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<br />-37- <br />deterioration of the quality of ground water flowing through abandoned coal <br />workings into coal aquifers, depletion of flow in the stream/alluvial aquifer <br />system, and a deterioration of water quality in the stream/alluvial aquifer <br />system. Water quality impacts to the Purgatoire River would be greatest <br />during operations when mine water is discharged from the two mines. <br />The Allen and Maxwell coal seams lie close to one another in the stratigraphic <br />column, separated by approximately 20 feet of interburden material. <br />Disturbance of roof, floor, and interburden material during mining, and <br />subsidence after mining, will result in the breakdown of the interburden <br />strata. As a result, hydrologic communication is expected to occur between <br />the two coal seams, and ground water impacts are expected to be cumulative. <br />The following assessment considers the two coal seams as one aquifer. <br />During operations, dewatering would occur in the coal aquifer and the drawdown <br />of the piezometric surface could extend outward to approximately 3 miles from <br />each mine. Since the mines are adjacent to each other, a portion of these <br />affected areas would overlap. Within that zone, drawdown effects would be <br />additive. <br />After the cessation of operations, mine water would no longer be discharged <br />and the abandoned workings would fill with water. The ground water level and <br />piezometric surface would partially recover. A permanent depression in the <br />piezometric surface of the coal aquifer would exist in the vicinity of the <br />flooded workings of the mines. The depression would not be large, but it may <br />extend 3 miles from each mine. Approximately twice•as much ground water would <br />flow through the flooded mine workings than flowed through the undisturbed <br />coal prior to mining. This mine water flow would, however, be restricted by <br />the low permeability of the undisturbed coal surrounding the mine workings. <br />Ground water would stagnate in the mine workings and react with fragmented <br />roof, floor, coal, rock dust, and other materials in the mine cavity. This <br />ground water would have a poorer quality than water currently pumped from <br />underground workings, which is similar to ground water observed in the Allen <br />refuse pile. The total dissolved solids levels are expected to equal or <br />exceed 2600 mg/1 (Exhibit 6, Table 13 o the permit application). This ground <br />water would spread as a plume down ~p _ /~, <br />The effect of having two mining operation/s/'~afufecting strata in hydrologic <br />communication with one another would be to decrease dilution within the <br />aquifers and increase the distance a detectable mine water plume would <br />spread. The degradation of water quality in the coal aquifers will not impact <br />ground water use in the general area, since the poor quality and depth limited <br />use originally. <br />The two operations are expected to cumulatively effect the flow in the <br />Purgatoire River stream/alluvial aquifer system. The Allen Mine is located or <br />the Middle Fork of the Purgatoire River. This fork joins the North Fork of <br />the Purgatoire to form the Purgatoire River. The Maxwell Mine is located <br />adjacent to the Purgatoire River i~nrnediately downstream from the Allen Mine. <br />Both operations have undermined and will further undermine the stream/alluvial <br />aquifer systems. The amount of depletion of flow in the Purgatoire River <br />alluvial aquifer has been estimated to be 5 gpm for the Allen Mine, and 2.3 <br />