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      Department of Public Works Bureau of Sanitation

From Sludge-Out to Full Secondary Treatment

November 23, 1998 is considered by many Southern Californians as the most important day in the history of healing Santa Monica Bay. On this day, the City of Los Angeles Hyperion Treatment Plant operated at full secondary treatment capacity for the first time in nearly half a century. This achievement assured the 4 million residents of Los Angeles and millions of more neighbors and visitors that the world-renowned Santa Monica Bay would be protected from wastewater pollution for future generations.

About HTP

Hyperion Treatment Plant (HTP) is the City’s oldest and largest wastewater treatment facility. The plant has been operating since 1894. Initially built as a raw sewage discharge point into the Santa Monica Bay, it had been upgraded over the years to partial secondary treatment (1950), and most recently to full secondary treatment (1998). The plant has a dry weather capacity of 450 MGD for full secondary treatment and an 850 MGD wet weather capacity. Current flow is 340 MGD.

The Division has 416 employees and performs wastewater treatment related duties. HTP is comprised of three sections with multiple functions. The sections are Engineering, Maintenance and Operations.

Related Links

History of Hyperion Treatment Plant

Terminal Island
Sewer System Facts:
Served Population: 4 million
Average Flow: 450 MGD
Collection System (in miles): 6,500

Q: Does Los Angeles have a combined sewer or separated sewer system?

A: The City of Los Angeles has two separate drainage systems, the stormwater system and the sanitary sewer system.

Q: How does the City handle large rain events which cause the flow to exceed capacity and escape untreated?

A: The climate in the Los Angeles area is generally considered arid and rainstorms are an infrequent occurrence.

And although the systems are separate, at times the sewer system can become inundated with stormwater overflow prompting (however infrequent) beach closures. This is more due to the age (70-80 years) and condition of the sewers and not so much to capacity limitations.

The City of Los Angeles is currently upgrading the sewer system lines in many parts of the city and the main treatment facility, the Hyperion Wastewater Treatment Plant, is a state-of-the-art full secondary treatment facility which recently won the