9343

• UCREFRP Catalog Number: 9343
• Author: Greve, A. I., N. E. Spahr, P. C. Van Metre and J. T. Wilson.
• Title: Identification of Water-Quality Trends Using Sediment Cores from Dillon Reservoir, Summit County, Colorado.
• USFW Year: 2001.
• USFW - Doc Type: Denver.
• Copyright Material: NO

Figure 7. Evidence of bank erosion on Dillon Reservoir, Colorado.

SUMMARY AND CONCLUSIONS

The drainage area of Dillon Reservoir, in
Summit County, Colorado, has been the site of
rapid urban development and the continued influence
of historical mining. Sediment cores were collected
at seven locations in Dillon Reservoir in an effort to
assess changes in the water quality. The sediment
cores were analyzed for pesticides, polychlorinated
biphenyls (PCBs), polycyclic aromatic hydrocarbons
(PAHs), and trace elements. Pesticides, PCBs, and
PAHs were used to determine the effects of urban
development, and trace elements were used to
identify mining contributions. Water-quality and
streambed-sediment samples also were collected
at the mouth of three streams that drain into the
reservoir.
The use of pesticides and PCBs can increase
with urban growth. Of the 14 pesticides and 3 PCBs
for which the sediment samples were analyzed,
only 2 pesticides were detected. Low amounts of
dichlorodiphenyldichloroethylene (DOE) and dichlo-
rodiphenyldichloroethane (ODD), metabolites of
dichlorodiphenyltrichloroethane (DOT), were found
at core depths of 5 cm and below 15 cm in a core
collected near the dam.
Historical mining and urban development
within the Dillon Reservoir watershed have affected
water quality. Combustion-derived PAH concentra-
tions and the ratio of fluoranthene to pyrene have

increased over time within the sediments of Dillon
Reservoir. A relation also was established between
resident population and total combustion PAH.
These upward trends and the relation between popula-
tion and total combustion PAH is likely due to the
growth in both the resident and tourist populations
in the region. Comparisons between core samples
gathered in each arm of the reservoir showed the
highest PAH concentrations were from the Tenmile
Creek arm, the only arm that has an urban area
on its shores, the town of Frisco. The levels of
PAHs, however, are low by comparison with lakes
and reservoirs in urban areas and are typical of
remote freshwater lakes. All PAH concentrations,
except pyrene concentration in one segment in the
core near the dam and acenaphthylene concentrations
in the tops of three cores taken in the reservoir arms,
were below Canadian interim freshwater sediment-
quality guidelines.
Trace-element concentrations of arsenic,
cadmium, chromium, copper, lead, and zinc in Dillon
Reservoir sediment exceeded freshwater sediment-
quality guidelines established by the Canadian
Council of Ministers of the Environment and likely
resulted from historical mining in the watershed. The
core data establish the presence of trace-element depo-
sition throughout the history of the reservoir. The anal-
ysis of stream data indicate that metals loads are
delivered through the system of tributaries draining

20 Identification of Water-Quality Trends Using Sediment Cores from Dillon Reservoir, Summit County, Colorado