The waste rock (including overburden) and tailings that we produce represent our largest volume waste. In 2011, we produced approximately 283 and 219 million metric tons of waste rock and tailings, respectively. The primary risks with managing waste rock stockpiles and tailings relate to structural stability, acid rock drainage (ARD) and dust generation. Management of this waste is highly regulated in the jurisdictions where we operate, and our programs are in compliance with applicable national, state and local laws, permits and approved Environmental Impact Studies.

Freeport-McMoRan currently operates 14 tailings storage facilities (TSFs) and manages 59 TSFs that are inactive or have been fully reclaimed. TSF stability is monitored by internal engineering personnel and contracted engineering firms utilizing instrumentation including manual and automated measurement equipment. At TSFs located in arid areas, the tailings management program includes measures to reduce fugitive dust emissions from the surface of tailings impoundments and the capture and reuse of tailings reclaimed water to reduce fresh water consumption. In the U.S. we had 14 reportable permit exceedances related to windblown dust from TSFs; 10 of these events occurred at our Sierrita mine in Arizona.

We conducted annual field inspections of 10 active and 35 inactive TSFs during 2011 under our tailings stewardship program. The program, which is directed by an interdisciplinary group of Company management, internal experts and external consultants, includes reviews of operational issues, phreatic level trends, deposition plans, hydrologic controls, seepage management, decant systems, structural integrity and stability evaluations.

As previously reported, at PTFI we use riverine transport of material from the concentrating complex in the mountains to a designated engineered and managed deposition zone in the lowlands and coastal zone as approved by the Government of Indonesia. PTFI's tailings management review board meets to review monitoring data and make specific operational recommendations for improving levee designs and construction, and system-wide performance. For more information on Controlled Riverine Tailings Management at PTFI please click here.

Waste rock and overburden are managed in stockpiles for possible future mineral recovery, reclamation or other projects. Overburden and waste rock stockpiles are evaluated for structural stability and local seismic design criteria and monitored regularly. Freeport-McMoRan is an active member of the International Network for Acid Prevention, which works to address management of ARD globally through sharing of best practice.

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