OFR-145-80 Instability Of Contoured Surface-Mined Landscapes In The Northern Great Plains: Causes And Implications

Reclamation of surface-mined landscapes is commonly defined only in terms of biological productivity. Other critical concerns associated with surface mining include the long-term quality of groundwater and stability of the postmining landscape. Meaningful reclamation design must address all these concerns. Reconnaissance of postmining landscapes indicates that three types of instability occur in these settings. These include: area-wide settling, localized collapse, and piping. Area-wide settling is most pronounced during the first year after contouring but appears in precontouring valley areas where frozen materials are contoured with a dozer. Although severe in some settings, development typically ends within one year. Piping appears to be a severe and long-term problem in some settings. Piping usually begins soon after contouring ceases and may continue for several years. In some postmining landscapes, piping has only started to develop after as many as five years of apparent stability. Piping is controlled by a combination of physical and chemical conditions in the spoil. A key factor is the presence of highly dispersive materials in the near surface. The design of a stable postmining landscape requires the integration of severe critical factors. These include: 1) detailed knowledge of the distribution of overburden materials with emphasis upon the delineation of highly sodic sediments; 2) proper equipment selection; and 3) a consideration of climatic factors. For reclamation to be successful, it must consider the entire landscape, not merely the soil zone. Any approach short of this will lead, at best, to temporary solutions.