Chrome-6

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Chromium is a naturally occurring metallic element found throughout the environment in rocks, soils, plants, and animals. The most common forms are trivalent Chromium (chromium 3) and hexavalent Chromium (chromium 6/chrome-6)—the numerals signifying their distinct oxidative state. Chromium 3 is found in foods and is an essential dietary nutrient. Chrome-6, on the other hand, can be toxic if ingested in large amounts.

Routine water monitoring has shown that three of our 18 groundwater wells located in the Seascape area (Bonita, San Andreas, and Seascape) contain chrome-6 above the State of California’s newly reestablished standard of 10 parts per billion (ppb). The average range for these three wells is 10.5 ppb to 12 ppb. This is not a result of any kind of industrial spill or discharge — it is naturally occurring. Scientists have estimated that up to 80% of the drinking water sources in the United States could have chrome-6.

Our chrome-6 exceedance is not an emergency. While recent water quality results show that levels of chrome-6 exceed the newly adopted State Maximum Contaminant Level (MCL), it’s important to emphasize that this is not a public health emergency. There is no immediate risk, and customers do not need to take any special actions such as boiling or avoiding water use. This new California regulatory threshold is based on long-term high levels of exposure, not short-term health concerns.

We are actively working to meet compliance regulations. Only three of our 18 groundwater wells require treatment to meet the new standard and the District has already completed the environmental review and a pilot test using Reduction Coagulation Filtration technology to remove chrome-6. Design of a new treatment plant is currently underway. A water system of our size is not considered in violation of the chrome-6 MCL until after October 1, 2026.

Chrome-6 MCL History and District Activities

What We've Done and are Doing to Address Chrome-6

The District has been, and continues to be, very proactive regarding Chromium 6. 

• April–August 2013: We conducted a successful pilot treatment project using a process called strong-base anion exchange, with grant funding by the Water Research Foundation. 
• October 2014–December 2017: We completed demonstration treatment using strong-base anion exchange. 
•  January–March 2017: We completed demonstration treatment testing using stannous chloride as a reducing agent (to convert Chromium 6 to Chromium 3) with filtration of the precipitate. Completed environmental permitting for a permanent treatment facility and installed new water transmission mains to treat at a centralized location. 
• 2017: MCL was rescinded by the State of California, and the District paused design and construction of its chrome-6 treatment facility to await further developments in the MCL by the state. 
• 2024 and beyond: 
  • The State reestablished the MCL in October of 2024.
  • The District piloted a new, lower-cost chrome-6 treatment and is designing a treatment facility. 
  • The state approved our compliance plan on October 3, 2025.