SLOPE STABILITY ISSUES AND CONSIDERATIONS AT SURFACE MINES IN CALIFORNIA

The California Surface Mining and Reclamation Act of 1975 (SMARA) and associated regulations became operative 34 years ago; however, statewide reclamation standards requiring reclaimed mine slopes to be stable were adopted into regulations only 17 years ago. Given that the operational life of many mines exceeds 40 years, older operating mines were approved prior to the standards. Although slope-stability issues have arisen at older mines, problems also occur at mines approved after 1992, when the reclamation standards were adopted. Many operators must weigh the pros and cons of creating steep mined slopes to maximize available resources versus creating reclamation slopes with gentler inclinations that generally promote slope stability, erosion control, and successful revegetation efforts. Slope stability problems typically are minimal or nonexistent at mines where appropriate stability studies have been completed or where lower slope inclinations are maintained during the mining process. Stability issues typically arise because necessary geologic and geotechnical studies are either lacking or inadequate, or because of improper management by operators or oversight by inspectors. Problems have occurred when slope stability studies 1) rely on overly optimistic site characterization based on little to no data, 2) fail to address all slope types and orientations, 3) do not consider all likely failure mechanisms, or 4) do not adequately consider project changes. Mines operations that fail to follow approved mining plans or that engage in questionable mining practices (e.g. side-cast waste) are often plagued by adverse slope stability or related issues. Slope stability problems at mines can be minimized or eliminated with careful pre-project planning that is supported by thorough technical studies and documentation of final slopes in reclamation plans, periodic review of site conditions by qualified professionals, proper management of the mining project by operators, and appropriate oversight by responsible agencies.