INSPEC01821 - Laserfiche WebLink

Home Browse Search

III. COMMENTS -COMPLIANCE Below are comments on the inspection. The comments include discussion of observations made during the inspection. Comments also describe any enforcement actions taken during the inspection and the facts or evidence supporting the enforcement action. Background This was a partial site inspection of the Munger Canyon Mine, conducted by pan Mathews of the DMG Grand Junction Field Otfice. Mine Manager Walter Whitledge had contacted me on the afternoon of August 2, to report a flooding problem that resulted from an intense rain storm event on the evening of July 25. A storm cell had tracked across an area of the Roan Cliffs, Bookcliffs, and the Grand Valley that afternoon and evening, causing flood damage in various locations. The main portion of the storm cell apparently bypassed the McClave Creek Drainage, but upper portions of the Munger Canyon watershed apparently received very intense rainfall. On August 2, Chuck Silengo of CAM had checked the roads and drainage structures at Munger, and discovered that Munger Creek and its tributaries had flowed very high, and that drainage structures in several locations had been impacted. The main problem was at the 36" road culvert that routes undisturbed drainage from watershed "F" beneath the Munger Canyon Haul Road. The culvert is located immediately adjacent to the coal waste disposal area sedimentation pond. The open channel emergency spillway for the pond discharges into the undisturbed watershed "F" drainage channel immediately upstream of the road culvert inlet. Flood flows in the watershed "F" drainage channel had carried large volumes of fine sediment, cobbles and small boulders from higher in the watershed. The culvert was clogged and buried by sediment, and water flowed out of the channel, over the road, and backed up through the open spillway, filling the pond to the level of the emergency spillway with water, and an unknown but likely substantial quantity of sediment. I had inspected the site on the afternoon of July 25, prior to the storm event that evening. At that time, the sediment pond was dry, with maximum sediment and water retention capacity (there had been no appreciable inflow to the sediment pond since it had been constructed). The 36" CMP was clear and unobstructed. All aspects of the drainage control plan appeared to be in compliance with the approved plan, just prior to the storm event. Site Observations Coal Waste Area Sediment Pond I arrived at the site at 08:30 on the morning of August 3. Weather was clear, warm, and humid. There had been light rain the previous evening. There was muddy flow in East Salt Creek, no flow in Munger Creek at the time of the inspection. Walter Whitledge of CAM, and Jim Stover of J.E. Stover and Associates, engineering consultant to CAM, accompanied me on the inspection. The waste disposal area sediment pond and adjacent culvert were as previously described. Sediment and rock had completely filled in the ephemeral channel upstream of the culvert for a distance of 150 feet or more. Flow had escaped the channel along this segment, and had come close to overtopping the low berm between the channel and the sediment pond, but apparently did not. Inflow to the pond was solely from water that backed up through the emergency spillway. There were cracks along the banks of the incised pond along the west side (adjacent to the channel) and along the haul road fill slope at the north edge of the sediment pond, apparently related to movement associated with the saturated materials. Water could be heard trickling into a submerged crack along the west side of the pond. The 36" CMP inlet was buried, pond was full of water and unknown quantity of sediment, which had obviously buried the inlet of the 6" CMP gated primary spillway. Based on my observations, it would appear that the intensity and duration of the storm within the upper Munger Creek watershed and its larger tributaries (including the Watershed "F" channel) was such that peak flows generated in the drainage channels significantly exceeded those associated with the 10 year, 3