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~ .: ~ iii iiiiiiiiuiiiiii INSPECTION REPORT Site: National King Coal Mine, Hesperus, Colorado Inspected By: Don R. May, P.E., Project Engineer Inspection Date: Quarterly Inspection, November 2, 1996 .e>` ~.a.D~ RE. ~1~7/> Note: Harry Ranney, Colorado Department of ~Ainerals and Geology, rep'0'rted~4o~lkie that he witnessed an intense storm (probably exceeding the 100-yr event) at the mine in August. This event caused erosion, blockage and partial failure in some of the drainage features. In general the drainage system worked quite well. Some adjustments are suggested that may improve the system. Ponds: The east and west sedimentation ponds and their embankments are in good condition. There are no signs of excessive erosion of the inlet channels or outlet spillways and all pipes are in good condition. As seen in photographs 1 and 2 the ponds both have standing water from recent snow and rain. The west pond low level outlet is approximately 5 feet above the pond invert. As pointed out in the last inspection report, this prevents the pond from completely draining except through evaporation and percolation. Harry Ranney's most recent survey of this pond should be checked to verify that this storage volume (below low level outlet) is not needed to meet the required design volume. Drainagg Ditches: Photograph 3 shows the east side drainage channel adjacent to the waste pile. It is in good condition with some signs of erosion from the August storm. Portions of this ditch should be protected with rock riprap or other suitable material to armor the channel bottom and sides. Photographs 4 and 5 show the drainage ditch along the top and tow of the waste pile. These are in good shape and appear to operating properly. Photograph 6 shows the westside interceptor pipe entrance at the mouth of the canyon. This entrance became blocked during the August event and has been cleaned and a trashrack installed immediately upstream. Further measures to prevent blockage may be necessary at this location and on the east side where the ditch enters the pipe. The yard is dry and drainage structures are in good shape. Runoff from the lower yard area is currently flowing along and in the access road, between the ponds and out into the adjacent pasture. The design calls for aditch/pipe diversion to intercept flow and channel it into the ponds. This feature needs to be constructed. All other ditches and structures were inspected and appear in good operating condition. Except for the conditions mentioned above, all drainage features have been constructed and are operating as stated in the drainage plan submitted to the Division of Minerals and Geology. Coal Waste Pile: There are no signs of structural instability on the waste pile. Photograph 5 shows the front face of the waste pile. The slope of the face appears to exceed the design slope of 3:1 (horz:vert). This should be confirmed and adjustments made to the face as needed to assure the design slope is met. Some erosion on the pile face has resulted in rill formation