Streamwater Quality at Selected Sites 

in the Fraser River Basin, Grand County, 

Colorado, Water Years 1991–2000

By Jeffrey B. Bails

Water-Resources Investigations Report 03–4087

U.S. Department of the Interior

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

Gale A. Norton, Secretary

U.S. Geological Survey

Charles G. Groat, Director

U.S. Geological Survey, Reston, Virginia: 2003

For sale by U.S. Geological Survey, Information Services

Box 25286, Denver Federal Center

Denver, CO 80225

For more information about the USGS and its products:

Telephone: 1-888-ASK-USGS

World Wide Web: http://www.usgs.gov/

Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply 

endorsement by the U.S. Government.
iii

Contents

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

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

Basin Characteristics.......................................................................................................................... 1

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

Data Collection and Analysis...................................................................................................................... 2

Streamwater-Quality Results...................................................................................................................... 4

Stream Standards................................................................................................................................ 4

Spatial Distribution of Selected Water-Quality Constituents, Water Year 2000 ........................ 5

Temporal Trends................................................................................................................................... 7

Summary ........................................................................................................................................................ 9

References Cited .......................................................................................................................................... 9

Figures

 1. Map showing the Fraser River Basin ....................................................................................... 2

 2. Map showing spatial distribution and magnitude of median concentrations of 

selected water-quality constituents in the Fraser River Basin, 1991–2000 ....................... 6

 3. Graph showing downstream median instantaneous load of selected constituents 

in the Fraser River Basin, 1991–2000 ........................................................................................ 7

 4. Graphs showing median instantaneous load for each month of selected constituents 

and monthly median discharge in the Fraser River at Tabernash, site 4, 1991–2000 ....... 8

Tables

 1. Characteristics of selected streamwater-quality sites in the Fraser River Basin............ 3

 2. Summary of median values of field-determined constituents at 13 sites in the 

Fraser River Basin, 1991–2000 ................................................................................................... 3

 3. Summary of median concentrations of selected water-quality constituents at 

13 sites in the Fraser River Basin, 1991–2000.......................................................................... 4

 4. Results of the seasonal Kendall test for trends on selected nutrient species in 

the Fraser River Basin, 1991 and 1995 through 2000.............................................................. 9
Abstract

To determine the effect of population growth on streamwater quality in the Fraser River Basin, the U.S. Geological 

Survey did a study in cooperation with the Grand County 

Commissioners and the East Grand County Water 

Quality Board. During water years 1991 through 2000, 

the study determined that concentrations of un-ionized ammonia and nitrite plus nitrate in the streamwater of the basin are 

within Colorado State streamwater–quality standards. The 

study also found that concentrations of chloride are largest at 

the headwaters and decrease downstream; however, chloride 

loading in the stream has the opposite relation. Most nutrient 

loading to the Fraser River happens January through May. 

Concentrations of ammonia at Fraser River downstream from 

Vasquez Creek at Winter Park had a downward trend through 

the period of the study. Nitrite plus nitrate had upward and 

downward trends at different sites and over different time 

spans. Orthophosphorus concentrations had upward trends 

at two sites. In general, the streamwater quality in the Fraser 

River Basin is good and is not out of compliance with State 

standards.

Introduction

The Fraser River Basin in the southeastern part of 

Grand County, Colorado, encompasses about 287 square 

miles (fig. 1). The Fraser River originates at the Continental 

Divide in the Arapaho National Forest, flows about 29 miles 

in a northerly direction through the towns of Winter Park, 

Fraser, Tabernash, and Granby, and joins the Colorado River 

2 miles downstream from Granby. A more detailed discussion 

of the characteristics of the Fraser River Basin is found in 

Apodaca and Bails (1999). The population of Grand County 

increased more than 56 percent between 1990 and 2000 

(2000 census population of 12,442) and increased more than 

300 percent since 1970 (U.S. Census Bureau, 2001). These 

population statistics do not include the thousands of people 

that visit the Fraser River Basin each year to enjoy the many 

year-round recreational activities and place demands on the 

water resources of the basin. The Fraser River upstream from 

the town of Tabernash is currently the recipient of wastewater 

discharges from three wastewater-treatment plants that serve 

the Winter Park ski area, the town of Winter Park, and the 

town of Fraser (fig. 1). Local water managers are concerned 

about the effects of population growth on streamwater quality. 

To address this need, the U.S. Geological Survey, in cooperation with the Grand County Commissioners and the East 

Grand County Water Quality Board, conducted a study of 

streamwater quality in the Fraser River Basin.

Basin Characteristics

The land-surface elevation of the Fraser River Basin 

ranges from about 12,500 feet at Berthoud Pass to about 

7,860 feet at the mouth of the Fraser River. The major tributaries to the Fraser River are Vasquez, St. Louis, Crooked, Ranch, 

Strawberry, and Tenmile Creeks. In the upper reaches of the 

Fraser River, three hydrologic modifications divert water from 

St. Louis Creek, Vasquez Creek, and the main stem of the 

Fraser River to the Moffat Water Tunnel system. According 

to the Colorado Water Quality Control Division (1989), these 

diversions have the potential to reduce streamflow substantially and compound water-quality problems in the Fraser 

River Basin.

Climatic data for Fraser from 1989 through the end of 

2000 indicate that the average monthly maximum and minimum temperatures are 75.7 degrees Fahrenheit in July and

–3.9 degrees Fahrenheit in December. Average annual precipitation for Fraser is 19.2 inches, which includes an average 

annual snowfall of 154 inches. At Berthoud Pass, the headwaters of the Fraser River, the average annual precipitation 

from 1950 through 1985 is 37.5 inches, which includes an 

average annual snowfall of 391 inches (Western Regional 

Climate Center, 2001).

Streamwater Quality at Selected Sites in the Fraser River 

Basin, Grand County, Colorado, Water Years 1991–2000

By Jeffrey B. Bails
2 Streamwater Quality at Selected Sites in the Fraser River Basin, Grand County, Colorado, Water Years 1991–2000

Purpose and Scope

This report presents an overview of the general streamwater quality at 13 sites in the Fraser River Basin during 

water years 1991–2000, and focuses primarily on chloride, 

nutrient, pH, dissolved oxygen, and fecal coliform bacteria 

data (a water year is defined as the 12-month period from 

October 1 through September 30 of the named year). Data 

from these sites were compared to Colorado’s current State 

stream-segment water-quality standards (hereinafter referred 

to as “State standards”) for the Fraser River established by the 

Colorado Water Quality Control Commission (2001). Under 

these guidelines, the Fraser River and its tributaries are under 

the designations of the Upper Colorado River segments 9 

and 10. The data were compared spatially in downstream 

order and assessed for trends at selected sites that had at 

least 5 years of monthly data.

Data Collection and Analysis

Water-quality data were collected between 

October 1, 1990, and September 30, 2000, at 13 stream 

sites (fig. 1, tables 1, 2, and 3). These sites include six 

sites on the main stem of the Fraser River, four sites 

on Crooked and Pole Creeks, and three sites on Ranch 

and Hurd Creeks. Three sites have data spanning the 

entire period of record while the other sites have partial 

records (table 1). All data for this report were collected 

and analyzed by the U.S. Geological Survey using 

methods described in Fishman (1993) and Fishman and 

Friedman (1989). Water-quality samples were collected 

using the equal-width increment (EWI) method and 

processed using steps outlined in the U.S. Geological 

Survey National Field Manual (U.S. Geological Survey, 

1999).

Figure 1. The Fraser River Basin.

Fraser

River

anch Creek

C

1

105°45'

105°52'30"

39°52'30"

40°

106°

0 2 4 6 MILES

0 2 4 6 KILOMETERS

Tabernash

R

Creek

reek

n

b

Fraser

4

5

8 9

10 12

13

Stra w erry

Te

mile

EXPLANATION

Wastewater treatment plant

Continental divide

Arapahoe National Forest

Private property

U.S. Highway 40

COLORADO

1 Sampling site with site number

6

11

2

3

7

Fraser River

Basin

Grand County

Granby

Pole Creek

CONTINENTAL DIVIDE

CONTIN

E

NTAL DIVIDE

Colorado River

Winter Park

Moffat Water Tunnel

Vasquez Water 

Tunnel

Berthoud

Pass

Vasquez Creek

Crooked Creek

Hurd Creek
Data Collection and Analysis 3

Table 1. Characteristics of selected streamwater-quality sites in the Fraser River Basin.

[USGS, U.S. Geological Survey]

Site

number

(fig. 1)

Site 

name

USGS station

identification

number

Period of 

record in 

water years1

Elevation,

in feet above

sea level

Fraser River

 1 Fraser River at Upper Station, near Winter Park, CO 09022000 1994–2000 9,520

 2 Fraser River below Buck Creek at Winter Park, CO 09023750 1991–2000 9,020

 3 Fraser River below Vasquez Creek at Winter Park, CO 09025010 1991–2000 8,710

 4 Fraser River at Tabernash, CO 09027100 1991–2000 8,350

 5 Fraser River below Crooked Creek at Tabernash, CO 09033300 1991–1994

1999–2000

8,270

 6 Fraser River at Highway 40 at Granby, CO 400453105554200 2000 7,920

Crooked and Pole Creeks

 7 Crooked Creek below Tipperary Creek near Tabernash, CO 395634105532401 1997–2000 8,690

 8 Crooked Creek above Pole Creek at Tabernash, CO 395927105505700 2000 8,360

 9 Pole Creek at Upper Station near Tabernash, CO 395901105550800 1997–2000 8,640

 10 Pole Creek at mouth near Tabernash, CO 395930105510700 1997–2000 8,320

Ranch and Hurd Creeks

 11 Ranch Creek near Fraser, CO 09032000 1997–2000 8,660

 12 Hurd Creek below Trail Creek near Tabernash, CO 395947105481000 1999–2000 8,860

 13 Ranch Creek below Meadow Creek near Tabernash, CO 09033100 1997–2000 8,350

1

A water year is the 12-month period from October 1 until September 30 of the named year.

Table 2. Summary of median values of field-determined constituents at 13 sites in the Fraser River Basin, 1991–2000.

[ft3/s, cubic feet per second; mg/L, milligrams per liter; cols/100ml, colonies per 100 milliliters; μS/cm, microsiemens per centimeter at 25 degrees Celsius; 

<1, not detected; --, no data]

Site

number

(fig. 1)

Site 

name

Discharge

(ft3

/s)

pH Dissolved

oxygen

(mg/L)

Fecal

coliform

bacteria

(cols/100ml)

Specific

conductance

(μS/cm)

 1 Fraser River at Upper Station, near Winter Park, CO 6.2 8.1 10.0 -- 84

 2 Fraser River below Buck Creek at Winter Park, CO 7.6 8.0 9.9 -- 91

 3 Fraser River below Vasquez Creek at Winter Park, CO 19 7.9 10.0 -- 78

 4 Fraser River at Tabernash, CO 28 8.0 9.9 -- 97

 5 Fraser River below Crooked Creek at Tabernash, CO 48 8.2 9.8 17 119

 6 Fraser River at Highway 40 at Granby, CO 47 8.1 10.3 <1 120

 7 Crooked Creek below Tipperary Creek near Tabernash, CO 2.2 8.1 9.8 <1 174

 8 Crooked Creek above Pole Creek at Tabernash, CO 4.3 8.1 10.1 5 218

 9 Pole Creek at Upper Station near Tabernash, CO 0.9 8.0 9.2 3 125

 10 Pole Creek at mouth near Tabernash, CO 2.3 8.1 9.6 <1 274

 11 Ranch Creek near Fraser, CO 4.2 8.0 10.4 <1 48

 12 Hurd Creek below Trail Creek near Tabernash, CO 3.4 7.8 10.5 <1 43

 13 Ranch Creek below Meadow Creek near Tabernash, CO 14.2 8.0 9.8 2 76
4 Streamwater Quality at Selected Sites in the Fraser River Basin, Grand County, Colorado, Water Years 1991–2000

Water samples were analyzed for dissolved chloride, dissolved or total ammonia, dissolved or total nitrite plus nitrate, 

dissolved and total phosphorus, dissolved orthophosphorus, 

and fecal coliform bacteria. Properties measured at the time 

of sample collection include water temperature, pH, specific 

conductance, and dissolved oxygen. The dissolved phase of 

water-quality constituents was obtained by filtering sampled 

water through a 0.45-μm (micrometer) filter; total concentrations are from unfiltered samples. Nutrient samples (ammonia, 

nitrite plus nitrate, phosphorus, and orthophosphorus) collected in the Fraser River Basin from October 1991 through 

September 2000 were analyzed for either total or dissolved 

concentrations. In general, most samples collected before calendar year 1992 were analyzed for total nutrients. From water 

year 1993 through 2000, water-quality samples were analyzed 

for dissolved nutrients. Total and dissolved concentrations 

only were determined for phosphorus from samples collected 

for the same sampling event. At sites where total and dissolved 

nutrient samples were collected over time, the data were 

aggregated for statistical analysis using the methods outlined 

in Mueller and others (1995). Unless otherwise specified, concentrations in this report represent aggregated concentrations.

Streamwater-Quality Results

Stream Standards

Specific properties and constituents compared to applicable State standards include pH, dissolved oxygen, fecal 

coliform bacteria, un-ionized ammonia, nitrite plus nitrate, and 

chloride. A summary of water-quality data for selected constituents is in tables 2 and 3. Analysis of the data for this report 

indicates that water quality in the Fraser River Basin is generally very good and compares favorably to State standards.

In general, pH measurements from the study sites were 

within the State standard range of 6.5–9. At site 4, the pH 

measurements were greater than the maximum State standard 

for less than 10 percent (29) of the total number (307) of measurements taken. Compliance with State standards, however, 

is determined by comparing the 15th and 85th percentiles 

of the representative water-quality data with the associated 

water-quality standard. For site 4, the 15th and 85th percentile 

values for pH were equal to 7.6 and 8.8, respectively, which is 

Table 3. Summary of median concentrations of selected water-quality constituents at 13 sites in the Fraser River Basin, 1991–2000.

[mg/L, milligrams per liter]

Site

number

(fig. 1)

Site 

name

Chloride

(mg/L)

Ammonia

(mg/L)

Nitrite

plus nitrate

(mg/L)

Dissolved

phosphorus

(mg/L)

Orthophosphorus

(mg/L)

Total

phosphorus

(mg/L)

 1 Fraser River at Upper Station, near

Winter Park, CO

 9.782 0.002 0.084 0.003 0.001 0.050

 2 Fraser River below Buck Creek at

Winter Park, CO

 8.370 0.003 0.075 0.004 0.002 0.050

 3 Fraser River below Vasquez Creek 

at Winter Park, CO

 5.40 0.018 0.127 0.012 0.009 0.050

 4 Fraser River at Tabernash, CO 4.835 0.065 0.169 0.062 0.051 0.102

 5 Fraser River below Crooked Creek 

at Tabernash, CO

 3.48 0.034 0.085 0.031 0.027 0.059

 6 Fraser River at Highway 40 at 

Granby, CO

 4.010 0.030 0.140 0.040 0.040 0.060

 7 Crooked Creek below Tipperary Creek

near Tabernash, CO

 0.280 0.004 0.006 0.007 0.005 0.041

 8 Crooked Creek above Pole Creek at 

Tabernash, CO

 2.915 0.007 0.005 0.015 0.010 0.041

 9 Pole Creek at Upper Station near 

Tabernash, CO

 0.380 0.005 0.008 0.017 0.013 0.050

 10 Pole Creek at mouth near Tabernash, CO 2.04 0.008 0.025 0.021 0.017 0.051

 11 Ranch Creek near Fraser, CO 0.251 0.002 0.033 0.004 0.003 0.030

 12 Hurd Creek below Trail Creek near 

Tabernash, CO

 0.405 0.004 0.005 0.004 0.002 0.050

 13 Ranch Creek below Meadow Creek 

near Tabernash, CO

 0.515 0.003 0.035 0.012 0.007 0.050
Streamwater Quality Results 5

within the range of 6.5–9. Dissolved-oxygen concentrations 

for all sites and samples exceeded the State standard for the 

Fraser River Basin set at a minimum of 6.0 mg/L (milligrams 

per liter). This is an indication that there were no detrimental 

processes taking place in the streamwater that would consume 

oxygen beyond a threshold that would make the water toxic to 

many aquatic species.

Fecal coliform bacteria samples were collected at 9 of 

the 13 study sites. The State standard for fecal coliform in the 

Fraser River Basin is 200 cols/100 mL (colonies per 100 milliliters), with compliance defined as when the geometric mean 

of all representative water samples at a site does not exceed 

the standard. The geometric mean for all nine sites ranged 

from 1.6 to 10.5 cols/100 mL. A few samples exceeded the 

State standard at sites 7, 8, and 9 during the summer. The 

larger concentrations may be attributed to reduced streamflows 

and increased recreational use, or the presence of livestock 

near the headwaters of these tributaries, or both.

Un-ionized ammonia (NH3

) concentrations were calculated from ammonium (NH4

+

) concentrations for all sites 

where dissolved ammonia, temperature, and pH data were 

collected. The percentage of ammonium ion concentration 

that is in the un-ionized form is a function of the pH and 

water temperature at the time of sample collection. Because 

the un-ionized form of ammonia is the most toxic to aquatic 

life, it is the one on which stream standards are based. The 

chronic State standard for un-ionized ammonia for the Fraser 

River Basin is set at 0.2 mg/L. The acute State standard for 

un-ionized ammonia is defined as a table value standard (TVS) 

(Colorado Water Quality Control Commission, 2001) and is 

a function of the pH and temperature of the water. The acute 

TVS concentration for un-ionized ammonia was calculated 

for each sample and compared to the calculated un-ionized 

ammonia concentration. Un-ionized ammonia concentrations 

in all streamwater samples did not exceed the calculated acute 

TVS or chronic standard.

State standards for nitrite plus nitrate (as nitrogen) and 

chloride in the Fraser River Basin are 10 mg/L and 250 mg/L, 

respectively, and concentrations did not exceed the standards 

at any site. The maximum concentration for nitrite plus nitrate 

for all samples was 0.88 mg/L at site 4. The maximum concentration of chloride for all samples was 75 mg/L at site 1. The 

highest concentrations for chloride were at site 1 for samples 

collected during the early spring. The high concentrations at 

site 1 may result from spring runoff flushing salts from the 

accumulated road gravel/salt applications on Berthoud Pass 

during the winter.

National or local standards for total phosphorus or 

orthophosphorus concentrations in streamwater have not 

been established, although the U.S. Environmental Protection 

Agency (USEPA) has set a recommended maximum concentration of 0.1 mg/L of total phosphorus for flowing water 

that does not directly discharge into a lake or reservoir 

(U.S. Environmental Protection Agency, 1986). Total phosphorus concentrations exceeded the guideline at three sites 

(sites 5, 10, and 12) during the period of record for this study 

in one or two samples per site. At site 4, 58 percent (18 of 

31 samples) of the samples collected exceeded the guideline. These large concentrations primarily happened during 

February through March, before spring runoff.

Currently (2002), the USEPA is revising its guidelines on 

nutrient concentrations in streams and rivers to focus on more 

regionally dependent recommendations for the prevention of 

eutrophication, or the excessive growth of aquatic plants.

Spatial Distribution of Selected Water-Quality 

Constituents, Water Year 2000

To spatially represent the condition of the streamwater 

quality in the Fraser River Basin, rankings of median concentrations for the nutrient constituents (ammonia, nitrite plus 

nitrate, dissolved phosphorus, orthophosphorus, and total 

phosphorus) and chloride were plotted in map form (fig. 2). 

The median concentrations at each site were compared to the 

25th, 50th, and 75th percentiles of all data collected during 

the study in order to assess the spatial variance for each 

constituent.

Nutrient concentrations in the Fraser River increased 

downstream as water flowed through the towns of Winter 

Park and Fraser. The most likely sources of these nutrients are 

the three wastewater-treatment plants that discharge effluent 

into the Fraser River. Some dilution and possible uptake by 

biological processes of nitrite plus nitrate and dilution of total 

phosphorus occurred downstream from the mouths of Ranch 

and Crooked Creeks where nutrient concentrations were 

lower than the Fraser River. At the most downstream site near 

Granby (site 6), concentrations of nitrite plus nitrate and total 

phosphorus were large, indicating that nutrient input exceeded 

the physical, chemical, and biological processes that tend to 

decrease nutrient concentrations and may be influenced by the 

agricultural land use that is prevalent in the lower part of the 

basin.

Chloride concentrations were highest in the upper 

reaches of the Fraser River and tended to decrease downstream. Tributaries to the Fraser River had the lowest chloride 

concentrations and contributed to the dilution of chloride as 

water traveled downstream. A likely source for the chloride in 

the upper reaches of the Fraser River is road salts applied with 

gravel for traffic safety.

In addition to concentrations, chemical loading also was 

evaluated for selected water-quality constituents. Although 

concentration data are useful for comparison to water-quality 

standards, loading data indicate the mass of a chemical transported past a site. Loading information is necessary for the 

State Total Maximum Daily Load (TMDL) process and can 

be useful in understanding chemical deposition in downstream 

surface-water storage features. Loads only were calculated 

at sites 1 through 5 on the main stem of the Fraser River. 

Many possible irrigation diversions exist between sites 5 

and 6 and could give rise to erroneous loading values. Values 

for constituent loading were calculated by multiplying the 
6 Streamwater Quality at Selected Sites in the Fraser River Basin, Grand County, Colorado, Water Years 1991–2000

instantaneous chemical concentration by the instantaneous discharge. Loading values then were multiplied by a conversion 

factor to yield values in tons per day. Median instantaneous 

loads were calculated for samples at each site from all data 

for the period of record.

Analysis of the instantaneous load data on the main stem 

of the Fraser River showed similar results to the concentration 

data: the majority of the inputs of nutrients in the streamwater 

was between sites 3 and 4 (fig. 3). The reduction of nitrite plus 

nitrate and orthophosphorus loads downstream from site 4 

indicated that physical, chemical, or biological processes that 

remove nutrients from the streamwater were greater than input 

sources. The continual increase in total phosphorus load may be 

a result of increased sediment loads in the river, which are commonly high in insoluble phosphorus. Data collected for chloride 

show that about one-third of the total load of chloride in the 

entire Fraser River is present by the time the water reaches 

site 1. The gradual increase in loads may be an indication 

of ground-water discharge to the stream, inputs from the 

wastewater-treatment plants, and inputs from tributaries.

In order to assess the monthly loading of nutrients and 

chloride in the Fraser River, median instantaneous loads for 

all monthly data from site 4 are shown in figure 4. This site 

is used because monthly samples are available for the entire 

period of study, and the site is located downstream from the 

wastewater-treatment plants. Monthly median stream discharge is included in figure 4 to show the relation between 

loads and streamflow conditions. Peak nutrient loads began in 

early spring before the onset of spring runoff, and loadings to 

the Fraser River were largest between January and May. The 

large loads in the Fraser River between January and May most 

likely resulted from the increased seasonal population and 

Fraser

River

St. Louis

Vasquez

Pole

Crooked

Ranch

Hurd

Moffat Water Tunnel

Vasquez

Water Tunnel

Creek

Creek

Creek

Creek

Creek

Creek

Creek

Creek

Tenmile

Stra wberry

7

12

0 2 4 6 MILES

0 2 4 6 MILES

39°52'30"

40°

106°

105°52'30"

105°45'

5

1

2

3

4

5

6

8 9 10

11

13

Fraser

Winter

Park

Tabernash

EXPLANATION

Sampling site with site number

Wastewater treatment plant

Median is greater than the 75th percentile

Median is greater than the 50th percentile and

less than or equal to the 75th percentile

Median is greater than the 25th percentile and

less than or equal to the 50th percentile

Median is less than or equal to the 25th percentile

No data available

Continental divide

Chloride Ammonia

Nitrite

plus

nitrate

Dissolved

phosphorus

Orthophosphorus

Total

phosphorus

Percentiles of nutrient concentrations

in milligrams per liter

Chloride Ammonia

Nitrite

plus

nitrate

Dissolved

phosphorus

Orthophosphorus phosphorus

Total

25th

50th

75th

0.525 0.002 0.005 0.006 0.002 0.018

2.925 0.006 0.064 0.014 0.010 0.041

6.510 0.014 0.125 0.029 0.023 0.059

Granby

Colorado

River

CONTINENTAL DIVIDE

CO

N

TINEN

TAL DIVIDE

Figure 2. Spatial distribution and magnitude of median concentrations of selected water-quality constituents in the Fraser River 

Basin, 1991–2000.
Streamwater Quality Results 7

associated inputs to the wastewater-treatment plants during 

the ski season. With the onset of high flow at the end of the 

ski season, loads decreased significantly. Chloride loading, 

however, seems to more closely reflect streamflow conditions. This scenario supports the concept that the source of 

chloride in the river is a combination of a nonpoint source, 

possibly from the salt and gravel applications on the roadways in the basin and discharges from the wastewatertreatment plants. The reduction in loads during early spring 

runoff is an indication that either most of the road salts are 

removed during initial runoff or runoff from near the highway 

is reduced.

Temporal Trends

The seasonal Kendall test (Helsel and Hirsh, 1992) was 

used to test for trends in water quality (table 4). Trend analysis 

was completed on sites 1–4 on the main stem of the Fraser 

River. These sites had at least 5 years of monthly data. Trend 

analysis was performed on ammonia, nitrite plus nitrate, 

and orthophosphorus because these constituents are directly 

related to biological responses in the river. The null hypothesis 

for trend testing in this report is no change in concentration 

over time when compared seasonally. The null hypothesis is 

rejected, indicating that there is a trend, if the p-value (or 

probability value) of the test is less than the alpha level, which 

for this report is set at 0.05. This alpha level (or acceptable 

error) requirement means that there is a 5-percent chance that 

a trend is mistakenly identified and the null hypothesis is true 

(Helsel and Hirsch, 1992). Trend analysis was done on the 

raw, or unadjusted, concentrations to assess trends in ambient stream conditions, which is desirable in relation to human 

or aquatic organism water use. Where applicable, a LOcally 

WEighted Scatterplot Smoothing (LOWESS) procedure 

(Cleveland, 1979) was used to flow-adjust concentrations 

before trend analysis. This procedure will account for variability of chemical concentrations due to streamflow (flow) 

and provide greater insight about the sources of nutrients to 

the Fraser River. The LOWESS smoothing procedure and 

recalculation of trends were performed only on data sets that 

contained less than 10 percent censored (less than the laboratory minimum reporting level) concentrations. If a trend was 

calculated on the flow-adjusted concentrations, the trend slope 

(the magnitude of the trend expressed in units per year) was 

listed only to indicate relative magnitude because the trend 

analyses for these sites were computed on flow-adjusted concentrations and not the raw concentrations. Where some of the 

concentrations were censored (below the laboratory reporting 

level), trend analyses on the raw data were performed twice 

at each site, once with the censored data set at the minimum 

reporting level and again with the censored data set to zero. In 

28 26 24 22 20 18 16 14 12 10

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

CHLORIDE LOAD, IN TONS PER DAY

MILES UPSTREAM OF MOUTH OF THE FRASER RIVER

0

0.002

0.004

0.006

0.008

0.010

0.012

0.014

0.016

0.018

0.020

NUTRIENT LOAD, IN TONS PER DAY

Wastewater-treatment

plant locations

Ammonia

Nitrite plus nitrate

Dissolved phosphorus

Orthophosphorus

Total phosphorus

Chloride

Site 1

Site 2

Site 3

Site 4

Site 5

Figure 3. Downstream median instantaneous load of selected constituents in the Fraser 

River Basin, 1991–2000.
8 Streamwater Quality at Selected Sites in the Fraser River Basin, Grand County, Colorado, Water Years 1991–2000

all cases, the two trend slopes were almost identical, indicating 

little sensitivity to the trend analysis because of the censored 

data.

Trend analyses for ammonia at sites 1 and 2 were not 

done because of the large number (greater than 20 percent) 

of censored concentrations. Only site 3 had a statistically 

significant trend for ammonia and showed a downward trend 

in concentration for 1991–2000.

Nitrite plus nitrate trend analysis revealed two sites 

(sites 1 and 4) with upward trends, although not over the same 

time period, and one site (site 2) with a downward trend. The 

upward trends at site 1 on both the raw and flow-adjusted data 

are likely due to an increase in nitrite plus nitrate sources in 

the upper reaches of the Fraser River. Because the period of 

record for site 1 is different from the other three sites, a direct 

relation in the trend for site 1 cannot be made with the other 

three sites. The trend analysis at site 2 resulted in a downward 

trend on the raw data and no trend on the flow-adjusted data. 

Site 2 results indicate that the inputs of nitrite plus nitrate to 

the Fraser River above site 2 are not changing, but some other 

factor, such as streamflow, chemistry, or biological uptake, 

is causing the concentrations to decrease. The trend results 

from site 4 show the opposite conditions. Although there is 

an upward trend for the flow-adjusted data, indicating a possible increase in the input of nitrite plus nitrate to the stream, 

the raw concentrations remain stable. Trend analysis on 

streamflow measurements at site 4 indicate an upward trend, 

and this relation may be caused by site 4 being located downstream from the three wastewater-treatment plants.

Trend analysis was not done for orthophosphorus 

at sites 1 and 2 because of the large number (greater that 

20 percent) of censored concentrations. Results for the trend 

analyses at sites 3 and 4 indicate upward trends in the orthophosphorus concentrations at both sites. The lack of a trend 

for the flow-adjusted orthophosphorus concentrations at site 4 

indicates that the upward trends may be caused by streamflow 

conditions and not increases in orthophosphorus inputs to the 

river.

MONTH

0

0.005

0.010

0.015

0.020

0.025

0.030

0.035

0.040

0.045

0.050

0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

NUTRIENT LOAD, IN TONS PER DAY CHLORIDE LOAD, IN TONS PER DAY

JAN FEB MAR APR MAY JUNE JULY AUG SEPT OCT NOV DEC

0

50

100

150

200

250

300

Ammonia

Nitrite plus nitrate

Dissolved phosphorus

Orthophosphorus

Total phosphorus

Discharge

0

50

100

150

200

250

300

Chloride

Discharge

DISCHARGE, IN CUBIC FEET 

PER SECOND

DISCHARGE, IN CUBIC FEET 

PER SECOND

Figure 4. Median instantaneous load for each month of selected constituents and monthly median 

discharge in the Fraser River at Tabernash, site 4, 1991–2000.
References Cited 9

Table 4. Results of the seasonal Kendall test for trends on selected nutrient species in the Fraser River Basin, 1991 and 1995 

through 2000.

[mg/L, milligrams per liter; (mg/L)/yr, milligrams per liter per year; <, less than; --, no data]

Site

number

(fig. 1)

Site 

name

Span 

of trend

analysis

Number of 

analyses

Number of 

censored

analyses

Minimum

reporting

level

(mg/L)

Data used 

in trend 

analysis

p-value 

of tau 

test

Trend

direction

Slope

[(mg/L)/yr]

Median

concentration

(mg/L)

Ammonia

3 Fraser River below Vasquez 

Creek at Winter Park, CO

1991–2000 108 22 < 0.002 Raw 0.0001 Down –0.002 0.018

4 Fraser River at Tabernash, CO 1991–2000 108 10 < 0.002 Raw

Flow-adjusted

0.1137

0.4003

None

None

--

--

0.058

Nitrite plus nitrate

1 Fraser River at Upper Station,

near Winter Park, CO

1995–2000 61 2 <0.005 Raw

Flow-adjusted

0.0032

0.0238

Up

Up

0.0057

0.007

0.084

2 Fraser River below Buck 

Creek at Winter Park, CO

1991–2000 100 2 <0.005 Raw

Flow-adjusted

0.0341

0.1335

Down

None

–0.0023

--

0.078

3 Fraser River below Vasquez 

Creek at Winter Park, CO

1991–2000 103 1 <0.010 Raw

Flow-adjusted

0.2056

0.9210

None

None

--

--

0.141

4 Fraser River at Tabernash, CO 1991–2000 105 1 <0.005 Raw

Flow-adjusted

0.2255

0.0414

None

Up

--

0.007

0.174

Orthophosphorus

3 Fraser River below Vasquez 

Creek at Winter Park, CO

1995–2000 61 7 <0.001 Raw 0.0125 Up 0.001 0.010

4 Fraser River at Tabernash, CO 1995–2000 66 0 --- Raw

Flow-adjusted

0.0076

0.0627

Up

None

0.004

--

0.052

Summary

In general, the water in the Fraser River Basin is of 

good quality and compares favorably with State standards. 

A few pH values were greater than State standards, and even 

in these instances, the river was not out of compliance because 

of the limited number of exceedances. Un-ionized ammonia, 

nitrite plus nitrate, and chloride concentrations did not exceed 

any applicable State standard. Concentrations and loads of 

nutrients increased downstream; the largest inputs into the river 

were between Fraser River below Vasquez Creek at Winter 

Park (site 3) and Fraser River at Tabernash (site 4). Wastewatertreatment-plant discharges enter the Fraser River upstream 

from site 4. Median monthly loading data for nutrients 

and chloride indicate that the largest nutrient and chloride 

loading happens during early spring before the onset of 

spring runoff.

Seasonal Kendall trend results indicate downward 

trends for ammonia concentration at Fraser River below 

Vasquez Creek at Winter Park (site 3) during the period of this 

study. Nitrite plus nitrate concentrations had upward trends at 

Fraser River at Tabernash (site 4) for the available data during 

1995 through 2000. Results from the trend testing on nitrite 

plus nitrate concentrations during 1991 through 2000 at Fraser 

River below Buck Creek (site 2) had a downward trend and 

Fraser River at Tabernash (site 4) had an upward trend. Concentrations of orthophosphorus showed consistently upward 

trends at both the Fraser River below Vasquez Creek at Winter 

Park and Fraser River at Tabernash sites.

References Cited

Apodaca, L.E., and Bails, J.B., 1999, Fraser River watershed, 

Colorado—Assessment of available water-quantity and waterquality data through water year 1997: U.S. Geological Survey 

Water-Resources Investigations Report 98–4255, 58 p.

Cleveland, W.S., 1979, Robust locally weighted regression and 

smoothing scatterplots: Journal of the American Statistical 

Association, v. 74, p. 829–836.

Colorado Water Quality Control Commission, 2001, June 30 

(2001) Classifications and numeric standards for Upper 

Colorado River Basin and North Platte River (Planning 

Region 12) Regulation 33: Colorado Department of Public 

Health and Environment, Water Quality Control Commission [variously paginated].

Colorado Water Quality Control Division, 1989, Colorado 

nonpoint assessment report: Denver, Colorado Department 

of Public Health and Environment, 189 p.
10 Streamwater Quality at Selected Sites in the Fraser River Basin, Grand County, Colorado, Water Years 1991–2000

Fishman, M.J., ed., 1993, Methods of analysis by the U.S. 

Geological Survey National Water Quality Laboratory—

Determination of inorganic and organic constituents in 

water and fluvial sediments: U.S. Geological Survey OpenFile Report 93–125, 217 p.

Fishman, M.J., and Freidman, L.C., eds., 1989, Methods for 

determination of inorganic substances in water and fluvial 

sediments: U.S. Geological Survey Techniques of WaterResource Investigations, book 5, chap. A1, 545 p.

Helsel, D.L., and Hirsch, R.M., 1992, Statistical methods in water 

resources: Amsterdam, The Netherlands, Elsevier, 522 p.

Mueller, D.K., Hamilton, P.A., Helsel, D.R., Hitt, K.J., and 

Ruddy, B.C., 1995, Nutrients in ground water and surface 

water of the United States—An analysis of data through 

1992: U.S. Geological Survey Water Resources Investigations Report 95–4031, 74 p.

U.S. Census Bureau, 2001, Grand County QuickFacts 

from the U.S. Census Bureau, accessed March 14, 2002, 

at http://quickfacts.census.gov/qfd/states/08/08049.html

U.S. Environmental Protection Agency, 1986, Quality criteria 

for water, 1986: Washington, D.C., U.S. Environmental 

Protection Agency Report 440/5–86–001, Office of Water 

[variously paginated].

U.S. Geological Survey, 1999, National field manual for 

the collection of water-quality data: U.S. Geological 

Survey Techniques of Water-Resources Investigations, 

book 9, chaps. A1–A9, two volumes [variously 

paged].

Western Regional Climate Center, 2001, Colorado 

climate summaries, accessed September 28, 2001, 

at http://www.wrcc.dri.edu/summary/climsmco.html