Laserfiche WebLink
-36- <br />Mining activities which affect subsidence are: <br />Size, shape, depth, location and real extent of workings; <br />Rate of development and extraction of resource; and, <br />Mining methods. <br />The possible impacts of subsidence include: <br />- Modification of surface water hydrology - channel and watershed <br />geometry and sediment erosion rates, <br />- Modification of ground water hydrology - changes in spring <br />discharge, aquifer characteristics and recharge, <br />- Loss of water from surface impoundments due to disruption by <br />surface cracking, and <br />- Increase in surficial mass movement activity - landsliding and rock <br />falling. <br />Natural physical influences upon subsidence can be controlled to the extent <br />that mine plans can be designed to avoid obvious hazards (e.g. shallow <br />openings beneath perennial streams, landslide bodies, impoundments, etc), or <br />to limit subsidence in accordance with the current state-of-the-art of ground <br />control (engineered control of roof and pillar failures in mines). Subsidence <br />predication and ground control engineering are not definitive sciences. <br />Design engineering concepts must be verified through continuous monitoring <br />(surface topography, ground water hydrology and surface water hydrology) and <br />observation. <br />Evaluation of the impacts of subsidence upon hydrologic systems requires the <br />collection of extensive baseline data consisting of surface water and ground <br />water monitoring (quantity and quality), precipitation gaging, <br />evapotranspiration rates, geological mapping, topographic surveying and <br />recording of mine inflow rates. The baseline data should be updated <br />continuously as mining progresses to improve engineering control design <br />parameters or to mitigate any unexpected subsidence occurrences. Such <br />procedures are necessary at each mine within the district in order to <br />coordinate a district wide subsidence control plan. These procedures are now <br />being required of all operators through the Permanent Colorado Coal Mine <br />Regulatory Program permitting process. <br />Subsidence in the area has been studied or observed at the Somerset Mine, the <br />Hawk's Nest Mine, the Bear Mine, and hypotheses forwarded concernin the <br />Oliver No. 2 Mine. Dunrud, in a study regarding the Somerset Mine ~USGS Prof <br />Paper 969), discussed numerous subsidence causes and effects, and while no <br />specific and consistent effects were delineated, it is evident that the <br />physical parameters mentioned above are important topics. For instance, the <br />presence of strong rock strata (such as sandstone) at the ground surface will <br />permit the opening of tension cracks which could extend through the affected <br />