PERMFILE57875

• Permit No: M1977004
• IBM Index Class Name: Permit File
• Doc Date: 3/28/1984
• Doc Name: Internal Memo
• From: DMG
• Media Type: D
• Archive: No

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diminished, now being limited to sloughage of the head scarp. Utilizing
measured material properties and observations of past slide movement, Call and
Nicholas project "a long-term geometry" for the landslide mass. Any such
projection, however, is extremely tentative, being dependent upon numerous
assumptions regarding mechanical and hydraulic performance of the
heterogeneous landslide mass. In addition, variation in meteorology, surface
drainage and mining or backfilling rates would further limit the reliability
of any such projection.
Homestake's consultants present a plausible scenario for landslide
adjustment. Movement will continue downs lope until equilibrium has been
achieved. The exact final configuration of the landslide mass, or the exact
rates of adjustment, however, are impossible to predict. Call and Nicholas'
brief geotechnical report appears to have been prepared in keeping with the
prudent state-of-the-art of slope stability and landslide analysis. In fact,
to attempt to predict or analyze adjustment of the landslide mass in
significantly more detail than presented within their report, might, indeed,
be imprudent, in suggesting any greater significance or accuracy in such an
endeavor.
As I observed in my earlier memo to you regarding this topic, dated September
8, 1983;
"The terrain between the crest of the northeastern pit wall of the
Northern Pit and the head scarp of the slide now consists of horst and
graben blocks of landslide-affected ground. Open fissures and scarps
are common, as is disorientation of trees and plant life within the
affected area. The magnitude of the slide suggests that it would be
impractical to attempt standard landslide control techniques. The only
conceivable control activity possible at this time appears to be the
backfilling of the North Pit, which could serve to resist continued
movement of the landslide mass. However, the greatly extended landslide
mass will probably continue to internally readjust itself under the
force of gravity, until it achieves both external and internal
equilibrium, at some unknown time in the future."
The applicant's consultant concludes, based upon observed movement rates of
the basal portions of the landslide, that their projected "final" topography
will be reached within five years after partial backfilling or ten years from
the present time, if there were no backfilling from the South Pit. Because of
possible variations in the hydrological and mechanical assumptions, this
conclusion could be subjected to lengthy discussion concerning actual rates of
movement and final configurations of the landslide body. The basic concept,
that the landslide will proceed towards equilibrium, however, is not disputed
by the Division.
One major topic that remains to be resolved prior to approval of any proposed
amendment, is determination of the term and nature of Homestake's
responsibility for final stabilization of the landslide mass. The applicant's
consultant may not be accurate in projecting the rate of adjustment.
Homestake Mining company, as the operator, is required to established the