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• MONTGOMERY WATSON ~ ~ <br />Mining Group <br />Date: 7-Maz-00 <br />To: Seneca Coal - 1342851 File <br />From: John Pellicer <br />Subject: Yoast Mine Pond 12 Area -Slope Stability <br />On March 6, 2000, Mike Altavilla with Seneca Coal informed Tom Leidich (Montgomery Watson) <br />that the slope on the north side of Pond 12 at the Yoast Mine was experiencing some deformation and <br />requested that someone from;the MW Steamboat Springs office make a site visit and provide some <br />recommendations to minimize slope deformation. <br />On March 7, 2000 Jay James and I ~ohn Pellicer) went to Pond 12 to review the slope deformation. <br />We met Mike Altavilla (Seneca) and Mike Boulpy(DMG) at Pond 12. The slope on the north side of <br />the pond had moved downslope. Mike Altavilla noted that the slide had moved substantially <br />• overnight. The slide body is estimated to be about 300 feet wide (along slope strike) by 100 feet long <br />(along the slope dip) in iu largest dimensions. The head scarp at tts maximum dimension is <br />approximately 20 feet. A portion of this area had previously experienced some deformation last fall <br />near the completion of the pond construction. The slide body has not impacted the Pond 12 <br />embankment and appears to terminate about 60 ft upstream of the embankment. The upstream <br />portion of the slide body terminates at about the upstream end of the pond. It appeared that the <br />s~u-face water coming down the haul road above the slide was on the slide side of the road. This may <br />have delivered enough water to the area to trigger the slide. Mike stated that a lot of snow had melted <br />in the past week on the south facing slopes. It appears that the majority of the snowpack on this slope <br />has melted. <br />We recommended that surface water above the slide be managed and monitored with caze. We <br />suggested that two ditches be put in across the road above the slide in the portion of the road where it <br />veers back to the east going up the hill. Any surface water in the road should be diverted to the ditch <br />on the inside road edge. This ditch may have to be enlarged to handle flows. In addition we <br />recommended that survey stakes be placed on the slide body toe just above the pond water level to <br />monitor deformation into the pond. This will allow some method to determine if the pond storage <br />volume is being substantially reduced. We also suggested survey stakes be placed at the pond water <br />level to enable water level monitoring within the pond. This will permit monitoring of available <br />storage volume in the pond as•snow melts in the drainage. Once the area has dried out, which we <br />estimated to be in another 1 to 2 months, the slide body should be re-graded to close up any surficial <br />cracking in order to reduce the potential for surface water infiltration. The slide body should be <br />• checked every day for the next several days to ensure that is has stabilized. Once it has stabilized, the <br />slide should be checked weekly or after any storm or melt events that could produce substantial <br />surface water runoff. <br />5.~185f ~Pord 11 Slope /mmin'liry Afrmo 7~Mai~I000.dor <br />