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).
|Figure 1. Map
of the study area.
The Cache la Poudre River originates in northern
Colorado near the 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 drinking-water 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 long-term 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
A quality-assurance sample was collected with
more than one-half of the environmental samples. Quality-assurance
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 contamination 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).
|Figure 2. Detections
in the Cache la Poudre River.
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-hexamethyl-tetrahydro-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
|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.
maximum contaminant level; --, no standard currently established;
µg/L, micrograms per liter]
The Cache la Poudre River was sampled as part
of an assessment of 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.
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