|
<br />(Summit County Government, 1999). Over that same
<br />period, the number of housing units in the county grew
<br />from 2,198 to 8,364, a 281-percent increase. By 1998,
<br />the area had a permanent population of more than
<br />19,000 that increased to more than 100,000 during the
<br />peak tourist season from December to mid-March.
<br />Similarly, the total number of housing units in the
<br />county reached more than 23,000 by 1998 (Summit
<br />County Government, 1999). This type of growth in
<br />population typically generates increased construction,
<br />numbers of automobiles, sewage waste, storm water
<br />runoff, and energy demands.
<br />The study area also has a long history of mining
<br />activity, which continues to affect water quality in
<br />Dillon Reservoir. The sources of some of the largest
<br />trace-element loads to reach Dillon Reservoir are more
<br />easily described on a sub watershed basis.
<br />
<br />Tenmile Creek
<br />
<br />The Climax Mine occupies the southernmost
<br />part of Tenmile Creek's 93.3-square-mile drainage
<br />area. The history of this molybdenum mine, changes
<br />in land use, and mine drainage as described by
<br />Voynick (1996) follow. The mine was operated,
<br />with few breaks, from 1917 to 1980 and intermittently
<br />between 1980 and 1992. Through most of its history,
<br />Climax was primarily an underground mining opera-
<br />tion, with only limited open-pit mining. Development
<br />of a large-scale open-pit mine began in 1972. In
<br />5 years, the pit mine produced an average of
<br />17,000 tons of ore per day. In addition to the Climax
<br />Mine, the Tenmile Creek drainage area contains
<br />hundreds of prospect holes, shafts, and tunnels from
<br />mining operations as early as the 1860's. The metal-
<br />laden runoff from active and abandoned mines
<br />destroyed all aquatic life in Tenmi1e Creek to its
<br />confluence with the Blue River until the 1970's.
<br />The first steps to reduce the effects of Climax
<br />Mine on water quality in Tenmile Creek were taken
<br />in 1936. In that year, a new tailings pond, Robinson
<br />Pond, was built as a closed system to replace previous
<br />free-draining ponds. In 1957, the filling of Robinson
<br />Pond necessitated construction of a second c1osed-
<br />system pond, the Tenmile Tailings Pond. Between
<br />1972 and 1978, the Mayflower Tailings Pond System
<br />was completed. This pond system was built down-
<br />stream from the mill, smelter wastes, and mine. Water
<br />from the mine was diverted into the pond system,
<br />and unaffected water was diverted in channels around
<br />
<br />the mine for release directly into Tenmile Creek.
<br />By 1978, an ionic-exchange treatment plant
<br />(Bryce Romig, Climax Mine, oral commun., 1999)
<br />was treating 2,000 gallons per hour of discharge from
<br />the Mayflower Tailings Pond System. As a result of
<br />the Mayflower Tailings Pond System, water quality
<br />in Tenmile Creek improved to the point that trout
<br />returned for the first time in the century. The treatment
<br />method at the Mayflower plant was changed in 1984 to
<br />a two-stage pH adjustment method to treat all flow,
<br />including spring runoff (Bryce Romig, Climax Mine,
<br />oral commun., 1999). The mine currently employs a
<br />small staff whose responsibilities include mine and
<br />mill maintenance, environmental quality and reclama-
<br />tion, and development of water resources.
<br />
<br />Snake River
<br />
<br />The remnants of a silver mining industry
<br />that peaked in the late 1800's and early 1900's are
<br />evident in Peru Creek, a tributary of the Snake River
<br />(drainage area approximately 115 square miles). Of
<br />the mines draining to Peru Creek, the Pennsylvania
<br />Mine contributes the largest metal loads, particularly
<br />zinc (Sullivan and others, 1998). Conditions in Peru
<br />Creek have been severe enough that, as recently as
<br />1998, no fish were found in the reach nearest the mine
<br />(Sullivan and others, 1998). In the 1990's, there have
<br />been several efforts to improve the environmental
<br />quality in Peru Creek. In 1990, a passive treatment
<br />system was installed to reduce metal concentrations in
<br />the drainage from the Pennsylvania Mine. The system
<br />was run as a pilot study from 1990 to 1993 (Northwest
<br />Colorado Council of Governments, written commun.,
<br />1999).
<br />
<br />
<br />The Snake River upstream from Dillon Reservoir.
<br />
<br />4 Identification of Water-Quality Trends Using Sediment Cores from Dillon Reservoir, Summit County, Colorado
<br />
<br />
|