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. Ground water in strata being mined, and in deeper strata below the mining <br />areas, has been shown by drilling to be non-existent to negligible. There- <br />- ~ fore present proposed mining is not expected to materially affect ground <br />water quality in any confined, bedded aquifers. Of greater concern is <br />the effect from mining on the hydrologic balance of Grassy Creek and the <br />ground water in adjacent alluvium. The mined area is all within the <br />Grassy Creek headwater basin. The surface water and the alluvial ground <br />water essentially belong to the same system. After spring runoff has taken <br />place, field data (especially conductivity readings) show very similar <br />water characteristics throughout the rest of the year. Ground water flows <br />into ponds and into the stream bed of Grassy Creek maintaining pond levels <br />and intermittent stream flow. Deterioration of water quality in either <br />stream flow or ground water would result in lowering of water quality <br />of the other. Thus far, we have not observed a lowering of water quality <br />in the system. Field data from the alluvial wells is attached. <br />A deterioration of water quality due to mining would probably mean an <br />increase in dissolved solids and rise in alkanity levels. TDS in Grassy <br />Creek waters leaving the mined area at Site 1 range seasonally from 400 <br />to 700. TDS in Grassy Creek doubles during transit from Site 1 to Seneca <br />Coals Ltd. final sample point upon leaving their mined area. Some of <br />this increase is natural due to the distance (about 2 miles) between <br />Site 1 and their initial sample point. Given this parameter it can be <br />fairly assumed that the maximum TDS increase due to the Grassy Gap Mine <br />operation could possibly be two times present values during low surface <br />flow. Downstream users of Grassy Creek water are limited to Seneca Coal <br />Ltd., stock water on ranches and by wildlife. It is not used for flood <br />or spray irrigation. Some minor sub or natural irrigation occurs. If <br />higher TDS and alkalinity levels occurred it might produce changes in <br />vegetative cover; more tolerant species replacing other species in the <br />areas of sub-irrigation. Mitigation of TDS/alkalinity levels of this <br />magnitude are not presently attempted in Routt County. <br />MW-1 and MW-3 are used as sample wells for chemical analysis to determine <br />if water quality is being affected by mining. The only samples analyzed <br />. since June, 1981 were collected in March, 1982 and results are attached. <br />Thus far, the monthly/quarterly data do not suggest that mining has affected <br />alluvial ground water quality in Grassy Creek. <br />2-85 II.E-3a <br />>--- _ - <br />