Twin Oaks Valley Water Treatment Plant Cited for Error

July 08, 2019

A malfunction at the Twin Oaks Valley Water Treatment Plant resulted in a citation from the state Division of Drinking Water, though the water in regional pipelines continued to be safe for all uses due to additional treatment processes that are in place.

The malfunction lasted for about 15 hours on April 21-22, when ozone dosage levels in the plant fell below state-mandated levels because a valve failed to fully open. Ozone is a common disinfectant used in water treatment systems to kill bacteria and other organisms. To be effective, water must be in contact with the proper dosage of ozone for specific amounts of time.

CH2M Hill/Jacobs operates the Twin Oaks plant under a contract with the Water Authority, but the citation was issued to the Water Authority as the plant owner and permit holder. This is the first citation issued at the Twin Oaks plant in more than a decade of service.

Corrective actions were taken immediately, and the lapse was reported to state regulators. The contractor has updated its operational procedures and installed additional monitoring equipment to prevent similar problems in the future.

If there had been a water quality emergency, the public would have been notified immediately. After the citation was issued on June 4, the Water Authority worked closely with impacted member agencies to follow state-mandated noticing requirements.

“This was an unfortunate event, and we’ve put new procedures and equipment in place to ensure it doesn’t happen again,” said Sandy Kerl, acting general manager of the Water Authority. “We are committed to maintaining the high levels of safety and reliability we’ve achieved over more than 75 years of service to the San Diego region.”

That process involved identifying and notifying all customers who may have received water from the Twin Oaks plant during the April 21-22 incident. Affected agencies are Carlsbad Municipal Water District, Helix Water District, City of Oceanside, Otay Water District, Padre Dam Municipal Water District, Rainbow Municipal Water District, Ramona Municipal Water District, Rincon del Diablo Municipal Water District, Vista Irrigation District, City of San Diego, Vallecitos Water District, and Valley Center Municipal Water District. Notices in English and Spanish are being mailed to potentially affected customers this week.

The notices include a hotline number that Water Authority set up to address questions from the public at (858) 284-4142. In addition, the Water Authority has provided online resources at Those resources include a map of affected areas searchable by address, the official public notice, the formal citation by the state and frequently asked questions.

During June, retail water agencies are distributing their annual water quality reports to customers. The Twin Oaks incident is not included in the current reports, which cover water quality during calendar year 2018. Since the event occurred in April 2019, it will be noted in the annual reports for calendar year 2019 which will be released next year.

  • The San Diego County Water Authority sustains a $268 billion regional economy and the quality of life for 3.3 million residents through a multi-decade water supply diversification plan, major infrastructure investments and forward-thinking policies that promote fiscal and environmental responsibility. A public agency created in 1944, the Water Authority delivers wholesale water supplies to 23 retail water providers, including cities, special districts and a military base.

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