into a fleet of 64 large dump trucks which each carry of ore at a time; the trucks themselves cost about $3 million each. There is a series of conveyors that take ore to the Copperton concentrator and flotation plant. The longest conveyor is long. As of 2010, Kennecott Utah Copper was the second largest copper producer in the US, and provided about 13-18% percent of the U.S.'s copper needs. It is one of the top producing copper mines in the world with production at more than 18.7 million short tons (16.7 million long tons; 17.0 Mt). Every year, Kennecott produces approximately 300 thousand short tons (272 kt or 268 thousand long tons) of copper, along with 400 thousand troy ounces (13.7 short tons 12.4 tonnes, or 12.2 long tons) of gold, 4 million troy ounces (124 tonnes, 137 short tons or 122 long tons) of silver, about 10 thousand short tons (9,100 tonnes or 8,900 long tons) of molybdenum, and about a million short tons (910 kt or 890 thousand long tons) of sulfuric acid, a by-product of the smelting process. Rio Tinto purchased Kennecott Utah Copper in 1989 and has invested about $2 billion in the modernization of KUC's operations. The current mine plan will expire in 2019. Rio Tinto has been studying a plan to extend the open pit southward, which would extend the life of the mine into the mid-2030s. The plan has been contingent on approval by the Rio Tinto board of directors and approximately 25 required environmental permits. Production Bingham Canyon has proven to be one of the world's most productive mines. As of 2004, its ore yielded more than 17 million tons (15.4 Mt) of copper, 23 million ounces (715 t) of gold, 190 million ounces (5,900 t) of silver, and 850 million pounds (386 kt) of molybdenum. The value of the resources extracted from the Bingham Canyon Mine is greater than the Comstock Lode, Klondike, and California gold rush mining regions combined. Mines in Chile, Indonesia, Arizona, and New Mexico now exceed Bingham Canyon's annual production rate. High molybdenum prices in 2005 made the molybdenum produced at Bingham Canyon in that year worth more than the copper. The value of metals produced in 2006 at Bingham Canyon was US$1.8 billion. Environmental impact In 1990, homes that had been built on former flood plains were discovered to be contaminated with high levels of