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~. Northern Coal Company The height of coal mining will not extend to the roof strata encompassing the coal seam and no disruption of these beds will take place. Consequently, the existing permeability and/or porosity of this strata will remain intact. kNo changes, in groundwater communication within the srtrata or along~~~f+ra~dt"ure~ 4lineame'nts and mine inflow should be expected over what is presently occurrjinga Additionally, monitoring of observation wells shows the "G" seam and other coals in the area are aquicludes. Under these conditions, it is expected that the joints and fractures and encompassing strata would be under a slightly higher than equilibrium pore pressure resulting from very low transmissivity of coals and encompassing strata. Ultimately reduction of these pressures could result from mining and may improve and lessen the potential for movement and subsidence. Subsidence is primarily dependent upon the amount of material extracted from the coal seam and is greatest with pillar extraction or with mining to extract a higher percentagz of coal than tJorthern has projected for the area under Curtis Creek. The roof control plan for the Rienau No. 2 Mine calls for pillars of 80 x 80 feet on 100 foot centers to be used when crossing under Curtis Creek. Pillars will not be robbed nor pulled at the end of mining. This will enable sufficiently large and competent material to support the roof conditions in this area. Northern Coal is complying and will continue to comply with 30 CFR Chapter 1, Sub-Part 75.200, Roof Control, as administered by Mine Safety and Health Administration, Department of Labor. These regulations are designed to prevent roof falls and protect the safety of the miners. Any roof fall that might occur in'spite of the compliance with these regi,lations - would be a failure of the strata along the bedding planes within the pressure :arch created 6y the opening of the mine entry. This ar-~ch.is showr.,in~,the t• attached copies of chapters from tests on roof support and ground con•trol~ From - these it will be plainly seen that any "what if" roof fall would not normally have vertical cracks, but rather the fall would be dome shaped and would be ,, roughly the height of the entry above the original mine roof. MSHA requires that any roof fall be fully re-supported before mining can continue. This eliminated fractures from entending further in the roof. *To summarize, there wirll be,no subsidence in that secondary miningh, e;:.gi.•, tfje,. .mining of pillars, is not planned in the area where the Rienau Nd•!~ 2 Mihe w~ihlll cross under State Highway 13/788 and Curtis Creek: The lack of subsidence coupled with the nature of the overlying sediments •.~e.g, fractures discontinuous and tendency to "heal" due to plastic response of sediments, would restrict fractures to the immediate area above the haulageways. F•• The maximum extent of possible fracturing into the roof would be~himited.by!~the 'pressure stabilization arch which forms above the haulageways;. Noy arch wou~lld~ abe present over the pillars since this will remain undisturbed gr,o,u~d~;~Max~4= mum height of this arch is equal to the width of the ha wlageway. (i20 fe'et). ! Northern's•roof control program should eliminate even these fractures from . forming.