Background on Hyperion Water Reclamation Plant

The Hyperion Water Reclamation Plant (Hyperion) is a sewage treatment plant operated by City of Los Angeles Sanitation & Environment located at 12000 Vista Del Mar, Playa Del Rey, CA 90293.

On July 11, 2021, Hyperion experienced a malfunction at its headworks facility when a series of bar screens were overwhelmed and unable to remove large quantities of trash and debris causing a system failure and raw sewage to flood the plant. As a result, elevated hydrogen sulfide levels produced odors that impacted residents' quality of life until the flood was cleared. After the initial malfunction, odors continued to intermittently impact the surrounding community. In December 2023, Hyperion installed new Primary Battery Tank Covers to reduce odors. All other tank covers were replaced by June 2024.

Wastewater treatment plants process water from homes and businesses, which contains human waste, food, and certain soaps and detergents. As such, odors may occur due to different factors. Common odors lingering in and around treatment plants smell like rotten eggs, ammonia, or garlic, among other things. Generally, they result from the decomposition of organic compounds, of which hydrogen sulfide (a gas that smells like rotten eggs) is a natural by-product. Odors may be most noticeable on hot days and when the levels of bioactivities are high and the percentage of humidity in the air is higher. The first step in solving any odor problem is identifying the source, which may be a combination of different things. The next step involves preventing the odor from being released to the air by installing covers and building containment around the odorous treatment processes. Finally, the odorous air should be properly treated before it is released.

Ongoing Hydrogen Sulfide Monitoring

LA Sanitation & Environment provides hourly data on levels of hydrogen sulfide in the air at Hyperion. The levels can be found on Hyperion Air Monitoring page (opens in a new tab).

The South Coast Air Quality Management District (SCAQMD) provides updates on the investigation on their Hyperion Water Reclamation Plant website (opens in a new tab).

Hydrogen Sulfide and Health Facts

Hydrogen Sulfide (H2S) is a gas that smells like rotten eggs. Industrial facilities such as sewage treatment plants can produce hydrogen sulfide.

People can generally smell hydrogen sulfide odors at around 3-5 parts per billion (ppb), although some people can smell hydrogen sulfide at even lower concentrations. This can be stressful and impact health and quality of life.

The health effects of hydrogen sulfide depend on how much you breathe and for how long. Hydrogen sulfide in low concentrations can cause symptoms such as:

  • Irritation to the eyes, nose, or throat
  • Difficulty in breathing, for people with asthma or other respiratory illnesses
  • Nausea
  • Headache
  • Dizziness

The California Environmental Protection Agency's Office of Environmental Health Hazard Assessment (OEHHA) reviews information about chemicals. OEHHA has determined that no adverse health effects are anticipated at hydrogen sulfide levels below 7 ppb in the air, even for chronic (long-term) exposures. Hyperion operates 3 continuous hydrogen sulfide monitors at their fenceline. For the majority of the time, hydrogen sulfide is measured at less than 3 ppb, historically, there have been 2 to 3 times a week that hydrogen sulfide is measured between 7 and 30 ppb and those elevations are generally short lived and go back down with an hour or two.

The California Ambient Air Quality Standard (opens in a new tab) for hydrogen sulfide is 30 parts per billion (ppb), averaged over one hour, and was adopted for the purpose of odor control.

Hydrogen sulfide in air is regulated by the South Coast Air Quality Management District (opens in a new tab).

What Can You Do To Protect Yourself?

If you experience odors, you can:

  • Use a portable indoor air filter such as a High Efficiency Particulate Air (HEPA) cleaner to improve air quality in your home. For more information on certified air filters, check EPA's Air Cleaners and Air Filters in the Home page (opens in a new tab).
  • Air out your home when odors are not present by temporarily opening windows and doors.
  • Contact your healthcare provider if you are experiencing health symptoms.
  • Report the odors.

To Report Concerns

If you notice "rotten egg" or "sulfur" odors, you can report them to the following agencies below:

Public Health & Safety Guides

Public Health Letters to Los Angeles Sanitation and Environment