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=rte ~~..:-..._:a <br />. _3_ <br />The Dorchester operation mines the Pine Gulch and Red Arrow seams by <br />underground methods. The Newlin Creek operation, also an underground <br />mine, currently works the Vento seam and proposes to ramp down to the <br />Black Hawk seam. It is difficult to detennine exactly which strata are <br />being mined at the GEC strip operat.i~an;probably the sequence from the <br />Black Hawk seam down to the Red Arrow seam. Because of differences in <br />nomenclature, it is nearly impossible to assess which seams were worked <br />at the Twin Pines underground operation. These correlation difficulties <br />further make this cummulative hydrologic impact assessment somewhat uncertain. <br />Partial Impacts <br />Ground Water <br />Two types of impacts are, likely to occur as a result of the current <br />mining in the Canon City Coal Field. First, as a result of mine-dewatering, <br />the piezometric surfaces of strata in the Veremejo Formation are likely <br />to be lowered. Second, water quality impacts are likely due to ground <br />water contact with leachates from mine wastes and spoil piles. These are <br />discussed individually below. <br />When mine workings encounter saturated portions of the coal seams, water <br />will accumulate and have to be pumped out. The removal of this water <br />will lower piezometric surfaces in the coal seams and immediately adjacent <br />strata. The distance from the mine that this impact will extend is <br />dependent upon the transmissivity and storage coefficient properties of <br />the strata. In most coal bearing strata, these properties are such that <br />the impact rarely extends more than a mile from the edge of the mine <br />workings. No values of transmissivity or storage coefficient are available <br />for the strata being evaluated. Because of past mine dewatering, most <br />of the strata in the vicinity of the mines are dry alteady. Therefore, <br />significant additional lowering of the piezometric surfaces is not anticipated. <br />The quality of ground water may become degraded as a result of the proposed <br />mining operations. All three of the underground mines (Dorchester, Newlin <br />Creek, and Twin Pines) will have to dispose of mine waste rock. When this <br />material comes in contact with water, a leachate water is produced which is <br />usually of worst quality then the natural waters. If the leachate were to <br />