‘Unlikely’ Power Failure and Series of Equipment Mishaps Led to Massive Oakland Sewage Spill

A sign warns people not to go in the water after 50,000 gallons of sewage spills into the Oakland Estuary.  (Lakshmi Sarah/KQED)

A major release of raw and partially treated sewage into the Oakland Estuary earlier this month was triggered by a rapid-fire series of electrical failures at the East Bay Municipal Utility District's main wastewater treatment plant, the agency says in a report filed with state regulators.

The spill took place during the Bay Area's mid-August heat wave and prompted the agency to post warnings along a nearly 4-mile stretch of the waterway separating Oakland and Alameda. Water quality samples taken in the estuary the day after the spill showed bacteria levels many times higher than the safety threshold for the area.

“These discharges resulted from an unprecedented confluence of several unlikely events and circumstances,” Eileen White, EBMUD's director of wastewater, wrote to state water regulators on Aug. 24.

In the hours after the Aug. 15 releases, EBMUD said the spills were caused by a PG&E power outage.

But the agency now says that the episode began with the failure of the wastewater plant's own internal power sources — three large generators — within a three-minute period starting at 5:11 p.m. Aug. 14. Then, just seconds after the last of the generators stopped running, two high-voltage PG&E lines providing electricity to the wastewater plant also lost power, knocking the facility offline.

Sewage began backing up through the plant and flooded a battery of five massive pumps that are not designed to be submerged — meaning they could not be brought back online when PG&E power was restored at 6:49 p.m.

With no way of processing incoming wastewater, EBMUD was forced to divert raw sewage to backup holding facilities in Richmond, East Oakland and Alameda. More than nine hours after the incident began, about 47,000 gallons of untreated sewage spilled from an outlet on Alice Street, just east of Jack London Square. A much larger amount of partially treated wastewater, about 3.7 million gallons, flowed into the harbor from an outlet adjacent to Oakland's Estuary Park.

The section of the estuary where the spill took place, the Oakland Inner Harbor, is already on a Clean Water Act watch list because it's contaminated with bacteria from human waste, notes Sejal Choksi-Chugh, executive director of San Francisco Baykeeper.

“So an accident of this scale is unacceptable and puts the community and wildlife at additional risk,” Choksi-Chugh said.

EBMUD and PG&E are investigating the cause of the outages that led to the spill. Both utilities say the power failures that occurred at the wastewater facility are unrelated to rotating blackouts that PG&E was ordered to implement in other parts of its service area that evening of Aug. 14.

Besides the power outage, EBMUD says a series of mechanical and maintenance issues at the sewage treatment plant also played a major role in the spill.

Sewage was able to flow back through one of the five huge “influent” pumps at the facility because of a leaking discharge valve. An adjacent pump was undergoing maintenance, and an inspection plate on the massive device had been removed to facilitate the work. The rapid overflow of sewage from the first pump spilled through the second pump and flooded a part of the facility that normally stays dry, so all of its pumps stopped working.

Crews worked overnight to lower sewage levels in the plant's “dry pit” using a vacuum truck and portable pump to pull out the flooding wastewater.

But EBMUD operators weren't able to get inside the area where the sewage was filling up “because the water level was rising very quickly and there was a risk of engulfment of personnel,” EBMUD's White wrote.

Andrea Pook, an EBMUD spokeswoman, said the spill could have been worse if the agency had not been able to store some of the sewage in multiple facilities.

“EBMUD took immediate action to mitigate the magnitude of the overflow,” Pook said.

Immediately after the overflow, crews began posting signs along both shores of the waterway warning people to avoid contact with the water.

Agency officials say they were concerned the ongoing heat wave would bring more people to the estuary so they began reaching out to local officials, news organizations, swim clubs and others to get the word out about the dangers of the spill and urge swimmers and boaters to stay away.

EBMUD took water quality tests near the site of the release in the following days. The results showed high levels of the bacteria enterococcus, which poses a risk of serious infections.

The day after the spill, tests in one location showed enterococcus levels 19 times higher than the safety threshold for swimming in the estuary.

EBMUD's Pook says the spill contributed to those high levels but the main culprit was the rain the region received that day after months of very little precipitation.

“The rains we had (that) Sunday morning actually result in more contaminants being added to the estuary in the form of ‘first flush’ runoff,” Pook said, adding that rain pushes runoff from roadways into the estuary.

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That morning there was a series of thunderstorms in the Bay Area that would eventually lead to the lightning-caused wildfires in and around the the region that have burned hundreds of thousands of acres and destroyed hundreds of homes.

But the storm did not produce much precipitation. On Aug. 16, the day after the spill, .02 of an inch fell at the Oakland Museum, a little more than half a mile from the estuary. And .04 of an inch fell at Oakland International Airport, according to Jan Null, a meteorologist at Golden Gate Weather Services.

The bacteria levels dropped the following day and the next Saturday the advisory was lifted.

In the meantime, the regional water quality control board is investigating the spill and the utility says it's making changes to prevent a similar release. EBMUD told the board that it plans to replace inspection plates faster and buy pumps that can be used in emergencies.

“EBMUD needs to modernize its backup protocols and perform extensive testing to be certain its system can withstand foreseeable threats like power outages, fires earthquakes and flooding,” said the Baykeeper's Choksi-Chugh.