0.182 0.156 – 1.010 16.1 91 32

Mercury, total 15 -3.957 – – 0.003 – – – -1.755 1.030 35.0 85 76

Site 5

Arsenic, dissolved 21 1.407 0.011 – – – 0.119 0.274 – 1.013 18.2 86 77

Antimony, dissolved 20 -0.867 0.021 – – – 0.151 0.410 – 1.032 29.1 90 75

Mercury, total 19 3.045 – – 0.010 – -0.369 -1.194 -7.644 1.367 109 87 82
Summary 37

Areas of Further Study

Additional samples collected on the rising and falling 

limbs of the streamflow hydrograph during summer storms 

would help validate all regression models presented in this 

report. Given the remote location of the study area and the 

flashiness of storm events, obtaining storm samples may 

require installation of auto-samplers. However, because 

concentrations of sediment and sediment-associated 

constituents may not be evenly distributed in the stream cross 

section, auto-samplers, which are point samplers, may not 

provide an adequate representation of stream concentrations. 

A continuous physical measure of sediment in the water 

column, or a surrogate such as turbidity, is not appropriate for 

the study area because most sediment transported is coarse 

(>0.0625 mm in diameter) and does not necessarily cause 

increases in turbidity. Acoustic backscatter may or may not be 

a significant predictor of sediment concentration at study-area 

sites and would require further investigation of feasibility. 

The steep gradient in the study area may contribute to bedload 

transport of coarse sediment and sediment-associated metals. 

Bedloads are not well characterized by surrogate measures of 

sediment concentrations in the water column. 

MGI-directed sample collection at various surface-water 

sites within the study area in addition to the five USGS 

monitoring sites operated and sampled during this study. 

Measured discrete loads at additional sites in the study area 

could be compared to load estimates in the Meadow Creek 

reach and the Glory Hole reach that are summarized in this 

report. Such comparisons may identify more specific source 

areas and validate LOADEST modeling results.

Tracer-injection methods also can be used to validate 

findings in this report and to identify more specific sources of 

contaminants. Tracer injection in discrete reaches of interest 

(such as the Glory Hole reach) can provide reliable streamflow 

measurements on a watershed scale in addition to spatially 

detailed concentration information when combined with 

synoptic sampling. Streamflow and concentration data then 

can be used to develop mass-loading profiles for metals of 

interest. Streamflow and loading profiles identify the primary 

sources in spatial detail and demonstrate the importance of 

unsampled, dispersed subsurface inflows and attenuation 

(Kimball and others, 2004). Longitudinal loading profiles 

generated from tracer injection studies, therefore, are useful 

for targeting remediation efforts.

With continued operation of continuous stream stage and 

specific conductance sensors at monitoring sites, real time 

estimates of arsenic, antimony, and mercury concentrations 

can be made publicly available on the USGS National Water 

Information System (U.S. Geological Survey, 2015). Changes 

in land use associated with mining activities may be detected 

with subsequent evaluation of regression model coefficients 

and inclusion of a predictor variable that accounts for trends.

Summary

Water-quality and streamflow monitoring during 2012–

2014 showed that concentrations of trace elements, except 

for mercury, generally do not exceed ambient water-quality 

criteria applicable in streams in the Stibnite mining area of 

central Idaho. Total mercury was detected at concentrations 

greater than the State of Idaho 0.012-microgram per liter 

(μg/L) chronic exposure limit for freshwater aquatic life at 

five monitoring sites used for the study. Arsenic and antimony 

concentrations exceeded human-health based water-quality 

criteria in Sugar Creek (site 5) and both monitoring sites 

located on the East Fork of the South Fork of the Salmon 

River (EFSFSR) downstream of the confluence with Meadow 

Creek. Arsenic concentrations exceeded the 10-μg/L humanhealth-based standard about one‐half the time in the EFSFSR 

upstream of the confluence with Meadow Creek (site 1), but 

did not exceed 10 μg/L at Meadow Creek (site 2). Site 2 was 

selected to represent background conditions, and the median 

total arsenic concentration in samples collected from site 2 

was 1.3 μg/L. Water temperature exceeded the 9 °C maximum 

daily average temperature criterion for salmonid spawning 

at least 29 percent of the time at each site. Water temperature 

at sites 3 and 4 in the EFSFSR and site 5 in Sugar Creek 

exceeded the 13 °C maximum daily maximum temperature 

criterion for salmonid spawning between 4 and 9 percent of 

the time. 

Two distinct constituent sources are present in the study 

area. Significant positive correlations between streamflow and 

concentrations of suspended sediment and sediment-associated 

constituents (total aluminum, total lead, and total mercury) 

indicate that surface runoff and stream-channel erosion deliver 

these constituents to streams during rainfall or snowmelt 

runoff. Significant negative correlations between streamflow 

and concentrations of arsenic, antimony, and dissolved iron 

and magnesium indicate that groundwater is the source 

for these constituents. Significant correlation between 

constituent concentrations and streamflow also showed that 

the U.S. Geological Survey LOAD ESTimation (LOADEST) 

program is a useful tool for estimating mean annual loads 

and streamflow-weighted concentrations (FWCs) of selected 

constituents in streams in the study area. 

Mass balance estimates show that concentrated sources 

of arsenic, antimony, and dissolved manganese are present 

in discrete reaches along Meadow Creek and between sites 3 

and 4 along the EFSFSR. Although they accounted for only 

25 percent of the total streamflow, the reaches along Meadow 

Creek (the Meadow Creek reach) and between sites 3 and 4 

(the Glory Hole reach) accounted for 80 percent of the total 

arsenic and antimony loads and 86 percent of the dissolved 

manganese load transported downstream of the study area. 

Estimated FWCs exceeded human-health based water-quality 

criteria for arsenic and antimony at sites 3 and 4 in the 

EFSFSR and for arsenic at site 5 in Sugar Creek.
38 Occurrence and Transport of Selected Constituents in Streams near the Stibnite Mining Area, Central Idaho, 2012–14

Continuously monitored specific conductance was 

statistically significant as a predictor (surrogate) for 

concentrations of dissolved arsenic and antimony at all 

study-area sites. Surrogate regression models using continuous 

stage and specific conductance, and, in some cases, functions 

of streamflow and time, can be used to estimate concentrations 

and loads of dissolved arsenic and antimony at all five 

study-area sites. 

The East Fork of Meadow Creek was not monitored 

as part of this study, but LOADEST model results indicate 

that the East Fork Meadow Creek, the only tributary stream 

in the Meadow Creek reach, likely accounts for most of the 

suspended sediment loading in the study area. Sediment and 

sediment-associated constituent loads from the East Fork of 

Meadow Creek are trapped in the Glory Hole between sites 

3 and 4. FWCs of suspended sediment, total aluminum, and 

total lead decrease in the Glory Hole reach between sites 3 

and 4. The Meadow Creek reach was the largest contributor 

of suspended sediment and the second largest contributor 

of total aluminum in the study area. The East Fork Meadow 

Creek in the Meadow Creek reach was not sampled, but 

likely contributes most of the sediment and aluminum 

attributed to the Meadow Creek reach. Because sediment and 

sediment-associated constituents from sources upstream of 

the Glory Hole are trapped in the Glory Hole, Sugar Creek 

accounts for most of the sediment and sediment-associated 

constituent loading transported downstream of the study 

area. Sugar Creek (site 5) is the second largest contributor 

of suspended sediment and the largest contributor of total 

aluminum in the study area. Sugar Creek accounted for 98 

percent of the total mercury load transported downstream of 

the study area. 

LOADEST model results indicated hysteresis in transport 

of suspended sediment and sediment-associated constituents 

within the study area. Biases in estimated loads were reduced 

using an additional predictor variable to describe streamflow 

variability relative to an n-day average streamflow. The 

ratio of estimated surface runoff to streamflow, known as 

the base-flow index, was tested for significance as another 

predictor variable to account for streamflow variability. 

Different streamflow variability terms were significant as 

predictor variables in different sub-watersheds, indicating 

that watershed characteristics and (or) conditions preceding 

erosional events may influence sediment transport in the study 

area. Results from samples collected during a summer storm in 

August 2014 showed that LOADEST and surrogate regression 

models may not produce reliable estimates of sediment and 

sediment-associated constituent concentrations and loads 

during rainfall runoff events. Regression models using 

streamflow and the base-flow index as predictor variables 

accounted for at least 80 percent of the variability in sampled 

concentrations of total mercury at sites 4 (EFSFSR above 

Sugar Creek) and 5 (Sugar Creek). With continued operation 

of continuous stage sensors, concentrations and loads of 

total mercury can be estimated in real time at sites 4 and 5. 

Additional sample results are necessary to evaluate LOADEST 

and surrogate models for total mercury concentrations and 

loads at remaining study area sites and during summer storms 

at sites 4 and 5. 

Acknowledgments

The author thanks Rhonda Weakland, Alvin Sablan, Pete 

Spatz, Russ Chirstensen, and Keith Hein for their dedication 

to collecting and processing water-quality samples, continuous 

water-quality data, and streamflow data at these remote sites 

under an extreme range of weather and streamflow conditions. 

Thanks also to members of the Boise Field Office and Idaho 

Falls Field Office for installation of bank-operated cableways 

at two of the monitoring sites in the study area.

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chemistry—A practical guide (3d ed.): Boca Raton, Fla., 

CRC Press, 618 p.

Wood, M.S., and Etheridge, A.B., 2011, Water-quality 

conditions near the confluence of the Snake and Boise 

Rivers, Canyon County, Idaho: U.S. Geological Survey 

Scientific Investigations Report 2011–5217, 70 p.

Woodworth, M.T., and Connor, B.F., 2003, Results of the 

U.S. Geological Survey’s analytical evaluation program for 

standard reference samples distributed in March 2003: U.S. 

Geological Survey Open-File Report 2003-261, 109 p.
42 Occurrence and Transport of Selected Constituents in Streams near the Stibnite Mining Area, Central Idaho, 2012–14

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Appendix A. Analysis of Quality-Assurance and Quality-Control Data from 

Field Samples in Streams in the Stibnite Mining Area, Central Idaho, and 

Laboratory Samples from the National Water-Quality Laboratory, 2012–14

Results from the National Water Quality Laboratory’s 

(NWQL) inorganic blind sampling project (IBSP) showed 

a positive bias for dissolved analyses of cadmium and lead. 

Wilcoxon signed-rank tests were used to assess bias relative 

to the median expected concentration in the reference sample 

(Woodworth and Connor, 2003; T. Struzenski, U.S. Geological 

Survey, written commun., 2013). Positive biases in dissolved 

cadmium and lead results were known to occur starting in 

October 2011 and January 2012, respectively, and were 

corrected by the end of water year 2013. Positive bias in 

dissolved cadmium results ranged from 13 to less than 

6 percent, and positive bias in dissolved lead results ranged 

from 7.4 to 5.8 percent (T. Struzenski, U.S. Geological Survey, 

written commun., 2013).

Positive bias in dissolved concentrations of cadmium 

and lead affected the quality of analytical results. Uncensored 

dissolved concentrations were greater than whole-water 

concentrations in 86 percent of cadmium results and 

24 percent of lead results (table A1). Consistent positive 

or negative bias in dissolved or whole-water results for 

zinc, copper, antimony, and arsenic was not documented. 

However, dissolved concentrations of zinc, copper, antimony, 

and arsenic also commonly exceeded concentrations 

from whole-water samples (table A1. Dissolved antimony 

concentrations that were commonly higher than total antimony 

concentrations resulted in model results with larger loads and 

streamflow-weighted concentrations for dissolved antimony 

than total antimony in some cases. However, this did not 

affect the interpretive results in the report because analytical 

data indicate that most of the antimony on site is dissolved. 

Numerous dissolved results were flagged in the National 

Water Information System (NWIS) database based on:

1. The known positive bias shown in IBSP analytical 

results for dissolved cadmium and lead,

2. The relative percent difference (RPD) between 

uncensored dissolved concentrations and censored or 

uncensored whole-water concentrations, and

3. The 2014 long-term method detection level (LT-MDL) 

for the dissolved constituent. The LT-MDL is determined 

based on the standard deviation of a minimum of 24 

method-detection-limit spike sample measurements 

over an extended period of time (Oblinger Childress and 

others, 1999).

The NWQL collects quality-control data on a 

continuous basis to assess variations in LT–MDLs and to 

determine or revise LT–MDLs from year to year. Several 

LT-MDLs changed during the study period (table A1). 

Dissolved concentrations were flagged as “estimated” in 

the NWIS database if they were reported as uncensored at 

a concentration lower than the latest LT-MDL regardless of 

the RPD compared to the whole-water concentration in the 

same sample. Uncensored dissolved constituents detected at 

higher concentrations than whole-water constituents were 

flagged as “reviewed and rejected” in the NWIS database if 

the RPD compared to the censored or uncensored whole-water 

concentration in the same sample was greater than 20 percent. 

In most of these cases, repeated laboratory analysis for 

dissolved and total constituents confirmed original results. 

Analysis of the quality-control dataset collected for this study 

includes rejected results, but they are not otherwise used, 

interpreted, or provided to the public. Estimated results are 

used, interpreted, and provided to the public. 

During water years 2012–14, 11 split replicate samples 

were collected on a rotating basis between the five study 

sites. Split-replicate RPDs greater than 20 percent for 

individual sets of samples generally occurred with rarely 

detected trace elements or trace elements detected near the 

applicable LT-MDL. Relatively large RPDs also occurred with 

concentrations of total iron, total aluminum, and suspended 

sediment in split-replicates collected at site 3 near the peak 

runoff event in May 2012 (table A2).

Results from the field blanks indicate overall acceptable 

quality (table A2). Four field blanks collected between 

May 17 and June 23, 2012, contained 29 out of a total of 

41 detections (table A3). Field equipment cleaning practices 

between May and June of 2012 may have been ineffective in 

removing residual contamination, which may have resulted in 

positive bias to sample results, but other sources of bias also 

were present during the period. Forty-eight percent of the field 

blank detections between May and June 2012 were associated 

with cadmium, lead, and manganese. Positive laboratory bias 

in dissolved cadmium and lead was confirmed in laboratory 

quality-assurance testing (T. Struzenski, U.S. Geological 

Survey, written commun., 2013). Eight detections of 

dissolved manganese out of 15 blanks probably resulted 

from bias introduced during filtration (S. Skrobialowski, 

U.S. Geological Survey, written commun., 2015). 
44 Occurrence and Transport of Selected Constituents in Streams near the Stibnite Mining Area, Central Idaho, 2012–14

Blank sample detections did not indicate consistent 

positive bias from sampling equipment cleaning procedures or 

ambient conditions during sample processing, but did indicate 

occasional contamination bias from the source blank solution, 

shipping, storing, or analytical procedures. Blank detections 

that exceeded the minimum detections in environmental 

samples from the same trip are further summarized in 

table A3. In some cases, the blank detection exceeded the 

maximum detected concentration in environmental samples 

collected during the same trip, ruling out contamination 

bias from ambient processing conditions or equipment. 

In other cases, the dissolved constituent was detected and 

the total constituent was not detected in the same blank 

sample, suggesting positive bias in analytical procedures for 

the dissolved constituent. One detection each of dissolved 

cadmium, total lead, and total aluminum were within the range 

Table A1. Quality-assurance summary for selected constituent analyses from streams in the Stibnite mining area, central Idaho, 

2012–14.

[Abbreviations: QA, quality assurance; QC quality control; RPD, relative percent difference; >, greater than; μg/L, micrograms per liter; NWIS, National Water 

Information System; LT-MDL, long-term method detection limit. Dissolved concentrations are determined from filtered samples and whole-water concentrations 

are determined from unfiltered samples]

Cadmium Copper Lead Zinc Antimony Arsenic

Number of environmental samples (including split replicate 

QA/QC samples)

118 115 118 118 115 118

Number of uncensored dissloved results 36 17 68 11 115 118

Number of uncensored dissolved concentrations > whole-water 

concentrations (censored or uncensored)

31 8 16 4 64 32

Percentage of uncensored dissolved concentrations > whole-water 

concentrations (censored or uncensored)

86 47 24 36 56 27

Average RPD between uncensored dissolved concentrations 

> whole-water concentrations (censored or uncensored)

91.1 42.3 32.9 63.2 8.15 5.58

Number of dissolved results flagged as “rejected” in the NWIS 

database

22 6 10 0 3 0

Long-term method detection limit October 1, 2011 to September 30, 

2013, μg/L (dissolved; whole-water)

0.016;

0.016

0.80;

0.70

0.025;

0.04

1.4;

3.0

0.027;

0.18

1

0.04;

0.28

Long-term method detection limit as of October 1, 2013, μg/L 

(dissolved; whole-water)

0.03;

0.03

0.80;

0.80

0.04;

0.04

2.0;

2.0

0.027;

0.18

0.10;

0.20

Number of dissolved results flagged as “estimated” because of 

increased LT-MDL

6 0 0 0 0 0

1

The LT-MDL for dissolved arsenic was 0.03 μg/L from October 1, 2011 to September 30, 2012 and increased to 0.04 μg/L until September 30, 2013.

of detections for the same analyte during the same sampling 

trip, suggesting possible field equipment contamination. 

Overall, split replicate, field blank, and IBSP 

quality-assurance sample results indicate that detections of 

dissolved cadmium and lead in environmental sample results 

should be used with caution. Blank results also suggest 

possible positive laboratory bias in dissolved chromium 

during May 2012. Manganese concentrations in environmental 

samples collected with potentially contaminated capsule 

filters were compared with environmental samples collected at 

similar streamflows at each site using uncontaminated capsule 

filters. The comparison showed that dissolved manganese 

introduced during sample filtration and quantified in blank 

results did not consistently bias environmental sample results 

for dissolved manganese.
Appendix A 45

Table A2. Results from quality-control samples collected in the Stibnite mining area, central Idaho, 2012–14.[Bold type indicates a relative percent difference of greater than 20 percent. Shaded cells indicate that the maximum field blank detection was higher than the minimum detection for an analyte in environmental samples. Abbreviations: CaCO3, carbonate; RPD, relative percent difference; mg/L, milligrams per liter; μg/L, micrograms per liter; (f), filtered; (unf), unfiltered; >, greater than; <, less than; mm, millimeter; 

NA, not applicable; N, no; Y, yes; 2×LT-MDL long-term method detection level multiplied by 2 (also known as the laboratory reporting level or LRL)]

Constituent

Number of 

field blank 

samples

Number of 

field blank 

detections

Number of 

field blank 

detections 

> 2×LT-MDL

Median detected 

field blank 

concentration

(μg/L)

Maximum 

detected 

field blank 

concentration

(μg/L)

Minimum 

detected 

concentration in 

environmental

samples

(μg/L)

Number of 

split replicate

pairs 

Split 

replicate 

minimum 

RPD

Split 

replicate 

75th percentile 

RPD

Split 

replicate 

maximum 

RPD

Hardness as CaCO3, mg/L 15 0 0 NA NA 13.5 9 0.00 1.66 6.67

Calcium (f), mg/L 15 2 0 NA 0.034 4.2 9 0.52 1.73 6.78

Magnesium, (f), mg/L 15 0 0 NA NA 0.72 9 0.00 1.95 7.55

Magnesium, (unf), mg/L 20 1 0 NA 0.009 0.72 11 0.37 5.00 8.40

Sodium, (f), mg/L 15 0 0 NA NA 1.25 9 0.00 4.46 7.96

Potassium, (f), mg/L 15 1 0 NA 0.008 0.46 9 0.30 4.15 29.1

Chloride, (f), mg/L 15 1 1 NA 6.07 0.10 9 0.00 3.07 3.82

Sulfate, (f), mg/L 15 1 1 NA 0.10 0.93 9 0.00 2.02 35.3

Fluoride, (f), mg/L 15 0 0 NA NA 0.03 8 0.00 5.17 22.2

Silica, (f), mg/L 15 2 0 NA 0.07 8.45 9 0.00 3.23 4.08

Arsenic, (f), μg/L 20 3 0 0.05 0.06 0.61 11 0.00 4.55 8.00

Arsenic, (unf), μg/L 20 0 0 NA NA 0.81 11 0.50 6.63 8.70

Cadmium, (f), μg/L 20 5 4 0.303 1.22 0.033 11 0.00 36.1 63.6

Cadmium, (unf), μg/L 20 4 1 0.036 0.101 0.016 11 0.00 30.3 119

Chromium, (f), μg/L 20 2 0 NA 0.09 0.052 11 0.00 16.7 57.8

Chromium, (unf), μg/L 20 0 0 NA NA 0.05 11 0.00 0.00 18.2

Copper, (f), μg/L 20 1 1 NA 2.00 0.117 11 0.00 0.00 40.0

Copper, (unf), μg/L 20 0 0 NA NA 0.30 11 0.00 0.00 117

Iron, (f), μg/L 20 1 0 NA 6.00 4.1 11 0.81 16.4 23.4

Iron, (unf), μg/L 20 0 0 NA NA 11.2 10 0.00 16.0 54.7

Lead, (f), μg/L 20 4 0 0.046 0.069 0.008 10 0.00 72.6 93.0

Lead, (unf), μg/L 20 1 0 NA 0.06 0.01 11 0.00 18.2 76.9

Manganese, (f), μg/L 15 8 1 0.21 0.59 0.36 9 1.28 23.5 54.8

Zinc, (f), μg/L 20 1 0 NA 3.30 1.4 10 0.00 0.00 38.2

Zinc, (unf), μg/L 20 1 1 NA 4.50 2.1 11 0.00 0.00 158

Antimony, (f), μg/L 20 1 0 NA 0.027 0.23 11 0.00 3.74 4.34

Antimony, (unf), μg/L 20 0 0 NA NA 0.21 11 0.00 4.58 7.23

Aluminum, (f), μg/L 20 0 0 NA NA 2.9 11 1.16 18.4 66.7

Aluminum, (unf), μg/L 20 1 1 NA 8.20 4.7 10 0.87 13.9 45.9

Suspended sediment, 

percent fines (<0.0625 mm)

0 0 0 NA NA 11 6 1.40 41.6 63.4

Mercury, (f), μg/L 8 0 0 NA NA 0.005 2 13.3 NA 18.2Mercury, (unf), μg/L 11 0 0 NA NA 0.005 2 7.41 NA 22.2

Suspended sediment 

concentration, mg/L

0 0 0 NA NA 1 6 0.00 65.6 66.7

Sum 549 41 11 NA NA NA 310 NA NA NA
46 Occurrence and Transport of Selected Constituents in Streams near the Stibnite Mining Area, Central Idaho, 2012–14

Table A3. Blank sample detections exceeding minimum detections in environmental samples collected in the Stibnite mining 

area, central Idaho, 2012–14.

[Likely source of contamination: Handling, likely contamination bias from any of the following sources—source blank solution, shipping, storing, or 

analytical procedures; Equipment, contamination bias from sampling equipment; Filter, likely contamination bias from a capsule filter. Abbreviations:

mg/L, milligrams per liter; μg/L, micrograms per liter; (f), filtered; (unf), unfiltered; <, less than; NA, not applicable]

Constituent Blank

detection date Blank

Detected in

dissolved and

total results?

Environmental 

range during 

sampling event

Likely source of 

contamination

Chloride (f), mg/L 05-23-12 6.07 NA 0.23–0.38 Handling

Aluminum (unf), μg/L 06-13-12 8.2 No 58.2–199 Equipment

Cadmium (f), μg/L 05-17-12 0.434 Yes 0.088–0.371 Handling

Cadmium (f), μg/L 05-18-12 1.22 Yes 0.088–0.371 Handling

Cadmium (f), μg/L 05-23-12 0.251 Yes 0.088–0.371 Handling

Cadmium (f), μg/L 11-06-12 0.017 No <0.016–0.056 Handling

Cadmium (f), μg/L 10-01-14 0.303 No <0.030–0.194 Handling

Cadmium (unf), μg/L 05-17-12 0.025 Yes 0.017–0.037 Equipment

Cadmium (unf), μg/L 05-18-12 0.046 Yes 0.017–0.037 Handling

Cadmium (unf), μg/L 05-23-12 0.101 Yes 0.017–0.037 Handling

Cadmium (unf), μg/L 06-13-12 0.021 No <0.016–0.156 Handling

Chromium (f), μg/L 05-17-12 0.09 No 0.17–0.36 Handling

Chromium (f), μg/L 05-18-12 0.09 No 0.17–0.36 Handling

Copper (f), μg/L 05-23-12 2.00 No <0.80 Handling

Iron (f), μg/L 05-23-12 6.00 No 18.0–33.6 Handling

Lead (f), μg/L 05-18-12 0.029 No 0.027–0.063 Handling

Lead (f), μg/L 05-23-12 0.069 No 0.027–0.063 Handling

Lead (f), μg/L 06-14-12 0.027 No 0.027–0.105 Handling

Lead (f), μg/L 05-19-14 0.062 No <0.040–0.048 Handling

Lead (unf), μg/L 06-13-12 0.06 No 0.04–0.10 Equipment

Manganese (f), μg/L 05-17-12 0.38 NA 1.16–6.29 Filter

Manganese (f), μg/L 05-18-12 0.59 NA 1.16–6.29 Filter

Manganese (f), μg/L 05-23-12 0.17 NA 1.16–6.29 Filter

Manganese (f), μg/L 06-13-12 0.14 NA 1.28–9.08 Filter

Manganese (f), μg/L 11-06-12 0.17 NA 0.57–37.5 Filter

Manganese (f), μg/L 03-26-13 0.25 NA 1.56–28.8 Filter

Manganese (f), μg/L 06-25-13 0.17 NA 0.83–18.5 Filter

Manganese (f), μg/L 04-25-14 0.29 NA 0.77–20.5 Filter

Zinc (f), μg/L 05-23-12 3.3 No <1.4–1.5 Handling

Zinc (unf), μg/L 08-28-12 4.5 No <3.0 Handling
Appendix B 47

Appendix B. Statistical Summary of Constituent Concentrations in Water-Quality 

Samples Collected at Streamflow-Gaging Stations in the Stibnite Mining Area, 

Central Idaho, 2012–14

Appendix B is a Microsoft Excel® file and is available for download at http://dx.doi.org/10.3133/sir20155166.
Publishing support provided by the U.S. Geological Survey 

Science Publishing Network, Tacoma Publishing Service Center

For more information concerning the research in this report, contact the 

Director, Idaho Water Science Center

U.S. Geological Survey 

230 Collins Road

Boise, Idaho 83702

http://id.water.usgs.gov
Etheridge—Occurrence and Transport of Selected Constituents in Streams near the Stibnite Mining Area, Central Idaho, 2012–14—Scientific Investigations Report 2015–5166

ISSN 2328-0328 (online)

http://dx.doi.org/10.3133/sir20155166