On August 6th, 2014 at Cananea, Sonora, 40,000 m3 of mining waste was spilled into the river Bacanuchi, continuing into the river Sonora. It was basically sulfuric acid leach solution, containing huge amounts of copper and other heavy metals. There is a probability that this waste has been transported up to 300 km downstream to the dam Rodolfo Felix Valdez (El Molinito). El Molinito dam is located about 23 km upstream from the Hermosillo City and partially supplies the city for human consumption and irrigation.
To promptly address the damages caused by the spill in Bacanuchi and Sonora rivers, a escrow called “Rio Sonora” was created in order to serve as a funding source and payment method to carry out remedial measures to repair and / or compensate for damages to the environment and human health caused by the spill. This escrow was established with funds provided by the mine owner, Grupo Mexico (Buenavista del Cobre, S.A. de C.V. y Operadora de Minas, S.A. de C.V.). Danael Aceves is there working for Universidad Nacional Autónoma de México (UNAM), a member of the technical committee appointed by the escrow.
The river and dam sediments, the surface water and the groundwater were sampled along the river and at different depths at the dam. The test results were compared with national standards regarding environmental health, water for human use, and consumption, to know the metals exceeding the limits permitted.
The test results were also compared with the geochemistry anomalies, determined before the spill, by the Mexican Geological Survey, and background values of neighbor basins to understand the nature of the metals in the water and sediments (geological or anthropogenic due to the historical mining in Sonora).