GENERAL32420 - Laserfiche WebLink

Home Browse Search

~~ It is not anticipated that the small Rimrock Strip Mines, with a disturbed area of 20 acres, will appreciably raise the TDS value even in the surface drainages nearby which are tributary to the Purgatoire River. As a result, the impacts of the Raton Creek and Rimrock Strip are cumulatively insignificant as regards the quality of water in the Purgatoire River. The Allen and Maxwell coal seams lie close to one another in the stratigraphic column, separated by approximately 20 feet of interburden material. Disturbance of roof, floor, and interburden material during mining, and subsidence after mining, will result in the breakdown of the interburden strata. As a result, hydrologic communication is expected to occur between the two coal seams, and ground water impacts are expected to be cumulative. The following assessment considers the two coal seams as one aquifer. During operations, dewatering would occur in the coal aquifer and the drawdown of the piezometric surface could extend outward to approximately 3 miles from each mine. Since the mines are adjacent to each other, a portion of these affected areas would overlap. Within that zone, drawdown effects would be additive. After the cessation of operations, mine water would no longer be discharged and the abandoned workings would fill with water. The ground water level and piezometric surface would partially recover. A permanent depression in the piezometric surface of the coal aquifer would exist in the vicinity of the flooded workings of the mines. The depression would not be large, but it may extend 3 miles from each mine. Approximately twice as much ground water would flow through the flooded mine workings than flowed through the undisturbed coal prior to mining. This mine water flow would, however, be restricted by the low permeability of the undisturbed coal surrounding the mine workings. Ground water would stagnate in the mine workings and react with fragmented roof, floor, coal, rock dust, and other materials in the mine cavity. This ground water would have a poorer quality than water currently pumped from underground workings, which is similar to ground water observed in the New Elk refuse pile. The total dissolved solids levels are expected to equal or exceed 2600 mg/1 (Exhibit 6, Table 13 of the permit application). This ground water would spread as a plume down dip. The effect of having two mining operations affecting strata in hydrologic communication with one another would be to decrease dilution within the aquifers and increase the distance a detectable mine water plume would spread. The degradation of water quality in the coal aquifers will not impact ground water use in the general area, since the poor quality and depth limited use originally. The two operations are expected to cumulatively effect the flow in the Purgatoire River stream/alluvial aquifer system. The New Elk Mine is located on the Middle Fork of the Purgatoire River. This fork joins the North Fork of the Purgatoire to form the Purgatoire River. The Golden Eagle Mine is located adjacent to the Purgatoire River immediately downstream from the New Elk Mine. Both operations have undermined and will further undermine the stream/alluvial aquifer systems. -23-