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South Permit Boundary Bowie #2 Mine Paonia, Colorado I• RESULTS Rockfall Hazard PROJECT N0.24004 Naturally occurring rockfall activity on the s-ope appears to be limited to the area where the resistant sandstone unit outcrops at midslope, from approximate elevations 6500 to 6900 feet. Without consideration of the effects of a ground vibration or movement due to the subsidence event, the probability of a naturally occurring rockfall event initiating from this area of the slope would be considered moderate with a recurrence interval of less than 50 years for larger rock falls. The outcropping sandstone unit is not within the draw angle of the subsidence and is several thousand feet from the underground workings. Ground vibrations of sufficient magnitude may initiate a rockfall event from this area of the slope. Prediction of the magnitude of the ground vibration is not within the scope of this study. • The majority of the slope does not show outcropping bedrock, is heavily vegetated and exists at slope angles that are considered stable. While it is possible for rocks embedded in the slope or lying on the surface to dislodge and begin rolling, it is unlikely without significant movement of the ground surface due to the subsidence. We considered rockfall initiating from these areas in our analysis only for areas near or within the projected draw angle, regardless of the probability of the occurrence of an event. Rockfall Simulation 7o estimate the probabilistic trajectories of the rocks, four profiles of the site were modeled using the Colorado Rockfall Simulation Program, Version 4.0 (CRSP). CRSP is the most widely used program for evaluating rockfall behavior. Information provided by the program includes rock bounce height, rock velocity • and kinetic energy. The model was developed using terrain survey provided by the client.