2019-06-28_REVISION - M1977004 (9)

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Homestake Mining Company May 10,2019 Regular(112d)Operation Reclamation Permit Application Package equilibrium is reached. A westward slope creep should be expected to continue until sufficient resistance is reached. • AAI (2000a) constructed a geotechnical model based on surface survey and inclinometer data to evaluate wedge failure conditions on the South Wall of the North Pit. The analysis was performed using XSTABL, a two-dimensional, limiting equilibrium slope stability software program. Results showed a relatively shallow failure plane and slope stability that are near limiting equilibrium, suggesting that only minor changes in conditions may be needed to trigger slope movement. This analysis was originally performed in 1998, but the final report was issued in 2000 (AAI, 2000a). As a result of this analysis, Inclinometers 198-1 and 198-2 were installed on the South Wall of the North Pit in November of 1998. Slope movement in the North Pit continued after regrading activities and stability assessments were completed. HMC therefore adopted an observational approach discussed in Section 4.2. 3.4.1.2. South Pit Slope movement at the South Pit began after excavation of the pit was initiated (AAI, 1999). Details regarding the date when slope movement was first observed, size, and characteristics of the movement are not included in the reporting reviewed, but tension cracks and scarps above the South Pit's East Wall were mapped in 1994, apparently as part of the Golder(1995) study as cited by Agapito (1999). The tension cracks and scarps are shown in maps by AAI (1999) and SRK (2007). The South Pit slopes were regraded in 1996 as part of mitigation effort to stabilize the pit slopes. Although AAI (1999) suggests that the regrading effort appeared to stabilize the slopes, at least one area of slope failure has become active(Figure 3-16). The landslide measures up to approximately 180 ft wide and approximately 250 ft long and annual survey data shows that his has been actively moving since at least 2006 (SRK, 2007). Previous slope stability models include: • SRK (1983) evaluated slope stability for the South Pit prior to its excavation, and the rock dumps. • DPI (1993) evaluated rotational failure for the South Pit and concluded that the pit slopes can be stabilized for Mine reclamation through backfilling, regrading, and revegetation. Pit slope movement in the South Pit temporarily ceased upon backfilling in in 1996, but shallow slope movement began in 2006 (SRK, 2007). HMC adopted an observational approach, as discussed in Section 4.2. 3.4.1.3. Tie Camp Rock Dump and Indian Rock Dump In 1995 multiple shallow slope failures occurred on the faces of both the TCRD and IRD (Figure 3-15) (Golder, 1996a). Two areas of slope movement are mapped on the face of the TCRD (Golder ,1 996a). The source of the slope failure is thought to be caused by saturation of the slope due to water that had bypassed the underdrain system. EXHIBIT E-RULE 6.4.5(AMENDED RECLAMATION PLAN) Page 42 HOMESTAKE MINING COMPANY