U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2005–3037

May 2005

The Cache la Poudre River, Colorado, as a Drinking-Water Source

By Jim A. Collins and Lori A. Sprague

Printed on recycled paper

From October 2002 through September 2003, the U.S. Geological

Survey conducted a study to assess 

the quality of a subset of the Nation’s 

drinking-water supplies. In the South 

Platte River Basin of Colorado, 

the Cache la Poudre River, one of 

two surface-water sources of drinking water for the city of Fort Collins, 

Colo., was included in the study. The 

study focused primarily on the presence or absence of organic chemicals 

in source water. The 271 compounds 

studied included dissolved organic 

carbon, 89 volatile organic compounds, 

123 pesticide compounds, and 59 wastewater compounds. Escherichia coli 

(E. coli) bacteria also was collected. Of 

the 271 compounds monitored, 257 were 

not detected. Low concentrations of 

dissolved organic carbon and E. coli

bacteria were detected throughout most 

of the study period. In addition, 3 volatile organic compounds, 1 pesticide, and 

10 wastewater compounds were detected 

in the Cache la Poudre River. All concentrations detected were below established water-quality standards. Most of 

the compounds detected appeared to be 

related to recreation, automobile emissions, or personal and household use of 

chemicals in the drainage area. Based 

on the results of this study, the Cache la 

Poudre River appears to provide a highquality source of drinking water for the 

city of Fort Collins.

The NAWQA Program

 In 2001, the U.S. Geological Survey’s 

(USGS) National Water-Quality Assessment (NAWQA) Program began its 

second decade of intensive water-quality 

assessments (Gilliom and others, 2001). 

The goals of the NAWQA Program are 

to assess the quality of surface water, 

ground water, and aquatic ecosystems 

throughout the Nation and to understand 

the primary natural and human factors 

affecting the quality of these resources. 

The South Platte River Basin is one of 

42 study areas included in the national 

assessment. 

One component of the NAWQA 

program is to evaluate the quality of a 

subset of the Nation’s publicly supplied 

drinking water. Surface water (rivers, 

lakes, and reservoirs) and ground water 

are used separately or in combination as 

source water for public-water supply in 

cities across the Nation. The NAWQA 

program is evaluating the quality of 

surface-water and ground-water sources 

in separate studies. The primary goals of 

the studies are to (1) evaluate the quality of the source water entering a subset 

of the Nation’s drinking-water treatment 

facilities, and (2) compare the quality 

of this source water to the quality of the 

treated water that is delivered to the public. The study is intended to complement 

drinking-water monitoring by Federal, 

State, and local programs, which focus 

primarily on post-treatment compliance 

monitoring (Gilliom and others, 2001).

The Source-Water Quality Assessment 

Study for surface water began in October 2002. First-year activities involved 

collecting untreated surface-water 

samples (source water) from nine rivers 

throughout the United States and analyzing them for a large number of primarily 

anthropogenic organic chemicals, most of 

which are not regulated currently (2004) 

by the U.S. Environmental Protection 

Agency (USEPA). All sites were at 

the drinking-water intakes located on 

major rivers that serve relatively large 

populations. Lakes and reservoirs are not 

included in this study. The second year 

included collecting treated water samples 

(finished water), along with additional 

source-water samples to characterize the 

occurrence and concentration of chemicals in finished water prior to distribution 

from municipal water-treatment facilities. 

This report describes the results from the 

first year of sampling in the South Platte 

River Basin study area. 

The Cache la Poudre River

In the South Platte River Basin, the 

Cache la Poudre River was chosen for 

one of the nine sampling sites because 

it serves as one of two surface-water 

sources (together with Horsetooth 

Reservoir) for the city of Fort Collins, 

Colo. (fig. 1). The city of Fort Collins 

water-treatment facility has an annual 

production of more than 10 billion 

gallons of finished water that serves a 

growing Colorado community of more 

than 125,800 residents (Kevin R. Gertig, 

Water Production Manager, City of 

Fort Collins Utilities, written commun., 

2005).

The Cache la Poudre River originates in northern Colorado near the 

The Cache la Poudre River.
Continental Divide. The river flows out of 

Rocky Mountain National Park, through 

the city of Fort Collins, and eventually 

into the South Platte River near Greeley, 

Colo. The sampling site was located in 

the sparsely populated Cache la Poudre 

Canyon upstream from the confluence of the North Fork of the Cache la 

Poudre River with the main stem of the 

Cache la Poudre River. The drainage 

area of the study site is approximately 

484 square miles, and the land cover is 

predominately forested (fig. 1). Upstream 

from the sampling site, a few homes and 

ranches are near the banks of the river. 

State Highway 14 parallels the river for 

approximately 40 miles within the study 

area. Snowmelt provides most of the flow 

in the river at the site, with contributions 

from storm runoff in the summer months 

and ground-water inflow throughout 

the year. Streamflows during the study 

ranged from a low of 20 cubic feet per 

second (ft3/s) during fall into spring to 

more than 1,000 ft3

/s during peak summer 

flows. The natural flows are augmented 

by transmountain and transbasin diversions that import water from the North 

Platte and Colorado River drainages with 

similar forest land use. A large diversion 

upstream from the site removes water 

from the stream for downstream agricultural use (Litke and Kimbrough, 1998). 

The river and surrounding area are very 

popular for whitewater rafting, canoeing, 

camping, hiking, and fishing. 

Water Sample Collection

Water samples were collected monthly 

from the river just upstream from the 

Fort Collins water-supply intake from 

October 2002 through September 2003; 

one additional sample was collected each 

month from May through September 

when recreational use of the river was at 

its peak. Water samples were analyzed 

for dissolved organic carbon (DOC), 

89 volatile organic compounds (VOCs), 

123 pesticide compounds, 59 wastewater 

compounds, and E. coli bacteria. In addition, water temperature, specific conductance, pH, and dissolved oxygen were 

measured at the time of each sampling. 

Streamflow also was measured when 

the samples were collected with exception of during the highest flow during 

snowmelt, when conditions were not safe 

for streamflow measurements.

DOC is a general measure of the 

thousands of compounds found in water 

that are derived from organic materials; it 

often is produced within a stream or lake 

from animal feces and decomposition of 

fish, insects, and plants (Boyer and others, 1997). Increased DOC in drinkingwater supplies has been associated with 

an increase in the creation of disinfection by-products during chlorination in 

water-treatment facilities; some of these 

compounds have been linked with longterm health effects (U.S. Environmental 

Protection Agency, 1998). VOCs are a 

group of largely anthropogenic organic 

chemicals that include solvents, petroleum distillates, some aerosol spray-can 

propellants, dry-cleaning products, and 

fumigants. Wastewater compounds are 

a collection of organic compounds commonly used in and around many households that may be found in septic leachate and wastewater effluent. They include 

caffeine (found in coffee and many other 

caffeinated beverages), DEET (found in 

insect repellent), and camphor (found 

in topical medications). Pesticides, 

including herbicides, insecticides, and 

fungicides, are used to control weeds, 

insects, and disease-carrying organisms. 

The E. coli bacteria found in streams is 

derived from a variety of sources, including animal waste or failed septic-system 

leach fields. Therefore, E. coli can be 

an indicator of fecal contamination and 

the possible presence of fecal pathogens 

(Wilhelm and Malik, 1998).

Water samples were collected, 

processed, and preserved onsite using 

standard methods described in the USGS 

National Field Manual (U.S. Geological 

Survey, 1997–present) and were analyzed 

at the USGS National Water-Quality 

Laboratory in Denver, Colo., using 

methods described in Brenton and Arnett 

(1993), Zaugg and others (1995), Connor 

and others (1997), and Zaugg and others 

(2002). E. coli samples were analyzed 

using the modified m-TEC membrane 

filtration method (U.S. Geological 

Survey, 1997–present) in the Colorado 

Water Science Center Laboratory in 

Denver. Analytical results are available 

in the USGS National Water Information 

System at http://water.usgs.gov/nwis.

A quality-assurance sample was 

collected with more than one-half of 

the environmental samples. Qualityassurance samples included blanks (used 

to assess potential sample contamination), replicates (used to assess environmental or laboratory variability), and 

spikes (used to assess environmental 

interference with the detection of VOC’s, 

pesticides, and wastewater compounds). 

Blank concentrations for all compounds 

were below laboratory reporting limits 

with the exception of phenol and caffeine. Phenol was detected in multiple 

blanks, indicating systematic contaminaFigure 1. Map of the study area.

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tion during sample collection, processing, or analysis. As a result, phenol 

detections in the water samples were 

considered suspect and were removed. 

Caffeine was detected only in one blank, 

and the concentration was near the 

laboratory-reporting limit. As a result, 

caffeine concentrations were left in the 

data set, but may be biased slightly high. 

Concentrations in the replicate samples 

were consistent with those in the water 

samples. All spike recoveries were 

within acceptable ranges. 

Detections in the Cache la

Poudre River

DOC concentrations were low 

throughout the year (fig. 2A). Concentrations were lowest during fall and 

winter months, with a marked increase 

during early spring runoff, followed by 

a decrease as runoff ended in early summer. A likely source of DOC in the river 

was decomposing plant and organic matter within the soil, which was released 

into the stream as the water table rose 

and flow increased during snowmelt 

(Boyer and others, 1997).

Three of the 89 VOC compounds—

acetone, benzene, and toluene—were 

detected during the study (fig. 2B). 

Sample detections of acetone occurred in 

May and September. Low-level detections of benzene and toluene occurred 

from October through February. Stream 

temperatures measured during the study 

ranged from –0.1 degrees Celsius (°C) 

in winter to 18°C in summer. At water 

temperatures below 25°C, the solubility of toluene and benzene, which are 

components of gasoline and other fuels, 

generally increases (Shaw, 1989), which 

may explain why they were detected only 

in the colder months. The detections of 

acetone in the spring and summer months 

may have been related to the increase 

in automobile traffic and the increase in 

DOC concentrations; sources of acetone 

include automobile exhaust and the 

oxidation of humic carbon substances 

(Verschueren, 1983). 

Siduron, a widely available herbicide 

used primarily for pre-emergent weed 

control (Chemical and Pharmaceutical Press, 1993), was the only pesticide 

of 123 to be detected during the study 

(fig. 2C). The one detection in June may 

be attributable to weed control along 

Highway 14 and on the yards of canyon 

residents in the spring and summer.

Ten of 59 wastewater compounds—

acetophenone, acetyl-hexamethyltetrahydro-naphthalene (AHTN), 

caffeine, camphor, DEET, diethoxynonylphenol, monoethoxyoctylphenol, 

para-Cresol, tetrachloroethylene, and triphenyl phosphate—were detected during 

the study (fig. 2D). Of these compounds, 

only para-Cresol (two detections) and 

DEET (seven detections) were detected 

more than once. With the exception of 

diethoxynonylphenol, all concentrations 

were less than 1 microgram per liter 

or one part per billion. The detections 

of acetophenone, AHTN, diethoxynonylphenol, monoethoxyoctylphenol, 

para-Cresol, tetrachloroethylene, and 

triphenyl phosphate likely are related to 

the seasonal use of various household 

and personal-care products. DEET, 

camphor, and caffeine had detections in 

the spring and summer months when recreational use and contact with the river 

was at its peak.

Low concentrations of E. coli bacteria 

were detected during the months of April 

through September (fig. 2A). Bacteria 

may have been in the river during this 

time of year due to increased recreation 

and cattle grazing in the drainage area, 

combined with warmer streamwater 

temperatures that can enhance bacterial 

survival. No bacteria were detected during the late fall and winter when water 

temperatures were low and use of the 

river was minimal.

Compared to other streams in urban 

and agricultural areas of the South Platte 

River Basin, the number of compounds 

detected at this site on the Cache la 

Poudre River was low. Previous studies 

in the basin have found up to 14 VOC 

compounds in a single urban stream sample (U.S. Geolgical Survey, 2005, data 

accessible at http://water.usgs.gov/nwis), 

19 pesticide compounds in a single agricultural stream sample (Sprague, 2005), 

and as many as 37 wastewater compounds in a single urban stream sample 

(Sprague and Battaglin, 2005).

Potential human-health risks of the 

compounds measured in this study can 

be assessed by comparing concentrations in the water samples to standards 

established by the USEPA and the State 

of Colorado. Current (2004) standards 

are listed in table 1 for all of the VOC, 

wastewater, and pesticide compounds 

detected in water samples during this 

study. All concentrations detected in this 

study were below established standards. These standards, however, do not 

completely address potential risks. Many 

of the compounds detected do not have 

established standards, and there are no 

standards that account for the potential 

effects of mixtures of chemicals.

Conclusions

The Cache la Poudre River was 

Figure 2. sampled as part of an assessment of Detections in the Cache la Poudre River.

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the quality of a subset of the Nation’s 

publicly supplied drinking water. The 

number of detections and concentrations 

of the largely unregulated chemicals 

sampled were low in the Cache la Poudre 

River compared to the other eight rivers 

sampled as part of this source-water quality assessment (Greg Delzer, U.S. Geological Survey, written commun., 2003). 

Because of the small number of detected 

compounds and the low concentrations 

measured in the Cache la Poudre River, 

major differences between the source 

water in the river and the treated water 

delivered to Fort Collins residents were 

not expected. Therefore, this site was not 

included during the second year of the 

source-water quality assessment study. 

The city of Fort Collins blends water 

from both the Cache la Poudre River and 

Horsetooth Reservoir throughout the year 

to supply water to residents, and further 

study of both water sources would be 

needed to assess the overall quality of 

source water for the city. Based on the 

results of this study, the Cache la Poudre 

River appears to provide high-quality 

source water for the city of Fort Collins.

References Cited

Boyer, E.W., Hornberger, G.M., Bencala, 

K.E., and McKnight, D.M., 1997, Response 

characteristics of DOC flushing in an alpine 

catchment: Hydrologic Processes, v. 11, 

p. 1,635–1,647.

Brenton, R.W., and Arnett, T.L., 1993, Methods of analysis by the U.S. Geological Survey National Water-Quality Laboratory—

Determination of dissolved organic carbon 

by UV-promoted persulfate oxidation and 

infrared spectrometry: U.S. Geological Survey Open-File Report 92–480, 12 p.

 Chemical and Pharmaceutical Press, 1993, 

Crop protection chemicals reference: New 

York, Wiley and Boris Chemical and Pharmaceutical Publishing Corporation, 9th ed., 

1,812 p. and supplement.

Colorado Department of Public Health and 

Environment Water-Quality Control Commission, 2001, The basic standards and 

methodologies for surface water: Regulation 

no. 31, 175 p.

Connor, B.F., Rose, D.L., Noriega, M.C., 

Murtagh, Lucinda, and Abney, S.R., 1997, 

Methods of analysis by the U.S. Geological 

Survey National Water-Quality Laboratory—Determination of 86 volatile organic 

compounds in water by gas chromatography/mass spectrometry, including detections 

less than reporting limits: U.S. Geological 

Survey Open-File Report 97–829, 78 p.

Gilliom, R.J., Hamilton, P.A., and Miller, T.M., 

2001, The National Water-Quality Assessment Program—Entering a new decade 

of investigations: U.S. Geological Survey 

Fact Sheet 071–01, 6 p.

Litke, D.W. and Kimbrough, R.A., 1998, 

Water-quality assessment of the South 

Platte River Basin, Colorado, Nebraska, 

and Wyoming—Environmental setting and 

water quality of fixed sites, 1993–1995: 

U.S. Geological Survey Water-Resources 

Investigations Report 97–422, 61 p.

Shaw, D.G., 1989, Hydrocarbon with water 

and seawater, Part I—Hydrocarbons C5 to 

C7: International Union of Pure and Applied 

Chemistry, v. 37, variously paged.

Sprague, L.A., 2005, Drought effects on 

water quality in the South Platte River 

Basin, Colorado: Journal of the American 

Water Resources Association, v. 41, no. 1, 

p. 11–24.

Sprague, L.A., and Battaglin, W.A., 2005, 

Wastewater chemicals in Colorado’s streams 

and ground water: U.S. Geological Survey 

Fact Sheet 2004–3127, 4 p.

U.S. Environmental Protection Agency, 

2003, National primary drinking water 

standards: Washington, D.C., EPA Report 

816–F–03–016.

U.S. Environmental Protection Agency, 

1998, National primary drinking water 

regulations—disinfectants and disinfection 

byproducts: Federal Register, v. 63, no. 241, 

p. 69,389–69,476.

U.S. Geological Survey, variously dated, 

National field manual for the collection of 

water-quality data: U.S. Geological Survey 

Techniques of Water-Resources Investigations, book 9, chaps. A1−A9, accessed 

September 14, 2004, at http://pubs.water.

usgs.gov/twri9A, variously paged.

Verschueren, Karel, 1983, Handbook of environmental data on organic chemicals: New 

York, Van Nostrand Rienhold, 1310 p.

Wilhelm, L.J., and Malik, T.L., 1998, Fecalindicator bacteria in surface waters of 

Santee River Basin and coastal drainages, 

North and South Carolina, 1995–98: U.S. 

Geological Survey Fact Sheet FS–085–98, 

6 p.

Zaugg, S.D., Smith, S.G., Schroeder, M.P., 

Barber, L.B., and Burkhardt, M.R., 2002, 

Methods of analysis by the U.S. Geological Survey National Water-Quality 

Laboratory—Determination of wastewater 

compounds by polystyrene-divinylbenzene 

solid-phase extraction and capillary-column

gas chromatography/mass spectrometry: 

U.S. Geological Survey Water-Resources 

Investigations Report 01–4186, 37 p.

Zaugg, S.D., Sandstrom, M.W., Smith, S.G., 

and Fehlberg, K.M., 1995, Methods of 

analysis by the U.S. Geological Survey

National Water-Quality Laboratory—Determination of pesticides in water by C–18 

solid-phase extraction and capillary-column 

gas chromatography/mass spectrometry 

with selected-ion monitoring: U.S. Geological Survey Open-File Report 95–181, 49 p.

Compound Common uses or sources

USEPA 

MCL1

(μg/L)

Colorado 

standard2

(μg/L)

Maximum 

study concentration

(μg/L)

Acetone Plastic, fibers, drugs, solvents, exhaust by-product -- -- 2.0

Acetophenone Fragrance in soap, detergent, tobacco -- -- 0.026

Acetyl-hexamethyl-tetrahydro-naphthalene (AHTN) Fragrance in musk, widespread usage -- -- 0.025

Benzene Plastics, fibers, lubricants, detergents, pharmaceuticals, fuels 5 1.2 0.020

Caffeine Coffee, soda, tea, and other beverages -- -- 0.016

Camphor Flavor, odorant, ointments -- -- 0.015

Diethoxynonylphenol Detergent degradation product -- -- 4.0

Monoethoxyoctylphenol Detergent degradation product -- -- 0.80

N,N-diethylmetatoluamide (DEET) Insect repellant -- -- 0.10

para-Cresol Wood preservative -- -- 0.030

Siduron Herbicide -- -- 0.010

Tetrachloroethylene Solvent, degreaser 5 5 0.10

Toluene Paints, adhesives, lacquers, rubber, paint thinner, fuels 1,000 1,000 0.030

Triphenyl phosphate Plasticizer, resins, finishes, waxes, and roofing paper -- -- 0.014

Table 1. Description of uses or sources, U.S. Environmental Protection Agency (USEPA) maximum contaminant levels, and State of 

Colorado basic standards for compounds detected during the study.

[MCL, maximum contaminant level; --, no standard currently established; μg/L, micrograms per liter]

1. From the National Primary Drinking Water Standards (U. S. Environmental Protection Agency, 2003).

2. From the basic standards for organic chemicals in surface water, human-health based water-supply standards (Colorado Department of Public Health and Environment, 2001).