Laserfiche WebLink
Memo to Bob Oswald 7 December 20, 2004 <br />Golden Wonder Mine Permit No. M-1978-091-UG <br />The minimum required overlying rock thickness at the bulkhead location is determined in accordance <br />with the following equation: <br />72B <br />H= r <br />Y <br />where: H =Required Rock Thickness above Bulkhead (feet) <br />BP =Formation Breakdown Pressure (psi) =design hydrostatic head <br />y =Rock Density (pounds per cubic foot) <br />H = (71)65 4) = 386 ft <br />Given the slope of the mountain above the proposed portal location, the foregoing analysis indicates that <br />the main water impounding bulkhead must be located approximately 800 feet inby of the portal. Since the <br />first 100 or so feet of the adit aze likely to make significant amounts of water due to open joints (limited <br />overburden pressure) the bulkhead 800 feet into the adit will not be capable of preventing 100 percent of <br />adit discharge in the post-mining setting. Additional, less robust bulkheads or adit linings can be installed <br />outby of the main bulkhead, but aze unlikely to be totally effective in elimination of adit dischazge. The <br />Operator must provide a plan for elimination of discharges to surface in the post mining setting. A <br />borehole to the Gold Quartz vein near the portal location was discussed during the October 13, 2004 site <br />inspection. However, boreholes for water management are problematic at reclaimed sites due to the need <br />for ongoing maintenance to keep the borehole open and flowing. <br />One of the primazy criteria to be evaluated for determination of required main bulkhead length is concrete <br />sheaz on the adit perimeter, which is determined as follows: <br />fs. = 2 f~ = 2 2500 =100 psi <br />(ACI 318-89, sec.11.3.1.1) <br />L = P(h)(l) <br />2(h + l) fs. <br />L _ 884(12)(12) <br />2(12 + 12)100 <br />L = 26.Sfeet <br />where.• fs- =concrete shear strength (psi) <br />f~~ =concrete compressive strength (psi) <br />L=bulkhead length (feet) <br />p=pressure head (psi) <br />h=adit height (feet) <br />l=adit width (feet) <br />The direct cost for the installation of a bulkhead of this length is estimated at $350,000.00. This estimate <br />is based on costs to install numerous bulkheads in San Juan County, Colorado over the past nine years. <br />With this cost for the main bulkhead alone, the Operator is forewarned to anticipate that the bond for the <br />