Laserfiche WebLink
The overburden units will be directly affected by the removal of the Wadge and Wolf Creek coal seams. Good <br />hydrologic communication with these units may occur through natural fractures and faults, which are enhanced <br />by stress- relief, and subsidence related to the mining activity. Partial dewatering of the immediately overlying <br />overburden units by gravity drainage is anticipated in active mine areas. Lateral movement of ground water in <br />the overburden unit toward the active mine areas will cause some dewatering and more general lowering of <br />potentiometric levels near the mine. <br />Historic Inflows - The Foidel Creek Mine has been in operation since 1983. Since that time, inflows and <br />discharges have been monitored. In addition, future inflows have been estimated. Past inflow estimates have <br />been made using theoretical models. At the time the most recent inflow estimates were made (using historic <br />inflow rates to 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 />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 />For mining to date, none of the faults identified in this report have yielded sustained inflows. In addition, no <br />evidence has been found that there is any significant hydraulic communication between the mine workings and <br />either the underlying Trout Creek Sandstone or the overlying Twentymile Sandstone. Only two significant <br />localized inflows were encountered; one in the 6 -Right Entry in late 1997, and one in the Northeast Mains fault <br />crossing 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, and the Wolf <br />Creek Reserve. Mining areas 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 µmhos /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, provided in Exhibit 49, Table E49 -1, indicates a mixed <br />cation sulfate /bicarbonate water with a conductivity of 3,610 µmhos /cm. In addition, most of this inflow has <br />been 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 were <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 approximately 55 gpm <br />resulted from mining activity in this area. Since the SWMD has been sealed, measurements of inflows and <br />discharge indicate that this rate has declined to 15 to 20 gpm. This inflow is further discussed in the mine water - <br />balance discussion. The historic inflows can be used to estimate overall inflows to the mine for areas that are <br />not near the sub -crop of the coal. Based upon the estimated inflow of 55 gpm and an affected mine area of <br />2,064 acres, the estimated inflow per unit area is 0.027 gpm /acre. An area is considered affected when the <br />entries are mined with the continuous miners. <br />TR13 -83 2.05 -135 11/03/14 <br />