2009-02-10_PERMIT FILE - C1981022 (5)

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Sa2ien - 2.04.7 Stored Mine Water System - Historical and ongoing coal mining in the area has resulted in extensive underground mine workings. In those areas where the mine workings are associated with perched ground water units or where mine subsidence results in fractures connecting to perched ground water occurrences, ground water inflow has occurred or is occurring, resulting in some accumulation of stored ground water in the mine workings. Both historic and potential future contributions to mine inflow from either surface water flows in the North Fork of the Gunnison River or the associated alluvial/colluvial system are considered negligible. The historic Blue Ribbon, Hawk's Nest Mine and the Elk Creek Mine workings are or will be well above the present level of the river. The Somerset Mine and Sanborn Creek Mine workings, while partially below river level, are in coal seams which are stratigraphically above river level and laterally separated from the margins of both the river and the associated alluvial/colluvial deposits. The only mine water discharge to date has been minor flow from Spring SP-8 (Oliver Mme) and pumped water from the Sanborn Creek Mme. While historic flows from this spring averaged 12gpm, recent flows are non-existent. When the Sanborn Crek mine was closed, pumped flows were halted. See the Annual Hydrology Reports (AHR's) for additional information. Total water storage capacity in the abandoned Somerset B and C seam workings located below the portal elevations (6090' elevation) is estimated to be in excess of 1 billion gallons. Historic Somerset mine inflow rates had been low to moderate, as discussed in the previous section, ranging from 0 to 400 gpm. Based on monitoring of initial flooding of the abandoned B-Seam workings in the Somerset Mute (Wells B-6 and H 10), the rate of flooding is relatively slow, occurring over a period of 5 to 10 years as illustrated by Figures 2.04.7-175, Water Level Hydrograph , Somerset Mine - B Coal Seam (Well B-6), and 2.04.7-F6, Water Level Hydrograph , Somerset Mine - B Coal Seam (Well H-10). Curiously, beginning in October 1999, both wells showed no measurable water level. The D2B water transfer well located in the Elk Creek drainage (TR 47) indicated a water table at the 6044' elevation. Flooding of the abandoned workings had been neither complete nor uniform, as evidenced by differences in equilibrium water level elevations between the referenced monitoring wells (Well B-6 at elevation 6,050' and Well H-10 at elevation 6,068). The water level in the abandoned Somerset Mine B-Seam workings have stabilized at an elevation well below any of the mine openings (-6090') and there has been no mine water discharge from the Somerset Mine nor is there expected to be any in the future. Some of the mine water which may potentially be stored in the upper mine workings (Hawk's Nest and Oliver Mines - D and E seams) may be drained by mining and related subsidence in the B and C seams by the Sanborn Creek Mine. Potential mine water inflows and drainage and the proposed related control and mitigation measures, are addressed by a detailed report titled, "Water Communication Potential From Overlying Workings at the Sanborn Creek Mine" (Abel, 1992), included in Exhibit 2.04-E4, Hydrologic Information. During active miring operations, minimal mine water inflows and operational water collected from dust control over spray, motor cooling, etc will also be collected and routed to underground sumps. . To the extent possible, water which collects in the sumps will be utilized to meet operational mine water needs for dust control and other purposes. Any excess mine water will be treated, if necessary, to meet applicable effluent standards and discharged to surface drainages or transferred via water transfer boreholes (D2B and Hubbard Fan) to the underlying abandoned B/C seam workings. Generally, following completion of mining, it is anticipated that ground water inflows to the mine workings will continue until equilibrium is established between inflows, any discharge or ground water recharge, and the associated perched water table(s). Ground Water Quality - Ground water quality for the mine and adjacent areas is highly variable dependent on the recharge source, flow path, strata with which the water comes in contact, and discharge mechanism Generally, water quality for alluvial/colluvial ground water is very similar to the surface water quality of the associated surface water source due to close surface and ground water interaction and limited residence time. Water quality for most shallow perched ground water sources TR-51 2.04-37 Revised July2005