McLaughlin Mine Project
Homestake Mining Company of California
Background
The McLaughlin Mine operated between 1985 and 2002, producing 3.5 million ounces of gold over its 17-year life. Napa, Lake, and Yolo Counties, along with the BLM, approved the McLaughlin Mine Plan of Operations and the Reclamation Plan in the early 1980s. In Lake County, Homestake placed approximately 38 million tons of mill tailings from its gold processing facilities into a Tailings Impoundment Facility (TIF), extending to a maximum depth of approximately 145 feet.
The approved reclamation plan called for a minimum of 3 feet of composite cover material over the tailings and establishment of shallow-rooted grassland. A diversion channel would be removed, and a cut in the tailings embankment would be excavated to facilitate the reestablishment of surface runoff from the surrounding watershed through the TIF and back into the native watercourses. Completion of closure was not envisioned for approximately 50 years.
Challenges
In 2007, reevaluation under current RWQCB regulations concluded certain aspects of the 1983 reclamation plan were determined infeasible with regard to post-closure water management, dam stability, and final reclamation scenarios. The need for complete on-site containment of TIF sediments under current RWQCB requirements, and the need to maintain the integrity over the impoundment (dam) under Division of Safety of Dams requirements made implementation of the plan approved 27 years ago infeasible today. Had the original plan been implemented without modification, the TIF could not have complied with the Regional Water Board requirement to maintain the TIF as a “zero-discharge facility.”
Solutions
Benchmark Resources developed an amendment to the reclamation and closure plan was developed is based on a series of technical studies completed to address soil cover quantity and placement, vegetation cover, wetland development and saline water habitats, water quality, dam safety, and long-term monitoring.
The Amendment called for the development of a mosaic of differing moisture regions on the TIF, resulting in upland grasslands in the dryer areas along with emergent marshes behind the berms on the surface of the TIF. Some run-on from the surrounding watershed would be allowed to flow into the TIF to provide a mix of fresher water habitats along with the more saline habitats associated with the internal pond (tailings) water. The Amendment provides a greater level of sustainability than the original plan and allows for adaptive management of the reclaimed mine surface into the future as on-site conditions and habitats evolve.