Quantification of Metal Loading by 

Tracer Injection and Synoptic Sampling, 

1996–2000

By Briant A. Kimball, Katherine Walton-Day, and Robert L. Runkel

Chapter E9 of

Integrated Investigations of Environmental Effects of Historical 

Mining in the Animas River Watershed, San Juan County, Colorado

Edited by Stanley E. Church, Paul von Guerard, and Susan E. Finger

Professional Paper 1651

U.S. Department of the Interior

U.S. Geological Survey
Contents

Abstract .......................................................................................................................................................423

Introduction.................................................................................................................................................423

Purpose and Scope ..........................................................................................................................424

Acknowledgments ............................................................................................................................424

Methods.......................................................................................................................................................424

Mass-Loading Analysis....................................................................................................................426

Multivariate Classification of Samples .........................................................................................427

Mass-Loading Studies ..............................................................................................................................428

Upper Animas River Basin, 1997, 1998, and 2000 .........................................................................428

Discharge ..................................................................................................................................428

Chemical Characterization of Synoptic Samples ...............................................................431

Mass-Load Profiles..................................................................................................................434

Principal Locations of Loading .....................................................................................437

Unsampled Inflow ...........................................................................................................438

Attenuation of Load ........................................................................................................438

Summary....................................................................................................................................438

Cement Creek Basin, 1996, 1999, and 2000 ...................................................................................438

Chemical Characterization of Synoptic Samples ...............................................................440

Inflows ..............................................................................................................................440

Stream ..............................................................................................................................440

Mass-Load Profiles..................................................................................................................443

Principal Locations of Loading .....................................................................................443

Unsampled Inflow ...........................................................................................................448

Attenuation of Load ........................................................................................................449

Summary....................................................................................................................................449

Mineral Creek Basin, 1999 ...............................................................................................................449

Chemical Characterization of Synoptic Samples ...............................................................449

Inflows ..............................................................................................................................454

Stream ..............................................................................................................................455

Mass-Load Profiles..................................................................................................................457

Principal Locations of Loading .....................................................................................458

Unsampled Inflow ...........................................................................................................458

Attenuation of Load ........................................................................................................460

Summary....................................................................................................................................460

Elk Park Basin, 1998—Summary of Watershed Contributions ..................................................460

Chemical Characterization of Synoptic Samples ...............................................................460

Inflows ..............................................................................................................................460

Stream ..............................................................................................................................462

Mass-Load Profiles..................................................................................................................463

Aluminum..........................................................................................................................466

Iron ....................................................................................................................................468
Copper ..............................................................................................................................471

Manganese ......................................................................................................................472

Zinc ..................................................................................................................................473

Summary and Conclusions .......................................................................................................................476

References Cited........................................................................................................................................476

Appendix 1. Methods .............................................................................................................................479

Sampling and Chemical Analysis ...................................................................................................479

Tracer Injections and Stream Discharge ......................................................................................479

Tracer-Dilution Case I: Uniform Background Concentrations ..........................................480

Tracer-Dilution Case II: Non-Uniform Background with a Presynoptic 

Sampling ......................................................................................................................480

Tracer-Dilution Case III: Non-Uniform Background without a Presynoptic 

Sampling ......................................................................................................................481

Synoptic Sampling and Analytical Methods ................................................................................481

Appendix 2. Details of Upper Cement Creek Mass-Loading Studies ............................................482

Upper Cement Creek Study Area and Experimental Design .....................................................482

Discharge ..................................................................................................................................482

Comparison of Conditions 1996 Versus 1999 .......................................................................488

Figures

 1. Map showing location of mass-loading study reaches, Animas River watershed 

study area, Colorado, 1996–2000 .............................................................................................425

 2. Map showing location of study reaches, alteration zones, key locations, and 

principal sites of inactive mines, upper Animas River basin, 1997, 1998, and 2000 ..........429

 3–6. Graphs showing:

 3. Variation of discharge with distance for three mass-loading studies, upper 

 Animas River basin, 1997, 1998, and 2000 ......................................................................430

 4. Variation of pH and total-recoverable concentrations of iron, copper, and 

 zinc with distance, upper Animas River basin, 1997, 1998, and 2000 ........................432

 5. Variation of dissolved zinc concentration with distance, upper Animas 

 River basin, from Arrastra Creek to Silverton, August 2002 .......................................435

 6. Variation of normalized instream loads for aluminum, iron, manganese, 

 cadmium, copper, zinc, strontium, and sulfate with distance, upper Animas 

 River basin, 1997, 1998, and 2000 .....................................................................................436

 7. Map showing location of study area, alteration zones, key locations, and 

principal sites of inactive mines, Cement Creek basin, 1996, 1999, and 2000 .................439

 8–10. Graphs showing:

 8. Variation of pH with distance for three mass-loading studies, Cement 

 Creek basin, 1996, 1999, and 2000 ...................................................................................441

 9. Variation of pH and dissolved and colloidal concentrations of iron, and 

 total-recoverable concentrations of copper and zinc with distance, 

 Cement Creek basin, 1996, 1999, and 2000 ....................................................................444

 10. Variation of normalized instream loads for cadmium, copper, zinc, aluminum, 

 iron, lead, manganese, strontium, and sulfate with distance, Cement Creek 

 basin, 1996 and 1999 ..........................................................................................................448
 11. Map showing location of study area, alteration zones, key locations, and principal 

sites of inactive mines, Mineral Creek basin, 1999 ...............................................................450

 12–14. Graphs showing:

 12. Variation of injected bromide concentration and calculated discharge with 

 distance, Mineral Creek basin, September 1999 ..........................................................451

 13. Variation of pH and dissolved and colloidal concentrations of iron, and total-

 recoverable concentrations of copper and zinc with distance, Mineral Creek 

 basin, 1999 ...........................................................................................................................452

 14. Variation of normalized instream loads for arsenic, copper, zinc, aluminum, 

 iron, manganese, strontium, and sulfate with distance, Mineral Creek basin, 

 September 1999 .................................................................................................................459

15. Map showing location of study reach, stream segments, and key locations, 

Animas River, Silverton to Elk Park, August 1997 and 1998 ...............................................461

 16–18. Graphs showing:

 16. Variation of chloride concentration and discharge with distance, Animas 

 River, Silverton to Elk Park, August 1997 and 1998 .......................................................462

 17. Variation of pH and dissolved and colloidal concentrations of iron, and total-

 recoverable concentrations of copper and zinc with distance, Animas River, 

 Silverton to Elk Park, August 1997 and 1998 ..................................................................464

 18. Variation of normalized instream loads for aluminum, copper, iron, manganese, 

 zinc, strontium, and sulfate with distance, Animas River, Silverton to Elk Park, 

 August 1997 and 1998 ........................................................................................................467

 19–24. Bar charts showing:

 19. Comparison of sampled instream load for Elk Park study reach (outlet load) 

 with cumulative instream load for the individual basin studies for aluminum, 

 iron, copper, and zinc ........................................................................................................469

 20. Areas of relative importance for aluminum mass loading, Animas River 

 watershed study area .......................................................................................................470

 21. Areas of relative importance for iron mass loading, Animas River watershed 

 study area ............................................................................................................................472

 22. Areas of relative importance for copper mass loading, Animas River 

 watershed study area .......................................................................................................473

 23. Areas of relative importance for manganese mass loading, Animas River 

 watershed study area .......................................................................................................474

 24. Areas of relative importance for zinc mass loading, Animas River watershed 

 study area ............................................................................................................................475

 25. Map showing location of selected synoptic sampling sites and inactive mines, 

upper Cement Creek, September 1999 ..................................................................................483

 26–33. Graphs showing:

 26. Variation of bromide concentration with time at three transport sites, and 

 with distance, upper Cement Creek, September 1999 ................................................485

 27. Variation of synoptic, plateau, and adjusted bromide concentrations with 

 distance along study reach, upper Cement Creek, September 1999 ........................487

 28. Variation of discharge measurements with distance, upper Cement Creek, 

 September 1996 and 1999 .................................................................................................489

 29. Relation of pH measured during three different studies, upper Cement Creek .........490
 30. Relation of copper concentrations and corresponding copper loads 

 measured during three different studies, upper Cement Creek ................................491

 31. Relation of iron concentrations and corresponding iron loads measured 

 during three different studies, upper Cement Creek ...................................................492

 32. Relation of manganese concentrations and corresponding manganese 

 loads measured during three different studies, upper Cement Creek .....................493

 33. Relation of zinc concentrations and corresponding zinc loads measured 

 during three different studies, upper Cement Creek ...................................................494

Tables

 1. Chemical composition of selected samples representing groups defined by 

principal component analysis, upper Animas River basin, 1997, 1998, and 2000 ...........434

 2. Summary of load calculations and cumulative instream load for selected 

subreaches, upper Animas River basin, 1997, 1998, and 2000 ..........................................437

 3. Chemical composition of selected inflow samples representing groups defined 

by principal component analysis, Cement Creek basin, 1996, 1999, and 2000 ....................442

 4. Chemical composition of selected stream samples representing groups defined 

by principal component analysis, Cement Creek basin, 1996, 1999, and 2000 ....................446

 5. Summary of load calculations and cumulative instream load for selected 

subreaches, Cement Creek basin, 1996 and 1999 ...............................................................447

 6. Chemical composition of selected inflow samples representing groups defined 

by principal component analysis, Mineral Creek basin, 1999 .............................................454

 7. Chemical composition of selected stream samples representing groups defined 

by principal component analysis, Mineral Creek basin, 1999 .............................................456

 8. Summary of load calculations and cumulative instream load for selected 

subreaches, Mineral Creek, September 1999 ......................................................................458

 9. Chemical composition of selected inflow samples representing groups defined 

by principal component analysis, Animas River, Silverton to Elk Park, August 1997 

and 1998 ......................................................................................................................................463

 10. Chemical composition of selected stream samples representing groups defined 

by principal component analysis, Animas River, Silverton to Elk Park, August 1997 

and 1998 ......................................................................................................................................466

 11. Summary of load calculations and change of instream load for selected sections 

of the study reach, Animas River, Silverton to Elk Park, August 1997 and 1998 .................468

 12. Summary of mass loading for selected metals, Animas River watershed study 

area .............................................................................................................................................471

 13. Site identification, downstream distance, source, label, principal component 

classification, site description, and selected characteristics for stream and 

inflow sites, upper Cement Creek, September 1999 ...........................................................484

 14. Bromide concentrations, discharge based on velocity meter, Parshall flume 

measurements, and discharge calculated from tracer concentrations, upper 

Cement Creek, September 1999 .............................................................................................486

 15. Relation of water quality and load for samples collected at the Mogul mine

inflow by the Colorado Division of Minerals and Geology (CDMG) in 1996 and

the U.S. Geological Survey (USGS) in 1999 and 2000, upper Cement Creek ...................495
Conversion Factors and Abbreviated Water-Quality Units

Multiply By To obtain

meter (m) 0.30481 foot (ft)

liter per second (L/s) 28.317 cubic foot per second (ft3

/s)

kilometer (km) .62137 mile (mi)

square kilometer (km2

) .3861 square mile (mi2)

kilogram per day (kg/day) 2.205 pounds per day (lb/day)

Temperature in degrees Celsius (°C) may be converted to temperature in degrees Fahrenheit 

(°F) by using the following equation:

°F=9/5°C+32

The following terms and abbreviations also are used in this report:

milligram per liter (mg/L)

microgram per liter (μg/L)

millimoles per liter (mmol/L)

milliliters per minute (mL/min)

milligram per second (mg/s)
Abstract

Prioritizing mine site remediation efforts at the watershed 

scale requires an understanding of all trace- and major-element 

sources in the watershed. We established a hydrologic framework to study metal loading in the Animas River watershed 

study area in Colorado by conducting a series of tracerinjection studies. Each study used the tracer-dilution method 

to quantify stream discharge in conjunction with synoptic 

sampling to provide downstream profiles of pH and solute 

concentration. Discharge and concentration data were then 

used to develop mass-loading profiles for the various solutes 

of interest. The discharge and load profiles (1) identify the 

principal sources of solute load to the streams; (2) demonstrate 

the scale of unsampled, dispersed subsurface inflows; and 

(3) estimate the amount of solute attenuation resulting from 

physical, chemical, and biological processes.

Weathering of extensive alteration zones in basins near 

Mineral and Cement Creeks contributes to metal loading in 

these areas. In contrast, alteration in the upper Animas River 

basin is focused along discrete veins, and metal loading corresponds closely with these features. Mass-loading analysis 

indicates that at base flow, Mineral Creek basin dominates 

the contribution of total copper load. Mineral Creek basin 

contributes 60 percent, Cement Creek contributes 30 percent, 

and the upper Animas River basin contributes 4 percent of 

the cumulative instream copper load in the watershed. The 

remaining 6 percent is from sources downstream from these 

three basins. Cement Creek had the greatest contribution of 

total zinc load: 40 percent of the cumulative instream load 

at the A72 gauging station, downstream from Silverton, was 

from Cement Creek, 31 percent was from the upper Animas 

River basin, and 24 percent was from Mineral Creek. The 

contribution of aluminum and iron loads from Cement Creek 

and Mineral Creek was more substantial than for copper and 

zinc. Mass-loading results indicate that 9 percent of the aluminum load was from the upper Animas River basin, 43 percent 

from Cement Creek, and 42 percent from Mineral Creek. The 

contribution of iron from the upper Animas River basin was 

4 percent, from Cement Creek 49 percent, and from Mineral 

Creek 43 percent. Manganese loading differed from the other 

metals because the greatest percentage, 49 percent, came from 

the upper Animas River basin, while 31 percent came from 

Cement Creek, and 15 percent came from Mineral Creek. A 

substantial part of the manganese load from the upper Animas 

River basin could result from the accumulation of large tailings piles from many different sources. Otherwise, the greater 

loads from Cement and Mineral Creeks correspond to geologic 

patterns of alteration. Within these basins, 24 locations have 

been identified that account for from 73 to 87 percent of the 

total mass loading of these selected metals. These locations 

include both mined and unmined areas. This detailed snapshot 

of mass loading can be used to support remediation decisions, 

and to quantify processes affecting metal transport.

Introduction

The Animas River Stakeholders Group, which includes 

State and Federal land-management agencies, is charged with 

the task of improving water quality in the Animas River watershed. Hundreds of inactive mines are scattered throughout the 

mountainous terrain that makes up San Juan County, Colo. 

(Church, Mast, and others, this volume, Chapter E5; Jones, 

this volume, Chapter C). The challenge facing the stakeholders 

group is to understand the complex variety of inflows and to 

determine which sources of loading have the greatest influence 

on water quality. These issues are of paramount importance to 

land managers who must implement remedial actions.

A great diversity among inflow chemistry provides a 

unique opportunity (1) to examine how the tracer-injection 

and synoptic-sampling methods, applied on a watershed scale, 

help to define the contributions to metal loads from many 

sources and (2) to understand the effects of instream processes 

on the transport of metals. Both mined and unmined areas 

contribute substantial loads of constituents to the streams that 

drain the Animas River watershed because of the widespread 

extensively altered and mineralized rocks in the area. Contributions to the stream from these sources range from welldefined tributary inflows to dispersed, ground-water inflows. 

Chapter E9

Quantification of Metal Loading by Tracer Injection 

and Synoptic Sampling, 1996–2000

By Briant A. Kimball, Katherine Walton-Day, and Robert L. Runkel
Mass-loading studies are useful to identify and compare the 

complex sources of loads in a watershed. These studies are 

based on two well-established techniques: the tracer-dilution 

method and synoptic sampling. The tracer-dilution method 

provides estimates of stream discharge that are in turn used 

to quantify the amount of water entering the stream, both 

tributary and ground-water inflow, in a given stream segment 

(Bencala and others, 1990). Synoptic sampling of instream 

and inflow chemistry provides a detailed longitudinal snapshot 

of stream-water quality and of the chemistry of inflows that 

influence changes in the stream. When used together, these 

techniques provide discharge and concentration data that are 

used to determine the mass loading associated with various 

sources of water.

For this chapter, the Animas River watershed study area 

has been divided into four basins (fig. 1). The upper Animas 

River basin extends from Silverton, Colo., to the headwaters 

of California Gulch and is detailed by the Howardsville (1997), 

Eureka (1998), and California Gulch (2000) mass-loading 

studies. The Cement Creek basin also extends upstream from 

Silverton to Ross Basin and is detailed by the lower Cement 

Creek (1996), upper Cement Creek (1999), and May Day (2000; 

Wright, Kimball, and Runkel, this volume, Chapter E23). The 

Mineral Creek basin was detailed by three mass-loading studies 

in 1999. The Elk Park basin was included to evaluate loading 

and transport in the Animas River downstream from Silverton 

and is detailed by the Silverton (1997) and Elk Park (1998) 

mass-loading studies.

The diversity among inflows results from the complex 

geologic history in the area of the Silverton caldera. Five 

distinct alteration mineral assemblages have been identified, 

including an acid-sulfate (AS) zone, a quartz-sericite-pyrite 

(QSP) zone, a vein-related quartz-sericite-pyrite (V-QSP) 

zone, a weak sericite-pyrite (WSP) zone, and a regional propylitic zone (Bove and others, this volume, Chapter E3; Yager 

and Bove, this volume, Chapter E1). In general, the rocks on 

both sides of the upper Animas River have propylitic alteration, but areas of QSP and V-QSP alteration also exist (Bove 

and others, this volume). Among the four basins discussed 

in this chapter, the upper Animas River basin only has one 

small area of AS alteration in the upper reaches of California 

Gulch. It mostly contains regional propylitic alteration with 

many locations of V-QSP alteration. Both Cement Creek and 

Mineral Creek basins are within the core of alteration in the 

Silverton caldera and contain substantial areas of AS and QSP 

alteration (Bove and others, this volume). There is little alteration in the Elk Park basin.

Purpose and Scope

The purpose of this chapter is to describe the application 

of the mass-loading studies to several stream reaches within 

the Animas River watershed study area. Application of the 

method results in mass-loading profiles that are used to answer 

three basic questions. First, where do the greatest loadings of 

metals and acidity occur? These locations will likely have the 

greatest effect on stream-water quality and may be the subject 

of further study and candidates for remedial action. Second, 

is the mass loading at these locations primarily composed of 

dispersed, ground-water inflow? Loading that is dominated 

by ground-water inflow may not be amenable to remediation 

because of more complex pathways from the source to the 

stream. Third, does substantial instream attenuation of metal 

loads take place? Attenuation of metal loads by geochemical processes should be considered as part of the remedial 

design, but also may change the nature of the toxic effect in 

the stream, and may lead to seasonal flushing of toxic metals. The analyses presented within this chapter are limited 

to the information that comes from mass-loading profiles; 

results of solute-transport simulations based on data described 

herein are discussed by Walton-Day and others (this volume, 

Chapter E24).

Acknowledgments

This work was done in cooperation with the Bureau 

of Land Management, which provided funding. Support 

was also provided by the U.S. Geological Survey Toxic 

Substances Hydrology Program. Many individuals helped 

with the synoptic sampling for the mass-loading studies, 

including Douglas Burkhardt, Melissa Cox, Jonathan Evans, 

Robert Jenkins, Kenneth Leib, Alisa Mast, Ed Vaill, 

Lawrence Schemel, Patricia Solberg, Paul von Guerard, 

Winfield Wright, and Tracy Yager, U.S. Geological 

Survey; Bill Carey, Cathleen Zillich, Stephanie O’Dell, and 

Loren Wickstrom, Bureau of Land Management; Carol Russell, 

U.S. Environmental Protection Agency; Paul Krabacher, 

James Herron, and Bruce Stover, Colorado Division of Minerals 

and Geology; Steve Ferron and William Simon from the Animas 

River Stakeholders Group; and volunteers including Anna Day, 

Andy Gleason, Adam Kimball, Daniel Kimball, Bryn Kimball, 

Aaron Packman, Francis ReMillard, Michael ReMillard, 

Brad Smith, and Joy von Guerard. The studies also benefited 

from the support of members of the Animas River Stakeholders 

Group.

Methods

Application of mass-loading methods to abandoned 

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

Survey’s (USGS) Toxic Substances Hydrology Program 

(Bencala and McKnight, 1987; Kimball and others, 1994; 

Kimball and others, 1995; Kimball and others, 2002). As 

described in Appendix 1, 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 

424 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
Quantification of Metal Loading 425

Figure 1. Location of mass-loading study reaches, Animas River watershed study area, Colorado, 1996–2000.

A68

C48

A72

Eureka

1998

Howardsville 1997

L

ower C

e

me

nt Creek 1996

Upper

Mineral

M

di d

el Min

eral Lower Mineral

Upper

Cement1999

C

aliforn

ai Gulch 2000

E

lk

P

a

rk

1

9

9

8

Silverton 1997

M

ni

eral Cre

e

k 19

9

9

U

n

stu

die

d re

a

ch

C48

EXPLANATION

U.S. Geological Survey

 streamflow gauging station

M

ay

Day

2000

M34

North Fork 2000

107o42’38” 107o

33’54”

37o

53’49”

37o48’02”

Animas River

watershed 

study area

C O L O R A D O

Durango
profiles. The appendix also includes a discussion of tracerinjection methods, equations for calculating discharge, methods 

for synoptic sampling, and analytical methods.

The studies described herein were undertaken during base-flow conditions (generally occurring from August 

to March when ground-water discharge predominates in 

the streamflow). Application of the method to base-flow 

conditions is appropriate for two reasons. First, the pattern 

of a mass-loading profile, expressed at base flow, reflects the 

importance of metal sources that enter the stream on a continuous basis. Remedial actions that address the sources identified 

at base flow will therefore improve water quality during the 

entire year; such actions will address chronic concerns. Second, the pattern of mass loading at base flow indicates those 

sources that contribute to high instream concentrations during 

the winter months, when the most toxic conditions likely 

occur (Besser and Leib, 1999). During the base-flow winter 

months, dilution of mine drainage by other sources of water is 

minimal, and toxicity standards are more likely to be exceeded 

(Besser and Leib, 1999). Although dissolved metal loads are 

greater during snowmelt runoff, truly dissolved metal concentrations generally are lower and pose less risk to aquatic life. 

Even with the focus on the base-flow period, we could identify 

differences in the flow regimes due to year-to-year variability 

in timing and quantity of snow and rain. As such, comparison 

of mass-loading profiles from the individual studies may be 

limited, but generalizations are possible.

To outline the chemical characteristics of water from 

each basin, downstream profiles are presented for pH and concentrations of iron, copper, and zinc. Many changes in stream 

chemistry arise from variations in pH, particularly the partitioning of iron between dissolved and colloidal phases. The 

fate and transport of many metals like copper and zinc in mine 

drainage are tied to the transport of the iron colloidal material 

(Kimball and others, 1995). Copper and zinc are two metals 

of particular concern because of their toxicity to aquatic life 

(Colorado Department of Public Health and Environment, 

2000). Acute and chronic toxicity standards, which are based 

on the hardness of the water, are presented in graphs of copper 

and zinc. Values of these standards are unique to each sample 

because the hardness of each sample varies. During base flow, 

hardness generally is higher than during runoff. This means 

that toxicity standards are higher, because the standards are 

directly proportional to the hardness.

Details of sampling, chemical analysis, and tracerinjection methods are in Appendix 1. These methods were 

used for each of the study basins.

Mass-Loading Analysis

To quantify load requires accurate measurements of both 

discharge and chemistry. 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 (2.4451) (1)

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 ft3/s,

and

 2.4451 is the conversion factor to obtain load in 

kg/day.

Sampled instream load is calculated from the totalrecoverable 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 presents 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:

ΔMs

 = Mb – Ma (2)

where

ΔMs is the change in sampled instream load for 

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

Mb

 and Ma are calculated for sites a and b from (1).

Gains in constituent load (ΔMs is greater than zero) imply 

the presence of 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 only 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 

it 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 any loss of a constituent to the streambed has 

occurred.

For those segments that include a sampled inflow, 

calculation of a second value for load is possible based 

upon the change in discharge between stream sites. This 

change, multiplied by constituent concentration in an 

inflow sample, produces an estimate of the inflow load 

for a stream segment. If stream sites a and b surround an 

inflow sample, location i:

ΔMi = Ci

 (Qb – Qa)(2.4451) (3)

426 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
Quantification of Metal Loading 427

where

ΔMi

 is the change in sampled infl ow load from 

location a to b, in kg/day,

Ci

 is the concentration of the selected constituent 

at infl ow location i, in mg/L,

Qa

 and Qb are defi ned as in (1),

and

 2.4451 is the conversion factor to obtain load in 

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. For a given stream segment, the cumulative instream and cumulative inflow loads 

would be equal if the sampled inflow was perfectly representative of the constituent concentration for all the water 

entering the stream in that segment, 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 

defined as:

 Unsampled infl ow = ΔMs –ΔMi (4)

This 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, we find it 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):

 Load error = Qa

2

'Ca

2 Ca2

'Qa

2

+ © 1 § ·  2.4451 (5)

where

Qa

 is the discharge at the upstream site, in ft3/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, 

in ft3

/s,

and

 2.4451 is the conversion factor to obtain load in 

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 load has changed significantly, and ΔMS

 is added 

to the sampled instream load. In developing the cumulative instream load profile, only the changes that are deemed 

significant according to this criterion are used. Otherwise, the 

cumulative instream load remains constant until there is the 

next significant change downstream.

In this accounting of mass loading to the stream, a 

contribution to the load of a particular stream segment can 

be missed if the net change in constituent load for the segment is negative. For example, a definite contribution to load 

could take place within a stream segment, but through chemical reaction, a greater amount of the constituent is removed 

within the segment than was added. Yet, a value for ΔMi

 in that 

stream segment could have a measurable value in that stream 

segment.

Multivariate Classification of Samples

Synoptic sampling results in a large number of stream 

and inflow samples. Because water-rock reactions with altered 

and unaltered mineral assemblages may lead to particular 

chemical signatures among inflows to the stream, classification of samples into groups of similar chemical characteristics 

helps to highlight their similarities and differences, distinguish 

different sources, and recognize geochemical processes.

Patterns in the chemistry and pH of stream and inflow 

samples can be evaluated by using Principal Component 

Analysis (PCA), a multivariate analysis technique (Daultry, 

1976). Principal components represent a set of new, transformed reference axes that are linear combinations of the 

original variables. 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 is easy to picture 

in two dimensions. One can imagine drawing a line that would 

go through the two most distant points in a bivariate plot of 

data; that line would show the direction of PC1 for those data. 

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

point along the line could be described by a linear combination of the original variables. PC2 would be drawn perpendicular to PC1 and it would have its own linear equation. In 

multidimensional space, each subsequent principal component 

is orthogonal to the other principal components 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. Using the scores 

for PC1 and PC2, which are the coordinates of the original 
samples on the new axes, groups were established by using 

a method of partitioning around medoids (a medoid is a 

multivariate median of a group of samples (Kaufman and 

Rousseeuw, 1990)). The appropriate number of groups was 

based on the ability to find chemical and geologic explanations for the differences among all the groups. To carry out 

this multivariate analysis, the chemical data were converted 

to millimoles per liter and then transformed to logarithmic 

values, a procedure that maximized the linear relations among 

solutes that result from stoichiometric chemical reactions. Calculations were done using the S-Plus 2000 software package 

(Mathsoft, Inc., 1999).

Mass-Loading Studies

Results of 10 mass-loading studies in the Animas River 

watershed study area are combined here to give summaries of 

the upper Animas River, Cement Creek, and Mineral Creek 

basins. An additional study reach, called the Elk Park basin 

herein, serves to summarize constituent loads for the whole 

watershed. This study reach starts at the south end of the 

upper Animas River basin, at U.S. Geological Survey gauging station 09358700 (A68), and continues past the mouths 

of Cement Creek and Mineral Creek all the way downstream 

to Elk Park (fig. 1). All the chemical determinations upon 

which these summaries are based, along with detailed site 

information, are presented in Sole and others (this volume, 

Chapter G). Designation of inflows as right or left bank is 

from a downstream view, which is the typical designation in 

hydrology.

Upper Animas River Basin, 1997, 1998, and 2000

The upper Animas River basin extends about 26 km 

upstream from the U.S. Geological Survey stream gauging 

station at A68 (figs. 1, 2). Five mass-loading studies have 

been completed in the upper Animas River basin, three of 

which are reported here. The most upstream study reach, 

along California Gulch to Animas Forks (fig. 2) was studied 

in August 2000. The North Fork of the Animas River also 

was studied in August 2000, but results of that study are not 

included here; however, the load of metals from the North Fork 

is included as part of the California Gulch study reach. The 

section from upstream of Eureka Gulch (fig. 2, A4) to downstream of Cunningham Creek was studied in August 1998. This 

corresponds with a relatively low gradient reach of the upper 

Animas River, and includes sections where the river is braided 

(Blair and others, 2002; Vincent and Elliott, this volume, 

Chapter E22). The section from upstream of Cunningham Creek 

to A68 was studied in August 1997. There were overlapping 

sites between these two downstream studies. In August 2002, 

the section of the Animas River from upstream of Arrastra 

Creek (fig. 2, A8) to A68 was studied again. Only results for 

zinc are available for this report. Distances used in this report 

add 17,611 m to those used in the 1997 study and 12,128 m to 

those used in the 1998 study to reflect the total distance in the 

upper Animas River basin for all three studies.

Certain factors complicate the combination of these data 

sets into one long view of the upper Animas River basin. First, 

discharge at individual sites where injection reaches overlapped varied between 1997 and 1998 (fig. 3), but the difference was not too great to reasonably make an adjustment to 

make them equal. Second, a segment approximately 6,000 m 

long between the California Gulch and Eureka study reaches 

was not studied. A difference in pH and in several constituent 

concentrations appeared between the California Gulch and 

Eureka data sets, and as we worked on combining the two, 

we have assumed that the differences are a result of instream 

processes along the 6,000-m reach that was not studied.

Inactive mines and prospects exist along the study reach; 

the discharge from tailings near the Pride of the West Mill 

area near Howardsville (fig. 2, A6) was one of the most visually 

significant for its iron staining in the stream (see Church, Mast, 

and others, this volume, Chapter E5 for AMLI mine inventory). Along California Gulch inflows from Mountain Queen 

adit (CGS-350)1

, Vermillion mine (CGS-3081), and Frisco 

tunnel (CGS-4794) were all sampled. Individual samples of 

mine drainage along North Fork are not reported in this study, 

but combined drainage from these mines was accounted for as 

water from North Fork Animas River joined California Gulch 

near Animas Forks (fig. 2, A3). Remnants of the Sunnyside 

Eureka Mill occur just upstream from Eureka Gulch (fig. 2, 

A4). Drainage from Forest Queen mine (UAEH-2090) enters 

the Animas River near the end of the braided reach (A5). The 

Kittimack tailings are near the river, just upstream from Maggie 

Gulch (UAEH-3435). Downstream from Arrastra Creek (fig. 2, 

A8) are several large tailings repositories (sites # 507–510) 

stored along the stream (Nash, 2000). This is also the location 

of the Mayflower Mill, and the site of large tailings piles that 

recently (since 1995) have received tailings from several locations in the Animas River watershed, particularly from Cement 

Creek.

A main objective of the mass-loading study from Eureka 

to Howardsville was to quantify the flow and metal loading 

through the braided reach between Eureka Gulch (fig. 2, A4) 

and the site UAEH-2240 (fig. 2, A5). This braided reach could 

act as a source or a sink for metals in the upper Animas River. 

Details of the mass-loading study for this reach have been 

published by Paschke and others (2005).

Discharge

Sodium chloride was used as the tracer for the Eureka 

and Howardsville studies, and sodium bromide was used for 

California Gulch. Discharge increased by about 80 ft3

/s along 

the study reach (fig. 3). Discharge consistently increased all 

along the California Gulch study reach, but the two greatest 

428 Environmental Effects of Historical Mining, Animas River Watershed, Colorado

1

Labels after sites, in the form such as CGS-350, refer to identifications 

in Sole and others (this volume, Chapter G).
Quantification of Metal Loading 429

Figure 2. Location of study reaches, alteration zones, key locations, and principal sites of inactive mines, upper Animas River 

basin, 1997, 1998, and 2000.

A68

A68

A4 - Eureka 

Gulch Key locations

Streamflow gauging station

Acid-sulfate

Quartz-sericite-pyrite

Vein-related quartz-sericite-p

Weak sericite-p

Regional propylitic

Alteration types

A1 - Mountain

Queen

Mountain

Queen

A3

A2

A4

A5 - End of

braids

A6

A7 - Howardsville gauge

A8

A9

A10

Eureka

Mill

Lackawanna

Mill

Mayflower

tailings

MinnieGulch

Braided reach

Inactive mine, mill, or tailings site Eureka

Mill

California Gulch

P lacer G

ulch

Animas River

CunninghamCreek

Arrastra Creek

Boulder Gulch

Eureka Gulch

Pride of the West

tailings

Maggie Gulch

Kittimack tailings

Nor ht Fork

37o

52’

30”

37o

45’

107o37’30”

0

0

1

1

2

2

3

3

4 MILES

4 KILOMETERS

Animas

Forks

yrite

EXPLANATION

yrite
increases occurred downstream from Placer Gulch (fig. 2, A2) 

and the North Fork Animas River (A3). Along the Eureka 

study reach, the greatest increases were at Eureka Gulch 

(A4), Minnie Gulch (UAEH-2620), and Cunningham Creek 

(UAEH-6618). Along the Howardsville study reach, discharge 

increased the most at Arrastra Creek (A8). At several locations 

between A9 and A10 (fig. 3), increases in discharge also 

occurred, but large, visible inflows were not observed. These 

increases were most likely a result of ground-water inflows, 

particularly upstream from 23,906 m (AMIN-6038). Note 

that in figure 3 and in subsequent figures that depict contributions of water or mass load to study reaches, vertical lines that 

DISCHARGE, IN CUBIC FEET PER SECOND

0.01

0.1

1

10

100

0 2,000 4,000 6,000 12,000 16,000 20,000 24,000 28,000

DISTANCE ALONG STUDY REACH, IN METERS

California Gulch, stream

Eureka, stream

Howardsville, stream

California Gulch, inflows

Eureka, inflows

Howardsville, inflows

EXPLANATION

Figure 3. Variation of discharge with distance for three mass-loading studies, upper Animas River basin, 1997, 1998, and 2000. 

Note break of 6,000 meters between California Gulch and Eureka study reaches. Vertical lines with letters refer to locations of

significant change along the study reach in figure 2.

430 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
Quantification of Metal Loading 431

indicate inflows are drawn at the location of the stream site 

downstream from the inflow, not at the inflow itself. This is 

because the accounting for any load from the inflow is done 

at the downstream site.

Chemical Characterization of Synoptic Samples

Concentrations of constituents and values of pH varied 

substantially along the 26,000 m study reach (fig. 4). Unless 

noted otherwise, dissolved concentrations are from ultrafiltration and colloidal concentrations are from the subtraction of 

ultrafiltrate concentration from the total-recoverable concentration (Appendix 1). Chemical changes in the stream were 

systematic in response to groups of inflows. Differences in 

chemical composition resulted in the classification of five 

groups of inflow samples and five groups of stream samples 

by PCA (table 1). Among the five inflow groups, the California 

Gulch study reach yielded samples classified in groups 1 

and 2; the Eureka and Howardsville study reaches yielded 

samples in groups 4 and 5; and each of the study reaches 

yielded group 3 samples. Values of pH were greater than 6.0 

at the beginning of the California Gulch study reach (stream 

group 1, table 1): at the head of the basin, the stream drained 

propylitically altered rocks (fig. 2). As a result of several acidic 

inflows, pH decreased to less than 5.5 (fig. 4A). These acidic 

inflows (inflow group 1, table 1) drain areas of QSP alteration 

to the south of California Gulch and V-QSP altered rocks that 

crop out near the stream (Bruce Stover, Colorado Division 

of Minerals and Geology, written commun., 2000). Some of 

these veins have high base-metal sulfide content (Bove and 

others, this volume). A distinct increase in the pH of inflows 

(inflow group 2, table 1) occurred downstream from 1,954 m 

(fig. 4A), and these inflows caused the stream pH to increase 

progressively to Placer Gulch (A2, fig. 4A; stream group 3, 

table 1). Some of these inflows were from wetland ponds and 

had much lower concentrations of major ions (inflow group 2, 

table 1). They were not free of manganese and zinc, but the 

metal concentrations were substantially lower than in group 1, 

and they likely drained the propylitic alteration assemblage. 

Downstream from Placer Gulch (A2) and the North Fork (A3), 

pH increased almost to 6.0 (stream group 2, table 1).

In the Eureka and Howardsville study reaches, pH generally was greater than 7.0 (fig. 4A). Many inflows from the end 

of the braided reach (A5) to Arrastra Creek (A8) had substantially higher pH (inflow group 4, table 1). Most of these 

inflows, like Minnie Gulch (UAEH-2465), drained only rocks 

of propylitic alteration to the southeast of the Animas River. 

Downstream from Arrastra Creek (A8), there were more acidic 

inflows (inflow group 5, table 1). Although the pH of these 

inflows was not as low as that of group 1, their sulfate and 

metal concentrations were higher.

Distinct changes occurred in the concentration of 

iron (fig. 4B) along the study reach, and particularly in the 

dissolved versus colloidal concentrations (table 1). Colloidal 

iron concentrations were greater than dissolved at the 

beginning of the study reach (stream group 1, table 1). Inflows 

along the California Gulch study reach (inflow groups 1, 2, 

and 3, table 1) initially caused instream iron concentrations to 

decrease, but then to increase toward Placer Gulch (A2) and 

North Fork (A3). At the beginning of the Eureka study reach 

(near A4), the instream iron concentration was 0.085 mg/L, 

a decrease from 0.2 mg/L measured downstream from the 

North Fork (A3, fig. 4B). Along most of the Eureka study 

reach, iron concentration decreased in response to low inflow 

concentrations (inflow group 4, table 1). The greatest increase 

of instream iron concentration was downstream from the tailings discharge (A6). The higher iron concentration was mostly 

colloidal for the inflow (inflow group 3, table 1), and for the 

stream (stream group 5, table 1).

Inflows near the beginning of California Gulch (inflow 

group 1, table 1) caused substantial increases in concentrations 

of copper (fig. 4C) and zinc (fig. 4D). Inflow concentrations of 

copper and zinc around 2,200 m were lower (inflow groups 2 

and 3, table 1), and instream concentrations decreased in 

response to these inflows. Concentrations of copper decreased 

from the end of the California Gulch study reach to the beginning of the Eureka study reach (fig. 4C). Copper concentration 

decreased substantially downstream from the braided reach (A5, 

fig. 4C). Downstream from Arrastra Creek (A8), copper concentrations increased in response to high inflow concentrations. 

Along the California Gulch study reach, and at the beginning of 

the Eureka study reach, copper concentrations exceeded chronic 

toxicity standards, but downstream from the braided reach (A5) 

instream concentrations were below the standards (fig. 4C).

The highest instream zinc concentrations occurred 

along the California Gulch study reach (stream groups 2 and 3, 

table 1; fig. 4D). Zinc weathers from sphalerite, which is prevalent in veins near the Eureka graben (Bove and others, this 

volume; Yager and Bove, this volume). There were differences 

in the zinc to manganese mole ratio among the acidic inflows 

in the upper part of the study reach, even though they all were 

classified as inflow group 1 (table 1). Manganese gangue minerals provide high manganese concentrations to inflows draining QSP and V-QSP alteration. Differences in the ratios likely 

reflect different amounts of sphalerite and manganese gangue 

minerals associated with individual occurrences because no 

clear spatial pattern exists. Chemical distinctions among these 

inflow samples, however, indicate variations in alteration 

mineralogy. Zinc concentration decreased substantially—from 

1.73 mg/L to 0.468 mg/L—between the California Gulch and 

Eureka study reaches (stream groups 2 and 4, table 1).

Like concentrations of copper, zinc concentration 

increased downstream from Arrastra Creek. Results of a 

more detailed sampling for zinc during extreme base flow 

in August 2002 indicate four locations where zinc increased 

downstream from Arrastra Creek. The first was just downstream 

from Arrastra Creek (site I, fig. 5) where very high concentrations of zinc were found in samples of inflows along the right 

bank. Downstream from Boulder Gulch (site II, fig. 5), a second 

increase was noted where acidic inflows from an alteration 

zone and a draining mine occurred along the left bank. Capped 

tailings repositories (sites # 507–510) along the right bank also 

occurred in that reach. The inflow concentrations were higher 
A1

A2

A3

A4

A5

A6

A7A8

A9 A10

A68

A1 A2

A3

A4 A5

A6 A7

A8

A9 A10

A68

0 2,000 4,000 6,000 12,000 16,000 20,000 24,000 28,000

DISTANCE ALONG STUDY REACH, IN METERS

0

10

1

0.1

0.01

1E-3

4

3

5

6

7

8

9

2,000 4,000 6,000 12,000 16,000 20,000 24,000 28,000

A

BpH, IN STANDARD UNITS

IRON CONCENTRATION,

IN MILLIGRAMS PER LITER

Figure 4. Variation of A, pH, and total-recoverable concentrations of B, iron, C, copper, and D, zinc with distance, upper 

Animas River basin, 1997, 1998, and 2000. Groups of stream samples (diamonds) and inflows (stars) are indicated by 

colors: 1, blue; 2, green; 3, yellow; 4, orange; 5, red. Groups were determined by principal component analysis, and their 

chemistry is summarized in table 1. Letters by vertical dashed lines refer to site descriptions in table 2. In C and D, blue 

line, acute toxicity standard; red line, chronic toxicity standard.

432 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
Quantification of Metal Loading 433

A1

A2 A3

A4 A5

A6 A7

A8

A9

A10

A68

A1

A2 A3

A4

A5

A6 A7A8

A9

A10

A68

0 2,000 4,000 6,000 12,000 16,000 20,000 24,000 28,000

D DISTANCE ALONG STUDY REACH, IN METERS

0 2,000 4,000 6,000 12,000 16,000 20,000 24,000 28,000

C

100

200

10

1

0.1

0.01

1E-3

ZINC CONCENTRATION,

IN MILLIGRAMS PER LITER

1

7

0.1

0.01

1E-3

COPPER CONCENTRATION,

IN MILLIGRAMS PER LITER

Figure 4—Continued. Variation of C, copper, and D, zinc with distance, upper Animas River basin, 1997, 1998, and 2000. 

Groups of stream samples (diamonds) and inflows (stars) are indicated by colors: 1, blue; 2, green; 3, yellow; 4, orange; 

5, red. Groups were determined by principal component analysis, and their chemistry is summarized in table 1. Letters 

by vertical dashed lines refer to site descriptions in table 2. Blue line, acute toxicity standard; red line, chronic toxicity 

standard.
along the right bank. Downstream from an area with substantial 

iron staining (site III, 23,876 m) was the third increase. Finally, 

there was an increase at 24,917 m, which was downstream 

from the Lackawanna Mill (site IV, fig. 5). Field observation 

indicated that tailings deposits along the right bank were a more 

likely source of this zinc increase, however.

Mass-Load Profiles

Constructing profiles of mass loading for the 26 km 

study reach required assumptions about the effects of inflows 

along the study reach. Loading profiles from the California 

Gulch study reach were used to the point downstream from 

the North Fork (A3). After that point, the change in load for 

stream segments of the Eureka study reach were applied to the 

new load just upstream from Eureka (A4). Downstream from 

the Howardsville gauge (A7), the changes in load for stream 

segments from the Howardsville study reach were applied. 

This method assumes that areas of loss and gain would be the 

same in all three years. Because the analysis uses the normalized load, it compares patterns rather than absolute values, and 

should be comparable among the different years.

Changes in concentrations of constituents need to be 

evaluated within the context of catchment hydrology, and this 

is accomplished by load calculations. Normalization of loads 

with respect to the cumulative instream load allows the comparison of patterns along the study reach (fig. 6). Constituents 

that are relatively conservative during transport have normalized values near 1 at the end of the study reach. The conservative constituents include aluminum, manganese, strontium, 

sulfate, and zinc. Cadmium, copper, and iron were reactive 

constituents, and lost mass load along the study reach.

Table 1. Chemical composition of selected samples representing groups defined by principal component analysis, upper Animas River 

basin, 1997, 1998, and 2000.

[Values are in milligrams per liter, except pH; Phase: Diss, dissolved; coll, colloidal; <, less than]

Inflows Stream

Group 1 2 3 4 5 1 2 3 4 5

SampleID CGS-1459 CGS-4382 CGS-3081 UAEH-2465 AMIN-5858 CGS-450 CGS-5466 CGS-2725 UAEH-3400 AMIN-2515

Distance (m) 1,459 4,382 3,081 14,593 23,726 450 5,466 2,725 15,528 20,383

SiteName Seep down 

slope from 

mine

Placer 

Gulch at 

mouth

Drains area 

down from 

Vermillion 

mine

Minnie 

Gulch

Seep along 

grassy bank

Stream 

down from 

Mtn Queen

Up from 

Columbus 

mine

Bracket 

for inflows 

upstream

Downstream 

from braids 

near 

Kittimack

Stream

pH, in standard units 3.98 5.74 7.09 7.93 5.67 6.97 5.81 4.98 7.05 7.55

Calcium 32.0 21.1 73.0 36.8 229 81.7 32.4 34.8 29.2 37.8

Magnesium 13.0 2.13 4.10 2.94 13.0 8.20 4.07 5.84 2.10 2.56

Sodium 2.30 .69 4.40 2.71 5.38 21.3 1.94 3.23 3.01 2.20

Alkalinity, as 

calcium carbonate

<1 <1 <1 47.6 8.85 <1 <1 <1 36.6 <1

Sulfate 262 59.6 151 61.0 861 192 112 157 64.0 77.6

Chloride .30 .15 .39 .21 1.74 .140 .190 .110 3.33 1.61

Fluoride 1.21 .25 .47 <0.1 <0.1 .260 1.89 2.98 <0.1 <0.1

Silica 13.0 .96 6.20 6.65 24.6 5.14 8.92 12.1 5.31 6.63

Aluminum Diss 12.9 .187 .080 .057 1.74 .083 2.26 6.41 .035 .024

Coll <.020 .372 .121 <.020 <.020 .053 .868 .218 .062 .065

Cadmium Diss .021 .004 <.001 <.001 .056 .003 .007 .011 .002 <.001

Coll .002 <.001 .002 <.001 <.001 <.001 <.001 <.001 <.001 <.001

Copper Diss .028 .017 .003 <.002 .248 <.002 .018 .023 .004 <.002

Coll .003 .005 <.002 <.002 <.002 .003 <.002 <.002 <.002 <.002

Iron Diss .044 .168 .052 .049 .020 .016 .144 .121 <.002 .017

Coll <.002 .056 1.62 <.002 <.002 .090 .107 .094 .032 .460

Lead Diss <.023 <.023 <.023 <.023 <.023 <.023 <.023 <.023 <.023 <.023

Coll <.023 <.023 <.023 <.023 <.023 <.023 <.023 <.023 <.023 <.023

Manganese Diss 29.0 .912 .110 .021 34.4 .037 7.24 15.0 .242 .459

Coll .557 .005 .282 <.001 <.001 .002 <.001 .068 .008 .016

Nickel Diss .021 .004 <.003 <.003 .045 <.003 .006 .008 <.003 <.003

Coll <.003 <.003 <.003 <.003 <.003 <.003 <.003 <.003 <.003 <.003

Strontium Diss .068 .121 .860 .504 2.13 .715 .173 .164 .261 .381

Coll .005 .002 .029 .504 2.13 <.001 <.001 .002 .008 .006

Zinc Diss 10.0 1.15 .082 .008 12.7 .051 1.80 2.44 .305 .273

Coll <.001 <.001 .186 <.001 <.001 <.001 .006 .030 .013 .056

434 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
Quantification of Metal Loading 435

Three patterns of load profiles existed among the solutes 

(fig. 6). Aluminum, manganese, and zinc increased substantially in the study reach upstream from Placer Gulch (A2) and 

North Fork (A3; fig. 6A, B). Cadmium, copper, and iron did 

not increase greatly in the California Gulch study reach, but 

did increase greatly in the Howardsville study reach (fig. 6A, 

B). Strontium and sulfate had similar patterns: Their greatest 

increases were at Placer Gulch (A2), the tailings discharge (A6), 

and the reach of capped tailings (sites # 507–509; A10, fig. 6C).

The summary of the mass-load calculations indicates a 

great variation in the magnitude of cumulative instream load 

among the selected constituents (table 2). Sulfate load comes 

from both mine and non-mine related sources, and was very 

large in comparison to the other constituents. Manganese load 

was large, reflecting the importance of manganese gangue minerals in QSP deposits near the headwaters of California Gulch 

(fig. 2). Aluminum, iron, strontium, and zinc loads also were 

sizable, much greater than the loading of cadmium and copper.

Figure 5. Variation of dissolved zinc concentration with distance, upper Animas River basin, from Arrastra Creek to 

Silverton, August 2002. Sites I–IV, locations of zinc increase discussed in text.

21,000 22,000 23,000 24,000 25,000 26,000

DISTANCE ALONG STUDY REACH, IN METERS

0.01

0.1

1

10

100

200

ZINC CONCENTRATION, IN MILLIGRAMS PER LITER

Boulder Gulch (A9)

Stream gauge (A68)

End of capped tailings (A10)

Arrastra Creek (A8)

EXPLANATION

Stream

Left bank inflow

Right bank inflow
Figure 6. Variation of normalized instream loads for A, aluminum, iron, and manganese; B, cadmium, copper, and zinc; 

C, strontium and sulfate with distance, upper Animas River basin, 1997, 1998, and 2000. Labels on vertical lines refer to 

locations of substantial change along the study reach in figure 2 and table 2. A1 A2 A3A4A5

A6

A7

A8

A9

A10

A68

A1

A2

A3

A4

A5

A6

A7

A8

A9

A10

A68

A1

A2

A3

A4

A5

A6

A7

A8

A9

A10

A68

A

B

C

0

2,000

4,000

6,000

12,00014,000

16,00018,000

20,00022,000

24,000

26,000

DISTANCE ALONG STUDY REACH, IN METERS

0.0

0.2

0.4

0.6

0.8

1.0

0.0

0.2

0.4

0.6

0.8

1.0

0.0

0.2

0.4

0.6

0.8

1.0

NORMALIZED LOAD

Strontium

Sulfate

Aluminum

Iron

Manganese

Cadmium

Copper

Zinc

436 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
Quantification of Metal Loading 437

Principal Locations of Loading

Aluminum and manganese profiles mostly increased at 

similar locations (fig. 6A). Their basic pattern consisted of 

many considerable inflows between 701 m and 1,586 m and a 

moderate loading from Placer Gulch (A2). Aluminum loading 

was substantially greater from the North Fork Animas River 

(A3) because the North Fork drains the large QSP alteration of 

Houghton Mountain (fig. 2). Note that a loss of 68.5 percent of 

the aluminum load to the streambed occurred along the study 

reach (table 2; fig. 6A). Much of this loss occurred between A3 

and A4 (fig. 6A), but started between A2 and A3 where the pH 

of the stream water exceeded 5.0. Between A2 and A3, there 

was not a net loss (fig. 6A), so the precipitate on the cobbles 

represents only a small mass of the colloidal aluminum, less 

than the error in the load calculation, that is integrated on the 

cobbles over time. The relatively high pH between A3 and A4 

(fig. 4A) was sufficiently high for the substantial loss of aluminum load to the streambed cobbles in that reach.

Downstream from a rhyolite outcrop (1,586 m), where 

the load of manganese and other metals increased substantially, there was a loss of manganese to the streambed (fig. 6A). 

Manganese loss did not result in a visible coating on the 

streambed; however, gravels along the stream bank between 

1,142 m and 1,310 m were coated with manganese precipitates. 

Visible cementing of streambed gravels with manganese forms 

a manganocrete that helps account for the loss of manganese 

load in the stream. Far downstream, along the Howardsville 

study reach, manganese loading from the capped tailings repositories (A10) was substantial, and manganocrete also occurred 

there, along the right stream bank.

The greatest increase of iron load was from the tailings 

discharge (A6, fig. 6A). Two other substantial loads occurred 

at 21,413 m and 22,084 m. Both increases occurred near 

old milling sites (site # 234) on the left and right banks. The 

second increase was downstream from a very acidic spring that 

discharged at stream level, and had very high iron concentrations. Downstream from each of these inflows, the iron load 

was transported mostly in the colloidal phase that made the 

iron transport relatively conservative despite some loss downstream from the tailings discharge inflow (A6, stream group 5, 

table 1).

Cadmium, copper, and zinc loading had similarities, yet 

each metal differed in principal locations of loading (fig. 6B). 

The greatest increase in cadmium load occurred near the 

Howardsville gauge (A7); an old mill site lies nearby (Nash, 

2000). Loading of copper was important from acidic inflows 

along the California Gulch study reach (downstream from A1, 

fig. 6B) and from North Fork (A3). Arrastra Creek (A8) was 

the location of the greatest increase in copper load (fig. 6B). 

The historical mines at Silver Lake (sites # 343, 345, 348) 

are located near Arrastra Creek headwaters, and Silver Lake 

Mill # 2 is on the left bank near mouth of Arrastra Creek. 

These features, along with mineralized veins of the South 

Silverton mining area, could be sources for copper load along 

this reach. Downstream from each of these locations of copper 

Table 2. Summary of load calculations and cumulative instream load for selected subreaches, upper Animas River basin, 1997, 1998, 

and 2000.

[Dist, distance along study reach, in meters; Al, aluminum; Cd, cadmium; Cu, copper; Fe, iron; Mn, manganese; Sr, strontium; Zn, zinc; SO4, sulfate; all values 

in kilograms per day, except percentages; numbers in parentheses indicate rank of five greatest loadings for each constituent (1, greatest)]

Al Cd Cu Fe Mn Sr Zn SO4

Cumulative instream load 116 1.51 4.60 82.9 333 84.5 129 22,500

Cumulative inflow load 72.7 0.53 2.28 24.6 185 62.4 87.9 12,200

Percent inflow load 62. 6 34.8 49.6 29.7 55.5 73.9 68.0 54.2

Unsampled inflow 43.5 .99 2.32 58.3 148 22.1 41.4 10,300

Percent unsampled inflow 37.4 65.2 50.4 70.3 44.5 26.1 32.0 45.8

Attenuation 79.5 0.46 2.53 29.1 133 8.50 54.7 3,440

Percent attenuation 68.5 30.6 55.0 35.1 40.1 10.1 42.3 15.3

Site description Dist Al Cd Cu Fe Mn Sr Zn SO4

Down from Placer Gulch (A2) 4,448 52.2 (1) 0.084 0.516 (3) 5.95 (5) 121 (1) 1.99 26.3 (2) 3,050 (2)

Second site down from North Fork (A3) 6,128 13.9 (2) 0.110 0.430 6.67 (4) 20.2 1.62 23.1 (3) 1,630

Downstream from Eureka Gulch (A4) 12,714 1.51 0.072 0.463 (4) 0.798 2.07 5.68 6.67 1,280

Downstream from braided reach (A5) 14,368 0.484 0.146 (4) 0.182 0.000 1.22 5.77 (5) 13.9 (5) 1,200

Downstream from tailings drainage (A6) 18,656 12.0 (3) 0.438 (1) 0.432 (5) 42.6 (1) 35.5 (3) 23.1 (1) 27.8 (1) 5,260 (1)

At State gauge at Howardsville (A7) 19,121 2.31 0.173 (3) 0.224 0.000 1.25 15.5 (2) 0.095 2,060 (4)

Downstream from Arrastra Creek (A8) 21,921 10.4 (4) 0.408 (2) 1.27 (1) 13.4 (2) 0.672 7.66 (4) 3.87 1,230

Downstream from Boulder Gulch (A9) 22,742 6.80 0.000 0.196 9.39 (3) 32.6 (4) 0.000 9.84 0

Downstream from capped tailings (A10) 23,899 9.22 (5) 0.139 (5) 0.792 (2) 0.000 87.9 (2) 9.44 (3) 14.9 (4) 2,850 (3)

Animas River at Silverton (A68) 25,469 3.68 0.000 0.304 0.728 25.2 (5) 0.000 0.000 1,720 (5)
loading, the load was attenuated. Loading of zinc also was 

important from the acidic inflows near the beginning of the 

study reach, but its pattern differed from those of aluminum 

and manganese (fig. 6A, B). Zinc load entered the stream at 

many more locations, including Placer Gulch (A2), Frisco 

tunnel (4,856 m), North Fork (A3), the braided reach (A5), 

the tailings discharge (A6), and the capped tailings repositories (A10).

The mass-loading profile of strontium and sulfate represents a final pattern that differs from that of the other constituents (fig. 6C). These loads resulted from weathering of both 

altered and unaltered rocks in the watershed. Because strontium was not associated with ore or gangue minerals, no loading came from the acidic springs between 859 m and 1,586 m 

that contributed large loads of aluminum and manganese. 

Sulfate load, on the other hand, was contributed by the acidic 

inflows between 859 m and 1,586 m. Both strontium and sulfate loads increased substantially downstream from the braided 

reach (A5), and remained elevated to the tailings discharge 

(A6), where both loads increased from the tailings discharge 

(A6). They both increased from the inflow of Cunningham 

Creek (18,746 m, downstream from A6). Cunningham Creek 

drains an area of propylitically altered rocks, which would be 

consistent with the loading of strontium. Several large sulfate 

loads entered the stream in the area of the capped tailings 

(A10).

Unsampled Inflow

Unsampled inflow mostly indicates loading from dispersed, subsurface inflow in most stream segments; however, 

it also can result from skipping some surface inflows along 

the study reach, either intentionally or unintentionally. To 

sample every inflow is not possible. Unsampled inflow was 

responsible for 66 percent of the loading of cadmium and 

70 percent of the loading of iron (table 2). Unsampled inflow 

was less important for aluminum, copper, manganese, strontium, zinc, and sulfate, but it did occur for each of the selected 

constituents. A very noticeable change occurred from sampled 

to unsampled inflow along the study reach. Two main locations of unsampled inflow loading occurred. First, the tailings 

drainage near Howardsville (A6) was important for unsampled 

inflow of iron. Second, downstream from Arrastra Creek (A8) 

to 23,899 m, a great increase was measured in the unsampled 

inflow load of all the metals, except iron and sulfate. The 

source of metals in this reach of the stream has not been 

determined, but mine wastes and old mill sites lie along on 

both sides of the stream. Sampling in 2002, however, indicated 

higher concentrations of zinc along the right bank than along 

the left bank (B.A. Kimball, unpub. data, 2002). Seeps along 

the right bank had iron and aluminum precipitates, and a substantial amount of manganocrete was observed in the area of 

the capped tailings repositories (A10). Most of this unsampled 

inflow occurred in the stream segments from 23,147 m to 

23,899 m. In 1997, these inflows were not visible, but in 2002 

during extreme base-flow conditions, some of these inflows 

were sampled; they are indicated by the plot of zinc concentration (fig. 5). Considering the relatively high flow of the upper 

Animas River compared to other streams in this study, the 

small increases in concentration (fig. 4) represent a substantial 

increase in metal load.

Attenuation of Load

Attenuation of cadmium and copper exceeded 30 percent 

along the study reach, but relatively little attenuation occurred 

for the other constituents, particularly strontium and sulfate 

(table 2). Much of the copper attenuation was in the braided 

reach of the stream (A5). Otherwise, no spatial pattern for the 

loss of constituent loads was observed. Between 15,528 m and 

15,793 m most constituent loads decreased. Downstream from 

Cunningham Creek (18,746 m) and Hematite Gulch (18,881 m) 

iron load decreased, as did the loads of aluminum, cadmium, 

and manganese. Downstream from the tailings discharge (A6) 

and past Cunningham Creek (18,746 m), the stream bank along 

the left side was heavily stained with iron precipitate. Most of 

the attenuation of aluminum was at 22,265 m and 22,527 m. 

The greatest attenuation of copper was downstream from the 

greatest loading of copper, at 22,084 m (fig. 6B). For both 

aluminum and copper, this attenuation was downstream from 

substantial unsampled inflow.

Summary

Mass loading of constituents along a study reach of 

almost 26 km in the upper Animas River basin was detailed by 

three different studies. Loading in the headwaters was dominated by drainage from zones of QSP alteration. A substantial 

change in the character of the water with respect to aluminum 

and copper occurred in the braided reach downstream from 

Eureka Gulch. Loading along the remainder of the study 

reach was dominated by inflows in the areas of tailings near 

Howardsville (tailings discharge, A6, site # 234) and a lower 

reach of capped tailings repositories (A10).

Cement Creek Basin, 1996, 1999, and 2000

Cement Creek originates above 3,000 m elevation and 

has a drainage area of about 52 square kilometers (Crowfoot 

and others, 1997). A stream gauge near the mouth of Cement 

Creek indicates that most of the streamflow occurs during 

snowmelt runoff during May and June. The best opportunity to quantify dispersed subsurface inflow to the stream 

is during late summer base flow. Both acidic and non-acidic 

inflows enter along Cement Creek, and they have a wide 

range of chemical composition. Among the acidic inflows, 

some are acidic from weathering of altered bedrock and 

others are acidic due to acceleration of weathering by mining 

activities. The most recent mining activity in the area was at 

Gladstone (fig. 7, C4).

438 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
Quantification of Metal Loading 439

Figure 7. Location of study area, alteration zones, key locations, and principal sites of inactive mines, Cement Creek basin, 

1996, 1999, and 2000.

Queen

Anne

C1 - Queen Anne

C2 - Mogul

C4

C6 -Prospect

Gulch

Mogul

Upper Gold King

Sunnyside

C5 - South Fork

C3 - North Fork

Gladstone

May Day

Yukon

Anglo-Saxon

Lark

Natalie/Occidental

Big

Colorado

C12 - Lower bog

C11 - Illinois Gulch

C10 - Ohio Gulch

C9 - Porcupine Gulch

C8 - Minnesota Gulch

C7 - Iron bog

Basin

boundary

C48

CementCreek

C48

C12 - Lower bog Key locations

Streamflow gauging station

Acid-sulfate

Quartz-sericite-pyrite

Vein-related quartz-sericite-pyrite

Weak sericite-pyrite

Regional propylitic

Alteration types

Inactive mine site

May Day

0

0

1

1

2

2

3

3

4 MILES

4 KILOMETERS

37o

52’

30”

107o37’30”

EXPLANATION
Four mass-loading studies have been completed in 

Cement Creek. The first, in 1996, started a short distance 

upstream from the North Fork Cement Creek (C3) and 

continued to the U.S. Geological Survey stream gauging 

station 09358550 (C48) near the mouth (Kimball and others, 

2002). The second, in 1999, started high in the basin, upstream 

from the Queen Anne mine (upstream from C1), and continued to a site downstream from the South Fork (C5) of Cement 

Creek. Also in 1999, a shorter injection study was done in 

Prospect Gulch (Wirt and others, 1999). In 2000, part of the 

1996 study reach was revisited, starting upstream from Ohio 

Gulch (C10), and continuing to a point downstream from the 

May Day mine (Wright, Kimball, and Runkel, this volume, 

Chapter E23). This last study had the purpose of evaluating 

effects of remediation at the May Day tailings. Some factors 

complicate the combination of these data sets into one long 

view of the Cement Creek basin. First, in 1996 there was 

active treatment of water from Cement Creek at the Sunnyside 

mine at Gladstone, and the water that was returned to Cement 

Creek after the treatment had a much higher pH and lower 

base-metal concentrations than the water upstream from the 

treatment (fig. 8). This high pH decreased because of many 

acidic inflows, and with the inflow from Prospect Gulch, 

the pH was again very acidic. Second, the stream chemistry 

changed upstream from North Fork Cement Creek between 

sampling in 1996 and 1999 (fig. 8). The pH decreased substantially. A detailed discussion of these changes and their implications is in Appendix 2. Third, pH downstream from Illinois 

Gulch (C11) increased more in 2000 than in 1996 (fig. 8).

Chemical Characterization of Synoptic Samples

The chemical composition of synoptic samples in the 

Cement Creek basin varied greatly. The combined data set 

was analyzed by PCA to define groups with similar chemical 

composition.

Inflows

Six groups of inflow samples were distinguished by PCA 

analysis. Inflow groups generally reflect the extent of waterrock interaction with particular alteration mineral assemblages 

(Kimball and others, 2002; Bove and others, 2000; Mast and 

others, 2000). Samples representing the median values of each 

group are listed in table 3. Samples of inflow group 1 were the 

least affected by interaction with alteration minerals, as indicated by relatively low concentrations of all the constituents 

and high values of pH. Concentrations of sulfate and the metals were particularly low with respect to other inflow groups 

(table 3). Samples from inflow group 5 also had high pH, but 

had higher concentrations of sulfate and other constituents 

than samples from group 1, suggesting that they had some 

interaction with alteration minerals.

Samples in each of the other groups indicated a wide 

range of interaction with alteration mineral assemblages. 

Groups 2, 3, and 6 (fig. 9A) had the lowest pH values and 

the highest concentrations of metals (table 3). Among these 

acidic samples, group 3 had the highest concentrations of copper (fig. 9C) and zinc (fig. 9D). Sample sites of groups 2 and 

3 included the Mogul mine (C2), North Fork Cement Creek 

(C3), Prospect Gulch (C6), Ohio Gulch (C10), and the Yukon 

tunnel (just downstream from C11, fig. 7; site designations 

also available in table 5). Each of these samples represents 

water from subbasins with V-QSP alteration, and most have 

come from locations of mining (fig. 7). Thus, group 2 likely 

represents many of the mine-related inflows.

Samples represented in group 4 included high-pH–highsulfate concentration inflows (table 3) such as Elk tunnel 

(CE-4493), Porcupine Gulch (C9), and Illinois Gulch (C11). 

These samples had high concentrations of calcium, manganese, and strontium (table 3), which may reflect the presence 

of neutralizing carbonate minerals from propylitic alteration 

minerals. However, the high manganese concentrations could 

indicate the influence of other alteration mineral assemblages. 

Metal concentrations could have been lowered because of the 

higher pH.

Samples from inflow group 6 occurred between South 

Fork Cement Creek (C5) and Prospect Gulch (C6), in the 

vicinity of the iron bog (C7) and also at the lower bog (C12; 

CE-9543). These samples are distinct because of high concentrations of silica, aluminum, and iron (table 3), but copper and 

zinc concentrations were low compared to those of samples 

from inflow group 3. This difference might suggest that these 

inflows of group 6 drain alteration assemblages that have 

lower base metal content. Many of the ferricretes in Cement 

Creek and other basins of the watershed study area predate 

mining, and the type of inflow represented by group 6 could 

be typical of sources for water that formed the ferricretes 

(Wirt and others, this volume, Chapter E17).

Stream

Principal changes in stream chemistry of Cement Creek 

occurred at the same locations as the major changes in pH 

(figs. 7 and 9A). Five groups of stream samples are represented 

by the samples in table 4, but this excludes those samples from 

1996 between South Fork (C5) and Prospect Gulch (C6) that 

were affected by the active treatment. Excluding those samples, 

the overall variation in pH of the stream was from 6.83 at the 

most upstream site to 3.32 at a site downstream from the North 

Fork inflow (C3). At the beginning of the study reach, the high 

pH decreased below 6.5 downstream from the first sampled 

inflow (upstream from C1). The next major decrease in pH 

was below the inflow from the Mogul mine (C2), where pH 

dropped below 4.5. Samples collected in 1999 and 2000 

indicated that pH remained less than 4.5 along the remainder 

of Cement Creek (fig. 8). The decrease in pH at 11,245 m 

(CE-8218; end of blue diamonds, fig. 8) reflects a difference 

between samples collected in 2000 (higher pH upstream) and 

1996 (lower pH downstream), an artifact of joining the two 

data sets.

440 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
Quantification of Metal Loading 441

Concentrations of major ions varied in downstream 

steps, similar to the pattern of pH (table 4). Upstream from 

the Mogul mine (C2; groups 1 and 2, table 4), concentrations 

were relatively low, but they increased substantially downstream from the Mogul mine (group 3, table 4). The next step 

occurred downstream from the North Fork (C3; still group 3, 

table 4). Inflow from the Sunnyside mine (C4) caused a 

substantial increase (group 4, table 4). A final step occurred 

downstream from Porcupine Gulch (C9, group 5, table 4).

Substantial colloidal iron concentrations (fig. 9B) 

occurred along the entire study reach but were greater than 

dissolved iron concentrations upstream from the Mogul mine 

inflow (C2). Colloidal aluminum also was important upstream 

from the Mogul mine inflow (C2). Values of pH in these 

reaches were consistent with the formation of iron and aluminum oxyhydroxide-mineral colloids, according to calculations 

with PHREEQC (Parkhurst and Appelo, 1999). Downstream 

from the Mogul mine inflow (C2), pH was less than 3.7, which 

Figure 8. Variation of pH with distance for three mass-loading studies, Cement Creek basin, 1996, 1999, and 2000. Labels 

on vertical lines refer to locations in figure 7. C1 C2 C3 C4 C5

C6

C7

C8

C9

C10

C11

C48

pH, IN STANDARD UNITS

2.5

0 2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000

3.0

3.5

4.0

4.5

5.0

5.5

6.0

6.5

7.0

7.5

8.0

DISTANCE ALONG STUDY REACH, IN METERS

EXPLANATION

1996

1999

2000

Inflows
rendered aluminum soluble, and colloid formation did not 

occur. Iron, however, was still insoluble and ferrihydrite or 

schwertmannite colloids occurred. Dissolved iron and aluminum were dominant along most of the remaining study reach, 

but colloidal iron increased downstream from the inflow of 

Illinois Gulch (C11) as a result of the higher pH. The similarity of iron concentrations for 1996 and 2000 between C9 and 

C10 (fig. 9B) might not be expected because most of the iron 

was removed from the stream water by the mine treatment 

in 1996 (Kimball and others, 2002). To have nearly equal 

concentrations is consistent with the geochemical control of 

dissolved iron concentrations by colloidal formation. This was 

indicated by the simulation of Walton-Day and others (this 

volume, Chapter E24).

For copper (fig. 9C), important differences appeared 

among data from 1996, 1999, and 2000. Concentrations of 

copper were high downstream from North Fork in 1996 but 

much lower upstream from North Fork (Kimball and others, 2002). Copper concentrations in samples collected in 

1999 were much higher upstream from North Fork. This, and 

other significant chemical changes upstream from North Fork 

between 1996 and 1999, are discussed in Appendix 2.

Another difference occurred downstream from South Fork 

(C5), where the dissolved copper concentration was 0.02 mg/L 

in 1996 (Kimball and others, 2002, table 3) but was 0.65 mg/L 

in 1999. Finally, in the interval between 9,409 and 11,018 m 

higher copper concentrations occurred in 2000 than in 1996 

(fig. 9C). These likely represent differences caused by the lack 

of treatment at the Sunnyside mine in 2000. Walton-Day and 

others (this volume) simulated the transport of copper along 

Cement Creek, using the results of the 1999 sampling and the 

calibration with inflow loads from 1996. These simulations 

indicated that the higher copper below South Fork (C5) would 

be 0.27 mg/L at the beginning of the May Day study reach. 

This prediction is substantially higher than the 0.076 mg/L at 

9,409 m measured in 2002 (Wright, Kimball, and Runkel, this 

volume; see fig. 9C, this report). Sorption of copper at the low 

pH near 4.0 would be minimal (Walton-Day and others, 2000), 

so this could indicate coprecipitation of copper with the iron 

colloids. Walton-Day and others (2000) suggested that this 

could occur in mixing zones, where higher values of pH might 

be locally important, even though the overall pH of the stream 

remains low (Kimball and others, 2002).

The pattern of zinc concentration had many similarities 

with that of copper (fig. 9D). Although zinc concentration was 

2.6 mg/L upstream from North Fork (C3) in 1996, the concentration at that point in 1999 was 10.9 mg/L. Downstream from 

South Fork (C5), zinc concentration was 0.82 mg/L in 1996 

and 4.27 mg/L in 1997, reflecting the treatment that occurred 

Table 3. Chemical composition of selected inflow samples representing groups defined by principal component analysis, Cement 

Creek basin, 1996, 1999, and 2000.

[RBI, right bank inflow; LBI, left bank inflow; concentrations in milligrams per liter; diss, dissolved; <, less than]

Group 1 2 3 4 5 6

Sample identification ROSS-1187 ROSS-2711 MD-852 MD-1230 CE-8860 CE-3180

Source RBI LBI LBI RBI LBI RBI

Downstream distance, in meters 1,237 2,761 10,261 10,678 11,887 6,207

Chemical character of group High pH, low 

sulfate

Acidic, moderate 

sulfate

Acidic, high 

sulfate and metal 

concentrations

Acidic, moderate 

concentrations

High pH, 

moderate 

concentrations

Acidic, high 

concentrations

Number of samples 10 10 3 21 11 22

Site description Drains across 

road

Draining Fe bog 

and Red and 

Bonita mine

Seeps down 

gradient of 

Yukon tunnel

Ferricrete spring Inflow Inflow

pH, in standard units 6.78 3.50 3.09 4.46 7.64 3.20

Calcium 19.4 25.8 165 103 41.3 164

Magnesium 1.35 3.90 19.7 5.28 2.94 9.74

Sodium .69 2.28 4.18 2.74 1.19 4.31

Sulfate 22.4 88.3 722 275 52.9 582

Chloride .06 .25 .52 .54 .37 .94

Silica, diss 3.46 23.3 61.0 20.3 6.97 44.1

Aluminum, diss .063 12.5 25.9 2.93 .041 8.19

Cadmium, diss <.001 .049 .052 .005 <.001 .041

Copper, diss <.002 .499 1.71 .012 .001 .006

Iron, diss <.002 .270 9.64 .029 .026 8.46

Lead, diss .023 .023 .345 .023 .023 .023

Manganese, diss .015 1.81 15.7 .651 .123 1.41

Nickel, diss <.003 .016 .050 .005 .003 .021

Strontium, diss .174 .221 1.83 1.38 .391 1.32

Zinc, diss .021 9.16 10.6 .377 .024 .521

442 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
Quantification of Metal Loading 443

during the 1996 sampling. At the start of the May Day study 

reach (9,409 m, fig. 9D), zinc concentration was near 1.0 mg/L 

in 1996 and 1.24 mg/L in 2000. The simulation of Walton-Day 

and others (this volume) predicts a concentration of about 

2.3 mg/L for the beginning of the May Day study reach. The 

lower observed concentration in 2000 likely is obtained from 

the effects of mixing zone processes, as suggested for copper 

(Walton-Day and others, 2000; Kimball and others, 2002).

Mass-Load Profiles

Constructing profiles of mass loading with the combined data sets required some assumptions about the effects 

of inflows along the study reach. Loading profiles from the 

1999 study reach were used to the point downstream from 

South Fork (C5). After that point, the change in load for 

stream segments of the 1996 study reach were applied to the 

new load at C5. This assumes that areas of loss and gain were 

the same downstream from the mine in 1999 as they were in 

1996, which essentially is the same assumption used for the 

solute-transport simulations (Walton-Day and others, this 

volume).

A summary of the mass-load calculations for selected 

constituents, and the sum of cumulative instream load for 

selected sections of the study reach, are given in table 5. 

The summary indicates the great variation in the magnitude 

of cumulative instream load. Iron mass load was greater than 

1,000 kg/day, and aluminum was about half that amount. 

These loads are substantially greater than those in the upper 

Animas River basin, indicating the importance of the acidsulfate and quartz-sericite-pyrite altered rock that crops out 

in the Cement Creek basin. Mass loading of base metals also 

was substantial for copper, lead, and zinc, but both copper 

and zinc loads were less than in the upper Animas River basin. 

Although lower in magnitude than copper and zinc loads, the 

mass loads of cadmium and lead were important.

Principal Locations of Loading

Normalized loads indicate the patterns of loading along 

the study reach (fig. 10). Normalization is with respect to the 

cumulative instream load in table 5. Constituents that are most 

conservative during transport had normalized values near 1 at 

the end of the study reach, including copper (because of the 

low pH of Cement Creek), manganese, strontium, and sulfate. 

Loads of reactive constituents, including zinc, cadmium, aluminum, iron, and lead decreased along the study reach. Three 

general patterns of load profiles emerged among the solutes 

(fig. 10; table 5). Copper and zinc loads increased substantially 

in the upper part of the study reach at the Mogul mine inflow 

(C2) and the North Fork (C3) (fig. 10A). Cadmium load also 

increased, but not as much as copper and zinc. Instead, downstream from the inflow of South Fork (C5), cadmium load 

increased similar to loads of aluminum and iron (fig. 10B). 

Aluminum and iron loads increased at many locations, but 

particularly at the iron bog (C7) and the lower bog (C12), 

and at 13,953 m (fig. 10B), where lead load also increased 

substantially. Finally, manganese, strontium and sulfate mostly 

increased at Sunnyside mine (C4), Minnesota Gulch (C8), and 

Yukon tunnel (downstream from C11; fig. 10C).

Despite differences in details among the load profiles, 

the metal loads collectively indicated the areas where most 

of the metal loads entered the stream. Although it might seem 

that loads from these sources could be divided into mined and 

unmined areas, mined and unmined sources exist in almost 

every subbasin along Cement Creek (Wright and Nordstrom, 

1999). Therefore, such a distinction is difficult. The summary of cumulative instream load in table 5 is similar to that 

presented for sampled instream load by Kimball and others 

(2002), but table 5 reports load calculations with an analysis of load error that was not applied in Kimball and others 

(2002). The principal locations of loading were defined by the 

same stream segments in both reports, except that some areas 

with little or no loading were combined to simplify table 5. 

Such a large number of contributing segments indicates the 

widespread effects of alteration and mining in the Silverton 

caldera (Bove and others, 2000). Considering the patterns of 

all these constituents (table 5; fig. 10), the principal locations 

of loading include:

1. Mogul mine (C2): This was the major source for cadmium, copper, and zinc, but loads of aluminum, iron, 

manganese, and sulfate also were substantial.

2. North Fork Cement Creek (C3): The North Fork of 

Cement Creek was the second greatest source of copper 

and zinc. In 1996 it was the greatest source of copper 

(Kimball and others, 2002).

3. Sunnyside mine (C4): Effluent from the Sunnyside 

mine (the American tunnel) was the greatest source of 

strontium, and the loads of manganese and sulfate were 

substantial. These are the constituents that also had substantial loads from the treatment that was in place in 1996 

(Kimball and others, 2002).

4. South Fork (C5): Inflow from South Fork Cement Creek 

was a considerable source for loads of iron, manganese, 

strontium, and sulfate.

5. Prospect Gulch (C6) and iron bog (C7): Kimball and others (2002) noted the substantial increase in many metal 

loads that occurred along a broad area around Prospect 

Gulch starting upstream from Prospect Gulch at CE-2785, 

and continuing downstream to CE-3185. This area 

includes both Prospect Gulch (C6) and the iron bog (C7). 

An adit contributed some drainage at CE-3425. Substantial mining took place in Prospect Gulch, and there are 

outcrops containing acid-sulfate and quartz-sericite-pyrite 

alteration assemblages in its headwaters (fig. 7). Taken 

together, this area was a substantial source of aluminum, 

cadmium, copper, iron, manganese, and sulfate. Because 

of the importance of Prospect Gulch to mass loading in 

Cement Creek, more detailed studies were done there and 

are summarized herein.
C1

C2

C3

C4

C5

C6

C7

C8

C9

C10

C11

C12

C48

C1

C2

C3

C4

C5

C6

C7

C8

C9

C10

C11

C12

C48

0 2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000

0

2

0

4

8

12

16

20

30

40

50

60

3

4

5

6

7

8

9

2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000

DISTANCE ALONG STUDY REACH, IN METERS

A

BpH, IN STANDARD UNITS

IRON CONCENTRATION,

IN MILLIGRAMS PER LITER

Figure 9. Variation of A, pH; of dissolved and colloidal concentrations of B, iron; and total-recoverable concentrations 

of C, copper; and D, zinc with distance, Cement Creek basin, 1996, 1999, and 2000. Groups of stream samples (diamonds, 

upward triangles, dissolved; downward triangles, colloidal), and inflows (stars) are indicated by colors: 1, blue, 2, green; 

3, yellow; 4, orange; 5, red; 6, lavender. Groups were determined by principal component analysis, and their chemistry is 

summarized in tables 3 and 4. Labels on vertical dashed lines refer to locations in figure 7. C, D, Blue line, acute toxicity 

standard; red line, chronic toxicity standard.

444 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
Quantification of Metal Loading 445

C1

C2

C3

C4

C5

C6

C7

C8

C9

C10

C11

C12

C48

C1

C2

C3

C4

C5

C6

C7

C8

C9

C10

C11

C12

C48

0 2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000

D DISTANCE ALONG STUDY REACH, IN METERS

0

1E-3

0.01

0.1

10

20

1

2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000

C

COPPER CONCENTRATION,

IN MILLIGRAMS PER LITER

ZINC CONCENTRATION,

IN MILLIGRAMS PER LITER

1E-3

0.01

0.1

10

100

1

Figure 9—Continued. Variation of total-recoverable concentrations of C, copper; and D, zinc with distance, Cement Creek 

basin, 1996, 1999, and 2000. Groups of stream samples (diamonds, upward triangles, dissolved; downward triangles, colloidal), 

and inflows (stars) are indicated by colors: 1, blue, 2, green; 3, yellow; 4, orange; 5, red; 6, lavender. Groups were determined 

by principal component analysis, and their chemistry is summarized in tables 3 and 4. Labels on vertical dashed lines refer to 

locations in figure 7. Blue line, acute toxicity standard; red line, chronic toxicity standard.
Prospect Gulch is a steep-gradient mountain catchment 

that is strongly affected by natural acidity from pyrite weathering. Metal content in the stream water is a composite of 

multiple sources affected by hydrologic, geologic, climatic, 

and anthropogenic conditions. We identified sources of metals from various drainage areas using tracer-injection and 

synoptic-sampling methods during base flow on September 29, 

1999. Tracer data were interpreted by Wirt and others (1999) 

in conjunction with detailed geologic mapping, topographic 

profiling, geochemical characterization, and the occurrence and 

distribution of trace metals to identify sources of ground-water 

inflows.

Samples of water affected by mining in Prospect Gulch 

characteristically had some of the lowest pH values and highest concentrations of aluminum, sulfate, and iron; but they 

also contained elevated dissolved metals from ore-bearing 

vein minerals such as copper, zinc, cadmium, nickel, and lead. 

In comparison, weathering of regional acid-sulfate mineral 

assemblages produced moderately low pH waters elevated in 

sulfate, aluminum, and iron, but generally lacking in copper, 

cadmium, nickel, and lead. Occurrences of the base metals 

were helpful in identification of ground-water sources and 

flow paths. For example, cadmium was greatest in inflows 

associated with drainage from inactive mine sites and was 

absent in inflows that were unaffected by past mining activities; thus cadmium appears to be an important indicator of the 

effect of mining in this setting.

The reach of Prospect Gulch most strongly affected by 

mining contributed substantial percentages of the total sulfate, 

aluminum, and iron loads, and also large percentages of the 

copper and zinc loads for the entire Cement Creek basin (Wirt 

and others, 1999). An acidic spring near the mouth of Prospect 

Gulch yielded much of the stream discharge, sulfate, aluminum, and iron loads but only small loads of copper and zinc. 

Watershed-scale remediation efforts targeted at reducing loads 

of sulfate, aluminum, and iron at inactive mine sites will likely 

be limited in their influence because of the major sources of 

these constituents in Prospect Gulch, which are predominantly 

Table 4. Chemical composition of selected stream samples representing groups defined by principal component analysis, Cement 

Creek basin, 1996, 1999, and 2000.

[Concentrations in milligrams per liter; diss, dissolved; coll, colloidal; <, less than]

Group 12 3 4 5

Sample identification ROSS-0234 ROSS-0345 ROSS-3272 MD-712 CE-6107

Downstream distance, in meters 234 345 3,358 10,121 9,134

Character Upstream from 

Queen Anne 

mine inflow

From Queen Anne 

mine inflow to 

Mogul mine inflow

From Mogul mine 

inflow to South 

Fork Cement Creek

From Prospect Gulch 

to downstream from 

Porcupine Gulch

Upstream from Ohio 

Gulch to end of 

study reach

Number of samples 5 11 19 31 28

Site description Above inflow 

from talus

Below Queen 

Anne inflow

At treatment intake 

for Sunnyside

Down 88 m from 

Illinois Gulch

200 m downstream 

from Porcupine Gulch

pH, in standard units 6.64 5.71 3.32 4.19 3.85

Calcium 29.3 30.9 48.6 205 149

Magnesium 2.58 3.61 5.38 7.63 8.39

Sodium 0.79 0.77 1.48 3.97 3.38

Sulfate 24.6 34.5 80.9 536 460

Chloride 0.04 0.05 0.16 0.58 2.88

Silica 1.61 2.58 5.01 31.3 27.4

Aluminum, diss .050 .722 8.63 5.37 5.15

Aluminum, coll .313 .462 .020 .111 .382

Cadmium, diss .003 .010 .153 .012 .050

Cadmium, coll <.001 <.001 <.001 <.001 <.001

Copper, diss .019 .175 1.76 .071 .039

Copper, coll .048 .021 .004 <.001 .003

Iron, diss .003 .036 11.9 4.03 8.13

Iron, coll .035 .617 .743 3.92 1.60

Lead, diss <.023 <.023 .026 <.023 .023

Lead, coll <.023 <.023 <.023 <.023 .023

Manganese, diss .123 1.22 4.11 1.78 2.67

Manganese, coll <.001 <.001 .174 .010 .107

Nickel, diss .003 .004 .018 .008 .015

Nickel, coll <.003 <.003 <.003 <.003 <.003

Strontium, diss .246 .169 .384 2.23 1.53

Strontium, coll .018 .016 .008 .008 .112

Zinc, diss .515 2.08 11.8 1.06 .992

Zinc, coll .007 .005 .183 <.001 .082

446 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
Quantification of Metal Loading 447

discharged from nonmining sources. Remediation goals targeting reductions in loads of copper and other base metals may 

have better success, however, because changes in these loads 

are disproportionately higher than increases in discharge over 

the same reach, and a substantial fraction of the source of 

these metals is from mine-influenced reaches.

6. Minnesota Gulch area (C8, fig. 7): The area around 

Minnesota Gulch contributed substantial loads of 

aluminum, iron, manganese, lead, and sulfate. This 

appears to be related to the vein-related QSP (V-QSP) 

alteration in that subbasin.

7. Porcupine Gulch area (C9, fig. 7): Segments around 

Porcupine Gulch contributed cadmium, lead, and sulfate.

8. Ohio Gulch (C10, fig. 7): The stream segment ending 

at 6,907 m accounted for the load added by Ohio Gulch, 

which was important for aluminum and manganese. 

There also was an iron load, but it was not as great as 

in other areas.

9. Illinois Gulch (C11, fig. 7): Loading from Illinois Gulch 

was represented in a single stream segment (C11), where 

loads of strontium and sulfate were substantial.

10. Yukon tunnel (downstream from C11, fig. 7): Seeps that 

were not visible in 1996 were sampled in 2000; the results 

of that sampling helped us to separate loading of the Yukon 

tunnel from that of Illinois Gulch. The loads of aluminum 

and manganese were substantial here.

11. Lower bog (C12, fig. 7): Significant loading of aluminum, iron, manganese, lead, and sulfate occurred in the 

area of the lower bog. This small bog is located where a 

fracture zone crosses the stream. It is a setting similar in 

appearance to the iron bog (C7; Bruce Stover, Colorado 

Department of Minerals and Geology, oral commun., 

1999). No mines were developed in this fault area; only 

prospects were observed. This area likely represents a 

nonmining contribution to the load of Cement Creek.

12. Gauge at C48: Most of the load accounted for at the last 

stream segment occurred at 13,953 m. Substantial percentages of the aluminum and lead loads were contributed 

in this segment. Although this stream segment passed 

the load error test, the dramatic increase and subsequent 

decrease might be attributed to sampling error of some 

kind, particularly because this area is not near mine sites 

or mapped altered areas.

Table 5. Summary of load calculations and cumulative instream load for selected subreaches, Cement Creek basin, 1996 and 1999.

[Distance, in meters along study reach; Al, aluminum; Cd, cadmium; Cu, copper; Fe, iron; Mn, manganese; Pb, lead; Sr, strontium; Zn, zinc; SO4, sulfate; all 

values in kilograms per day, except percents; rank of loading for each element indicated by number in parentheses; blank entries indicate loading less than load 

error]

Al Cd Cu Fe Mn Pb Sr Zn SO4

Cumulative instream load 531 3.83 14.0 1,039 210 6.94 77.7 166 35,000

Cumulative inflow load 148.7 1.15 11.4 374 97.2 0.35 97.7 83.7 21,200

Percent inflow load 28.0 30.1 81.2 35.9 46.3 5.1 >100 50.4 60.7

Unsampled inflows 382 2.67 2.64 666 113 6.59 0.00 82.5 13,800

Percent unsampled inflow 72.0 69.9 18.8 64.1 53.7 94.9 <1 49.6 39.3

Attenuation 206 1.18 0.03 436.7 59.4 4.39 7.17 38.2 5,700

Percent attenuation 38.8 30.7 <1 42.0 28.3 63.3 9.24 23.0 16.3

Area or site designation Distance Al Cd Cu Fe Mn Pb Sr Zn SO4

ROSS-0345 Queen Anne (C1) 345 3.68 0.042 0.620 (4) 2.02 3.77 0.014 0.559 6.31 312

ROSS-1317A Mogul mine (C2) 1,367 32.3 (4) .994 (1) 8.30 (1) 25.8 19.0 (3) .214 .707 61.6 (1) 665

ROSS-3057 North Fork (C3) 3,107 23.9 3.87 (2) 96.5 (3) 8.59 .000 .872 37.0 (2) 560

ROSS-3845 Sunnyside mine (C4) 3,931 16.2 .159 20.8 (1) 5,660 (1)

ROSS-4047 South Fork (C5) 4,133 20.4 64.7 13.3 12.9 (4) 2,810 (3)

CE-2425 Upstream from Prospect Gulch 5,452 14.9 .868 (2) 47.5 2.95 .631 (4) 2.35 1,230

CE-3185 Prospect Gulch area (C6) 6,212 74.8 (2) .484 (3) .852(3) 229 (1) 19.1 (2) .259 5.97 (5) 8.07 2,650 (4)

CE-3317 Iron bog (C7) 6,344 22.2 .169 68.9 (4) 6.20 1.71

CE-5215 Upstream from Minnesota Gulch 8,242 16.2 134 (2) 17.2 (5) .752 (3) 2.70 2,630 (5)

CE-5767 Minnesota Gulch area (C8) 8,794 87.4 (1) .308 (5) 0.402 (5) 57.1 33.4 (1) .000 18.7 (2) 13.3 (3) 1,960

CE-6107 Porcupine Gulch area (C9) 9,134 .440 (4) 12.2 .481 (5) 7.56 (4) 2,650 (4)

CE-6742 Upstream from Ohio Gulch 9,769 15.8 .306 4.65 .422 4.75 889

CE-6907 Ohio Gulch (C10) 9,934 31.3 (5) 33.4 18.0 (4) 4.02

CE-7131 Illinois Gulch (C11) 10,158 .215 17.2 (3) 2,520

CE-7331 Yukon tunnel 10,358 25.8 14.5 .422 6.13

CE-7501 Topeka Gulch (May Day mine) 10,528 36.4 1,470

CE-9360 Upstream from lower bog 12,387 65.4 (3) 54.5 8.07 

CE-9905 Lower bog area (C12) 12,932 32.1 (4) .000 68.7 (5) 12.8 1.34 (2) 6.79 (5) 4,100 (2)

CE-11558 End of study reach (C48) 14,585 64.9 (3) .000 .000 36.0 1.48 (1) 1,900
Unsampled Inflow

Unsampled inflow was important for mass loading in 

Cement Creek. Over half the cumulative instream loads for 

aluminum, cadmium, iron, manganese, lead, and zinc entered 

the stream as unsampled inflow (table 5). Only copper and 

sulfate had smaller unsampled inflow. This indicates two 

aspects of the geology in the Cement Creek basin. First, there 

are a large number of outcrops of the AS- and QSP-altered 

rocks, and many of these may contribute loading to the 

stream through dispersed, subsurface inflow, most likely 

through the large alluvial fans at the mouths of many side 

drainages. These fans also could contain substantial amounts 

of unweathered, altered rock that could be contributing to 

these loads. Second, there are areas where fracture flow is 

important for the contribution of mass load to the stream, 

principally the Prospect Gulch area (C6) and the lower bog 

area (C12).

Figure 10. Variation of normalized instream loads for A, cadmium, copper, zinc; B, aluminum, iron, lead; 

C, manganese, strontium, and sulfate with distance, Cement Creek basin, 1996 and 1999. Labels on vertical lines 

refer to locations of substantial change along the study reach in table 5. C1 C2 C3 C4C5C6C7C8C9 C10

C11

C12

C48

C1

C2

C3

C4

C5

C6

C7

C8

C9

C10

C11

C12

C48

C1

C2

C3

C4

C5

C6

C7

C8

C9

C10

C11

C12

C48

0 2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000

DISTANCE ALONG STUDY REACH, IN METERS

A

B

C

0.0

0.2

0.4

0.6

0.8

1.0

0.0

0.2

0.4

0.6

0.8

1.0

0.0

0.2

0.4

0.6

0.8

1.0

NORMALIZED LOAD

Cadmium

Copper

Zinc

Aluminum

Iron

Lead

Manganese

Strontium

Sulfate

448 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
Quantification of Metal Loading 449

Kimball and others (2002) indicated several important 

areas where unsampled inflow occurred in the Cement Creek 

basin. These included the area around Prospect Gulch (C6), 

the area around Minnesota Gulch (C8), the Yukon tunnel 

area (downstream from C11), and the lower bog (C12). 

Another important area was near the end of the study reach, 

near 13,953 m. From results of the work upstream from 

North Fork in 1999, two areas can be added: (1) substantial 

unsampled inflow upstream from the Mogul mine inflow (C2), 

which could indicate that drainage from the mine seeps into 

the ground and enters the stream upstream from the visible 

inflows; (2) unsampled inflow near North Fork (C3) (better 

observed in 1999 than in 1996). The normalized load profiles 

indicate additional, smaller inflows (fig. 10). Although these 

smaller inflows may not be substantial sources of metal load 

individually, together they represent a large, dispersed contribution to the metal loads, and they may complicate remediation goals.

Attenuation of Load

Net attenuation of constituent loads ranged from less than 

1 percent for copper to 63 percent for lead (table 5). Copper, 

strontium, and sulfate were the most conservative in Cement 

Creek: all three showed less than 20 percent attenuation. Copper commonly is attenuated in streams affected by mine drainage, but at a pH less than 4.5 in Cement Creek, copper is mostly 

conservative. Aluminum, cadmium, iron, manganese, and zinc 

had from 20 to 50 percent attenuation. These results differ from 

those of Kimball and others (2002) because the accounting 

here used the total metal concentrations rather than the filtered 

concentrations.

Not many areas occurred along the study reach where 

attenuation took place for all the elements simultaneously 

(fig. 10). The greatest amount of attenuation occurred downstream from the Sunnyside mine discharge in 1996, but no 

attenuation was measured in the same reach in 1999, when 

treatment was temporarily stopped during the mass-loading 

study. The normalized loading curves for the combined data 

sets do not show the 1996 attenuation (fig. 10). Attenuation 

occurred in several other areas as follows:

Area Attenuation

Near Minnesota and 

Porcupine Gulches

Substantial for aluminum, cadmium, 

and manganese

Downstream from 

Illinois Gulch

Aluminum, manganese, lead, 

zinc (Kimball and others, 2002; 

Walton-Day and others, 2002)

Last few segments 

of study reach

Aluminum, iron, lead, zinc, and 

sulfate

From about 6,000 m to 10,000 m, a reach that includes Illinois 

Gulch, some of the attenuation could result from higher pH 

waters along the left bank (east side of the canyon) that drain 

the propylitized rocks.

Summary

With many outcrops of AS- and QSP-altered rock in 

the Cement Creek basin, loadings of many constituents were 

substantial. Cement Creek had a pH less than 4.5 along much 

of the study reach, and so changes between dissolved and 

colloidal phases were not substantial. Important changes 

occurred between sampling in 1996 and 1999 and are detailed 

in Appendix 2.

Mineral Creek Basin, 1999

Three tracer injections were needed to assess the 15 km 

study reach of Mineral Creek. Basic details of all three studies 

are combined here to give a framework for the entire Mineral 

Creek basin. The study reach started on a tributary to Mineral 

Creek near Red Mountain Pass. The injection was upstream 

from the Junction mine inflow (M1, fig. 11), which collects 

water from the Longfellow mine and the Koehler tunnel, and 

continued downstream to the U.S. Geological Survey stream 

gauging station 09359010 (M34), near the confluence with the 

Animas River (figs. 1 and 11). The upstream injection ended 

just upstream from Mill Creek (M6). The middle injection 

started at this same location and continued to the site just 

upstream from South Fork (M11). The lower injection started 

upstream from South Fork (M11), and continued to the gauging station (M34). Overall, there were 84 stream segments and 

65 sampled inflows. Locations where changes in stream chemistry occurred are indicated by the labels M1 through M34 in 

figure 11 and subsequent figures.

For each of the three injections, the bromide tracer 

provided a clear tracer signal that was elevated above the 

low background concentrations (fig. 12). Calculated stream 

discharge from the tracer dilution indicates that the greatest 

increases in stream discharge occurred at Mill Creek, Middle 

Fork Mineral Creek, South Fork, and along the section of 

stream from South Fork to Bear Creek (fig. 12).

Chemical Characterization of Synoptic Samples

The chemical character of stream water in Mineral Creek 

is dominated by distinct changes in response to a few key 

inflows (fig. 13). Many substantial changes in pH and constituent concentrations occurred in the upstream part of the study 

reach, from M1 to M6, where the stream was relatively small. 

Thus, small inflows had a large effect on concentrations. 

Inflow from the Longfellow mine and the Koehler tunnel are 

combined herein and called the Junction mine inflow (M1) for 

this discussion. The inflow caused a substantial decrease in pH 

from greater than 6.5 to less than 3.0 (fig. 13A). Subsequent 

inflows downstream from M1 caused the pH to increase back 

to values greater than 6.0. Many inflows from M1 to M6 had 

substantial concentrations of iron, copper, and zinc, and the 

concentrations in the stream were high.
Figure 11. Location of study area, alteration zones, key locations, and principal sites of inactive mines, Mineral Creek basin, 1999.

Bear

Creek

M9-Middle Fork

107o45’

37o

52’

30”

Longfellow

M1 - Junction mine

M2 - Mineral Creek inflow

M4 - Porphyry Gulch

M3 - Carbon Lakes

M5- Big Horn Gulch

Red tributary

M6- Mill Creek

M10

M7 - Browns

Gulch

M12

M8

Brooklyn

Brooklyn

North

Star

Silver Ledge

K

Inactive mine site

ey locations

Acid-sulfate

Quartz-sericite-pyrite

Vein-related quartz-sericite-pyrite

Weak sericite-pyrite

Regional propylitic

Streamflow gauging station

Alteration types

3,792 m

M34

M34

Mineral

Creek

0 1 2 3

0 1 2 3

4 MILES

4 KILOMETERS

M9 - Middle Fork

M11 - South Fork

EXPLANATION

450 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
Quantification of Metal Loading 451

Figure 12. Variation of injected bromide concentration and calculated discharge with distance, Mineral Creek basin, September 1999. 

Note the start of the two downstream injection reaches where bromide concentration is higher than at the end of each upstream 

injection reach. M1 M2

M3

M4

M5

M6

M7

M8

M9

M10

M11

M12

M34

0 0.01 0

20

40

60

80

100

120

0.1

1

10

100

300

2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000

DISTANCE ALONG STUDY REACH, IN METERS

BROMIDE CONCENTRATION, IN MILLIGRAMS PER LITER

DISCHARGE, IN CUBIC FEET PER SECOND

EXPLANATION

Stream bromide

Stream discharge

Inflow discharge
Figure 13. Variation of A, pH; of dissolved and colloidal concentrations of B, iron; and total-recoverable concentrations 

of C, copper, and D, zinc with distance, Mineral Creek basin, 1999. Groups of stream samples (diamonds or upward 

triangles, dissolved; downward triangles, colloidal), and inflows (stars) are indicated by colors: 1, blue (darker); 2, green; 

3, yellow; 4, orange; 5, red; 6, purple; 7, cyan (lighter). Groups were determined by principal component analysis; their 

chemistry is summarized in tables 6 and 7. Labels on vertical dashed lines refer to site locations in figure 11. C, D, Blue 

line, acute toxicity standard; red line, chronic toxicity standard. M1 M2M3 M4 M5M6M7 M8 M9

M10

M11

M12

M34

M1 M2

M3

M4

M5

M6

M7

M8

M9

M10

M11

M12

M34

2

1E-3

0.01

0.1

1

10

100

300

3

4

5

6

7

8

A

BpH, IN STANDARD UNITS

IRON CONCENTRATION,

IN MILLIGRAMS PER LITER

0 2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000

0 2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000

DISTANCE ALONG STUDY REACH, IN METERS

452 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
Quantification of Metal Loading 453

M1

M2

M3

M4

M5

M6

M7

M8

M9

M10

M11

M12

M34

M1

M2

M3

M4

M5

M6

M7

M8

M9

M10

M11

M12

M34

1E-3

0.01

0.1

1

10

100

D

ZINC CONCENTRATION,

IN MILLIGRAMS PER LITER

COPPER CONCENTRATION,

IN MILLIGRAMS PER LITER

0 2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000

DISTANCE ALONG STUDY REACH, IN METERS

1E-3

0.01

0.1

1

C

0 2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000

Figure 13—Continued. Variation of total-recoverable concentrations of C, copper, and D, zinc with distance, Mineral 

Creek basin, 1999. Groups of stream samples (diamonds or upward triangles, dissolved; downward triangles, colloidal), 

and inflows (stars) are indicated by colors: 1, blue (darker); 2, green; 3, yellow; 4, orange; 5, red; 6, purple; 7, cyan 

(lighter). Groups were determined by principal component analysis; their chemistry is summarized in tables 6 and 7. 

Labels on vertical dashed lines refer to site locations in figure 11. Blue line, acute toxicity standard; red line, chronic 

toxicity standard.
Inflows

Classification of inflow samples, based on PCA, is 

illustrated by the chemical composition of representative 

samples from each of four inflow groups (table 6). The chemical composition of samples in the groups range from acidic 

(inflow groups 1 and 4) with high sulfate concentrations to 

near neutral with lower sulfate concentrations (inflow groups 2 

and 3, table 6). Sulfate concentrations among these representative samples are very different, ranging from 6.81 to 346 mg/L 

(table 6). The most acidic, sulfate-rich samples (inflow group 1) 

also had some of the highest base metal concentrations. The 

four groups of inflows in this report do not directly relate to 

groups or categories suggested by Mast and others (2000) and 

Mast and others (this volume, Chapter E7). The classification 

of Mast and others (2000) sought to evaluate the potential for 

the effects of mining activity on water quality of seeps and 

springs throughout the Animas River watershed study area, and 

was constructed on the basis of field observations, topographic 

maps, geologic maps, geologic and mining publications, 

aerial photographs, and PCA. Inflow samples from the tracer 

studies differ from the data of Mast and others (2000) in that 

the tracer inflow samples were collected at the stream rather 

than at the sources away from the stream to obtain a representation of the water quality that directly affects the stream 

chemistry. The tracer inflow samples do not meet the goals 

of the Mast and others (2000) study.

Variations in the chemistry of inflows reflect the differences that result from weathering of the particular alteration suites in the Mineral Creek basin (Bove and others, 

this volume). The sample at the Junction mine inflow (M1, 

inflow group 1) is influenced by weathering of the AS-altered 

rocks and breccia pipes that are rich in copper and zinc sulfides (Bruce Stover, Colorado Department of Minerals and 

Geology, written commun., 1999). This produces the high 

concentrations of almost all the metals, but especially copper and zinc. The inflow from Middle Fork Mineral Creek 

(M9, group 4) is influenced by weathering of QSP-altered 

rocks on peak 3,792 m (fig. 11), which produces very high 

Table 6. Chemical composition of selected inflow samples representing groups defined by principal component analysis, Mineral 

Creek basin, 1999.

[Sample identification, key to samples in database; distance, in meters along study reach; specific conductance in microsiemens per centimeter; all concentrations 

in milligrams per liter; <, less than; NM, no measurement]

Group 1 2 3 4

Chemical character Acidic, high sulfate 

and metal concentrations

Near neutral, 

moderate sulfate and 

metal concentrations

Near neutral, low 

sulfate and metal 

concentrations

Acidic, moderate 

sulfate and metal 

concentrations

Number of samples 6 26 20 19

Site description Small spring near

 highway 550

Draining marsh from 

alluvial fan

From culvert under 

highway 550

Draining over 

ferricrete and moss

Downstream distance, in meters 297 5,883 518 6,994

Sample identification MIN3-00121 MIN2-05667 MIN3-00292 MIN2-06768

pH, in standard units 2.83 7.50 6.71 3.64

Specific conductance 958 262 59.0 392

Calcium 43.0 38.3 8.39 36.4

Magnesium 7.16 2.85 .69 4.19

Sodium 4.47 3.84 1.48 3.88

Potassium <.001 .87 .51 1.32

Alkalinity <.001 NM 33.6 <.001

Sulfate 346 93.4 6.81 148

Chloride .96 .46 .94 1.55

Fluoride .56 .43 <.001 .18

Silica as SiO2 23.4 9.67 2.39 16.9

Aluminum 10.5 .016 .058 3.56

Arsenic .078 .008 .002 .026

Cadmium .047 <.001 <.001 <.001

Copper 4.43 .002 .003 .005

Iron 23.1 .037 .088 .943

Lead .092 .006 .008 .045

Lithium .044 <.001 .001 <.001

Manganese 4.35 .064 .006 .524

Nickel .042 <.001 <.001 .004

Strontium .659 .228 .125 .265

Zinc 13.2 .024 .010 .055

454 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
Quantification of Metal Loading 455

aluminum and iron concentrations. A few other inflows 

(inflow group 4 between M9 and M12) also had high basemetal concentrations, and like the Junction mine inflow had 

high zinc to aluminum mole ratios. The zinc to aluminum ratio 

helps us distinguish between drainage from the AS and QSP 

alteration zones. Samples of water draining the AS alteration zones are relatively high in zinc concentration, whereas 

samples of water draining QSP alteration zones, such as 

Middle Fork Mineral Creek (M9), are relatively lower in zinc 

and higher in aluminum concentration.

Stream

Classification of stream samples into groups that have 

similar chemistry yielded seven distinguishable groups along 

the 15 km study reach (table 7). Unlike the groups of inflow 

samples, these groups of stream samples indicate sequential 

chemical changes along the study reach. Groups assigned by 

the multivariate analysis differ slightly from the sequential 

order downstream; however, the groups are ordered in table 7 

according to their sequential occurrence in downstream order. 

PCA for stream samples used both dissolved and colloidal 

concentrations. Calcium and sulfate were the major ions 

throughout the study reach (table 7). Values of pH were less 

than 4.5 in several sections of the study reach (fig. 13A), and 

alkalinity was absent in those sections. The highest instream 

concentration of iron exceeded 100 mg/L (fig. 13B); concentrations of copper (fig. 13C) and zinc (fig. 13D) were greater 

than 15 mg/L and 35 mg/L, respectively, in stream group 3. 

Concentrations of arsenic, cadmium, and lead were relatively 

high also. There were measurable colloidal concentrations 

of all the metals, and the colloidal concentrations of iron and 

copper were greater than dissolved concentrations in several 

sections along Mineral Creek (fig. 13). The method for determining colloidal concentrations usually is not sensitive enough 

to measure colloidal concentrations of arsenic, cadmium, 

nickel, and lead, but these concentrations were measurable 

in Mineral Creek (Kimball and others, 1995).

Each of the metal concentrations, and especially the partitioning between dissolved and colloidal phases, varied considerably along the study reach in response to inflows of differing 

pH (fig. 13 and table 7). Details of these spatial patterns help 

to indicate the chemical reactions that affect the metal loading 

and transport. Metals affected the most by colloid formation 

were aluminum, arsenic, copper, iron, and lead. Those least 

affected were manganese and zinc.

Iron colloids (fig. 13B) affect the transport and partitioning of other metals (Kimball and others, 1992, 1995). 

Sorption of arsenic and lead to the abundant colloidal iron 

has been simulated for the upstream injection reach (Runkel 

and Kimball, 2002). Downstream from the Junction mine 

inflow (M1) where pH was less than 3.0, iron was not yet 

diluted or partitioned to the colloidal phase. As pH increased 

downstream, the streambed became coated with iron colloidal 

material along much of the study reach, particularly downstream from inflows that had higher pH (downstream from 

M2, M3, M6, and M11). Dissolved iron concentrations substantially decreased downstream from the inflow of Mill Creek 

(M6) and South Fork (M11), but they increased downstream 

from Middle Fork Mineral Creek (M9). Colloidal concentrations were substantial in groups 2 through 7; they were 

substantially greater than dissolved iron in stream groups 4, 5, 

6, and 7 (table 7). A notable decrease in colloidal iron concentration was evident at the last two stream sites along the study 

reach (fig. 13B). Colloidal aluminum concentrations also 

showed a decrease in these samples.

Because of the AS and QSP alteration of bedrock in 

the Middle Fork Mineral Creek subbasin and the low pH of 

the stream water, aluminum concentrations were unusually 

high in Mineral Creek (table 7). Dynamic changes between 

dissolved and colloidal aluminum occurred at the locations 

where pH changed across a value of about 5.3 (fig. 13A). In 

general, when pH was less than 5.5 (stream groups 3, 4, 5, 

and 7), aluminum was mostly transported in the dissolved 

phase; when pH was greater than 5.3 (stream groups 1, 2, 

and 6), colloidal aluminum exceeded dissolved aluminum. 

This behavior is consistent with the observations of aluminum 

solubility by Nordstrom and Ball (1986) for waters affected 

by mine drainage. The greatest changes occurred downstream 

from the Junction mine inflow (M1), the inflow of Mill Creek 

(M6), the inflow of Middle Fork Mineral Creek (M9), and the 

inflow of South Fork (M11). The pattern was similar to that 

of iron (fig. 13B). Because these changes occurred within the 

time frame of transport through an individual stream segment, 

the rate of precipitation and dissolution reactions had to be on 

the order of seconds to minutes.

Important similarities were observed between the spatial 

variations of copper (fig. 13C) and iron (fig. 13B) concentrations. Copper concentration increased at many, but not all, of 

the same locations as iron, which suggests either that some 

sources of iron did not include copper mineralization or that 

copper had been removed before it reached the stream. Colloidal copper concentrations became increasingly more important 

downstream from Big Horn Gulch (M5) and Mill Creek (M6). 

At M8, no increase in total-recoverable copper occurred, but 

instead an increase in dissolved copper was observed, indicating partitioning from colloidal to dissolved phases. The 

change was consistent with the decrease in pH that occurred 

at M8 (fig. 13A). No significant increase in copper took place 

downstream from Middle Fork Mineral Creek, and yet Mast 

and others (2000) found substantial sources of copper load in 

Middle Fork subbasin that most likely was from QSP veins. 

Thus, the relatively low concentration of copper in the Middle 

Fork Mineral Creek sample from this synoptic study likely 

reflects the removal of copper between the informally named 

Red tributary and the mouth of Middle Fork. Dissolved copper 

concentrations were greater than acute and chronic standards 

(Colorado Department of Public Health and Environment, 

2000) along the entire study reach, except downstream from 

the South Fork, where the concentration was less than the 

acute standard (fig. 13C).
Concentrations of zinc were remarkably high in 

Mineral Creek; the highest concentration was 35.6 mg/L, 

downstream from the Junction mine inflow (M1), and 

the median dissolved concentration was 0.829 mg/L (fig. 13D). 

Dissolved concentrations exceeded both acute and chronic 

standards along the entire study reach (Colorado Department 

of Public Health and Environment, 2000). Zinc concentrations consistently decreased downstream from each major 

Table 7. Chemical composition of selected stream samples representing groups defined by principal component analysis, Mineral 

Creek basin, 1999.

[Sample identification, key to samples in database; distance, in meters along study reach; specific conductance in microsiemens per centimeter; all concentrations 

in milligrams per liter; diss, dissolved; coll, colloidal; <, less than; NM, no measurement]

Group 1 Group 3 Group 4 Group 5 Group 2 Group 6 Group 7

Group characteristic Upstream from 

acid inflows; 

generally low 

concentrations

Downstream from 

Junction mine 

inflow; high 

concentrations 

from inflow

From highway 550 

culvert to inflow 

of Mineral Creek; 

dilution of high 

concentrations

Mineral Creek 

to Porphyry 

Gulch; 

substantial 

colloidal 

concentration

From Porphyry 

Gulch to Mill 

Creek; colloidal 

iron higher than 

dissolved iron

From Mill Creek 

to Middle Fork 

and downstream 

from South 

Fork; higher pH 

and colloidal 

concentrations, 

upstream 

From Middle 

Fork to South 

Fork; high 

dissolved 

and colloidal 

concentrations

Number of samples 3 2 8 17 11 34 15

Sample identification MIN3-UP103 MIN3-00050 MIN3-00550 MIN3-01450 MIN3-02170 MIN2-03945 MIN2-09372

Downstream distance 103 226 776 1,676 2,396 4,171 9,598

pH, in standard units 6.61 2.84 3.24 3.93 5.48 6.55 4.87

Specific conductance 286 1,531 638 226 139 270 414

Calcium 10.3 59.9 24.7 15.9 15.3 43.8 62.6

Magnesium 2.14 10.7 3.63 1.65 1.55 2.06 5.12

Sodium .64 7.72 4.40 2.23 1.69 2.92 3.30

Potassium .40 1.09 1.88 .61 .62 .82 .18

Alkalinity 36.0 <.001 <.001 <.001 NM 14.85 NM

Sulfate 14.3 664 234 81.2 55.2 111 198

Chloride .51 2.64 1.86 .98 .67 .62 .68

Fluoride .01 1.76 .52 .16 .07 .32 .69

Silica 1.34 9.33 4.21 2.54 2.19 3.93 7.39

Aluminum, diss .012 15.0 5.26 1.39 .232 .012 2.18

Aluminum, coll .133 <.001 <.001 .198 .531 .332 1.97

Arsenic, diss .008 2.12 .303 .010 .118 .007 .018

Arsenic, coll .006 .530 .565 .274 <.001 .020 <.001

Cadmium, diss .002 .143 .048 .010 .005 .002 <.001

Cadmium, coll .003 .015 .007 .006 .005 .005 <.001

Copper, diss .007 15.0 5.25 1.48 .658 .073 .089

Copper, coll .007 <.001 <.001 .033 .080 .173 .020

Iron, diss .013 123 37.6 5.68 2.25 .106 4.36

Iron, coll .598 4.20 3.46 6.44 2.48 1.48 1.62

Lead, diss .005 .109 .066 .003 .052 <.001 .022

Lead, coll .004 <.001 <.001 .011 .041 .051 .017

Manganese, diss .055 5.34 1.71 .472 .289 .260 .567

Manganese, coll .026 <.001 <.001 .024 .003 <.001 .051

Nickel, diss <.003 .035 .004 .007 <.003 <.003 <.003

Nickel, coll <.003 .021 .003 <.003 <.003 <.003 <.003

Strontium, diss .249 1.77 .748 .372 .299 .584 .620

Strontium, coll .004 <.001 <.001 .008 .011 .011 .068

Zinc, diss .013 35.6 12.5 3.41 2.07 .861 .495

Zinc, coll .008 <.001 <.001 .074 .014 <.001 .024

inflow, and each downstream group of samples, from 2 

through 7, had lower dissolved zinc concentrations (table 7). 

Downstream from South Fork (M11 to M34) zinc was partitioned to the colloidal phase. Even with a small amount of 

partitioning to colloids, zinc concentration in the bed material, 

including biofilm, can be substantial because the streambed 

integrates colloidal concentrations through time (Kimball 

and others, 2002).

456 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
Quantification of Metal Loading 457

Arsenic is an important component of the arsenopyrite 

found in the AS-altered rocks (D.B. Yager, written commun., 

2003). Although concentrations were not measurable along 

much of the study reach (table 7), dissolved arsenic concentration was high in stream group 2, which was downstream from 

the Junction mine inflow (M1). In groups 3 and 4, colloidal 

arsenic concentration was greater than the dissolved concentration, suggesting the sorption of arsenic to iron colloids (Runkel 

and Kimball, 2002). This process has been described in streams 

affected by mine drainage by Fuller and Davis (1989) and 

Fuller and others (1993). This association of arsenic and other 

toxic metals with colloidal material could provide a means for 

arsenic’s introduction into the food web (Besser and others, 

2001). Arsenic is also elevated in bed sediments near locations 

M1 and M2 (Church, Fey, and Unruh, this volume).

Concentrations of dissolved lead were similar to those of 

arsenic; measurable concentrations of colloidal lead occurred 

downstream from the Junction mine inflow (M1; table 7), 

and were detectable for the first 3,500 m of Mineral Creek. 

Two relatively high inflow concentrations occurred at 1,781 

and 1,921 m; both inflows were near the Silver Ledge mine 

(upstream from M4, fig. 11). Downstream from Mill Creek 

(M6), however, their concentrations mostly were less than 

detection along the rest of the study reach.

Manganese did not partition to the colloidal phase; its 

pattern was similar to that of zinc (fig. 13D). Downstream 

from South Fork (M11, stream group 6, table 7), where other 

metals transformed to the colloidal phase, manganese mostly 

remained in the dissolved phase. Manganese concentration is 

a good indication of metal sources because manganese comes 

from the weathering of gangue minerals in some alteration 

zones and is not highly reactive once in solution. Variation of 

manganese was similar to variation of other metals until the 

inflow of Mill Creek (M6); downstream from that point were 

substantial increases in concentration at Browns Gulch (M7) 

and Middle Fork (M9).

Variation of strontium concentrations along the study 

reach differed from that of the other metals (table 7). Strontium did not partition to the colloidal phase. Downstream from 

Mill Creek (M6), strontium concentrations increased substantially. Where there were large increases in concentration of 

other metals downstream from Middle Fork (M9), strontium 

concentration did not increase. These differences imply a 

source for strontium that was different from the alteration 

assemblages that provided other metals, mined or unmined. 

Strontium likely comes from substitution for calcium in plagioclase of propylitized intermediate-composition lavas of the 

San Juan Formation and Silverton Volcanics (D.B. Yager, written commun., 2003). Thus, its source is not always associated 

with the alteration zones that produced ores in the watershed.

Mass-Load Profiles

A summary of the loading calculations for each constituent and the sum of cumulative instream load for selected 

sections of the study reach are given in table 8. Cumulative 

instream loads varied substantially, from more than 

30,000 kg/day for sulfate to less than 5 kg/day for arsenic. 

Normalized loading profiles indicate three general patterns 

among the solutes: (1) arsenic, copper, and zinc mostly 

increased in the upper part of the study reach, upstream from 

Mill Creek (M6; fig. 14A); (2) aluminum, iron, and manganese mostly increased from the inflow of Middle Fork (M9, 

fig. 14B); and (3) strontium and sulfate increased at these 

and other locations (fig. 14C).

The first load pattern is illustrated by zinc (fig. 14A). The 

Junction mine inflow (M1) was the single largest load among 

all the stream segments, but the sum of cumulative instream 

load along the reaches to M2 and M3 was 35.0 kg/day, greater 

than the amount from the Junction mine inflow (table 8). 

Much of this zinc loading was from AS alteration in rocks that 

crop out near Red Mountain Pass (Bove and others, this volume) and the breccia pipes that also crop out near the stream 

(Bruce Stover, Colorado Division of Mines and Geology, written commun., 1999). Two inflows near the Silver Ledge mine 

also contributed to the zinc load in this part of Mineral Creek 

(upstream from M4). Between Middle Fork (M9) and the 

gauge at M34 a substantial increase in zinc load was observed, 

which was likely a result of weathering areas of QSP alteration 

in the Middle Fork Mineral Creek subbasin (Mast and others, 

2000), and AS-altered rock that crops out on Anvil Mountain 

(fig. 11).

Loading for arsenic mostly occurred upstream from 

Mill Creek (M6, fig. 14A). To some extent, patterns of cadmium and nickel mass loading (not shown in fig. 14A) resembled that of arsenic, but their concentrations were too variable 

to calculate reliable mass-loading profiles. Loads for arsenic 

that are listed in table 8 only include the subreach down to 

Mill Creek (M6). Some indications of loading for arsenic 

were observed at Porphyry Gulch (M4) and downstream from 

South Fork (M11 to M34), near the AS-altered rock of Anvil 

Mountain (fig. 11).

Inflow from Middle Fork Mineral Creek (M9) dominated 

the second pattern (fig. 14B). This load is a result of weathering in the QSP alteration zone of peak 3,792 m (fig. 11; Mast 

and others, 2000; Mast and others, this volume). Iron and 

aluminum both had the same general pattern, particularly with 

the dynamic changes in partitioning between dissolved and 

colloidal phases (shown for iron in fig. 13B). The normalized 

load profile for aluminum (fig. 14B) does not indicate this 

partitioning because the total instream load did not change 

greatly; the partitioning occurred in the water column and total 

aluminum concentrations remained nearly constant. A substantial increase in pH with the inflow of South Fork Mineral 

Creek (pH 7.2) was responsible for partitioning essentially all 

the aluminum to the colloidal phase. An increase at M12 was 

observed, near the Anvil Mountain alteration, but over a short 

distance downstream from there most of the colloidal load was 

removed.

The third pattern included both strontium and sulfate 

loads (fig. 14C). In addition to substantial mass loading from 

Middle Fork Mineral Creek (M9), increases came from Mill 
Creek (M6) and South Fork (M11). Strontium represents the 

weathering of carbonate-bearing propylitized rocks in Middle 

Fork subbasin (D.B. Yager, written commun., 2003). There 

also were locations where these constituents were not lost like 

the others, and along with manganese (fig. 14B) they were the 

most conservative during transport.

Principal Locations of Loading

Cumulative instream loads for each constituent are the 

best estimate of the total loading along the study reach (table 8). 

Although different patterns appear among loading profiles of 

the metals, their similarities identify certain locations as the 

most important for metal loading. Cumulative instream load 

for individual stream segments have been summed for the 

subreaches identified in figure 11. Subreaches that contributed 

the greatest load to Mineral Creek are indicated by ranks in the 

table.

The three patterns of loading for Mineral Creek suggest 

those areas of the study reach where the majority of loading 

occurred. In upstream to downstream order, these sources are 

as follows:

1. Junction mine inflow (M1), Red Mountain mining district, 

and associated AS alteration (fig. 11). Downstream from 

Junction mine inflow (M1) to Porphyry Gulch (M4) 

substantial sources enter the stream from dispersed, 

ground-water inflows. These sources account for the 

majority of arsenic, copper, and zinc (fig. 14A).

2. Middle Fork Mineral Creek (M9) contributes the greatest loads of aluminum, iron, manganese, strontium, and 

sulfate. Upstream from Middle Fork, there also are substantial loads of aluminum, manganese, and sulfate from 

Browns Gulch (M7), and the subbasin at M8.

3. AS-altered rock that crops out in Anvil Mountain downstream from South Fork Middle Creek (fig. 11). This was 

most important for zinc loading.

Unsampled Inflow

More than 40 percent of the loads of arsenic, copper, 

manganese, strontium, and zinc occurred as unsampled inflow 

(table 8). The most important location for unsampled inflow 

along the Mineral Creek study reach was between M1 and M3, 

near the upper part of the study reach. This area was responsible for much of the loading for arsenic, copper, and zinc 

(fig. 14A). Data in Runkel and Kimball (2002) also indicate 

that this area was an important source of lead. Unsampled 

inflows also occurred near Anvil Mountain where there was 

substantial outcrop of AS-altered rock (near M12, fig. 11).

Table 8. Summary of load calculations and cumulative instream load for selected subreaches, Mineral Creek, September 1999.

[Distance, in meters along study reach; Al, aluminum; As, arsenic; Cu, copper; Fe, iron; Mn, manganese; Sr, strontium; Zn, zinc; SO4, sulfate; all values in 

kilograms per day, except percents; rank of load for each constituent indicated by number in parentheses after load value; blank entries indicate loading less 

than load error. Note that “below” and “above” indicate “downstream from” and “upstream from”]

Al As Cu Fe Mn Sr Zn SO4

Cumulative instream load 526 4.18 27.4 910 102 128 99 30,638

Cumulative inflow load 418 1.82 10.7 731 53 71.2 52.1 24,574

Percent inflow 80 44 39 80 52 56 53 80

Unsampled inflow 107 2.35 16.7 180 49 57.0 46.7 6,064

Percent unsampled 20 56 61 20 48 44 47 20

Attenuation 359 2.58 18.5 521 15 13.8 39.6 1,857

Percent attenuation 68 62 68 57 15 11 40 6

Description Distance Al As Cu Fe Mn Sr Zn SO4

Below Junction mine 

inflow (M1)

226 7.99 1.41 (2) 7.99 (2) 67.6 (5) 2.84 0.941 18.9 (2) 353

Below Mineral Creek (M2) 888 3.35 .882 (3) 3.54 (3) 37.1 0.486 1.72 7.85 234

Above Porphyry Gulch 

(upstream from M4)

1,989 6.59 1.48 (1) 9.04 (1) 70.1 (4) 1.81 0.804 27.1 (1) 436

Below Porphyry Gulch (M4) 2,041 72.1

Below Big Horn Gulch (M5) 2,396 0.398 (4) 1.16 40.4

Below Mill Creek (M6) 4,090 4.25 17.8 (4) 3,370 (4)

Below Browns Gulch (M7) 5,406 29.3 (5) 8.17 (5) 6.87 3.40 912 (5)

Below left bank drainage (M8) 6,350 29.4 (4) 14.0 0.0 0.0 412

Below Middle Fork (M9) 6,981 293 (1) 1.15 450 (1) 36.2 (1) 31.9 (1) 10.5 (5) 14,200 (1)

Below acid springs (M10) 9,298 51.2 (3) 2.63 (4) 159 (3) 11.2 (4) 3.53 9.74

Below South Fork (M11) 10,943 28.5 42.9 28.3 (2) 2.95 6,360 (2)

Below Anvil Mountain 

alteration (near M12)

14,033 105 (2) 0.775 160 (2) 21.0 (2) 21.6 (3) 11.7 (4) 4,220 (3)

Mineral Creek at gauge (M34) 15,436 1.74 (5) 16.2 (3) 13.5 (5) 17.1 (3)

458 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
Quantification of Metal Loading 459

0 2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000

DISTANCE ALONG STUDY REACH, IN METERS

A

B

C

0.0

0.2

0.4

0.6

0.8

1.0

0.0

0.2

0.4

0.6

0.8

1.0

0.0

0.2

0.4

0.6

0.8

1.0

NORMALIZED LOAD

Aluminum

Iron

Manganese

Arsenic

Copper

Zinc

Strontium

Sulfate

Figure 14. Variation of normalized instream loads for A, arsenic, copper, zinc; B, aluminum, iron, manganese; C, strontium, 

and sulfate with distance, Mineral Creek basin, September 1999. Labels on vertical lines refer to locations of substantial change 

along the study reach of figure 11 and table 8.
Attenuation of Load

The net attenuation of metal loads ranged from 6 percent 

for sulfate to 68 percent for aluminum and copper (table 8). 

Spatially, most of the attenuation occurred at three locations 

along the study reach. Downstream from the inflow of Mill 

Creek (M6), substantial attenuation of copper occurred. There 

could have been sorption of copper onto the iron colloidal 

material with the increase in pH in this part of the stream. 

Downstream from the inflow of Middle Fork (M9), sulfate was 

attenuated. The removal of sulfate could have been associated 

with the formation of aluminum hydroxysulfates and schwertmannite. Finally, a large amount of attenuation took place for 

aluminum, copper, and iron loads in the last few segments of 

the study reach, downstream from M12 (fig. 11). The cause 

of this loss is not clear, but it could be related to inflow from 

Bear Creek, 1,922 m upstream, which drains a large component of propylitized rocks (Yager and Bove, 2002). These 

areas of attenuation could result in substantial input of metals 

to the food web (Besser and others, 2001).

Summary

Loadings of aluminum, copper, iron, manganese, and 

zinc into Mineral Creek were substantial. The mass-loading 

studies support the conclusions of Mast and others (2000) 

that much of this loading was from nonmining sources, but 

there were very substantial loads from the Junction mine 

inflow (M1) and near the Silver Ledge mine (upstream from 

M4). Few streams have such dynamic chemical reactions 

causing the partitioning of metals back and forth between 

dissolved and colloidal phases (fig. 13B, C). These reactions 

were rapid enough to occur during stream transport of a few 

hundred meters downstream from the inflows that affected 

the changes.

Elk Park Basin, 1998—Summary of Watershed 

Contributions

The Elk Park study reach, near Silverton, Colo., 

was selected in order to include the confluences of Cement 

Creek and Mineral Creek with the Animas River. Downstream 

from these confluences, the study reach extended to Elk Park 

(fig. 15). This section combines the results of a mass-loading 

study in 1997 that began upstream from the mouth of Cement 

Creek (C48) and continued to the A72 gauge downstream 

from Silverton, and results from a study that began at the 

stream gauging station in Mineral Creek (M34) and continued 

to Elk Park in 1998 (fig. 15). The two studies had overlapping 

sites that allowed for scaling of the loads calculated from each. 

In the Elk Park study reach, problems occurred with copper 

contamination in ultrafiltrate samples; thus, total-recoverable 

concentrations are used for load calculations and the 0.45-μm 

concentrations are used as the dissolved concentration in 

this study reach. The objectives of combining the studies 

were (1) to evaluate the relative contributions of the three 

main basins of the Animas River upstream from Silverton, 

(2) to quantify the chemical and physical processes that 

affect metals in the mixing zones along the study reach, and 

(3) to quantify the transport of dissolved and colloidal metals 

in the reach of the Animas River from Silverton to Elk Park. 

Transport of metals downstream from the Silverton area, to a 

large degree, is facilitated by iron and aluminum colloids that 

form in the mixing zones as these three major tributaries of 

the Animas converge (Church and others, 1997; Schemel and 

others, 2000).

The systematic decrease of chloride concentration 

along the study reach represented dilution by inflows. In 

1997, discharge at several sites along the upstream part of 

the study reach was measured by the area-velocity method 

as well as tracer dilution because the stream was divided 

into several braids downstream from Cement Creek (from 

1,818 m to 1,998 m). A synoptic discharge profile was calculated from chloride concentrations for both data sets (fig. 16). 

Background concentrations of chloride were low compared 

to the injected concentrations. The increase of chloride 

downstream from Deer Park Creek (E5) is unexplained. In 

that stream segment we had to use conservative solutes like 

calcium, strontium, and sulfate to estimate the increase in 

flow from Deer Park Creek (E5) (Bencala and McKnight, 

1987). The discharge profile indicates a gain of 166 ft3

/s. 

Stream segments with sampled inflows contributed 123 ft3/s, 

or 74 percent of the total increase. The remaining 26 percent 

of the increase in streamflow was contributed as dispersed, 

subsurface inflow.

Chemical Characterization of Synoptic Samples

Inflows

The spatial variation of concentrations distinguished 

four groups of inflow samples (table 9). Inflows from Cement 

Creek (C48, inflow group 1) and Mineral Creek (M34, inflow 

group 2) were distinct from all of the other inflow samples 

and also from each other. Cement Creek (C48) was acidic at 

pH 4.11, and thus, aluminum and copper mostly occurred in 

the dissolved phase; iron was split between the dissolved and 

colloidal phases. Owing to the neutralization of Mineral Creek 

by the inflow of the South Fork (M11), Mineral Creek at the 

mouth (M34) is more basic with a pH of 6.87, and the colloidal concentrations of aluminum, copper, and iron were greater 

than the dissolved concentrations. Downstream from Mineral 

Creek, all the other inflow samples (inflow groups 3 and 4, 

table 9) had near-neutral pH, relatively low concentrations of 

metals, and low sulfate concentrations. These two groups of 

samples generally did not influence the stream to any great 

extent.

460 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
Quantification of Metal Loading 461

E1 - 1,818

E2 - 2,793

3,778

E3 - 4,528 

E4 - 5,328

E5 - 5,989 

A72

M34

E6 - 7,479 

A68

1,100 - Upper Animas River

E7 - 10,637 

E8 - 12,607 

Key locations — Number

 is downstream distance along

 study reach, in meters

E2 2,793 

Stream segments — 

 Number is downstream

 distance along study

 reach, in meters

4,018

4,258

A68

Gauging station

107°42' 00" 107°37'00"

37°

49'

00"

37°

44'

00"

0

0 500 1,000 METERS

0.5 1 MILE

Animas River

Molas Lake

Molas Creek

Creek

Elk 

Whitehead Gulch

Sultan Creek

Kendall Gulch

Deadwood

Deer Park Creek

Gulch

Mineral Creek

SILVERTON

Cement

Cr

Animas River

EXPLANATION

C48

Figure 15. Location of study reach, stream segments, and key locations, Animas River, Silverton to Elk Park, 

August 1997 and 1998.
Stream

The greatest changes in stream chemistry occurred 

downstream from Cement Creek (E1) and Mineral Creek (E2; 

figs. 15 and 17). Four distinct groups of stream samples were 

classified by PCA as a result of these changes (table 10). The 

Animas River at Silverton (A68) yielded a unique sample at 

the beginning of the study reach (stream group 1, table 10); 

the sample had a pH of 7.60. The acidic inflow from Cement 

Creek (inflow group 1; table 9) decreased the pH to less than 

7.0 in samples between Cement Creek and Mineral Creek 

(stream group 2). Mineral Creek inflow (inflow group 2, 

table 9), was also slightly acidic, which caused the instream 

pH to decrease below 7.0 in the sample just downstream 

from Mineral Creek (E2); but the remaining samples between 

Mineral Creek and the end of the study reach had pH values 

near 7.0 (stream groups 3 and 4, table 10).

Instream concentrations of iron and copper (fig. 17B, C) 

increased downstream from the inflows of Cement Creek (E1) 

and Mineral Creek (E2). Iron concentration was highest downstream from Cement Creek (E1); iron was present mostly as 

colloidal (fig. 17, downward triangles), rather than dissolved 

(upward triangles). The sample from Cement Creek (C48) 

had 54 percent colloidal iron, and the sample from the upper 

Animas River (A68) had more than 99 percent colloidal iron. 

The sample collected downstream from Cement Creek (E1) 

had 87 percent colloidal iron. Schemel and others (2000) have 

documented the transformation of iron from the dissolved to 

the colloidal iron in this mixing zone. The maximum concentration of colloidal iron occurred downstream from Deer 

Park Creek (E5, fig. 17B), and concentrations consistently 

decreased downstream from there. The pattern of aluminum 

concentration was very similar to that of iron because both 

formed colloids in the mixing zones (Schemel and others, 

2000).

The pattern of copper concentration was similar to the 

pattern of iron concentration (fig. 17C). The greatest increase 

was downstream from Cement Creek (E1), but the concentration also increased downstream from Mineral Creek (E2), 

which had the highest inflow concentration of copper (inflow 

group 2, table 9). Downstream from Cement Creek (E1) and 

Mineral Creek (E2) copper was predominantly in the colloidal phase, which likely was copper sorbed to the abundant 

iron colloids (Runkel and Kimball, 2002). Copper concentrations remained nearly constant along the remainder of the 

study reach (fig. 17C), but the concentration in bed sediment increased (Church and others, 1997), suggesting that 

some colloidal copper was lost to the bed. Total-recoverable 

Figure 16. Variation of chloride concentration and discharge with distance, Animas River, Silverton to Elk Park, 

August 1997 and 1998.

0

0

1

2

3

4

5

2,000 4,000

DISTANCE ALONG STUDY REACH, IN METERS

CHLORIDE CONCENTRATION, IN MILLIGRAMS PER LITER

DISCHARGE, IN CUBIC FEET PER SECOND

6,000 8,000 10,000 12,000

50

100

150

200

EXPLANATION

Chloride, stream, 1997

Chloride, stream, 1998

Chloride, inflows

Calculated discharge

462 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
Quantification of Metal Loading 463

concentrations of copper were near the chronic toxicity 

standard, but dissolved copper was lower than both standards 

along the entire study reach.

Concentrations of dissolved zinc decreased slightly with 

the inflow of Cement Creek (E1) but with the increase in colloidal zinc concentration, the total zinc increased (fig. 17D). 

There was a decrease in both dissolved and colloidal concentrations with the inflow of Mineral Creek (E2). A decrease in 

dissolved zinc concentration upstream from Deer Park Creek 

(E5) corresponded to an equal increase in colloidal zinc concentration. This corresponds to an increase in colloidal iron in 

the same location (fig. 17B). Both dissolved and colloidal zinc 

concentrations remained mostly constant for the remainder of 

the study reach. Dissolved concentrations of zinc exceeded the 

acute and chronic standards along the entire study reach.

Other metal concentrations were also distinct among the 

groups of stream samples (table 10). Manganese concentrations 

systematically decreased from group to group downstream. 

Lead concentrations were less than detection in all the groups; 

however, bed sediment contained substantial lead (Church 

and others, 1997). Besser and others (2001) found that the colloidal concentrations of copper, lead, and zinc are significant to 

the aquatic health in these reaches of the Animas River.

Mass-Load Profiles

Because the Elk Park study includes all three upstream 

basins, it provides the opportunity to compare the basin contributions to the Animas River downstream from Silverton, and in 

doing so, to compare the principal locations of loading among 

the three upstream basins. The load profiles fall into two groups 

(fig. 18), those solutes that were affected by colloidal concentrations (including aluminum, copper, and iron), and those that 

were not (sulfate, strontium, manganese, and zinc). A summary of load calculations, indicating the change in cumulative 

instream load along selected sections of the study reach, is 

presented in table 11.

Table 9. Chemical composition of selected inflow samples representing groups defined by principal component analysis, Animas 

River, Silverton to Elk Park, August 1997 and 1998.

[Phase: Diss, dissolved; Coll, colloidal; all concentrations in milligrams per liter; (97), 1997 only; <, less than; NM, not measured]

Phase Inflows

1 2 34

Site description Cement Creek 

at mouth (97)

Mineral Creek 

at mouth (97)

Deer Park 

Creek

Whitehead 

Gulch

Distance (m) 1,166 2,538 5,749 9,482

pH, in standard units 4.11 6.87 7.74 7.91

Calcium Diss 155 47.2 21.4 20.5

Magnesium Diss 7.77 3.83 2.59 2.04

Sodium Diss 6.27 2.34 1.32 1.54

Alkalinity, as CaCO3 Diss <1 NM NM 50.1

Sulfate Diss 473 131 11.9 13.2

Chloride Diss 4.35 .550 .170 .140

Silica Diss 12.4 5.38 1.62 1.80

Aluminum Diss 4.53 .025 .020 .020

Coll .403 1.71 .020 .020

Cadmium Diss <.001 <.001 <.001 <.001

Coll <.001 <.001 <.001 .002

Copper Diss .021 .003 .013 .005

Coll <.002 .046 <.002 <.002

Iron Diss 2.97 .237 .007 .002

Coll 3.92 2.07 .009 .009

Manganese Diss 1.59 .254 .001 .000

Coll .086 .002 .001 .001

Nickel Diss .006 <.003 .005 <.003

Lead Diss .037 <.023 <.023 .034

Coll <.023 <.023 <.023 <.023

Strontium Diss 1.62 .412 .193 .222

Coll .084 .008 .012 <.008

Zinc Diss .620 .212 .025 .007

Coll .028 .032 <.001 <.001
B

0 2,000 4,000 6,000 8,000 10,000 12,000 14,000

A

0 2,000 4,000 6,000 8,000 10,000 12,000 14,000

DISTANCE ALONG STUDY REACH, IN METERS

4.0

4.5

5.0

5.5

6.0

6.5

7.0

7.5

8.0

8.5

pH, IN STANDARD UNITS

1E-3

0.01

0.1

1

10

IRON CONCENTRATION,

IN MILLIGRAMS PER LITER

A68 A68

A72

A72

E1 E1

E2 E2

E8 E8

E7 E7

E5 E5

Figure 17. Variation of A, pH; of dissolved and colloidal concentrations of B, iron; and total-recoverable concentrations 

of C, copper; and D, zinc, with distance, Animas River, Silverton to Elk Park, August 1997 and 1998. Groups of stream 

samples (diamonds or upward triangles, dissolved; downward triangles, colloidal), and inflows (stars) are indicated 

by colors: 1, blue; 2, green, 3, yellow; 4, orange. Groups were determined by principal component analysis, and their 

chemistry is summarized in tables 9 and 10. Labels on vertical dashed lines refer to locations in figure 15. C, D, Blue line, 

acute toxicity standard; red line, chronic toxicity standard.

464 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
Quantification of Metal Loading 465

D

0 2,000 4,000 6,000 8,000 10,000 12,000 14,000

C

0 2,000 4,000 6,000 8,000 10,000 12,000 14,000

DISTANCE ALONG STUDY REACH, IN METERS

COPPER CONCENTRATION,

IN MILLIGRAMS PER LITER

1E-3

0.01

0.1

1E-3

0.01

0.1

1

ZINC CONCENTRATION,

IN MILLIGRAMS PER LITER

A68

A72

E1

E2

E8

E7

E5

A68

A72

E1

E2

E8

E7

E5

Figure 17—Continued. Variation of total-recoverable concentrations of C, copper; and D, zinc, with distance, Animas 

River, Silverton to Elk Park, August 1997 and 1998. Groups of stream samples (diamonds or upward triangles, dissolved; 

downward triangles, colloidal), and inflows (stars) are indicated by colors: 1, blue; 2, green, 3, yellow; 4, orange. Groups 

were determined by principal component analysis, and their chemistry is summarized in tables 9 and 10. Labels on 

vertical dashed lines refer to locations in figure 15. Blue line, acute toxicity standard; red line, chronic toxicity standard.
The colloidal phase was the dominant form of transport 

for aluminum, iron, and copper (table 10). Inflows of Cement 

Creek (C48) and Mineral Creek (E2) added substantial aluminum load to the stream (fig. 18A). Mass-loading patterns of 

five metals, described next, illustrate the contributions of the 

different basins.

Aluminum

Aluminum loading for the Elk Park study reach reveals 

an important difference between two methods of accounting 

for a watershed load. The first method is to account for the 

load at the outlet of a basin, catchment, or watershed; this is 

a traditional way to account for load and has many uses. The 

second method is to account for load by using the cumulative 

instream load from the mass-loading analysis within the basin, 

catchment, or watershed. These two methods differ between 

a generalized view for the outlet method and a detailed view 

for the instream method. Mass-loading data from the Elk Park 

study reach (table 11) represent an outlet view, or the contributions of the Animas River, Cement Creek, and Mineral 

Creek by just accounting for the load observed in the Animas 

River. With the outlet view the Animas River contributes 

1.6 percent of the cumulative load of aluminum (10.1 kg/day 

divided by 640 kg/day), Cement Creek contributes 33 percent, and Mineral Creek contributes 45 percent (table 11). 

The remaining 20 percent of load for aluminum along the 

Elk Park study reach comes from sources downstream from 

Mineral Creek (table 11). These sampled instream loads for 

individual stream segments along the Elk Park study reach differ substantially from the instream view that comes from the 

cumulative instream load determined for each of the upstream 

basins (tables 2, 5, and 8). For example, the inflow load for 

the Animas River in the Elk Park study was 10.1 kg/day 

(table 11), but the cumulative instream load for the Animas 

River from combining the California Gulch, Eureka, and 

Howardsville studies was 116 kg/day (table 2). The difference 

Table 10. Chemical composition of selected stream samples representing groups defined by principal component analysis, Animas 

River, Silverton to Elk Park, August 1997 and 1998.

[Phase: Diss, dissolved; Coll, colloidal; all concentrations in milligrams per liter; (97), 1997 only; <, less than; TR, tracer salt; NM, not measured]

Phase Stream

12 3 4

Site description Animas River at 

Silverton A68 (97)

Upstream from 

Mineral Creek (97)

Downstream from 

Deadwood Gulch

Downstream from 

small inflow

Distance (m) 1,100 2,478 4,528 7,894

pH, in standard units 7.60 6.99 7.00 6.86

Calcium Diss 45.8 68.7 56.6 55.3

Magnesium Diss 2.72 3.83 3.73 3.69

Sodium Diss TR TR TR TR

Alkalinity, as CaCO3 Diss NM NM 19.7 27.4

Sulfate Diss 90.0 174 161 153

Chloride Diss TR TR TR TR

Silica Diss 3.50 5.39 5.27 5.03

Aluminum Diss .020 .047 .038 .040

Coll .051 1.098 1.417 1.225

Cadmium Diss <.001 .004 .003 .003

Coll <.001 <.001 <.001 <.001

Copper Diss .002 .002 .004 .006

Coll <.002 .012 .012 .013

Iron Diss .002 .250 .164 .004

Coll .324 1.50 1.32 1.46

Manganese Diss 1.20 1.12 .649 .594

Coll .026 .042 .027 .020

Nickel Diss <.003 .004 <.003 .004

Lead Diss <.023 <.023 <.023 <.023

Coll <.023 <.023 <.023 <.023

Strontium Diss .450 .697 .537 .527

Coll <.008 .018 .025 .015

Zinc Diss .409 .368 .282 .223

Coll .040 .084 .029 .077

466 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
Quantification of Metal Loading 467

Figure 18. Variation of normalized instream loads for A, aluminum, copper, iron; B, manganese, zinc; C, strontium, and 

sulfate with distance, Animas River, Silverton to Elk Park, August 1997 and 1998. Labels on vertical lines refer to locations 

of substantial change along the study reach in figure 15.

0 2,000 4,000 6,000 8,000 10,000 12,000

C DISTANCE ALONG STUDY REACH, IN METERS

A

B

0.0

0.2

0.4

0.6

0.8

1.0

0.0

0.2

0.4

0.6

0.8

1.0

0.0

0.2

0.4

0.6

0.8

1.0

NORMALIZED LOAD

A68 A68 A68

A72 A72 A72

E1 E1 E1

E2 E2 E2

E8 E8 E8

E7 E7 E7

E5

E5

E5

Manganese

Zinc

Strontium

Sulfate

Aluminum

Copper

Iron
can be attributed to the attenuation of aluminum load that 

occurs upstream from the A68 gauge. Much of the aluminum 

load from the California Gulch study is effectively removed 

from the stream water through the braided reach downstream 

from Eureka (Paschke and others, 2005). Attenuation within 

the basin, upstream from the accounting site at the outlet, 

makes the apparent contribution from the upper Animas River 

basin at A68 (the outlet method) much smaller than the cumulative instream load from the detailed studies upstream from 

A68 (fig. 19A).

The large difference for aluminum and other metal 

loads (fig. 19) points out the difference between having the 

outlet view and the instream view. The outlet view gives 

an accounting of the load that affects the Animas River 

downstream from these basins, but it cannot indicate where the 

greatest sources of aluminum load occur. Indeed, some of the 

most substantial sources of constituent loading could go undetected using the outlet view because of the possible effects of 

attenuation. None of the detail that is necessary to make decisions about remediation is available. On the other hand, the 

instream view provides the detailed understanding that helps 

to facilitate decisions. This is all a matter of scale for a loading 

study. For example, the detailed loadings from the studies in 

the Animas River, Cement Creek, and Mineral Creek all use 

the outlet view to account for inflows within those basins 

along the study reaches. An appropriate scale must be selected 

depending on the questions being asked and the resources 

available for the study.

Taking the instream view from each of the basins, the principal locations of mass loading for aluminum can be compared 

among the basins for the entire watershed study area (fig. 20; 

table 12). The bars for aluminum load indicate that the load 

from Middle Fork Mineral Creek (M9) was the greatest of all 

sources, accounting for 23 percent of the combined cumulative 

instream loads (table 12). Combined with the other locations 

that are listed in table 12, these locations account for 73 percent 

of the total aluminum load. In Cement Creek, the Prospect 

Gulch area and the Minnesota Gulch area were both important for contributions of aluminum load. In the Animas River, 

downstream from Silverton, the area below the Mineral Creek 

confluence also was important.

Iron

Like aluminum loads, iron loads differ between outlet 

and cumulative instream views for each of the basins. The outlet loads only represent a fraction of the cumulative instream 

load that was determined for each of the basins (fig. 19B). 

Taking the more detailed view of the cumulative instream 

loads, Cement Creek contributed 49 percent of the load at A72 

(gauge location, fig. 15), Mineral Creek contributed 43 percent, 

and the Animas River contributed 4 percent (table 12). These 

differences reflect the location of Cement Creek and Mineral 

Creek mostly within the altered rock of the Silverton caldera 

and the location of the upper Animas River more in areas 

that were affected by propylitic alteration and not AS or QSP 

alteration. This pattern also corresponds with the majority of 

ferricrete occurrences in the watershed (Yager and Bove, this 

volume, pl. 2). Substantial iron load entered the Animas River 

with the inflow of Deer Park Creek (E5, fig. 18). Most of the 

iron load downstream from Deer Park Creek was transported 

downstream. This might, in part, account for the iron stain 

on streamside boulders along much of the canyon. Iron stain 

Table 11. Summary of load calculations and change of instream load for selected sections of the study reach, Animas River, Silverton 

to Elk Park, August 1997 and 1998.

[Al, aluminum; Cu, copper; Fe, iron; Mn, manganese; Sr, strontium; Zn, zinc; SO4, sulfate; distance, in meters; all loads in kilograms per day; number in parentheses indicates ranking of load for each constituent. Note that “below” and “above” indicate “downstream from” and “upstream from”]

Al Cu Fe Mn Sr Zn SO4

Cumulative instream load 640 11.2 914 300 241 144 68,890

Cumulative inflow load 532 11.5 746 290 207 132 56,893

Percent inflow 83.2 102 81.6 96.7 85.8 91.4 82.6

Unsampled inflow 108 <0 169 9.88 34.3 12.4 11,998

Percent unsampled 16.8 <1 18.4 3.29 14.2 8.59 17.4

Attenuation 49.4 4.28 148 52.1 0.00 0.00 2,510

Percent attenuation 7.72 38.1 16.2 17.4 0.00 0.00 3.64

Site Dist Al Cu Fe Mn Sr Zn SO4

Animas River above Silverton (A68) 1,100 10.1 (5) 1.14 (3) 40.7 (5) 174 (1) 59.3 (3) 59.4 (1) 12,679 (3)

Downstream from Cement Creek (E1) 1,818 208 (2) 1.81 (2) 290 (1) 48.3 (3) 61.8 (2) 25.6 (3) 19,261 (2)

Downstream from Mineral Creek (E2) 2,793 289 (1) 5.06 (1) 253 (2) 49.4 (2) 75.8 (1) 30.6 (2) 22,520 (1)

A72 gauge (A72) 3,778 71.2 (3) 0.0 75.4 (4) 28.5 (4) 16.1 (4) 17.4 (4) 6,137 (4)

Below Deer Park Creek (E5) 5,989 62.7 (4) 0.8 (4) 185 (3) 0.0 14.0 (5) 0.0 2,604

Below Whitehead Gulch (E7) 9,772 0.0 0.0 0.0 0.0 13.9 0.0 0.0

Below Elk Park Creek (E8) 12,607 0.0 0.0 0.0 0.0 0.0 11.2 (5) 3,991 (5)

468 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
Quantification of Metal Loading 469

A

B

C

D

0

50

100

150

200

ZINC LOAD,

IN KILOGRAMS PER DAY

0

5

10

15

20

25

30

COPPER LOAD,

IN KILOGRAMS PER DAY

0

200

400

600

800

1,000

1,200

IRON LOAD,

IN KILOGRAMS PER DAY

0

100

200

300

400

500

600

ALUMINUM LOAD,

IN KILOGRAMS PER DAY

ANIMAS RIVER CEMENT CREEK MINERAL CREEK

ANIMAS RIVER CEMENT CREEK MINERAL CREEK

ANIMAS RIVER CEMENT CREEK MINERAL CREEK

ANIMAS RIVER CEMENT CREEK MINERAL CREEK

Outlet load

Cumulative instream load

Outlet load

Cumulative instream load

Outlet load

Cumulative instream load

Outlet load

Cumulative instream load

Figure 19. Comparison of sampled instream load for the Elk Park study reach (outlet load) with cumulative 

instream load for the individual basin studies for A, aluminum; B, iron; C, copper; D, zinc.

extended above stream level and most likely was deposited 

on the rocks during high flow. Church and others (1997) 

detailed how the colloidal iron load continued all the way 

into New Mexico, more than 180 km downstream.

Also like aluminum, iron was transported mostly in 

the colloidal phase (for example, see each stream group, 

table 10), and the segments that were important for aluminum loading also were important for iron loading (fig. 18A). 

On a watershed scale, mass loading of iron was dominated 

by the inflow from Middle Fork Mineral Creek, which was 

21 percent of the watershed total upstream from the A72 

gauge (fig. 21). In Cement Creek, Prospect Gulch contributed 11 percent and the iron bog contributed 6 percent of 

the watershed total. The contribution around Prospect Gulch 

was mostly unsampled inflow. In Mineral Creek, the Anvil 

Mountain area and the dispersed inflow above Porphyry 

Gulch each contributed more than 5 percent to the total iron 

load (fig. 21; table 12). The 23 locations in table 12 account 
for 74 percent of the cumulative instream load of iron. This 

is similar to the percentages for aluminum and zinc, and is 

lower than the percentage for copper because sources of iron 

throughout the watershed are more dispersed, and not just 

present with base-metal deposits.

Iron colloids in the Animas River watershed study area 

have a role in the transport of copper, zinc, and other metals 

(Schemel and others, 2000). The sequence of iron transformation has been studied in laboratory experiments (Grundl 

and Delwiche, 1993) and quantified in streams affected 

by mine drainage (Kimball and others, 1994). Steps of this 

transformation occur within the time frame of transport 

through individual stream segments in the Animas River, 

indicating rates of reaction on the order of seconds. The presence of high concentrations of colloidal iron can have two 

effects. First, the high concentrations of colloidal iron affect the 

streambed habitat as this material is trapped by algae on cobbles 

and fills interstices in the cobbles and gravels (Woodward and 

others, 1995; Clements, 1994). This decreases the pore space 

that is inhabited by benthic invertebrates. Second, the colloidal 

iron surface accumulates metals through sorption (Webster 

and others, 1998). Benthic invertebrates consume iron colloids 

Figure 20. Areas of relative importance for aluminum mass loading, Animas River watershed study area.

EXPLANATION

Surface inflow

Unsampled inflow

0

50

100

150

200

250

300

ALUMINUM LOAD, IN KILOGRAMS PER DAY

470 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
Quantification of Metal Loading 471

Table 12. Summary of mass loading for selected metals, Animas River watershed study area.

[Label, symbol used on maps and figures; Al, aluminum; Fe, iron; Cu, copper; Mn, manganese; Zn, zinc; all loads are in kilograms per day; numbers in parentheses 

indicate stream segments that were combined for these sums within each subbasin; blanks indicate no significant loading]

Basin Label Description Al Fe Cu Mn Zn

Animas Total (California Gulch + Eureka + Howardsville – overlaps) 116 82.9 4.60 333 129

Cement Total (Upper + Lower minus North/South Forks) 531 1,040 14.0 210 166

Mineral Total 526 910 27.4 102 99

Elk Total (between A68 and A72, less Cement and Mineral) 71.2 75.4 0 28.5 17.4

Total at A72 1,240 2,110 46 674 411

Basin Segment or area description

Mineral M1 Junction mine inflow 7.99 67.6 7.99 2.84 18.9

Mineral M4 Dispersed inflow upstream from Porphyry Gulch 9.94 107 12.6 2.30 35.0

Mineral M9 Middle Fork 293 450 1.15 36.2 10.5

Mineral Near M12 Anvil Mountain area 105 160 .78 21.0 11.7

Cement C1 Grand Mogul and Queen Anne 3.68 2.02 .62 3.77 6.31

Cement C2 Mogul mine 32.3 25.8 8.30 19.0 61.6

Cement C3 North Fork 23.9 96.5 3.87 8.59 37.0

Cement C4 Sunnyside mine 16.2

Cement C5 South Fork 20.4 64.7 13.3

Cement C6 Prospect Gulch area (2785, 2970, 3125, 3185) 74.8 229 .85 19.1 8.07

Cement C7 Iron bog (3230, 3317) 22.2 68.9 6.20 1.71

Cement C8 Minnesota Gulch area (5356, 5652, 5767) 87.4 57.1 .40 33.4 13.3

Cement C10 Ohio Gulch 31.3 33.4 18 4.02

Cement C11 Illinois Gulch / Yukon 25.8 14.5 6.13

Cement C12 Lower bog (9643, 9905) 32.1 68.7 12.8 6.79

1

Animas Downstream 

from A1

Acid springs (790 through 1586) 43.5 0.959 0.20 105 15.9

Animas A2 Placer Gulch (4448, 4762) 4.98 2.23 0.17 15.5 9.24

Animas A3 North Fork area (5634 through 6128) 23.0 5.87 0.36 11.2 18.7

Animas A4 Eureka Mill 1.51 .80 .46 2.07 6.67

Animas A6 Tailings drainage near Howardsville 12.0 42.6 .43 35.5 27.8

Animas A8 to A9 Arrastra Creek to Boulder Gulch 6.80 9.39 1.12 32.6 9.84

Animas A9 to A10 Downstream from Boulder Gulch to end of tailings 9.22 0 0.79 87.9 14.9

Elk A72 Downstream from Mineral Creek 71.2 75.4 0 28.5 17.4

Total 910 1,567 40.0 586 318

Percent of total 73 74 87 87 77

1

Several of the Animas sums are calculated differently from sums in table 2.

along with algae in biofilm, introducing sorbed metals to the 

food chain. Colloidal iron has been shown to dissolve in the 

digestive system of fish and release metals (Gasser and others, 

1996).

Copper

Even though problems of copper contamination arose 

for the ultrafiltrate samples, we could still calculate loads 

using the total-recoverable concentrations (fig. 18A). In general, the pattern of copper load resembled that of aluminum 

and iron because of the tendency of copper to be sorbed by 

colloidal solids at the near-neutral pH values of the Animas 

River (Smith, 1999). Accounting for copper load through the 

individual cumulative instream loads from the three upstream 

basins gives differences with the outlet view that are similar to 

the differences for aluminum and iron (fig. 19C). The copper 

load from the Mineral Creek basin was 60 percent of the total 

at A72. Cement Creek contributed 30 percent of the load and 

the Animas River contributed 4 percent. Large differences 

between the outlet view and the cumulative instream loads for 

copper again point out the need for a detailed spatial accounting to understand the scale of metal loading (fig. 19C).

The partitioning of copper was similar to that of iron 

because the relatively low pH inflow of Cement Creek had 

mostly dissolved copper, and the higher pH inflow of Mineral 

Creek had mostly colloidal copper. Dissolved copper from 

Cement Creek was transformed to colloidal copper in the mixing zone downstream (Schemel and others, 2000). Through the 

canyon to Elk Park, the total copper load increased at 4,258 m 

(fig. 15), but the source of this copper load was not obvious.

The 23 areas that are listed in table 12 account for 

87 percent of the copper loading in the watershed study 

area. Among those areas, the Junction mine inflow (M1), 

the dispersed inflow above Porphyry Gulch (M4), the Anvil 

Mountain area (near M12), the Mogul mine (C2), and North 
Fork Cement Creek (C3) contributed the greatest loads 

(fig. 22). A substantial part of this mass loading is due to 

alteration zones dispersed throughout the watershed, which 

is reflected in the large portion of load that occurred as 

unsampled inflow.

Manganese

Dissolved manganese concentration was much greater 

than the colloidal concentration along the entire study reach 

(similar to zinc, fig. 17D; table 10). The normalized load 

profile of manganese indicates the large contribution from 

the upper Animas River basin (A68 gauge), and smaller 

loads from Cement Creek (E1) and Mineral Creek (E2). 

A substantial increase in manganese load also occurred near 

the A72 gauge. Through the Animas River canyon loss of 

manganese was minimal. Percent contribution for each of 

the basins, which was calculated by using the cumulative 

instream loads, indicates that 49 percent of the load at A72 

comes from the upper Animas River, 31 percent from Cement 

Creek, 15 percent from Mineral Creek, and 4 percent from 

sources near A72 (table 12). The areas listed in table 12 

accounted for 87 percent of the total load of manganese 

at A72.

Figure 21. Areas of relative importance for iron mass loading, Animas River watershed study area.

0

100

200

300

400

500

IRON LOAD, IN KILOGRAMS PER DAY

EXPLANATION

Surface inflow

Unsampled inflow

472 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
Quantification of Metal Loading 473

Mass loading of manganese, slightly different from that 

of other metals, points out additional locations that are significant for metal loading in the watershed (fig. 23). The greatest 

contributions to manganese load are from the acid springs in 

California Gulch (downstream from A1; 15 percent), downstream from Boulder Gulch (A9 to A10, but not including 

Boulder Gulch) to the end of tailings in the upper Animas 

(13 percent), the Anvil Mountain area (near C12; 5 percent), 

and Middle Fork Mineral Creek (M9; 5 percent), and the tailings drainage near Howardsville (A6; 5 percent) (figs. 2, 7, 

11). Manganese load principally results from the weathering 

of gangue minerals near the Eureka graben (Bove and others, 

this volume). Some of this load in the downstream subreach 

of the upper Animas River basin could be the result of the 

accumulated tailings piles that have been used to store tailings 

from many sites throughout the watershed study area.

Zinc

The pattern of zinc loading is comparable to the pattern 

of manganese, mostly because of the large contribution from the 

upper Animas River basin (fig. 18B). Dissolved zinc concentrations were much greater than colloidal concentrations along 

0

2

4

6

8

10

12

14

COPPER LOAD, IN KILOGRAMS PER DAY

EXPLANATION

Surface inflow

Unsampled inflow

Figure 22. Areas of relative importance for copper mass loading, Animas River watershed study area.
the entire study reach (table 10). Even though zinc transport 

was conservative along the Elk Park study reach (fig. 18B), 

attenuation of zinc was still substantial within the three 

upstream basins. This attenuation is indicated by the substantial 

differences for zinc in the comparison between the outlet view 

and the instream views (fig. 19D). The greatest contribution to 

the load of zinc at A72 was from Cement Creek, which contributed 40 percent. The Animas River contributed 31 percent and 

Mineral Creek contributed 24 percent (table 12). The greatest 

source of zinc was in the core of the Silverton caldera where 

the Eureka graben structures and other caldera-related basemetal-bearing structures were weathered or mined.

Mass loading of zinc was more evenly dispersed 

among the 23 areas, but the combined loading from these 

areas accounted for 77 percent of the cumulative instream 

load of zinc upstream from A72 (fig. 24; table 12). This 

Figure 23. Areas of relative importance for manganese mass loading, Animas River watershed study area.

0

25

50

75

100

125

MANGANESE LOAD, IN KILOGRAMS PER DAY

EXPLANATION

Surface inflow

Unsampled inflow

474 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
Quantification of Metal Loading 475

more dispersed pattern reflects the widespread occurrence of 

zinc in alteration zones. Areas with the greatest mass loading 

were the dispersed inflows upstream from Porphyry Gulch 

in Mineral Creek and the Mogul mine in Cement Creek. 

These two accounted for 9 and 14 percent of the cumulative 

instream zinc load, respectively. Several major contributions 

of zinc load occurred as unsampled inflow. Similar to the 

sources for copper loads, the dispersed inflows upstream from 

Porphyry Gulch in Mineral Creek had a substantial amount 

of unsampled inflow. In addition, the contributions in the 

upper Animas River basin, downstream from Boulder Gulch 

to the end of the capped tailings repositories, and in the Elk 

Park basin, below Mineral Creek, were principally unsampled 

inflow.

Figure 24. Areas of relative importance for zinc mass loading, Animas River watershed study area.

0

20

40

60

ZINC LOAD, IN KILOGRAMS PER DAY

EXPLANATION

Surface inflow

Unsampled inflow
Summary and Conclusions

Tracer-injection and synoptic-sampling methods determined the locations and quantity of loading to three basins in 

the Animas River watershed. Much of the metal loading can 

be attributed to 23 specific areas in the watershed. Although 

these areas are prominent because of the large loads, numerous other sources exist, even though their loads were small in 

comparison to loads from these 23 areas. After transport in 

Cement Creek and the Animas River, many of the metals are 

partitioned between dissolved and colloidal phases by chemical reactions in mixing zones downstream from the confluence 

of these two streams. These reactions produce substantial 

colloidal material that affects the transport of metals that sorb 

to the colloids. Deposition of this material on the streambed 

provides a route for metals to enter the food web and affect 

the chronic toxicity in fish populations downstream. However, 

part of the colloidal load is transported for more than 100 km 

downstream, possibly affecting aquatic health for a long distance from the Animas River watershed study area.

Loading patterns that have been documented from the 

mass-loading studies have important implications for possible remediation. When a watershed is dominated by distinct 

sources, and those sources contribute such a high percentage 

of the total loads, it is obvious that the most effective remediation could be done by focusing efforts on those sources. Remediation efforts of the many smaller sources of metals would 

have limited influence on stream recovery if no improvements 

to the larger sources took place.

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478 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
Quantification of Metal Loading 479

Sampling and Chemical Analysis

A general discussion of the sampling procedure is 

included here, although procedural details among the 

10 studies actually varied as noted. Investigators began synoptic sampling at the downstream end of the study reach and 

moved upstream to avoid sampling suspended materials that 

they disturbed by walking in the streambed. Inflows and stream 

sites that were considered to be well mixed were sampled by 

using grab techniques. Sites that were not well mixed (commonly determined by specific-conductance measurements 

across the stream) were sampled by equal-width integration 

(Ward and Harr, 1990). An inflow is designated left or right 

bank looking downstream.

Samples were collected in 1.8-L bottles and were transported to a central processing area after being placed in black 

plastic bags, to avoid exposure to direct sunlight (McKnight 

and others, 1988). The collected samples for each study except 

the 1996 Cement Creek study were divided into raw (unfiltered) unacidified samples (RU), raw acidified samples (RA), 

filtered unacidified samples (FU), filtered acidified samples 

(FA), and ultra-filtered acidified samples (UFA). Filtration was 

with a tangential flow unit equipped with a 0.45-μm membrane for the FA and FU samples, and with 10,000-Dalton 

molecular-weight membranes for the UFA samples. Filtration 

equipment was acid-rinsed between samples and each new 

membrane was rinsed with reagent-grade water, followed by 

250 mL of sample before collecting the filtrates. Aliquots for 

Fe speciation were placed in amber bottles and were preserved 

with concentrated HCl to fix the Fe(II)/Fe(III) ratio in UFA 

samples (To and others, 1998). Specific conductance and pH 

were determined from the RU sample. Aliquots for metal analysis were acidified to pH less than 2.0 with ultrapure HNO3

. 

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 ion chromatography 

(Kimball and others, 1999). Total alkalinity was determined 

from the FU sample by titration.

Use of two filtration membranes provides for three operationally defined concentrations for each metal. The RA sample 

provides a measure of the total-recoverable metal concentration (dissolved+colloidal), and the UFA sample provides the 

dissolved metal concentration. Filtration for metals with the 

0.45-μm membranes (FA) is used for comparison with the 

UFA filtration because aquatic standards commonly are in 

terms of 0.45-μm filtration. Colloidal metal concentrations are 

defined as the difference between the total-recoverable (RA) 

and the ultrafiltrate metal concentrations (UFA) (Kimball 

and others, 1995). For the 1996 Cement Creek study, there 

was only one filtration using a 0.1-mm filter and a pressure 

filtration system (Kimball and others, 2002). This filtration 

led to an operationally different, but comparable definition 

of dissolved and colloidal concentrations.

An unexpected result occurred with the filtration of 

samples collected for the Eureka study reach. Concentrations 

of dissolved copper in ultrafiltrates were consistently higher 

than concentrations of 0.45-μm-filtered copper and sometimes 

greater than the total-recoverable concentration. This likely 

indicates contamination of copper in the ultrafiltrate sample 

that did not occur in the other filtrates, nor for other metals. 

This contamination occurred in both mass-loading studies in 

1998, and was a factor in the Elk Park study reach also. Generally, this only affected samples in which copper concentration 

was less than about 30 μg/L. Because of this contamination, 

the 0.45-μm concentration was used as the dissolved copper 

concentration for this study reach. Because total-recoverable 

concentrations were used to calculate loads, those calculations 

were not affected by the contamination.

Tracer Injections and Stream Discharge

Quantifying discharge in mountain streams by the 

traditional velocity-area method (Rantz and others, 1982) 

is compromised by 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, a condition that may result in an underestimate of 

constituent loads (Zellweger and others, 1989). Measurement 

of discharge using the velocity-area method does not account 

for flow through the hyporheic zone. 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 herein, numerous (often, about 60) instream samples were collected during 

a single day to characterize stream chemistry at steady state. 

To perform velocity-area discharge measurements in conjunction with sample collection at the large number of sites that are 

needed is problematic, if not impossible.

An alternative means of estimating discharge used here 

is the tracer-dilution method (Kilpatrick and Cobb, 1985). 

The tracer-dilution method uses an inert tracer that is continuously injected into the stream at a constant rate and 

concentration. Given sufficient time, all parts of the stream 

including side pools and the hyporheic zone will become 

saturated with tracer and instream concentrations will reach 

a plateau (Kimball and others, 2002). Decreases in plateau 

concentration with stream length reflect the dilution of tracer 

by additional water entering the channel (surface- and groundwater inflow). Consideration of this dilution allows for the 

calculation of discharge at each stream site. Application of 

Appendix 1. Methods
the tracer-dilution method addresses both limitations of the 

area-velocity method because (1) the tracer enters porous areas 

of the streambed such that flow through the hyporheic zone is 

accounted for; and (2) the collection of tracer samples when 

plateau concentrations are achieved provides the ability to 

obtain discharge estimates at numerous locations.

Successful implementation of the tracer-dilution method 

is dependent on several key factors. (1) First and foremost, 

the injected tracer must be transported through the stream 

system in a conservative manner; that is, concentrations of 

the tracer should be unaffected by biogeochemical reactions. 

Tracers used include dyes and inorganic salts. The degree 

to which a given tracer is conservative is often a function of 

stream pH. Inorganic salts containing lithium, for example, 

are often used in acidic environments due to the conservative 

nature of lithium at low pH. In consideration of the range of 

pH found in the Animas River watershed, our investigations 

used a number of different inorganic salts in the individual 

studies described herein. Previous studies have documented 

the transport, chemistry, and toxicity of these inorganic tracers (Bencala and others, 1990; Broshears and others, 1993; 

Zellweger, 1994; Tate and others, 1995). (2) Another key 

factor is the ability to maintain a constant rate during the continuous tracer injection. For the studies described here, 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. Additional details on specific tracer 

injections are included in the sections describing the basins.

Kilpatrick and Cobb (1985) presented a simple mass 

balance equation used to determine discharge when fluorescent dyes are used to implement the tracer-dilution method. 

Although the use of dyes is straightforward, their use is 

precluded in acidic waters due to sorption reactions that act to 

artificially dilute the added tracer (Bencala and others, 1983). 

Simple inorganic salts (sodium chloride, for example) were 

used instead. Use of these salt tracers necessitates the use of 

alternate equations for discharge determination, as described 

here. As in the work of Kilpatrick and Cobb (1985), these 

equations are based on a simple mass balance that considers 

the concentration and injection rate of the added tracer. Owing 

to the different types of tracers used in the Animas River studies, three different sets of equations are needed. Each equation 

set assumes that the concentration of the added tracer is much 

greater than the naturally occurring concentration. All concentration variables expressed herein refer to tracer concentrations 

at the time of synoptic sampling, except for those including 

the superscript “P,” which refers to a “presynoptic” sample.

Tracer-Dilution Case I: Uniform Background 

Concentrations

Inorganic salts containing lithium and bromide were used 

in several of the tracer injections. In mountain stream environments in which the rocks are mainly igneous, concentrations 

of lithium and bromide are typically low, with background 

concentrations at or near the detection limits. Spatial variability in background concentrations is also low, such that 

background concentrations are nominally uniform. Given the 

assumption of uniform background concentrations, stream 

discharge at any location downstream from the injection is 

given by:

D B

INJ INJ

D C

Q C Q = (1)

where

QD is stream discharge, in L/s,

QINJ is the injection rate, in L/s,

CINJ is the injectate concentration, in mg/L,

CD is the tracer concentration at plateau, in mg/L,

and

CB is the naturally occurring background 

concentration, in mg/L.

Tracer-Dilution Case II: Non-Uniform Background 

with a Presynoptic Sampling

Due to their low background concentrations, lithium 

and bromide are ideal tracers for use in tracer-dilution studies. 

Inorganic salts containing lithium and bromide are relatively 

expensive, however, and alternate tracers may be preferable 

when discharge rates are high, or when the injection will be 

for a long period or will cover a long stream reach. Several 

studies described herein, therefore, involve the injection of 

sodium chloride, where the chloride ion is used as a conservative tracer. Because of the effects of natural sources and 

anthropogenic activities (road salting and dust management, 

for example), background chloride concentrations are neither 

low nor uniform in many situations.

Non-uniform background conditions may be addressed 

by the addition of presynoptic sampling, just prior to the start 

of the tracer injection. During presynoptic sampling, samples 

are collected at each of the stream sites that are to be sampled 

during the main synoptic. These presynoptic samples are analyzed for the tracer of interest (chloride, for example) and used 

to correct the observed tracer concentrations for the spatially 

variable background concentrations. Presynoptic and synoptic 

discharges are assumed equal, and stream discharge at any 

location downstream from the injection is given by:

P

D D

INJ INJ

D C

Q C Q = (2)

where

P CD is the presynoptic estimate of the naturally 

occurring background concentration, in 

mg/L, and all the other terms are defi ned 

as in equation 1.

480 Environmental Effects of Historical Mining, Animas River Watershed, Colorado

-C

- C
Quantification of Metal Loading 481

Tracer-Dilution Case III: Non-Uniform 

Background without a Presynoptic Sampling

The final case concerns the use of a tracer with nonuniform background concentration, such as chloride, when 

a presynoptic either is not conducted or is invalid owing to a 

change in flow regimes. In this situation, non-uniform background concentrations are addressed by considering the tracer 

concentrations of the inflow waters entering the channel within 

each subreach. For some subreaches, these inflow waters will 

be well-defined surface inflows that are easily sampled during 

the main synoptic. In other subreaches, inflow waters may be 

primarily dispersed, ground-water inflows that are unsampled 

during the main synoptic. These subreaches require estimation 

of the tracer-inflow concentration, a process that can lead to 

considerable uncertainty in the discharge calculations.

Tracer-dilution estimates of discharge for this final case 

are made in downstream order, starting with the first synoptic 

site below the injection. Under the assumption that negligible 

inflow enters the stream between the injection site and the first 

synoptic site, stream discharge at the first synoptic site is given 

by:

C 0

Q C Q

D

INJ INJ

D = (3)

where

 C0

 is the naturally occurring background 

concentration upstream of the injection, in 

mg/L, and all the other terms are defi ned as 

in equation 1. Discharge estimates for the 

remaining synoptic sites are given by:

D L

U U L

D C

Q C Q = ( ) (4)

where

 QU is the stream discharge for the synoptic site 

immediately upstream, in L/s,

 CU is the plateau tracer concentration for the 

synoptic site immediately upstream,

and

 CL is tracer concentration in the infl ow waters 

entering a given subreach, in mg/L, and all 

the other terms are defi ned as in equation 1.

Synoptic Sampling and Analytical Methods

Synoptic sampling is needed to quantify water chemistry 

and discharge for instream load calculations. This sampling 

scheme is appropriate for streams and small rivers in which 

the most significant chemical gradients occur in the longitudinal direction. Under ideal conditions, samples at all of the 

sampling locations would be collected simultaneously, providing data for stream-water quality at steady state. Personnel 

limitations generally preclude simultaneous sample collection, 

but the synoptic studies described herein provide an approximate means of defining steady-state conditions. This approximation is achieved by collection of all the stream samples 

during a relatively short time period (less than 8 hours). When 

this is done under base-flow conditions, the effects of diurnal 

flow variation are minimized.

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) dispersed subsurface 

inflow within each segment. Changes in stream chemistry and 

discharge between stream sampling sites reflect a net metal 

load for specific segments, but the loads cannot always be 

attributed to specific sources.

If stream sites downstream from inflows are considered 

well mixed, grab samples are collected. The extent of mixing is determined by pH or water conductance cross sections 

before sampling. Sites that are not well mixed are sampled 

by equal width integration (Ward and Harr, 1990). Water 

temperature is measured at the time of collection. Samples 

are transported to a central location for further processing, 

having been placed in black plastic bags to prohibit sunlight 

from altering the sample (McKnight and others, 1988). The 

collected samples are divided into several 125 mL bottles with 

different treatments at the central processing location: a raw 

(unfiltered) unacidified 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 are determined from the 

RU sample within hours of sample collection. Tangentialflow filtration is used with 0.45-μm membranes (FU and FA 

samples) and 10,000-Dalton molecular weight membranes 

(UFA ultrafiltration sample). Metal concentrations for the RA, 

FA, and UFA samples are determined by inductively coupled 

plasma–atomic emission spectrometry (Lichte and others, 

1987). Anion concentrations are determined from FU samples 

using ion chromatography (Kimball and others, 1999). Ferrous 

iron is determined colorimetrically from the UFA samples 

(Kimball and others, 1992), and total alkalinity is determined 

by titration.

Use of three processing treatments provides for different 

operationally defined concentrations for each metal. The unfiltered sample (RA) provides a measure of the total-recoverable 

metal concentration (dissolved+colloidal), whereas the ultrafiltrate concentration (UFA) is considered the dissolved metal 

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

comparison purposes, as a means of quantifying the colloids 

having a size between 0.45-μm and 10,000-Dalton molecular 

weight, but also to compare the 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).

- C

- C

- C
Upper Cement Creek Study Area 

and Experimental Design

The tracer injection and synoptic sampling for upper 

Cement Creek covered approximately 4,133 m of stream 

starting downstream from Ross Basin and continuing to just 

downstream from the confluence with South Fork Cement 

Creek near Gladstone (figs. 7 and 25). Synoptic sampling sites 

and their site numbers are listed in table 13. This stream reach 

included inflows from the Grand Mogul and Queen Anne 

mines at 271 and 298 m and the Mogul mine at 1,318 and 

1,348 m. North Fork Cement Creek, which contains several 

inactive mines and is affected by mine drainage, joins Cement 

Creek at approximately 3,076 m (table 13). Treated effluent 

from the American tunnel/Sunnyside mine enters the stream at 

3,853 m. The American tunnel effluent contains mine drainage 

that is collected from underground workings associated with 

the Sunnyside mine and that is treated and released to Cement 

Creek under a National Pollutant Discharge Elimination 

System (NPDES) permit (Chris Gates, Colorado Water Quality 

Control Commission, oral commun., 2001). This source will 

be referred to as Sunnyside mine effluent. South Fork Cement 

Creek enters Cement Creek at approximately 4,001 m. Numerous additional inactive mines and prospects exist in the basin 

(see Church, Mast, and others, this volume). Stream elevation 

ranges from approximately 3,600 m at the injection site to 

3,170 m at the downstream end of the reach. Average stream 

gradient is approximately 10 percent. Geology of the basin is 

described in Yager and Bove (this volume) and Bove and others (this volume).

A total of 36 stream sites and 21 inflow sites were 

sampled. Stream-discharge measurements using a velocity 

meter were made at 3,844 m (T3), and 4,133 m. A Parshall 

flume located at the Sunnyside mine effluent provided an 

independent measure of that inflow. A few additional inflow 

and stream samples were collected during August 2000 

to aid in water-quality characterization for the basin.

Discharge

Profiles of bromide at sites T1 (507 m), T2 (2,885 m), 

and T3 (3,844 m) are shown in figure 26. Discharge calculated 

by use of equations 3 and 4 is shown in table 14. Independent 

velocity meter and Parshall-flume measurements also are 

shown in table 14. Two problems with the tracer data necessitated our making adjustments to the data and using slightly 

different techniques to calculate discharge from the tracer data 

than indicated in equations 1–4: (1) tracer was not at plateau at 

all sites when synoptic samples were collected; (2) discharge 

estimates made using equations 1–4 do not compare favorably with independent measurements of discharge made using 

velocity meters and Parshall flumes.

The first problem with the tracer data is that the synoptic 

samples collected between the bottom of the reach and site T2 

(2,885 m) were collected before the tracer concentration had 

reached plateau or steady-state values (fig. 26A). Plateau concentrations at T3 were reached at approximately 1415 hours 

(MDT) on September 20, whereas the synoptic sample at that 

site was collected at 0915 hours. In contrast, it appears that 

tracer concentrations at site T2 (2,885 m) reached plateau 

at about the same time the synoptic sample was collected 

(1100 hours). Therefore, the tracer concentrations in synoptic 

samples collected at all sites downstream from T2 are lower 

than they would have been had the tracer reached plateau. 

It is possible to correct this problem and adjust the tracer concentrations at sites between T2 and T3 with the help of a few 

assumptions.

The first assumption is that the concentration of bromide in the synoptic sample collected at site T2 (2.73 mg/L) 

represents plateau, or steady-state concentration. The second 

assumption is that the proportional change in bromide concentrations (Brprop) between stream sites relative to the change 

in bromide concentrations between sites T2 and T3 would be 

the same before plateau as after plateau. At each site, Brprop

 is 

defined as:

( )

( )

C C

C C

up down

T T

−

2 3 − = Brprop = ( )

( )

' '

' '

C C

C C

up down

T T

−

2 3 − (6)

where

 Cup is the concentration of bromide in the synoptic 

sample collected at a stream site, in mg/L,

 Cdown is the concentration of bromide in the synoptic 

sample from the adjacent downstream site,

in mg/L,

 CT2 is the concentration of bromide in the synoptic 

sample collected at site T2, in mg/L,

 CT3 is the concentration of bromide in the 

synoptic sample collected at T3, in mg/L,

 C'up is the plateau concentration of bromide at a 

stream site, in mg/L,

 C'down is the plateau concentration of bromide at 

the adjacent downstream site, in mg/L,

 C'T2 is the plateau concentration of bromide at 

site T2, in mg/L, 

and

 C'T3 is the plateau concentration of bromide at T3.

Solving for C'down:

C C C C

C C down up C C T T

T T

up down

' '

' ' ( )

( ) = − ( ) −− − 2 3

2 3

 (7)

We can solve for C'down at 2,976 m using site T2 (2,885 m) as 

Cup: Cup = C'up = 2.73 mg/L bromide; Cdown = 2.63 mg/L bromide; CT2 – CT3 = 0.64 mg/L bromide; C'T2 – C'T3 = 2.73 –2.34 

Appendix 2. Details of Upper Cement Creek Mass-Loading Studies

482 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
Quantification of Metal Loading 483

(from fig. 26B) = 0.39 mg/L bromide. Therefore, the adjusted 

bromide concentration at 2,976 m is C'down = 2.67 mg/L. The 

results of applying the correction moving downstream to T3 

are listed in table 14, and shown graphically in figure 27. The 

adjustment procedure results in proportionally greater adjustments to the bromide concentration moving downstream. This 

type of proportional adjustment is appropriate considering that 

the samples were collected in an upstream direction, so the difference between the time the synoptic samples were collected 

and the time of plateau concentrations at each site decreased 

as sampling approached site T2.

The second problem with the tracer data is that the 

discharge values calculated from the tracer concentration 

are as much as three times greater than independent measurements of discharge made using velocity meters (table 14). 

This discrepancy indicates either a large hyporheic zone that 

carries one-half to two-thirds of the flow near the bottom of 

the stream reach, or a loss of tracer in the stream reach. To 

assign a large hyporheic zone to this stream seems unrealistic. 

The cross-sectional area of the hyporheic zone can be calculated using Darcy’s law: Q = KIA, where K is the hydraulic 

conductivity (units length/time), I is the ground-water gradient 

Figure 25. Location of selected synoptic sampling sites and inactive mines, upper Cement 

Creek, September 1999. Dashed blue line segments indicate drainage to stream.

Gladstone

37°

54'

00"

Ross Basin

Cement Creek

North

South Fork

Fork

Queen Anne and

Grand Mogul 

Mogul

Pride of Bonita 

Adams 

Red and Bonita 

Upper Gold King 

American tunnel

Sunnyside

Synoptic-sampling site

 and downstream

 distance along study

 reach

Inactive mine site

EXPLANATION

, ,

0 1 MILE

0 1 KILOMETER

107°39'00" 107°38'00"
Table 13. Site identification, downstream distance, source, label, principal component classification, site description, and selected 

characteristics for stream and inflow sites, upper Cement Creek, September 1999.

[Site identification, reference to site in database; Distance, in meters along the study reach; Source: S, stream; RBI, right bank inflow; LBI, left bank inflow; Label, 

map and discussion label used in fig. 7; PCA group, classification from principal component analysis; pH in standard units; SO4, sulfate, in milligrams per liter]

Site 

identification Distance Source Label PCA group

Site 

description pH SO4

ROSS-0000 0 S 1 T0 transport site—up from injection site 6.83 73.4

ROSS-0041 41 S 1 First site below injection 6.75 73.3

ROSS-0084 84 S 1 After braids 6.71 73.6

ROSS-0234 234 S 1 Above inflow from talus 6.64 73.8

ROSS-0237 237 LBI 1 Draining talus slope 6.72 64.2

ROSS-0259 259 S 1 Below first inflow 6.46 69.0

ROSS-0271 271 RBI 3 From stope with Fe stain 3.27 205

ROSS-0293 293 S 1 Above Queen Anne inflow 5.14 77.8

ROSS-0298 298 RBI 3 Drainage from Queen Anne mine 5.73 143

ROSS-0345 345 S C1 1 Below Queen Anne inflow 5.71 104

ROSS-0440 440 S 1 Above small mine dump 5.71 103

ROSS-0457 507 S 1 T1 transport site—above Texas crossing 6.24 101

ROSS-0577 627 S 1 Before first cascade of canyon 6.04 101

ROSS-0777 827 S 1 At head of deep canyon 6.44 98.3

ROSS-0877 927 S 1 At mouth of canyon 5.15 98.2

ROSS-0883 933 RBI 1 Drains prevailing fracture set 6.60 41.4

ROSS-0933 983 S 1 Below inflow for mixing 5.07 93.9

ROSS-1092 1,142 S 1 Above road to Mogul 5.75 94.5

ROSS-1187 1,237 RBI 1 Drains across road 6.78 44.7

ROSS-1237 1,287 RBI 1 Mossy inflow 6.47 34.8

ROSS-1242 1,292 S 1 Above first Mogul inflow 4.59 90.2

ROSS-1265 1,315 S 1 Above Mogul inflow—some Mogul inflow 4.27 83.9

ROSS-1268 1,318 LBI 2 Mogul mine inflow 2.85 1,010

ROSS-1283 1,333 S 2 Between Mogul inflows 3.65 203

ROSS-1298 1,348 LBI 3 Second, more dilute Mogul inflow 3.89 126

ROSS-1317 1,367 S C2 2 Below Mogul inflows—replicate samples 3.65 200

ROSS-1361 1,411 RBI 1 Draining catchment 6.74 24.5

ROSS-1491 1,541 S 3 Below catchment inflow 0.00 189

ROSS-1629 1,679 LBI 3 Draining lineament 6.39 572

ROSS-1664 1,714 S 2 Below lineament inflow 3.72 193

ROSS-1669 1,719 LBI 1 Draining second fracture lineament 4.34 16.4

ROSS-1819 1,869 S 2 Above iron soil zone on right bank 3.66 182

ROSS-1834 1,884 RBI 3 Iron bog—dip sample 3.42 72.9

ROSS-2034 2,084 S 2 Below slumped soil zone on right bank 3.66 186

ROSS-2184 2,234 S 2 Near start of left bank iron soil zone 3.66 195

ROSS-2357 2,407 LBI 3 Draining iron soil zone on left bank 3.64 87.0

ROSS-2456 2,506 S 2 Below left bank iron soil zone 3.70 189

ROSS-2668 2,718 S 2 Below clean inflows 3.73 183

ROSS-2711 2,761 LBI 3 Draining iron bog and Red and Bonita mine 3.50 177

ROSS-2713 2,763 LBI 2 Second inflow draining iron bog 3.23 248

ROSS-2835 2,885 S 2 T2 transport site—below left bank iron soil zone 3.67 191

ROSS-2926 2,976 S 2 Above North Fork Cement Creek 3.57 191

ROSS-3026 3,076 LBI 2 North Fork 2.87 993

ROSS-3057 3,107 S C3 3 30 m below North Fork 3.45 245

ROSS-3122 3,172 S 3 96 m below North Fork 3.45 236

ROSS-3205 3,255 S 3 129 m below North Fork 3.35 248

ROSS-3272 3,358 S 3 At treatment intake for Sunnyside 3.32 243

ROSS-3362 3,448 LBI 3 Pond at base of rocks 3.46 170

ROSS-3430 3,516 S 3 Above culvert at Sunnyside mine 3.44 234

ROSS-3432 3,518 LBI 3 Upper discharge pipe 6.35 288

ROSS-3547 3,633 S 3 Upstream of culvert 3.39 237

ROSS-3758 3,844 S 3 T3 transport site—above treatment inflow 3.39 267

ROSS-3767 3,853 LBI 3 Inflow from Sunnyside treatment 7.87 1,460

ROSS-3845 3,931 S C4 3 Below Sunnyside treatment 3.67 610

ROSS-3915 4,001 LBI 3 South Fork Cement Creek 5.54 240

ROSS-3916 4,002 RBI 1 Inflow from iron-stained seep 3.66 198

ROSS-4047 4,133 S C5 3 Below South Fork 4.02 407

484 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
Quantification of Metal Loading 485

B

A

0

0

5

10

15

20

25

30

500 1,000 1,500 2,000 2,500 3,000 3,500 4,000 4,500

DISTANCE ALONG STUDY REACH, IN METERS

9/19/1999 12:00 9/20/1999 00:00 9/21/1999 00:00 9/21/1999 12:00 9/20/1999 12:00

TIME, IN HOURS

BROMIDE CONCENTRATION,

IN MILLIGRAMS PER LITER

0

1

2

3

4

5

6

7

BROMIDE CONCENTRATION,

IN MILLIGRAMS PER LITER

T1

T2

T3

Start of plateau at T2

Start of plateau at T3

Smoothed bromide

T1 – 507

T2 – 2,885

T3 – 3,844

Figure 26. Variation of bromide concentration with A, time at three transport sites, and B, distance, upper Cement Creek, 

September 1999.
(dimensionless), and A is the cross-sectional area over which 

flow occurs (the area of the hyporheic or storage zone). In 

the hyporheic zone, I is assumed to be equal to the stream 

gradient, which in this case is 0.1. Values of K in sand and 

gravel range from 10–1 to 102

 cm/s (Freeze and Cherry, 1979, 

p. 29). At site T3, approximately 180 L/s discharge was unaccounted for by the velocity meter and may be flowing in the 

hyporheic zone. Assuming a hydraulic conductivity of 10 cm/s, 

which is approximately one-third stream velocity, the crosssectional area of the hyporheic zone required to carry this flow 

is 18.3 m2

 or more than 60 times the cross-sectional area of the 

stream, which was measured as 0.296 square meters during 

the velocity-meter measurement. Considering the cemented 

and indurated nature of the streambed, this estimated hydraulic 

Table 14. Bromide concentrations, discharge based on velocity meter, Parshall flume measurements, and discharge calculated from 

tracer concentrations, upper Cement Creek, September 1999.

[Distance, along the study reach, in meters; all concentrations in milligrams per liter; all discharge in liters per second; NA, no analysis; dash, no measurement]

Distance

Smoothed 

bromide 

concentration

Initial 

discharge 

estimate

Discharge measured 

with velocity meter

Discharge 

(upstream velocity 

measurement plus Parshall 

flume measurement)

Adjusted 

bromide 

concentration

Adjusted 

discharge 

estimate

Discharge 

from CDMG1

0 0.00 21.0 -- -- 0.0 8.68 --

41 27.2 21.0 -- -- 27.2 8.68 17.9

84 27.3 20.9 -- -- 27.2 8.70 --

234 26.7 21.4 -- -- 26.7 8.85 --

259 15.0 39.3 -- -- 15.0 15.8 --

293 11.7 50.5 -- -- 11.7 20.3 14.8

345 6.75 87.2 -- -- 6.75 35.0 --

440 6.65 88.5 -- -- 6.65 35.5 --

507 6.41 91.9 -- -- 6.41 36.9 --

627 6.42 91.7 -- -- 6.39 37.0 --

827 6.17 95.5 -- -- 6.17 38.3 --

927 6.12 96.3 -- -- 6.12 38.6 --

983 5.83 101 -- -- 5.83 40.6 --

1,142 5.74 103 -- -- 5.74 41.2 2

40.1

1,292 5.27 112 -- -- 5.27 44.8 --

1,315 4.51 131 -- -- 4.51 52.4 --

1,333 4.09 144 -- -- 4.09 57.8 --

1,367 3.91 151 -- -- 3.91 60.4 52.07

1,367

(replicate)

3.84 153 -- -- 3.84 61.5 --

1,541 3.60 164 -- -- 3.60 65.6 --

1,714 3.45 171 -- -- 3.45 68.4 --

1,869 3.14 188 -- -- 3.14 75.4 40.24

2,084 3.14 188 -- -- 3.14 75.5 --

2,234 3.12 189 -- -- 3.12 75.7 --

2,506 2.93 201 -- -- 2.93 80.6 40.97

2,718 2.78 212 -- -- 2.78 84.9 --

2,885 (T2) 2.73 216 -- -- 2.73 86.6 50.74

2,976 2.63 224 -- -- 2.67 88.6 --

3,107 2.32 254 -- -- 2.48 95.4 --

3,172 2.32 254 -- -- 2.48 95.4 --

3,255 2.32 254 -- -- 2.48 95.4 32.62

3,358 2.13 277 -- -- 2.36 100 --

3,516 2.13 277 -- -- 2.36 100 --

3,633 2.01 293 -- -- 2.34 101 --

3,844 (T3) 2.09 282 101 -- 2.34 101 --

3,931 1.33 443 -- 147 NA 147 3

64.28

4,133 0.62 954 300 -- NA 300 123.5

1

Jim Herron, Bruce Stover, and Paul Krabacher, Unpublished Cement Creek reclamation feasibility report, Upper Animas River Basin, Colorado Division 

of Minerals and Geology, 1998.

2

Colorado Division of Minerals and Geology distance is 1,070 meters.

3

Colorado Division of Minerals and Geology distance is 4,001 meters.

486 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
Quantification of Metal Loading 487

conductivity probably overestimates the actual hydraulic 

conductivity. Lower values of hydraulic conductivity would 

increase the calculated area of the hyporheic zone and the value 

of the ratio of the storage zone cross-sectional area to stream 

cross-sectional area. The ratio of the hyporheic, or storage 

zone to stream cross-sectional area is reported in many studies 

of stream transport. One such compilation showed the greatest value of this ratio to be 4.6 (Harvey and Wagner, 2000). 

Another compilation shows values ranging from 0.04 to 1.81 

for cobble-bottom streams similar in character to upper Cement 

Creek (Broshears and others, 1993, table 4). Based on this 

comparison, it seems unreasonable to ascribe the differences 

between discharge measured by velocity meter and tracer dilution at T3 to flow in the hyporheic zone.

Therefore, we hypothesize that streamflow and tracer 

were lost near the top of the study reach. The large decrease in 

tracer concentration that occurred in the upper reaches of the 

stream (fig. 26B) seems too large to account for the increases 

Figure 27. Variation of synoptic, plateau, and adjusted bromide concentrations with distance along study reach, upper 

Cement Creek, September 1999.

2,000 2,500 3,000 3,500 4,000

DISTANCE ALONG STUDY REACH, IN METERS

BROMIDE CONCENTRATION, IN MILLIGRAMS PER LITER

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

T2 – 2,885

T3 – 3,844

EXPLANATION

Synoptic

Plateau

Adjusted
in streamflow observed in that reach. This stream reach contains glacial, colluvial, and alluvial deposits and some fracture zones (Burbank and Luedke, 1969; Yager and Bove, this 

volume; Blair and others, 2002) that could represent recharge 

zones for deeper circulating ground water. Therefore, flow was 

calculated using the discharge measured by velocity meter at 

T3 as the starting point. At sites upstream from T3, discharge 

was calculated by rearranging equation 4, and assuming the 

concentration of bromide in inflows was zero:

QU QD

CD

CU

------- © 1 § · = (8)

The velocity-meter measurement and Parshall-flume measurement were used to complete the discharge profile at 

sites downstream from T3. Because tracer was lost, and the 

discharge measurements are being calculated to velocitymeter measurements, the discharge (flow in the hyporheic 

zone is unaccounted for) and the metal loads in this reach 

of Cement Creek are underestimated by an unknown amount. 

However, comparison of these data with flow measurements 

collected by the Colorado Division of Minerals and Geology 

(CDMG) under similar flow conditions shows that the 

adjusted discharge estimates are more similar to the CDMG 

values than are the initial discharge estimates (table 14; 

fig. 28). This favorable comparison lends credibility to the 

adjusted discharge values. In addition, certain trends in the 

loads of conservative constituents indicate that the error 

in the method used in this study is probably minimal.

Based on the adjusted discharge estimates (table 14; 

fig. 28), the largest contributor to flow is South Fork, which 

contributes 51 percent of the flow. The second largest contributor of flow is the Sunnyside mine effluent at the American 

tunnel, contributing 15.2 percent of the flow. The reaches 

containing the Queen Anne and Grand Mogul mines contribute slightly more than 6.4 percent of the flow. The two inflows 

from the Mogul mine account for 4.2 percent of the flow, 

and North Fork contributes 2.2 percent of the flow. Together 

these six distinct sources account for 79 percent of the flow. 

The remaining 21 percent of the flow originates in smaller 

tributaries, seeps, springs, and dispersed, subsurface flow that 

discharge to the stream.

Comparison of Conditions 1996 Versus 1999

In 1996 the CDMG conducted a study in Cement Creek 

to identify locations of waste rock and mine drainage within 

the Cement Creek basin (Jim Herron, Bruce Stover, and 

Paul Krabacher, Unpublished Cement Creek reclamation feasibility report, Upper Animas River Basin, Colorado Division 

of Minerals and Geology, 1998). As part of this investigation, 

stream samples and streamflow discharge measurements were 

collected from Cement Creek to enable calculation of load 

values during base flow in October 1996. In addition, during 

the USGS lower Cement Creek synoptic sampling experiment, 

conducted in September 1996, samples were collected along 

the downstream portions of upper Cement Creek. Comparison 

of the results of these two samplings with the 1999 results 

is instructive. Since 1996, some conditions have changed in 

upper Cement Creek. For instance, in early September 1996 

a bulkhead was closed in the American tunnel that drains the 

Sunnyside mine workings (see Leib and others, this volume, 

Chapter E11). Closure of the bulkhead might force static 

water levels in the mountain to rise and cause re-plumbing 

and rerouting of the acid water intercepted in the American 

tunnel. The net result could be emergence of acidic, metal-rich 

water at higher elevations than before the placement of the 

bulkhead. In addition, in 1996, the treatment system for the 

American tunnel was collecting almost all of the water from 

upper Cement Creek just downstream from the confluence of 

North Fork. The collection and treatment of the upper Cement 

Creek water had stopped temporarily in 1999 during the massloading study. Both of these changes could produce poorer 

water quality in upper Cement Creek in 1999 relative to 1996.

The variation of discharge, pH, total copper, iron, manganese, and zinc concentration and load with distance are 

shown for the three data sets (USGS 1996 and 1999 studies; 

CDMG 1996 study) in figures 28 and 29–33. Discharge results 

(fig. 28) indicate that the CDMG data were collected at the 

lowest flow. In addition, at the North Fork, the CDMG noted, 

“***during August 1996, all the flow from North Fork was 

observed to infiltrate into the alluvial gravels prior to reaching Cement Creek,” and “***the flow in Cement Creek was 

visibly reduced near the confluence with the North Fork” 

(Unpub. Cement Creek reclamation feasibility report, CDMG, 

1998, p. 34). Therefore, water from North Fork and Cement 

Creek was recharging the ground-water system at the time 

of the CDMG sampling. In contrast, both USGS data sets 

indicate measurable surface flow from North Fork to Cement 

Creek at the time of sampling. The CDMG data show lower 

values of pH (fig. 29) upstream of the Mogul mine than the 

USGS data show for that area, but greater values downstream 

from the Mogul mine. The 1996 USGS data show greater 

pH values at all locations than are shown in the 1999 USGS 

data. Despite slightly different flow conditions, copper, iron, 

manganese, and zinc concentration and load data are remarkably similar between the USGS 1999 and CDMG 1996 data 

sets upstream from the Mogul mine (figs. 30–33). For the area 

downstream from the Mogul mine, the data sets do not show 

similar results; the 1999 USGS data generally have lower pH 

values and greater concentrations and loads than do either of 

the other two data sets.

The differences among the three data sets are partially 

the result of different hydrologic conditions. In particular, 

the different patterns between the 1996 CDMG and USGS 

data sets downstream from the North Fork confluence are 

attributed to the lack of surface flow in North Fork during 

the CDMG sampling. The different pH values reported for the 

1999 USGS and 1996 CDMG data upstream from the Mogul 

mine also may be due to the lower flow that occurred during 

the CDMG sampling: at the lowest flow conditions perhaps 

only acid springs flow, whereas at slightly higher flow, there 

488 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
Quantification of Metal Loading 489

is still some higher pH runoff or spring flow related to the 

latest storm events. In 1999, a major rainstorm had occurred a 

few days prior to the USGS synoptic sampling. Dilution from 

precipitation runoff would be expected to increase stream pH 

in the acidic conditions of Cement Creek.

Lower flow conditions in 1996 relative to 1999 cannot 

explain the higher values for copper, iron, manganese, and 

zinc concentrations and loads that occurred downstream from 

the Mogul mine in 1999 relative to 1996. Lower flow in 1996 

should have caused more acid conditions similar to what 

occurred upstream from the Mogul mine. This was not the 

case. In addition, even considering the lower flow and lower 

pH in 1996 relative to 1999, copper, iron, manganese, and zinc 

concentrations and loads are remarkably similar between the 

two data sets upstream from the Mogul mine.

The differences in copper, iron, and zinc concentrations 

and loads downstream from the Mogul mine between 1996 

and 1999 are caused by different chemistry and higher flow of 

the Mogul mine inflow between the 2 years. Flow and constituent concentrations are greater at the larger of the two Mogul 

mine inflows sampled by the USGS in 1999 than at the Mogul 

mine adit as represented by CDMG data in 1996 (table 14). As 

a result, metal loads are from 5 to more than 80 times greater 

in 1999 than in 1996. The differences between the 2 years 

do not seem to be related to higher flow alone, as the CDMG 

high-flow data for the Mogul mine adit (Unpub. Cement Creek 

reclamation feasibility report, CDMG, 1998) indicate a flow 

rate of 1.7 L/s, and more dilute chemistry than that represented 

in table 15. Changes that have occurred at the site of the 

Mogul inflow between 1996 and 1999 include collection and 

0

0

50

100

150

200

250

300

500 1,000 1,500 2,000 2,500 3,000 3,500 4,000 4,500

DISTANCE ALONG STUDY REACH, IN METERS

DISCHARGE, IN LITERS PER SECOND

Grand Mogul and Queen Anne inflows

Mogul mine

North Fork

Sunnyside mine

South Fork

USGS, 1999 data

USGS, 1996 data

CDMG, 1996 data

EXPLANATION

Figure 28. Variation of discharge measurements with distance along the study reach, upper Cement Creek, September 1996 

and 1999.
rerouting of flow from the Mogul mine around mine-waste 

deposits to help improve water quality (Jim Herron, CDMG, 

oral commun., 2001). This change cannot account for the large 

loading increases observed at the Mogul mine between 1996 

and 1999. Rather, it seems that some fundamental change 

occurred in the flow rate and composition of flow exiting the 

Mogul mine between 1996 and 1999. Hydrologic changes 

resulting from placement of the bulkhead in the American 

tunnel could be responsible for the change, as maps of underground workings indicate an underground connection between 

the American tunnel and the Mogul mine (Burbank and 

Luedke, 1969, pl. 8). However, this direct connection requires 

a static water-level altitude of approximately 12,200 ft. Pressure behind the bulkheads in the American tunnel and Terry 

tunnel indicated water levels of approximately 11,600 ft in 

commun., 2001), which is above the altitude of the Mogul 

mine adit (approximately 11,300 ft).

The change in chemistry of the Mogul mine inflow from 

1996 to 1999 indicates that a change in hydraulics (plumbing) involving the addition of water from east of Cement 

Creek has occurred. The Mogul mine drainage sampled by 

the USGS in 1999 and 2000 (table 15) is exceptionally rich in 

manganese (concentration greater than 25 mg/L). In 1999, the 

manganese load had increased more than 20 times relative to 

1996. Studies of mine drainage in other parts of the Animas 

River watershed study area have indicated that drainage waters 

similarly elevated in manganese are typical of, and unique 

to, the Eureka vein systems that formed part of the ore mined 

at the Sunnyside mine (Bove and others, this volume). The 

0

3.0

3.5

4.0

4.5

5.0

5.5

6.0

6.5

7.0

7.5

8.0

1,000 2,000 3,000 4,000

DISTANCE ALONG STUDY REACH, IN METERS

pH, IN STANDARD UNITS

Grand Mogul and

Queen Anne inflows (C1)

Mogul mine (C2)

Sunnyside mine (C4)

North Fork (C3)

South Fork (C5)

USGS, 1999 data

USGS, 1996 data

CDMG, 1996 data

EXPLANATION

Figure 29. Relation of pH measured during three different studies, upper Cement Creek.

490 Environmental Effects of Historical Mining, Animas River Watershed, Colorado

October 1999 (Larry Perino, Sunnyside Corporations, oral 
Quantification of Metal Loading 491

0

0

2

4

6

8

10

12

14

16

18

500 1,000 1,500 2,000 2,500 3,000 3,500 4,000 4,500

DISTANCE ALONG STUDY REACH, IN METERS

COPPER LOAD, IN KILOGRAMS PER DAY

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

COPPER CONCENTRATION,

IN MILLIGRAMS PER LITER

B

0 500 1,000 1,500 2,000 2,500 3,000 3,500 4,000 4,500

A

Grand Mogul and Queen Anne mines (C1)

Grand Mogul and Queen Anne mines (C1)

Mogul mine (C2) Mogul mine (C2)

Sunnyside mine (C4) Sunnyside mine (C4)

North Fork (C3)

North Fork (C3)

South Fork (C5) South Fork (C5)

USGS, 1999

CDMG, 1996

USGS, 1996

EXPLANATION

USGS, 1999

CDMG, 1996

USGS, 1996

EXPLANATION

Figure 30. Relation of A, copper concentrations and B, corresponding copper loads measured during three different studies, upper 

Cement Creek.
0 500 1,000 1,500 2,000 2,500 3,000 3,500 4,000 4,500

B DISTANCE ALONG STUDY REACH, IN METERS

0 500 1,000 1,500 2,000 2,500 3,000 3,500 4,000 4,500

A

0

20

40

60

80

100

120

140

160

180

IRON LOAD, IN KILOGRAMS PER DAY

0

2

4

6

8

10

12

14

IRON CONCENTRATION,

IN MILLIGRAMS PER LITER

Grand Mogul and Queen Anne mines (C1)

Mogul mine (C2)

Sunnyside mine (C4)

North Fork (C3)

South Fork (C5)

Grand Mogul and Queen Anne mines (C1)

Mogul mine (C2)

Sunnyside mine (C4)

North Fork (C3)

South Fork (C5)

USGS, 1999

CDMG, 1996

USGS, 1996

EXPLANATION

USGS, 1999

CDMG, 1996

USGS, 1996

EXPLANATION

Figure 31. Relation of A, iron concentrations and B, corresponding iron loads measured during three different studies, upper Cement 

Creek.

492 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
Quantification of Metal Loading 493

0 500 1,000 1,500 2,000 2,500 3,000 3,500 4,000 4,500

B DISTANCE ALONG STUDY REACH, IN METERS

0 500 1,000 1,500 2,000 2,500 3,000 3,500 4,000 4,500

A

Grand Mogul and Queen Anne mines (C1)

Mogul mine (C2)

Sunnyside mine (C4)

North Fork (C3)

South Fork (C5)

Grand Mogul and Queen Anne mines (C1)

Mogul mine (C2)

Sunnyside mine (C4)

North Fork (C3)

South Fork (C5)

USGS, 1999

CDMG, 1996

USGS, 1996

EXPLANATION

USGS, 1999

CDMG, 1996

USGS, 1996

EXPLANATION

0

20

40

60

80

MANGANESE LOAD, IN KILOGRAMS PER DAY

0

2

4

6

8

10

MANGANESE CONCENTRATION,

IN MILLIGRAMS PER LITER

Figure 32. Relation of A, manganese concentrations and B, corresponding manganese loads measured during three different studies, 

upper Cement Creek.
0 500 1,000 1,500 2,000 2,500 3,000 3,500 4,000 4,500

B DISTANCE ALONG STUDY REACH, IN METERS

0 500 1,000 1,500 2,000 2,500 3,000 3,500 4,000 4,500

A

Grand Mogul and Queen Anne mines (C1) Grand Mogul and Queen Anne mines (C1)

Mogul mine (C2)

Mogul mine (C2)

Sunnyside mine (C4)

Sunnyside mine (C4)

North Fork (C3)

North Fork (C3)

South Fork (C5) South Fork (C5)

USGS, 1999

CDMG, 1996

USGS, 1996

EXPLANATION

USGS, 1999

CDMG, 1996

USGS, 1996

EXPLANATION

0

20

40

60

80

100

120

ZINC LOAD, IN KILOGRAMS PER DAY

0

2

4

6

8

14

12

10

ZINC CONCENTRATION,

IN MILLIGRAMS PER LITER

Figure 33. Relation of A, zinc concentrations and B, corresponding zinc loads measured during three different studies, upper Cement 

Creek.

494 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
Quantification of Metal Loading 495

Table 15. Relation of water quality and load for samples collected at the Mogul mine inflow by the Colorado Division of Minerals and 

Geology (CDMG) in 1996 and the U.S. Geological Survey (USGS) in 1999 and 2000, upper Cement Creek.

[Concentrations measured in total-recoverable sample except calcium, magnesium, sodium, sulfate, and silica, which are from dissolved sample; L/s, liters per 

second; Spec. cond., specific conductance; μS/cm, microsiemens per centimeter at 25°C; mg/L, milligrams per liter; kg/day, kilograms per day; NM, not measured; LDL, less than detection limit]

Constituent CDMG1

1996

USGS 12

1999

USGS 23

1999

USGS

20004 CDMG USGS5

Load ratio 

USGS/CDMG Water-quality data Load

Discharge (L/s) 0.68 5.37 3.17 NM NM NM NM

pH 2.89 2.85 3.89 3.11 NM NM NM

Spec. cond. (μS/cm) 1,098 1,869 318 1,084 NM NM NM

Concentration (mg/L) Load (kg/day)

Calcium 83.53 169 34.5 179 4.91 87.9 18

Magnesium 4.2 11.7 3.3 11.6 .25 6.33 26

Sodium 3.32 3.4 1.5 4.6 .20 1.99 10

Sulfate 449 1,009 126 820 26.4 503 19

Aluminum 5.24 44.2 3.4 20.5 .29 23.0 78

Cadmium .15 1.50 .054 .62 .01 .75 82

Copper 6.42 12.6 .5 4.6 .38 5.91 16

Iron 51.2 36.2 .3 25.4 2.84 16.3 6

Manganese 9.7 28.5 1.74 26.7 .57 12.3 22

Nickel .015 .058 .007 LDL .00 .03 22

Lead .21 .211 .003 .137 .01 .10 9

Silica 9.5 44.5 17.2 40.4 .56 25.4 45

Zinc 28.1 82.2 4 53.8 1.73 38.1 22

1

Colorado Division of Minerals and Geology, base-flow synoptic, Mogul mine sample (Unpub. Cement Creek reclamation feasibility report, CDMG, 1998).

2

Sample from 1,318 m, 1999 USGS synoptic.

3

Sample from 1,348 m, 1999 USGS synoptic.

4

Sample from 1,318 m, 2000 USGS reconnaissance.

5

Load is the sum of the loads for USGS 1 and USGS 2.

change in chemistry at the Mogul mine to values more typical 

of drainages occurring east of the Mogul and associated with 

the Sunnyside supports the idea that placing a plug in the 

American tunnel (that drained the Sunnyside mine) has altered 

the hydrology and chemistry of flow from the Mogul mine. 

An official of the Sunnyside mine (Larry Perino, Sunnyside 

Corporation, oral commun., 2001) has hypothesized that the 

increased water level resulting from the American tunnel bulkhead has caused water that formerly flowed to the Sunnyside 

mine and the American tunnel to now divert to the Mogul 

mine.

Another explanation of the changes observed between 

the 1996 and 1999 flow and water quality of the Mogul mine 

drainage is that the CDMG collected their sample at the outflow from the adit, whereas the USGS samples were collected 

where the flow from the adit joins Cement Creek. Conceivably, water is added to the mine effluent as it flows across the 

surface between the two locations (a distance of approximately 

200 m). The CDMG data indicate a gain of approximately 

12 L/s in Cement Creek between their monitoring stations 

located upstream and downstream from the Mogul mine 

inflow. They measured the Mogul mine inflow at 0.57 L/s. 

Therefore, possibly as much as 11.4 liters per second of flow 

is being added to the reach where the water from the Mogul 

adit flows before entering Cement Creek. In addition, the 

unsampled load at the Mogul mine, as calculated from the 

CDMG samples, did not account for approximately 0.1 kg/day 

of the copper load and 3 kg/day of the zinc load increases 

observed within the reach of Cement Creek that contains the 

Mogul mine inflow. The CDMG data showed a loss of iron in 

that reach. These small loads of zinc and copper are still much 

smaller than the differences noted between the 1996 CDMG 

and 1999 USGS data sets (35 kg/day zinc and 5.4 kg/day copper) at the stream sites just downstream from the Mogul mine. 

Therefore, in 1996, the 11.4 L of missing flow did not contain 

metals in sufficient concentrations to augment the loading in 

Cement Creek and account for the differences between the 

1996 and 1999 data sets. If this substantial inflow between 

Mogul adit and the stream exists, then the chemistry of that 

inflow may have changed between 1996 and 1999.