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t <br /> TR-25 Submittal <br /> Page 2 <br /> American Tunnel closure. WQCD has stipulated by Amendment to the Consent Decree <br /> (attached)to allow placement of the additional American Tunnel bulkheads needed for <br /> final mine closure under a modified schedule thereby, allowing placement during the <br /> 2001 construction season. The following outlines the proposed technical revisions to the <br /> respective sections of MLR Permit M-77-378. <br /> MINING PLAN <br /> The conceptual closure plan for the American Tunnel anticipated placement of a <br /> bulkhead in the portal to eliminate drainage to surface. This concept was modified to <br /> include an internal bulkhead with TR-14 after completion of technical studies(placement <br /> and design, hydrologic and geochemical) commissioned to provide DMG with the <br /> technical details for closure. TR-14 did not include placement and design details for the <br /> additional bulkheads needed for tunnel closure. These details are summarized below and <br /> attached is the design report by John F. Abel Jr., design engineer for the Sunnyside Mine <br /> bulkheads. <br /> Two bulkheads are proposed. The interior bulkhead(American Tunnel Bulkhead#2)will <br /> be placed to isolate the water bearing fault zone from the near surface fracture zone and <br /> the near surface bulkhead(American Tunnel Bulkhead#3) will be placed to minimize the <br /> near surface fracture zone drainage to surface through the portal. In combination, they <br /> will provide an approximation of the pre-mining hydrologic conditions. Each of these <br /> bulkheads is designed for the maximum pressure (ie pressure resulting from distance to <br /> surface) and the maximum credible earthquake. <br /> Bulkhead#2 Details <br /> Location: Approximately 2000' from surface <br /> Design Head: 640 feet <br /> Concrete Design Strength 3000 psi <br /> Bulkhead Length 10, <br /> Cross-section Dimensions: 13.5' wide x 14' high <br /> Rebar: <br /> Upstream: #10 rebar @ 6.5" centers—vertical and horizontal <br /> Downstream: #10 rebar @ 6"centers—vertical and horizontal <br /> Rebar Cover: 3.5"—both faces <br /> Perimeter Irregularity: 8.3 %perimeter irregularities projecting 0.16"minimum <br /> Drainage Pipe: 8" Schedule 40 SS with 1 - 3/8"thick thrust ring and 2— <br /> seep rings <br />