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-35- <br />- Modification of ground water hydrology -changes in spring discharge, <br />aquifer characteristics and recharge; <br />- Loss of water from surface impoundments due to disruption by surface <br />cracking; and <br />- Increase in surficial mass movement activity -landslides and rock <br />falls. <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 />workings 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 />prediction and ground control engineering are not definitive sciences. Design <br />engineering concepts must be verified through continuous monitoring (surface <br />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 monitoring data consisting of surface water and ground <br />water monitoring (quantity and quality), precipitation gaging, <br />evapotranspiration rates, geological mapping, topography surveying and <br />recording of mine inflow discharge and consumption rates. The monitoring data <br />should be updated continuously as mining progresses to improve engineering <br />control design parameters or to mitigate any unexpected subsidence <br />occurrences. Such procedures are necessary at each mine within the Somerset <br />Coal Field in order to coordinate a comprehensive subsidence control plan. <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 have been forwarded concerning <br />the inactive and abandoned Oliver No. 2 Mine. The Oliver Mine, since <br />abandoned and not anticipated to open, is not by definition a "coal mine <br />operation" that was or could be considered in this CHIS. However, literature <br />on this mine was reviewed for general information purposes. Dunrud (1976) <br />discussed numerous subsidence causes and effects, and while no specific and <br />consistent effects were delineated, it is evident that the physical parameters <br />mentioned above are important topics. For instance, the presence of strong <br />rock strata, such as sandstone, at the ground surface will permit the opening <br />of tension cracks which could extend through the affected rock unit. Such a <br />condition could significantly affect the interception of surface water and the <br />recharge of ground water. The existence of weak rocks, such as shale, or <br />soils at the ground surface could result in much less pronounced surface <br />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 overburden, <br />and the location of crack occurrence. Cracks in competent rocks tend to <br />remain open while cracks in incompetent rocks and soils are likely to fill. <br />