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GENERAL45390
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Last modified
8/24/2016 8:14:36 PM
Creation date
11/23/2007 1:46:10 PM
Metadata
Fields
Template:
DRMS Permit Index
Permit No
C1981025
IBM Index Class Name
General Documents
Doc Date
7/8/1983
Doc Name
Proposed Decision and Findings of Compliance
Permit Index Doc Type
Findings
Media Type
D
Archive
No
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-21- <br />Thompson Creek Mine loadout. These wells are pumped at a combined rate <br />of 50 gpm in the summer and 15 gpm during the winter. The water is <br />considered tributary water to the Roaring Fork River, and is under an <br />augmentation plan, which permits water uses of dust suppression, 6.14 <br />acre-feet; plant washdown, 2.88 acre-feet; sanitation, 0.02 acre-feet; <br />and irrigation, 9.0 acre-feet, for a total of 18.04 acre-feet per year. <br />The alluvium at the North Thompson Creek Mine loadout consists of medium <br />to coarse grained sand and gravels. The aquifer's transmissivity is <br />51,200 gpd/f t. and storativity was estimated to be 0.3. The water <br />quality of the Roaring Fork alluvium is similar to the Roaring Fork <br />River. Total dissolved solids (TUS) range between 280 and 500 mg/1; and <br />iron (Fe) varies between U and 0.08 mg/1. The pH is neutral to slightly <br />alkaline, and the water type is a calcium, magnesium-bicarbonate, sulfate. <br />The Coal Basin Mine loadout obtains domestic, irrigation, and industrial <br />water from three ground water wells completed in the Roaring Fork <br />alluvium. Wells No. 1 and 2 have a combined withdrawal rate of 3 <br />acre-feet/year. Well No. 3 is used as a backup well. <br />In general, the alluvial deposits along Fourmile Creek, Thompson Creek, <br />and Coal Creek are restricted to thin, discontinuous, narrow bands along <br />the strewn channels. Wider bodies of alluvia are located at the <br />confluences of two or more streams. Alluvial bodies are broken at water <br />gaps (e.g., narrow passes through resistant units). At these points, the <br />upstream alluvial body discharges to the surf ace stream and the <br />downstream alluvial body is recharged by the stream. Therefore, the <br />alluvia of these streams do not represent a continuous band tributary <br />from the mine sites to the Crystal River and the Roaring Fork River <br />alluvia. As a result of this phenomenon any impacts to the alluvial <br />ground water quality or quantity at the mine sites will directly impact <br />the quality of quantity in the associated stream. The alluvial ground <br />water flows are the most significant sources of base flows in the streams <br />during low flow periods. <br />The alluvium of North Thompson Creek ranges in thickness from zero feet <br />at the western end of the mine site to 33 feet at the lower end of the <br />refuse pile. The alluvium below the refuse pile has a higher clay and <br />silt content than other alluvium along North Thompson Creek. The <br />estimated transmissivity from slug tests in this area is 31 gpd/f t. The <br />water quality below the refuse pile and downgradient of the two wash <br />plant settling ponds has high total dissolved solids (3498 to 3982 mg/1) <br />and sulfate concentrations (1900 to 2700 mg/1). The water type is <br />calcium-magnesium sulfate. This water quality may be the result of both <br />the salinity of the underlying Mancos shale and the effects of the mining <br />operations at the North Thompson Creek i'~ines. <br />The alluvium of Coal Creek and its tributaries consists of sands and <br />gravels derived from the Mesaverde Group, Mancos shale, and reworked <br />glacial and terrace deposits. This alluvium is discontinuous, varies <br />between 0 and 75 feet and is nignly permeable. The Coal Creek alluvium <br />
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