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<br />Mr. Noon Roche <br />Mazch 7, 2001 <br />Page 4 <br />Inc <br />distances to structures, differing structure geometries, and the presence or absence of stockpile berms. <br />All six of the geometries are from the north part of the mine where stability issues are more critical due to <br />the deeper mine depth and relative proximity of structures. The six geometries analyzed and the critical <br />structures are outlined below. All mine highwall heights are based on the exploratory boring logs. <br />1. North 75ih Street near the northwest corner of the ntine -This situation was modeled with a <br />22-foot highwall sloping %:l (horizontal to vertical) with the top of the highwall located 52 feet <br />from North 75's Street right-of--way. The stockpile berm was modeled with a 25-foot wide <br />surcharge load of 1,200 psf. The resulting factor of safety (FOS) was 2.1. <br />2. Southwest part of the west Pella Pond near the northwest corner ojtlte mine -The slope <br />geometry at the west Pella Pond near the northwest comer of the mine was also analyzed with <br />22-foot highwall sloping,''/~:1 (horizontal to vertical) with the top of the highwall located 80 feet <br />from the top of the pond. The Pella Pond was modeled at a slope of 2: I (horizontal to vertical). <br />No stockpile berm will be present in this area so no surcharge load was included in the model. <br />The resulting FOS was 2.9. <br />3. Southeast part of tl:e west Pella Pond near the north parr of t{te mine -The slope geometry <br />in this area was modeled with a 20-foot highwall sloping'h:l (horizontal to vertical). The top of <br />the highwall was modeled 50 feet from the top of the pond, and Pella Pond was sloped at Z: I <br />(horizontal to vertical). No surcharge load was approved as no stockpile will be present in this <br />area. The resulting FOS was 2.1. <br />4. The east Pella Pond near the north central part of the mine -This slope was modeled with a <br />19-foot highwall sloping '/z:l (horizontal to vertical) and located 80 feet from the top of the Pella <br />Pond. The slope of the Pella Pond was input at 2:1 (horizontal to vertical) and a 45-foot wide <br />surcharge load of 1200 psf was input to simulate the stockpile berm in this area. The resulting <br />FOS was 3. I . <br />5. The railroad lute located near the northeast corner of the mitre -The area was modeled with <br />a l9 foot high highwall sloping''/z:l (horizontal to vertical) and located 65 feet from the mine <br />highwall. No stockpile is planned in this area, so no surcharge was applied. The resulting FOS <br />was 2.7. <br />6. The water pipeline easement on the north part of the east ntltte bouttdarv -This area was <br />modeled with a 19 foot highwall sloping %z:l (horizontal to vertical) and located 60 feet from the <br />mine highwall. No surcharge was applied as stockpile berms are not planned between the mine <br />and the easement. The resulting FOS was 2.4. <br />r~ <br />Copies of the stability analysis input files and cross-sections are attached to this letter. <br />