Laserfiche WebLink
-30- <br /> year. The alluvium at the North Thompson Creek Mine load-out consists of <br /> medium to coarse grained sand and gravels. The aquifer' s transmissivity is <br /> 51 ,200 gpd/ft. and storativity was estimated to be 0.3. The water quality of <br /> the Roaring Fork alluvium is similar to the Roaring Fork River. Total <br /> dissolved solids - TDS) range between 280 and 500 mg/l ; and iron (Fe) varies <br /> between 0 and 0.08 mg/l . The pH is neutral to slightly alkaline, and the <br /> water type is a calcium, magnesium-bicarbonate, sulfate. <br /> The Coal Basin Mine load-out obtains domestic, irrigation, and industrial <br /> water from three ground water wells completed in the Roaring Fork alluvium. <br /> Wells No. 1 and 2 have a combined withdrawal rate of 3 acre-feet/year. Well <br /> No. 3 is used as a backup well . <br /> In general , the alluvial deposits along Fourmile Creek, Thompson Creek, and <br /> Coal Creek are restricted to thin, discontinuous, narrow bands along the <br /> stream channels. Wider bodies of alluvia are located at the confluences of <br /> two or more streams. Alluvial bodies are broken at water gaps (e.g. , narrow <br /> passes through resistant units) . At these points, the upstream alluvial body <br /> discharges to the surface stream and the downstream alluvial body is recharged <br /> by the stream. Therefore, the alluvia of these streams do not represent a <br /> continuous band tributary from the mine sites to the Crystal River and the <br /> Roaring Fork River alluvia. As a result of this phenomenon any impacts to the <br /> alluvial ground water quality or quantity at the mine sites will directly <br /> impact 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 at the <br /> western end of the mine site to 33 feet at the lower end of the refuse pile. <br /> The alluvium below the refuse pile has a higher clay and silt content than <br /> other alluvium along North Thompson Creek. The estimated transmissivity from <br /> slug tests in this area is 31 gpd/ft. The water quality below the refuse pile <br /> and downgradient of the two wash plant settling ponds has high total dissolved <br /> solids (3498 to 3982 mg/1) and sulfate concentrations (1900 to 2700 mg/1 ) . <br /> The water type is calcium-magnesium sulfate. This water quality may be the <br /> result of both the salinity of the underlying Mancos shale and the effects of <br /> the mining operations at the North Thompson Creek Mines. <br /> The alluvium of Coal Creek and its tributaries consists of sands and gravels <br /> derived from the Mesaverde Group, Mancos Shale, and reworked glacial and <br /> terrace deposits. This alluvium is discontinuous, varies between 0 and 75 <br /> feet and is highly permeable. The Coal Creek alluvium is isolated into <br /> separate narrow alluvial bodies by water gaps formed by the resistant <br /> sandstone strata. The alluvial ground water is predominantly a calcium, . <br /> sodium, magnesium bicarbonate type. The total dissolved solids concentration <br /> is about 350 mg/l . Alluvial ground water is utilized by Coal Creek Mine for <br /> domestic and industrial uses. The alluvial ground water discharges to Dutch, <br /> Coal, Bear and Porcupine Creeks, providing base flow in the creeks during low <br /> flow periods. The alluvium is recharged directly from the streams during <br /> snowmelt and during precipitation events. <br />