U.S. GEOLOGICAL SURVEY

Water-Resources Investigations Report 02–4151

Characterization of Selenium in the 

Lower Gunnison River Basin, Colorado, 

1988–2000

By David L. Butler and Kenneth J. Leib

Denver, Colorado

2002

Prepared in cooperation with

DELTA COUNTY and the

SHAVANO SOIL CONSERVATION DISTRICT
For additional information write to:

District Chief

U.S. Geological Survey

Box 25046, Mail Stop 415

Denver Federal Center

Denver, CO 80225-0046

U.S. DEPARTMENT OF THE INTERIOR

GALE A. NORTON, Secretary

U.S. GEOLOGICAL SURVEY

Charles G. Groat, Director

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

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

Copies of this report can be purchased 

from:

U.S. Geological Survey

Information Services

Box 25286

Denver Federal Center

Denver, CO 80225
CONTENTS III

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

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

Characterization of Selenium in the Lower Gunnison River................................................................................................. 4

North Fork Basin ......................................................................................................................................................... 6

Smith Fork to the Uncompahgre River, Excluding the North Fork............................................................................. 8

Uncompahgre River to Whitewater ............................................................................................................................. 8

Characterization of Selenium in Cedar Creek and Loutzenhizer Arroyo.............................................................................. 12

Cedar Creek ................................................................................................................................................................. 13

Loutzenhizer Arroyo.................................................................................................................................................... 17

Summary................................................................................................................................................................................ 24

References Cited.................................................................................................................................................................... 26

FIGURES

1–5. Maps showing:

1. Location of the Lower Gunnison River Basin................................................................................................... 3

2. Location of sampling sites in the North Fork Basin.......................................................................................... 7

3. Location of sampling sites from the Smith Fork to the Uncompahgre River.................................................... 9

4. Location of sampling sites from the Uncompahgre River to Whitewater......................................................... 10

5. Cedar Creek and location of sampling sites ...................................................................................................... 14

6. Graph showing selenium concentrations and specific conductance in Cedar Creek, November 16–17, 1999 ........ 15

7. Graph showing selenium loads in Cedar Creek, November 16–17, 1999 ................................................................ 16

8. Map showing Loutzenhizer Arroyo and location of sampling sites.......................................................................... 18

9. Graph showing selenium concentrations and specific conductance in Loutzenhizer Arroyo, 

February 28–29, 2000 ............................................................................................................................................... 19

TABLES

1. Summary of selenium data for the lower Gunnison River Basin, 1988–2000 ........................................................ 4

2. Synoptic data for upper Cedar Creek Basin, November 18, 1999 .......................................................................... 16

3. Streamflow, specific conductance, and selenium concentrations for the west tributary of Loutzenhizer Arroyo,

February 29, 2000.................................................................................................................................................... 19

4. Selected streamflow and selenium load data for Loutzenhizer Arroyo, February 28–29, 2001 ............................. 20

5. Selenium data for the upper Loutzenhizer Arroyo Basin and lower Bostwick Park, 1992–2000........................... 22

CONVERSION FACTORS, VERTICAL DATUM, AND ABBREVIATIONS

Multiply By To obtain

Length

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

acre 4,047 square meter (m2)

square mile (mi2) 2.590 square kilometer (km2)

Volume

cubic foot (ft3) 0.028317 cubic meter (m3)

acre-foot (acre-ft) 1,233 cubic meter (m3)

Flow

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

Mass

pound avoirdupois (lb avdp) 0.4536 kilogram (kg)

pound per day (lb/d) 0.9072 kilogram per day

pound per year (lb/yr) 0.9072 kilogram per year

CONTENTS
IV CONTENTS

Temperature in degrees Celsius (C) may be converted to degrees Fahrenheit (F) as follows:

F = 9/5 C + 32

Sea level: In this report “sea level” refers to the National Geodetic Vertical Datum of 1929—

a geodetic datum derived from a general adjustment of the first-order level nets of the United States 

and Canada, formerly called Sea Level Datum of 1929.

Altitude, as used in this report, refers to distance above sea level.

Specific conductance is given in microsiemens per centimeter at 25 degrees Celsius (S/cm).

Concentrations of chemical constituents in water are given either in milligrams per liter (mg/L) or 

micrograms per liter (g/L). Concentrations in milligrams per liter are commonly expressed as parts 

per million (ppm), and concentrations in micrograms per liter are commonly expressed as parts per 

billion (ppb).

ADDITIONAL ABBREVIATIONS

g gram

L liter

g/L micrograms per liter

S/cm microsiemens per centimeter at 25 degrees Celsius

mg/L milligrams per liter

ACRONYMS

BOR Bureau of Reclamation

NIWQP National Irrigation Water Quality Program

USGS U.S. Geological Survey

MRL Minimum reporting limit
1

Characterization of Selenium

in the Lower Gunnison River Basin, 

Colorado, 1988–2000

By David L. Butler and Kenneth J. Leib

Abstract

Selenium concentrations in certain water 

bodies in the lower Gunnison River Basin, 

including the lower Gunnison River and lower 

Uncompahgre River, have exceeded the Colorado 

water-quality standard of 5 micrograms per liter 

for selenium. A task force was formed in 1998 

that consists of various government agencies, 

private irrigation companies, and local residents 

to address the selenium concerns in the lower 

Gunnison River Basin. The task force, working 

with the National Irrigation Water Quality 

Program, needed more detailed information on 

selenium loading in the basin to develop viable 

alternatives for remediating selenium in the lower 

Gunnison River Basin.

In 1999–2000, the U.S. Geological Survey 

collected selenium data for tributaries of the 

Gunnison River downstream from the North Fork 

of the Gunnison and in the North Fork Basin. The 

largest selenium load in a tributary stream was in 

the Uncompahgre River, which accounted for 

about 38 percent of the selenium load in the 

Gunnison River at Whitewater. The North Fork of 

the Gunnison River accounted for about 7 percent 

of the selenium load in the Gunnison River. Two 

tributaries east of Delta, Sunflower Drain and 

Bonafide Ditch, consist primarily of irrigation 

return flows and were other major selenium 

sources to the Gunnison River.

Some tributaries in the lower North Fork 

Basin had selenium concentrations exceeding 

5 micrograms per liter. Except for several streams 

draining the Uncompahgre Plateau, many tributaries to the Gunnison River downstream from the 

North Fork had selenium concentrations 

exceeding 5 micrograms per liter. Except during 

occasional rain and snowmelt events, selenium 

loading from nonirrigated desert areas was 

minimal.

Detailed characterization studies were done 

in 1999–2000 on Cedar Creek and Loutzenhizer 

Arroyo, which contribute the largest tributary 

selenium loads to the Uncompahgre River. Selenium concentrations in Cedar Creek downstream 

from Miguel Road ranged from 12 to 28 micrograms per liter in November 1999. Montrose 

Arroyo was the largest selenium source to Cedar 

Creek. On an annual basis, about 20 percent of the 

selenium load in Cedar Creek originates in the 

basin upstream from Miguel Road.

Selenium concentrations in Loutzenhizer 

Arroyo ranged from 157 to 347 micrograms per 

liter in February 2000. A significant increase in 

selenium concentrations occurred in the stream 

reach between the Selig Canal and Falcon Road 

(LZU7). Although selenium concentrations in the 

west tributary of Loutzenhizer Arroyo were lower 

than in the main stem, the west tributary contributed about 41 percent of the selenium load. 

Downstream from the confluence with the west 

tributary to the mouth, selenium concentrations in 

the arroyo gradually decreased, and the increase 

in selenium load in the lower reach was small.
2 Characterization of Selenium in the Lower Gunnison River Basin, Colorado, 1988–2000

INTRODUCTION

Selenium is a water-quality concern in the 

Gunnison River Basin. Since 1985, a multiagency 

program within Department of the Interior, the 

National Irrigation Water Quality Program (NIWQP), 

has done investigations at various irrigation projects in 

the Western United States to determine if irrigation 

drainage was having adverse effects on water quality 

and on fish and wildlife. Beginning in 1988, NIWQP 

studies have been done in the Uncompahgre River 

Basin, a major tributary of the Gunnison River, and in 

the Grand Valley in west-central Colorado. High levels 

of selenium were reported in some water, sediment, 

and biota samples in both areas (Butler and others, 

1996). Selenium concentrations in some fish- and 

bird-tissue samples were at levels of concern, and in 

late 1994 NIWQP initiated the planning phase for 

remediation. One objective of the NIWQP planning 

phase was to determine what, if any, remediation 

methods could be used to reduce selenium loading 

from irrigation sources to the Uncompahgre and 

Gunnison Rivers (fig. 1).

Prior to 1997, the chronic criterion for aquatic 

life for dissolved selenium in Colorado was 17g/L. 

In 1997, the State Water Quality Control Commission 

adopted the 5-g/L chronic criterion for selenium for 

surface waters in Colorado (Colorado Department of 

Public Health and Environment, 1998). Because the 

criterion is based on the dissolved-selenium concentration, all selenium concentrations and loads discussed 

in this report are for dissolved selenium. Also in 1997, 

the triennial review of the water-quality standards for 

the Gunnison River Basin was completed and the 

5-g/L criterion was applied to streams with aquaticlife classifications in the basin. The more stringent 

selenium standard caused the lower Uncompahgre 

River (from Montrose to the mouth) and the lower 

Gunnison River (downstream from the Uncompahgre 

River to the mouth), along with some tributary streams 

to the North Fork of the Gunnison River, to be listed as 

out of compliance for selenium. Temporary modifications were put in place for the affected water bodies to 

allow time for measures to be taken at the local level to 

address the selenium issue. A local watershed initiative began in February 1998 with formation of the 

Gunnison Basin Selenium Task Force (Task Force). 

The Task Force is a group of private, local, State, and 

Federal interests, including NIWQP, whose goal is to 

examine projects or methods that could be feasible for 

reducing selenium levels in the Uncompahgre and 

Gunnison Rivers.

The Task Force needed to examine possible 

remediation methods to address selenium loading to 

the Gunnison and Uncompahgre Rivers. Previous 

NIWQP studies (Butler and others, 1996) indicated 

that Cedar Creek and Loutzenhizer Arroyo were the 

largest contributors to the selenium load in the 

Uncompahgre River and that the Uncompahgre River 

was the single largest selenium source to the Gunnison 

River. However, data for determining selenium loading 

to the lower Gunnison River from tributary streams 

other than the Uncompahgre River were limited. Selenium data were available only for a few tributaries in 

the North Fork Basin, and much of this information 

was for streams in the upper basin where selenium 

concentrations are low. Few or no data were available 

for many of the tributaries to the Gunnison River 

downstream from the North Fork to Whitewater 

(fig. 1). The Task Force and the NIWQP realized that 

if selenium load, and subsequently selenium concentration, in the Uncompahgre River was to be significantly reduced, some of the remediation alternatives 

would need to address selenium loading in the Cedar 

Creek and Loutzenhizer Arroyo Basins. However, 

other than general synoptic data collected by NIWQP 

in these basins (Butler and others, 1994; Butler and 

Osmundson, 2000), data were lacking to describe areal 

distribution of selenium concentrations and loads in 

great detail. More specific data were needed to focus 

potential remediation efforts in the Cedar Creek and 

Loutzenhizer Arroyo Basins to areas with the highest 

selenium loading.

The U.S. Geological Survey (USGS), in cooperation with Delta County and the Shavano Soil Conservation District, developed a characterization study to 

provide more detailed selenium information for the 

lower Gunnison River Basin. The selenium characterization study objectives are:

1. To characterize selenium concentrations and loads 

in tributary streams of the North Fork of the 

Gunnison and tributaries of the Gunnison River 

downstream from the Smith Fork to Whitewater.

2. To characterize selenium concentrations and loads 

in Cedar Creek and Loutzenhizer Arroyo.

This report summarizes selenium data for 

streams in the North Fork Basin and for tributary 

streams of the lower Gunnison River. Selenium data 

were collected in water years 1999–2000 and supplemented with historical data collected since water year
INTRODUCTION 3

 Lower 

Gunnison 

 Basin

Delta

Montrose

Ridgway

Sweitzer 

 Lake

Gunnison

River

Gunnison 

River

Gunnison River

North 

Fork

 Ridgway 

Reservoir

Uncompahgre

River

Whitewater

DENVER

Grand Junction

C O L O R A D O

0

25

25 50 KILOMETERS

0 50 MILES

Cedar Creek

Loutzenhizer Arroyo

Olathe

Smith Fork

108°27'30"

108°02'30"

107°37'30"

107°12'30"

38°42'30"

38°57'30"

38°27'30"

38°12'30"

Study area

South

River

River

River

Platte

Arkansas

Colorado

Figure 1. Location of the Lower Gunnison River Basin.
4 Characterization of Selenium in the Lower Gunnison River Basin, Colorado, 1988–2000

1988, where water year is defined as the period beginning on October 1 and ending on September 30 of the 

following year. The report also describes results of 

detailed characterization studies done in 1999 and 

2000 in the Cedar Creek and Loutzenhizer Arroyo 

Basins.

CHARACTERIZATION OF SELENIUM IN 

THE LOWER GUNNISON RIVER

The characterization of selenium loads in the 

North Fork Basin and tributary streams to the lower 

Gunnison River began in the spring of 1999. A list of 

sampling sites was developed using previous selenium 

data that had been collected by the USGS and by the 

Colorado Department of Public Health and Environment (CDPHE). Generally, major tributaries and 

selected small washes and drainages were sampled. 

Basins with significant areas of irrigation were 

included, especially in areas with outcrops of Mancos 

Shale of Cretaceous age. According to Butler and 

others (1996), basins that have the highest selenium 

levels also have extensive outcrops of Mancos Shale. 

Synoptic sampling was done by the USGS, starting in 

the North Fork Basin and then sampling downstream 

to Whitewater. The study area (fig. 1) was separated 

into three major sections for the synoptic sampling 

runs: (1) the North Fork Basin, (2) the reach from 

Smith Fork to the Uncompahgre River, and (3), the 

reach from the Uncompahgre River to Whitewater. All 

the sampling sites are listed in table 1. Selenium data 

also were collected by the CDPHE and USGS in 

March 1999 from a few tributary streams of the 

Gunnison River and from the Gunnison River between 

Delta and Whitewater. The major synoptic sampling 

runs were done in April and May 1999 (runoff), late 

August and early September 1999 (late summer, irrigation effects), in November 1999 (nonirrigation 

season), and in March 2000 (base flow). During the 

major synoptic sampling runs, all sites that had 

flowing water were sampled. Additional sampling for 

this study also was done in June and July 1999 at a 

limited number of sites. Selenium data and field

Table 1. Summary of selenium data for the lower Gunnison River Basin, 1988–2000

[Selenium concentrations in micrograms per liter, or parts per billion; mean load in pounds per day; <, less than; --, no data; data collected in 1999–2000 unless 

otherwise noted in remarks; years are in water years (October 1–September 30)] 

Site

number

(figs. 2–4)

Site name

(U.S. Geological

Survey streamflow-gaging 

station number)

Number 

of 

samples

Selenium

concentration Mean

load Remarks

Median Range

North Fork Basin

2 North Fork near Somerset (09132500) 4 <1 <0.7–<1 1.56

3 Hubbard Creek at mouth 4 <1 <.7–<1 .10

4 Terror Creek at mouth 4 <1 <.7–<1 .04

5 Stevens Gulch at Paonia 0 -- -- -- No flow when visited—no samples.

6 Minnesota Creek at Paonia 5 1.3 <1–1.5 .04

7 Roatcap Creek at Highway 133 4 1.7 <2–5 .06

8 Reynolds Creek near mouth 4 4.6 <1–8 .02

9 Bell Creek near mouth 6 4.4 2–7 .19

10 Jay Creek at Highway 133 4 13 6–19 .06

11 Cottonwood Creek near mouth 7 7.3 4–13 .33

12 Short Draw at Hotchkiss 7 11 8–29 .37

13 Leroux Creek at Highway 92 13 13 1–21 .57 All but one sample from 1990 to 1993.

14 Leroux Creek at mouth 6 7.9 5–9 .29

15 Alum Gulch at mouth 5 2.4 1–3 .11

16 Big Gulch at Highway 92 4 7.6 6–9 .13

17 North Fork at mouth 39 2.5 <1–6 3.93 Data from 1991 to 2000.

Smith Fork to the Uncompahgre River

1 Smith Fork at mouth 5 2.7 1–4 .06

18 Sulphur Gulch at Highway 92 4 11 4–21 .01
CHARACTERIZATION OF SELENIUM IN THE LOWER GUNNISON RIVER 5

measurements made during each sample collection for 

the 1999–2000 characterization are published in the 

USGS annual data report for 2000 (Crowfoot and 

others, 2001). Much of the selenium data collected for 

the NIWQP prior to 1999 are published in Butler and 

others (1994) and in Butler and Osmundson (2000). 

For some sites, the data summary in table 1 

includes other selenium data that were collected at that 

site in addition to data collected for the characterization study. A majority of such data were collected for 

NIWQP studies, but some of the data were collected 

for several water-quality programs by USGS. Because 

Uncompahgre River to Whitewater—Continued

19 Lawhead Gulch at Highway 92 4 7.0 5–8 0.01

20 Oasis Ditch below Oasis Pond 6 9.5 5–15 .30

21 Currant Creek below Dry Creek 8 19 10–45 .68

22 Gunnison River at Austin 5 1.2 1–2 9.34 One sample from 1991.

23 Peach Valley Arroyo near mouth 10 6.5 5–95 .39 Includes data from 1991 to 1998.

24 Alfalfa Run at Austin 6 16 11–18 .32

25 Sunflower Drain at Highway 92 61 20 6–200 3.67 Data from 1992 to 2000.

26 Tongue Creek near Cory 8 4.7 4–10 .70 One sample in 1991.

27 Hartland Ditch diversion 3 2.2 1–3 .35 Diversion on Gunnison River.

28 Bonafide Ditch at Delta 19 12 4–95 4.57 Data from 1992 to 2000.

29 Gunnison River at Delta (09144250) 27 3.8 <1–8 27.2 Data from 1988 to 2000.

Uncompahgre River to Whitewater

30 Uncompahgre River at Delta 

(09149500)

84 12 2–34 21.4 Data from 1988 to 2000.

31 East Ditch at Highway 50, north Delta 4 6.2 5–65 .08

32 West Ditch at Highway 50, north Delta 4 3.2 2–5 .11

33 Cummings Gulch at mouth 14 8.7 3–16 .87 Data from 1991 to 1995 and 1999 to 2000.

34 Roubideau Creek at upper site 6 <1 <1–<1 .20 Mean load biased high by 1 sample.

35 Roubideau Creek at mouth 16 3.0 <1–5 .97 Data from 1991 to 1995 and 1999 to 2000.

36 Alkali Creek below Highway 50 11 85 18–150 .04 Data from 1996 to 2000. Additional 

samples in January 2000.

37 Gunnison River above Escalante Creek 8 5 3–10 48.3 Data for 1987 to 1988 and 1991 included.

38 Escalante Creek at mouth 5 <1 <1–<1 .13

39, 40 Wells Gulch (2 sites below Highway 

50)

8 2.6 <1–10 <.01 Additional runoff samples.

41 Beaver Gulch at Highway 50 0 –- -- -- No flow observed.

42 Dominguez Creek at mouth 3 <1 <1–1.5 .02

43, 44 Deer Creek (2 sites below Highway 50) 6 7.2 2–11 <.01 Five of six samples snowmelt runoff.

45 Kannah Creek below city diversion 7 <.7 <.7–<1 .05 Background site for Kannah Creek.

46 Kannah Creek below Indian Creek 10 10.5 4–31 .41

47 East Creek at Highway 141 3 1.3 1–1.5 .01

48 Brandon Ditch near Whitewater 7 <.7 <.7–1.5 .01 Water from upper Whitewater Creek.

49 Whitewater Creek near mouth 10 27 13–48 .59

50 Gunnison River at Whitewater 

(Gunnison River near Grand Junction, 09152500)

103 5.0 <1–11 55.3 Data for 1988 to 2000.

51 Callow Creek at Whitewater 3 11 5–13 <.01

52 Bangs Canyon at mouth 1 <1 -- .01

Table 1. Summary of selenium data for the lower Gunnison River Basin, 1988–2000—Continued

[Selenium concentrations in micrograms per liter, or parts per billion; mean load in pounds per day; <, less than; --, no data; data collected in 1999–2000 unless 

otherwise noted in remarks; years are in water years (October 1–September 30)] 

Site

number

(figs. 2–4)

Site name

(U.S. Geological

Survey streamflow-gaging 

station number)

Number 

of 

samples

Selenium

concentration Mean

load Remarks

Median Range
6 Characterization of Selenium in the Lower Gunnison River Basin, Colorado, 1988–2000

some sites have much more selenium data than only 

the samples collected for this study, data for water 

years 1988–2000 also are included in the summaries in 

table 1. 

Mean selenium load from table 1 is calculated 

by taking the average of all load values at a given site. 

Individual selenium loads at each site are calculated 

using the following equation:

L = (28.32 Q) (C/453,600,000)  (1)

where

L is selenium load, in pounds per day;

28.32 converts cubic feet to liters;

Q is streamflow discharge, in cubic feet 

per second; 

C is selenium concentration, in micrograms per liter; (C/453,600,000) 



453,600,000 converts pounds to micrograms; and

86,400 converts days to seconds.

Some selenium concentrations in table 1 were reported 

as less than a minimum reporting limit (MRL) of 

either 1 g/L or 0.7 g/L. For samples with selenium 

concentrations reported as a “less than” value, a 

concentration of 0.7 times the MRL was used to 

compute the selenium load.

Data interpretation for the characterization 

study of the lower Gunnison River Basin identified 

streams that have selenium concentrations that exceed 

the State standard of 5 g/L. Tributary basins that are 

contributing the largest selenium loads to the 

Gunnison River and, therefore, have the largest effect 

on selenium concentrations at the Whitewater site, the 

compliance point for the lower Gunnison River 

(fig. 1), were determined. Many sites have fewer than 

10 samples; therefore, data interpretation should be 

viewed with caution, especially when examining selenium loads. The mean loads shown in table 1 for sites 

with a small number of samples may or may not accurately represent the mean daily load throughout the 

year. Also, for sites where most or all of the selenium 

concentrations were reported as “less than” values, 

using 0.7 times the MRL to calculate loads could overestimate loads, especially for samples collected at high 

flows during snowmelt runoff from high-altitude 

areas.

North Fork Basin

Selenium sampling in the North Fork Basin was 

done at sites 2 through 17 (fig. 2), and the selenium 

data are summarized in table 1. The main stem was 

sampled at the USGS streamflow-gaging station 

(09132500) near Somerset and at the mouth. Additional sampling of the North Fork at the mouth was 

done using resources from NIWQP to develop a better 

estimate of annual selenium loading. All major tributary streams downstream from the site near Somerset 

were sampled.

In the North Fork Basin, selenium concentrations were less than 5 g/L in tributary streams at and 

upstream from Paonia (fig. 2). Based on historical data 

and data collected for this study at the Somerset gage 

(site 2) and from several tributaries upstream from 

Paonia, selenium concentrations in the upper North 

Fork Basin are equal to or less than 1 g/L. Some 

outcrops of Mancos Shale are present along the North 

Fork in the vicinity of Terror Creek, but the shale 

outcrops are much more extensive downstream from 

Paonia, especially on the south side of the river. Selenium concentrations in all or nearly all samples from 

Jay Creek, Cottonwood Creek, Short Draw, Leroux 

Creek, and Big Gulch were equal to or greater than 

5 g/L. The largest selenium loads from tributaries 

were in Bell, Cottonwood, and Leroux Creeks and in 

Short Draw. Based on the selenium data for the mainstem sites (sites 2 and 17) and the measured tributaries, there is an unmeasured selenium load between 

the Somerset site and the mouth. The unmeasured 

selenium load probably is from diffuse ground-water 

inflow and from tributary streams and ditches that 

were not sampled.

Annual selenium loads for water years 1999 and 

2000 were computed for the North Fork at mouth 

(site 17) to enable comparison to the selenium load in 

the Gunnison River at the Whitewater site (Site 50, 

USGS streamflow-gaging station 09152500, also 

referred to as “Gunnison River near Grand Junction”). 

For computing the annual load for the North Fork at 

the mouth, a linear regression equation relating selenium load to streamflow was computed using selenium data and streamflow measurements collected at 

site 17. Regression analysis was done using logarithmtransformed data from 40 samples collected at various 

flow regimes during the study period. Statistical diagnostics indicate that the regression was able to explain 

approximately 60 percent of the variation in the data
CHARACTERIZATION OF SELENIUM IN THE LOWER GUNNISON RIVER 7

Somerset

Big Gl

Hubbard Creek

Terror Creek Minnesota Creek Reynolds Creek

Roatcap Creek

Paonia

Bell Creek

Jay Creek

Hotchkiss

Cottonwood

Short Draw

Crawford

Crawford

Leroux Creek

Alum Gulch

Smith

Fork

North Fork Gunnison

River

PR

Hwy 92

Stevens Gulch

0

0 4

4

8

8

E

MILES

KILOMETERS

Hwy 133

3

Gunnison River

17

16

15

14

13 12

11

10 9

8

7 6

5

4

3 2

39°00'

107°45' 107°30'

38°45'

 Creek

 Reservoir

Base from U.S. Geological Survey1:24,000 digital data, 1927 North American Datum,Universal Transverse Mercator projection,Zone 13

Figure 2. Location of sampling sites in the North Fork Basin.
8 Characterization of Selenium in the Lower Gunnison River Basin, Colorado, 1988–2000

set (r squared = 0.6). The regression equation was 

applied to estimated daily streamflow values for site 

17 to estimate a daily selenium load. The sum of the 

daily loads for the water year results in the annual 

load. The North Fork at the mouth does not have a 

gage; therefore, daily streamflow for site 17 was estimated using the instantaneous streamflow measurements made at site 17 during sample collection and the 

daily streamflow records for USGS streamflow-gaging 

station 09135950, located on the North Fork about 

0.7 mi downstream from Leroux Creek (fig. 2). The 

method to compute annual load is similar for the 

Gunnison River at Whitewater except that a second 

regression equation relating selenium load to streamflow and specific conductance was computed because 

daily specific-conductance data are available for most 

days at that site. When specific conductance is 

included in the regression, the coefficient of determination increases and the standard error of estimate 

decreases compared to a regression based solely on 

streamflow. These regression equations are then used 

to compute daily selenium loads by using the streamflow and daily specific-conductance records for the 

Whitewater site (USGS streamflow-gaging station 

09152500).

For water year 1999, the estimated selenium 

load for the North Fork was 1,400 lb, which is about 

7 percent of the selenium load in the Gunnison River 

at Whitewater (20,100 lb). For 2000, the estimated 

load was 1,300 lb, which was about 8 percent of the 

selenium load in 2000 in the Gunnison River 

(16,200 lb). Based on the information in 1999 and 

2000, the North Fork Basin contributes a relatively 

small part of the selenium load in the Gunnison River.

Smith Fork to the Uncompahgre River, 

Excluding the North Fork

This reach includes the Smith Fork (site 1) and 

tributary and main-stem sites (sites 18–29) of the 

Gunnison River downstream from the North Fork to 

the USGS streamflow-gaging station (09144250) 

Gunnison River at Delta. The confluence of the 

Uncompahgre River with the Gunnison River is downstream from the Gunnison River at Delta gage. Sites 

are shown in figure 3, and selenium results are summarized in table 1.

All the sampled tributary streams in this reach 

except the Smith Fork and Tongue Creek had median 

selenium concentrations greater than 5 g/L. The 

largest measured selenium loads in tributaries were 

from Sunflower Drain (site 25) and the Bonafide Ditch 

(site 28). Streamflow in Sunflower Drain consists 

entirely of irrigation drainage and tailwater from irrigated areas on Mancos Shale south of the Gunnison 

River. The Bonafide Ditch also receives irrigation tailwater from areas south of the Gunnison River, but part 

of the flow in the ditch is water from two canals that 

divert water from the Gunnison River upstream from 

Austin. Based on samples collected at the Austin site 

(table 1) and on other data collected from the canals 

upstream from Austin (Butler and Osmundson, 2000), 

the Gunnison River upstream from Austin probably 

has selenium concentrations of 2 g/L or less during 

the irrigation season. Selenium loads from the north 

side of the river are discharged by Oasis Ditch, Currant 

Creek, Alfalfa Run, and Tongue Creek, but loads are 

considerably smaller than loads in Sunflower Drain 

and Bonafide Ditch (table 1). Considerable acreage 

from Currant Creek to Tongue Creek (fig. 3) is irrigated, and some of that area contains outcrops of 

Mancos Shale. Samples from small drainages such as 

Sulphur Gulch and Lawhead Gulch contain selenium; 

but the measured flows were small, and the selenium 

loads were insignificant. 

The small number of samples for the site on the 

Gunnison River at Austin (site 22) adds uncertainty to 

analysis of selenium loading in the reach from Austin 

to Delta. The loading data listed in table 1 indicate a 

considerable amount of unmeasured selenium load in 

that reach. Only major tributary streams or ditches 

were sampled in this reach. Numerous surface inflows 

were not sampled, and selenium load from direct 

ground-water discharge into the Gunnison River and 

from the adjacent alluvium were not assessed. Based 

on the data for the site at Delta, selenium concentrations in the Gunnison River upstream from the 

Uncompahgre River usually do not exceed 5 g/L.

Uncompahgre River to Whitewater

This reach, which includes the lower Gunnison 

River and tributaries from the Uncompahgre River to 

Whitewater (sites 30–52; fig. 4), has mixed geology 

and land uses. Generally, tributaries on the north or 

east side of the Gunnison River between Delta and 

Grand Junction drain areas that contain outcrops of 

Mancos Shale. The west side of the Gunnison River
CHARACTERIZATION OF SELENIUM IN THE LOWER GUNNISON RIVER

9

S

Sulphur 

Gulch

Gunnison River

Uncompahgre

River

Bonafide Ditch

Fruit Growers

Reservoir

Gunnison 

Lawhead

Oasis

Pond

Peach

Valley

Arroyo

Sunflower Drain

Currant Creek

Tongue

Sweitzer Lake

River

Alfalfa

Run

Delta

Hwy 92

Hwy 50

Hwy 65

Oasis Ditch

Hartland Ditch 

29 28

27

26

25

24

23

22

21

20

19

18

1

Creek

Dry Creek

Cory

00

2

2

4 MILES

4 KILOMETERS

20

OrchardCity

108°05' 108°00' 107°55' 107°50'

38°50'38°45'

Austin

Gulch

Base from U.S. Geological Survey1:24,000 digital data, 1927 North American Datum,Universal Transverse Mercator projection,Zone 13

Figure 3. Location of sampling sites from the Smith Fork to the Uncompahgre River.
10 Characterization of Selenium in the Lower Gunnison River Basin, Colorado, 1988–2000 

Callow 

Kannah Creek

East Cree

Bangs Cany

k

on

Dominguez Creek

Beaver Gulch

Wells Gulch

Escalante 

Alkali Creek

Roubideau 

Cummings

Delta

Sweitzer L

Hwy 50

Deer Creek

Brandon 

Whitewater

Uncompahgre River

Whitewater

Gunnison River

Hwy 92

GRAND MESA

30

West Ditch

East Ditch

32 31

33

34

35

36

37

38

39

40

42 41

43 44

45

46

48

49

50

51

47

52

Indian

City or town

Irrigated land

Sampling site and number (table 1)

EXPLANATION

37

38°45'

39°00'

108°30' 108°15' 108°

0

0

5

5

10 MILES

10 KILOMETERS

 Creek

Ditch

Creek

 Creek

Creek

Cr

 Gl

Base from U.S. Geological Survey1:24,000 digital data, 1927 NorthAmerican Datum, UniversalTransverse Mercator projection,Zone 13

Figure 4. Location of sampling sites from the Uncompahgre River to Whitewater.
CHARACTERIZATION OF SELENIUM IN THE LOWER GUNNISON RIVER 11

between Roubideau Creek and East Creek (fig. 4) does 

not have outcrops of Mancos Shale and is composed 

primarily of outcrops of sandstone, siltstone, and shale 

of Cretaceous age.

Nearly all selenium concentrations in the 

Uncompahgre River at Delta exceeded 5 g/L during 

water years 1988–2000 (table 1). The lower 

Uncompahgre River is listed by the State as out of 

compliance for selenium. Annual selenium loads for 

the Uncompahgre River were computed using the 

same method described for the North Fork. Daily 

streamflow data are available for the Uncompahgre 

River at the USGS streamflow-gaging station 

09149500 located in Delta (site 30 in fig. 4). Based 

on a mean annual selenium load for 1988–2000 of 

7,600 lb/yr at the Delta site, the Uncompahgre River 

accounted for about 38 percent of the mean annual 

load in the Gunnison River at Whitewater for 1988–

2000 (20,100 lb/yr) and is the largest loading source to 

the Gunnison River. 

Selenium concentrations for tributary streams 

and washes on the north or east side of the Gunnison 

River downstream from Delta were variable. Four of 

the five sites affected by irrigation drainage from shale 

areas north or east of the river had median concentrations greater than 5 g/L: the East Ditch in north 

Delta, Alkali Creek, Kannah Creek below Indian 

Creek, and Whitewater Creek near the mouth (fig. 4; 

table 1). Only the West Ditch in north Delta had a 

median concentration less than 5 g/L. There is a 

marked contrast in selenium concentrations between 

upstream and downstream sites on Kannah Creek and 

on Whitewater Creek. Selenium concentrations at the 

upper site on Kannah Creek (site 45) and the Brandon 

Ditch (site 48), which represents water diverted from 

upper Whitewater Creek, were less than the MRL 

(0.7 g/L) except for one sample from Brandon Ditch. 

Selenium concentrations at the downstream sites on 

the two creeks were much higher, with median 

concentrations of 10.5 g/L for Kannah Creek below 

Indian Creek (site 46) and 27 g/L for Whitewater 

Creek near mouth (site 49) (table 1). Water samples 

collected at the two upper sites are representative of 

streamflow off the Grand Mesa, which is upstream 

from irrigation and Mancos Shale outcrops. 

The highest selenium concentrations sampled in 

the Uncompahgre River to Whitewater reach were 

from Alkali Creek (site 36; fig. 4), a basin that is 

affected by irrigation and a small reservoir located on 

Mancos Shale. Some additional samples were 

collected from Alkali Creek during snowmelt and rainfall runoff in January 2000. The runoff caused an 

increase in selenium concentrations and a small 

increase in streamflow. However, the maximum load 

was only 0.14 lb/d (at a concentration of 150 g/L), 

and that sample was the only sample that had a selenium load greater than 0.10 lb/d from Alkali Creek.

The other three tributaries on the east side of the 

Gunnison River—Wells Gulch, Beaver Gulch, and 

Deer Creek—drain essentially nonirrigated areas. A 

small reservoir occasionally releases water into Deer 

Creek. The irrigated areas shown in figure 4 in the tributary basin of Deer Creek have had little irrigation in 

recent years. These streams probably are ephemeral 

and normally flow only after rain or snowmelt. No 

streamflow was observed in Beaver Gulch despite 

numerous visits during or after rain or snowmelt. The 

runoff measured in Wells Gulch and Deer Creek did 

mobilize selenium from the shale areas, but the selenium loads were small (maximum load was 0.03 lb/d 

in Wells Gulch) because measured streamflow was 

low. The highest streamflow measured for the 

14 samples collected from Wells Gulch and Deer 

Creek was 0.74 ft3/s in March 2000 at Wells Gulch, 

but 11 of the 14 samples collected from these two 

drainages had a measured streamflow of less than 

0.10 ft3/s. Much larger runoff has undoubtedly 

occurred in this area than what was measured during 

1999–2000.

On the south and west side of the Gunnison 

River (Cummings Gulch to Bangs Canyon in fig. 4), 

selenium concentrations were less than 2 g/L except 

for samples from Cummings Gulch and the downstream site on Roubideau Creek (table 1). These 

streams generally drain areas containing no Mancos 

Shale. Cummings Gulch and the downstream reach of 

Roubideau Creek (at mouth) receive considerable 

quantities of irrigation return flows from the west side 

of the Uncompahgre Valley. The streams downstream 

from Roubideau Creek have little or no irrigation and 

no outcrops of Mancos Shale. The upstream site on 

Roubideau Creek is upstream from irrigation return 

flows from the Uncompahgre Valley. Nearly all selenium concentrations from the upstream Roubideau 

Creek (at upper) site, Escalante Creek, Dominguez 

Creek, East Creek, and Bangs Canyon were less than 

or equal to 1.3 g/L (table 1).

The largest selenium loads in tributary streams 

of the Gunnison River downstream from the 

Uncompahgre River were in basins affected by irriga-
12 Characterization of Selenium in the Lower Gunnison River Basin, Colorado, 1988–2000

tion drainage and return flows: Kannah Creek and 

Whitewater Creek on the north and east side of the 

river, and Cummings Gulch and lower Roubideau 

Creek (at mouth) on the south and west side (table 1). 

Selenium loads from other areas in this reach seems to 

be minor. Large, widespread rainstorms or significant 

snowmelt in the Mancos Shale areas north and east of 

the river could increase selenium loads to the lower 

Gunnison River for a short period. Such events are 

infrequent and of short duration, but snowmelt and 

rain did occur in January 2000. In the latter one-half of 

the month, a combination of low-elevation snowmelt 

and rain apparently caused an increase in selenium 

loads from Mancos Shale areas in the Delta area and 

the east side of the Uncompahgre Valley to the south. 

Selenium concentrations increased about 1-2 g/L in 

the Gunnison River at Whitewater (site 50) and loads 

increased about 5–10 lb/d for about 2 weeks in the 

latter one-half of January 2000.

For water years 1988–2000, the median selenium concentration was 5 g/L at the compliance 

point for the Gunnison River at the USGS streamflowgaging station at the Whitewater site (site 50; fig. 4), 

which equals the selenium standard for the lower 

Gunnison River. Based on the median concentration, 

the lower Gunnison River would not seem to be out of 

compliance for selenium; however, the determination 

of whether a water body exceeds a water-quality standard in Colorado is based on the 85th-percentile 

concentration, not the median. For the Whitewater site 

the 85th percentile was 8 g/L, and that is why the 

State set the temporary modification at 8 g/L for selenium in the lower Gunnison River.

CHARACTERIZATION OF SELENIUM IN 

CEDAR CREEK AND LOUTZENHIZER 

ARROYO 

The tributaries of the Uncompahgre River with 

the largest selenium loads are Cedar Creek and 

Loutzenhizer Arroyo (fig. 1). To aid remediation planning for reducing selenium in the Uncompahgre River, 

more detailed information about selenium loading in 

the Cedar Creek and Loutzenhizer Basins was needed 

by the Task Force and the NIWQP. The USGS has 

collected a considerable amount of selenium data at 

outflow sites on these tributaries, but selenium data 

generally were sparse for upstream areas. To fill in 

data gaps and help focus remediation efforts, the 

USGS conducted detailed sampling of Cedar Creek 

and Loutzenhizer Arroyo in 1999–2000 to determine 

the distribution of selenium loading in these basins.

One method of evaluating constituent loading to 

a stream is to make streamflow measurements and 

collect water samples for analysis of the constituents 

of interest at numerous main-stem sites and at major 

inflows. Because load is calculated using streamflow 

and concentration, both parameters must be known for 

every site. Streamflow measurements are usually 

measured using the current-meter method (Rantz and 

others, 1982), which involves measuring the water 

depth and velocity at numerous locations across a 

stream cross section. Accurate streamflow measurements can be made with ideal cross sections that are 

smooth and uniform. Measurements become less accurate as streambeds become rocky and banks and 

streambeds become irregular. Undercut banks and 

irregular stream channels with heavy brush are a 

common feature of Cedar Creek and Loutzenhizer 

Arroyo, which can degrade the accuracy of currentmeter streamflow measurements. Less accurate 

streamflow measurements mean the loads calculated 

from those measurements will be less accurate, and 

evaluating loading inputs becomes subject to more 

uncertainty. This is especially true when attempting to 

determine loading from diffuse ground-water sources 

because ground-water discharge into a relatively short 

stream reach can be quite small compared to the flow 

in the stream.

Streamflow can be measured in streams with 

good precision by using the tracer-dilution method 

(Bencala and others, 1990; Kimball, 1997). A conservative salt tracer such as bromide, chloride, or lithium 

is commonly used and is injected into the stream at a 

known concentration and rate. The tracer is injected in 

sufficient quantities to raise the concentration of the 

tracer in the stream much higher than the background 

concentration in the stream. As the tracer moves 

downstream, it is diluted by inflow from tributaries 

and from diffuse ground water, and the discharge at 

any one point is related to the amount of dilution that 

has occurred downstream from the injection point. 

After the tracer concentration in the stream has 

reached a steady concentration, water sampling is 

done at preselected stations in the stream reach. The 

samples are analyzed for the tracer concentration and 

for the constituent concentrations of interest. The 

tracer concentration is used to calculate streamflow at 

each sampling station, and with the constituent 
CHARACTERIZATION OF SELENIUM IN CEDAR CREEK AND LOUTZENHIZER ARROYO 13

concentration, a load can be calculated for each site. 

When using the tracer-dilution method, manual 

streamflow measurements are not required; however, a 

few measurements are usually made for comparison to 

the flows determined from the tracer data.

For this study, bromide was used as the tracer. 

After a preliminary reconnaissance, tracer-injection 

sites and sampling sites were selected. For each 

sampling site, water temperature, pH, and specific 

conductance were measured, and water samples were 

collected for analysis of dissolved selenium and 

bromide. At a few selected locations, streamflow was 

measured with a current meter for comparison to 

streamflow determined using the tracer method.

Cedar Creek

The characterization of Cedar Creek was done 

November 16–17, 1999. The stream reach where the 

tracer study was done was between Miguel Road (site 

CD1) and below Highway 50 (site CD26; fig. 5). The 

stream was separated into two reaches for tracer injections. The upper reach is from sites CD1 to CD13, the 

lower reach from site CD13 to site CD26 (fig. 5). In 

the upper reach, 12 main-stem sites and 3 inflows were 

sampled. In the lower reach, 16 main-stem and 

3 inflow sites were sampled. Main-stem sites are 

designated “CD” and inflow sites “TR”.

Selenium concentrations and specific-conductance measurements at the main-stem sites are shown 

in figure 6, and selenium loads are shown in figure 7. 

In general, significant changes in selenium concentrations and loads occurred in reaches with major surface 

inflows, either from drainage ditches and washes or 

from discharge of ground-water seepage that is 

discharged from canals and laterals. Montrose Arroyo 

was the largest single source of selenium to Cedar 

Creek downstream from Miguel Road (fig. 7) and 

accounted for 32 percent of the load at the outflow site 

below Highway 50 (CD26) on November 16–17, 

1999. Selenium load did not increase between 

sites CD1 and CD10, although the bromide concentrations indicate about a 3-ft3

/s gain in streamflow in this 

reach. The selenium concentrations in Cedar Creek 

decreased slightly between sites CD1 and CD10, indicating that the selenium concentrations in the gaining 

water were low. The only notable increase in selenium 

load in the upper reach (sites CD1–CD13 in fig. 5) 

was between sites CD10 and CD11(fig. 6) where 

seepage water from the AM lateral (fig. 5) would 

discharge into Cedar Creek. The AM lateral was not 

sampled, so the cause of the increase in load (about 

0.4 lb/d) between sites CD10 and CD11 is not known.

About one-half of the increase in selenium load 

in the lower reach (sites CD13 to CD26 in fig. 5) was 

discharged from Montrose Arroyo (1.5 lb/d). The selenium load increases about 0.5 lb/d between 6700 Road 

(site CD15) and the cemetery downstream from the 

Loutzenhizer Canal (site CD17B). The increase in 

load between sites CD16 and CD17 was from the 

Loutzenhizer Canal, which has a small flow during the 

winter that apparently is the result of shallow groundwater seepage. The canal flow at the time of the tracer 

study was diverted into Cedar Creek. The remaining 

increase in load between sites CD15 and CD17B probably is diffuse ground-water discharge. The decrease 

in selenium load from site CD18 (Hillcrest Drive) to 

site CD19 (at Highway 50) was the result of a 3-g/L 

decrease in the selenium concentration. The computed 

streamflows at sites CD18 and CD19 were equal 

(20.5 ft3/s). The specific-conductance measurements 

at sites CD18 and CD19 were almost equal (fig. 6); 

therefore, it is possible that the selenium concentration 

for site CD19 might be too low because of sampling or 

analytical error. Inflow from a drainage ditch accounts 

for the increase in load between sites CD21B and 

CD21 (fig. 7). Downstream from Montrose Arroyo, 

the selenium load increased 0.56 lb/d between sites 

CD22 and CD23. The tracer data indicate a gain in 

streamflow of only 0.3 ft3/s in this reach, which means 

the selenium concentration of the gaining flow would 

be 346 g/L to account for a load of 0.56 lb/d. The 

specific conductance readings (fig. 6) were identical at 

sites CD22, CD23, and CD24, which indicates that the 

selenium concentration for the sample at site CD23 

(28.2 g/L) might be high, resulting in a selenium load 

for site CD23 that is too high. Therefore, the selenium 

gain between sites CD22 and CD23 could be overestimated. Inflow into Cedar Creek with a selenium 

concentration of 346 g/L that has virtually no salinity 

(as measured by specific conductance) seems unlikely.

A review of the Cedar Creek tracer study for 

November 16–17, 1999, indicates that selenium 

concentrations at main-stem sites ranged from 

12 to 28 g/L. The increase in selenium load between 

Miguel Road and Highway 50 was about 3.5 lb/d. This 

increase indicates that 27 percent of the load was from 

the basin upstream from Miguel Road, 23 percent 

from the reach between Miguel Road and Montrose
14 Characterization of Selenium in the Lower Gunnison River Basin, Colorado, 1988–2000 Montrose Regional Airport

Mesa Rd (6450)

Stough Ave 26

Hwy 50

Uncompahgre

River

MA

Hwy 550

25

CD19

CD18

CD20

CD17 CD15

CD14

CD16

CD17B

Loutzenhizer

canal

TR17

Montrose

CD7

CD4 CD3

CD2

CD6 CD1

CD5 TR4

CD13

CD12

TR11 CD11

CD9

TR9

CD10

Fairview Hwy 50

Hillcrest Drive

6700 Road

Fairview

Reservoir

Montrose Arroyo

Cedar Creek

South Canal

Kinikin Road

Vernal

Mesa

Bostwick

Park

B

Landfill

Road

Cedar Creek

Miguel Road

CU7

CU6

CU5

C

AM 

Lateral 

AM Lateral 

CU3

TR4

Niagara St

CD24

CD23

CD22

CD21

TR21

CD21B

CD

CD

E

CD7

0

0

1

1

2 MILES

2 KILOMETERS

38°25'38°30'

107°55' 107°50' 107°45' 

Shinn Park

Dry 

Base from U.S. Geological Survey1:24,000 digital data, 1927 North American Datum,Universal Transverse Mercator projection,Zone 13

Figure 5. Cedar Creek and location of sampling sites.
CHARACTERIZATION OF SELENIUM IN CEDAR CREEK AND LOUTZENHIZER ARROYO 15

Arroyo, 32 percent from Montrose Arroyo, and 

18 percent was downstream from Montrose Arroyo. 

That loading distribution for Cedar Creek is applicable 

to the conditions of November 1999 when the tracer 

study was done. The relative percentages of the selenium loading in Cedar Creek from the reaches 

described may be different at different times of the 

year.

Several sources of selenium to Cedar Creek in 

the tracer-study reach from Miguel Road (site CD1) to 

Highway 50 (site CD26) are possible, but irrigationrelated sources would seem to be the largest single 

source of selenium. Seepage from canals, laterals, and 

ditches and deep percolation from irrigated fields 

provide recharge to shallow ground water in shale or 

unconsolidated deposits derived from shale, and water 

movement through those materials can mobilize selenium (Wright and Butler, 1993). The Cedar Creek 

Basin has about 6,650 acres of irrigated land (Bureau 

of Reclamation, written commun., 2001), most of 

which is downstream from site CD1 (fig. 5). A demonstration project in the Montrose Arroyo Basin in 

1998–2000 indicated that piping of 7.5 mi of laterals 

in that basin caused about a 27-percent decrease in 

selenium load in Montrose Arroyo at Niagara Street 

(fig. 5) (Butler, 2001). Other sources of selenium 

loading, like deep percolation from residential lawn 

and garden and golf-course watering, septic systems, 

ponds, and natural runoff, also would be a source of 

selenium load. 

The relatively high percentage of the selenium 

load in Cedar Creek from the upper basin (upstream 

from site CD1 at Miguel Road) is typical of the 

nonirrigation season (November–March) based on 

selenium data collected since 1991 at sites CD1 and 

CD26 (downstream from Highway 50) for the 

NIWQP. The percentage of the selenium load in Cedar 

Creek at site CD26 representing selenium load from 

the upper basin was considerably less during the irrigation season compared to the nonirrigation season 

and averaged about 12 percent of the load at site CD26 

for seven sets of concurrent irrigation-season samples.

Figure 6. Selenium concentrations and specific conductance in Cedar Creek, November 16–17, 1999.

10

12

14

16

18

20

22

24

26

28

30

1,300

1,400

1,500

1,600

1,700

1,800

1,900

2,000

2,100

2,200

2,300

2,400

2,500

2,600

Selenium concentration

Specific conductance

UPSTREAM DOWNSTREAM At Fairview Wash north of Highway 50 At Highway 50 At 6700 Road Seepage from Loutzenhizer Canal At Hillcrest Drive At Stough Avenue Montrose Arroyo inflow At 6450 Road

SELENIUM CONCENTRATION, IN MICROGRAMS PER LITER

SPECIFIC CONDUCTANCE, IN MICROSIEMENS PER CENTIMETER

CD1CD2CD3CD4CD5CD6CD7CD9

CD10CD11CD12CD13CD14CD15CD16CD17

CD17B

CD18CD19CD20

CD21B

CD21CD22CD23CD24CD25CD26
16 Characterization of Selenium in the Lower Gunnison River Basin, Colorado, 1988–2000

Selenium loads at site CD1 generally were lower in 

irrigation-season samples than in nonirrigation season 

samples; the opposite was true for loads at site CD26. 

Reasons for lower irrigation-season loads at site CD1 

have not been studied but could be related to higher 

consumptive-use losses in the irrigation season 

compared to the nonirrigation season in the upper 

Cedar Creek Basin. During the summer, water and 

selenium could be lost from irrigation use and water 

uptake by the extensive natural vegetation present in 

much of the basin upstream from site CD1. Estimates 

of annual loads for sites CD1 and CD26 using selenium data for 1991–2000 indicate that the selenium 

load from the Cedar Creek Basin upstream from site 

CD1 accounted for about 20 percent of the annual 

selenium load in Cedar Creek below Highway 50 (site 

CD26).

Synoptic sampling was done at seven sites on 

November 18, 1999, in the upper basin, upstream from 

Miguel Road, to provide information on selenium 

concentrations and loads in the upper Cedar Creek 

Basin (table 2; sites CU1–CU7 in fig. 5). Streamflow

Figure 7. Selenium loads in Cedar Creek, November 16–17, 1999.

was measured using a current meter for the upper-basin 

synoptic sampling. Selenium concentrations were high at 

the uppermost sites: 181 g/L in Cedar Creek above 

Hairpin Creek (site CU1) and 361 g/L in Hairpin Creek 

at the mouth (site CU2). The selenium load in Cedar 

Creek below Hairpin Creek was about 38 percent of the 

Table 2. Synoptic data for upper Cedar Creek Basin, 

November 18, 1999

[Streamflow in cubic feet per second; specific conductance in microsiemens 

per centimeter at 25o Celsius; selenium concentration in micrograms per liter; 

selenium load in pounds per day; <, less than]

Site

(fig. 5) Streamflow Specificconductance

Selenium

concentration

Selenium

load

CU1 0.24 7,890 181 0.23

CU2 .10 8,520 361 .19

CU3 .24 7,040 190 .25

CU4 1.33 595 <2.4 <.02

CU5 3.06 2,000 26 .43

CU6 3.78 964 6 .12

CU7 .79 1,020 20 .09

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

UPSTREAM DOWNSTREAM At FairviewWash north of Highway 50 At Highway 50 At 6700 Road Seepage from Loutzenhizer Canal At Hillcrest Drive At Stough Avenue Montrose Arroyo inflow At 6450 Road

CD1

CD2

CD3

CD4

CD5

CD6

CD7

CD9

CD10

CD11

CD12

CD13

CD14

CD15

CD16

CD17

CD17B

CD18

CD19

CD20

CD21B

CD21

CD22

CD23CD24

CD25

CD26

SELENIUM LOAD, IN POUNDS PER DAY
CHARACTERIZATION OF SELENIUM IN CEDAR CREEK AND LOUTZENHIZER ARROYO 17

load measured at site CD1 the previous day (using 

streamflow from current-meter measurements for 

calculating load). The synoptic sampling was not a 

detailed study of the upper basin, and about 40 percent 

of the selenium load at site CD1 was unmeasured. 

Landslide areas in the upper Cedar Creek Basin are 

composed primarily of material derived from Mancos 

Shale. Irrigation ditches in the headwater areas of 

Cedar Creek and Hairpin Creek are dug through the 

landslide deposits. Also, several areas in the upper 

basin and along Cedar Creek downstream from 

Rawhide Gulch have irrigated lands (fig. 5). The selenium load in the upper Cedar Creek Basin is probably 

derived from a combination of natural recharge and 

runoff from the landslide areas, from deep percolation 

from irrigated fields, and from irrigation canal and 

ditch seepage.

Loutzenhizer Arroyo

The Loutzenhizer Arroyo characterization study 

was done February 28–29, 2000. The tracer study was 

done in the stream reach between the Selig Canal 

(site LZ1) and the mouth (site LZ26 in fig. 8). The 

stream was separated into two reaches for tracer injections. The upper reach was from sites LZ1 to LZ15 

and the lower reach was from site LZ15 to site LZ26. 

In the upper reach, 12 main-stem sites and 4 inflows 

were sampled. In the lower reach, 12 main-stem and 

2 inflow sites were sampled (East and West Drains). 

Main-stem sites are designated “LZ” and inflow sites 

“TR”.

Unexpected problems adversely affected 

obtaining loading information for the Loutzenhizer 

Arroyo study. Initially, three stream reaches were 

selected for tracer studies, two on the main stem of 

Loutzenhizer Arroyo and one on the west tributary 

(fig. 8). A lack of access in certain areas made doing 

a tracer study on the west tributary impractical; 

therefore, the only data collected on the west tributary 

were synoptic samples at the six “WT” sites shown in 

figure 8. The streamflow and selenium data for the 

west tributary samples are listed in table 3. During the 

tracer runs on the main stem of the arroyo, various 

problems occurred during both runs that invalidated 

some of the bromide data. Therefore, streamflow 

could be calculated from the tracer data for only a 

limited number of sites, which means that determination of loads also was limited. However, seleniumconcentration and specific-conductance data are available for all the sites that were sampled (fig. 9). Streamflow was measured with a current meter at all sites in 

the west tributary basin and at sites LZ1, LZ14, and 

LZ26 on the main stem of the arroyo. 

The most apparent changes in selenium concentrations and in specific conductance in Loutzenhizer 

Arroyo were the increases between sites LZ2 and LZ4 

and the decreases between sites LZ14 and LZ14b 

(fig. 9). The selenium concentration increased from 

184 g/L at site LZ2 to 331 g/L at site LZ4. Because 

the bromide data for these sites were available, the 

selenium loads could be calculated; there was an 

increase of about 1.4 lb/d of selenium between sites 

LZ2 and LZ4. A small ditch (site TR3; fig. 8) between 

sites LZ2 and LZ4 had a selenium concentration of 

655 g/L, and the ditch accounted for at least part of 

the increase in selenium load in that reach. The reach 

between sites LZ2 and LZ4 and the area drained by the 

ditch are downgradient from the Selig Canal (fig. 8), 

which cuts through Mancos Shale in this area. Part of 

the increase in selenium load in the arroyo between 

sites LZ2 and LZ4 might be from canal seepage.

Selenium concentrations were relatively 

unchanged in the main stem of Loutzenhizer Arroyo 

between sites LZ4 and the confluence with the west 

tributary at site LZ14 (fig. 9). Concentrations were 

between 310 and 347 g/L. Detailed selenium-load 

data could not be determined for the reach between 

sites LZ4 and LZ14. Inflow from the west tributary 

(site WT7) caused a decrease in selenium concentrations and specific conductance in Loutzenhizer Arroyo 

(fig. 9). The selenium and specific-conductance data 

shown for site LZ14b in figure 9 were back calculated 

using the measured streamflow and the selenium and 

specific-conductance data for sites LZ14 and WT7. 

The synoptic data (streamflow measured with a 

current meter) for the west tributary (table 3) indicate 

downstream increases in streamflow and selenium 

load from Ida Road (WT1) to the mouth (WT7). 

Site WT4 is on a drainage ditch. The largest increase 

in selenium load (about 1.7 lb/d) occurred in the reach 

between WT1 and WT2 and accounted for 50 percent 

of the total load in the west tributary. However, the 

reach between sites WT1 and WT2 also is 52 percent 

of the total stream length between sites WT1 and the 

mouth, so the loading is directly proportional to the 

length of the reach. The selenium load downstream
18 Characterization of Selenium in the Lower Gunnison River Basin, Colorado, 1988–2000

0

0

1

1

2 MILES

2 KILOMETERS

38°35'38°40'

108°00' 107°55' 107°50'

Gunnison

North

Branch

River

East

Selig

Canal

Canal

Canal

Middle Branch

South

Branch

Loutzenhizer

Loutzenhizer

Arroyo

West Tributary

River

Creek

Spring

Uncompahgre

Hwy 50

Hwy 50

M 

M6TR5

WT6

I

W 

S 

EXP

LZ2

Peach Valley

Red Bostwi

Ditch

Rock Canyon

Amber

Banner

Carnation

River Road

David

Falcon

Jade

Holly

Jay-Jay

East

5900

6000

6200

6450

Drain Ditch

Ida

Flat Top

LZ26

LZ25

LZ24 LZ20

LZ19

LZ18

LZ17

LZ16

LZ15

LZ14

LZ13

LZ11

LZ10

LZ8

LZ7

LZ6

LZ4

LZ1

LZ2

TR9

TR5

TR3

M6

M5

M4

M2

M

M3

WT7

WT6

WT5

WT4

WT2

WT1

LZ14b

LZ21

LZ22

LZ23

Diversion

Ditch

W. Drain

E. Drain

Olathe

Base from U.S. Geological Survey1:24,000 digital data, 1927 North American Datum,Universal Transverse Mercator projection,Zone 13

Ir

Figure 8. Loutzenhizer Arroyo and location of sampling sites.
CHARACTERIZATION OF SELENIUM IN CEDAR CREEK AND LOUTZENHIZER ARROYO 19

from the East Canal (WT6), despite a small gain in 

streamflow (table 3), did not change.

In the lower reach of Loutzenhizer Arroyo 

(sites LZ15 to LZ26; fig. 9), downstream from the 

west tributary, selenium concentrations were 

unchanged to Banner and 6000 Roads (site LZ18), and 

then concentrations to the mouth decrease gradually. 

Specific conductance throughout the lower reach was 

essentially unchanged, varying by no more than 

3 percent. Therefore, surface and subsurface inflows in

Table 3. Streamflow, specific conductance, and selenium concentrations for the west 

tributary of Loutzenhizer Arroyo, February 29, 2000

[Streamflow in cubic feet per second; specific conductance in microsiemens per centimeter at 25o Celsius;

selenium concentration in micrograms per liter; selenium load in pounds per day]

Site

(fig. 8) Streamflow Specificconductance

Selenium

concentration

Selenium

load

WT1 1.11 4,790 125 0.75

WT2 2.98 5,110 151 2.43

WT4 .34 7,560 45 .08

WT5 3.40 5,280 149 2.73

WT6 4.55 5,200 139 3.41

WT7 4.85 5,160 130 3.40

Figure 9. Selenium concentrations and specific conductance in Loutzenhizer Arroyo, February 28–29, 2000. At 6400 Road At Falcon Road At David Road Below East Canal At Carnation Road At Banner and 6000 Roads At 5900 Road At North River Road

SPECIFIC CONDUCTANCE, IN MICROSIEMENS PER CENTIMETER

SELENIUM CONCENTRATION, IN MICROGRAMS PER LITER

Below east drain, near Banner Road

Below west drain, near Banner Road

Above west tributary

Below west tributary

Tributary inflow, below David Road

5,000

5,200

5,400

5,600

5,800

6,000

6,200

6,400

6,600

6,800

7,000

140

160

180

200

220

240

260

280

300

320

340

360

LZ1

LZ4LZ6LZ7LZ8

LZ10LZ13LZ14

LZ14b

LZ11

LZ15LZ16LZ17LZ18LZ19LZ20

LZ21

LZ22LZ23LZ24LZ25LZ26

LZ2

Selenium

Specific conductance
20 Characterization of Selenium in the Lower Gunnison River Basin, Colorado, 1988–2000

the lower reach had little effect on salinity (as approximated by specific conductance) in the arroyo and had a 

dilution effect on selenium concentrations. Some of 

the bromide data were usable in this reach, allowing 

limited analysis of selenium loads. The streamflow 

computed by tracer dilution was about 9.8 ft3

/s at 

sites LZ15 and LZ16, compared to the measured 

streamflow of 7.2 ft3/s at site LZ14b (sum of measured 

flows at sites LZ14 and WT7). Between sites LZ16 

and LZ18 there was a gain of about 0.7 ft3/s and a 

small increase in selenium load using the streamflow 

computed by tracer dilution. Streamflow and load data 

could not be determined for sites LZ19 through LZ24. 

The selenium concentrations sampled in two tributaries (east and west drains) between sites LZ19 and 

LZ22 had relatively low selenium concentrations 

compared to the main-stem arroyo (fig. 8). Selenium 

concentrations were 49 g/L in the east drain and only 

8 g/L in the west drain (fig. 8). The sampling site on 

the west drain is at the mouth of a drainage that flows 

through a densely vegetated swale above Banner Road 

and then through a small wetland and pond below 

Banner Road. Such a flow pathway could be conducive to removal of selenium from the water column by 

chemical and biological processes. 

The calculated streamflow at sites LZ25 and 

LZ26 using the bromide data indicate a gain in streamflow of about 1.3 ft3/s between sites LZ18 and LZ25 

and a gain of 0.5 ft3/s between sites LZ25 and LZ26. 

The total gain in streamflow for the lower reach was 

about 2.5 ft3/s. The calculated streamflow at site LZ26 

using the bromide data of 12.3 ft3

/s was about 

40 percent greater than the measured streamflow at 

that site of about 8.8 ft3

/s. Because the selenium 

concentrations at sites LZ25 and LZ26 were lower 

than sites LZ16–LZ18, the load increase from site 

LZ16 to LZ26 was small despite a gain in streamflow. 

From site LZ16 to LZ26, the selenium load increase 

was about 0.9 lb/d.

Because it was not possible to obtain detailed 

loading information from the Loutzenhizer tracer 

study at all sites, analysis of selenium loading into 

Loutzenhizer Arroyo was limited to major stream 

reaches and the west tributary. Loads were computed 

using streamflow measured with a current meter at 

sites LZ1, LZ14, WT7, and LZ26 (table 4). Streamflow and selenium load for site LZ14b (below the 

confluence of the main stem of the arroyo with the 

west tributary) was computed as the sum of measured 

streamflow and loads for sites LZ14 and WT7. Selenium loads for the upper basin (the load at site LZ1), 

for the reach on the main stem between the Selig 

Canal and the west tributary (load difference between 

sites LZ14 and LZ1), the load from the west tributary 

(load at site WT7), and the selenium load into the 

lower main stem of the arroyo (load difference 

between sites LZ26 and LZ14b) were compared to the 

selenium load at the mouth (site LZ26). Using the 

measured streamflow data for February 28–29, 2000, 

about 10 percent of the selenium load in Loutzenhizer 

Arroyo was from the upper basin, 43 percent from the 

reach between the Selig Canal and the west tributary, 

46 percent from the west tributary, and only 1 percent 

from the lower reach downstream from the west tributary confluence to the mouth. 

An analysis of the selenium loading in the 

Loutzenhizer Arroyo Basin for the same reaches or 

subbasins also was done using the tracer data, but 

several assumptions are necessary to do this analysis. 

If site LZ2 is considered equivalent to site LZ1 and 

site LZ15 equivalent to site LZ14b, then there are 

usable tracer data for three of the five sites where 

streamflow was directly measured (table 4). Tracer 

data were not available for sites LZ14 and WT7. 

However, the selenium loads for sites LZ14 and WT7 

were approximated for the tracer-data set. From the 

measured data (table 4), selenium load increased by 

6.59 lb/d between sites LZ1 and LZ14b (7.34–0.75). 

Of that increase, 3.40 lb/d was from the west tributary

Table 4. Selected streamflow and selenium load data 

for Loutzenhizer Arroyo, February 28–29, 2001

[Streamflow in cubic feet per second; selenium concentration in 

micrograms per liter; selenium load in pounds per day]

Site

(fig. 8) Streamflow Seleniumconcentration

Selenium

load

Loads Computed From Measured Streamflow

LZ1 0.74 188 0.75

LZ14 2.36 310 3.94

WT7 4.85 130 3.40

LZ14b1 7.21 189 7.34

LZ26 8.78 157 7.43

Loads Computed From Streamflow Computed

Using Tracer Data 

LZ2 1.34 184 1.33

LZ15 9.80 180 9.51

LZ26 12.30 157 10.41

1Computed as the sum of measured streamflow and loads 

for sites LZ14 and WT7.
CHARACTERIZATION OF SELENIUM IN CEDAR CREEK AND LOUTZENHIZER ARROYO 21

(site WT7), which is 52 percent of the load increase in 

that reach. The remaining increase of 3.19 lb/d (6.59–

3.40 or 3.94–0.75) was in the reach between LZ1 and 

LZ14. If the loads computed from the tracer data are 

used, there was a gain of 8.18 lb/d between sites LZ2 

and LZ15 (9.51–1.33; table 4), which for this analysis, 

was considered equivalent to the loading for the reach 

between sites LZ1 and LZ14b. If it is assumed that the 

west tributary accounted for 52 percent of the gain in 

selenium load between sites LZ1 and LZ14b that was 

determined using the measured streamflow data, then 

the selenium load from the west tributary at site WT7 

was 4.25 lb/d (0.52 times 8.18 lb/d). The remaining 

load of 3.93 lb/d is the selenium load gain between 

sites LZ2 (or LZ1) and site LZ14, which is the reach 

on the main stem between the Selig Canal and the west 

tributary. Using the estimated selenium loads based on 

the tracer data indicates that on February 28–29, 2000, 

about 12 percent of the selenium load in Loutzenhizer 

Arroyo was from the upper basin, 38 percent from the 

upper main-stem reach between the Selig Canal and 

the west tributary, 41 percent from the west tributary, 

and 9 percent from the lower reach downstream from 

the west tributary. The percentage for the upper basin 

was rounded to 12 percent so that the total percentages 

add up to 100 percent. Differences in the relative 

loading percentages between the two data sets are not 

large, except for the lower reach of the arroyo between 

the west tributary confluence (site LZ14b) and the 

mouth (site LZ26). The increase in selenium load in 

the lower reach was only 0.09 lb/d (1 percent of the 

load at site LZ26) using the measured streamflow data 

compared to 0.90 lb/d (9 percent of the load at site 

LZ26) using the tracer data.

For the entire study reach of Loutzenhizer 

Arroyo in February 2000, selenium concentrations 

ranged from 157 g/L at site LZ26 to 347g/L at site 

LZ11 (fig. 9). Selenium load in the reach (where 

streamflow values were available for use in load calculations) ranged from 0.75 lb/d (LZ1) to 7.43 lb/d 

(LZ26) using measured streamflow and 1.33 lb/d 

(LZ2) to 10.41 lb/d (LZ26) using streamflow values 

calculated from the tracer data (table 4).

Because detailed selenium-load information 

could not be obtained for Loutzenhizer Arroyo using 

tracer data, selenium data collected prior to 2000 by 

the USGS for the NIWQP also were examined in an 

attempt to augment the results of the tracer study. 

However, most of the selenium data collected by the 

USGS in the Loutzenhizer Arroyo Basin prior to the 

tracer study were collected at River Road (site LZ25) 

for the purpose of estimating the outflow load from the 

basin. Limited data were collected elsewhere in the 

basin, so not much information is available to augment 

the results of the Loutzenhizer tracer study.

One data set that can be used to examine selenium loading for Loutzenhizer Arroyo was collected 

for synoptic sampling of the Loutzenhizer Basin on 

March 9–10, 1992. Those samples were collected for 

the NIWQP detailed study of the Uncompahgre 

Project. Results are discussed in Butler and others 

(1996), and the data were published in Butler and 

others (1994). The sampling in 1992 was limited in 

scope, and only five sites were sampled on the main 

stem of the arroyo (sites LZ2, LZ11, LZ14, LZ18, and 

LZ25) and three sites on the west tributary (sites WT2, 

WT5, and WT7). When the 1992 samples were 

collected, snowmelt runoff from shale areas in the 

upper basin was discharging into the main stem of the 

arroyo. The selenium load at 6400 Road (site LZ2) 

accounted for about 36 percent of the load at River 

Road (site LZ25 in fig. 8) in March 1992. By contrast, 

in February 2000, the selenium load at site LZ1 

accounted for about 12 percent of the selenium load at 

site LZ25. Other results from March 1992 are not 

consistent with results for February 2000. The March 

1992 data indicate a smaller increase in selenium load 

between 6400 Road (site LZ2) and the west tributary 

(site LZ14) and a much larger increase in load in the 

lower reach downstream from Carnation Road 

(site LZ15) than in February 2000. For the March 

1992 samples, the selenium concentrations were 

160 g/L at site LZ18 and 190 g/L at site LZ25, 

which is different from the results of the sampling in 

2000 when concentrations gradually decreased 

throughout that reach from 183 g/L at site LZ18 to 

155 g/L at site LZ25. Because many more samples 

were collected in 2000 than in 1992, the selenium 

concentrations shown in figure 9 are assumed to be 

more representative of present-day selenium concentrations during low-flow conditions in the lower reach 

of Loutzenhizer Arroyo than are the two samples from 

March 1992. For the west tributary, the selenium load 

at site WT2 was 64 percent higher in February 2000 

than in March 1992, but the loads at sites WT5 and 

WT7 were only 7 percent higher in February 2000 

than in March 1992.

Questions have been raised at Task Force meetings about selenium loading in the Loutzenhizer 

Arroyo Basin from the upper part of the drainage basin 

upstream from the Loutzenhizer and Selig Canals 
22 Characterization of Selenium in the Lower Gunnison River Basin, Colorado, 1988–2000

(fig. 8). Selenium data have been collected since 1992 

at a few locations that provide a minimal amount of 

information to address such questions. During 1992–

2000, 13 samples were collected on the middle branch 

of Loutzenhizer Arroyo at sites M3, M5, LZ1, and 

LZ2 (fig. 8; table 5). The mean selenium load for the 

13 samples is 1.39 lb/d. Assuming that the mean load 

for the 13 samples represents daily selenium loads 

throughout the year, the annual load in the middle 

branch is about 507 lb/yr, or about 10 percent of the 

estimated annual selenium load of 4,900 lb/yr for 

Loutzenhizer Arroyo at River Road (site LZ25). The 

selenium load for the middle branch is considered 

uncertain because it is based on data collected at four

Table 5. Selenium data for the upper Loutzenhizer Arroyo Basin and lower Bostwick Park, 1992–2000

[Streamflow in cubic feet per second; specific conductance in microsiemens per centimeter at 25o Celsius; selenium concentration in micrograms per liter; 

selenium load in pounds per day; E, estimated; --, no data; <, less than]

Site

(fig. 8) Site location Sampling date Streamflow

Specific

conductance

Selenium, 

dissolved

Selenium 

load

M1 Drain in lower Bostwick Park 04–10–00 E3.0 1,220 36 E0.58

M1 05–15–00 7.9 930 29 1.23

M1 07–26–00 18.3 856 20 1.97

M1 10–05–00 7.8 1,130 29 1.22

M2 South branch of Loutzenhizer Arroyo at Landfill Road 

bridge

11–21–95 E.05 11,060 1,500 E.40

M2 02–14–96 .01 10,600 1,700 .10

M2 07–19–00 .21 1,110 69 .08

M2 10–05–00 2.49 492 20 .27

M3 Loutzenhizer Arroyo upstream from Loutzenhizer Canal 05–14–93 .88 3,040 96 .46

M4 Loutzenhizer Canal at Holly Road 07–14–93 7.52 406 4 .16

M4 08–13–93 15.7 443 5 .42

M4 09–08–93 3.30 488 7 .12

M5 Loutzenhizer Arroyo downstream from Loutzenhizer 

Canal

07–14–93 8.27 591 12 .53

M5 08–13–93 16.8 552 8 .72

M5 09–08–93 5.48 1,190 19 .56

LZ1 Loutzenhizer Arroyo upstream from Selig Canal 02–29–00 .74 5,370 188 .75

LZ1 04–10–00 15.0 684 13 1.05

LZ1 07–26–00 2.42 813 14 .18

LZ1 10–05–00 14.9 1,260 36 2.89

LZ2 Loutzenhizer Arroyo at 6400 Road 03–10–92 4.74 3,830 220 5.62

LZ2 03–02–93 1.37 4,010 190 1.40

LZ2 03–23–93 27.8 1,150 21 3.15

LZ2 05–14–93 3.87 472 2 .04

LZ2 10–03–96 -- 1,470 26 --

LZ2 02–29–00 .74 5,400 184 .73

M6 North branch of Loutzenhizer Arroyo upstream from 

Selig Canal

05–15–00 .34 3,930 23 .04

M6 07–26–00 .86 1,820 9 .04

M6 10–05–00 .01 6,940 52 <.01
CHARACTERIZATION OF SELENIUM IN CEDAR CREEK AND LOUTZENHIZER ARROYO 23

sites over a period of almost 9 years, and selenium 

loads at the four sites are not equivalent.

Additional factors complicate obtaining an 

accurate estimate of selenium loading from the upper 

Loutzenhizer Arroyo Basin using the available data. 

During the irrigation season, tailwater from the 

Loutzenhizer Canal (site M4 in fig. 8 and table 5) 

discharges into the middle branch, so some of the load 

measured in the middle branch of the arroyo downstream from that site might include part of the load 

associated with the canal tailwater. However, not all of 

the tailwater necessarily remains in the middle branch 

because there is a diversion ditch on the arroyo 

between sites M5 and LZ1, and the ditch discharges 

into the Selig Canal immediately downstream from 

site LZ1 (fig. 8). Therefore, throughout the irrigation 

season (April through October), an unknown portion 

of the flow in Loutzenhizer Arroyo upstream from 

site LZ1 is diverted into the Selig Canal and flows out 

of the Loutzenhizer Arroyo drainage basin. Site M3 

would be a better location to determine selenium load 

for the middle branch, but only one sample was 

collected at that site. Natural runoff from the Mancos 

Shale hills in the upper basin was accounted for in the 

sampling because two samples for site LZ2 were 

collected in March 1992 and March 1993 during 

snowmelt runoff. Data probably are not sufficient to 

determine annual selenium loads for the south branch 

(site M2) and north branch (site M6) of Loutzenhizer 

Arroyo, but the data in table 5 indicate that the loads in 

those branches are relatively small. At low streamflow, 

high selenium concentrations at site M2 (table 5) in 

the south branch along Landfill Road were likely 

caused by some saline seeps near the head of the 

drainage. Because the south branch discharges into the 

Loutzenhizer Canal near Flat Top (fig. 8), an unknown 

part of the selenium load in the canal came from the 

south branch of Loutzenhizer Arroyo.

To further complicate the determination of selenium loading and sources in the upper Loutzenhizer 

Arroyo Basin, part of the selenium load is composed 

of irrigation-drainage water and tailwater from 

Bostwick Park (fig. 8), which is not in the Loutzenhizer drainage basin. During the irrigation season, irrigation tailwater is occasionally discharged from the 

west side of Bostwick Park into the south branch of the 

arroyo. The samples collected at site M2 in July and 

October 2000 reflect tailwater discharge into the south 

branch (table 5). Part of the tailwater and drainage 

water collected in a drainage ditch in lower Bostwick 

Park (site M1; fig. 8) is used to irrigate some fields in 

the upper Loutzenhizer Basin. Before the Bostwick 

Ditch flows into Red Rock Canyon, a diversion from 

the Bostwick Ditch carries part of flow into the head of 

the middle branch (fig. 8). The diverted Bostwick 

Ditch water is used for irrigation of the fields (fig. 8) in 

the middle and north branch drainages. The Bostwick 

Ditch water has moderate levels of selenium and selenium load (site M1 in table 5). The selenium load 

diverted into Loutzenhizer Arroyo from Bostwick Park 

has not been quantified.

 Because much of the Loutzenhizer Arroyo 

Basin contains Mancos Shale outcrops or soils derived 

from the shale, sources of selenium are widespread in 

the Loutzenhizer Basin. About 12,000 acres of irrigated land in the Loutzenhizer Arroyo Basin are 

served by the Uncompahgre Project (Bureau of Reclamation, 1982) with the associated canals, laterals, and 

ditches. The Uncompahgre Project lands are essentially all irrigated land shown in figure 8 west of the 

Loutzenhizer and Selig Canals. A hydrosalinity study 

of the Uncompahgre Project (Bureau of Reclamation, 

1982) concluded that salt loading from the project was 

primarily from distribution-system leakage and deep 

percolation from fields. If selenium loading is occurring from the same sources as salt, then much of the 

selenium load in Loutzenhizer Arroyo probably is 

derived from irrigation drainage. Because there is less 

residential and urban development in the Loutzenhizer 

Arroyo Basin compared to the Cedar Creek Basin, 

sources of selenium from septic tanks, lawns and 

gardens, golf courses, and ponds would be less important in the Loutzenhizer Basin than in the Cedar Creek 

Basin at this time (2001). Except for surface inflows 

measured upstream from the Selig Canal, the hydrosalinity study assumed that natural sources of salt load 

on the east side of the Uncompahgre Valley were small 

and attributed less than 1 percent of the salt load to 

natural ground-water discharge (Bureau of Reclamation, 1982). The study by Bureau of Reclamation used 

mass-balance methods and investigations of shallow 

ground water in the Loutzenhizer Arroyo Basin to estimate salt loads. Studies of deep ground-water flow in 

the Mancos Shale in the lower Gunnison River Basin 

have not been done. Selenium sources in the Loutzenhizer Basin outside of the Uncompahgre Project 

include episodic periods of natural runoff from the 

upper basin, discharge of irrigation return flows and 

drainage water from Bostwick Park, and subsurface 

drainage and return flows from irrigated fields upgradient from the project.
24 Characterization of Selenium in the Lower Gunnison River Basin, Colorado, 1988–2000

SUMMARY

Studies by the National Irrigation Water Quality 

Program (NIWQP) since 1988 have reported high 

selenium concentrations in some water, bottom sediment, and biota samples collected in the lower 

Gunnison River Basin. A planning effort was started in 

1994 by the NIWQP to examine possible remediation 

methods for selenium in the basin. In 1997, the State 

Water Quality Control Commission changed the selenium standard for the Gunnison River Basin from 

17 g/L to 5 g/L, which resulted in the lower 

Gunnison River, the lower Uncompahgre River, and 

some other water bodies in the lower basin being out 

of compliance for selenium. The Gunnison River 

Basin Selenium Task Force (Task Force), composed of 

various government agencies, irrigators, and local residents in the lower Gunnison River Basin, was formed 

in 1998 to address the selenium concerns. As part of 

its investigations, the Task Force decided more information was needed about tributary selenium loading to 

the Gunnison River. Data collected previously for the 

NIWQP indicated that Cedar Creek and Loutzenhizer 

Arroyo contributed the largest selenium loads to the 

Uncompahgre River. In 1999, the USGS began studies 

to characterize tributary selenium concentrations and 

loads to the lower Gunnison River and to characterize 

selenium concentrations and loads within the Cedar 

Creek and Loutzenhizer Arroyo Basins.

Sampling of Gunnison River tributaries 

included the North Fork Basin plus tributary streams 

downstream from the Smith Fork to Whitewater. 

Seasonal sampling was done from April 1999 to 

March 2000. To provide detailed characterization of 

selenium loads in Cedar Creek and Loutzenhizer 

Arroyo, tracer studies using bromide were done. The 

Cedar Creek study was done in November 1999 and 

the Loutzenhizer Arroyo study in February 2000.

In water years 1999 and 2000, the North Fork of 

the Gunnison River accounted for about 7 percent of 

the selenium load in the Gunnison River at Whitewater. Selenium concentrations in the main stem of the 

North Fork and in tributaries at or upstream from 

Paonia were less than 5 g/L, and many concentrations were less than 1 g/L. Selenium concentrations 

were greater than 5 g/L in most of the tributaries 

sampled downstream from Paonia. The largest selenium loads were from Bell, Cottonwood, and Leroux 

Creeks and Short Draw.

In the reach downstream from the North Fork to 

the Uncompahgre River (including the Smith Fork), 

the Smith Fork and Tongue Creek had median selenium concentrations less than 5 g/L, and the eight 

other sampled tributaries had selenium concentrations 

greater than 5 g/L. The largest measured selenium 

loads into the Gunnison River between the North Fork 

and Delta were from Sunflower Drain and the 

Bonafide Ditch, where selenium loads are derived 

primarily from irrigation drainage and return flows 

from the east side of the Uncompahgre Valley, south of 

the Gunnison River. The selenium loads in each of 

those two drains were equal to or slightly greater than 

the selenium load from the entire North Fork Basin. 

Selenium loads in tributaries north of the river were 

much less than from Sunflower Drain and Bonafide 

Ditch, but there were moderate selenium loads in 

Currant Creek and Tongue Creek. Small streams such 

as Sulphur Gulch and Lawhead Gulch had selenium 

concentrations greater than 5 g/L, but selenium loads 

were not significant because of low measured streamflow in those gulches.

The Uncompahgre River accounted for about 

38 percent of the load in the Gunnison River in water 

years 1988–2000 and discharges the largest selenium 

load to the Gunnison River. Between the 

Uncompahgre River and Whitewater, many samples 

collected from tributaries on the north or east side of 

the Gunnison River had selenium concentrations 

exceeding 5 g/L. Areas north and east of the 

Gunnison River contain outcrops of Mancos Shale. By 

contrast, all samples collected from the tributaries on 

the west side of the Gunnison River downstream from 

Roubideau Creek had selenium concentrations less 

than 2 g/L, and most concentrations were less than 

1 g/L. The largest selenium loads in this reach were 

from Cummings Gulch and lower Roubideau Creek, 

which receive considerable amounts of irrigation tailwater from the west side of the Uncompahgre Valley, 

and in Kannah and Whitewater Creeks, which drain 

some irrigated lands in the Whitewater area. The tributaries in the desert area north of Delta and south of 

Kannah Creek that are unaffected by irrigation probably are ephemeral streams and had low selenium 

loads. Alkali Creek, which drains a small area of irrigated land in Mancos Shale terrain, had much higher 

selenium concentrations, but the selenium loads were 

small because of low streamflow. Runoff from occasional rain and snowmelt events in the nonirrigated 
SUMMARY 25

shale areas can temporarily increase selenium loads 

and concentrations in the lower Gunnison River.

A tracer study was done on Cedar Creek from 

Miguel Road to below Highway 50 in November 

1999. Selenium concentrations at main-stem sites 

ranged from 12 to 28 g/L. The gain in selenium load 

between Miguel Road and Highway 50 was about 

3.5 lb/d. The largest selenium load into Cedar Creek 

was from Montrose Arroyo, which accounted for 

about 32 percent of the load in Cedar Creek that was 

measured downstream from Highway 50. The Cedar 

Creek Basin upstream from Miguel Road accounted 

for 27 percent of the selenium load in November 1999. 

Of the remaining selenium load, 23 percent was from 

the reach between Miguel Road and Montrose Arroyo 

and 18 percent from the lower reach downstream from 

Montrose Arroyo. Load increases were associated 

with surface inflows from drainage ditches and from 

canals and laterals that were carrying small quantities 

of ground-water seepage. Selenium loading from 

diffuse ground-water discharge into Cedar Creek probably was widespread, but generally the loads were 

small. This study did not distinguish selenium sources, 

but it is likely that the largest source of selenium to 

Cedar Creek downstream from Miguel Road is the 

result of seepage from canals, laterals, and ditches and 

deep percolation from irrigated fields. Other sources 

include deep percolation from residential lawn and 

garden watering, golf course watering, septic systems, 

and natural runoff and leakage from ponds.

Using periodic data collected from 1991 to 

2000, the estimated annual selenium load from upper 

Cedar Creek Basin (upstream from Miguel Road) was 

about 20 percent of the annual load in Cedar Creek 

downstream from Highway 50. A limited synoptic 

study of the upper basin in November 1999 indicates 

highly variable selenium concentrations. The selenium 

load in the upper Cedar Creek Basin is probably 

derived from a combination of natural recharge and 

runoff from the landslide areas, deep percolation from 

irrigated fields, and irrigation canal and ditch seepage. 

A tracer study on Loutzenhizer Arroyo was 

done between the Selig Canal and the mouth of the 

arroyo in February 2000. Synoptic sampling was done 

on the west tributary of Loutzenhizer Arroyo. Selenium concentrations ranged from 155 to 347 g/L in 

the main arroyo and 125 to 151 g/L in the west tributary. Detailed determination of selenium loading was 

limited because of various problems that invalidated 

some of the tracer data that were needed to calculate 

stream discharges. 

Selenium concentrations increased from 184 to 

331 g/L in a 1.4-mi reach in upper Loutzenhizer 

Arroyo between site LZ2 and site LZ4 with an associated increase in load of 1.4 lb/d. Selenium concentrations were greater than 300 g/L in Loutzenhizer 

Arroyo from LZ4 to the confluence with the west tributary. Inflow from the west tributary caused a decrease 

in selenium concentrations in the main stem of the 

arroyo from 310 to 189 g/L. Downstream from the 

west tributary, selenium concentrations gradually 

decreased in Loutzenhizer Arroyo. There was a gain in 

streamflow in the lower reach; however, selenium 

concentrations in the arroyo generally decreased from 

this point. The reduction most likely resulted from 

drain ditch inflows and diffuse ground-water inputs 

downstream from the west tributary having lower selenium concentrations.

In February 2000, an estimated 12 percent of the 

selenium load in Loutzenhizer Arroyo was from the 

upper basin upstream from the Selig Canal, 38 percent 

from the reach between the Selig Canal and the west 

tributary, 41 percent from the west tributary, and 

9 percent from the lower reach downstream from the 

west tributary. Results of the 2000 study differ from 

those of a synoptic study of Loutzenhizer Arroyo done 

in March 1992. The study in March 1992 had a much 

higher percentage (36 percent) of the selenium load 

from areas upstream from the Selig Canal, which 

might have been caused in part by snowmelt runoff, 

which did not occur during the February 2000 study. 

Because many more samples were collected in 2000 

than in 1992, the selenium concentrations shown in 

figure 9 are assumed to be more representative of 

present-day selenium concentrations during low-flow 

conditions in the lower reach of Loutzenhizer Arroyo 

than are the two samples from March 1992.

The major land use in the Loutzenhizer Arroyo 

Basin is irrigated agriculture, and the largest source of 

selenium loading in the basin is expected to be from 

canal and lateral leakage and deep percolation from 

fields. A part of the selenium load in Loutzenhizer 

Arroyo probably is from natural runoff in the upper 

basin from episodic rain and snowmelt events. Selenium also is transported into the headwater drainages 

of Loutzenhizer Arroyo in irrigation tailwater diverted 

from Bostwick Park.
26 Characterization of Selenium in the Lower Gunnison River Basin, Colorado, 1988–2000

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