Jun 25, 2020

Potable Water System Likely Caused Sewage Spill at Nuclear Plant

7,000 gallons of non-radiological wastewater released into the ocean in late March are connected to a large influx from the potable water system into the sewage treatment plant on the grounds of the San Onofre Nuclear Generating Station.

sewage spill

7,000 gallons of non-radiological wastewater released into the ocean in late March are connected to a large influx from the potable water system into the sewage treatment plant on the grounds of the San Onofre Nuclear Generating Station, according to a report submitted to the San Diego Regional Water Quality Control Board.

The sewage treatment plant collects raw sewage from existing facilities used by people at SONGS, a now-closed nuclear plant. The spill was mostly human waste, which was expelled by a conduit that runs 1.1 miles and 50 feet below the surface of the ocean from SONGS.

The report included analysis from an engineering firm specializing in the assessment of environmental risk, GSI Environmental Inc. The firm concluded there was no evidence of impacts on human health from the spill, as toxicity testing showed no observed impacts on kelp or in sea urchins.

The spill was triggered after approximately 28,000 gallons of water swamped the plant’s sewage treatment plant on Mar. 24. Combined with an influent pump, which was plugged, the result was the discharge of 4,200 to 7,000 gallons of wastewater about a mile into the ocean.

The source of the 28,000 gallons of water is still not completely known, according to the San Diego Tribune.

According to the report, the plant’s potable water system was the only reasonable source of the unexpected influx because the potable water system is capable of supplying enough water to cause such a surge.

The report also notes it is not possible that the source of the inflow into the sewage treatment plant was radioactive, since there were no unexplained transfers of radioactive water or radioactive systems at SONGS.

According to the report, when a high-level alarm was received from an equalization basin in the sewage treatment plant, appropriate personnel were not contacted in as timely a manner. The next day at about 5:30 a.m. on Mar. 25, the day-shift station operator unplugged the influent pump discharge line, which increased the flow rate through the sewage treatment plant.

“Had this action not occurred,” the report said, Integrated Performance Consultants, “Might have arrived on site in time to prevent an unpermitted release, even with the delay in communication.”

Edison officials said they have taken steps to avoid a repeat of the spill, including: installing a submersible pump with auto start capability; improving the timing of alarm notifications; making modifications to the sewage treatment plant; And employing enhanced training and operating procedures.

In April, in the Water Board’s letter calling for Edison to file a report, the board listed its enforcement actions for potential violations. 

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