Laserfiche WebLink
per minute (92 gpm from the aquifer and 218 gpm from the three faults) and to <br />develop a map of the total projected water level decline in the affected <br />aquifer (see Figure 5). A description of the modeling can be found in Exhibit <br />39 of the permit application. <br />The applicant has projected that mining will dewater undermined portions of <br />the Wadge coal overburden aquifer and that the cone of depression will extend <br />to the margins of the Twentymile Park Basin. Also if faults are intercepted <br />that are in hydrologic communication with the underlying Trout Creek <br />sandstone, a local reduction in the hydrostatic head of the Trout Creek <br />sandstone can be expected. <br />The maximum 310 gpm mine inflows projected by the applicant for the life of <br />mine represent a removal of ground water stored within the Wadge <br />coal-overburden aquifer and Trout Creek sandstone. Figure 4 shows the <br />projected decline of the piezometric surface within the Wadge coal-overburden <br />aquifer. <br />The dewatering of the Wadge coal-overburden aquifer and the fault zones by the <br />mine workings may impact the recharge of the Fish Creek alluvial aquifer and <br />base flow in Fish Creek. This has been estimated to be between 8 and 20 gpm. <br />However, during the five-year permit period, the applicant projects only minor <br />decreases. The applicant predicts a 0.14 cfs maximum decrease in ground water <br />contribution to Fish Creek due to the loss of ground water currently <br />discharging to the streams from the Wadge coal-overburden (p. 2.05-49). This <br />number reflects a maximum loss of ground water tributary to Fish Creek. <br />There also is the potential of depleting water from the Fish Creek <br />stream-alluvial system by recharging the underlying Wadge coal-overburden <br />aquifer over four miles from the mine in Section 2, T6N, R86W. This depletion <br />would occur when the drawdown cone produced by the mine extends to the present <br />discharge area. This may occur by year 10 of mining. After this the <br />gradients will reverse and the waters of Fish Creek will discharge to the <br />overburden aquifer. The quantities of water removed from Fish Creek may be on <br />the order of 9 gpm. This calculation was made based on permeabilities of 0.4 <br />ftlday, reverse gradients of 7.5 percent and is bedrock - AVF contact of <br />60,000 ft2. <br />The applicant used a maximum design inflow rate of 310 gpm in their mine plan <br />and in their assessments of hydrologic impacts. Most of the projected mine <br />inflows will be discharged to sediment ponds and eventually to Foidel Creek <br />and Fish Creek. Any water required for operations within the mine will be <br />supplied by TCC well No. 1. A minor amount of inflow water will be consumed <br />as increased humidity in ventilation air (9 gpm) and increased moisture <br />absorbed on the coal leaving the mine (35 gpm). The applicant will monitor <br />mine inflow rates, ground water level declines, discharge rates, and <br />consumption of water within the mine (see Hydrologic Monitoring Plan, Exhibit <br />14 of the revision application). Results of the monitoring will be submitted <br />quarterly to the Division to verify the applicant's predictions. <br />Springs and seeps which discharge from the Wadge coal-overburden aquifer may <br />experience diminished flows. However, the applicant has located only one <br />-41- <br />