BACKFILLING OF METALLIC AND NON-METALLIC OPEN-PIT MINES IN CALIFORNIA

Thirty years ago, the Congress of the United States required that coal mines be backfilled as a routine element of reclamation when it passed the Surface Mining Control and Reclamation Act. Until recently, the concept has not been generally applied to non-coal surface mines. In 2003, California's State Mining and Geology Board (Board) evaluated reclamation of open pit mines in the state. Numerous examples that backfilling occurs at large open pits resulting from aggregate mining were identified. These pits are generally located in or near urban areas. Although there is little residual mined material, high property values encourage backfilling with inert soils from construction projects in the surrounding area to achieve a productive end use. Metallic mines, however, were not being reclaimed, despite California's Surface Mining and Reclamation Act of 1975 (SMARA). As a result, the Board issued regulations for the backfilling of open-pit metallic mines. The need for such regulation reflected several issues. Open-pit metallic mineral mines often create very large excavations. In addition, metallic mineral mines that employ the cyanide heap leach method for mineral segregation and collection frequently generate very large leach piles which create long term soil and groundwater contamination conditions. It is the intent of SMARA that completed mine sites present no additional dangers to the public health and safety, and that the mined lands are returned to an alternate, useful condition. To date, no large, open pit metallic mines in California have been returned to the conditions contemplated by SMARA, and these sites continue to pose significant environmental problems. The goal of the Board's regulations was to require mining companies to address the problems identified above and to take responsibility for cleaning up their mine sites after the completion of surface mining operations, and return them to a condition that allows alternative uses and avoids environmental harms, thereby meeting the purpose and intent of SMARA. Board regulations, which took effect in 1993, establish performance standards for reclamation pursuant to SMARA, including standards for backfilling which provide that, where backfilling is required for resource conservation purposes, fill material must be backfilled “to the standards required for the resource conservation use involved”.