Prepared in cooperation with the 

City of Creede, Colorado and the U.S. Forest Service 

Evaluation of Metal Loading to Streams near Creede, 

Colorado, August and September 2000 

Scientific Investigations Report 2004–5143


U.S. Department of the Interior 

U.S. Geological Survey 

Evaluation of Metal Loading to Streams near Creede, 

Colorado, August and September 2000

Prepared in cooperation with the

CITY OF CREEDE, COLORADO,

and the U.S. FOREST SERVICE

By B.A. Kimball, R.L. Runkel, K. Walton-Day, and B.K. Stover

Salt Lake City, Utah

2006

U.S. Geological Survey

SCIENTIFIC INVESTIGATIONS REPORT 2004-5143
U.S. DEPARTMENT OF THE INTERIOR

GALE A. NORTON, Secretary

U.S. GEOLOGICAL SURVEY

P. Patrick Leahy, Acting Director

For additional information write to: Copies of this report can be purchased from:

U.S. Geological Survey

Branch of Information Services

Box 25286, Federal Center

Denver, CO 80225-0286

1-888-ASK-USGS

Any use of trade, product, or firm names in this publication is for descriptive purposes only and does 

not imply endorsement by the U.S. Government.

Director, Utah Water Science Center

U.S. Geological Survey

2329 West Orton Circle

Salt Lake City, UT 84119

http://ut.water.usgs.gov
iii

CONTENTS

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

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

Purpose and Scope ...................................................................................................................................... 3

Methods................................................................................................................................................................ 3

Approach ..................................................................................................................................................... 3

Tracer Injections and Stream Discharge ..................................................................................................... 3

Synoptic Sampling and Analytical Methods............................................................................................... 4

Mass-Loading Analysis............................................................................................................................... 5

Principal Components Analysis .................................................................................................................. 6

Evaluation of Metal Loading................................................................................................................................ 7

West Willow Creek ..................................................................................................................................... 7

Discharge ........................................................................................................................................... 10

Chemical Characterization of Synoptic Samples............................................................................... 10

Load Profiles ...................................................................................................................................... 20

Principal Locations of Mass Loading ................................................................................................ 23

Unsampled Inflow.............................................................................................................................. 31

Attenuation of Load ........................................................................................................................... 31

East Willow Creek ...................................................................................................................................... 31

Discharge ........................................................................................................................................... 31

Chemical Characterization of Synoptic Samples............................................................................... 34

Load Profiles ...................................................................................................................................... 40

Principal Locations of Mass Loading ................................................................................................ 40

Unsampled Inflow.............................................................................................................................. 40

Attenuation of Metals......................................................................................................................... 40

Lower Willow Creek................................................................................................................................... 40

Discharge ........................................................................................................................................... 49

Chemical Characterization of Synoptic Samples............................................................................... 49

Load Profiles ...................................................................................................................................... 57

Summary—Implications for Remediation ........................................................................................................... 57

References Cited .................................................................................................................................................. 62

Appendix—Results of Chemical Analyses for Synoptic Samples Collected near Creede, Colorado ................. 64
iv

FIGURES

Figure 1. Map showing location of the Willow Creek watershed, indicating study reaches for tracerinjection study reaches and principal mines along the study reach near Creede, Colorado .............. 2

Figure 2. Map showing location of stream segments and inflow samples for East and West Willow 

Creeks, Colorado ............................................................................................................................... 8

Figure 3. Graph showing variaton of bromide concentration and calculated discharge with distance along 

the study reach, West Willow Creek, Colorado, September 2000..................................................... 11

Figure 4. Graph showing variation of (a) pH and (b) calcium, sulfate, and alkalinity concentration with 

distance along the study reach, West Willow Creek, Colorado, September 2000............................. 12

Figure 5. Box plot showing distribution of dissolved (blue) and collodial (orange) metal concentrations in

synoptic stream samples, West Willow Creek, Colorado, September 2000...................................... 14

Figure 6. Graph showing variation of aluminum concentration in ultrafiltrate, 0.45-μm filtered, and

total-recoverable samples with distance along the study reach, West Willow Creek, Colorado, 

September 2000 ................................................................................................................................. 15

Figure 7. Graph showing variation of iron concentration in ultrafiltrate, 0.45-μm filtered, and totalrecoverable samples with distance along the study reach, West Willow Creek, Colorado, 

September 2000 ................................................................................................................................. 16

Figure 8. Graph showing variation of zinc concentration in ultrafiltrate, 0.45-μm filtered, and totalrecoverable samples with distance along the study reach, West Willow Creek, Colorado, 

September 2000 ................................................................................................................................. 17

Figure 9. Graphs showing biplot of principal component scores for synoptic samples and loadings for 

chemical constituents, West Willow Creek, Colorado, September 2000 .......................................... 18

Figure 10. Graphs showing (A) variation of aluminum load with distance and (B) changes in aluminum 

load for individual stream segments, West Willow Creek, Colorado, September 2000 ................... 22

Figure 11. Graphs showing (A) variation of manganese load with distance and (B) changes in manganese 

load for individual stream segments, West Willow Creek, Colorado, September 2000 ................... 24

Figure 12. Graphs showing (A) variation of zinc load with distance and (B) changes in zinc load for 

individual stream segments, West Willow Creek, Colorado, September 2000................................. 25

Figure 13. Graphs showing (A) variation of strontium load with distance and (B) changes in strontium 

load for individual stream segments, West Willow Creek, Colorado, September 2000 ................... 26

Figure 14. Graphs showing (A) variation of sulfate load with distance and (B) changes in sulfate load for

individual stream segments, West Willow Creek, Colorado, September 2000................................. 27

Figure 15. Graphs showing (A) variation of iron load with distance and (B) changes in iron load for 

individual stream segments, West Willow Creek, Colorado, September 2000................................. 28

Figure 16. Graphs showing (A) variation of cadmium load with distance and (B) changes in cadmium 

load for individual stream segments, West Willow Creek, Colorado, September 2000 ................... 29

Figure 17. Graphs showing (A) variation of lead load with distance and (B) changes in lead load for 

individual stream segments, West Willow Creek, Colorado, September 2000................................. 30

Figure 18. Graph showing variation of bromide concentration and calculated discharge, East Willow 

Creek, Colorado, August 2000 .......................................................................................................... 33

Figure 19. Graphs showing variation of (A) pH and (B) calcium, sulfate, and alkalinity concentration 

with distance along the study reach, East Willow Creek, Colorado, August 2000 ........................... 35

Figure 20. Box plot showing distribution of dissolved (blue) and collodial (orange) metal concentration 

in synoptic stream samples, East Willow Creek, Colorado, August 2000 ........................................ 36
 v

Figure 21. Graph showing variation of zinc concentration with distance along the study reach, East 

Willow Creek, Colorado, August 2000 ............................................................................................. 37

Figure 22. Graph showing variation of iron concentration with distance along the study reach, East 

Willow Creek, Colorado, August 2000 ............................................................................................. 38

Figure 23. Biplot indicating classification of synoptic samples from East Willow Creek, Colorado, 

August 2000....................................................................................................................................... 39

Figure 24. Graphs showing (A) variation of sulfate load with distance and (B) changes in sulfate load 

for individual stream segments, East Willow Creek, Colorado, August 2000 .................................. 42

Figure 25. Graphs showing (A) variation of strontium load with distance and (B) changes in strontium 

load for individual stream segments, East Willow Creek, Colorado, August 2000 .......................... 43

Figure 26. Graphs showing (A) variation of manganese load with distance and (B) changes in manganese

load for individual stream segments, East Willow Creek, Colorado, August 2000 .......................... 44

Figure 27. Graphs showing (A) variation of zinc load with distance and (B) changes in zinc load for 

individual stream segments, East Willow Creek, Colorado, August 2000........................................ 45

Figure 28. Graphs showing (A) variation of aluminum load with distance and (B) changes in aluminum

load for individual stream segments, East Willow Creek, Colorado, August 2000 .......................... 46

Figure 29. Graphs showing (A) variation of iron load with distance and (B) changes in iron load 

for individual stream segments, East Willow Creek, Colorado, August 2000 .................................. 47

Figure 30. Map showing location of synoptic sampling sites, lower Willow Creek, near Creede, Colorado, 

August 2000....................................................................................................................................... 48

Figure 31. Graph showing discharge at sampling sites along the study reach, lower Willow Creek, 

Colorado, August 2000 ...................................................................................................................... 51

Figure 32. Graph showing variation of pH with distance along the study reach, indicating paths of braids, 

lower Willow Creek, Colorado, August 2000 ................................................................................... 52

Figure 33. Box plot showing distribution of selected dissolved (blue) and colloidal (orange) metal 

concentrations, lower Willow Creek, Colorado, August 2000 .......................................................... 53

Figure 34. Graph showing variation of sulfate concentration with distance along the study reach, 

indicating paths of braids, lower Willow Creek, Colorado, August 2000......................................... 54

Figure 35. Graph showing variation of manganese concentration with distance along the study reach, 

indicating paths of braids, lower Willow Creek, Colorado, August 2000......................................... 55

Figure 36. Graph showing variation of zinc concentration with distance along the study reach, indicating 

paths of braids, lower Willow Creek, Colorado, August 2000.......................................................... 56

Figure 37. Graph showing total strontium load at synoptic sampling sites, lower Willow Creek, 

Colorado, August 2000 ...................................................................................................................... 58

Figure 38. Graph showing total sulfate load at synoptic sampling sites, lower Willow Creek, Colorado,

August 2000....................................................................................................................................... 59

Figure 39. Graph showing total manganese load at synoptic sampling sites, lower Willow Creek, 

Colorado, August 2000 ...................................................................................................................... 60

Figure 40. Graph showing total zinc load at synoptic sampling sites, lower Willow Creek, Colorado, 

August 2000....................................................................................................................................... 61
vi 

TABLES

Table 1. Sample identification, source, distance along the injection study reach, site description, pH, 

specific conductance, tracer concentration, and calculated discharge for synoptic samples 

from West Willow Creek, Colorado, September 2000 .................................................................. 9

Table 2. Median composition of stream and inflow groups distinguished by principal components

analysis, West Willow Creek, Colorado, September 2000............................................................ 19

Table 3. Summary of load calculations, West Willow Creek, Colorado, September 2000......................... 21

Table 4. Synoptic sampling sites, East Willow Creek, Colorado, August 2000.......................................... 32

Table 5. Summary of load calculations, East Willow Creek, Colorado, August 2000................................ 41

Table 6. Synoptic sampling sites, lower Willow Creek, Colorado, August 2000 ....................................... 50

Table 7. Change in load through study reach of lower Willow Creek, Colorado, August 2000................. 57

Table A-1. Physical properties of synoptic samples collected near Creede, Colorado, August and 

September 2000.............................................................................................................................. 64

Table A-2. Concentration of chemical constituents in synoptic samples collected near Creede, 

Colorado, August and September 2000 ......................................................................................... 64
 vii

CONVERSION FACTORS, DATUMS, AND ABBREVIATED WATER-QUALITY 

UNITS

Water temperature in degrees Celsius (oC) can be converted to degrees Fahrenheit (oF) by using the 

following equation:

oF = 9/5(oC)+32.

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

Chemical concentration and water temperature are reported only in metric units. Chemical concentration is reported in milligrams per liter (mg/L), micrograms per liter (μg/L), or millimoles per liter 

(mM/L). Milligrams per liter is a unit expressing the mass of solute per unit volume (liter) of water. 

For concentrations less than 7,000 milligrams per liter, the numerical value is about the same as for 

concentrations in parts per million. Specific conductance is reported in microsiemens per centimeter at 

25 degrees Celsius (μS/cm).

Multiply By To obtain

kilogram per day (kg/day) 2.2 pound per day (lb/day)

milligram per second (mg/s) .1901 pound per day (lb/day)

liter per second (L/s) .0353 cubic foot per second (ft3/s)

meter (m) 3.281 foot (ft)

micrometer (μm) .000003281 foot (ft)

milliliter (mL) .000264 gallon (gal)

square kilometer (km2) .03861 square miles (mi2)
viii Conversion Factors, and Abbreviated Water-Quality Units
Abstract 1

Evaluation of Metal Loading to Streams near Creede, Colorado, 

August and September 2000

By B.A. Kimball, R.L. Runkel, K. Walton-Day, and B.K. Stover

ABSTRACT

Decisions about remediation of mine drainage on 

the watershed scale require an understanding of metal 

contributions from all sources to be able to choose the 

best sites for remediation. A hydrologic framework to 

study metal loading in the Willow Creek watershed, a 

tributary to the Rio Grande River near Creede, 

Colorado, was established by conducting a series of 

tracer-injection studies. Each study used the tracerdilution method in conjunction with synoptic sampling 

to determine the spatial distribution of discharge and 

concentration. Discharge and concentration data were 

then used to develop mass-loading curves for the 

metals of interest. The discharge and load profiles (1) 

identify the principal sources of load to the streams; (2) 

demonstrate the scale of unsampled, dispersed 

subsurface inflows; and (3) estimate the amount of 

natural attenuation. The greatest source of metal loads 

was from the Nelson Tunnel on West Willow Creek, 

which contributed 158 kilograms per day of zinc to the 

stream. Additional loading from other dispersed, 

subsurface inflows along West Willow Creek added 

substantial loads, but these were small in comparison to 

the loads from the Nelson Tunnel. No significant 

contributions of metal load from potential sources 

occurred along East Willow Creek. The lack of 

measurable loading may be a result of previous 

remedial actions along that stream. The lower Willow 

Creek section had relatively small contributions of load 

compared to what had been contributed upstream. This 

watershed approach provides a detailed snapshot of 

metal load for the watershed to support remediation 

decisions and quantifies processes that affect metal 

transport.

INTRODUCTION

Historical mining near Creede, Colorado, has 

produced silver, lead, zinc, and gold. Production of 

metals has been from veins along faults that formed 

during subsidence of the Creede caldera (Steven and 

Ratté, 1965). The mining activity in the Willow Creek 

watershed has affected conditions in the streams. A 

technical advisory group (TAC) has been working to 

make decisions about what might be done to improve 

stream conditions and to lessen the effect of metals in 

Willow Creek and downstream in the Rio Grande 

River. To support the decision-making process of the 

stakeholder group, the U.S. Geological Survey 

conducted three tracer-injection studies in the Willow 

Creek watershed in August and September 2000 to 

assess metal loading.

The Willow Creek watershed covers an area of 

about 26 km2. To study metal loading from the 

headwaters of Willow Creek to the Rio Grande River, 

the study area was separated into three separate tracer 

injections (fig. 1). Two injections were upstream from 

the town of Creede, Colorado. One was in West Willow 

Creek and started upstream from the Last Chance Mine 

and continued past the confluence with East Willow 

Creek to the streamflow-gaging station upstream from 

Creede. The second injection was in East Willow 

Creek, starting upstream from the Outlet Mine and 

continuing past the confluence with West Willow 

Creek to the same gaging station. The third injection 

started just downstream from the town of Creede and 

continued to the mouth of Willow Creek. It also 

included sampling sites in the Rio Grande River, 

upstream and downstream from Willow Creek. Much 

of this lower study reach included braids of Willow 

Creek and irrigation diversions. Area-velocity 

discharge measurements were included to supplement 

the discharge information from the tracer injection in 

that reach. 
2 Evaluation of Metal Loading to Streams near Creede, Colorado, August and September 2000

Figure 1. Location of the Willow Creek watershed, indicating study reaches for tracer-injection study reaches and principal mines along the study reach near 

Creede, Colorado.

2 Report Title
Methods 3

Purpose and Scope

This report presents the results of the three tracer 

injections in Willow Creek. The results will help 

determine where the greatest metal loading to the 

stream occurs, the extent of loading from dispersed, 

subsurface inflow to the stream, and the extent of metal 

attenuation from physical, chemical, and biological 

processes. The study treats the major ions calcium 

(Ca), magnesium (Mg), sodium (Na), sulfate (SO4), 

and bicarbonate (alkalinity as CaCO3), and the trace 

metals aluminum (Al), cadmium (Cd), copper (Cu), 

iron (Fe), manganese (Mn), lead (Pb), and zinc (Zn).

METHODS

Approach

Application of the combined tracer-dilution and 

synoptic-sampling methods to abandoned mine lands 

has been developed as part of the U.S. Geological 

Survey's Toxic Substances Hydrology Program 

(Bencala and McKnight, 1987; Bencala and others, 

1990; Broshears and others, 1993; Kimball and others, 

1994; Kimball, 1997; Zellweger, 1994). As described 

below, the approach includes tracer injections to 

quantify discharge by tracer-dilution (Kilpatrick and 

Cobb, 1985) and synoptic sampling to provide spatial 

concentration profiles of pH and inorganic constituents. 

Discharge and concentration data are then combined to 

develop mass-loading curves.

The studies described below were undertaken 

during low-flow conditions in late summer for two 

reasons. First, the mass-loading pattern expressed at 

low flow reflects the importance of metal sources that 

enter the stream on a continuous basis. Remedial 

actions that address the sources identified at low flow 

will therefore improve water quality during the entire 

year. These sources can include mine waste sources 

such as waste rock piles, tailings piles, and mine 

workings and also drainage from adits, tunnels, or 

ground-water pathways to the stream. Some of these 

sources contribute water and solutes to the stream as 

distinct surface inflows, but some contribute water 

through dispersed, subsurface inflows to the stream. 

Second, the pattern of metal loading at low flow 

indicates which sources contribute to high 

concentrations during the winter months, when the 

most toxic conditions likely occur (Besser and Leib, 

1999). During the low-flow winter months, mine 

drainage is less diluted by other sources of water, and 

limits of toxicity are more likely to be exceeded 

(Besser and others, 2001). Although dissolved metal 

loads are greater during snowmelt runoff, truly 

dissolved metal concentrations generally are lower, and 

the risk to aquatic life is not as great. 

Tracer Injections and Stream Discharge

Quantifying discharge in mountain streams by 

the traditional velocity-area method (Rantz and others, 

1982) is compromised because of the roughness of the 

streambed and the variability caused by pools and 

riffles (Jarrett, 1992). Further, a substantial percentage 

of discharge may be flowing through porous areas of 

the streambed that make up the hyporheic zone 

(Zellweger and others, 1989). Measurement of 

discharge with the velocity-area method does not 

account for flow through the hyporheic zone, and 

discharge estimates based on the velocity-area method 

may result in an underestimate of metal loads 

(Zellweger and others, 1989; Kimball and others, 

2002). Another limitation of the velocity-area method 

for the characterization of metal loads is the time and 

personnel requirements associated with each discharge 

measurement. In the studies described below, 

numerous instream samples were collected during a 

single day to characterize stream chemistry at steady 

state. Velocity-area discharge measurements made in 

conjunction with sample collection at a large number of 

sites would be difficult, if not impossible.

An alternative means of estimating discharge 

that was used for this study is the tracer-dilution 

method (Kilpatrick and Cobb, 1985). With the tracerdilution method, an inert tracer is continuously injected 

into the stream at a constant rate and concentration. 

Given sufficient time, all of the stream, including side 

pools and the hyporheic zone, becomes saturated with 

tracer and instream concentration reaches a plateau 

(Bencala and others, 1990). Decreases in plateau 

concentration with stream length reflect the dilution of 

tracer by additional water entering the channel (surface 

and ground-water inflow). Consideration of this 

dilution allows for the calculation of discharge at each 

stream site. Application of the tracer-dilution method 

addresses both of the problems noted above: (1) the 
4 Evaluation of Metal Loading to Streams near Creede, Colorado, August and September 2000

tracer enters porous areas of the streambed such that 

flow through the hyporheic zone is accounted for; and 

(2) collection of tracer samples when plateau 

concentration is achieved provides the ability to obtain 

discharge estimates at numerous locations during a 

short period.

Successful implementation of the tracer-dilution 

method is dependent on several key factors. First and 

foremost, the injected tracer must be transported 

through the stream system in a conservative manner; 

concentrations of the tracer should be unaffected by 

biogeochemical reactions. Potential tracers include 

dyes and inorganic salts. The degree to which a given 

tracer is conservative is often a function of stream pH. 

Because of the circum-neutral pH of waters within the 

Willow Creek watershed, a sodium bromide (NaBr) 

salt was used, and bromide (Br) was used as the 

conservative tracer. Another key factor is the ability to 

maintain a constant rate during the continuous tracer 

injection. For the study described below, tracer 

injections were controlled with precision metering 

pumps linked to a Campbell CR-10 data logger. Use of 

the data logger provides a means to maintain a constant 

injection rate as battery voltage decreases.

Kilpatrick and Cobb (1985) present a simple 

mass-balance equation used to determine discharge 

when fluorescent dyes are used to implement the 

tracer-dilution method. This equation is also 

applicable to the Br tracer as background Br 

concentrations in the Willow Creek watershed are 

uniform and much lower than that of the injected tracer 

(Kimball and others, 2002). Stream discharge at any 

location downstream from the injection site is therefore 

determined by: 

(1)

where 

is stream discharge, in L/s,

is the injection rate, in L/s,

is the injectate concentration, in mg/L,

 is the tracer concentration at plateau, in 

mg/L, and

is the naturally occurring background 

concentration.

Synoptic Sampling and Analytical Methods

The spatial distribution of metal sources may be 

characterized by synoptic sampling. Under ideal 

conditions, samples at all of the sampling locations 

would be collected simultaneously, providing a 

description of stream water quality at steady state. 

Personnel limitations generally preclude simultaneous 

sample collection, but the synoptic studies described 

below provide an approximate means of describing 

steady-state conditions. This approximation is 

achieved by collecting samples over a relatively short 

time period (less than 8 hours) and by conducting the 

studies under low-flow conditions such that the effects 

of diurnal flow variation are minimized. By 

approximating steady-state conditions, synoptic 

sampling provides a spatially intensive “snapshot” of 

chemistry and discharge that is used to quantify 

instream loads. 

During a synoptic study, samples are collected at 

a number of stream and inflow sites. Stream sites 

along the study reach are spaced such that they bracket 

the sampled inflows and areas of likely subsurface 

inflow. Subreaches that are bracketed by two adjacent 

stream sites are referred to as stream segments. The 

intent of this bracketing is to capture the changes in 

load that are attributable to visible surface inflow and 

(or) diffuse subsurface inflow within each segment. At 

this level of spatial detail, changes in stream chemistry 

and discharge between stream sampling sites reflect a 

net metal load for specific segments that incorporates 

all sources that reach the stream in that segment and 

instream reactions that affect metal concentrations. 

Loads for a particular segment cannot always be 

attributed to specific sources.

For each of the tracer injections described below, 

stream and inflow samples were collected at numerous 

predetermined locations, beginning at the downstream 

end of the study reach and ending upstream of the 

tracer-injection site. This downstream to upstream 

sampling order was followed to avoid disturbing 

streambed materials. Inflow and stream sites that were 

considered well mixed were sampled by using grab 

techniques. Sites that were not well mixed were 

sampled by equal-width integration (Ward and Harr, 

1990). Water temperature was measured on site and 

the collected samples were transported to a central 

location for further processing. The collected samples 

were divided into several 125-mL bottles at the central 

processing location: a raw (unfiltered) unacidified 

QD

QINJCINJ

CD CB – = ----------------------

QD

QINJ

CINJ

CD

CB
Methods 5

sample (RU), a raw acidified sample (RA), a filtered 

unacidified sample (FU), a filtered acidified sample 

(FA), and an ultra-filtered acidified sample (UFA). 

Specific conductance and pH were determined 

from the RU sample within hours of sample collection. 

Tangential-flow filtration was used with 0.45-μm 

membranes (FU and FA samples) and 10,000-Dalton 

molecular weight membranes (UFA sample, giving an 

effective pore size on the order of 0.001 μm). Metal 

concentrations for the RA, FA, and UFA samples were 

determined by inductively coupled plasma-atomic 

emission spectrometry (Lichte and others, 1987). 

Anion concentrations were determined from FU 

samples by using ion chromatography (Kimball and 

others, 1999). Ferrous iron was determined 

colorimetrically from the UFA (Kimball and others, 

1992), and total alkalinity was determined by titration 

from the FU samples.

Use of two filtration techniques provides for 

three different operationally defined concentrations for 

each metal. The unfiltered sample (RA) provides a 

measure of the total-recoverable metal concentration 

(dissolved plus colloidal) and the ultrafiltrate 

concentration (UFA) is considered the dissolved metal 

concentration. The 0.45-μm concentration (FA) is used 

to compare ultrafiltrate concentrations to aquatic 

standards that are written with 0.45-μm filtration. 

Colloidal metal concentrations are defined as the 

difference between the total-recoverable (RA) and the 

ultrafiltrate metal concentrations (UFA) for stream 

samples (Kimball and others, 1995).

Mass-Loading Analysis

To quantify load requires accurate discharge and 

chemical measurements. Profiles of mass load along 

the study reach use three different views of load. 

Sampled instream load at individual sampling sites is 

calculated as:

Ma = CaQa (0.0864) (2)

where

Ma is the constituent load at location a, in 

kg/day,

Ca is the concentration of the selected 

constituent at location a, in mg/L, 

 Qa is the discharge at location a, in L/s, and

0.0864 is the conversion factor from mg/s to 

kg/day.

Sampled instream load is calculated from the 

total-recoverable concentration of the constituent, but 

this value for load can be divided between the 

dissolved and the colloidal load if both filtered and 

total-recoverable samples are collected. The 

longitudinal profile of sampled instream load is the 

basic data from the mass-loading study. 

The change in load between a pair of stream 

sites, or for a stream segment, accounts for the gain or 

loss of constituent load for that segment. For the 

change in load for the segment starting at location a 

and ending at location b, we calculate:

(3)

where

ΔMs is the change in sampled instream load 

for the segment from a to b, in kg/day,

Cb is the concentration of the selected 

constituent at location b, in mg/L, 

Qb is the discharge at location b, in L/s, 

 Ca and Qa are defined above, and

0.0864 is the conversion factor from mg/s to 

kg/day.

Gains in constituent load (ΔMs is greater than 

zero) imply that there is a source that contributes to the 

stream between the two stream sites. Instream load also 

can decrease within a stream segment (ΔMs is less than 

zero), meaning that a net loss of the constituent 

occurred as a result of physical, chemical, or biological 

processes. Summing all the increases in load between 

sampling sites along the study reach (positive values of 

ΔMs) leads to the cumulative instream load. At the end 

of the study reach, the cumulative instream load is the 

best estimate of the total load added to the stream but is 

likely a minimum estimate because it only measures 

the net loading between sites and does not account for 

loss resulting from reaction. The cumulative instream 

load will be greater than the sampled instream load at 

the end of the study reach if there has been any loss of a 

constituent to the streambed.

For those segments that include a sampled 

inflow, it is possible to calculate a second value for load 

that is based upon the change in discharge between 

stream sites. This change, multiplied by constituent 

concentration in an inflow sample, produces an 

ΔMs CbQb CaQa = ( ) – ( ) 0.0864
6 Evaluation of Metal Loading to Streams near Creede, Colorado, August and September 2000

estimate of the inflow load for a stream segment. If 

stream sites a and b surround an inflow sample, 

location i:

(4)

where 

ΔMi is the change in sampled inflow load 

from location a to b, in kg/day,

Ci is the concentration of the selected 

constituent at inflow location i, in mg/L,

Qb and Qa are defined above, and 

0.0864 is the conversion factor from mg/s to 

kg/day.

Summing the inflow loads along the study reach 

produces a longitudinal profile of the cumulative 

inflow load. This sum can be compared to the 

cumulative instream load to indicate how well the 

sampled inflows account for the load measured in the 

stream. The cumulative instream and cumulative inflow 

profiles would be equal if the sampled inflows were 

representative of the constituent concentration for all 

the water entering the stream, but that is rarely the case. 

It is common in streams affected by mine drainage that 

dispersed, subsurface inflow can have higher 

concentrations of metals than the surface-water inflows 

in the same stream segment. This causes the profile of 

cumulative instream load to be greater than the profile 

of cumulative inflow load and can indicate important 

areas of unsampled inflow, which is defined as:

Unsampled inflow = ΔMs - ΔMi. (5)

Unsampled inflow can be calculated for 

individual stream segments if the segment included a 

sampled inflow, or for the entire study reach. If the 

value is negative for the entire study reach, however, it 

can still be positive for some individual stream 

segments.

In considering estimates of stream discharge and 

metal concentration at each stream site, it is possible to 

predict an error for the change in load along a stream 

segment. The error is determined by the precision of 

both discharge and chemical measurements (Taylor, 

1997), according to an equation from McKinnon 

(2002):

(6)

where

Qa is the discharge at the upstream site, in 

L/s,

ΔCa is the concentration error at the upstream 

site, in mg/L,

Ca is the concentration at the upstream site, 

in mg/L, 

ΔQa is the discharge error at the upstream 

site, and

0.0864 is the conversion factor from mg/s to 

kg/day.

Load error can be calculated for each stream site 

and compared to the change in load from that site to the 

next site downstream, ΔMs. If ΔMs is greater than the 

calculated load error, then there has been a significant 

change in load. Only the changes of instream load that 

are greater than the load error are included in the 

longitudinal profiles of sampled instream load and the 

cumulative instream load.

Principal Components Analysis

Synoptic sampling results in a large number of 

stream and inflow samples. Classification of these 

samples into groups of similar chemical characteristics 

helps highlight their similarities and differences. 

Because water-rock reactions with altered and 

unaltered mineral assemblages may lead to particular 

chemical signatures among inflows to the stream, the 

classification can help to distinguish different sources 

and also to recognize geochemical processes.

Patterns in the chemistry and pH of stream and 

inflow samples were evaluated by using Principal 

Components Analysis (PCA), a multivariate analysis 

technique (Daultrey, 1976; Joreskog and others, 1976). 

Principal components represent a set of new, 

transformed reference axes that are linear combinations 

of the original variables; it is a transformation of data, 

not a statistical treatment. A principal components 

transformation orients the data points so that the first of 

the new axes, principal component 1 (PC1), is oriented 

along the direction of the greatest variance in the data. 

The second principal component (PC2) is orthogonal to 

PC1 and is oriented to show the next greatest amount of 

variance in the data. This can be pictured in two 

dimensions if one imagines drawing a line that would 

go through the two most distant points in a bivariate 

plot of data; that would be the direction of PC1. It 

would be at some angle to the original x and y axes, but 

ΔMi Ci Qb Qa = ( ) – ( ) 0.0864

Loaderror Qa

2

ΔCa

2 Ca2

ΔQa

2 = ( ) + ( ) 0.0864
Evaluation of Metal Loading 7

any point along the line could be described by a linear 

equation. PC2 would be drawn perpendicular to PC1 

and would have its own linear equation. In 

multidimensional space, each subsequent principal 

component is orthogonal to the first two and represents 

a decreasing amount of the total variance.

Typically, the first two or three principal 

components show enough of the variance in the data set 

to enable the recognition of groups among samples; 

this is the advantage of using the method for 

multivariate data. Synoptic samples are plotted by their 

PCA scores, which are the coordinates of the original 

data points on the new principal component axes. 

Adding vectors representing the correlations of original 

variables with the new principal component axes to the 

plot of scores creates what is called a biplot. The 

vectors help identify variations in chemistry among the 

groups of samples. For the PCA analysis, totalrecoverable chemical concentrations, including pH (in 

millimoles per liter) were used after log transformation. 

Conversion to millimoles per liter and transformation 

to logs can maximize the linear relations among solutes 

that result from stoichiometric chemical reactions. 

Calculations were done using the U.S. Geological 

Survey STATPAC programs (Grundy and Miesch, 

1985).

EVALUATION OF METAL LOADING

Results from the three tracer injections will be 

presented individually and the results can be combined 

for a discussion of watershed implications. A complete 

listing of the results of chemical analyses for synoptic 

samples is contained in the appendix. The tracerinjection study reaches in East and West Willow Creeks 

overlapped downstream from the confluence of the 

streams and both ended at the discontinued gaging 

station at the north end of Creede. This allowed for a 

comparison between the two reaches. The lower study 

reach started at the south end of Creede. The section of 

Willow Creek that was not included in a tracerinjection study reach flows through a concrete channel 

that extends through the town of Creede. 

West Willow Creek

The tracer injection in West Willow Creek 

investigated a 6,602 m section of the Willow Creek 

watershed, starting upstream from the Last Chance 

Mine, and continuing past the confluence with East 

Willow Creek to the gaging station just upstream from 

the town of Creede (fig. 1). East Willow Creek was the 

only major surface-water inflow to the study reach, but 

there were many small seeps, springs, and minedrainage tunnels. Drainage from the Amethyst Mine, 

the Commodore Tunnel, and the Nelson Tunnel all 

entered the study reach. A reconnaissance geologic 

traverse was mapped in the field for much of this study 

reach and provides details of the near-stream geology 

and structure (Bruce Stover, Colorado Division of 

Minerals and Geology, written commun., 2000).

The 6,602-m study reach was divided into 34 

segments by the stream sampling sites (fig. 2). Stream 

segments bracketed eight major and minor tributary 

inflows and areas of likely subsurface inflow. Site 

designations for stream segments came from the 

previous studies of the stakeholder group: sites WW-A 

through WW-L, in an upstream direction. Additional 

sites use the designations for West Willow (WW), East 

Willow (EW), and lower Willow (LW) along with the 

measured downstream distance to the site. Downstream 

distance in East Willow Creek continued past the 

confluence with West Willow Creek all the way to the 

Rio Grande River. Distances in West Willow Creek 

only went as far as the confluence with East Willow 

Creek. Site designations and information about the 

sampling sites in West Willow Creek are listed in table 

1. In choosing stream-sampling sites, locations were 

selected that should be sufficiently downstream from 

inflows to capture both visible tributary inflow and 

additional subsurface inflow. Only eight stream 

segments contained sampled inflows; the other 

segments represented dispersed, subsurface inflow. 
8 Evaluation of Metal Loading to Streams near Creede, Colorado, August and September 2000

Figure 2. Location of stream segments and inflow samples for East and West Willow Creeks, Colorado.

Colors indicate the different stream segments.

  

	


	












	











	 



 

 


 


 







 
	


	


























 




















 













	


 	

 




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Evaluation of Metal Loading 9

Table 1. Sample identification, source, distance along the injection study reach, site description, pH, specific conductance, tracer concentration, and 

calculated discharge for synoptic samples from West Willow Creek, Colorado, September 2000—Continued

Sample 

identification

Source

Downstream 

distance, 

in meters

Site description

pH, 

in 

standard 

units

Specific 

conductance, in 

microsiemens 

per centimeter

Bromide 

concentration, in 

milligrams per 

liter

Calculated

discharge, 

in liters per 

second

WW-430 Stream 430 T0 - Above injection site 7.91 105 0.09 92

WW-634 Stream 634 T1 - First site below injection site 8.02 111 4.07 92

WW-846 Stream 846 West Willow Creek where gradient increases 8.11 111 4.07 92

WW-1096 Inflow 1,096 Drainage from gully 6.75 58 .10

WW-1296 Stream 1,296 Below rhyolite outcrop 8.09 111 4.07 92

WW-1350 Inflow 1,350 Left bank inflow 6.99 95 .10

WW-1729 Stream 1,729 Stream site to check mixing of tracer 8.08 110 4.07 92

WW-2054 Stream 2,054 Last site in moraine deposits 7.97 111 3.98 95

WW-L Stream 2,304 Stakeholder site above Last Chance Mine 8.01 111 3.83 100

WW-2464 Stream 2,464 Above Last Chance talus pile 7.86 111 3.83 100

WW-2627 Stream 2,627 Above Amethyst Tunnel 7.93 111 3.83 100

WW-K Stream 2,667 Below Amethyst Tunnel 7.95 111 3.80 100

WW-J Stream 2,829 T2 - Above Nelson Creek 7.99 112 3.74 106

NC-E Inflow 2,847 Nelson Creek above Midwest Mine

NC-B Inflow 2,847 Nelson Creek at mouth

WW-I Stream 3,021 Below Nelson Creek 7.97 112 3.66 106

WW-3186 Stream 3,186 West Willow Creek above right bank spring 

at fault

7.94 112 3.55 110

WW-3221 Inflow 3,221 Spring from fault 6.92 101 4

WW-3299 Stream 3,299 West Willow Creek at rhyolite outcrop 7.91 112 3.45 114

WW-3489 Stream 3,489 West Willow Creek at log waterfall 7.87 110 3.41 116

WW-3520 Inflow 3,520 Spring near stream level on right bank 7.13 90 1

WW-3600 Stream 3,600 West Willow Creek at top of cascades 7.96 110 3.38 117

WW-3728 Stream 3,728 West Willow Creek at culvert above Burro 

Bridge

7.94 110 3.36 118

WW-HH Stream 3,858 West Willow Creek at Burro Bridge 7.96 110 3.32 120

WW-4100 Inflow 3,885 Water coming off rock face 7.73 32 2

WW-4081 Stream 4,081 West Willow Creek below Burro Bridge 7.94 110 3.27 122

WW-H Stream 4,245 West Willow Creek in cascades 7.88 109 3.18 126

WW-4401 Stream 4,401 100 meters above old buildings by 

Commodore Tunnel

7.93 109 3.15 128

WW-G Stream 4,577 West Willow Creek above Commodore 

Tunnel

7.91 109 3.09 131

WW-4710 Stream 4,710 Above Nelson Tunnel 7.73 109 3.09 131

WW-NT Inflow 4,730 Nelson Tunnel discharge 4.45 1,521 22

WW-F Stream 4,766 West Willow Creek down from Nelson 

Tunnel (not WW-F)

7.26 328 2.72 153

WW-4866 Stream 4,866 West Willow Creek below culvert 7.37 344 2.63 158

WW-4930 Inflow 4,930 Spring on right bank with aluminum 

precipitate

5.46 646 5

WW-4980 Stream 4,980 Below Commodore mine dump 7.30 351 2.57 163

WW-D Stream 5,063 West Willow Creek below mine dump 7.74 349 2.55 164

WW-5189 Stream 5,189 West Willow Creek at point of good mixing 7.77 349 2.55 131

Table 1. Sample identification, source, distance along the injection study reach, site description, pH, specific conductance, tracer concentration, and 

calculated discharge for synoptic samples from West Willow Creek, Colorado, September 2000
10 Evaluation of Metal Loading to Streams near Creede, Colorado, August and September 2000

Discharge

Precision for the Br analyses was better than 1 

percent over the range of concentrations. This allows 

the detection of very small changes in discharge. In a 

cascading, cobble-bottom stream like West Willow 

Creek, an area-velocity measurement might have a 

precision closer to 20 percent, or as much as 28 L/s. A 

NaBr tracer with a Br concentration of 145,250 mg/L 

was injected at a rate of 0.0034 L/s. The systematic 

decrease of Br concentration downstream from the 

injection site allowed the calculation of discharge at 

each of the stream sampling sites (fig. 3). There were 

no inflows with Br concentrations above the lower 

detection limit. Thus, with a uniform background 

concentration of tracer, equation 1 can be used to 

calculate discharge for the stream sites. The change in 

discharge for each stream segment represents the 

combination of surface and subsurface inflow to the 

stream and is the total inflow discharge for a given 

stream segment. The increase in discharge along the 

study reach was 476 L/s. Only about 7 percent of the 

increase in discharge was from segments that had no 

sampled inflow. However, subtracting the surfacewater inflow from East Willow Creek, about 55 percent 

of the remaining increase in discharge along West 

Willow Creek was from unsampled inflow. 

The Amethyst Fault intersects West Willow 

Creek in the vicinity of stream site WW-5189 (Bruce 

Stover, Colorado Division of Minerals and Geology, 

written commun., 2000). The Amethyst Fault trends 

north-northwest and has a dip of 50 to 70 degrees 

southwest (Steven and Ratté, 1965). Area-velocity 

measurements made upstream and downstream from 

the area of the fault indicated a loss of 34 L/s in that 

segment of the stream. A loss of water would result in a 

constant tracer constant, and tracer concentrations 

remained constant in segments WW-D through WW-B. 

So the tracer pattern is consistent with a measured loss 

of streamflow. The discharge profile reflects this loss of 

streamflow at WW-5189 (fig. 3). 

Chemical Characterization of Synoptic Samples

Synoptic sampling of inflows provides the range 

of chemistry affecting the stream and provides a 

context for understanding the changes in stream 

chemistry and solute loads. Water-rock interactions 

with bedrock throughout the watershed can generate 

inflows that are affected by acid rock drainage as well 

as inflows that are affected by rocks that have acidneutralizing capacity. Thus, inflow chemistry can range 

from acidic and metal-rich to alkaline and essentially 

metal-free and both kinds of inflow chemistries can 

affect the stream chemistry.

Streamwater at the injection point in West 

Willow Creek was a CaHCO3-CaSO4 type water, 

reflecting the chemical weathering of bedrock in the 

watershed (Steven and Ratté, 1965). Both major ions 

and pH remained nearly constant along the study reach 

from the injection site until the inflow of the Nelson 

Tunnel at WW-F (fig. 4). At that point, the chemical 

character changed to a CaSO4 type, and pH was lower. 

With the inflow of East Willow Creek, at W-A ́, 

WW-B Stream 5,282 West Willow Creek up from bridge at photo 

stop

7.75 350 2.55 131

WW-5383 Stream 5,383 West Willow Creek above possible Amethyst 

Fault

7.72 349 2.53 132

WW-A Stream 5,540 T3 - West Willow Creek above confluence 7.64 350 2.49 135

EW-A Inflow 5,614 East Willow Creek near mouth 8.01 53 .03 434

W-A Stream 5,716 Willow Creek down from confluence 7.82 145 .7 568

EW-5892 Stream 6,450 Willow Creek above pond near Windy Gulch 7.46 147 .7 568

EW-6044 Stream 6,602 Willow Creek down from Windy Gulch at 

gage

7.59 146 .7 568

Table 1. Sample identification, source, distance along the injection study reach, site description, pH, specific conductance, tracer concentration, and 

calculated discharge for synoptic samples from West Willow Creek, Colorado, September 2000—Continued

Sample 

identificationSource

Downstream 

distance, 

in meters

Site description

pH, 

in 

standard 

units

Specific 

conductance, in 

microsiemens 

per centimeter

Bromide 

concentration, in 

milligrams per 

liter

Calculated

discharge, 

in liters per 

second
Evaluation of Metal Loading 11

Figure 3. Variaton of bromide concentration and calculated discharge with distance along the study reach, West Willow Creek, Colorado, September 

2000.

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12 Evaluation of Metal Loading to Streams near Creede, Colorado, August and September 2000

Figure 4. Variation of (A) pH and (B) calcium, sulfate, and alkalinity concentration with distance along the study reach, West Willow Creek, Colorado, 

September 2000.

       









       





















3TREAMCALCIUM

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Evaluation of Metal Loading 13

pH became more basic again; Ca and SO4 were diluted, 

and alkalinity remained nearly constant. 

Several metals were present in relatively high 

concentrations, most notably Fe, Mn, Pb, Sr, and Zn 

(fig. 5). Dissolved Al, dissolved Fe, and nickel (Ni) 

mostly were near limits of detection, but colloidal 

concentrations of Al and Fe were measurable along 

most of the study reach. Colloidal Pb concentrations 

generally were higher than dissolved Pb 

concentrations, but both collodial and dissolved 

concentrations of Pb were relatively high compared to 

many streams affected by mine drainage. Although no 

great variation in major-ion concentrations or pH 

occurred along the study reach (fig. 4), a substantial 

difference in metal concentrations upstream and 

downstream from the Nelson Tunnel did occur, with 

higher concentrations occurring downstream.

A substantial amount of spatial variation in Al 

concentrations occurred (fig. 6). From the injection site 

to the Nelson Tunnel, which entered in segment WW-F, 

both the ultrafiltrate and 0.45-μm filtered 

concentrations were less than detection. Only the totalrecoverable concentration was measurable, but a 

considerable amount of analytical variation occurred 

with the ICP-AES analysis for Al concentrations less 

than 0.1 mg/L. With the inflow of the Nelson Tunnel at 

WW-F, total-recoverable and 0.45-μm-filtered 

concentrations increased, while the ultrafiltrate 

concentration remained low. Between the Nelson 

Tunnel inflow and the inflow of East Willow Creek at 

W-A', a distinct difference occurred between the 

ultrafiltrate and the 0.45-μm filtered concentrations, 

indicating the possible distribution in size of the 

colloidal particles. Downstream from the inflow of East 

Willow Creek, an even more clear distinction occurred, 

and the ultrafiltrate and the 0.45-μm filtered 

concentrations were again near the lower detection 

limit for analysis.

Ultrafiltrate Fe concentrations essentially were 

less than detection along the entire study reach (fig. 7). 

However, the 0.45-μm filtrate concentrations were 

measurable and followed the pattern of totalrecoverable Fe concentrations. The clear distinction 

between total-recoverable and ultrafiltrate Fe 

concentrations indicates the presence of colloidal Fe. 

As with Al, the difference between total-recoverable 

and 0.45-μm concentrations indicates the size 

distribution of colloidal particles, but also indicates the 

importance of ultrafiltration to determine truly 

dissolved Fe concentrations in a stream affected by 

mine drainage. 

The importance of the Fe and Al colloids is seen 

by their effect on other metals. Zinc and Cu sorb to the 

Fe hydroxides (Runkel and others, 1999). The presence 

of Cu and Zn in the colloidal material could have 

effects on the chronic toxicity of the stream (Clements, 

1994; Besser and others, 2001). Colloidal concentrations contribute to the high concentrations of Cu 

and Zn in the bed sediments of many streams affected 

by mine drainage (Kimball and others, 2002). 

The pattern of Zn concentration in each of the 

filtrations differed substantially from the patterns of Al 

and Fe. Concentrations of Zn were essentially near 

detection from the beginning of the study reach to the 

area near the Amethyst Mine, where concentrations 

increased to more than 0.2 mg/L (fig. 8). Downstream 

from the inflow of the Nelson Tunnel at WW-4766, Zn 

concentration increased to more than 10 mg/L. The 

Nelson Tunnel inflow caused all the filtrate 

concentrations to increase, and they all decreased with 

the inflow of East Willow Creek at W-A'. This pattern 

indicates that Zn occurred in the dissolved, rather than 

the colloidal, phase. The concentration profile of Mn 

was very similar to that of Zn, but the concentration of 

Mn did not increase until inflow of the Nelson Tunnel 

joined the flow.

All the variations in stream chemistry are 

summarized in the biplot of principal component 

scores and loadings (fig. 9). Each of the chemical 

constituents used in the analysis is represented by an 

arrow, or vector, in the biplot. Each vector points in the 

direction of increasing concentration for a given 

constituent. For example, all the constituents except Fe 

increase from left to right on the diagram. The value of 

pH decreases (direction of increasing hydrogen ion 

concentration) in the direction of WW-NT and WW4930 (group 6). Thus, the change along the PC1 axis 

represents the effects of mine drainage, namely, the 

lowering of pH and the increase of metal 

concentrations. Changes along the PC2 axis mostly 

represent variations in Fe concentration, but Al 

concentration also increases slightly in that direction. 

Note that total-recoverable Fe was used in the PCA, 

therefore this includes dissolved plus colloidal 

concentrations.
14 Evaluation of Metal Loading to Streams near Creede, Colorado, August and September 2000

Figure 5. Distribution of dissolved (blue) and collodial (orange) metal concentrations in synoptic stream samples, West Willow Creek, Colorado, 

September 2000.

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Evaluation of Metal Loading 15

Figure 6. Variation of aluminum concentration in ultrafiltrate, 0.45-μm filtered, and total-recoverable samples with distance along the study reach, 

West Willow Creek, Colorado, September 2000.

       















77
,OSSOFFLOW	

77
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16 Evaluation of Metal Loading to Streams near Creede, Colorado, August and September 2000

Figure 7. Variation of iron concentration in ultrafiltrate, 0.45-μm filtered, and total-recoverable samples with distance along the study reach, West 

Willow Creek, Colorado, September 2000.

Heading 1 7

       

















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Evaluation of Metal Loading 17

Figure 8. Variation of zinc concentration in ultrafiltrate, 0.45-μm filtered, and total-recoverable samples with distance along the study reach, West 

Willow Creek, Colorado, September 2000.

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18 Evaluation of Metal Loading to Streams near Creede, Colorado, August and September 2000

Figure 9. Biplot of principal component scores for synoptic samples and loadings for chemical constituents, West Willow Creek, Colorado, September 

2000.


 
 
 
 
             
























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Evaluation of Metal Loading 19

Within this framework of chemical changes, the 

classification of samples into the different groups 

indicates important changes along the study reach. 

Three groups of stream samples and three groups of 

inflow samples were distinguished (table 2). Stream 

samples of group 1 have the lowest concentrations of 

all the stream samples and represent water unaffected 

by mine drainage. In a sense, this group is like an 

inflow group, indicating the composition of recharge 

waters at the head of the stream. Inflows of group 4

also plot far to the left of the biplot and have relatively 

low concentrations of all the constituents. A unique 

sample, WW-1350, was sufficiently different to be 

considered separately as group 5, and had the lowest 

concentrations of all the constituents, but a lower pH. 

Two inflow samples make up group 6; these had the 

highest concentrations and lowest pH values among all 

the inflow samples. The effects of these inflow groups 

on the stream samples is evident by changes among 

groups of stream samples.

Table 2. Median composition of stream and inflow groups distinguished by principal components analysis, West Willow Creek, Colorado, September 

2000

[Dis, dissolved; Col, colloidal; mg/L, milligrams per liter; LD, less than detection limit]

Constituent Phase

Group 1

Streamheadwater 

samples

Group 2a

Stream from 

Amethyst 

Mine to 

Nelson 

Tunnel

Group 2b

downstream 

from East 

Willow 

Creek

Group 3

Stream from 

Nelson 

Tunnel to 

East Willow 

Creek

Group 4

Inflows—

Dilute

Group 5

Inflow WW1350

Group 6

Inflows—

Nelson 

Tunnel and 

WW-4930 

spring

pH, in standard units Dis 8.02 7.94 7.59 7.67 7.13 6.99 4.96

Calcium, in mg/L Dis 14.9 14.9 17.6 43.9 9.27 12.9 145

Magnesium, in mg/L Dis 1.60 1.65 1.69 3.89 1.30 1.51 12.8

Sodium, in mg/L Dis 4.15 3.81 4.66 10.1 2.47 2.86 33.2

Chloride, in mg/L Dis .160 .170 .220 .278 .260 .240 1.13

Sulfate, in mg/L Dis 17.3 18.9 43.1 143 3.58 14.2 653

Alkalinity, in mg/L as CaCO3 Dis 31.1 31.0 23.8 25.2 24.5 28.8 .245

Silica, in mg/L Dis 17.0 17.3 19.2 18.1 17.8 17.3 28.2

Aluminum, in mg/L Dis .007 .006 .022 .045 .032 LD .988

Col .061 .090 .120 .115 .032 LD .988

Cadmium, in mg/L Dis .001 .001 .018 .038 .003 LD .388

Col LD LD .003 .002 .003 LD .388

Copper, in mg/L Dis LD .004 .008 .005 .004 LD .278

Col LD LD LD LD .004 LD .278

Iron, in mg/L Dis LD LD LD LD .024 LD .007

Col .186 .109 .125 .233 .024 LD .007

Manganese, in mg/L Dis .021 .035 .636 2.42 .038 .038 13.1

Col LD .003 .005 LD .038 .038 13.1

Nickel, in mg/L Dis LD LD LD LD LD LD .009

Col LD LD LD LD LD LD .009

Lead, in mg/L Dis LD LD .012 .081 .004 LD 1.30

Col .001 .026 .047 .117 .004 LD 1.30

Strontium, in mg/L Dis .159 .152 .137 .395 .114 .113 1.24

Col LD .005 .007 LD .114 .113 1.24

Zinc, in mg/L Dis .002 .253 4.22 14.1 .194 .012 86.9

Col LD .015 .122 .162 .194 .012 86.9
20 Evaluation of Metal Loading to Streams near Creede, Colorado, August and September 2000

The first effect on stream samples is seen by the 

change from group 1 to group 2a. This change occurred 

downstream from the Last Chance Mine (WW-2304) 

and occurred in stream samples collected from 

upstream of the Amethyst Mine to the sample collected 

upstream from the Nelson Tunnel, WW-4710. A 

second group of stream samples with slightly higher 

concentrations is classified as group 2b and included 

the three samples collected downstream from the 

confluence of East and West Willow Creeks. The 

greatest shift in concentration among the stream 

samples occurred downstream from the inflow of the 

Nelson Tunnel (WW-NT). At that point, the samples 

shift to the higher concentrations measured in group 3. 

Thus, the stream samples change systematically to the 

right on the biplot with increasing concentrations from 

group 1 in the recharge area, to group 2a near the 

Amethyst Mine, to group 3 downstream from the 

Nelson Tunnel. Then the shift is back to the left, to 

group 2b, downstream from the confluence with East 

Willow Creek. This shift is in the direction of the East 

Willow sample, EW-A.

Load Profiles

Transferring chemical data into a hydrologic 

context provides information that can be useful for 

remediation decisions and for quantifying the physical, 

chemical, and biological processes that affect metal 

transport and availability. This hydrologic context 

comes from detailed spatial profiles of load that are 

possible from combining the tracer-injection study with 

synoptic sampling for chemistry. As defined in the 

“Methods” section, load profiles provide the sampled 

instream load, which yields the data on net loading or 

attenuation for each stream segment. These data can be 

used to calculate the cumulative instream load, which 

gives the best estimate of the total loading for an 

element in a study reach. An evaluation of how well the 

sampled inflows account for the cumulative instream 

load comes from the cumulative inflow load. The 

cumulative instream load is calculated from totalrecoverable concentrations, but sampled instream load 

can be calculated by using the dissolved or colloidal 

concentrations. This permits an evaluation of instream 

chemical reactions.

A summary of load calculations for selected 

metals in West Willow Creek is listed in table 3. Values 

in table 3 come from the load profiles of each solute. 

The five stream segments that have the greatest loading 

are indicated in each column. Concentrations of Cu and 

Ni were too low to be able to calculate load profiles, 

therefore, they are not included in table 3.

As an example of how the profiles are used, the 

load profile of Al (fig. 10) shows five different curves, 

as described in the “Methods” section. Cumulative 

instream load is the best estimate of the total quantity 

of a metal entering the stream along the study reach, 

which was 9.17 kg/day for total Al. Cumulative inflow 

load shows whether or not the sampled inflows account 

for that total instream load. For Al, the cumulative 

inflow load was only 33 percent of the cumulative 

instream load. Subtracting the inflow load from the 

instream load gives the unsampled load, which was 67 

percent for Al. The difference between the cumulative 

instream load and the total instream load, including 

both dissolved and colloidal load, is the amount of 

attenuation along the study reach. This was 27 percent 

of the cumulative instream load for Al. Only a small 

part of that attenuation was from the loss of load at 

WW-5189 because Al concentrations were low. 

Cumulative instream loads varied considerably 

among these solutes (table 3). Because SO4 is a product 

of pyrite oxidation as well as the oxidation and 

dissolution of other metal-bearing sulfide minerals, it 

commonly has a much greater load than any of the 

metals. However, SO4 can be added to the stream 

through dissolution reactions of gypsum or anhydrite, 

which may be present as accessory minerals. Among 

the metals, Zn and Mn have substantially greater loads 

than the others. In fact, the cumulative instream load of 

Zn is one of the highest of all the watersheds in the 

Rocky Mountains where tracer-injection studies have 

been used to quantify loadings (Kimball and others, 

1994; Kimball and others, 1999a; Kimball and others, 

1999b; Cleasby and others, 2000; Kimball and others, 

2001; Kimball and others, 2002). 
Evaluation of Metal Loading 21

Table 3. Summary of load calculations, West Willow Creek, Colorado, September 2000

[Loads reported in kilograms per day, except for percent values; italicized bold numbers in parentheses indicate rank for the five greatest loads of each 

constituent]

Segment ID Distance,

in meters Aluminum Cadmium Iron Manganese Lead Strontium Zinc Sulfate

WW-430 (T-0) 430 (3)0.527 0.015 (3)1.71 0.193 0.014 (2)1.27 0.022 (4)139 

WW-634 634 .056 .003 -.015 -.018 .015 .065 .016 -.239

WW-846 846 .067 -.008 .040 -.002 -.020 -.140 -.033 .638 

WW-1296 1,296 .115 .018 -.244 .168 .045 .110 .009 -1.04

WW-1729 1,729 .000 .000 .000 .000 .000 .000 .000 .000 

WW-2054 2,054 -.086 -.011 -.115 -.023 .073 .041 .056 4.02 

WW-L 2,304 .059 -.002 -.015 .071 .054 -.000 .054 8.04 

WW-2464 2,464 .075 -.003 -.060 .062 -.016 .104 .007 .259 

WW-2627 2,627 -.257 -.001 -.187 .087 -.150 -.155 .400 2.33 

WW-K 2,667 .140 .017 .107 -.228 (5).203 .112 .143 1.24 

WW-J 2,829 .000 .000 .000 .000 .000 .000 .000 .000 

WW-I 3,021 .098 .023 -.035 .057 .145 -.030 1.42 17.2 

WW-3186 3,186 .067 .008 .004 -.018 .043 .097 .385 8.30 

WW-3299 3,299 -.018 .000 -.115 .162 -.072 .027 .196 10.2 

WW-3489 3,489 .087 .004 .075 -.152 .036 -.002 .117 .540 

WW-3600 3,600 .114 .006 -.041 -.037 .031 .100 .145 1.10 

WW-3728 3,728 .127 -.002 .061 .259 -.002 .001 .032 1.48 

WW-HH 3,858 -.126 -.001 -.141 -.136 -.083 -.090 -.090 2.83 

WW-4081 4,081 .001 .029 .120 -.020 .009 .042 .219 3.53 

WW-H 4,245 .025 -.023 -.158 -.041 .071 .101 -.087 6.29 

WW-4401 4,401 (4).443 -.056 -.161 .062 -.284 -.084 .152 .093 

WW-G 4,577 -.486 .000 -.017 .204 -.071 .110 .073 6.73 

WW-4710 4,710 .099 .069 .169 -.197 (3).315 .201 .624 1.61 

WW-F 4,766 (2).934 (1).475 (2)2.65 (1)28.4 (1)2.26 (1)3.04 (1)158 (1)1,540 

WW-4866 4,866 -.134 -.195 -.221 (2)4.93 .062 (5).448 (4)19.8 (2)174 

WW-4980 4,980 (5).374 (5).137 -.184 (3)2.87 .166 .160 (3)21.2 (5)98.4 

WW-D 5,063 .134 (3).297 (5).312 -.583 .133 .125 -1.10 17.0 

WW-5189 5,189 -.646 -.407 -1.04 -6.24 -.846 -1.18 -39.7 -417

WW-B 5,282 .101 (4).214 .133 -3.26 (4).176 .056 -.411 1.24 

WW-5383 5,383 .125 .020 .069 .074 .044 -.064 -.100 11.2 

WW-A 5,540 -.288 -.076 -.211 (5)1.76 -.160 .279 1.3 25.0 

W-A 5,716 (1)5.22 (2).387 (1)3.90 3.44 (2).913 (3)2.00 (2)36.2 (3)433 

EW-5892 6,450 -.461 -.010 -.545 -.633 -.506 -.712 3.91 23.1 

EW-6044 6,602 .177 .118 (4).319 (4)2.64 .113 (4).663 (5)15.5 4.91 

Cumulative instream load 9.17 1.84 9.66 45.5 4.92 9.16 269 2,540

Cumulative inflow load 3.07 .890 2.68 37.5 3.29 6.55 215 2,200

Percent inflow load 33 48 28 82 67 72 80 87

Attenuation 2.5 .790 3.51 11.6 2.21 2.47 41.6 418

Percent attenuation 27 43 36 25 45 27 15 16

Unsampled inflow 6.10 .950 6.98 8.00 1.63 2.61 54.0 340

Percent unsampled inflow 67 52 72 18 33 28 20 13
22 Evaluation of Metal Loading to Streams near Creede, Colorado, August and September 2000

Figure 10. (A) Variation of aluminum load with distance and (B) changes in aluminum load for individual stream segments, West Willow Creek, 

Colorado, September 2000.

       


















       



















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Evaluation of Metal Loading 23

Differences in the amount of unsampled inflow 

were noted among the solutes. The unsampled inflows 

of Mn, Sr, Zn, and SO4 were much smaller than those 

of Al and Fe (table 3). This grouping is consistent with 

the geochemical behavior of these solutes. Aluminum 

and Fe are among the most reactive constituents and 

Mn, Zn, and SO4 are less reactive. Thus, Mn, Zn, and 

SO4 were not lost from the aqueous phase during 

transport to the stream from metal sources away from 

the stream. For this same reason, Zn and SO4 had the 

least amount of attenuation in the stream. Attenuation 

of Mn was measurable, but much less than attenuation 

of Al, Cd, Fe, and Pb. Given these general 

characteristics of loading, the loading profiles mostly 

fall into two groups that include Mn, Zn, and SO4 in 

one group and Al, Fe, and Cd in another. Strontium and 

Pb had characteristics of both groups. 

Loading profiles for Mn (fig. 11), Zn (fig. 12), Sr 

(fig. 13), and SO4 (fig. 14) are dominated by loading 

from the Nelson Tunnel (accounted for at stream site 

WW-F), and the substantial loading in the two stream 

segments just downstream from the Nelson Tunnel 

(WW-4866 and WW-4930). The inflow at WW-4866 

was “unsampled” inflow for Mn, Zn, and SO4 (figs. 

11B, 12B, and 14B). White Al precipitate in a sampled 

inflow in segment WW-4930 coated logs and rocks 

before the inflow entered the stream. Both Sr and SO4

have sources from non-ore minerals, and their loading 

profiles indicate sources upstream from the beginning 

of the study reach.

Although substantial loads of Al (fig. 10) and Fe 

(fig. 15) were added to West Willow Creek by the 

Nelson Tunnel discharge, East Willow Creek also had 

substantially greater loads of these solutes. East Willow 

Creek also was an important source for Cd (fig. 16) and 

Pb (fig. 17). Much of the cumulative instream load for 

Fe came from unsampled inflow, similar to the load for 

Al. If the loads come from dispersed, subsurface 

inflow, the Al and Fe can enter the stream before being 

removed if they have remained soluble in the 

subsurface. Once in the stream, however, they have a 

tendency to precipitate and form colloidal particles. 

This is evident by the relatively large percentage of Al 

and Fe that were removed by attenuation. Slightly 

greater percentages of Cd and Pb were removed, and 

this was most likely through sorption to the Fe colloidal 

material that was formed.

Principal Locations of Mass Loading

Net instream load for each stream segment 

allows for a ranking of segments according to their 

contribution of mass to the stream. Mass of a 

constituent, not its concentration in an inflow, 

determines the real effects on the stream (Kimball and 

others, 2002). The change in mass for any stream 

segment can be divided by the cumulative instream 

load to give a percentage of the total load contributed 

by each segment. However, this percentage may be 

affected by a net loss of solute for a stream reach. For 

example, stream segments with sampled inflows may 

have a positive inflow load and yet may have a negative 

instream load because chemical reactions are fast 

enough to remove the solutes before transport to the 

downstream end of the stream segment. 

Two clear patterns emerge from these loadings 

(table 3). First, the Nelson Tunnel (accounted for at 

WW-F) contributed the greatest loads of Cd, Mn, Pb, 

Sr, Zn, and SO4. Generally, this was greater than 50 

percent of the load along the study reach. For some of 

these solutes, the Nelson Tunnel contributed about 10 

times the load contributed by any other stream 

segment. Not only did the Nelson Tunnel contribute the 

majority of load for most solutes, but there were also 

substantial loads contributed for Cd, Mn, Pb, Zn, and 

SO4 in the two segments downstream from the Nelson 

Tunnel (WW-4866 and WW-4980). These loads could 

result from leakage of Nelson Tunnel discharge into the 

large waste-rock pile at the Commodore Mine and then 

discharge of this leakage to the stream.

The second pattern is that Al and Fe, and to some 

extent Pb and Sr, are substantially contributed in the 

stream segment that includes East Willow Creek (WA'). For each of these solutes, except Sr, this 

contribution was mostly transformed to the colloidal 

phase within the stream segment W-A'. The majority of 

this load, however, was unsampled inflow. It is not 

clear if this unsampled inflow came from the discharge 

of East Willow Creek, or perhaps upwelling of water 

from the drainage of East Willow, West Willow, or 

both.
24 Evaluation of Metal Loading to Streams near Creede, Colorado, August and September 2000

Figure 11. (A) Variation of manganese load with distance and (B) changes in manganese load for individual stream segments, West Willow Creek, 

Colorado, September 2000.

       























       























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Evaluation of Metal Loading 25

Figure 12. (A) Variation of zinc load with distance and (B) changes in zinc load for individual stream segments, West Willow Creek, Colorado, September 

2000.

       

























       















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26 Evaluation of Metal Loading to Streams near Creede, Colorado, August and September 2000

Figure 13. (A) Variation of strontium load with distance and (B) changes in strontium load for individual stream segments, West Willow Creek, Colorado, 

September 2000.

       




























       























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Evaluation of Metal Loading 27

Figure 14. (A) Variation of sulfate load with distance and (B) changes in sulfate load for individual stream segments, West Willow Creek, Colorado, 

September 2000.

       

























       















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28 Evaluation of Metal Loading to Streams near Creede, Colorado, August and September 2000

Figure 15. (A) Variation of iron load with distance and (B) changes in iron load for individual stream segments, West Willow Creek, Colorado, September 

2000.

       

















       























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Evaluation of Metal Loading 29

Figure 16. (A) Variation of cadmium load with distance and (B) changes in cadmium load for individual stream segments, West Willow Creek, Colorado, 

September 2000.

       






























       

















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30 Evaluation of Metal Loading to Streams near Creede, Colorado, August and September 2000

Figure 17. (A) Variation of lead load with distance and (B) changes in lead load for individual stream segments, West Willow Creek, Colorado, 

September 2000.

       





















       























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Evaluation of Metal Loading 31

Unsampled Inflow

There were three locations with considerable 

amounts of unsampled inflow (figs. 10-17). The first 

was segment WW-4866, downstream from the Nelson 

Tunnel. Unsampled inflow of Mn, Sr, Zn, and SO4

occurred in this segment. As noted above, this 

unsampled inflow was likely from infiltration of 

Nelson Tunnel discharge and subsequent discharge 

downstream. It also could be from an alternative 

pathway from the mine workings to the stream. The 

second location was at the confluence of East and West 

Willow Creeks, segment W-A'. The unsampled inflow 

was greatest for Al, Fe, and Pb in that segment. 

Loading from subsurface water in this segment could 

be from East or West Willow, or both. Data from these 

tracer studies cannot distinguish between the two 

sources. The third location of unsampled inflow was in 

the last segment of the study reach, EW-6044. This 

loading could represent subsurface inflow from Windy 

Gulch and was most important for Mn, Sr, and Zn. It is 

not possible to distinguish the inflow between Windy 

Gulch and other possible sources because it could also 

be from mine wastes within the Willow Creek 

drainage. Most of the alluvial material near the end of 

the canyon has been reworked and could contain source 

material.

Attenuation of Load

Attenuation of metal loads ranged from a high of 

45 percent for Pb, to 15 percent for Zn (table 3). In an 

Fe-rich system where there is abundant formation of Fe 

colloids, it is common to see substantial metal 

attenuation (Kimball and others, 1994). In West Willow 

Creek, pH was greater than 7.0, even downstream from 

metal-rich inflows. At this pH, it would be reasonable 

to expect substantial sorption of metals to the iron 

hydroxide colloids. Yet, relatively little attenuation 

occurred. After the inflow of the Nelson Tunnel 

discharge and the two subsequent stream segments that 

had substantial unsampled inflow, some attenuation of 

Cd, Fe, Mn, and Zn occurred in segments WW-5189, 

WW-B, WW-5383, and WW-A. Subsequently, 

downstream from the inflow of East Willow Creek, in 

segments W-A' and EW-5892, attenuation of Fe, Mn, 

Pb, and Sr was measurable. No attenuation of SO4

occurred, however, which is consistent with the pH 

value greater than 7.5 in these stream segments.

East Willow Creek

Load profiles from West Willow Creek indicated 

increases in the load of some constituents in the 

segment that included the inflow of East Willow Creek. 

To determine where these loads originated in East 

Willow Creek, a tracer injection was used to identify 

possible sources in that drainage. 

The East Willow Creek tracer injection covered a 

6,044-m section of the Willow Creek watershed, 

starting upstream from the Outlet Mine and continuing 

past the confluence with West Willow Creek to the 

gaging station just upstream from the town of Creede 

(fig. 2). There were no major inflows to the stream 

along the study reach, but discharge did increase from 

some discharge of dispersed, subsurface flow and 

mine-drainage tunnels. The Solomon Mine was the 

principal mine drainage entering the stream in the 

study reach. 

The 6,044-m study reach was divided into 21 

segments by the stream sampling sites (fig. 2). Stream 

segments bracketed 12 inflow samples, but there likely 

were areas of subsurface inflow also bracketed by 

stream samples. Segment designations, downstream 

distance, and information about the sampling sites are 

listed in table 4. Only 9 stream segments contained 

sampled inflows; the other 12 segments had no 

sampled inflow. 

Discharge

A NaBr tracer with a Br concentration of 

151,250 mg/L was injected at a rate of 0.004 L/s. The 

systematic decrease of Br concentration downstream 

from the injection site allowed the calculation of 

discharge at each of the stream sampling sites (fig. 18). 

The increase in discharge along the study reach was 

from 341 L/s at the injection site to 619 L/s at the 

downstream gage. West Willow Creek accounted for 

199 L/s of the increase, or 72 percent. Discharge 

increased by 79 L/s upstream from the confluence with 

West Willow Creek, and 39 percent of that increase was 

from segments that had no sampled inflows.
32 Evaluation of Metal Loading to Streams near Creede, Colorado, August and September 2000

Table 4. Synoptic sampling sites, East Willow Creek, Colorado, August 2000

[Distance, in meters along the study reach; dashed line indicates samples that were collected upstream from the confluence with West Willow Creek]

Site 

designation Source Distance,in meters Site description

pH,

in standard 

units

Discharge,

(in liters per 

second

EW-T0 Stream 947 Upstream from injection site 7.90 341

TRN Inflow 1,079 Left bank drainage through culvert 7.78 .10

TRS Inflow 1,129 Spring discharging from hill 7.57 .10

EW-K Stream 1,157 East Willow Creek upstream from Outlet Mine 7.91 341

EW-J Stream 1,447 T1-East Willow Creek downstream from Outlet Mine 7.90 348

EW-1807 Stream 1,807 Along road to check for ground-water inflow 7.92 350

EW-2175 Stream 2,175 In canyon to check for ground-water inflow 8.03 350

EW-I Stream 2,405 Upstream from Solomon and Ridge Mines 7.95 353

PC Inflow 2,695 Pipe on left bank 7.18 4.4

EW-H Stream 2,735 Upstream from Solomon wetland 7.91 358

SMA Inflow 2,790 Solomon adit 4.71 .10

EW-2830 Inflow 2,811 Spring discharge from Solomon Tunnel 7.02 2.25

EW-2825 Inflow 2,825 Drainage from Solomon ponds along road 5.68 2.25

EW-2995 Stream 2,995 T2 - Stream downstream from Solomon ponds 7.95 363

EW-G Stream 3,135 Downstream from Solomon tailings 8.01 367

EW-3525 Stream 3,525 Upstream from spring on right bank at base of talus 7.79 373

EW-3533 Inflow 3,533 Spring from talus slope 7.33 6.23

EW-E Stream 3,602 East Willow Creek as valley gets constricted 7.90 380

EW-D Stream 3,970 East Willow Creek upstream from old diversions 7.93 385

SWI Inflow 4,015 Discharge at concrete diversion structure 7.33 5.74

EW-4107 Stream 4,107 Upstream end of culvert 7.62 391

EW-4121 Inflow 4,121 Small spring downstream from culvert 7.33 7.39

EW-C Stream 4,157 East Willow Creek upstream from Mammoth adit 7.73 398

MA Inflow 4,183 Pipe upstream hill discharging Mammoth adit flow 7.66 17.3

EW-B Stream 4,613 East Willow Creek upstream from North Creede site 7.62 416

EW-A Stream 4,968 T3-East Willow Creek near mouth 7.67 419

WW-A Inflow 5,056 West Willow Creek near mouth 7.23 199

W-A 'Stream 5,158 Willow Creek downstream from confluence 7.45 618

EW-5292 Stream 5,292 Willow Creek in reaction zone 7.34 618

EW-5492 Stream 5,492 Willow Creek upstream from braids and dam 7.47 618

EW-5892 Stream 5,892 Willow Creek upstream from pond near Windy Gulch 6.79 618

EW-5944 Inflow 5,944 Drainage from right bank pond near Windy Gulch 7.06 1.07

EW-6044 Stream 6,044 Willow Creek at Army Corps of Engineer gage 7.12 619
Evaluation of Metal Loading 33

Figure 18. Variation of bromide concentration and calculated discharge, East Willow Creek, Colorado, August 2000.

















       



















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34 Evaluation of Metal Loading to Streams near Creede, Colorado, August and September 2000

Chemical Characterization of Synoptic Samples

Analysis of synoptic samples collected along 

East Willow Creek indicates that the pH along the 

study reach to the confluence with West Willow Creek 

was near 8.0 (fig. 19A) and that the principal ions were 

Ca, Na (not shown in figure), and HCO3 (fig. 19B). 

These major ions result mostly from weathering of 

non-ore minerals. In these upper reaches, the SO4

concentration of East Willow Creek is very low, 

indicating little effect from sulfide minerals. 

Downstream from the confluence with West Willow 

Creek, pH was less than 7.5 and the dominant ions 

were Ca and SO4. The sample at W-A' represents the 

mixing of East and West Willow Creeks.

Metal concentrations were high in some of the 

synoptic samples, but considerably lower than in West 

Willow Creek (fig. 20). Concentrations of dissolved Zn 

were the highest among the metals, with a maximum 

concentration of 4.1 mg/L, and a median of 0.11 mg/L. 

Colloidal concentrations of Al, Fe, and Pb were greater 

than the dissolved concentrations. Colloidal Zn 

concentration was not higher than dissolved Zn 

concentration, but was greater than detection in many 

of the stream samples. Concentrations of dissolved Cu 

were greater than those of colloidal Cu; only a few 

samples indicated measurable colloidal Cu. 

Although metal concentrations were high in the 

sample from the Solomon Mine adit, no substantial 

change in the stream concentrations along East Willow 

Creek occurred downstream from the adit. 

Concentrations of Zn increased downstream from the 

area of the Solomon Tunnel, but this increase was small 

in comparison to the increase downstream from the 

confluence for West Willow Creek (fig. 21). 

Concentrations of Mn were similar to those of 

Zn. Although Mn concentrations were high in samples 

collected at the Solomon Mine adit (SMA), instream 

concentrations did not increase greatly until the 

confluence with West Willow Creek. In contrast to this, 

concentrations of Al and Fe were low (fig. 22). 

Concentrations of Fe and Al also were high in samples 

collected from the Solomon Mine adit, but these 

concentrations did not affect the stream concentrations. 

This could be from the effects of the constructed 

wetland, or because there is little hydrologic input from 

the adit to the stream.

These trends in composition are summarized by 

the groups of inflows and stream samples in a biplot of 

PCA results (fig. 23). Vectors for the constituents fall 

into two groups that are distinguished by those 

constituents that increase from the inflow of West 

Willow Creek (Ca, Mg, SO4, Cd, Sr, pH, Zn, Na, Pb, 

and Cl), and those that vary to some degree in East 

Willow Creek (Fe, Al, and Cu). Within this framework, 

there are only two groups of stream samples. Group 1 

includes all the samples in East Willow Creek upstream 

from West Willow Creek, and the inflows TRN and 

TRS, which had a chemistry similar to that of the 

stream samples. These samples vary somewhat in their 

Fe and Al concentrations, and there is some variation in 

Zn, but overall there is not a great amount of variation 

along that part of East Willow Creek. Group 2 includes 

those stream samples that are downstream from the 

confluence, and this group is shifted to the right on the 

biplot, indicating the increase in all those constituents 

that are dominant in West Willow Creek. The shift is 

toward the West Willow sample, WW-A. 

The highest concentrations of metals, including 

Al, Fe, and Cu, were measured in the sample collected 

from the Solomon Mine adit (SMA, group 4). EW2825 (group 5) originated from the same source but had 

lower metal concentrations because the adit water had 

passed through constructed wetlands before the sample 

was collected. EW-2830 (group 2) originated from the 

Solomon Mine but was collected from a spring that 

issued near the stream, downstream from the Solomon 

adit and the constructed wetlands. It was not clear if 

that water drained from the adit or from the wetlands, 

but the sample had lower concentrations of metals than 

did sample EW-2825. Despite high concentrations of 

metals, these inflows had little effect on the stream 

chemistry. There was only a slight shift toward SMA 

among stream samples of group 1; group 1 samples 

that plot to the right generally were collected 

downstream from the Solomon Mine area. This mostly 

reflects the increase in Zn concentration, as mentioned 

above. A lack of the shift indicates that the Solomon 

Mine and the associated inflows had little influence on 

the stream chemistry. The only major shift in the 

stream chemistry came downstream from the 

confluence with West Willow Creek (group 2). The 

sample from Windy Gulch, EW-5944, was 

distinguished by low concentrations of Al, Fe, and Cu, 

but relatively high concentrations of other metals.
Evaluation of Metal Loading 35

Figure 19. Variation of (A) pH and (B) calcium, sulfate, and alkalinity concentration with distance along the study reach, East Willow Creek, Colorado, 

August 2000.

     









       



















3ULFATEGREEN	

#ALCIUMRED	

3TREAM

)NFLOW

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3OLOMON-INE

#/.#%.42!4)/.).-),,)-/,%30%2,)4%2

$)34!.#%!,/.'345$92%!#().-%4%23

!LKALINITYBLUE	

"

7EST7ILLOW#REEK

3OLOMON-INE

3TREAM

)NFLOW

7
!©

P().34!.$!2$5.)43

!
36 Evaluation of Metal Loading to Streams near Creede, Colorado, August and September 2000

Figure 20. Distribution of dissolved (blue) and collodial (orange) metal concentration in synoptic stream samples, East Willow Creek, Colorado, August 2000.

!L$!L#

#D$#U$

&E$&E#

-N$

0B$0B#

3R$

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8
AXISLABELS

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$ISSOLVED

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Evaluation of Metal Loading 37

Figure 21. Variation of zinc concentration with distance along the study reach, East Willow Creek, Colorado, August 2000.

       



































%7
$OWNSTREAMFROM3OLOMONMINETAILINGS	

%7


7
!©7EST7ILLOW#REEK	

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3TREAMULTRAFILTRATE

3TREAM
MICROMETERFILTRATE

3TREAM4OTALRECOVERABLE

)NFLOW
MICROMETERFILTRATE
38 Evaluation of Metal Loading to Streams near Creede, Colorado, August and September 2000

Figure 22. Variation of iron concentration with distance along the study reach, East Willow Creek, Colorado, August 2000.

       





















3-!

7
!©7EST7ILLOW#REEK	

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3OLOMON-INE	

)2/.#/.#%.42!4)/.).-),,)'2!-30%2,)4%2

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3TREAMULTRAFILTRATE

3TREAM
MICROMETERFILTRATE

3TREAM4OTALRECOVERABLE

)NFLOW
MICROMETERFILTRATE
Evaluation of Metal Loading 39

Figure 23. Biplot indicating classification of synoptic samples from East Willow Creek, Colorado, August 2000.

For both stream (diamonds) and inflow (stars) samples, groups are indicated by color: Group 1 (blue), group 2 (green), group 3 (yellow), group 4 (orange), group 5 (red), 

and group 6 (magenta). 


 
 
 
           



























 
 
 
           


























3-!

#HLORIDE

:INC

3TRONTIUM

,EAD

.ICKEL

3ODIUM

-AGNESIUM

)RON

#OPPER

#ADMIUM

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!LUMINUM

-ANGANESE

3ULFATE

#ALCIUM

3#!,%$02).#)0!,#/-0/.%.4,/!$).'3

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3#!,%$02).#)0!,#/-0/.%.43#/2%3
40 Evaluation of Metal Loading to Streams near Creede, Colorado, August and September 2000

Load Profiles

Load profiles for solutes in East Willow Creek 

are presented for the entire study reach (table 5). To 

compare the summary values for cumulative instream 

load in table 5 to the inflow values in table 2, the sum 

should only be through EW-A. For example, the 

cumulative instream load for Al along the East Willow 

Creek study reach was 7.94 kg/day, but 2.38 kg/day of 

that total was added by West Willow Creek in segment 

W-A'. Therefore, the load from East Willow Creek 

would be only 5.56 kg/day. Copper is not included in 

the summary because concentrations were too close to 

the detection limit.

Load profiles for East Willow Creek had two 

patterns. First, those elements that had very little 

loading along the study reach upstream from EW-A 

included SO4 (fig. 24), Sr (fig. 25), Mn (fig. 26), and 

Zn (fig. 27). Load profiles of these elements indicate 

that essentially all of the load came from West Willow 

Creek. The sample from WW-A accounted for all the 

increase in SO4 (fig. 24B), Sr (fig. 25B), and Mn (fig. 

26B). Part of the increase in Zn was unsampled inflow 

(fig. 27B). This could indicate the occurrence of 

substantial subsurface inflow that had high Zn 

concentrations from West Willow Creek.

Load profiles for Al (fig. 28) and Fe (fig. 29) 

were very different from those of the first group. The 

cumulative loads at the mouth of East Willow Creek 

were comparable to the loads from West Willow Creek, 

and so downstream from the confluence, both these 

loads essentially doubled. The mass balance between 

the two tracer-injection studies was very good. For both 

Al and Fe the load was transported in the colloidal 

phase, unlike SO4, Sr, Mn, and Zn, which were 

transported in the dissolved phase.

Although the Solomon Mine area provided an 

increase in the Al load, the majority of Al was 

contributed upstream from the study reach. A 

considerable load of Fe also was contributed upstream 

from the study reach, but very little was contributed by 

the Solomon Mine. The small loading of Al and the 

lack of loading for other metals except Zn could be a 

result of the passive wetlands at the Solomon adit. No 

historical data are included in this study to enable a 

comparison, but the stakeholder group has collected 

data that may help evaluate the influence of the 

wetland.

Principal Locations of Mass Loading

Only Al and Fe had significant loadings in the 

study reach upstream from West Willow Creek (table 

5). However, the magnitude of the Al and Fe loads in 

comparison to those of West Willow Creek were about 

equal (figs. 28 and 29). Among the other solutes, only 

Zn had any substantial loading, but the Zn load was 

very small in comparison to the loading from West 

Willow Creek. Thus, in comparison to West Willow 

Creek and the portion of Willow Creek downstream 

from the confluence, the study reach of East Willow 

Creek upstream from the confluence with West Willow 

Creek was not a significant contributor to metal and 

SO4 loads.

Unsampled Inflow

For the entire study reach, most of the unsampled 

inflow occurred downstream from the confluence with 

West Willow Creek. The reach upstream from the 

confluence accounted for only a small portion of the 

overall load of any metal, and the unsampled inflow 

ranged from less than 1 percent for Mn and SO4 to 49 

percent for Fe. 

Attenuation of Metals

Attenuation ranged from less than 1 percent for 

Fe to 28 percent for Zn in East Willow Creek (table 5). 

However, the magnitude of loads was so small in 

comparison to West Willow Creek that it was not 

comparable.

Lower Willow Creek

The tracer injection in lower Willow Creek 

investigated a 2,912-m section of the Willow Creek 

drainage, starting near the end of the engineered 

section of the stream at the south end of Creede, and 

continued to the Rio Grande River downstream from 

the confluence with Willow Creek (fig. 30). The 

hydrology of this stream reach was complicated by 

braids in the stream, and samples did not represent a 

longitudinal profile of stream segments as they did in 

East and West Willow Creeks. However, it was possible 

to calculate mass balance for important aspects of the 

study reach. Sample sites for the Lower Willow 

injection reach as well as important field and discharge
Evaluation of Metal Loading 41

Table 5. Summary of load calculations, East Willow Creek, Colorado, August 2000

[Loads reported in kilograms per day, except percentages; italicized bold numbers in parentheses indicate rank for the five greatest loads of each constituent]

Segment 

name

Distance, 

in meters Aluminum Cadmium Iron Manganese Lead Strontium Zinc Sulfate

East Willow Creek

EW-T0 947 (1)3.39 (4)0.048 (2)3.22 0.109 0.048 (3)0.943 0.197 (3)53.9

EW-K 1,157 .002 .0 .002 .030 .0 -.058 .678 .916

EW-J 1,447 .066 .001 (5).062 .033 .001 .017 -.644 5.57

EW-1807 1,807 .019 .0 .018 .001 .0 .065 .122 2.44

EW-2175 2,175 -.006 .0 -.006 .099 .0 -.002 -.022 -.720

EW-I 2,405 .044 .0 .042 -.158 .0 .073 .148 1.70

EW-H 2,735 .044 .0 .042 .165 .0 -.080 .324 2.04

EW-2995 2,995 .046 .0 .043 -.037 .001 .106 1.00 9.30

EW-G 3,135 .049 .0 .046 -.028 .001 -.017 -.887 -.884

EW-3525 3,525 (3)1.41 .012 .055 (5).207 (4).2365 .081 (3)2.30 11.2

EW-E 3,602 .084 .001 .059 -.059 -.022 .052 1.374 7.00

EW-D 3,970 .079 -.011 .055 -.028 -.212 -.048 .403 7.08

EW-4107 4,107 -.554 .0 .054 -.140 .0 .051 -.939 7.23

EW-C 4,157 (5).088 .001 (4).070 .152 .001 -.012 (5)1.48 .985

EW-B 4,613 (4).207 (5).014 (3).163 -.068 .002 (5).410 (4)2.04 7.19

EW-A 4,968 .034 -.012 .027 -.023 (3).273 -.278 -1.06 8.03

Downstream from confluence with West Willow Creek

W-A 5,158 (2)2.38 (1).828 (1)3.53 (1)31.8 (1)3.39 (1)5.64 (1)250 (1)2,070

EW-5292 5,292 .0 (2).138 .0 (3).534 -.350 (4).534 -74.8 (2)60.3

EW-5492 5,492 .0 -.011 .0 -.534 -.460 .0 .0 (5)9.08

EW-5892 5,892 .0 -.038 .0 (4).497 (2).380 .0 .0 -52.3

EW-6044 6,044 .0 (3).124 .0 (2).534 (5).066 (2)1.60 (2)21.4 (4)52.3

Cumulative instream load 7.94 1.17 7.48 34.2 4.40 11.0 281 2,320

Cumulative inflow load 6.48 .98 3.79 37.7 2.40 7.63 158 2,560

Percent inflow load 82.0 84 51 110 55 69 56 110

Attenuation .560 .07 <.01 1.08 1.04 .58 78 54.0

Percent attenuation 7 6 < 1 3 24 5 28 2

Unsampled inflow 1.46 .19 3.69 < 1 2.00 3.37 123 < 1

Percent unsampled inflow 18.0 16 49 < 1 45 31 44 < 1
42 Evaluation of Metal Loading to Streams near Creede, Colorado, August and September 2000

Figure 24. (A) Variation of sulfate load with distance and (B) changes in sulfate load for individual stream segments, East Willow Creek, Colorado, 

August 2000.

       















       
















7
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3URFACE
WATERINFLOW

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,OSS

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7INDY'ULCH	

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3OLOMON-INE

35,&!4%,/!$).+),/'2!-30%2$!9

3AMPLEDDISSOLVEDLOAD

#UMULATIVEINSTREAMLOAD

#UMULATIVEINFLOWLOAD
Evaluation of Metal Loading 43

Figure 25. (A) Variation of strontium load with distance and (B) changes in strontium load for individual stream segments, East Willow Creek, Colorado, 

August 2000.

       













       

















%7
7INDY'ULCH	

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342/.4)5-,/!$).+),/'2!-30%2$!9

3AMPLEDDISSOLVEDLOAD

#UMULATIVEINSTREAMLOAD

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44 Evaluation of Metal Loading to Streams near Creede, Colorado, August and September 2000

Figure 26. (A) Variation of manganese load with distance and (B) changes in manganese load for individual stream segments, East Willow Creek, 

Colorado, August 2000.

       






















       



















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3AMPLEDDISSOLVEDLOAD

3AMPLEDCOLLOIDALLOAD

4OTALINSTREAMLOAD

#UMULATIVEINSTREAMLOAD

#UMULATIVEINFLOWLOAD
Evaluation of Metal Loading 45

Figure 27. (A) Variation of zinc load with distance and (B) changes in zinc load for individual stream segments, East Willow Creek, Colorado, August 

2000.

       





















       















%7
7INDY'ULCH	

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3AMPLEDDISSOLVEDLOAD

3AMPLEDCOLLOIDALLOAD

4OTALINSTREAMLOAD

#UMULATIVEINSTREAMLOAD

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46 Evaluation of Metal Loading to Streams near Creede, Colorado, August and September 2000

Figure 28. (A) Variation of aluminum load with distance and (B) changes in aluminum load for individual stream segments, East Willow Creek, Colorado, 

August 2000.

       

























       





















"EGINNINGOFSTUDYREACH

7
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3AMPLEDDISSOLVEDLOAD

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#UMULATIVEINSTREAMLOAD

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Evaluation of Metal Loading 47

Figure 29. (A) Variation of iron load with distance and (B) changes in iron load for individual stream segments, East Willow Creek, Colorado, August 

2000.

       






















       



















"EGINNINGOFSTUDYREACH

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4OTALINSTREAMLOAD

#UMULATIVEINSTREAMLOAD

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48 Evaluation of Metal Loading to Streams near Creede, Colorado, August and September 2000

Figure 30. Location of synoptic sampling sites, lower Willow Creek, near Creede, Colorado, August 2000.



	










	























	

+,,-.#/&(,#-





























	


















	


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Evaluation of Metal Loading 49

data are listed in table 6. Inflow from the Creede 

sewage treatment plant may have occurred along the 

west side of the study reach. Along the east side, acidic 

inflow was likely from the Imperious tailings (fig. 30). 

Otherwise, only a few obvious inflows along the study 

reach were observed. A diversion of 29 percent of the 

water occurred at the Wasson gate (LW-10150). 

Although this resulted in a loss of mass, it was possible 

to account for this in the load calculations.

Discharge

A NaBr tracer with a Br concentration of 

151,900 mg/L was injected at a rate of 0.0043 L/s. 

Straightforward application of equation 1 for 

determining discharge was not possible because of 

extensive braiding that occurs in this lower reach. 

Numerous discharge estimates based on traditional 

velocity-area measurements (Rantz and others, 1982) 

were therefore combined with tracer-dilution data to 

provide a description of discharge. Discharge 

estimates for sites above the braided area (W-D, W-E, 

and LW-8220) were first calculated by using equation 

1. Velocity-area measurements were then used to 

assign discharge to a number of additional sites (LW9500, LW-9520, LW-9540, W-H, LW-10150, W-I, and 

W-J). Discharges at the remaining sites were given by:

(7)

where:

= stream discharge at the upstream site, 

in L/s,

= the tracer concentration at the 

upstream site, in mg/L,

= the tracer concentration at the 

downstream site, in mg/L, and

= the inflow concentration (of water 

entering between two stream sites).

For example, discharge at W-I, which is 

downstream from LW-10082, was estimated from the 

upstream discharge at LW-10082 (QU), the upstream 

concentration at LW-10082 (CU), the downstream 

concentration at W-I (CD), and the inflow 

concentration at LW-10090 (CL) (fig. 31).

Chemical Characterization of Synoptic Samples

Concentrations along the study reach are difficult 

to track because the braiding of the stream caused 

variations to a simple longitudinal profile. There were 

essentially three different longitudinal paths through 

the study reach, defined as follows:

1. From the injection site, path 1 follows the eastern 

braid to W-H, and then a part goes to LW-9520 and 

from there to the mouth of Willow Creek at W-J.

2. From the central braid, at W-G, the stream 

continues to the mouth of Willow Creek at W-I.

3. On the west side of the study reach, a stream starts 

upstream from W-G West, passes the Sewage 

Treatment Plant (STP), and joins path 2 at LW9482.

The stream was mostly a calcium sulfate type 

water in all of the braids. The Rio Grande River near 

Willow Creek was a calcium bicarbonate type. Values 

of pH were generally between 7.0 and 7.5 (fig. 32). The 

effect of acidic inflows may have started at LW-8220, 

but values just downstream were again near 7.5. pH in 

the Rio Grande River was higher than in the study 

reach of Willow Creek.

Concentrations of Al, Fe, Mn, and Zn were 

relatively high along the study reach (fig. 33). Both Al 

and Fe were present mostly as colloids. There was 

some colloidal Zn, but concentrations of dissolved Zn 

were much higher. The spatial variation of metals gives 

an indication of the importance of the Imperious 

tailings and other sources. The pattern of SO4

concentration indicates that concentrations were higher 

in the east braid (path 1) than in the central braid (fig. 

34). This could be from the inflow of W-F and LW8340. However, the concentration of SO4 in the west 

braid (path 3) was substantially higher. The source of 

this SO4 is not clear because this braid started just 

upstream from the sampling site. Water entering the 

Rio Grande River along path 1 had a higher SO4

concentration than along path 2, but they were not very 

different.

The pattern of Mn was different from that of SO4

(fig. 35). There was a distinction between 

concentrations in the east and middle braids (paths 1 

and 2), but concentrations in the west braid (path 3) 

were lower. Concentrations of Zn were similar to those 

of SO4 because the west braid (path 3) had higher Zn 

concentrations than the other two paths (fig. 36).

QD

QU CU CD ( ) –

CD CL – = ---------------------------------

QU

CU

CD

CL
50 Evaluation of Metal Loading to Streams near Creede, Colorado, August and September 2000

Table 6. Synoptic sampling sites, lower Willow Creek, Colorado, August 2000

[-—, no data]

Segment 

identification Source Distance, in meters Site description

pH, in 

standard 

units

Specific 

conductance, 

in microsiemens per 

centimeter

Discharge, in 

liters per 

second

Smoothed 

bromide, in 

milligrams 

per liter

LW-T0 Stream 7,443 Upstream from injection 7.46 137 582 0.04

LW-7586 Stream 7,586 At the end of the channel at railroad bridge 7.31 143 582 .73

W-D Stream 7,716 Down from trailer park sewage disposal 7.39 142 582 1.02

W-E Stream 7,830 T1 - Up from braided reach 7.43 141 588 1.05

LW-8170 Inflow 8,170 Stream return flow—may have tailings 

seepage

7.50 139 — — 

LW-8220 Stream 8,220 Where braids come back together 6.84 145 599 1.03

LW-8340 Inflow 8,340 Seep with Ulothrix algae 3.42 2,050 — .01

W-F Inflow 8,450 Seep from tailings 2.95 2,770 — .01

W-G Stream 8,725 Stream in middle braid 170 m before split 7.46 144 304 1.01

W-G-East Stream 8,725 East channel 7.40 149 263 .99

W-G-West Stream 8,725 West channel with little flow 7.17 176 31.7 .94

LW-9075 Stream 9,075 T2 - Right part of middle braid 7.49 143 250 .89

LW-9335 Inflow 9,335 Seepage from sewage treatment plant 7.46 172 55.4 .01

LW-9482 Stream 9,482 Down from sewage treatment plant 7.45 146 305 .87

LW-9500 Stream 9,500 Upstream from Wasson return 7.28 148 40.3 .87

LW-9520 Inflow 9,520 Wasson return 7.11 149 99.1

LW-9540 Stream 9,540 Down from Wasson return 7.10 149 148 .87

LW-9782 Stream 9,782 Right part of middle braid 7.38 147 308 .88

LW-10082 Stream 10,082 Another right part of the middle braid 6.74 149 322 .88

LW-10090 Inflow 10,090 Flow along base of high berm 6.96 166 — .01

W-H Stream 10,100 Wasson gate 7.21 150 265 .88

LW-10150 Stream 10,150 Irrigation diversion — — — —

W-I Stream 10,324 Stream near mouth of upstream braid 7.37 147 333 .82

W-J Stream 10,324 Stream near mouth of downstream braid 7.42 147 163 .60

RG-A Stream 10,350 Rio Grande River up from Willow Creek 8.13 80 7,074 .29

RG-B Stream 10,355 Rio Grande River down from Willow Creek 7.45 82 7,570 .04
Evaluation of Metal Loading 51

Figure 31. Discharge at sampling sites along the study reach, lower Willow Creek, Colorado, August 2000.



	

	












	


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Figure 32. Variation of pH with distance along the study reach, indicating paths of braids, lower Willow Creek, Colorado, August 2000.

       





















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Evaluation of Metal Loading 53

Figure 33. Distribution of selected dissolved (blue) and colloidal (orange) metal concentrations, lower Willow Creek, Colorado, August 2000.

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54 Evaluation of Metal Loading to Streams near Creede, Colorado, August and September 2000

Figure 34. Variation of sulfate concentration with distance along the study reach, indicating paths of braids, lower Willow Creek, Colorado, August 2000.

       























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Evaluation of Metal Loading 55

Figure 35. Variation of manganese concentration with distance along the study reach, indicating paths of braids, lower Willow Creek, Colorado, August 

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56 Evaluation of Metal Loading to Streams near Creede, Colorado, August and September 2000

Figure 36. Variation of zinc concentration with distance along the study reach, indicating paths of braids, lower Willow Creek, Colorado, August 2000.

       























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Summary—Implications for Remediation 57

Load Profiles

Patterns of loading are difficult to display in a 

longitudinal view for the lower Willow Creek study 

area. With the braiding in the stream, loads are split and 

at other places, they recombine. To avoid the 

complexity of such a plot, the loads are presented in a 

schematic map view, similar to the presentation of 

discharge. It is also difficult to present a summary of 

loading calculations that is similar to those for West 

and East Willow Creeks. However, some load 

calculations help identify the effect of this study reach 

on loads to the Rio Grande River (table 7). The first 

calculation is the sum of W-I and W-J. The net gain 

through the study reach takes this sum, adds the load 

leaving by the Wasson diversion, and subtracts the load 

at LW-8220, upstream from the beginning of braiding. 

Finally, the net gain for the Rio Grande River is from 

the difference between loads at RG-A and RG-B. 

The overall effect of the lower Willow study 

reach was a net loss of Fe, Mn, and Zn, and a net gain 

of Al and SO4. Overall, however, there appeared to be a 

net gain of Al, Fe, Mn, Zn, and SO4 to the Rio Grande 

River between the two sampling sites. Without the 

longitudinal profiles of load, it is difficult to determine 

if this increase was from unsampled inflow, but it most 

likely was ground-water contribution to the Rio Grande 

River from sources within the Willow Creek watershed. 

To interpret the load diagrams for the lower 

Willow study, strontium can be viewed as a 

conservative solute through the study reach. Strontium 

concentration did not vary by more than a few 

hundredths of a milligram per liter. With that 

assumption, the percentage of Sr load at W-G and WG-East was 51 (3.70 of 7.25) and 44 (3.19 of 7.25) 

percent, respectively, of the load at LW-8220 (fig. 37). 

If other metals have different percentages, particularly 

at W-GE, then we might assume that there was some 

loading along the east braid, most likely from the

Imperious tailings. The same reasoning might be used 

at other sites, but this one is of particular interest for 

metal loading. For SO4 loading, the percentages are 

comparable: 52 percent for W-G and 48 percent for WG-East (fig. 38). For Mn (fig. 39) and Zn (fig. 40) 

loads, however, the percentages are reversed, and W-G 

only accounts for 46 and 43 percent, respectively. Thus, 

there is some indication of loading in this small reach 

of stream because of the highly acidic inflows of W-F 

and LW-8340.

SUMMARY—IMPLICATIONS FOR 

REMEDIATION

Metal loading in the Willow Creek watershed 

was quantified by establishing the hydrologic 

framework for chemical synoptic sampling in a series 

of tracer injections. Mass-loading results have shown 

that there is not a substantial contribution from any of 

the possible sources in lower Willow Creek, although 

the loads from sources upstream of Creede, Colorado, 

mostly are transported to the Rio Grande River through 

the lower Willow Creek area. Load profiles from West 

Willow Creek indicate that the greatest loading of 

metals in the Willow Creek watershed comes from the 

Nelson Tunnel inflow, accounted for at sampling site 

WW-F. This is a particularly substantial loading for Zn 

and other metals. Other stream segments, just 

downstream from WW-F, contribute substantial 

amounts of metals, including additional Zn load. It is 

possible that these secondary loadings result from 

water that leaks into the waste-rock pile and enters the 

stream farther down the drainage. Any remediation 

plan should account for those secondary sources, 

whether they are part of the Nelson Tunnel loading or 

not. East Willow Creek is not a significant source of 

metal loads. This could be a result of previous, 

Table 7. Change in load through study reach of lower Willow Creek, Colorado, August 2000

[All values reported in kilograms per day; <, less than]

Calculation Aluminum

Cadmium Copper Iron Manganese

Strontium Zinc Sulfate

Sum of load from two braids of Willow Creek 7.3 0.6 0.8 2.7 17.0 6.0 93.7 2,062

Net gain through study reach (including Wasson diversion) 1.1 0 .4 -.9 -1.1 .8 -14.2 436

Net gain in the Rio Grande River 13.4 .5 -13.9 19.0 21.3 4.7 89.7 2,088

Unsampled inflow to Rio Grande River 6.1 < 1 < 1 16.3 4.3 < 1 < 1 22
58 Evaluation of Metal Loading to Streams near Creede, Colorado, August and September 2000

Figure 37. Total strontium load at synoptic sampling sites, lower Willow Creek, Colorado, August 2000.

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Summary—Implications for Remediation 59

Figure 38. Total sulfate load at synoptic sampling sites, lower Willow Creek, Colorado, August 2000.

 

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Figure 39. Total manganese load at synoptic sampling sites, lower Willow Creek, Colorado, August 2000.

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Figure 40. Total zinc load at synoptic sampling sites, lower Willow Creek, Colorado, August 2000.

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62 Evaluation of Metal Loading to Streams near Creede, Colorado, August and September 2000

remediation efforts in that drainage. In summary, these 

tracer-injection studies have given a watershed picture 

of the metal-loading in streams near Creede, Colorado. 

Metal loading is dominated by the inflow from the 

Nelson Tunnel, however, there also were dispersed, 

subsurface inflows that add substantial loads. 

REFERENCES CITED

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Mich., Lewis Publishers, Inc., p. 255-269.

Bencala, K.E., McKnight, D.M., and Zellweger, G.W., 1990, 

Characterization of transport in an acidic and metal-rich 

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simulations of transient storage: Water Resources 

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Besser, J.M., Brumbaugh, W.G., May, T.W., Church, S.E., 

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Broshears, R.E., Bencala, K.E., Kimball, B.A., and 

McKnight, D.M., 1993, Tracer-dilution experiments 

and solute-transport simulations for a mountain stream, 

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Water-Resources Investigations Report 92-4081, 18 p.

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synoptic sampling methods in Cataract Creek, Jefferson 

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4237, 39 p.

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responses to heavy metals in the upper Arkansas River 

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Daultrey, S., 1976, Principal components analysis: Concepts 

and techniques in modern geography No. 8: London, 

Institute of British Geographers, 50 p.

Grundy, W.D., and Miesch, A.T., 1985, Brief descriptions of 

STATPAC and related statistical programs for the IBM 

personal computer: U.S. Geological Survey Open-File 

Report 87-411-A, 34 p.

Jarrett, R.D., 1992, Hydraulics of mountain rivers, in Yen, 

B.C., ed., Channel Flow Resistance Centennial of 

Manning's Formula: International Conference of the 

Centennial of Manning's and Kuichling's Rational 

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Publications, p. 287-298.

Joreskog, K.G., Klovan, J.E., and Reyment, R.A., 1976, 

Geological factor analysis: New York, Elsevier 

Scientific Publishing Co., 178 p.

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discharge using tracers: Techniques of Water-Resources 

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Chap. A16.

Kimball, B.A., 1997, Use of tracer injections and synoptic 

sampling to measure metal loading from acid mine 

drainage: U.S. Geological Survey Fact Sheet FS-245-

96.

Kimball, B.A., Bencala, K.E., and Broshears, R.E., 1994, 

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Colorado, in, Dutton, A., ed., Toxic Substances in the 

Hydrologic Sciences: Minneapolis, Minn., American 

Institute of Hydrology, p. 80-94.

Kimball, B.A., Callender, E., and Axtmann, E.V., 1995, 

Effects of colloids on metal transport in a river 

receiving acid mine drainage, Upper Arkansas River, 

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306.

Kimball, B.A., McKnight, D.M., Wetherbee, G.A., Harnish, 

R.A., 1992, Mechanisms of iron photoreduction in a 

metal-rich, acidic stream, St. Kevin Gulch, Colorado, 

U.S.A.: Chemical Geology, v. 96, p. 227-239.

Kimball, B.A., Nimick, D.A., Gerner, L.J., and Runkel, R.L., 

1999a, Quantification of metal loading in Fisher Creek 

by tracer injection and synoptic sampling, Park County, 

Montana, August 1997: U.S. Geological Survey WaterResources Investigations Report 99-4119, 40 p.

Kimball, B.A., Runkel, R.L., and Gerner, L.J., 1999b, 

Quantification of metal loading in French Gulch, 

Summit County, Colorado, using a tracer-injection 

study: U.S. Geological Survey Water-Resources 

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Quantification of mine-drainage inflows to Little 

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10, p. 1390-1404.
References Cited 63

Kimball, B.A., Runkel, R.L., Walton-Day, K., and Bencala, 

K.E., 2002, Assessment of metal loads in watersheds 

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K.E., 1999, Reactive solute transport in streams: A 

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

processing of surface-water and bed-material samples 

for physical and chemical analyses: U.S. Geological 

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tracers to measure stream flow loss by multiple tracer 

injection: Hydrological Processes, v. 8, p. 155-165.

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4150, 20 p.
64 Evaluation of Metal Loading to Streams near Creede, Colorado, August and September 2000

APPENDIX—RESULTS OF CHEMICAL ANALYSES FOR SYNOPTIC SAMPLES COLLECTED 

NEAR CREEDE, COLORADO

The appendix consists of two tables available as PDF files. These files are linked from their titles below. 

Table A-1. Physical properties of synoptic samples collected near Creede, Colorado, August and September 2000

Table A-2. Concentration of chemical constituents in synoptic samples collected near Creede, Colorado, August and September 2000
Printed on recycled paper