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<br />into the reservoir. The data gathered, however, are
<br />not detailed enough to firmly establish a specific
<br />source for individual trace elements within a specific
<br />subwatershed. The downward trends identified for
<br />copper, iron, lithium, nickel, scandium, titanium, and
<br />vanadium may be due in part to the mine-restoration
<br />efforts and the decrease in active mining in the water-
<br />shed. In addition to the monotonic trend in trace
<br />elements, several elements had a number of high
<br />concentrations or spikes, which indicate that loads
<br />entering the reservoir may have been higher in the
<br />past. These spikes occurred in concentrations of
<br />copper, lead, manganese, mercury, and zinc during
<br />the late 1970's and early 1980's.
<br />Although concentrations of many trace
<br />elements in sediment samples exceeded the probable
<br />effects levels for freshwater lakes established by the
<br />Canadian Council of Ministers of the Environment,
<br />under current (1997) limnological conditions, elevated
<br />sediment concentrations do not appear to significantly
<br />affect water quality in Dillon Reservoir. The concen-
<br />trations of trace elements in the reservoir water
<br />column did not exceed the water-quality standards
<br />established by the Colorado Water Quality Control
<br />Commission.
<br />
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