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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 geologic <br /> units is not reconstructed during this backfill process. Placed backfill materials are not as dense as in <br /> situ geologic formations. Being less dense, they have more voids, are more permeable, and have <br /> higher transmissivity values. As precipitation penetrates these areas, it 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 of <br /> developed groundwater are not deemed aquifers and the water is known to be of degraded quality. <br /> Thus the Division determined that points of groundwater compliance are not required in areas of <br /> 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. In <br /> the event that groundwater reservoirs do develop, it is the determination of the Division, as with <br /> backfilled areas, that groundwater points of compliance are not required in excess spoil fills. Spoil <br /> 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 with <br /> Good Spring Creek has a high transmissivity and is unconfined. Possible impacts to this aquifer <br /> would be associated with the infiltration of water from the pit and water quality deviations caused by <br /> infiltration of runoff water. Colowyo further states that "meteoric water infiltrating into the <br /> reclaimed pit should enter the bedrock aquifer and eventually contribute to seeps and springs <br /> tributary to Good Spring Creek and possibly Taylor Creek." These statements are consistent with <br /> Division findings. Therefore,the Division concludes that the Colowyo Mine <br /> 38 <br /> Permit Revision No.5(PR-05),G 1981-019 <br />