A civil defense official says that about 10 million gallons of mining acid leaked into a river that supplies water to tens of thousands of people. Carlos Arias, director of civil defense for the northern state of Sonora, said that the sulfuric acid spill last Thursday was detected by residents downstream the next day, and that the mine operators had not immediately notified state authorities. He attributed the problem at the Buenavista mine in Cananea, Sonora, to defects in newly built retaining ponds that hold the overflow of acids used to leach metal out of crushed rock. The operator of the mine, the Grupo Mexico, did not respond to requests for comment on Tuesday.