The Grupo Mexico Cananea Buena Vista mine spilled millions of gallons of sulfuric acid leach solution on Thursday, Aug. 7 containing huge amounts of copper and other metals and contaminants into the Rio Bacanuchi, continuing into the Rio Sonora south and east of Cananea, according to a mine and governmental officials.
The contamination has resulted in many miles of a red-flowing river south at least 150 miles to Mazacahui, Sonora leaving dead fish, dead cattle who likely drank from the river and seven municipal-county areas receiving bottled water -- prohibited for an indefinite period to drink from municipal and private potable wells, and a population wondering how long their lands and water would be polluted.
The amount discharged had been reported as approximately 40,000 cubic meters or 10.6 million gallons by government officials, however Grupo Mexico's director of Ecology, Victor del Castillo Alarcon, said last Tuesday that the actual amount was approximately 15 million gallons.
The spill had been aggravated by heavy rains saturating the region, said Del Castillo.
Del Castillo told the Sierra Vista Herald that although he was personally confident of the causes of the problem, that until an investigation was complete, "he did not want to discuss how the acid was discharged from a holding area where the acid that had been through an acidic 'solvent extraction process' to leach copper ore that would normally be transported to an 'electrowinnowing' plant to produce cathode copper. Del Castillo said that "the solution contained about 1.5 percent copper and other metals present in the ore that had been leached by the acid."
According to public statements from the Attorney General for Environment (PROFEPA), Jorge Carlos Flores Monge, and the Sonoran Delegate of Civil Protection, Carlos Arias, "the acid was released from a broken pipe, attached to an acid retention dam, as a result of human engineering error." It was not made clear whether a retaining wall constructed by the mine above the Rio Bacanuchi was broken by the spill or how the acid was transported to the river. Arias' office told the Herald that all agencies are coordinating continually to determine how to respond to the crisis.
Grupo Mexico did not file an emergency release report with PROFEPA for nearly 24 hours, instead of immediately as required by law. Flores of PROFEPA said that until the scale of ecological impact was known, the mine would be fined a minimum of 20 000 "daily minimum wages" for the failure to report and for the costs of officials responding. This would be around $105,000 U.S.
Grupo Mexico, including U.S. affiliate ASARCO, had $9.4 billion in sales in 2013, a relatively sub-average year for the mining industry.*
Del Castillo said that Grupo Mexico had constructed a lime dam across the river to capture the acid and neutralize it and that the river is quickly "stabilizing." He also said that the contamination problem of surfacewater would be solved very quickly and that he doubted that the contamination would infiltrate to groundwater and he did not yet know whether sediments in the river would remain contaminated.
Del Castillo said that he believed "the health of the river would be good in little time and that most of the fears over contamination came from those who were poorly informed."
Del Castillo said that the mine was coordinating with various governmental officials to provide drinking water to municipios (county-cities) including Arizpe, Huepac, Banamichi, Sinoquipe, Aconchi, Baviacora and Mazocahui. Sonoran capitol Hermosillo is in theory impacted by the spill, although Del Castillo said that only 3 percent of their drinking water utilizes the Rio Sonora as a source.
Arizpe Municipal Secretary Ramon Acedo told the Herald last Tuesday that six tanker trucks and trucks with bottled water were providing drinking water to the city. Acedo also reported that one cow had been found dead by the river near the town and that it was currently being autopsied by the Secretaria of Agrarian Reform to determine whether river contamination caused the death.
The National Commission for Water or CONAGUA, an arm of the environmental ministry, said that pH levels in the Rio Sonora were "within acceptable standards" on Monday. However, a small CONAGUA summary of sampling data taken of river water was published in the Hermosillo newspaper 'Imparcial,' showed elevated levels of metals, including aluminum at 307 times standards, manganese at 676 times standards, nickel 8 times, cadmium four times and copper at close to three times standards. CONAGUA warned affected residents, estimated at 22,000 inhabitants, to avoid drinking water from any well within 500 meters of the river.
Del Castillo of Grupo Mexico said that the acid that was released into the Rio Bacanuchi watershed had a pH of 2.9 at the time of discharge although the Bacanuchi River pH had returned to 7.1 by August 13. Acceptable potable and surface water pH in Mexico and the U.S, would be 6.5 to 9.
The mine released huge amounts of similar contaminants during rains into the San Pedro River in 1979 (photo) and some localized visual contamination could still be seen by a reporter near Cananea in the San Pedro basin as of 2010. However political pressure from the U.S. State Department resulted in the mine moving much of its dams containing contaminants into the basins of the Rio Bacanuchi and the Rio Sonora. Spills continued flowing to the south, but no longer crossing the border and this was a major problem in the region during the 1980s
before tapering off.
Historical research on past Cananea spills indicates that river contamination diminished over years. University of Sonora researcher Agustin Gomez Alvarez tracked contamination in the Rio Sonora along with Sonora-Arizona research teams in the San Pedro River from the late 1980s through 2002 and found that pollution levels from spills in both river basins declined steadily as distance increased from the source. However levels of contamination remained high near the mine in both river basins and some shallow wells on the mine above the Rio Bacanuchi were still very acidic. Del Castillo confirmed last Tuesday that the University of Sonora has research teams sampling in the Rio Sonora with government and mining officials.
Geochemist Dr. Ann Maest was a principal author in a 2003 Border Ecology Project study completed for the Municipio of Cananea on the mine, how it could prevent future contamination and develop a closure plan that utilized the University of Sonora water contamination data.
Maest said last Tuesday that contamination from the spill could manifest itself in several ways and that levels of contaminants reported were not inconsistent with contaminants left behind by past mine spills.
"Aluminum appears as a whitish deposit and copper can precipitate out from the lime used by the mine to increase pH (reduce acidity) in the river," she said. Maest added that University of Sonora water samples
in Arroyo Salto, which travels from the Cananea mine to an area above the Rio Bacanuchi, had such precipitates of metals in 2002 that indicated past spills.
Maest said that aquatic standards for certain metals could be lower than those used by CONAGUA for drinking water, because of the higher sensitivity of aquatic life to metals such as copper or cadmium. Even low concentrations of cadmium, she added, could quickly kill aquatic life.
Rio Sonora Banamichi resident Tom Matthew, owner of the Los Arcos hotel, said that he could "see what looked like literal sheets of copper on rocks where the water had passed through, and that white solids were present in the water," consistent with Maest's description of aluminum and copper precipitates.
Matthew said that all wells in Banamichi, including the municipal wells, tended to be alluvial shallow wells connected with the river "no more than 20-40 feet deep." He added that the local Santa Elena silver mine
was sampling community water supply daily and providing test results to the local mayor, whohas sent some samples to the University of Arizona and is awaiting lab results.
Several Banamichi and Aconchi residents indicated that nobody would consume local cheese for the time being over fears that the local cows had either drank contaminated water or were grazing on contaminated grass.
Sonoran State Human Rights Commission President Raul Ramirez Arturo Ramirez said, "The commission saw a high risk to the ecology and health of the residents from the spill and the authorities have full responsibility to ensure that the mine was fined given that there would be impacts to the ecosystem."
Legal concerns were more fearfully expressed by several residents along the river. Banamichi resident Gerlinda Helge said, "What does this pollution do to our land values and to the cattle and cheese produced by local residents? The Cananea mine has felt for decades that they have the right to contaminate this river and this is the worst spill I have seen and will take years to clean itself. We need some form of legal defense."
FULL DISCLOSURE: Dick Kamp was Director of the Border Ecology Project when it produced the aforementioned 2003 report on the Cananea mine for the city of Cananea.