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Memo to Christine Johnston Mountain Coal T.R. 69 Adequacy page 3 If Mountain Coal desires to complete this application, they will have to complete an appropriately comprehensive evaluation of the stability of the site. My review of the boring loge suggests that basal landsliding planes may be evident in bore LPG-2 at 15 to 20 feet in depth, in LPG-4 at 25 to 30 feet in depth, in LPG-5 at 20 to 25 feet in depth, and in LPG-7 at 20 to 25 feet in depth. A significantly more detailed site investigation will be necessary to define the preexisting basal failure planes and the specific landsliding mechanisms manifested at the site. Once this data collection and evaluation has been completed, it may be possible to design an appropriate facility to resist the effects of slope instability at this site. In my experience, however, it may be more cost effective to select an alternative site for the installation of the ventilation fan and its attendant facilities. Light Use Road Similarly to the proposed fan bench, a major proportion of the existing light use road which will service the fan facility passes through prehistoric and historic landslide complexes. The road is maintainable, and less susceptible to minor disorientation than the fan and motor. However, it is important to maintain access to the fan for maintenance and emergency access. In addition the road must comprise a stable component of the reclaimed landscape. In several locations, such as the tight bend in the southeastern extremity of Lone Pine Gulch, the radius of the existing curves will have to be increased. This will result in cut slopes of significant size in these locations. If located in historic landslide deposits, these cuts may result in cut slopes which will be difficult to stabilize. An appropriate reconnaissance investigation should be completed to identify potentially susceptible locations along the road alignment. These locations should be properly designed to assure long term stability of the resulting cutslopes. Fan Bench Area Cut and Fill Balance The brief references to material balances within the application suggest that an approximately 9,600 cubic yard surplus of material will result from the cut and fill at the fan bench area. The indiscriminant placement of this dead weight could destabilize the slopes within the impacted area. The brief application does not specify where the surplus material is intended to be placed. Mountain Coal will need to provide this information, including appropriate stability analyses for any fills.