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2009-10-30_PERMIT FILE - C1982056A (5)
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2009-10-30_PERMIT FILE - C1982056A (5)
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Last modified
8/24/2016 3:56:36 PM
Creation date
2/9/2010 10:39:29 AM
Metadata
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Template:
DRMS Permit Index
Permit No
C1982056A
IBM Index Class Name
Permit File
Doc Date
10/30/2009
Doc Name
Pages 2.05-123 to 2.05-197.3
Section_Exhibit Name
2.05.5 Postmining Land Uses
Media Type
D
Archive
Yes
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Ground Water Inflow to the Mine <br /> The underground mining activities at the Foidel Creek Mine have the potential to drain ground water from the <br /> mined coal seam, and overlying and immediately underlying rock units. Bedrock units overlying and <br /> underlying the Wadge Coal Seam, which contain ground water, would typically have formation pressures higher <br /> that the atmospheric pressure that would exist in any open mine workings. Consequently, if there is sufficient <br /> hydrologic communication, there will be movement of ground water from these units into the active mine - <br /> workings. <br /> The overburden unit will be directly affected by the removal of the Wadge Coal Seam. Good hydrologic <br /> communication with the unit may occur through natural fractures and faults, which are enhanced by stress - relief, <br /> and subsidence related to the mining activity. Partial dewatering of the immediately overlying overburden unit <br /> by gravity drainage is anticipated in active mine areas. Lateral movement of ground water in the overburden unit <br /> toward the active mine areas will cause some dewatering and more general lowering of potentiometric levels <br /> near the mine. <br /> Historic Inflows - The Foidel Creek Mine has been operated since 1983. Since that time, inflows and discharges <br /> have been monitored. In addition, future inflows have been estimated. Past inflow estimates have been made <br /> using theoretical models. At the time the most recent inflow estimates were made (using historic inflow rates to <br /> project future inflows), approximately 9,000 acres of area had been mined. <br /> The quantity of mine inflow and the resultant effects on potentiometric levels on the Wadge overburden unit <br /> were studied using a two - dimensional finite - difference, simulation model for the original Foidel Creek Mine <br /> permit application (Exhibit 13, Ground Water Model Documentation). The results and predictions of the model <br /> were used in the development of a Mine Water Control Plan included in Exhibit 33. Most of the estimated <br /> inflow was projected to occur as leakage from the Trout Creek Sandstone through faults intersecting the mine. <br /> This is based on the assumption that the faults would act as conduits and allow for flow of ground water into the <br /> 0 _ mine. The mine has intercepted several faults, however, because the faults are typically in compression they are <br /> relatively tight and inflows through the faults have been limited. <br /> Through June 2006, none of the faults identified in this report had yielded sustained inflows. In addition, no <br /> evidence has been found that there is any significant connection between the mine workings and either the <br /> underlying Trout Creek Sandstone or the overlying Twentymile Sandstone. Only two significant localized <br /> inflows were encountered; one in the 6 -Right Entry in late 1997, and one in the Northeast Mains fault crossing <br /> in August 1999. <br /> The discussion of the historic inflows are presented by mining area: 1) The North Mains and portal areas <br /> (NMS); 2) The 1 -South Panel plus the Southwest panels (Panels 1 -SW to 3 -SW) plus the South Panels (1 -Left to <br /> 6 -Left) which will be called the Southwest Mining District (SWMD); 3) The East Mining District (EMD) <br /> consisting of Panels 2Right to 9- Right; and 4) The North Mining District (NMD) consisting of Panels 12 -Right <br /> through 16- Right. Future mining areas include the remaining panels in the North Mining District (NMD) and <br /> the Western Mining District (WMD) containing the reserves to the north and west of the SWMD. Mining areas <br /> and designations are shown on the Mine Plan Map, Map 23. <br /> Inflows have historically been encountered in the NMS area. From 1993 to 2006, the inflows to the (NMS, <br /> water from overlying surface -mined spoils), as measured in the annual mine inflow surveys, remained constant <br /> at approximately 30 to 40 gpm. The conductivity of this water, which ranged from approximately 2,500 to <br /> 4,500 gmhos /cm, indicates that it is primarily derived from ground water that has been mixed with spoil water <br /> from the up -dip spoils. A typical spoil well analysis is shown in Exhibit 49, Table E49 -1. It has a mixed cation - <br /> sulfate/bicarbonate water with a conductivity of 3,610 gmhos /cm. In addition, most of this inflow has been <br /> observed from seeps that are within 2,000 feet of the portal. <br /> • No specific areas of high inflow occurred during development of the SWMD. Also, because the panels where <br /> sealed sequentially after mining, these areas could not be accessed for the more recent mine inflow surveys, so <br /> detailed information on mine inflows for this area could not be obtained. Estimates based on a composite of <br /> several prior inflow studies and dewatering rates indicate that flows on the order of approximately55 gpm <br /> PR09 -08 2.05 -135 04/22/09 <br />
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