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mining operation and the assessment of the probable cumulative impact of all anticipated mining <br />in the area on the hydrologic balance, as described in Rule 2.05.6(3), have been made. The <br />proposed operation has been found to be designed to prevent material damage to the hydrologic <br />balance outside the permit area. <br />During the review of Permit Revision Number 2, the Division further evaluated potential impacts <br />to groundwater within and adjacent to the permit area and with regard to establishing <br />groundwater points of compliance. Three specific zones of groundwater that have the potential <br />to be impacted were evaluated. These include bedrock groundwater, backfill and excess spoil <br />groundwater, and alluvial groundwater. A synopsis of the Division's review is provided below. <br />Bedrock Groundwater <br />The Division has determined that coal mining operations at the Mine do not have the potential to <br />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 (materials are blast cast, back -cast by dragline, end - <br />dumped from trucks). Being less dense, they have more voids, are more permeable, and have <br />higher transmissivity values. In addition, the up to 450 -foot backfill section becomes a more <br />homogenous section. 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 <br />of developed groundwater are not deemed aquifers and the water is known to be of degraded <br />quality. Thus the belief of the Division is that points of groundwater compliance are not required <br />in 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 belief of the Division, as with <br />backfilled areas, 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 />Proposed Decision and Findings of Compliance January 2012 <br />Permit Renewal 06 Page 138 <br />