Equipment failure causes lapse in quality of water discharged to Bay

Filtration system back online as of early Sunday

A damaged filtration system at the City of Palo Alto's Regional Water Quality Control Plant -- which led to a small change for three days in the quality of water being discharged into the San Francisco Bay -- was back online as of Sunday morning, according to the Public Works department.

An equipment failure, which occurred Wednesday evening, resulted in the flooding of the plant's filtration building. While efforts were taking place to repair the damage, wastewater had to skip the filtration step, one of the last processes the water undergoes during its treatment. An estimated 55 million gallons of water were discharged while the system was shut off; the plant typically discharges 18 million gallons per day.

Assistant Director of Public Works Phil Bobel said Monday morning that, while not all damage has been repaired, the filtration system went back online early Sunday and the quality of water discharged was back within legal compliance during samples taken from Saturday to Sunday morning.

On Saturday, Bobel emphasized that the lapse in water quality was only slight and should not be worrisome, as almost all the treatment processes, including disinfection, were still in place. The change posed no danger to the public or wildlife, he said.

"While we've had this technical problem and had to bypass one of our treatment units, it hasn't resulted in any impact in the Bay or to human health," he told the Weekly.

The problem arose during routine maintenance when an air plug blocking the flow of water failed and the filtration building was flooded, damaging the electrical motors for the filtration pumps. No one was injured. Pumping of the building began early on Thursday, and the building was emptied by midday.

Following the failure, wastewater was redirected past the building, skipping the filtration step, which typically removes a portion of suspended solids -- that is, particles remaining from earlier steps in which bacteria are used to treat the sewage water.

The limit of parts per million of suspended solids allowed by the plant's permit is 20, and measurements of the unfiltered water yielded levels as high as 26 parts per million. However, Bobel noted that the increase isn't large, and bacteria levels in the water are still within safe limits.

"The Bay has far more suspended solids than 26 parts per million," Bobel said.

Still, as required by its permit, the plant's staff notified the San Francisco Regional Water Quality Control Board and the state's Office of Emergency Services of the change. The water quality control board has been in contact daily with the plant, Bobel said, asking questions and ensuring that the situation is resolved quickly.

After the incident, the damaged motors were rushed off to be repaired, and Bobel said that most of them were returned to the plant on Saturday and are being reinstalled. To pay for the repairs, the department has authorized $25,000 in emergency funds; Bobel hopes the staff will not expend the entire amount.

In the future, the water quality control board may have to levy fines -- as stipulated by state law -- for the plant's exceeding its suspended solids limit, but that determination won't be made until a later date.

On Monday morning, Bobel noted that a composite analysis sample taken from Saturday morning to Sunday morning -- in which water is tested every 30 minutes and then averaged -- was below the limit at 13 parts per million of suspended solids. He said that should go down even further; ordinarily, the level can be as low as one part per million.

"We hope to get back to that within a few days," Bobel said.

Editorial Assistant Sam Sciolla can be emailed at

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