SAN DIEGO -- The city of San Diego has become the state's last holdout from a federal law requiring secondary treatment for sewage discharged into the ocean, 10News reported.

It gained that status after two central coast agencies recently committed to complying with the mandate. About 40 sewage treatment plants statewide pump their effluent into the Pacific Ocean, The San Diego Union-Tribune reported.

Mayor Jerry Sanders is expected to make an announcement Tuesday about future operations at the city's Point Loma Wastewater Treatment Plant, which still processes sewage at the advanced primary level, according to the newspaper.

Secondary and tertiary treatments remove more solids and other pollutants from wastewater than the primary or advanced primary processes.

San Diego's options include spending up to $1.5 billion to retrofit the facility, requesting another exemption from the Clean Water Act or adopting a hybrid plan that seeks a waiver while pledging to retrofit the plant at a later time.

To afford an upgrade, city officials almost certainly would have to raise sewer rates again for residents and businesses in San Diego and 15 other agencies that use the facility.

Despite the costs, environmentalists have increased their demands for a Point Loma retrofit after Morro Bay and the Cayucos Sanitary District agreed in recent weeks to boost their sewage treatment level from advanced primary to tertiary by March 2014, the newspaper reported.

Orange County and Goleta, the two other wastewater districts in California that still don't have secondary treatment, are following schedules to improve their operations by 2012 and 2014, respectively.