LA’s Hyperion Experiences Overwhelming Flood of Debris Clogging Headworks

Sunday, July 11th Emergency Led to Brief Bypass of Screened Sewage
Emerging Issues

Friday, 7/23 – Los Angeles County has released a third-party report that looked at what happened during the incident when Hyperion was inundated with debris. Hyperion is owned and operated by the City of Los Angeles.

Download LA County’s Hyperion incident report here > (pdf)

Highlights from the report include:

  • On Sunday, July 11, at approximately 2:00 pm the Plant began to receive a very high volume of large trash pieces.
  • The large trash flow began to overwhelm the screens.
  • As clearing the debris became more difficult, Plant executive staff were called to the site.
  • By late afternoon the debris flow had completely overwhelmed the (headworks) building, requiring the evacuation of personnel due to increasingly life-threatening circumstances.
  • Plant staff had prepared for this and quickly installed pre-configured filter screens on all storm drain inlets to remove as many of the solids as possible.
  • By early evening the flows were so high approximately 50 percent of the Plant had flooded and the secondary pump system was unable to keep up.
  • The Plant team was between two outcomes either the incoming effluent would back up into the nearest public streets or the secondary containment pumping system could discharge the excess over what could be handled into the emergency one-mile offshore pipe.
  • At approximately 8:10 pm the Plant followed its regulatory requirements to file a Hazardous Material Spill/Release Report with the 24-hour duty officer at the California Office of Emergency Services (Cal OES)
  • The Board of Supervisors, the Los Angeles City Council, and contract cities in the Plant’s system should redouble public education efforts to keep debris out of the sanitary sewer system. To allow otherwise, places the public at as much risk as a loss of electric power or drinking water. These plants are essential to modem urban society.

The preliminary report compiled by Citygate Associations consulting firm concludes:

The handling of this release and the necessary public notification were failures. The fact that the Plant staff saved their Plant, with limited ocean damage and no water samples the day of or after detected contamination is due to current Plant design and what the Plant staff did under extraordinary circumstances and pressure. Next time, however, it may not be enough.

A 2019 photo of Hyperion’s bar screens and headworks building, photo by Headworks Inc (View the video on YouTube).


Wednesday, 7/21 – the City of Los Angeles, Bureau of Sanitation and Environment has released the following statement.

The hard working and dedicated frontline staff of LA Sanitation and Environment consider themselves guardians of the Santa Monica Bay and Hyperion Water Reclamation Plant as their home. Just as they have done during rain or shine, 24 hours per day, 365 days per year, and even through a major pandemic, they put up a valiant struggle to save Hyperion and the Santa Monica Bay during the emergency overflow discharge that began on July 11th. Their heroic efforts averted a much larger catastrophe, and limited the discharge of untreated wastewater to 17 million gallons, which is a small fraction of the 260 million gallons per day that could have polluted Santa Monica Bay for days on end.

On the afternoon of Sunday July 11, 2021, the Hyperion Water Reclamation Plant became inundated with overwhelming quantities of debris, causing backup of the headworks facilities. The plant’s relief system was triggered and wastewater overflows were controlled through use of the plant’s one-mile outfall system at 7 pm which resulted in the discharge of untreated wastewater into Santa Monica Bay. Normally the discharge of secondary-treated effluent is through the five-mile outfall. During the over eight hours of discharge through the one-mile outfall, approximately 17 million gallons of wastewater (representing six percent of an average daily load) was discharged as a controlled emergency measure through its one-mile outfall relief system to prevent the plant from going completely offline and discharging much more untreated wastewater. The overflow of wastewater was through the one-mile outfall rather than the five-mile outfall because the plant’s internal storm drains are connected to the one-mile outfall to ensure stormwater flows do not overwhelm wastewater treatment processes.

Per established protocols, the State of California Office of Emergency Services (Cal OES) and the National Response Center were notified respectively at 8:10 pm and at 8:18 pm on July 11th. State Law requires that an unauthorized discharge of sewage [as defined in 23 California Code of Regulations (CCR) 2250 (b)] into or onto state waters must be reported to Cal OES. Cal OES will then immediately notify the appropriate Regional Water Quality Control Board, the local public health department, and the local office of environmental health. These offices are responsible for determining appropriate public and environmental safety measures.

Plant staff was onsite all night and resolved the issue early Monday morning. Overflow of wastewater from the plant headworks flowed through roadways within the plant, inundated multiple buildings on site, flooded underground pipe galleries, submerged equipment and caused significant damage. On Monday July 12th during low influent into the plant at around 4:30 am, a previously submerged metal plate was lifted to provide an opening for plant flows to bypass the bar screen filters at the plant headworks and flow downstream into treatment processes. The opening of the bypass gate stopped flooding within the plant and overflow of wastewater into the one-mile outfall.

Numerous improvements over the years, in partnership with several environmental groups, helped to mitigate the flow into the ocean, including reconfiguration of in-plant storm basins to pump sewage back into the plant in cases of emergency; installation of screens on all catch basins to prevent untreated debris from entering the storm drains and discharging out to the ocean; and installation of a Headworks Bypass to allow diversion of flow away from the bar screen filters and into a bypass channel directed back to the treatment process.

Water quality sampling and testing of shoreline (beach) samples were conducted, and our monitoring vessel traveled to both outfalls to make observations and take samples for analyses following regulatory permit protocols. Sampling locations were centered along the shoreline at the 1-Mile Outfall pipe. From there staff went north and south at distances of 100 meters, 0.5 mile, 1 mile, 3 miles, 5 miles, and 7 miles; these sampling sites extended from the Santa Monica Pier south to Avenue A in Redondo Beach. Samples were collected for total coliforms, E. coli, and Enterococcus. Five days of testing revealed normal bacteria levels, well below the state water quality limits for each type of bacteria.

The nearly catastrophic flooding of the Hyperion Water Reclamation Plant on July 11, 2021 resulted in significant areas of the plant being submerged under water and major damage to equipment and processes that treat and clean wastewater. Despite these impacts, Hyperion continues to treat wastewater through its secondary treatment process before discharge through its standard five-mile outfall.

City of Los Angeles forces and contractors are working around the clock to pump wastewater out of inundated facilities, sanitize facilities and equipment, and mitigate hazardous conditions inside the facilities caused by the flooding. It is expected to take a month or more to repair damaged facilities and equipment in order to restore full functionality to Hyperion. Our commitment is to complete the repairs as soon as possible.

Hyperion generates digester gas which is a byproduct of wastewater that the plant receives each day. Since April 2017, digester gas, a renewable energy, is used to generate over 20 megawatts (MW) of power each day from the state-of-the-art Hyperion Bioenergy Facility. The 20 MW of power which is used to meet the plant’s power demand is enough to power about 30,000 homes and is the equivalent of removing about 95,000 tons/year of greenhouse gases from the environment, and about 20,000-cars equivalent.

The flooding of Hyperion on July 11, 2021 significantly reduced the amount of digester gas available to generate power, which resulted in a temporary shutdown of the Hyperion Bioenergy Facility. Because the production of digester gas is low and insufficient to run the Hyperion Bioenergy Facility, the unused gas is combusted by utilizing plant equipment permitted by AQMD, which may intermittently produce visible smoke or flames.

We ask for your patience during the reconstruction period as you may experience intermittent odors, noise, or see smoke or flames emitting from plant equipment permitted by AQMD to combust unutilized digester gas. Hyperion is taking all measures to minimize and mitigate impacts (odors, noise, etc.) to the community during the cleanup and repairs to fully restore functionality of the plant.

We sincerely apologize for any inconvenience experienced as a result of the flooding incident on July 11, 2021. Please contact LA Sanitation & Environment’s 24-hour Customer Care Center at 1-800-773-2489 to express specific concerns or to file a complaint. If you feel that you have lost money or property as a result of any action or inaction by the City of Los Angeles, you can file a claim by clicking here.

– end of statement –


Here’s what we know day-by-day according to information released by LA City Sanitation & Environment and other groups:

  • Thursday 7/14 – Beaches reopened. LA County Department of Public Health announced all ocean waters and beaches near the one mile outlet are reopened after tests showed no threat to public health.
  • Thursday 7/14 – Non-profit group Heal the Bay broadcast an interview with their Executive Director Dr. Shelly Lucy. Dr. Lucy reported LA City Sanitation team members were monitoring the beach and ocean waters looking for trash that may have come from the bypass flow and found no sewage related debris so far.
  • Monday 7/12 – The LA County Department of Public Health closed ocean access at nearby beaches out of an abundance of caution and began water quality testing
  • Monday 7/12 – After repairs, the plant resumed full treatment levels and ended the overflow bypass.
  • Sunday 7/11 – Late that night all headworks equipment became clogged and inoperable and the emergency one mile ocean outlet was used to keep the treatment plant from flooding. 17 million gallons of screened sewage was sent to the outfall for eight hours, that is 6% of Hyperion’s average daily flow.
  • Sunday 7/11 – Operators implemented the treatment plants emergency procedures including rerouting flows to a new equalization treatment tank that was recently constructed for emergency storm flows.
  • Sunday 7/11 – On Sunday afternoon influent coming into the plant contained overwhelming quantities of debris including chunks of wood, concrete and other debris according to a statement by Hyperion Plant executive manager Timeyin Dafeta.

Additional Background

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