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2019-06-28_REVISION - M1977004 (9)
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2019-06-28_REVISION - M1977004 (9)
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Last modified
1/5/2025 7:35:53 AM
Creation date
7/1/2019 2:03:06 PM
Metadata
Fields
Template:
DRMS Permit Index
Permit No
M1977004
IBM Index Class Name
REVISION
Doc Date
6/28/2019
Doc Name
Request For Amendment To Permit
From
Homestake Mining
To
DRMS
Type & Sequence
AM1
Email Name
DMC
THM
Media Type
D
Archive
No
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Homestake Mining Company May 10,2019 <br /> Regular(112d)Operation Reclamation Permit Application Package <br /> • CNI (1995) evaluated five alternative failure models for the East Wall of the North Pit, <br /> including: 1)deep seated rotational failure through bedrock and/or structures that extends <br /> from the East Wall main scarp to the floor of the North Pit, 2) two rotational failures, an <br /> upper rotational failure involving a pre-existing slide, and failure through rock mass below <br /> the 10,600 ft level, 3)failure above the 10,500 ft level along a pre-existing rotational failure <br /> surface, and failure along intermediate geologic structures below 10,600 ft level, <br /> 4) pre-existing slide above the 10,500 ft level and plastic deformation below the 10,600 ft <br /> level along faults within bedrock, and 5) both upper and lower slope failures, with <br /> progressive (retrogressive) failure in the upper slide. Six alternative strategies for <br /> reclamation of the East Wall were provided and include: <br /> 1. No Action -Allow pit slope to stabilize naturally. <br /> 2. Unload slide and backfill pit. <br /> 3. Backfill the pit without unloading. <br /> 4. Unload slide without backfilling of pit. <br /> 5. Depressurize slope and install permanent surface drainage. <br /> 6. Combination of unloading, backfilling and slope drainage. <br /> • Golder (1996b) constructed a geotechnical model, performed a back analysis, and a <br /> sensitivity analysis of the"Pinnacle slopes"on the south wall of the North Pit. The analysis <br /> considered a circular failure scenario within Paleozoic bedrock stratigraphy using XSTABL <br /> limiting equilibrium software. Golder (1996b) concludes that the slope is sensitive to a <br /> curvilinear groundwater surface reaches above the 10,400 ft level and that the slope is <br /> likely more stable than the two adjacent slopes which failed previously. <br /> • AAI (1999) performed the most recent slope stability analysis of the East Wall of the North <br /> Pit. This study simulated slope failure of a complex three-block geologic model using used <br /> Universal Distinct Element Code(UDEC). The AAI (1999)three-block model uses different <br /> block geometry than the previous CNI (1982). The simulation showed that rotational failure <br /> of the "lower" and "middle" blocks resulted in explaining slope deformation features <br /> observed at the site and that translational failure of the "upper" block occurs in response <br /> to failure of the"middle"block. Their results show a decrease in slope movement velocities <br /> over time that may increase periodically in response to unusual extreme climatic <br /> conditions. AAI (1999) makes the following conclusions about rates of slope movement: <br /> o Northwest Corner: The potential for slope failure in the Northwest Corner is <br /> perceived to be low due to backfilling and slope regrading. <br /> o South Wall: The potential for slope failure at the South Wall is perceived to be low <br /> due to observed low rates of slope movement. AAI (1999)suggests that significant <br /> changes in slope geometry or ambient conditions would be required to affect the <br /> rates of slope movement at the South Wall. <br /> o East Wall: Although the eastern extent of the East Wall is defined by a prominent <br /> set of tension cracks and scarps, AAI (1999) states that the East Wall has never <br /> exhibited large scale rapid slope failure. They state that decreasing slope <br /> movement rates between 1994 and 1999 are likely the result of slope regrading <br /> operations in 1996 and that rates should continue to decrease until a state of quasi- <br /> EXHIBIT E-RULE 6.4.5(AMENDED RECLAMATION PLAN) Page 41 <br /> HOMESTAKE MINING COMPANY <br />
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