The equivalent of more than six million gallons a day of raw sewage has been spilling into the Tijuana River since Monday night, according to federal officials. The U.S. section of the International Boundary and Water Commission, or IBWC, said Tuesday that counterparts in Mexico informed the agency that the cause of the sewage leak was a ruptured collector pipe. Federal officials said the aging collector underwent millions of dollars in upgrades over the last year but had yet to be fully rehabilitated.