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negatively impact bedrock groundwater, and that no point of compliance need be established for <br /> bedrock groundwater. <br /> Backfill and Excess Spoil Groundwater <br /> The Mine is a multi-seam, open-pit, operation. The pits are excavated to approximately 450 feet <br /> deep, and are then backfilled to approximate original contour. The original stratification of <br /> geologic units is not reconstructed during this backfill process. Placed backfill materials are not <br /> as dense as in situ geologic formations. Being less dense, they have more voids, are more <br /> permeable, and have higher transmissivity values. As precipitation penetrates these areas, it <br /> becomes groundwater. <br /> Such groundwater would develop as a result of the mining method and is not considered a pre- <br /> existing groundwater aquifer/saturated zone that would be impacted by the mining. These zones <br /> of developed groundwater are not deemed aquifers and the water is known to be of degraded <br /> quality. Thus the Division determined that points of groundwater compliance are not required in <br /> areas of mine pit backfill. <br /> During the open-pit mining process, the replacement volume of mined materials expands by <br /> approximately 20 percent, requiring the development of excess spoil fills for the excess material. <br /> These fills approximate the pit depths in thickness and are similar to characteristics of backfilled <br /> areas. However, they include underdrain systems designed to minimize groundwater reservoirs. <br /> In the event that groundwater reservoirs do develop, it is the determination of the Division, as <br /> with backfilled areas, that groundwater points of compliance are not required in excess spoil fills. <br /> Spoil groundwater is of known degraded quality and is not intended for use as an aquifer. <br /> Alluvial Groundwater <br /> Activities at the Mine have the potential to impact alluvial groundwater in those areas of Taylor <br /> Creek, Wilson Creek„ Good Spring Creek, Collom Gulch and Jubb Creek that are hydrologically <br /> down-gradient of mining activity. Sources of impact include discharges of runoff from surface <br /> disturbed areas, discharges or seepage from backfill and excess spoil areas, and from surface and <br /> subsurface flows from the coal stockpiles at the Gossard Loadout. <br /> The findings by the Division, for alluvial groundwater as described above, is substantiated by the <br /> information in the application. In the PAP, Colowyo indicates that the alluvial aquifer associated <br /> with Good Spring Creek has a high transmissivity and is unconfined. Possible impacts to this <br /> aquifer would be associated with the infiltration of water from the pit and water quality <br /> deviations caused by infiltration of runoff water. Colowyo further states that "meteoric water <br /> infiltrating into the reclaimed pit should enter the bedrock aquifer and eventually contribute to <br /> seeps and springs tributary to Good Spring Creek and possibly Taylor Creek." These statements <br /> are consistent with Division findings. Therefore, the Division concludes that the Colowyo Mine <br /> Proposed Decision and Findings of Compliance January 5,2023 <br /> Permit Renewal No. 8 Page 142 <br />