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' I:d Haker April 8, 2002 ' Page 8 contaminate the USDW aquifers with high TDS water from the dissolution surface aquifer. The ' volume of llow, if any, will depend upon any changes in conductivity, the magnitude of the natural hydraulic gradient, and regional groundwater flow. The formulas in Table l correspond well with computer model predictions of fracture zone height for earlier Panel 1 mining. Fracture zone height estimates given by 'fable 1 for a 15-ft cavity height9 are consistent with analytical conclusions made in [he 1995 AAI report2. The 1995 analytical results showed insignifcant changes to hydraulic conductivity at the bottom of the R-6 aquitard (assuming weak roof strata), indicating that the fracture zone would not reach the R-6 unit. This corresponds with conclusions derived from the Table 1 formula for weak rock, which estimates that the fracture zone will terminate approximately 201•t or more below the base of the R-6 unit. The numerical model, if utilized to assess Panel 2 mining plans, would be expected to corroborate estimates shown in Table 2. Long-term surface subsidence is difficult to predict without detailed knowledge of cavity shape. Within the range of economic mining, it is possible for peak subsidence to range from zero to more than 10 ft, depending upon the extent of resource recovery. Notably, even for large subsidence, the B Groove and higher aquifers are likely to lie in the zone of continuous deformation and above the fracture zone. Mn/iognny Oil Shnle Zone The Mahogany oil shale zone overlies the top of the solution cavities (assumed to be the dissolution surface) by more than 440 ft. Hydraulic impacts are expected to be insignificant at this horizon due to attenuated connectivity between mining-induced fractures and separations. However, while continuous channels for groundwater flow may not exist, there is potential for localized rock mass disturbance resulting from overburden settlement. Possible damage features include bed separation, tensile fracturing, and strata shearing, as identified in the 1995 report2. Longwall operators have reported lateral movements along bedding of up to three inches as high as 90 times the mining hei~ht (I~'. Studies have shown that the greatest potential for interseam shearing lies within 12H °. The Mahogany Zone lies approximately 12 times above the maximum height of the solution cavities. Tensile fractures are most prevalent around the periphery of mining where bending strata are subjected to peak tensile stresses, but decrease substantially in the continuous deformation zone where strata bend more gradually and stresses are more widely distributed. The LISBM reports that some ground control problems can be expected where mining is conducted closer than SOH over caved longwall panelstl. However, it is suggested that mining is v Basis for high extraction solution mining in Panel 1 (1995 AAI report). 10 Haycocks, C., M. Karmic, E. Barko, J. Carman, B. Ehganner, S. Hudock, and S. Webster (1983), "Ground Control Mechanisms in Multi-Seam Mining," (Grants G t 105050 and G 111551 I, VAPolytech. Institute and State University), BuMines OFR 7-84, 328 pp. (cited on p. 14, IC 4360). ~ ~ Chekan, G. J. and 1. M. Listak (1993), "Design Practices for Multiple-Seam Longwall Mines," U.S. Department of the Interior, Bureau of Mines IC 9360. Agapito Associates, Inc.