PERMFILE114605 - Laserfiche WebLink

Home Browse Search

therefore: Qr = (0.17 ft/day)(0.5 ft)(I,500 ft Q, 127.5 cubic tUday for outcrop area one, and Q2 (0.17 ft/day)(0.5 ft)(22,440 ft2) Qr = 1,907.4 cubic ft/day for outcrop area two The combined total recharge for both outcrops using a hydraulic conductivity of 0.17 ft/day is 2,034.9 cubic ft/day. This value increases to a combined total of 3,352 cubic f1/day when using the higher hydraulic conductivity of 0.28 fUday. By using a total dissolved solid concentration of 2,392 mg/L in the Foidel Creek water, it is possible to calculate a recharge to the sandstone that ranges from 137.8 1cg/day to 227 kg/day. This is certainly aworst-case scenario because the water m Foidel Creek is separated from the Twentymile Sandstone by a silty-clay that forms the bed of the creek. It is estimated that a reduction from 50% to more than an order of magnitude could be expected from the theoretical seepage calculation. Therefore, recharge of total dissolved solids should also be substantially less than calculated. Fractures aze expected to form in the Twentymile Sandstone as subsidence occurs. These fractures would normally increase the hydrauhc conductivity and recharge to the sandstone. @ is, however, expected that these fractures will rapidly be filled with clay and silt from the streambed. Sub Terra, the same consultant who prepared the subsidence predictions for Fish Creek, has prepared subsidence predictions for the Eastern Mining District. This work is presented in Exhibit 7E, Prediction of Subsidence, Eastem Section of the Foidel Creek Mine. The subsidence predictions vary from .2 feet to 6 feet. This prediction is presented th Table 19 and shown on Figure l7, Exhibit 7E. The valley floor is not actively managed, i.e.: no flood imgation network estabhshed, and therefore, will not cause any major dismption to the system. The most likely effect will be a ponding of water within the subsided area, which should not cause any significant problems to the grazing of the area. • )n reference to Middle Creek, subsidence will vary from .2 feet to 7.2 feet. This prediction is presented in Table 21 and shown on Figure 19 in Exhibit 7E. The valley floor is managed the same as above and no major disruptions to the system are anticipated from the subsidence in the area. A program will be developed for monitoring the subsidence impacts to the valley floor. This program is detailed in the subsidence monitoring section of the pemrit application. NORTHERN MINING DISTRICT (12 Right through 16 Right) (PR99-OS) TCC's mining operation will result in subsiding Fish Creek and its alluvial valley floor. The impact to the ranches is discussed in the following paragraphs. The ranches are shown on Map 1B. Given the fact that the valley floor will subside the area will be flooded. TCC is not proposing any reclamation activities for the flooded areas. The extent of flooding and loss of acreage is described in the following paragraphs. The extent of flooding is controlled by the elevation overlying the gateroads and bank height immediately upstream from that point. In reference to Fish Creek, Twentymile is of the opinion that its mining operation will not impact enough of the valley floor to be significant to the ranching operation. Twentymile Coal Company, through its Trout Crcek Ranch, manages all of its lands, approximately 24,000 acres, for the grazing of cattle. Given the active status of its mining operation, not all of this acreage is utilized for pasturing livestock. Presently, there are no irrigation ditches established along Fish Crcek, which irrigate a designated alluvial floor within the limits of longwall panels 13 Right through 16 Right. This is due to the fact that it is not economically feasible to establish an irrigation system on the limited acres formed by the meandering Fish Creek. Given the • extensive irrigation systems set up when the area was originally developed, it is reasonable to conclude that this segment of Fish Creek is not conducive to flood imgation. PR 99-OS 2.06-25 11/17/99