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ENFORCE37929
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Entry Properties
Last modified
8/24/2016 7:46:46 PM
Creation date
11/21/2007 3:49:42 PM
Metadata
Fields
Template:
DRMS Permit Index
Permit No
C1980007
IBM Index Class Name
Enforcement
Doc Date
6/11/1998
Doc Name
TECHNICAL DISCUSSION OF THE GEOLOGY AND GEOTECHNICAL ASPECTS OF THE BEAR 3 LANDSLIDE WITH
From
WRIGHT WATER ENGINEERS INC
To
MOUNTAIN COAL CO
Violation No.
CV1997022
Media Type
D
Archive
No
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' Memorandum to Kathy Welt <br />June 11, 1998 <br />' Page 2 <br />We reviewed the plan and section drawings and the slope stability chart which were <br />presented to CDMG in our eazlier submittal. Key points made during this discussion <br />included our opinion that the slide initiated with a translational failure at the top of the <br />current observable scarp. As this translational block moved downslope, it overloaded the <br />lower slope elevations causing progressive failures and the dilatancy of the slide at the <br />approximate mid-height between the toe of the slope and the top of the scarp. This <br />mechanism is confirmed by field observations showing several progressively smaller grabens <br />downslope of the top of the scarp to the mid-height of the slide. <br />' The important implications of previous slope stability analyses done for the Bear Mine by <br />Hazding Lawson Associates (HLA) was discussed with CDMG representatives. HLA did a <br />cazeful analysis of the hillside stability in the azea of the Beaz Mine focusing on the <br />translational failures between the colluvium and the underlying bedrock. These analyses <br />indicate that the slopes aze meta-stable, having a factor of safety of one or less under dry <br />' conditions. If moisture or groundwater is introduced into the hillside, the factor of safety is <br />significantly diminished. This information is important because it supports the irrefutable <br />conclusion that all of the slopes in the area of the subject slide aze, and have been, unstable <br />' for a long time. In particular, John Rold presented a topographic map, which was taken from <br />a Bear Coal submission to CDMG in 1995. John pointed out numerous locations on the <br />topography where the configuration of the contour lines cleazly indicated historic downslope <br />' movements. <br />We concluded our presentation by stating that, particulazly in light of the recent data <br />' collected, we believe the recent landslide movement occurred as a result of an oiler-steepened <br />dry slope reactivated by high precipitation and interruption of surface drainage patterns. <br />' After we concluded the presentation of the data, Dr. Pendleton commented that we had <br />presented a compelling case and that he was nearly ready to recommend to Mr. Berry that <br />Mountain Coal Company had met the test of describing the geology of the slide and its <br />' trigger mechanism. However, he stated that the key "to ending the issue" would be a water <br />balance on the MCC sump which indicated very little water loss. Dr. Pendleton also posed <br />several questions concerning the longer-term management of the slide with regazd to the <br />' health and safety of citizens and the regulatory aspects of the mine reclamation. He <br />specifically suggested that a monitoring plan and worst-case projection for slide movement <br />' should be developed to deal with long-term reclamation and health and safety issues. <br />Mr. Berry commented that his field observations indicated that recent downslope movements <br />may be occurring west of the subject slide, particularly a new debris flow. We agreed that a <br />recent debris flow is present and pointed out that its origin is the unstable slopes above the <br />subject landslide which have been observed by all investigators. <br />C:\631-032\411ard\cdmgprcsenu[ion.dmj.doc <br />
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