Quantification and Simulation of Metal 

Loading to the Upper Animas River, Eureka 

to Silverton, San Juan County, Colorado, 

September 1997 and August 1998

By Suzanne S. Paschke, Briant A. Kimball, and Robert L. Runkel

Prepared in Cooperation with the Bureau of Land Management

Scientific Investigations Report 2005–5054

U.S. Department of the Interior

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

Gale A. Norton, Secretary

U.S. Geological Survey

Charles G. Groat, Director

U.S. Geological Survey, Reston, Virginia: 2005

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Box 25286, Denver Federal Center

Denver, CO 80225

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

reproduce any copyrighted materials contained within this report.
iii

Contents

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

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

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

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

Study Methods .......................................................................................... 4

Tracer-Injection and Synoptic-Sampling Methods ............................................. 4

Sampling and Analytical Methods ............................................................... 5

Discharge and Traveltime Calculations ......................................................... 5

Mass-Loading Calculations ........................................................................ 6

Solute-Transport Simulations ..................................................................... 8

Metal Loading to the Upper Animas River, Eureka to Howardsville, Colorado, 

Study Reach, August 1998 ..................................................................... 9

Tracer-Injection Study Objectives ............................................................... 9

Tracer-Injection Study Methods .................................................................. 9

Synoptic Sampling and Analyses ............................................................... 10

Tracer-Injection Study Results .................................................................. 11

Arrival Times ................................................................................. 11

Discharge Profile .............................................................................. 14

Synoptic-Sampling and Mass-Loading Calculation Results ................................. 14

pH .......................................................................................... 14

Aluminum .................................................................................... 16

Calcium and Magnesium ..................................................................... 16

Copper .......................................................................................... 16

Iron .......................................................................................... 20

Manganese .................................................................................... 20

Zinc .......................................................................................... 20

Sulfate .......................................................................................... 24

Discussion of Sources and Loadings, Eureka to Howardsville Study Reach ............... 24

Zinc Solute-Transport Simulations ............................................................... 26

Conservative and First-Order Decay Simulations ....................................... 26

Remediation Simulations ..................................................................... 26

Metal Loading to the Upper Animas River, Howardsville to Silverton, Colorado, 

Study Reach, September 1997 .................................................................. 31

Tracer-Injection Study Objectives ............................................................... 31

Tracer-Injection Study Methods .................................................................. 31

Synoptic Sampling and Analyses ............................................................... 31

Tracer-Injection Study Results .................................................................. 31

Arrival Times ................................................................................. 31

Discharge Profile .............................................................................. 38

Synoptic-Sampling and Mass-Loading Calculation Results ................................. 38

pH .......................................................................................... 38

Aluminum .................................................................................... 40

Calcium and Magnesium ..................................................................... 41
iv

Copper .......................................................................................... 41

Iron .......................................................................................... 41

Manganese .................................................................................... 41

Zinc .......................................................................................... 44

Sulfate .......................................................................................... 49

Discussion of Sources and Loadings Howardsville to Silverton Study Reach ...... 50

Zinc Solute-Transport Simulations ............................................................... 51

Conservative and First-Order Decay Simulation Results ................................. 51

Remediation Simulations ..................................................................... 54

Summary ................................................................................................... 54

References ................................................................................................ 58

Appendixes ................................................................................................ 63

Figures

1. Location of study area and study reaches, upper Animas River, Colorado. ...................... 3

2. Eureka to Howardsville study reach, upper Animas River, Colorado, August 1998 ....... 10

3. Dissolved chloride concentrations with time at transport sites T1 and T2, 

Eureka to Howardsville study reach, upper Animas River, Colorado, August 1998. ....... 13

4. Dissolved chloride concentrations and calculated discharges with distance 

downstream from the injection site, Eureka to Howardsville study reach, 

upper Animas River, Colorado, August 14, 1998 ................................................................... 15

5. Instream and inflow pH with distance from the injection site, upper Animas 

River, Eureka to Howardsville, Colorado, August 14, 1998 .................................................. 15

6. Instream and inflow colloidal aluminum concentrations with distance from the 

injection site, upper Animas River, Eureka to Howardsville, Colorado, 

August 14, 1998. .......................................................................................................................... 17

7. Sampled instream load, cumulative instream load, and cumulative inflow 

load of colloidal aluminum with distance from the injection site, upper 

Animas River, Eureka to Howardsville, Colorado, August 14, 1998 ................................... 17

8. Instream and inflow dissolved calcium concentrations with distance from the 

injection site, upper Animas River, Eureka to Howardsville, Colorado, 

August 14, 1998. .......................................................................................................................... 18

9. Instream and inflow dissolved magnesium concentrations with distance 

from the injection site, upper Animas River, Eureka to Howardsville, Colorado, 

August 14, 1998. .......................................................................................................................... 18

10. Instream and inflow dissolved copper concentrations, copper acute toxicity 

standard, and copper chronic toxicity standard with distance from the 

injection site, upper Animas River, Eureka to Howardsville, Colorado, 

August 14, 1998. .......................................................................................................................... 19

11. Sampled instream load, cumulative instream load, and cumulative inflow load 

of dissolved copper with distance from the injection site, upper Animas 

River, Eureka to Howardsville, Colorado, August 14, 1998. ................................................. 19

12. Sampled instream load, cumulative instream load, and cumulative inflow load 

of dissolved iron with distance from the injection site, upper Animas River, 

Eureka to Howardsville, Colorado, August 14, 1998. ............................................................ 21

13. Sampled instream load, cumulative instream load, and cumulative inflow 

load of colloidal iron with distance from the injection site, upper Animas 

River, Eureka to Howardsville, Colorado, August 14, 1998 .................................................. 21
v

14. Instream and inflow dissolved manganese concentrations with distance from the 

injection site, upper Animas River, Eureka to Howardsville, Colorado, 

August 14, 1998. .......................................................................................................................... 22

15. Sampled instream load, cumulative instream load, and cumulative inflow load 

of dissolved manganese with distance from the injection site, upper Animas 

River, Eureka to Howardsville, Colorado, August 14, 1998 .................................................. 22

16. Instream and inflow dissolved zinc concentrations, zinc acute toxicity standard, 

and zinc chronic toxicity standard with distance from the injection site, upper 

Animas River, Eureka to Howardsville, Colorado, August 14, 1998 ................................... 23

17. Sampled instream load, cumulative instream load, and cumulative inflow load 

of dissolved zinc with distance from the injection site, upper Animas River, 

Eureka to Howardsville, Colorado, August 14, 1998. ............................................................ 24

18. Instream and inflow dissolved sulfate concentrations with distance from the 

injection site, upper Animas River, Eureka to Howardsville, Colorado, 

August 14, 1998. .......................................................................................................................... 25

19. Sampled instream load, cumulative instream load, and cumulative inflow load 

of dissolved sulfate with distance from the injection site, upper Animas River, 

Eureka to Howardsville, Colorado, August 14, 1998 ............................................................. 25

20. OTIS lateral inflow concentrations and measured inflow concentrations for 

dissolved zinc with distance from the injection site, upper Animas River, 

Eureka to Howardsville, Colorado. .......................................................................................... 28

21. OTIS results for conservative and first-order decay simulations, upper Animas 

River, Eureka to Howardsville, Colorado. ............................................................................... 28

22. OTIS results for remediation simulations 3 and 4, upper Animas River, Eureka 

to Howardsville, Colorado ........................................................................................................ 30

23. OTIS results for remediation simulations 5 and 6, upper Animas River, Eureka 

to Howardsville, Colorado ........................................................................................................ 30

24. Howardsville to Silverton study reach, upper Animas River, Colorado, 

September 1997. ......................................................................................................................... 32

25. Dissolved chloride concentrations with time at (A) transport sites T1, T2, and 

T3, and (B) transport sites T4, T5, and T6, upper Animas River, Howardsville to 

Silverton, Colorado, September 1997 ..................................................................................... 37

 26. (A) Dissolved chloride concentrations, and (B) calculated discharge with distance 

downstream from the injection site, upper Animas River, Howardsville to 

Silverton, Colorado, September 14, 1997 ............................................................................... 39

27. Instream and inflow pH with distance from the injection site, upper Animas 

River, Howardsville to Silverton, Colorado, September 14, 1997 ....................................... 40

28. Instream and inflow dissolved calcium concentrations with distance from 

the injection site, upper Animas River, Howardsville to Silverton, Colorado, 

September 14, 1997 .................................................................................................................... 42

29. Instream and inflow dissolved magnesium concentrations with distance from 

the injection site, upper Animas River, Howardsville to Silverton, Colorado, 

September 14, 1997. ................................................................................................................... 42

30. Instream dissolved copper concentrations, copper acute toxicity standard, and 

copper chronic toxicity standard with distance from the injection site, upper 

Animas River, Howardsville to Silverton, Colorado, September 14, 1997 ......................... 43

31. Instream and inflow dissolved iron concentrations and instream colloidal iron 

concentrations with distance from the injection site, upper Animas River, 

Howardsville to Silverton, Colorado, September 14, 1997 .................................................. 43
vi

32. Sampled instream load, cumulative instream load, and cumulative inflow load 

of colloidal iron with distance from the injection site, upper Animas River, 

Howardsville to Silverton, Colorado, September 14, 1997 .................................................. 44

33. Instream and inflow dissolved manganese concentrations with distance from the 

injection site, upper Animas River, Howardsville to Silverton, Colorado, 

September 14, 1997 .................................................................................................................... 45

34. Sampled instream load, cumulative instream load, and cumulative inflow load 

of dissolved manganese with distance from the injection site, upper Animas River, 

Howardsville to Silverton, Colorado, September 14, 1997 .................................................. 45

35. Instream dissolved zinc concentrations, zinc acute toxicity standard, and zinc 

chronic toxicity standard with distance from the injection site, upper Animas 

River, Howardsville to Silverton, Colorado, September 14, 1997 ....................................... 46

36. Instream and inflow dissolved zinc concentrations with distance from the 

injection site, upper Animas River, Howardsville to Silverton, Colorado, 

September 14, 1997. ................................................................................................................... 47

37. Sampled instream load, cumulative instream load, and cumulative inflow load 

of dissolved zinc with distance from the injection site, upper Animas River, 

Howardsville to Silverton, Colorado, September 14, 1997 .................................................. 47

38. Dissolved sulfate concentrations with distance from the injection site, upper 

Animas River, Howardsville to Silverton, Colorado, September 14, 1997. ........................ 49

39. Sampled instream load, cumulative instream load, and cumulative inflow load 

of dissolved sulfate with distance from the injection site, upper Animas River, 

Howardsville to Silverton, Colorado, September 14, 1997 .................................................. 50

40. OTIS lateral inflow concentrations and measured inflow concentrations for 

dissolved zinc with distance from the injection site, upper Animas River, 

Howardsville to Silverton, Colorado ....................................................................................... 53

41. OTIS results for conservative and first-order decay simulations, upper Animas 

River, Howardsville to Silverton, Colorado ............................................................................ 53

 42. OTIS results for remediation simulations, 3, 4, and 5, upper Animas River, 

Howardsville to Silverton, Colorado ....................................................................................... 56

 43. OTIS results for remediation simulations 6 and 7, upper Animas River, 

Howardsville to Silverton, Colorado ....................................................................................... 57

Tables

1. Analytical methods for tracer and synoptic water samples collected during the 

Eureka to Howardsville tracer-injection study, August 1998, and the 

Howardsville to Silverton tracer-injection study, September 1997 ..................................... 6

2. Equations defining calculated quantities in tracer-injection studies (modified 

from Kimball and others, 1999a) [Subscripts correspond to sites illustrated in 

the diagram]. . 7

3. Probable explanations for various cumulative stream-load relations (modified 

from Kimball and others, 1999a) ................................................................................................ 8

4. Tracer-injection study sequence of events, upper Animas River, Eureka to 

Howardsville, Colorado, August 1998 ..................................................................................... 11

5. Synoptic-sampling sites and discharge calculated from tracer-dilution, 

upper Animas River, Eureka to Howardsville, Colorado, August 14, 1998 ........................ 12
vii

 6. OTIS setup and input parameters for zinc solute-transport model, upper 

Animas River, Eureka to Howardsville, Colorado ................................................................. 27

7. OTIS results for zinc solute-transport and remediation simulations, upper 

Animas River, Eureka to Howardsville, Colorado ................................................................. 29

8. Tracer-injection study sequence of events, upper Animas River, Howardsville

 to Silverton, Colorado, September 1997 ................................................................................ 32

9. Tracer arrival data and traveltime calculations for transport sites downstream 

from the tracer-injection site, upper Animas River, Howardsville to Silverton, 

Colorado, September 1997 ....................................................................................................... 33

10. Synoptic-sampling sites and discharge calculated from tracer-dilution, upper 

Animas River, Howardsville to Silverton, Colorado, September 14, 1997 ......................... 36

11. Zinc loads calculated from tracer-dilution results, upper Animas River, 

Howardsville to Silverton, Colorado, September 14, 1997 ................................................. 48

 12. OTIS setup and input parameters for zinc solute-transport model, upper 

Animas River, Howardsville to Silverton, Colorado .............................................................. 52

13. OTIS results for zinc solute-transport and remediation simulations, upper 

Animas River, Howardsville to Silverton, Colorado .............................................................. 55

Appendix 1. Field measurements and major ion concentrations for synoptic water 

samples, upper Animas River, Eureka to Howardsville, Colorado, 

August 14, 1998 ........................................................................................................................... 65

Appendix 2. Inductively coupled plasma-atomic emissions spectrometry (ICP-AES) 

results for synoptic water samples, upper Animas River, Eureka to 

Howardsville, Colorado, August 14, 1998 ............................................................................... 66

Appendix 3. Field measurements and major ion concentrations for synoptic water 

samples, upper Animas River, Howardsville to Silverton, Colorado, 

September 14, 1997 .................................................................................................................... 68

Appendix 4. Inductively coupled plasma-atomic emissions spectrometry (ICP-AES) 

results for synoptic water samples, upper Animas River, Howardsville to 

Silverton, Colorado, September 14, 1997 ............................................................................... 70
viii

Conversion Factors, Vertical Datum, Acronyms, and Abbreviations

Multiply By To obtain

centimeter (cm) 0.3937 inch

cubic meter (m3) 35.31 cubic foot (ft3)

kilogram 2.205 pound

kilometer (km) 0.6214 mile

liter (L) 0.2642 gallon

liter per minute (L/min) 5.886 x 10–4 cubic foot per second (ft3/s)

liter per second (L/s) 0.0353 cubic foot per second (ft3/s)

meter 3.281 foot

square meter (m2) 10.76 square foot

Temperature in degrees Celsius (oC) may be converted to degrees Fahrenheit (oF) as follows:

 oF = (1.8 x oC ) + 32

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

Horizontal coordinate information is referenced to North American Datum of 1927 (NAD 27) except as 

noted.

Acronyms and Abbreviations

kilogram per day (kg/d)

meters per second (m/s)

microsiemens per centimeter at 25 degrees Celsius (μS/cm)

micrometer (μm)

milligrams per liter (mg/L)

milliliter (mL)

milliliters per minute (mL/min)

AMD acid mine drainage

ARD acid rock drainage

ARSG Animas River Stakeholders Group

BLM Bureau of Land Management

CLATIN OTIS input parameter for lateral inflow concentration

Ma million years before present

USEPA U.S. Environmental Protection Agency

USGS U.S. Geological Survey
Abstract

Drainage from abandoned and inactive mines and from 

naturally mineralized areas in the San Juan Mountains of 

southern Colorado contributes metals to the upper Animas 

River near Silverton, Colorado. Tracer-injection studies and 

associated synoptic sampling were performed along two 

reaches of the upper Animas River to develop detailed profiles 

of stream discharge and to locate and quantify sources of 

metal loading. One tracer-injection study was performed in 

September 1997 on the Animas River reach from Howardsville to Silverton, and a second study was performed in August 

1998 on the stream reach from Eureka to Howardsville. 

Drainage in the upper Animas River study reaches contributed 

aluminum, calcium, copper, iron, magnesium, manganese, 

sulfate, and zinc to the surface-water system in 1997 and 1998. 

Colloidal aluminum, dissolved copper, and dissolved zinc 

were attenuated through a braided stream reach downstream 

from Eureka. Instream dissolved copper concentrations were 

lower than the State of Colorado acute and chronic toxicity 

standards downstream from the braided reach to Silverton. 

Dissolved iron load and concentrations increased downstream 

from Howardsville and Arrastra Gulch, and colloidal iron 

remained constant at low concentrations downstream from 

Howardsville. Instream sulfate concentrations were lower than 

the U.S. Environmental Protection Agency’s secondary 

drinking-water standard of 250 milligrams per liter throughout 

the two study reaches. 

Elevated zinc concentrations are the primary concern for 

aquatic life in the upper Animas River. In the 1998 Eureka to 

Howardsville study, instream dissolved zinc load increased 

downstream from the Forest Queen mine, the Kittimack 

tailings, and Howardsville. In the 1997 Howardsville to 

Silverton study, there were four primary areas where zinc 

load increased. First, was the increase downstream from 

Howardsville and abandoned mining sites downstream from 

the Cunningham Gulch confluence, which also was measured 

during the 1998 study. The second affected reach was downstream from Arrastra Gulch, where the increase in zinc load 

seems related to a series of right-bank inflows with low pH 

Quantification and Simulation of Metal Loading to the 

Upper Animas River, Eureka to Silverton, San Juan County, 

Colorado, September 1997 and August 1998

By Suzanne S. Paschke, Briant A. Kimball, and Robert L. Runkel

and elevated dissolved zinc concentrations. A third increase 

in zinc load occurred 6,100 meters downstream from the 1997 

injection site and may have been from ground-water discharge 

with elevated zinc concentrations based on mass-loading 

graphs and the lack of visible inflow in the reach. A fourth but 

lesser dissolved zinc load increase occurred downstream from 

tailings near the Lackawanna Mill.

Results of the tracer-injection studies and the effects of 

potential remediation were analyzed using the onedimensional stream-transport computer code OTIS. Based 

on simulation results, instream zinc concentrations downstream from the Kittimack tailings to upstream from Arrastra 

Gulch would approach 0.16 milligram per liter (the upper 

limit of acute toxicity for some sensitive aquatic species) if 

zinc inflow concentrations were reduced by 75 percent in the 

stream reaches receiving inflow from the Forest Queen mine, 

the Kittimack tailings, and downstream from Howardsville. 

However, simulated zinc concentrations downstream from 

Arrastra Gulch were higher than approximately 0.30 milligram 

per liter due to numerous visible inflows and assumed groundwater discharge with elevated zinc concentrations in the lower 

part of the study reach. Remediation of discrete visible inflows 

seems a viable approach to reducing zinc inflow loads to the 

upper Animas River. Remediation downstream from Arrastra 

Gulch is more complicated because ground-water discharge 

with elevated zinc concentrations seems to contribute to the 

instream zinc load.

Introduction

The upper Animas River drains an extensively mineralized area of the San Juan Mountains near Silverton, Colorado. 

Gold deposits were first discovered in 1871 in Arrastra Gulch, 

and mining activity continued in the watershed at various 

levels of activity until the Sunnyside Mine was closed in 1991 

(Church and others, 1997). The Animas River drainage basin 

contains more than 300 formerly producing metal mines that 

have affected water quality in the watershed (Church and others, 1997). Acid mine drainage (AMD) from abandoned and 
2 Quantification and Simulation of Metal Loading to the Upper Animas River, Eureka to Silverton, San Juan County, Colorado, 

 September 1997 and August 1998

inactive mines and mine-related wastes, as well as naturally 

occurring acid rock drainage (ARD) from mineralized areas, 

contributes acidic, metal-rich water to the upper Animas River. 

Environmental characterization of the upper Animas 

River basin upstream from Silverton began in 1991 under the 

auspices of the Colorado Department of Public Health and 

Environment (Church and others, 1997). These initial studies showed seasonal and regional variation in water quality 

and noted several acidic tributaries upstream from Silverton. 

Although pH was variable, aluminum and iron concentrations 

in the acidic waters exceeded the solubility products of various 

iron and aluminum hydroxides, and iron- and aluminumhydroxide-coated bed sediments were noted in many stream 

reaches. Additional reconnaissance sampling of water and 

bed sediments was conducted by Church and others (1997) 

during 1995 and 1996 to identify the sources, movement, and 

partitioning of metals in the upper Animas River. Results of 

that investigation indicated that most of the aluminum, arsenic, 

cadmium, copper, iron, lead, and zinc in the Animas River 

originated within the upper Animas River drainage basin 

upstream from Silverton (Church and others, 1997). Aquatic 

habitats in the upper Animas River and its tributaries are 

affected by the presence of acidic, metal-rich water and by aluminum and iron oxyhydroxide precipitates on bed sediments 

(Besser and others, 2001). 

The Bureau of Land Management (BLM) and the Animas 

River Stakeholders Group (ARSG) are planning possible 

remedial actions along the upper Animas River to alleviate 

water-quality degradation. An evaluation of remedial actions 

requires a detailed understanding of the primary metal sources 

to the river and any instream geochemical processes controlling metal transport. River and tributary discharge measurements, which allow calculation of metal loads, are available 

for a few sites along the stream. However, a more detailed 

profile of discharge distribution and resultant metal loading is 

needed to evaluate specific locations for remedial actions.

The U.S. Geological Survey (USGS), in cooperation with 

the Bureau of Land Management, conducted two tracerinjection and synoptic-sampling studies during September 

1997 and August 1998. The purpose of these studies was to 

provide an evaluation of metal loading to the upper Animas 

River and instream geochemical processes, which will aid in 

the selection of remedial alternatives. The principal objectives of the studies were to: (1) locate, identify, and quantify 

increases in metal loading, by surface and subsurface flow, 

to the upper Animas River between Eureka and Silverton, 

Colorado, using tracer-dilution methods; and (2) identify and 

describe any instream geochemical processes affecting metal 

concentrations and natural attenuation of metals in 

streamwater.

Purpose and Scope

The purpose of this report is to document quantification 

and simulation of metal loading to the upper Animas River 

that was based on two tracer-injection and synoptic-sampling 

studies performed in 1997 and 1998. The methods used to calculate stream discharge and chemical mass loading from the 

collected data are described. Additionally, this report describes 

the computer simulations using the one-dimensional computer 

program OTIS (Runkel, 1998) to simulate the effects of potential remediation plans.

Study Area Description

The upper Animas River study area is in San Juan County 

in southwestern Colorado near Silverton. The study area 

encompasses the upper Animas River from the historical mining town of Eureka to the town of Silverton (fig. 1). The river 

and its major tributaries originate at an altitude of more than 

3,000 meters (m). The watershed receives as much as 

80–100 centimeters (cm) of annual precipitation principally 

as snow in winter (Yager and Bove, 2002), and the principal 

source of streamwater is snowmelt runoff, which usually 

occurs from May through July. Major tributaries to this reach 

of the upper Animas River include Eureka Gulch, Minnie 

Gulch, Maggie Gulch, Otto Gulch, Porcupine Gulch, Cataract 

Gulch, Cunningham Gulch, Hematite Gulch, Arrastra Gulch, 

Boulder Gulch, Blair Gulch, and Swansea Gulch (fig. 1).

Bedrock beneath much of the study area consists of 

Tertiary volcanic rocks of the Silverton caldera, underlain by 

Precambrian igneous and metamorphic rocks and Paleozoic 

sedimentary rocks that outcrop in the southern part of the 

study area (Luedke and Burbank, 1996a; 1996b; Yager and 

Bove, 2002). Tertiary volcanism in the San Juan volcanic 

field began between 35 and 30 million before present (Ma), 

and later caldera-related eruptions occurred between 28.2 and 

27.6 Ma (Yager and Bove, 2002). Caldera-bounding ring and 

tangential radial fractures associated with the Silverton caldera 

provided pathways for later intrusive magmas and hydrothermal fluids, which contain gold and silver mineral deposits in 

the area (Yager and Bove, 2002). Subsequent uplift, erosion, and glaciation of the area in more recent geologic time 

resulted in surficial exposure of the hydrothermally altered 

rock, and continued weathering of the bedrock and derived 

surficial materials released acid and metals to surface and 

ground waters in the drainage basin prior to mining (Bove 

and others, 2000; Church and others, 2000; Mast and others, 

2000).

Placer gold deposits were discovered in 1871 on Arrastra 

Creek upstream from Silverton, and hard-rock gold and silver 

mining activity spread rapidly through the area following the 

1873 treaty with the Ute Indians (U.S. Geological Survey, 

2000). Mining continued in the Animas River watershed 

at various levels of activity until 1991 when the Sunnyside 

Mine was closed (U.S. Geological Survey, 2000). More than 

100 years of historical mining activity created many kilometers of underground workings and produced large volumes of 

waste rock. The mine workings provide pathways for ground 

water and surface water to react with mineralized rock 
Figure 1. Location of study area and study reaches, upper Animas River, Colorado.

Introduction 3

Eureka

Forest Queen

mine

Kittimack

tailings

Howardsville

Tailings nearMayflower Mill

Cement Creek

Lackawanna

Mill

COLORADO

Primary

braided

reach

Upstream end

and injection site

1998 study reach

Upstream

end and

injection site

1997 study reach

Downstream end

1998 study reach

Downstream

end 

1997 study reach 1 MILE

1⁄2

00

0.5 1 KILOMETER

Mayflower

Mill

107o40’ 107o35’

37o50’

37o53’30”

Base from U.S. Geological Survey, 1955Handies Peak, Howardsville, and Silverton 7.5 minute quadrangles1927 North American DatumUniversal Transverse Mercator projection, Zone 13

Seconday

braided

reach

EXPLAN

ATION

TailingsStudy reach boundary

Index map

Silverton

Eureka Gulch

M ni n ei Gulch

Maggie Gulch

Porcupine

Gulch

Cataract Gulch

Hematite Gulch

Cunningham Gulch

A

N

MI AS

RIVER

Otto Gulch

Bo l u ed r Gu cl h

Blair Gulch

Arrastra Gulch

Swansea Gulch

Pride of the 

West Mill
4 Quantification and Simulation of Metal Loading to the Upper Animas River, Eureka to Silverton, San Juan County, Colorado, 

 September 1997 and August 1998

producing low-pH, metal-rich waters that flow from mine adits 

(U.S. Geological Survey, 2000). Ground-water and surfacewater flow in and over waste rock piles also can contribute 

acidic metal-rich drainage to the Animas River and its tributaries. Mineralization and historical mining sites are present 

throughout the area, but several specific areas are possible 

contributors of metals to the Animas River: Eureka Gulch, the 

Forest Queen mine downstream from Eureka, the Kittimack 

tailings, mill tailings near Howardsville, Arrastra Gulch, mill 

tailings near the Mayflower Mill, and mill tailings near the 

Lackawanna Mill (fig. 1).

Study Methods

Metal loading to the upper Animas River was quantified 

by performing two tracer-injection and synoptic-sampling 

studies and by simulating study results with the onedimensional solute-transport code OTIS (Runkel, 1998). One 

tracer-injection and synoptic-sampling study was performed 

on the upper Animas River reach from Howardsville to Silverton in September 1997, and a second study was performed 

on the stream reach from Eureka to Howardsville in August 

1998 (fig. 1). This section of the report describes the methods used for tracer injection and synoptic sampling and for 

sampling and analyzing surface-water samples. Methods used 

for calculating discharge, traveltime, and mass loading also are 

described. A general overview of the one-dimensional computer code OTIS (Runkel, 1998) used for simulating solute 

transport also is provided.

Tracer-Injection and Synoptic-Sampling 

Methods

The methodology of tracer-injections studies was 

developed as part of the USGS Toxic Substances Hydrology Program to identify and enumerate sources of acid and 

metals to streams (Bencala and McKnight, 1987; Bencala 

and others, 1990; Broshears and others, 1995; Kimball and 

others, 1991; 1994; Kimball, 1997; Kimball and others, 

1999a, 1999b, 1999c; Runkel and others, 1996; Walton-Day 

and others, 1999). As described in this section of the report, a 

tracer-injection study includes a tracer injection to quantify 

discharge (Kilpatrick and Cobb, 1985) and synoptic sampling 

to provide spatial concentration profiles of pH and inorganic 

constituents. Discharge and concentration data then are combined to develop mass-loading profiles for the stream.

Quantification of metal loads requires accurate discharge 

measurements and representative chemical concentrations. 

However, quantifying discharge in mountain streams by the 

traditional velocity-area method (Rantz, 1982) is complicated 

by streambed roughness and variability caused by pools and 

riffles (Jarrett, 1992). In addition, some percentage of discharge cannot be measured by the traditional method because 

of flow through the streambed (hyporheic zone) (Bencala 

and Walters, 1983; Bencala and others, 1991; Harvey and 

Bencala, 1993; Zellweger and others, 1988). Because velocity-area discharge measurements cannot measure flow through 

the hyporheic zone, metal-loading calculations based on 

traditional discharge measurements may underestimate metal 

loads (Kimball, 1997; Zellweger and others, 1988). Application of the velocity-area method for quantifying metal loads 

also is limited by the time and personnel required to measure 

discharge at numerous stream sampling sites in a single day.

The tracer-injection study is an alternative method of 

estimating discharge in gaining mountain streams (Kilpatrick 

and Cobb, 1985). A tracer injection consists of continuously 

injecting an inert chemical tracer into the stream at a constant 

rate and concentration and measuring the downstream dilution 

of the tracer at various locations. Given sufficient time during 

a tracer injection, all parts of the stream including side pools 

and the hyporheic zone become saturated with tracer, and 

instream tracer concentrations will reach a plateau (Kimball, 

1997). Downstream decreases in tracer plateau concentration 

indicate tracer dilution by surface- and ground-water inflow 

to the stream, and stream discharge is calculated from the 

downstream dilution. The downstream arrival, concentration 

plateau, and departure (upon cessation of the injection) of the 

tracer also are monitored at selected transport sites to compute 

stream velocities and other streamflow properties. Discharge 

computed from tracer concentrations accounts for both the 

surface and the hyporheic flow because the tracer follows 

the water through cobbled bed sediment. The tracer-injection 

method also allows discharge estimates at numerous locations 

in a short timeframe. Zellweger and others (1988) provide 

additional details of tracer-injection methods.

Synoptic sampling is a one-time detailed sampling of 

stream sites and all visible tributary inflows to the stream 

performed during the plateau period of the tracer injection. 

Synoptic sampling provides a description of the stream and 

tributary inflow chemistry during the tracer injection. By 

combining discharge, computed from the tracer injection, 

with synoptic metal concentrations, metal-loading profiles 

are developed for the stream using mass-balance calculations. Results of the tracer-injection study can identify where 

changes in stream load occur. However, study results do 

not identify specific pathways to the stream from particular 

sites, except for visible surface inflows. The detailed loading 

information provides insight to the key geochemical processes 

affecting stream pH and metal concentrations, and it provides 

the hydrologic framework for solute-transport simulations 

(Bencala, 1983; Bencala and others, 1988; Broshears and 

others, 1993; Broshears and others, 1996; Harvey and others, 

1996; McKnight and Bencala, 1989; Runkel, 1998; Runkel 

and others, 1996; Runkel and others, 1999; Wagner and 

Harvey, 1997).

Both of the upper Animas River tracer-injection studies 

were conducted during fall base-flow (low-flow) conditions. 

Application of tracer-injection studies to low-flow condi-
tions is appropriate for two reasons. First, the mass-loading 

profiles developed for low-flow conditions reflect base-flow 

metal-loading conditions, which are present all year long. 

Remediation that addresses sources identified during low flow 

therefore will improve water quality during the entire year. 

Second, mass-loading profiles developed for low-flow conditions indicate those sources contributing to elevated instream 

concentrations during the winter months when conditions 

most toxic to aquatic organisms likely occur (Besser and Leib, 

1999). During the low-flow winter months, dilution of metals 

is minimal, and toxicity standards based on metal concentrations are more likely exceeded (Besser and others, 2001). 

Testing during low-flow conditions also makes it possible to 

measure discharge and collect samples at many synoptic-sampling sites during the tracer plateau.

Successful implementation of a tracer-injection study 

requires that the injected tracer be transported through the 

stream system in a conservative manner unaffected by biogeochemical reactions. Potential tracers include dyes and 

inorganic salts. Dye tracers have the disadvantage of being 

unstable at low pH, and they adsorb to solids and organic matter in the hyporheic zone (Bencala and others, 1986). Chloride 

and bromide salts of sodium and lithium are suitable tracers in 

environments where naturally occurring chloride or bromide 

concentrations are low. Lithium works well in streams with 

low pH, and chloride and bromide work well in streams with 

higher pH (Bencala and others, 1990). Sodium chloride tracer 

was used for both of the upper Animas River tracer injections 

where stream pH was circumneutral. 

Sampling and Analytical Methods

Surface-water samples were collected at downstream 

transport sites and synoptic-sampling sites during the tracer 

injection. Sampling sites are referenced by their distance in 

meters downstream from the injection, and inflow samples 

were referenced as being on the right or left streambank looking downstream.

Frequent surface-water samples were collected at the 

transport sites during the tracer injections to observe the 

arrival, plateau, and departure of the sodium-chloride tracer. 

Transport-site samples were collected as manual grab samples 

and with auto samplers and were filtered upon collection 

through 0.45-micrometer (μm) in-line capsule filters into 

polyethylene bottles. Transport-site samples were analyzed for 

chloride concentrations using ion chromatography (table 1) at 

the USGS laboratory in Salt Lake City, Utah, using analytical techniques and quality assurance procedures described by 

Kimball and others (1999a).

Synoptic samples were collected from instream and 

inflow sites during the tracer plateau. Instream and inflow 

samples were collected into polyethylene bottles, and water 

temperature was measured at each site upon sample collection. For the instream sites, samples were collected using 

equal-width integration (EWI) and a DH-81 sampler (Wilde 

and others, 1998). Manual grab samples were collected at 

inflow sites. A temporary field laboratory was used to process 

the synoptic samples, measure pH and specific conductance, 

and filter the samples for the remaining analyses (table 1). To 

prevent photoreduction of iron, all samples were kept out of 

the light in dark plastic bags until processing at the temporary 

field laboratory.

Synoptic samples were analyzed for anions and iron 

speciation at the USGS laboratory in Salt Lake City, Utah. 

Chloride and sulfate concentrations were determined using ion 

chromatography (Kimball and others, 1999a), alkalinity was 

determined using Gran titration (Stumm and Morgan, 1981), 

and iron speciation was determined colorimetrically (table 1). 

Precision of the ion chromatography results was less than 

5 percent for chloride analyses and less than 10 percent for 

sulfate analyses (Kimball and others, 1999a).

Dissolved and total-recoverable concentrations for aluminum, barium, calcium, cadmium, copper, iron, potassium, 

magnesium, manganese, sodium, silica, strontium, and zinc 

were determined by inductively coupled argon plasma atomic 

emissions spectrometry (ICP-AES, table1). The dissolved 

concentrations for instream samples were obtained by filtering samples through a tangential-flow filter apparatus with 

a 10,000-Dalton molecular-weight nominal pore size (Benoit and Rozan, 1999; Kimball and others, 1992; Moran and 

Moore, 1989). For inflow samples, dissolved concentrations 

were obtained from a 0.45-μm filtration using the same apparatus. For both instream and inflow samples, total-recoverable 

concentrations were obtained from an unfiltered sample. The 

colloidal concentration was calculated indirectly by subtracting the dissolved concentration from the total-recoverable 

concentration (Kimball and others, 1995). Synoptic samples 

for ICP-AES analyses were acidified at the field laboratory 

using 1 milliliter (mL) of ultrapure nitric acid. ICP-AES 

analyses of synoptic samples from the September 1997 tracerinjection study (Howardsville to Silverton study reach) were 

performed at the USGS laboratories in Boulder, Colorado, and 

ICP-AES analyses of synoptic samples from the August 1998 

tracer-injection study (Eureka to Howardsville study reach) 

were performed at the Colorado School of Mines laboratories in Golden, Colorado. ICP-AES analytical techniques are 

described in Taylor (1982) and Garbarino and Taylor (1984a; 

1984b), and quality-assurance procedures followed the methods described by Friedman and Erdmann (1982). 

Discharge and Traveltime Calculations

During a tracer injection, the tracer reaches a steady 

plateau concentration in the stream, and discharge can be 

calculated by the amount of tracer dilution at each successive instream site by using the conservation of mass. If stream 

discharge increases downstream, the tracer will have successively lower downstream plateau concentrations. The 

synoptic sampling is conducted during the plateau period 

of the tracer injection, and tracer concentrations from the 

Study Methods 5
6 Quantification and Simulation of Metal Loading to the Upper Animas River, Eureka to Silverton, San Juan County, Colorado, 

 September 1997 and August 1998

synoptic sampling are used to compute stream discharge as 

discussed herein.

Conservation of mass requires the load of tracer in the 

stream at B to be equal to the load at A, upstream from the 

injection, plus the load added by the injection (table 2, equation 1). In addition, by flow balance, the discharge at B must 

equal the discharge at A plus the discharge of the injection. 

Discharge at the downstream site B then is computed from the 

injection flow rate and concentration and the measured tracer 

concentrations at sites A and B (table 2, equation 2). Mass and 

flow balance relations also are used to develop a discharge 

equation for site C and all subsequent sites downstream based 

on the flow and measured tracer concentration computed for 

the upstream site B and the measured tracer concentration of 

any inflow between sites B and C (table 2, equation 3). 

Inflow to the stream can include visible tributaries, seeps, 

springs, and diffuse ground-water inflow. Inflow discharge 

is computed as the difference in discharge between sites C 

and B (table 2, equation 4). If a visible tributary is present in 

the reach between two sites, calculated inflow discharge is 

assigned to the tributary inflow. If there is no visible inflow 

between two sites, calculated inflow discharge is assigned as 

unsampled ground-water inflow.

During the tracer injection, the arrival, plateau, and 

departure of tracer in the stream are monitored at several 

downstream transport sites, and the transport graphs are used 

to calculate traveltime between sites as well as stream-channel 

parameters used for solute-transport simulations. The tracer 

arrival time at a site (t

50) is defined as the time at which the 

instream tracer concentration reaches one-half of the plateau 

concentration (C50) (Zellweger and others, 1988). Traveltime 

between two sites is the difference in arrival times.

Mass-Loading Calculations

Discharge values computed from a tracer-injection study 

are combined with synoptic-sampling results to compute 

mass-loading graphs for various constituents of interest. The 

constituent load at the downstream end of a stream segment 

includes the load from the upstream end plus the load contributed by all surface and subsurface inflows between the sites 

(table 2, equation 5). The sampled instream load (Ms) and the 

sampled inflow load (MI) are two ways to consider the load of 

a stream segment (Kimball and others, 1999a). The sampled 

instream load at site C, Mc, is calculated as the product of the 

discharge (Q) and synoptic constituent concentration (C) at 

each stream sampling site (table 2, equation 5). The sampled 

instream load represents the effect of constituent sources in the 

watershed on the stream, and it is used to identify changes in 

constituent load because it can increase, decrease, or remain 

constant between stream sites. An increase generally indicates 

a source of constituent loading, and the magnitude of the 

increase compared to other stream segments ranks the sources 

in the context of the watershed. A decrease generally indicates 

a loss of metal from the water through chemical reactions such 

as precipitation or adsorption. Both reactions can result in loss 

to the streambed or a transformation from the dissolved phase 

to a colloidal solid phase.

The net change in sampled instream load between stream 

sites includes the instream load at site B plus the inflow load 

contributed by all the surface and subsurface inflow between 

sites B and C (table 2, equation 5). Because it is not possible to sample all the inflow affecting the stream, especially 

the diffuse ground-water inflow, the inflow concentration in 

equation 5 (table 2) represents an effective inflow concentra-

 Analysis Field treatment Analytical method

Chloride tracer concentrations and sulfate Filtered (0.45 μm), unacidified Ion chromatography (Kimball and others, 

1999a)

pH, specific conductance Unfiltered, unacidified Ion-sensitive electrode measured at field 

laboratory

Filtered ferrous iron Filtered (0.45 μm), unacidified Bipyridine, colorimetric method for ferrous 

iron

Filtered metal concentrations Filtered (10,000 Dalton), acidified 

Filtered (0.45 μm), acidified

ICP-AES (Taylor, 1982; Garbarino and 

Taylor, 1984a; 1984b; Friedman and 

Erdmann, 1982)

Total-recoverable metal concentrations Unfiltered, acidified ICP-AES with standard U.S. Environmental 

Protection Agency digestion for total-recoverable concentrations (Taylor, 1982; 

Garbarino and Taylor, 1984a; 1984b; 

Friedman and Erdmann, 1982)

Table 1. Analytical methods for tracer and synoptic water samples collected during the Eureka to Howardsville tracerinjection study, August 1998, and the Howardsville to Silverton tracer-injection study, September 1997.

[μm, micrometer; ICP-AES, inductively coupled plasma atomic emissions spectrometry]
Calculated quantity Tracer-dilution equations Variables

(1) Mass balance downstream from the 

injection site

MB = CBQB

 = CAQA + CinjQinj

QB = QA + Qinj

MB, Load at site B

CB, Concentration at site B

QB, Discharge at site B

CA, Concentration at site A

QA, Discharge at site A

Cinj, Concentration of injectate solution

Qinj, Discharge of injection pump

(2) Discharge at first site downstream from 

tracer injection QB = Qinj (Cinj - CA)

 (CB - CA)

All variables defined above

(3) Discharge at subsequent downstream 

sites QC = QB (CB - CI

)

 (CC - CI)

QC, Discharge at downstream site C

CC, Concentration of tracer at site C

CI, Sampled inflow concentration of tracer

(4) Inflow discharge QI

 = QC - QB QI, Computed inflow discharge. If visible inflow is present in the reach, QI is 

assigned inflow discharge, otherwise, QI

is assigned to unsampled ground-water 

discharge.

Solute-loading equations

(5) Sampled instream load at subsequent 

stream sites

MC = CC QC

 = CBQB + CI 

E (QC - QB)

MC, Load at site C or subsequent sites 

downstream

CI

E, Effective inflow concentration

(6) Effective inflow concentration CI

E =

 (CC QC - CB QB)

 (QC - QB)

All variables defined above

(7) Change in sampled instream load ∆MS = CC QC - CB QB

 = CI 

E (QC - QB)

∆MS, Net change in load between sites B 

and C

(8) Change in sampled inflow load ∆MI

 - CI (QC - QB) ∆MI, Net change in load between sites B 

and C based on sampled inflow concentration 

CI, Sampled inflow concentration

Table 2. Equations defining calculated quantities in tracer-injection studies (modified from Kimball and others, 

1999a) [Subscripts correspond to sites illustrated in the diagram].

Study Methods 7
8 Quantification and Simulation of Metal Loading to the Upper Animas River, Eureka to Silverton, San Juan County, Colorado, 

 September 1997 and August 1998

tion (CI

E), which is a discharge-weighted mean concentration 

of all surface and subsurface inflow contributions within the 

stream segment (table 2, equation 6). 

The change in instream load between two stream sites 

(∆MS) is defined as the downstream load minus the upstream 

load (table 2, equation 7), and the cumulative instream load is 

defined as the sum of the positive values of ∆MS. Each negative value of ∆MS indicates a stream segment where there is a 

net reduction in constituent load, and the cumulative instream 

load is held constant for a segment with a negative ∆MS. The 

cumulative instream load represents the minimum total load 

added to the stream over the study reach. Comparison of ∆MS

to MS indicates the extent of instream constituent attenuation 

along the study reach, because ∆MS is greater than MS when 

MS is reduced by physical, chemical, or biological process.

The change in sampled inflow load, ∆MI, represents the 

load contributed to the stream from visible inflows and is 

calculated for each stream reach as the product of the sampled inflow concentrations, CI, and the change in discharge 

between stream sites, QI (table 2, equation 8). The change 

in sampled inflow load represents the net change in stream 

loading from the sampled inflow concentrations. For stream 

segments with no visible inflow, ∆MI is set to zero. The cumulative inflow load is the sum of the values for ∆MI along the 

study reach.

Table 3 presents probable explanations for the various 

relations between ∆MS and ∆MI. If ∆MS and ∆MI are nearly 

equal for a stream segment, then the sampled inflow concentrations, CI, approximate the effective inflow concentrations, 

CI

E, and the sampled inflow loads account for the change in 

stream loading. If ∆MS is greater than ∆MI, then CI

E is greater 

than CI, presumably because there is unsampled inflow such 

as ground-water discharge to the stream with high constituent concentrations. For colloidal constituent loads, if ∆MS is 

greater than ∆MI, chemical precipitation of colloidal material 

is indicated. For dissolved constituent loads, if ∆MS is less 

than ∆MI, then there has been a reduction in load by chemical 

reaction.

Solute-Transport Simulations

To interpret mass-loading calculations and simulate the 

effects of potential remediation plans in the basin, surfacewater flow and zinc solute transport were simulated for the 

Eureka to Howardsville and the Howardsville to Silverton 

study reaches using the one-dimensional computer program 

OTIS (Runkel, 1998). A general overview of OTIS is provided 

in this section of the report. Details on the site-specific application of OTIS to the Eureka to Howardsville and Howardsville to Silverton study reaches are provided in subsequent 

sections.

OTIS is a computer code for simulating onedimensional solute transport of a single solute in a stream 

based on the advection-dispersion equation with additional 

terms to account for transient storage, lateral inflow, first-order 

decay, and adsorption (Runkel, 1998). Transient storage refers 

to the temporary storage of streamwater in the stream and 

adjacent streambed, and OTIS accounts for transient storCondition Probable explanation

∆MS = ∆MI The sampled inflow concentrations approximate the effective inflow 

concentrations, and the sampled inflow load accounts for the change 

in sampled stream load.

∆MS > ∆MI The sampled stream load is greater than the sampled inflow load, and 

the sampled inflow load does not account for the change in sampled 

stream load. For dissolved constituents, ground-water discharge 

with elevated constituent concentrations is indicated. For colloidal 

constituents, transfer from the dissolved to the colloidal phase by 

chemical precipitation is indicated.

∆MS < ∆MI The sampled inflow load is greater than the sampled stream load indicating a loss of stream load through physical, chemical, or biological 

reaction or dilution by ground-water inflow.

∆MS < 0 There is a net loss of load through physical, chemical, or biological reaction in the stream reach.

Table 3. Probable explanations for various cumulative stream-load relations (modified from Kimball 

and others, 1999a).

[∆MS, change in sampled instream load; MI, change in sampled inflow load; <, less than; >, greater than]
age by solving separate mass-balance equations for the main 

stream channel and the stream storage zone. The main channel 

is defined as the stream portion where advection and dispersion are the dominant transport processes, and the storage zone 

is defined as the stream portion where transient storage occurs. 

Advection and dispersion are not included in the storage zone, 

where downstream transport is negligible. Lateral inflow 

represents additional water coming into the main channel as 

overland flow, interflow, and ground-water discharge. Chemical reactions can be specified within the main channel, the 

storage zone, or both.

OTIS can be used in conjunction with data from fieldscale tracer-injection studies to quantify the hydrologic parameters affecting surface-water flow (Runkel, 1998). The application of OTIS to tracer-injection results generally involves a 

trial-and-error process where estimates for the hydrologic 

parameters of channel cross-sectional area, transient storage 

cross-sectional area, and solute dispersion are adjusted to 

obtain an acceptable match between simulated and measured 

tracer concentrations for the tracer-transport sites and synoptic 

sampling. OTIS-P is a modified version of OTIS that couples 

OTIS with a nonlinear regression package to automate the 

hydrologic parameter-estimation process.

Once the hydrologic parameters are established for the 

conservative tracer, OTIS is used to simulate measured mass 

loading and solute transport for constituents of interest. For 

the two upper Animas River study reaches, the measured 

inflow concentrations (CI) are used as lateral inflow values to 

simulate conservative solute transport for zinc. The simulated 

instream concentration profile is compared to the measured 

synoptic instream concentration profile to identify potential 

instream physical, chemical, or biological processes in the 

stream reach. If the simulated instream concentrations for 

a given constituent are higher than the measured synoptic 

instream concentrations, then removal of the constituent by 

physical, chemical, or biological processes is indicated. For 

the two upper Animas River study reaches, the effects of 

instream chemical reactions are simulated using first-order 

decay. The resulting OTIS simulations then are used to predict 

the effects of hypothetical remedial actions for the upper 

Animas River.

Metal Loading to the Upper Animas 

River, Eureka to Howardsville, 

Colorado, Study Reach, August 1998

The Eureka to Howardsville tracer-injection study 

started near the historical mining town of Eureka and ended 

downstream from Howardsville at the USGS gaging station 

09358750 (referenced herein using the Colorado State 

gaging station number A53). This study reach encompassed a 

7,250-m reach of the upper Animas River (fig. 2).

Tracer-Injection Study Objectives

There were three primary objectives for the Eureka to 

Howardsville tracer-injection study. The first objective was to 

identify and locate metal loading in the stream study reach. 

Although a tracer-injection study can help identify where load 

increases occur, it does not identify specific pathways to the 

stream from particular sites, except for visible surface inflows. 

Possible sources of metal loading include Eureka Gulch, the 

Forest Queen mine discharge, the Kittimack mill tailings, 

and tailings near Howardsville. The second objective was to 

determine (for low-flow conditions) if the stream reach is a 

net sink or source of metals to the downstream areas. This 

objective was accomplished by identifying and describing any 

instream physical, chemical, or biological processes affecting 

metal concentrations and natural attenuation. A third objective for the Eureka to Howardsville study was to characterize 

the effects of braided stream reaches on streamwater quality. 

There is a primary braided reach just downstream from Eureka 

from 786 to 2,030 m and a secondary braided reach near the 

Kittimack tailings from 3,150 to 3,435 m. Channel restoration is being considered for these braided reaches, and an 

understanding of 1998 conditions will aid in rechannelization 

planning.

Tracer-Injection Study Methods

The Eureka to Howardsville tracer-injection study was 

conducted August 11 through August 14, 1998. A solution 

containing 166,700 milligrams per liter (mg/L) of sodium 

chloride was injected into the upper Animas River at an average flow rate of 1.784 liters per minute (L/min). The injection started at 1000 hours on August 11, 1998, but the pump 

stopped at approximately 1200 hours the same day. The injection began again at 1002 hours on August 12, 1998 and ran 

continuously until 1930 hours on August 14, 1998 (table 4). 

For reporting results, time 0.0 is the beginning of experiment 

time, which was midnight on August 11, 1998, and subsequent 

times are reported as decimal hours.

The Eureka to Howardsville injection site was located 

approximately 347 m upstream from Eureka Gulch so inflow 

from Eureka Gulch could be quantified as tributary inflow. 

The arrival of the sodium-chloride pulse and the development 

of a plateau concentration were measured at four downstream 

locations, transport sites T1 through T4 (fig. 2). Transport 

site T1 was located upstream from Eureka Gulch at 282 m. 

Transport site T2 was located at 2,240 m, downstream from 

the braided reach, and site T3 was located at 5,467 m at the 

same location as the tracer injection for the Howardsville to 

Silverton tracer-injection study conducted in 1997. Transport 

site T4 was located at 6,993 m at the Howardsville gaging 

station A53.

Metal Loading to the Upper Animas River, Eureka to Howardsville, Colorado, Study Reach, August 1998 9
10 Quantification and Simulation of Metal Loading to the Upper Animas River, Eureka to Silverton, San Juan County, Colorado, 

 September 1997 and August 1998

Figure 2. Eureka to Howardsville study reach, upper Animas River, Colorado, August 1998.

Synoptic Sampling and Analyses

Synoptic samples were collected from 34 instream sites, 

including the 4 transport sites and 4 sites in the breaded reach 

at 1,618 m, and 17 inflows on August 14, 1998, during the 

plateau period of the tracer injection. Although there was 

rain before and after the synoptic sampling, there was no rain 

during the sampling, so steady-state conditions were achieved 

during the synoptic sampling. Instream sampling sites were 

located upstream and downstream from identified inflows to 

allow mass-balance calculations for each inflow, and additional sites were located in longer subreaches between inflows 

to account for subsurface inflow. Seventeen inflow-sampling 

sites were chosen to represent the range of pH and specific 

conductance of water entering the stream. Although there were 

several sampling sites in the braided reach, only the samples 

upstream and downstream from the braided reach can account 

for the metal loading or loss that could occur in the braided 

reach. The instream sample at 786 m represents input to the 

braided reach, and the instream sample at 2,030 m represents 

output from the braided reach.

Instream and inflow water samples were analyzed in the 

field and laboratory for various constituents as presented in the 

Eureka

Forest Queen

mine

Kittimack

tailings

Howardsville

Primary

braided

reach

Seconday

braided

reach

Porcupine Gulch

Cataract Gulch

Otto Gulch

Upstream end and

injection site

1998 study reach

(0 meters)

Downstream end

1998 study reach

(7,250 meters)

ANIMAS RIVER

Hematite Gulch

(6,633 meters)

Cunningham Gulch (6,558 meters)

Maggie Gulch (3,450 meters)

Minnie Gulch

Eureka Gulch (347 meters)

T1

(282 m)

T2

(2,240 m)

T3

T4 and (4,567 m)

gaging station 

A53

(6,993 m)

(2,465 meters)

37o53’30”

107o32’30”

37o50’

Base from U.S. Geological Survey, 1955

Handies Peak and Howardsville 

7.5 minute quadrangles

1927 North American Datum

Universal Transverse Mercator

projection, Zone 13

Transport site and distance

 downstream from injection

 site, in meters—Distance of

 features downstream from

 injection site, in meters,

 shown in parentheses

T1

(282 m)

107o35’

0 1⁄2 1 MILE

0 0.5 1 KILOMETER

EXPLANATION

Tailings

Study reach boundary

COLORADO

Index map
“Study Methods” section of this report. The analytical methods are listed in table 1.

Tracer-Injection Study Results

Chemical analyses results for chloride tracer concentrations at the Eureka to Howardsville transport and synoptic 

sites were used to compute traveltime, stream discharge, and 

chemical mass loading as discussed herein. The 1998 synoptic-sampling site locations are listed in table 5, field measurements and major ion concentrations are listed in Appendix 1, 

and ICP-AES synoptic-sampling results are listed in 

Appendix 2. Data are sorted in downstream order within 

groups of instream and inflow sites to emphasize the downstream changes.

Arrival Times

Information from the arrival and departure of tracer from 

the transport sites was used to calculate the traveltime between 

sites. Despite the complication caused by the pumps stopping 

on the first day of injection, the arrival times of the tracer at 

the downstream sites during the subsequent injection were not 

affected, and data from the restarted continuous injection are 

reported herein. 

Data for transport sites T1 and T2 are used to demonstrate how arrival times of the chloride tracer were calculated 

and to discuss traveltime through the braided reach (fig. 3). At 

transport site T1, an abrupt chloride arrival is noted; indicating 

that the interval of time between sample collections was too 

large to discern a gradual tracer arrival. However, the tracer 

arrival curve is well defined at transport site T2. After the 

initial arrival of chloride tracer at sites T1 and T2, the plateau 

concentration decreased between 35 and 40 hours because of a 

decrease in the upstream tracer injection rate (table 4). A second decrease in the tracer plateau is noted at both sites T1 and 

T2 at approximately 75 hours because of a local rainstorm, 

which diluted the instream tracer concentrations. Because of 

variations in tracer plateau concentration at sites T1 and T2, an 

assumed average tracer plateau concentration for each site was 

used to compute the traveltime between sites. An average plateau concentration of 11.0 mg/L was assumed at site T1, and 

an average plateau concentration of 5.5 mg/L was assumed at 

T2, resulting in C50 values of 5.5 mg/L and 2.25 mg/L for sites 

T1 and T2, respectively. Interpolations of C50 arrival times 

Date Clock time

Experiment 

time

(hours)

Activity

08/09/1998–

08/10/1998

Stream reconnaissance and discharge measurements

08/11/1998 0000

1000

1800

 0.0

10.0

18.0

Start of experiment time

Start of initial injection

Initial injection pump stopped

08/12/1998 1002

1115

1135

1705

1920

1932

34.03

35.25

35.58

41.08

43.33

43.53

Started injection pump

Injectate sample, measured pump rate at 2,517 mL/min

Adjusted pump rate to approximately 1,833 mL/min

Injectate sample, measured pump rate at 1,783 mL/min

Finished refilling the tank with injectate solution

Injectate sample, measured pump rate at 1,817 mL/min

08/13/1998 1056

1115

1538

1600

58.93

59.25

63.63

64.00

Finished refilling the tank with injectate solution

Measured pump rate at 1,725 mL/min

Measured pump rate at 1,800 mL/min

Finished refilling the tank with injectate solution

08/14/1998 1000 –1830

1135

1520

1930

 82.0 – 90.5

83.58

87.33

91.50

Synoptic sample collection

Injectate sample, measured pump rate at 1,790 mL/min

Measured pump rate at 1,767 mL/min

Stopped pumps

Table 4. Tracer-injection study sequence of events, upper Animas River, Eureka to Howardsville, 

Colorado, August 1998.

[mL/min, milliliters per minute]

Metal Loading to the Upper Animas River, Eureka to Howardsville, Colorado, Study Reach, August 1998 11
12 Quantification and Simulation of Metal Loading to the Upper Animas River, Eureka to Silverton, San Juan County, Colorado, 

 September 1997 and August 1998

Table 5. Synoptic-sampling sites and discharge calculated from tracer-dilution, upper Animas River, Eureka to 

Howardsville, Colorado, August 14, 1998.

[distance, distance downstream from injection site; L/s, liters per second; ft3/s, cubic feet per second; --, not applicable] 

Distance

(meters) Site name Source

Inflow 

location

Discharge

(L/s)

Discharge

(ft3/s)

0 Upstream from injection site Stream -- 261 9.2

80 First site downstream from injection Stream -- 261 9.2

282 T1 site—Upstream from Eureka Gulch Stream -- 310 11.0

347 Eureka Gulch Inflow Right bank 162 5.7

586 Downstream from Eureka Gulch Stream -- 472 16.7

786 Near right bank talus slope Stream 473 16.7

906 Upstream from first braids Stream 477 16.8

1,061 Upper braided reach Stream 481 17.0

1,411 Left braid near Forest Queen Stream -- 491 17.3

1,618 1618 Braids Stream -- 496 17.5

1,918 Left braid upstream from Forest Queen Stream -- 505 17.8

2,030 Upstream from Forest Queen inflow Stream -- 706 25.0

2,090 Inflow from Forest Queen mine Inflow Left bank 80.2 2.8

2,240 T2 site—Downstream from end of braids Stream -- 786 27.8

2,420 Upstream from Minnie Gulch Stream -- 786 27.8

2,465 Minnie Gulch Inflow Left bank 90.3 3.2

2,860 Near braided area Strean -- 877 31.0

3,150 Upstream from inflow near Kittimack Stream -- 948 33.5

3,165 Upstream from Otto Gulch fan Inflow Right bank 104 3.7

3,400 Downstream from braids near Kittimack Stream -- 1,052 37.2

3,405 Drains hillslope or alluvium Inflow Left bank 168 5.9

3,435 Upstream Maggie Gulch downstream Kittimack tailings Stream -- 1,200 43.1

3,450 Maggie Gulch Inflow Right bank 80.5 2.8

3,665 Downstream from Maggie Gulch Stream -- 1,301 46.0

3,905 Upstream from braided reach Stream -- 1,328 46.9

3,954 Drains large area of willows Inflow Right bank 29.3 1.0

4,164 Near beaver ponds on left bank Stream -- 1,357 48.0

4,189 Inflow from beaver ponds Inflow Left bank 84.2 3.0

4,430 Downstream from beaver ponds on left bank Stream -- 1,441 50.9

4,670 Downstream from braids Stream -- 1,560 55.1

4,970 Along smooth reach of stream Strean -- 1,570 55.5

5,190 Upstream from beaver pond inflow Strean -- 1,595 56.4

5,210 Drains beaver pond Inflow Right bank 0.8 0.03

5,407 Drains ponds Inflow Right bank 0.8 0.03

5,467 T3 site--Site of 1997 Howardsville injection Inflow Left bank 0.8 0.03

5,648 Drains upstream from tailings piles Stream -- 1,597 56.4

6,038 Along tailings piles (1997 T1) Inflow Left bank 30.2 1.1

6,438 Inflow from Howardsville Mill Stream -- 1,627 57.5
Table 5. Synoptic-sampling sites and discharge calculated from tracer-dilution, upper Animas River, Eureka to 

Howardsville, Colorado, August 14, 1998.—Continued

[distance, distance downstream from injection site; L/s, liters per second; ft3/s, cubic feet per second; --, not applicable] 

Distance

(meters) Site name Source

Inflow 

location

Discharge

(L/s)

Discharge

(ft3/s)

6,528 Downstream from Howardsville Mill Inflow Left bank 15.7 0.6

6,558 Cunningham Gulch Stream -- 1,662 58.7

6,618 Downstream from Cunningham Gulch Inflow Left bank 445 15.7

6,633 Hematite Gulch Stream -- 2,107 74.4

6,753 Downstream from Hematite Gulch Inflow Right bank 65 2.3

6,993 T4 site—Howardsville gage Stream -- 2,172 76.8

7,008 Drains left bank adit up hill Inflow Left bank 30.6 1.1

7,013 Drains old mill site Inflow Right bank 30.6 1.1

7,063 Also drains old mill site (?) Inflow Right bank 30.6 1.1

7,250 End of study reach Stream -- 2,319 81.9

Metal Loading to the Upper Animas River, Eureka to Howardsville, Colorado, Study Reach, August 1998 13

Figure 3. Dissolved chloride concentrations with time at transport sites T1 and T2, Eureka to Howardsville study 

reach, upper Animas River, Colorado, August 1998.

20 30 40 50 60 70 80 90 100 110 120

0

2

4

6

8

10

12

T1 Tracer arrival time at one-half the plateau

concentration (C50 ) = 34.20 hours

T2 Tracer arrival time at one-half the plateau

concentration (C50 ) = 35.54 hours

Traveltime from T1 to T2 = 1.34 hours (80.4 minutes)

TIME SINCE START OF EXPERIMENT, IN HOURS

DISSOLVED CHLORIDE CONCENTRATION, IN 

MILLIGRAMS PER LITER

 Transport site T1

 Transport site T2
14 Quantification and Simulation of Metal Loading to the Upper Animas River, Eureka to Silverton, San Juan County, Colorado, 

 September 1997 and August 1998

(t

50 values) from figure 3 result in an arrival time of 34.2 hours 

for T1 and an arrival time of 35.54 hours for site T2.

The difference between the T1 and T2 arrival times is 

1.34 hours (80.4 minutes) and represents the average traveltime from site T1 to site T2. Site T2 is located downstream 

from the braided reach of interest, and the traveltime calculated for this stream reach indicates relatively rapid flow of 

water through the braided reach. A stream velocity of 

0.47 meter per second (m/s) was computed for the open stream 

channel from the injection site to site T1, and a stream velocity of 0.45 m/s was computed for the braided reach from site 

T1 to T2. This small difference in stream velocity between 

reaches indicates that the braided reach did not substantially 

reduce water flow velocity under low-flow conditions. 

Discharge Profile

A detailed discharge profile for the 1998 Eureka to 

Howardsville study reach was developed using the chloride 

tracer concentrations that were measured in the synoptic 

samples and adjusted for analytical precision. Discharge 

calculations based on chloride concentrations for a given 

tracer-injection study depend on two conditions. First, the 

instream tracer concentration should be consistently higher 

than the inflow tracer concentrations, and this condition was 

generally met during the 1998 Eureka to Howardsville tracerinjection study (fig. 4). Second, the tracer concentration in the 

synoptic samples must represent the steady-state tracer-plateau 

concentration at that sampling site. For the 1998 Eureka to 

Howardsville study, the tracer-plateau chloride concentrations 

at the transport sites do match the synoptic-sampling chloride 

concentrations (fig. 4).

Concentrations of chloride, in a downstream direction, 

indicate the initial addition of the tracer and then the dilution 

due to surface and subsurface inflows (fig. 4). For a decrease 

of chloride to be considered a measurable change and not 

a product of analytical error, the decrease in concentration 

between stream samples must be higher than the precision of 

the chemical analyses. Error bars are indicated for chloride 

concentrations to show the precision of 1.75 percent for the 

1998 data set (fig. 4). If a change in instream chloride concentration was lower than the precision of the analysis, the 

downstream chloride concentration was held constant for 

discharge calculations until a change higher than the precision 

of the analysis was measured.

The resulting profile of chloride concentration was used 

to calculate discharge according to the equations presented in 

table 2. Discharge results are presented in table 5 and in fig. 4. 

The total flow increase through the study reach was 2,058 L/s 

(72.7 ft3/s), with visible tributary inflow contributing 

1,449 L/s (51.1 ft3/s) or about 70 percent of the total flow 

increase. By difference, unsampled ground-water inflow 

accounted for 609 L/s (21.6 ft3/s) or about 30 percent of the 

total flow increase through the study reach. Cunningham 

Gulch (distance 6,558 m) was the largest tributary inflow, 

accounting for 445 L/s (15.7 ft3/s) or about 22 percent of the 

total flow increase. The change in flow through the braided 

reach was the difference in flow between sites at 2,030 m and 

786 m and was 233 L/s (8.2 ft3/s) or about 11 percent of the 

total flow increase. Eureka Gulch (586 m) contributed 162 L/s 

(5.7 ft3/s) or about 8 percent of the total flow increase. Notable 

flow increases also occurred downstream from the Kitty 

Mack tailings at 3,405 m (168 L/s, 5.9 ft3/s, 8 percent of total 

increase), Otto Gulch at 3,165 m (104 L/s, 3.7 ft3/s, 5 percent 

of total increase), Minnie Gulch at 2,465 m (90 L/s, 3.2 ft3/s, 

4 percent of total increase), willows and beaver ponds at 

4,189 m (84 L/s, 3.0 ft3/s, 4 percent of total increase), Maggie 

Gulch at 3,450 m (80 L/s, 2.8 ft3/s, 4 percent of total increase), 

and Hematite Gulch at 6,633 m (65 L/s, 2.3 ft3/s, 3 percent of

total increase).

A streamflow-gage measurement at the downstream 

monitoring site (gaging station A53) did not compare well 

with the discharge values calculated from tracer dilution 

(fig. 4). Similar to other streams, the volume of flow measured 

by tracer dilution was much higher than concurrent flowmeter 

measurements because of flow through streambed cobbles 

(Kimball, 1997; Kimball and others, 1999a, 1999c).

Synoptic-sampling and Mass-Loading 

Calculation Results

This section presents results for the 1998 Eureka to Howardsville synoptic-sampling results and mass-loading calculations for constituents of interest. Synoptic-sampling data are 

presented in Appendixes 1 and 2, and the data are contained in 

USGS digital database for the Animas River watershed Abandoned Mine Land Program (Sole and others, 2005). Although 

concentrations of many metals were determined in the study, 

constituents of interest in the Eureka to Howardsville reach 

of the upper Animas River included pH, aluminum, calcium, 

magnesium, copper, iron, manganese, zinc, and sulfate.

pH

Instream pH is an important chemical parameter used 

to evaluate ARD effects and instream chemical reactions 

because pH can control chemical reactions such as aluminum 

or iron hydroxide precipitation and adsorption of metals onto 

sediment. The downstream profile of instream and inflow pH 

values for the Eureka to Howardsville study reach is presented 

in figure 5. Instream pH values were near neutral, ranging 

from about 6.6 at 1,918 m to 7.6 at 3,905 m. There was no 

clear downstream trend to the instream pH values; however, 

instream pH did appear to be affected by inflow pH. Instream 

pH values decreased downstream from inflows with pH values 

lower than the stream (3,165-m inflow, 3,954-m inflow, and 

6,438-m inflow), and instream pH values increased downstream from inflows with high pH values (Minnie Gulch, 

Maggie Gulch, beaver ponds at 5,210 m, Cunningham Gulch, 
Figure 4. Dissolved chloride concentrations and calculated discharges with distance downstream 

from the injection site, Eureka to Howardsville study reach, upper Animas River, Colorado, 

August 14, 1998.

0

10

20

30

40

50

60

70

80

90

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000

0

2

4

6

8

10

12

14

Transport

site T4

Transport

site T3

Transport site T2

Transport site T1

DISTANCE DOWNSTREAM FROM INJECTION SITE, IN METERS

DISSOLVED CHLORIDE CONCENTRATION, IN MILLIGRAMS PER LITER

 Instream chloride concentration

 with error bar indicating precision of 1.75 percent

 Inflow chloride concentraion

 Plateau chloride concentration at

 transport sites

T4

Discharge

08/14/1998 Hematite Gulch (6,633 meters)

Cunningha

m

 Gulch (6,558 meters)

Maggie Gulch (3,450 meters)

Minnie Gulch (2,465 meters)

Eureka Gulch (347 meters)

 Calculated stream discharge

 Measured stream discharge

 DISCHARGE, IN CUBIC FEET PER SECOND

Metal Loading to the Upper Animas River, Eureka to Howardsville, Colorado, Study Reach, August 1998 15

Figure 5. Instream and inflow pH with distance from the injection site, upper Animas River, Eureka to 

Howardsville, Colorado, August 14, 1998.

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000

5.5

6.0

6.5

7.0

7.5

8.0

8.5

Maggie Gulch

(3,450 meters)

(3,954 meters)

Beaver ponds

(5,210 meters)

Cunningham Gulch

(6,558 meters)

Minnie Gulch

(2,465 meters)

Eureka Gulch

(347 meters)

(3,165 meters)

Hematite Gulch

(6,633 meters)

Downstream

from Howardsville

(6,438 meters) 

DISTANCE DOWNSTREAM FROM INJECTION SITE, IN METERS

pH, IN STANDARD UNITS

 Instream

 Inflow
16 Quantification and Simulation of Metal Loading to the Upper Animas River, Eureka to Silverton, San Juan County, Colorado, 

 September 1997 and August 1998

and Hematite Gulch) (fig. 5). The inflow sample from 6,438 m 

had the lowest pH of all sampled inflows (5.7), and there were 

no acidic inflows (pH lower than 5.0) identified during the 

synoptic sampling.

Aluminum 

There was little variability in dissolved aluminum 

instream and inflow concentrations (Appendix 2). Instream 

aluminum concentrations ranged from 0.014 to 0.084 mg/L 

with a mean of 0.049 mg/L, and inflow aluminum concentrations ranged from 0.014 to 0.56 mg/L with a mean of 

0.067 mg/L. The maximum dissolved aluminum inflow concentration of 0.56 mg/L occurred at 6,438 m.

Instream colloidal aluminum concentrations decreased 

downstream from Eureka to just upstream from Howardsville 

at 6,038 m (fig. 6). The maximum instream colloidal aluminum concentration of 0.226 mg/L occurred at the upstream 

end of the study reach near the injection site, indicating that 

colloidal aluminum was contributed to the Eureka to 

Howardsville study reach from sources upstream from Eureka. 

Instream colloidal aluminum concentrations decreased through 

the primary braided reach from a concentration of 

0.172 mg/L at 786 m to a concentration of 0.077 mg/L at 

2,030 m (fig. 6). Colloidal aluminum loss also occurred 

through a secondary braided reach where the colloidal aluminum concentration decreased from 0.088 mg/L at 3,150 m to 

0.036 mg/L at 3,435 m (fig. 6). A graph of sampled instream 

load (fig. 7) also shows a loss of colloidal aluminum through 

the braided reaches and supports conclusions that the braided 

reaches contributed to attenuation of colloidal aluminum probably by settling and entrapment of colloidal particles through 

the shallow water. Downstream from transport site T3 at 5,467 

m, colloidal aluminum concentrations increased slightly in 

response to inflows with elevated colloidal aluminum concentrations (fig. 6). The instream colloidal aluminum load also 

increased downstream from the inflow at 6,438 m (fig. 7).

Calcium and Magnesium

Calcium and magnesium concentrations in the upper 

Animas River for 1998 were controlled by the calcium and 

magnesium concentrations of surface-water inflows. Instream 

concentrations of calcium ranged from approximately 25 to 

37 mg/L with a mean of 30 mg/L, and inflow calcium concentrations ranged from 27 to 96 mg/L with a mean of 43 mg/L. 

Instream calcium concentrations increased in a downstream 

direction, from approximately 26 mg/L at Eureka to approximately 37 mg/L at the downstream end of the study reach, in 

response to elevated inflow calcium concentrations (fig. 8).

Magnesium concentrations in the stream ranged from 

approximately 2.0 to 2.4 mg/L with a mean of 2.2 mg/L, and 

inflow magnesium concentrations ranged from approximately 

1.9 to 8.8 mg/L with a mean of 3.0 mg/L. Magnesium concentrations increased slightly in the downstream direction from 

2.2 mg/L at Eureka to 2.4 mg/L at the downstream end of the 

study reach. Inflow magnesium concentrations were similar 

to stream concentrations with the exception of the inflow at 

6,438 m (fig. 9).

Copper

Instream dissolved copper concentrations were compared 

to acute and chronic toxicity standards for aquatic life. These 

standards were computed for each water sample as a function 

of hardness (the sum of calcium, magnesium, barium, and 

strontium concentrations in milligrams per liter as calcium 

carbonate) according to the following relations (Colorado 

Department of Public Health and Environment, written 

commun., 1997):

Copper Acute Toxicity Standard = 0.5*

(e ) (0.9422*1n(hardness) –0.7703)

1,000 , and

Copper Chronic Toxicity Standard = 

(e ) (0.8545*1n(hardness) –1.465)

1,000 .

Figure 10 presents a graph of instream and inflow dissolved copper concentrations for the Eureka to Howardsville 

1998 synoptic sampling and the acute and chronic toxicity 

standards computed for each instream sample. The highest 

dissolved copper concentrations were in the upstream part of 

the study reach, indicating that dissolved copper was contributed by sources upstream from Eureka. Similar to colloidal 

aluminum, dissolved copper concentrations decreased through 

the primary braided reach downstream from Eureka from 

approximately 0.033 mg/L at 906 m to less than the method 

detection limit of 0.002 mg/L at 2,030 m (fig. 10). A graph of 

sampled instream copper load (fig. 11) also shows a loss of 

dissolved copper at the downstream end of the primary braided 

reach at 2,030 m. Adsorption of dissolved copper was the 

likely mechanism of copper attenuation through the primary 

braided reach.

Instream dissolved copper concentrations remained lower 

than both the acute and chronic toxicity standards downstream 

from the primary braided reach at 2,030 m to the end of the 

study reach (fig. 10), and the mass-loading graph for copper 

also indicates a relatively constant instream copper load downstream from the primary braided reach (fig. 11). An increase in 

copper load at the downstream end of the study reach (fig. 11) 

seems to be related to inflows from abandoned mines downstream from Hematite Gulch (6,633 m), although the instream 

dissolved copper concentrations remained lower than the acute 

and chronic toxicity standards downstream from Hematite 

Gulch (fig. 10). Dissolved copper was not detected in the 

6,438-m inflow downstream from Howardsville in 1998.
Metal Loading to the Upper Animas River, Eureka to Howardsville, Colorado, Study Reach, August 1998 17

Figure 7. Sampled instream load, cumulative instream load, and cumulative inflow load 

of colloidal aluminum with distance from the injection site, upper Animas River, Eureka to 

Howardsville, Colorado, August 14, 1998.

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 0

2

4

6

8

10

12

14

16

18

20

22

 DISTANCE DOWNSTREAM FROM INJECTION SITE, IN METERS

 COLLOIDAL ALUMINUM LOAD, IN KILOGRAMS PER DAY

 Sampled instream load

 Cumulative instream load

 Cumulative inflow load

Secondary braided reach

Primary

braided

reach Colloidal

aluminum

loss

Figure 6. Instream and inflow colloidal aluminum concentrations with distance from the 

injection site, upper Animas River, Eureka to Howardsville, Colorado, August 14, 1998.

0

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

Downstream from

Howardsville

(6,438 meters)

Beaver ponds

(5,210 meters)

Secondary braided reach

Primary

braided

reach

DISTANCE DOWNSTREAM FROM THE INJECTION SITE, IN METERS

COLLOIDAL ALUMINUM CONCENTRATION, IN 

MILLIGRAMS PER LITER

 Instream

 Inflow
18 Quantification and Simulation of Metal Loading to the Upper Animas River, Eureka to Silverton, San Juan County, Colorado, 

 September 1997 and August 1998

Figure 9. Instream and inflow dissolved magnesium concentrations with distance from 

the injection site, upper Animas River, Eureka to Howardsville, Colorado, August 14, 1998.

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000

1

2

3

4

5

6

7

8

9

Left bank adit

(7,008 meters)

Downstream from

Kittimack tailings

(3,165 meters)

Eureka Gulch

(347 meters)

Downstream from

Howardsville

(6,438 meters)

DISSOLVED MAGNESIUM CONCENTRATION, IN 

MILLIGRAMS PER LITER

DISTANCE DOWNSTREAM FROM INJECTION SITE, IN METERS

 Instream

 Inflow

Figure 8. Instream and inflow dissolved calcium concentrations with distance from the 

injection site, upper Animas River, Eureka to Howardsville, Colorado, August 14, 1998.

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 20

40

60

80

100

Old mill site

(7,063 meters)

Left bank adit

(7,008 meters)

Downstream from

Howardsville

(6,438 meters)

Beaver ponds

(5,210 meters)

Downstream from

Kittimack tailings

(3,165 meters) Eureka Gulch

(347 meters)

DISTANCE DOWNSTREAM FROM INJECTION SITE, IN METERS

DISSOLVED CALCIUM CONCENTRATION, IN 

MILLIGRAMS PER LITER

 Instream

 Inflow
Figure 10. Instream and inflow dissolved copper concentrations, copper acute toxicity standard, and copper chronic toxicity standard with distance from the injection site, upper Animas 

River, Eureka to Howardsville, Colorado, August 14, 1998.

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000

0

0.02

0.04

0.06

0.08

0.10

0.12

0.14

Hematite

Gulch

(6,633 meters)

Secondary braided reach

Primary braided reach DISTANCE DOWNSTREAM FROM INJECTION SITE, IN METERS

DISSOLVED COPPER CONCENTRATION, 

IN MILLIGRAMS PER LITER

 Instream

 Inflow

 Copper acute toxicity standard

 Copper chronic toxicity standard

Figure 11. Sampled instream load, cumulative instream load, and cumulative inflow load 

of dissolved copper with distance from the injection site, upper Animas River, Eureka to 

Howardsville, Colorado, August 14, 1998.

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 0

1

2

3

4

Hematite Gulch

(6,633 meters)

Secondary

braided reach

Primary braided reach DISTANCE DOWNSTREAM FROM INJECTION SITE, IN METERS

 DISSOLVED COPPER LOAD, IN KILOGRAMS PER DAY

 Sampled instream load

 Cumulative instream load

 Cumulative inflow load

Metal Loading to the Upper Animas River, Eureka to Howardsville, Colorado, Study Reach, August 1998 19
20 Quantification and Simulation of Metal Loading to the Upper Animas River, Eureka to Silverton, San Juan County, Colorado, 

 September 1997 and August 1998

Iron

Instream dissolved and colloidal iron concentrations during the 1998 Eureka to Howardsville study generally were low 

or not detected upstream from Howardsville, where dissolved 

iron concentrations were less than 0.014 mg/L, and colloidal 

iron concentrations were less than 0.088 mg/L. There was 

essentially no change in the instream load, the cumulative 

instream load, or the cumulative inflow load for dissolved or 

colloidal iron upstream from Howardsville (figs. 12 and 13).

Downstream from Howardsville, the sampled instream 

load for dissolved iron increased because of the elevated iron 

concentration from the inflow at 6,438 m (11.7 mg/L) and 

then decreased downstream probably because iron colloids 

precipitated in the near-neutral pH streamwater (fig. 12). A 

second but smaller increase in the dissolved iron instream load 

occurred at 7,008 m where an adit inflow contributed additional dissolved (1.03 mg/L) and colloidal (1.13 mg/L) iron 

to the stream. Downstream from Howardsville, the dissolved 

iron cumulative inflow load was higher than the cumulative 

instream and sampled instream loads indicating chemical 

removal probably as precipitation of iron colloids (fig. 12).

The sampled instream load for colloidal iron increased 

downstream from Howardsville because of the elevated colloidal iron concentration from the inflow at 6,438 m (3.87 mg/L) 

and likely from precipitation of iron colloids from the dissolved iron. For colloidal iron, the cumulative instream load 

was higher than the cumulative inflow load (fig. 13), indicating that the source of iron colloids was instream chemical 

precipitation rather than inflow contributions. The decrease 

in the colloidal iron instream load between Howardsville and 

the adit drainage at 7,008 m likely reflects the settling of iron 

colloids onto the streambed.

Based on synoptic-sampling concentration data and massloading calculations, the inflow at 6,438 m was a substantial 

source of dissolved and colloidal iron to the upper Animas 

River from Eureka to Howardsville in 1998. This inflow drains 

the area of tailings near Howardsville and the Pride of the 

West Mill. Some of these tailings were relocated during 1997 

and 1998, and the effects of tailings removal on stream inflow 

quality are undocumented. Inflow from a draining adit at 

7,008 m was a secondary source of dissolved and colloidal 

iron to the study reach. The instream dissolved iron load 

downstream from each of these inflows first increased in 

response to the inflow and then decreased in response to precipitation of iron colloids in the near-neutral pH stream. The 

colloidal iron load increased downstream from each of these 

inflows in response to the elevated inflow concentrations of 

colloidal iron and the chemical precipitation of iron colloids.

Manganese

Instream dissolved manganese concentrations in the 

Eureka to Howardsville study reach ranged from 0.14 to 

0.78 mg/L in 1998. The highest instream manganese concentration (fig. 14) was upstream from the injection site at 

0 m (0.78 mg/L) indicating that dissolved manganese was 

contributed by sources upstream from Eureka. Downstream 

from Eureka to upstream from Howardsville, instream manganese concentrations decreased (fig. 14), and the cumulative instream manganese load remained relatively constant 

(fig. 15). Inflows dissolved manganese concentrations 

upstream from Howardsville ranged from less than the method 

detection limit of 0.01 to 0.26 mg/L and generally were lower 

than the instream manganese concentrations from Eureka to 

Howardsville. The highest manganese inflow concentration in 

the Eureka to Howardsville study reach in 1998 was from the 

inflow at 6,438 m (18.5 mg/L), and the second highest manganese inflow concentration was downstream from Howardsville 

at 7,008 m where visible drainage from an adit contributed 

1.0 mg/L dissolved manganese to the upper Animas River.

The mass-loading graphs for dissolved manganese 

showed little increase in sampled instream load, cumulative 

instream load, or cumulative inflow load upstream from 

Howardsville (fig. 15). All three loads increased downstream 

from Howardsville in response to the elevated manganese 

concentrations from the inflows at 6,438 m and 7,008 m. The 

manganese cumulative inflow loads were higher than the 

cumulative instream loads downstream from Howardsville, 

indicating chemical removal of manganese possibly by precipitation of manganese oxyhydroxides.

Zinc

Instream dissolved zinc concentrations were compared 

to acute and chronic toxicity standards for aquatic life. These 

standards were computed for each water sample as a function of hardness (in milligrams per liter as calcium carbonate) 

according to the following relations (Colorado Department of 

Public Health and Environment, written commun., 1997):

Zinc Acute Toxicity Standard = 

(e ) (0.8473*1n(hardness) +0.8604)

1,000 , and

Zinc Chronic Toxicity Standard = 

(e ) (0.8473*1n(hardness) +0.7614)

1,000 .

Instream dissolved zinc concentrations ranged from 0.27 

to 0.54 mg/L and exceeded the acute and chronic aquatic-life 

standards along the entire study reach (fig. 16). The highest 

dissolved zinc concentrations were upstream from the primary 

braided reach, indicating that dissolved zinc was contributed 

by sources upstream from Eureka. Dissolved zinc concentrations decreased through the primary braided reach similar 

to colloidal aluminum and dissolved copper concentrations 

(fig. 16), and the graph of sampled instream zinc load (fig. 17) 

also shows slight dissolved zinc loss through the primary 

braided reach. Adsorption of dissolved zinc likely contributed 

to its attenuation through the braided reach.
Figure 12. Sampled instream load, cumulative instream load, and cumulative inflow load of 

dissolved iron with distance from the injection site, upper Animas River, Eureka to Howardsville, 

Colorado, August 14, 1998.

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000

0

5

10

15

20

25

30

35

40

45

50

Downstream from 

Howardsville

 (6,438 meters)

Cumulative inflow load

greater than instream load

indicates iron colloid precipitation

 DISTANCE DOWNSTREAM FROM INJECTION SITE, IN METERS

 DISSOLVED IRON LOAD, IN KILOGRAMS PER DAY

 Sampled instream load

 Cumulative instream load

 Cumulative inflow load

Figure 13. Sampled instream load, cumulative instream load, and cumulative inflow load of 

colloidal iron with distance from the injection site, upper Animas River, Eureka to Howardsville, 

Colorado, August 14, 1998.

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 0

10

20

30

40

50

60

Downstream from Howardsville (6,438 meters)

 DISTANCE DOWNSTREAM FROM INJECTION SITE, IN METERS

 COLLOIDAL IRON LOAD, IN KILOGRAMS PER DAY

 Sampled instream load

 Cumulative instream load

 Cumulative inflow load

Metal Loading to the Upper Animas River, Eureka to Howardsville, Colorado, Study Reach, August 1998 21
22 Quantification and Simulation of Metal Loading to the Upper Animas River, Eureka to Silverton, San Juan County, Colorado, 

 September 1997 and August 1998

Figure 14. Instream and inflow dissolved manganese concentrations with distance from 

the injection site, upper Animas River, Eureka to Howardsville, Colorado, August 14, 1998.

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

16

18

20

Left bank adit

(7,008 meters)

Downstream from

Howardsville

(6,438 meters)

DISTANCE DOWNSTREAM FROM INJECTION SITE, IN METERS

DISSOLVED MANGANESE CONCENTRATION, 

IN MILLIGRAMS PER LITER

 Instream

 Inflow

Figure 15. Sampled instream load, cumulative instream load, and cumulative inflow load 

of dissolved manganese with distance from the injection site, upper Animas River, Eureka 

to Howardsville, Colorado, August 14, 1998.

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000

10

20

30

40

50

60

70

80

90

 DISTANCE DOWNSTREAM FROM INJECTION SITE, IN METERS

 DISSOLVED MANGANESE LOAD, IN KILOGRAMS PER DAY

 Sampled instream load

 Cumulative instream load

 Cumulative inflow load

Downstream from Howardsville (6,438 meters)
The zinc concentration of inflow samples varied more 

than instream zinc concentrations. Inflow zinc concentrations 

ranged from a minimum value of 0.008 mg/L to a maximum 

value of 7.3 mg/L for the inflow downstream from 

Howardsville at 6,438 m (fig. 16). Increases in the dissolved 

zinc sampled instream load, cumulative instream load, and 

cumulative inflow load are noted at approximately 2,000 m, 

3,500 m, and 6,500 m downstream from the 1998 injection site 

(fig. 17). Corresponding increases in instream dissolved zinc 

concentrations also occurred in these reaches (fig. 16). 

The dissolved zinc load increase at approximately 

2,000 m apparently was the result of elevated dissolved zinc 

concentrations in unsampled inflow at the downstream end 

of the primary braided reach and the Forest Queen inflow at 

2,090 m (0.48 mg/L). Zinc loading from unsampled inflow 

could be from ground-water and/or surface-water interaction 

with historical tailings dispersed from Eureka, which now are 

located in and downstream from the braided reach (Vincent 

and others, 1999). A smaller load increase at 2,090 m was 

attributed to visible inflow from the Forest Queen mine 

(fig. 2). However, in the fall of 1998, a wetland was constructed at the mouth of the Forest Queen mine, and dissolved 

zinc concentrations in the Forest Queen discharge to the 

Animas River had decreased to near detection limits 

(0.003 mg/L) in 2000 as a result of this remedial action 

(M.A. Mast, U.S. Geological Survey, oral commun., 2000).

Downstream from the Kittimack tailings, from approximately 3,000 to 3,500 m, the dissolved zinc loads again 

increased (figs. 16 and 17). This area included the secondary 

braided reach and is identified as a contributor of dissolved 

zinc to the Eureka to Howardsville study reach. The effects of 

remediating this area are addressed through solute-transport 

simulations later in the “Zinc Solute-Transport Simulations” 

section.

The large increases in dissolved zinc load and instream 

dissolved zinc concentration at approximately 6,500 m likely 

were the result of inflow downstream from Howardsville at 

6,438 m, where the maximum dissolved zinc inflow concentration of 7.3 mg/L was measured. Some of the tailings near 

Howardsville were relocated during 1997 and 1998, and the 

effects of tailings removal on instream zinc concentrations are 

undocumented. Inflows downstream from Howardsville and 

Cunningham Gulch drain abandoned adits and other historical 

mining sites and contribute dissolved zinc to the upper Animas 

River including the inflow at 7,063 m (1.4 mg/L dissolved 

zinc). Summing all the positive changes in zinc load between 

stream sites provides a minimum estimate of the total mass of 

zinc entering the study reach, which was approximately 

76 kilograms per day (kg/d) for low-flow conditions in 1998. 

Metal Loading to the Upper Animas River, Eureka to Howardsville, Colorado, Study Reach, August 1998 23

Figure 16. Instream and inflow dissolved zinc concentrations, zinc acute toxicity 

standard, and zinc chronic toxicity standard with distance from the injection site, upper 

Animas River, Eureka to Howardsville, Colorado, August 14, 1998.

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000

0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

7

8

Primary braided reach

Secondarybraided reach

Forest

Queen

inflow

(2,090 meters)

Downstream from

Kittimack tailings

(3,165 meters)

Old mill site

(7,063 meters)

Downstream from

Howardsville

(6,438 meters)

DISTANCE DOWNSTREAM FROM INJECTION SITE, IN METERS

DISSOLVED ZINC CONCENTRATION, IN MILLIGRAMS PER LITER

 Instream

 Inflow

 Zinc acute toxicity standard

 Zinc chronic toxicity standard

6
24 Quantification and Simulation of Metal Loading to the Upper Animas River, Eureka to Silverton, San Juan County, Colorado, 

 September 1997 and August 1998

Figure 17. Sampled instream load, cumulative instream load, and cumulative inflow 

load of dissolved zinc with distance from the injection site, upper Animas River, Eureka to 

Howardsville, Colorado, August 14, 1998.

10

20

30

40

50

60

70

80

 DISSOLVED ZINC LOAD, IN KILOGRAMS PER DAY

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000

 DISTANCE DOWNSTREAM FROM INJECTION SITE, IN METERS

 Sampled instream load

 Cumulative instream load

 Cumulative inflow load

Primary braided reach

Secondayr braided reach

Sulfate

Instream sulfate concentrations ranged from 55 to 

74 mg/L and were lower than the U.S. Environmental Protection Agency’s (USEPA) secondary drinking-water standard 

of 250 mg/L (U.S. Environmental Protection Agency, 1992). 

A slight increase of instream sulfate concentration occurred 

downstream from the Eureka Gulch inflow, and concentrations 

remained nearly constant downstream from Eureka Gulch 

(fig. 18). Inflow sulfate concentrations in the study reach were 

more variable, ranging from 44 to 307 mg/L. The highest 

inflow sulfate concentrations were from Eureka Gulch at 

347 m (90.7 mg/L), inflow downstream from the Kittimack 

tailings at 3,165 m (128 mg/L), inflow downstream from 

Howardsville at 6,438 m (307 mg/L), adit inflow at 7,008 m 

(266 mg/L), and inflow downstream from an old mill site at 

7,063 m (108 mg/L) (fig. 18). 

The mass-loading graphs for sulfate show increases in the 

sampled instream load, cumulative instream load, and cumulative inflow load from Eureka to Howardsville, indicating a 

general increase in instream and inflow sulfate load through 

the study reach. The sampled instream load and the cumulative 

instream load were approximately equal throughout the entire 

study reach, indicating no loss of sulfate because of chemical 

reaction (fig. 19).

Discussion of Sources and Loadings, Eureka to 

Howardsville Study Reach 

Surface-water drainage in the Eureka to Howardsville 

study reach contributed aluminum, calcium, copper, iron, magnesium, sulfate, and zinc to the upper Animas River in 1998. 

Based on the 1998 synoptic-sampling results and mass-loading 

graphs, sources upstream from Eureka contributed aluminum, 

copper, manganese, and zinc to the Eureka to Howardsville 

study reach.

Colloidal aluminum, dissolved copper, and dissolved zinc 

were attenuated through the primary reach downstream from 

Eureka indicating that the braided reach is a sink for these 

metals. Colloidal aluminum attenuation through the primary 

braided reach likely was the result of physical processes such 

as particle settling and entrapment. Attenuation of dissolved 

copper and zinc through the primary braided reach likely was 

the result of adsorption of the dissolved constituents onto 

colloidal iron particles or streambed coatings. Instream colloidal aluminum concentrations were low downstream from 

the braided reaches to upstream from Howardsville (less than 

approximately 0.05 mg/L). The instream dissolved copper 

concentrations were lower than both the acute and chronic 

toxicity standards downstream from the primary braided reach 

to the end of the study reach. 

Instream loads for colloidal aluminum, dissolved iron, 

colloidal iron, dissolved manganese, dissolved zinc, and dis-
Figure 18. Instream and inflow dissolved sulfate concentrations with distance from the 

injection site, upper Animas River, Eureka to Howardsville, Colorado, August 14, 1998.

0

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000

50

100

250

300

350

 DISTANCE DOWNSTREAM FROM INJECTION SITE, IN METERS

DISSOLVED SULFATE CONCENTRATION, IN MILLIGRAMS PER LITER

Left bank adit

(7,008 meters)

Old mill site

Downstream from (7,063 meters)

Kittimack tailings

(3,165 meters) Eureka Gulch

(347 meters)

Downstream from

Howardsville

(6,438 meters)

 Instream

 Inflow

Figure 19. Sampled instream load, cumulative instream load, and cumulative inflow load 

of dissolved sulfate with distance from the injection site, upper Animas River, Eureka to 

Howardsville, Colorado, August 14, 1998.

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000

0

2,000

4,000

6,000

8,000

10,000

12,000

14,000

16,000

 DISTANCE DOWNSTREAM FROM INJECTION SITE, IN METERS

DISSOLVED SULFATE LOAD, IN KILOGRAMS PER DAY

 Sampled instream load

 Cumulative instream load

 Cumulative inflow load

Metal Loading to the Upper Animas River, Eureka to Howardsville, Colorado, Study Reach, August 1998 25
26 Quantification and Simulation of Metal Loading to the Upper Animas River, Eureka to Silverton, San Juan County, Colorado, 

 September 1997 and August 1998

solved sulfate all increased substantially downstream from 

the inflow at 6,438 m. The inflow at 6,438 m drains the area 

of tailings near Howardsville and the Pride of the West Mill. 

Some of these tailings were relocated during 1997 and 1998, 

and the effects of tailings removal on streamwater quality are 

uncertain. Upstream from Howardsville, dissolved manganese was diluted by inflow, and dissolved and colloidal iron 

concentrations generally were low or not detected. Although 

instream sulfate loads increased in a downstream direction, 

instream sulfate concentrations were lower than the USEPA’s 

secondary drinking-water standard of 250 mg/L.

Based on synoptic-sampling results, dissolved zinc was 

the primary constituent of concern in the Eureka to Howardsville study reach of the upper Animas River, and a cumulative 

instream zinc load of 76 kg/d was calculated for low-flow 

conditions in 1998. Increases in zinc load were measured 

downstream from Howardsville at 6,438 m (19 percent of the 

total load), downstream from the braided reach near the Forest 

Queen mine at 2,090 m (13 percent of the total load), near the 

Kittimack tailings at 3,165 m (12 percent of the total load), 

downstream from site T4 at 6,993 m (10 percent of the total 

load), and downstream from Eureka Gulch at 347 m 

(6 percent of the total load). Zinc loading from the upper 

Animas drainage upstream from the study area also was substantial (14 percent of the total load). A constructed wetland 

installed at the mouth of the Forest Queen mine in 1998 was 

successfully reducing zinc concentrations in the Forest Queen 

discharge to near detection limits (0.003 mg/L) in 2000.

Zinc Solute-Transport Simulations

 To interpret mass-loading calculations and to evaluate 

the effects of potential remediation, one-dimensional surface-water transport of dissolved zinc was simulated for the 

Eureka to Howardsville study reach using OTIS. This section 

of the report describes the conservative and first-order decay 

simulations and the remediation simulations for the Eureka to 

Howardsville reach.

Conservative and First-Order Decay Simulations

The Eureka to Howardsville study reach was divided into 

14 model reaches based on discharge calculations and massloading graphs. Main channel cross-sectional area, storage 

zone cross-sectional area, and storage-zone exchange coefficients were determined using OTIS-P simulations of the transport site data, and a uniform dispersion coefficient of 1.0 m 

was used for all model reaches. For each model reach, a lateral 

inflow discharge was computed based on the stream discharge 

profile, and lateral inflow concentrations were assigned to 

each model reach based on measured inflow concentrations for 

1998 (table 6 and fig. 20).

 Using lateral inflow concentrations representative 

of measured inflow concentrations (table 6), the conservative 

(no decay) OTIS simulation computed instream zinc concentrations higher than the measured instream concentrations 

downstream from reach 2 (Eureka Gulch) (fig. 21). Consistent 

with the mass-loading graphs, this simulation result indicates 

removal of dissolved zinc from the stream. The loss of dissolved zinc likely was caused by zinc adsorption onto colloidal particles or streambed sediment and was represented 

as a first-order decay process using OTIS. First-order decay 

rates determined from best-fit trial and error simulations were 

assigned to model reaches 3, 5, 8, and 13 (table 6) to represent the decrease of sampled instream zinc load through these 

reaches (fig. 17). The OTIS result for instream zinc concentrations using measured lateral inflow concentrations and firstorder decay is shown in figure 21 and is a reasonable match to 

the measured instream zinc concentrations.

Remediation Simulations

Two remediation alternatives were evaluated for the 

Eureka to Howardsville study reach using the first-order 

decay zinc solute-transport simulation described in the previous section. The first set of remediation simulations evaluated the effects of remediating inflow zinc concentrations in 

model reaches representing the Forest Queen mine inflow 

and unsampled inflow downstream from the braided reach 

in model reach 4 and inflow downstream from the Kittimack 

tailings in model reach 6. The second set of remediation 

simulations evaluates the effects of remediating inflow zinc 

concentrations in model reaches 4 and 6 in addition to inflow 

downstream from Howardsville in model reach 10.

To simulate remediation of stream reaches, the zinc 

lateral inflow concentrations were reduced from the measured 

inflow concentrations to hypothetical concentrations representative of inflow after remediation. Because these postremediation concentrations are uncertain, remediation simulations of the Eureka to Howardsville study reach used a 

50-percent reduction and then a 75-percent reduction in zinc 

concentrations for the lateral inflow concentrations of remediated reaches. A list of remediation simulations, zinc lateral 

inflow concentrations, and simulation results are presented in 

table 7.

The first set of remediation simulations address remediation of zinc concentrations in the model reaches representing 

the Forest Queen mine inflow and inflow below the 

Kittimack tailings (table 7, simulations 3 and 4). Model reach 

4 represents the zinc inflow from the Forest Queen mine 

and unsampled inflow downstream from the braided reach, 

and model reach 6 represents the Kittimack tailings inflow. 

The zinc lateral inflow concentrations for these reaches were 

reduced by 50 percent and by 75 percent, and the simulations 

were run with first-order decay. Simulation results are shown 

in figure 22 and indicate that instream zinc concentrations 

downstream from the Kittimack tailings and upstream from 

Howardsville (end of model reach 7) would approach concentrations near 0.16 mg/L (fig. 22 and table 7) if zinc inflow 
Model 

reach

Distance

 from

injection

site

(m)

Reach 

length

(m)

Main

channel 

cross-sectional area

(m2)

Lateral 

inflow rate

(m3/s-m)

Lateral 

inflow

concentration

 (mg/L)

First-order 

decay rate

(/s)

Description (see figure 2)

1 282 282 0.65 1.767 x 10-4 0.008 -- T1

2 586 304 1.20 5.329 x 10-4 0.299 Downstream from Eureka 

Gulch

3 1,918 1,332 1.20 2.445 x 10-5 0.008 4.0 x 10-5 Downstream from braided 

reach

4 2,240 322 1.20 8.751 x 10-4 0.483 T2 and downstream from 

Forest Queen mine

5 3,150 910 1.50 1.777 x 10-4 0.008 2.5 x 10-5 Upstream from Kittimack 

tailings

6 3,400 250 1.50 4.169 x 10-4 0.879 Downstream from Kittimack 

tailings

7 3,435 35 1.50 4.806 x 10-3 0.325 Downstream from flow 

increase at 3,405 m

8 4,670 1,235 1.50 2.754 x 10-4 0.229 1.0 x 10-4 Increase in flow from willows 

and beaver ponds

9 5,467 797 1.50 4.584 x 10-5 0.115 T3 and upstream from 

Howardsville

10 6,528 1,061 3.00 6.112 x 10-5 2.62 Downstream from 

Howardsville and upstream 

from Cunningham Gulch

11 6,618 90 3.00 4.947 x 10-3 0.020 Downstream from 

Cunningham Gulch

12 6,993 375 3.00 3.217 x 10-4 0.400 T4

13 7,250 257 3.00 3.570 x 10-4 1.37 5.0 x 10-4 End of study reach

14 7,350 100 3.00 -- -- -- Downstream boundary

Table 6. OTIS setup and input parameters for zinc solute-transport model, upper Animas River, Eureka to Howardsville, Colorado.

[m, meters; m2, square meters; m3/s-m, cubic meters per second per meter; mg/L, milligrams per liter; /s, per second; --, not applicable]

Metal Loading to the Upper Animas River, Eureka to Howardsville, Colorado, Study Reach, August 1998 27

concentrations were reduced by 75 percent in model reaches 

4 and 6. An instream zinc concentration of 0.16 mg/L is the 

upper limit of acute toxicity for some sensitive aquatic species 

(Besser and others, 2001).

For the second set of remediation simulations, the effects 

of remediating model reaches representing the Forest Queen 

mine (model reach 4), inflow downstream from the Kittimack 

tailings (model reach 6), and inflow downstream from 

Howardsville (model reach 10) were evaluated (table 7, 

simulations 5 and 6). The zinc lateral inflow concentrations for 

these reaches were reduced by 50 percent and by 75 percent, 

and the simulations were run with first-order decay. Simulation results are shown in figure 23 and indicate that instream 

zinc concentrations downstream from the Kittimack tailings 

and downstream from Howardsville would approach concentrations near 0.16 mg/L (fig. 23 and table 7) if zinc inflow 

concentrations were reduced by 75 percent in model reaches 4, 

6, and 10.
28 Quantification and Simulation of Metal Loading to the Upper Animas River, Eureka to Silverton, San Juan County, Colorado, 

 September 1997 and August 1998

0

1

2

3

7

8

DISSOLVED ZINC CONCENTRATION, IN MILLIGRAMS PER LITER

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000

 DISTANCE DOWNSTREAM FROM INJECTION SITE, IN METERS (4,670 meters)

1 2 3 4 5 6 7 8 9 10 11 12 13 14

Model reach number

Increase in flow (3,435 meters)

Upstream from Kittimack tailings (3,165 meters)

End of study reach (7,250 meters)

T4 (6,993 meters)

Downstream from

Cunningham Gulch

(6,618 meters)

Downstream from Howardsville (6,528 meters)

T3 (5,467 meters)

Downstream from Kittimack tailings (3,435 meters)

T2 (2,240 meters)

Downstream from braided reach and upstream from Forest Queen inflow (1,918 meters)

Downstream from Eureka Gulch (586 meters)

T1 (282 meters)

Downstream from

Howardsville

(6,438 meters)

 OTIS lateral inflow concentration (CLATIN) input values

 Measured concentration of visible inflow

Figure 20. OTIS lateral inflow concentrations and measured inflow concentrations for 

dissolved zinc with distance from the injection site, upper Animas River, Eureka to 

Howardsville, Colorado.

 Measured instream

 OTIS result with no decay (table 7, simulation 1)

 OTIS result with first-order decay in reaches 3, 5, 8, and 13 (table 7, simulation 2)

 Zinc acute toxicity standard

 Zinc chronic toxicity standard

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 0

0.2

0.4

0.6

0.8

 DISTANCE DOWNSTREAM FROM INJECTION SITE, IN METERS

DISSOLVED ZINC CONCENTRATION, IN MILLIGRAMS PER LITER

Forest Queen 

and unsampled inflow

T4

8 9 10 11 12

Kittimack tailings

T2

1 2 3 4 5 6 7

Model reach number

13 14

T1

T3

Braided reach Braided reach

Figure 21. OTIS results for conservative and first-order decay simulations, upper Animas River, 

Eureka to Howardsville, Colorado.
Metal Loading to the Upper Animas River, Eureka to Howardsville, Colorado, Study Reach, August 1998 29

Table 7. OTIS results for zinc solute-transport and remediation simulations, upper Animas River, Eureka to 

Howardsville, Colorado.

[CLATIN, OTIS input parameter for lateral inflow concentration; m, meters; mg/L, milligrams per liter; %, percent]

Reach 4 Reach 6 Reach 10 End of

 reach 7

(3,435 m)

End of study 

reach

(7,250 m)

1 0.483 0.879 2.615 0.372 0.383 Zinc CLATIN represents measured inflows with 

no decay.

2 0.483 0.879 2.615 0.346 0.295 Zinc CLATIN represents measured inflows

with first-order decay in reaches 3, 4, 8, and

13.

3 0.242 0.440 2.615 0.255 0.259 Forest Queen and Kittimack remediation.

50% reduction in zinc CLATIN in reaches 4 and

6 with first-order decay in reaches 3, 5, 8, and

13.

4 0.121 0.220 2.615 0.165 0.238 Forest Queen and Kittimack remediation. 

75% reduction in zinc CLATIN in reaches 4 and

6 with first-order decay in reaches 3, 5, 8 and 13.

5 0.242 0.440 1.308 0.255 0.229 Forest Queen, Kittimack, and Howardsville

remediation. 50% reduction in zinc CLATIN in

reaches 4, 6, and 10 with first-order decay in

reaches 3, 5, 8, and 13.

6 0.121 0.220 0.654 0.165 0.191 Forest Queen, Kittimack, and Howardsville

remediation. 75% reduction in zinc CLATIN in

reaches 4, 6, and 10 with first-order decay in

reaches 3, 5, 8 and 13.

Simulation 

number

OTIS input lateral inflow 

concentration (CLATIN)

(mg/L)

OTIS result — computed 

instream 

zinc concentration 

(mg/L)

Description
30 Quantification and Simulation of Metal Loading to the Upper Animas River, Eureka to Silverton, San Juan County, Colorado, 

 September 1997 and August 1998

Figure 22. OTIS results for remediation simulations 3 and 4, upper Animas River, Eureka to 

Howardsville, Colorado.

 Measured instream

 OTIS result based on 50 percent reduction in zinc inflow in reaches 4 and 6 and first-order decay in 

 reaches 3, 5, 8, and 13 (table 7, simulation 3)

 OTIS result based on 75 percent reduction in zinc inflow in reaches 4 and 6 and with first-order decay 

 in reaches 3, 5, 8, and 13 (table 7, simulation 4)

 Zinc acute toxicity standard

 Zinc chronic toxicity standard

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

 DISTANCE DOWNSTREAM FROM INJECTION SITE, IN METERS

DISSOLVED ZINC CONCENTRATION, IN MILLIGRAMS PER LITER

0.16 milligram per liter = Upper limit of acute toxicity for sensitive aquatic species Forest Queen and unsampled inflow

T4

8 9 10 11 12

Kittimack

T2

1 2 3 4 5 6 7

Model reach number

13 14

T1

T3

Braided reach Braided reach

Figure 23. OTIS results for remediation simulations 5 and 6, upper Animas River, Eureka to 

Howardsville, Colorado.

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

 DISTANCE DOWNSTREAM FROM INJECTION SITE, IN METERS

DISSOLVED ZINC CONCENTRATION, IN MILLIGRAMS PER LITER

0.16 milligram per liter = Upper limit of acute toxicity for sensitive aquatic species

Forest Queen

and unsampled inflow

T4

Howardsville

8 9 10 11 12

Kittimack

T2

1 2 3 4 5 6 7

Model reach number

13 14

T1

T3

 Measured instream

 OTIS result based on 50 percent reduction in zinc inflow in reaches 4, 6, and 10 and first-order decay in 

 reaches 3, 5, 8, and 13 (table 7, simulation 5)

 OTIS result based on 75 percent reduction in zinc inflow in reaches 4, 6, and 10 and first-order decay in 

 reaches 3, 5, 8, and 13 (table 7, simulation 6)

 Zinc acute toxicity standard

 Zinc chronic toxicity standard

Braided reach Braided reach
Metal Loading to the Upper Animas 

River, Howardsville to Silverton, 

Colorado, Study Reach, September 

1997

The Howardsville to Silverton tracer-injection study 

started near the historical mining town of Howardsville and 

ended just upstream from Silverton at the USGS gaging station 09358000 (referenced herein using the Colorado State 

gaging station number A68). The study reach encompassed a 

7,858-m reach of the upper Animas River (fig. 24).

Tracer-Injection Study Objectives

There were two primary objectives for the Howardsville 

to Silverton tracer-injection study. The first objective was to 

identify and locate where metal loading occurred in the study 

reach. Although a tracer-injection study can help identify 

where load increases occur, it does not identify specific 

pathways to the stream from particular sites, except for visible 

surface inflows. Potential sources of metal loading included 

the tailings near Howardsville, Arrastra Gulch, tailings near 

the Mayflower Mill, and tailings near the Lackawanna Mill. 

The second objective was to determine (for low-flow conditions) if the stream reach is a net sink or source of metals to 

the downstream areas. Identifying and describing any instream 

geochemical processes that affect metal concentrations and 

natural attenuation accomplished this objective.

Tracer-Injection Study Methods

The Howardsville to Silverton tracer-injection study 

began at 1206 on September 13, 1997, and ran continuously 

until 0900 on September 15, 1997 (table 8). A solution containing 128,200 mg/L of sodium chloride (or 77,760 mg/L of 

chloride) was injected into the upper Animas River at an average rate of 1.098 L/min. A leak in the injectate pool prior to 

the injection start likely resulted in elevated preinjection chloride concentrations at the transport sites. For reporting results, 

time 0.0 is the beginning of the experiment time, which was 

midnight on September 13, 1997, and subsequent times are 

reported as decimal hours.

The Howardsville to Silverton injection site was located 

approximately 180 m upstream from a ditch near Howardsville so that inflow near Howardsville and Cunningham Gulch 

could be quantified as tributary inflow to the stream. The 

arrival of the sodium-chloride pulse and the development of a 

plateau concentration were measured at six downstream locations, transport sites T1 through T6 (fig. 24). Transport site 

T1 was located upstream from a channelized stream reach at 

595 m, and transport site T2 was located at 1,059 m, which is 

downstream from Howardsville and upstream from Cunningham Gulch, to differentiate between these inflows. Transport 

site T3 was located upstream from a canyon in the river at 

2,800 m, and transport site T4 was located upstream from 

Arrastra Gulch at 4,166 m. Transport site T5 was located at 

6,038 m, and transport site T6 was located at 7,858 m at 

gaging station A68. 

Synoptic Sampling and Analyses

Synoptic samples were collected from 41 instream sites, 

including the 6 transport sites, and 46 inflows on 

September 14, 1997, during the plateau period of the tracer 

injection. Instream sampling sites were located upstream and 

downstream from identified inflows to allow mass-balance 

calculations for each inflow, and additional sites were located 

in longer subreaches between inflows to account for subsurface inflow. Forty-six inflow sites were chosen to represent 

the range of pH and specific conductance of water entering the 

stream. Instream and inflow water samples were analyzed in 

the field and laboratory for various constituents as presented 

in the “Study Methods” section of this report. The analytical 

methods are listed in table 1.

Tracer-Injection Study Results

Chemical analyses results for chloride tracer concentrations at the Howardsville to Silverton transport and synoptic 

sites were used to compute traveltime, stream discharge, and 

chemical mass loading as discussed herein. The 1997 

synoptic-sampling site locations are listed in table 9, field 

measurements and major ion concentrations are listed in 

Appendix 3, and the ICP-AES synoptic-sampling results are 

listed in Appendix 4. Data are sorted in downstream order 

within groups of stream and inflow sites to emphasize the 

downstream changes.

Arrival Times

Tracer arrival data and traveltime calculations for the six 

transport sites from Howardsville to Silverton are listed in 

table 10. The tracer sampling frequency provided well-defined 

tracer arrival graphs at sites T1, T2, T4, T5, and T6 

(figs. 25a and 25b). A complete arrival curve was not obtained 

for site T3. However, a complete departure curve for site T3 

was obtained, and the departure curve was used to compute 

traveltime between sites T2 and T3. Instream chloride concentrations increased to a maximum of 5.22 mg/L at sites T4, 

T5, and T6 from approximately 18 to 28 hours because of a 

rainstorm and the possible associated runoff of magnesium 

chloride road salts from the adjacent roadway. 

The tracer moved quickly from the injection site 

upstream from Howardsville to the downstream transport site 

T6 (gaging station A68) at Silverton (table 10). The injection 

began at 12.1 hours, and the tracer arrival time at site T1 was 

Metal Loading to the Upper Animas River, Howardsville to Silverton, Colorado, Study Reach, September 1997 31
32 Quantification and Simulation of Metal Loading to the Upper Animas River, Eureka to Silverton, San Juan County, Colorado, 

 September 1997 and August 1998

Figure 24. Howardsville to Silverton study reach, upper Animas River, Colorado, September 1997.

Arrastra Gulch (4,186 

m)

Blair Gulch (5,221 m)

Porcupine Gulch

Hematite Gulch

(1,150 m)

Cunningham Gulch (1,075 m)

Cataract Gulch

Boulder Gulch (4,951 m)

Swansea Gulch

Howardsville

Tailings 

Silverton

Cement Creek

Lackawanna

Mill

Downstream

end

1998 study

Mayflower

Mill

T1

(595 m)

T2

(1,059 m)

T3

(2,800 m) T4

(4,166 m)

A53

(1,510 m)

A53

T5

(6,038 m)

Canyon

T6 and

gaging station A68

(7,858 m)

Gaging station and number

107o40’

37o50’

37o51’15”

37o48’45”

107o35’

Base from U.S. Geological Survey, 1955

Handies Peak, Howardsville, and Silverton 

7.5 minute quadrangles

1927 North American Datum

Universal Transverse Mercator

projection, Zone 13

Transport site and distance

 downstream from injection

 site, in meters— Distance of

 features downstream from

 injection site, in meters,

 shown in parentheses

T1

(282 m)

1⁄2 1 MILE

0

0

0.5 1 KILOMETER

EXPLANATION

Study reach boundary

Upstream end and

injection site

1998 study reach

(0 meters)

Downstream end

1997 study reach

ANIMAS RIVER

COLORADO

Index map

Tailings

Date Clock 

time

Experimental 

time

(hours)

Activity

09/12/1997 Stream reconnaissance and discharge 

 measurements

09/13/1997 0000

0900

1206

1400

1630

1810

0.0

9.0

12.10

14.00

16.50

18.17

Start of experimental time

Scheduled injection start, but injectate pool leaked

Started injection; measured pump rate of 1,075 mL/min

Measured pump rate at 1,100 mL/min

Measured pump rate at 1,100 mL/min

Measured pump rate at 1,100 mL/min

09/14/1997

0905

1330

33.08

 37.50

Synoptic sampling

Measured pump rate at 1,080 mL/min; mixed more salt into pool

Measured pump rate at 1,070 mL/min

09/15/1997 0900

1100

57.00

59.00

Stopped injection

Slug injection of remaining solution

Table 8. Tracer-injection study sequence of events, upper Animas River, Howardsville to Silverton, 

Colorado, September 1997.

[mL/min, milliliters per minute]
Table 9. Synoptic-sampling sites and discharge calculated from tracer-dilution, upper Animas River, Howardsville to 

Silverton, Colorado, September 14, 1997.

[distance, distance downstream from injection sites; L/s, Liters per second; ft3/s, cubic feet per second; RB, right bank; LB, left bank; --, not 

applicable]

Distance 

(meters) Site name Source

Inflow

 location

Discharge 

(L/s)

Discharge 

(ft3/s)

 0 Upstream from injection site Stream -- 1,107 39.1

 160 Downstream from injection site Stream -- 1,107 39.1

 181 Dredged ditch from Howardsville Ponds Inflow Left bank 1.6 0.05

 213 Stream from beaver ponds Inflow Right bank 1.6 0.05

 310 Downstream from RB ponds Stream -- 1,110 39.2

 315 RB seep from talus Inflow Right bank 0 0

 595 T1—near construction Stream -- 1,110 39.2

 745 Drains beaver pond Inflow Right bank 35 1.2

 905 Upstream from RB inflow Stream -- 1,145 40.4

 910 From cobble road bank RB Inflow Right bank 10.5 0.37

 955 Upstream from Howardsville Mill Stream -- 1,156 40.8

 965 Mill discharge Inflow Left bank 14.4 0.51

1,059 T2—Downstream from Howardsville Mill Stream -- 1,170 41.3

1,075 Cunningham Gulch Inflow Left bank 386 13.6

1,135 Downstream from Cunningham Gulch Stream -- 1,556 54.9

1,150 Hematite Gulch Inflow Right bank 56.6 2.0

1,270 Downstream from bridge Stream -- 1,612 56.9

1,510 At State gage (A53) Stream -- 1,615 57.0

1,605 Draining LB adit—large inflow Inflow Left bank 6.4 0.23

1,648 RB road bank seep (old mill site) Inflow Right bank 6.4 0.23

1,665 RB seep beneath old road bank Inflow Right bank 6.4 0.23

1,725 Downstream from clean and dirty inflows Stream -- 1,634 57.7

1,745 Water across road RB Inflow Right bank 88.6 3.1

1,925 At upper “campground” A Stream -- 1,723 60.8

1,925 At upper “campground” B Stream -- 1,723 60.8

2,050 LB spring inflow Inflow Left bank 3.6 0.13

2,110 Downstream from campground Stream -- 1,726 61.0

2,125 Drains LB ponds with iron precipitate Inflow Left bank 3.7 0.13

2,360 LB inflow Inflow Left bank 3.7 0.13

2,361 LB rapid inflow from marsh Inflow Left bank 3.7 0.13

2,425 Swift inflow from marshy area Inflow Left bank 3.7 0.13

2,515 Upstream from draining adit Stream -- 1,737 61.4

2,522 Drains old mining Inflow Left bank 16.9 0.60

Metal Loading to the Upper Animas River, Howardsville to Silverton, Colorado, Study Reach, September 1997 33
34 Quantification and Simulation of Metal Loading to the Upper Animas River, Eureka to Silverton, San Juan County, Colorado, 

 September 1997 and August 1998

Table 9. Synoptic-sampling sites and discharge calculated from tracer-dilution, upper Animas River, Howardsville 

to Silverton, Colorado, September 14, 1997.—Continued

[distance, distance downstream from injection sites; L/s, Liters per second; ft3/s, cubic feet per second; RB, right bank; LB, left bank; --, not 

applicable]

Distance 

(meters) Site name Source

Inflow

location

Discharge 

(L/s)

Discharge 

(ft3/s)

2,572 Downstream from adit Stream -- 1,754 61.9

2,605 RB inflow from willows Inflow Right bank 0.3 0.01

2,709 RB inflow Inflow Right bank 0.3 0.01

2,800 T3—Truck park Stream -- 1,754 61.9

3,040 Narrow chute within canyon Stream -- 1,788 63.1

3,235 RB cascade across road Inflow Right bank 0.0 0.00

3,295 Downstream from first cableway Stream -- 1,788 63.1

3,555 Mid canyon Stream -- 1,788 63.1

3,682 RB drainage off grassy hillside Inflow Right bank 21.2 0.75

3,820 RB cascade from rocky bank Inflow Right bank 21.2 0.75

4,023 Between RB inflows in canyon Stream -- 1,830 64.6

4,033 RB cascade from rocky bank Inflow Right bank 2.8 0.10

4,166 T4—upstream from Arrastra Gulch Stream -- 1,833 64.7

4,186 Arrastra Gulch Inflow Left bank 218 7.7

4,190 Inflow from pipe RB Inflow Right bank 2.8 0.10

4,310 Downstream from Arrastra Gulch Stream -- 2,053 72.5

4,334 From “pipe bridge” Inflow Right bank 3.2 0.11

4,353 Stream level spring RB Inflow Right bank 3.2 0.11

4,473 Downstream from river level spring Stream -- 2,060 72.7

4,533 Marsh area RB Inflow Right bank 27.1 0.96

4,581 Downstream from LB abandoned mill Stream -- 2,087 73.7

4,586 Ponded water RB Inflow Right bank 12.0 0.42

4,656 Upstream from Pinnacle Gap Stream -- 2,099 74.1

4,816 Upstream from acid inflows Stream -- 2,099 74.1

4,886 Seep w/acid algae Inflow Right bank 2.8 0.10

4,916 Downstream from acid inflows Stream -- 2,102 74.2

4,951 Boulder Gulch Inflow Right bank 39.0 1.4

4,970 RB inflow—substantial Inflow Right bank 39.0 1.4

5,131 Downstream from Boulder Gulch Stream -- 2,180 77.0
Table 9. Synoptic-sampling sites and discharge calculated from tracer-dilution, upper Animas River, Howardsville to 

Silverton, Colorado, September 14, 1997.—Continued

[distance, distance downstream from injection sites; L/s, Liters per second; ft3/s, cubic feet per second; RB, right bank; LB, left bank; --, not 

applicable]

Distance 

(meters) Site name Source

Inflow

location

Discharge 

(L/s)

Discharge 

(ft3/s)

5,161 Pond to stream LB with fish Inflow Left bank 14.2 0.50

5,221 Blair Gulch Inflow Left bank 14.2 0.50

5,306 Downstream from Blair Gulch Stream -- 2,208 78.0

5,355 LB inflow from willow bog Inflow Left bank 0.3 0.01

5,356 Small ponds RB in cobbles Inflow Right bank 0.3 0.01

5,446 LB inflow near wells Inflow Left bank 0.3 0.01

5,536 Downstream from first of capped tailings Stream -- 2,208 78.0

5,756 Upstream from drain from tails Stream -- 2,233 78.3

5,766 Drains tailings RB in “ditch” Inflow Right bank 0.3 0.01

5,858 Seep along 60 m of grass Inflow Right bank 0.3 0.01

6,038 T5—Downstream from capped tailings Stream -- 2,233 78.8

6,105 LB inflow from willows Inflow Left bank 24.2 0.86

6,288 Downstream from toe of Mayflower Stream -- 2,257 79.7

6,528 Upstream from Lackawanna Bridge Stream -- 2,257 79.7

6,768 Downstream from Lackawanna Bridge Stream -- 2,257 79.7

7,008 Upstream from Lackawanna Mill Stream -- 2,257 79.7

7,103 Discharge from Lackawanna Mill Inflow Left bank 0.00 0.00

7,163 LB inflow Inflow Left bank 0.30 0.01

7,283 Downstream from Lackawanna Mill Stream -- 2,257 79.7

7,483 LB inflow Inflow Left bank 2.8 0.10

7,523 Among braids near town Stream -- 2,257 79.7

7,688 RB drainage from Mayflower Inflow Right bank 7.1 0.25

7,858 T6—At bridge/gage A68 - end of study reach Stream -- 2,264 79.9

Metal Loading to the Upper Animas River, Howardsville to Silverton, Colorado, Study Reach, September 1997 35
36 Quantification and Simulation of Metal Loading to the Upper Animas River, Eureka to Silverton, San Juan County, Colorado, 

 September 1997 and August 1998

Transport

site

Distance 

downstream 

from

injection

site

(m)

Distance 

between 

transport 

sites

(m)

Arrival 

time

(t

50)

(hours)

Traveltime

from

injection

site

(hours)

Traveltime

between 

transport

sites

(hours)

Average 

velocity

between 

transport 

sites

(m/s)

Comments

T1 595 595 12.38 0.28 0.28 0.59 Injection start time = 

12.1 hours

T2 1,059 464 12.60 0.50 0.22 0.59

T3 2,800 1741 NM(13.4) 1.30 0.80 0.60 T3 traveltime computed from departure 

curve instead of 

arrival curve

T4 4,166 1,366 14.07 1.97 0.67 0.57

T5 6,038 1,872 14.90 2.80 0.83 0.63

T6 7,858 1,820 15.68 3.58 0.78 0.65

Table 10. Tracer arrival data and traveltime calculations for transport sites downstream from the tracer-injection 

site, upper Animas River, Howardsville to Silverton, Colorado, September 1997.

[m, meters; m/s, meters per second; mg/L, milligrams per liter; NM, not measured (arrival time computed from departure curve for 

transport site T3)]
Figure 25. Dissolved chloride concentrations with time at (A) transport sites T1, T2, and T3, and 

(B) transport sites T4, T5, and T6, upper Animas River, Howardsville to Silverton, Colorado, 

September 1997.

0 5 10 15 20 25 30 35 40 45 50 55 60 65

1

2

3

4

 TIME SINCE START OF TRACER INJECTION, IN HOURS

DISSOLVED CHLORIDE CONCENTRATION, IN MILLIGRAMS PER LITER

 Transport site T1

 Transport site T2

 Transport site T3

0

A

0 10 15 20 25 30 35 40 45 50 55 60 65 0

1

2

3

4

5

6

 TIME SINCE START OF TRACER INJECTION, IN HOURS

DISSOLVED CHLORIDE CONCENTRATION, 

IN MILLIGRAMS PER LITER

 Transport site T4

 Transport site T5

 Transport site T6

B

Metal Loading to the Upper Animas River, Howardsville to Silverton, Colorado, Study Reach, September 1997 37
38 Quantification and Simulation of Metal Loading to the Upper Animas River, Eureka to Silverton, San Juan County, Colorado, 

 September 1997 and August 1998

12.38 hours, indicating a traveltime of 0.28 hour (16 minutes) 

and an average flow velocity of 0.59 m/s between the injection 

site and site T1. A similar traveltime (0.22 hour) and velocity 

(0.59 m/s) were measured for a similar distance between sites 

T1 and T2. The tracer arrival time at site T3, computed from 

the T3 departure curve, was 13.4 hours, indicating a traveltime 

of 1.3 hours from the injection site. The total traveltime from 

the injection site to site T6 was 3.58 hours. The average flow 

velocity generally increased downstream to a maximum value 

of 0.65 m/s between sites T5 and T6.

Discharge Profile

A detailed discharge profile for the Howardsville to 

Silverton study reach was developed using the chloride tracer 

concentrations measured in the synoptic samples. For the 

Howardsville to Silverton study reach, synoptic instream 

chloride concentrations generally were higher than the inflow 

chloride concentrations, and chloride concentrations decreased 

downstream due to dilution (fig. 26a). However, several inflow 

chloride concentrations were higher than instream chloride 

concentrations, and downstream increases of instream chloride 

concentrations were measured in the synoptic chloride profile. 

The inflows with higher chloride concentrations were located 

primarily on the right streambank, and some possibly were the 

result of runoff containing magnesium chloride road salts from 

the roadway, which also is located on the right streambank. 

For stream reaches where chloride was not an appropriate 

indicator of dilution because of higher inflow concentrations, 

the conservative ions strontium, manganese, and sulfate were 

used to calculate discharge.

For a decrease in chloride concentration to be considered 

a measurable change and not a product of analytical error, the 

decrease in concentration between instream samples must be 

higher than the precision of the chemical analyses. Error bars 

are indicated for chloride concentrations to show the precision 

of 1.83 percent for the 1997 data set (fig. 26a). If a change in 

instream chloride concentration was lower than the precision 

of the analysis, the downstream chloride concentration was 

held constant for discharge calculations until a change higher 

than the precision of the analysis was measured.

The synoptic-sampling profile of chloride concentration 

(fig. 26a), supplemented by strontium, manganese, and sulfate 

concentrations, was used to calculate discharge according 

to the relations presented in table 2. Discharge results are 

presented in table 9 and in figure 26b. The resulting discharge 

profile for the Howardsville to Silverton study reach indicates 

stream discharge ranged from 1,107 L/s (39.1 ft3/s) at the 

injection site to 2,264 L/s (79.9 ft3/s) at gaging station A68 

(fig. 26b), and the total increase of discharge through the study 

reach was 1,157 L/s (40.8 ft3/s). The largest inflow was Cunningham Gulch (1,075 m) with a computed inflow discharge 

of 386 L/s (13.6 ft3/s) or 33 percent of the total flow increase. 

Arrastra Gulch (4,186 m) contributed 218 L/s (7.7 ft3/s) or 

19 percent of the total flow increase. The contributions from 

Hematite Gulch (1,150 m) and Boulder Gulch (4,951 m) were 

5 percent and 3 percent, respectively, of the total increase in 

stream discharge. Small surface inflows and ground-water 

seeps caused the remaining streamflow increase along the 

study reach. Discharge values computed from the synopticsampling results compare well with discharge measured at the 

six transport sites (fig. 26b). 

The Howardsville to Silverton discharge values computed 

from the September 1997 tracer-injection study were higher 

than the discharge values computed from the August 1998 

Eureka to Howardsville tracer-injection study. At the instream 

site immediately downstream from Cunningham Gulch, the 

1997 computed discharge at site 1,135 m was 1,556 L/s 

(54.9 ft3/s), whereas the 1998 computed discharge at this 

same site (6,618 m in 1998 study) was 2,107 L/s (74.4 ft3/s) 

(table 5). The difference in discharge from 1997 to 1998 is 

attributed to seasonal variation.

Synoptic-Sampling and Mass-Loading 

Calculation Results

This section presents results for the 1997 Howardsville to 

Silverton synoptic-sampling results and mass-loading calculations for constituents of interest. Synoptic-sampling data are 

presented in Appendixes 3 and 4, and the data are contained 

in the USGS digital database for the Animas River watershed 

Abandoned Mine Land Program (Sole and others, 2005)

pH

The downstream profile of instream and inflow pH values 

for the 1997 Howardsville to Eureka study reach is presented 

in figure 27. Instream pH values were near neutral and ranged 

from a minimum of 7.4 at 4,581 m to a maximum of 7.8 at 

3,295 m. Although there was no clear downstream trend for 

the instream pH values, instream pH did appear to vary with 

inflow pH. Instream pH values increased downstream from 

inflows with high pH values, such as those from Cunningham 

and Hematite Gulches, and instream pH values decreased 

downstream from inflows with pH values lower than the 

stream. 

Based on the pH downstream profile, the study reach 

can be subdivided into sections with similar characteristics. 

First is the upper part of the stream from the injection site to 

Cunningham Gulch where the inflows at 181 m and 965 m 

had pH values of 6.9. These inflows lowered the instream 

pH to 7.4 upstream from Cunningham Gulch. The 1997 pH 

from the inflow downstream from Howardsville (965 m) was 

higher than the pH for this same inflow in the 1998 Eureka to 

Howardsville synoptic sampling (pH of 5.7 for the 6,438-m 

inflow). Instream pH increased to 7.7 downstream from 

Cunningham Gulch because of the high-pH inflow from 

Cunningham (8.0) and Hematite (8.1) Gulches. 
0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 0

1

2

3

4

5

6

7

8

9

20

25

30

Stream synoptic

chloride profile

Right bank

march

(4,533 meters)

Right bank

ditch

(7,688 meters)

Right bank

spring

(4,353 meters)

Old mill site

(1,648 meters)

Downstream from

Howardsville

(965 meters)

Ditch

downstream from

Howardsville

(181 meters) 

DISTANCE DOWNSTREAM FROM INJECTION SITE, IN METERS

DISSOLVED CHLORIDE CONCENTRATION, IN 

MILLIGRAMS PER LITER

 Instream chloride

 concentration with

 error bar indicating

 precision of

 1.83 percent

 Inflow chloride

 concentration

A

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 500

1,000

1,500

2,000

2,500

DISTANCE DOWNSTREAM FROM INJECTION SITE, IN METERS

DISCHARGE, IN LITERS PER SECOND

 Calculated stream discharge

 Measured discharge on 9/12/1997

20

30

40

50

60

70

80

T5

Blair Gulch (5,221 meters)

Boulder Creek (4,951 meters)

Arrastra Gulch (4,186 meters)

T6

T4

T3

T2

T1

Hematite Gulch (1,150 meters)

Cunningham Gulch (1,075 meters)

DISCHARGE, IN CUBIC FEET PER SECOND

B

Figure 26. (A) Dissolved chloride concentrations, and (B) calculated discharge with distance 

downstream from the injection site, upper Animas River, Howardsville to Silverton, Colorado, 

September 14, 1997.

Metal Loading to the Upper Animas River, Howardsville to Silverton, Colorado, Study Reach, September 1997 39
40 Quantification and Simulation of Metal Loading to the Upper Animas River, Eureka to Silverton, San Juan County, Colorado, 

 September 1997 and August 1998

The second area affected by low-pH inflows was from 

1,605 to 2,572 m, where inflows with pH values lower than 

instream values lowered instream pH (fig. 27). The lowest inflow pH in this reach (4.8) was from ponds on the left 

bank at 2,125 m. Between the site at 2,572 m and site T4 at 

4,166 m, the upper Animas River flows through a steep-walled 

canyon. The visible inflows in this reach are primarily from 

the right bank, with inflow pH values ranging from a minimum of 7.9 to a maximum of 8.2, and instream pH ranging 

from 7.7 to 7.8 (fig. 27). 

A third area affected by AMD and ARD was downstream 

from 4,353 m, where a series of low-pH right bank inflows 

lowered the instream pH. The lowest inflow pH in the entire 

study reach emanated from a right bank spring at 4,353 m 

(pH of 4.2), and additional right bank low-pH inflows were at 

4,533 m (pH of 4.9) and 4,586 m (pH of 4.9) (fig. 27).

Aluminum 

Instream dissolved aluminum concentrations were low 

and had little variability, although concentrations increased 

slightly downstream due to inflows with elevated dissolved 

aluminum concentrations. Instream dissolved aluminum concentrations ranged from less than the method detection limit of 

0.01 to 0.98 mg/L. Inflow dissolved aluminum concentrations 

were more variable than instream concentrations and ranged 

from less than the method detection limit of 0.01 to 

23.5 mg/L. The inflows with elevated dissolved aluminum 

concentrations included the right bank inflows downstream 

Figure 27. Instream and inflow pH with distance from the injection site, upper Animas River, 

Howardsville to Silverton, Colorado, September 14, 1997.

3

4

5

6

7

8

9

 pH, IN STANDARD UNITS

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000

 DISTANCE DOWNSTREAM FROM INJECTION SITE, IN METERS

Right bank

inflows

in canyon

Cunningham

and Hematite

Gulches

 Instream

 Inflow

Downstream from

Howardsville

(965 meters)

Downstream from adit and upstream from canyon (2,572 meters)

T4 – Upstream from Arrastra Gulch (4,166 meters)

Left bank ponds

at 2,125 meters

Right bank pond

Right bank spring

(4,353 meters)

Right bank marsh (4,533 meters)

and ponded water (4,386 meters)

Right bank

seep/inflows

Right bank

ditch

(7,688 meters)
from Arrastra Gulch. Dissolved aluminum was not elevated in 

the ditch upstream from Howardsville (0.060 mg/L at 181 m) 

or the inflow downstream from Howardsville (0.012 mg/L 

at 965 m). Instream colloidal aluminum concentrations also 

appeared to increase slightly in a downstream direction 

because of the inflow of elevated dissolved aluminum concentrations and the subsequent precipitation of aluminum 

oxyhydroxide.

Calcium and Magnesium

Calcium and magnesium concentrations in the upper 

Animas River for 1997 are controlled by the calcium and 

magnesium concentrations of surface-water inflows. Instream 

concentrations of calcium ranged from approximately 35 to 

40 mg/L with a mean of 37 mg/L, and inflow calcium concentrations ranged from 12 to 344 mg/L with a mean of 81 

mg/L. Instream calcium concentrations increased slightly in a 

downstream direction from about 36 mg/L at Howardsville to 

about 39 mg/L at gaging station A68 in response to elevated 

inflow calcium concentrations (fig. 28).

Instream magnesium concentrations had little variability 

and ranged from about 2.4 to 2.7 mg/L, generally increasing 

in a downstream direction. Inflow magnesium concentrations 

varied more than instream concentrations ranging from 0.8 

to 35.3 mg/L (fig. 29). The inflows with elevated magnesium 

concentrations included the ditch upstream from Howardsville 

(10.6 mg/L), inflow downstream from Howardsville 

(7.55 mg/L), and a right bank ditch at 7,688 m (14.2 mg/L), 

as well as four right bank inflows downstream from Arrastra 

Gulch with magnesium concentrations ranging from 14.4 to 

35.3 mg/L.

Copper

Instream dissolved copper concentrations were compared 

to acute and chronic toxicity standards for aquatic life. 

Figure 30 presents a graph of instream dissolved copper concentrations for the Howardsville to Silverton study reach 1997 

synoptic sampling and the acute and chronic toxicity standards 

computed for each instream sample. Instream copper concentrations were near or estimated less than the method detection 

limit of 0.002 mg/L and were lower than the acute and chronic 

toxicity standards throughout the study reach (fig. 30). The 

maximum inflow copper concentrations were from the right 

bank inflows downstream from Arrastra Gulch (5.2 mg/L at 

4,353 m; 0.36 mg/L at 4,533 m; 0.20 at 4,586 m; and 2.4 mg/L 

at 5,356 m).

Iron

Instream dissolved iron concentrations in the 

Howardsville to Silverton study reach generally were low or 

not detected except immediately downstream from Howardsville in 1997 (fig. 31). Instream colloidal iron also was not 

detected upstream from Howardsville (fig. 31). The dissolved 

iron concentration of inflow downstream from Howardsville 

(965 m) was 1.2 mg/L in 1997, which was an order of magnitude lower than the inflow dissolved iron concentration in 

1998 (11.7 mg/L at 6,438 m in 1998 study). The maximum 

instream dissolved iron concentrations occurred immediately 

downstream from Howardsville at 1,059 m (0.13 mg/L) and 

downstream from Arrastra Gulch at 4,310 m (0.16 mg/L). 

Instream dissolved iron concentrations decreased and instream 

colloidal iron concentrations increased downstream from both 

the Howardsville and Arrastra Gulch inflows probably in 

response to iron oxyhydroxide precipitation.

The sampled instream, cumulative instream, and cumulative inflow loads for colloidal iron all increased downstream 

from Howardsville (fig. 32). The colloidal iron loads increased 

in response to the elevated inflow colloidal iron concentrations downstream from Howardsville (12.4 mg/L at 965 m) 

and the precipitation of iron oxyhydroxides from the elevated 

inflow dissolved iron concentrations. Downstream from 

Howardsville, the cumulative instream colloidal iron load was 

higher than the cumulative inflow load (fig. 32) indicating that 

mineral precipitation was a source of instream iron colloids. 

Downstream from Arrastra Gulch, from approximately 4,166 

to 6,000 m, there was an increase of sampled instream colloidal iron load but no increase of cumulative inflow load, which 

indicates ground-water discharge of dissolved iron, possible 

precipitation of iron colloids, or both (fig. 32).

Based on synoptic-sampling concentration data and 

mass-loading calculations, inflow downstream from Howardsville at 965 m was a source of dissolved and colloidal iron to 

the upper Animas River reach from Eureka to Howardsville in 

1998 and from Howardsville to Silverton in 1997. Inflow from 

a draining adit at 7,008 m in the Eureka to Howardsville study 

reach (1,605 m in the Howardsville to Silverton study reach) 

was a secondary source of dissolved and colloidal iron in both 

studies. The stream reach downstream from Arrastra Gulch 

and the right bank ditch inflow at 7,688 m were secondary 

sources of iron (fig. 31). The sampled instream dissolved iron 

load downstream from each of these inflows first increased in 

response to the inflow and then decreased as iron oxyhydroxides precipitated in the near-neutral pH stream.

Manganese

Instream manganese concentrations upstream from 

Howardsville decreased downstream due to dilution in 1998 

(fig. 14). In contrast, instream dissolved manganese concentraMetal Loading to the Upper Animas River, Howardsville to Silverton, Colorado, Study Reach, September 1997 41
42 Quantification and Simulation of Metal Loading to the Upper Animas River, Eureka to Silverton, San Juan County, Colorado, 

 September 1997 and August 1998

Figure 28. Instream and inflow dissolved calcium concentrations with distance from the 

injection site, upper Animas River, Howardsville to Silverton, Colorado, September 14, 1997.

0

50

100

150

200

250

300

350

DISSOLVED CALCIUM CONCENTRATION, IN 

MILLIGRAMS PER LITER

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000

 DISTANCE DOWNSTREAM FROM INJECTION SITE, IN METERS

Right bank

ditch

(7,688 meters)

Right bank inflows

downstream from

Arrastra Gulch

Right bank seep

with acid algae

(4,886 meters)

Downstream from

Howardsville

(965 meters)

 Instream

 Inflow

Figure 29. Instream and inflow dissolved magnesium concentrations with distance from the 

injection site, upper Animas River, Howardsville to Silverton, Colorado, September 14, 1997.

0

5

10

15

20

25

30

35

40

DISSOLVED MAGNESIUM CONCENTRATION, IN 

MILLIGRAMS PER LITER

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000

Right bank

ditch

(7,688 meters)

Downstream from

Howardsville

(965 meters)

Ditch upstream

from Howardsville

(181 meters)

Right bank inflows

downstream from

Arrastra Gulch

 DISTANCE DOWNSTREAM FROM INJECTION SITE, IN METERS

 Instream

 Inflow
Figure 30. Instream dissolved copper concentrations, copper acute toxicity standard, and 

copper chronic toxicity standard with distance from the injection site, upper Animas River, 

Howardsville to Silverton, Colorado, September 14, 1997.

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 0

0.01

0.02

0.03

2

4

6

8

10

Right bank inflows

downstream from

Arrastra Gulch

Old mill site

(1,648 meters)

DISTANCE DOWNSTREAM FROM INJECTION SITE, IN METERS

DISSOLVED COPPER CONCENTRATION, IN MILLIGRAMS PER LITER

 Instream

 Inflow

 Copper acute toxicity standard

 Copper chronic toxicity standard

Figure 31. Instream and inflow dissolved iron concentrations and instream colloidal 

iron concentrations with distance from the injection site, upper Animas River, Howardsville to Silverton, Colorado, September 14, 1997.

 Instream dissolved iron

 Inflow dissolved iron

 Instream colloidal iron

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000

0

0.5

1.0

1.5

Right bank

ditch

(7,688 meters)

Left bank adit

(1,605 meters)

Downstream from

Howardsville

(965 meters)

 DISTANCE DOWNSTREAM FROM INJECTION SITE, IN METERS

IRON CONCENTRATION, IN MILLIGRAMS PER LITER

Metal Loading to the Upper Animas River, Howardsville to Silverton, Colorado, Study Reach, September 1997 43
44 Quantification and Simulation of Metal Loading to the Upper Animas River, Eureka to Silverton, San Juan County, Colorado, 

 September 1997 and August 1998

Figure 32. Sampled instream load, cumulative instream load, and cumulative inflow load of 

colloidal iron with distance from the injection site, upper Animas River, Howardsville to Silverton, 

Colorado, September 14, 1997.

tions from the 1997 Howardsville to Silverton study ranged 

from 0.12 to 1.1 mg/L and generally increased in the downstream direction because of elevated inflow manganese concentrations (fig. 33). Inflow dissolved manganese concentrations ranged from less than the method detection limit of 0.001 

to 284 mg/L (right bank marsh at 4,533 m). The dissolved 

manganese concentration from inflow downstream from 

Howardsville at 965 m was 15.9 mg/L during 1997, slightly 

lower than the manganese concentration measured for the 

inflow in 1998 (18.6 mg/L). Several right bank inflows 

downstream from Arrastra Gulch also had elevated manganese 

concentrations (55.5 mg/L at 4,353 m; 4.7 mg/L at 4,586 m; 

75.6 mg/L at 4,886 m; 3.1 mg/L at 4,970 m; 34.4 mg/L at 

5,858 m; and 39.7 mg/L at 7,688 m).

The mass-loading graphs for dissolved manganese reflect 

the downstream increase in manganese load caused by inflows 

with elevated manganese concentrations. Consistent with the 

Eureka to Howardsville study results for manganese, sampled 

instream, cumulative instream, and cumulative inflow loads 

generally did not increase upstream from Howardsville 

(figs. 15 and 34). All three manganese-loading graphs in

 figure 34 showed increases downstream from Howardsville. 

Immediately downstream from Howardsville, the sampled 

instream and cumulative instream manganese loads increased, 

and this increase was greater than the cumulative inflow load 

increase for the same reach, indicating that ground-water 

inflow possibly contributed to the sampled instream manganese load. The sampled instream and cumulative instream 

manganese loads remained relatively constant downstream 

from Howardsville to Arrastra Gulch. A second increase in 

sampled instream and cumulative instream dissolved manganese loads occurred downstream from Arrastra Gulch where 

several right bank inflows had elevated manganese concentrations. However, the increases of sampled instream and 

cumulative instream manganese loads were greater than the 

increase of cumulative inflow load from approximately 5,000 

to 6,500 m, again indicating that ground-water inflow possibly was contributing to the sampled instream manganese load 

downstream from Boulder Gulch.

Zinc

Instream dissolved zinc concentrations for 1997 were 

compared to acute and chronic toxicity standards for aquatic 

life. Instream dissolved zinc concentrations ranged from 0.24 

to 0.45 mg/L, and exceeded the acute and chronic aquatic-life 

standards along the entire study reach (fig. 35). With a spatial 

distribution similar to manganese, dissolved zinc concentra0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000

0

20

40

60

80

100

120

Possible ground-water

discharge of iron,

iron colloid precipitation,

or both 

DISTANCE DOWNSTREAM FROM INJECTION SITE, IN METERS

 COLLOIDAL IRON LOAD, IN KILOGRAMS PER DAY

 Sampled instream load

 Cumulative instream load

 Cumulative inflow load
Figure 34. Sampled instream load, cumulative instream load, and cumulative inflow 

load of dissolved manganese with distance from the injection site, upper Animas River, 

Howardsville to Silverton, Colorado, September 14, 1997.

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000

50

0

100

150

200

250

Arrastra Gulch (4,186 meters)

T2—Downstream from Howardsville (1,059 meters)

Possible

ground-water

discharge

of manganese 

 DISTANCE DOWNSTREAM FROM INJECTION SITE, IN METERS

 DISSOLVED MANGANESE LOAD, IN KILOGRAMS PER DAY

 Sampled instream load

 Cumulative instream load

 Cumulative inflow load

Figure 33. Instream and inflow dissolved manganese concentrations with distance 

from the injection site, upper Animas River, Howardsville to Silverton, Colorado, 

September 14, 1997.

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000

0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

50

100

150

200

250

300

Right bank

ditch

(7,688 meters)

Right bank inflows

downstream from

Arrastra Gulch

Left bank ponds

(2,515 meters)

Left bank adit

(1,605 meters)

Right bank marsh

(4,533 meters) 

Downstream from

Howardsville

(965 meters) 

Ditch upstream

from Howardsville

(181 meters)

 DISTANCE DOWNSTREAM FROM INJECTION SITE, IN METERS

DISSOLVED MANGANESE CONCENTRATION, IN 

MILLIGRAMS PER LITER

 Instream

 Inflow

Metal Loading to the Upper Animas River, Howardsville to Silverton, Colorado, Study Reach, September 1997 45
46 Quantification and Simulation of Metal Loading to the Upper Animas River, Eureka to Silverton, San Juan County, Colorado, 

 September 1997 and August 1998

Figure 35. Instream dissolved zinc concentrations, zinc acute toxicity standard, and zinc chronic 

toxicity standard with distance from the injection site, upper Animas River, Howardsville to Silverton, 

Colorado, September 14, 1997.

tions generally increased in a downstream direction because of 

inflows with elevated zinc concentrations (fig. 36). The highest instream dissolved zinc concentrations were downstream 

from Howardsville and downstream from Arrastra Gulch.

The variability of zinc concentrations for inflow samples 

was much higher than for instream samples and ranged from 

0.004 to 130 mg/L (right bank inflow at 4,353 m) 

(fig. 36). The highest inflow dissolved zinc concentrations 

were from right bank inflows downstream from Arrastra Gulch 

(130 mg/L at 4,353 m; 53.2 mg/L at 4,533; 9.3 mg/L at 

4,586 m; 19.4 mg/L at 4,886 m; 3.8 mg/L at 4,970 m; 

39.8 mg/L 5,356 m; and 12.7 mg/L at 5,858 m). The dissolved 

zinc concentration from inflow downstream from Howardsville (965 m) was 2.5 mg/L during 1997, which was considerably lower than the zinc concentration measured for the inflow 

in 1998 (7.3 mg/L). 

Increases in the dissolved zinc loads corresponded to 

increases of instream dissolved zinc concentrations. Zinc load 

increases occurred downstream from Howardsville, through 

the reach with right bank inflows downstream from Arrastra 

Gulch, and downstream from Boulder Gulch (4,951 m) 

(fig. 37). Sampled instream load and cumulative instream load 

for dissolved zinc were higher than the cumulative inflow load 

immediately downstream from Howardsville, indicating that 

ground-water discharge possibly contributed dissolved zinc to 

the river in this area (table 11). From downstream of Howardsville to the reach immediately upstream from Arrastra Gulch 

at 4,166 m, the instream zinc load increased 7.6 kg/d from surface inflows and ground-water discharge (table 11 and fig. 37). 

The largest instream zinc load increase was observed downstream from Arrastra Gulch (4,186 m) from surface inflows 

and apparent ground-water discharge (table 11). For reaches 

where the sampled instream load and cumulative instream 

load increased but cumulative inflow load remained constant, 

unsampled inflow, possibly from ground-water discharge, 

is indicated. Possible ground-water discharge is evident for 

several reaches downstream from 5,131 to 7,523 m (table 11 

and fig. 37). The instream zinc load increase of 15.3 kg/d 

from 6,038 to 6,288 m probably is caused by ground-water 

discharge with elevated zinc concentrations, because no visible 

inflows occurred in this reach (table 11 and fig 36). The loading graphs (fig. 37) also indicate locations downstream from 

Boulder Gulch where the dissolved zinc sampled instream 

load decreases possibly in response to zinc adsorption onto 

iron colloids or stream sediment. The total sampled instream 

load for dissolved zinc was approximately 83 kg/d, and the 

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000

0

0.1

0.2

0.3

0.4

0.5

 Instream

 Zinc acute toxicity standard

 Zinc chronic toxicity standard

DISSOLVED ZINC CONCENTRATION, IN MILLIGRAMS PER LITER

DISTANCE DOWNSTREAM FROM INJECTION SITE, IN METERS
Figure 37. Sampled instream load, cumulative instream load, and cumulative inflow load 

of dissolved zinc with distance from the injection site, upper Animas River, Howardsville to 

Silverton, Colorado, September 14, 1997.

Metal Loading to the Upper Animas River, Howardsville to Silverton, Colorado, Study Reach, September 1997 47

Figure 36. Instream and inflow dissolved zinc concentrations with distance from the 

injection site, upper Animas River, Howardsville to Silverton, Colorado, 

September 14, 1997.

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

20

40

60

80

100

120

140

Arrastra Gulch (4,186 meters)

Right bank

ditch

(7,688 meters)

Right bank inflows

downstream from

Arrastra Gulch

Right bank

inflow

(4,353 meters)

Old mill site

(1,648 meters)

Downstream from

Howardsville

(965 meters)

Ditch

upstream

from

Howardsville

(181 meters)

DISTANCE DOWNSTREAM FROM INJECTION SITE, IN METERS

DISSOLVED ZINC CONCENTRATION, IN MILLIGRAMS PER LITER

 Instream

 Inflow

 Sampled instream load

 Cumulative instream load

 Cumulative inflow load

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000

20

30

40

50

60

70

80

90

100

110

 DISTANCE DOWNSTREAM FROM INJECTION SITE, IN METERS

 DISSOLVED ZINC LOAD, IN KILOGRAMS PER DAY

Zinc loss

Right bank inflows downstream from

Arrastra Gulch and Boulder Gulch 

(4,310-5,100 meters)

T2—Downstream from Howardsville (1,059 meters)

Possible

ground-water

discharge

of zinc

Arrastra Gulch (4,186 meters)

T4—Upstream from Arrastra Gulch (4,166 meters)
48 Quantification and Simulation of Metal Loading to the Upper Animas River, Eureka to Silverton, San Juan County, Colorado, 

 September 1997 and August 1998

Table 11. Zinc loads calculated from tracer-dilution results, upper Animas River, Howardsville to Silverton, Colorado, September 14, 1997.

[Distance, distance downstream from injection site; kg/d, kilograms per day; RB, right bank; LB, left bank]

Distance 

(meters) Stream reach name

Instream 

zinc 

load 

(kg/d)

Cumulative 

instream 

zinc 

load 

(kg/d)

Cumulative 

inflow zinc 

load 

(kg/d)

Change 

in 

instream 

zinc load 

(kg/d)

Change 

in 

inflow 

zinc load 

(kg/d)

Possible 

explanation

 160 Downstream from injection site–B 26.7 26.7 26.7 26.7 0.0

 310 Downstream from RB ponds 26.7 26.7 26.8 0.1 0.1

 595 T1—near construction 26.7 26.7 26.8 0.0 0.0

 905 Upstream from RB inflow 27.6 27.6 26.8 0.8 0.0

 955 Upstream from Howardsville Mill 27.8 27.8 26.8 0.3 0.0

1,059 T2—Downstream from Howardsville Mill 37.3 37.3 30.0 9.4 3.2 Ground-water discharge

1,135 Downstream from Cunningham Gulch 35.2 37.3 30.9 -2.1 0.9 Zinc loss—adsorption

1,270 Downstream from bridge 36.5 38.6 30.9 1.3 0.1

1,510 At State gage (A53) 36.5 38.6 30.9 0.1 0.0

1,725 Downstream from clean/ dirty inflows 37.0 39.0 32.6 0.4 1.7 Surface inflow

1,925 At upper “campground” 39.0 41.1 32.6 2.0 0.0 Unsampled inflow

2,110 Downstream from campground 39.1 41.1 32.6 0.1 0.0

2,515 Upstream from draining adit 39.3 41.4 32.7 0.2 0.0

2,572 Downstream from adit 39.7 41.8 32.7 0.4 0.1

2,800 T3—Truck park 39.7 41.8 32.7 0.0 0.0

3,040 Narrow chute within canyon 40.4 42.5 32.7 0.8 0.0

3,295 Downstream from first cableway 41.8 43.9 32.7 1.4 0.0

3,555 Mid canyon 41.8 43.9 32.7 0.0 0.0

4,023 Between RB inflows in canyon 42.8 44.9 33.0 1.0 0.2

4,166 T4—Upstream from Arrastra Gulch 46.9 49.0 33.0 4.1 0.0

4,310 Downstream from Arrastra Gulch 49.3 51.4 35.6 2.4 2.6 Surface inflow

4,473 Downstream from river level spring 49.9 52.0 35.7 0.7 0.1

4,581 Downstream from LB abandoned mill 56.1 58.2 35.7 6.2 0.0 Ground-water discharge

4,656 Upstream from Pinnacle Gap 58.0 60.1 45.3 1.9 9.6 Surface inflow

4,816 Upstream from acid inflows 58.0 60.1 45.3 0.0 0.0

4,916 Downstream from acid inflows 63.8 65.9 50.1 5.8 4.7 Surface inflow

5,131 Downstream from Boulder Gulch 64.1 66.2 50.5 0.3 0.4 Surface inflow

5,306 Downstream from Blair Gulch 73.6 75.7 51.9 9.5 1.5 Ground-water discharge

5,536 Downstream from first of capped tailings 77.0 79.1 53.1 3.4 1.2 Ground-water discharge

5,756 Upstream from drain from tailings 72.1 79.1 53.1 -4.9 0.0 Zinc loss—adsorption

6,038 T5—Downstream from capped tailings 72.1 79.1 53.1 0.0 0.0

6,288 Downstream from toe of Mayflower 87.4 94.4 53.1 15.3 0.0 Ground-water discharge

6,528 Upstream from Lackawanna Bridge 83.4 94.4 53.1 -4.0 0.0 Zinc loss—adsorption

6,768 Downstream from Lackawanna Bridge 83.4 94.4 53.1 0.0 0.0

7,008 Upstream from Lackawanna Mill 83.4 94.4 53.1 0.0 0.0

7,283 Downstream from Lackawanna Mill 75.2 94.4 53.1 -8.2 0.0 Zinc loss—adsorption

7,523 Among braids near town 81.7 100.9 53.1 6.5 0.0 Ground-water discharge

7,858 T6—At bridge/gage A68 83.3 102.4 54.4 1.5 1.3 Surface inflow
total cumulative load for zinc was approximately 102 kg/d at 

gaging station A68 (table 11).

Sulfate

Dissolved sulfate concentrations in the upper Animas 

River for 1997 were controlled by the sulfate concentrations of 

surface-water inflows. Instream sulfate concentrations ranged 

from 63.5 to 85.3 mg/L and were lower than the USEPA’s 

secondary drinking-water standard of 250 mg/L. Instream 

sulfate concentrations increased downstream from Howardsville, and concentrations remained relatively constant downstream from Cunningham Gulch (fig. 38).

Inflow sulfate concentrations in the study reach were 

more variable than instream concentrations and ranged from 

12.8 to approximately 1,400 mg/L. Inflows with elevated 

sulfate concentrations in the upper part of the study reach 

included the ditch upstream from Howardsville at 181 m 

(212 mg/L), right bank drainage at 910 m (243 mg/L), inflow 

downstream from Howardsville at 965 m (549 mg/L), adit 

inflow at 1,605 m (256 mg/L) (7,008 m in the Eureka to 

Howardsville study reach), inflow from an old mill site at 

1,648 m (116 mg/L) (7,063 m in the Eureka to Howardsville 

study reach), and abandoned mining sites at 2,125 m 

(222 mg/L) and 2,522 (224 mg/L) (fig. 38). In the lower part 

of the study reach, the right bank inflows downstream from 

Arrastra Gulch contributed elevated sulfate concentrations to 

the stream. Inflows with the highest sulfate concentrations in 

this area were the right bank inflows at 4,353 m (1,053 mg/L); 

4,533 m (1,353 mg/l); 4,886 m (1,408 mg/L); 5,356 m 

(1,378 mg/L); 5,858 m (861 mg/L); and the ditch at 7,688 m 

(1,103 mg/L).

The mass-loading graphs for sulfate show the sampled 

instream load, the cumulative instream load, and the cumulative inflow load as approximately equal, indicating little to 

no sulfate loss or gain due to chemical reaction. The sulfate 

cumulative instream load was approximately equal to the 

cumulative inflow load upstream from Blair Gulch (5,221 m) 

indicating that instream concentrations were a result of the 

measured inflow concentrations (fig. 39). However, downstream from approximately 5,500 m, the sulfate cumulative 

instream load curve is slightly greater than the cumulative 

inflow load curve (fig. 39), indicating that the measured inflow 

load did not account for the entire instream load with the 

remainder probably resulting from ground-water discharge 

with elevated sulfate concentrations.

Metal Loading to the Upper Animas River, Howardsville to Silverton, Colorado, Study Reach, September 1997 49

Figure 38. Dissolved sulfate concentrations with distance from the injection site, upper 

Animas River, Howardsville to Silverton, Colorado, September 14, 1997.

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 0

25

50

75

100

1,000

3,000

 DISTANCE DOWNSTREAM FROM INJECTION SITE, IN METERS

DISSOLVED SULFATE CONCENTRATION, IN MILLIGRAMS PER LITER

Cunningham

Gulch

Downstream from

Howardsville

(965 meters)

Right bank inflows

downstream from

Arrastra Gulch

Right bank 

ditch

(7,688 meters)

 Instream

 Inflow
50 Quantification and Simulation of Metal Loading to the Upper Animas River, Eureka to Silverton, San Juan County, Colorado, 

 September 1997 and August 1998

Figure 39. Sampled instream load, cumulative instream load, and cumulative inflow load of 

dissolved sulfate with distance from the injection site, upper Animas River, Howardsville to

Silverton, Colorado, September 14, 1997.

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000

6,000

8,000

10,000

12,000

14,000

16,000

18,000

20,000

 DISTANCE DOWNSTREAM FROM INJECTION SITE, IN METERS

SULFATE LOAD, IN KILOGRAMS PER DAY

 Sampled instream load

 Cumulative instream load

 Cumulative inflow load

Discussion of Sources and Loadings 

Howardsville to Silverton Study Reach 

Surface-water drainage in the Howardsville to Silverton 

study reach contributed aluminum, copper, iron, manganese, 

zinc, and sulfate to the upper Animas River surface-water 

system in 1997. Instream dissolved and colloidal aluminum 

concentrations generally were low and near detection limits. 

Dissolved iron concentrations and loads increased downstream 

from Howardsville and Arrastra Gulch, and colloidal iron 

remained constant at low concentrations downstream from 

Howardsville. The concentrations and mass loads of instream 

dissolved manganese and zinc increased substantially downstream from Arrastra Gulch to the end of the study reach 

from surface and subsurface inflows, and instream dissolved 

zinc concentrations exceeded acute and chronic aquatic-life 

standards along the entire reach. Instream dissolved copper 

concentrations were lower than the acute and chronic toxicity standards throughout the study reach, and instream sulfate 

concentrations were lower than the USEPA’s secondary drinking water standard of 250 mg/L throughout the study reach. 

Based on the 1997 synoptic-sampling results and massloading graphs, there were four primary areas where metal 

concentrations and loads increased within the Howardsville to 

Silverton study reach. The first increase was the reach downstream from Howardsville to downstream from Cunningham 

Gulch where the sampled instream loads of dissolved and 

colloidal iron, dissolved manganese, dissolved zinc, and dissolved sulfate all increased in a downstream direction during 

1997 and 1998. The second increase was downstream from 

Arrastra Gulch, from approximately 4,186 to 5,900 m, where 

sampled instream loads of colloidal iron, dissolved manganese, dissolved zinc, and dissolved sulfate increased. The load 

increases in this reach appear to result from a series of right 

bank inflows downstream from the Mayflower Mill tailings 

with low pH and elevated constituent concentrations. A third 

increase of sampled instream loads occurred at approximately 

6,100 m where load increases were measured for colloidal 

iron, dissolved manganese, dissolved zinc, and dissolved sulfate. The source of these load increases may have been from 

discharge of ground water with elevated constituent concentrations, based on mass-loading graphs and the lack of visible 

inflow in the reach. A fourth but lesser load increase for 

dissolved zinc and dissolved sulfate occurred at the end of the 

study reach, near the Lackawanna Mill, from approximately 

7,283 to 7,850 m.

Based on the 1997 synoptic-sampling results, dissolved 

zinc is the primary constituent of concern in the Howardsville 

to Silverton study reach of the upper Animas River, and the 
total cumulative load for zinc was approximately 102 kg/d at 

gaging station A68. Listed below are locations where instream 

dissolved zinc load increased and the percentage of the total 

load attributed to the reach:

• Downstream from tailings near the Mayflower Mill 

 (15 percent), 

• Downstream from Blair Gulch (9 percent), 

• Downstream from Howardsville (9 percent), 

• Downstream from tailings near the Lackawanna Mill 

 (6 percent),

• Downstream from abandoned mill at 4,581 m 

 (6 percent),

• Downstream from acidic inflows at 4,916 m 

 (6 percent), and 

• Downstream from Arrastra Gulch (4 percent).

A substantial dissolved zinc load also was contributed 

from the upper Animas drainage upstream from the study area 

(26 percent of the total load).

The 1997 Howardsville to Silverton study reach overlaps 

with the 1998 Eureka to Silverton study reach from a point 

upstream from Howardsville to a point downstream from 

Cunningham Gulch. Although seasonal variability was not 

specifically addressed by the studies, a general relation 

between constituent concentrations and stream discharge is 

noted in the overlapping part of the two data sets. Stream 

discharge near Howardsville was lower in 1998 than in 1997, 

the pH values were higher in 1997 than in 1998, and dissolved 

iron, manganese, zinc, and sulfate concentrations were lower 

in 1997 than in 1998. These observations indicate chemical 

constituents were diluted in 1997 relative to 1998, and that the 

effects of metal-rich inflow on water quality were greater at 

low flow. 

Zinc Solute-Transport Simulations

To interpret mass-loading calculations and to evaluate 

the effects of potential remediation, one-dimensional surfacewater transport of dissolved zinc was simulated for the Howardsville to Silverton study reach using OTIS. This section 

of the report describes the conservative and first-order decay 

simulations and the remediation simulations for the 

Howardsville to Silverton reach.

Conservative and First-Order Decay Simulation 

Results

The Howardsville to Silverton study reach was divided 

into 15 model reaches based on discharge calculations and 

mass-loading graphs. Main-channel cross-sectional area, 

storage-zone cross-sectional area, and storage-zone exchange 

coefficients were determined using OTIS-P simulations of the 

transport site data. A uniform dispersion coefficient of 1.0 m 

was used for all model reaches. For each model reach, a lateral 

inflow discharge was computed based on the stream discharge profile. Upstream from Arrastra Gulch, lateral inflow 

concentrations were assigned to model reaches 1 through 7 

based on measured inflow concentrations for 1997 (table 12 

and fig. 40). Downstream from Arrastra Gulch, lateral inflow 

concentrations and first-order decay rates were adjusted as discussed herein to obtain a reasonable match between simulated 

and measured instream zinc concentrations.

Numerous low-pH inflows with elevated zinc concentrations occurred in model reach 8 downstream from Arrastra 

Gulch (fig. 40), and a flow-weighted average dissolved zinc 

inflow concentration of 42 mg/L was computed for reach 8. 

Using a lateral inflow concentration of 42 mg/L also required 

using a first-order decay constant in reach 8 to achieve a match 

between simulated and measured instream dissolved zinc 

concentrations. However, no dissolved zinc loss was indicated 

for reach 8 based on the sampled instream load graph (fig. 37). 

Therefore, the lateral inflow concentration for dissolved zinc 

in reach 8 was adjusted by trial-and-error to a value of 

4.5 mg/L, and first-order decay was not simulated for this 

reach, to achieve a match between simulated and measured 

instream dissolved zinc concentrations (figs. 40 and 41). 

Model reach 9 represents Boulder Gulch inflow. Using 

the lateral inflow rate and lateral inflow concentration representative of Boulder Gulch (0.06 mg/L), simulated zinc 

concentrations for reach 9 matched the measured instream zinc 

concentrations, so first-order decay was not simulated for this 

reach (table 12, fig. 41).

Instream concentrations and sampled instream load for 

dissolved zinc increased through model reaches 10, 12, and 

14; however, there was little to no increase in the cumulative 

inflow load through these reaches (fig. 37). Unsampled inflow 

is indicated in these reaches, and the increase in instream 

zinc concentrations in this stream reach may be attributed to 

ground-water discharge with elevated zinc concentrations. 

Lateral inflow concentrations for model reaches 10, 12, and 14 

therefore were increased by trial-and error to obtain a match 

between simulated and measured instream zinc concentrations. 

For model reach 10, a flow-weighted average inflow zinc concentration of 1.04 mg/L was computed for the visible inflows 

in the reach. However, using a lateral inflow concentration of 

1.04 mg/L in reach 10 resulted in simulated zinc concentrations for the reach that were lower than the measured instream 

zinc concentrations. Consistent with the mass-loading graphs, 

this result indicates that effective lateral inflow zinc concentrations in reach 10 were higher than measured inflow 

concentrations. A lateral inflow concentration of 5.0 mg/L was 

used for model reach 10 to obtain a match between simulated 

and measured instream zinc concentrations (table 12 and 

fig. 40). The only visible inflow in model reach 12 had a 

low zinc concentration of 0.024 mg/L. However, measured 

instream zinc concentrations increased through reach 12. 

Ground-water discharge with elevated zinc concentrations 

again is indicated, and a lateral inflow concentration of 

Metal Loading to the Upper Animas River, Howardsville to Silverton, Colorado, Study Reach, September 1997 51
52 Quantification and Simulation of Metal Loading to the Upper Animas River, Eureka to Silverton, San Juan County, Colorado, 

 September 1997 and August 1998

Table 12. OTIS setup and input parameters for zinc solute-transport model, upper Animas River, Howardsville to 

Silverton, Colorado.

[m, meters; m2, square meters; m3/s-m, cubic meters per second per meter; mg/L, milligrams per liter; /s, per second; --, not applicable]

Model 

reach

Distance

from 

injection

 site 

(m)

Reach

 length

(m)

Main

channel 

crosssectional 

area

(m2)

Lateral

 inflow 

rate

( m3/s-m)

Lateral

 inflow

concentration

simulation

(mg/L)

Firstorder

 decay 

rate

(/s)

Description

1 595 595 1.713 5.24 x 10-6 0.94 -- T1

2 955 360 1.730 1.25 x 10-4 0.02 -- Upstream from 

 Howardsville

3 1,059 104 1.730 1.39 x 10-4 5.00 -- T2 — Downstream 

from Howardsville

4 1,135 76 2.816 5.08 x 10-3 0.03 -- Downstream from 

 Cunningham Gulch

5 2,800 1,665 2.816 1.19 x 10-4 0.48 -- T3

6 4,166 1,366 2.740 5.76 x 10-5 0.01 -- T4 — Upstream from 

 Arrastra Gulch

7 4,310 144 2.851 1.53 x 10-3 0.20 -- Downstream from 

 Arrastra Gulch

8 4,916 606 2.851 7.99 x 10-5 4.50 -- Downstream from right 

bank acid inflows 

and Boulder Gulch

9 5,131 215 2.851 3.68 x 10-4 0.06 -- Downstream from 

Boulder Gulch

10 5,536 405 2.851 6.99 x 10-5 5.00 -- Downstream from Blair 

Gulch

11 6,038 502 2.851 4.74 x 10-5 6.38 4.0 x 10-4 T5

12 6,288 250 3.188 9.74 x 10-5 7.20 -- Downstream from 

zinc concentration 

increase

13 7,283 995 3.188 8.54 x 10-8 0.20 1.0 x 10-4 Downstream from zinc 

loss

14 7,858 575 3.188 1.23 x 10-6 10.0 -- T6 — End of study 

reach

15 7,958 100 3.188 -- -- -- Downstream boundary
Figure 40. OTIS lateral inflow concentrations and measured inflow concentrations for 

dissolved zinc with distance from the injection site, upper Animas River, Howardsville to 

Silverton, Colorado.

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000

0

5

10

15

20

25

30

35

40

45

50

125

150

14 15

Downstream from zinc loss (7,283 meters)

Downstream from zinc concentration increase (6,288 meters)

Downstream from Blair Gulch (5,536 meters)

12 13

Upstream from Boulder Gulch (4,916 meters)

Downstream from Boulder Gulch (5,131 meters)

T6 (7,858 meters)

T5 (6,038 meters)

Downstream from Arrastra Gulch (4,310 meters)

T4—Upstream from Arrastra Gulch (4,166 meters)

Downstream from Cunningham Gulch (1,135 meters)

T2—Downstream from Howardsville (1,059 m)

Upstream from Howardsville (955 meters)

1 2 3 4 5 6 7 8 9 10 11

Model reach number

T3 (2,800 meters)

T1 (595 meters)

 OTIS CLATIN input values

 Measured concentration of visible inflow

DISTANCE DOWNSTREAM FROM INJECTION SITE, IN METERS

DISSOLVED ZINC CONCENTRATION, IN MILLIGRAMS PER LITER

Figure 41. OTIS results for conservative and first-order decay simulations, upper Animas 

River, Howardsville to Silverton, Colorado.

 Measured instream

 OTIS result with no decay (table 13, simulation 1)

 OTIS result with first-order decay in reaches 11 and 13 (table 13, simulation 2)

 Zinc acute toxicity standard

 Zinc chronic toxicity standard

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

 DISTANCE DOWNSTREAM FROM INJECTION SITE, IN METERS

DISSOLVED ZINC CONCENTRATION, IN MILLIGRAMS PER LITER

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Model reach number

0.16 milligram per liter = Upper limit of acute toxicity for sensitive aquatic species

Metal Loading to the Upper Animas River, Howardsville to Silverton, Colorado, Study Reach, September 1997 53
54 Quantification and Simulation of Metal Loading to the Upper Animas River, Eureka to Silverton, San Juan County, Colorado, 

 September 1997 and August 1998

7.2 mg/L was used for model reach 12 to obtain a match 

between simulated and measured instream zinc concentrations 

(table 12 and fig. 40). In model reach 14, a lateral inflow concentration of 10.0 mg/L was used to obtain a match between 

simulated and measured instream zinc concentrations (table 12 

and fig. 40).

Using the lateral inflow concentrations listed in table 12, 

the conservative OTIS simulation computed instream zinc 

concentrations higher than the measured instream concentrations downstream from Blair Gulch (model reach 10) (fig. 41). 

Consistent with the mass-loading graphs, this simulation result 

indicates that chemical removal of dissolved zinc from some 

stream reaches likely is caused by zinc adsorption onto iron 

colloids or streambed sediment. Loss of a dissolved constituent is represented as a first-order process in OTIS, and firstorder decay rates were assigned to model reaches 11 and 13 to 

represent the decrease of sampled instream zinc load through 

these reaches (table 12). The flow-weighted average zinc 

concentration of the two visible inflows in model reach 11 was 

6.38 mg/L (table 12 and fig. 40). A first-order decay rate of 

4.0 x 10-4/s was assigned to model reach 11 to obtain a match 

between simulated and measured instream zinc concentrations 

(table 12 and fig. 41). In model reach 13, the flow-weighted 

average zinc concentration for the two inflows was 0.20 mg/L, 

and a first-order decay rate of 1.0 x 10-4/s was assigned to 

obtain a match between simulated and measured instream zinc 

concentrations (table 12 and fig. 41). 

Remediation Simulations

 Two remediation alternatives were evaluated for the 

Howardsville to Silverton study reach using the first-order 

decay zinc transport simulation described in the previous 

section. To simulate remediation of stream reaches, the zinc 

lateral inflow concentrations were reduced from the model 

inflow concentrations to hypothetical concentrations representative of inflow after remediation. Because these postremediation concentrations are uncertain, remediation for the 

Howardsville to Silverton study reach was simulated using a 

50-percent reduction and then a 75-percent reduction in zinc 

lateral inflow concentrations of remediated reaches. A list of 

remediation simulations, zinc lateral inflow concentrations, 

and simulation results are presented in table 13.

The first set of remediation simulations addresses reducing zinc inflow concentrations in the model reach representing 

the inflow downstream from Howardsville (model reach 3). 

The zinc lateral inflow concentration for reach 3 (5.0 mg/L) 

was reduced by 50 percent and by 75 percent, and the simulations were run with first-order decay (table 13, simulations 3 

and 4). A third simulation evaluated reducing the dissolved 

zinc upstream boundary condition from 0.28 to 0.19 mg/L 

to represent a 75-percent reduction in zinc concentrations 

from the Forest Queen mine and Kittimack tailings inflows 

(table 13, simulation 5). This simulation is similar to those 

presented for the Eureka to Howardsville 1998 study (table 7, 

simulations 5 and 6) and is repeated here for the 1997 data 

set to examine the effects of remediation on stream reaches 

downstream from Howardsville. Results from simulations 3, 4, 

and 5 indicate that instream zinc concentrations downstream 

from Howardsville to upstream from Arrastra Gulch would 

approach concentrations near 0.16 mg/L if zinc inflow concentrations were reduced by 75 percent in the stream reaches 

receiving inflow from the Forest Queen mine, the Kittimack 

tailings, and downstream from Howardsville (fig. 42).

For the second set of remediation simulations, the anticipated effects of reducing zinc inflow concentrations in model 

reach 12 in addition to the upstream model reaches were 

evaluated (table 13, simulations 6 and 7). Remediation of the 

upstream inflows was represented using an upstream boundary 

condition of 0.19 mg/L zinc, a 75-percent reduction in zinc 

lateral inflow concentration for model reach 3, and then a 

50- and a 75-percent reduction in zinc lateral inflow concentration for model reach 12. These simulations represent the 

effects of remediating reaches receiving inflow from the Forest 

Queen mine, Kittimack tailings, inflow downstream from 

Howardsville, presumed ground-water discharge in model 

reach 12, and include first-order decay in model reaches 11 

and 13. Results of simulations 6 and 7 indicate that instream 

zinc concentrations would be higher than approximately 

0.20 mg/L downstream from Arrastra Gulch because of visible 

inflows and ground-water discharge with elevated zinc concentrations in the lower part of the study reach (fig. 43).

SUMMARY

Drainage from abandoned and inactive mines and naturally mineralized areas in the San Juan Mountains of southern Colorado contributes metals to the upper Animas River 

near Silverton, Colorado. The Bureau of Land Management 

(BLM) and the Animas River Stakeholders Group (ARSG) are 

planning possible remedial actions along the upper Animas 

River to alleviate water-quality degradation, and tracer-injection studies and associated synoptic sampling were performed 

along two reaches of the upper Animas River to locate and 

quantify the sources of metal loading. One tracer-injection 

study was performed in September 1997 on the Animas River 

reach from Howardsville to Silverton, and a second study was 

performed in August 1998 on the stream reach from Eureka 

to Howardsville. Detailed profiles of stream discharge and 

chemical mass loading were obtained from the tracer-injection 

and synoptic-sampling studies. The one-dimensional stream 

transport computer code OTIS was used to evaluate results of 

the tracer-injection studies and to evaluate potential effects of 

remediation.

Tributary drainage in the upper Animas River study 

reaches contributed aluminum, calcium, copper, iron, magnesium, manganese, sulfate, and zinc to the surface-water system 

in 1997 and 1998. Based on the 1998 synoptic-sampling

results and mass-loading graphs, sources upstream from 
Table 13. OTIS results for zinc solute-transport and remediation simulations, upper Animas River, Howardsville to Silverton, Colorado.

[CLATIN, OTIS input parameter for lateral inflow concentrations; m, meters; mg/L, milligrams per liter; %, percent]

Simulation 

number

OTIS CLATIN

(mg/L)

Reach Reach

3 12

OTIS result —computed 

instream zinc 

concentration (mg/L)

Description

1 5.0 7.2 0.269 0.574 Zinc CLATIN represents measured inflows with 

adjusted values in reaches 10, 11, 12 and 14 for 

ground-water discharge and no decay.

2 5.0 7.2 0.269 0.417 Zinc CLATIN represents measured inflows with 

adjusted values in reaches 10, 11, 12 and 14 for 

ground-water inflow and first-order decay in reaches 

11 and 13.

3 2.5 7.2 0.249 0.406 Howardsville remediation.

50% reduction in zinc CLATIN in reach 3

and first-order decay in reaches 11 and 13.

4 1.25 7.2 0.239 0.401 Howardsville remediation.

75% reduction in zinc CLATIN in reach 3

and first-order decay reaches 11 and 13.

5 1.25 7.2 0.184 0.371 Howardsville remediation. 

75% reduction in zinc CLATIN in reach 3 with 

first-order decay in reaches 11 and 13 and upstream 

boundary = 0.19 mg/L.

6 2.5 3.6 0.194 0.343 Reach 12 remediation.

50% reduction in zinc CLATIN in reaches 3 and 

12 with first-order decay in reaches 11 and 13 and 

upstream boundary = 0.19 mg/L.

7 1.25 1.8 0.184 0.321 Reach 12 remediation. 

75% reduction in zinc CLATIN in reaches 3 and 

12 with first-order decay in reaches 11 and 13 and 

upstream boundary = 0.19 mg/L.

End of

reach 6

(4,166 m)

End of study

reach 6

(4,166 m)

Summary 55
56 Quantification and Simulation of Metal Loading to the Upper Animas River, Eureka to Silverton, San Juan County, Colorado, 

 September 1997 and August 1998

Figure 42. OTIS results for remediation simulations, 3, 4, and 5, upper Animas River, Howardsville to Silverton, 

Colorado.

0.16 milligram per liter = Upper limit of acute toxicity for sensitive aquatic species

1 2 3 4 5 6 7 8 9 10 11 12 13 14

Model reach number

 Measured instream

 EXPLANATION

 OTIS result based on 50 percent reduction in zinc inflow reach 3 and first-order decay 

 reaches 11 and 13 (table 13, simulation 3)

 OTIS result based on 75 percent reduction in zinc inflow reach 3 and first-order decay 

 reaches 11 and 13 (table 13, simulation 4)

 OTIS result based on 75 percent reduction in zinc inflow reach 3, first-order decay 

 reaches 11 and 13, and upstream boundary = 0.19 milligram per liter (table 13, 

 simulation 5) 

 OTIS result based on 75 percent reduction in zinc inflow reach 3, first-order decay 

 reaches 11 and 13, and upstream boundary = 0.19 milligram per liter 

 (table 13, simulation 5) 

 Zinc acute toxicity standard 

 Zinc chronic toxicity standard

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000

0

0.1

0.2

0.3

0.4

0.5

0.6

DISSOLVED ZINC CONCENTRATION, IN MILLIGRAMS PER LITER

0.7

 DISTANCE DOWNSTREAM FROM INJECTION SITE, IN METERS
Figure 43. OTIS results for remediation simulations 6 and 7, upper Animas River, Howardsville to 

Silverton, Colorado.

0.16 milligram per liter = Upper limit of acute toxicity for sensitive aquatic species

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

1 2 34 5 6 7 8 9 10 11 12 13 14

Model reach number

 DISTANCE DOWNSTREAM FROM INJECTION SITE, IN METERS

DISSOLVED ZINC CONCENTRATION, IN MILLIGRAMS PER LITER

 Measured instream

 EXPLANATION

 OTIS result based on 50 percent reduction in zinc inflow in reaches 3 and 12, first-order decay in 

 reaches 11 and 13, and upstream boundary = 0.19 milligram per liter (table 13, simulation 6)

 OTIS result based on 75 percent reduction in zinc inflow in reaches 3 and 12, first-order decay in 

 reaches 11 and 13, and upstream boundary = 0.19 milligram per liter (table 13, simulation 7)

 Zinc acute toxicity standard 

 Zinc chronic toxicity standard

Eureka contributed aluminum, copper, manganese, and zinc 

to the upstream end of the study reaches. Colloidal aluminum, 

dissolved copper, and dissolved zinc were attenuated through a 

braided reach downstream from Eureka. Instream copper concentrations were lower than the State of Colorado acute and 

chronic toxicity standards downstream from the braided reach 

to Silverton. Dissolved iron load and concentrations increased 

downstream from Howardsville and Arrastra Gulch, and colloidal iron remained constant at low concentrations downstream from Howardsville. Dissolved manganese was diluted 

by inflows downstream from Eureka, but the sampled instream 

manganese load increased downstream from Howardsville 

and downstream from Arrastra Gulch to Silverton. Instream 

sulfate concentrations were lower than the U.S. Environmental 

Protection Agency’s secondary drinking-water standard of 

250 milligrams per liter (mg/L) throughout the study reaches. 

Elevated zinc concentrations are the primary concern 

for aquatic life in the upper Animas River. In the Eureka to 

Howardsville 1998 study, the sampled instream dissolved zinc 

load increased downstream from the Forest Queen mine, the 

Kittimack tailings, and Howardsville. In the Howardsville to 

Silverton 1997 study, there were four primary areas where 

zinc load increased. First was the increase downstream from 

Howardsville and abandoned mining sites downstream from 

Cunningham Gulch, which also was measured during the 1998 

study. The second increase was downstream from Arrastra 

Gulch, from approximately 4,186 meters (m) to downstream 

from the 1997 injection site at 5,900 m where the sampled 

instream zinc load increased because of a series of right bank 

inflows with pH values lower and dissolved zinc concentrations higher than those of the stream. A third increase of sampled instream dissolved zinc load occurred at approximately 

6,100 m and may have been from ground-water discharge with 

elevated zinc concentrations, based on mass-loading graphs 

and the lack of visible inflow in the reach. A fourth but lower 

zinc load increase occurred near the end of the study reach 

Summary 57
58 Quantification and Simulation of Metal Loading to the Upper Animas River, Eureka to Silverton, San Juan County, Colorado, 

 September 1997 and August 1998

and downstream from tailings near the Lackawanna Mill, from 

approximately 7,283 to 7,850 m.

The 1997 Howardsville to Silverton study reach overlaps 

with the 1998 Eureka to Silverton study reach from a point 

upstream from Howardsville to a point downstream from 

Cunningham Gulch. Although seasonal variability was not 

specifically addressed by these studies, a general relation 

between constituent concentrations and stream discharge 

was noted in the overlapping part of the two data sets. River 

discharge near Howardsville was lower in 1998 than in 1997, 

instream pH values were higher in 1997 than in 1998, and 

instream dissolved iron, manganese, sulfate, and zinc concentrations were lower in 1997 than in 1998. These observations 

indicate that instream chemical constituents were diluted in 

1997 relative to 1998, and that the effects of metal-rich inflow 

on water quality were greater at low flow.

Zinc solute transport in the river was simulated for both 

study reaches to interpret mass-loading calculations and to 

evaluate potential effects of remediation. Using lateral inflow 

concentrations representative of measured inflow concentrations, the conservative simulations computed instream zinc 

concentrations higher than the measured instream concentrations downstream from Eureka Gulch and downstream from 

Arrastra Gulch. Consistent with the mass-loading graphs, 

these simulation results indicate chemical removal of dissolved zinc from some stream reaches. The loss of dissolved 

zinc likely was caused by zinc adsorption onto iron oxyhydroxide colloids or streambed sediment and was represented 

as a first-order decay process using OTIS. First-order decay 

rates were assigned to selected reaches in both simulations to 

represent zinc adsorption, and lateral inflow zinc concentrations were adjusted to represent ground-water discharge of 

elevated zinc concentrations downstream from Arrastra Gulch 

in the Howardsville to Silverton simulations. The simulated 

results for instream zinc concentrations provided reasonable 

matches to the measured instream zinc concentrations for both 

study reaches. 

Two remediation alternatives were evaluated for each 

study reach using the first-order decay zinc transport simulations. For the Eureka to Howardsville study reach, one set of 

simulations evaluated remediation of model reaches representing the Forest Queen mine inflow and inflow downstream 

from the Kittimack tailings, and the second set of simulations 

evaluated remediation of the model reach representing inflow 

downstream from Howardsville in addition to the Forest 

Queen mine inflow and inflow downstream from the Kittimack tailings. For the Howardsville to Silverton study reach, 

one set of simulations evaluated remediation of the model 

reach representing the inflow downstream from Howardsville, 

and the second set of simulations evaluated remediation of 

ground-water inflow in model reach 12. Based on simulation 

results, instream zinc concentrations downstream from the 

Kittimack tailings to upstream from Arrastra Gulch might 

approach 0.16 mg/L (the upper limit of acute toxicity for some 

sensitive aquatic species) if zinc inflow concentrations were 

reduced by 75 percent in the stream reaches receiving inflow 

from the Forest Queen mine, the Kittimack tailings, and downstream from Howardsville. However, simulated zinc concentrations downstream from Arrastra Gulch were higher than 

approximately 0.20 mg/L because of numerous visible inflows 

and assumed ground-water discharge with elevated zinc concentrations in the lower part of the study reach. Removal of 

zinc from discrete visible inflows such as the Forest Queen 

mine discharge seems a viable approach to reducing zinc 

inflow loads to the upper Animas River. Remediation downstream from Arrastra Gulch is more complicated because 

ground-water discharge with elevated zinc concentrations 

seems to contribute to the instream zinc load.

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Water Resources Research, v. 35, no. 2, p. 3829–3840.

Runkel, R.L., McKnight, D.M, Bencala, K.E., and Chapra, 

S.C., 1996, Reactive solute transport in streams, 2. Simulation of a pH modification experiment: Water Resources 

Research, v. 32, no. 2, p. 419–430.

Sole, T.C., Granitto, Matthew, Rich, C.L., Litke, D.W., and 

Pelltier, R.T., 2005, Digital databases and CD-ROM for the 

Animas River watershed, Chapter G in Church, S.E., von 

Guerard, Paul, and Finger, S.E., eds., U.S. Geological 

Survey Professional Paper 1651, 27 p., 6 plates, 1 DVD.

 Stumm, W. and J.J. Morgan, 1981, Aquatic Chemistry: New 

York, Wiley-Interscience, 780 p.

Taylor, H.E., 1982, Atomic emission spectrometric methods, 

in Fishman, M.J., and Bradford, W.L., eds., A supplement 

to methods for the determination of inorganic substances in 

water and fluvial sediments: U.S. Geological Survey OpenFile Report 82–272, 136 p.

U.S. Environmental Protection Agency, 1992, Secondary 

Drinking Water Regulations: Guidance for Nuisance 

Chemicals: U.S. Environmental Protection Agency Report 

810/K–92–001, http://www.epa.gov/safewater/consumer/

2ndstandards.html, accessed February 8, 2005.

U.S. Geological Survey, 2000, Interim report on the scientific 

investigations in the Animas River watershed, Colorado, to 

facilitate remediation decisions by the U.S. Bureau of Land 

Management and the U.S. Forest Service, March 29, 2000 

meeting, Denver, Colorado: U.S. Geological Survey OpenFile Report 00–245, 34 p.
Vincent, K.R., Church, S.E., and Fey, D.L., 1999, Geomor

-

phological context of metal-laden sediments in the Animas 

River floodplain, Colorado, in Morganwalp, D.W., and 

Buxton, H.T., eds., U.S. Geological Survey Toxic Sub-

stances Hydrology Program—Proceedings of the Technical 

Meeting, Charleston, South Carolina, March 8-12, 1999—

Volume 1 of 3—Contamination from Hardrock Mining: 

U.S. Geological Survey Water-Resources Investigations 

Report 99–4018A, p. 99–105.

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estimating parameters of rate-limited mass transfer — Anal-

ysis of stream tracer studies: Water Resources Research, 

v. 33, no. 7, p. 1731–1741.

Walton-Day, Katherine, Runkel, R.L., Kimball, B.A., and Ben-

cala, K.E., 1999, Application of the solute-transport models 

OTIS and OTEQ and implications for remediation in a 

watershed affected by acid mine drainage, Cement Creek, 

Animas River Basin, Colorado, in Morganwalp, D.W., and 

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stances Hydrology Program—Proceedings of the Technical 

Meeting, Charleston, South Carolina, March 8-12, 1999—

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of part of the upper Animas River watershed and vicinity, 

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Field Studies Map MF–2377.

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p. 125–130.

References 61

APPENDIXES

Appendix 1. Field measurements and major ion concentrations for synoptic water samples, upper Animas River, Eureka to 

Howardsville, Colorado, August 14, 1998.

[Source, 0=stream, 1=inflow; Distance, distance downstream from injection site; Temp, water temperature in degrees Celsius; pH, in standard units; SC, specific 

conductance, in microsiemens per centimeter at 25 degrees Celsius; Alkalinity, in milligrams per liter calcium carbonate; all major ion concentrations in milligrams per liter; method detection limits in milligrams per liter listed in parentheses below constituent names; 1,618A, 1,618B, 1,618C, and 1,618D, instream 

samples collected from individual braids listed from left bank to right bank of main channel looking downstream; --, not measured]

Source Distance 

(meters) Time Temp pH SC Calcium (0.02)

Magnesium 

(0.001)

Sodium 

(0.20)

Chloride 

(0.30)

Sulfate 

(0.09) Alkalinity

0 0 -- 12.0 7.35 165 26.4 2.18 0.92 0.20 54.7 21.7

0 80 1855 12.5 7.34 210 25.8 2.14 8.72 13.35 55.2 34.4

0 282 1845 13.1 7.41 210 25.2 2.16 7.35 11.24 55.2 22.5

0 586 1830 11.9 7.21 220 30.9 2.23 5.44 7.43 66.4 20.5

0 786 1825 11.9 7.28 205 30.7 2.23 5.46 7.41 66.5 20.0

0 906 1820 12.1 7.44 225 28.8 2.23 5.49 7.44 66.0 21.3

0 1,061 1815 15.9 7.36 215 28.2 2.23 5.42 7.41 65.5 21.6

0 1,411 1800 14.9 7.27 185 29.8 2.32 5.60 7.34 66.5 --

0 1,618A 1740 13.0 6.98 210 30.0 2.20 5.30 7.35 66.1 36.8

0 1,618B 1750 12.9 7.45 225 29.1 2.25 5.92 9.02 66.1 20.2

0 1,618C 1750 12.8 7.27 210 30.4 2.31 5.74 7.40 66.1 35.7

0 1,618D 1755 14.4 7.17 210 28.5 2.21 5.25 7.27 66.1 23.0

0 1,918 1720 14.0 6.59 220 29.1 2.15 4.98 6.96 65.9 37.0

0 2,030 1700 11.7 7.13 185 27.6 2.04 4.03 5.00 61.3 --

0 2,240 1640 11.9 6.78 145 27.9 2.03 3.35 4.45 62.2 33.2

0 2,420 1630 12.2 6.65 145 26.9 1.95 4.14 4.51 61.8 30.8

0 2,620 1605 13.0 7.03 145 29.0 2.04 3.44 3.93 61.9 20.7

0 2,620 1610 12.7 7.16 150 29.6 2.07 3.55 3.93 61.9 20.9

0 2,860 1555 13.4 7.34 185 28.0 2.05 4.56 4.00 62.2 24.5

0 3,150 1540 13.8 7.30 190 29.3 2.13 4.67 3.72 61.7 20.0

0 3,400 1513 13.5 7.05 195 27.8 2.08 2.78 3.33 64.0 36.6

0 3,435 1505 13.4 6.88 195 29.7 2.14 3.90 2.94 63.5 35.0

0 3,665 1450 12.5 7.22 195 29.8 2.17 3.96 2.77 62.6 23.8

0 3,905 1435 12.0 7.64 190 27.8 2.07 2.53 3.11 62.2 22.5

0 4,164 1415 11.9 6.89 150 30.6 2.20 2.46 2.64 63.4 22.1

0 4,430 1400 11.6 7.05 200 30.4 2.21 3.12 2.51 65.3 23.8

0 4,670 1345 12.1 6.79 155 32.2 2.26 2.31 2.33 67.9 22.6

0 4,970 1333 12.5 7.04 210 33.4 2.28 2.71 2.33 69.3 23.4

0 5,190 1320 12.4 7.00 215 34.3 2.31 2.77 2.30 68.9 23.0

0 5,467 1240 11.1 7.37 210 31.6 2.24 2.85 2.30 70.6 24.6

0 6,038 1215 11.4 7.14 215 31.6 2.22 2.41 2.26 70.7 24.3

0 6,528 1145 10.7 7.33 220 35.3 2.34 2.73 2.26 74.0 23.9

0 6,618 1135 10.9 6.98 220 35.0 2.37 2.29 2.08 70.7 24.3

0 6,753 1115 10.5 7.09 145 33.3 2.28 2.40 1.80 70.4 29.2

0 6,993 1105 10.5 6.86 220 35.3 2.35 2.14 1.76 70.4 27.7

0 7,250 1024 9.4 7.13 235 37.0 2.35 2.77 1.84 71.0 31.1

1 347 1845 12.3 7.38 230 38.0 2.34 1.23 0.27 90.7 37.6

1 2,090 1705 10.5 7.22 175 26.9 2.32 1.47 1.35 63.6 32.7

1 2,465 1625 11.2 7.93 225 36.5 2.91 2.40 0.21 61.0 47.6

1 3,165 1540 12.4 6.32 240 49.5 3.72 2.24 0.24 128 24.3

1 3,405 1525 8.0 7.11 175 30.7 1.99 1.60 0.65 58.9 20.6

1 3,450 1500 13.5 7.95 195 33.4 2.84 2.60 0.19 43.8 52.8

1 3,954 1426 10.8 6.51 245 38.9 2.54 1.76 0.27 94.9 34.6

1 4,189 1415 12.0 6.99 165 33.5 2.14 1.45 0.36 77.1 11.7

1 5,210 1317 15.4 7.74 315 54.8 2.45 3.33 0.28 85.8 65.7

1 5,407 1307 17.9 6.83 210 32.5 1.93 2.07 1.58 58.9 28.8

1 5,648 1235 13.7 7.30 210 32.4 2.55 2.79 2.52 73.8 20.9

1 6,438 1151 15.5 5.68 610 77.5 8.78 2.77 5.17 307 --

1 6,558 1140 10.5 7.60 210 36.2 2.16 1.79 0.28 54.1 46.4

1 6,633 1128 9.3 7.81 245 43.6 2.02 2.44 0.25 69.3 50.7

1 7,008 1052 7.9 7.09 540 95.7 6.14 5.21 0.30 266 23.1

1 7,013 1045 10.1 7.25 185 30.9 1.96 2.48 3.79 46.6 27.1

1 7,063 1038 9.6 6.90 300 52.7 2.61 3.43 4.79 108 30.3

Appendixes 65
Appendix 2. Inductively coupled plasma-atomic emissions spectrometry (ICP-AES) results for synoptic water samples, 

upper Animas River, Eureka to Howardsville, Colorado, August 14, 1998.

[Source, 0=stream, 1=inflow; Distance, distance downstream from injection site; Silica as SiO2; all concentrations in milligrams per liter; 

method detection limits in milligrams per liter listed in parentheses below constituent names; 1,618A, 1,618B, 1,618C, and 1,618D, instream 

samples collected from individual braids listed from left bank to right bank of main channel looking downstream; < constituent not detected; 

E, estimated concentration less than method detection limit]

Source Distance 

(meters)

Aluminum, 

dissolved 

(0.01)

Aluminum, 

colloidal 

(0.01)

Barium, 

dissolved 

(0.002)

Cadmium, 

dissolved 

(0.001)

Copper, 

dissolved 

(0.002)

Copper, 

colloidal 

(0.002)

Iron, 

dissolved 

(0.003)

Iron, 

colloidal 

(0.003)

0 0 0.066 0.222 0.0119 0.0021 0.0232 <0.002 <0.003 0.085

0 80 0.060 0.225 0.0114 0.0030 0.0845 <0.002 0.008 0.075

0 282 0.074 0.226 0.0116 0.0026 0.0170 <0.002 <0.003 0.088

0 586 0.084 0.155 0.0117 0.0024 0.0068 0.0037 <0.003 0.078

0 786 0.065 0.172 0.0119 0.0018 0.0201 <0.002 <0.003 0.078

0 906 0.053 0.180 0.0112 <0.001 0.0330 <0.002 0.006 0.073

0 1,061 0.053 0.180 0.0120 0.0024 0.0063 0.0058 <0.003 0.081

0 1,411 0.065 0.159 0.0121 0.0018 0.0334 <0.002 0.005 0.072

0 1,618A 0.076 0.134 0.0113 0.0021 0.0060 0.0030 <0.003 0.062

0 1,618B 0.079 0.130 0.0125 0.0035 0.141 <0.002 0.014 0.049

0 1,618C 0.053 0.014 0.0118 0.0028 0.0046 <0.002 0.005 <0.003

0 1,618D 0.077 0.117 0.0112 0.0020 0.0078 <0.002 <0.003 0.049

0 1,918 0.083 0.103 0.0109 0.0019 0.0040 0.0036 <0.003 0.055

0 2,030 0.059 0.077 0.0116 0.0017 0.0062 <0.002 <0.003 0.032

0 2,240 0.039 0.081 0.0118 <0.001 0.0065 <0.002 <0.003 0.029

0 2,420 0.048 0.070 0.0110 <0.001 0.0044 <0.002 <0.003 0.032

0 2,620 0.067 0.053 0.0152 <0.001 0.0036 <0.002 <0.003 0.048

0 2,620 0.058 0.098 0.0161 0.0015 0.0036 <0.002 <0.003 0.061

0 2,860 0.055 0.065 0.0162 <0.001 0.0038 <0.002 <0.003 0.044

0 3,150 0.037 0.088 0.0168 <0.001 0.0030 <0.002 <0.003 0.045

0 3,400 0.035 0.062 0.0157 0.0020 0.0040 <0.002 <0.003 0.034

0 3,435 0.053 0.036 0.0185 <0.001 0.0031 <0.002 <0.003 0.031

0 3,665 0.035 0.037 0.0199 <0.001 0.0037 <0.002 <0.003 0.023

0 3,905 0.021 0.059 0.0189 <0.001 0.0038 <0.002 <0.003 0.021

0 4,164 0.032 0.014 0.0195 <0.001 0.0046 <0.002 <0.003 <0.003

0 4,430 0.031 0.054 0.0199 <0.001 0.0045 <0.002 <0.003 0.023

0 4,670 0.028 0.049 0.0196 <0.001 0.0032 <0.002 <0.003 0.021

0 4,970 0.053 0.014 0.0195 <0.001 0.0020 <0.002 <0.003 0.015

0 5,190 0.046 0.014 0.0197 <0.001 0.0023 <0.002 <0.003 0.019

0 5,467 0.024 0.055 0.0184 <0.001 0.0050 <0.002 <0.003 0.023

0 6,038 0.014 0.058 0.0184 0.0017 0.0022 <0.002 <0.003 0.031

0 6,528 0.040 0.059 0.0183 <0.001 0.0015E <0.002 0.059 0.240

0 6,618 0.036 0.034 0.0242 <0.001 0.0023 <0.002 0.013 0.213

0 6,753 0.014 0.076 0.0237 <0.001 0.0060 <0.002 0.008 0.152

0 6,993 0.026 0.049 0.0236 0.0015 0.0109 <0.002 0.020 0.121

0 7,250 0.041 0.033 0.0232 0.0017 0.0018E 0.0012E <0.003 0.171

1 347 0.064 0.071 0.0121 0.0017 0.0144 <0.002 <0.003 0.076

1 1,940 0.154 0.014 0.0150 0.0020 0.0070 <0.002 0.029 <0.003

1 2,090 0.025 0.035 0.0093 0.0031 0.0060 0.0034 0.130 0.163

1 2,465 0.057 0.079 0.0485 <0.001 0.0018E <0.002 0.049 0.144

1 3,165 0.085 0.014 0.0161 0.0028 0.0019E <0.002 <0.003 0.008

1 3,405 0.028 0.014 0.0267 0.0018 0.0025 <0.002 <0.003 0.019

1 3,450 0.014 0.021 0.0468 <0.001 0.0023 <0.002 <0.003 <0.003

1 3,954 0.023 0.014 0.0247 0.0019 0.0043 <0.002 <0.003 <0.003

1 4,189 0.014 0.014 0.0182 <0.001 0.0013E <0.002 <0.003 0.796

1 5,210 0.014 0.043 0.0105 <0.001 0.0010E 0.0015E 0.037 0.070

1 5,407 0.014 0.383 0.0110 <0.001 0.0027 0.0251 <0.003 0.796

1 5,648 0.031 0.073 0.0167 <0.001 0.0036 <0.002 0.036 0.041

1 6,438 0.563 0.141 0.0298 0.0091 <0.002 0.0225 11.7 3.87

1 6,558 0.023 0.014 0.0434 <0.001 <0.002 <0.002 <0.003 0.024

1 6,633 0.014 0.014 0.0019E <0.001 0.0011E <0.002 <0.003 <0.003

1 7,008 0.023 0.024 0.0093 0.0021 <0.002 <0.002 1.03 1.13

1 7,013 0.026 0.014 0.0043 0.0034 0.0399 0.0048 <0.003 0.040

1 7,063 0.032 0.014 0.0101 0.0100 0.0254 0.0018E <0.003 <0.003

66 Quantification and Simulation Of Metal Loading to the Upper Animas River, Eureka to Silverton, San Juan County, Colorado, 

 September 1997 and August 1998
Appendix 2. Inductively coupled plasma-atomic emissions spectrometry (ICP-AES) results for synoptic water samples, 

upper Animas River, Eureka to Howardsville, Colorado, August 14, 1998.—Continued

[Source, 0=stream, 1=inflow; Distance, distance downstream from injection site; Silica as SiO2; all concentrations in milligrams per liter; method 

detection limits in milligrams per liter listed in parentheses below constituent names; 1,618A, 1,618B, 1,618C, and 1,618D, instream samples 

collected from individual braids listed from left bank to right bank of main channel looking downstream; < constituent not detected; 

E, estimated concentration less than method detection limit]

Source Distance 

(meters)

Manganese, 

dissolved 

(0.001)

Manganese, 

colloidal 

(0.001)

Silica, 

dissolved 

(0.009)

Silica, 

colloidal 

(0.009)

Strontium, 

dissolved 

(0.0005)

Strontium, 

colloidal 

(0.0005)

Zinc, dissolved 

(0.003)

Zinc, 

colloidal 

(0.003)

0 0 0.779 <0.001 3.94 0.449 0.172 <0.0005 0.467 <0.003

0 80 0.754 0.005 4.03 0.227 0.165 <0.0005 0.541 <0.003

0 282 0.766 0.016 4.01 0.436 0.167 0.0049 0.391 0.0270

0 586 0.576 0.006 4.11 0.689 0.241 0.0035 0.365 0.0185

0 786 0.574 0.013 4.25 0.604 0.244 0.0029 0.382 <0.003

0 906 0.566 0.012 4.54 0.215 0.239 0.0088 0.418 <0.003

0 1,061 0.567 0.007 4.69 0.058 0.244 <0.0005 0.335 0.0293

0 1,411 0.583 <0.001 4.67 0.136 0.248 <0.0005 0.414 <0.003

0 1,618A 0.552 0.013 4.49 0.021 0.238 0.0022 0.302 0.0217

0 1,618B 0.582 <0.001 4.71 0.021 0.248 <0.0005 0.339 <0.003

0 1,618C 0.562 0.018 4.61 0.156 0.242 0.0067 0.651 <0.003

0 1,618D 0.564 0.023 4.41 0.383 0.237 0.0069 0.326 0.0233

0 1,918 0.527 <0.001 4.35 0.269 0.232 0.0011 0.301 0.0130

0 2,030 0.377 0.007 4.90 0.160 0.232 0.0042 0.347 0.0136

0 2,240 0.343 <0.001 5.13 0.031 0.242 <0.0005 0.353 0.0019E

0 2,420 0.327 0.018 4.95 0.176 0.227 0.0117 0.332 0.0266

0 2,620 0.301 0.059 4.81 1.23 0.265 0.0528 0.292 0.0679

0 2,620 0.290 0.010 4.60 0.662 0.254 0.0097 0.284 0.0189

0 2,860 0.299 0.004 5.08 0.258 0.263 0.0048 0.294 0.0134

0 3,150 0.296 <0.001 5.23 0.021 0.276 <0.0005 0.302 0.0078

0 3,400 0.242 0.008 5.33 0.152 0.261 0.0081 0.304 0.0132

0 3,435 0.222 <0.001 5.61 0.134 0.284 <0.0005 0.337 <0.003

0 3,665 0.210 <0.001 5.52 0.076 0.290 <0.0005 0.291 0.0107

0 3,905 0.196 0.015 5.25 0.505 0.270 0.0216 0.286 0.0265

0 4,164 0.192 <0.001 5.62 0.021 0.288 0.0037 0.288 <0.003

0 4,430 0.172 0.003 5.65 0.021 0.292 0.0039 0.286 0.0071

0 4,670 0.158 0.004 5.86 0.021 0.305 0.0046 0.278 0.0159

0 4,970 0.154 <0.001 5.87 0.050 0.311 <0.0005 0.286 <0.003

0 5,190 0.149 <0.001 5.77 0.292 0.318 <0.0005 0.284 <0.003

0 5,467 0.137 0.004 5.90 0.021 0.306 0.0069 0.276 0.0087

0 6,038 0.135 0.004 5.94 0.178 0.312 0.0045 0.272 0.0186

0 6,528 0.365 0.011 5.82 0.561 0.324 0.0079 0.364 0.0238

0 6,618 0.292 0.005 5.99 0.033 0.341 <0.0005 0.298 0.0118

0 6,753 0.279 0.011 5.95 0.021 0.345 0.0034 0.282 0.0130

0 6,993 0.284 <0.001 5.95 0.021 0.346 <0.0005 0.321 <0.003

0 7,250 0.287 <0.001 5.68 0.483 0.348 <0.0005 0.286 0.0103

1 347 0.118 0.005 5.58 0.228 0.398 0.0197 0.299 0.0095

1 1,940 0.562 <0.001 6.15 0.021 0.281 <0.0005 0.728 <0.003

1 2,090 0.193 0.005 6.79 0.146 0.228 <0.0005 0.483 0.0094

1 2,465 0.021 0.008 6.44 0.413 0.504 0.0161 0.008 <0.003

1 3,165 0.073 0.003 11.9 0.021 0.405 0.0046 0.879 0.0027E

1 3,405 0.003 0.006 6.39 0.344 0.304 0.0014 0.325 <0.003

1 3,450 <0.001 <0.001 4.99 0.021 0.378 <0.0005 0.008 <0.003

1 3,954 0.122 0.002 8.38 0.021 0.367 0.0039 0.456 <0.0

1 4,189 0.038 0.002 6.90 0.245 0.328 0.0084 0.222 0.0063

1 5,210 0.056 0.013 6.62 0.058 0.646 <0.0005 0.012 0.0059

1 5,407 0.100 0.314 9.24 5.10 0.336 0.0085 0.218 0.0732

1 5,648 0.259 <0.001 6.69 0.085 0.304 <0.0005 0.308 <0.003

1 6,438 18.6 0.419 15.0 0.363 0.516 <0.0005 7.28 0.4317

1 6,558 0.005 0.001 5.23 0.200 0.363 0.0090 0.026 <0.003

1 6,633 <0.001 0.001 5.99 0.139 0.596 0.0086 0.013 <0.003

1 7,008 1.04 <0.001 20.9 0.021 0.885 <0.0005 0.368 <0.003

1 7,013 0.011 0.009 7.47 0.120 0.307 <0.0005 0.298 <0.003

1 7,063 0.001 <0.001 10.1 0.168 0.596 0.0192 1.37 0.0232

Appendixes 67
68 Quantification and Simulation of Metal Loading to the Upper Animas River, Eureka to Silverton, San Juan County, Colorado, 

 September 1997 and August 1998

Appendix 3. Field measurements and major ion concentrations for synoptic water samples, upper Animas River, 

Howardsville to Silverton, Colorado, September 14, 1997.

[Source, 0=stream, 1=inflow; Distance, distance downstream from injection site; Temp, water temperature, in degrees Celsius; pH, in standard 

units; SC, specific conductance, in microsiemens per centimeter at 25 degrees Celsius; Alkalinity, in milligrams per liter calcium carbonate; 

all major ion concentrations in milligrams per liter, method detection limits in milligrams per liter listed in parentheses below constituent 

names; --, not measured]

Source Distance 

(meters)

Sample 

Time Temp pH SC Calcium (0.20)

Magnesium 

(0.001)

Sodium 

(0.20)

Chloride 

(0.30)

Sulfate 

(0.09) Alkalinity

0 160 1815 9.5 7.55 203 35.9 2.44 2.53 2.24 78.6 21.8

0 310 1755 10.0 7.50 228 35.4 2.47 2.30 2.20 79.7 --

0 595 1735 11.0 7.40 230 36.0 2.45 2.53 2.23 78.4 23.0

0 905 1710 11.8 7.46 229 35.3 2.40 2.48 2.17 78.5 21.4

0 955 1701 12.0 7.63 232 36.3 2.41 10.2 2.18 81.5 23.3

0 1,059 1645 12.0 7.65 244 37.6 2.62 2.15 2.41 89.6 0.00

0 1,135 1630 12.5 7.69 229 36.9 2.52 2.32 1.53 71.8 29.0

0 1,270 1615 -- 7.64 235 36.4 2.48 2.29 1.68 73.2 32.8

0 1,510 1610 -- 7.60 234 36.5 2.47 2.31 1.61 73.0 30.4

0 1,725 1555 -- 7.58 235 37.6 2.56 2.31 1.69 77.4 28.0

0 2,110 1525 -- 7.68 235 36.6 2.49 2.79 1.52 78.2 28.1

0 2,515 1450 -- 7.55 237 37.6 2.54 2.21 1.61 77.6 --

0 2,572 1442 -- 7.53 240 36.6 2.47 2.13 1.60 77.7 27.8

0 2,800 1430 12.5 7.73 239 37.7 2.64 2.32 1.60 78.5 29.7

0 3,040 1420 12.5 7.78 238 36.6 2.52 2.12 1.58 80.4 29.9

0 3,295 1410 -- 7.84 237 37.8 2.62 2.24 1.63 77.2 38.4

0 3,555 1405 11.5 7.78 238 37.8 2.58 3.22 1.72 78.0 29.8

0 4,023 1335 -- 7.73 237 37.7 2.61 2.19 1.86 69.9 28.2

0 4,166 1320 -- 7.75 238 38.8 2.65 2.93 1.69 78.8 22.7

0 4,310 1300 9.5 7.72 232 36.9 2.46 2.56 1.57 74.6 --

0 4,473 1240 9.0 7.68 232 36.4 2.48 2.15 1.60 75.0 29.6

0 4,581 1200 8.0 7.36 232 36.8 2.56 3.30 1.70 73.1 31.1

0 4,656 1150 -- 7.71 234 37.8 2.52 2.32 1.62 75.7 2.62

0 4,816 1145 8.0 7.70 233 37.6 2.56 2.15 1.63 63.5 23.7

0 4,916 1125 8.0 7.61 236 38.4 2.52 2.18 1.59 78.0 30.2

0 5,131 1115 7.5 7.62 231 37.7 2.58 2.11 1.54 75.2 26.4

0 5,306 1100 7.5 7.55 237 39.5 2.58 3.48 1.58 77.2 32.8

0 5,536 1040 7.0 7.50 239 39.6 2.64 3.64 1.60 79.2 31.9

0 5,756 1030 7.0 7.42 239 38.8 2.61 3.50 1.54 80.2 31.9

0 6,038 1018 7.0 7.57 239 37.4 2.49 2.18 1.54 79.7 26.2

0 6,288 1005 7.0 7.49 244 38.8 2.61 4.78 1.56 81.9 33.1

0 6,528 1000 7.0 7.66 245 39.3 2.60 2.11 1.58 71.3 29.8

0 6,768 948 7.0 7.65 244 39.3 2.59 2.20 1.57 79.7 26.0

0 7,008 938 7.0 7.69 243 39.2 2.62 2.34 1.63 80.6 30.0

0 7,283 925 7.0 7.64 243 37.6 2.52 2.10 1.60 80.7 32.7

0 7,523 915 7.0 7.63 243 39.2 2.61 4.60 1.69 83.7 32.9

0 7,858 900 7.0 7.63 250 39.4 2.57 1.91 1.64 83.2 35.0

1 181 1805 18.0 6.92 443 70.4 10.6 2.10 26.9 212 3.73

1 213 1800 12.5 7.53 134 24.5 0.93 2.21 0.17 39.8 29.6

1 315 1750 6.5 7.59 183 30.5 1.59 2.32 0.34 38.9 44.6

1 745 1730 9.5 7.63 245 41.8 1.62 2.32 0.36 75.3 33.8

1 795 1725 12.0 7.36 -- -- -- 1.59 78.0 21.1 --

1 910 1710 9.0 7.65 482 99.6 2.60 2.42 0.58 243 54.4

1 965 1700 18.0 6.88 839 171 7.55 1.25 7.86 549 22.9

1 1,075 1645 -- 8.04 211 37.9 2.47 2.42 0.32 53.6 44.4

1 1,150 1620 9.5 8.12 259 44.6 2.10 2.35 0.23 74.1 52.8

1 1,605 1605 11.0 6.98 456 107 7.33 4.79 0.40 256 22.4

1 1,648 1605 9.5 6.74 297 52.9 2.69 2.35 8.31 116 31.5

1 1,665 1600 9.5 6.80 267 -- -- -- 1.76 80.5 29.1

1 1,745 1550 11.0 7.89 191 30.4 1.85 1.86 0.94 51.1 40.7

1 2,050 1535 8.5 7.23 194 31.4 1.94 2.38 1.40 48.7 34.6

1 2,125 1520 11.0 4.76 354 67.8 5.87 4.65 0.39 222 0.00

1 2,360 1510 11.0 6.43 246 34.1 3.91 3.30 0.56 105 4.34

1 2,361 1510 9.5 7.30 177 24.4 2.80 2.43 0.37 62.9 24.1

1 2,425 1500 10.0 7.15 152 21.3 2.14 2.29 0.33 47.5 29.0
Appendix 3. Field measurements and major ion concentrations for synoptic water samples, upper Animas River, Howardsville to 

Silverton, Colorado, September 14, 1997.—Continued

[Source, 0=stream, 1=inflow; Distance, distance downstream from injection site; Temp, water temperature, in degrees Celsius; pH, in standard units; SC, specific 

conductance, in microsiemens per centimeter at 25 degrees Celsius; Alkalinity, in milligrams per liter calcium carbonate; all major ion concentrations in milligrams per liter, method detection limits in milligrams per liter listed in parentheses below constituent names; --, not measured]

Source Distance 

(meters)

Sample 

Time Temp pH SC Calcium (0.20)

Magnesium 

(0.001)

Sodium 

(0.20)

Chloride 

(0.30)

Sulfate 

(0.09) Alkalinity

1 2,522 1445 9.0 6.10 383 64.2 6.38 2.21 0.42 224 3.08

1 2,605 1440 14.5 7.92 291 -- -- -- 1.63 77.2 63.1

1 2,709 1430 14.0 7.92 315 -- -- -- 1.58 80.4 66.6

1 3,235 1415 12.5 8.20 276 46.9 2.75 2.24 1.28 56.4 78.5

1 3,682 1400 15.5 8.14 245 40.8 2.53 2.41 2.17 49.1 64.2

1 3,820 1350 13.0 7.93 240 38.3 3.06 2.24 2.54 48.0 64.5

1 4,033 1325 9.5 8.17 295 53.4 3.59 2.34 2.39 65.3 72.8

1 4,186 1310 -- 7.92 184 32.1 1.68 9.31 0.23 43.9 41.6

1 4,190 1305 6.5 7.77 187 32.2 1.65 2.39 0.31 40.8 32.4

1 4,334 1255 -- 7.75 187 30.8 1.62 2.54 0.23 45.0 40.8

1 4,353 1245 12.0 4.17 1,543 192 35.3 1.20 26.0 1,053 0.00

1 4,533 1225 14.5 4.90 1,929 205 31.4 6.83 8.85 1,353 0.00

1 4,586 1200 10.5 4.89 710 114 14.4 5.28 1.96 442 0.00

1 4,886 1135 12.5 5.92 1,824 344 24.7 6.65 2.49 1,408 18.0

1 4,951 1120 8.5 7.53 126 21.1 1.07 2.25 0.18 30.8 27.1

1 4,970 1125 9.5 6.04 478 78.7 5.78 5.23 0.85 249 10.8

1 5,161 1110 9.5 7.47 687 137 3.00 7.26 0.33 364 44.6

1 5,221 1107 8.0 7.52 673 135 3.04 2.43 0.51 360 50.0

1 5,355 1055 7.0 6.95 80 12.8 0.81 2.44 0.18 15.5 30.3

1 5,356 1055 11.0 5.14 691 230 17.9 1.01 1.01 1,378 0.00

1 5,446 1045 7.0 6.72 75 12.1 0.81 1.88 0.26 12.8 23.1

1 5,766 1045 8.0 7.80 236 40.8 2.77 2.24 0.47 55.2 59.9

1 5,858 1025 11.0 5.67 242 226 12.7 1.25 1.74 861 8.85

1 6,105 1010 6.5 7.03 120 18.5 1.41 2.34 0.32 31.3 21.9

1 7,103 935 9.0 7.61 272 46.4 3.13 4.45 0.42 89.1 44.8

1 7,163 935 6.0 7.66 123 19.3 1.50 2.27 0.22 30.8 26.4

1 7,483 915 7.5 7.64 129 19.6 1.54 1.20 0.30 33.5 26.8

1 7,688 905 10.5 7.14 1,522 307 14.2 1.22 5.64 1,103 35.2

Appendixes 69
70 Quantification and Simulation of Metal Loading to the Upper Animas River, Eureka to Silverton, San Juan County, Colorado, 

 September 1997 and August 1998

Appendix 4. Inductively coupled plasma-atomic emissions spectrometry (ICP-AES) results for synoptic water 

samples, upper Animas River, Howardsville to Silverton, Colorado, September 14, 1997.

[Source, 0=stream, 1=inflow; Distance, distance downstream from injection site; Silica as SiO2; all concentrations in milligrams per liter; 

method detection limits in milligrams per liter listed in parentheses below constituent names; <, constituent not detected; E, estimated 

concentration less than method detection limit; --, not measured]

Source Distance 

(meters)

Aluminum, 

dissolved 

(0.01)

Aluminum 

colloidal 

(0.01)

Barium, 

dissolved 

(0.002)

Cadmium, 

dissolved 

(0.001)

Copper, 

dissolved 

(0.002)

Copper, 

colloidal 

(0.002)

Iron, 

dissolved 

(0.003)

Iron, 

colloidal 

(0.003)

0 160 0.006E 0.083 0.0208 0.0018 0.0038 0.0020E 0.002E 0.030

0 310 0.031 0.036 0.0207 0.0014 0.0028 0.0006E 0.006 0.032

0 595 0.009E 0.001E 0.0205 0.0018 0.0036 <0.002 <0.003 <0.003

0 905 0.036 0.026 0.0203 0.0013 0.0019E <0.002 0.016 0.015

0 955 0.005E 0.057 0.0198 0.0018 0.0027 0.0012E 0.007 0.026

0 1,059 0.017 0.039 0.0200 0.0012 0.0012E 0.0031 0.130 0.304

0 1,135 0.015 0.040 0.0304 0.0012 0.0020E 0.0021 0.084 0.389

0 1,270 0.011 0.051 0.0276 0.0013 0.0020E 0.0014E 0.016 0.455

0 1,510 0.012 0.062 0.0277 0.0012 0.0020E 0.0012E 0.076 0.375

0 1,725 0.010E 0.064 0.0278 0.0018 <0.002 0.0025 0.036 0.412

0 1,925 0.011 0.051 0.0272 0.0013 <0.002 0.0029 0.023 0.428

0 1,925 0.022 0.036 0.0267 0.0011 0.0011E 0.0028 0.037 0.419

0 2,110 0.025 0.042 0.0269 0.0012 0.0011E 0.0023 0.012 0.443

0 2,515 0.024 0.065 0.0268 0.0014 0.0017E 0.0020E 0.017 0.460

0 2,572 0.033 0.033 0.0261 0.0018 <0.002 0.0035 0.009 0.445

0 2,800 0.022 0.070 0.0275 0.0012 <0.002 0.0030 0.005 0.436

0 3,040 0.035 0.039 0.0255 0.0016 0.0011E 0.0029 0.010 0.431

0 3,295 0.035 0.048 0.0268 <0.001 0.0013E 0.0025 0.013 0.434

0 3,555 0.017 0.069 0.0265 0.0017 0.0017E 0.0027 0.014 0.424

0 4,023 0.038 0.075 0.0260 0.0012 <0.002 0.0016E 0.009 0.464

0 4,166 0.023 0.087 0.0272 0.0014 0.0017E 0.0022 0.009 0.468

0 4,310 0.027 0.069 0.0262 0.0017 0.0035 0.0050 0.163 0.233

0 4,473 0.009E 0.098 0.0257 0.0016 <0.002 0.0041 <0.003 0.457

0 4,581 0.017 0.102 0.0264 0.0020 0.0018E 0.0020E 0.005 0.446

0 4,656 0.039 0.057 0.0262 0.0012 0.0010E 0.0030 0.009 0.457

0 4,816 0.049 0.092 0.0260 0.0013 <0.002 0.0021 0.004 0.493

0 4,916 0.041 0.065 0.0263 0.0011 <0.002 0.0034 0.007 0.482

0 5,131 0.021 0.079 0.0267 0.0015 0.0015E 0.0024 0.018 0.445

0 5,306 0.041 0.072 0.0264 0.0018 <0.002 0.0037 0.015 0.421

0 5,536 0.052 0.095 0.0265 0.0011 <0.002 0.0027 0.004 0.460

0 5,756 0.021 0.109 0.0261 0.0015 0.0019E 0.0038 0.018 0.457

0 6,038 0.040 0.070 0.0244 0.0015 0.0019E 0.0028 0.014 0.406

0 6,288 0.041 0.083 0.0261 0.0016 0.0028 0.0034 0.010 0.409

0 6,528 0.054 0.071 0.0253 0.0018 <0.002 0.0057 0.012 0.425

0 6,768 0.055 0.056 0.0260 0.0015 <0.002 0.0049 0.002E 0.406

0 7,008 0.043 0.079 0.0261 0.0021 0.0027 0.0021 0.013 0.406

0 7,283 0.034 0.106 0.0247 0.0015 0.0021 0.0028 0.009 0.414

0 7,523 0.041 0.101 0.0260 0.0017 0.0020E 0.0020E 0.011 0.419

0 7,858 0.058 0.081 0.0249 0.0017 <0.002 0.0047 0.003E 0.423
Appendix 4. Inductively coupled plasma-atomic emissions spectrometry (ICP-AES) results for synoptic water 

samples, upper Animas River, Howardsville to Silverton, Colorado, September 14, 1997.—Continued

[Source, 0=stream, 1=inflow; Distance, distance downstream from injection site; Silica as SiO2; all concentrations in milligrams per liter; 

method detection limits in milligrams per liter listed in parentheses below constituent names; <, constituent not detected; E, estimated 

concentration less than method detection limit; --, not measured]

Source Distance 

(meters)

Aluminum, 

dissolved 

(0.01)

Aluminum 

colloidal 

(0.01)

Barium, 

dissolved 

(0.002)

Cadmium, 

dissolved 

(0.001)

Copper, 

dissolved 

(0.002)

Copper, 

colloidal 

(0.002)

Iron, 

dissolved 

(0.003)

Iron, 

colloidal 

(0.003)

1 181 0.060 0.698 0.0211 0.0045 0.0022 0.0149 0.154 0.925

1 213 0.018 0.003E 0.0057 <0.001 0.0022 0.0020E 0.021 0.054

1 315 <0.01 0.003E 0.0039 0.0011 0.0011E 0.0012E 0.003 0.007

1 745 0.006E 0.014 0.0042 <0.001 <0.002 0.0006E 0.010 0.024

1 910 0.002E 0.079 0.0032 0.0013 <0.002 <0.002 0.011 0.074

1 965 0.012 0.329 0.0286 0.0038 0.0013E 0.0070 1.202 12.382

1 1,075 0.017 0.026 0.0508 <0.001 0.0017E <0.002 0.008 0.038

1 1,150 0.013 0.011 0.0023 <0.001 <0.002 <0.002 0.008 0.011

1 1,605 0.051 0.010E 0.0111 0.0031 <0.002 <0.002 1.172 0.732

1 1,648 0.002E 0.016 0.0108 0.0122 0.0355 0.0068 <0.003 0.006

1 1,745 0.007E 3.975 0.0029 <0.001 <0.002 0.0092 0.004 3.775

1 2,050 0.002E 0.001E 0.0031 <0.001 <0.002 <0.002 0.001E <0.003

1 2,125 1.323 0.001E 0.0111 <0.001 0.0109 0.0070 0.556 0.036

1 2,360 0.329 -- 0.0140 0.0040 0.0180 -- 0.222 --

1 2,361 0.060 0.064 0.0106 0.0018 <0.002 <0.002 0.011 <0.003

1 2,425 <0.01 0.031 0.0131 <0.001 <0.002 <0.002 0.007 0.048

1 2,522 0.565 0.454 0.0101 0.0035 <0.002 0.0008E <0.003 1.016

1 3.235 <0.01 0.190 0.0035 <0.001 <0.002 <0.002 <0.003 0.225

1 3,682 0.035 0.001E 0.0071 <0.001 <0.002 <0.002 0.006 <0.003

1 3,820 0.020 1.392 0.0080 0.0021 0.0039 0.0056 <0.003 1.54

1 4,033 0.022 0.071 0.0068 0.001E <0.002 <0.002 <0.003 0.119

1 4,186 0.021 0.020 0.0254 0.0016 0.0034 <0.002 <0.003 0.006

1 4,190 0.016 0.004E 0.0315 0.0021 0.0043 0.0012E 0.002E 0.011

1 4,334 0.026 0.001E 0.0304 0.0025 0.0075 <0.002 0.008 <0.003

1 4,353 23.5 11.695 0.0153 0.610 5.20 0.0604 0.044 9.81

1 4,533 9.76 0.403 0.0162 0.188 0.358 0.0677 0.552 0.170

1 4,586 2.43 0.524 0.0190 0.0370 0.203 0.0454 0.309 0.776

1 4,886 0.394 0.001E 0.0209 0.0458 0.0238 <0.002 0.013 0.006

1 4,951 0.046 0.001E 0.0077 <0.001 <0.002 0.0020E <0.003 0.009

1 4,970 0.145 0.001E 0.0088 0.0131 0.0381 0.0040 <0.003 0.025

1 5,161 0.004E 0.018 0.0257 0.0021 <0.002 0.0010E <0.003 0.026

1 5,221 0.030 0.001E 0.0251 0.0029 <0.002 <0.002 0.010 0.025

1 5,355 0.046 0.023 0.0151 <0.001 <0.002 <0.002 0.011 0.050

1 5,356 20.0 0.001E 0.0193 0.1244 2.42 <0.002 0.023 0.084

1 5,446 0.037 0.200 0.0133 <0.001 <0.002 <0.002 0.013 0.523

1 5,766 0.055 0.226 0.0052 0.0013 0.0018E 0.0069 0.002E 0.388

1 5,858 1.74 0.892 0.0156 0.0555 0.248 0.0460 0.020 0.957

1 6,105 0.015 0.015 0.0080 <0.001 <0.002 <0.002 0.009 0.013

1 7,103 <0.01 0.035 0.0299 0.0017 <0.002 0.0017E 0.022 0.112

1 7,163 0.025 0.032 0.0257 0.0017 0.0029 0.0010E 0.017 0.135

1 7,483 0.015 -- 0.0290 0.0020 0.0020E -- 0.009 --

1 7,688 0.067 0.170 0.0306 0.0144 0.0040 0.0107 1.12 0.772

Appendixes 71
72 Quantification and Simulation of Metal Loading to the Upper Animas River, Eureka to Silverton, San Juan County, Colorado, 

 September 1997 and August 1998

Appendix 4. Inductively couple plasma-atomic emissions spectrometry (ICP-AES) results for synoptic water samples, 

upper Animas River, Howardsville to Silverton, Colorado, September 14, 1997.—Continued

[Source, 0=stream, 1=inflow; Distance, distance downstream from injection site; Silica as SiO2; all concentrations in milligrams per liter; 

method detection limits in milligrams per liter listed in parentheses below constituent names; <, constituent not detected; E, concentration 

estimated less than method detection limit; --, not measured]

Source Distance 

(meters)

Manganese, 

dissolved 

(0.001)

Manganese, 

colloidal 

(0.001)

Silica, 

dissolved 

(0.009)

Silica, 

colloidal 

(0.009)

Strontium, 

dissolved 

(0.0005)

Strontium, 

colloidal 

(0.0005)

Zinc, 

dissolved 

(0.003)

Zinc, 

colloidal 

(0.003)

0 160 0.134 0.0010E 6.56 <0.009 0.354 <0.0005 0.291 <0.003

0 310 0.131 0.0060 6.38 0.205 0.348 0.3562 0.278 0.0158

0 595 0.135 <0.001 6.55 <0.009 0.352 -- 0.288 <0.003

0 905 0.124 <0.001 6.23 0.778 0.353 <0.0005 0.274 0.0079

0 955 0.125 0.0005E 6.35 0.158 0.363 0.366 0.266 0.0062

0 1,059 0.585 <0.001 6.67 <0.009 0.370 0.3700 0.369 0.0298

0 1,135 0.442 0.0020 6.20 0.052 0.371 0.371 0.265 0.0276

0 1,270 0.458 0.0076 6.08 0.163 0.371 0.375 0.261 0.0436

0 1,510 0.446 0.0040 6.06 0.255 0.371 0.376 0.258 0.0444

0 1,725 0.446 0.0040 6.27 <0.009 0.385 0.374 0.266 0.0379

0 1,925 0.444 <0.001 6.30 <0.009 0.380 0.375 0.266 0.0345

0 1,925 0.437 0.0115 5.90 0.377 0.367 0.383 0.252 0.0556

0 2,110 0.446 <0.001 6.16 0.235 0.373 0.375 0.258 0.0492

0 2,515 0.459 0.0157 6.63 0.335 0.381 0.387 0.273 0.0558

0 2,572 0.410 0.0301 5.96 0.705 0.374 0.383 0.242 0.0620

0 2,800 0.435 0.0034 6.62 <0.009 0.386 0.380 0.262 0.0410

0 3,040 0.403 0.0338 6.26 0.254 0.364 0.385 0.235 0.0642

0 3,295 0.433 0.0146 6.60 0.200 0.382 0.381 0.265 0.0443

0 3,555 0.454 <0.001 6.68 0.178 0.384 0.383 0.285 0.0139

0 4,023 0.431 0.0193 6.52 0.467 0.379 0.385 0.263 0.0586

0 4,166 0.453 <0.001 6.76 <0.009 0.389 0.387 0.296 0.0268

0 4,310 0.407 <0.001 6.25 0.732 0.390 <0.0005 0.278 <0.003

0 4,473 0.412 0.0288 6.21 0.622 0.387 0.385 0.281 0.0635

0 4,581 0.497 <0.001 6.54 0.034 0.388 0.384 0.311 0.0223

0 4,656 0.499 0.0030 6.42 0.080 0.389 0.382 0.317 0.0402

0 4,816 0.497 0.0252 6.26 0.446 0.387 0.392 0.323 0.0555

0 4,916 0.576 0.0220 6.23 0.376 0.392 0.395 0.352 0.0437

0 5,131 0.601 0.0501 5.94 0.593 0.397 0.395 0.341 0.0569

0 5,306 0.693 <0.001 6.69 <0.009 0.409 0.388 0.386 0.0152

0 5,536 0.787 <0.001 6.58 0.091 0.412 0.401 0.404 0.0371

0 5,756 0.786 <0.001 6.52 0.456 0.407 0.402 0.379 0.0685

0 6,038 0.737 0.0224 6.39 0.260 0.387 0.399 0.370 0.0498

0 6,288 1.10 <0.001 6.67 <0.009 0.410 0.407 0.448 0.0217

0 6,528 1.05 0.0339 6.35 0.441 0.400 0.407 0.428 0.0550

0 6,768 0.972 0.0184 6.38 0.231 0.399 0.400 0.418 0.0375

0 7,008 1.02 0.0020 6.60 0.354 0.410 0.407 0.436 0.0427

0 7,283 0.962 0.0515 6.10 0.707 0.389 0.409 0.386 0.0735

0 7,523 1.01 <0.001 6.36 0.262 0.410 0.398 0.420 0.0398
Appendix 4. Inductively couple plasma-atomic emissions spectrometry (ICP-AES) results for synoptic water 

samples, upper Animas River, Howardsville to Silverton, Colorado, September 14, 1997.—Continued

[Source, 0=stream, 1=inflow; Distance, distance downstream from injection site; Silica as SiO2; all concentrations in milligrams per liter; method detection limits in milligrams per liter listed in parentheses below constituent names; <, constituent not detected; E, concentration estimated less than method 

detection limit; --, not measured]

Source Distance 

(meters)

Manganese, 

dissolved 

(0.001)

Manganese, 

colloidal 

(0.001)

Silica, 

dissolved 

(0.009)

Silica, 

colloidal 

(0.009)

Strontium, 

dissolved 

(0.0005)

Strontium, 

colloidal 

(0.0005)

Zinc, 

dissolved 

(0.003)

Zinc, 

colloidal 

(0.003)

0 7,858 1.08 0.0584 6.33 0.478 0.403 0.421 0.426 0.0591

1 181 1.27 0.0583 21.9 1.29 0.652 0.645 0.645 0.0424

1 213 0.092 0.0183 4.29 <0.009 0.278 0.275 0.094 0.0033

1 315 0.003 0.0029 7.24 0.101 0.303 0.305 0.0411 0.0062

1 745 0.030 0.0022 7.79 0.075 0.472 0.474 0.0142 0.0017E

1 910 0.011 <0.001 12.8 0.551 1.49 1.55 0.0161 <0.003

1 965 15.9 0.5434 6.83 3.43 0.592 0.591 2.53 2.37

1 1,075 0.007 <0.001 5.51 <0.009 0.399 0.369 0.0267 <0.003

1 1,150 <0.001 0.0013 6.11 0.259 0.622 0.619 0.0106 0.0017E

1 1,605 1.12 <0.001 26.4 <0.009 0.992 0.792 0.476 <0.003

1 1,648 <0.001 <0.001 9.99 0.131 0.653 0.656 1.54 0.0173

1 1,745 0.003 0.1647 7.80 16.8 0.332 0.351 0.0040 0.0446

1 2,050 0.0010E <0.001 7.63 <0.009 0.332 -- 0.0043 <0.003

1 2,125 1.04 <0.001 30.9 <0.009 <0.0005 0.551 0.218 <0.003

1 2,360 0.249 -- 21.2 -- 0.0010 -- 0.533 --

1 2,361 0.0181 0.0140 17.9 0.380 0.205 0.0010 0.0293 <0.003

1 2,425 0.0021 0.0066 16.0 <0.009 0.161 0.165 0.0115 0.0024E

1 2,522 0.0072 0.0158 25.1 2.26 0.704 0.711 0.0409 0.0024E

1 3,235 <0.001 0.0117 9.59 0.75 0.488 0.503 0.0056 0.0080

1 3,682 0.0054 <0.001 7.80 <0.009 0.373 -- 0.0078 <0.003

1 3,820 0.0556 0.0152 8.12 5.76 0.344 0.353 0.126 <0.003

1 4,033 0.0025 0.0014 9.41 <0.009 0.526 0.488 0.0089 <0.003

1 4,186 0.0018 0.0006E 4.69 <0.009 0.457 0.449 0.138 0.0087

1 4,190 0.0021 <0.001 4.69 <0.009 0.457 0.435 0.199 <0.003

1 4,334 0.218 <0.001 4.53 0.171 0.441 0.447 0.221 <0.003

1 4,353 55.5 2.09 38.5 40.6 1.23 1.24 130 8.15

1 4,533 284 <0.001 33.8 0.292 0.989 0.971 53.2 <0.003

1 4,586 4.70 <0.001 31.0 0.921 0.564 0.557 9.32 <0.003

1 4,886 75.6 <0.001 16.5 0.093 2.04 2.02 19.4 <0.003

1 4,951 0.193 0.0115 3.98 0.092 0.211 0.210 0.0594 0.0109

1 4,970 3.11 <0.001 6.60 <0.009 <0.0005 <0.0005 3.77 <0.003

1 5,161 0.070 0.0007E 13.0 <0.009 1.23 1.21 0.424 0.0167

1 5,221 0.012 <0.001 12.3 0.075 1.16 1.15 0.776 0.0247

1 5,355 0.019 <0.001 5.83 0.279 <0.0005 <0.0005 0.0041 <0.003

1 5,356 <0.001 210 30.5 <0.009 <0.0005 2.08 39.8 <0.003

1 5,446 0.0032 0.131 5.98 1.02 <0.0005 <0.0005 0.0047 0.0098

1 5,766 0.0231 0.0120 10.4 0.532 0.455 0.429 0.0425 0.0181

1 5,858 34.4 0.960 24.6 4.18 2.13 2.19 12.7 0.6015

1 6,105 0.0012 0.0017 8.09 0.213 <0.0005 <0.0005 0.0239 0.0019E

1 7,103 0.940 <0.001 11.5 <0.009 <0.0005 <0.0005 0.0835 0.0037

1 7,163 0.0510 0.0094 4.86 0.226 <0.0005 <0.0005 0.2087 0.0240

1 7,483 0.0070 -- 4.92 -- 0.0010 -- 0.395 --

1 7,688 39.7 1.07 15.5 0.087 3.75 3.79 2.08 0.0142

Appendixes 73