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This material was cast onto the slope as a large fan, loading the dipping <br />sedimentary strata on the highest part of the west quarry wall. <br />16. The CGS Report on p. 7 describes the fourth contributing factor as: <br />Deviation from the mining plan: the mining of the hole [Area H] exposed too <br />much of the base of the quarry wall. The mine permit amendment stated that, <br />"it is not expected that any more than '/ of the total length of the west- wall of <br />the Hole will be unsupported by backfill (or unmined rock) at any one time. <br />Thus, any large scale instability that might occur would be limited in scope <br />simply because most of the west wall will either be supported by backf ll or by <br />native rock yet to be mined. " That does not appear to be the case. [An <br />oblique aerial photo of the quarry wall failure looking west] illustrates that <br />much of the hole was open and the quarry wall was essentially unsupported <br />prior to the failure. The limited amount of fine-material fill located on the <br />south end to develop the access ramp was not effective in supporting the slope <br />and was displaced laterally about 80 feet by the rockslide. <br />17. The CGS Report concludes: <br />Based on the site observations and the material reviewed, it is the opinion of <br />the CGS that, even though the adverse geologic and structural conditions were <br />known, or should have been well known, they were not given the <br />consideration they required during mining activities, even though past failures <br />had occurred... At these potentially unstable conditions, continued deepening <br />of the open-pit mine in Area H at the base of the west quarry wall ultimately <br />resulted in slope failure. <br />CGS Report p. 9. <br />18. The CGS Report concludes that the quarry wall failure was a combination of <br />daylighted adverse steeply inclined strata; the inherent weakness of the rockmass; the loading <br />of the benches at the top of the quarry with spoils from the more recent expansion and <br />excavation into granite at the top of the quarry; "further undermining and steepening of the <br />rock slope related to mining and removal of rock in Area H (the Hole)," and to a lesser <br />extent, blasting causing rock damage at the toe of the slope; and the effects of water from <br />off-site drainage. <br />19. The MSHA also concluded that in addition to the geologic formation factors, <br />"[t]he current pit mining operation was likely removing material that had provided a buttress <br />to the rock material above the critical discontinuity, ultimately triggering the slope failure." <br />MSHA Memo p.10. <br />20. The quarry slope at the failure location is currently stable. <br />21. However, both the CGS Report and the MSHA Memo conclude that the area <br />above the slide area is at risk of sliding. Tension cracks appeared above the head scarp of the <br />slide area. The CGS Report states "CGS has concerns about large unstable rock blocks that <br />Continental Materials <br />Pike View Quarry, M-1977-211 <br />MV-2009-012 4