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Page 16 <br />` Limestone` ~ ~` / ~~ <br />Coal <br />j ~ -~ <br />-t- ~ <br />_ - ~/ .. ~ <br />Sandstone <br />Sandstone. ~ ~ ` <br />/: <br />Barrier Dillar <br />`~- - - <br /> <br /> <br />Figure 4-2. Interseam Shearing (adapted from Holland 194'n <br />active and that the greatest potential for shearing occurs in coal beds lying either within twelve <br />times the extracted seam height or in the caved zone. Fractures and joint systems inherent to the <br />strata aze also critical factors in interseam shearing. Faults may complicate or contribute to shear <br />7 failure. <br />4.2.2 Effect of Underground Mining on Groundwater <br />The effects of mining on groundwater have been the subject of many investigations <br />(Booth 1992; Elsworth et al. 1994, etc.). In general, the major factors controlling the groundwa- <br />ter level aze summarized as (1) the vertical position of the aquifer relative to the deformed zones <br />in the overburden, (2) the deformed zone in which the aquifer is located, (3) the characteristics of <br />the aquifer, and (4) the permeability of the underlying strata. <br />The water levels are not usually affected by the mining when the aquifer is located in the <br />continuous deformation and minor fractured zones. If the aquifer is underlain by good permeable <br />strata, the water level will never change. If the aquifer is located above regulaz coal measure <br />rock, the water level will change somewhat as the face of the longwall approaches. When the <br />strata movement ceases, the water level will recover either partially or completely. <br />The fractures in the regulaz and severe fractured zones cut through the entire zone and aze <br />well connected both horizontally and vertically. When the aquifer is located in the regular and <br />~ severe fractured zones with a highly permeable underlying strata, water will most likely drain to <br />the caving zone during mining and will seldom recover after mining. <br />Agapito Associates, Inc <br />