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-40- <br /> monitoriny of ;nine inflow, discharge, and consumption rates. The <br /> monitoring data should be updated continuously as mining progresses to <br /> improve engineering control design parameters or to mitigate any <br /> unexpected hydrologic impacts of subsidence. Such procedures .are <br /> necessary at each mine within the Roaring Fork Drainage in order to <br /> coordinate a comprehensive subsidence control plan. This monitoring is <br /> now being required of operators through the Colorado Permanent Regulatory <br /> Program permitting process. <br /> Subsidence in the adjacent North Fork of the Gunnison River Basin has <br /> been studied or observed at the Somerset Mine, the Hawk' s Nest mine, the <br /> Bear Mine, and hypotheses have been forwarded concerning the inactive and <br /> abandoned Oliver, No. 2 Mine. Dunrud (1976) discussed numerous subsidence <br /> causes and effects, and while no specific and consistent effects were <br /> delineated, it is evident that the physical parameters mentioned above <br /> are important topics. For instance, the presence of strong rock strata <br /> (such as sandstone) at the ground surfaced will permit the opening of <br /> tension cracks which could extend through the affected rock unit. Such a <br /> condition could significantly affect the interception of surface water <br /> and the recharge of ground water. The existence of weak rocks (such as <br /> shale) or soils at the ground surface could result in much less <br /> pronounced surface cracking. <br /> The dimensions of surface cracks appear to relate to the type of rocks in <br /> which they occur, the thickness of coal removed, the depth of the <br /> overburden, and the location of crack occurrence. Cracks in competent <br /> rocks tend to remain open, while cracks in incompetent rocks ar.d soils <br /> are likely to fill . _`__7 <br /> In light of these observations a range of subsidence impact scenarios are <br /> possible. Subsidence related cracking could increase surface and <br /> overburden infiltration rates, diverting water from streams and <br /> impoundments above the affected areas. Related changes in local <br /> piezometric surfaces could result in the modification of springs and <br /> seeps. Waters, having entered the sub-surface strata, could migrate <br /> towards the underground workings, eventually permeating the strata and <br /> gradually migrating downdip to the axis of the Piceance Basin. <br /> None of the three ;nines will affect the use of ground water from bedrock <br /> aquifers either separately or cumulatively, since there are no bedrock <br /> :,,ate.r supply wells completed in the region hydrologically adjacent to the <br /> .nines. Also, the potential for impacting future use of bedrock ground <br /> eater is low due to the depth of`u�1 required and to the problems <br /> of accessing steep slopes on private and U.S. Forest Service land. <br /> The quality and quantity of the .alluvial aquifers of Fournile Creek, <br /> Theuipson Creek ano Coal Creek Nill not oe cumulatively impacted during <br /> the first 5-Year permit period of the three mines. There is a <br /> possioility of quality and quantity impacts on Coal Cree' in the distant <br /> future when, and if, the north Thompson Creek ,tines progress into the <br /> Coal .,ree{ Drainace. <br />