A sewage spill in Oceano following heavy rain last December might have been prevented but for two errors at the South San Luis Obispo County Sanitation District.
Because of a closed discharge valve, a pump was not able to push the raw sewage quickly enough through the plant. If it had, the probability of a sewage spill would have been very low, according to a report the district sent this week to the state Water Resources Control Board.
Sanitation district Administrator John Wallace said Wednesday he believes the valve was inadvertently left closed after maintenance had taken place at the plant.
“I’m not sure how that happened,” he said. The plant staff “responded as quickly as they could through the sequence of events.”
District staff has estimated that 384,000 gallons of sewage spilled after floodwater flowed into the wastewater treatment plant and caused an electrical short that shut down four influent pumps about 10:30 a.m. on Dec. 19.
In April, the state water board sent the sanitation district a notice of violation requiring it to submit a technical report outlining the cause of the spill, the district’s response and detailed information about the agency by Tuesday. Water board staff was trying to determine whether the sanitation district underreported the amount of sewage spilled in December, water board spokesman Dave Clegern said.
Clegern verified Thursday that the district’s documents had been received. “Any penalties would be dependent on what the whole body of information shows,” he wrote.
The state water code allows fines of up to $10 per gallon for a spill. A civil penalty of up to $1,000 per day can also be levied if required information is not furnished or is falsified.
The original estimate of the sewage spill was much higher. An analysis by the plant superintendent, which assumed the “worst case conditions,” put the spill amount at 1.8 million gallons to 2.3 million gallons.
But that number was later reduced after staff analyzed data recorded during the spill, reviewed sewage line storage capacity and interviewed local residents.
The South County treatment plant was not the only one to report a sewage spill in December. Clegern said the Vandenberg Village Community Services District was sent a notice of violation in March, and another is being prepared for the Cambria Community Services District.
Floodwater started pouring into the treatment plant, located in Oceano near the Oceano County Airport, about 7:35 a.m. on Dec. 19, according to the district’s response.
Plant employees first tried unsuccessfully to reset the breakers to restart the pumps to process the wastewater. Then, they started the backup, motor-driven diesel pump and immediately discovered it couldn’t work to its maximum capacity because a valve that is normally open was shut.
The plant superintendent was able to open the valve only a third of the way before it was submerged in water.
The valve was fully open by 2:30 p.m. but by that time, sewage had overflowed from 21 manholes in the Oceano area. In the meantime, other pumps were brought in to help contain untreated sewage spilling within the plant.
Floodwaters took most of the sewage through the Oceano Lagoon area to the mouth of Arroyo Grande Creek and then to the ocean at Oceano State Beach.
Since the spill, the valve has been chained open, Wallace said. Thoma Electric is also conducting a study of all the plant’s breakers.
The sanitation district responded to numerous questions from the state water board about the spill and cleanup. Here are a few district responses:
The district’s response to the spill was hampered by the county’s evacuation order and severe flooding. “Floodwaters of up to 2 to 3 feet covered a number of manholes that were potentially spilling,” the report states. “As a result, it was not possible to stop or contain the spilling of wastewater in some locations outside the plant.”
In response to a question on water quality monitoring after the spill, the district referred to the sampling done by the county’s Environmental Health Department. The department conducts weekly sampling at three locations at Oceano State Beach but did not sample the week of Dec. 19 because of safety concerns, including high surf. Samples were taken Dec. 28, and all results were within allowed limits.
The state water board asked whether the sanitation district had assessed short- and long-term impacts on public health, animals and plants. The district is interested in contracting with Douglas Rischbieter, a state Department of Water Resources employee, who prepared a monitoring report on the lower Arroyo Grande Creek in 2006. District staff has called and emailed Rischbieter, who was out of town in May.