Prepared in cooperation with Colorado River Water Conservation District, Eagle 

County, Eagle River Water and Sanitation District, Upper Eagle Regional Water 

Authority, Colorado Department of Transportation, City of Aurora, Town of Eagle, 

Town of Gypsum, Town of Minturn, Town of Vail, Vail Resorts, City of Colorado 

Springs, Colorado Springs Utilities, and Denver Water

Assessment of Surface-Water Quantity 

and Quality, Eagle River Watershed,

Colorado, 1947–2007

Scientific Investigations Report 2011–5075

U.S. Department of the Interior

U.S. Geological Survey
Cover.

Large photo: Eagle River at the mouth near Minturn, Colorado. Photograph by Jennifer Moore, September 15, 2010.

Small photos from top to bottom: Vail Pass, Vail, Colorado. Photograph by Jennifer Moore, February 1, 2009.

Beaver Creek Ski Resort, Beaver Creek, Colorado. Photograph by Jennifer Moore, February 1, 2009.

Bridge near Red Cliff, Colorado. Photograph by Jennifer Moore, September 14, 2010.

Old mining area near Gilman, Colorado. Photograph by Jennifer Moore, September 14, 2010.
Assessment of Surface-Water Quantity and 

Quality, Eagle River Watershed, Colorado, 

1947–2007

By Cory A. Williams, Jennifer L. Moore, and Rodney J. Richards

Prepared in cooperation with Colorado River Water Conservation District, Eagle 

County, Eagle River Water and Sanitation District, Upper Eagle Regional Water 

Authority, Colorado Department of Transportation, City of Aurora, Town of Eagle, 

Town of Gypsum, Town of Minturn, Town of Vail, Vail Resorts, City of Colorado 

Springs, Colorado Springs Utilities, and Denver Water

Scientific Investigations Report 2011–5075

U.S. Department of the Interior

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

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia: 2011

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U.S. Government.

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

reproduce any copyrighted material contained within this report.

Suggested citation:

Williams, C.A., Moore, J.L., and Richards, R.J., 2011, Assessment of surface-water quantity and quality, Eagle River 

watershed, Colorado, 1947–2007: U.S. Geological Survey, Scientific Investigation Report 2011–5075, 139 p.
iii

Contents

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

Introduction.....................................................................................................................................................2

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

Relevant Publications ..........................................................................................................................3

Description of Study Area ...................................................................................................................3

Geology..........................................................................................................................................7

Mining Activity..............................................................................................................................7

Data Sources, Compilation, Review, and Analysis.................................................................................11

Surface-Water Quantity.....................................................................................................................11

Surface-Water Quality .......................................................................................................................28

Data Sources and Compilation................................................................................................28

Data Review and Analysis........................................................................................................28

Assessment of Surface-Water Quantity ..................................................................................................32

Assessment of Surface-Water Quality.....................................................................................................37

Field Properties ...................................................................................................................................37

Specific Conductance...............................................................................................................37

pH..................................................................................................................................................37

Water Temperature ...................................................................................................................41

Dissolved Oxygen.......................................................................................................................49

Hardness .....................................................................................................................................49

Dissolved Solids and Major Ions......................................................................................................53

Nutrients...............................................................................................................................................77

Trace Elements....................................................................................................................................97

Suspended Sediment .......................................................................................................................125

Summary......................................................................................................................................................132

Acknowledgments............................................................................................................................137

References Cited........................................................................................................................................137

Figures

1–12. Map showing:

 1. Location of the Eagle River watershed, Colorado, and location of major streams, 

tributaries, and urban development within the watershed ............................................4

 2. Variation in precipitation throughout the Eagle River watershed, Colorado 

(Western Regional Climate Center, 2009) ..........................................................................5

 3. Land use in the Eagle River watershed, Colorado, 2008.................................................6

 4. Surficial geology of the Eagle River watershed, Colorado (from Tweto, 1979)...........9

 5. Location of hard-rock mining and related superfund remediation in the Eagle

River watershed, Colorado, 2008 ......................................................................................11

 6. Streamflow-gaging station locations and streamflow distribution for selected 

streams in the Eagle River watershed, Colorado, by subwatershed..........................12
iv

 7. Locations of surface-water-monitoring sites within the Eagle River watershed, 

Colorado, 1947–2007............................................................................................................23

 8. Locations of surface-water-monitoring sites in the lower Eagle River 

subwatsershed, Colorado, 1947–2007..............................................................................24

 9. Location of surface-water-monitoring sites in the middle Eagle River 

subwatershed, Colorado, 1947–2007................................................................................25

 10. Location of surface-water-monitoring sites in the Upper Eagle River 

subwatershed, Colorado, 1947–2007 ...............................................................................26

 11. Location of surface-water-monitoring sites in the Gore Creek subwatershed, 

Colorado, 1947–2007 ...........................................................................................................27

 12. Colorado Department of Public Health and Environment stream-segment 

designations for the Eagle River watershed, Colorado (Colorado Department 

of Public Health and Environment and U.S. Environmental Protection 

Agency, 2008) .......................................................................................................................31

13. Hydrographs of selected sites in the Eagle River watershed, Colorado...........................33

14. Graph showing lowess Smooth of annual-mean streamflow at selected sites in 

the Eagle River watershed, Colorado, 1947–2007 .................................................................34

15. Arrow schematic of major streams and diversion mean annual streamflow 

volume in the Eagle River watershed .....................................................................................35

16. Graph showing comparison of streamflow prediversion (1945–1965) and postdiversion (1966–2008) from Homestake Reservoir at site 27, Homestake Creek 

near Red Cliff, Colorado ............................................................................................................36

17. Map showing spatial distribution of median-concentration percentiles and 

monotonic trends in specific conductance at selected sites in the Eagle River 

watershed, Colorado, 1990–2007 .............................................................................................40

18. Graph showing seasonal pattern of pH at selected sites in the Eagle River 

watershed, Colorado, 1947–2007..............................................................................................42

19–21. Map showing:

 19. Spatial distribution of median-concentration percentiles and monotonic pH 

trends at selected sites in the Eagle River watershed, Colorado, 1990–2007.........43

 20. Number of exceedances of the Colorado water-quality standard for pH at

selected sites in the Eagle River watershed, Colorado, 1947–2007..........................45

 21. Spatial distribution of median-concentration percentiles and monotonic

water temperature trends at selected sites in the Eagle River watershed, 

Colorado, 1990–2007 .........................................................................................................46

22. Graph showing seasonal pattern of water temperature at selected sites in the 

Eagle River watershed, Colorado, 1947–2007 ........................................................................47

23. Map showing number of exceedances of the Colorado water-quality standard 

for water temperature at selected sites in the Eagle River watershed, Colorado, 

1947–2007 .....................................................................................................................................48

24. Map showing spatial distribution of median-concentration percentiles and 

monotonic dissolved-oxygen concentration trends at selected sites in the 

Eagle River watershed, Colorado, 1990–2007 ........................................................................50

25. Graph showing seasonal pattern of dissolved oxygen at selected sites in the 

Eagle River watershed, Colorado, 1947–2007 ........................................................................51

26. Map showing number of exceedances of the Colorado water-quality standard 

for dissolved oxygen at selected sites in the Eagle River watershed, Colorado, 

1947–2007 .....................................................................................................................................52
v

27. Map showing spatial distribution of median-concentration percentiles and 

monotonic hardness concentration trends at selected sites in the Eagle River watershed, Colorado, 1994–2007 ........................................................................................................54

28. Graph showing seasonal pattern of hardness concentrations at selected sites in the 

Eagle River watershed, Colorado, 1947–2007 ........................................................................55

29. Map showing spatial distribution of median-concentration percentiles and 

monotonic sum of constituent trends at selected sites in the Eagle River 

watershed, Colorado, 1995–2007..............................................................................................57

30–37. Graphs showing:

 30. Seasonal pattern of sum of constituents at selected sites in the Eagle River 

watershed, Colorado, 1947–2007 ....................................................................................58

 31. Seasonality of water chemistry at site 13, Eagle River watershed, Colorado, 

1947–2007............................................................................................................................61

 32. Seasonality of water chemistry at site 160, Eagle River watershed, Colorado, 

1947–2007............................................................................................................................62

 33. Seasonality of water chemistry at site 173, Eagle River watershed, Colorado, 

1947–2007............................................................................................................................63

 34. Seasonality of water chemistry at site 201, Eagle River watershed, Colorado, 

1947–2007............................................................................................................................64

 35. Seasonality of water chemistry at site 224, Eagle River watershed, Colorado, 

1947–2007............................................................................................................................65

 36. Seasonality of water chemistry at selected streamflow-gaging station 

locations, in the Eagle River watershed, Colorado, 1947–2007..................................66

 37. Spatial distribution of median-concentration percentiles and monotonic 

calcium concentration trends at selected sites in the Eagle River watershed, 

Colorado, 1995–2007 .........................................................................................................67

38–50. Map showing:

 38. Spatial distribution of median-concentration percentiles and monotonic 

magnesium trends at selected sites in the Eagle River watershed, Colorado, 

1995–2007............................................................................................................................68

 39. Spatial distribution of median-concentration percentiles and monotonic 

sodium trends at selected sites in the Eagle River watershed, Colorado, 

1995–2007............................................................................................................................69

 40. Spatial distribution of median-concentration percentiles and monotonic 

potassium trends at selected sites in the Eagle River watershed, Colorado, 

1995–2007............................................................................................................................70

 41. Spatial distribution of median-concentration percentiles and monotonic 

chloride trends at selected sites in the Eagle River watershed, Colorado, 

1995–2007............................................................................................................................71

 42. Spatial distribution of median-concentration percentiles and monotonic 

sulfate trends at selected sites in the Eagle River watershed, Colorado, 

1995–2007............................................................................................................................72

 43. Spatial distribution of median-concentration percentiles and monotonic 

silica trends in at selected sites in the Eagle River watershed, Colorado, 

1995–2007............................................................................................................................73

 44. Spatial distribution of median-concentration percentiles and monotonic 

alkalinity trends at selected sites in the Eagle River watershed, Colorado, 

1995–2007............................................................................................................................74
vi

 45. Number of exceedances of the Colorado water-quality standard for major 

ions at selected sites in the Eagle River watershed, Colorado, 1947–2007 .............75

 46. Spatial distribution of median-concentration percentiles and monotonic 

nitrate trends at selected sites in the Eagle River watershed, Colorado, 

1995–2007............................................................................................................................80

 47. Spatial distribution of median-concentration percentiles and monotonic nitrite 

trends at selected sites in the Eagle River watershed, Colorado, 1995–2007.........81

 48. Spatial distribution of median-concentration percentiles and monotonic ammonia 

trends at selected sites in the Eagle River watershed, Colorado, 1995–2007.........82

 49. Spatial distribution of median-concentration percentiles and monotonic total 

phosphorus trends at selected sites in the Eagle River watershed, Colorado, 

1995–2007............................................................................................................................83

 50. Spatial distribution of median-concentration percentiles and monotonic 

orthophosphate trends at selected sites in the Eagle River watershed, 

Colorado, 1995–2007 .........................................................................................................84

51–60. Graphs showing:

 51. Seasonal patterns of nitrate concentrations at selected sites in the Eagle 

River watershed, Colorado, 1947–2007..........................................................................85

 52. Seasonal patterns of nitrite concentrations at selected sites in the Eagle 

River watershed, Colorado, 1947–2007..........................................................................86

 53. Seasonal patterns of total phosphorus concentrations at selected sites in 

the Eagle River watershed, Colorado, 1947–2007 ........................................................87

 54. Seasonal patterns of orthophosphate concentrations at selected sites in 

the Eagle River watershed, Colorado, 1947–2007 ........................................................88

 55. Temporal distribution of total phosphorus concentrations at site 110, Eagle 

River watershed, Colorado, 1997–2004..........................................................................90

 56. Temporal distribution of total phosphorus concentrations at site 157, Eagle 

River watershed, Colorado, 1974–2006..........................................................................90

 57. Temporal distribution of total phosphorus concentrations at site 160, Eagle 

River watershed, Colorado, 1996–2007..........................................................................91

 58. Temporal distribution of total phosphorus concentrations at site 180, Eagle 

River watershed, Colorado, 1970–2002..........................................................................91

 59. Temporal distribution of total phosphorus concentrations at site 224, Eagle 

River watershed, Colorado, 1980–2007..........................................................................92

 60. Temporal distribution of total phosphorus concentrations at site 227, Eagle 

River watershed, Colorado, 1974–2007..........................................................................92

61. Map showing number of exceedances of the Colorado chronic water-quality 

standard for nutrients at selected sites in the Eagle River watershed, Colorado, 

1970–2007 .....................................................................................................................................94

62. Map showing number of exceedances of the Colorado acute water-quality 

standard for nutrients at selected sites in the Eagle River watershed, Colorado, 

1947–2007 .....................................................................................................................................95

63. Graph showing correlation between suspended-sediment concentration and 

total phosphorus concentration in the Eagle River watershed, Colorado........................96

64–68. Map showing:

 64. Spatial distribution of median-concentration percentiles and monotonic 

dissolved cadmium trends at selected sites in the Eagle River watershed, 

Colorado, 1994–2006 .......................................................................................................101

 65. Spatial distribution of median-concentration percentiles for dissolved 

copper at selected sites in the Eagle River watershed, Colorado, 1966–2007......102
vii

 66. Spatial distribution of median-concentration percentiles and monotonic 

dissolved iron trends at selected sites in the Eagle River watershed, 

Colorado, 1994–2006 .......................................................................................................103

 67. Spatial distribution of median-concentration percentiles and monotonic 

dissolved manganese trends at selected sites in the Eagle River watershed, 

Colorado,1994–2006 ........................................................................................................104

 68. Spatial distribution of median-concentration percentiles and monotonic 

dissolved zinc concentration trends at selected sites in the Eagle River 

watershed, Colorado, 1994–2006 ..................................................................................105

69–75. Graphs showing:

 69. Seasonal pattern of dissolved cadmium concentrations at selected sites 

in the Eagle River watershed, Colorado, 1966–2007..................................................106

 70. Seasonal pattern of dissolved copper concentrations at selected sites 

in the Eagle River watershed, Colorado, 1966–2007..................................................107

 71. Seasonal pattern of dissolved iron concentrations at selected sites in the 

Eagle River watershed, Colorado, 1966–2007.............................................................108

 72. Seasonal pattern of dissolved manganese concentrations at selected 

sites in the Eagle River watershed, Colorado, 1970–2007 ........................................109

 73. Seasonal patterns of dissolved zinc concentrations at selected sites 

in the Eagle River watershed, Colorado, 1966–2007..................................................110

 74. Seasonal pattern relation between trace elements concentrations 

and hardness at site 72 in the Eagle River watershed, Colorado............................111

 75. Seasonal patterns of total recoverable iron concentrations at site 224 

in the Eagle River watershed, near Gypsum, Colorado ............................................112

76. Map showing number of exceedances of the Colorado acute water-quality 

standard for concentration of trace elements (dissolved arsenic, dissolved 

selenium, dissolved uranium) at selected sites in the Eagle River watershed, 

Colorado, 1971–2007.................................................................................................................113

77. Map showing number of exceedances of the Colorado chronic water-quality 

standard for concentration of trace elements (dissolved arsenic, dissolved 

selenium, dissolved uranium) at selected sites in the Eagle River watershed, 

Colorado, 1968–2001.................................................................................................................114

78–96. Graphs showing:

 78. Temporal distribution of dissolved cadmium concentrations at site 28, 

in the Eagle River watershed, Colorado, 1984–2003..................................................117

 79. Temporal distribution of dissolved cadmium concentrations at site 66, 

in the Eagle River watershed, Colorado, 1985–2007..................................................118

 80. Temporal distribution of dissolved cadmium concentrations at site 173, 

in the Eagle River watershed, 1997–2007 ....................................................................118

 81. Temporal distribution of dissolved copper concentrations at site 28, 

in the Eagle River watershed, Colorado, 1985–2003..................................................119

 82. Temporal distribution of dissolved copper concentrations at site 66, 

in the Eagle River watershed, Colorado, 1981–2007..................................................119

 83. Temporal distribution of dissolved copper concentrations at site 173, 

in the Eagle River watershed, Colorado, 1994–2007..................................................120

 84. Temporal distribution of dissolved iron concentrations at site 28, 

in the Eagle River watershed, Colorado, 1984–2003..................................................120

 85. Temporal distribution of dissolved iron concentrations at site 66, 

in the Eagle River watershed, Colorado, 1985–2005..................................................121
viii

 86. Temporal distribution of dissolved iron concentrations at site 173, 

in the Eagle River watershed, Colorado, 1978–2003..................................................121

 87. Temporal distribution of total recoverable iron concentrations at site 28, 

in the Eagle River watershed, Colorado, 1984–2004..................................................122

 88. Temporal distribution of total recoverable iron concentrations at site 66, 

in the Eagle River watershed, Colorado, 1985–2007..................................................122

 89. Temporal distribution of total recoverable iron concentrations at site 173, 

in the Eagle River watershed, Colorado, 1994–2006..................................................123

 90. Temporal distribution of dissolved manganese concentrations at site 28, 

in the Eagle River watershed, Colorado, 1984–2003..................................................124

 91. Temporal distribution of dissolved manganese concentrations at site 66, 

in the Eagle River watershed, Colorado, 1986–2007..................................................124

 92. Temporal distribution of dissolved manganese concentrations at site 173, 

in the Eagle River watershed, Colorado, 1994–2007..................................................125

 93. Temporal distribution of dissolved zinc concentrations at site 23, in the 

Eagle River watershed, Colorado, 1985–2003.............................................................126

 94. Temporal distribution of dissolved zinc concentrations at site 66, in the 

Eagle River watershed, Colorado, March–April 1986–2007 .....................................126

 95. Temporal distribution of dissolved zinc concentrations at site 66, in the 

Eagle River watershed, Colorado, May–February 1986–2007..................................127

 96. Temporal distribution of dissolved zinc concentrations at site 173, in the 

Eagle River watershed, 1994–2006 ...............................................................................127

97–99. Maps showing:

 97. Number of exceedances of the Colorado acute water-quality standard 

for metals concentrations at selected sites in the Eagle River watershed, 

Colorado, 1966–2006 .......................................................................................................128

 98. Number of exceedances of the Colorado chronic water-quality standard 

for metals concentrations at selected sites in the Eagle River watershed, 

Colorado, 1966–2007 .......................................................................................................129

 99. Spatial distribution of median-concentration percentiles and monotonic 

suspended-sediment concentration trends at selected sites in the Eagle 

River watershed, Colorado, 1995–2007........................................................................133

100. Graph showing seasonal pattern in suspended-sediment concentration at 

selected sites in the Eagle River watershed, Colorado, 1947–2007........................134

Tables

1. Sources of water-related data for the Eagle River watershed.............................................2

2. Eagle Mine Superfund Site major construction milestones (Colorado Department of Public 

Health and Environment and U.S. Environmental Protection Agency, 2008)........................... 10

3. Hydrologic characteristics for streamflow-gaging stations in the Eagle River 

watershed ....................................................................................................................................13

4. Summary of the mean annual runoff, median annual maximum daily streamflow, 

annual flood frequency, and low-flow statistics for selected sites in the Eagle 

River watershed..........................................................................................................................14

5. Historic and current surface-water quantity and quality sites in the Eagle River 

watershed, Colorado..................................................................................................................15

6. Eagle River watershed quality-assurance results by sample source agency.................29
ix

7. Federal Clean Water Act Section 303(d) listings for the Eagle River watershed.............30

8. Summary statistics of field properties and suspended-sediment data in the Eagle 

River watershed by subwatershed, 1947–2007......................................................................38

9. Summary of monotonic temporal trends for field properties and 

suspended-sediment concentrations in the Eagle River watershed, Colorado...............39

10. Summary of Colorado exceedances of water-quality standards for field 

properties in the Eagle River watershed, Colorado by subwatershed..............................44

11. Summary statistics of dissolved solids and major ions data in the Eagle 

River watershed, Colorado by subwatershed 1947–2007 ....................................................56

12. Summary of monotonic temporal trends for dissolved solids and major ions in 

the Eagle River watershed, Colorado......................................................................................59

13. Summary of exceedences of Colorado water-quality standard (250 milligrams 

per liter) for chloride for surface-water samples collected in the Eagle River 

watershed, 1947–2007................................................................................................................76

14. Comparison of cation and anion concentration, Gore Creek subwatershed, 

Colorado, 1947–2007...................................................................................................................76

15. Median nutrient concentrations for selected sites in the Eagle River watershed, 

Colorado, 1968–2007 and background regional reference values .....................................77

16. Summary statistics of nutrients data in the Eagle River watershed, Colorado, 

by subwatershed ........................................................................................................................78

17. Summary of water-quality standard or recommendation exceedances for 

nutrients in the Eagle River watershed by subwatershed...................................................89

18. Summary of monotonic temporal trends for nutrients in the Eagle River watershed.....93

19. Summary statistics of trace element data in the Eagle River watershed by 

subwatershed 1947–2007 ..........................................................................................................98

20. Summary of water-quality standard exceedances for trace elements in the 

Eagle River watershed by subwatershed.............................................................................115

21. Summary of step-trends assessment for select sites affected by Eagle Mine 

Superfund remediation, water years 1972–1991, and 1992–2007 .....................................130

22. Summary of monotonic temporal trends for metals in the Eagle River watershed.......131

Assessment of Surface-Water Quantity and Quality, 

Eagle River Watershed, Colorado, 1947–2007

By Cory A. Williams, Jennifer L. Moore, and Rodney J. Richards

Abstract

From the early mining days to the current tourismbased economy, the Eagle River watershed (ERW) in central 

Colorado has undergone a sequence of land-use changes that 

has affected the hydrology, habitat, and water quality of the 

area. In 2000, the USGS, in cooperation with the Colorado 

River Water Conservation District, Eagle County, Eagle 

River Water and Sanitation District, Upper Eagle Regional 

Water Authority, Colorado Department of Transportation, 

City of Aurora, Town of Eagle, Town of Gypsum, Town 

of Minturn, Town of Vail, Vail Resorts, City of Colorado 

Springs, Colorado Springs Utilities, and Denver Water, initiated a retrospective analysis of surface-water quantity and 

quality in the ERW.

Surface-water quantity data and surface-water quality data 

were obtained from local, State, and Federal agencies to assist 

in the analysis of surface-water conditions in the ERW 1947–

2007. Surface-water-quality data from 293 sites and 12 different 

source agencies were compiled into 192 unique sites located 

on streams and rivers in the ERW. Approximately 39 percent of 

the unique sites had fewer than 5 samples; while 23 percent of 

the sites had more than 100 samples. Physical properties were 

the most abundant type of samples collected, with major ions, 

nutrients, and trace elements also commonly collected.

For selected water-quality properties and constituents in 

the watershed, this report: (1) characterizes available waterquantity and water-quality data, (2) identifies spatial and 

seasonal variability in water quantity and water quality, (3) 

provides comparisons to Federal and State water-quality standards or recommendations, (4) characterizes temporal changes 

in water quality, and (5) where possible, identifies potential 

causes of these changes. This report provides reconnaissancelevel statistical summaries and comparisons of water-quality 

conditions and characteristics using available data within the 

ERW. The report also includes streamflow statistics such as: 

mean annual runoff totals, peak-flood-frequency recurrence 

intervals, and minimum 7-day mean streamflows for selected 

sites within the watershed.

The spatial patterns for concentrations of trace metals 

(aluminum, cadmium, copper, iron, manganese, and zinc) 

indicate an increase in dissolved concentrations of these 

metals near historical mining areas in the Eagle River and 

several tributaries near Belden. In general, concentrations 

decrease downstream from mining areas. Concentrations 

typically are near or below reporting limits in Gore Creek 

and other tributaries within the watershed. Concentrations 

for trace elements (arsenic, selenium, and uranium) in the 

watershed usually are below the reporting limit, and no 

prevailing spatial patterns were observed in the data. Steptrend analysis and temporal-trend analysis provide evidence 

that remediation of historical mining areas in the upper Eagle 

River have led to observed decreases in metals concentrations in many surface-waters. Comparison of pre- and 

post-remediation concentrations for many metals indicates 

significant decreases in metals concentrations for cadmium, 

manganese, and zinc at sites downstream from the Eagle 

Mine Superfund Site. Some sites show order of magnitude 

reductions in median concentrations between these two 

periods. Evaluation of monotonic trends for dissolved metals 

concentrations show downward trends at numerous sites in, 

and downstream from, historic mining areas.

The spatial pattern of nutrients shows lower concentrations on many tributaries and on the Eagle River upstream 

from Red Cliff with increases in nutrients downstream of 

major urban areas. Seasonal variations show that for many 

nutrient species, concentrations tend to be lowest May–June 

and highest January–March. The gradual changes in concentrations between seasons may be related to dilution effects 

from increases and decreases in streamflow. Upward trends 

in nutrients between the towns of Gypsum and Avon were 

detected for nitrate, orthophosphate, and total phosphorus. 

An upward trend in nitrite was detected in Gore Creek. No 

trends were detected in un-ionized ammonia within the ERW. 

Exceedances of State water-quality standards (nitrite, nitrate, 

and un-ionized ammonia) and levels higher than U.S. Environmental Protection Agency recommendations (total phosphorus) occur in several areas within the ERW. The majority 

of the exceedances are from comparisons to the U.S. Environmental Protection Agency total phosphorus recommendations. 

A positive correlation was observed between suspended sediment and total phosphorus. 

An upward trend in total dissolved solids in Gore Creek 

may be the result of increases in chloride salts. Highly 

significant trends were detected in sodium, potassium, and 

chloride with a significant upward trend in magnesium and 
2 Assessment of Surface-Water Quantity and Quality, Eagle River Watershed, Colorado, 1947–2007

a weakly significant upward trend in calcium. A quantitative 

analysis of the relative abundance of calcium, magnesium, 

sodium, and potassium to the available anions suggests that 

chloride salts likely are the source for the detected upward 

trends because chloride is the only commonly occurring 

anion with a trend in Gore Greek. A potential source for the 

observed chloride salts may be the chemical anti-icing and 

deicing products used during winter road maintenance in 

municipal areas and on Interstate-70. 

A downward trend in dissolved solids in the Eagle 

River between Gypsum and Avon may be contributing to 

the detected trend on the Eagle River at Gypsum. Significant downward trends were detected in specific ions such as 

calcium, magnesium, sulfate, and silica. Measures of total 

dissolved solids as well as comparisons to specific ions show 

that in water-quality samples within the ERW concentrations 

generally are lower in the headwaters, with increases downstream from Wolcott. Differences in concentrations likely 

result from increased abundance of salt-bearing geologic units 

downstream from Avon. Few sites had measured concentrations that exceeded the State standards for chloride.

Introduction

From the early mining days to the current tourism-based 

economy, the Eagle River watershed (ERW) (fig. 1) in central 

Colorado has undergone a sequence of land-use changes 

that has affected the hydrology, habitat, and water quality 

of the area. Although intensive hard-rock mining has all but 

stopped in the ERW, elevated concentrations of metals, such 

as cadmium, copper, iron, manganese, and zinc, in streams are 

prevalent as a result of long-standing mining activity in the 

watershed (Colorado Department of Public Health and Environment, 2008). A 235-acre site encompassing the Eagle Mine 

and associated mining wastes between Gilman and Minturn 

was placed on the Superfund site list in 1986 (Colorado 

Department of Public Health and Environment, 2008). Remediation of the Eagle Mine site began in 1988 and continues 

today (2008). Eagle County has become a four-season resort 

destination. Ski resorts such as Vail and Beaver Creek have 

brought increased tourism and development to the area.

Although remediation of mining-affected areas continues, expansion of development, tourism, and transportation 

place new and varied demands on the water resources of the 

ERW. Local entities in the watershed that rely on and manage these water resources are interested in the assessment of 

water quantity and water quality to aid in the preservation 

and management of the ERW. Beginning in 1997, in cooperation with the Gore Creek Management Program partners, 

the U.S. Geological Survey (USGS) began a water-quality 

monitoring program on Gore Creek. The evaluation of this 

monitoring program was completed in 2001 and summarized 

in a USGS report (Wynn and others, 2001). The program 

was expanded in 1999 to include additional water-quantity 

and water-quality monitoring throughout the ERW. In order 

to evaluate the water quality, assess effects of growth and 

associated land-use change, identify temporal and spatial 

gaps within available water-quality data, and evaluate spatial 

and temporal trends in water quality, an analysis of historical 

data was done. In 2000, the USGS, in cooperation with the 

Colorado River Water Conservation District, Eagle County, 

Eagle River Water and Sanitation District, Upper Eagle 

Regional Water Authority, Colorado Department of Transportation, City of Aurora, Town of Eagle, Town of Gypsum, 

Town of Minturn, Town of Vail, Vail Resorts, City of Colorado Springs, Colorado Springs Utilities, and Denver Water, 

initiated a retrospective analysis of surface-water quantity 

and quality in the ERW.

Purpose and Scope

This report presents an assessment of the available surfacewater quantity and quality data from 1947 to 2007 for the ERW. 

Surface water in this study refers to rivers and streams; analysis 

of wells, groundwater, mine drainage, and ditch diversions were 

not included in this report. For selected water-quality properties 

and constituents in the watershed, this report: (1) characterizes 

available water-quantity and water-quality data, (2) identifies 

spatial and seasonal variability in water quantity and water quality, (3) provides comparisons to Federal and State water-quality 

standards or recommendations, (4) characterizes temporal 

changes in water quality, and (5) where possible, identifies 

potential causes of these changes. 

The analysis done by the U.S. Geological Survey used 

electronic data obtained from Federal, State, and local 

sources for the period 1947–2007 and includes data gathered and reported from the USGS, the U.S. Environmental 

Protection Agency (USEPA), U.S. Department of Agriculture 

Forest Service (USFS), Colorado Department of Natural 

Resources, Colorado Department of Public Health and Environment (CDPHE), Colorado Division of Water Resources, 

Colorado Department of Transportation, Colorado Division of Wildlife (River Watch), Eagle Mine Superfund 

Site Assessment, Colorado Springs Utilities, Eagle River 

Water and Sanitation District, Grand River Consulting, and 

Advanced Sciences Inc. (table 1).

Table 1. Sources of water-related data for the Eagle River 

watershed.—Continued

[NA, not applicable; No., number]

Agency No. of

sites

No. of

samples

Streamflow

City of Colorado Springs 1 NA

Colorado Division of Water Resources 5 NA

U.S. Geological Survey 37 NA
Introduction 3

Relevant Publications

Several previous studies have investigated the water quality in the ERW. The Eagle River Watershed Plan (1996) was 

initiated by local governments after protection of the Eagle 

River was identified as a top community concern through 

town and county planning forums and surveys (Eagle River 

Watershed Plan, 1996). The purpose of the plan was to outline 

a collaborative, local philosophy for protecting and improving 

water quantity, water quality, wildlife habitat, and recreational 

opportunities, while promoting compatible land-use practices.

The USEPA and the State of Colorado have an agreement that designates the CDPHE as the lead agency on the 

Eagle Mine Superfund Site project. Surface-water monitoring 

stations were established in 1985 at the onset of the superfund 

investigation. In 2009, surface-water data were collected at 

seven monitoring stations on the Eagle River and tributaries. 

Annual reports and 5-year review reports are written to summarize and analyze changes in water quality. The first 5-year 

review was completed in October 2000. Documents related 

to the superfund cleanup can be found at http://www.epa.gov/

Region8/superfund/co/eagle (January 2009) and at http://www.

cdphe.state.co.us/hm/rpeagle.htm (January 2009).

The USGS studied the water quantity, quality, and 

aquatic ecology of Gore Creek (Wynn and others, 2001). The 

study summarized available water quantity, water quality, 

and aquatic-ecology data collected from 1968 through 1998 

by various agencies. Wynn and others (2001) concluded that 

geology and land use in the watershed affects the water quality 

and stream biota.

Bledsoe and others (2005) developed a report that served 

as an inventory and assessment of the ERW. The report concluded that the greatest threats to the ERW are flow regime 

changes, nutrient loading, metals loading, land-use change, 

and cumulative effects from recreationalists.

Rupert and Plummer (2009) studied groundwater 

quality, age, and susceptibility to contamination in the ERW 

and the corresponding relation to land use. The project developed groundwater-susceptibility maps at 1:24,000 scale and 

incorporated new tracers for calibrating the groundwatersusceptibility models. 

Zuellig and others (2010) conducted a study to analyze 

invertebrate data for sites in the ERW to help identify and 

highlight information gaps relative to water-resource management in the watershed. These data were analyzed to assess 

the biological condition of selected sites using invertebrate 

indicators. The results were integrated with previous studies to 

better understand the connection between human actions (land 

use, water-resource management, and so on) and biological 

conditions in the watershed.

Description of Study Area

The Eagle River drains approximately 963 square miles 

(mi2) west of the Continental Divide in central Colorado 

before flowing into the Colorado River (Seaber and others, 

1987). Located in central Colorado west of Vail Pass, the ERW 

is almost entirely contained within Eagle County, with a small 

portion in Pitkin County. The watershed extends from the 

eastern boundary near Vail Pass to the western boundary near 

Dotsero. The headwaters of the Eagle River are located in the 

southernmost region of the watershed near Tennessee Pass. 

Major tributaries within the watershed include Gore Creek, 

Homestake Creek, Cross Creek, Lake Creek, and Brush Creek 

(fig. 1). Gore Creek drains approximately 102 mi2 and flows 

westward 19 miles (mi) out of the Gore mountain range [highest elevation 13,200 feet (ft)] through Vail to the confluence 

with the Eagle River near Minturn (7,730 ft). The Eagle River 

headwaters flow northward from Tennessee Pass (10,000 ft) 

on the Continental Divide through the towns of Red Cliff and 

Minturn to the confluence with Gore Creek. The main stem 

of the Eagle River then flows westerly through the towns of 

Avon, Wolcott, Eagle, Gypsum, and Dotsero before flowing 

into the Colorado River. 

The study area was divided into four subwatersheds for 

this analysis: (1) Upper Eagle, Eagle River including all tributaries upstream from Gore Creek; (2) Gore Creek, including all 

tributaries: (3) Middle Eagle, Eagle River including all tributaries downstream from Gore Creek and upstream of the USGS 

streamflow-gaging station near Wolcott (394220106431500); 

(4) Lower Eagle, Eagle River including all tributaries downstream from the USGS streamflow-gaging station near Wolcott 

and upstream from the Colorado River (fig 1).

Table 1. Sources of water-related data for the Eagle River 

watershed.—Continued

[NA, not applicable; No., number]

Agency No. of

sites

No. of

samples

Surface-water quality

Advanced Sciences Inc. 13 299

Colorado Department of Natural 

Resources 4 171

Colorado Department of Public Health 

and Environment 40 2,340

Colorado Department of Transportation 3 122

Colorado Springs Utilities 9 262

Division of Wildlife (River Watch) 23 539

Eagle Mine Superfund Site Assessment 44 2,116

Eagle River Water and Sanitation 

District 10 997

Grand River Consulting 5 26

U.S. Environmental Protection Agency 3 18

U.S. Forest Service 7 53

U.S. Geological Survey 131 9,085
4 Assessment of Surface-Water Quantity and Quality, Eagle River Watershed, Colorado, 1947–2007

Upper Eagle subwatershed

EXPLANATION

Urban areas

Gore Creek subwatershed

Lower Eagle subwatershed

Middle Eagle subwatershed

Streams

Road

County

COLORADO

UTAH

WYOMING NEBRASKA

KANSAS

ARIZONA NEW MEXICO

TEXAS

OKLAHOMA

DENVER

Grand Junction

Tennessee

Pass

Vail

Pass

Wolcott

106°15'

106°45'

39°45'

39°30'

Base from U.S. Geological Survey digital data, 2007,

Universal Transverse Mercator projection

Zone 13 

Gilman

Belden

0 5 10 KILOMETERS

0 5 10 MILES

Gore

Range

CONTINENTAL

DIVIDE

EAGLE

COUNTY

70

24

70

Eagle

Gypsum

Minturn

Red Cliff

Dotsero

Edwards

Avon Vail

Colorado River

Gunnison River

Colorado River

PITKIN

COUNTY

Eagle River

Lake Creek

Gypsum Creek

Brush Creek

East Brush Creek Squaw Creek

East Lake Creek

Beaver Creek

Cross Creek

Fall Creek

Homestake Creek

Rock Creek

Black Gore Creek

Alkali Creek

Eagle River watershed

West Lake Creek

Gore Creek

Homestake

Reservoir

131

Figure 1. Location of the Eagle River watershed, Colorado, and location of major streams, tributaries, and urban development within the 

watershed.
Introduction 5

Monthly average temperatures in the Vail area range from 

14 degrees Fahrenheit (°F) (-10 degrees Celsius) in January to 

56 °F (13 degrees Celsius) in July. Temperatures in Eagle range 

from 18 °F (-8 degrees Celsius) in January to 67 °F (19 degrees 

Celsius) in July. Precipitation in the ERW ranges from 

52 inches per year in the higher elevations to 11 inches in the 

lower valleys (fig. 2) (Western Regional Climate Center, 2009). 

Much of the precipitation in the watershed falls in the form 

of snow throughout the winter months. The annual cycle of 

streamflow in the ERW is marked by spring snowmelt, which 

causes water levels in the river to rapidly rise. Streamflow 

usually peaks mid June, followed by moderate flows throughout the summer months. Streamflow in autumn and winter are 

characterized by low flows until the snowmelt cycle starts over.

Water management within the ERW provides for municipal (including domestic and industrial), agricultural, and 

recreational uses. Diversion structures were constructed as 

early as the 1880s to deliver water for both in and out-of-basin 

purposes (Bledsoe and others, 2005). Several substantial transbasin diversions direct water from the headwaters of the ERW 

to adjacent hydrologic basins for agriculture and to provide 

water for the cities east of the Continental Divide.

The population of Eagle County within the ERW in 2008 

was estimated at 52,331 (U.S. Census Bureau, 2009). The 

largest townships in the ERW in 2004 include: Avon (6,755), 

Gypsum (4,944), Vail (4,806), Eagle (3,816), and Minturn 

(1,115) (Eagle County, 2009). The population of Eagle County 

has increased 625 percent between 1970 and 2004 (Eagle 

EXPLANATION

11.0 to 14.0

14.1 to 22.5

22.6 to 27.5

27.6 to 35.0

35.1 to 52.0

Average annual precipitation (1904-1994)

in the Eagle River watershed, in inches 

106°15'

106°45'

39°45'

39°30'

0 5 10 KILOMETERS

0 5 10 MILES

Base from U.S. Geological Survey digital data, 2007,

Universal Transverse Mercator projection

Zone 13 

Figure 2. Variation in precipitation throughout the Eagle River watershed, Colorado (Western Regional Climate Center, 2009).
6 Assessment of Surface-Water Quantity and Quality, Eagle River Watershed, Colorado, 1947–2007

County, 2009). The ERW attracts many visitors for recreational activities like fishing, hiking, camping, biking, ice 

climbing, and skiing.

The primary industries within the watershed are mining 

and recreation/tourism. Mining activities historically have 

included the extraction of base and precious metals from ore 

deposits in the Upper Eagle subwatershed as well as gypsum 

in the Lower Eagle subwatershed since the late 1800s (Bledsoe and others, 2005). Very little hard-rock metals mining 

activity presently (2009) exists in the watershed, however, 

gypsum mining continues near the town of Gypsum. Ski tourism, second-home development, and outdoor recreation are 

large contributors to the growing economy of Eagle County 

(Eagle County, 2009). 

Land-use patterns within the ERW have been shaped by 

economic and development trends. The economy is shifting 

toward tourism, although ranching, mining, and farming still 

exist. Currently, within the ERW 49 percent of total lands 

are forested, 40 percent are shrubs, grasses, agricultural, and 

rangeland, 9 percent are tundra, wetlands, and barren lands, 

and 2 percent are developed lands (U.S. Geological Survey, 

2010). Vegetation throughout the watershed is diverse. Land 

cover in the headwater elevations close to 10,000 ft are dominated by rock, alpine tundra, evergreen forest, and herbaceous 

vegetation. Elevations at 8,000–10,000 ft are dominated by 

evergreen and aspen forests. The lower regions of the Eagle 

River flow through an alluvial valley consisting of rangeland, 

shrubs, and grassland (fig. 3). 

EXPLANATION

Agriculture

Barren

Forest

Rangeland, shrub, grassland

Tundra

Urban or developed land

Water

Wetland

Eagle River watershed land use:

City

Streams

106°15'

106°45'

39°45'

39°30'

0 5 10 KILOMETERS

0 5 10 MILES

Base from U.S. Geological Survey digital data, 2007,

Universal Transverse Mercator projection

Zone 13 

Vail

Avon

Eagle

Minturn

Red Cliff

Gilman

Belden

Dotsero Gypsum

Wolcott

Edwards

Figure 3. Land use in the Eagle River watershed, Colorado, 2008.
Developed land within the watershed is increasing, which 

can lead to associated water-quality issues and the introduction of new contaminants (Rupert and Plummer, 2009). A 

major factor arising from development and the changing land 

use of the region is a decrease in vegetative buffers in riparian 

areas (Wynn and others, 2001). As runoff approaches surface 

waters, soil and vegetation act as filters for contaminants and 

nutrients, thus preventing them from entering at high concentrations. Construction of Interstate-70 (I-70) began in the 

early 1970s. Historically, suspended sediment associated with 

construction of I-70 has been a primary water-quality concern; 

however, recent data indicate that streambed aggradation of 

sediment originating from I-70 traction sanding is a greater 

concern (Wynn and others, 2001).

Geology

The ERW geologically is diverse and has more than a 

billion years of geologic history in the rock record including 

deposition, deformation, metamorphism, and related change. 

There are geologic deposits that vary from Precambrian metamorphic rocks to Quaternary alluvium and volcanic deposits 

(fig. 4). The wide range of geologic units contributes major 

ions and metals to the river system thereby affecting water 

quality. For example, saline shales and sandstones, along with 

evaporite deposits can contribute selenium and total-dissolved 

solids, commonly described as an estimate of salinity, to the 

water (Tweto, 1979; Hem, 1989). A geologically active region 

during the Laramide orogeny, in the southern part of the ERW, 

is recognized as being part of the Colorado Mineral Belt 

(Wilson and Sims, 2003). The Colorado Mineral Belt extends 

in a northeast direction from the San Juan Mountains in the 

southwest to just west of Boulder, Colorado, and is shown on 

figure 4. Igneous intrusions, hydrothermal alteration, mineralization, and various ore deposits are typically associated with 

the Colorado Mineral Belt. These economic ores, which can 

include copper, gold, lead, molybdenum, silver, tungsten, and 

zinc have contributed to a multibillion-dollar industry for the 

State (Wilson and Sims, 2003).

The ERW contains a mix of lithologies including sedimentary, metamorphic, and intermixed igneous intrusions 

(Tweto, 1979). The sedimentary rocks are Pennsylvanian 

in age conglomerate, sandstone, shale, and limestone in the 

eastern portion of the ERW; and Cretaceous and Pennsylvanian in age siltstone, shale, gypsum and salt-bearing deposits 

in the central and western areas. The northern portion of the 

watershed contains Cretaceous sandstone and shale deposits. 

These deposits include Pierre Shale and Dakota Sandstone. 

The Pierre Shale is a marine deposit that contains salt and has 

been indicated as a contributor of selenium to water supplies 

(Butler, 2001). The metamorphic rocks occurring along the 

eastern and southern portion of the ERW are Precambrian in 

age gneiss, schist, migmatite, and granite. The igneous rocks 

are Quaternary and Tertiary in age basalt flows, tuffs, and 

breccias, with various age intrusive deposits in the western 

portion of the ERW. 

Three formations that are in contact with the main 

stem Eagle River are the Eagle Valley Evaporite, Minturn 

Formation, and the Belden Formation (Tweto, 1979). The 

Eagle Valley Evaporite, an evaporite facies of the Eagle Valley Formation, is Pennsylvanian in age and predominantly 

composed of gypsum, anhydrite, and interbedded siltstone 

and shale with thick salt deposits located sporadically underneath. The Belden Formation, also Pennsylvanian in age, is a 

dark-colored shale, limestone, and sandstone (Tweto, 1979). 

The Minturn Formation, Pennsylvanian in age, is a yellow to 

red sandstone and conglomerate that has interbedded layers of 

carbonate rocks (Tweto, 1979). 

Mining Activity

Mining first began in the Gilman area in the late 1870s 

with the discovery of gold and silver deposits. The Gilman 

area is located between the towns of Minturn and Red Cliff 

along the Eagle River (fig. 5). Mining of lead and zinc became 

common in the mid 1890s. The Eagle Mine is one of the 

largest zinc mines in the United States, and a major domestic 

source of zinc (Colorado Department of Public Health and 

Environment and U.S. Environmental Protection Agency, 

2008). Copper and silver were the last mining activities near 

Belden with production ending in 1984 (Colorado Department 

of Public Health and Environment and U.S. Environmental 

Protection Agency, 2008).

The Eagle Mine and associated mining wastes between 

Gilman and Minturn (which encompass about 235 acres), was 

placed on the Superfund sites list in 1986 (Colorado Department of Public Health and Environment and U.S. Environmental Protection Agency, 2008). Remediation of the Eagle 

Mine site began in 1988 through the relocation of processed 

mine wastes and contaminated soils to an on-site tailing pile. 

A water-treatment plant was constructed in 1990 to collect and 

treat mine seepage, tailing-pile groundwater, and accumulated 

precipitation runoff. Major remediation generally was completed by 1996. A list of major construction milestones for the 

Eagle Mine Superfund Site is provided in table 2.

In 2000, the first 5-year review report was written to identify human health risks and restoration of the Eagle River (Colorado Department of Public Health and Environment, 2000). The 

second 5-year review report was written in 2005 and concluded 

that remedies at the mine site continue to be protective to human 

health (Colorado Department of Public Health and Environment 

and U.S. Environmental Protection Agency, 2005). The third 

5-year report was completed in 2008 and concluded that efforts 

to protect human health are working but additional actions are 

necessary to achieve protection of the aquatic ecosystem (Colorado Department of Public Health and Environment and U.S. 

Environmental Protection Agency, 2008).

Regional mining of gypsum and gravel near Gypsum 

still occurs today. The American Gypsum Plant in Gypsum 

produced more than 408,000 metric tons of gypsum in 1999 

(Bledsoe and others, 2005). Gravel mining also is an active 

industry near the towns of Edwards and Gypsum. 

Introduction 7
8 Assessment of Surface-Water Quantity and Quality, Eagle River Watershed, Colorado, 1947–2007

Base from U.S. Geological Survey digital data, 1992,

1:100,000, Universal Transverse Mercator projection

Zone 13 

Eagle River watershed

EXPLANATION

Colorado Mineral Belt

0 5 10 KILOMETERS

0 5 10 MILES

Eagle Denver

Durango

Boulder

Grand

Junctiion

COLORADO

SAN JUAN MOUNTAINS

FRONT RANGE

Xb

Kp

Xg

Xg

Kc

Kc

Qg

Ql

Kd

Kd

TKi

Tbb

Ql

Qd

Tbp

Tbp

Kp

Ql

Qd

Qd

Qd

Qg

Jme

Jme

Xb

Xb

Xb

Xb

TKi

Qd Ql

Qd

Qd

Qd

Xb

Xb Xb

Ql

Qd

Qg

Xg

Kd

Tbb

Qg

Qd

Tbb

Tbb

Qg

Xfh

Tmi

Tmi

Jme

Qd

Xfh

Xfh

Kd

KJde

Kc

Ql

Ql

Kp

Tbb

Qd

Xb

Xb

Xg

Qdo

Qd

Kc

Qd

Kc

Yg Yg

Kd

Ql

Qd

Qd

Jmce

Yg

Qd

Ql

Xg

Qdo

Qdo

Ql

Qd

Ql

Ql Ql

Qd

Qd Qdo

Xfh

Ql

TKi Xfh

Ql

Qgo

Xg

Qd

Ql

Ql

KJde

Qa

Qb Tbb

KJde

KJde

KJde

Xb

Xb

Qd

Qdo

QTa

Qd

TKi

Qd

Qb

Qdo

Tbb

TKi

Kc

Qd

TKi

Qd

Qd

TKi

Pcs Pcs

Pcs

Pcs

Pcs

Pcs

Pcs

P	wm

P	m P	m

P	m

	e

	e

	e

	e

	ee

	ee

	ee

	ee

	ee

P	wm

P	wm

P	wm

P	wm

P	m

P	m

P	m

P	m

	m

	m

	m

	m

	m 	m

	m

	m

P	m

	ee

	ee

	mb

	mb

	b M

M

M

M

M

M

M

M

M	 MD

O

O O

O

s

s s

s

	ee

c

Ps

Ps

M

Tbb

P	m
Introduction 9

Modern alluvium—Includes Holocene Piney Creek Alluvium and

 younger deposits

Gravels and alluviums (Pinedale and Bull Lake age)—Includes

 Broadway and Louviers Alluviums

Glacial drift of Pinedale and Bull Lake glaciations—Includes some

 unclassified glacial deposits

Landslide deposits—Locally includes talus, rock-glacier, and thick

 colluvium deposits

Ancient alluvium—In isolated patches that may not all be of the

 same age

Older Gravels and alluviums (Pre-Bull Lake age)

Older glacial drift (Pre-Bull Lake age)

Basalt flows (age less than 1.8 million years)

Unconsolidated Surficial Deposits and

 Rocks of Quaternary and Tertiary Age 

Qa

Browns Park Formation—Sandstone and siltstone, west of

 Park Range

Sedimentary Rocks of Tertiary Age

Tbp

Qg

Qgo

Chinle Formation—Red siltstone, sandstone, and limestone pellet

 conglomerate

State Bridge Formation—Red and orange silstone and sandstone

Chinle and State Bridge Formations, undivided

Sedimentary Rocks of Triassic and Permian Age

EXPLANATION

c

Ps

Pcs

Maroon Formation—Arkosic sandstone, siltstone, conglomerate,

 and local limestone

Weber Sandstone and Maroon Formation

Sedimentary Rocks of Permian and Pennsylvania Age

Pm

Pwm

Basalt flows and associated tuff, breccia, and conglomerate

 of late volcanic bimodal suite

Middle Tertiary intrusive rocks (age 20–40 million years)—

 Intermediate to felsic compositions

Laramide intrusive rocks (age 20–72 million years)

Ingneous Rocks of Teriary and Cretaceous Age

Tbb

Tmi

Morrison Formation and Entrada Sandstone

Morrison, Curtis, and Entrada Formations

Sedimentary rocks of Jurassic Age

Jme

Jmce

TKi

Qd

Colorado Group—Consists of Niobrara Formation and either Benton

 Shale or Carlile, Greenhorn, and Graneros Formations

Dakota Sandstone or Group

Dakota, Morrison, and Entrada Formations

Pierre Shale, undivided

Sedimentary Rocks of Cretaceous and Jurassic Age

Kc

Kd

Kp

KJde

Qdo

Minturn Formation—Arkosic sandstone, conglomerate, shale, and

 limestone

Belden Formation—shale, limestone, and sandstone

Eagle Valley Evaporite—Gypsum, siltstone and shale, anhydrite,

 salt, present in deep borings 

Eagle Valley formation—Siltstone, shale, and gypsum

Minturn and Belden Formations

Sedimentary Rocks of Pennsylvanian Age

m

b

e

ee

mb

Leadville Limestone

Leadville, Gilman, Dyer, Parting, Fremont, Harding, Manitou,

 Dotsero, Peerless, and Sawatch Formations

Sawatch Formation—Locally includes Peerless Formation

Ordovician rocks

Sedimentary Rocks of Pre-Pennsylvania Paleozoic Age

MD

M


O



s

Biotite gneiss, schist, and migmatite—Locally contains minor

 hornblende gneiss, quartzite, and marble

Felsic and hornblende gneisses—Includes metabasalt, metatuff,

 and interbedded metagraywacke

Granitic rocks 1,700 million years

Granitic rocks 1,400 million years

Sedimentary, Metamorphic, and Igneous Rocks of

 Precambrian Age

Xb

Xfh

Yg

Xg

Ql

Qb

QTa

Figure 4. Surficial geology of the Eagle River watershed, Colorado (from Tweto, 1979).
10 Assessment of Surface-Water Quantity and Quality, Eagle River Watershed, Colorado, 1947–2007

Table 2. Eagle Mine Superfund Site major construction milestones (Colorado Department of Public 

Health and Environment and U.S. Environmental Protection Agency, 2008).

Major construction milestones Date completed

Rex Flats tailing removal 1988, 1996

Roaster Pile #5 removal 1988

Consolidated tailings pile groundwater extraction system completed 1989

Roaster Pile #4 removal 1989

Roaster Piles #1, 2, 3 removal 1989

Package water treatment plant installed 1990

Roaster Gulch sediment and sediment basin removal 1990, 1992, 1994

Old tailings pile tailing removal 1991

Pipeline trestle tailing removal 1991

Customized water treatment plant constructed 1991

Sludge Press added to water treatment plant operation 1994

Maloit Park soil removal 1995, 1996

Consolidated tailings pile cap completed 1996

Belden “concentrate” removal 1997
Data Sources, Compilation, Review, and Analysis 11

Data Sources, Compilation, Review, 

and Analysis

The availability of multiple digital surface-water data 

sources within the ERW provides extensive information to 

support an assessment of the surface-water conditions within 

the watershed; however, these data sources are the product of 

multiple data-collection objectives, collection methodologies, 

and temporal scales within the watershed. Details relevant 

to the sources of data used in the analysis, methods used to 

generate the analysis dataset structure, and limitations inherent 

in the data analysis are presented. 

106°22'30"

106°38'

39°41'

39°25'30"

ENLARGED

AREA

Minturn

Red Cliff

Eagle River

Base from U.S. Geological Survey digital data, 2007,

Universal Transverse Mercator projection

Zone 13 

0 5 10 KILOMETERS

0 5 10 MILES

!(

Waterbodies

EXPLANATION

Urban areas

Eagle Mine structures

City

Upper Eagle subwatershed

Middle Eagle subwatershed

Gore Creek subwatershed

Superfund restoration boundary

Streams

Highways

Lower Eagle subwatershed

Avon Vail

Edwards

24

70

!(

!( !(

!( !(

!(

!(

Rex Flats

Belden

Gilman

Roaster Pile

Roaster Pile

Old Tailings Pile

Eagle Mine Workings

Water Treatment Plant

Consolidated

Tailings Pile

Bolt Lake

Eagle River

24

Figure 5. Location of hard-rock mining and related superfund remediation in the Eagle River watershed, Colorado, 2008.

Surface-Water Quantity

Available surface-water quantity data were obtained 

from the USGS National Water Information System 

(NWIS, URL: http://waterdata.usgs.gov/nwis) and the City 

of Colorado Springs (URL: http://www.springsgov.com/

Index.aspx). Streamflow-gaging stations have monitored 

surface-water quantity in the ERW at up to 39 different 

locations in the watershed since water year 1911 (fig. 6, 

table 3). In 2009, the USGS monitored surface-water 

quantity (streamflow) at 14 sites, and the City of Colorado 

Springs operated a streamflow gaging-station on the outflow from Homestake Reservoir. The Homestake Reservoir 
12 Assessment of Surface-Water Quantity and Quality, Eagle River Watershed, Colorado, 1947–2007

outfall is used in this report for information pertaining to 

water management and flow augmentation within the ERW 

and is not shown in figure 6 or in table 3. No other streamflow-gaging stations currently (2009) are operated by other 

agencies within the ERW. 

A summary of streamflow statistics for selected streamflow-gaging stations is available in table 4. Median annual 

maximum daily streamflow and median annual minimum 

7-day mean streamflow were calculated from available annual 

summary statistics between 1968‒2008 to provide estimates 

of typical high and low-flow conditions (NWIS, URL: http://

waterdata.usgs.gov/nwis). The mean annual runoff, daily mean 

streamflow exceedance, and flood frequency statistics are of 

value to water managers because these data provide a historical summary that aids in the prediction of recurrence of highand low-flow conditions.

Characterization of the prevailing climatic conditions for 

sites was done using a Locally Weighted Scatterplot Smoothing (LOWESS Smooth) of the annual mean streamflow at 

selected sites (Helsel and Hirsh, 1992). Selection of the appropriate smoothing factor was completed iteration until the best 

fit was obtained for each of the selected sites.

106°15'

106°45'

39°45'

39°30'

0 5 10 KILOMETERS

0 5 10 MILES # #

##

#

#

## ## ##

#

#

#

#

# #

##

#

##

#

#

#

#

#

#

#

#

#

#

#

##

# #

#

Gypsum

Creek

Brush

Creek

Lake

Creek Beaver

Creek

Cross 

Creek

Homestake Creek

MissouriCreek

Creek

Creek

Creek

Creek

Creek

Creek

Turkey Wearymann

East Fork Eagle

Pitkin

Bighorn

Booth

Red

Sandstone

Gore

Gore Creek

Black 

Gore

Creek

Eagle

Creek

River

Eagle

River

Creek

Middle

Active streamflow-gaging

 stations and site number

 (site name given in table 5)

Discontinued streamflow-gaging

 stations and site number

 (site name given in table 5)

Waterbodies

EXPLANATION

Cities

Gore Creek subwatershed

Upper Eagle subwatershed

Streams

Middle and Lower subwatersheds

Gore Creek subwatershed

18 #

Base from U.S. Geological Survey digital data, 2007,

Universal Transverse Mercator projection

Zone 13 

229

233

204.1

217

212

193

194

184 176

169

160

157.1

139

78

66

17

xd-3 13

27

14

15

110

1

1.2 1.1

xd-1 xd-2 24

22

111

102

114

120 116 125

135

141

138

173

19 #

Alkali Creek

Figure 6. Streamflow-gaging station locations and streamflow distribution for selected streams in the Eagle River watershed, Colorado, by

subwatershed.
Table 3. Hydrologic characteristics for streamflow-gaging stations in the Eagle River watershed.[no., number; USGS, U.S. Geological Survey; CDWR, Colorado Division of Water Resources; CO, Colorado; water year, continuous period from October 1 through September determined by the ending calendar year; --, no data; xd, transmountain diversion]

Site no. Site name Source

agency

Site

identifier

Period of record 

stored in a database, 

in water years1

Drainage area,

in square miles2

Mean annu

streamflow, in 

feet per seco

1 East Fork Eagle River near Climax, CO USGS 09061600 2002–08 7.78 4.77 xd-1 Wurtz Extension Ditch near Tennessee Pass, CO CDWR WUREXDCO 1967–91 -- -- 

xd-2 Wurtz Extension CDWR WUREXTCO 1991–2006 -- -- 

1.1 Wurtz Ditch near Tennessee Pass, CO USGS CDWR 09062500 WURDITCO 1948–67 1947–2006 -- -- 

1.2 Ewing Ditch at Tennessee Pass, CO USGS CDWR 09062000 EWIDITCO 1948–67 1947–2006 -- -- 

13 Eagle River at Red Cliff, CO USGS 09063000 1911–25, 1945–2008 70.0 45.3 xd-3 Eagle River at Red Cliff Plus Columbine, Ewing, and Wurtz5 USGS 09063001 1947–1967 70.0 48.04 

14 Wearyman Creek near Red Cliff, CO USGS 09063200 1965–2008 9.53 8.24 15 Turkey Creek near Red Cliff, CO USGS 09063400 1964–2008 23.8 21.7 16.1 Turkey Creek at Red Cliff, CO USGS 09063500 1914–21, 1945–56 29.4 28.64 22 Missouri Creek near Gold Park, CO USGS 09063900 1972–2008 6.39 7.37 24 Homestake Creek at Gold Park, CO USGS 09064000 1948–54, 1972–2008 36.0 27.0 

27 Homestake Creek near Red Cliff, CO USGS 09064500 1911–18, 1945–2008 58.2 41.6 66 Eagle River near Minturn, CO USGS 09064600 1990–2008 186 122 78 Cross Creek near Minturn, CO USGS 09065100 1957–64, 1968–2008 34.2 51.9 102 Gore Creek at Upper Station, near Minturn, CO USGS CDWR 09065500 GORMINCO 1948–56, 1964–2008 1963–66 14.4 29.7-- 

110 Black Gore Creek near Minturn, CO USGS 09066000 1948–56, 1964–2008 12.6 16.7 111 Black Gore Creek near Vail, CO USGS 09066050 1974–80 19.6 28.74 

114 Bighorn Creek near Minturn, CO USGS 09066100 1964–2008 4.54 9.77 116 Pitkin Creek near Minturn, CO USGS 09066150 1967–2008 5.32 11.6 120 Booth Creek near Minturn, CO USGS 09066200 1965–2008 6.02 11.8 125 Gore Creek at Vail, CO USGS 09066250 1974–79 57.3 95.54 135 Middle Creek near Minturn, CO USGS 09066300 1965–2008 5.94 5.63 138 Gore Creek, Lower Station at Vail, CO USGS 09066310 1988–99 77.1 1184 139 Gore Creek above Red Sandstone Creek at Vail, CO USGS 09066325 2000–08 77.1 101 141 Red Sandstone Creek near Minturn, CO USGS 09066400 1964–2008 7.32 8.85 157.1 Gore Creek near Minturn, CO USGS 09066500 1945–56 101 1294 160 Gore Creek at Mouth, near Minturn, CO USGS 09066510 1996–2008 102 128 

169 Beaver Creek at Avon, CO USGS 09067000 1974–2008 14.8 13.0 173 Eagle River At Avon, CO USGS 09067005 1989–99 395 3864 

176 Eagle River below Wastewater Treatment Plant at Avon, CO USGS 09067020 2000–08 402 317 184 Lake Creek near Edwards, CO USGS 09067200 1994–2008 49.0 57.6 194 Alkali Creek near Wolcott, CO USGS 09067300 1959–65 27.3 2.134 201 Eagle River below Milk Creek near Wolcott, CO USGS 394220106431500 2006–2008 600 -- 204.1 Eagle River at Eagle, CO USGS 09067500 1912–24 629 6763 212 East Brush Creek at Yeoman Park, near Eagle, CO USGS 09067700 1966–72 9.74 14.94 217 Brush Creek near Eagle, CO USGS 09068000 1951–72 71.4 44.14 229 Gypsum Creek near Gypsum, CO USGS 09069500 1951–55, 1966–72 62.7 32.44 233 Eagle River below Gypsum, CO USGS 09070000 1947–2008 944 566 

1Water year from October 1–September 30.2Data obtained from USGS National Water Information System: Web Interface URL: http://waterdata.usgs.gov/nwis.3Mean annual streamflow for period of record; data obtained from USGS Water-Data Report 2007 unless otherwise indicated.4Mean annual streamflow for period of record calculated from USGS National Water Information System: Web Interface URL: http://waterdata.usgs.gov/nwis.5Does not have a physical location, streamflow is calculated using nearby gages.
Table 4. Summary of the mean annual runoff, median annual maximum daily streamflow, annual flood frequency, and low-flow statistics for selected 

watershed. [no., number; %, percent of time per year; --, no data; yr, year] Site no.1 Period of record, in water years Mean annual runoff, in acre-feet2 Daily mean streamflow that was exceeded the specified percent of time per year, in cubic feet per second2 Median annual maximum daily streamflow, in cubic feet per second3 Peak flood-frequency recurrence interval, in cubic feet per second4 

10% 50% 90% 2 yr 5 yr 10 yr 10

13 1911–25, 1945–2008 32,800 122 15 9.0 251 -- -- -- 

14 1965–2008 5,970 23 2.4 1.2 69 83 124 150 

15 1964–2008 15,730 33 5.8 2.8 170 236 370 460 

22 1972–2008 5,340 18 2.4 .60 63 -- -- -- 

24 1948–54, 1972–2008 19,560 59 12 4.4 177 -- -- -- 

27 1911–18, 1945–2008 30,170 109 17 6.2 275 805 997 1,107 1,

66 1990–2008 88,490 339 48 25 740 -- -- -- 

78 1957–64, 1968–2008 37,570 174 12 2.4 415 -- -- -- 

102 1948–56, 1964–2008 21,520 99 7.1 2.5 250 334 441 506 

110 1948–56, 1964–2008 12,100 50 3.9 2.0 164 215 274 308 

114 1964–2008 7,080 32 2.4 .70 75 86 132 163 

116 1967–2008 8,410 37 3.4 1.2 78 -- -- -- 

120 1965–2008 8,550 40 2.3 .77 106 143 182 205 

135 1965–2008 4,080 19 .95 .22 55 74 107 128 

141 1964–2008 6,410 28 1.8 .88 84 11 156 183 

169 1974–2008 9,450 38 4.5 2.1 82 -- -- -- 

233 1947–2008 409,900 1,540 242 158 3,425 3,870 5,100 5,840 7,

1 Sites names are shown in table 3.2 U.S. Geological Survey, 2007.3 Data calculated from available continuous data, 1968 to 2008, from U.S. Geological Survey National Water Information System: Web Interface database: URL: http:// water4 Ries III and others, 2008.
Table 5. Historic and current surface-water quantity and quality sites in the Eagle River watershed, Colorado.[no., number; USGS, U.S. Geological Survey; CDPHE, Colorado Department of Public Health and Environment; CO, Colorado; WWTP, wastewater treatment plant; CSU, ColGRC, Grand River Consulting, EMSSA, Eagle Mine Superfund Site Assessment; DOW-RW, Division of Wildlife, River Watch; CDNR, Colorado Division of Natural ResourceIncorporated; CDOT, Colorado Department of Transportation; ERWSD, Eagle River Water and Sanitation District; USFS, U.S. Forest Service; USEPA, U.S. Environmental Proproperties; MI, major ions; TE, trace elements; O, other constituents; AE, aquatic ecology; S, sediment; N, nutrients; R, radionuclide]

Site

no.

Site name Data

sources

Site

identifiers Latitude Longitude Type of data

Period of 

discharge record

(water year)

1 East Fork Eagle River near Climax, CO USGS 09061600 39.41027 –106.24975 FP 2002–08 2 East Fork Eagle River above Sheep Gl near Camp 

Hale, CO 

USGS 392440106150400 39.41110 –106.25169 FP, MI, TE 

3 East Fork Eagle River near Red Cliff, CO USGS

CDPHE

392511106164000392511106164000

39.41971 –106.27836 O, FP, MI, AE, S, N, TE

FP, MI, TE

4 Cataract Creek at mouth near Camp Hale, CO USGS 392514106165800 39.42055 –106.28293 FP, MI, TE 5 East Fork Eagle River, CO CSU E8_EFORK 39.42028 –106.29944 FP, TE, MI, AE 6 East Fork Eagle River above Camp Hale, CO GRC EAG1_EFE 39.41944 –106.30333 FP, MI, N, TE 7 East Fork Eagle River at mouth below Climax, CO USGS 392518106184700 39.42112 –106.31212 O, FP, TE, MI, N 8 South Fork Eagle River above Camp Hale ,CO GRC EAG3_SFE 39.41222 –106.31583 FP, MI, N, TE 9 South Fork Eagle River above East Fork Eagle 

River near Red Cliff, CO

USGS

CDPHE

392513106184500392513106184500

39.42027 –106.31294 FP, AE

FP, MI, TE

10 Resolution Creek near Eagle River, CO GRC EAG2_RESCK 39.44778 –106.31944 FP, MI, N, TE 

11 Eagle River at Camp Hale, CO CSU E7_CHALE 39.44833 –106.32750 O, FP, TE, MI, AE 

12 Eagle River below Camp Hale, CO GRC EAG4_BCH 39.46056 –106.32944 FP, MI, N, TE 13 Eagle River at Red Cliff, CO USGS 

CDPHE

0906300009063000

39.50838 –106.36598 AE, O, FP, MI, S, N, TE

FP, TE, MI, AE, N

1911–25, 1945–2008 

14 Wearyman Creek near Red Cliff, CO USGS 09063200 39.52238 –106.32357 FP 1965–2008 15 Turkey Creek near Red Cliff, CO USGS 09063400 39.52276 –106.33614 FP 1964–2008 16 Turkey Creek at Red Cliff intake near Red Cliff, CO USGS 393109106210600 39.51915 –106.35225 O, FP, MI, AE, N, TE 17 Turkey Creek at Red Cliff, CO CDPHE 12590 39.51402 –106.36687 FP, MI, AE, S, N, TE 20 Eagle River above Homestake Creek, CO CDPHE

EMSSA

DOW-RWDOW-RW

CSU

E-1RE-1R328438E7_AHMCR

39.5083339.5083439.5083339.50825

–106.37656–106.37640–106.37691–106.37584

FP, MI, TEO, FP, MI, N, TEFP, MI, TEFP, MI, TEFP

22 Missouri Creek near Gold Park, CO USGS 09063900 39.38986 –106.46961 FP 1972–2008 24 Homestake Creek at Gold Park, CO USGS 09064000 39.40554 –106.43336 FP 1948–54, 1972–2008 27 Homestake Creek near Red Cliff, CO USGS

CDPHECDPHE

GRC

090645000906450012564EAG5_HSC

39.4733239.4731339.47306

–106.36781–106.36833–106.36861

AE, O, FP, MI, S, N, TEFP, TE, R, MI, AE, S, N, OFP MI, AE, S, N, TEFP, MI, N, TE

1911–1918, 1945–20

28 Eagle River below Homestake Creek near Red 

Cliff, CO

USGS 393030106224700 39.50833 –106.37972 AE, O, FP, MI, S, N, TE 

29 Eagle River below Homestake Creek and at B CSU E4_BHMCR 39.51194 –106.38459 FP, MI, N 30 Eagle River above Peterson Gulch CDPHE EAGLE07 39.51416 –106.38684 FP, MI, TE 

31 Peterson Creek at mouth USGS 393057106232301 39.51570 –106.39009 FP, MI, S, TE 

32 Eagle River below Peterson Creek CDPHE EAGLE06 39.51722 –106.39222 FP, MI, TE 

34 Eagle River above Belden Mine USGS

CDPHE

DOW-RW

3931231062345013931231062345013285

39.5230439.52288

–106.39642–106.39625

FP, MI, S, TEFP, MI, TEFP, MI, TE
Table 5. Historic and current surface-water quantity and quality sites in the Eagle River watershed, Colorado.—Continued [no., number; USGS, U.S. Geological Survey; CDPHE, Colorado Department of Public Health and Environment; CO, Colorado; WWTP, wastewater treatment plant; CSU, ColGRC, Grand River Consulting, EMSSA, Eagle Mine Superfund Site Assessment; DOW-RW, Division of Wildlife, River Watch; CDNR, Colorado Division of Natural ResourceIncorporated; CDOT, Colorado Department of Transportation; ERWSD, Eagle River Water and Sanitation District; USFS, U.S. Forest Service; USEPA, U.S. Environmental Proproperties; MI, major ions; TE, trace elements; O, other constituents; AE, aquatic ecology; S, sediment; N, nutrients; R, radionuclide] Site no. Site name Data sources Site identifiers Latitude Longitude Type of data Period of discharge record (water year) 

35 Eagle River, right bank 450 feet upstream E-4BR EMSSA E-4AR1 39.52522 –106.39451 FP, TE 

37 Belden USGS DOW-RW EMSSA 393132106233601 3286 E-3 39.52554 39.52553 39.52556 –106.39392 –106.39396 –106.39389 FP, TE, MI, N FP, MI, TE O, FP, MI, N, TE 

39 Eagle River, right bank 175 feet upstream E-4BR EMSSA E-4AR2 39.52592 –106.39424 FP, TE 

40 Eagle River, 25 feet upstream culvert EMSSA EMSSA E-4BR E-4BL 39.52639 –106.39447 FP, TE FP, TE 

41 Eagle River above Belden Power Station EMSSA E-4A 39.52660 –106.39459 FP, MI, N, TE 

42 Eagle River, right bank 100 feet downstream E-4BR EMSSA E4-R1 39.52662 –106.39461 FP, TE 

43 Eagle River, right bank 200 feet downstream E-4BR EMSSA E4-R2 39.52684 –106.39485 FP, TE 

44 Eagle River, right bank 300 feet downstream E-4BR EMSSA E4-R3 39.52700 –106.39519 FP, TE 

45 Eagle River, right bank 400 feet downstream E-4BR EMSSA E4-R4 39.52715 –106.39556 FP, TE 

46 Eagle River, right bank 500 feet downstream E-4BR EMSSA E4-R5 39.52729 –106.39595 FP, TE 

47 Eagle River, right bank 550 feet downstream E-4BR EMSSA E4-R5A 39.52731 –106.39620 FP, TE 

48 Eagle River at Belden Power Station EMSSA E-4 39.52724 –106.39647 FP, TE 

49 Eagle River above Fall Creek EMSSA EMSSA EMSSA EMSSA EMSSA E-5 E-5D E-5W CC-6D CC-6W 39.52667 –106.39917 O, FP, MI, N, TE FP, TE FP, TE FP, TE FP, TE 

50 Eagle River, 40 feet upstream Fall Creek EMSSA EMSSA E-5AR E-5AL 39.52726 –106.40007 FP, TE FP, TE 

51 Fall Creek above power plant diversion USGS 393125106241601 39.52360 –106.40503 FP, MI, TE 

52 Fall Creek at mouth USGS EMSSA 393137106240001 T-8B 39.52705 39.52725 –106.40074 –106.40035 FP, MI, S, TE FP, TE 

54 Eagle River, right bank at Fall Creek EMSSA E-5BR 39.52732 –106.40025 FP, TE 

56 Eagle River below Fall Creek USGS EMSSA EMSSA 393139106240101 E-9R E-9L 39.52749 39.52743 –106.40062 –106.40031 FP, MI, S, TE FP, TE FP, TE 

57 Eagle River above Rock Creek EMSSA E-10 39.53146 –106.40050 O, FP, MI, N, TE 

58 Rock Creek at mouth USGS EMSSA 393157106235501 T-10 39.53249 –106.39920 FP, MI, S, TE O, FP, MI, N, TE 

59 Eagle River above Bishop Gulch EMSSA

DOW-RW

E-113287

39.5416639.54224

–106.40288–106.40354

O, FP, MI, N, TEFP, MI, TE

61 Bishop Gulch at mouth USGS

EMSSA

393233106241401T-11

39.5424939.54271

–106.40447–106.40402

FP, MI, S, TEFP, TE

63 Eagle River below Bishop Gulch USGS

CDPHE

USEPA

393245106241501393245106241501393245106241501

39.54582 –106.40475 FP, MI, S, TE

FP, TE, MIFP, MI, N, TE
Table 5. Historic and current surface-water quantity and quality sites in the Eagle River watershed, Colorado.—Continued[no., number; USGS, U.S. Geological Survey; CDPHE, Colorado Department of Public Health and Environment; CO, Colorado; WWTP, wastewater treatment plant; CSU, ColGRC, Grand River Consulting, EMSSA, Eagle Mine Superfund Site Assessment; DOW-RW, Division of Wildlife, River Watch; CDNR, Colorado Division of Natural ResourceIncorporated; CDOT, Colorado Department of Transportation; ERWSD, Eagle River Water and Sanitation District; USFS, U.S. Forest Service; USEPA, U.S. Environmental Proproperties; MI, major ions; TE, trace elements; O, other constituents; AE, aquatic ecology; S, sediment; N, nutrients; R, radionuclide]

Site

no.

Site name Data

sources

Site

identifiers Latitude Longitude Type of data

Period of 

discharge record

(water year)

64 Eagle River below Belden CDPHE EAGLE04 39.55028 –106.40575 FP, MI, TE 

66 Eagle River near Minturn, CO USGS

EMSSAEMSSAEMSSAEMSSAEMSSA

09064600E-12AE-12ADE-12AWCC-42DCC-42W

39.5538739.55361

–106.40253–106.40167

AE, O, FP, MI, S, N, TEO, FP, MI, N, TEFP, TEFP, TEFP, TEFP, TE

1990–2008 

67 Eagle River above Cross Creek near Minturn, CO USGS

CDNR

CDPHE

393318106240400393318106240400EAGLE03

39.5549939.55473

–106.40170–106.40142

O, FP, TE, MI, AE, NFP, MI, TEFP, MI, TE

68 Eagle River above Two Elk Creek USGS

EMSSA

393336106235701E-13

39.55999 –106.39975 FP, MI, S, TE

O, FP, MI, N, TE

69 Eagle River at Two Elk (3) DOW–RW 3289 39.56462 –106.40203 FP, MI, TE 

70 Two Elk Creek at mouth USGS

EMSSA

393353106240301T-14

39.5648139.56470

–106.40151–106.40143

FP, MI, S, TEFP, TE

72 Eagle River above Cross Creek USGS

CDNR

CSU

EMSSA

393411106242001393411106242001393411106242001E-13B

39.56986 –106.40554 FP, MI, S, TE

FP, TE, MIO, FP, TE, MI, AEO, FP, MI, N, TE

73 Cross Creek above Battle Mountain School 

near Minturn, CO

USGS 393350106251200 39.56313 –106.41946 O, FP, TE, MI, AE, N 

74 Cross Creek at Maloit CDPHE 12563 39.56389 –106.41806 FP, MI, AE, S, N, TE 

76 Cross Creek at Minturn intake CSU

DOW-RW

E3_CRSSMIN98

39.5650039.56474

–106.41639–106.41642

O, FP, TE, MI, AE, NFP, MI, TE

77 Gravel Pit: Cross Creek above Tailings Outfall USGS 393400106244701 39.56665 –106.41364 FP, TE, MI, N 

78 Cross Creek near Minturn, CO USGS

CDPHE

0906510009065100

39.56805 –106.41202 AE, O, FP, TE, MI, S, N

FP, TE, R, MI, AE, S, N, O

1957–1963, 1967-200

79 Cross Creek near mouth EMSSA

CDNR

USGSUSGS

T-18MINT03393413106242301393413106242300

39.5697239.5701539.57026

–106.40778–106.40701–106.40697

O, FP, MI, N, TEFP, MI, TEFP, MI, S, TEFP, MI, TE

82 Eagle River below Cross Creek DOW-RW 3288 39.57093 –106.40597 FP, TE 

83 Eagle River below Cross Creek USGS

CDNR

USEPA

393422106242001393422106242001393422106242001

39.57276 –106.40614 FP, TE, MI, N

FP, MI, TEFP, MI, N, TE

84 Eagle River below Cross Creek EMSSA

CSU

DOW-RW

E-14E1_BCRSS3290

39.5747239.5747239.57493

–106.40694–106.40750–106.40850

O, FP, MI, N, TEFP, NFP, MI, TE

88 Eagle River below Cross Creek EMSSA

DOW-RW

E-153291

39.5769439.57606

–106.41139–106.41015

O, FP, MI, N, TETE
Table 5. Historic and current surface-water quantity and quality sites in the Eagle River watershed, Colorado.—Continued [no., number; USGS, U.S. Geological Survey; CDPHE, Colorado Department of Public Health and Environment; CO, Colorado; WWTP, wastewater treatment plant; CSU, ColGRC, Grand River Consulting, EMSSA, Eagle Mine Superfund Site Assessment; DOW-RW, Division of Wildlife, River Watch; CDNR, Colorado Division of Natural ResourceIncorporated; CDOT, Colorado Department of Transportation; ERWSD, Eagle River Water and Sanitation District; USFS, U.S. Forest Service; USEPA, U.S. Environmental Proproperties; MI, major ions; TE, trace elements; O, other constituents; AE, aquatic ecology; S, sediment; N, nutrients; R, radionuclide] Site no. Site name Data sources Site identifiers Latitude Longitude Type of data Period of discharge record (water year) 

89 Unnamed tributary Eagle River above Minturn USGS 393443106245201 39.57860 –106.41503 FP, MI, S, TE 

90 Eagle River above Minturn, CO USGS CSU EMSSA 393454106252201 E5_MIN E5_MIN 39.58165 39.58174 –106.42336 –106.42332 FP, MI, S, TE O, FP, TE, MI, AE FP, MI, TE 

92 Martin Creek at mouth USGS 393454106252301 39.58165 –106.42364 FP, MI, S, TE 

93 Eagle River at county bridge DOW-RW 39 39.58190 –106.42358 FP, MI, TE 

94 Eagle River at Minturn CDPHE EMSSA E-21 E-21 39.58940 –106.43139 FP, MI, AE, N, TE FP, MI, TE 

95 Grouse Creek at mouth USGS 393543106260001 39.59526 –106.43392 FP, MI, S, TE 

96 Game Creek at mouth USGS 393548106255201 39.59665 –106.43170 FP, MI, S, TE 

97 Eagle River below Minturn, CO USGS EMSSA 393550106262001 E-22 39.59744 39.59778 –106.43356 –106.43361 FP, TE O, FP, MI, N, TE 

100 Eagle River above Gore Creek near Minturn, CO USGS ASI CDPHE DOW-RW 393627106264000 393627106264000 12503G 3292 39.60749 39.60789 39.60582 –106.44503 –106.44657 –106.44192 AE, O, FP, MI, S, N, TE FP, MI, TE FP, TE, MI, AE, S, N FP, MI, TE 

102 Gore Creek at Upper Station, near Minturn, CO USGS ASI 09065500 09065500 39.62582 –106.27808 AE, O, FP, TE, MI, S, N FP, MI, TE 1948–1956, 1964–20103 Black Gore Creek above Black Lake USGS ASI 393212106125800 393212106125800 39.53665 –106.21669 O, FP, MI, S, N, TE FP, MI, TE 

105 Black Gore Creek below Black Lake No. 2 USGS ASI 393307106133200 393307106133200 39.55193 –106.22614 O, FP, MI, S, N, TE FP, MI, TE 

106 Polk Creek above US6 CDOT PC-2 39.59018 –106.24166 FP, MI, N, TE 107 Polk Creek at Interstate 70 USGS 393527106143500 39.59082 –106.24364 O, FP, MI, S, N, TE 

108 Miller Creek near mouth CDOT UN-1 39.59556 –106.25167 FP, MI, N, TE 

110 Black Gore Creek near Minturn, CO USGS CDOT 09066000 BG-2 39.59637 39.59641 –106.26503 –106.26421 AE, O, FP, MI, S, N, TE FP, MI, N, TE 1948–1956, 1964–20

111 Black Gore Creek near Vail, CO USGS ASI 09066050 09066050 39.62332 –106.28030 AE, O, FP, MI, S, N, TE FP, MI, TE 1974–1979 

112 Gore Creek below Black Gore Creek near Vail, CO USGS 393737106165900 39.62693 –106.28364 O, FP, TE, R, MI, AE, S, N 

113 Gore Creek above Bighorn Creek near Vail, CO USGS 393807106174600 39.63526 –106.29669 O, FP, MI, S, N, TE 

114 115 Bighorn Creek near Minturn, CO Bighorn Creek near Vail, CO USGS USGS 09066100 393813106174500 39.63999 39.63792 –106.29336 –106.29687 O, FP, MI, S, N, TE AE 1964–2008 

116 Pitkin Creek near Minturn, CO USGS 09066150 39.64360 –106.30253 O, FP, MI, S, N, TE 1967–2008 

117 Gore Creek at Bighorn Subdivision below 

Pitkin Creek

USGS

ASI

CDPHE

USGS

393831106181900393831106181900393831106181900393836106182500

39.6419339.64332

–106.30586–106.30753

O, FP, MI, S, N, TEFP, MI, TEFP, TE, R, MI, AE, S, N, OAE, FP

119 Gore Creek below Katsos USGS 393848106185900 39.64600 –106.31699 AE 
Table 5. Historic and current surface-water quantity and quality sites in the Eagle River watershed, Colorado.—Continued[no., number; USGS, U.S. Geological Survey; CDPHE, Colorado Department of Public Health and Environment; CO, Colorado; WWTP, wastewater treatment plant; CSU, ColGRC, Grand River Consulting, EMSSA, Eagle Mine Superfund Site Assessment; DOW-RW, Division of Wildlife, River Watch; CDNR, Colorado Division of Natural ResourceIncorporated; CDOT, Colorado Department of Transportation; ERWSD, Eagle River Water and Sanitation District; USFS, U.S. Forest Service; USEPA, U.S. Environmental Proproperties; MI, major ions; TE, trace elements; O, other constituents; AE, aquatic ecology; S, sediment; N, nutrients; R, radionuclide]

Site

no.

Site name Data

sources

Site

identifiers Latitude Longitude Type of data

Period of 

discharge record

(water year)

120 Booth Creek near Minturn, CO USGS

USGS

09066200393849106192000

39.6483239.64693

–106.32300–106.32281

AE, O, FP, MI, S, N, TEAE

1965–2008 

122 Gore Creek above well field, near Vail, CO USGS

ASI

393844106192100393844106192100

39.64554 –106.32308 O, FP, MI, S, N, TE

FP, MI, TE

123 Gore Creek at Booth Creek Road USGS 393851106193100 39.64554 –106.32577 AE, FP 

124 Gore Creek at Golf Course at Vail, CO USGS 393844106195300 39.64533 –106.33204 FP, MI, N, TE 

125 Gore Creek at Vail, CO USGS

ASI

0906625009066250

39.64242 –106.34589 O, FP, MI, S, N, TE

FP, MI, TE

1974–1979 

126 Gore Creek at Vail WWTP Intake USGS 393826106212900 39.64036 –106.35864 O, FP, TE, MI, AE, S, N 

127 Gore Creek downstream of Pulis Bridge USGS 393825106213400 39.64026 –106.36003 AE, FP 

128 Gore Creek at bike path bridge DOW-RW 526 39.63876 –106.36458 FP, MI, TE 

129 Gore Creek below golf course, at Vail, CO USGS 393825106220000 39.64026 –106.36725 O, FP, MI, S, N, TE 

130 Mill Creek on Vail Mountain USGS 393726106212000 39.62527 –106.35617 AE 

131 Mill Creek at ski area at Vail, CO USGS

ASI

393814106221500393814106221500

39.63721 –106.37099 O, FP, MI, S, N, TE

FP, MI, TE

132 Mill Creek near Vail, CO USGS

USGS

393824106221700393827106222100

39.6399139.64075

–106.37211–106.37266

AE, O, FP, MI, S, N, TEO, FP, TE, MI, AE, N

134 Gore Creek at Middle Creek USGS 393826106223800 39.64104 –106.37782 AE, FP 

135 Middle Creek near Minturn, CO USGS 09066300 39.64571 –106.38189 O, FP, MI, S, N, TE 1965–2008 136 Middle Creek near Vail, CO USGS 393836106230100 39.64320 –106.38391 AE 

137 Gore Creek above STP near Vail, CO USGS 393901106231400 39.64167 –106.38893 O, FP, TE, MI, AE, N 

139 Gore Creek above Red Sandstone Creek at Vail, CO USGS

USGS

ERWSD

ASI

CDPHE

0906632509066310090663250906631009066310

39.6410039.64110

–106.39473–106.39420

FPAE, O, FP, MI, S, N, TEFP, TE, MI, AE, NFP, MI, N, TEFP, MI, AE, N, TE

2000–20081988–1999

140 Gore Creek below Vail WWTP outfall at Vail, CO USGS

ERWSD

393829106234000393829106234000

39.64096 –106.39493 FP

FP, TE, MI, AE, N

141 Red Sandstone Creek near Minturn, CO USGS 09066400 39.68276 –106.40142 FP 1964–2008 142 Red Sandstone Creek near Vail, CO USGS 393852106234300 39.64776 –106.39619 AE 

143 Red Sandstone Creek near Vail, CO USGS 393841106234200 39.64470 –106.39594 AE 

144 Red Sandstone Creek at mouth at Vail, CO USGS 393829106234400 39.64132 –106.39571 O, FP, MI, S, N, TE 

145 Gore Creek below WWTP USGS 393826106235300 39.64018 –106.39852 AE, FP 

146 Gore Creek below Red Sandstone Creek at Vail, CO USGS

ASI

393823106240000393823106240000

39.63947 –106.40002 O, FP, MI, S, N, TE

FP, MI, N, TE

148 Gore Creek 0.5 miles downstream of WWTP ERWSD GC1/2MDNSTP 39.63750 –106.40130 FP 

149 Gore Creek 1 mile downstream of WWTP ERWSD GC1MDNSTP 39.63361 –106.40917 FP 

150 Buffehr Creek near Vail, CO USGS 393801106244800 39.63360 –106.41392 AE, FP 

151 Gore Creek below Buffehr Creek near West Vail, CO USGS 393756106244300 39.63185 –106.41263 O, FP, MI, S, N, TE 
Table 5. Historic and current surface-water quantity and quality sites in the Eagle River watershed, Colorado.—Continued [no., number; USGS, U.S. Geological Survey; CDPHE, Colorado Department of Public Health and Environment; CO, Colorado; WWTP, wastewater treatment plant; CSU, ColGRC, Grand River Consulting, EMSSA, Eagle Mine Superfund Site Assessment; DOW-RW, Division of Wildlife, River Watch; CDNR, Colorado Division of Natural ResourceIncorporated; CDOT, Colorado Department of Transportation; ERWSD, Eagle River Water and Sanitation District; USFS, U.S. Forest Service; USEPA, U.S. Environmental Proproperties; MI, major ions; TE, trace elements; O, other constituents; AE, aquatic ecology; S, sediment; N, nutrients; R, radionuclide] Site no. Site name Data sources Site identifiers Latitude Longitude Type of data Period of discharge record (water year) 

152 Gore Creek 1.5 miles downstream of WWTP ERWSD GC15MDNSTP 39.62944 –106.41472 FP 

153 Gore Creek at West Vail exit USGS 393738106251000 39.62721 –106.42003 O, FP, MI, S, N, TE 

154 Gore Creek 2 miles downstream of WWTP ERWSD GC2MDNSTP 39.62556 –106.42194 FP 

155 Gore Creek at Stephens Park USGS 393715106253600 39.62082 –106.42725 AE, FP 

156 Gore Creek at West Vail, CO USGS 393713106253900 39.62026 –106.42809 O, FP, MI, S, N, TE 

157 Gore Creek at mouth CDPHE 000074 39.61675 –106.43608 FP, TE, R, MI, AE, S, N 

160 Gore Creek at mouth, near Minturn, CO USGS ASI 09066510 09066510 39.60943 –106.44781 AE, O, FP, TE, R, MI, S, N FP, MI, TE 1996–2008 

161 Eagle River below Gore Creek USGS ASI 393638106271401 393638106271401 39.61054 –106.45447 FP, MI, S, TE FP, MI, TE 

163 Eagle River below Gore Creek below Eagle-Vail Intake at Dowds Junction USGS DOW-RW 393711106275200 151 39.61971 39.61935 –106.46503 –106.46546 O, FP, TE, MI, AE, S, N FP, MI, TE 

164 SC00508117BCA Eagle-Vail USGS 393708106291701 39.61888 –106.48864 FP, MI, N, TE 

165 Beaver Creek downstream Beaver Lake CDPHE 12542D 39.56536 –106.53480 FP, MI, AE, S, N, TE 166 Beaver Creek above Avon, CO USGS 393501106313200 39.58361 –106.52556 AE, O, FP, MI, S, N, TE 167 Beaver Creek above Town USGS 393552106311800 39.59776 –106.52225 AE 168 Beaver Creek at top of Golf Course at Avon, CO USGS 393633106311000 39.60917 –106.51853 AE 169 Beaver Creek at Avon, CO USGS 09067000 39.62971 –106.52281 AE, O, FP, MI, S, N, TE 1974–2008 

171 Beaver Creek near mouth USGS CDPHE CDPHE 393752106312700 000143 12541 39.63119 39.63111 –106.52167 –106.52139 AEFP, TE, MI, AE, S, N FP, MI, AE, S, N, TE 

172 Eagle River at Avon DOW-RW 41 39.63187 –106.52228 FP, MI, TE 

173 Eagle River at Avon, CO USGS CDPHE CSU ERWSD CDPHE 09067005 09067005 09067005 09067005 12503D 39.63212 39.63194 –106.52422 –106.52500 AE, O, FP, R, MI, S, N, TE FP, TE, MI, AE, N O, FP, TE, MI, AE FP, TE, MI, AE, N FP, TE, MI, AE, S, N 1989–2000 

175 Eagle River at Edwards CDPHE 12502E 39.63334 –106.52500 FP, TE, MI, AE, S, N 

176 Eagle River below WWTP at Avon, CO USGS ERWSD 09067020 09067020 39.63500 –106.53250 FPFP, TE, MI, AE, N 2000–2008 

177 June Creek USGS 394005106330001 39.66764 –106.55298 FP, MI, N, TE 

178 Eagle River below Beaver Creek EMSSA

DOW-RW

E-283293

39.6399039.64006

–106.56218–106.56226

O, FP, MI, N, TEFP, MI, TE

180 Eagle River at Edwards, CO USGS

CDPHE

393845106353000393845106353000

39.64582 –106.59226 AE, O, FP, MI, S, N, TE

FP, TE, R, MI, AE, S, N, O

181 Berry Creek USGS 393940106345501 39.66098 –106.58173 FP, MI, N, TE 

182 West Lake Creek near Edwards, CO USGS 393523106364700 39.58972 –106.61306 AE, O, FP, MI, S, N, TE 

183 East Lake Creek USGS 393720106370001 39.62211 –106.61607 FP, TE 
Table 5. Historic and current surface-water quantity and quality sites in the Eagle River watershed, Colorado.—Continued[no., number; USGS, U.S. Geological Survey; CDPHE, Colorado Department of Public Health and Environment; CO, Colorado; WWTP, wastewater treatment plant; CSU, ColGRC, Grand River Consulting, EMSSA, Eagle Mine Superfund Site Assessment; DOW-RW, Division of Wildlife, River Watch; CDNR, Colorado Division of Natural ResourceIncorporated; CDOT, Colorado Department of Transportation; ERWSD, Eagle River Water and Sanitation District; USFS, U.S. Forest Service; USEPA, U.S. Environmental Proproperties; MI, major ions; TE, trace elements; O, other constituents; AE, aquatic ecology; S, sediment; N, nutrients; R, radionuclide]

Site

no.

Site name Data

sources

Site

identifiers Latitude Longitude Type of data

Period of 

discharge record

(water year)

184 Lake Creek near Edwards, CO USGS

CDPHE

0906720012502D

39.6474939.64807

–106.60920–106.60955

AE, O, FP, MI, S, N, TEFP, MI, AE, S, N, TE

1994–2008 

186 Eagle River above Edwards WWTP DOW-RW 3294 39.65303 –106.62098 TE 

187A Eagle River 50 feet upstream Squaw WWTP ERWSD ER50FTUPSWWTP 39.65250 –106.62361 FP, TE, MI, AE, N 

187B Eagle River 50 feet downstream Squaw WWTP ERWSD ER50FTDNSWWTP 39.65250 –106.62361 FP, TE, MI, AE, N 

188 Eagle River below Edwards WWTP DOW-RW 3295 39.65419 –106.62772 FP, MI, TE 

189 Squaw Creek USGS

CDPHE

39393010638200112502C

39.6583639.65838

–106.63819–106.63819

AE, O, FP, TE, MI, S, NFP, MI, AE, S, N

190 Eagle River at Eagle Springs golf course CDPHE 12502A 39.69056 –106.66000 FP, TE, MI, AE, S, N 191 Eagle River at Eagle Springs golf course near 

Wolcott, CO

USGS

CDPHE

394129106393300394129106393300

39.69138 –106.65976 AE, O, FP, MI, S, N, TE

FP, TE, MI, AE, N

193 Eagle River at Wolcott, CO CDPHE

DOW-RW

125023296

39.7013939.70144

–106.67833–106.67805

FP, MI, AE, N, TEFP, MI, TE

194 Alkali Creek near Wolcott, CO USGS 09067300 39.75610 –106.67059 FP 1959–1965 

195 Alkali Creek near Wolcott CDPHE 12575 39.72948 –106.67875 FP, MI, AE, S, N, TE 

196 Alkali Creek below Muddy Creek, near Wolcott, CO USGS 394259106405900 39.71639 –106.68306 O, FP, MI, AE, S, N, TE 

197 Milk Creek 2 miles above mouth USGS 394415106424200 39.73750 –106.71167 O, FP, MI, S, N, TE 

198 Milk Creek at mouth near Wolcott, CO USGS 394240106433200 39.71164 –106.70942 O, FP, MI, N, TE 

199 Milk Creek at mouth, near Wolcott USGS 394240106423200 39.71164 –106.70933 O, FP, MI, AE, S, N, TE 

200 Milk Creek at I-70 near Wolcott CDPHE 12574 39.71115 –106.70928 FP, MI, AE, S, N, TE 

201 Eagle River below Milk Creek near Wolcott, CO USGS 394220106431500 39.70554 –106.72142 AE, O, FP, TE, R, MI, S, N 

202 Eagle River at Hwy 6 Bridge above Eagle, CO USGS 393937106485400 39.66026 –106.81559 FP, MI, N, TE 

203 Eagle River at Eagle DOW-RW 3297 39.65680 –106.82516 FP, MI, TE 

204 Eagle River at Hwy 6 bridge DOW-RW 686 39.65679 –106.82521 FP, MI, N, TE 

206 Eby Creek at mouth near Eagle, CO, Site 1B USGS

CDPHE

39393010649400112520

39.6594439.66000

–106.82975–106.82966

FP, TE, MI, NFP, MI, AE, S, N

208 Eagle River above Brush Creek at Eagle, CO USGS

CDPHE

39385210650320012501

39.6485639.64859

–106.84332–106.84331

AE, O, FP, MI, S, N, TEFP, MI, AE, S, N, TE

209 West Brush Creek at Adam camp ground USFS 35-005 39.46994 –106.72910 FP, MI, AE, N, TE 210 West Brush Creek above Sylvan Lake near Eagle USGS 392814106434600 39.47055 –106.72935 O, FP, TE, MI, AE, N 

211 West Brush Creek below Sylvan Lake USFS 35-004 39.47917 –106.73750 FP, MI, AE, N, TE 

212 East Brush Creek at Yeoman Park, near Eagle, CO USGS

USFS

USGS

0906770009067700393045106404000

39.5041539.50417

–106.67809–106.67804

FP, MI, TEFP, MI, AE, N, TEO, FP, MI, AE, S, N, TE

1966–1972 

213 Nolan Creek at Middle Bridge USFS 35-006 39.52599 –106.69230 FP, MI, AE 

214 East Brush Creek at Fisher Gulch USFS 35-002 39.53750 –106.74167 FP, MI, AE, N, TE 

215 East Brush Creek above confluence USGS 393221106450700 39.53920 –106.75255 AE, O, FP, MI, S, N, TE 

216 East Brush Creek at mouth near Eagle USGS 393227106451700 39.54082 –106.75531 O, FP, TE, MI, AE, S, N 
Table 5. Historic and current surface-water quantity and quality sites in the Eagle River watershed, Colorado.—Continued [no., number; USGS, U.S. Geological Survey; CDPHE, Colorado Department of Public Health and Environment; CO, Colorado; WWTP, wastewater treatment plant; CSU, ColGRC, Grand River Consulting, EMSSA, Eagle Mine Superfund Site Assessment; DOW-RW, Division of Wildlife, River Watch; CDNR, Colorado Division of Natural ResourceIncorporated; CDOT, Colorado Department of Transportation; ERWSD, Eagle River Water and Sanitation District; USFS, U.S. Forest Service; USEPA, U.S. Environmental Proproperties; MI, major ions; TE, trace elements; O, other constituents; AE, aquatic ecology; S, sediment; N, nutrients; R, radionuclide] Site no. Site name Data sources Site identifiers Latitude Longitude Type of data Period of discharge record (water year) 

217 Brush Creek near Eagle, CO USGS USFS 09068000 09068000 39.55721 –106.76309 FP, TE, R, MI FP, MI, AE, N, TE 1951–1972 

218 Salt Creek above Trail Gulch near Eagle, CO USGS 393558106452200 39.59943 –106.75670 FP, MI, TE 

219 Salt Creek below Brush Creek near Eagle, CO USGS 393655106453001 39.61420 –106.76379 FP, TE 

220 Abrams Creek USGS 393710106492001 39.61903 –106.82055 FP, MI, N, TE 

221 Brush Creek at Highway 6 CDPHE 12503 39.64622 –106.84109 FP, MI, AE, S, N, TE 

222 Brush Creek at Mouth at Eagle WWTP CDPHE 12530 39.64660 –106.84117 FP, MI, AE, S, N, TE 

223 Brush Creek at Mouth near Eagle, CO USGS 393851106503400 39.64818 –106.84362 AE, O, FP, TE, MI, S, N 

224 Eagle River at Gypsum, CO USGS 09069000 39.64999 –106.95227 AE, O, FP, TE, R, MI, S, N 

225 Eagle River at Gypsum, CO DOW-RW DOW-RW 3298 3331 39.64997 39.64997 –106.95230 –106.95232 FP, MI, TE FP, MI, TE 

227 Eagle River at Gypsum, CO CDPHE 000052 39.64989 –106.95221 FP, TE, R, MI, AE, S, N 

228 Red Creek Tributary USFS 37-001 39.47077 –106.85146 FP, MI, TE 

229 Gypsum Creek near Gypsum, CO USGS 09069500 39.54554 –106.93477 FP, TE, R, MI 1951–1955, 1966–19

230 Gypsum Creek at Gypsum, CO USGS USGS 393842106571900 393842106571901 39.64492 –106.95077 FP, MI, N, TE FP, MI, N, TE 

232 Gypsum Creek at Gypsum, CO USGS CDPHE 09069900 12510 39.64887 39.64887 –106.95227 –106.95233 AE, O, FP, TE, MI, S, N FP, MI, AE, S, N, TE 

233 Eagle River below Gypsum, CO USGS 09070000 39.64943 –106.95366 FP, MI, S, N, TE 1947–2008 234 Eagle River below Gypsum, CO DOW-RW 42 39.65505 –106.97821 FP, MI, TE 

235 Eagle River at Mouth, near Dotsero, CO USGS USEPA 09070400 09070400 39.64615 –107.05674 FP, R, MI FP, O, TE 
Data Sources, Compilation, Review, and Analysis 23

Figure 7. Locations of surface-water-monitoring sites within the Eagle River watershed, Colorado, 1947–2007.

Upper Eagle subwatershed

EXPLANATION

Urban areas

Gore Creek subwatershed

Lower Eagle subwatershed

Middle Eagle subwatershed

Streams

Highways

Water-monitoring site and site number 

 (site name given in table 5)

!(

!(

!( !(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!( !( !( !( !( !(

!(

!(

!(!( !(

!(

!(

!(

!(

!(

!(

!( !(!(

!( !(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(!( !( !(

!(

!(

!(

!(!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(!(

!(

!(

!(

!(

!(

!(!(

!(

!(

!(!(

!(

!(

!(

!(

!(

!(!( !(!(

!(

!( !( !(

!( !( !( !( !(

!(

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!( !(

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!( !(!( !(

!(

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!( !(!(!( !( !( !( !(

!( !( !( !( !( !( !( !( (! !( !(!( !( !( !( !(!( !(!(!(!(!(!( !( !(

!(

!( !( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(!(!(!(

!(

!(

197

106°15'

106°45'

39°45'

39°30'

0 5 10 KILOMETERS

0 5 10 MILES

Base from U.S. Geological Survey digital data, 2007,

Universal Transverse Mercator projection

Zone 13 

!(

235

234

233

232 230 222

221

220 219

218

217

216

215

229 214

213

212

211

210

209 228

182

165

166

167

164 168

176

178 180 184

183

187A

187B

188

189

190

191

193

196

195

194

197

198 200

199

201

186

181

177

169-175

163

149-157

141

160

161

100

126-148

29-97

17

15

14

16

13 28 20

27 12

11

10

24

22

8

9

6 1 2 3

57 4

208 206

223 202 224-227

203-204

103

105

107 106

110 108

102

111

112 130

115113

114

116

117

119-124

125

24

70

70
24 Assessment of Surface-Water Quantity and Quality, Eagle River Watershed, Colorado, 1947–2007

Figure 8. Locations of surface-water-monitoring sites in the lower Eagle River subwatsershed, Colorado, 1947–2007.

!13

!

!

! !

!

!

!

!

! !!

!

!

!

! !

!!

!

!

!

!

229

211

209

210

228

212

213

214

215

216

217

218

219 220

230 232

233

234 224-227

235

70 !

!

! !!

!

!

EXPLANATION

Urban areas

City

Lower Eagle subwatershed

Streams

Highways

Surface water-quality site and site number

 (site name given in table 5)

0 4 8 KILOMETERS

0 4 8 MILES

106°45'

107°00'

39°45'

39°30'

Base from U.S. Geological Survey digital data, 2007,

Universal Transverse Mercator projection

Zone 13 

!!

!!

!

! !

!

221

223

208

222

203

204

206 202

6 Eagle

Gypsum

70 6

Eagle
Data Sources, Compilation, Review, and Analysis 25

Figure 9. Location of surface-water-monitoring sites in the middle Eagle River subwatershed, Colorado, 1947–2007.

EXPLANATION

Urban areas

City

Middle Eagle subwatershed

Streams

Highways

Surface water-quality site and site number

 (site name given in table 5) !194

!

!

!

!

!

!

!

!

!

!

!

!

!

!

!! !

!

!!

!

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!

!

!

!

!

!

!

!

!

!

!

!

!

178

Base from U.S. Geological Survey digital data, 2007,

Universal Transverse Mercator projection

Zone 13 

0 5 10 KILOMETERS

0 5 10 MILES

Avon

39°40'

106°40'

106°30'

39°30'

6

131

70

197

199 198

200

201 193

190

189

188

187A 187B

186

191

196

195

194

182

183

184 180

177

165

166

161

163

167

!

178

181

167

168

164

169

173

171

172

175

176

70

6

Avon
26 Assessment of Surface-Water Quantity and Quality, Eagle River Watershed, Colorado, 1947–2007

Figure 10. Location of surface-water-monitoring sites in the Upper Eagle River subwatershed, Colorado, 1947–2007.

Urban areas

City

Upper Eagle subwatershed

Streams

Highways

EXPLANATION

Superfund boundary

Surface water-quality site and site number

 (site name given in table 5) ! 72

!

!

!

!! !! !!

!!

! ! !

! !

!

!

!! !!!!

!!

!!! ! !

!!!!!

!!

!

!

!!

!

!! !!!!!!!!!

!!! !!

!

!

!!

! 100

97

95 96

94

64

63

61

59

32

31 30

29

28 20 13

27

12

11

10

9 5 4

3

2 1

67

24 8

22

17 15

16 14

90-93 ! 89

24

!

!

!!

!

!

!

!

!!! !!!

! !

!!

!

!

!

51

52

56

58

57

54

50

49

48 47 46 4544

4342

41 40

39

37 35

34

!

89

!

!

!

!!

! !

!

!

!

! !

!

!

!

69 70

68

67

66

73 74

76

77 78

79 72

82

83

84

88

Base from U.S. Geological Survey digital data, 2007,

Universal Transverse Mercator projection

Zone 13 

0 4 8 KILOMETERS

0 4 8 MILES

Red Cliff

Minturn

39°20'

39°30'

106°30'

106°20'

!

!

24

24
Data Sources, Compilation, Review, and Analysis 27

Figure 11. Location of surface-water-monitoring sites in the Gore Creek subwatershed, Colorado, 1947–2007.

! !

!

!

!

!

!

! !

!

!

!

!

!

!

!

!

! !

! !

!

!! ! ! ! ! !! ! ! ! ! ! !

!

!

103

105

106

107

108 110

!

! !

!

!

!

!

!

!

!

!

!

70

102

!194

111

112

113

114

116

117

119

122123

120

125 124

126

127 134 132

142 135

141

143

146

150

154

160

157

156

155

153 152

148

145 149

151

144 137 136

139-140

130

131 129 128

EXPLANATION

Urban areas

City

Gore Creek subwatershed

Streams

Highway

Surface water-quality site and site number

 (site name given in table 5)

Base from U.S. Geological Survey digital data, 2007,

Universal Transverse Mercator projection

Zone 13 

106°15'

106°25'

39°40'

39°35'

0 2 4 KILOMETERS

0 2 4 MILES

Vail

Gilman

Belden
28 Assessment of Surface-Water Quantity and Quality, Eagle River Watershed, Colorado, 1947–2007

Surface-Water Quality

Data Sources and Compilation

Available surface-water quality data were obtained from 

local, State, and Federal agencies and entered into a relational 

database to assist in the analysis of water-quality conditions 

in the ERW 1947–2007. Digital data were obtained from the 

USEPA web-based STORage and RETrieval (STORET, 

http://www.epa.gov/storet/dbtop.html) system, the USGS 

web-based National Water Information System (NWIS, 

http://waterdata.usgs.gov/nwis), and from local agencies and 

stakeholders. The data used in the analysis described in this 

report are available in a web-based repository at http://rmgsc.

cr.usgs.gov/cwqdr/Eagle/index.shtml (5/21/2011). A summary 

of the data sources and data abundance is provided in table 1.

Incorporation of multiple-data sources into a common 

repository required combining data into a single, uniform 

data structure. Data compilation, including changes to data 

format and consistent scaling for each parameter code as well 

as aggregation of similar constituents into common parameter 

codes, was done to homogenize the datasets and simplify the 

data structure. The determination of the chemical properties of 

waters can result in censored data because of analytical limits 

of the laboratory analysis. Censored data provide a range of 

possible values expressed as (1) less than the reporting limit, 

or (2) values greater than the maximum value reported. For 

left-censored data in this report (data reported as less than 

the reporting limit), the most common reporting limit (most 

frequently used) for each parameter code was kept; censored 

values greater than the common reporting limit were deleted; 

censored values below the common reporting limit were 

converted to the common reporting limit. For right-censored 

data in this report (data reported as greater-than the maximum 

value reported), the most common maximum value reported 

(most frequently used) for each parameter code was kept; 

the values greater than the maximum value reported were set 

equal to the censored value. In addition, aggregation of parameters was done following guidance outlined in Mueller and 

others (1995) to simplify the analysis procedures. This aggregation was done for nutrients such as nitrate, nitrite, ammonia, 

un-ionized ammonia, total phosphorous, and orthophosphate. 

Spatial comparisons of water-quality site locations were 

done to determine if collection of water-quality samples 

occurred at the same location under different site identifications. Aggregation of multiple sites into a single identifier 

provides greater efficiency and increased statistical merit 

during analysis. The validity of the aggregation of sites was 

determined by evaluation of the hydrologic complexity of a 

location and its proximity to additional site locations. Care was 

taken when aggregating two sites with the same source agency; 

it was assumed that each agency already had taken care not 

to duplicate sites unnecessarily. In some instances, however, 

aggregating more than one site from the same source agency 

was deemed warranted. This aggregation most often was 

done when two sites were in close proximity, and one of the 

sites had few samples (one or two samples as compared with 

dozens). A summary of the available data for these sites along 

with the aggregation of these sites is presented in table 5 and 

figures 7–11. When sites are referenced throughout this report, 

the subwatershed is included in addition to the site number.

Data Review and Analysis

Review of the water-quality datasets was completed 

prior to analysis through several quality-assurance methods. 

Initial data review began with identification of gross errors in 

the data through use of USEPA guidelines for typical ranges 

of values for constituents and properties of natural waters 

(National Park Service, 1998). Values outside these identified 

ranges provided a basis to characterize samples as suspect. 

In natural waters, the electrostatic charges of positive ions 

(cations) and negative ions (anions) are balanced. The ioniccharge balance of a water-quality sample was evaluated for 

samples with sufficient data (at a minimum samples must have 

values reported for calcium, magnesium, sodium, potassium, 

alkalinity (or acid-neutralizing capacity), sulfate, and chloride) using methods outlined in Hem (1989). Samples with 

excessive differences in charge-balances (usually greater than 

5-percent difference) were considered suspect and reviewed 

to determine if they should be removed from the dataset. 

An additional comparison between filtered (dissolved) and 

unfiltered (total) concentrations for a constituent also were 

applied to samples that had both analytical results available. 

If the filtered concentrations were greater than the unfiltered 

concentrations, the samples were removed from the dataset.

Samples also were reviewed in the context of geologic 

setting, land use, season, consistency, and comparison to 

values from adjacent sites for validation. Questionable or 

inconsistent samples were removed from the dataset. Quality 

assurance results are presented in table 6. Samples lacking 

sufficient analytical results for ion-balance and filteredunfiltered comparisons were assumed to be accurate if the 

values were within the range of typical values. A large 

portion of the data has limited quality assurance review and 

may contain errors. Further exploration of the dataset was 

beyond the scope of this analysis. 

This report provides reconnaissance-level statistical summaries and comparisons of water-quality conditions and characteristics using available data within the ERW. An inclusive 

approach was taken to expand the number of samples and sites 

available for analysis in order to provide greater spatial and 

temporal coverage of water-quality conditions in the watershed. A large portion of the data has limited metadata and (or) 

quality-assurance data. Therefore, it is possible that some data 

may contain errors that were not detected during the waterquality data review. Assumptions regarding water-quality collection methods and laboratory-analytical techniques used on 

data from different data sources were made based on available 

information. No distinctions between water-quality data collection methods and laboratory-analytical techniques were made 

when metadata were unavailable to support these distinctions. 
Data Sources, Compilation, Review, and Analysis 29

Disparities between data from different sources resulting from 

differences in water-quality collection methods and laboratoryanalytical techniques may affect the precision and accuracy 

of the statistical results. Although the effect of methodological differences could not be quantified in this analysis, robust 

statistical methods were employed to limit the effect of outliers 

on statistical results of the analysis.

Summary statistics in this report were calculated using 

methods described in Helsel (2005) and in Helsel and Hirsch 

(1992) based on the number of samples available and the 

percentage of the data that was left-censored (nondetects). 

Summary statistics for minimum, 25th, 50th (median), and 

75th percentiles, and maximum are calculated using traditional 

statistical methods when the datasets included only uncensored data. For datasets with less than 50 percent nondetects, 

the Kaplan-Meier method (Helsel and Hirsch, 1992) was used; 

where 50–80 percent of the data were nondetects and there 

were more than 50 samples, the adjusted maximum likelihood 

estimator was used (Helsel, 2005).

Graphical representations of water-quality results are 

presented in this report using boxplots, bar graphs, line graphs, 

and maps. Boxplots are used to show the ranges of concentrations observed within particular groupings of data. These 

plots show a range of data including the 25th, 50th (median), 

and 75th percentiles of data for groupings with more than 

four samples. In map form, depictions of the median constituent concentrations from sampling sites within the ERW are 

displayed for sites with a minimum of five samples and a 

time span of 5 years between the first and last samples. These 

medians are normalized to the percentiles of data from the 

whole watershed as follows: (1) for sample-site medians less 

than the 25th percentile, (2) for sample-site medians between 

the 25th and less than the 50th percentile, (3) for sample-site 

medians between the 50th and less than the 75th percentile, 

and (4) for sample-site medians equal to or greater than the 

75th percentile.

Determination of temporal trends for select constituents 

was done using nonparametric statistical methods. Nonparametric statistical methods were selected because the 

statistical results are not strongly affected by outliers, and 

there are minimal assumptions regarding the distribution 

shape of the datasets (Helsel and Hirsch, 1992). Step-trend 

and monotonic-trend analyses were performed. Step trends are 

appropriate when identifiable, abrupt changes occur in either 

the hydrologic system or in the source area for water-quality 

constituents, resulting in two discrete groups of data (Helsel 

and Hirsch, 1992). For step-trend assessments, the Wilcoxon 

rank-sum test was used to compare the median values between 

two time periods defined as pre- and post-change periods 

(Helsel and Hirsch, 1992). The Peto-Prentice test was used if 

the concentration data included nondetects. 

Monotonic-trend assessments (single-direction, upward, 

or downward) were done on selected water-quality constituents to identify changes to stream conditions at sites with 

Table 6. Eagle River watershed quality-assurance results by sample source agency.

[No., number; USEPA, U.S. Environmental Protection Agency; --, no data; Count, the number of samples compared to the quality-assurance test; Rejected, the 

number of samples that failed the quality-assurance test]

Source agency No. of 

samples

Charge-balance

equation

Filtered 

and unfiltered

USEPA Typical

Range Guideline

Count/rejected Count/rejected Count/rejected

Surface-water quality

Advanced Sciences Inc. 299 --/-- 282/18 299/0

Colorado Department of Natural Resources 171 --/-- --/-- 171/0

Colorado Department of Public Health and Environment 2,340 --/-- 336/0 2,340/0

Colorado Department of Transportation 122 --/-- 68/0 122/0

Colorado Springs Utilities 262 --/-- 58/1 262/0

Division of Wildlife (River Watch) 539 --/-- 374/133 539/0

Eagle Mine Superfund Site Assessment 2,116 --/-- 819/209 2,116/0

Eagle River Water and Sanitation District 997 --/-- 6/1 997/0

Grand River Consulting 26 --/-- 25/0 26/0

U.S. Environmental Protection Agency 18 --/-- 1/0 18/0

U.S. Forest Service 53 --/-- --/-- 53/0

U.S. Geological Survey 9,085 1,432/4 929/173 9,085/2
30 Assessment of Surface-Water Quantity and Quality, Eagle River Watershed, Colorado, 1947–2007

sufficient data. To account for sampling bias and to ensure 

independence of the sample data, a subset of the data was used 

in each trend test. The subset limited the data to one sample 

each month (step-trend analysis) or one sample each season 

(monotonic-trend analysis) within the same calendar year in 

order to meet the assumptions and requirements, or both, of 

each test. Sites with sufficient data had (1) adequate seasonal 

characterization, (2) a minimum of 7-years of data with at 

least one sample collected after January 1, 2003, (3) less than 

50 percent censoring of the data, and (4) adequate distribution 

of samples in the first and last one-third of the record (Lanfear 

and Alexander, 1990). Monotonic trends in concentration data 

were tested using the seasonal Kendall test (Helsel and Hirsch, 

1992). The seasonal Kendall test accounts for seasonal effects 

in the concentration data through the separation and comparisons of data by each season. Where adequate streamflow 

data are available, and the amount of censored water-quality 

data is less than 8 percent, flow-adjusted concentration data 

were used in the trend analysis to account for the variation in 

concentrations that is related to streamflow (Helsel and Hirsch, 

1992). Trends in unadjusted concentrations may be due to 

trends in concentrations or trends in streamflow quantity or 

timing. Flow-adjusted analysis better quantifies changes in 

constituent concentrations over time that are not the result 

of changes in streamflow; therefore, where both trend tests 

have been evaluated, preference is given to flow-adjusted 

trends. Trend tests for cadmium, iron, manganese, and zinc 

excluded data from February and March for each year because 

of observed variability during this time period attributed to 

known hydrological processes (Colorado Department of Public Health and Environment and U.S. Environmental Protection Agency, 2000) that may not be well characterized based 

on assumptions and procedures used in the seasonal Kendall 

test, the Wilcoxon rank sum test, and the Peto-Prentice test.

In this report, temporal trends were evaluated based on 

statistical significance and are considered highly significant 

when the trend test reports a greater than 99-percent confidence level (p-value less than 0.01), significant when the trend 

test reports a greater than 95-percent confidence level (p-value 

less than 0.05), and weakly significant when the trend test 

reports a greater than 85-percent confidence level (p-value less 

than 0.15). For all trend-test results, the calculated level of significance (p-value) is given; for trend-test results with p-values 

less than 0.15, the trend direction (upward or downward) is 

reported; for highly significant and significant trends, the slope 

or magnitude of the trend also is reported. 

The trend magnitude from the seasonal Kendall test is the 

median slope of all pair-wise comparison of points used in the 

seasonal Kendall test. This slope is not the amount of change 

expected to be observed each year and does not require that 

the change in concentrations recognized in the test occur in 

any distribution within the trend period, so it is possible for a 

linear or nonlinear trend to be occurring. As a result, the slope 

better describes the trend observed over the entire trend period 

instead of an average annual slope. The trend slope should not 

be used to forecast future stream conditions.

Temporal trends have both a statistical significance and 

environmental significance. The trend magnitude provides 

information on the significance of the trend from an environmental perspective, but often is a subjective decision based 

on the context of the current stream conditions. It is important 

when reviewing trend summaries to consider the specific constituent of concern and any corresponding standard.

The Colorado Water Quality Control Commission 

(CWQCC), supported by the CDPHE, sets stream classifications and water-quality standards for rivers and other water 

bodies across the state; they also are required under Section 

303(d) of the Federal Clean Water Act to submit a list of 

Table 7. Federal Clean Water Act Section 303(d) listings for the Eagle River watershed.

[Cd, cadmium; Mn, manganese; Zn, zinc; Cu, copper; --, no data]

Reach Federal Clean Water Act Section 303(d) listing cycle1

1996 1998 20002 2002 2004 2006 2008

Black Gore Creek -- -- -- Sedimentation/

siltation

Sedimentation/ 

siltation

Sedimentation/ 

siltation

Sedimentation/ 

siltation

Cross Creek (except segment 1) Metals (other 

than mercury)

Cd, Mn, Zn -- Mn, Zn Cu, Zn Zn Cu, Zn

Eagle River–Belden to Gore confluence -- Cd, Mn, Zn -- Mn, Zn (entire 

reach), and Cu 

(above Rex Flats)

Cu, Zn Cu, Zn Cu3

, Zn

Eagle River–Gore confluence to 

Colorado River

Metals (other 

than mercury)

Mn -- -- -- -- --

1

Data obtained from U.S. Environmental Protection Agency National Assessment Database and http://www.cdphe.state.co.us/wq/Assessment/TMDL/303dlists.html, 

accessed July 2009.

2

2000 303(d) list was suspended.

3

Cu only on Eagle River from Belden to Highway 24 Bridge.
Data Sources, Compilation, Review, and Analysis 31

Figure 12. Colorado Department of Public Health and Environment stream-segment designations for the Eagle River watershed, Colorado 

(Colorado Department of Public Health and Environment and U.S. Environmental Protection Agency, 2008).

106°15'

106°45'

39°45'

39°30'

0 5 10 KILOMETERS

0 5 10 MILES

Base from U.S. Geological Survey digital data, 2007,

Universal Transverse Mercator projection

Zone 13 

Stream segment designations

EXPLANATION

Segment 1

Segment 2

Segment 3

Segment 4

Segment 5a

Segment 5b

Segment 5c

Segment 6

Segment 7a

Segment 7b

Segment 8

Segment 9

Segment 10

Segment 11

Segment 12

City

Vail

Avon

Eagle

Minturn

Red Cliff

Gilman

Belden

Gypsum

Dotsero

Wolcott

Edwards

identified waters within Colorado which have “water-qualitylimited segments still requiring Total Maximum Daily Loads” 

(Colorado Department of Public Health and Environment, 

2009). The water-quality standards are established to protect 

specific classified uses. In addition, numeric standards exist for 

physical, biological, inorganic, and metal constituents. Comparisons of water-quality conditions to available water-quality 

standards were done to provide environmentally relevant 

context to observations of stream conditions. The objective of 

this report is not to characterize or rate the “condition” of any 

stream, or to assess the impairment or health of the watershed. Available information on Section 303(d)-listed stream 

segments within the ERW is presented in table 7 to provide 

additional context to aid in the determination of the environmental significance of water quality in the ERW.

Surface-water-quality data were compared to CDPHE 

in-stream water-quality State standards, which are based on 

the stream-reach classification. The stream segments within 

the ERW (segments 1, 2, 3, 4, 5a, 5b, 5c, 6, 7a, 7b, 8, 9, 10, 11, 

and 12) are classified for cold-water aquatic life, recreational, 

domestic-water supply, and agricultural use. Stream segments 

generally are delineated at points on a water course that separate reaches with significant differences in classification and 

change, or both, in water-quality standard (Colorado Department of Public Health and Environment, 2008). Figure 12 

shows the location of defined stream segments in the ERW. 
32 Assessment of Surface-Water Quantity and Quality, Eagle River Watershed, Colorado, 1947–2007

Many State water-quality standards use Table Value 

Standards (TVS), some of which are based on site-specific 

hardness calculations. Calculations of hardness values at each 

site resulted from four different calculation methods from a 

regression analysis of site-specific data (Colorado Department of Public Health and Environment, 2008). The following 

calculations were done in decreasing order of preference: (1) 

for sites with 6 or more hardness samples during the low-flow 

period, hardness values were calculated as the lower 95th 

confidence interval about the mean hardness value for only the 

samples from the low-flow period; (2) for sites with 1–5 hardness samples during the low-flow period, hardness values were 

calculated as the mean hardness value for only those samples 

collected during the low-flow period; (3) for sites without 

low-flow hardness samples and 6 or more hardness samples, 

hardness values were calculated as the lower 95th confidence 

interval about the mean hardness value for all samples; (4) for 

sites without low-flow hardness samples and less than 6 hardness samples, hardness values were calculated as the mean 

hardness value for all samples.

CDPHE has established State standards for acute and 

chronic exposure levels for many constituents of in-stream 

water quality (http://www.cdphe.state.co.us/regulations/

wqccregs/index.html). The acute State standard refers to the 

level that is not to be exceeded by the concentration for either 

a single sample or is calculated as an average of all samples 

collected during a one-day period. The chronic State standard 

is defined as the level not to be exceeded by the concentration 

for either a single representative sample or calculated as an 

average of all samples collected during a thirty-day period. 

State standards for water temperature (chronic) in the ERW 

are specific to CDPHE Regulation 33 (effective September 1, 

2007) designating stream reaches above and below elevations 

of 7,000 ft.

Assessment of Surface-Water Quantity

Streamflow conditions of the Eagle River follow a 

consistent seasonal pattern. Low-flow conditions (base flow) 

typically occur in October–March, with the start of the snowmelt-runoff generally beginning in late March and early April 

(fig. 13). As the snowpack begins to melt, streamflows begin 

to rise and increase to peak streamflow conditions in late May 

and early June. As available snowpack levels are depleted in 

late spring and early summer, streamflow levels return to the 

base-flow conditions of the fall (fig. 13). Occasional increases 

in flow during the summer and fall months can occur because 

of precipitation events within the ERW.

Many sites within the ERW show patterns of wet and dry 

years. The mid 1980s and 1990s are two wet periods within 

the last several decades, separated by average to dry periods in 

1990 and 2000 (fig. 14). The wettest and driest years on record 

at most sites are 1984 and 2002, respectively (U.S. Geological Survey, 2007). Seasonal and multiyear patterns in streamflow can affect water quality through chemical processes and 

through dilution. Understanding the seasonal and multi-year 

patterns of streamflow within the watershed is important in 

interpreting patterns in water quality.

Variations in snowmelt timing can be important to 

water managers and can affect the streamflow characteristics 

throughout the year. Understanding runoff intensity and timing is important in order to properly manage the storage and 

release of snowmelt runoff in reservoirs. If snowmelt runoff is 

different than expected and if storage opportunities are missed, 

decreased water availability may result later in the year when 

municipal and agriculture demands increase.

The Eagle River contributes an average of 409,900 acreft per year to the Colorado River system (based on USGS 

streamflow-gaging station Eagle River below Gypsum, CO, 

09070000, water years 1947–2007; U.S. Geological Survey, 

2007). Much of the water that flows out of the ERW originates 

from snow accumulations during the winter months. The 

ERW is a complex system of tributaries, lakes, and reservoirs 

that supply year-round water for agriculture, industrial, and 

municipal uses. The largest storage structure in the ERW is 

Homestake Reservoir (45,000 acre-ft), located in the southeast part of the ERW (fig. 15). There are several other smaller 

reservoirs in the watershed used for recreation, irrigation, 

snowmaking, flow augmentation, and domestic-water supply. 

Homestake Reservoir is part of the transmountaindiversion system that moves water through the Continental 

Divide to supply water to cities east of the Continental Divide 

(U.S. Geological Survey, 2008). Diversions from the ERW 

into the reservoir began in 1966. Water is then conveyed 

through the Homestake Tunnel to the Arkansas River Basin, 

thereby depleting the ERW by an average of 30,580 acre-ft 

per year (fig. 15). Records indicate that the largest diversions 

from Homestake Reservoir occur May–July, with smaller 

diversions sporadically throughout the rest of the year (Colorado Division of Water Resources, 2009). The Homestake 

Tunnel is the largest diversion from the ERW and spans 

5.2 miles. The Ewing Ditch (constructed 1880), Wurtz Ditch 

(constructed 1929), Columbine Ditch (constructed 1931), also 

divert water from the upper Eagle River watershed across 

the Continental Divide into the Arkansas River Basin (Eagle 

River Watershed Plan, 1996). Average annual diversion totals 

from other diversion structures include the Wurtz Ditch with 

2,210 acre-ft; the Columbine Ditch with 1,520 acre-ft; and 

the Ewing Ditch with 820 acre-ft (fig. 15). Diversions in these 

and other ditches typically occur May–October and represent 

less than 8 percent of the annual total streamflow that originates in the ERW (fig. 15).

Homestake Reservoir also supplies water to the ERW. 

Releases from the reservoir are important to urban centers 

within the ERW. Large releases from the reservoir occur at two 

times during the year, March–April, and September–October. 

Dividing the ERW into smaller subwatersheds is a useful 

way to compare streamflow distributions and to understand 

water balances within the watershed. For this report, the 

ERW was divided into four subwatersheds: the Upper Eagle, 

Gore Creek, Middle Eagle, and Lower Eagle subwatersheds 
Assessment of Surface-Water Quantity 33

450 Site 66, 1990−2008

500

400

350

300

50

100

150

200

250

0

January February March April May June July August September October November December

Site 233, 1947−2008

500

1,000

1,500

2,000

2,500

0

January February March April May June July August September October November December

Streamflow, in cubic feet per second

Site 78, 1957−1964; 1968−2008

50

100

150

200

250

300

0

January February March April May June July August September October November December

Site 160, 1996−2008

100

200

300

400

500

600

700

0

January February March April May June July August September October November December

Monthly mean flow Mean annual flow

EXPLANATION

Figure 13. Hydrographs of selected sites in the Eagle River watershed, Colorado.
34 Assessment of Surface-Water Quantity and Quality, Eagle River Watershed, Colorado, 1947–2007

1950 1960 1970 1980 1990 2000

Site 233

Site 160

(includes

Site 157.1)

Site 116

Site 110

Site 78

Site 27

Site 66

Site 184

Missing data,

annual means unavailable for this period

Year

Figure 14. Lowess Smooth of annual-mean streamflow at selected sites in the Eagle River watershed, Colorado, 1947–2007.
Eagle River

409,900 acre-feet

92.1 percent

Brush Creek31,890 acre-feet7.2 percent Lake Creek

41,730 acre-feet

9.4 percent

Gypsum Creek23,420 acre-feet 5.3 percent 

Cross Creek

37,570 acre-feet

8.4 percent

Beaver Creek

9,450 acre-feet

2.1 percent

Homestake Creek

30,170 acre-feet

6.8 percent 

Homestake Tunnel

30,580 acre-feet

6.9 percent 

Wurtz Ditch

 2,210 acre-feet

0.5 percent

Ewin820 a0.2 p

Upper Eagle River126,060 acre-feet28.3 percent

Turkey Creek

15,730 acre-feet

3.5 percent

Black G

20,740 

4.

Gore Creek

93,060 acre-feet

20.9 percent

B

 8,5

 

Middle Creek

 4,080 acre-feet

 0.9 percent

Red Sandstone Creek

6,410 acre-feet

1.4 percent

Alkali Creek 1,540 acre-feet 0.3 percent

106°45'

39°45'

39°30'

0 5 10 KILOMETERS0 5 10 MILES

Base from U.S. Geological Survey digital data, 2007,Universal Transverse Mercator projectionZone 13 

Homestake

Reservoir

East 32,807.4 p

Water inputs to the Eagle River watershedWater from the Eagle River watershed

Arrow size increases relative to annual streamflow 

volume, percentage derived from total streamflow 

in the Eagle River watershed

EXPLANATION

Figure 15. Arrow schematic of major streams and diversion mean annual streamflow volume in the Eagle River watershed.
36 Assessment of Surface-Water Quantity and Quality, Eagle River Watershed, Colorado, 1947–2007

Figure 16. Comparison of streamflow prediversion (1945–1965) and post-diversion (1966–2008) from Homestake Reservoir at site 27, 

Homestake Creek near Red Cliff, Colorado. Streamflow, in cubic feet per second

450

400

350

300

250

200

150

100

40

0

January February March April May June July August September October November December

Monthly mean streamflow Monthly mean streamflow

Mean annual streamflow Mean annual streamflow

Prediversion Post-diversion

EXPLANATION

(fig.7–11). Comparisons of water quantities within the ERW 

show that 92 percent of the streamflow that originates within 

the watershed is accounted for at site 233 (Lower Eagle 

subwatershed) (09070000, Eagle River below Gypsum, CO). 

The remaining 8 percent is diverted near the headwaters to 

supplement water supplies east of the Continental Divide in 

Colorado (fig. 1 and fig. 15). 

The Upper Eagle subwatershed contributes 126,060 acreft annually (U. S. Geological Survey, 2007); this mean annual 

streamflow volume represents approximately 28.3 percent of the 

total annual streamflow volume that originates within the ERW 

for the period of record (fig. 15). It is the only subwatershed with 

transmountain diversions. In 2009 seven active streamflow-gaging 

stations in the Upper Eagle subwatershed. Major tributaries within 

the Upper Eagle subwatershed include Homestake Creek, Cross 

Creek, and Turkey Creek; contributing 30,170 acre-ft; 37,570 

acre-ft; and 15,730 acre-ft, respectively (fig. 15). 

The Gore Creek subwatershed contributes 93,060 acre-ft. 

The Gore Creek subwatershed contributes 20.9 percent of the 

annual streamflow volume that originates within the ERW. 

The Gore Creek subwatershed currently (2009) has three 

active streamflow-gaging stations with numerous discontinued 

stations, many of which were discontinued in 2008 (table 3, 

fig. 6). Major tributaries of Gore Creek include Black Gore 

Creek, Bighorn Creek, Pitkin Creek, Booth Creek, Middle 

Creek, and Red Sandstone Creek. The largest mean annual 

streamflow volume of these tributaries is Black Gore Creek 

with 20,740 acre-ft (fig. 15). 

The combined Middle and Lower Eagle subwatersheds 

contribute 43 percent of the mean annual streamflow volume 

originating within the ERW and are currently (2009) monitored by 5 active streamflow-gaging stations. Many USGS 

streamflow-gaging stations in the Lower and Middle Eagle 

subwatersheds were discontinued in 1972 (table 3, fig. 6). The 

largest mean annual streamflow volumes within the Middle 

Eagle subwatershed are from Lake Creek with 41,730 acre-ft; 

and in the Lower Eagle subwatershed are from Brush Creek 

with 31,890 acre-ft (fig. 15).

The effects of diversions in the Upper Eagle subwatershed, primarily from Homestake Reservoir, are evident when 

comparing pre-diversion and post-diversion flow record at 

Homestake Creek near Red Cliff, Colorado (Upper Eagle subwatershed, site 27; fig. 6) in figure 16. Streamflow May–July 

decreased during the post-diversion period. Base flow through 

the summer, fall, and winter months remained similar to the 

pre-diversion period (fig. 16).
Assessment of Surface-Water Quality 37

Assessment of Surface-Water Quality

Natural and human factors can affect surface-water quality. Natural factors affecting water quality include geology, 

snowpack, soil type, vegetation, topography, streamflow, 

precipitation, climate, and ecology. Many human effects such 

as urbanization and agriculture are part of a larger process of 

watershed-wide land-use or land-cover change that can affect 

water quality. Understanding the relation between land use and 

water quality is particularly useful when considering nonpointsource contaminants. Diffuse sources of suspended sediments, 

pathogens, nutrients, pesticides, emerging contaminants, 

heavy metals, oil, and road salt often are less visibly obvious 

than point-source contamination. 

In order to pinpoint diffuse sources of contamination, 

studies often require more intensive monitoring programs and 

special research efforts. Correlations between land use and 

water quality often are complex and, in general, are likely to be 

site or region specific. Understanding the relation between land 

use and water quality in each watershed is useful for the landuse management specific to that region. The inclusive approach 

to this study and associated data limitations does not allow 

for the analysis to convey specific conclusions which identify 

stressors and their immediate effects within the watershed.

Surface-water-quality data from 293 sites and 12 different 

source agencies were complied into 192 unique sites located 

on streams and rivers in the ERW (table 5). Nearly 39 percent 

(74 sites) of the unique sites had fewer than 5 samples. In 

comparison, 23 percent (44 sites) of the sites have more than 

100 samples. Physical properties were the most abundant type 

of samples collected, with major ions, nutrients, and trace elements also commonly collected.

As mentioned in “Data Review and Analysis,” where 

adequate data existed, determination of summary statistics, 

comparisons to State standards and Federal recommendations, 

and trend analysis was done. Discussion of surface-water quality is presented in the following sections based on constituent 

groupings: “field properties, dissolved solids and major ion, 

nutrients, trace elements, and suspended sediment.”

Field Properties

Agriculture, industry, urbanization, and mining all affect 

field properties. Field properties analyzed for in this study 

included specific conductance, pH, water temperature, dissolved oxygen, and hardness (table 8). These constituents are 

indicators of water-quality conditions. 

Specific Conductance

Specific conductance is proportional to the dissolvedsolids concentration within the stream and has the ability to 

conduct an electric current. The presence of charged ionic 

species in a solution makes the solution conductive. The 

weathering of minerals in soil and bedrock contribute as a 

primary source of major dissolved constituents. The major 

ions that comprise the total dissolved solids in the water column are presented in “Dissolved solids and Major Ions.”

Specific conductance in the ERW was measured at 

163 sites from January 12, 1968, to 2007, and ranged from 

less than 50 to 4,550 μS/cm depending on site and time of 

year. The 25th, 50th, and 75th percentiles for specific conductance at sites in the ERW were 97, 152, and 250 μS/cm, 

respectively. Median values for the subwatersheds ranged 

from 105 μS/cm in Gore Creek, 138 μS/cm in the Upper 

Eagle, 295 μS/cm in the Middle Eagle, to 809 μS/cm in the 

Lower Eagle (table 8). The spatial pattern shows an increase 

in specific conductance as water moves downstream, with 

a defined increase in specific conductance occurring near 

the mouth of Gore Creek and downstream of Gore Creek. 

Additionally, there also may be a localized area of increased 

values within Black Gore Creek near Vail (site 11) and Turkey Creek near Red Cliff (site 15) (fig. 17).

Evaluation of temporal trends was done for all sites with 

specific conductance data; trend analysis was done at the 8 

sites meeting the criteria set in the “Data Sources, Compilation, Review, and Analysis” section of this report. Findings 

from the trend analysis are presented in table 9 and figure 17. 

A comparison between sites where trend assessments were 

completed was done to find areas within the ERW that may 

be contributing to the observed trends. Seasonal Kendall Trend tests were done based on data availability for 

1990–2007. There is a significant downward trend (p-value 

of 0.03) in specific conductance (flow-adjusted) at site 59 

(Upper Eagle subwatershed), which represents a 47.8-μS/cm 

decrease over the time period. Upstream at site 37 (Upper 

Eagle subwatershed) near Gilman there is no flow-adjusted 

trend for 1990–2007. The area between these sites (59 and 

37) may represent the area within the ERW contributing to 

the observed trend at site 59 and this area contains Fall Creek 

and Rock Creek (fig 1. and fig. 17). 

pH

The pH is an important property of water that can limit 

the diversity and quantity of biota of aquatic communities 

(Allan, 1996) and can be a controlling component of solubility 

(Stumm and Morgan, 1996). The pH is calculated as the negative log10 of hydrogen ions concentration occurring between 

0 and 14 (Brown and others, 2006). The pH is a measure of 

how acidic or basic a solution is. Acids are represented by 

values 0–7 and bases are represented by values 7–14; a value 

of 7 is neutral. Lower pH can contribute to increased solubility 

of metals (Hem, 1989).

The pH of a stream is affected by biological processes, 

geology, precipitation, and human activities. Within the ERW, 

pH in streams may be altered by minerals within the geologic 

formations (Tweto, 1979). The Colorado Mineral Belt contains 

metal ores that when oxidized by water produce acidic water. 

This process is naturally occurring within the ERW, but may 

be accelerated within mining areas. Numerous sedimentary 
38 Assessment of Surface-Water Quantity and Quality, Eagle River Watershed, Colorado, 1947–2007

Table 8. Summary statistics of field properties and suspended-sediment data in the Eagle River watershed by subwatershed, 1947–2007.

[No., number; --, undetermined; MRL, Minimum Reporting Limit; μS/cm, microsiemens per centimeter at 25 degrees Celsius; °C , degrees Celsius; ntu, 

nephelometric turbidity units; mg/L, milligrams per liter; CaCO3, calcium carbonate]

Constituent 

or property

No. of 

censored 

values

No. of

samples MRL Minimum1

Concentration or value 

at indicated percentile2 Maximum

25 50 75

Gore Creek subwatershed

Specific conductance (μS/cm) 268 3,117 50.0 2.0 67 105 193 1,690

pH (standard units) 0 1,423 -- 5.62 7.9 8.1 8.3 10.0

Water temperature (°C) 0 4,403 -- –2.0 1.0 4.0 7.0 21.0

Turbidity (ntu) 0 277 -- .30 2.4 5.0 28.0 1,100

Dissolved oxygen (mg/L) 0 1,073 -- 5.0 8.8 9.6 10.4 19.0

Hardness (mg/L as CaCO3

) 1 1,059 10.0 6.0 57 86 140 660

Suspended sediment (mg/L) 0 186 -- .1 1.0 3.0 9.0 172

Upper Eagle subwatershed

Specific conductance (μS/cm) 58 4,544 50.0 12.0 68 138 212 4,550

pH (standard units) 0 2,564 -- 4.2 7.3 7.7 8.0 10.7

Water temperature (°C) 0 5,493 -- –1.0 1.0 5.0 9.0 22.0

Turbidity (ntu) 4 984 1.0 0.1 1.2 2.0 4.3 106

Dissolved oxygen (mg/L) 0 647 -- 3.4 8.6 9.7 10.8 18.1

Hardness (mg/L as CaCO3

) 2 914 10.0 3.0 52 89 124 765

Suspended sediment (mg/L) 0 69 -- 0.7 2.0 4.0 7.0 549

Middle Eagle subwatershed

Specific conductance (μS/cm) 0 1,230 -- 36.5 180 295 393 1,500

pH (standard units) 0 1,540 -- 5.5 7.8 8.0 8.3 9.3

Water temperature (°C) 0 1,956 -- –2.0 2.0 6.0 10.0 23.55

Turbidity (ntu) 0 257 -- 0.2 2.2 3.9 6.7 654

Dissolved oxygen (mg/L) 0 1,402 -- 3.5 8.3 9.5 10.8 35.3

Hardness (mg/L as CaCO3

) 0 1,314 -- 25.0 100 156 200 1,400

Suspended sediment (mg/L) 0 122 -- 0.4 4.0 7.0 24.0 1,330

Lower Eagle subwatershed

Specific conductance (μS/cm) 0 1,578 -- 100 426 809 1,020 1,980

pH (standard units) 0 1,345 -- 6.5 7.7 8.0 8.3 9.6

Water temperature (°C) 0 1,524 -- –2.0 2.2 7.8 11.7 24.0

Turbidity (ntu) 0 235 -- .02 2.3 4.7 17.3 1,500

Dissolved oxygen (mg/L) 0 714 -- 6.0 9.0 10.0 11.4 15.4

Hardness (mg/L as CaCO3

) 0 1,007 -- 34 169 300 380 1,100

Suspended sediment (mg/L) 0 102 -- 1.0 8.0 23.5 70.0 814.0

1

Uncensored values.

2

Percentile values can be less than the MRL values due to multiple MRLs within the combined dataset.
Assessment of Surface-Water Quality 39

Table 9. Summary of monotonic temporal trends for field properties and suspended-sediment concentrations in the Eagle River 

watershed, Colorado.

[No., number; --, undetermined; μS/cm, microsiemens per centimeter at 25 degrees Celsius; mg/L, milligrams per liter; CaCO3, calcium carbonate]

Site 

no.

Trend 

period

No. of 

samples

Flow

adjustment

Trend slope,

units per year

Percent change,

per year p-value Trenddirection

Median 

value

Specific conductance, μS/cm

13 1990–2007 88 No -- -- 0.58 No trend 223

13 1990–2007 88 Yes -- -- .87 No trend 223

37 1990–2007 79 No -- -- .05 Upward 132

37 1990–2007 28 Yes -- -- .26 No trend 132

59 1990–2007 76 No -- -- .66 No trend 133

59 1990–2007 33 Yes –2.99 –2.26 .03 Downward 133

66 1990–2007 95 No -- -- .85 No trend 155

66 1990–2007 95 Yes -- -- .58 No trend 155

72 1990–2007 85 No –4.45 –1.89 .03 Downward 235

72 1990–2007 23 Yes -- -- .50 No trend 235

160 1995–2007 69 No -- -- .21 No trend 324

160 1995–2007 69 Yes -- -- .53 No trend 324

173 1990–2007 95 No -- -- .38 No trend 287

173 1990–2007 93 Yes -- -- .18 No trend 287

224 1992–2007 75 No -- -- .39 No trend 838

224 1992–2007 75 Yes -- -- .15 Downward 838

pH, standard units

37 1990–2007 49 No -- -- .95 No trend 7.9

37 1990–2007 26 Yes -- -- .30 No trend 7.9

59 1990–2007 48 No -- -- .11 Upward 7.7

59 1990–2007 29 Yes -- -- .21 No trend 7.7

66 1990–2007 51 No -- -- .06 Upward 7.6

66 1990–2007 51 Yes -- -- .11 Upward 7.6

72 1990–2007 49 No .03 .38 .04 Upward 7.6

72 1990–2007 24 Yes -- -- .24 No trend 7.6

160 1995–2007 33 No -- -- .10 Upward 8.7

160 1995–2007 33 Yes -- -- .10 Upward 8.7

173 1990–2007 50 No .02 .21 .01 Upward 8.1

173 1990–2007 40 Yes .03 .32 .01 Upward 8.1

224 1991–2007 44 No -- -- .07 Upward 8.3

224 1991–2007 43 Yes -- -- .14 Upward 8.3

Water temperature, degrees Celsius

13 1990–2005 130 No -- -- .07 Upward 5.7

66 1990–2006 164 No -- -- .56 No trend 5.0

160 1995–2007 120 No .10 2.2 .03 Upward 4.6

173 1990–2005 165 No -- -- .97 No trend 5.0

224 1998–2007 85 No -- -- .90 No trend 7.4

Dissolved oxygen, mg/L

160 1995–2007 113 No -- -- .06 Downward 10.2

160 1995–2007 113 Yes -- -- .07 Downward 10.2

173 1990–2007 153 No .10 1.1 .02 Upward 9.2

173 1990–2007 136 Yes .14 1.5 .01 Upward 9.2

224 1998–2007 83 No -- -- .93 No trend 9.9

224 1998–2007 82 Yes -- -- .35 No trend 9.9

Hardness as CaCO3

, mg/L

160 1994–2007 69 No -- -- .34 No trend 150

160 1994–2007 69 Yes -- -- .22 No trend 150

173 1994–2007 70 No -- -- .74 No trend 132

173 1994–2007 58 Yes -- -- .21 No trend 132

224 1994–2007 64 No -- -- .44 No trend 290

224 1994–2007 64 Yes –3.85 –1.33 .02 Downward 290

Suspended sediment concentration, mg/L

160 1995–2007 54 No -- -- .87 No trend 3.0

160 1995–2007 54 Yes -- -- .22 No trend 3.0

224 1995–2007 37 No -- -- .11 Upward 9.0

224 1995–2007 37 Yes -- -- .78 No trend 9.0
40 Assessment of Surface-Water Quantity and Quality, Eagle River Watershed, Colorado, 1947–2007

Figure 17. Spatial distribution of median-concentration percentiles and monotonic trends in specific conductance at selected sites in the Eagle 

River watershed, Colorado, 1990–2007.

EXPLANATION

Waterbodies

Upper Eagle subwatershed

Middle Eagle subwatershed

Gore Creek subwatershed Streams

Lower Eagle subwatershed

Monotonic trend in specific conductance, 1990 to 2007

Specific conductance

5–40 0–25

41–150 greater than 25–50

151–440 greater than 50–75

greater than 75–100

Number of samples

Grouping of median concentrations

by Eagle River watershed percentile 

City

77

224

59

No trend

Upward trend

Downward trend

 p-value greater than 0.05–0.15

 p-value greater than 0.01–0.05

 p-value 0.00–0.01

Base from U.S. Geological Survey digital data, 2007,

Universal Transverse Mercator projection

Zone 13 

!(

!(

!(

!(!(

!(

!(

!(

!(

!(

!(

!(

!(

!(!( !(!(

!(

!(

!(!(

!( !(!(

!( !(

!(

!(!(

!(

!(

!(!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!( !(

!(

224

173

Minturn

Vail

Red Cliff

Gore Creek

Turkey Creek

Edwards

Eagle

Gypsum

Wolcott

Avon

Dotsero

106°15'

106°45'

39°45'

39°30'

0 5 10 KILOMETERS

0 5 10 MILES

Fall

Creek

!(

!(

!( !(

!(

!(

!(

!(

!(

!( !( !( !(

!(

!(

!(

!(!(

!(

!(

!(

!(

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!(

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!(

!(

!(

!(

!( !(

!(

13

Minturn

Vail

Red Cliff

Black Gore Creek

72

160

59

37

Rock Creek

Fall

Creek

Eagle River

East Fork

Eagle River 

Eagle

River

Black Gore Creek

Cross Creek

Alkali Creek

Gore Creek

(!(!

Turkey Creek
Assessment of Surface-Water Quality 41

units, including the Minturn Formation and the Belden Formation contain carbonate minerals. When these minerals are 

dissolved in water, pH increases. This process also occurs 

naturally within the ERW but also may be increased through 

water storage and irrigation within the watershed. If storage or 

irrigation is occurring in formations containing metal ores, the 

pH could decrease.

Seasonal variations in pH occur in two general patterns 

within the Eagle River watershed based on how much influence the mining area has on the pH (fig. 18). In areas heavily 

affected by mining, pH tends to be lowest during February 

and March; the median concentrations are lower than areas 

less affected by mining. In areas less affected or unaffected by 

mining, pH tends to be lowest during peak streamflows during 

May and June and highest during late fall and early spring.

The pH in the ERW has been measured at 175 sites from 

January 12, 1968, to the present (2009), and ranged from 4.2 

to 10.7. The 25th, 50th, and 75th percentiles for the ERW were 

7.7, 8.0, and 8.2, respectively. Median concentrations for the 

subwatersheds were 8.1 in Gore Creek, 7.7 in the Upper Eagle, 

8.0 in the Middle Eagle, and 8.0 in the Lower Eagle (table 8). 

The spatial pattern shows increase in pH as water moves 

downstream, both within the subwatersheds and the watershed 

as a whole; with the exception of the main stem Eagle River 

near areas subject to acid-mine drainage from several tributaries in mining areas near Belden (fig. 19). In the mining area, 

many locations show lower pH values, with the lowest median 

concentration occurring near the mouths of Cross and Rock 

Creeks (7.2 and 7.1, respectively). Additionally, there also 

may be two localized areas of higher pH values, within Black 

Gore Creek near Vail and the East Fork of the Eagle River 

near Red Cliff. 

State standards for pH are set as a range of acceptable 

values between 6.5 and 9.0 (Colorado Department of Public Health and Environment, 2008). Measurements of pH in 

streams with values outside this range are considered exceedances of the State standard and may indicate possible waterquality concerns. The minimum pH standard of 6.5 units was 

exceeded less than 10 times over a period of several years 

for most sites in the ERW (fig. 20); approximately 1 percent 

(86 comparisons) of the total number of measurements (6,872) 

exceeded the minimum pH standard (table 10). The maximum 

pH standard of 9.0 units was exceeded less than 5 times over 

a period of several years for most sites in the ERW; approximately 1 percent (73 comparisons) of the total number of measurements (6,872) exceeded the maximum standard (table 10).

Evaluation of temporal trends was done for all sites 

with pH data; trend analysis was done at the 7 sites that met 

the minimum criteria set in the “Data Sources, Compilation, 

Review, and Analysis” section of this report. Findings from 

the trend analysis are presented in table 9 and figure 19. A 

comparison between sites where trend assessments were completed was done to find areas within the ERW that may be contributing to the observed trends. Seasonal Kendall Trend tests 

were done based on data availability for 1990–2007. There 

is a weakly significant flow-adjusted upward trend (p-value 

of 0.11) at site 66 (Upper Eagle subwatershed) (table 9). 

Upstream a short distance at site 59 (Upper Eagle subwatershed), no flow-adjusted trend was detected. The area between 

these sites may be contributing to the detected trend at site 66, 

and includes the areas located downstream of the Belden mining area. No other trends exist upstream of this area. Downstream near Avon, a highly significant upward trend (p-value 

of 0.01) exists at site 173 (Middle Eagle subwatershed). This 

trend represents an increase of 0.5 standard pH units over the 

entire specified time period. A flow-adjusted upward trend is 

detected as weakly significant (p-value of 0.14) at a site downstream near Gypsum (site 224, Lower Eagle subwatershed). 

No flow-adjusted trends were detected at site 72 (Upper Eagle 

subwatershed), which limits the potential area contributing to 

the trend detected at site 173 (Middle Eagle subwatershed) to 

a large area of the ERW as shown in figure 19. 

Water Temperature

Temperature is an important physical property of water 

that can affect aquatic biota and stream chemistry. Water temperature affects larval maturation rates and other life cycles 

of biota in aquatic habitats (Allan, 1996). The rate of many 

chemical reactions is related proportionally to temperature. 

For example, as temperature increases, the rates of reaction also can increase. Water temperature often is related to 

ambient-air temperature, but also is affected by the source of 

the water (groundwater, lake, or snow melt), the geomorphology of the stream channel, and various human effects.

Water temperature in the ERW has been measured at 181 

sites from April 30, 1958, to the present (2009), and ranged 

from -2 to 24 degrees Celsius (table 8). The 25th, 50th, and 

75th percentiles for the ERW were 1.4, 4.9, and 8.9 degrees 

Celsius, respectively. Summary statistics for temperature are 

shown in table 8. Median temperatures for the ERW generally increase in the downstream direction as evidenced by the 

subwatershed median temperatures (50th 

percentile) that ranged from 4.0 degrees Celsius in Gore 

Creek, 5.0 degrees Celsius in the Upper Eagle, 6.0 degrees 

Celsius in the Middle Eagle, to 7.8 degrees Celsius in the 

Lower Eagle (fig 21). The highest median temperature 

observed in the ERW occurred near Gypsum (9.0 degrees 

Celsius). Seasonal variations in the median temperatures show 

that water temperatures tend to be coldest December–February 

and warmest July–August following ambient air-temperature 

patterns (fig 22). The greatest rates of temperature change 

occur as an increase between June–July and as a decrease 

between September–October (fig. 22).

State standards for water temperature (chronic) are 

specific to CDPHE Regulation 33 (Colorado Department of 

Public Health and Environment, 2007). The water-temperature 

State standard was exceeded less than 10 times over a period 

of several years for most sites in the ERW; less than 1 percent (89 comparisons) of the total number of measurements 

(13,376) exceed the State standard for chronic water temperature (table 10 and fig 23).
42 Assessment of Surface-Water Quantity and Quality, Eagle River Watershed, Colorado, 1947–2007 pH, in standard units

Site 160

x

x

x

x

o

x

x

7.5

8.0

8.5

9.0

9.5

10.0

10.5

11.0

14 11 19 22 2 6 21 13 14 12 9 14 14

Site 173

x

x

x

x

x

x

x

x x

xx

x

x

6.5

7.0

7.5

8.0

8.5

9.0

9.5

10.0

18 20 29 24 34 32 20 30 26 28 20 29

Site 201

x x

7.5

8.0

8.5

9.0

9.5

10.0

6 7 7 8 10 9 8 8 7 5 8 7

Site 224 

x

x

x

x

x

x

x

x

x

x

x

x

x

x xxx

x

x

x x

x

x

x x

x

x

x

6.5

7.0

7.5

8.0

8.5

9.0

9.5

10.0

54 53 63 79 89 79 74 81 59 51 48 55

January February March April May June July August September October November December

EXPLANATION

30 Number of values

o Upper detached

Upper outside

Lower adjacent

Upper adjacent

x

x Lower outside

o Lower detached

90th percentile

75th percentile

25th percentile

10th percentile

median

Figure 18. Seasonal pattern of pH at selected sites in the Eagle River watershed, Colorado, 1947–2007.
Assessment of Surface-Water Quality 43

Figure 19. Spatial distribution of median-concentration percentiles and monotonic pH trends at selected sites in the Eagle River watershed, 

Colorado, 1990–2007.

EXPLANATION

Waterbodies

Upper Eagle subwatershed

Middle Eagle subwatershed

Gore Creek subwatershed Streams

Lower Eagle subwatershed

Monotonic pH trend, 1990 to 2007

pH

5–40 0–25

41–150 greater than 25–50

151– 303 greater than 50–75

greater than 75–100

Number of samples

Grouping of median concentrations,

by Eagle River watershed percentile 

City

77

224

59

No trend

Upward trend

Downward trend

 p-value greater than 0.05–0.15

 p-value greater than 0.01–0.05

 p-value 0.00–0.01

Base from U.S. Geological Survey digital data, 2007,

Universal Transverse Mercator projection

Zone 13 

!(

!(

!(

!(

!(

!(

!(

!(!(

!(

!(

!(!(

!(

!(

!( !(

!(

!(

!(!(

!(

!(

!(

!(!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!( !( !( !( !(

!(

!(

224

173

!(

!(

!(

!(

!(

!(

!(

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37

Eagle

Gypsum

Wolcott

Avon

Minturn

Vail

Red Cliff

Black Gore Creek

Gore Creek

Dotsero

Gore Creek

Turkey Creek

Minturn

Vail

Red Cliff

Eagle River

Cross Creek

East Fork

Eagle River 

Edwards

106°15'

106°45'

39°45'

39°30'

0 5 10 KILOMETERS

0 5 10 MILES

72

160

66

59Rock Creek

Fall

Creek

Turkey Creek

(!

Eagle

River

Black Gore Creek

Alkali Creek
44 Assessment of Surface-Water Quantity and Quality, Eagle River Watershed, Colorado, 1947–2007

Table 10. Summary of Colorado exceedances of water-quality standards for field properties in the Eagle River watershed, Colorado by 

subwatershed.

[No., number; --, no data; <, less than; mg/L, milligrams per liter; μg/L, micrograms per liter; °C, degrees Celsius]

Constituent 

or property

No. of 

censored

values

No. of

samples 

No. of standard

exceedances

Percent of

standard

exceedences

Minimum

date

Maximum

date

Gore Creek subwatershed

pH maximum (standard units) 0 1,423 48 3 July 25, 1969 April 18, 2007

pH minimum (standard units) 0 1,423 2 <1 June 18, 1997 April 10, 2002

Water temperature (°C) 0 4,403 5 <1 Aug. 16, 1973 July 31, 2002

Dissolved-oxygen minimum (mg/L) 0 1,073 7 <1 Dec. 6, 1978 May 30, 2005

Oxygen, dissolved fish spawn (mg/L) 0 1,073 21 2 Dec. 6, 1978 May 30, 2005

Upper Eagle subwatershed

pH maximum (standard units) 0 2,564 4 <1 Nov. 20, 1975 March 7, 1989

pH minimum (standard units) 0 2,564 80 3 July 14, 1966 Oct. 23, 2006

Water temperature (°C) 0 5,493 31 <1 July 27, 1964 Aug. 13, 2003

Dissolved-oxygen minimum (mg/L) 0 647 16 2 June 4, 1997 Aug. 27, 1997

Dissolved-oxygen spawning (mg/L) 0 647 23 4 Sept. 6, 1979 July 25, 2001

Middle Eagle subwatershed

pH maximum (standard units) 0 1,540 8 <1 May 15, 1970 Sept. 12, 2006

pH minimum (standard units) 0 1,540 3 <1 Feb. 18, 1997 Nov. 7, 2001

Water temperature (°C) 0 1,956 36 2 June 20, 1961 June 26, 2007

Dissolved-oxygen minimum (mg/L) 0 1,402 25 2 Nov. 14, 1990 Sept. 13, 2004

Dissolved-oxygen spawning (mg/L) 0 1,402 23 2 Sept. 6, 1979 July 25, 2001

Lower Eagle subwatershed

pH maximum (standard units) 0 1,345 13 <1 May 15, 1970 April 17, 2001

pH minimum (standard units) 0 1,345 1 <1 Oct. 15, 1999 Oct. 15, 1999

Water temperature (°C) 0 1,524 17 1 July 30, 1964 July 13, 2004

Dissolved-oxygen minimum (mg/L) 0 714 0 0 -- --

Dissolved-oxygen spawning (mg/L) 0 714 23 3 Sept. 6, 1979 July 25, 2001
Assessment of Surface-Water Quality 45

EXPLANATION

Waterbodies

Upper Eagle subwatershed

Middle Eagle subwatershed

Gore Creek subwatershed Streams

Lower Eagle subwatershed

pH

5–40 0–25

41–150 1–10

151–785 11–22

Number of samples Number of exceedances

City

Base from U.S. Geological Survey digital data, 2007,

Universal Transverse Mercator projection

Zone 13 

!(

!(

!(

!( !(

!(

!(

!(

!(

!

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(!( !( !( !( !(

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!(

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!( !(

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!(

!(

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!(

!(

!(

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!(

!(

!(

!(

!(

!(

!(

!( !(

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!(

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!( !( !(

!(

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!( !( !( !(!(!( !( !( !(!( !( !( !( !(

!(

!( !(!(!(!(

(

Creek

!(

(!

Edwards !!!!

Eagle

Gypsum

Wolcott

Avon

Minturn

Vail

Red Cliff

Gore Creek

Black Gore Creek

Dotsero

Eagle River

Cross Creek

East Fork

Eagle River 

Gore Creek

Turkey Creek

Minturn

Vail

Red Cliff

Black Gore Creek

Eagle

River

Turkey

Rock Creek

Fall Creek

106°15'

106°45'

39°45'

39°30'

0 5 10 KILOMETERS

0 5 10 MILES

Alkali Creek

!

(

Figure 20. Number of exceedances of the Colorado water-quality standard for pH at selected sites in the Eagle River watershed, Colorado, 

1947–2007.
46 Assessment of Surface-Water Quantity and Quality, Eagle River Watershed, Colorado, 1947–2007

Figure 21. Spatial distribution of median-concentration percentiles and monotonic water temperature trends at selected sites in the Eagle 

River watershed, Colorado, 1990–2007.

EXPLANATION

Waterbodies

Upper Eagle subwatershed

Middle Eagle subwatershed

Gore Creek subwatershed Streams

Lower Eagle subwatershed

Monotonic water temperature trend, 1990 to 2007

Water temperature

5–40 0–25

41–150 greater than 25–50

151–458 greater than 50–75

greater than 75–100

Number of samples

Grouping of median concentrations

by Eagle River watershed percentile 

City

77

224

59

No trend

Upward trend

Downward trend

 p-value greater than 0.05–0.15

 p-value greater than 0.01–0.05

 p-value 0.00–0.01

Base from U.S. Geological Survey digital data, 2007,

Universal Transverse Mercator projection

Zone 13 

!(

!(

!(

!(

!(

!(

!(!(

!( !(

!(

!(

!(

!(

!(

224

173

!(

!(

!( !(

!(

!(

!(

!(

!(

!( !( !( !(

!(

!(

!(

!(

!(!(

!(

!(

!(

!(

!(

!(

!(

!(

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!(

!(

!(

!( !( !(

!(

66

13

106°15'

106°45'

39°45'

39°30'

0 5 10 KILOMETERS

0 5 10 MILES

Gore Creek

!( !(

Eagle

Gypsum

Wolcott

Avon

Minturn

Vail

Red Cliff

Black Gore Creek

Dotsero

Eagle River

Cross Creek

East Fork

Eagle River 

Gore Creek

Minturn

Vail Edwards

Red Cliff

Eagle

River

Black Gore Creek

Turkey Creek

160

Rock Creek

Fall

Creek

(!

(

!(

(

((

(

(

!

(

!!

!

!

! !

!

!

!

!

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(

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(

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(

( (

(

!(!

(!

!

!( (!(

(

(!

Alkali Creek

(!

(

( (

!

! !

!!!

Turkey Creek
Assessment of Surface-Water Quality 47

Water temperature, in degrees Celsius

Site 224 

0

5

10

15

20

25

18 20 27 19 24 27 20 23 17 19 22 21

x

x

o

January February March April May June July August September October November December

EXPLANATION

30 Number of values

o Upper detached

Upper outside

Lower adjacent

Upper adjacent

x

x Lower outside

o Lower detached

90th percentile

75th percentile

25th percentile

10th percentile

median

o

x

x

Site 201

0

5

10

15

20

25

6 7 7 8 10 9 8 8 7 5 8 7

Site 173

0

5

10

15

20

25

26 24 48 34 42 46 30 37 28 39 31 32

x

x

o

x

x

x

x

x

x

o

Site 160

18 14 35 30 30 29 16 18 16 10 20 18

0

5

10

15

20

x

x

o

x

Figure 22. Seasonal pattern of water temperature at selected sites in the Eagle River watershed, Colorado, 1947–2007.
48 Assessment of Surface-Water Quantity and Quality, Eagle River Watershed, Colorado, 1947–2007

Figure 23. Number of exceedances of the Colorado water-quality standard for water temperature at selected sites in the Eagle River 

watershed, Colorado, 1947–2007.

EXPLANATION

Waterbodies

Upper Eagle subwatershed

Middle Eagle subwatershed

Gore Creek subwatershed Streams

Lower Eagle subwatershed

Water temperature

5–40 0

41–150 1–10

151–581

Number of samples Number of exceedances

City

Base from U.S. Geological Survey digital data, 2007,

Universal Transverse Mercator projection

Zone 13 

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(!( !( !( !( !(

!(

!(

!(

!(

!(

!(

!(

!(

!( !(!(

!( !(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!( !( !(

!(

!(

!(

!(!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(!(

!(

!(

!(

!(

!(!(

!(

!( !(!( !(

!(

!(

!(

!(!( !(

!(

!( !( !(

!(

!( !( !(!(

!(

!( !(

!(!( !(

!( !( !(

!( !( !(!(

!(!(! !( !( !(

!(!(!( !( !(!( !( !( !( !( !( !( !( !( !(!( !( !( !(!(!(!( !(!(!(!(!( !( !( !( !(!(

!(

!(

!(

!(

!(

!(!(!(!(!(

27

180

194

227

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(!(

!(

!(

!(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(!(

!( !(

!( !(

!(!(!(

!(

!(

!(

!(

!( !( !(

!(

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!(

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!(!(

!( !(

!( !(!(

!(

!( !( !( !(!(!( !( !( !(!( !( !( !( !(

!(

!( !(!(!(!(

106°15'

106°45'

39°45'

39°30'

0 5 10 KILOMETERS

0 5 10 MILES

Edwards Gore Creek

Turkey Creek

Minturn

Vail

Red Cliff

Minturn

!(!(

!(

Creek

(!(!

!(

!(

!((

Eagle

Gypsum

Wolcott

Dotsero

East Fork

Eagle River 

Avon

Eagle River

Cross Creek

Eagle

River

Black Gore Creek

Vail

Red Cliff

Black Gore Creek

Gore Creek

Turkey

Rock Creek

Fall Creek

(!

Alkali Creek
Assessment of Surface-Water Quality 49

Evaluation of temporal trends was done for all sites 

with water temperature data; trend analysis was done at the 

5 sites that met the criteria set in the “Data Sources, Compilation, Review, and Analysis” section of this report. Findings 

from trend analysis are presented in table 9 and figure 21. 

A comparison between sites where trend assessments were 

completed was done to locate areas within the ERW that may 

be contributing to the observed trends. Upward trends at sites 

13 (Upper Eagle subwatershed) (p-value of 0.07) and 160 

(Gore Creek subwatershed) (p-value of 0.03) indicate increasing water temperatures at (1) the Eagle River above Red Cliff 

and (2) in Gore Creek. The trend on Gore Creek (table 9) is 

equivalent to a 1.3 degrees Celsius change over the entire 

specified time period (1995–2007).

Dissolved Oxygen

Dissolved oxygen is an important property of water that 

can affect both aquatic biota and chemical reactions within 

streams. Dissolved oxygen is important for all respiratory 

functions of aquatic life including both plant and animal species. Dissolved-oxygen levels are important components of 

oxidation-reduction reactions (redox) and can be important to 

oxidation states of transition metals like copper, iron, manganese, and zinc (Stumm and Morgan, 1996). Iron and manganese are the predominant participants in redox processes. In 

the presence of oxygen, iron and manganese are stable only as 

solid oxides. Soluble forms are present at concentrations less 

than 10-9 molar (Stumm and Morgan, 1996). The oxidation 

state of transition metals is important in determining solubility 

and mobility of these compounds in natural waters especially 

downstream of mining areas in the watershed. 

The concentration of dissolved oxygen within a stream 

is dependent on many processes. Dissolved oxygen enters a 

stream through reactions between the stream and the atmosphere along the surface of the water, and through mechanical 

mixing of air and water in turbulent areas. Dissolved oxygen 

also can be introduced directly by aquatic plants during photosynthesis. Contrarily, dissolved oxygen can be consumed and 

therefore reduced as organic matter dies and decomposes. This 

important process relates primarily to algal blooms. Dissolvedoxygen concentrations are inversely related to water temperatures; as temperatures increase the capacity of water to hold a 

given quantity of dissolved oxygen is reduced (Hem, 1989).

Dissolved oxygen-concentration in the ERW has been 

measured at 121 sites from March 15, 1973, to the present 

(2009), and ranged from 3.4 to 35.3 mg/L shown in table 8. 

The 25th, 50th, and 75th percentiles for the watershed were 

8.4, 9.5, and 10.5 mg/L respectively. Median concentrations 

for the subwatersheds ranged from 9.6 mg/L in Gore Creek, 

9.7 mg/L in the Upper Eagle, 9.5 mg/L in the Middle Eagle, 

to 10.0 mg/L in the Lower Eagle (table 8). The spatial pattern 

is variable, with the highest median concentration occurring 

in the Eagle River around Edwards (10.9 mg/L) (fig. 24). 

Seasonal variations in dissolved-oxygen concentrations show 

that concentrations tend to be lowest from July–September 

and highest from November–March, which is the inverse of 

patterns in water temperature (fig. 25).

State standards for dissolved oxygen (chronic) are set for 

both minimum dissolved oxygen (6.0 mg/L) and minimum 

dissolved oxygen for fish spawning (7.0 mg/L) (Colorado 

Department of Public Health and Environment, 2007). The 

minimum dissolved oxygen State standard was exceeded less 

than 10 times over a period of several years for most sites in 

the ERW; approximately 1 percent (48 comparisons) of the 

total number of measurements (3,836) exceeded the State 

standard (6.0 mg/L) for chronic dissolved oxygen (table 10 

and fig 26). Sites exceeding the minimum dissolved oxygen 

(spawning) State standard (7.0 mg/L) typically have less than 

10 exceedances over a period spanning several years for most 

sites in the ERW; approximately 3 percent (90 comparisons) 

of the total number of measurements (3,836) exceeded the dissolved oxygen (spawning) State standard (table 10).

Evaluation of temporal trends was done for all sites 

with dissolved oxygen data; trend analysis was done at the 

3 sites that met the minimum criteria set in the “Data Sources, 

Compilation, Review, and Analysis” section of this report. 

Findings from the trend analysis are presented in table 9 and 

figure 24. A comparison between sites where trend assessments were completed was done to find areas within the ERW 

that may be contributing to the observed trends. A weakly 

significant flow-adjusted downward trend (p-value less than 

0.07) at site 160 (Gore Creek subwatershed) (1995–2007) 

was detected. A highly significant flow-adjusted upward trend 

(p-value less than 0.01) at site 173 (Middle Eagle subwatershed) (1990–2007) was detected. No trend was detected at 

site 224 (Lower Eagle subwatershed). No other sites were 

available to compare to this trend for the same time period, 

so it is not possible to limit the area contributing to the trend. 

The upward trend represents a 2.5-mg/L change over the 

entire specified time period. 

Hardness

Hardness is an important property of water because it can 

be used to calculate the toxicity of metals in aquatic environments, and it also is an important consideration for municipalwater supply purposes. Hardness can be important to aquatic 

life because it can have an effect on the toxicity of metals; as 

hardness increases, trace-metal toxicity can decrease (Santore 

and others, 2001). For municipal water suppliers, the term 

“hard water” is used to describe the reaction of water with 

soaps and detergents to produce insoluble soap scum or the 

scale left when water is heated. Although hardness can have 

many definitions, in this analysis it will be interpreted as a 

measure of calcium and magnesium abundance (Hem, 1989).

Hardness within the ERW is likely related to the geology (Tweto, 1979). Geologic units rich in calcium, magnesium, other alkaline earth metals, and some heavy metals, 

can contribute to increases in hardness (Hem, 1989). In the 

ERW, sedimentary formations containing carbonates, such as 

the Minturn Formation and the Belden Formation, as well as 
50 Assessment of Surface-Water Quantity and Quality, Eagle River Watershed, Colorado, 1947–2007

Figure 24. Spatial distribution of median-concentration percentiles and monotonic dissolved-oxygen concentration trends at selected sites in 

the Eagle River watershed, Colorado, 1990–2007.

EXPLANATION

Waterbodies

Upper Eagle subwatershed

Middle Eagle subwatershed

Gore Creek subwatershed Streams

Lower Eagle subwatershed

Monotonic dissolved oxygen trend, 1990 to 2007

Dissolved oxygen

5–40 0–25

41–150 greater than 25–50

151–261 greater than 50–75

greater than 75–100

Number of samples

Grouping of median concentrations

by Eagle River watershed percentile 

City

77

224

59

No trend

Upward trend

Downward trend

 p-value greater than 0.05–0.15

 p-value greater than 0.01–0.05

 p-value 0.00–0.01

Base from U.S. Geological Survey digital data, 2007,

Universal Transverse Mercator projection

Zone 13 

!(

!(

!(

!(

!(!(

!(

!(

!(!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!( !( !( !(

!( 224

173

!(

!(

!(

!(

!(

!(

!(

!(!(

!(

!( !( !(

Gore Creek

Turkey Creek

Minturn

Vail Edwards

Red Cliff

106°15'

106°45'

39°45'

39°30'

0 5 10 KILOMETERS

0 5 10 MILES

!

!(

Eagle

Gypsum

Wolcott

Minturn

Vail

Red Cliff

Black Gore Creek

Avon

Dotsero

Eagle River

Cross Creek

East Fork

Eagle River 

Eagle

River

Black Gore Creek

Turkey Creek

160

Rock Creek

Fall

Creek

!(

(

Alkali Creek

Gore Creek
Assessment of Surface-Water Quality 51

Figure 25. Seasonal pattern of dissolved oxygen at selected sites in the Eagle River watershed, Colorado, 1947–2007. Dissolved oxygen, in milligrams per liter

Site 224 

6

8

12

10

14

16

18

16 19 24 17 22 25 20 19 14 17 21 18

o

o

x

x

xx

January February March April May June July August September October November December

EXPLANATION

30 Number of values

o Upper detached

Upper outside

Lower adjacent

Upper adjacent

x

Lower outside x

Lower detached o

90th percentile

75th percentile

25th percentile

10th percentile

median

Site 201

0

8

10

12

14

16

6 7 7 8 10 9 8 8 7 5 8 7

o

o

o

oo o

o

o

o

x

Site 173

0

5

10

15

20

25

16 16 32 20 27 23 17 24 21 22 20 23

x

x

xx

xxx xx

x

x x

o

oo

o o

o

14 11 30 21 21 20 11 13 12 9 14 13

6

8

12

14

16

10

x

x

x

x

x

x

x

Site 160
52 Assessment of Surface-Water Quantity and Quality, Eagle River Watershed, Colorado, 1947–2007

Figure 26. Number of exceedances of the Colorado water-quality standard for dissolved oxygen at selected sites in the Eagle River 

watershed, Colorado, 1947–2007.

EXPLANATION

Waterbodies

Upper Eagle subwatershed

Middle Eagle subwatershed

Gore Creek subwatershed Streams

Lower Eagle subwatershed

Dissolved oxygen

5–40 0

41–150 1–10

151–303 11–31

Number of samples Number of exceedances

City

Base from U.S. Geological Survey digital data, 2007,

Universal Transverse Mercator projection

Zone 13 

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!( !(

!( !(!(

!(

!( !( !( !(!(!( !( !( !( !(!( !( !( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(!( !( !( !( !(

!(

!(

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!(

!(

!(

!(

!( !(

!(

!(

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!(

!(

!( !( !(

!(

!( !( !(

!(

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!(

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!(

!(

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!(

!(

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!(

!(

!(

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!(

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!(

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!(!( !( !( !( !( !( !( !(!( !( !( !(!(!(!( !(!( !( !( !( !(!(

! !( !(

106°15'

106°45'

39°45'

39°30'

0 5 10 KILOMETERS

0 5 10 MILES

!(

(

(!(!!(!(!((! Edwards

(

!(

Dotsero

Eagle River

Cross Creek

East Fork

Eagle River 

Eagle

Gypsum

Wolcott

Avon

Gore Creek

Turkey Creek

Minturn

Vail

Red Cliff

Eagle

River

Black Gore Creek

Minturn

Vail

Red Cliff

Black Gore Creek

Gore Creek

Turkey

Rock Creek

Fall Creek

Creek

(!(

!

!(

Alkali Creek
Assessment of Surface-Water Quality 53

sandstones or shales containing carbonate cement may contribute to increases in hardness (Tweto, 1979). The Eagle Valley 

Evaporite may also be a source of calcium from the minerals 

gypsum and anhydrite. Human effects on hardness may result 

from water storage (reservoirs), which can cause increases in 

hardness through evapoconcentration and increased infiltration 

of water into the surrounding geologic units; municipal-watertreatment operations, which use additives such as carbonates 

in the treatment process; agriculture soil amendments and 

fertilizers; and winter road maintenance.

Hardness in the ERW has been measured at 116 sites from 

1970 to 2009, and ranged from less than 10 to 1,400 mg/L 

shown in table 8. The 25th, 50th, and 75th percentiles for 

the ERW were 76, 130, and 188 mg/L, respectively. Median 

concentrations for the subwatersheds ranged from 86 mg/L 

in Gore Creek, 89 mg/L in the Upper Eagle, 156 mg/L in the 

Middle Eagle, to 300 mg/L in the Lower Eagle (table 8). The 

spatial pattern shows an increase in hardness concentration as 

water moves downstream, with a defined increase in hardness 

in areas draining the Eagle Valley Evaporite and downstream 

of Edwards. Additionally, there also may be a localized area 

of higher concentrations within Black Gore Creek near Vail 

(fig. 27). Seasonal variations in hardness show that concentrations tend to be lowest May–June and highest January–March 

which is the inverse of patterns in streamflow (fig. 28). Snowmelt derived waters tend to have lower hardness concentrations 

compared to waters derived from groundwater sources. The 

greatest rate of hardness concentration change occurs as an 

increase July–August and as a decrease March–May.

Evaluation of temporal trends was done for all sites with 

hardness data; trend analysis was done at the 3 sites that met 

the criteria set in the “Data Sources, Compilation, Review, 

and Analysis” section of this report. Findings from the trend 

analysis are presented in table 9 and figure 27. A comparison 

between sites where trend assessments were completed was 

done to find areas within the ERW that may be contributing to 

the observed trends. Seasonal Kendall Trend tests were done 

for the time period 1994–2007. There is a significant downward trend (p-value of 0.02) in hardness at site 224 (Lower 

Eagle subwatershed). This trend represents a 53.9-mg/L 

decrease over the entire specified time period. Upstream at 

site 173 (Middle Eagle subwatershed) near Avon there is no 

trend. The area between these sites may represent the area 

within the ERW contributing to the observed trend.

Dissolved Solids and Major Ions

Dissolved solids (TDS) typically are measured using 

two different analytical methods. When dissolved solids are 

calculated through the sum of concentrations of commonly 

occurring major ions (calcium, magnesium, sodium, potassium, alkalinity, sulfate, chloride, fluoride, and silica) within 

a water-quality sample, this method is referred to as sum of 

constituents (SOC). Measures of the solids or salt remaining after evaporation of a water sample is another common 

method for the determination of dissolved solids in water 

samples; this method is referred to as residue on evaporation 

(ROE) (Hem, 1989).

Higher concentrations of dissolved solids can reduce the 

value of water for agricultural uses and human consumption. 

The relative percentages of the major ion concentrations in a 

water sample can be used to classify the water type and can 

help identify water sources (Freeze and Cherry, 1979). Understanding the source of a water sample can provide insight into 

important hydrologic processes within a watershed. This can 

provide useful ancillary data for consideration in the interpretation of water-quality findings. The major ions dissolved in 

most natural waters typically include calcium, magnesium, 

sodium, potassium, bicarbonate, carbonate, sulfate, chloride, 

fluoride, and silicate. 

Although complete major-ion data have not been routinely collected at many sites within the watershed, TDS (SOC 

method) in the ERW has been measured at 72 sites from 

April 1, 1947, to September 30, 2007, and ranged from 20 to 

1,680 mg/L. The 25th, 50th, and 75th percentiles for the ERW 

were 95, 159, and 290 mg/L, respectively). Median values for 

the subwatersheds ranged from 130 mg/L in Gore Creek, 

120 mg/L in the Upper Eagle, 191 mg/L in the Middle Eagle, 

to 526 mg/L in the Lower Eagle (table 11). TDS (ROE method) 

data are available at additional sites in the ERW that do not 

have SOC samples. ROE and SOC provide comparable measurements of the TDS concentrations within a water sample. 

ROE has been measured at 73 sites in the ERW from 

April 1, 1947, to September 30, 2007. Concentrations ranged 

from 8 to 1,410 mg/L throughout the watershed. The 25th, 

50th, and 75th percentiles for the ERW were 110, 190, and 

310 mg/L, respectively. Median values for the subwatersheds 

ranged from 92 mg/L in Gore Creek, 110 mg/L in the Upper 

Eagle, 200 mg/L in the Middle Eagle, to 553 mg/L in the 

Lower Eagle (table 11). The spatial patterns for TDS concentrations (SOC method) show increasing concentrations from 

upstream to downstream with a defined increase occurring near 

Wolcott. Higher concentrations near the mouth of Gore Creek 

appear to be diluted by streamflow from the upper Eagle River. 

Differences in concentrations likely result from increased abundance of salt-bearing geologic formations, such as the Eagle 

Valley Evaporite, downstream from Avon (Tweto, 1979). Seasonal variations for TDS (SOC method) show that concentrations tend to be lowest May–June and highest October–March, 

which is the inverse of patterns in streamflow (fig. 30). 

Evaluation of temporal trends was done for all sites with 

TDS (SOC method) data; trend analysis was done at the 4 sites 

that met the criteria set in the “Data Sources, Compilation, 

Review, and Analysis” section of this report. Findings from the 

trend analysis are presented in table 12 and figure 29. A comparison between sites where trend assessments were completed 

was done to find areas within the ERW that may be contributing 

to the observed trends. A significant flow-adjusted upward trend 

(p-value of 0.03) at site 160 (Gore Creek subwatershed 1995–

2007) shows increasing TDS concentrations in Gore Creek. This 

trend represents a 34.3-mg/L change over the entire specified 

time period. A weakly significant flow-adjusted downward trend 
54 Assessment of Surface-Water Quantity and Quality, Eagle River Watershed, Colorado, 1947–2007

Figure 27. Spatial distribution of median-concentration percentiles and monotonic hardness concentration trends at selected sites in the 

Eagle River watershed, Colorado, 1994–2007.

EXPLANATION

Waterbodies

Upper Eagle subwatershed

Middle Eagle subwatershed

Gore Creek subwatershed Streams

Lower Eagle subwatershed

Monotonic hardness trend, 1994 to 2007

Hardness as calcium carbonate

5–40 0–25

41–150 greater than 25–50

151–268 greater than 50–75

greater than 75–100

Number of samples

Grouping of median concentrations

by Eagle River watershed percentile 

City

77

224

59

No trend

Upward trend

Downward trend

 p-value greater than 0.05–0.15

 p-value greater than 0.01–0.05

 p-value 0.00–0.01

Base from U.S. Geological Survey digital data, 2007,

Universal Transverse Mercator projection

Zone 13 

!(

!(!(

!(

!(

!(!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!( !( 224 !( !( 173

106°15'

106°45'

39°45'

39°30'

0 5 10 KILOMETERS

0 5 10 MILES

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!

Eagle

Gypsum

Wolcott

Avon

Dotsero

Eagle River

Cross Creek

East Fork

Eagle River 

Eagle

River

Black Gore Creek

Gore Creek

Turkey Creek

Minturn

Vail

Red Cliff

Red Cliff

Edwards

(!

!(

!(

Turkey Creek

Fall

Creek

Minturn

Vail Black Gore Creek

160

Rock Creek

(

Alkali Creek

Gore Creek
Assessment of Surface-Water Quality 55

Figure 28. Seasonal pattern of hardness concentrations at selected sites in the Eagle River watershed, Colorado, 1947–2007. Hardness as calcium bicarbonate, in milligrams per liter

Site 224 

0

200

600

400

800

1,000

1,200

52 54 62 82 93 82 73 82 58 51 48 54

o

o

x

xxx

o

x

x

x x

x

January February March April May June July August September October November December

EXPLANATION

30 Number of values

o Upper detached

Upper outside

Lower adjacent

Upper adjacent

x

x Lower outside

o Lower detached

90th percentile

75th percentile

25th percentile

10th percentile

median

Site 201

0

50

150

100

200

350

300

250

400

6 7 7 8 9 9 8 9 7 5 8 7

o

x

x x

x

x x

x

Site 173

0

50

100

200

150

300

350

14 20 26 22 29 30 17 28 25 26 20 26

250 x

x

x

x

x

x x

x x

o

o

o

14 10 18 20 21 20 10 11 12 9 14 14

0

50

200

250

300

150

100

Site 160

x

x

x

x

x

o x
56 Assessment of Surface-Water Quantity and Quality, Eagle River Watershed, Colorado, 1947–2007

Table 11. Summary statistics of dissolved solids and major ions data in the Eagle River watershed, Colorado by subwatershed 1947–2007.

[No., number; MRL, Minimum Reporting Limit; --, undetermined; ROE, residue on evaporation; SOC, sum of constituents]

Constituent 

or property

No. of 

censored 

values

No. of 

samples MRL Minimum1

Concentration or value 

at indicated percentile2 Maximum

25 50 75

Gore Creek subwatershed

Calcium, dissolved (mg/L) 1 454 0.02 0.02 17.0 24.0 38.7 170

Magnesium, dissolved (mg/L) 1 477 .014 .014 2.8 4.0 6.9 56

Sodium, dissolved (mg/L) 1 324 .2 .2 2.3 7.0 14.0 140

Potassium, dissolved (mg/L) 1 219 1.5 .2 .6 .8 1.3 5.6

Bicarbonate, dissolved (mg/L) 0 150 -- 26.0 70 104 123 158

Alkalinity, dissolved (mg/L) 1 351 5.0 5.0 48 80 108 154

Alkalinity, total (mg/L) 0 560 -- 6.8 55 77 110 174

Sulfate, dissolved (mg/L) 71 616 5.0 1.0 4.1 21.0 50 590

Chloride, dissolved (mg/L) 11 506 .1 .1 1.7 3.7 8.7 130

Fluoride, dissolved (mg/L) 59 207 .1 .06 .08 .1 .1 .5

Silica, dissolved (mg/L) 1 219 .2 .2 4.1 4.6 5.3 9.5

Dissolved solids, ROE (mg/L) 0 581 -- 21.0 66 92 170 1,300

Dissolved solids, SOC (mg/L) 0 212 -- 25.0 81 130 198 1,210

Upper Eagle subwatershed

Calcium, dissolved (mg/L) 0 784 -- 2.5 15.0 18.9 23.7 181

Magnesium, dissolved (mg/L) 1 784 .014 .014 5.9 7.6 10.2 258

Sodium, dissolved (mg/L) 0 380 -- .3 1.4 1.9 2.5 29.9

Potassium, dissolved (mg/L) 4 372 1.5 .01 .5 .8 .9 6.5

Bicarbonate, dissolved (mg/L) 0 95 -- 13.0 67 89 116 140

Alkalinity, dissolved (mg/L) 1 741 5.0 3.0 54 66 80 353

Alkalinity, total (mg/L) 2 538 5.0 4.0 20.0 53 74 160

Sulfate, dissolved (mg/L) 26 561 5.0 1.0 9.0 15.0 48 800

Chloride, dissolved (mg/L) 2 570 .1 .1 .60 .9 2.2 28.0

Fluoride, dissolved (mg/L) 23 312 .1 .04 .05 .08 .1 .8

Silica, dissolved (mg/L) 0 370 -- .3 5.6 6.3 7.3 12.4

Dissolved solids, ROE (mg/L) 0 389 -- 8.0 44 110 150 843

Dissolved solids, SOC (mg/L) 0 291 -- 20.0 83 120 160 1,680

Middle Eagle subwatershed

Calcium, dissolved (mg/L) 0 375 -- 6.8 26.9 40 51 143

Magnesium, dissolved (mg/L) 0 376 -- 1.7 6.0 9.5 13.2 86.6

Sodium, dissolved (mg/L) 0 348 -- 1.0 2.5 4.6 26.2 182

Potassium, dissolved (mg/L) 0 265 -- .5 .9 1.2 2.5 19

Bicarbonate, dissolved (mg/L) 0 195 -- 36 78 102 121 456

Alkalinity, dissolved (mg/L) 0 239 -- 29.0 62 86 100 378

Alkalinity, total (mg/L) 0 930 -- 1.0 67 86 102 320

Sulfate, dissolved (mg/L) 3 930 5.0 1.4 41 68 98 490

Chloride, dissolved (mg/L) 0 504 -- .1 1.9 5.5 14.9 308

Fluoride, dissolved (mg/L) 44 231 .1 .06 .1 .1 .2 .8

Silica, dissolved (mg/L) 0 265 -- 3.6 5.2 6.1 7.2 15.4

Dissolved solids, ROE (mg/L) 0 654 -- 26.0 130 200 252 1,192

Dissolved solids, SOC (mg/L) 0 260 -- 40 126 191 406 925

Lower Eagle subwatershed

Calcium, dissolved (mg/L) 0 711 -- 14 54 95 117 343

Magnesium, dissolved (mg/L) 0 711 -- 1.9 11.0 19.0 24.0 65.0

Sodium, dissolved (mg/L) 0 599 -- 1.0 15.5 44 69 131

Potassium, dissolved (mg/L) 0 497 -- .3 1.6 2.7 3.3 6.9

Bicarbonate, dissolved (mg/L) 0 103 -- 51 98 135 149 281

Alkalinity, dissolved (mg/L) 0 105 -- 43 82 114 128 230

Alkalinity, total (mg/L) 2 701 5.0 5.0 92 126 144 430

Sulfate, dissolved (mg/L) 0 1,103 -- 13.0 91 190 244 830

Chloride, dissolved (mg/L) 0 1,050 -- .2 18.0 60 98 404

Fluoride, dissolved (mg/L) 32 361 .1 .05 .1 .2 .2 1.2

Silica, dissolved (mg/L) 0 673 -- 3.2 6.7 8.3 10.0 45

Dissolved solids, ROE (mg/L) 0 1,087 -- 60 282 553 686 1,410

Dissolved solids, SOC (mg/L) 0 500 -- 54 268 526 655 1,370

1

Uncensored values.

2

Percentile values can be less than the MRL values due to multiple MRLs within the combined dataset.
Assessment of Surface-Water Quality 57

!(

!(

!( !(

!(

!(

224

173 160

13

Gore Creek

EXPLANATION

Waterbodies

Upper Eagle subwatershed

Middle Eagle subwatershed

Gore Creek subwatershed Streams

Lower Eagle subwatershed

Monotonic sum of constituents trend, 1995 to 2007

Sum of constituents

5–40 0–25

41–150 less than 25–50

less than 50–75

less than 75–100

Number of samples

Grouping of median concentrations

by Eagle River watershed percentile

City

77

224

59

No trend

Upward trend

Downward trend

 p-value less than 0.05–0.15

 p-value less than 0.01–0.05

 p-value 0.00–0.01

Base from U.S. Geological Survey digital data, 2007,

Universal Transverse Mercator projection

Zone 13 

0 5 10 KILOMETERS

0 5 10 MILES

Eagle

Gypsum

Minturn

Red Cliff

Wolcott

Dotsero

Edwards

Avon Vail

106°15'

106°45'

39°45'

39°30'

!

(!

Figure 29. Spatial distribution of median-concentration percentiles and monotonic sum of constituent trends at selected sites in the Eagle 

River watershed, Colorado, 1995–2007.
58 Assessment of Surface-Water Quantity and Quality, Eagle River Watershed, Colorado, 1947–2007

Figure 30. Seasonal pattern of sum of constituents at selected sites in the Eagle River watershed, Colorado, 1947–2007. Sum of constituents, in milligrams per liter

Site 224 

0

200

800

600

1,000

1,400

1,600

26 31 35 38 41 40 31 40 31 31 31 33

400

1,200

o

o

x

x

x xx

January February March April May June July August September October November December

EXPLANATION

30 Number of values

o Upper detached

Upper outside

Lower adjacent

Upper adjacent

x

x Lower outside

o Lower detached

90th percentile

75th percentile

25th percentile

10th percentile

median

Site 201

0

200

400

800

600

1,000

6 7 7 8 9 9 8 9 7 5 8 7

o

o

x

x

x

x

x

x

x

x

x

Site 173

50

100

200

150

300

5 6 7 9 15 7 4 9 7 7 7 6

250

x

x

x

x

o

o

11 9 14 18 19 18 8 9 9 7 11 10

50

100

250

300

350

200

150

Site 160

x

x

x

x

x
Assessment of Surface-Water Quality 59

Table 12. Summary of monotonic temporal trends for dissolved solids and major ions in the Eagle River watershed, Colorado.

[No., number; --, undetermined, mg/L, milligrams per liter]

Site no. Trend period No. of

samples

Flow

adjustment

Trend slope,

units per year

Percent change,

percent per year p-value Trenddirection

Median

value

Dissolved solids (sum of constituents), mg/L

13 1995–2007 36 No -- -- 0.08 Upward 123

13 1995–2007 36 Yes -- -- .37 No trend 123

160 1995–2007 47 No -- -- .15 Upward 184

160 1995–2007 47 Yes 2.64 1.43 .03 Upward 184

173 1997–2007 36 No -- -- .80 No trend 149

173 1997–2007 36 Yes -- -- 1.00 No trend 149

224 1995–2007 44 No -- -- .45 No trend 493

224 1995–2007 43 Yes -- -- .08 Downward 493

Calcium, mg/L

160 1995–2007 47 No -- -- .23 No trend 46

160 1995–2007 47 Yes -- -- .10 Upward 46

224 1995–2007 44 No -- -- .70 No trend 89

224 1995–2007 43 Yes –1.09 –1.23 .03 Downward 89

Magnesium, mg/L

160 1995–2007 47 No -- -- .17 No trend 8

160 1995–2007 47 Yes .10 1.24 .04 Upward 8

224 1995–2007 44 No -- -- .91 No trend 17

224 1995–2007 43 Yes –.22 –1.29 .03 Downward 17

Sodium, mg/L

160 1995–2007 47 No .28 4.05 .01 Upward 7

160 1995–2007 47 Yes .30 4.31 .002 Upward 7

224 1995–2007 44 No -- -- .17 No trend 52

224 1995–2007 43 Yes -- -- .13 Upward 52

Potassium, mg/L

160 1995–2007 47 No .02 1.71 .04 Upward 1

160 1995–2007 47 Yes .03 2.27 .003 Upward 1

224 1995–2007 44 No -- -- .13 Upward 2

224 1995–2007 43 Yes -- -- .11 Upward 2

Alkalinity, mg/L

160 1995–2007 46 No -- -- .48 No trend 98

160 1995–2007 46 Yes -- -- .58 No trend 98

224 1997–2007 37 No -- -- .17 No trend 116

224 1997–2007 36 Yes -- -- .15 No trend 116

Sulfate, mg/L

160 1995–2007 47 No -- -- .78 No trend 39

160 1995–2007 47 Yes -- -- .82 No trend 39

224 1995–2007 44 No -- -- .29 No trend 166

224 1995–2007 43 Yes –4.46 –2.69 .04 Downward 166

Chloride, mg/L

160 1995–2007 47 No .93 6.97 .004 Upward 13

160 1995–2007 47 Yes 1.07 7.98 .001 Upward 13

224 1995–2007 44 No -- -- .10 Upward 78

224 1995–2007 43 Yes -- -- .06 Upward 78

Silica, mg/L

160 1995–2007 47 No -- -- .72 No trend 5

224 1995–2007 44 No -- -- .11 Downward 6

224 1995–2007 43 Yes –.06 –.97 .03 Downward 6
60 Assessment of Surface-Water Quantity and Quality, Eagle River Watershed, Colorado, 1947–2007

(p-value of 0.08) at site 224 (Lower Eagle subwatershed) shows 

decreasing TDS concentrations upstream from Gypsum. No 

flow-adjusted trend was detected on the Eagle River upstream 

from Avon (site 173) (Middle Eagle subwatershed) or upstream 

of Red Cliff (site 13) (Upper Eagle subwatershed). Areas 

between Gypsum and Avon may be contributing to the detected 

trend on the Eagle River at Gypsum.

A comparison of available data for major ions was 

done to determine ion-specific trends in the ERW. Spatial 

patterns were consistent with the patterns observed for the 

SOC method (fig. 29). Identification of the specific cations 

(positively charged ions) and anions (negatively charged ions) 

within a watershed can help identify likely source areas and 

also can aide in the evaluation of the causes of detected trends. 

Trilinear diagrams or “Piper plots” are useful representations of the relative percentages of major ions within a waterquality sample and allow for the characterization of water 

types for specific sites and seasons. Trilinear diagrams are 

presented for selected sites from different areas of the ERW 

in figures 31–36. Separation of the data into three month time 

periods based on collection date (October–December, January–

March, April–June, and July–September) allows for an examination of seasonal variations in water chemistry at each site. 

At sites 13 (Upper Eagle subwatershed) and 173 (Middle 

Eagle subwatershed), relative percentages of calcium, magnesium, and sodium plus potassium are consistent throughout 

the year, with changes occurring in the relative percentages of 

sulfate and bicarbonate with higher concentrations of bicarbonate potentially related to changes in water chemistry from 

snowmelt runoff April–June. Similar patterns are present in 

the relative abundance of calcium, magnesium, and sodium 

plus potassium and in the occurrence of higher concentrations 

of bicarbonate April–June in data from Gore Creek (site 160; 

Gore Creek subwatershed); however, variations exist in 

the concentrations of chloride plus fluoride with the higher 

concentrations occurring for some samples January–June. At 

sites 201 (Middle Eagle subwatershed) and 224 (Lower Eagle 

subwatershed), relative percentages of several ions vary by 

season. For the most part, the April–June time period shows 

relative increases in calcium and bicarbonate and decreases in 

chloride and sulfate (figs. 34 and 35). 

In addition to temporal variations, regional variations in 

the relative percent of major ions also appear to exist. Sites in 

areas downstream from the Eagle Valley Evaporite (site 224) 

appear to have higher relative percentages of sodium plus 

potassium and chloride plus fluoride than sites upstream 

from the Eagle Valley Evaporite. These differences appear 

to be consistent with the geology of the two areas, with an 

exception during the January–June time period in Gore Creek 

where increases in chloride do not appear to strongly correlate 

to geologic sources.

The spatial patterns of each major ion were similar to 

the patterns observed in the SOC method and ROE method 

data (figs. 37–44). Localized areas with higher concentrations of calcium were observed on Rock Creek and Alkali 

Creek (fig. 37). Localized areas with higher concentrations of 

magnesium were observed on the East Fork of the Eagle River 

near Red Cliff, Rock Creek, and Alkali Creek (fig. 38). Localized areas with higher concentrations of sodium were observed 

on Black Gore Creek and Alkali Creek (fig. 39). These localized areas may be related to human or geologic effects and 

there is insufficient data to determine an exact source. Localized areas with higher concentrations of alkalinity (fig. 44) 

were observed on the East Fork of the Eagle River near Red 

Cliff, Black Gore Creek, and Alkali Creek.

Chloride concentrations measured in samples were 

compared to the State standards within the ERW to provide 

an environmentally relevant context to observations of stream 

condition. The State standard for chloride (250 mg/L) (Colorado Department of Public Health and Environment, 2008) 

was exceeded less than 1 percent (3 comparisons) out of the 

2,630 comparisons in the ERW (table 13 and fig. 45).

The two sites with detected trends in TDS (SOC 

method), site 160 (Gore Creek subwatershed upward trend) 

and site 224 (Lower Eagle subwatershed downward trend), 

were evaluated for trends in calcium, magnesium, sodium, 

potassium, alkalinity, sulfate, chloride, and silica for the time 

period 1995–2007 (table 12, figs. 37–44). At site 160 (Gore 

Creek subwatershed), highly significant flow-adjusted upward 

trends were found for sodium (p-value of 0.002), potassium 

(p-value of 0.003), and chloride (p-value of 0.001); with a 

significant upward trend in magnesium (p-value of 0.04); and 

a weakly significant trend in calcium (p-value of 0.10). At 

site 160 (Gore Creek subwatershed), no trends were observed 

in alkalinity, sulfate, or silica. At site 224 (Lower Eagle subwatershed), significant flow-adjusted downward trends were 

detected in calcium (p-value of 0.03), magnesium (p-value 

of 0.03), sulfate (p-value of 0.04), and silica (p-value of 

0.03); and weakly significant upward trends were observed 

in sodium (p-value of 0.13), potassium (p-value of 0.11), and 

chloride (p-value of 0.06). At site 224 (Lower Eagle subwatershed), no trend was detected in alkalinity.

A quantitative analysis of the relative abundance of calcium, magnesium, sodium, and potassium [cations with a significant upward trend at site 160 (Gore Creek subwatershed)] 

to the available anions (anions with a significant upward 

trend at site 160) indicates that chloride salts likely are the 

source for the detected upward trends because chloride is the 

only commonly occurring anion with a trend at site 160. To 

deduce the source minerals contributing to the observed trends 

the rate-of-change (increase in ions in mg/L per year) for 

each cation and anion was converted to milliequivalents. For 

example, if chloride is the anion related to increases in sodium 

there needs to be an equal increase in chloride to balance the 

atomic ratio of sodium chloride (NaCl); the same one-to-one 

ratio is needed for potassium chloride (KCl). Likewise, for 

chloride to be the anion related to the observed increases in 

magnesium there needs to be twice the increase in chloride to 

balance the atomic ratio of magnesium chloride (MgCl2

); the 

same one-to-two ratio is needed for calcium chloride (CaCl2

). 

To show strong evidence that chloride is the anion related to 

the cation trends at site 160, the number of milliequivalents of 
Assessment of Surface-Water Quality 61

Figure 31. Seasonality of water chemistry at site 13, Eagle River watershed, Colorado, 1947–2007.

Data points

October − December

January − March

April − June

July − September

EXPLANATION Sulfate plus chloride

Calcium plus magnesium

80

60

40

20

80

60

40

20

20

40

60

80

80

60

40

20

Calcium

80

60

40

20

20

40

60

80

Magnesium

20

40

60

80

Chloride, fluoride

20

40

60

80

80

60

40

20

Bicarbonate

80

60

40

20

Sulfate

PERCENT MILLIEQUIVALENTS PER LITER

Sodium plus potassium

Sulfate plus chloride 80

60

40

20

Calcium plus magnesium

80

60

40

20

Ca + Mg

Cl + SO4

Na + K

HCO3

20

40

60

80

20

40

60

80

Calcium

80

60

40

20

Magnesium

20

40

60

80

Sodium plus potassium

80

60

40

20

Magnesium

type

No

dominant

type

Calcium

type

Sodium

type or

potassium type

Chloride, fluoride

20

40

60

80

80

60

40

20

Sulfate

20

40

60

80

No

dominant

type

Bicarbonate

type

Chloride

type

Sulfate

type Bicarbonate
62 Assessment of Surface-Water Quantity and Quality, Eagle River Watershed, Colorado, 1947–2007

Figure 32. Seasonality of water chemistry at site 160, Eagle River watershed, Colorado, 1947–2007.

Data points

October − December

January − March

April − June

July − September

EXPLANATION Sulfate plus chloride

Calcium plus magnesium

80

60

40

20

80

60

40

20

20

40

60

80

80

60

40

20

Calcium

80

60

40

20

20

40

60

80

Magnesium

20

40

60

80

Chloride, fluoride

20

40

60

80

80

60

40

20

Bicarbonate

80

60

40

20

Sulfate

PERCENT MILLIEQUIVALENTS PER LITER

Sodium plus potassium

Sulfate plus chloride 80

60

40

20

Calcium plus magnesium

80

60

40

20

Ca + Mg

Cl + SO4

Na + K

HCO3

20

40

60

80

20

40

60

80

Calcium

80

60

40

20

Magnesium

20

40

60

80

Sodium plus potassium

80

60

40

20

Magnesium

type

No

dominant

type

Calcium

type

Sodium

type or

potassium type

Chloride, fluoride

20

40

60

80

80

60

40

20

Sulfate

20

40

60

80

No

dominant

type

Bicarbonate

type

Chloride

type

Sulfate

type Bicarbonate
Assessment of Surface-Water Quality 63

Figure 33. Seasonality of water chemistry at site 173, Eagle River watershed, Colorado, 1947–2007.

Data points

October − December

January − March

April − June

July − September

EXPLANATION Sulfate plus chloride

Calcium plus magnesium

80

60

40

20

80

60

40

20

20

40

60

80

80

60

40

20

Calcium

80

60

40

20

20

40

60

80

Magnesium

20

40

60

80

Chloride, fluoride

20

40

60

80

80

60

40

20

Bicarbonate

80

60

40

20

Sulfate

PERCENT MILLIEQUIVALENTS PER LITER

Sodium plus potassium

Sulfate plus chloride 80

60

40

20

Calcium plus magnesium

80

60

40

20

Ca + Mg

Cl + SO4

Na + K

HCO3

20

40

60

80

20

40

60

80

Calcium

80

60

40

20

Magnesium

20

40

60

80

Sodium plus potassium

80

60

40

20

Magnesium

type

No

dominant

type

Calcium

type

Sodium

type or

potassium type

Chloride, fluoride

20

40

60

80

80

60

40

20

Sulfate

20

40

60

80

No

dominant

type

Bicarbonate

type

Chloride

type

Sulfate

type Bicarbonate
64 Assessment of Surface-Water Quantity and Quality, Eagle River Watershed, Colorado, 1947–2007

Figure 34. Seasonality of water chemistry at site 201, Eagle River watershed, Colorado, 1947–2007.

Data points

October − December

January − March

April − June

July − September

EXPLANATION Sulfate plus chloride

Calcium plus magnesium

80

60

40

20

80

60

40

20

20

40

60

80

80

60

40

20

Calcium

80

60

40

20

20

40

60

80

Magnesium

20

40

60

80

Chloride, fluoride

20

40

60

80

80

60

40

20

Bicarbonate

80

60

40

20

Sulfate

PERCENT MILLIEQUIVALENTS PER LITER

Sodium plus potassium

Sulfate plus chloride 80

60

40

20

Calcium plus magnesium

80

60

40

20

Ca + Mg

Cl + SO4

Na + K

HCO3

20

40

60

80

20

40

60

80

Calcium

80

60

40

20

Magnesium

20

40

60

80

Sodium plus potassium

80

60

40

20

Magnesium

type

No

dominant

type

Calcium

type

Sodium

type or

potassium type

Chloride, fluoride

20

40

60

80

80

60

40

20

Sulfate

20

40

60

80

No

dominant

type

Bicarbonate

type

Chloride

type

Sulfate

type Bicarbonate
Assessment of Surface-Water Quality 65

Figure 35. Seasonality of water chemistry at site 224, Eagle River watershed, Colorado, 1947–2007.

Data points

October − December

January − March

April − June

July − September

EXPLANATION Sulfate plus chloride

Calcium plus magnesium

80

60

40

20

80

60

40

20

20

40

60

80

80

60

40

20

Calcium

80

60

40

20

20

40

60

80

Magnesium

20

40

60

80

Chloride, fluoride

20

40

60

80

80

60

40

20

Bicarbonate

80

60

40

20

Sulfate

PERCENT MILLIEQUIVALENTS PER LITER

Sodium plus potassium

Sulfate plus chloride 80

60

40

20

Calcium plus magnesium

80

60

40

20

Ca + Mg

Cl + SO4

Na + K

HCO3

20

40

60

80

20

40

60

80

Calcium

80

60

40

20

Magnesium

20

40

60

80

Sodium plus potassium

80

60

40

20

Magnesium

type

No

dominant

type

Calcium

type

Sodium

type or

potassium type

Chloride, fluoride

20

40

60

80

80

60

40

20

Sulfate

20

40

60

80

No

dominant

type

Bicarbonate

type

Chloride

type

Sulfate

type Bicarbonate
66 Assessment of Surface-Water Quantity and Quality, Eagle River Watershed, Colorado, 1947–2007

Figure 36. Seasonality of water chemistry at selected streamflow-gaging station locations, in the Eagle River watershed, Colorado, 1947–2007.

Site number

 13

160

173

201

224

EXPLANATION Sulfate plus chloride

Calcium plus magnesium

80

60

40

20

80

60

40

20

20

40

60

80

80

60

40

20

Calcium

80

60

40

20

20

40

60

80

Magnesium

20

40

60

80

Chloride, fluoride

20

40

60

80

80

60

40

20

Bicarbonate

80

60

40

20

Sulfate

PERCENT MILLIEQUIVALENTS PER LITER

Sodium plus potassium

Sulfate plus chloride 80

60

40

20

Calcium plus magnesium

80

60

40

20

Ca + Mg

Cl + SO4

Na + K

HCO3

20

40

60

80

20

40

60

80

Calcium

80

60

40

20

Magnesium

20

40

60

80

Sodium plus potassium

80

60

40

20

Magnesium

type

No

dominant

type

Calcium

type

Sodium

type or

potassium type

Chloride, fluoride

20

40

60

80

80

60

40

20

Sulfate

20

40

60

80

No

dominant

type

Bicarbonate

type

Chloride

type

Sulfate

type Bicarbonate
Assessment of Surface-Water Quality 67

Figure 37. Spatial distribution of median-concentration percentiles and monotonic calcium concentration trends at selected sites in the Eagle 

River watershed, Colorado, 1995–2007.

EXPLANATION

Waterbodies

Upper Eagle subwatershed

Middle Eagle subwatershed

Gore Creek subwatershed Streams

Lower Eagle subwatershed

Monotonic calcium trend, 1995 to 2007

Calcium

5–40 0–25

41–150 greater than 25–50

greater than 50–75

greater than 75–100

Number of samples

Grouping of median concentrations

by Eagle River watershed percentile 

City

77

224

59

No trend

Upward trend

Downward trend

 p-value greater than 0.05–0.15

 p-value greater than 0.01–0.05

 p-value 0.00–0.01

Base from U.S. Geological Survey digital data, 2007,

Universal Transverse Mercator projection

Zone 13 

!(

!(

!(

!(

!(

!( !(

!(

!(!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

224

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

160

Creek

Eagle

Gypsum

Wolcott

Avon

Dotsero

Eagle River

Cross Creek

East Fork

Eagle River 

Eagle

River

Black Gore Creek

Edwards

106°15'

106°45'

39°45'

39°30'

0 5 10 KILOMETERS

0 5 10 MILES

Gore Creek

Turkey Creek

Minturn

Vail

!( Red Cliff

Minturn

Vail

Red Cliff

Black Gore Creek Gore Creek

Turkey

Rock Creek

Fall Creek

Alkali Creek
68 Assessment of Surface-Water Quantity and Quality, Eagle River Watershed, Colorado, 1947–2007

Figure 38. Spatial distribution of median-concentration percentiles and monotonic magnesium trends at selected sites in the Eagle River 

watershed, Colorado, 1995–2007.

EXPLANATION

Waterbodies

Upper Eagle subwatershed

Middle Eagle subwatershed

Gore Creek subwatershed Streams

Lower Eagle subwatershed

Monotonic magnesium trend, 1995 to 2007

Magnesium

5–40 0–25

41–150 greater than 25–50

greater than 50–75

greater than 75–100

Number of samples

Grouping of median concentrations

by Eagle River watershed percentile 

City

77

224

59

No trend

Upward trend

Downward trend

 p-value greater than 0.05–0.15

 p-value greater than 0.01–0.05

 p-value 0.00–0.01

!(

!(

!(

!(

!( !(

!(

!(!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

224

Base from U.S. Geological Survey digital data, 2007,

Universal Transverse Mercator projection

Zone 13 

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

160

!(

!(

Creek

Minturn

Vail

Red Cliff

Black Gore Creek

Gore Creek

Turkey

Rock Creek

Fall Creek

Eagle

Gypsum

Wolcott

Avon

Dotsero

Eagle River

Cross Creek

East Fork

Eagle River 

Eagle

River

Black Gore Creek

Edwards

106°15'

106°45'

39°45'

39°30'

0 5 10 KILOMETERS

0 5 10 MILES

Gore Creek

Turkey Creek

Minturn

Vail

Red Cliff

Alkali Creek
Assessment of Surface-Water Quality 69

Figure 39. Spatial distribution of median-concentration percentiles and monotonic sodium trends at selected sites in the Eagle River 

watershed, Colorado, 1995–2007.

EXPLANATION

Waterbodies

Upper Eagle subwatershed

Middle Eagle subwatershed

Gore Creek subwatershed Streams

Lower Eagle subwatershed

Monotonic sodium trend, 1995 to 2007

Sodium

5–40 0–25

41–150 greater than 25–50

greater than 50–75

greater than 75–100

Number of samples

Grouping of median concentrations

by Eagle River watershed percentile 

City

77

224

59

No trend

Upward trend

Downward trend

 p-value greater than 0.05–0.15

 p-value greater than 0.01–0.05

 p-value 0.00–0.01

Base from U.S. Geological Survey digital data, 2007,

Universal Transverse Mercator projection

Zone 13 

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

224

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

160

Creek

Eagle

Gypsum

Wolcott

Avon

Dotsero

Eagle River

Cross Creek

East Fork

Eagle River 

Eagle

River

Black Gore Creek

Edwards

106°15'

106°45'

39°45'

39°30'

0 5 10 KILOMETERS

0 5 10 MILES

Gore Creek

Turkey Creek

Minturn

Vail

Red Cliff

Alkali Creek

Minturn

Vail

Red Cliff

Black Gore Creek

Gore Creek

Turkey

Rock Creek

Fall Creek

!(

!(
70 Assessment of Surface-Water Quantity and Quality, Eagle River Watershed, Colorado, 1947–2007

Figure 40. Spatial distribution of median-concentration percentiles and monotonic potassium trends at selected sites in the Eagle River 

watershed, Colorado, 1995–2007.

EXPLANATION

Waterbodies

Upper Eagle subwatershed

Middle Eagle subwatershed

Gore Creek subwatershed Streams

Lower Eagle subwatershed

Monotonic potassium trend, 1995 to 2007

Potassium

5–40 0–25

41–150 greater than 25–50

greater than 50–75

greater than 75–100

Number of samples

Grouping of median concentrations

by Eagle River watershed percentile 

City

77

224

59

No trend

Upward trend

Downward trend

 p-value greater than 0.05–0.15

 p-value greater than 0.01–0.05

 p-value 0.00–0.01

Base from U.S. Geological Survey digital data, 2007,

Universal Transverse Mercator projection

Zone 13 

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

224

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

160

Creek

Eagle

Gypsum

Wolcott

Avon

Dotsero

Eagle River

Cross Creek

East Fork

Eagle River 

Eagle

River

Black Gore Creek

Edwards

106°15'

106°45'

39°45'

39°30'

0 5 10 KILOMETERS

0 5 10 MILES

Gore Creek

Turkey Creek

Minturn

Vail

Red Cliff

Alkali Creek

Minturn

Vail

Red Cliff

Black Gore Creek

Gore Creek

Turkey

Rock Creek

Fall Creek

!

!(

(
Assessment of Surface-Water Quality 71

Figure 41. Spatial distribution of median-concentration percentiles and monotonic chloride trends at selected sites in the Eagle River 

watershed, Colorado, 1995-2007.

EXPLANATION

Waterbodies

Upper Eagle subwatershed

Middle Eagle subwatershed

Gore Creek subwatershed Streams

Lower Eagle subwatershed

Monotonic chloride trend, 1995 to 2007

Chloride

5–40 0–25

41–150 greater than 25–50

greater than 50–75

greater than 75–100

Number of samples

Grouping of median concentrations

by Eagle River watershed percentile 

City

77

224

59

No trend

Upward trend

Downward trend

 p-value greater than 0.05–0.15

 p-value greater than 0.01–0.05

 p-value 0.00–0.01

Base from U.S. Geological Survey digital data, 2007,

Universal Transverse Mercator projection

Zone 13 

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

224

!

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

(

160

Creek

Minturn

Vail

Red Cliff

Black Gore Creek

Gore Creek

Turkey

Rock Creek

Fall Creek

Eagle

Gypsum

Wolcott

Avon

Dotsero

Eagle River

Cross Creek

East Fork

Eagle River 

Eagle

River

Edwards

106°15'

106°45'

39°45'

39°30'

0 5 10 KILOMETERS

0 5 10 MILES

Gore Creek

Turkey Creek

Minturn

Vail

Red Cliff

Alkali Creek

Black Gore Creek

!(
72 Assessment of Surface-Water Quantity and Quality, Eagle River Watershed, Colorado, 1947–2007

Figure 42. Spatial distribution of median-concentration percentiles and monotonic sulfate trends at selected sites in the Eagle River 

watershed, Colorado, 1995–2007.

EXPLANATION

Waterbodies

Upper Eagle subwatershed

Middle Eagle subwatershed

Gore Creek subwatershed Streams

Lower Eagle subwatershed

Monotonic sulfate trend, 1995 to 2007

Sulfate

5–40 0–25

41–150 greater than 25–50

greater than 50–75

greater than 75–100

Number of samples

Grouping of median concentrations

by Eagle River watershed percentile 

City

77

224

59

No trend

Upward trend

Downward trend

 p-value greater than 0.05–0.15

 p-value greater than 0.01–0.05

 p-value 0.00–0.01

Base from U.S. Geological Survey digital data, 2007,

Universal Transverse Mercator projection

Zone 13 

!(

!(

!(

!(

!(

!(

!(

!(

!(!(

!(

!(

!( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

Eagle

Gypsum

Wolcott

Avon

Dotsero

Eagle River

Cross Creek

East Fork

Eagle River 

Eagle

River

Black Gore Creek

Edwards

106°15'

106°45'

39°45'

39°30'

0 5 10 KILOMETERS

0 5 10 MILES

Gore Creek

Turkey Creek

Minturn

Vail

Red Cliff

Minturn

Avon

Gore Creek

Alkali Creek

(!

160

224
Assessment of Surface-Water Quality 73

Figure 43. Spatial distribution of median-concentration percentiles and monotonic silica trends in at selected sites in the Eagle River 

watershed, Colorado, 1995–2007.

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

EXPLANATION

Waterbodies

Upper Eagle subwatershed

Middle Eagle subwatershed

Gore Creek subwatershed Streams

Lower Eagle subwatershed

Monotonic silica trend, 1995 to 2007

Silica

5–40 0–25

41–150 greater than 25–50

greater than 50–75

greater than 75–100

Number of samples

Grouping of median concentrations

by Eagle River watershed percentile 

City

77

224

59

No trend

Upward trend

Downward trend

 p-value greater than 0.05–0.15

 p-value greater than 0.01–0.05

 p-value 0.00–0.01

Base from U.S. Geological Survey digital data, 2007,

Universal Transverse Mercator projection

Zone 13 

(!

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

Eagle

Gypsum

Wolcott

Avon

Dotsero

Eagle River

Cross Creek

East Fork

Eagle River 

Eagle

River

Black Gore Creek

Edwards

106°15'

106°45'

39°45'

39°30'

0 5 10 KILOMETERS

0 5 10 MILES

Gore Creek

Turkey Creek

Minturn

Vail

Red Cliff

Minturn

Red Cliff

Alkali Creek

224

160

Gore Creek
74 Assessment of Surface-Water Quantity and Quality, Eagle River Watershed, Colorado, 1947–2007

Figure 44. Spatial distribution of median-concentration percentiles and monotonic alkalinity trends at selected sites in the Eagle River 

watershed, Colorado, 1995–2007.

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

EXPLANATION

Waterbodies

Upper Eagle subwatershed

Middle Eagle subwatershed

Gore Creek subwatershed Streams

Lower Eagle subwatershed

Monotonic alkalinity trend, 1995 to 2007

Alkalinity

5–40 0–25

41–150 greater than 25–50

greater than 50–75

greater than 75–100

Number of samples

Grouping of median concentrations

by Eagle River watershed percentile 

151–165

City

77

224

59

No trend

Upward trend

Downward trend

 p-value greater than 0.05–0.15

 p-value greater than 0.01–0.05

 p-value 0.00–0.01

Base from U.S. Geological Survey digital data, 2007,

Universal Transverse Mercator projection

Zone 13 

!(

!(

!(!(

!(

!(

!(

!( !(

!(

!(!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!( !(

!(

224

Eagle

Gypsum

Wolcott

Avon

Dotsero

Eagle River

Cross Creek

East Fork

Eagle River 

Eagle

River

Black Gore Creek

Edwards

106°15'

106°45'

39°45'

39°30'

0 5 10 KILOMETERS

0 5 10 MILES

Gore Creek

Turkey Creek

Minturn

Vail

Red Cliff

Alkali Creek

224

Minturn

Red Cliff

160

Gore Creek
Assessment of Surface-Water Quality 75

Figure 45. Number of exceedances of the Colorado water-quality standard for major ions at selected sites in the Eagle River watershed, 

Colorado, 1947–2007.

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!( !(

!(

!(

!(

!( !(

!( !(

!( !( !( !( !(

!(

EXPLANATION

Waterbodies

Upper Eagle subwatershed

Middle Eagle subwatershed

Gore Creek subwatershed Streams

Lower Eagle subwatershed

Major ions

5–40 0

41–150 1

Number of samples Number of exceedances

151–794

City

Base from U.S. Geological Survey digital data, 2007,

Universal Transverse Mercator projection

Zone 13 

Eagle

Wolcott

Avon

Dotsero

Edwards

Minturn

Gypsum

East Fork

Eagle River 

Eagle

River

106°15'

106°45'

39°45'

39°30'

0 5 10 KILOMETERS

0 5 10 MILES

Gore Creek

Alkali Creek

Turkey

Minturn

Vail

Red Cliff

Black Gore Creek

Rock Creek

Fall

Creek

Turkey Creek

Vail

!(

!(

( !(

!(

!(

!(

!(

!(

!(

!(

!(

!( !(

!(

!(!(

!(

!(

(! !(

!( !(!(

!(

!(

!( !( !(

!(

!(

!(

!(

!(

!(

!(

!(!(

!( !

!(

!( !( !(

!(

!( !(

!( !(

!(!( !( !( !( !(!(!(!(

!( !( !(

!(

!( !( !( !( !( !( !( !( !(!(!( !(

!( !( !(!(

!( !(

!(

!(

180

201

227

Cross Creek

Red Cliff

Black Gore Creek

Eagle River

!

Gore Creek
76 Assessment of Surface-Water Quantity and Quality, Eagle River Watershed, Colorado, 1947–2007

chloride needs to be equal or greater than the sum of the milliequivalents of all cations with an upward trend at site 160. 

The quantity of increase in chloride at site 160 can account for 

all of the anions needed to balance magnesium, sodium, and 

potassium with a small amount of additional chloride remaining (table 14). This excess chloride may be related to the 

weakly significant trend observed in calcium at site 160.

Comparison of the chloride salts to minerals commonly 

found in the geologic formations within the Gore Creek subwatershed provides evidence that the trend source may not be 

natural. Chloride salts are ionic solids that are highly soluble 

and primarily are found in nature as evaporite deposits. Evaporite deposits occur in the ERW primarily in the Eagle Valley 

Evaporite. These evaporite deposits occur in areas downstream from Edwards, but do not appear to be present in the 

Gore Creek watershed (fig. 4) (Tweto, 1979). Additionally, if 

evaporite deposits were the source for the detected trends, it is 

Table 13. Summary of exceedances of Colorado water-quality standard (250 milligrams per liter) for chloride 

for surface-water samples collected in the Eagle River watershed, 1947–2007.

[No., number; --, no data]

Constituent

or property

No. of 

censored values

No. of 

samples

No. of standard

exceedances

Minimum 

date

Maximum 

date

Gore Creek subwatershed

Chloride 11 506 0 -- --

Upper Eagle subwatershed

Chloride 2 570 0 -- --

Middle Eagle subwatershed

Chloride 0 504 2 Feb. 24, 1977 Sept. 4, 2002

Lower Eagle subwatershed

Chloride 0 1,050 1 Feb. 24, 1977 Feb. 24, 1977

Table 14. Comparison of cation and anion concentration, Gore Creek subwatershed, Colorado, 1947–2007.

[mg/L, milligrams per liter; --, no data; Ca2+, calcium; Mg2+, magnesium; Na+, sodium; K+, potassium; CO3

2-, carbonate; SO42-, sulfate; Cl–

, chloride; F–, 

floride; SiO2

2-, silicate]

Ion Trend slope, 

mg/L per year

Atomic 

mass

Abundance of ions

relative to potassium2

Ionic 

charge

Milliequivalents 

relative to potassium

Cations

Calcium1 -- 40.078 -- Ca2+ --

Magnesium 0.1 24.305 5.4 Mg2+ 10.8

Sodium .3 22.99 17.0 Na+ 17.0

Potassium .03 39.098 1.0 K+ 1.0

Total 28.8

Anions

Carbonate No trend 60.0089 0 CO3

2– 0

Sulfate No trend 96.0626 0 SO4

2– 0

Silicate No trend 60.0843 0 SiO2

2– 0

Chloride 1.07 35.453 39.3 Cl– 39.3

Fluoride No trend 18.9984 0 F– 0

Total 39.3

1

Trend slope for calcium not reported because p-value is between 0.05–0.15, a weakly significant trend.

2

Obtained by dividing the trend slope by the atomic mass and normalizing results for cations and anions to the smallest value (potassium, 0.0008).

likely that there would be an upward trend in sulfates in addition to chloride salts because of the abundance of gypsum and 

anhydrite (calcium-sulfate minerals) within the Eagle Valley 

Evaporite (Tweto, 1979). A potential source for the observed 

chloride salts may be the chemical anti-icing and deicing 

products used during winter road maintenance in municipal areas and on Interstate-70. Various magnesium chloride 

(MgCl2) deicers and anti-icers, along with solid deicers (NaCl, 

MgCl2, KCl, CaCl2, and traction sand) commonly are used by 

the Colorado Department of Transportation (CDOT) to assist 

in winter road maintenance operations in Colorado (Colorado 

Department of Transportation, 2008). Application of these 

anti-icing and deicing products may explain the upward trend 

detected at site 160. 

Potential effects on water quality, aquatic life, and riparian 

vegetation are numerous and variable and beyond the scope 

of this study. If the present trends are the result of winter-road 
Assessment of Surface-Water Quality 77

maintenance operations, then the timing and instream concentration are likely to occur in a highly variable pattern both 

spatially and temporally because salt contribution to the stream 

from these types of sources would likely coincide with the 

episodic melt cycles of the snow along the roadways periphery. 

Additionally, the pattern and concentrations of these salts in 

the stream also could be affected by the transient storage of an 

unquantified amount of these salts in the shallow groundwater 

system in municipal areas and roadways. These variations in 

concentration currently (2009) are not well represented by the 

data collection within the Gore Creek watershed. 

Nutrients

Nutrients provide food to plants and animals but excessive 

concentrations in streams can have adverse effects to both biota 

and human health. Nitrogen and phosphorous occur naturally 

in streams at “background” levels, even in pristine watersheds 

(table 15). It is well established that a variety of watershed land 

uses alter the amounts of nutrients reaching surface waters. 

Nitrogen and phosphorus are two nutrients that can be 

present in varying chemical forms within the watershed. 

Nitrogen species include ammonia, nitrate, nitrite, and other 

compounds; phosphorus species include orthophosphate and 

other compounds. The chemical form of these nutrients can be 

related to the bioavailability of the compound to an organism or 

how the compounds are transported in the environment. Eutrophication of streams or other waterbodies is possible when 

excessive concentrations of nitrogen or phosphorus are present, 

resulting in algae growth and decomposition that can affect the 

availability of dissolved oxygen for aquatic communities (Center for Disease Control and Prevention, 2011). Algal blooms 

can result in an initial increase in dissolved oxygen followed by 

decay and decomposition, which lead to decreases in dissolved 

Table 15. Median nutrient concentrations for selected sites in the Eagle River watershed, 

Colorado, 1968–2007 and background regional reference values.

[mg/L, milligrams per liter; --, no data; <, less than]

Site name (sample dates)

Nitrate 

concentration, 

mg/L

Total phosphorous 

concentration, 

mg/L

Gore Creek background1 (1968–1997) 0.11 <0.01

Gore Creek at the mouth site 160 (1996–2007) .657 .088

Eagle River at Red Cliff site 3 (1996–2007) -- .004

Eagle River at Avon site 173 (1996–2007) .282 .037

Eagle River at Gypsum site 224 (1996–2007) .585 .088

Colorado Rockies Ecoregion 21 regional reference values2 (2000) <.10 .02

1

Wynn and others (2001).

2

U.S. Environmental Protection Agency, Nutrient criteria technical guidance manual: rivers and streams. Report 

No. EPA-822B-00-002 (2000).

oxygen that can result in a decline in the health and diversity 

of invertebrates and fish. Eutrophication of source waters can 

cause associated problems such as clogging water intakes, 

habitat alteration, toxic algal blooms, reduction in biodiversity, 

pH fluctuations, and taste-and-odor, among others (Center for 

Disease Control and Prevention, 2011). Additionally, elevated 

concentrations of un-ionized ammonia (NH3) in a stream can 

be toxic to fish (Fairchild and others, 2002).

In the ERW, natural sources of nutrients (nitrogen and 

phosphorus) to streams may include chemical dissolution or 

reaction with nitrogen- and phosphorus-rich minerals within 

soils and geologic formations, decomposition of organic 

matter, and atmospheric deposition. Additional sources may 

include human activities related to agriculture such as fertilizers, phosphate detergents, effluent from wastewater treatment 

plants, seepage from septic systems, and fossil-fuel combustion. Nitrate is the most stable nitrogen species found in 

natural waters and can exist in a wide range of environmental 

conditions (Mueller and others, 1995). Nitrite is an intermediate form of nitrogen that is unstable in most natural waters. 

High concentrations of nitrite can be associated with untreated 

sewage, fertilizers, and (or) other organic waste such as decaying plant debris. Phosphate is the only significant form of dissolved phosphorus in natural water (Hem, 1989) and it is only 

moderately soluble. Phosphorus often adsorbs to the surface of 

sediment and organic particles and when found in waterways, 

can indicate that erosion and sediment transport is occurring 

(Mueller and others, 1995).

Nutrients in the ERW have been measured at 114 sites 

from February 21, 1968, through September 30, 2007. Median 

nutrient concentrations within the ERW were compared 

to regional reference values (table 15). The data analysis 

throughout this report did not differentiate if a sampling site 

was within a mixing zone as defined by CDPHE (Colorado 

Department of Public Health and Environment, 2002).
78 Assessment of Surface-Water Quantity and Quality, Eagle River Watershed, Colorado, 1947–2007

Concentrations of nitrate ranged from less than 0.02 to 

84 mg/L depending on location and time of year. The 25th, 

50th, and 75th percentiles for the ERW are 0.2, 0.6, and 

1.2 mg/L, respectively. Median concentrations for the subwatersheds ranged from 0.2 mg/L in Gore Creek subwatershed, 

0.06 mg/L in the Upper Eagle subwatershed, to 0.5 mg/L in 

the Middle Eagle subwatershed, and 0.2 mg/L in the Lower 

Eagle subwatershed (table 16).

Concentrations of nitrite ranged from less than 0.01 to 

1.8 mg/L depending on location and time of year. The 25th, 

50th, and 75th percentiles for the ERW are 0.002, 0.004, and 

0.01 mg/L, respectively. Median concentrations for the subwatersheds ranged from 0.004 mg/L in Gore Creek subwatershed, 

0.003 mg/L in the Upper Eagle subwatershed, 0.006 mg/L in 

the Middle Eagle subwatershed, to 0.003 mg/L in the Lower 

Eagle subwatershed (table 16).

Concentrations of ammonia ranged from less than 0.1 

to 18.3 mg/L depending on location and time of year. The 

25th, 50th, and 75th percentiles for the ERW are 0.01, 0.02, 

and 0.05 mg/L, respectively. Median concentrations for the 

subwatersheds were 0.02 mg/L in Gore Creek subwatershed, 

0.03 mg/L in the Upper Eagle subwatershed, 0.03 mg/L in 

the Middle Eagle subwatershed, and 0.04 mg/L in the Lower 

Eagle subwatershed (table 16).

Concentrations of un-ionized ammonia ranged from less 

than 0.01 to 1.47 mg/L depending on location and time of 

year. The 25th, 50th, and 75th percentiles for the ERW are 

0.0003, 0.001, and 0.004 mg/L, respectively. Median concentrations for the subwatersheds ranged from 0.001 mg/L 

in Gore Creek subwatershed, 0.001 mg/L in the Upper Eagle 

subwatershed, to 0.003 mg/L in the Middle Eagle subwatershed (table 16).

Concentrations of total phosphorus ranged from less than 

0.05 to 17 mg/L depending on location and time of year. The 

25th, 50th, and 75th percentiles for the ERW are 0.02, 0.04, 

and 0.1 mg/L, respectively. Median concentrations for the subwatersheds ranged from 0.05 mg/L in Gore Creek subwatershed, 0.01 mg/L in the Upper Eagle subwatershed, 0.06 mg/L 

Table 16. Summary statistics of nutrients data in the Eagle River watershed, Colorado, by subwatershed.

[No., number; MRL, Minimum Reporting Limit; <, less than; --, undetermined]

Constituent 

or property

No. of 

censored values

No. of

samples MRL Minimum1

Concentration or value 

at indicated percentile2 Maximum

25 50 75

Gore Creek subwatershed

Nitrate 32 313 0.02 0.005 0.09 0.2 0.7 9.4

Nitrite 188 371 .01 .0003 .002 .004 .01 .08

Ammonia 615 862 .1 .002 .01 .02 .06 3.8

Un-ionized ammonia 32 140 .01 .0001 .0005 .001 .003 <.01

Total phosphorus 163 514 .05 .007 .02 .05 .10 3.2

Orthophosphate 172 419 .01 .001 .01 .01 .05 .6

Upper Eagle subwatershed

Nitrate 39 143 .02 .009 .017 .06 .20 1.7

Nitrite 144 215 .01 .0009 .001 .003 .005 <.01

Ammonia 392 888 .1 .002 .01 .03 .07 4.1

Un-ionized ammonia 23 295 .01 .0001 .0003 .001 .003 1.47

Total phosphorus 286 456 .05 .002 .006 .01 .02 .7

Orthophosphate 122 462 .01 .001 .003 .003 .004 .2

Middle Eagle subwatershed

Nitrate 11 329 .02 .02 .3 .5 1.2 84

Nitrite 82 376 .01 .0009 .003 .006 .02 1.8

Ammonia 771 1,275 .1 .002 .01 .03 .1 18.3

Un-ionized ammonia 22 295 .01 .0001 .001 .003 .006 0.24

Total phosphorus 131 630 .05 .004 .03 .06 .1 2.1

Orthophosphate 101 387 .01 .001 .007 .01 .04 .7

Lower Eagle subwatershed

Nitrate 35 722 .02 .009 .09 .2 .4 4.1

Nitrite 81 293 .01 .0003 .002 .003 .007 .07

Ammonia 225 470 .1 .006 .02 .04 .08 .7

Un-ionized ammonia 2 3 .01 .01 -- -- -- .02

Total phosphorus 100 455 .05 .008 .03 .07 .1 17.0

Orthophosphate 68 356 .01 .0003 .01 .01 .04 4.89

1

Uncensored values.

2 Percentile values can be less than the MRL values due to multiple MRLs within the combined dataset.
Assessment of Surface-Water Quality 79

in the Middle Eagle subwatershed, to 0.07 mg/L in the Lower 

Eagle subwatershed (table 16).

Concentrations of orthophosphate ranged from less than 

0.01 to 4.89 mg/L depending on location and time of year. 

The 25th, 50th, and 75th percentiles for the ERW are 0.003, 

0.006, and 0.03 mg/L, respectively. Median concentrations 

for the subwatersheds ranged from 0.01 mg/L in Gore Creek 

subwatershed, 0.003 mg/L in the Upper Eagle subwatershed, 

0.01 mg/L in the Middle Eagle subwatershed, to 0.01 mg/L in 

the Lower Eagle subwatershed (table 16).

The spatial pattern of nutrients (figs. 46–50) shows lower 

concentrations on many tributaries and on the Eagle River 

upstream from Red Cliff with increases in nutrients downstream 

of major urban areas. Seasonal variations show that for many 

nutrient species, concentrations tend to be lowest May–June 

and highest January–March (figs. 51–54). The gradual changes 

in concentrations between seasons may be related to dilution 

effects from increases and decreases in streamflow. Downstream 

in the Eagle River near Gypsum (site 224), total phosphorus 

concentrations are elevated January–May and July–September 

with concentrations highest in April. These higher concentrations may be related to sediment transported by snowmelt runoff 

(January–April) and rainfall (July–September). 

Water-quality State standards have been established 

by CDPHE for nitrate (10 mg/L), nitrite (0.05 mg/L), and 

un-ionized ammonia (TVS) for selected stream segments in 

the watershed (Colorado Department of Public Health and 

Environment, 2007) (fig. 12). CDPHE has not established an 

in-stream State standard for total phosphorus. The State of 

Colorado Water Quality Control Division currently (2009) is 

working to understand the link between nutrient criteria for 

streams and their designated uses (Colorado Water Quality 

Forum, 2008). General recommendations for total phosphorus concentration exist from the USEPA at concentrations of 

0.01 and 0.1 mg/L (U.S. Environmental Protection Agency, 

1986). In this report, 0.1 mg/L was used to compare sample 

concentrations. This was done in recognition that this concentration is only a recommendation, not an actual standard, 

and because many of the method reporting limits (MRLs) 

used in ERW data collection are equal to or exceed the lower 

0.01 mg/L recommendation.

The State standard value for chronic nitrate set by the 

CDPHE is 10.0 mg/L for all reaches of the ERW except for segment 11 (100.0 mg/L) (Colorado Department of Public Health 

and Environment, 2008). The State standard for chronic nitrate 

(10 mg/L) was exceeded less than 1 percent (2 comparisons) of 

the 1,507 comparisons in the ERW (table 17).

The State standard for chronic nitrite set by the CDPHE 

is 0.05 mg/L for all reaches of the ERW except for segment 

11 (10.0 mg/L) (Colorado Department of Public Health and 

Environment, 2008). The State standard for chronic nitrite was 

exceeded 9 percent (70 comparisons) of the 1,255 comparisons in the ERW (table 17).

The State standard for un-ionized ammonia is set by the 

CDPHE as a TVS. The TVS are site-specific for both acute and 

chronic exposure levels based on pH and water temperature. In 

samples where either pH or water temperature was not measured, the sample was not compared to the TVS. At present, 

segment 11 of the ERW does not have a State standard for 

un-ionized ammonia (fig. 12). ERW had 7 sites with samples 

with exceedances of the un-ionized ammonia chronic TVS. 

The State standard for un-ionized ammonia was exceeded less 

than 5 times over a period of several years for most sites in 

the ERW, although some sites exhibited exceedances multiple times within a given year. Out of the 3,495 comparisons 

of un-ionized ammonia measurements to State standards, 

less than 1 percent (21 comparisons) of the total number 

of measurements exceeded the chronic State standard. The 

ERW had 7 sites with samples with exceedances of the acute 

State standard. Out of the 3,495 comparisons of un-ionized 

ammonia measurements to State standards, less than 1 percent 

(28 comparisons) of the total number of measurements 

exceeded the acute State standard (table 17).

The USEPA recommendation for total phosphorus is 

0.1 mg/L (Colorado Department of Public Health and Environment, 2008) and is used in this report for all reaches of the 

ERW. The total phosphorus recommended concentration was 

exceeded 10 or less times over a period of several years for 

most sites in the ERW; approximately 24 percent (511 comparisons) of the total number of comparisons (2,055) were higher 

than the recommended concentration (table 17). Figures 55–60 

show the concentrations for total phosphorus through time at 

sites with numerous comparisons that were higher than the 

recommended concentrations.

To better represent exceedances of State standards for 

nutrients in the ERW as a whole, the combined number of 

samples with detected exceedances for any of the nutrient species discussed was made into map form. Maps summarizing 

the spatial extent of chronic-nutrient exceedances and acutenutrient exceedances are presented in figures 61–62.

Evaluation of temporal trends was done for all sites with 

nitrate data; trend analysis was done at the 3 sites that met the 

criteria set in the “Data Sources, Compilation, Review, and 

Analysis” section of this report. Findings from the trend analysis are presented in table 18 and figures 46–50. Seasonal Kendall Trend tests were done for various time periods between 

1994–2007 depending on the data available at each site. A significant upward trend (p-value of 0.015) in nitrate at site 224 

(Lower Eagle subwatershed) occurs for 1994–2007. This trend 

represented a 0.30-mg/L increase over the entire specified time 

period. Upstream at sites 173 (Middle Eagle subwatershed) 

and 160 (Gore Creek subwatershed) there was no trend. The 

area between sites 224 (Lower Eagle subwatershed) and 173 

(Middle Eagle subwatershed) contains several tributaries and 

urban areas including Avon, Edwards, Eagle, and Gypsum 

(fig. 46) which may contribute to the observed trend.

Evaluation of temporal trends was done for all sites with 

nitrite data; trend analysis was done at the 3 sites that met the 

criteria set in the “Data Sources, Compilation, Review, and 

Analysis” section of this report. Findings from the trend analysis are presented in table 18 and figure 47. Seasonal Kendall 

Trend tests were done for the time period 1999–2007. There is 
80 Assessment of Surface-Water Quantity and Quality, Eagle River Watershed, Colorado, 1947–2007

Figure 46. Spatial distribution of median-concentration percentiles and monotonic nitrate trends at selected sites in the Eagle River watershed, 

Colorado, 1995–2007.

!

!

224

173

160

EXPLANATION

Waterbodies

Upper Eagle subwatershed

Middle Eagle subwatershed

Gore Creek subwatershed Streams

Lower Eagle subwatershed

Monotonic nitrate trend, 1994 to 2007

Nitrate

5–40 0–25

41–150 less than 25–50

less than 50–75

less than 75–100

Number of samples

Grouping of median concentrations

by Eagle River watershed percentile

City

77

224

59

No trend

Upward trend

Downward trend

 p-value less than 0.05–0.15

 p-value less than 0.01–0.05

 p-value 0.00–0.01

Base from U.S. Geological Survey digital data, 2007,

Universal Transverse Mercator projection

Zone 13 

0 5 10 KILOMETERS

0 5 10 MILES

Eagle

Gypsum

Minturn

Red Cliff

Wolcott

Dotsero

Edwards

Avon Vail

106°15'

106°45'

39°45'

39°30'

!

! Gore Creek
Assessment of Surface-Water Quality 81

Figure 47. Spatial distribution of median-concentration percentiles and monotonic nitrite trends at selected sites in the Eagle River watershed, 

Colorado, 1995–2007.

!(

!

!( !(

!(

224

173

160

Gore Creek

106°15'

106°45'

39°45'

39°30'

0 5 10 KILOMETERS

0 5 10 MILES

EXPLANATION

Waterbodies

Upper Eagle subwatershed

Middle Eagle subwatershed

Gore Creek subwatershed Streams

Lower Eagle subwatershed

Monotonic nitrate trend, 1994 to 2007

Nitrate

5–40 0–25

41–150 less than 25–50

less than 50–75

less than 75–100

Number of samples

Grouping of median concentrations

by Eagle River watershed percentile

City

77

224

59

No trend

Upward trend

Downward trend

 p-value less than 0.05–0.15

 p-value less than 0.01–0.05

 p-value 0.00–0.01

Eagle

Gypsum

Minturn

Red Cliff

Wolcott

Dotsero

Edwards

Avon Vail

Base from U.S. Geological Survey digital data, 2007,

Universal Transverse Mercator projection

Zone 13 

(

(!
82 Assessment of Surface-Water Quantity and Quality, Eagle River Watershed, Colorado, 1947–2007

Figure 48. Spatial distribution of median-concentration percentiles and monotonic ammonia trends at selected sites in the Eagle River 

watershed, Colorado, 1995–2007.

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

(

EXPLANATION

Waterbodies

Upper Eagle subwatershed

Middle Eagle subwatershed

Gore Creek subwatershed Streams

Lower Eagle subwatershed

Monotonic ammonia trend, 1995 to 2007

Ammonia

5–40 0–25

41–150 greater than 25–50

greater than 50–75

greater than 75–100

Number of samples

Grouping of median concentrations

by Eagle River watershed percentile 

151–249

City

77

224

59

No trend

Upward trend

Downward trend

 p-value greater than 0.05–0.15

 p-value greater than 0.01–0.05

 p-value 0.00–0.01

Base from U.S. Geological Survey digital data, 2007,

Universal Transverse Mercator projection

Zone 13 

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!( !(

!(

!(

(!! Avon

Eagle

Gypsum

Wolcott

Avon

Dotsero

Eagle River

Cross Creek

East Fork

Eagle River 

Eagle

River

Black Gore Creek

Edwards

106°15'

106°45'

39°45'

39°30'

0 5 10 KILOMETERS

0 5 10 MILES

Gore Creek

Turkey Creek

Minturn

Vail

Red Cliff

Alkali Creek

224

187B

160

Minturn
Assessment of Surface-Water Quality 83

Figure 49. Spatial distribution of median-concentration percentiles and monotonic total phosphorus trends at selected sites in the Eagle River 

watershed, Colorado, 1995–2007.

!

!

!

!(

!(

!

!(

!( !(

!(

!

!(

224

3

160

173

Gore Creek

EXPLANATION

Waterbodies

Upper Eagle subwatershed

Middle Eagle subwatershed

Gore Creek subwatershed Streams

Lower Eagle subwatershed

Monotonic total phosphorus trend, 1995 to 2007

Total phosphorus

5–40 0–25

41–150 less than 25–50

less than 50–75

less than 75–100

Number of samples

Grouping of median concentrations

by Eagle River watershed percentile

City

77

224

59

No trend

Upward trend

Downward trend

 p-value less than 0.05–0.15

 p-value less than 0.01–0.05

 p-value 0.00–0.01

Base from U.S. Geological Survey digital data, 2007,

Universal Transverse Mercator projection

Zone 13 

0 5 10 KILOMETERS

0 5 10 MILES

Eagle

Gypsum

Minturn

Red Cliff

Wolcott

Dotsero

Edwards

Avon Vail

!

!!

106°15'

106°45'

39°45'

39°30'

(!

!
84 Assessment of Surface-Water Quantity and Quality, Eagle River Watershed, Colorado, 1947–2007

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

224

173

160

Gore Creek

EXPLANATION

Waterbodies

Upper Eagle subwatershed

Middle Eagle subwatershed

Gore Creek subwatershed Streams

Lower Eagle subwatershed

Monotonic orthophosphate trend, 1996 to 2007

Orthophosphate

5–40 0–25

41–150 less than 25–50

less than 50–75

less than 75–100

Number of samples

Grouping of median concentrations

by Eagle River watershed percentile

City

77

224

59

No trend

Upward trend

Downward trend

 p-value less than 0.05–0.15

 p-value less than 0.01–0.05

 p-value 0.00–0.01

Base from U.S. Geological Survey digital data, 2007,

Universal Transverse Mercator projection

Zone 13 

0 5 10 KILOMETERS

0 5 10 MILES

Eagle

Gypsum

Minturn

Red Cliff

Wolcott

Dotsero

Edwards

Avon Vail

(!

106°15'

106°45'

39°45'

39°30'

!(

(!

Figure 50. Spatial distribution of median-concentration percentiles and monotonic orthophosphate trends at selected sites in the Eagle River 

watershed, Colorado, 1995–2007.
Assessment of Surface-Water Quality 85

Figure 51. Seasonal patterns of nitrate concentrations at selected sites in the Eagle River watershed, Colorado, 1947–2007. Nitrate, in milligrams per liter

Site 224 

1.0

0.5

1.5

2.5

3.0

35 36 36 50 51 48 45 48 44 31 28 38

0.0

2.0 o

o x

x x

x

x xx

x

x

x

x

January February March April May June July August September October November December

EXPLANATION

30 Number of values

o Upper detached

Upper outside

Lower adjacent

Upper adjacent

x

x Lower outside

o Lower detached

90th percentile

75th percentile

25th percentile

10th percentile

median

Site 180

0.0

0.5

1.0

2.0

1.5

3.0

13 11 12 11 11 8 8 12 6 10 10 6

2.5

x

x

x

o

o

9 8 10 6 4 7 4 8 5 4 8 10

0

1

3

4

2

Site 160

x

x

x

o

o
86 Assessment of Surface-Water Quantity and Quality, Eagle River Watershed, Colorado, 1947–2007

Figure 52. Seasonal patterns of nitrite concentrations at selected sites in the Eagle River watershed, Colorado, 1947–2007.

EXPLANATION

30 Number of values

o Upper detached

Upper outside

Lower adjacent

Upper adjacent

x

x Lower outside

o Lower detached

90th percentile

75th percentile

25th percentile

10th percentile

median

Nitrite, in milligrams per liter

Site 224 

0.08

0.06

0.04

0.02

0.0

10 6 8 11 10 12 12 10 9 9 7 11

x

o

o

o

o

January February March April May June July August September October November December

1.0

0.8

0.6

0.4

0.2

0.0

7 6 7 6 8 10 9 8 9 7 5 8

Site 201

x

x o

o oo

o o

1.0

0.8

0.6

0.4

0.2

0.0

8 7 6 12 8 15 11 8 11 8 9 10

o o

ooo

o

o

o

o

o

o

Site 173

Site 160

0.30

0.25

0.20

0.15

0.10

0.05

0.0

10 11 9 13 18 19 18 8 9 9 7 11

x x x

o o

o
Assessment of Surface-Water Quality 87

Figure 53. Seasonal patterns of total phosphorus concentrations at selected sites in the Eagle River watershed, Colorado, 1947–2007.

EXPLANATION

30 Number of values

o Upper detached

Upper outside

Lower adjacent

Upper adjacent

x

x Lower outside

o Lower detached

90th percentile

75th percentile

25th percentile

10th percentile

median

Total phosphorus, in milligrams per liter

Site 224 

1.0

0.8

0.6

0.4

0.2

0.0

8 11 13 11 12 13 10 11 10 8 12 10

x

x

x

o

o

January February March April May June July August September October November December

1.6

1.2

1.4

1.0

0.8

0.6

0.4

0.2

0.0

6 7 6 8 10 9 8 9 7 5 8 8

Site 201

x

x x

x

x x

o

o

0.7

0.6

0.5

0.3

0.4

0.2

0.1

0.0

8 6 8 9 13 15 11 10 10 7 8 8

Site 173

x

o

o

o

o

o

Site 160

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0.0

11 9 13 18 19 18 8 9 9 7 11 10

x x x x

x

o

o

o

o

o
88 Assessment of Surface-Water Quantity and Quality, Eagle River Watershed, Colorado, 1947–2007

Figure 54. Seasonal patterns of orthophosphate concentrations at selected sites in the Eagle River watershed, Colorado, 1947–2007.

EXPLANATION

30 Number of values

o Upper detached

Upper outside

Lower adjacent

Upper adjacent

x

x Lower outside

o Lower detached

90th percentile

75th percentile

25th percentile

10th percentile

median

Orthophosphate, in milligrams per liter

Site 224 

0.20

0.15

0.10

0.05

0.0

19 19 25 22 25 27 24 25 19 19 23 22

x

x

x

x

x

x

x

x

o

o

ooooooooo

o

0.35

0.30

0.25

0.20

0.15

0.10

0.05

0.0

6 7 6 8 10 9 8 9 7 5 8 7

Site 201

x

x

x

x

x

0.6

0.5

0.3

0.4

0.2

0.1

0.0

6 6 10 8 13 10 7 11 8 9 9 8

Site 173

o

ooo

o o oo o

o x

x

x

Site 160

0.5

0.4

0.3

0.2

0.1

0.0

11 9 13 18 19 18 8 9 9 7 10 10 o

o

x

x

x

xx

x

January February March April May June July August September October November December
Assessment of Surface-Water Quality 89

Table 17. Summary of water-quality standard or recommendation exceedances for nutrients in the Eagle River watershed by 

subwatershed.

[No., number; <, less than;--, no data]

Constituent 

or property

No. of 

censored 

values

No. of

samples

No. of standard 

or recommendation 

exceedances

Percent of 

standard 

exceedances

Minimum 

date

Maximum 

date

Gore Creek subwatershed

Nitrate, chronic 32 313 0 0 -- --

Nitrite, chronic 188 371 19 5 Feb. 4, 1971 Mar. 22, 2005

Un-ionized ammonia, acute 615 862 3 <1 Mar. 12, 1970 Feb. 19, 1976

Un-ionized ammonia, chronic 615 862 3 <1 Mar. 12, 1970 Feb. 19, 1976

Total phosphorous, chronic1 163 514 159 31 Apr. 8, 1974 Mar. 21, 2007

Upper Eagle subwatershed

Nitrate, chronic 39 143 0 0 -- --

Nitrite, chronic 144 215 1 <1 Oct. 27, 1976 Oct. 27, 1976

Un-ionized ammonia, acute 392 888 11 1 Nov. 12, 1974 Sept. 2, 1992

Un-ionized ammonia, chronic 392 888 7 <1 Nov. 12, 1974 Sept. 2, 1992

Total phosphorous, chronic1 286 456 6 1 Jan. 28, 1975 Jan. 8, 1998

Middle Eagle subwatershed

Nitrate, chronic 11 329 2 <1 Sept. 26, 1990 Feb. 22, 1991

Nitrite, chronic 82 376 48 13 Sept. 26, 1990 Feb. 19, 2003

Un-ionized ammonia, acute 771 1,275 14 1 Mar. 6, 1975 Feb. 13, 2007

Un-ionized ammonia, chronic 771 1,275 11 <1 Mar. 6, 1975 Feb. 13, 2007

Total phosphorous, chronic1 131 630 203 32 Jan. 6, 1970 Dec. 5, 2007

Lower Eagle subwatershed

Nitrate, chronic 35 722 0 0 -- --

Nitrite, chronic 81 293 2 <1 Nov. 12, 2002 Oct. 7, 2003

Un-ionized ammonia, acute 225 470 0 0 -- --

Un-ionized ammonia, chronic 225 470 0 0 -- --

Total phosphorous, chronic1 100 455 143 31 May 16, 1974 July 26, 2007

1

Water-quality recommended level set by U.S. Environmental Protection Agency (2000), no State standard.
90 Assessment of Surface-Water Quantity and Quality, Eagle River Watershed, Colorado, 1947–2007 Total phosphorous, in milligrams per liter

3

2

1

0

January 1995 January 2005

EXPLANATION

Total phosphorus

Censored value

U.S. Environmental Protection Agency

 Recommendation concentration

Figure 55. Temporal distribution of total phosphorus concentrations at site 110, Eagle River watershed, Colorado, 1997–2004.

Figure 56. Temporal distribution of total phosphorus concentrations at site 157, Eagle River watershed, Colorado, 1974–2006.

EXPLANATION

Total phosphorus

Censored value

U.S. Environmental Protection Agency

 Recommendation concentration

Total phosphorous, in milligrams per liter

0.8

0.6

0.2

0.4

0

January 1970 January 1980 January 1990 January 2000
Assessment of Surface-Water Quality 91

Figure 57. Temporal distribution of total phosphorus concentrations at site 160, Eagle River watershed, Colorado, 1996–2007.

Figure 58. Temporal distribution of total phosphorus concentrations at site 180, Eagle River watershed, Colorado, 1970–2002.

EXPLANATION

Total phosphorus

Censored value

U.S. Environmental Protection Agency

 Recommendation concentration

Total phosphorous, in milligrams per liter

0.6

0.2

0.4

0

January 1995 January 2005

EXPLANATION

Total phosphorus

Censored value

U.S. Environmental Protection Agency

 Recommendation concentration

Total phosphorous, in milligrams per liter

1.2

1

0.8

0.4

0.2

0.6

0

January 1970 January 1980 January 1990 January 2000
92 Assessment of Surface-Water Quantity and Quality, Eagle River Watershed, Colorado, 1947–2007

EXPLANATION

Total phosphorus

Censored value

U.S. Environmental Protection Agency

 Recommendation concentration

Total phosphorous, in milligrams per liter

3

1

2

0

January 1980 January 1990 January 2000

Figure 59. Temporal distribution of total phosphorus concentrations at site 224, Eagle River watershed, Colorado, 1980–2007.

Figure 60. Temporal distribution of total phosphorus concentrations at site 227, Eagle River watershed, Colorado, 1974–2007.

EXPLANATION

Total phosphorus

Censored value

U.S. Environmental Protection Agency

 Recommendation concentration

Total phosphorous, in milligrams per liter

0.4

0.3

0.1

0.2

0

January 1965 January 1975 January 1985 January 1995 January 2005
Assessment of Surface-Water Quality 93

Table 18. Summary of monotonic temporal trends for nutrients in the Eagle River watershed.

[No., number; --, undetermined; mg/L, milligrams per liter]

Site no. Trend

period

No. of

samples

Flow

adjustment

Trend slope, 

units per year

Percent change,

percent per year p-value Trenddirection

Median

value

Nitrate, mg/L

160 1996–2007 29 No -- -- 0.31 No trend 0.657

160 1996–2007 29 Yes -- -- .97 No trend .657

173 1996–2007 22 No -- -- .17 No trend .282

173 1996–2007 21 Yes -- -- .82 No trend .282

224 1994–2007 31 No -- -- .26 No trend .585

224 1994–2007 31 Yes 0.022 3.8 .015 Upward .585

Nitrite, mg/L

160 1999–2007 24 No -- -- .15 Upward .004

173 1999–2007 23 No -- -- .22 No trend .001

224 1999–2007 24 No -- -- .51 No trend .009

Ammonia, mg/L

160 1996–2007 33 No -- -- .64 No trend .008

187B 1996–2007 30 No -- -- .85 No trend .100

224 1996–2007 33 No -- -- .16 No trend .023

Total phosphorous, mg/L

3 1996–2007 30 No -- -- .95 No trend .004

160 1995–2007 33 No -- -- .20 No trend .088

173 1996–2007 29 No -- -- .80 No trend .037

224 1995–2007 36 No .0073 8.4 .021 Upward .088

Orthophosphate, mg/L

160 1996–2007 33 No -- -- .56 No trend .080

173 1996–2007 32 No -- -- .59 No trend .011

224 1996–2007 33 No -- -- .056 Upward .031
94 Assessment of Surface-Water Quantity and Quality, Eagle River Watershed, Colorado, 1947–2007

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!( !(

!( !(

!( !( !( !( !( !( !(

!(

!(

EXPLANATION

Waterbodies

Upper Eagle subwatershed

Middle Eagle subwatershed

Gore Creek subwatershed Streams

Lower Eagle subwatershed

Nutrients

5–40 0

41–150 1–10

11–40

41–80

81–107

Number of samples Number of exceedances

151–527

City

Base from U.S. Geological Survey digital data, 2007,

Universal Transverse Mercator projection

Zone 13 

Eagle

Wolcott

Avon

Dotsero

Edwards

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!( !( !( !( !(

!(

!(!(!(

!(

!(

!(

!(!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!(!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!( !(

!(

!( !(

!(

!( !(

!( !(

!(!( !( !(

!( !(

!(!(

!( !( !( !(

!(

!( !( !( !( !( !( !(!( !(!(!( !( !( !(!(

!( !(

!(

!(

!(

Minturn

Red Cliff

Gypsum Eagle River

East Fork

Eagle River 

Eagle

River

Black Gore Creek

106°15'

106°45'

39°45'

39°30'

0 5 10 KILOMETERS

0 5 10 MILES

Gore Creek

Alkali Creek

Turkey Creek

Minturn

Vail

Red Cliff

Black Gore Creek

Rock Creek

Fall

Creek

Turkey Creek

Cross Creek

Vail

!

(!

Gore Creek

Figure 61. Number of exceedances of the Colorado chronic water-quality standard for nutrients at selected sites in the Eagle River 

watershed, Colorado, 1970–2007.
Assessment of Surface-Water Quality 95

Figure 62. Number of exceedances of the Colorado acute water-quality standard for nutrients at selected sites in the Eagle River watershed, 

Colorado, 1947–2007.

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!( !(

!( !(

!( !( !( !( !( !( !(

!(

!(

EXPLANATION

Waterbodies

Upper Eagle subwatershed

Middle Eagle subwatershed

Gore Creek subwatershed Streams

Lower Eagle subwatershed

Nutrient

5–40 0

41–150 1–10

11–40

41–80

81–107

Number of samples Number of exceedances

151–527

City

Base from U.S. Geological Survey digital data, 2007,

Universal Transverse Mercator projection

Zone 13 

Eagle

Wolcott

Avon

Dotsero

Edwards

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!( !( !( !( !(

!(

!(!(!(

!(

!(

!(

!(!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!(!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!( !(

!(

!( !(

!(

!( !(

!( !(

!(!( !( !(

!( !(

!(!(

!( !( !(

!(

!(

!( !( !( !( !( !( !(!( !(!(!( !( !( !(!(

!( !(

!(

!(

!(

Minturn

Red Cliff

Gypsum Eagle River

East Fork

Eagle River 

Eagle

River

Black Gore Creek

106°15'

106°45'

39°45'

39°30'

0 5 10 KILOMETERS

0 5 10 MILES

Gore Creek

Alkali Creek

Turkey Creek

Minturn

Vail

Red Cliff

Black Gore Creek

Rock Creek

Fall

Creek

Turkey Creek

Cross Creek

Vail

!

!

Gore Creek
96 Assessment of Surface-Water Quantity and Quality, Eagle River Watershed, Colorado, 1947–2007

Figure 63. Correlation between suspended-sediment concentration and total phosphorus concentration 

in the Eagle River watershed, Colorado.

Gore subwatershed

Middle subwatershed

Lower subwatershed

EXPLANATION 

Regression line for suspended-sediment

concentrations greater than or equal to 40 mg/L

adjusted R2

 = 0.8385

adjusted p-Value = 0 

Suspended-sediment concentration, in milligrams per liter

Total phosphorus concentration, in milligrams per liter 1.0

1.5

0

0 500 1,000 1,500

1.5

a weakly significant upward trend (p-value of 0.15) in nitrite 

at site 160 (Gore Creek subwatershed). This trend is localized 

to contributing areas upstream from the mouth of Gore Creek 

(fig. 47). No trends were detected at sites 173 (Middle Eagle 

subwatershed) or 224 (Lower Eagle subwatershed).

Evaluation of temporal trends was done for all sites with 

ammonia data; trend analysis was done at the 3 sites that met 

the criteria set in the “Data Sources, Compilation, Review, 

and Analysis” section of this report. Findings from the trend 

analysis are presented in table 18 and figure 48. Seasonal Kendall Trend tests were done for the time period 1996–2007. No 

significant trends in ammonia were detected at site 160 (Gore 

Creek subwatershed), 187B (Middle Eagle subwatershed), or 

224 (Lower Eagle subwatershed) (fig. 48).

Evaluation of temporal trends was done for all sites with 

total phosphorus data; trend analysis was done at the 4 sites 

that met the criteria set in the “Data Sources, Compilation, 

Review, and Analysis” section of this report. Findings from 

the trend analysis are presented in table 18 and figure 49. 

Seasonal Kendall Trend tests were done for the time periods 

1996–2007 and 1995–2007 depending on the data available 

at each site. There was a significant upward trend (p-value of 

0.021) in total phosphorus at site 224 (Lower Eagle subwatershed) for 1995–2007. This trend represents a 0.095-mg/L 

increase over the entire specified time period. Upstream at 

sites 173 (Middle Eagle subwatershed), 160 (Gore Creek 

subwatershed), and 3 (Upper Eagle subwatershed) there were 

no trends. The area between sites 224 (Lower Eagle subwatershed) and 173 (Middle Eagle subwatershed) contains several 

tributaries and urban areas including the towns of Gypsum, 

Eagle, Edwards, and Avon (fig. 49), which may contribute to 

the observed trend.

Evaluation of temporal trends was done for all sites with 

orthophosphate data; trend analysis was done at the 3 sites that 

met the criteria set in the “Data Sources, Compilation, Review, 

and Analysis” section of this report. Findings from the trend 

analysis are presented in table 18 and figure 50. The orthophosphate trend at site 224 was weakly significant (p-value of 

0.056). Upstream at sites 173 (Middle Eagle subwatershed) 

and 160 (Gore Creek subwatershed) there were no trends in 

orthophosphate. The area between sites 224 (Lower Eagle 

subwatershed) and 173 (Middle Eagle subwatershed) contains 

several tributaries and urban areas including the towns of Gypsum, Eagle, Wolcott, and Edwards (fig. 50).

Three surface-water quality monitoring sites (site 140, 

Gore Creek below Vail wastewater treatment plant outfall 

at Vail; site 176, Eagle River below wastewater treatment 

plant at Avon; and site 187B, Eagle River 50 ft downstream 

Squaw wastewater treatment plant) were sampled directly 

downstream from wastewater treatment plant outfalls. The 

streams at these sampling locations are likely not well mixed 

and corresponding data at these sites could potentially bias 

the exceedances and trend analysis. As a result these data 

may have increased the level and number of exceedances and 

affected the trend values reported. 

Comparisons of nutrient concentrations to suspendedsediment concentrations were done in the ERW. A positive correlation was observed between concentrations of 
Assessment of Surface-Water Quality 97

Trace metal concentrations (aluminum, cadmium, iron, 

manganese, and zinc) in the ERW have been measured at 

154 sites from April 1, 1947, through September 30, 2007. 

Concentrations for dissolved aluminum ranged from less 

than 50 to 266 μg/L. The 25th, 50th, and 75th percentiles 

for the ERW were 14.0, 25.1, and 38.9 μg/L, respectively. 

Median concentrations for the subwatersheds ranged from 

8.0 μg/L in Gore Creek, 39.0 μg/L in the Upper Eagle, 

20.7 μg/L in the Middle Eagle, to 20.7 μg/L in the Lower 

Eagle (table 19).

Concentrations for dissolved cadmium ranged from 

less than 0.3 to 2,500 μg/L. The 25th, 50th, and 75th percentiles for the ERW were 0.1, 0.2, and 0.5 μg/L, respectively. 

Median concentrations for the subwatersheds ranged from 

0.5 μg/L in the Upper Eagle to 0.1 μg/L in the Middle Eagle 

(table 19 and fig. 64).

Concentrations for dissolved copper were less than 5.0 to 

150 μg/L. The 25th, 50th, and 75th percentiles for the ERW 

were 1, 2.2, and 5.0 μg/L, respectively. Median concentrations 

for the subwatersheds were 1.4 mg/L in Gore Creek, 3.0 μg/L 

in the Upper Eagle, 2.0 μg/L in the Middle Eagle, to 1.9 μg/L 

in the Lower Eagle (table 19 and fig. 65).

Concentrations for dissolved iron ranged from less than 

3 to 39,000 μg/L. The 25th, 50th, and 75th percentiles for 

the ERW were 22, 90, and 200 μg/L, respectively. Median 

concentrations for the subwatersheds were 13.0 μg/L in Gore 

Creek, 140 μg/L in the Upper Eagle, 40 μg/L in the Middle 

Eagle, and 30 μg/L in the Lower Eagle (table 19 and fig. 66).

Concentrations for dissolved manganese ranged from 

less than 10 to 100,000 μg/L. The 25th, 50th, and 75th 

percentiles for the ERW were 13.0, 62.0, and 310 μg/L, 

respectively. Median concentrations for the subwatersheds 

were 6.0 μg/L in Gore Creek, 160 μg/L in the Upper Eagle, 

71 μg/L in the Middle Eagle, and 31.7 μg/L in the Lower 

Eagle (table 19 and fig. 67).

Concentrations for dissolved zinc ranged from less than 

10 to 240,000 μg/L. The 25th, 50th, and 75th percentiles for 

the ERW were 10.0, 70, and 330 μg/L, respectively. Median 

concentrations for the subwatersheds were 5.7 μg/L in Gore 

Creek, 180 μg/L in the Upper Eagle, 50 μg/L in the Middle 

Eagle, and 22.2 μg/L in the Lower Eagle (table 19 and fig. 68).

The spatial pattern shows an increase in dissolved 

trace-metals concentrations as water moves downstream from 

historic mining areas (fig. 5), with a defined increase in the 

Eagle River and several tributaries near Belden (figs. 64–68). 

Concentrations often decreased or are below reporting limits 

in Gore Creek and other tributaries within the ERW. Seasonal 

variations generally show that many trace metals concentrations tend to be lowest May–June and highest November–

April. A gradual change in concentrations between seasons 

may be related to dilution effects from streamflow. A notable 

exception to this pattern occurs in early spring (February–

April) along the leading edge of snowmelt (figs. 69–73). 

Increases in melt waters moving along intermittent flow paths 

interact with mine shafts and (or) adits, mineralized rock 

units, and other areas affected by processed mine wastes and 

suspended sediment greater than 40 mg/L and total phosphorus (fig. 63). Seasonal variations in total phosphorus observed 

within the ERW may be related to sediment transported 

by snowmelt runoff (February–May) and rainfall (July–

September) with increases in sediment possibly resulting in 

increases in total phosphorus concentration. No such similar 

correlations were detected for nitrate, nitrite, ammonia, and 

orthophosphate.

Trace Elements

Many trace elements in natural waters are essential to 

humans, plants, and aquatic life. However, trace elements can 

be toxic in sufficient concentrations. Trace elements often are 

defined as those elements that generally occur in concentrations less than 1,000 micrograms per liter (Hem, 1989). There 

are natural (geology) and human sources of trace elements in 

streams. Human sources can increase trace-element contributions to streams and can include mining, urban runoff, and 

municipal and industrial wastewaters. Mining (both active and 

historical) in the ERW has provided conduits for water and 

air to come in contact with the underlying geologic material, 

where both physical and chemical weathering can dissolve 

and transport these constituents into streams. Streams draining areas affected by human activities in urban areas also can 

mobilize trace elements. 

The discussion of trace elements has been separated into 

two groups. Arsenic, selenium, and uranium are discussed 

separately from several commonly occurring trace metals 

(aluminum, cadmium, copper, iron, manganese, and zinc) in 

the following discussion. 

Trace elements concentrations (arsenic, selenium, and 

uranium) in the ERW have been measured at 72 sites from 

June 8, 1966, through September 30, 2007. Concentrations 

for dissolved arsenic ranged from less than 1.0 to 6.0 μg/L. 

The 25th, 50th, and 75th percentiles for the ERW were 0.2, 

0.2, and 5.0 μg/L, respectively. Median concentration for the 

Upper Eagle subwatershed was 5.0 μg/L (table 19).

Concentrations for dissolved selenium ranged from less 

than 1.0 to 10.0 μg/L. The 25th, 50th, and 75th percentiles for 

the ERW were 0.2, 0.3, and 0.6 μg/L, respectively. Median 

concentrations for the subwatersheds were 0.2 μg/L in the 

Upper Eagle, 0.4 μg/L in the Middle Eagle, and 0.6 μg/L in 

the Lower Eagle (table 19).

Concentrations for dissolved uranium ranged from less 

than 1.0 to 9.0 μg/L. The 25th, 50th, and 75th percentiles for 

the ERW were all less than 1.0 μg/L. Median concentrations 

for the subwatersheds ranged from 1.0 μg/L in Gore Creek, 

2.0 μg/L in the Upper Eagle, 2.0 μg/L in the Middle Eagle, 

and 2.0 μg/L in the Lower Eagle (table 19).

Concentrations of trace elements in the ERW usually are 

below the reporting limit, and no prevailing spatial pattern was 

observed in the data. Areas of the Upper Eagle subwatershed 

and Lower Eagle subwatershed have increased concentrations 

relative to other areas in the ERW, and these concentrations 

likely are related to source geology.
98 Assessment of Surface-Water Quantity and Quality, Eagle River Watershed, Colorado, 1947–2007

Table 19. Summary statistics of trace element data in the Eagle River watershed by subwatershed 1947–2007.—Continued

[No., number; MRL, Minimum Reporting Limit; <, less than; --, undetermined]

Constituent 

or property

No. of 

censored 

values

No. of

samples MRL Minimum1

Concentration or value 

at indicated percentile2 Maximum

25 50 75

Gore Creek subwatershed

Aluminum, dissolved (μg/L) 19 40 50 2.0 5.0 8.0 12.0 50

Aluminum, total (μg/L) 2 22 15.0 15.0 28.0 65 195 1,288

Arsenic, dissolved (μg/L) 66 66 1.0 1.0 -- -- -- <1.0

Arsenic, total (μg/L) 101 103 1.0 1.0 -- -- -- 8.0

Barium, dissolved (μg/L) 0 21 -- 18.0 58 118 127 190

Barium, total (μg/L) 0 0 -- -- -- -- -- --

Cadmium, dissolved (μg/L) 201 219 .3 .10 -- -- -- 1.2

Cadmium, total (μg/L) 88 91 1.0 .10 -- -- -- <1.0

Chromium, dissolved (μg/L) 30 35 1.0 1.0 -- -- -- 23.0

Chromium, total (μg/L) 12 12 1.0 1.0 -- -- -- <1.0

Copper, dissolved (μg/L) 218 304 5.0 .4 .9 1.4 2.4 60

Copper, total (μg/L) 50 91 1.0 1.0 .3 0.8 1.4 47

Iron, dissolved (μg/L) 154 393 20.0 3.0 8.0 13.0 20.0 190

Iron, total (μg/L) 51 338 20.0 18.0 24.0 70 190 1,900

Lead, dissolved (μg/L) 230 247 5.0 .04 -- -- -- 14.0

Lead, total (μg/L) 88 91 3.0 .8 -- -- -- 4.2

Manganese, dissolved (μg/L) 189 525 10.0 .8 2.4 6.0 10.0 530

Manganese, total (μg/L) 73 324 10.0 1.6 6.7 10.0 21.0 320

Mercury, dissolved (μg/L) 15 15 .1 .1 -- -- -- <0.1

Mercury, total (μg/L) 72 73 .2 .2 -- -- -- 0.3

Molybdenum, dissolved (μg/L) 20 21 1.0 1.0 -- -- -- 4.0

Molybdenum, total (μg/L) 0 0 -- -- -- -- -- --

Nickel, dissolved (μg/L) 24 35 1.0 .04 .01 .2 .7 26.0

Nickel, total (μg/L) 12 12 1.0 1.0 -- -- -- <1.0

Selenium, dissolved (μg/L) 56 70 1.0 .08 -- -- -- 4.4

Selenium, total (μg/L) 87 98 2.0 1.0 -- -- -- 5.0

Silver, dissolved (μg/L) 133 139 .2 .1 -- -- -- .3

Silver, total (μg/L) 51 51 .2 .2 -- -- -- <.2

Uranium, dissolved (μg/L) 13 37 1.0 1.0 -- 1.0 2.0 4.1

Zinc, dissolved (μg/L) 257 425 10.0 .6 3.2 5.7 10.0 149

Zinc, total (μg/L) 158 202 10.0 5.0 .9 2.7 8.1 370

Upper Eagle subwatershed

Aluminum, dissolved (μg/L) 34 86 50 10.0 24.0 39.0 54 180

Aluminum, total (μg/L) 0 17 -- 90 106 140 153 189

Arsenic, dissolved (μg/L) 75 338 1.0 .1 .2 5.0 5.0 6.0

Arsenic, total (μg/L) 66 69 1.0 -- -- -- -- --

Barium, dissolved (μg/L) 0 14 -- 12.0 30.0 41.5 51 100

Cadmium, dissolved (μg/L) 281 1,805 .3 .02 .2 .5 1.0 2,500

Cadmium, total (μg/L) 33 131 1.0 .14 .4 .7 1.3 4.56

Chromium, dissolved (μg/L) 42 47 1.0 -- --- -- -- --

Chromium, total (μg/L) 0 0 -- -- -- -- -- --

Copper, dissolved (μg/L) 268 1,828 5.0 .2 1.0 3.0 5.0 150

Copper, total (μg/L) 100 250 1.0 1.0 1.0 3.0 12.9 1,150

Iron, dissolved (μg/L) 62 1,636 20.0 10.0 80 140 270 39,000

Iron, total (μg/L) 9 903 20.0 20.0 300 600 1,510 1,000,000

Lead, dissolved (μg/L) 527 1,780 5.0 .04 1.0 1.0 3.0 40

Lead, total (μg/L) 207 242 3.0 -- -- -- -- --

Manganese, dissolved (μg/L) 106 1,926 10.0 1.5 30.0 160 605 100,000

Manganese, total (μg/L) 31 414 10.0 3.3 21.7 325 1,600 156,000

Mercury, dissolved (μg/L) 41 42 .1 -- -- -- -- --

Mercury, total (μg/L) 28 28 .2 -- -- -- -- --

Molybdenum, dissolved (μg/L) 0 1 5.0 -- -- -- -- --

Molybdenum, total (μg/L) 1 1 50 -- -- -- -- --

Nickel, dissolved (μg/L) 8 23 1.0 .1 .5 .8 .9 30

Nickel, total (μg/L) 0 0 -- -- -- -- -- --
Assessment of Surface-Water Quality 99

Table 19. Summary statistics of trace element data in the Eagle River watershed by subwatershed 1947–2007.—Continued

[No., number; MRL, Minimum Reporting Limit; <, less than; --, undetermined]

Constituent 

or property

No. of 

censored 

values

No. of

samples MRL Minimum1

Concentration or value 

at indicated percentile2 Maximum

25 50 75

Upper Eagle subwatershed—Continued

Selenium, dissolved (μg/L) 113 153 1.0 0.06 0.09 0.2 0.6 10.0

Selenium, total (μg/L) 64 72 2.0 -- -- -- -- --

Silver, dissolved (μg/L) 170 238 .2 .1 .02 .06 .2 5.0

Silver, total (μg/L) 30 33 .2 -- -- -- -- --

Uranium, dissolved (μg/L) 4 15 1.0 1.0 1.0 2.0 2.1 9.0

Zinc, dissolved (μg/L) 129 2,292 10.0 .3 30.0 180 460 240,000

Zinc, total (μg/L) 34 297 10.0 2.0 113 438 1,208 20,000

Middle Eagle subwatershed

Aluminum, dissolved (μg/L) 44 62 50 16.0 22.0 20.7 34.2 86

Aluminum, total (μg/L) 4 30 15.0 15.0 21.0 34.0 98 285

Arsenic, dissolved (μg/L) 67 82 1.0 .1 -- -- -- 2.0

Arsenic, total (μg/L) 46 51 1.0 1.0 -- -- -- 47.9

Barium, dissolved (μg/L) 0 2 -- 58 63 8 72 77

Cadmium, dissolved (μg/L) 171 317 .3 .02 .06 .1 .3 4.0

Cadmium, total (μg/L) 11 56 1.0 .1 .2 .4 .6 1.4

Chromium, dissolved (μg/L) 19 20 1.0 .8 -- -- -- 1.0

Chromium, total (μg/L) 0 0 -- -- -- -- -- --

Copper, dissolved (μg/L) 153 338 5.0 .6 1.4 2.0 3.0 20.0

Copper, total (μg/L) 1 65 1.0 1.0 2.2 3.5 6.0 23.4

Iron, dissolved (μg/L) 50 238 20.0 5.0 19.0 40.0 110 560

Iron, total (μg/L) 0 210 -- 24.0 240 405 980 560

Lead, dissolved (μg/L) 259 331 5.0 .04 .1 .4 .5 <5.0

Lead, total (μg/L) 58 65 3.0 2.2 -- -- -- 11.3

Manganese, dissolved (μg/L) 41 385 10.0 1.3 18.0 71 230 3,960

Manganese, total (μg/L) 0 187 -- 17.5 70 136 440 4,120

Mercury, dissolved (μg/L) 43 46 .1 .01 -- -- -- <.1

Mercury, total (μg/L) 178 181 .2 .2 -- -- -- 1.4

Molybdenum, dissolved (μg/L) 0 0 -- -- -- -- -- --

Molybdenum, total (μg/L) 0 0 -- -- -- -- -- --

Nickel, dissolved (μg/L) 4 20 1.0 .1 .3 .7 1.1 1.8

Nickel, total (μg/L) 0 0 -- -- -- -- -- --

Selenium, dissolved (μg/L) 99 139 1.0 .1 .2 .4 .6 5.2

Selenium, total (μg/L) 65 77 2.0 1.0 -- -- -- 7.8

Silver, dissolved (μg/L) 153 158 .2 .1 -- -- -- <.2

Silver, total (μg/L) 27 29 .2 .2 -- -- -- 11.0

Uranium, dissolved (μg/L) 1 13 1.0 1.0 1.0 2.0 2.5 7.0

Zinc, dissolved (μg/L) 32 340 10.0 1.4 19.0 50 110 1,830

Zinc, total (μg/L) 39 135 10.0 10.0 -- 70 203 1,600

Lower Eagle subwatershed

Aluminum, dissolved (μg/L) 64 82 50 7.0 12.5 20.7 34.2 266

Aluminum, total (μg/L) 0 35 -- 27.0 94 205 440 6,466

Arsenic, dissolved (μg/L) 98 109 1.0 1.0 -- -- -- 5.0

Arsenic, total (μg/L) 87 108 1.0 1.0 -- -- -- 27.0

Barium, dissolved (μg/L) 1 39 47 25.0 38.4 46.0 57 83.1

Cadmium, dissolved (μg/L) 172 207 .3 .02 -- -- -- 2.3

Cadmium, total (μg/L) 78 138 1.0 .1 .2 .3 .5 4.1

Chromium, dissolved (μg/L) 42 48 1.0 .4 -- -- -- 2.1

Chromium, total (μg/L) 16 44 1.0 .6 .6 1.5 4.0 18.0

Copper, dissolved (μg/L) 113 232 5.0 .8 1.4 1.9 3.0 54

Copper, total (μg/L) 26 139 1.0 1.0 1.2 2.8 4.7 22.1

Iron, dissolved (μg/L) 84 410 20.0 3.0 14.0 30.0 50 2,258

Iron, total (μg/L) 30 145 20.0 20.0 90 349 736 8,098

Lead, dissolved (μg/L) 235 258 5.0 .05 -- -- -- 51

Lead, total (μg/L) 97 142 3.0 .8 .8 1.5 3.0 24.5

Manganese, dissolved (μg/L) 23 405 10.0 2.0 17.7 31.7 70 620
100 Assessment of Surface-Water Quantity and Quality, Eagle River Watershed, Colorado, 1947–2007

Table 19. Summary statistics of trace element data in the Eagle River watershed by subwatershed 1947–2007.—Continued

[No., number; MRL, Minimum Reporting Limit; <, less than; --, undetermined]

Constituent 

or property

No. of 

censored 

values

No. of

samples MRL Minimum1

Concentration or value 

at indicated percentile2 Maximum

25 50 75

Lower Eagle subwatershed—Continued

Manganese, total (μg/L) 25 135 10.0 9.2 21.4 64 137 805

Mercury, dissolved (μg/L) 48 56 .1 .01 -- -- -- .4

Mercury, total (μg/L) 79 88 .2 .01 -- -- -- <.2

Molybdenum, dissolved (μg/L) 0 0 -- -- -- -- -- --

Molybdenum, total (μg/L) 0 0 -- -- -- -- -- --

Nickel, dissolved (μg/L) 28 34 1.0 .08 -- -- -- 15.0

Nickel, total (μg/L) 5 29 1.0 1.0 1.1 2.0 4.0 15.1

Selenium, dissolved (μg/L) 94 148 1.0 .2 .4 .6 1.0 4.5

Selenium, total (μg/L) 94 128 2.0 1.0 .7 1.1 1.7 8.4

Silver, dissolved (μg/L) 95 97 .2 .1 -- -- -- 2.0

Silver, total (μg/L) 28 29 .2 .2 -- -- -- 6.0

Uranium, dissolved (μg/L) 0 13 -- 1.0 2.0 2.0 3.0 3.5

Zinc, dissolved (μg/L) 23 246 10.0 4.0 13.4 22.2 40.0 800

Zinc, total (μg/L) 27 277 10.0 10.0 37.5 68 120 1,044 1

Uncensored values.

2

Percentile values can be less than the MRL values due to multiple MRLs within the combined dataset.

contaminated soils. Increases in melt water also mobilize 

localized areas of concentrated metals, leading to increases in 

some metal concentrations in streams. The increase in metal 

concentrations represents a seasonal “flushing” that becomes 

less pronounced as snowmelt increases (Colorado Department 

of Public Health and Environment and U.S. Environmental 

Protection Agency, 2000). In addition, the increase in median 

metal concentrations coincides with the reduction in hardness 

concentrations; this is illustrated for cadmium (fig. 74). Reductions in hardness can be an important consideration in the 

assessment of metals toxicity to aquatic biota (see “Hardness” 

section of this report). 

The seasonal pattern of dissolved iron at site 224 (Lower 

Eagle subwatershed) is different from other metals and other 

sites within the ERW (fig. 71). At site 224, dissolved iron 

concentrations are relatively stable for most of the year with 

higher concentrations April–July. These increased concentrations are not representative of the rest of the ERW where 

increases in streamflow result in dilution of many constituents. The increased concentrations of dissolved iron may 

best be explained by the colloidal behavior of iron. Colloidal 

iron is suspended iron that is not dissolved, but can potentially be included in concentrations of dissolved iron because 

of the nature of sample-collection techniques (Stumm and 

Morgan, 1996). Commonly, water samples are filtered using 

0.45-micron filters. Iron colloids can be less than the filterpore size, in which case not all colloids would be restricted 

from passing through the filter. If colloidal forms of iron are 

included in dissolved iron concentrations at this site, this may 

account for the difference in seasonal patterns at site 224 

because higher concentrations of total iron also occur March–

May at site 224 (fig. 75). The increases in iron concentrations during high flow may be the result of re-suspension of 

deposited iron colloids in the stream sediments during higher 

streamflows when increases in turbulence and stream power 

increase transport and suspension of bed sediments (Church 

and others, 1997; Schemel and others, 1999). Another possible explanation for the observed increases in dissolved iron 

at site 224 in April–June may be from seasonal variations in 

iron sources from areas downstream from site 66 (Upper Eagle 

subwatershed), although no specific source has been identified.

Arsenic, selenium, uranium, in addition to several commonly occurring metals (aluminum, cadmium, copper, iron, 

lead, manganese, mercury, nickel, silver, and zinc) in this report 

were compared to available State standards set by the CDPHE 

Regulation no. 33 (Colorado Department of Public Health and 

Environment, 2007). Number of exceedances is based on dissolved sample concentrations, except for iron which is based 

on dissolved and total recoverable concentrations.

A chronic State standard of 150 μg/L applies statewide 

for arsenic in the ERW, except for segment 11 which uses a 

TVS based on total recoverable concentrations (100 μg/L). All 

reaches of the ERW use the acute TVS for arsenic (50 μg/L) 

except for segment 11 (340 μg/L) (fig. 12). There are no exceedances of the chronic State standards for arsenic in the ERW out 

of 331 comparisons. There is 1 exceedance of the acute State 

standard at site 27 (Upper Eagle subwatershed) in 1971.

State standards for selenium are designated by the 

CDPHE and apply to all reaches of the ERW. The chronic 

State standard for dissolved selenium is 4.6 μg/L, and the 

acute State standard is 18.4 μg/L for dissolved selenium. 

Out of the 510 comparisons of selenium measurements to 

State standards, approximately 1 percent (5 comparisons) 

exceeded the chronic State standard for selenium. There were 

no exceedances out of 510 comparisons of the acute State 

standard for selenium (table 20).
Assessment of Surface-Water Quality 101

Figure 64. Spatial distribution of median-concentration percentiles and monotonic dissolved cadmium trends at selected sites in the Eagle 

River watershed, Colorado, 1994–2006.

!(

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(

72

88

66

59

58 57

49

EXPLANATION

Waterbodies

Upper Eagle subwatershed

Middle Eagle subwatershed

Gore Creek subwatershed Streams

Lower Eagle subwatershed

Monotonic cadmium trend, 1994 to 2006

Cadmium

5–40 0–25

41–150 greater than 25–50

greater than 50–75

greater than 75–100

Number of samples

Grouping of median concentrations

by Eagle River watershed percentile 

151–163

City

72

59

No trend

Downward trend

 p-value greater than 0.05–0.15

 p-value greater than 0.01–0.05

 p-value 0.00–0.01

Base from U.S. Geological Survey digital data, 2007,

Universal Transverse Mercator projection

Zone 13 

!(

!(

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!(

!(

!(

!(

!(

!(

!(

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!(

!(

!(

!(!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!( !(

!(

173

Minturn

!

Eagle

Gypsum

Wolcott

Avon

Dotsero

Eagle River

Cross Creek

East Fork

Eagle River 

Eagle

River

Black Gore Creek

Edwards

106°15'

106°45'

39°45'

39°30'

0 5 10 KILOMETERS

0 5 10 MILES

Gore Creek

Turkey Creek

Minturn

Vail

Red Cliff

Alkali Creek
102 Assessment of Surface-Water Quantity and Quality, Eagle River Watershed, Colorado, 1947–2007

Figure 65. Spatial distribution of median-concentration percentiles for dissolved copper at selected sites in the Eagle River watershed, 

Colorado, 1966–2007.

!(

!(

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!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

EXPLANATION

Waterbodies

Upper Eagle subwatershed

Middle Eagle subwatershed

Gore Creek subwatershed Streams

Lower Eagle subwatershed

Copper

5–40 0–25

41–150 greater than 25–50

greater than 50–75

greater than 75–100

Number of samples

Grouping of median concentrations

by Eagle River watershed percentile 

151–161

City

Base from U.S. Geological Survey digital data, 2007,

Universal Transverse Mercator projection

Zone 13 

173

Minturn

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(!(

!(

!(

!(

!(!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!( !(

!(

!(

Eagle

Gypsum

Wolcott

Avon

Dotsero

Eagle River

Cross Creek

East Fork

Eagle River 

Eagle

River

Black Gore Creek

Edwards

106°15'

106°45'

39°45'

39°30'

0 5 10 KILOMETERS

0 5 10 MILES

Gore Creek

Turkey Creek

Minturn

Vail

Red Cliff

Alkali Creek

!(

(!

(!
Assessment of Surface-Water Quality 103

Figure 66. Spatial distribution of median-concentration percentiles and monotonic dissolved iron trends at selected sites in the Eagle River 

watershed, Colorado, 1994–2006.

!(

!(

!(

!(

!(

!(

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!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

(

79

72

66

59

57

49

EXPLANATION

Waterbodies

Upper Eagle subwatershed

Middle Eagle subwatershed

Gore Creek subwatershed Streams

Lower Eagle subwatershed

Monotonic iron trend, 1994 to 2006, and site number

Iron

5–40 0–25

41–150 greater than 25–50

greater than 50–75

greater than 75–100

Number of samples

Grouping of median concentrations

by Eagle River watershed percentile 

151–530

City

59

79

No trend

Downward trend

 p-value greater than 0.05–0.15

 p-value greater than 0.01–0.05

 p-value 0.00–0.01

Base from U.S. Geological Survey digital data, 2007,

Universal Transverse Mercator projection

Zone 13 

!(

173

Minturn

!(

!(

!(

!(

!(

!(

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!(

!(

!(

!(

!(!(

!(

!(

!(!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!( !( !( !(

!(

!(

!

Eagle

Gypsum

Wolcott

Avon

Dotsero

Eagle River

Cross Creek

East Fork

Eagle River 

Eagle

River

Black Gore Creek

Edwards

106°15'

106°45'

39°45'

39°30'

0 5 10 KILOMETERS

0 5 10 MILES

Gore Creek

Turkey Creek

Minturn

Vail

Red Cliff

Alkali Creek
104 Assessment of Surface-Water Quantity and Quality, Eagle River Watershed, Colorado, 1947–2007

!(

!(

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!(

160

100

88

79 72

66

59

58

57

49 37

EXPLANATION

Waterbodies

Upper Eagle subwatershed

Middle Eagle subwatershed

Gore Creek subwatershed Streams

Lower Eagle subwatershed

Monotonic manganese trend, 1994 to 2006, and site number

Manganese

5–40 0–25

41–150 greater than 25–50

greater than 50–75

greater than 75–100

Number of samples

Grouping of median concentrations

by Eagle River watershed percentile 

151–237

City

49

224

No trend

Downward trend

 p-value greater than 0.05–0.15

 p-value greater than 0.01–0.05

 p-value 0.00–0.01

Base from U.S. Geological Survey digital data, 2007,

Universal Transverse Mercator projection

Zone 13 

173

!(

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!(

!(

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227 224

173

13

3

Eagle

Wolcott

Avon

Dotsero

Edwards

Minturn

Vail

Red Cliff

Minturn

(!

(!

!(!(

(!

(!

Gypsum Eagle River

Cross Creek

East Fork

Eagle River 

Eagle

River

Black Gore Creek

106°15'

106°45'

39°45'

39°30'

0 5 10 KILOMETERS

0 5 10 MILES

Gore Creek

Turkey Creek

Alkali Creek

Figure 67. Spatial distribution of median-concentration percentiles and monotonic dissolved manganese trends at selected sites in the Eagle 

River watershed, Colorado, 1994–2006.
Assessment of Surface-Water Quality 105

Figure 68. Spatial distribution of median-concentration percentiles and monotonic dissolved zinc concentration trends at selected sites in the 

Eagle River watershed, Colorado, 1994–2006.

!(

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88

79 72

66

59

49

58

EXPLANATION

Waterbodies

Upper Eagle subwatershed

Middle Eagle subwatershed

Gore Creek subwatershed Streams

Lower Eagle subwatershed

Monotonic dissolved zinc trend, 1994 to 2006, and site number

Zinc

5–40 0–25

41–150 greater than 25–50

greater than 50–75

greater than 75–100

Number of samples

Grouping of median concentrations

by Eagle River watershed percentile 

151–314

City

88

224

No trend

Downward trend

 p-value greater than 0.05–0.15

 p-value greater than 0.01–0.05

 p-value 0.00–0.01

Base from U.S. Geological Survey digital data, 2007,

Universal Transverse Mercator projection

Zone 13 

173

224

Eagle

Wolcott

Avon

Dotsero

Edwards

Vail

Red Cliff

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(!(

!(

!(

!(

!(!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

Minturn

Minturn

(!

(

!

Gypsum Eagle River

Cross Creek

East Fork

Eagle River 

Eagle

River

Black Gore Creek

106°15'

106°45'

39°45'

39°30'

0 5 10 KILOMETERS

0 5 10 MILES

Gore Creek

Turkey Creek

Alkali Creek
106 Assessment of Surface-Water Quantity and Quality, Eagle River Watershed, Colorado, 1947–2007

EXPLANATION

30 Number of values

o Upper detached

Upper outside

Lower adjacent

Upper adjacent

x

x Lower outside

o Lower detached

90th percentile

75th percentile

25th percentile

10th percentile

median

Dissolved cadmium, in milligrams per liter

Site 100

7

6

5

4

3

2

1

0

11 11 15 16 11 6 6 6 8 7

x

x

o

o

x o

January February March April May June July August September October November December

3.0

2.5

2.0

1.5

1.0

0.5

0

6 7 6 8 10 9 8 9 7 5 8

Site 78 o

o

o

oo

o o

o o

o

6

5

3

4

2

1

0

14 7 7 14 12 8 9 14 20 15 8 5

Site 72

x x x

o

o

o

o

o o

o

Site 66

10

8

6

4

2

0

17 7 24 28 17 12 9 13 23 16 7 7

x

x

x

x x x

x

o

o

o

o

o

o

o

o

o

Figure 69. Seasonal pattern of dissolved cadmium concentrations at selected sites in the Eagle River watershed, Colorado, 1966–2007.
Assessment of Surface-Water Quality 107

Figure 70. Seasonal pattern of dissolved copper concentrations at selected sites in the Eagle River watershed, Colorado, 1966–2007.

EXPLANATION

30 Number of values

o Upper detached

Upper outside

Lower adjacent

Upper adjacent

x

x Lower outside

o Lower detached

90th percentile

75th percentile

25th percentile

10th percentile

median

Dissolved copper, in micrograms per liter

16

14

12

10

8

6

4

2

0

7 7 10 13 8 9 9 9 8 7 7 7

Site 84

January February March April May June July August September October November December

25

20

10

15

5

0

17 7 26 25 13 12 9 14 23 16 7 7

Site 66

o

o o

x

Site 56B

200

150

100

50

0

15 5 12 13 11 6 8 11 15 14 6 6

o

o

o

o

o

o

x

x x

x

o

o

o

x

x
108 Assessment of Surface-Water Quantity and Quality, Eagle River Watershed, Colorado, 1947–2007

Figure 71. Seasonal pattern of dissolved iron concentrations at selected sites in the Eagle River watershed, Colorado, 1966–2007.

EXPLANATION

30 Number of values

o Upper detached

Upper outside

Lower adjacent

Upper adjacent

x

x Lower outside

o Lower detached

90th percentile

75th percentile

25th percentile

10th percentile

median

Dissolved iron, in micrograms per liter 400

300

100

200

0

17 7 26 25 13 12 9 14 23 16 7 7

Site 224

o

o

o

x

x

x

x

x

o

Site 66

2,000

1,500

1,000

500

0

16 7 12 16 16 11 9 15 19 13 7 6

o x

x

x

x

o

o

x

x

January February March April May June July August September October November December
Assessment of Surface-Water Quality 109

Figure 72. Seasonal pattern of dissolved manganese concentrations at selected sites in the Eagle River watershed, Colorado, 1970–2007.

EXPLANATION

30 Number of values

o Upper detached

Upper outside

Lower adjacent

Upper adjacent

x

x Lower outside

o Lower detached

90th percentile

75th percentile

25th percentile

10th percentile

median

Dissolved manganese, in micrograms per liter

Site 224

700

600

500

400

300

200

100

0

11 14 19 15 18 21 11 19 10 16 17 12

o

o

o

x x

x

x x x

o

o

o

x

x

x

1,200

1,000

800

600

400

200

0

2 2 7 8 16 8 2 11 7 5 6 4

Site 173

x

x

x

o

o

4,000

3,000

1,000

2,000

0

17 7 40 75 18 11 9 19 24 19 7 6

Site 66

x

o

o

o o

o

o o

o

o

o

x

x

xx

x

x

xx

x x

x

Site 13

25

20

15

10

5

0

2 3 5 5 10 5 1 5 2 6 9 4

o

x

x

January February March April May June July August September October November December
110 Assessment of Surface-Water Quantity and Quality, Eagle River Watershed, Colorado, 1947–2007

EXPLANATION

30 Number of values

o Upper detached

Upper outside

Lower adjacent

Upper adjacent

x

x Lower outside

o Lower detached

90th percentile

75th percentile

25th percentile

10th percentile

median

Dissolved zinc, in micrograms per liter

Site 224

100

80

60

40

20

0

2 3 8 5 6 7 0 6 3 5 6 3

x

o

o

500

400

300

200

100

0

2 2 7 7 16 8 2 11 6 5 6 3

Site 173

x

x

x

50

40

20

10

30

0

4 2 5 6 6 6 2 4 3 3 4 5

Site 160

o

Site 66

5,000

4,000

3,000

2,000

1,000

0

17 7 66 123 18 12 9 18 26 19 7 7

x

x

x

x

x x

x

x

x x x

o o

o

o

oo

o

o

o o

o

January February March April May June July August September October November December

Figure 73. Seasonal patterns of dissolved zinc concentrations at selected sites in the Eagle River watershed, Colorado, 1966–2007.
Assessment of Surface-Water Quality 111

EXPLANATION

30 Number of values

o Upper detached

Upper outside

Lower adjacent

Upper adjacent

x

x Lower outside

o Lower detached

90th percentile

75th percentile

25th percentile

10th percentile

median

Dissolved cadmium, in micrograms per liter Hardness ad CaCO3, in milligrams per liter

6

5

3

2

1

4

0

14 7 7 14 12 8 9 14 20 15 8 5

o

o

o

x x x

o

o o

o

1,000

800

600

400

200

0

3 5 10 5 6 12 6 8 8 10 3 8

o

o

x

x

January February March April May June July August September October November December

Figure 74. Seasonal pattern relation between trace elements concentrations and hardness at site 72 in the Eagle River watershed, Colorado.

Table value standards for uranium are designated by the 

CDPHE and applies to all reaches of the ERW. The acute and 

chronic TVS for uranium are site-specific based on hardness. 

There were no exceedances of the acute or chronic State standards for uranium out of 78 comparisons.

To better represent exceedances of State standards for 

trace-elements in the ERW as a whole, the combined number of samples with detected exceedances for any of the 

trace-element species State standards discussed was made 

into maps. Maps summarizing the spatial extent of acute 

and chronic State standards exceedances are presented in 

figures 76 and 77.

Extensive sampling for metals has been done in select 

areas of the ERW related to the Eagle Mine Superfund Site to 

address site remediation and compliance investigations. Sampling within specific reaches of the Eagle River and tributaries 

are closely spaced together making graphical presentation and 

resolution of the data difficult. Discussion of metals exceedances of State standards will focus on three sites that represent each of 3 conditions present within the ERW: (1) stream 

conditions upstream from the Eagle Mine area Upper Eagle 

subwatershed; (site 28); (2) stream conditions in the Eagle 

Mine area Upper Eagle subwatershed; (site 66); and (3) stream 

conditions downstream from the Eagle Mine area Middle 

Eagle subwatershed; (site 173). Table 20 provides information 

on metals exceedances within the (Upper Eagle, Middle Eagle, 

Lower Eagle and Gore Creek) subwatersheds of the ERW.

State standards for cadmium are designated by the 

CDPHE. The chronic TVS for cadmium are site-specific based 

on hardness, except for segment 11 (10 μg/L total recoverable 

cadmium). The chronic State standards for cadmium were 

exceeded less than 20 times over a period of several years for 

most sites in the ERW; approximately 20 percent (507 comparisons) of the total number of measurements (2,548) exceeded 

the chronic State standards (table 20). 

The acute TVS for cadmium are site-specific based on 

hardness, except for segment 11 (10 μg/L total recoverable 

cadmium). Most sites in the ERW exceeded the acute State 

standard for cadmium fewer than 5 times; approximately 

2 percent (44 comparisons) of the total number of measurements (2,548) exceeded the acute State standard for cadmium 

(table 20). Additionally, an acute(trout) State standard exists 

for cadmium. Using this standard as a comparative reference 

approximately 3 percent (86 comparisons) of the total number of measurements (2,548) exceeded the acute(trout) State 

standard (table 20). Figures 78–80 show the concentrations for 

dissolved cadmium through time at selected sites in comparison to State standards.
112 Assessment of Surface-Water Quantity and Quality, Eagle River Watershed, Colorado, 1947–2007 Total recoverable iron, in milcrograms per liter

January February March April May June July August September October November December

1,000

2,000

3,000

4,000

5,000

6,000

7,000

0

Figure 75. Seasonal patterns of total recoverable iron concentrations at site 224 in the Eagle River watershed, near 

Gypsum, Colorado.
Assessment of Surface-Water Quality 113

EXPLANATION

Waterbodies

Upper Eagle subwatershed

Middle Eagle subwatershed

Gore Creek subwatershed Streams

Lower Eagle subwatershed

Trace elements

5–40 0

41–101 1

Number of samples Number of exceedances

City

!

!

!

!

!

!

!

!

!

!

!

!(

Gore Creek

Base from U.S. Geological Survey digital data, 2007,

Universal Transverse Mercator projection

Zone 13 

Turkey Creek

Rock Creek

Fall Creek

!( !(

!

!(

!

!

!(

!(

!

!(

!(

!(!

!(

!(

!

!(

!(

!(

!(

!(

!(

!(

!(

!

!

!

!(

(

(

(

(

(

!!(!(

!(

!(

!(

!(!(

!( (!

(!

(

(

Eagle

Gypsum

Wolcott

Avon

Minturn

Vail

Red Cliff

Dotsero

Eagle River

Cross Creek

East Fork

Eagle River 

Eagle

River

Black Gore Creek

Edwards

106°15'

106°45'

39°45'

39°30'

0 5 10 KILOMETERS

0 5 10 MILES

Gore Creek

Turkey Creek

Minturn

Vail

Red Cliff

Alkali Creek

!

!

!

!

! !

Figure 76. Number of exceedances of the Colorado acute water-quality standard for concentration of trace elements (dissolved arsenic, 

dissolved selenium, dissolved uranium) at selected sites in the Eagle River watershed, Colorado, 1971–2007.
114 Assessment of Surface-Water Quantity and Quality, Eagle River Watershed, Colorado, 1947–2007

Figure 77. Number of exceedances of the Colorado chronic water-quality standard for concentration of trace elements (dissolved arsenic, 

dissolved selenium, dissolved uranium) at selected sites in the Eagle River watershed, Colorado, 1968–2001.

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!( !(

EXPLANATION

Waterbodies

Upper Eagle subwatershed

Middle Eagle subwatershed

Gore Creek subwatershed Streams

Lower Eagle subwatershed

Chronic trace elements

5–40 0

41–101 1–2

Number of samples Number of exceedances

City

Base from U.S. Geological Survey digital data, 2007,

Universal Transverse Mercator projection

Zone 13 

!( !(

!(

!(

!(

!(

!(

!(

!(

!(!

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!( Eagle

Gypsum

Wolcott

Avon

Minturn

Vail

Red Cliff

Dotsero

Eagle River

Cross Creek

East Fork

Eagle River 

Eagle

River

Black Gore Creek

Edwards

106°15'

106°45'

39°45'

39°30'

0 5 10 KILOMETERS

0 5 10 MILES

Gore Creek

Turkey Creek

Minturn

Vail

Red Cliff

Alkali Creek

!

!

(!

Turkey Creek

Rock Creek

Fall Creek

!

(!

!

!

!

! !

Gore Creek
Assessment of Surface-Water Quality 115

Table 20. Summary of water-quality standard exceedances for trace elements in the Eagle River watershed by subwatershed.—Continued

[Exceedances based on dissolved concentrations, unless otherwise noted; No., number; --, no data]

Constituent 

or property1

No. of 

censored 

values

No. of

samples

No. of 

standard 

exceedances

Percent of 

standard

exceedances

Minimum 

date

Maximum 

date

Gore Creek subwatershed

Aluminum, acute 2 22 2 9 Oct-18-99 Sep-25-00

Aluminum, chronic 2 22 10 45 May-19-99 Oct-16-01

Arsenic, acute 101 103 0 0 -- --

Arsenic, chronic 101 103 0 0 -- --

Cadmium, acute 201 219 0 0 -- --

Cadmium, acute (trout) 201 219 0 0 -- --

Cadmium, chronic 201 219 4 2 Mar-14-89 Jun-18-97

Copper, acute 218 304 1 <1 Sep-06-89 Sep-06-89

Copper, chronic 218 304 5 2 Sep-06-89 Aug-30-07

Iron, chronic1 205 731 8 1 Apr-25-89 Jun-04-03

Lead, acute 230 247 0 0 -- --

Lead, chronic 230 247 0 0 -- --

Manganese, acute 189 525 0 0 -- --

Manganese, chronic 189 525 0 0 -- --

Nickel, acute 24 35 0 0 -- --

Nickel, chronic 24 35 0 0 -- --

Selenium, acute 56 70 0 0 -- --

Selenium, chronic 56 70 0 0 -- --

Silver, acute 133 139 0 0 -- --

Silver, chronic 133 139 0 0 -- --

Silver, chronic (trout) 133 139 3 2 Dec-28-88 Sep-20-89

Uranium, acute 13 37 0 0 -- --

Uranium, chronic 13 37 0 0 -- --

Zinc, acute 257 425 0 0 -- --

Zinc, chronic 257 425 0 0 -- --

Upper Eagle subwatershed

Aluminum, acute 0 17 0 0 -- --

Aluminum, chronic 0 17 17 100 Oct-11-68 Apr-03-01

Arsenic, acute 66 69 1 1 Dec-06-71 Dec-06-71

Arsenic, chronic 66 69 0 0 -- --

Cadmium, acute 281 1,805 44 2 Oct-11-68 Apr-13-06

Cadmium, acute (trout) 281 1,805 82 5 Oct-11-68 Apr-13-06

Cadmium, chronic 281 1,805 469 26 Oct-11-68 Apr-20-06

Copper, acute 268 1,828 59 3 Oct-27-70 Apr-20-06

Copper, chronic 268 1,828 96 5 Oct-27-70 Apr-20-06

Iron, chronic1 71 2,539 687 27 Apr-25-66 Apr-13-06

Lead, acute 527 1,780 0 0 -- --

Lead, chronic 527 1,780 190 11 Oct-11-68 Mar-30-99

Manganese, acute 106 1,926 39 2 Dec-13-88 Mar-10-93

Manganese, chronic 106 1,926 96 5 Oct-27-70 Mar-07-95

Nickel, acute 8 23 0 0 -- --

Nickel, chronic 8 23 0 0 -- --

Selenium, acute 113 153 0 0 -- --

Selenium, chronic 113 153 4 3 Jun-28-68 Oct-27-70

Silver, acute 170 238 7 3 Oct-27-70 Mar-23-01

Silver, chronic 170 238 11 5 Oct-27-70 Mar-23-01

Silver, chronic (trout) 170 238 30 13 Oct-27-70 Apr-17-02

Uranium, acute 4 15 0 0 -- --

Uranium, chronic 4 15 0 0 -- --

Zinc, acute 129 2,292 583 25 Oct-05-66 Oct-23-06

Zinc, chronic 129 2,292 610 27 Oct-05-66 Oct-23-06
116 Assessment of Surface-Water Quantity and Quality, Eagle River Watershed, Colorado, 1947–2007

Table 20. Summary of water-quality standard exceedances for trace elements in the Eagle River watershed by subwatershed.—Continued

[Exceedances based on dissolved concentrations, unless otherwise noted; No., number; --, no data]

Constituent 

or property1

No. of 

censored 

values

No. of

samples

No. of 

standard 

exceedances

Percent of 

standard

exceedances

Minimum 

date

Maximum 

date

Middle Eagle subwatershed

Aluminum, acute 4 30 0 0 -- --

Aluminum, chronic 4 30 8 27 Dec-04-00 Sep-11-03

Arsenic, acute 46 51 0 0 -- --

Arsenic, chronic 46 51 0 0 -- --

Cadmium, acute 171 317 0 0 -- --

Cadmium, acute (trout) 171 317 4 1 Sep-14-89 Mar-08-95

Cadmium, chronic 171 317 32 10 Oct-26-88 Sep-09-98

Copper, acute 153 338 0 0 -- --

Copper, chronic 153 338 3 <1 Jan-10-91 Sep-14-99

Iron, chronic1 50 448 58 13 May-19-76 Aug-28-07

Lead, acute 259 331 0 0 -- --

Lead, chronic 259 331 0 0 -- --

Manganese, acute 41 385 3 <1 Jan-18-90 Mar-15-90

Manganese, chronic 41 385 10 3 Mar-14-89 Mar-15-90

Nickel, acute 4 20 0 0 -- --

Nickel, chronic 4 20 0 0 -- --

Selenium, acute 99 139 0 0 -- --

Selenium, chronic 99 139 1 <1 Feb-15-01 Feb-15-01

Silver, acute 153 158 0 0 -- --

Silver, chronic 153 158 0 0 -- --

Silver, chronic (trout) 153 158 0 0 -- --

Uranium, acute 1 13 0 0 -- --

Uranium, chronic 1 13 0 0 -- --

Zinc, acute 32 340 45 13 Jan-5-77 Feb-18-97

Zinc, chronic 32 340 56 16 Jan-5-77 Feb-18-97

Lower Eagle subwatershed

Aluminum, acute 0 35 4 11 Aug-29-00 May-23-03

Aluminum, chronic 0 35 28 80 Dec-02-98 May-23-03

Arsenic, acute 87 108 0 0 -- --

Arsenic, chronic 87 108 0 0 -- --

Cadmium, acute 172 207 0 0 -- --

Cadmium, acute (trout) 172 207 0 0 -- --

Cadmium, chronic 172 207 2 1 Aug-18-86 Apr-28-92

Copper, acute 113 232 0 0 -- --

Copper, chronic 113 232 0 0 -- --

Iron, chronic1 114 555 31 6 May-18-76 Apr-10-06

Lead, acute 235 258 0 0 -- --

Lead, chronic 235 258 1 <1 Nov-20-69 Nov-20-69

Manganese, acute 23 405 0 0 -- --

Manganese, chronic 23 405 0 0 -- --

Nickel, acute 28 34 0 0 -- --

Nickel, chronic 28 34 0 0 -- --

Selenium, acute 94 148 0 0 -- --

Selenium, chronic 94 148 0 0 -- --

Silver, acute 95 97 0 0 -- --

Silver, chronic 95 97 0 0 -- --

Uranium, acute 0 13 0 0 -- --

Uranium, chronic 0 13 0 0 -- --

Zinc, acute 23 246 0 0 -- --

Zinc, chronic 23 246 0 0 -- --

1

Counts include both total recoverable and dissolved iron.
Assessment of Surface-Water Quality 117

EXPLANATION

Cadmium

Acute standard concentration

Acute trout standard concentration

Colorado chronic standard concentration

Dissolved cadmium, in milligrams per liter

2.5

2

1

0.5

1.5

0

January 1970 January 1980 January 1990 January 2000 January 2010

Figure 78. Temporal distribution of dissolved cadmium concentrations at site 28, in the Eagle River watershed, Colorado, 1984–2003.

The chronic TVS for copper is site-specific based 

on hardness except reach 11 (200 μg/L total recoverable) 

(fig. 12). The chronic State standard for copper was exceeded 

less than 10 times over a period of several years for most sites 

in the ERW; approximately 4 percent (104 comparisons) of the 

total number of measurements (2,702) exceeded the chronic 

State standard (table 20). 

The acute TVS for copper set by the CDPHE is site 

specific based on hardness. Reach 11 does not have an acute 

TVS for copper (fig. 12). The acute TVS was exceeded fewer 

than 10 times at most sites within the ERW; approximately 

2 percent (60 comparisons) of the total number of measurements (2,702) exceeded the acute TVS (table 20). Figures 

81–83 show the concentrations for dissolved copper through 

time at selected sites in comparison to State standards.

Chronic State standards for iron are designated by the 

CDPHE for both dissolved iron and total recoverable iron. 

Reach 11 has no State standard for iron (fig. 12). For total 

recoverable iron, the chronic State standard is 1,000 μg/L. The 

chronic State standard for total recoverable iron was exceeded 

less than 20 times over a period of several years for most sites 

in the ERW; 26 percent (421 comparisons) of the total number 

of measurements (1,596) exceeded the chronic State standard.

For dissolved iron, the chronic State standard is 300 μg/L. 

Most sites in the ERW exceeded the chronic State standard 

fewer than 20 times; 14 percent (363 comparisons) of the total 

number of measurements (2,624) exceeded the chronic State 

standard (table 20). Figures 84–89 show the concentrations for 

dissolved iron through time at selected sites in comparison to 

the State standard. Figures 87–89 show the concentrations for 

total iron through time at selected sites in comparison to the 

State standard.

Standards for manganese are designated by the 

CDPHE. The chronic State standard for manganese is determined by the less restrictive value of either the TVS, which 

is site-specific based on hardness, or 50 μg/L dissolved 

for all reaches of the ERW except for reach 11 (200 μg/L 

total recoverable) (fig. 12). The manganese State standards 

were exceeded less than 20 times over a period of several 

years for most sites in the ERW; approximately 3 percent 

(106 comparisons) of the total number of measurements 

(3,241) exceeded the chronic State standards.

The acute State standard for manganese is the less 

restrictive value of either the TVS or 50 μg/L dissolved for 

all reaches of the ERW except for reach 11 (200 μg/L total 

recoverable) (fig. 12). Most sites in the ERW exceeded the 

acute State standards for manganese fewer than 15 times; 

approximately 1 percent (42 comparisons) of the total number 

of measurements (3,241) exceeded the acute State standard 

(table 20). Figures 90–92 show the concentrations for dissolved manganese through time at selected sites in comparison 

to acute and chronic State standards.
118 Assessment of Surface-Water Quantity and Quality, Eagle River Watershed, Colorado, 1947–2007

EXPLANATION

Cadmium

Acute standard concentration

Acute trout standard concentration

Colorado chronic standard concentration

Dissolved cadmium, in milligrams per liter

4.5

3.5

4

3

2

1.5

1

0.5

2.5

0

January 1970 January 1980 January 1990 January 2000 January 2010

Figure 80. Temporal distribution of dissolved cadmium concentrations at site 173, in the Eagle River watershed, 1997–2007.

EXPLANATION

Cadmium

Acute standard concentration

Acute trout standard concentration

Colorado chronic standard concentration

Dissolved cadmium, in milligrams per liter

10

8

4

2

6

0

January 1970 January 1980 January 1990 January 2000 January 2010

Figure 79. Temporal distribution of dissolved cadmium concentrations at site 66, in the Eagle River watershed, Colorado, 1985–2007.
Assessment of Surface-Water Quality 119

EXPLANATION

Cadmium

Acute standard concentration

Colorado chronic standard concentration

Dissolved copper, in milligrams per liter

12

10

6

4

2

0

January 1970 January 1980 January 1990 January 2000 January 2010

8

Figure 81. Temporal distribution of dissolved copper concentrations at site 28, in the Eagle River watershed, Colorado, 1985–2003.

EXPLANATION

Copper

Acute standard concentration

Colorado chronic standard concentration

Dissolved copper, in milligrams per liter

25

20

10

0

5

January 1970 January 1980 January 1990 January 2000 January 2010

15

Figure 82. Temporal distribution of dissolved copper concentrations at site 66, in the Eagle River watershed, Colorado, 1981–2007.
120 Assessment of Surface-Water Quantity and Quality, Eagle River Watershed, Colorado, 1947–2007

Figure 83. Temporal distribution of dissolved copper concentrations at site 173, in the Eagle River watershed, Colorado, 1994–2007.

EXPLANATION

Copper

Acute standard concentration

Colorado chronic standard concentration

Dissolved copper, in milligrams per liter

25

20

10

0

5

January 1970 January 1980 January 1990 January 2000 January 2010

15

Figure 84. Temporal distribution of dissolved iron concentrations at site 28, in the Eagle River watershed, Colorado, 1984–2003.

EXPLANATION

Dissolved iron

Colorado chronic standard concentration

Dissolved iron, in milligrams per liter

300

0

100

January 1970 January 1980 January 1990 January 2000 January 2010

200
Assessment of Surface-Water Quality 121

Figure 85. Temporal distribution of dissolved iron concentrations at site 66, in the Eagle River watershed, Colorado, 1985–2005.

EXPLANATION

Dissolved iron

Colorado chronic standard concentration

Dissolved iron, in milligrams per liter

1,800

0

200

January 1970 January 1980 January 1990 January 2000 January 2010

1,000

400

600

800

1,200

1,400

1,600

Figure 86. Temporal distribution of dissolved iron concentrations at site 173, in the Eagle River watershed, Colorado, 1978–2003.

EXPLANATION

Dissolved iron

Colorado chronic standard concentration

Dissolved iron, in milligrams per liter

400

0

January 1970 January 1980 January 1990 January 2000 January 2010

100

200

300
122 Assessment of Surface-Water Quantity and Quality, Eagle River Watershed, Colorado, 1947–2007

Figure 87. Temporal distribution of total recoverable iron concentrations at site 28, in the Eagle River watershed, Colorado, 1984–2004.

EXPLANATION

Total recoverable iron

Colorado chronic standard concentration

Total recoverable iron, in milligrams per liter

1,200

0

January 1970 January 1980 January 1990 January 2000 January 2010

400

800

Figure 88. Temporal distribution of total recoverable iron concentrations at site 66, in the Eagle River watershed, Colorado, 1985–2007.

EXPLANATION

Total recoverable iron

Colorado chronic standard concentration

Total recoverable iron, in milligrams per liter

6,000

5,000

3,000

2,000

1,000

0

January 1970 January 1980 January 1990 January 2000 January 2010

4,000
Assessment of Surface-Water Quality 123

Figure 89. Temporal distribution of total recoverable iron concentrations at site 173, in the Eagle River watershed, Colorado, 1994–2006.

EXPLANATION

Total recoverable iron

Colorado chronic standard concentration

Total recoverable iron, in milligrams per liter

1,200

200

0

January 1970 January 1980 January 1990 January 2000 January 2010

400

600

800

1,000

1,400

State standards for zinc are designated by CDPHE. 

Zinc has a seasonally modified standard within certain 

reaches of the ERW or a TVS for acute and chronic exposure levels of zinc (Colorado Department of Public Health 

and Environment, 2008). Two seasons are used to divide 

the year, March–April and May–February. Reaches 5a, 5b, 

5c, and 7b have a seasonal designation for the zinc chronic 

and acute State standards (fig. 12). All other reaches have a 

TVS that is site specific based on hardness, except for reach 

11. The chronic State standards for reach 5a are 410 μg/L 

(March–April) and 166 μg/L (May–February); for reach 5b, 

310 μg/L (March–April) and 123 μg/L (May–February); 

for reach 5c, 257 μg/L (March–April) and a TVS (May–

February); and for reach 7b, 193 μg/L (March–April) and 

116 μg/L (May–February). Reach 11 has a chronic State 

standard of 2,000 μg/L total recoverable. Acute standards 

for reach 5a are 472 μg/L (March–April) and 178 μg/L 

(May–February); for reach 5b, 332 μg/L (March–April) and 

153 μg/L (May–February); for reach 5c, 275 μg/L (March–

April) and 127 μg/L (May–February); and for reach 7b, 

254 μg/L (March–April) and 120 μg/L (May–February). 

Reach 11 does not have an acute State standard for zinc.

The chronic State standards for zinc were exceeded less 

than 20 times over a period of several years for most sites in 

the ERW; approximately 20 percent (666 comparisons) of the 

total number of measurements (3,303) exceeded the chronic 

State standards (table 20).

The acute State standards for zinc were exceeded less 

than 15 times over a period of several years for most sites in 

the ERW; approximately 19 percent (628) of the total number of measurements (3,303) exceeded the State standards 

(table 20). Figures 93–96 show the concentrations for dissolved zinc through time at selected sites in comparison to 

acute and chronic State standards. 

To better represent exceedances of State standards for 

trace-metals in the ERW as a whole, the combined number of samples with detected exceedances for any of the 

trace-metals species discussed was made into maps. Maps 

summarizing the spatial extent of exceedances of acute and 

chronic State standards for trace metals are presented in 

figures 97–98.

Evaluation of temporal trends for metals in the ERW 

includes the evaluation of step trends and monotonic trends. 

Remediation of the Eagle Mine Superfund site occurred over 

several years, with the major completion occurring by 1994 

(table 2). Comparisons of pre- and post-remediation concentrations for many trace metals shows highly significant 

decreases in concentrations for cadmium, manganese, and 

zinc at sites on the Eagle River downstream from the remediation sites and in tributaries affected by remediation activities 
124 Assessment of Surface-Water Quantity and Quality, Eagle River Watershed, Colorado, 1947–2007

Figure 90. Temporal distribution of dissolved manganese concentrations at site 28, in the Eagle River watershed, Colorado, 1984–2003.

Figure 91. Temporal distribution of dissolved manganese concentrations at site 66, in the Eagle River watershed, Colorado, 1986–2007.

EXPLANATION

Total recoverable iron

Colorado acute standard concentration

Colorado chronic standard concentration

Dissolved manganese, in milligrams per liter

3,000

0

January 1970 January 1980 January 1990 January 2000 January 2010

1,000

2,000

EXPLANATION

Manganese

Colorado acute standard concentration

Colorado chronic standard concentration

Dissolved manganese, in milligrams per liter

4,000

0

January 1970 January 1980 January 1990 January 2000 January 2010

1,000

2,000

3,000
Assessment of Surface-Water Quality 125

Figure 92. Temporal distribution of dissolved manganese concentrations at site 173, in the Eagle River watershed, Colorado, 1994–2007.

EXPLANATION

Manganese

Colorado acute standard concentration

Colorado chronic standard concentration

Dissolved manganese, in milligrams per liter

4,000

0

January 1970 January 1980 January 1990 January 2000 January 2010

1,000

2,000

3,000

(table 21). Some sites show order of magnitude reductions in 

median concentrations between these two periods (table 21). 

However, iron concentrations do not appear to show the same 

step-trend reductions between these two periods.

Evaluation of monotonic trends for dissolved trace metals (cadmium, iron, manganese, and zinc) was done for all 

sites with data that met the criteria set in the “Data Sources, 

Compilation, Review, and Analysis” section of this report. 

Findings from the trend analysis are presented in table 22 and 

figures 64–68. Seasonal Kendall Trend tests were done for 

the time period 1994–2006 depending on the data available at 

each site. Numerous downward trends and no upward trends 

were detected during the study period. Statistically significant 

trends occur in areas in and downstream from historic mining 

areas. Spatial continuity of trends within and downstream 

from the mine area was not always consistent. There were 

several sites that had no detected trends separating sites with 

significant downward trends. In general, however, step-trend 

analysis and temporal-trend analysis provided good evidence 

that remediation of historic mine areas in the Upper Eagle 

River subwatershed has lead to observed decreases in many 

metal concentrations.

Suspended Sediment

The size and quantity of sediments within streams and 

the types of sediments transported by a stream are important 

factors affecting aquatic ecosystems and water management. 

Sediment can be transported in the water column as suspended 

sediment or moved along the bed of a stream as bedload. 

Sediment transport is a combination of the sediment particle 

size and the transport forces within a stream. Larger particles 

require larger, continual forces for transport while smaller particles, once in suspension, can remain within a tranquil water 

column for days before settling out of suspension (Julien, 

2010). Varying geologic settings, geologic lithology, and channel form contribute to the sizes and abundance of sediments 

within a stream (Knighton, 1998).

Sedimentation has been identified by the Colorado 

Water-Quality Control Commission as a water-quality concern 

in Black Gore Creek. Black Gore Creek was placed on the 

Section 303(d) list in 2002, 2004, and 2006. Wynn and others 

(2001) indicate 4,000 tons of coarse sand and fine gravel are 

washed into Black Gore Creek each year as a result of traction 

sanding along I-70. Annual amounts of traction sand applied 
126 Assessment of Surface-Water Quantity and Quality, Eagle River Watershed, Colorado, 1947–2007

Figure 93. Temporal distribution of dissolved zinc concentrations at site 23, in the Eagle River watershed, Colorado, 1985–2003.

Figure 94. Temporal distribution of dissolved zinc concentrations at site 66, in the Eagle River watershed, Colorado, March–April 1986–2007.

EXPLANATION

Zinc

Colorado acute standard concentration

Colorado chronic standard concentration

Dissolved zinc, in milligrams per liter

160

0

January 1970 January 1980 January 1990 January 2000 January 2010

40

80

120

EXPLANATION

Zinc

Colorado acute standard concentration

Colorado chronic standard concentration

Dissolved zinc, in milligrams per liter

4,000

0

January 1970 January 1980 January 1990 January 2000 January 2010

1,000

2,000

3,000
Assessment of Surface-Water Quality 127

Figure 95. Temporal distribution of dissolved zinc concentrations at site 66, in the Eagle River watershed, Colorado, May–February 1986–2007.

Figure 96. Temporal distribution of dissolved zinc concentrations at site 173, in the Eagle River watershed, 1994–2006.

EXPLANATION

Zinc

Colorado acute standard concentration

Colorado chronic standard concentration

Dissolved zinc, in milligrams per liter

3,000

0

January 1970 January 1980 January 1990 January 2000 January 2010

1,000

2,000

EXPLANATION

Zinc

Colorado acute standard concentration

Colorado chronic standard concentration

Dissolved zinc, in milligrams per liter

500

0

January 1970 January 1980 January 1990 January 2000 January 2010

300

200

100

400
128 Assessment of Surface-Water Quantity and Quality, Eagle River Watershed, Colorado, 1947–2007

Figure 97. Number of exceedances of the Colorado acute water-quality standard for metals concentrations at selected sites in the Eagle River 

watershed, Colorado, 1966–2006.

!(

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!(

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Gore Creek

EXPLANATION

Waterbodies

Upper Eagle subwatershed

Middle Eagle subwatershed

Gore Creek subwatershed Streams

Copper and zinc

Zinc

Lower Eagle subwatershed

Water quality impaired by metals according to Section 303(d)

of the Federal Clean Water Act of 1972

Metals

5–40 0

41–150 1–10

11–40

41–80

81–205

Number of samples Number of exceedances

151–330

City

Base from U.S. Geological Survey digital data, 2007,

Universal Transverse Mercator projection

Zone 13 

173

224

Eagle

Wolcott

Avon

Dotsero

Edwards

! !(

Red Cliff

(

!(

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!(!(!( !( !( !( !(!(!( !( !(!( !( !( !( !( !( !( !( !( !( !(!( !(!(!(

Minturn (!

Vail

Gypsum Eagle River

Cross Creek

East Fork

Eagle River 

Eagle

River

Black Gore Creek

106°15'

106°45'

39°45'

39°30'

0 5 10 KILOMETERS

0 5 10 MILES

Gore Creek

Turkey Creek

Alkali Creek

Turkey Creek

Minturn

Vail

Red Cliff

Black Gore Creek

Rock Creek

Fall

Creek

(!

!!!

!!

(!
Assessment of Surface-Water Quality 129

Figure 98. Number of exceedances of the Colorado chronic water-quality standard for metals concentrations at selected sites in the Eagle 

River watershed, Colorado, 1966–2007.

!(

!(

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!(

!(

!(

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!( !( !( !( !( !( !( !( !( !(

!(

!( !(!(!(!(

EXPLANATION

Waterbodies

Upper Eagle subwatershed

Middle Eagle subwatershed

Gore Creek subwatershed Streams

Copper and zinc

Zinc

Lower Eagle subwatershed

Water quality impaired by metals according to Section 303(d)

of the Federal Clean Water Act of 1972

Metals

5–40 0

41–150 1–10

11–40

41–80

81–234

Number of samples Number of exceedances

151–330

City

Base from U.S. Geological Survey digital data, 2007,

Universal Transverse Mercator projection

Zone 13 

Eagle

Wolcott

Avon

Dotsero

Edwards

!(

!( !(

!(

!(

!(

!(

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!(

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!( !( !(!(

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Minturn

Red Cliff

Gypsum Eagle River

East Fork

Eagle River 

Eagle

River

Black Gore Creek

106°15'

106°45'

39°45'

39°30'

0 5 10 KILOMETERS

0 5 10 MILES

Gore Creek

Alkali Creek

!

Turkey Creek

Minturn

Vail

Red Cliff

Black Gore Creek

Rock Creek

Fall

Creek

Turkey Creek

Cross Creek

!

!

Vail !

!

!

!

!

Gore Creek
130 Assessment of Surface-Water Quantity and Quality, Eagle River Watershed, Colorado, 1947–2007

Table 21. Summary of step-trends assessment for select sites affected by Eagle Mine Superfund remediation, water years 1972–1991, 

and 1992–2007.

[No., number; μg/L, micrograms per liter]

Site 

no.

Site

Pre-remediation Post-remediation Difference 

in median 

concentrations

No. of p-value Significance

samples

Median 

concentration 

in μg/L

No. of 

samples

Median 

concentration 

in μg/L

Cadmium

49 E-5 23 1.0 68 0.4 –0.6 0 Highly significant

57 E-10 10 .6 74 .3 –.3 .0001 Highly significant

58 393157106235501 20 79 71 13.0 –66 0 Highly significant

59 E-11 24 1.0 71 .5 –.5 0 Highly significant

66 09064600 25 1.0 84 .5 –.5 0 Highly significant

72 393411106242001 15 1.0 81 .4 –.6 0 Highly significant

79 T-18 14 1.0 79 .2 –.8 0 Highly significant

84 E-14 24 1.0 45 .50 –.5 0 Highly significant

Iron

49 E-5 18 150 65 135 –15.0 .20 Not significant

57 E-10 10 115 71 130 15.0 .45 Not significant

58 393157106235501 16 50 59 65 15.0 .73 Not significant

59 E-11 20 130 68 130 0 .53 Not significant

66 09064600 23 440 79 350 –90 .20 Not significant

72 393411106242001 21 220 68 300 80 .93 Not significant

79 T-18 15 100 68 115 15.0 .43 Not significant

84 E-14 21 180 45 265 85 .92 Not significant

Manganese

49 E-5 18 145 69 62.5 –82.5 0 Highly significant

57 E-10 10 179 74 62.0 –117 .0002 Highly significant

58 393157106235501 16 3,610 71 3,555 –55 .73 Not significant

59 E-11 20 190 71 150 –40 .002 Highly significant

66 09064600 23 630 87 270 –360 .0001 Highly significant

72 393411106242001 21 1,630 73 445 –1,185 0 Highly significant

79 T-18 15 830 79 210 –620 .004 Highly significant

84 E-14 21 1,000 45 673 –327 .091 Highly significant

Zinc

49 E-5 23 162 69 63 –99 0 Highly significant

57 E-10 10 182 74 69 –113 .049 Significant

58 393157106235501 20 27,450 71 6,940 –20,510 .0001 Highly significant

59 E-11 24 245 72 350 105 .0004 Highly significant

66 09064600 25 280 86 320 40 0 Highly significant

72 393411106242001 23 380 73 179 –201 0 Highly significant

79 T-18 14 177 79 45.0 –132 .0033 Highly significant

84 E-14 24 280 45 280 0 .038 Significant
Assessment of Surface-Water Quality 131

Table 22. Summary of monotonic temporal trends for metals in the Eagle River watershed.—Continued

[No., number; μg/L, micrograms per liter; --, no data]

Site 

no.

Trend

period

No. of

samples

Flow

adjustment

Trend slope,

units per year

Percent change,

percent per year p-value Trenddirection

Median

value

Cadmium, μg/L

49 1994–2005 30 No -- -- 0.06 Downward 0.2

57 1994–2005 30 No –0.020 –8.9 .04 Downward .2

58 1994–2006 34 No -- -- .37 No trend 13.0

58 1994–2006 32 Yes -- -- .60 No trend 13.0

59 1994–2005 30 No –.030 –10.0 .03 Downward .3

59 1994–2005 14 Yes -- -- .06 Downward .3

66 1994–2006 35 No -- -- .12 Downward .3

66 1994–2006 35 Yes -- -- .08 Downward .3

72 1994–2005 30 No –.033 –11.1 .03 Downward .3

72 1994–2005 12 Yes -- -- .31 No trend .3

88 1998–2004 16 No -- -- .60 No trend .2

173 1995–2006 25 No –.020 –20.0 .03 Downward .1

Iron, μg/L

49 1994–2004 28 No -- -- .49 No trend 135

49 1994–2004 13 Yes -- -- .69 No trend 135

57 1994–2004 29 No -- -- .54 No trend 130

57 1994–2004 11 Yes -- -- .29 No trend 130

59 1994–2004 27 No -- -- .56 No trend 150

59 1994–2004 12 Yes -- -- .90 No trend 150

66 1994–2006 34 No -- -- .06 Downward 340

66 1994–2006 34 Yes –28.4 –8.3 .02 Downward 340

72 1994–2004 27 No -- -- .08 Downward 270

79 1994–2006 33 No -- -- .27 No trend 120

79 1994–2006 28 Yes –9.90 –8.2 .04 Downward 120

Manganese, μg/L

3 1996–2006 21 No -- -- .27 No trend 14.3

3 1996–2006 21 Yes –1.38 –9.6 .02 Downward 14.3

13 1996–2006 22 No -- -- .68 No trend 4.5

37 1994–2003 26 No -- -- .08 Downward 19.0

49 1994–2005 30 No -- -- .52 No trend 53

57 1994–2005 10 No -- -- 1.00 No trend 174

57 1994–2005 6 Yes -- -- .45 No trend 174

58 1994–2006 34 No –398 –12.4 .005 Downward 3,200

58 1994–2006 32 Yes –332 –10.4 .01 Downward 3,200

59 1994–2005 30 No –11.0 –13.3 .01 Downward 83

59 1994–2005 14 Yes –8.75 –10.5 .001 Downward 83

66 1994–2006 35 No -- -- .11 Downward 235

66 1994–2006 35 Yes –20.6 –8.8 .003 Downward 235

72 1994–2005 30 No –46.7 –14.1 .01 Downward 330

72 1994–2005 12 Yes –59 –17.9 .01 Downward 330

79 1994–2006 35 No –12.5 –7.4 .05 Downward 170

79 1994–2006 30 Yes –21.2 –12.5 .002 Downward 170

88 1998–2004 16 No -- -- .13 Downward 192

88 1998–2004 7 Yes -- -- .15 No trend 192

100 1997–2006 13 No -- -- .12 Downward 180

100 1997–2006 2 Yes -- -- 1.00 No trend 180

160 1995–2006 26 No -- -- .67 No trend 2.0

173 1994–2006 29 No –6.37 –9.0 .02 Downward 71

173 1994–2006 28 Yes –7.33 –10.3 .004 Downward 71

224 1994–2006 28 No -- -- .31 No trend 23.5

224 1994–2006 28 Yes -- -- .10 Downward 23.5

227 1994–2004 27 No –3.42 –12.7 .03 Downward 27.0
132 Assessment of Surface-Water Quantity and Quality, Eagle River Watershed, Colorado, 1947–2007

Table 22. Summary of monotonic temporal trends for metals in the Eagle River watershed.—Continued

[No., number; μg/L, micrograms per liter; --, no data]

Site 

no.

Trend

period

No. of

samples

Flow

adjustment

Trend slope,

units per year

Percent change,

percent per year p-value Trenddirection

Median

value

Zinc, μg/L

49 1994–2005 30 No -- -- 0.40 No trend 84

58 1994–2006 34 No –642 –9.4 .03 Downward 6,800

58 1994–2006 32 Yes -- -- .34 No trend 6,800

59 1994–2005 30 No -- -- .10 Downward 156

59 1994–2005 14 Yes -- -- .48 No trend 156

66 1994–2006 35 No -- -- .08 Downward 170

66 1994–2006 35 Yes –12.4 –7.3 .01 Downward 170

72 1994–2005 30 No -- -- .06 Downward 169

72 1994–2005 12 Yes -- -- .14 Downward 169

79 1994–2006 35 No -- -- .13 Downward 29.0

79 1994–2006 30 Yes –3.58 –12.4 .01 Downward 29.0

88 1998–2004 16 No -- -- .13 Downward 129

88 1998–2004 7 Yes -- -- .15 No trend 129

173 1994–2006 29 No –3.50 –6.7 .02 Downward 52

173 1994–2006 27 Yes –4.27 –8.2 .02 Downward 52

224 1994–2006 20 No -- -- .06 Downward 13.0

to Black Gore Creek along the I-70 corridor are approximately 

500 times the expected natural sediment inputs within the 

basin of Black Gore Creek (Black Gore Creek Executive Summary, 2006). The accumulation of sediment in streams reduces 

available spawning habitat for fish species and reduces habitat 

for macroinvertebrates (Wynn and others, 2001). Increases in 

the size of sediment particles, along with the total volume of 

sediments entering a stream, can affect the shape of streams 

and the size of the bed materials stored within a stream 

system. Introduction of sediments into a stream from human 

sources can affect the mobility of sediments within a stream 

and can lead to aggradation of the streambed. Larger sediment 

particles require more stream energy to move downstream.

Suspended-sediment concentration has been measured 

at 72 sites from October 2, 1959, to 2007, and ranged from 

0.1 to 1,330 mg/L. The 25th, 50th, and 75th percentiles for 

the ERW were 2.0, 4.0, and 15.0 mg/L, respectively. Median 

concentrations for the subwatersheds were 3.0 mg/L in Gore 

Creek, 4.0 mg/L in the Upper Eagle, 7.0 mg/L in the Middle 

Eagle, and 23.5 mg/L in the Lower Eagle (table 8). The spatial 

pattern shows an increase in suspended-sediment concentration as water moves downstream, with a defined increase in 

suspended-sediment concentration occurring downstream from 

Edwards (fig. 99).

Suspended-sediment concentrations indicate variations 

in seasonal pattern. In Gore Creek, the suspended sediment is 

highest May–June and lowest December–February (fig. 100). 

Suspended-sediment concentrations decrease sharply at the 

end of the runoff period and remain steady through the rest 

of the year. In the Eagle River, the availability of suspendedsediment data is limited, but available data indicate that suspended sediment is greatest during spring snowmelt runoff. 

Evaluation of temporal trends was done for all sites with 

suspended sediment data; trend analysis was done at the 2 

sites that met the criteria set in the “Data Sources, Compilation, Review, and Analysis” section of this report. Findings 

from the trend analysis are presented in table 9 and figure 99. 

Seasonal Kendall Trend tests were done for the time period 

1995–2007. At sites 224 (Lower Eagle subwatershed) and 

160 (Gore Creek subwatershed), no flow-adjusted trends were 

detected (fig. 99).

Summary

From the early mining days to the current tourismbased economy, the ERW has undergone a sequence of 

land-use changes that has affected the hydrology, habitat, 

and water quality of the area. Although intensive hardrock mining has all but stopped in the watershed, elevated 

concentrations of metals, such as cadmium, copper, iron, 

manganese, and zinc, in streams are prevalent as a result of 

long-standing mining activity in the watershed. A 235-acre 

site encompassing the Eagle Mine and associated mining 

wastes between Gilman and Minturn was placed on the 

Superfund site list in 1986. Remediation of the Eagle Mine 

site began in 1988 and continues today.

In order to evaluate the water quality, assess effects of 

growth and associated land-use change, identify temporal and 

spatial gaps within available water-quality data, and evaluate 

spatial and temporal trends in water quality, an analysis of 

historical data was done. In 2000, the USGS, in cooperation 

with the Colorado River Water Conservation District, Eagle 
Summary 133

!(

(

!(

!( !(

224

160

Gore Creek

EXPLANATION

Waterbodies

Upper Eagle subwatershed

Middle Eagle subwatershed

Gore Creek subwatershed Streams

Lower Eagle subwatershed

Monotonic suspended-sediment trend, 1995 to 2007

Suspended sediment

5–40 0–25

41–150 less than 25–50

less than 50–75

less than 75–100

Number of samples

Grouping of median concentrations

by Eagle River watershed percentile

City

77

224

59

No trend

Upward trend

Downward trend

 p-value less than 0.05–0.15

 p-value less than 0.01–0.05

 p-value 0.00–0.01

Base from U.S. Geological Survey digital data, 2007,

Universal Transverse Mercator projection

Zone 13 

0 5 10 KILOMETERS

0 5 10 MILES

Eagle

Gypsum

Minturn

Red Cliff

Wolcott

Dotsero

Edwards

Avon Vail

106°15'

106°45'

39°45'

39°30'

151

!

(!

Figure 99. Spatial distribution of median-concentration percentiles and monotonic suspended-sediment concentration trends at selected 

sites in the Eagle River watershed, Colorado, 1995–2007.
134 Assessment of Surface-Water Quantity and Quality, Eagle River Watershed, Colorado, 1947–2007

EXPLANATION

30 Number of values

o Upper detached

Upper outside

Lower adjacent

Upper adjacent

x

x Lower outside

o Lower detached

90th percentile

75th percentile

25th percentile

10th percentile

median

Suspended sediment concentration, in milligrams per liter

Site 224

600

500

400

300

100

200

0

2 3 3 4 7 7 6 6 2 2 4 3

o

o

January February March April May June July August September October November December

200

150

50

100

0

2 3 3 4 7 6 6 6 2 2 5 2

Site 201

Site 160

160

140

120

100

80

60

40

20

0

9 9 11 20 24 22 15 11 7 6 8 9

o o

o

o

o oo

x

x

x

o

o x

Figure 100. Seasonal pattern in suspended-sediment concentration at selected sites in the Eagle River watershed, Colorado, 1947–2007.
Summary 135

County, Eagle River Water and Sanitation District, Upper 

Eagle Regional Water Authority, Colorado Department of 

Transportation, City of Aurora, Town of Eagle, Town of Gypsum, Town of Minturn, Town of Vail, Vail Resorts, Colorado 

Springs Utilities, and Denver Water initiated a retrospective 

analysis of surface-water quantity and quality in the ERW. 

Data were gathered and reported from the U.S. Geological 

Survey, the U.S. Environmental Protection Agency, U.S. Forest Service, Colorado Department of Natural Resources, Colorado Department of Public Health and Environment, Colorado 

Division of Water Resources, Colorado Department of Transportation, Colorado Division of Wildlife (River Watch), Eagle 

Mine Superfund Site Assessment, Colorado Springs Utilities, 

Eagle River Water and Sanitation District, Grand River Consulting, and Advanced Sciences Incorporated.

The Eagle River drains approximately 963 square miles 

(mi2

) west of the Continental Divide in central Colorado 

before flowing into the Colorado River. Located in central 

Colorado west of Vail Pass, the Eagle River watershed (ERW) 

is almost entirely contained within Eagle County. The watershed extends from the eastern boundary near Vail Pass to the 

western boundary near Dotsero. 

For selected water-quality properties and constituents in the 

watershed, this report: (1) characterizes available water-quantity 

and water-quality data, (2) identifies spatial and seasonal 

variability in water quantity and water quality, (3) provides comparisons to Federal and State water-quality standards or recommendations, (4) characterizes temporal changes in water quality, 

and (5) where possible, identifies potential causes of these 

changes. The study area was divided into four subwatersheds 

for this analysis: (1) Upper Eagle, Eagle River including all 

tributaries upstream from Gore Creek; (2) Gore Creek, including 

all tributaries upstream from the Eagle River: (3) Middle Eagle, 

Eagle River including all tributaries downstream from Gore 

Creek and upstream of the USGS streamflow-gaging station at 

Wolcott; (4) Lower Eagle, Eagle River including all tributaries 

downstream from the USGS streamflow-gaging station at Wolcott and upstream from the Colorado River. 

Available surface-water quantity data were obtained from 

the USGS National Water Information System and the City of 

Colorado Springs. Available surface-water quality data were 

obtained from local, State, and Federal agencies and entered 

into a relational database to assist in the analysis of waterquality conditions in the ERW 1947–2007. The data used in the 

analysis described in this report are available in a web-based 

repository at http://rmgsc.cr.usgs.gov/cwqdr/Eagle/index.shtml. 

An inclusive approach was taken to expand the number 

of samples and sites available for analysis in order to provide 

greater spatial and temporal coverage of water-quality conditions in the watershed. A large portion of the data has limited 

metadata and (or) quality-assurance data. Therefore, it is possible that some data may contain errors that were not detected 

during the water-quality data review. 

Streamflow conditions of the Eagle River follow a 

consistent seasonal pattern. Low-flow conditions (base 

flow) typically occur in October–March, with the start of the 

snowmelt-runoff generally beginning in late March and early 

April. As the snowpack begins to melt, streamflows begin to 

rise and increase to peak streamflow conditions in late May 

and early June. As available snowpack levels are depleted in 

late spring and early summer streamflow levels return to the 

base-flow conditions. Occasional increases in flow during the 

summer and fall months can occur because of precipitation 

events within the ERW.

Many sites within the ERW show patterns of wet and dry 

years. The mid 1980s and 1990s are two wet periods within 

the last several decades, separated by average to dry periods in 

1990 and 2000. The wettest and driest years on record at most 

sites are 1984 and 2002, respectively.

Surface-water-quality data from 293 sites and 12 different 

source agencies were complied into 191 unique sites located 

on streams and rivers in the ERW. Nearly 39 percent (74 sites) 

of the unique sites had fewer than 5 samples. In comparison, 

23 percent (44 sites) of the sites have more than 100 samples. 

Physical properties were the most abundant type of samples 

collected, with major ions, nutrients, and trace elements also 

commonly collected. As mentioned in “Data Review and 

Analysis,” where adequate data existed, determination of 

summary statistics, comparisons to State standards and Federal recommendations, and trend analysis were done. Analysis 

results were separated into different sections of the report 

based on constituent groupings.

Field properties analyzed for in this study included specific conductance, pH, water temperature, dissolved oxygen, 

and hardness. 

Specific conductance is proportional to the dissolved-solids 

concentration within the stream and has the ability to conduct an 

electric current. The spatial pattern shows an increase in specific 

conductance as water moves downstream. There is a significant 

downward trend at site 59 (Upper Eagle subwatershed). 

The pH is a measure of how acidic or basic a solution 

is. In areas heavily affected by mining the median concentrations are lower, with seasonally lower pH during February and 

March. In other areas within the basin, pH tends to be lowest 

during peak streamflows (May and June) and highest during 

late fall and early spring. The spatial pattern shows increase 

in pH as water moves downstream. Approximately 2 percent 

of measurements in the ERW are outside the State’s range of 

acceptable values. There is a weakly significant upward trend 

in pH at site 66 (Upper Eagle subwatershed); a highly significant upward trend at site 173 (Middle Eagle subwatershed); 

and a weakly significant upward trend at site 224 (Lower 

Eagle subwatershed). 

Water temperatures in the ERW generally increase in the 

downstream direction with the highest median temperature 

observed near Gypsum. Water temperatures tend to be coldest 

December–February and warmest July–August following 

ambient air-temperature patterns. Less than 1 percent of the 

total numbers of measurements exceed the State standard for 

chronic water temperature. There are significant upward trends 

at site 13 (Upper Eagle subwatershed) and site 160 (Gore 

Creek subwatershed).
136 Assessment of Surface-Water Quantity and Quality, Eagle River Watershed, Colorado, 1947–2007

Dissolved-oxygen concentrations are inversely related to 

water temperatures; as temperatures increase the capacity of 

water to hold a given quantity of dissolved oxygen is reduced. 

The spatial pattern for dissolved oxygen is variable within the 

ERW. Concentrations tend to be lowest from July–September 

and highest from November–March. Approximately 4 percent 

of measurements exceed the State standards for dissolved oxygen. There is a highly significant upward trend (p-value less 

than 0.01) at site 173 (Middle Eagle subwatershed).

Hardness can have many definitions, in this analysis it 

will be interpreted as a measure of the calcium and magnesium 

abundance. The spatial pattern for hardness shows increases in 

concentration as water moves downstream in the ERW. Concentrations tend to be lowest May–June and highest January–

March, which is the inverse of patterns in streamflow. There 

is a significant downward trend in hardness at site 224 (Lower 

Eagle subwatershed).

Dissolved solids are calculated from (or a measures of) 

ions within a water-quality sample, and can be thought of as 

the dissolved salts that are present. The major ions dissolved 

in most natural waters typically include calcium, magnesium, 

sodium, potassium, alkalinity, sulfate, chloride, fluoride, and 

silica. The spatial pattern for dissolved solids shows increasing 

concentrations from upstream to downstream with a defined 

increase occurring near the town of Wolcott and likely resulted 

from salt-bearing geologic formations (such as the Eagle 

Valley Evaporite) within the area. Concentrations tend to be 

lowest May–June and highest October–March, which is the 

inverse of patterns in streamflow. There is a significant upward 

trend at site 160 (Gore Creek subwatershed), a weakly significant downward trend at site 224 (Lower Eagle subwatershed). 

Less than 1 percent of the measurements exceeded the State 

standards for chloride. 

The two sites with detected trends in dissolved solids 

(site 160 and site 224) were evaluated for trends in calcium, 

magnesium, sodium, potassium, alkalinity, sulfate, chloride, 

and silica. At site 160 (Gore Creek subwatershed), highly significant upward trends were found for sodium, potassium, and 

chloride; with a significant upward trend in magnesium; and a 

weakly significant trend in calcium. At site 224 (Lower Eagle 

subwatershed), significant downward trends were detected in 

calcium, magnesium, sulfate, and silica; and weakly significant upward trends were observed in sodium, potassium, 

and chloride. At site 160 (Gore Creek subwatershed) relative 

abundances of the ions indicates that chloride salts likely are 

the source for the detected upward trends. A potential source 

for the observed chloride salts may be the chemical anti-icing 

and deicing products used during winter road maintenance in 

municipal areas and on Interstate-70.

Nitrogen and phosphorus are two nutrients that can be 

present in varying chemical forms within the watershed. The 

spatial pattern of nutrients shows lower concentrations on many 

tributaries and on the Eagle River upstream from the town 

of Red Cliff with increases in nutrients downstream of major 

urban areas. Seasonal variations show that for many nutrient 

species, concentrations tend to be lowest May–June and highest 

January–March. At site 224 (Lower Eagle subwatershed), total 

phosphorus concentrations are elevated January–May and 

July–September with concentrations highest in April. These 

higher concentrations may be related to sediment transported 

by snowmelt runoff and rainfall. From less than 1 percent to 

9 percent of nitrogen nutrients measurements exceeded the 

State standards. Approximately 24 percent of phosphors nutrients measurements exceeded Federal recommendations. There 

is a significant upward trend in nitrate at site 224 (Lower Eagle 

subwatershed); a weakly significant upward trend in nitrite at 

site 160 (Gore Creek subwatershed); and a significant upward 

trend in total phosphorus and a weakly significant upward trend 

in orthophosphate at site 224 (Lower Eagle subwatershed). A 

positive correlation was observed between concentrations of 

suspended sediment and total phosphorus.

Trace elements often are defined as those elements that 

generally occur in concentrations less than 1,000 micrograms 

per liter. The discussion of trace elements has been separated into two groups: trace elements (arsenic, selenium, and 

uranium) and trace metals (aluminum, cadmium, copper, iron, 

manganese, and zinc).

The spatial pattern showed an increase in trace-metal 

concentrations downstream from historic mining areas and 

decreased concentrations or concentrations below reporting 

limits in Gore Creek and other tributaries within the ERW. 

Concentrations tend to be lowest May–June and highest 

November–April for many metals. Concentration in early spring 

(February–April) can be substantially higher as the leading edge 

of snowmelt waters interacts with mine shafts and (or) adits, 

mineralized rock units, and other areas affected by processed 

mine wastes and contaminated soils. The seasonal pattern of 

dissolved iron at site 224 (Lower Eagle subwatershed) is different from other metals in that dissolved iron concentrations 

are relatively stable for most of the year with higher concentrations April–July. The increased concentrations of dissolved 

iron may best be explained by the colloidal behavior of iron. 

Trace-element exceedances of State standards are generally less 

than 1 percent of the measurements. Trace-metal exceedances of 

State standards varied by metal but were generally more numerous than the exceedances for the trace elements. Step-trend 

analysis of trace-metal concentrations at some sites show order 

of magnitude reductions in median concentrations following 

major completion of remediation in the Eagle Mine Superfund 

Site. In general, step-trend analysis and monotonic-trend 

analysis provided good evidence that remediation of historic 

mine areas in the upper Eagle River subwatershed has lead to 

observed decreases in many metal concentrations.

Sediment can be transported in the water column as 

suspended sediment or moved along the bed of a stream as 

bedload. Sedimentation has been identified by the Colorado Water-Quality Control Commission as a water-quality 

concern in Black Gore Creek and was placed on the Section 303(d) list in 2002, 2004, and 2006. Traction sanding 

of Interstate-70 in the Gore Creek subwatershed has been 

identified as a source of sands to Black Gore Creek. The 

spatial pattern from available sampling locations shows an 
References Cited 137

increase in suspended-sediment concentration as water moves 

downstream in the ERW, with a defined increase in suspendedsediment concentration occurring downstream from the town 

of Edwards. In the ERW available data indicate that suspended 

sediment is greatest during spring snowmelt-runoff (MayJune). No trends in suspended sediment were detected.

Acknowledgments

The authors wish to express thanks and appreciation to 

the many agencies that provided data for this report. A special 

thanks to Ray Merry with Eagle County and Caroline Byus 

with Eagle River Water and Sanitation for their assistance 

and continued support in the watershed. The authors express 

gratitude to USGS employees Jude Thomas, Jean Dupree, and 

Bob Zuellig for their contributions. Acknowledgments are 

extended to Jason Gurdak, Liza Miller, and Dave Kanzer for 

their technical review of the manuscript.

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Publishing support provided by: 

Denver Publishing Service Center

For more information concerning this publication, contact:

Director, USGS Colorado Water Science Center

Box 25046, Mail Stop 415

Denver, CO 80225

(303) 236-4882

Or visit the Colorado Water Science Center Web site at:

http://co.water.usgs.gov/
Williams and others—Assessment of Surface-Water Quantity and Quality, Eagle River Watershed, Colo., 1947–2007—Scientific Investigations Report 2011–5075