1986-06-13_GENERAL DOCUMENTS - C1981018

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li -34- The permittee will be obtaining part of the required water supply from wells completed in the White River alluvium as discussed earlier. Approximately 600 gpm will be pumped from the aquifer to a head tank in the D-Portal Area. This is less than one percent of the low flow of the White River. Therefore impacts will not be significant. Recharge of the ground water is not expected to be impacted significantly by the proposed mining operation. Most of the recharge area for the Mesaverde aquifers is outside of the :mine plan area. It is possible that surface fracturing resulting from subsidence could increase recharge to the Upper Williams Fork. However, these cracks, if they occur, are expected to exist for only a short period of time before they seal up. Recharge of the White River Alluvium by bedrock aquifers is not considered to be significant because of the low transmissivities of the aquifers. The permittee has estimated that total discharge could be 1 .3 gpm through bedrock aquifers to the White River, which is less than a tenth of a percent of the base flow of the river. Therefore, changes in the recharge capacity of the bedrock aquifers is not expected to be a significant impact to the alluvial aquifer. The surface recharge capacity of the alluvial material in Scullion Gulch may be reduced due to the construction of cuts and fills in the portal areas. This disturbed area is small relative to the total area of Scullion Gulch and therefore impacts are expected to be very minor. Due to the presence of Kenney Reservoir, water withdrawal from the White River alluvial aquifer will not cause measurable drawdown in the alluvium at the well field site. The quantity of water which will be pumped is less than one percent of the low flow of the river. Subsidence from underground mine working could potentially impact both Red Wash and Scullion Gulch. The effect on Red Wash is of greatest importance because it drains approximately 122 square miles at the location where mining will extend beneath it. Alithough predictions indicate that maximum vertical subsidence could-approach six feet, large crevasses or collapse of the surface should not occur because there is approximately 600 to 1200 feet of overburden above the coal seam in that area. Furthermore, the swelling of shales and overburden from the caved roof should effectively fill the open mine cavity. An on-going monitoring program will be implemented to detect subsidence on the first longwall panel and first room and pillar section to be mined during the initial years of production. Predictions of probable disruption of the hydrologic regime from subsidence will be based on an analysis of that data. Tension cracks from subsidence may develop in formations directly underlying Red Wash. It appears that these cracks may extend upward for several tens of feet (oral communication with experts in this field; Page II. C-106b of the permit application). These cracks will be of limited extent, therefore a minimal amount of surface water will be siphoned into them. Furthermore, sediment accumulating in the cracks, and clays in the overburden may ultimately seal them off from surface inflow. Impacts on Scullion Gulch are expected to be similar to those on Red Wash, although maximum vertical a',fter room and pillar mining is only predicted to be one foot. The subsidence monitoring program previously mentioned will be used