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• offer greater potential for reliable long term water supply. In addition, <br />even if a hydrologic connection exists between the abandoned workings on <br />the Vento Seam and Southfield's active workings, it is doubtful that the <br />overlying workings would ever be totally dewatered. Flows from the <br />abandoned workings would be limited by subsidence and caving which could <br />isolate entire sections of the mine, sediment deposition in the subsidence <br />fractures which act as flow conduits would gradually reduce flows, and <br />continuous. groundwater inflows to the mine would at least in part offset <br />any seepage losses. <br />Assuming that some dewatering of the Vento workings may occur, resulting <br />dewatering would be temporary in nature with gradual restoration of the <br />piezometric surface upon abandonment and sealing of the Southfield Mine <br />workings. Upon completion of mining it is anticipated that the Southfield <br />workings will gradually fill with water, essentially limiting groundwater <br />inflows as a result of any vertical infiltration. As discharge from <br />overlying abandoned workings declines, any reduction in the volume of <br />groundwater stored in the Vento workings is expected to be replenished by <br />• continuous natural recharge. <br />The mechanisms of mine drainage and dewatering as discussed in the <br />previous two sections are expected to result in some localized reductions <br />in the level of the piezometric surface. Any reductions are expected to <br />be limited to the immediate area surrounding the active mine workings with <br />the overlying Vento Coal Seam serving as a upper limit. Dependent upon <br />the extent of subsidence fracturing and resulting discharge from <br />associated perched groundwater reservoirs, changes in the piezometric <br />surface will be limited both horizontally and vertically by the relatively <br />low permeability of the interbedded siltstones and shales characteristic <br />of the Vermejo formation. Localized changes in the piezometric surface <br />are not expected to effect groundwater levels or flow rates in those <br />groundwater aquifers utilized for beneficial groundwater usage. <br />Localized reductions in the piezometric surface will result in a cone of <br />depression in and surrounding the active mining area. Upon completion of <br />• Southfield operations, and abandonment and sealing of the mine workings, <br />the abandoned workings are expected to gradually fill with water resulting <br />2.05.6-43 <br />~~. <br />.3' <br />