REV103244 - Laserfiche WebLink

Home Browse Search

N^ T e r r a M a t r i x MONTGOMERY WATSON Mining Group RECEIVED March 27, 1998 Mr. Tom Kaldenbach Environmental Protection Specialist Colorado Division of Minerals and Geology 1313 Sherman Street, Room 215 Denver, Colorado 80203 Re: Hayden Gulch Mine (Permit No. C-80-003) Minor Revision Request Slump Mitigation Dear Mr. Kaldenbach: III IIIIIIIIIIIII III APR O 1 1998 Division of Minerals 8 Geobgy Enclosed are three (3) copies of an application for minor revision of the permit application (H-G Coal Company [HGCC for the reclaimed Hayden Gulch Coal Mine (Permit No. C-80- 003). This minor revision is submitted for the purpose of conducting additional mitigation work to stabilize the earthen slump located in the southeast corner of the reclaimed mine sice near the former mine high-wall. This application consists of a competed permit revision application form and a copy of the Slump Investigation and Mitigation Report (Montgomery Watson Americas, Inc., [MWA]1998), which is presented in Attachment A. In 1994, as per Minor Revision MR-07, HGCC installed a French drain above the head scarp of the slump to a depth of approximately 20 feet. At chat time, as now, it was thought that lubrication due to infiltration of water along the contact between bedrock and reclaimed spoils was the cause of [he slump. The French drain was designed to prevent or minimize the infiltration of water along the sliding surface of the slump. Subsequent to installing the French drain, HGCC installed a line of temporary movement markers across the upslope portion of the slump to monitor potential continuing movement of the slump. Field observations by HGCC and the Colorado Division of Minerals and Geology (CDMG) personnel during 1997 indicated that additional movement of the slump had occurred and that the French drain apparently had not prevented additional movement. i Consequently, as per Minor Revision MR-12, in the fall of 1997, HGCC conducted further investigation of the slump to evaluate the reason for continued movement. Results of this investigation are presented in the Slump Investigation and Mitigation Report (MWA, 1998), included in Attachment A. This investigation included a trench across the slump to observe subsurface conditions, installation of piezometers co evaluate groundwater conditions, installation of additional temporary movement markers to monitor movement of the slump, and development of potential mitigative measures. The results of the investigation indicated that movement of the slump was probably due to subsurface infiltration of rain water and snow melt in the vicinity of the slump, thereby lubricating the sliding surface. P.0. Box 774016 Te1:979 879 646U Serving the World's Environmental Needs 1475 Pine Grove Road Fax: 970 879 9048 Steamboat Springs, Colorado 80477