U.S. GEOLOGICAL SURVEY

Water-Resources Investigations Report 

Sources of Metal Loads to the Alamosa 

River and Estimation of Seasonal and 

Annual Metal Loads for the Alamosa 

River Basin, Colorado, 1995–97

By Roderick Ortiz, Patrick Edelmann, Sheryl Ferguson, and

Robert Stogner, Sr.

Denver, Colorado

2002

02-4128

Prepared in cooperation with the

U.S. ENVIRONMENTAL PROTECTION AGENCY
U.S. DEPARTMENT OF THE INTERIOR

GALE A. NORTON, Secretary

U.S. GEOLOGICAL SURVEY

Charles G. Groat, Director

The use of firm, trade, and brand names in this report is for identification purposes only and does

not constitute endorsement by the U.S. Geological Survey.

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

U.S. Geological Survey

Information Services

Box 25286

Federal Center

Denver, CO 80225

from:

District Chief

U.S. Geological Survey

Box 25046, Mail Stop 415

Denver Federal Center

Denver, CO 80225-0046
CONTENTS III

CONTENTS

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

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

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

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

Methods of Data Collection and Analysis ............................................................................................................................. 4

Methods of Collection and Analysis Used to Quantify Contamination from Various Source Areas.......................... 5

Methods of Collection and Analysis Used to Estimate Seasonal and Annual Metal Loads ....................................... 8

Sources of Metal Loads to the Alamosa River ...................................................................................................................... 9

Alamosa River Upstream from Wightman Fork (Exposure Area 3a).......................................................................... 10

Alamosa River from Wightman Fork to Fern Creek (Exposure Area 3b)................................................................... 15

Alamosa River from Fern Creek to Terrace Reservoir (Exposure Area 3c) ................................................................ 20

Estimation of Seasonal and Annual Metal Loads at Selected Sites....................................................................................... 20

Wightman Fork at WF5.5 (Exposure Area 1).............................................................................................................. 20

Wightman Fork at WF0.0 (Exposure Area 2).............................................................................................................. 28

Alamosa River at AR45.5 (Exposure Area 3a)............................................................................................................ 31

Alamosa River at AR43.6 (Exposure Area 3b) ........................................................................................................... 32

Alamosa River at AR41.2 and AR34.5 (Exposure Area 3c) ....................................................................................... 35

Alamosa River at AR31.0 (Exposure Area 5) ............................................................................................................. 39

Summary................................................................................................................................................................................ 48

Selected References ............................................................................................................................................................... 49

FIGURES

1. Map showing location of study area, risk assessment exposure areas, and water-quality sampling 

sites in the Alamosa River Basin............................................................................................................................ 2

2. Graph showing daily mean streamflow and number of water-quality samples collected at AR34.5, 1995–97 ..... 5

3. Depiction of hypothetical hydrographs showing selected sample points and estimated traveltime 

of theoretical parcel of water between downstream sites ....................................................................................... 7

4. Example diagram of a boxplot................................................................................................................................ 10

5–16. Boxplots showing:

5. Percentage of contribution of aluminum load from Exposure Area 3a (Alamosa River 

and tributary sites upstream from Wightman Fork), 1995–97................................................................................. 11

6. Percentage of contribution of copper load from Exposure Area 3a (Alamosa River

and tributary sites upstream from Wightman Fork), 1995–97 ................................................................................. 12

7. Percentage of contribution of iron load from Exposure Area 3a (Alamosa River 

and tributary sites upstream from Wightman Fork), 1995–97................................................................................. 13

8. Percentage of contribution of zinc load from Exposure Area 3a (Alamosa River and 

tributary sites upstream from Wightman Fork), 1995–97 ....................................................................................... 14

9. Percentage of contribution of aluminum load from Exposure Area 3b (Alamosa River 

and tributary sites from Wightman Fork to Fern Creek), 1995–97 ......................................................................... 16

10. Percentage of contribution of copper load from Exposure Area 3b (Alamosa River and 

tributary sites from Wightman Fork to Fern Creek), 1995–97................................................................................ 17

11. Percentage of contribution of iron load from Exposure Area 3b (Alamosa River and 

tributary sites from Wightman Fork to Fern Creek), 1995–97................................................................................ 18

12. Percentage of contribution of zinc load from Exposure Area 3b (Alamosa River and 

tributary sites from Wightman Fork to Fern Creek), 1995–97................................................................................ 19

13. Percentage of contribution of aluminum load from Exposure Area 3c (Alamosa River

and tributary sites from Fern Creek to Terrace Reservoir), 1995–97...................................................................... 21

14. Percentage of contribution of copper load from Exposure Area 3c (Alamosa River and 

tributary sites from Fern Creek to Terrace Reservoir), 1995–97............................................................................ 22
IV CONTENTS

5–16. Boxplots showing—Continued

15. Percentage of contribution of iron load from Exposure Area 3c (Alamosa River and 

tributary sites from Fern Creek to Terrace Reservoir), 1995–97 ........................................................................... 23

16. Percentage of contribution of zinc load from Exposure Area 3c (Alamosa River and 

tributary sites from Fern Creek to Terrace Reservoir), 1995–97 ........................................................................... 24

17–36. Graphs showing:

17. Cumulative streamflow for selected flow periods, Exposure Area 1 (site WF5.5), 1995–97 ................................ 25

18. Mass of aluminum and copper for selected flow periods, Exposure Area 1 (site WF5.5), 1995–97 ..................... 26

19. Mass of iron and zinc for selected flow periods, Exposure Area 1 (site WF5.5), 1995–97 ................................... 27

20. Cumulative streamflow for selected flow periods, Exposure Area 2 (site WF0.0), 1995–97 ................................ 28

21. Mass of aluminum and copper for selected flow periods, Exposure Area 2 (site WF0.0), 1995–97..................... 29

22. Mass of iron and zinc for selected flow periods, Exposure Area 2 (site WF0.0), 1995–97 ................................... 30

23. Cumulative streamflow for selected flow periods, Exposure Area 3a (site AR45.5), 1995–97 ............................. 32

24. Mass of aluminum and copper for selected flow periods, Exposure Area 3a (site AR45.5), 1995–97.................. 33

25. Mass of iron and zinc for selected flow periods, Exposure Area 3a (site AR45.5), 1995–97................................ 34

26. Cumulative streamflow for selected flow periods, Exposure Area 3b (site AR43.6), 1995–97............................. 36

27. Mass of aluminum and copper for selected flow periods, Exposure Area 3b (site AR43.6), 1995–97 ................. 37

28. Mass of iron and zinc for selected flow periods, Exposure Area 3b (site AR43.6), 1995–97 ............................... 38

29. Cumulative streamflow for selected flow periods, Exposure Area 3c (sites AR41.2 and AR34.5), 1995–97 ....... 40

30. Mass of aluminum for selected flow periods, Exposure Area 3c (sites AR41.2 and AR34.5), 1995–97 .............. 41

31. Mass of copper for selected flow periods, Exposure Area 3c (sites AR41.2 and AR34.5), 1995–97.................... 42

32. Mass of iron for selected flow periods, Exposure Area 3c (sites AR41.2 and AR34.5), 1995–97 ........................ 43

33. Mass of zinc for selected flow periods, Exposure Area 3c (sites AR41.2 and AR34.5), 1995–97........................ 44

34. Cumulative streamflow for selected flow periods, Exposure Area 5 (site AR31.0), 1995–97............................... 45

35. Mass of aluminum and copper for selected flow periods, Exposure Area 5 (site AR31.0), 1995–97 ................... 46

36. Mass of iron and zinc for selected flow periods, Exposure Area 5 (site AR31.0), 1995–97 ................................. 47

TABLES

1. Ecological risk exposure areas, corresponding stream reach, and U.S. Geological Survey sampling sites ....... 3

2. Flow periods and duration of flow periods in the Alamosa River Basin, 1995–97 ............................................ 6

3. Approximate periods of operation for streamflow gages on the Alamosa River and 

Wightman Fork, 1995–97 ................................................................................................................................... 9
CONTENTS V

CONVERSION FACTORS, ABBREVIATED UNITS, AND ACRONYMS

Sea level: In this report, “sea level” refers to the National Geodetic Vertical Datum of 1929 (NGVD of 1929)—a geodetic datum derived 

from a general adjustment of the first-order level nets of both the United States and Canada, formerly called Sea Level Datum of 1929.

Other abbreviation used in this report:

USGS U.S. Geological Survey

USEPA U.S. Environmental Protection Agency

ARL Analytical reporting limit

Multiply By To obtain

cubic foot per second (ft3/s) 0.02832 cubic meter per second (m3/s)

foot (ft) 0.3048 meter (m)

inch 25.4 millimeter (mm)

mile 1.609 kilometer (km)

square mile (mi2

) 2.590 square kilometer (km2)
Abstract 1

Abstract

Metal contamination in the upper Alamosa 

River Basin has occurred for decades from the 

Summitville Mine site, from other smaller mines, and 

from natural, metal-enriched acidic drainage in the 

basin. In 1995, the need to quantify contamination 

from various source areas in the basin and to quantify 

the spatial, seasonal, and annual metal loads in the 

basin was identified. Data collection occurred from 

1995 through 1997 at numerous sites to address data 

gaps. Metal loads were calculated and the percentages 

of metal load contributions from tributaries to three 

risk exposure areas were determined. Additionally, a 

modified time-interval method was used to estimate 

seasonal and annual metal loads in the Alamosa River 

and Wightman Fork. 

Sources of dissolved and total-recoverable 

aluminum, copper, iron, and zinc loads were determined for Exposure Areas 3a, 3b, and 3c. Alum Creek 

is the predominant contributor of aluminum, copper, 

iron, and zinc loads to Exposure Area 3a. In general, 

Wightman Fork was the predominant source of metals 

to Exposure Area 3b, particularly during the snowmelt 

and summer-flow periods. During the base-flow 

period, however, aluminum and iron loads from Exposure Area 3a were the dominant source of these metals 

to Exposure Area 3b. Jasper and Burnt Creeks generally contributed less than 10 percent of the metal loads 

to Exposure Area 3b. On a few occasions, however, 

Jasper and Burnt Creeks contributed a substantial 

percentage of the loads to the Alamosa River. The 

metal loads calculated for Exposure Area 3c result 

from upstream sources; the primary upstream sources 

are Wightman Fork, Alum Creek, and Iron Creek. 

Tributaries in Exposure Area 3c did not contribute 

substantially to the metal load in the Alamosa River.

In many instances, the percentage of dissolved 

and/or total-recoverable metal load contribution from 

a tributary or the combined percentage of metal load 

contribution was greater than 100 percent of the metal 

load at the nearest downstream site on the Alamosa 

River. These data indicate that metal partitioning and 

metal deposition from the water column to the 

streambed may be occurring in Exposure Areas 3a, 3b, 

and 3c. Metals that are deposited to the streambed 

probably are resuspended and transported downstream 

during high streamflow periods such as during snowmelt runoff and rainfall runoff.

 Seasonal and annual dissolved and totalrecoverable aluminum, copper, iron, and zinc loads 

for 1995–97 were estimated for Exposure Areas 1, 2, 

3a, 3b, and 3c. During 1995–97, many tons of metals 

were transported annually through each exposure 

area. Generally, the largest estimated annual totalrecoverable metal mass for most metals was in 1995. 

The smallest estimated annual total-recoverable metal 

mass was in 1996, which also had the smallest annual 

streamflow. In 1995 and 1997, more than 60 percent of 

the annual total-recoverable metal loads generally was 

transported through each exposure area during the 

snowmelt period. A comparison of the estimated storm 

load at each site to the corresponding annual load indicated that storms contribute less than 2 percent of the 

annual load at any site and about 5 to 20 percent of the 

load during the summer-flow period. 

INTRODUCTION

The upper Alamosa River Basin is a heavily 

mineralized area located in the San Juan Mountains of 

southwestern Colorado (fig. 1). Metal contamination 

has occurred for decades from the Summitville Mine 

Sources of Metal Loads to the Alamosa River and 

Estimation of Seasonal and Annual Metal Loads for 

the Alamosa River Basin, Colorado, 1995–97

By Roderick Ortiz, Patrick Edelmann, Sheryl Ferguson, and Robert Stogner, Sr.
2 Sources of Metal Loads to the Alamosa River and Estimation of Seasonal and Annual Metal Loads for the Alamosa River Basin, 

Colorado, 1995–97 37 ̊28'

37 ̊22'30" 

106 ̊37'30" 106 ̊37'30"

Alamosa River

Ranger Cr

LieutenantCreek

Creek

Cr

Cr

Silver

Fern

Spring

Burnt Creek

Jasper

Creek

Castleman Gulch

Wightman

Fork

Cropsy Cr

Bitter

Cr

Cr

Alum

Iron

Creek

Hydrology modified by Denver Water Board, 1998 Base from U.S. Geological Survey Digital Line Graphs, 1:100,000, 1982

Universal Transverse Mercator projection, Zone 13

Approximate extent of hydrothermal  alteration

Water-quality sampling site and number

EXPLANATION

C O L O R A D O

TERRACERESERVOIR

Water-quality sampling site and  streamflow-gaging station

Exposure areas

Summitville Mine Site

0 1 2 3 4 5 MILES0 1 2 3 4 5 KILOMETERS

Figure 1. Location of study area, risk assessment exposure areas, and water-quality sampling sites in the Alamosa River Basin.
INTRODUCTION 3

site, from other smaller mines, and from natural, 

metal-enriched acidic drainage in the basin (Miller and 

McHugh, 1994). Mining activities have occurred intermittently in the Summitville area since the late 1800’s. 

Large-scale open-pit mining began at the Summitville 

Mine site in the mid-1980’s and continued until the 

mine site was suddenly abandoned in late 1992. At 

that time, the State of Colorado requested the U.S. 

Environmental Protection Agency (USEPA) to assume 

site-maintenance responsibilities under the emergency 

response provisions of Superfund. Since 1992, the site 

has undergone substantial waste-pile consolidation, 

runoff rerouting, water treatment, and reclamation. In 

1998, the State of Colorado assumed shared site 

responsibility of the Summitville site with the USEPA.

Data-collection activities by the U.S. Geological 

Survey (USGS) began in 1993 and included streamflow measurements and water-quality sampling at 

several surface-water sites on the Alamosa River and 

Wightman Fork. In 1994, investigative work by the 

USGS was limited to Terrace Reservoir and the inflow 

and outflow sites to the reservoir (fig. 1). In 1995, 

Morrison-Knudsen Corporation and ICF Kaiser

Engineers (1995) identified multiple data gaps needed 

for ecological risk assessment of the Summitville 

Superfund site. Two of the data gaps identified were 

the need to quantify metal contamination from various 

source areas in the basin and the need to quantify the 

spatial, seasonal, and annual metal loads in the basin. 

As a result, the USGS developed a comprehensive 

data-collection plan for the basin to address these data 

gaps (Patrick Edelmann, U.S. Geological Survey, 

written commun., 1995). The plan included the use of 

several continuous streamflow gages and water-quality 

monitors. In addition, periodic water-quality sampling 

on the Alamosa River, Wightman Fork, and several 

other tributaries was established. Data collected from 

the network from 1995 through 1997 were used to 

address the data gaps identified in the risk assessment. 

Purpose and Scope

The purposes of this report are (1) to quantify 

metal contamination and contribution from various 

source areas and (2) to estimate seasonal and annual 

metal loads at selected sites in the Alamosa River 

Basin from 1995 through 1997. 

 This study was done to address specific data 

gaps identified in the original risk assessment of the 

Summitville Superfund site. The risk assessment 

addendum (Camp Dresser and McKee Inc., 2000) will 

provide the results from this and several other studies 

to the USEPA so that informed decisions regarding the 

need for remedial actions can be made. As part of the 

risk assessment addendum, the potentially impacted 

region downstream from the Summitville Mine site 

was divided into six exposure areas to address risks 

related to specific contaminants of concern on an areaby-area basis. The locations of the six exposure areas 

are described in table 1 and are shown in figure 1. 

The contaminants of concern addressed in the risk 

assessment and in this report are dissolved and totalrecoverable aluminum, copper, iron, and zinc. 

Table 1. Ecological risk exposure areas, corresponding stream reach, and U.S. Geological Survey sampling sites

[EA, exposure area; USGS, U.S. Geological Survey]

Exposure area

(see figure 1) Stream reach

USGS sampling site 

within the exposure area

(see figure 1)

EA1 Summitville Mine site WF5.5

EA2 Wightman Fork downstream from WF5.5 WF0.0

EA3a Alamosa River upstream from Wightman Fork AR45.5

EA3b Alamosa River from Wightman Fork to Fern Creek AR43.6

EA3c Alamosa River from Fern Creek to Terrace Reservoir AR41.2 and AR34.5

EA4 Terrace Reservoir Not addressed in this report

EA5 Alamosa River downstream from Terrace Reservoir AR31.0
4 Sources of Metal Loads to the Alamosa River and Estimation of Seasonal and Annual Metal Loads for the Alamosa River Basin, 

Colorado, 1995–97

Description of Study Area

The upper Alamosa River Basin is located in the 

San Juan volcanic fields of southwest Colorado 

(fig. 1). The study area has a drainage area of approximately 110 square miles and extends from near the 

headwaters of the Alamosa River to just above Terrace 

Reservoir (Stogner and others, 1996). Elevations in the 

study area range from 8,400 feet to nearly 13,000 feet 

above sea level. Annual precipitation ranges from 

approximately 12 inches at the lower elevations to as 

much as 40 inches at the top of the highest peaks 

(Miller and McHugh, 1994). Most of the precipitation 

is in the form of snowfall. The Alamosa River 

upstream from Wightman Fork receives water from 

the Iron, Alum, and Bitter Creek drainages, which are 

geomorphically degraded and have been for nearly 

5 million years (Bove and others, 1996). Low-pH 

water with high concentrations of trace metals from 

the Summitville Mine site adversely affects Wightman 

Fork and several miles of the Alamosa River downstream from the confluence with Wightman Fork. The 

oxidation of the ubiquitous pyrite stock in the area 

results in acidic water and the release of metals. The 

oxidation of pyrite is summarized in Wentz (1974) and 

in Nordstrom (1982). From the mouth of Wightman 

Fork, the Alamosa River flows east through the 

Alamosa Canyon for about 14 miles before reaching 

Terrace Reservoir. Several small tributary flows enter 

the Alamosa River along this reach including Jasper 

and Burnt Creeks, which drain hydrothermally altered 

areas. Terrace Reservoir is a small irrigation reservoir 

that supplies water for agricultural use in the San Luis 

valley (Ferguson and Edelmann, 1996).

METHODS OF DATA COLLECTION 

AND ANALYSIS

 To meet the objectives of this study, the USGS 

collected instantaneous streamflow and periodic 

water-quality data at five sites on the Alamosa River 

(AR45.5, AR43.6, AR41.2, AR34.5, and AR31.0) and 

two sites on Wightman Fork (WF5.5 and WF0.0) from 

1995 through 1997 (fig. 1). Site nomenclature uses a 

two-letter designation for the stream followed by a 

river mileage (in miles) from the mouth. Hence, 

WF5.5 is on Wightman Fork 5.5 miles upstream from 

the mouth of the Alamosa River. Routine water-quality 

samples were collected 8 to 12 times per year at these 

sites; figure 2 illustrates the temporal distribution of 

the sampling events over the 3 years of data collection. 

One additional site on the Alamosa River (AR49.5) 

was designated as a background site. Several other 

tributaries were sampled less often, based on their 

potential metal contribution to the Alamosa River. 

Tributaries that drain hydrothermally altered areas 

were sampled seven to nine times per year from April 

through October. These sites include Iron Creek 

(IC0.0), Alum Creek (AC0.0), Bitter Creek (BI0.0), 

Jasper Creek (JC0.0) and Burnt Creek (BC0.0) (fig. 1). 

Other tributaries that drained areas unaffected by 

mining were sampled four to five times per year, 

primarily during the snowmelt and summer flow. 

These tributaries were Spring Creek (SC0.0), Fern 

Creek (FC0.0), Castleman Gulch (CG0.0), Silver 

Creek (SI0.0), Lieutenant Creek (LC0.0), and 

Ranger Creek (RC0.0). The samples were collected 

as described by Horowitz and others (1994) and 

in the USGS comprehensive data-collection plan 

(Patrick Edelmann, U.S. Geological Survey, written 

commun., 1995). Streamflow measurements were 

done at all tributary sites at the time of sample 

collection.

The concentration and streamflow data used 

in the analyses of this report are available from 

the Colorado Department of Public Health and 

Environment, Hazardous Materials and Waste 

Management Division, 4300 Cherry Creek Drive 

South, Denver, CO, 80222–1530. The data include 

all instantaneous streamflow values from 1995 

through 1997. In addition, the data include dissolved 

and total-recoverable metal concentrations for grab 

samples, discrete samples collected using automatic 

samplers, and flow-weighted composite samples 

collected during the same period. Water-quality 

data collected during storm events also are included. 

Grab samples (discrete and equal-width increment), 

composite, and storm samples can be found in the data 

base under the general heading of “sample type.” 

The annual hydrograph has four distinct 

seasonal flow regimes or flow periods: base flow, early 

snowmelt, snowmelt, and summer flow (fig. 2). The 

timing and duration of these flow periods vary from 

year to year depending on the weather conditions and 

the available snowpack at the higher elevations 
METHODS OF DATA COLLECTION AND ANALYSIS 5

0

1,000

100

200

300

400

500

600

700

800

900

DAILY MEAN STREAMFLOW, IN CUBIC 

FEET PER SECOND

JFMAMJ J ASON

1995

D JFMAMJ J ASO

1996

ND A SON D J FMAMJ J

1997

SUMMER FLOW

SUMMER FLOW

BASE FLOW

BASE FLOW

BASE FLOW

SNOWMELT

BASE FLOW

SUMMER FLOW

SNOWMELT

EARLY SNOWMELT

EARLY SNOWMELT

EARLY SNOWMELT

SNOWMELT

STREAMFLOW

GRAB SAMPLE

STORM SAMPLE

COMPOSITE WITH MULTIPLE

 DISCRETE SAMPLES

EXPLANATION

(table 2). The water-quality data were analyzed and 

summarized for each of these four flow periods. The 

base-flow period is characterized by relatively steadystate low-flow conditions. Typically, base flow extends 

from early October through early April. The early 

snowmelt flow regime is delineated by a departure 

from base flow as the first substantial snowmelt conditions become apparent. This “first flush” period is relatively short in duration but can be associated with large 

metal loading to the river. The snowmelt-flow regime 

is characterized by the annual peak streamflow and 

provides the largest percentage of the annual streamflow in the river. The extent of the snowmelt period in 

the basin from 1995 to 1997 was highly variable 

depending on the amount of snowpack and the 

prevailing weather patterns. The summer-flow regime 

is delineated by a decrease in streamflow and a gradual 

return to base-flow conditions; nearly all significant 

rainfall events occur during this period. 

Methods of Collection and Analysis Used 

to Quantify Contamination from Various 

Source Areas

Selected water-quality and streamflow data 

collected from all sites were used to quantify contamination and assess the metal contribution from various 

exposure areas in the basin. Metal concentrations from 

analysis of water-quality samples and corresponding 

streamflow measurements were used to calculate metal 

Figure 2. Daily mean streamflow and number of water-quality samples collected at AR34.5, 1995–97.
6 Sources of Metal Loads to the Alamosa River and Estimation of Seasonal and Annual Metal Loads for the Alamosa River Basin, 

Colorado, 1995–97

loads at each sampling site for each sampling date. 

The following equation was used to compute metal 

loads:

where

Load is mass of metal, in tons per day,

Cmetal is concentration of metal, in micrograms

 per liter,

Qsite is streamflow, in cubic feet per second,

and

M is conversion factor of 26.98×10–7.

Generally, less than 3 percent of the total-recoverable concentrations at gaged stations were less than 

the reporting limit. Less-than values were more prevalent among dissolved concentrations but most were 

associated with aluminum values. If censored concentration data were reported, the reporting limit was 

substituted for the analytical value in the analysis. 

AR45.5 had the largest overall percentage of less-than 

values among the gaged sites.

Percentages of metal load contributions from 

tributaries were determined for each sample collected 

by dividing the metal load at the tributary site by the 

metal load at the nearest downstream Alamosa River 

site. For example, the percentage of metal load contribution from Alum Creek to AR45.5 was determined 

by dividing the metal load at Alum Creek by the metal 

load from the corresponding sample collected at 

AR45.5. The formula is as follows:

= percentage of metal load

contribution from Alum 

Creek

Percentages of metal load contributions were 

calculated for each tributary and flow period and 

grouped by exposure area.

During base-flow conditions, water-quality 

samples were collected only once at each site during a 

sampling event because relatively little diurnal variation in metal load was expected between October and 

March. Water-quality samples generally were 

collected from all Alamosa River sites, Wightman 

Fork sites, and sites on Iron, Alum, Bitter, Jasper, and 

Burnt Creeks. Instantaneous streamflow measurements were done at all sites during base flow. 

Dissolved and total-recoverable aluminum, copper, 

iron, and zinc loads were calculated and percentage of 

contributions to downstream sites were calculated as 

described previously.

During nonsteady-state streamflow conditions, 

large diurnal variations in streamflow and metal 

concentrations occur in the Alamosa River and 

Wightman Fork (Ortiz and Stogner, 2000). Consequently, large variations in metal loads also occur 

during these periods. In an effort to collect comparable 

samples, multiple water-quality samples were 

collected at WF5.5, WF0.0, AR45.5, AR43.6, 

AR41.2, and AR34.5 using automatic samplers. The 

automatic samplers were programmed to collect as 

many as six discrete sample sets at each site during a 

diurnal period (24 hours). The first sample at each 

site was collected from the same parcel of water as 

the parcel moved downstream from the Summitville 

Mine to Terrace Reservoir; samples at WF0.0 and 

AR45.5 were collected at the same time because of 

the close proximity of the two sites (fig. 1). The other 

sets of samples accomplished in the same manner but 

on different parts of the hydrograph (fig. 3). The 

specific timing of the sample collection at each site 

was determined just prior to the start of sampling by 

using satellite-transmitted streamflow data from each 

gaging station to compare and determine traveltimes 

between downstream sites. A description of these 

methods used can be found in Ortiz and Stogner 

(2000). 

Table 2. Flow periods and duration of flow periods in the 

Alamosa River Basin, 1995–97

Flow

periods Date range Duration, 

(in days)

1995

Base flow January 1–March 20 79

Early snowmelt March 21–April 29 40

Snowmelt April 30–August 1 94

Summer flow August 2–October 5 65

1995–1996

Base flow October 6–March 28 175

Early snowmelt March 29–April 25 28

Snowmelt April 26–June 20 56

Summer flow June 21–October 5 107

1996–1997

Base flow October 6–April 18 195

Early snowmelt April 19–May 5 17

Snowmelt May 6–July 5 61

Summer flow July 6–October 18 105

Load Cmetal Qsite = ( ) × × M

[ ] Load AC ( ) 0.0

[ ] Load AR ( ) 45.5 ----------------------------------------- × 100
METHODS OF DATA COLLECTION AND ANALYSIS 7

Sites AR49.5 and AR31.0 were not equipped 

with automatic samplers and were only sampled once 

during each sampling event. The background site, 

AR49.5, was sampled upstream from its confluence 

with Iron Creek at approximately the same time as 

IC0.0 (Iron Creek). The loads from AR49.5 were used 

to determine the contribution of metal loads entering 

Exposure Area 3a. Hereafter in this report, Exposure 

Area will be designated as “EA.” The metal load at 

AR31.0 (Alamosa River below Terrace Reservoir) was 

not expected to change throughout a diurnal cycle and, 

as such, a single sample was deemed representative of 

the daily mean concentration.

Water-quality samples also were collected from 

tributaries other than Wightman Fork during each 

sampling event. Typically, only one sample was 

collected at each tributary site. The tributary sites were 

located at or near the mouth of (in downstream order) 

Iron Creek, Alum Creek, Bitter Creek, Jasper Creek, 

Burnt Creek, Spring Creek, Fern Creek, Castleman 

Gulch, Silver Creek, Lieutenant Creek, and Ranger 

Creek (fig. 1).

Sources of metals to the Alamosa River were 

evaluated using data collected from a specific parcel of 

water as it flowed through the study area. The specific 

parcel was identified from those sites equipped with 

automatic samplers and was chosen to coincide with 

the approximate traveltime of water sampled at tributary sites. Generally, tributary sites were collected 

within a 6-hour period around noon. Occasionally, 

tributaries were not sampled on the same day as the 

sites equipped with automatic samplers. In these cases, 

an effort was made to ensure that the data used from 

the automatic samplers were collected at approxiSITE 1

SITE 2

SITE 3

Downstream direction

Traveltime

Traveltime

Stream hydrograph

STREAMFLOW, IN CUBIC FEET PER SECOND

TIME, IN HOURS

A1

A2

A3

B1 B2

B3

C1

C2

C3

D1

D2

D3

E1

E2

E3

Figure 3. Depiction of hypothetical hydrographs showing selected sample points and estimated 

traveltime of theoretical parcel of water between downstream sites.
8 Sources of Metal Loads to the Alamosa River and Estimation of Seasonal and Annual Metal Loads for the Alamosa River Basin, 

Colorado, 1995–97

mately the same time of day that the tributaries were 

sampled and that no major changes in streamflow had 

occurred. Storm samples were not included in the data 

set when evaluating loads and percentage of contributions from source areas. 

Streamflow data accompanied most waterquality samples collected during nonsteady-state 

periods. Generally, instantaneous data were retrieved 

from the data loggers at gaged sites providing the 

gage was operational. Streamflow measurements 

were not made at AR41.2, AR43.6, AR45.5, WF0.0, 

and WF5.5 from April through June 1995 because 

streamflow gages had not been installed and high 

streamflow conditions were unwadeable. As a result, 

load calculations, could not be made for these 

samples. Streamflow measurements were done in 

conjunction with water-quality samples collected at 

tributary sites. 

Methods of Collection and Analysis Used 

to Estimate Seasonal and Annual Metal 

Loads

Several methods can be used to compute 

seasonal and annual metal loads. Estimates using 

regression equations can be used where there are 

strong correlations between constituents. In the 

Alamosa River, however, relations between the logarithms of metal concentrations and streamflow 

generally were not statistically significant (p<0.10). 

Standard time-interval methods divide the data record 

into discrete intervals and estimate load as the product 

of the concentration for that discrete period and the 

sum of the streamflow for that period (Scheider and 

others, 1979). For the purposes of this report, a modified time-interval method was used to estimate metal 

loads. In the modified time-interval method, the data 

record is divided into several discrete time intervals 

based on changes in streamflow or flow periods. The 

mean concentration of the values that occurred during 

each flow period was multiplied by the total streamflow for the period to determine metal loads for the 

flow period. Estimates of the metal loads for each flow 

period were summed to estimate annual metal loads.

Grab samples collected during steady-state 

streamflow conditions and flow-weighted composite 

samples collected during nonsteady-state streamflow 

conditions were used to compute an average metal 

concentration at each site for each flow period from 

1995 through 1997. Methods for processing flowweighted composite samples were consistent with 

those described by the USEPA (1991). Appropriate 

concentration data were logarithmically transformed 

(log base 10) and averaged. The averages then were 

retransformed (antilog of the transformed averages) to 

obtain nonskewed, estimated average metal concentrations. This type of data transformation is commonly 

used with water-quality data because of the generally 

log-normal distribution of the positively skewed data 

(Helsel and Hirsch, 1992). However, the statistical 

certainties of the average concentrations determined 

by this method are unknown because of the small 

number of samples collected during each flow period 

(fig. 2).

Streamflow for each flow period was determined by summing the reported daily streamflow for 

the flow period at each gaged site. Streamflow gages at 

sites AR34.5 and AR31.0 were operated throughout 

much of the year by the Colorado Division of Water 

Resources (McDonald, 1996, 1997, and 1998). 

Streamflow gages at sites WF5.5, WF0.0, AR45.5, 

AR43.6, and AR41.2 were installed by the USGS in 

mid- to late July 1995. The USGS-gaged streamflow 

records are reported in the annual water-resources data 

reports for Colorado (Crowfoot and others, 1996, 

1997, and 1998). Table 3 shows the periods of operation for all the gages from 1995 to 1997. 

In certain cases, daily streamflow was not available at a site and was estimated by computing the 

proportion of instantaneous streamflow measured at 

the site during the flow period to the streamflow 

measured at AR34.5. Depending on the number of 

instantaneous measurements made during the flow 

period, either one proportion or multiple proportions 

were used to estimate the cumulative or total streamflow for the flow period for the ungaged period at the 

site.

Metal concentrations associated with rainstorm 

runoff were not used to compute the average metal 

concentrations for the summer-flow period because 

too few storm samples were collected to adequately 

characterize metal concentrations at each site during 

storms. As a result, the average metal concentrations 

and, therefore, loads may be underestimated for the 

summer-flow period. The available storm data, 

however, were analyzed and a semiquantitative discussion of seasonal and annual storm load contribution is 

presented. First, the storm data were grouped by site 

and a log-transformed average was computed as 
SOURCES OF METAL LOADS TO THE ALAMOSA RIVER 9

described previously. The average concentrations were 

multiplied by the median change in streamflow and the 

median duration of a storm as presented by Rupert 

(2001). The product (load in tons per day) was multiplied by the number of rainstorm runoff events per 

year to estimate the load contributed by storms. 

Generally, 18 storms were identified during the 

summer period for each year (Rupert, 2001). A 

comparison of the estimated storm load at each site to 

the corresponding annual load indicated that storms 

contribute less than 2 percent of the annual load at any 

site. When compared to the summer load, storms 

appeared to contribute from 5 to 20 percent of the 

load. The highest percentage of contribution was for 

total-recoverable aluminum and iron.

In addition to the underestimation of loads due 

to storms, the Summitville Mine treatment plant periodically released water with high metal concentrations 

and low pH that was not sampled (Rupert, 2001). The 

releases were generally associated with variations in 

the operations at the mine site. These releases affect 

the accuracy of the estimates of metal loads used in 

this report.

SOURCES OF METAL LOADS TO THE 

ALAMOSA RIVER

Sources of dissolved and total-recoverable 

aluminum, copper, iron, and zinc loads were determined for Exposure Areas 3a, 3b, and 3c (fig. 1) by 

computing the percentage of contribution of metal 

load for each site relative to the downstream mainstem site. The equation to calculate the percentage of 

contribution of metal load from each tributary was 

Table 3. Approximate periods of operation for streamflow gages on the Alamosa River and Wightman Fork, 1995–97

[1234, denotes approximate number of weeks during a month; -, denotes inactive; x, denotes active]

Site Jan Feb Mar Apr May June July Aug Sept Oct Nov Dec

1234 1234 1234 1234 1234 1234 1234 1234 1234 1234 1234 1234

1995

AR31.0 ---- ---- ---- xxxx xxxx xxxx xxxx xxxx xxxx xx-- ---- ----

AR34.5 ---- ---- ---- xxxx xxxx xxxx xxxx xxxx xxxx xx-- ---- ----

AR41.2 ---- ---- ---- ---- ---- ---- -xxx xxxx xxxx xx-- ---- ----

AR43.6 ---- ---- ---- ---- ---- ---- -xxx xxxx xxxx xx-- ---- ----

AR45.5 ---- ---- ---- ---- ---- ---- --xx xxxx xxxx xx-- ---- ----

WF0.0 ---- ---- ---- ---- ---- ---- --xx xxxx xxxx xx-- ---- ----

WF5.5 ---- ---- ---- ---- ---- ---- --xx xxxx xxxx xx-- ---- ----

1996

AR31.0 ---- ---- ---- xxxx xxxx xxxx xxxx xxxx xxxx x--- ---- ----

AR34.5 ---- ---- ---- xxxx xxxx xxxx xxxx xxxx xxxx x--- ---- ----

AR41.2 ---- ---- ---- -xxx xxxx xxxx xxxx xxxx xxxx x--- ---- ----

AR43.6 ---- ---- ---- -xxx xxxx xxxx xxxx xxxx xxxx x--- ---- ----

AR45.5 ---- ---- ---- -xxx xxxx xxxx xxxx xxxx xxxx x--- ---- ----

WF0.0 ---- ---- ---- -xxx xxxx xxxx xxxx xxxx xxxx x--- ---- ----

WF5.5 ---- ---- ---- -xxx xxxx xxxx xxxx xxxx xxxx x--- ---- ----

1997

AR31.0 ---- ---- ---- xxxx xxxx xxxx xxxx xxxx xxxx xx-- ---- ----

AR34.5 ---- ---- --- xxxx xxxx xxxx xxxx xxxx xxxx xx-- ---- ----

AR41.2 ---- ---- ---- --xx xxxx xxxx xxxx xxxx xxxx xx-- ---- ----

AR43.6 ---- ---- ---- --xx xxxx xxxx xxxx xxxx xxxx xx-- ---- ----

AR45.5 ---- ---- ---- --xx xxxx xxxx xxxx xxxx xxxx xx-- ---- ----

WF0.0 ---- ---- ---- --xx xxxx xxxx xxxx xxxx xxxx xx-- ---- ----

WF5.5 ---- ---- ---- ---- xxxx xxxx xxxx xxxx xxxx xx-- ---- ----
10 Sources of Metal Loads to the Alamosa River and Estimation of Seasonal and Annual Metal Loads for the Alamosa River Basin, 

Colorado, 1995–97

Interquartile range

(one-half of data is

within this range)

Outlier data value greater than 3 times the

interquartile range outside the quartile

Data value less than or equal to 1.5 times the

interquartile range outside the quartile

75th percentile (three quarters of data are less than

this value)

25th percentile (one quarter of data are less than

this value)

Outlier data value less than or equal to 3

and more than 1.5 times the

interquartile range outside the quartile

50th percentile (median)

described in a previous section of this report. In addition, the percentage of contribution of metal load from 

the upstream main-stem site to the closest downstream 

main-stem site was calculated in the same manner. 

This provides a percentage of contribution of the metal 

load that can be attributed to the Alamosa River 

upstream from the exposure areas. The percentage of 

contribution of metal loads determined in this manner 

provides an estimate of the contribution of metals from 

a particular area. In some instances, the percentage of 

contribution of metal loads from the tributary site(s) or 

the upstream main-stem site is larger than 100 percent 

of the metal load measured at the downstream mainstem site. This indicates that some reaction or process 

occurred within the stream reach that decreased the 

dissolved and/or total-recoverable metal load in the 

water column. Iron and aluminum hydroxide precipitates are commonly found on the stream bottom in 

certain areas of the Alamosa River and Wightman 

Fork. The following sections present the data as 

boxplots, which show the variation around the median 

value of the data. An example of a boxplot is given in 

figure 4. 

Alamosa River Upstream from Wightman 

Fork (Exposure Area 3a)

Sources of metals to the Alamosa River 

upstream from Wightman Fork, EA3a, were determined for each flow period: base flow, early snowmelt, 

snowmelt, and summer flow. The source area evaluated in EA3a includes the Stunner hydrothermally 

altered area (fig. 1). The water-quality sites evaluated 

for EA3a were: AR49.5 (Alamosa River upstream 

from Iron Creek), IC0.0 (Iron Creek at the mouth), 

AC0.0 (Alum Creek at the mouth), and BI0.0 (Bitter 

Creek at the mouth). The percentage of contribution of 

metal loads from each of these sites is shown in 

figures 5–8. The percentage of contribution of metal 

loads for AR49.5, IC0.0, AC0.0, and BI0.0 were 

Figure 4. Example diagram of a boxplot.
SOURCES OF METAL LOADS TO THE ALAMOSA RIVER 11

0

l

DISSOLVED ALUMINUM

TOTAL-RECOVERABLE ALUMINUM

INSTANTANEOUS DISSOLVED ALUMINUM

INSTANTANEOUS TOTAL-RECOVERABLE ALUMINUM

EXPLANATION

CONTRIBUTION OF ALUMINUM LOAD, IN PERCENT

AR49.5 IC0.0 AC0.0 BI0.0

Maximum tota

value=7,200

SNOWMELT PERIOD

AR49.5 IC0.0 AC0.0 BI0.0

SUMMER-FLOW PERIOD

0

0

7,000

1,000

2,000

3,000

4,000

5,000

6,000

0

3,500

500

1,000

1,500

2,000

2,500

3,000

0

450

50

100

150

200

250

300

350

400

CONTRIBUTION OF ALUMINUM LOAD, IN PERCENT

BASE-FLOW PERIOD EARLY SNOWMELT PERIOD

140

20

40

60

80

100

120

Figure 5. Percentage of contribution of aluminum load from Exposure Area 3a (Alamosa River and tributary 

sites upstream from Wightman Fork), 1995–97.
12 Sources of Metal Loads to the Alamosa River and Estimation of Seasonal and Annual Metal Loads for the Alamosa River Basin, 

Colorado, 1995–97

0

180

20

40

60

80

100

120

140

160

CONTRIBUTION OF COPPER LOAD, IN PERCENT

0

160

20

40

60

80

100

120

140

CONTRIBUTION OF COPPER LOAD, IN PERCENT

0

80

10

20

30

40

50

60

70

0

350

50

100

150

200

250

300

BASE-FLOW PERIOD EARLY SNOWMELT PERIOD

SNOWMELT PERIOD SUMMER-FLOW PERIOD

AR49.5 IC0.0 AC0.0 BI0.0 AR49.5 IC0.0 AC0.0 BI0.0

DISSOLVED COPPER

TOTAL-RECOVERABLE COPPER

INSTANTANEOUS DISSOLVED COPPER

INSTANTANEOUS TOTAL-RECOVERABLE COPPER

EXPLANATION

Figure 6. Percentage of contribution of copper load from Exposure Area 3a (Alamosa River and tributary sites 

upstream from Wightman Fork), 1995–97.
SOURCES OF METAL LOADS TO THE ALAMOSA RIVER 13

300

50

100

150

200

250

0

300

50

100

150

200

250

BASE-FLOW PERIOD EARLY SNOWMELT PERIOD

SNOWMELT PERIOD

0

700

100

200

300

400

500

600

SUMMER-FLOW PERIOD

0

CONTRIBUTION OF IRON LOAD, IN PERCENT

0

800

100

200

300

400

500

600

700

CONTRIBUTION OF IRON LOAD, IN PERCENT

AR49.5 IC0.0 AC0.0 BI0.0 AR49.5 IC0.0 AC0.0 BI0.0

EXPLANATION

DISSOLVED IRON

TOTAL-RECOVERABLE IRON

INSTANTANEOUS DISSOLVED IRON

INSTANTANEOUS TOTAL-RECOVERABLE IRON

Figure 7. Percentage of contribution of iron load from Exposure Area 3a (Alamosa River and tributary sites upstream 

from Wightman Fork), 1995–97.
14 Sources of Metal Loads to the Alamosa River and Estimation of Seasonal and Annual Metal Loads for the Alamosa River Basin, 

Colorado, 1995–97

0

SNOWMELT PERIOD

AR49.5 IC0.0 AC0.0 BI0.0 AR49.5 IC0.0 AC0.0 BI0.0

DISSOLVED ZINC

TOTAL-RECOVERABLE ZINC

INSTANTANEOUS DISSOLVED ZINC

INSTANTANEOUS TOTAL-RECOVERABLE ZINC

EXPLANATION

10

20

30

CONTRIBUTION OF ZINC LOAD, IN PERCENT

0

140

0

20

40

60

80

100

120

CONTRIBUTION OF ZINC LOAD, IN PERCENT

0

10

20

30

40

50

60

70

80

SUMMER-FLOW PERIOD

0

90

40

50

60

70

80

BASE-FLOW PERIOD EARLY SNOWMELT PERIOD

50

90

5

10

15

20

25

30

35

40

45

Figure 8. Percentage of contribution of zinc load from Exposure Area 3a (Alamosa River and tributary sites 

upstream from Wightman Fork), 1995–97.
SOURCES OF METAL LOADS TO THE ALAMOSA RIVER 15

computed relative to the metal loads measured at 

AR45.5.

Alum, Iron, and Bitter Creeks contribute 

substantially to the metal loads in EA3a. The predominant contributor of dissolved and total-recoverable 

aluminum, copper, iron, and zinc loads to EA3a is 

Alum Creek. Frequently, the percentage of contribution of metal loads from Alum Creek was greater than 

the combined metal load contribution from Iron Creek 

and Bitter Creek. Generally, Iron Creek was a greater 

source of metals to EA3a than Bitter Creek. The 

Alamosa River upstream from Iron Creek (AR49.5) is 

shown to contribute a fair percentage of copper and 

zinc for some flow regimes or periods. It should be 

noted that much of the copper and zinc concentration 

data at AR49.5 were reported as less than the analytical reporting limit (ARL). A decision was made to use 

the ARL when calculating loads because, generally, 

the ARL was representative of other reported concentrations. As such, the use of the ARL to calculate loads 

at AR49.5 provides a relatively good estimate, albeit a 

slightly higher estimate, of the copper and zinc load 

contribution to EA3a. 

As shown in figures 5–8, there were several 

instances where the percentage of metal load contribution from a tributary or several tributaries was greater 

than 100 percent of the measured metal load at 

AR45.5. This indicates that, with respect to dissolved 

metal loads, the dissolved metal partitioned to the 

suspended or particulate phase within the exposure 

area; and with respect to total-recoverable metal loads, 

the suspended or particulate metal settled from the 

water column to the streambed within the exposure 

area. Metals that are deposited to the streambed are 

probably resuspended and transported downstream 

during high streamflow associated with snowmelt 

runoff and during rainfall runoff in the summer.

Alamosa River from Wightman Fork to 

Fern Creek (Exposure Area 3b)

Sources of metals to the Alamosa River from 

Wightman Fork to Fern Creek, EA3b, were determined for each flow period: base flow, early snowmelt, 

snowmelt, and summer flow. The source areas evaluated in EA3b include Wightman Fork and the Jasper 

hydrothermally altered area (fig. 1). The water-quality 

sites evaluated for EA3b were: AR45.5 (Alamosa 

River upstream from Wightman Fork), WF0.0 

(Wightman Fork at mouth), AR43.6 (Alamosa River 

upstream from Jasper), JC0.0 (Jasper Creek at the 

mouth), BC0.0 (Burnt Creek at the mouth), and SC0.0 

(Spring Creek at the mouth). The percentage of contribution of metal loads from each of these sites are 

shown in figures 9–12. The percentage of contribution 

of metal loads from AR45.5 and WF0.0 were 

computed relative to the metal loads measured at 

AR43.6, and the percentage of contribution of metal 

loads from AR43.6, JC0.0, BC0.0, and SC0.0 were 

computed relative to AR41.2.

During the base-flow period, the pH of the 

Alamosa River at AR45.5 was at its annual minimum 

and the pH of the Wightman Fork generally was at its 

annual maximum. During this period, the predominant 

contribution of dissolved and total-recoverable 

aluminum and iron loads to EA3b was from EA3a, as 

indicated by the metal loads at AR45.5 (figs. 9 and 

11). Additionally, EA3a generally contributed more 

than 30 percent of the dissolved and total-recoverable 

zinc loads to EA3b during base flow (fig. 12). EA3a 

generally was the predominant contributor of totalrecoverable iron load to EA3b during the early snowmelt period (fig. 11). 

During early snowmelt, snowmelt, and summerflow periods, Wightman Fork was the predominant 

contributor of dissolved aluminum. Wightman Fork 

was the predominant contributor of dissolved iron load 

to AR43.6 during snowmelt periods. During base flow, 

early snowmelt, snowmelt, and summer flow, 

Wightman Fork was the predominant contributor of 

dissolved and total-recoverable copper loads. 

Throughout the year, Wightman Fork was the predominant contributor of dissolved and total-recoverable 

zinc loads. There were several instances where the 

percentages of dissolved aluminum, copper, iron, and 

zinc loads and total-recoverable copper and zinc loads 

from Wightman Fork were greater than 100 percent of 

the metal load at AR43.6. Additionally, there were 

occurrences where the dissolved and total-recoverable 

aluminum and iron loads at AR45.5 were greater than 

100 percent of the metal load at AR43.6. These data 

indicate that, during certain times, metal partitioning 

and metal deposition from the water column to the 

streambed may be occurring in the reach between 

Wightman Fork and AR43.6, a distance of 2.1 miles.

Downstream from AR43.6, Jasper and Burnt 

Creeks generally contributed less than 10 percent of 

the metal loads relative to AR41.2. However, on a few 

occasions, Burnt Creek contributed a substantial 
16 Sources of Metal Loads to the Alamosa River and Estimation of Seasonal and Annual Metal Loads for the Alamosa River Basin, 

Colorado, 1995–97

NO DATA

DISSOLVED ALUMINUM

TOTAL-RECOVERABLE ALUMINUM

INSTANTANEOUS DISSOLVED ALUMINUM

INSTANTANEOUS TOTAL-RECOVERABLE ALUMINUM

EXPLANATION

AR45.5 WF0.0 AR43.6 JC0.0 BC0.0 SC0.0 AR45.5 WF0.0 AR43.6 JC0.0 BC0.0 SC0.0

0

100

200

300

400

CONTRIBUTION OF ALUMINUM LOAD, IN PERCENT

0

100

200

300

0

1,000

200

400

600

800

CONTRIBUTION OF ALUMINUM LOAD, IN PERCENT

SNOWMELT PERIOD

0

1,000

200

400

600

800

SUMMER-FLOW PERIOD

Maximum

dissolved

value=1,850

600

400

500

BASE-FLOW PERIOD EARLY SNOWMELT PERIOD

700

500

600

NO DATA

NO DATA

NO DATANO DATANO DATA

NO DATA

Figure 9. Percentage of contribution of aluminum load from Exposure Area 3b (Alamosa River and tributary sites from 

Wightman Fork to Fern Creek), 1995–97.
SOURCES OF METAL LOADS TO THE ALAMOSA RIVER 17

BASE-FLOW PERIOD EARLY SNOWMELT PERIOD

SNOWMELT PERIOD SUMMER-FLOW PERIOD

CONTRIBUTION OF COPPER LOAD, IN PERCENT CONTRIBUTION OF COPPER LOAD, IN PERCENT

0

200

20

40

60

80

100

120

140

160

180

0

150

25

50

75

100

125

0

350

50

100

150

200

250

300

0

400

50

100

150

200

250

300

350

AR45.5 WF0.0 AR43.6 JC0.0 BC0.0 SC0.0 AR45.5 WF0.0 AR43.6 JC0.0 BC0.0 SC0.0

DISSOLVED COPPER

TOTAL-RECOVERABLE COPPER

INSTANTANEOUS DISSOLVED COPPER

INSTANTANEOUS TOTAL-RECOVERABLE COPPER

EXPLANATION NO DATA NO DATA

NO DATA

NO DATANO DATANO DATA

NO DATA

Maximum

dissolved

value = 1,250

Maximum

dissolved

value = 1,040

Figure 10. Percentage of contribution of copper load from Exposure Area 3b (Alamosa River and tributary sites 

from Wightman Fork to Fern Creek), 1995–97.
18 Sources of Metal Loads to the Alamosa River and Estimation of Seasonal and Annual Metal Loads for the Alamosa River Basin, 

Colorado, 1995–97

DISSOLVED IRON

TOTAL-RECOVERABLE IRON

INSTANTANEOUS DISSOLVED IRON

INSTANTANEOUS TOTAL-RECOVERABLE IRON

EXPLANATION

AR45. 5 WF0. AR43. 6 JC0. 0 BC0.0 SC0.0 AR45.5 WF0.0 AR43. 6 JC0.0 BC0.0 SC0.0

0

700

100

200

300

400

500

600

SUMMER-FLOW PERIOD

700

600

CONTRIBUTION OF IRON LOAD, IN PERCENT 300

400

500

0

100

200

SNOWMELT PERIOD

0

0

BASE-FLOW PERIOD

Maximum

dissolved

value = 596 

Maximum

dissolved

value = 355

Maximum

dissolved

value = 1,780

Maximum

dissolved

value = 8,850

300

200

250

50

100

150

CONTRIBUTION OF IRON LOAD, IN PERCENT

EARLY SNOWMELT PERIOD

0

150

25

50

75

100

125

NO DATA

NO DATANO DATA

NO DATA

NO DATA

NO DATA

NO DATA

Figure 11. Percentage of contribution of iron load from Exposure Area 3b (Alamosa River and tributary sites from 

Wightman Fork to Fern Creek), 1995–97.
SOURCES OF METAL LOADS TO THE ALAMOSA RIVER 19

DISSOLVED ZINC

TOTAL-RECOVERABLE ZINC

INSTANTANEOUS DISSOLVED ZINC

INSTANTANEOUS TOTAL-RECOVERABLE ZINC

EXPLANATION

AR45. 5 WF0. 0 AR43. 6 JC0.0 BC0.0 SC0.0 AR45. 5 WF0. 0 AR43. 6 JC0. 0 BC0.0 SC0.0

0

150

25

50

75

100

125

CONTRIBUTION OF ZINC LOAD, IN PERCENT

SNOWMELT PERIOD SUMMER-FLOW PERIOD

0

0

200

25

50

75

100

125

150

175

140

20

40

60

80

100

120

BASE-FLOW PERIOD EARLY SNOWMELT PERIOD

160

20

40

60

80

100

120

140

CONTRIBUTION OF ZINC LOAD, IN PERCENT

0

NO DATA

NO DATA

NO DATA

NO DATANO DATANO DATA

NO DATA

Figure 12. Percentage of contribution of zinc load from Exposure Area 3b (Alamosa River and tributary sites 

from Wightman Fork to Fern Creek), 1995–97.
20 Sources of Metal Loads to the Alamosa River and Estimation of Seasonal and Annual Metal Loads for the Alamosa River Basin, 

Colorado, 1995–97

percentage of the dissolved aluminum load and the 

dissolved and total-recoverable iron loads to the 

Alamosa River in EA3b. Also, on a few occasions, 

Jasper Creek contributed a substantial percentage of 

the dissolved and total-recoverable iron loads to the 

Alamosa River in EA3b. Spring Creek did not 

contribute substantially to the metal loading of the 

Alamosa River in EA3b.

Alamosa River from Fern Creek to Terrace 

Reservoir (Exposure Area 3c)

Sources of metals to the Alamosa River from 

Fern Creek to Terrace Reservoir, EA3c, were determined for each flow period—base flow, early snowmelt, snowmelt, and summer flow. The tributaries 

evaluated in EA3c do not drain any hydrothermally 

altered areas (fig. 1). The water-quality sites evaluated 

for EA3c are FC0.0 (Fern Creek at mouth), CG0.0 

(Castleman Gulch at the mouth), AR41.2 (Alamosa 

River downstream from Castleman Gulch), SI0.0 

(Silver Creek at the mouth), LC0.0 (Lieutenant Creek 

at the mouth), and RC0.0 (Ranger Creek at the mouth). 

The percentages of contribution of metal loads from 

each of these sites are shown in figures 13–16. The 

percentage of contribution of metal loads from FC0.0 

and CG0.0 were computed relative to the metal loads 

measured at AR41.2, and the percentage of contribution of metal loads from AR41.2, SI0.0, LC0.0, and 

RC0.0 were computed relative to AR34.5.

None of the five tributaries sampled in EA3c 

contributed substantially to dissolved or totalrecoverable aluminum, copper, iron, and zinc loads. 

The combined streamflow for these tributaries contributed less than 2 percent of the streamflow to EA3c. 

Therefore, the tributaries do not provide substantial 

dilution to the metal loads measured in EA3c. The 

metal loads in EA3c result from upstream sources; the 

primary upstream sources are Wightman Fork in EA1 

and Alum and Iron Creeks in EA3a.

Throughout the year, the contributions of 

dissolved aluminum, copper, iron, and zinc loads and 

total-recoverable copper and iron loads at AR41.2 

were frequently greater than 100 percent of the respective metal loads at AR34.5. Except during the early 

snowmelt period, total-recoverable zinc loads (fig. 16) 

were frequently greater than 100 percent of the respective metal loads at AR34.5. These data indicate that 

metal partitioning and metal deposition from the water 

column to the streambed may be occurring in the last 

8.5 miles of EA3c.

ESTIMATION OF SEASONAL AND 

ANNUAL METAL LOADS AT SELECTED 

SITES

Seasonal and annual dissolved and total-recoverable aluminum, copper, iron, and zinc loads for 

1995–97 were estimated for Exposure Areas 1, 2, 3a, 

3b, and 3c. As indicated in table 2, the duration of flow 

varied from year to year for the same flow period. For 

example, the base-flow period for 1995 had a duration 

of 79 days, the base-flow period for 1996 had a duration of 175 days, and the base-flow period for 1997 

had a duration of 195 days. The duration of the flow 

period affects the mass of metals estimated for each 

flow period. Therefore, it is important to remember 

this when making year-to-year comparisons of metal 

loads for the same flow period. Additionally, the 

magnitude of streamflow varied from year to year; 

1995 and 1997 were above-normal flow years, 

whereas 1996 was a below-normal flow year. The 

streamflow in 1995 had the highest total flow with a 

94-day snowmelt period, and the streamflow in 1996 

had the lowest total flow with a 56-day snowmelt 

period. 

Wightman Fork at WF5.5 (Exposure 

Area 1)

The cumulative streamflow and estimates of the 

mass of dissolved and total-recoverable aluminum, 

copper, iron, and zinc for each of the four seasonal 

flow regimes (flow periods) and the annual streamflow 

and metal mass for 1995–97 at WF5.5 are presented in 

figures 17–19. In 1995, streamflow measurements and 

water-quality samples were not collected from WF5.5 

until the snowmelt period. Therefore, metal loads were 

not estimated for the 1995 base flow and early snowmelt periods. The annual streamflow and estimates of 

metal mass shown for 1995 in figures 17–19 were 

based on partial year records and included estimates 

only for the snowmelt and summer-flow periods.

 Many tons of metals were transported past 

WF5.5 from 1995 through 1997. Between 49 and 

246 tons of total-recoverable aluminum (fig. 18), 

between 6 and 44 tons of total-recoverable copper 
ESTIMATION OF SEASONAL AND ANNUAL METAL LOADS AT SELECTED SITES 21

DISSOLVED ALUMINUM

TOTAL-RECOVERABLE ALUMINUM

INSTANTANEOUS DISSOLVED ALUMINUM

INSTANTANEOUS TOTAL-RECOVERABLE ALUMINUM

EXPLANATION

FC0.0 CG0.0 AR41.2 SI0.0 LC0.0 RC0.0 FC0.0 CG0.0 AR41.2 SI0.0 LC0.0 RC0.0

0

0

800

100

200

300

400

500

600

700

CONTRIBUTION OF ALUMINUM LOAD, IN PERCENT

0

0

8,000

1,000

2,000

3,000

4,000

5,000

6,000

7,000

BASE-FLOW PERIOD EARLY SNOWMELT PERIOD

SNOWMELT PERIOD SUMMER-FLOW PERIOD

14,000

2,000

4,000

6,000

8,000

10,000

12,000

CONTRIBUTION OF ALUMINUM LOAD, IN PERCENT

4,000

500

1,000

1,500

2,000

2,500

3,000

3,500

NO DATANO DATA

NO DATANO DATA

NO DATANO DATANO DATANO DATANO DATANO DATA

NO DATA

NO DATANO DATANO DATANO DATA

NO DATA

NO DATA

NO DATA

NO DATA

NO DATA

NO DATANO DATA

NO DATA

NO DATA

NO DATA

Figure 13. Percentage of contribution of aluminum load from Exposure Area 3c (Alamosa River and tributary sites 

from Fern Creek to Terrace Reservoir), 1995–97.
22 Sources of Metal Loads to the Alamosa River and Estimation of Seasonal and Annual Metal Loads for the Alamosa River Basin, 

Colorado, 1995–97

0

1,000

200

400

600

800

EXPLANATION

DISSOLVED COPPER

TOTAL-RECOVERABLE COPPER INSTANTANEOUS TOTAL-RECOVERABLE COPPER

INSTANTANEOUS DISSOLVED COPPER

SNOWMELT PERIOD SUMMER-FLOW PERIOD

0

500

100

200

300

400

CONTRIBUTION OF COPPER LOAD, IN PERCENT

0

BASE-FLOW PERIOD EARLY SNOWMELT PERIOD

1,250

250

500

750

1,000

CONTRIBUTION OF COPPER LOAD, IN PERCENT

0

1,000

200

400

600

800

NO DATANO DATA

NO DATANO DATA

NO DATANO DATANO DATANO DATANO DATANO DATA

NO DATA

NO DATANO DATANO DATANO DATA

NO DATA

NO DATA

NO DATA

NO DATA

NO DATA

NO DATANO DATA

NO DATA

NO DATA

NO DATA

FC0.0 CG0.0 AR41.2 SI0.0 LC0.0 RC0.0 FC0.0 CG0.0 AR41.2 SI0.0 LC0.0 RC0.0

Figure 14. Percentage of contribution of copper load from Exposure Area 3c (Alamosa River and tributary sites from 

Fern Creek to Terrace Reservoir), 1995–97.
ESTIMATION OF SEASONAL AND ANNUAL METAL LOADS AT SELECTED SITES 23

EXPLANATION

SNOWMELT PERIOD SUMMER-FLOW PERIOD

Maximum

dissolved

value=47,000 Maximum

dissolved

value=3,400

0

1,200

200

400

600

800

1,000

CONTRIBUTION OF IRON LOAD, IIN PERCENT

0

4,000

500

1,000

1,500

2,000

2,500

3,000

3,500

BASE-FLOW PERIOD EARLY SNOWMELT PERIOD

0 0

2,000

250

500

750

1,000

1,250

1,500

1,750

CONTRIBUTION OF IRON LOAD, IN PERCENT

20,000

2,000

4,000

6,000

8,000

10,000

12,000

14,000

16,000

18,000

INSTANTANEOUS DISSOLVED IRON

INSTANTANEOUS TOTAL-RECOVERABLE IRON

FC0.0 CG0.0 AR41.2 SI0.0 LC0.0 RC0.0 FC0.0 CG0.0 AR41.2 SI0.0 LC0.0 RC0.0 NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA

TOTAL-RECOVERABLE IRON

DISSOLVED IRON

Figure 15. Percentage of contribution of iron load from Exposure Area 3c (Alamosa River and tributary sites from 

Fern Creek to Terrace Reservoir), 1995–97.
24 Sources of Metal Loads to the Alamosa River and Estimation of Seasonal and Annual Metal Loads for the Alamosa River Basin, 

Colorado, 1995–97

DISSOLVED ZINC

TOTAL-RECOVERABLE ZINC

INSTANTANEOUS DISSOLVED ZINC

INSTANTANEOUS TOTAL-RECOVERABLE ZINC

EXPLANATION

BASE-FLOW PERIOD EARLY SNOWMELT PERIOD

CONTRIBUTION OF ZINC LOAD, IN PERCENT CONTRIBUTION OF ZINC LOAD, IN PERCENT

SNOWMELT PERIOD SUMMER-FLOW PERIOD

50

400

100

150

200

250

300

350

0

120

20

40

60

80

100

0

320

40

80

120

160

200

240

280

0

300

50

100

150

200

250

FC0.0 CG0.0 AR41.2 SI0.0 LC0.0 RC0.0 FC0.0 CG0.0 AR41.2 SI0.0 LC0.0 RC0.0 NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA

Figure 16. Percentage of contribution of zinc load from Exposure Area 3c (Alamosa River and tributary sites from 

Fern Creek to Terrace Reservoir), 1995–97.
ESTIMATION OF SEASONAL AND ANNUAL METAL LOADS AT SELECTED SITES 25

BASE FLOW EARLY SNOWMELT SNOWMELT SUMMER FLOW TOTAL ANNUAL

Based on partial year records

0

10,000

1,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

9,000

1995

1996

1997

No data collected

No data collected

CUMULATIVE STREAMFLOW, IN CUBIC FEET PER SECOND

(fig. 18), between 39 and 342 tons of total-recoverable 

iron (fig. 19), and between 4 and 20 tons of totalrecoverable zinc (fig. 19) were estimated to have been 

transported annually past WF5.5 from 1995 through 

1997. The largest estimated annual mass for dissolved 

and total-recoverable aluminum, copper, iron, and zinc 

occurred in 1995. The annual metal mass estimated for 

1995 was between 5 and 10 times larger than the 

annual metal mass estimated for 1996 and about 

2 times the annual metal mass estimated for 1997. The 

annual mass of dissolved aluminum, copper, iron, and 

zinc substantially decreased after 1995.

More than 60 percent of the annual streamflow 

occurred during the 8 to 13 weeks of the snowmelt 

period (fig. 17). For 1995 and 1997, the mass of 

dissolved and total-recoverable aluminum, copper, 

iron, and zinc transported during the snowmelt period 

generally constituted between about 70 and 90 percent 

of the corresponding annual metal mass. During 1996, 

the metal mass transported during the snowmelt period 

generally constituted between 25 and 50 percent of the 

annual metal mass.

From 1995 through 1997, generally more than 

95 percent of the annual copper and zinc mass was 

transported past WF5.5 in the dissolved fraction. In 

1995 and 1997, 85 percent of the annual aluminum 

mass was transported past WF5.5 in the dissolved 

fraction; in 1996, about 40 percent of the annual 

aluminum mass was transported past WF5.5 in the 

dissolved fraction. Between 1995 and 1997, between 

40 and 60 percent of the annual iron mass was transported past WF5.5 in the dissolved fraction.

Figure 17. Cumulative streamflow for selected flow periods, Exposure Area 1 (site WF5.5), 1995–97.
26 Sources of Metal Loads to the Alamosa River and Estimation of Seasonal and Annual Metal Loads for the Alamosa River Basin, 

Colorado, 1995–97 No data collected No data collected No data collected

No data collectedNo data collected

Based on partial year

DISSOLVED ALUMINUM, IN TONS

TOTAL-RECOVERABLE ALUMINUM, IN TONS

DISSOLVED COPPER, IN TONS

TOTAL-RECOVERABLE COPPER, IN TONS

BASE FLOW

EARLY SNOWMELT

SNOWMELT

SUMMER FLOW

TOTAL ANNUAL

BASE FLOW

EARLY SNOWMELT

SNOWMELT

SUMMER FLOW

TOTAL ANNUAL

BASE FLOW

EARLY SNOWMELT

SNOWMELT

SUMMER FLOW

TOTAL ANNUAL

BASE FLOW

EARLY SNOWMELT

SNOWMELT

SUMMER FLOW

TOTAL ANNUAL

0

45

5

10

15

20

25

30

35

40

0

45

5

10

15

20

25

30

35

40

0

250

50

100

150

200

Based on partial year

1995

1996

1997

Based on partial year Based on partial year

0

250

50

100

150

200

No data collectedNo data collected

No data collected

No data collected

Figure 18. Mass of aluminum and copper for selected flow periods, Exposure Area 1 (site WF5.5), 1995–97.
ESTIMATION OF SEASONAL AND ANNUAL METAL LOADS AT SELECTED SITES 27 No data collected No data collected

350

0

50

100

150

200

250

300

DISSOLVED IRON, IN TONS

1995

1996

1997

25

10

15

20

DISSOLVED ZINC, IN TONS

0

5

Based on partial year

Based on partial year

Based on partial year Based on partial year

0

350

50

100

150

200

250

300

TOTAL-RECOVERABLE IRON, IN TONS

BASE FLOW

EARLY SNOWMELT

SNOWMELT

SUMMER FLOW

TOTAL ANNUAL

BASE FLOW

EARLY SNOWMELT

SNOWMELT

SUMMER FLOW

TOTAL ANNUAL

0

25

5

10

15

20

TOTAL-RECOVERABLE ZINC, IN TONS

BASE FLOW

EARLY SNOWMELT

SNOWMELT

SUMMER FLOW

TOTAL ANNUAL

BASE FLOW

EARLY SNOWMELT

SNOWMELT

SUMMER FLOW

TOTAL ANNUAL

No data collected

No data collected

No data collectedNo data collected

No data collected

No data collected

Figure 19. Mass of iron and zinc for selected flow periods, Exposure Area 1 (site WF5.5), 1995–97.
28 Sources of Metal Loads to the Alamosa River and Estimation of Seasonal and Annual Metal Loads for the Alamosa River Basin, 

Colorado, 1995–97

0

10,000

1,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

9,000

CUMULATIVE STREAMFLOW, IN CUBIC FEET PER SECOND

1995

1996

1997

BASE FLOW EARLY SNOWMELT SNOWMELT SUMMER FLOW TOTAL ANNUAL

Wightman Fork at WF0.0 (Exposure 

Area 2)

The cumulative streamflow and estimates of the 

mass of dissolved and total-recoverable aluminum, 

copper, iron, and zinc for each of the four seasonal 

flow regimes (flow periods) and the annual streamflow 

and metal mass for 1995–97 at WF0.0 are presented in 

figures 20–22.

Many tons of metals were transported past 

WF0.0 from 1995 through 1997. Between 55 and 

220 tons of total-recoverable aluminum (fig. 21), 

between about 8 and 42 tons of total-recoverable 

copper (fig. 21), between 40 and 240 tons of totalrecoverable iron (fig. 22), and between about 5 and

19 tons of total-recoverable zinc (fig. 22) were estimated to have been transported annually past WF0.0 

from 1995 through 1997. The largest estimated annual 

mass for dissolved and total-recoverable aluminum, 

copper, iron, and zinc occurred in 1995. The annual 

metal mass estimated for 1995 was between 3 and 6 

times larger than the annual metal mass estimated for 

1996 and generally was between about 1 and 2 times 

the annual metal mass estimated for 1997. The annual 

mass of dissolved copper, iron, and zinc substantially 

decreased after 1995. However, the estimated annual 

Figure 20. Cumulative streamflow for selected flow periods, Exposure Area 2 (site WF0.0), 1995–97.
ESTIMATION OF SEASONAL AND ANNUAL METAL LOADS AT SELECTED SITES 29

BASE FLOW

EARLY SNOWMELT

SNOWMELT

SUMMER FLOW

TOTAL ANNUAL

BASE FLOW

EARLY SNOWMELT

SNOWMELT

SUMMER FLOW

TOTAL ANNUAL

0

45

5

10

15

20

25

30

35

40

DISSOLVED COPPER, IN TONS

0

45

5

10

15

20

25

30

35

40

TOTAL-RECOVERABLE COPPER, IN TONS

BASE FLOW

EARLY SNOWMELT

SNOWMELT

SUMMER FLOW

TOTAL ANNUAL

BASE FLOW

EARLY SNOWMELT

SNOWMELT

SUMMER FLOW

TOTAL ANNUAL

0

250

50

100

150

200

DISSOLVED ALUMINUM, IN TONS

1995

1996

1997

0

250

50

100

150

200

TOTAL-RECOVERABLE ALUMINUM, IN TONS

Figure 21. Mass of aluminum and copper for selected flow periods, Exposure Area 2 (site WF0.0), 1995–97.
30 Sources of Metal Loads to the Alamosa River and Estimation of Seasonal and Annual Metal Loads for the Alamosa River Basin, 

Colorado, 1995–97

0

25

5

10

15

20

TOTAL-RECOVERABLE ZINC, IN TONS

BASE FLOW

BASE FLOW

EARLY SNOWMELT

SNOWMELT

SUMMER FLOW

TOTAL ANNUAL

BASE FLOW

EARLY SNOWMELT

SNOWMELT

SUMMER FLOW

TOTAL ANNUAL

0

25

5

10

15

20

DISSOLVED ZINC, IN TONS

BASE FLOW

EARLY SNOWMELT

SNOWMELT

SUMMER FLOW

TOTAL ANNUAL

EARLY SNOWMELT

SNOWMELT

SUMMER FLOW

TOTAL ANNUAL

0

350

50

100

150

200

250

300

DISSOLVED IRON, IN TONS

0

350

50

100

150

200

250

300

TOTAL-RECOVERABLE IRON, IN TONS

1995

1996

1997

Figure 22. Mass of iron and zinc for selected flow periods, Exposure Area 2 (site WF0.0), 1995–97.
ESTIMATION OF SEASONAL AND ANNUAL METAL LOADS AT SELECTED SITES 31

mass of dissolved aluminum was similar in 1995 and 

1997.

More than 60 percent of the annual streamflow 

occurred during the snowmelt period (fig. 20). For 

1995 and 1997, the mass of aluminum, copper, iron, 

and zinc transported during the snowmelt period 

generally constituted between 50 and 90 percent of the 

annual metal mass. During 1996, the metal mass transported during the snowmelt period constituted 

between 14 and 56 percent of the annual metal mass.

From 1995 through 1997, between 10 and 

approximately 45 percent of the annual aluminum 

mass, between 60 and 90 percent of the annual copper 

mass, between 17 and 25 percent of the annual iron 

mass, and between 90 and 100 percent of the annual 

zinc mass were transported past WF0.0 in the 

dissolved fraction. The dissolved fraction of 

aluminum, copper, and iron mass tended to be smaller 

at WF0.0 than the dissolved-metal mass fraction at 

WF5.5, indicating that the dissolved fraction of 

aluminum, copper, and iron partitioned to the solid 

phase in the intervening reach between WF5.5 and 

WF0.0. There was no appreciable change to the 

dissolved zinc fraction between WF5.5 and WF0.0, 

indicating that little metal partitioning of zinc 

occurred. 

A comparison of the annual streamflow at 

WF0.0 to the annual streamflow at WF5.5 showed that 

about 40 percent of the annual streamflow at WF0.0 

was attributable to WF5.5, indicating that the intervening 11.7 square miles of drainage between WF5.5 

and WF0.0 contributed about 60 percent of the annual 

streamflow. However, a comparison of the annual 

metal mass at WF0.0 and WF5.5 in 1995 and 1997 

indicated that estimates of annual mass of totalrecoverable aluminum, copper, iron, and zinc were 

generally equivalent. Based on data collected from 

tributaries to the Wightman Fork in the reach between 

WF5.5 and WF0.0 during 1998 and 1999 

(K. Nordstrom, U.S. Geological Survey, written 

commun., 2000), it appears unlikely that there are any 

appreciable sources of metals downstream from 

WF5.5 along Wightman Fork. In 1996, however, the 

estimates of annual mass of total-recoverable metals at 

WF5.5 were 84 percent (aluminum), 75 percent 

(copper), 95 percent (iron), and 69 percent (zinc) of 

the annual mass of metals estimated at WF0.0. Additionally, the annual dissolved aluminum and iron 

masses were larger at WF5.5 than at WF0.0, indicating 

that these metals partitioned to the solid phase. However, the annual dissolved copper and zinc masses 

were smaller at WF5.5 than at WF0.0, indicating that 

other sources of metals contributed to the metal mass 

at WF0.0 during 1996. A plausible explanation is that 

metal loads associated with instream sources or storm 

runoff during 1996 contributed to the increases in estimated metal mass at WF0.0. Also, potential estimation 

errors could account for the estimated differences in 

metal loads. 

Alamosa River at AR45.5 (Exposure 

Area 3a)

The cumulative streamflow and estimates of the 

mass of dissolved and total-recoverable aluminum, 

copper, iron, and zinc for each of the four seasonal 

flow regimes and the annual streamflow and metal 

mass for 1995–97 at AR45.5 are presented in 

figures 23–25.

Many tons of total-recoverable aluminum and 

iron were transported past AR45.5 between 1995 and 

1997. Between 120 and 185 tons of total-recoverable 

aluminum (fig. 24), and between 230 and 400 tons of 

total-recoverable iron (fig. 25) were estimated to have 

been transported annually past AR45.5 from 1995 

through 1997. A relatively small mass of totalrecoverable copper and zinc was transported past 

AR45.5 during 1995–97. Less than 1 ton of totalrecoverable copper (fig. 24) and less than 2 tons of 

total-recoverable zinc (fig. 25) were estimated to have 

been transported annually past AR45.5 from 1995 

through 1997. The estimated annual mass for totalrecoverable aluminum, copper, iron, and zinc was 

similar in 1995 and 1997; the estimated annual mass 

for total-recoverable aluminum, copper, and iron in 

1996 was about 60 to 70 percent of the respective 

annual metal mass estimated for 1995 and 1997. The 

estimated annual mass of dissolved copper, iron, and 

zinc substantially decreased after 1995.

Less than 14 percent of the annual streamflow 

occurred during the base flow period. However, during 

this flow regime, the pH of the Alamosa River at 

AR45.5 generally is at its annual minimum and most 

of the annual dissolved aluminum and iron, and a 

considerable portion of the annual dissolved copper 

and zinc, were transported during the 1996 and 1997 

base-flow period. More than 65 percent of the annual 
32 Sources of Metal Loads to the Alamosa River and Estimation of Seasonal and Annual Metal Loads for the Alamosa River Basin, 

Colorado, 1995–97

0

32,000

4,000

8,000

12,000

16,000

20,000

24,000

28,000

CUMULATIVE STREAMFLOW, IN CUBIC FEET PER SECOND

BASE FLOW EARLY SNOWMELT SNOWMELT SUMMER FLOW TOTAL ANNUAL

1995

1996

1997

streamflow occurred during the snowmelt period 

(fig. 23), and the largest mass of total-recoverable 

aluminum, copper, iron, and zinc generally was transported during this period. However in 1996, the mass 

of total-recoverable aluminum, copper, iron, and zinc 

transported during the snowmelt period constituted of 

less than one-third of the annual metal mass. In 1995 

and 1997, the mass of total-recoverable aluminum, 

copper, iron, and zinc transported during the snowmelt 

period constituted between about 40 and 71 percent of 

the annual metal mass.

From 1995 through 1997, between 15 and about 

30 percent of the annual aluminum mass and between 

about 15 and 25 percent of the annual iron mass was 

transported past AR45.5 in the dissolved fraction. 

More than 50 percent of the annual copper and zinc 

mass was in the dissolved fraction. This indicated that, 

with the exception of zinc and copper, the vast 

majority of metals transported past AR45.5 was in the 

particulate or suspended fraction. However, as stated 

earlier, a large dissolved metal fraction was transported during the base-flow period.

Alamosa River at AR43.6 (Exposure

Area 3b)

The cumulative streamflow and estimates of the 

mass of dissolved and total-recoverable aluminum, 

copper, iron, and zinc for each of the four seasonal 

flow regimes and the annual streamflow and metal 

mass for 1995–97 at AR43.6 are presented in 

figures 26–28. In 1995, streamflow measurements and 

water-quality samples were not collected from AR43.6 

until the snowmelt period. Therefore, metal loads were 

not estimated for the 1995 base-flow and early snowmelt periods. The annual streamflow and estimates of 

Figure 23. Cumulative streamflow for selected flow periods, Exposure Area 3a (site AR45.5), 1995–97.
ESTIMATION OF SEASONAL AND ANNUAL METAL LOADS AT SELECTED SITES 33

0

200

20

40

60

80

100

120

140

160

180

DISSOLVED ALUMINUM, IN TONS

0

0.8

0.1

0.2

0.3

0.4

0.5

0.6

0.7

DISSOLVED COPPER, IN TONS

BASE FLOW

EARLY SNOWMELT

BASE FLOW

EARLY SNOWMELT

SNOWMELT

SUMMER FLOW

TOTAL ANNUAL

BASE FLOW

EARLY SNOWMELT

SNOWMELT

SUMMER FLOW

TOTAL ANNUAL

0

200

20

40

60

80

100

120

140

160

180

TOTAL-RECOVERABLE ALUMINUM, IN TONS

0

0.8

0.1

0.2

0.3

0.4

0.5

0.6

0.7

TOTAL-RECOVERABLE COPPER, IN TONS

BASE FLOW

EARLY SNOWMELT

SNOWMELT

SUMMER FLOW

TOTAL ANNUAL

SNOWMELT

SUMMER FLOW

TOTAL ANNUAL

1995

1996

1997

Figure 24. Mass of aluminum and copper for selected flow periods, Exposure Area 3a (site AR45.5), 1995–97.
34 Sources of Metal Loads to the Alamosa River and Estimation of Seasonal and Annual Metal Loads for the Alamosa River Basin, 

Colorado, 1995–97

BASE FLOW

EARLY SNOWMELT

SNOWMELT

SUMMER FLOW

TOTAL ANNUAL

BASE FLOW

EARLY SNOWMELT

SNOWMELT

SUMMER FLOW

TOTAL ANNUAL

BASE FLOW

EARLY SNOWMELT

SNOWMELT

SUMMER FLOW

TOTAL ANNUAL

BASE FLOW

EARLY SNOWMELT

SNOWMELT

SUMMER FLOW

TOTAL ANNUAL

0

2.5

0.5

1.0

1.5

2.0

DISSOLVED ZINC, IN TONS

0

2.5

0.5

1.0

1.5

2.0

TOTAL-RECOVERABLE ZINC, IN TONS

0

450

50

100

150

200

250

300

350

400

TOTAL-RECOVERABLE IRON, IN TONS

0

450

50

100

150

200

250

300

350

400

DISSOLVED IRON, IN TONS

1995

1996

1997

Figure 25. Mass of iron and zinc for selected flow periods, Exposure Area 3a (site AR45.5), 1995–97.
ESTIMATION OF SEASONAL AND ANNUAL METAL LOADS AT SELECTED SITES 35

metal mass shown for 1995 in figures 26–28 were 

based on partial year records and included estimates 

only for the snowmelt and summer-flow periods.

Many tons of metals were transported past 

AR43.6 between 1995 and 1997. Between 185 and 

415 tons of total-recoverable aluminum (fig. 27), 

between 7 and 40 tons of total-recoverable copper 

(fig. 27), between 285 and 760 tons of totalrecoverable iron (fig. 28), and between 6 and 20 tons 

of total-recoverable zinc (fig. 28) were estimated to 

have been transported annually past AR43.6 from 

1995 through 1997. The largest estimated annual mass 

for dissolved aluminum, dissolved and totalrecoverable copper, dissolved iron, and dissolved and 

total-recoverable zinc occurred in 1995. The smallest 

annual mass, with the exception of dissolved 

aluminum, occurred in 1996. The annual totalrecoverable metal mass estimated for 1995 was 

between 2 and 5 times larger than the annual metal 

mass estimated for 1996 and about the same or just 

slightly larger than the annual metal mass estimated 

for 1997. The annual mass of dissolved aluminum, 

copper, iron, and zinc substantially decreased after 

1995.

More than 60 percent of the annual streamflow 

occurred during the snowmelt period (fig. 26). For 

1995 and 1997, the mass of total-recoverable 

aluminum, copper, iron, and zinc transported during 

the snowmelt period constituted between about 70 and 

90 percent of the annual metal mass. However during 

1996, the total-recoverable metal mass transported 

during the snowmelt period was between about 25 and 

42 percent of the annual total-recoverable metal mass. 

During 1996, a large percentage of the dissolved 

aluminum (92 percent), copper (85 percent), iron 

(80 percent), and zinc (59 percent) for the year was 

transported past AR43.6 during the base-flow period. 

From 1995 through 1997, between 8 and 

25 percent of the annual aluminum mass, between 60 

and 75 percent of the annual copper mass, between 12 

and 22 percent of the annual iron mass, and between 

85 and 100 percent of the annual zinc mass was transported past AR43.6 in the dissolved fraction.

A comparison of the annual streamflow at 

AR43.6 to the annual streamflow at AR45.5 and 

WF0.0 indicated that about 75 percent of the annual 

streamflow at AR43.6 was attributable to streamflow 

upstream from AR45.5 (EA3a), and about 25 percent 

from Wightman Fork (EA2). A comparison of the 

annual metal mass at AR43.6 to the annual mass at 

AR45.5 and WF0.0 indicated that 45–65 percent of the 

annual total-recoverable aluminum mass at AR43.6 

may be attributed to EA3a (AR45.5) and about 

30–55 percent may be attributed to contributions from 

Wightman Fork. Less than 4 percent of the annual 

total-recoverable copper mass at AR43.6 may be 

attributed to EA3a (AR45.5) and more than 85 percent 

of the annual total-recoverable copper mass at AR43.6 

may be attributed to contributions from Wightman 

Fork. About 50–80 percent of the annual total-recoverable iron mass at AR43.6 may be attributed to EA3a 

(AR45.5) and about 15–40 percent of the annual totalrecoverable iron mass at AR43.6 may be attributed to 

contributions from Wightman Fork. About 10–25 

percent of the annual total-recoverable zinc mass at 

AR43.6 may be attributed to EA3a (AR45.5) and 

about 80-90 percent of the annual total-recoverable 

zinc mass at AR43.6 may be attributed to contributions 

from Wightman Fork.

Alamosa River at AR41.2 and AR34.5 

(Exposure Area 3c)

The cumulative streamflow and estimates of the 

mass of dissolved and total-recoverable aluminum, 

copper, iron, and zinc for each of the four seasonal 

flow regimes and the annual streamflow and metal 

mass for 1995–97 at AR41.2 and AR34.5 are 

presented in figures 29–33.

Many tons of metals were transported past 

AR41.2 and AR34.5 between 1995 and 1997. Between 

180 and 500 tons of total-recoverable aluminum 

(fig. 30) were estimated to have been transported 

annually past AR41.2, and between 170 and 670 tons 

of total-recoverable aluminum (fig. 30) were estimated 

to have been transported annually past AR34.5. 

Between 7 and 36 tons of total-recoverable copper 

(fig. 31) were estimated to have been transported 

annually past AR41.2, and between 7 and 32 tons of 

total-recoverable copper (fig. 31) were estimated to 

have been transported annually past AR34.5. Between 

320 and 880 tons of total-recoverable iron (fig. 32) 

were estimated to have been transported annually past 

AR41.2, and between 280 and 1,140 tons of totalrecoverable iron (fig. 32) were estimated to have been 

transported annually past AR34.5. Between 6 and 

20 tons of total-recoverable zinc (fig. 33) were estimated to have been transported annually past AR41.2, 

and 5 and 18 tons of total-recoverable zinc (fig. 33) 
36 Sources of Metal Loads to the Alamosa River and Estimation of Seasonal and Annual Metal Loads for the Alamosa River Basin, 

Colorado, 1995–97

0

40,000

5,000

10,000

15,000

20,000

25,000

30,000

35,000

CUMULATIVE STREAMFLOW, IN CUBIC FEET PER SECOND

BASE FLOW EARLY SNOWMELT SNOWMELT SUMMER FLOW TOTAL ANNUAL

Based on partial year record

1995

1996

1997

No data collected

No data collected

were estimated to have been transported annually past 

AR34.5.

The largest estimated annual mass for dissolved 

aluminum, copper, iron, and zinc and total-recoverable 

copper and zinc was measured in 1995. The smallest 

annual mass for all dissolved and total-recoverable 

constituents was measured in 1996. The annual totalrecoverable metal mass estimated for 1995 was 

between 2 and 5 times larger than the annual totalrecoverable metal mass estimated for 1996 and just 

slightly larger than the annual total-recoverable metal 

mass estimated for 1997; total-recoverable aluminum 

and iron were larger in 1997. The annual mass of 

dissolved aluminum, copper, iron, and zinc at AR41.2 

substantially decreased after 1995. The annual mass of 

dissolved aluminum, copper, and iron at AR34.5 

substantially decreased after 1995.

More than 58 percent of the annual streamflow 

occurred during the snowmelt period (fig. 29). The 

mass of total-recoverable aluminum, copper, iron, and 

zinc transported during the snowmelt period in 1995 

and 1997 constituted between about 70 and 85 percent 

of the annual metal mass at AR41.2 and AR34.5. 

During 1996, the total-recoverable metal mass transported during the snowmelt period was between about 

30 and 45 percent of the annual total-recoverable 

metal mass at AR41.2 and between about 45 and 

60 percent of the annual total-recoverable metal mass 

at AR34.5. 

 From 1995 through 1997, between 6 and 16 

percent of the annual aluminum mass, between about 

55 and 61 percent of the annual copper mass, between 

about 12 and 26 percent of the annual iron mass, and 

between about 88 and 94 percent of the annual zinc 

mass was transported past AR41.2 in the dissolved 

Figure 26. Cumulative streamflow for selected flow periods, Exposure Area 3b (site AR43.6), 1995–97.
ESTIMATION OF SEASONAL AND ANNUAL METAL LOADS AT SELECTED SITES 37

BASE FLOW

EARLY SNOWMELT

SNOWMELT

SUMMER FLOW

TOTAL ANNUAL

BASE FLOW

EARLY SNOWMELT

SNOWMELT

SUMMER FLOW

TOTAL ANNUAL

BASE FLOW

EARLY SNOWMELT

SNOWMELT

SUMMER FLOW

TOTAL ANNUAL

BASE FLOW

EARLY SNOWMELT

SNOWMELT

SUMMER FLOW

TOTAL ANNUAL

Based on partial year

Based on partial year

Based on partial year Based on partial year

1995

1996

1997

0

450

50

100

150

200

250

300

350

400

DISSOLVED ALUMINUM, IN TONS

0

450

50

100

150

200

250

300

350

400

TOTAL-RECOVERABLE ALUMINUM, IN TONS

0

40

5

10

15

20

25

30

35

DISSOLVED COPPER, IN TONS

0

40

5

10

15

20

25

30

35

TOTAL-RECOVERABLE COPPER, IN TONS

No data collectedNo data collectedNo data collected

No data collected

No data collectedNo data collectedNo data collectedNo data collected

Figure 27. Mass of aluminum and copper for selected flow periods, Exposure Area 3b (site AR43.6), 1995–97.
38 Sources of Metal Loads to the Alamosa River and Estimation of Seasonal and Annual Metal Loads for the Alamosa River Basin, 

Colorado, 1995–97

BASE FLOW

EARLY SNOWMELT

SNOWMELT

SUMMER FLOW

TOTAL ANNUAL

BASE FLOW

EARLY SNOWMELT

SNOWMELT

SUMMER FLOW

TOTAL ANNUAL

0

25

5

10

15

20

TOTAL-RECOVERABLE ZINC, IN TONS

BASE FLOW

Based on partial year

Based on partial year

0

25

5

10

15

20

DISSOLVED ZINC, IN TONS

BASE FLOW

EARLY SNOWMELT

SNOWMELT

SUMMER FLOW

TOTAL ANNUAL

EARLY SNOWMELT

SNOWMELT

SUMMER FLOW

TOTAL ANNUAL

0

900

100

200

300

400

500

600

700

800

DISSOLVED IRON, IN TONS

0

800

100

200

300

400

500

600

700

TOTAL-RECOVERABLE IRON, IN TONS

Based on partial year

Based on partial year

1995

1996

1997

No data collectedNo data collectedNo data collected

No data collected

No data collectedNo data collectedNo data collectedNo data collected

Figure 28. Mass of iron and zinc for selected flow periods, Exposure Area 3b (site AR43.6), 1995–97.
ESTIMATION OF SEASONAL AND ANNUAL METAL LOADS AT SELECTED SITES 39

fraction. From 1995 through 1997, less than 2 percent 

of the annual aluminum mass, between about 14 and 

32 percent of the annual copper mass, between about 3 

and 8 percent of the annual iron mass, and between 55 

and 80 percent of the annual zinc mass were transported past AR34.5 in the dissolved fraction. The 

smaller dissolved-metal mass fraction at AR34.5 relative to AR41.2, which is located in the upper part of 

EA3c (fig. 1), indicates that a large portion of the 

dissolved aluminum, copper, iron and, to a lesser 

extent, zinc mass (figs. 30, 31, 32, and 33) is partitioned to the particulate or suspended fraction in the 

stream reach.

A comparison of the annual streamflow at 

AR41.2 to the annual streamflow at AR43.6 (EA3b) 

indicated that about 80 to 90 percent of the annual 

streamflow at AR41.2 was attributable to streamflow 

upstream from AR43.6. A comparison of the annual 

metal mass at AR41.2 to the mass at AR43.6 indicated 

that the total-recoverable metal mass at AR41.2 was 

approximately equivalent to the total-recoverable 

metal mass at AR43.6. The only exceptions were for 

the total-recoverable aluminum mass in 1997 and the 

total-recoverable iron mass in 1995, 1996, and 1997. 

This comparison indicates that there were no appreciable sources of total-recoverable metals entering the 

intervening drainage area between AR43.6 and 

AR41.2. 

A comparison of the annual streamflow at 

AR34.5 and AR41.2 indicated that between 88 and 

100 percent of the annual streamflow at AR34.5 was 

attributable to streamflow upstream from AR41.2 

(fig. 29). A comparison of the annual metal masses at 

AR34.5 and AR41.2 indicated that the annual totalrecoverable copper and zinc mass at AR34.5 was 

similar to the annual mass at AR41.2. This comparison 

indicated there were no appreciable sources of totalrecoverable copper and zinc entering the intervening 

drainage area between AR41.2 and AR34.5. In 1995 

and 1997, however, the annual total-recoverable 

aluminum and iron mass at AR34.5 was about 

30 percent greater than the annual total-recoverable 

aluminum and iron mass at AR41.2. A plausible explanation for these increases is that aluminum and iron 

deposited in the streambed were resuspended and 

contributed to the increases in estimated aluminum 

and iron mass estimated at AR34.5. 

Alamosa River at AR31.0 (Exposure 

Area 5)

The cumulative streamflow and estimates of 

the mass of dissolved and total-recoverable aluminum, 

copper, iron, and zinc for each of the four seasonal 

flow regimes and the annual streamflow and metal 

mass for 1995–97 at AR31.0 are presented in 

figures 34–36. Estimates of metal mass presented in 

this section of the report represent: (1) the mass of 

metals being transported past AR31.0 and the mass of 

metals available for risk exposure in EA5, and (2) the 

mass of metals being transported out of Terrace Reservoir that were available for risk exposure in EA4. 

Terrace Reservoir has a capacity of about 

17,000 acre-ft (Watts, 1996) and is primarily used as 

storage for irrigation water. Streamflow at AR31.0 is 

lowest between November and about mid-April. when 

the outlet works are closed. During this time, storage 

is gradually increased in the reservoir. From May 

through June, reservoir releases for downstream irrigation users generally match reservoir inflow. From July 

through October, reservoir releases are generally 

greater than the reservoir inflow (as measured at 

AR34.5) thus reducing the reservoir storage substantially.

Many tons of metals were transported past 

AR31.0 between 1995 and 1997. Between 25 and 

85 tons of total-recoverable aluminum (fig. 35), 

between about 2 and 25 tons of total-recoverable 

copper (fig. 35), between about 80 and 170 tons of 

total-recoverable iron (fig. 36), and between about 3 

and 20 tons of total-recoverable zinc (fig. 36) were 

estimated to have been transported annually past 

AR31.0 from 1995 through 1997. 

The largest estimated annual mass for dissolved 

and total-recoverable aluminum, copper, iron, and zinc 

was in 1995, and the smallest annual mass was in 

1996. The annual total-recoverable metal mass estimated for 1995 was between about 2 and 12 times 

larger than the annual metal mass estimated for 1996 

and was less than 4 times the annual metal mass estimated for 1997. The annual mass of dissolved 

aluminum, copper, iron, and zinc substantially 

decreased after 1995.

Between 70 and 85 percent of the annual 

streamflow at AR31.0 occurred during the snowmelt 

period (fig. 34). From 1995 through 1997, between 87 

and 94 percent of the total-recoverable aluminum 

mass, between 55 and 70 percent of the total-
40 Sources of Metal Loads to the Alamosa River and Estimation of Seasonal and Annual Metal Loads for the Alamosa River Basin, 

Colorado, 1995–97

60,000

10,000

20,000

30,000

40,000

50,000

CUMULATIVE STREAMFLOW, IN CUBIC FEET PER SECOND

AR41.2

60,000

10,000

20,000

30,000

40,000

50,000

AR34.5

BASE FLOW EARLY SNOWMELT SNOWMELT SUMMER FLOW TOTAL ANNUAL

0

0

1995

1996

1997

Figure 29. Cumulative streamflow for selected flow periods, Exposure Area 3c (sites AR41.2 and 

AR34.5), 1995–97.
ESTIMATION OF SEASONAL AND ANNUAL METAL LOADS AT SELECTED SITES 41

BASE FLOW

EARLY SNOWMELT

SNOWMELT

SUMMER FLOW

TOTAL ANNUAL

BASE FLOW

EARLY SNOWMELT

SNOWMELT

SUMMER FLOW

TOTAL ANNUAL

BASE FLOW

EARLY SNOWMELT

SNOWMELT

SUMMER FLOW

TOTAL ANNUAL

BASE FLOW

EARLY SNOWMELT

SNOWMELT

SUMMER FLOW

TOTAL ANNUAL

0

700

100

200

300

400

500

600

DISSOLVED ALUMINUM, IN TONS

0

700

100

200

300

400

500

600

TOTAL-RECOVERABLE ALUMINUM, IN TONS

AR34.5 AR34.5

AR41.2 AR41.2

0

700

100

200

300

400

500

600

DISSOLVED ALUMINUM, IN TONS

0

700

100

200

300

400

500

600

TOTAL-RECOVERABLE ALUMINUM, IN TONS

1995

1996

1997

Figure 30. Mass of aluminum for selected flow periods, Exposure Area 3c (sites AR41.2 and AR34.5), 1995–97.
42 Sources of Metal Loads to the Alamosa River and Estimation of Seasonal and Annual Metal Loads for the Alamosa River Basin, 

Colorado, 1995–97

AR41.2 AR41.2

AR34.5 AR34.5

0

40

5

10

15

20

25

30

35

DISSOLVED COPPER, IN TONS

BASE FLOW

EARLY SNOWMELT

SNOWMELT

SUMMER FLOW

TOTAL ANNUAL

0

40

5

10

15

20

25

30

35

TOTAL-RECOVERABLE COPPER, IN TONS

BASE FLOW

EARLY SNOWMELT

SNOWMELT

SUMMER FLOW

TOTAL ANNUAL

BASE FLOW

EARLY SNOWMELT

SNOWMELT

SUMMER FLOW

TOTAL ANNUAL

BASE FLOW

EARLY SNOWMELT

SNOWMELT

SUMMER FLOW

TOTAL ANNUAL

0

40

5

10

15

20

25

30

35

DISSOLVED COPPER, IN TONS

0

5

TOTAL-RECOVERABLE COPPER, IN TONS

40

10

15

20

25

30

35

1995

1996

1997

Figure 31. Mass of copper for selected flow periods, Exposure Area 3c (sites AR41.2 and AR34.5), 1995–97.
ESTIMATION OF SEASONAL AND ANNUAL METAL LOADS AT SELECTED SITES 43

AR41.2 AR41.2

AR34.5 AR34.5

BASE FLOW

EARLY SNOWMELT

SNOWMELT

SUMMER FLOW

TOTAL ANNUAL

0

1,200

200

400

600

800

1,000

DISSOLVED IRON, IN TONS

0

1,200

200

400

600

800

1,000

TOTAL-RECOVERABLE IRON, IN TONS

BASE FLOW

EARLY SNOWMELT

SNOWMELT

SUMMER FLOW

TOTAL ANNUAL

BASE FLOW

EARLY SNOWMELT

SNOWMELT

SUMMER FLOW

TOTAL ANNUAL

BASE FLOW

EARLY SNOWMELT

SNOWMELT

SUMMER FLOW

TOTAL ANNUAL

1995

1996

1997

0

1,200

200

400

600

800

1,000

DISSOLVED IRON, IN TONS

0

1,200

200

400

600

800

1,000

TOTAL-RECOVERABLE IRON, IN TONS

Figure 32. Mass of iron for selected flow periods, Exposure Area 3c (sites AR41.2 and AR34.5), 1995–97
44 Sources of Metal Loads to the Alamosa River and Estimation of Seasonal and Annual Metal Loads for the Alamosa River Basin, 

Colorado, 1995–97

AR41.2 AR41.2

AR34.5 AR34.5

0

25

5

10

15

20

DISSOLVED ZINC, IN TONS

1995

1996

1997

BASE FLOW

EARLY SNOWMELT

SNOWMELT

SUMMER FLOW

TOTAL ANNUAL

BASE FLOW

EARLY SNOWMELT

SNOWMELT

SUMMER FLOW

TOTAL ANNUAL

0

25

5

10

15

20

TOTAL-RECOVERABLE ZINC, IN TONS

0

25

5

10

15

20

DISSOLVED ZINC,IN TONS

BASE FLOW

EARLY SNOWMELT

SNOWMELT

SUMMER FLOW

TOTAL ANNUAL

BASE FLOW

EARLY SNOWMELT

SNOWMELT

SUMMER FLOW

TOTAL ANNUAL

0

25

5

10

15

20

TOTAL-RECOVERABLE ZINC, IN TONS

Figure 33. Mass of zinc for selected flow periods, Exposure Area 3c (sites AR41.2 and AR34.5), 1995–97.
ESTIMATION OF SEASONAL AND ANNUAL METAL LOADS AT SELECTED SITES 45

0

60,000

10,000

20,000

30,000

40,000

50,000

CUMULATIVE STREAMFLOW, IN CUBIC FEET PER SECOND

1995

1996

1997

BASE FLOW EARLY SNOWMELT SNOWMELT SUMMER FLOW TOTAL ANNUAL

recoverable copper mass, between 63 and 91 percent 

of the total-recoverable iron mass, and between 48 and 

71 percent of the total-recoverable zinc mass were 

transported during the snowmelt period. 

From 1995 through 1997, between 5 and 

23 percent of the annual aluminum mass, between 

about 40 and 66 percent of the annual copper mass, 

between about 3 and 16 percent of the annual iron 

mass, and between 78 and 95 percent of the annual 

zinc mass were transported past AR31.0 in the 

dissolved fraction.

A comparison of the annual streamflow at 

AR31.0 to the annual streamflow at AR34.5 (EA3c) 

indicated that about 85 to more than 100 percent of the 

annual streamflow at AR31.0 was attributable from 

streamflow upstream from Terrace Reservoir. Downstream irrigation needs and storage limitations in 

Terrace Reservoir drive the operation of the reservoir. 

A comparison of the annual metal mass at AR31.0 to 

the annual metal mass at AR34.5 indicated that 

between 1995 and 1997, the annual total-recoverable 

aluminum mass at AR31.0 was about 15 percent of 

annual total-recoverable aluminum mass at AR34.5, 

the annual total-recoverable copper mass at AR31.0 

was between about 25 and 75 percent of annual totalrecoverable copper mass at AR34.5, the annual totalrecoverable iron mass at AR31.0 was between 13 and 

28 percent of annual total-recoverable iron mass at 

AR34.5, and the annual total-recoverable zinc mass at 

AR31.0 was between about 50 and 100 percent of 

annual total-recoverable zinc mass at AR34.5. These 

data indicate that Terrace Reservoir serves as a sink for 

metals. This conclusion is consistent with a previous 

report by Ferguson and Edelmann (1996). 

Figure 34. Cumulative streamflow for selected flow periods, Exposure Area 5 (site AR31.0), 1995–97.
46 Sources of Metal Loads to the Alamosa River and Estimation of Seasonal and Annual Metal Loads for the Alamosa River Basin, 

Colorado, 1995–97

BASE FLOW

EARLY SNOWMELT

SNOWMELT

SUMMER FLOW

TOTAL ANNUAL

BASE FLOW

EARLY SNOWMELT

SNOWMELT

SUMMER FLOW

TOTAL ANNUAL

BASE FLOW

EARLY SNOWMELT

SNOWMELT

SUMMER FLOW

TOTAL ANNUAL

BASE FLOW

EARLY SNOWMELT

SNOWMELT

SUMMER FLOW

TOTAL ANNUAL

0

25

5

10

15

20

TOTAL-RECOVERABLE COPPER, IN TONS

0

25

5

10

15

20

DISSOLVED COPPER, IN TONS

0

100

20

40

60

80

DISSOLVED ALUMINUM, IN TONS

1995

1996

1997

0

100

20

40

60

80

TOTAL-RECOVERABLE ALUMINUM, IN TONS

Figure 35. Mass of aluminum and copper for selected flow periods, Exposure Area 5 (site AR31.0), 1995–97.
ESTIMATION OF SEASONAL AND ANNUAL METAL LOADS AT SELECTED SITES 47

20

2

4

6

8

10

12

14

16

18

DISSOLVED ZINC, IN TONS

0 0

BASE FLOW

EARLY SNOWMELT

SNOWMELT

SUMMER FLOW

TOTAL ANNUAL

BASE FLOW

EARLY SNOWMELT

SNOWMELT

SUMMER FLOW

TOTAL ANNUAL

BASE FLOW

EARLY SNOWMELT

SNOWMELT

SUMMER FLOW

TOTAL ANNUAL

BASE FLOW

EARLY SNOWMELT

SNOWMELT

SUMMER FLOW

TOTAL ANNUAL

20

2

4

6

8

10

12

14

16

18

TOTAL-RECOVERABLE ZINC, IN TONS

0

200

20

40

60

80

100

120

140

160

180

TOTAL-RECOVERABLE IRON, IN TONS

0

200

20

40

60

80

100

120

140

160

180

DISSOLVED IRON, IN TONS

1995

1996

1997

Figure 36. Mass of iron and zinc for selected flow periods, Exposure Area 5 (site AR31.0), 1995–97.
48 Sources of Metal Loads to the Alamosa River and Estimation of Seasonal and Annual Metal Loads for the Alamosa River Basin, 

Colorado, 1995–97

SUMMARY

The upper Alamosa River Basin is a heavily 

mineralized area located in the San Juan Mountains of 

southwestern Colorado. Metal contamination has 

occurred for decades from the Summitville Mine site, 

from other smaller mines, and from natural, metalenriched acidic drainage in the basin. In 1995, 

multiple gaps in data needed for an ecological risk 

assessment of the Summitville Superfund site were 

identified. Specifically, the need to quantify contamination from various source areas in the basin and the 

need to quantify the spatial, seasonal, and annual 

metal loads in the basin was identified. As a result, the 

USGS developed a comprehensive data-collection 

plan for the basin to address these data gaps. 

To meet the objectives of this study, instantaneous streamflow data and periodic water-quality data 

were collected from 1995 through 1997 at 6 sites on 

the Alamosa River, 2 sites on Wightman Fork, and 11 

other tributary sites. Concentrations of metals and 

values of streamflow measurements were used to 

determine metal loads for each sampling date. Percentages of metal load contributions from tributaries were 

determined for each sample collected. A modified 

time-interval method was used to estimate seasonal 

and annual metal loads in the Alamosa River and 

Wightman Fork. 

Sources of dissolved and total-recoverable 

aluminum, copper, iron, and zinc loads were determined for three risk exposure areas. EA3a extends 

upstream from Wightman Fork along the Alamosa 

River. EA3b extends along the Alamosa River from 

Wightman Fork to Fern Creek. EA3c extends along 

the Alamosa River from Fern Creek to Terrace Reservoir. Alum Creek is the predominant contributor of 

aluminum, copper, iron, and zinc loads to EA3a. The 

percentage of contribution of metal loads from Alum 

Creek was often greater than the combined metal load 

contribution from Iron and Bitter Creeks. In general, 

Wightman Fork was the predominant source of metals 

to EA3b particularly during the snowmelt and summer 

flow periods. During the base-flow period, however, 

aluminum and iron loads from EA3a were the dominant source of these metals to EA3b. Jasper and Burnt 

Creeks generally contributed less than 10 percent of 

the metal loads to EA3b. On a few occasions, however, 

Burnt Creek contributed a substantial percentage of 

the dissolved aluminum load, and Jasper and Burnt 

Creeks contributed a substantial percentage of the iron 

loads to the Alamosa River in EA3b. The metal loads 

observed in EA3c result from upstream sources; the 

primary upstream sources are Wightman Fork in EA1 

and Alum and Iron Creeks in EA3a. Tributaries in 

EA3c did not contribute substantially to the metal load 

in the Alamosa River.

In many instances, the percentage of dissolved 

and/or total-recoverable metal load contribution from 

a tributary or the combined percentage of metal load 

contribution was greater than 100 percent of the metal 

load at the nearest downstream site on the Alamosa 

River. These data indicate that metal partitioning and 

metal deposition from the water column to the 

streambed may be occurring in Exposure Areas 3a, 3b, 

and 3c. Metals that are deposited to the streambed 

probably are resuspended and transported downstream 

during high-streamflow periods such as during snowmelt runoff and rainfall runoff.

 Seasonal and annual dissolved and totalrecoverable aluminum, copper, iron, and zinc loads for 

1995–97 were estimated for Exposure Areas 1, 2, 3a, 

3b, and 3c. EA1 incorporates the Summitville Mine 

site, and EA2 extends along Wightman Fork. During 

1995–97, many tons of metals were transported annually through each exposure area. Generally, the largest 

estimated annual total-recoverable metal mass for 

most metals was in 1995. The smallest estimated 

annual total-recoverable metal mass was in 1996, 

which also coincided with the smallest annual streamflow. In 1995 and 1997, more than 60 percent of the 

annual total-recoverable metal loads generally was 

transported through each exposure area during the 

snowmelt period; however, in 1996, generally less than 

40 percent of the annual total-recoverable metal loads 

was transported through the exposure areas during the 

snowmelt period. A comparison of the estimated storm 

load at each site to the corresponding annual load indicated that storms contribute less than 

2 percent of the annual load at any site and about 5 to 

20 percent of the load during the summer-flow period. 

The highest percentage of contribution was observed 

for total-recoverable aluminum and iron.

A comparison of the annual metal mass at 

WF5.5 (EA1) to annual metal mass estimated at 

WF0.0 (EA2) indicated that estimates of totalrecoverable metal mass for the two exposure areas 

were approximately equivalent in 1995 and 1997. The 

annual dissolved aluminum and iron mass was larger 
SELECTED REFERENCES 49

at WF5.5 (EA1) than at WF0.0 (EA2), indicating these 

metals partitioned to the solid phase. Between 1995 

and 1997, many tons of total-recoverable aluminum 

and iron were transported past AR45.5, whereas only a 

relatively small mass of total-recoverable copper and 

zinc was transported past AR45.5. Most of the 

dissolved metals transported past AR45.5 occurred 

during base flow even though only 14 percent of the 

annual streamflow occurred during this period. A 

comparison of the annual metal mass at AR43.6 to the 

annual mass at AR45.5 and WF0.0 indicated that most 

of the annual total-recoverable aluminum and iron 

mass may be attributed to EA3a (AR45.5) and most of 

the annual total-recoverable copper and zinc mass may 

be attributed to contributions from Wightman Fork. A 

comparison of the annual metal masses at AR34.5 and 

AR41.2 indicated that the annual total-recoverable 

copper and zinc mass was similar, which indicated that 

there were no appreciable sources of total-recoverable 

copper and zinc entering the intervening drainage area. 

A comparison of the annual metal mass at AR31.0 to 

the annual metal mass at AR34.5 indicated that the 

annual total-recoverable aluminum and iron mass at 

AR31.0 was about 15–30 percent of annual totalrecoverable mass at AR34.5, which indicated that 

Terrace Reservoir served as a sink for most contaminants of concern.

SELECTED REFERENCES

Bove, D.J., Wilson, A.B., and Barry, T.H., Hon, K., 

Kurtz, J., Van Loenen, R.E., and Calkin, W.S., 1996, 

Geology, alteration, and rock and water chemistry of 

the Iron, Alum, and Bitter Creek area, upper Alamos 

River, southwestern Colorado: U.S. Geological Survey 

Open–File Report 96–0039, 34 p. 

Camp Dresser and McKee Inc., 2000, Final report- Tier 2 

Summitville Ecological Risk Assessment addendum 

for Summitville Mine Superfund site, Rio Grande, 

Conejos, and Alamosa counties, Colorado: prepared 

for the U.S. Environmental Protection Agency, 

November 2000.

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