Laserfiche WebLink
under other lakes and that cover d stances below Eureka Gulch are substantial and not <br /> likely to eollapm. <br /> Stability above underground openings, in general, will be governed by the depth of <br /> overburden. In areas where the ratio of undisturbed overburden to width of opening(the <br /> workings average about 1448 feet in diameter) is greater than S, no in mediate swfaee <br /> effects are expected. In areas where this ratio is less, subsidence over the long tern may <br /> occur. Future mining plans may require removal of material in areas where the overburden <br /> to width ratio is less than S. At the present time, only the Lake Emma area is in this <br /> category. In this area bacI911 ng q%v mining will be done. If other areas are encountered <br /> during the continuing development of mining plans, the mining permit will be modified to <br /> present areas to be mineQ methods of mining and long term stability methods such as rock <br /> reinforcement,backfilling, and Instrumentation. <br /> The only areas where current concern exists would be for the workings immediately <br /> beneath the Lake Emma area. These areas of thin roof will be removed based on current <br /> mining plans and backfilled as pan of reclamation,as specified in Exhibit E. <br /> Closure of adits. As discussed with the MLRD stag at the September 18, 1986 <br /> meeting, it is anticipated that, to alleviate the need for indefinite mine drainage treatment,a <br /> hydraulic seal will be installed in both the Terry and American Tunnels upon closure of the <br /> mine. The seal will act to prevent any substantial releases of underground waters from the <br /> tunnels to the ground surface. <br /> Portal closure is planned for the American Tunnel and Terry Tunnels. Detailed plans are <br /> not available at the present and will be developed prior to acnW construction. Conceptual <br /> plans would be to place a by-pass pipe for the water flows with a valve in it. A rubble or <br /> concrete temporary buLthead with supports into the bedrock would then be constructed as <br />-`; necessary. The valve would then be closed and a plug of concrete placed immedately QW <br /> closure to provide an adequate factor of safety against blow-out under full head(refer to <br /> Appendix 2 F'). The plug would be placed back in the tunnel so additional hydrostatic <br /> pressure will have limited effect on the overburden rock. <br /> Waters that currently discharge from the tunnels are thought to be from near surface <br /> sources, which &filtrate into fracnves/pina that penetrate the various workings within the <br /> mine. No specific data related to underground waters within the mine or the sources of <br /> these waters exist for the site. However,based on the physical ground conditions that exist <br /> at mining sites similar to the Sunnyside Mine, certain conclusions can be drawn regarding <br /> potential discharges of impacted mine water to the surface. <br /> Obviously, without any form of hydraulic seal, the tunnels will continue to discharge water <br /> from the mine workings. The source of the water in the workings has to be attributed to <br /> water infiltrating(recharging)from the near surface environment. With the hydraulic seals <br /> in place water will acewnulate within the underground workings until some equilibrium <br /> conditions prevail. It is conceivable that water that is stored in this manner may arise at the <br /> ground surface through the various near surface jointlfi amm system(s)associated with the <br /> mine. Likewise due to the physical(small exposure)and chemical(reducing environment) <br /> characteristics of the sealed mine, the quality of this water would be of a better quality than <br /> what is currently produced from cannel discharges. <br /> Any attempt to evaluate the quantity and quality of water that may eventually seep from the <br /> mine would require a very in-depth and sophisticated investigative process. <br /> With regard to the Terry Tunnel, and again qualitatively speaking,flow from the tunnel <br /> occurred only afar the failure of Lake Emma. The source of water to the tunnel is thus <br /> through i filtration of surface water to and through the disturbed rock associated with this <br /> failure. Therefore, with the planned reclamation of Lake Emma, the flow to the Terry <br /> Tunnel is expected to be reduced. However,since some of the surfacelnear surface water <br /> Consolidated Permit Application G:26 1-13-87 <br />