Laserfiche WebLink
Ground water within the Mesaverde Formation has been found to be of limited <br />extent, occurring only as isolated perched water bearing zones. These zones are not <br />currently exploited and, because of their limited extent, have no potential for future <br />development. Disruption of local, perched water bearing zones may occur due to mining <br />where they lie in the immediate vicinity of the mine roof. Because of the nature of this <br />ground water, this will not constitute an impact on the area's resources. <br />Colluvial deposits are the source for local springs within the mine area. These are <br />generally located where there is sufficient overburden thickness and /or over areas where <br />low recovery rates will occur. The risk of the development of surface subsidence cracks is <br />low. <br />It is not expected that the subsidence will deteriorate the stability of old landslides to <br />the extent that their deformations could be renewed. Attention will have to be paid to <br />mining close to the coal outcrop and to the outcrop barrier pillars. <br />4.3 POTENTIAL MITIGATING MEASURES <br />Subsidence in areas where damage to resources is expected can be minimized by <br />leaving coal pillars for permanent support. Most features identified as requiring some form <br />of protection against the effects of subsidence lie within relatively small areas. This <br />enables the possibility of providing protection against subsidence by designing the mine to <br />appropriately locate partial extraction zones, such as main entries, without reducing <br />recoverable reserves. <br />The locations of proposed partial extraction zones are shown on Map 27. They are <br />generally limited by the 500 foot or less overburden zone, which corresponds with the limit <br />of the zone of high potential for the development of subsidence cracks at the surface, <br />unless there are site - specific justifications for extending the protective zone further. The <br />planned partial extraction zones (i.e. main entries and panel development pillars), form <br />protective pillars, the limits of which are defined according to the requirements of the <br />surface area being protected. The limits have been defined by extending a safety zone a <br />distance of fifty feet around the surface feature being protected, and then projecting a line <br />downward at the angle of draw until it intersects the coal seam. <br />PR -14 -34- 03/14 <br />