2009-04-27_REPORT - C1981012 - Laserfiche WebLink

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Historic Allen Mine waste materials appear to be the major contributors to saline alluvial ground water quality in the vicinity of the New Elk Mine (PAW-3 and PAW-4) (Figure • 3.2-3). Saline conditions were anticipated in the PHC, and conductivities and TDS concentrations have been far lower than expected. During March and April of 1985,500 feet of the Middle Fork of the Purgatoire River was diverted to the north to create additional room for the coal stockpile at the New Elk Preparation Plant. The original channel was backfilled with mine waste, and two alluvial wells, PAW-3 and PAW-4, were established -o monitor water elevation and chemical parameters. Water quality does not appear to deteriorate significantly due to the presence of refuse in the backfill between PAW-3 and PAW-4 and measures of salinity, sodium, and sulfate are far lower than predicted by the PHC. A threefold increase over historic values in iron quantities in PAW - 3 and PAW-4 may be due to the steel casing of the wells. No further monitoring is required for PAW-3 and PAW-4. Data on PAW-8 (Table B-5) and the Stiff Diagram indicate that seepage from the current refuse disposal area contains similar concentrations of sodium, potassium and calcium to the pre-law mine waste (PAW-4). Leaching may be a cause for lower values from the old materials. Data from PAW-9 downstream of the New Elk facilities indicated dilution having an effect on concentrations. 3.2.4 New Elk Mine Water During the third quarter of 1989, the New Elk Mine was sealed and access to the mine workings terminated. Mine inflows are flooding the abandoned mine workings. Previous studies and reports suggested an inflow of 177 gallons per minute (gpm) and calculated inflows ranged from 142 to 468 gpm based on measurements taken at Station NEW-4. A number of approximations were made in the calculation of rates of inflow. From mine maps, the dip of the mine floor was determined to be 5 percent, and the water line crosses approximately 12,000 linear feet of mined areas. The available volume is based on an average extraction of 60 per cent. The calculations assume that the entire mined area below the water level measured in NEW-4 is flooded (i.e., no trapped air pockets). Figure 3.2-4, Mine Water Levels, portrays a lineal increase in the mine water level in the sealed New Elk Mine from 1994 through 2001. From mid-2001 through 2003, the rate of increase in mine water level appears to have diminished, only to resume its previous rate of increase during 2004. The water level at NEW-2 remained constant during 2006 through 2008. It is thought that water was flooding the East Mains area as water levels increased more rapidly at the Apache Canyon airshaft (NEW-3) during 2006 only to stabilize in 2007 and resume rising in 2008. Continued monitoring will provide the information to clarify the phenomena, and permit a more accurate projection of hydrologic consequences. The surface elevation given for NEW-4 has been adjusted to the CF&I elevation system used for NEW-2. Similarly, a GPS surface elevation determined for NEW-3 has been adjusted to a CFI surface elevation. Inflow water quality information is being obtained at the sealed New Elk Mine (see NEW - 2, Table B-7; NEW -3, Table B-8; and NEW -4, Table B-9). Stiff diagrams of mine water quality are provided in Figure 3.2.5. This water is of relatively high conductivity, and high concentrations of total dissolved solids, bicarbonate, and sodium. NECC installed a pump at the East Portal airshaft and started dewatering in December 2008.Water quality and • quantity information can be found in Appendix C. 36