2011-09-26_PERMIT FILE - C1981012 (24)

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0 Probable Hydrologic Consequences New Elk Mine 1 1. INTRODUCTION This report presents the results of hydrologic studies that were prepared to support underground mining and associated surface operations at the New Elk Mine in Las Animas County, Colorado. Previous mining at New Elk produced coal from the Allen seam in the lower portion of the Raton Formation. The permit revision that is the focus of this report is for mining in the Allen and Apache coal seams. 2. MINE HISTORY AND PLANNED OPERATION Previous production from the New Elk Mine occurred from the Allen coal seam between 1952 and 1988. The mining method was predominantly room and pillar. The areal extent of the existing underground workings is shown on Figure 1. The mine was temporarily sealed in 1988 and allowed to flood. The water elevation in the underground workings was measured to be 7,112 feet amsl on November 7, 2008 at the East Portal Shaft'. Under the existing permits, the mine pool has been pumped down and the underground workings are being rehabilitated to resume production from the Allen and Apache Coal seams. Approval to reopen the East Portal Airshaft and install a turbine pump to dewater the mine was granted by MSHA in 2007. The pump was installed in 2008 and dewatering started in December of the same year. Water from the mine is pumped to a storage pond adjacent to the East Portal Airshaft where it is held for settlement and treatment prior to discharge to the Purgatoire River. Discharge from the settlement pond is covered under the mine's existing NPDES permit. The mine is a typical underground operation with access the Allen and Apache seams through a set of inclined slopes that are driven from the surface at the East and West Portals. Mine ventilation is provided by two air return fans located at the East Portal and West Portal air shafts, two intake airshafts located in Apache Canyon, and four access slopes. Two of the access slopes are located at the East Portal and two are located at the West Portal. Mining in the Apache and Allen coal seams will be a room and pillar operation using continuous mining methods. Surface facilities include a raw coal stockpile, preparation plant, conveyor belt, clean coal stockpile, development waste disposal area (DWDA), refuse disposal area (RDA), sediment ponds, shops, warehouses, administrative buildings, and a bathhouse (Plate 1). Development waste from the underground mine is placed in the DWDA south of Highway 12 (Plate 1). The material is similar to other waste rock that has been previously stockpiled on site and has low potential to form acidic drainage. Appropriate controls have been implemented in the DWDA to capture runoff and comply with all conditions prescribed by the applicable permits. Mine development will advance down dip to the east and south. Two sets of mains will be advanced east from the existing workings to the outermost extent of the economically recoverable coal. Production panels will be developed from the mains by room and pillar mining methods. An analysis prepared by Agapito Associates, Inc (AAI, 2011) projects that subsidence at the surface will range from 2.0 to 2.6 feet depending on coal thickness and the depth of mining below ground surface. Areas below and adjacent to the Purgatoire River will not be undermined and no surface subsidence is predicted below the river bed. Coal refuse from the mining operation will be permanently placed in the RDA. The RDA is an existing facility that was permitted in 1984. Both the RDA and the DWDA have been undermined and no vertical displacement has been observed as a result of subsidence. The depth to the underground mine workings below the RDA ranges from about 320 to 900 feet, and since the area has been undermined for more than 35 years, no future settlement is expected. 1 Elevation based on CFI underground datum corrected to conform with USGS surface topography by subtracting 100.73 feet. • 4164A.110130 Whetstone Associates • PR 02 Exhibit 8(4) Page 122 Revised 1/31/11