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Last modified
8/11/2009 11:32:57 AM
Creation date
8/10/2009 4:56:06 PM
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UCREFRP
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
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<br /> <br />Blue River <br /> <br />French Gulch is a small tributary of the Blue <br />River. It drains more than 10 square miles of the <br />121-square-mile Blue River drainage area upstream <br />from Dillon Reservoir. There have been several mining <br />operations along French Gulch. In total, more than <br />600,000 tons of gold, silver, lead, and zinc were <br />removed along French Gulch (Miller, 1995). The <br />largest metal loads to reach the stream originate from <br />the Wellington-Oro Mine (Kimball and others, 1999), <br />located 2 miles upstream from the confluence with the <br />Blue River, near Breckenridge. The mine was operated <br />from 1882 to 1930 and again from 1940 to 1970. In <br />1972, in an attempt to reopen the mine, the flooded <br />underground mine shafts were pumped for more <br />than a year at a rate of 600 to 1,000 gallons per minute <br />(American Geological Services, written commun., <br />1999). <br />In the late 1980's, the Colorado Department <br />of Public Health and Environment began monitoring <br />in the French Gulch drainage area to investigate <br />increased fish mortality rates (Bails, 1998). This moni- <br />toring began to identify the sources of the most <br />contaminated discharge. The Colorado Division of <br />Minerals and Geology has since identified four likely <br />sources of metal loading to French Gulch: mill tail- <br />ings, discarded waste-rock piles, roaster fines, and <br />flooded portions of the Wellington-Oro Mine (Science <br />Applications International Corporation, written <br />commun., 1995). The largest loads originate in <br />the flooded mine. It was estimated that six levels, <br />80 percent of the mine workings, were currently <br />below the water table in 1995 (Science Applications <br />International Corporation, written commun., 1995). A <br />considerable amount of reclamation has been done to <br />improve water quality within French Gulch, including <br />the sealing of a mine shaft in 1992, streambed clearing <br />and revegetation in 1993, and the removal of roaster <br />fines and tailings piles in 1998 (Science Applications <br />International Corporation, written commun., 1995). <br /> <br />STUDY METHODS <br /> <br />Seven sediment-core samples were collected <br />from Dillon Reservoir. Streambed-sediment and <br />water-quality samples were gathered from the three <br />main streams draining into the reservoir and the Blue <br />River exiting the reservoir. Water-quality samples <br />also were gathered at four sites on the reservoir. <br /> <br />The water-quality samples and streambed-sediment <br />samples were gathered to complement the sediment- <br /> <br />core data. <br /> <br />Reservoir Bottom-Sediment Core <br />Samples <br /> <br />Sediment-core samples were collected at <br />seven locations within Dillon Reservoir, two in each <br />of the three arms of the reservoir and one near the <br />dam (fig. 2), in August 1997. Samples were analyzed <br />for pesticides, PCBs, PAHs, and major and trace <br />elements (Appendix 1-3). Samples were collected <br />from a pontoon boat. The sediment cores from each <br />arm of the reservoir were collected using a 15- by <br />15- by 20-cm-deep box corer. A 50-cm-deep box <br />corer was used to collect the core near the dam. The <br />corers were fitted with an acrylic liner, used to hold <br />the sample after collection. The samples were divided <br />into discrete segments I or 2 cm in thickness. Each <br />segment was further divided: one-half for organic <br />compound analysis and one-half for analysis for <br />inorganic compounds. All samples were stored a~d <br />shipped on ice until received by USGS laboratones <br />in Arvada, Colorado, or Reston, Virginia. <br /> <br /> <br />Collecting sediment-core sample from Dillon <br />Reservoir. <br /> <br />STUDY METHODS 5 <br />
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