Cananea Mine discharging wastes into San Pedro and Rio Sonora Basins

Cananea Mine discharging wastes into San Pedro and Rio Sonora Basins

Dick Kamp, Wick Communications Environmental Liaison  22 Sept 2014 

In 1979 the San Pedro River seen in Palominas ran red for a hundred miles with rain floodwater and Cananea tailings wastes.

photo Marty Cordano

An undetermined amount of what looks like sulfuric acid leaching solution from the Grupo Mexico Buenavista Cananea, Sonora mine has entered the north-flowing San Pedro River on the Sonoran side of the  border.  The overflow of mine wastes resulted from heavy rains September 17-18 said a company representative. 

A bulletin from Proteccion Civil Sonora (civil protection agency) indicated that an overflight following the rains provided evidence that other discharges from two mine waste retention dams appeared to also be entering the southeast flowing Rio Bacanuchi, a tributary to the south flowing Rio Sonora.                                              

This spill follows an August 7 discharge of 15 million metric gallons of sulfuric acid from a solvent extraction plant at the mine spilled into the Rio Bacanuchi and the Rio Sonora and resulted in an estimated 32,000 residents drinking bottled water over a stretch of more than 100 miles.

The newest spill resulted in a “preventative binational alert” issued by the agency Proteccion Civil (Civil Protection).to the International Boundary and Water Commission (IBWC) Nogales, Arizona office.  The Hermosillo Proteccion Civil office said Monday that they had also immediately alerted the environmental agency SEMARNAT and the National Water Commission (CONAGUA) who conducted surface water testing in the San Pedro.  

The Proteccion Civil bulletin did not state that the contamination is known to be entering Arizona. Ivan Valerio Cortes, Chief of the Cananea municipal Proteccion Civil office, said Monday that he has seen no test results but that the appearance of the contaminatedwater seems to be a mix of reddish acid, mud, and rain water. 

Valerio added that he could not accurately describe the source of contamination, which had been viewed by the Sonora state head of the agency, Carlos Jesus Arias.  However Valerio said that it appeared to be a leaching solution of “cobreza” or copper sulfate that has been utilized to leach metals.  

“The solution had been diverted to an arroyo and overflowed into a tributary of the San Pedro and appears to be impacting the Cananea Vieja ejido(collective land) area north of the mine.   Proteccion Civil is advising ranchers in that area to not allow cattle to drink from the river”

There are several other ejidos between the mine and the Arizona border, but Valerio said he did not know if they were impacted by mine discharges.

Victor Del Castillo, Director of Ecology for Grupo Mexico said Monday that “what is entering the river is 100% rainwater in quality and that CONAGUA and PROFEPA (the enforcement arm of SEMARNAT) have declared that the pH (acidity) is within Mexican norms.”

Del Castillo added that the mine had used lime and magnesium hydroxide to neutralize pH in the waters as a “preventative measure” but that “there is no problem with mining contamination impacting the San Pedro as we have often told the Arizona-Mexico Commission. There are levels of iron present in these discharges that are within the norms for surface water.  Proteccion Civil has a policy of exercising caution; they do not know whether waters are contaminated.”

On Monday, Arias told several Sonoran publications, including Sinembargo, an online newspaper, that in an overflight over the mine this past weekend he had viewed ruptures in two dams that were leaking oranges fluid—Campo Frio and La Mexicana.   According to the newspapers, Arias stressed that he had no idea what the orange chemicals that he saw were but that the earthen “curtain” that was retaining wastes from leaving the waste dams appeared to be leaking above the Rio Bacanuchi and that other wastes were entering the San Pedro basin.  Arias told the papers that he saw other discharges that appeared to be infiltrating into the ground.

Del Castillo and Valerio both indicated that, without giving a figure for the latest spill, it was far smaller than the August 7 spill of acid and is being diluted by copious amounts of rainwater.

Arizona Department of Environmental Quality spokesman Mark Shaffer said Monday evening that ADEQ has no additional information from Federal authorities in either country but that they would be monitoring for acidity and metals near their sampling station by Palominas on Tuesday.   Shaffer said that pH/acidity results could be immediately reported and that the Arizona state lab should have metals levels reported within a week. 

Shaffer suggested that the river is flowing at around 600 feet per second near the border and that contaminants may have been diluted.  “At this time we are not issuing any health alert pending the test results,” added Shaffer.

Acidic spills from the Cananea mine between 1977 and 1979 resulted in devastating impacts on the San Pedro River.   Pollution levels declined dramatically as, under U.S. diplomatic pressure, the mine began to divert newer wastes to the Rio Sonora basin which suffered numerous spills in the 1980s that appeared to have diminished greatly prior to the August 7 acid spill. 

Photographs taken by the Sierra Vista Herald on Monday afternoon did not show obvious discolorations in the river as it entered Cochise County.

One Sonoran resident on Monday, who asked not be identified, described contamination entering the San Pedro River as “a potential opportunity.   Maybe people in Arizona will notice that the mine pollutes and understand better how our lives have been impacted by contamination in the Rio Sonora.”