A major cleanup is underway after about 40 million liters of wastewater were discharged into the River Bacanuchi, a tributary of the Sonora, on Thursday 7 August 2014. The precise nature of the event at the Buenavista Copper Mine at Cananea in Sononra State, Mexico, is unclear but it has been linked to heavy rainfall in the area, and is therefore likely to relate to the failure of a tailings pond. A 420 km long stretch of the two rivers has reportedly turned orange following the spill, and the water supply to the towns of Arizpe, Banamichi, San Felipe de Jesus, Aconchi, Baviacora and Ures, and the state capitol Hermosillo, with a combined population of about 800 000 people. Fish and livestock deaths have been reported along the affected stretches of river.
The approximate location of the Buenavista Copper Mine. Google Maps.
Tailings ponds are used to store sediment-laden waters from mines; such waters typically contain a high proportion of fine silt and clay particles, which take time to settle out of the water. The resulting water may be fairly clean, or may contain other pollutants (typically acids, either generated by the local geology or used in the mining process), and need further treatment. The water from the Buenavista Copper Mine spill has been described as containing sulphuric acid, though it is not clear if this originates from the mine tailings (many metal ores are sulphur rich, making sulphuric acid a common problem at metal mines), or whether acid had been added to the water to dissolve metals from the tailings for later recovery (acid leaching). Either way it presents a major environmental problem, and lime has been added to the affected waterways to attempt to neutralize the acid.
See also...
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Heavy rainfall associated with Cyclone Grant (now downgraded to Tropical Storm Grant) has caused...
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