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<br />Effects of Mining on Identified Alluvial Uallev F1 <br />Mining operations are not, or will not be, located within the Trout Creek <br />alluvial valley floor. Therefore, the AVF will not be physically disturbed. <br />Because mining does not extend onto the alluvial valley floor boundary, direct <br />impacts resulting from the physical disruption of alluvial and/or channel <br />materials will not occur. However, secondary effects, including minor <br />dewatering of the alluvium and water quality impacts due to the leaching of <br />dissolved salts from the spoil material, have been identified and have the <br />potential to impact the AVF. The significance of these secondary impacts are <br />discussed below. <br />Dewatering of the Alluvium <br />Mining operations in both the West Ridge and Moffat Areas have produced mine <br />inflows from the alluvial terraces. Mine inflows are directly related to <br />distance of the mining edge to the AVF alluvium, the further away operations, <br />the less the inflow. <br />The original permit application indicated that mining would induce inflows <br />from the Trout Creek alluvium. This impact has occurred in both the West <br />Ridge and the Moffat Areas where the floor of the box cut was at an elevation <br />below the alluvial water table elevation. Mining created a reverse gradient <br />allowing alluvial ground water to enter the pit following migration through <br />the undisturbed materials between the box cut and the alluvium. <br />In the original research, the orientation of the box cut was determined to be <br />a factor in the amount of inflow from the alluvium. Since more terrace area <br />and subsequent water flow would be encountered down dip if the pit was <br />oriented north-south, an east-west direction was chosen for coal removal. The <br />subsequent mine inflow seems to be within the estimated amounts of 29 gpm at <br />West Ridge, where the edge of the operation is 50 feet from Trout Creek, and <br />16 gpm at Moffat, where the edge of the operation is 400 feet from the creek. <br />Inflow has been observed to occur at discreet locations, and not in a <br />continual manner from the Moffat pit face. <br />As the Moffat pit proceeds northward, and above hydraulic gradient, pit inflow <br />from the alluvium is predicted to decrease. All reports indicate that the <br />inflow is temporary in nature. The data to date supports that the inflow will <br />cease and the water will reverse direction once the pit is backfilled. <br />Therefore, the quantity of water lost to the pit face is minimal and will be <br />restored when the post-mining hydraulic gradient is restored. <br />Data submitted by the applicant illustrate that impact to the alluvium is <br />minimal with a gradual lowering of the water level. The amount of flow from <br />the alluvium into Trout Creek is negligible when compared to the total flow of <br />Trout Creek. The impacts observed are temporary in nature occurring only for <br />the duration of mining. <br />An analysis done by the Division showed that a maximum drawdown of 1.6 feet <br />could occur where the alluvium is closest to the West Ridge box cut. Data <br />from the alluvial wells do not indicate that drawdown to this degree has <br />occurred. Orawdown in the alluvium adjacent to the Moffat Area has been <br />-31- <br />