What Went Wrong at the International Wastewater Treatment Plant

Published Nov. 29, 2011 by Imperial Beach Patch.

Officials from the South Bay International Wastewater Treatment Plant talked about multiple problems that have kept its secondary treatment plant from meeting Clean Water Act standards at a U.S. International Boundary and Water Commission Citizens Forum held earlier this month in Imperial Beach.

A pumping station a few miles south of the border in Tijuana sends the sewage to the International Wastewater Treatment Plant north of the border in San Ysidro.

There an average 25 million gallons of Mexican sewage is treated daily, though at peak hours the plant can handle rates up to 50 millions gallons a day. Water treated at the plant is then released three miles out in the ocean by the South Bay Ocean Outfall.

The primary treatment facility opened in 1999 and cost more than $140 million. The U.S. Environmental Protection Agency spent a combined $127 million to build the primary treatment plant and $89 million for the City of San Diego and Army Corps of Engineers to build the South Bay Ocean Outfall.

The secondary treatment facility opened in November 2010 and cost more than $90 million.

In the secondary treatment process at the plant, first a population of bacteria in aerations tanks eat away at solids. Air blowers provide gases necessary to fuel the bacteria. Then solids and liquids are separated in secondary clarifiers tanks.

Flights, which rotate in the tank and pull solid material into hoppers, failed for the first time May 16, said Robert Nienhuis with Veolia Water North America, the company who built the new secondary plant.

“An operator was walking by and noticed that the flights weren’t there,” he said. “So we shut it down, pumped all the sludge out and these flights looked like Pixie Sticks at the bottom [of the tank].”

Four violations of Clean Water Act standards were detected in May, June and July 2011, the Water Quality Control Board said in the continuation court document. Exceedances allowed solid materials wash out into the ocean, said U.S. IBWC Area Operations Manager Steve Smullen.

After that repair was made, a month later there was another failure. After the second failure a contractor came into check each of the 10 secondary clarifier tanks.

Surveys found that wrong sized washers were used in some cases, and some misaligned flights scraped against the side of the tank.

“These are like two bicycle chains that these two things are attached to so there’s a lot of little parts and things that have to go together to make these things run correctly,” Smullen said.

Currently, two of the 10 tanks remain offline due to problems with flights. The plant hopes to have them back online within the next month, Smullen said.

“The misalignment of these two, they’re still not sure where that misalignment occurred but if we leave it the way it’s set now, we could run into major failure.”

“When they fail, they really fail catastrophically,” Smullen said.

Due to an engineering oversight, an emergency bypass of secondary treatment when the plant reaches maximum capacity at 50 million gallons a day was programmed to release at 41 million gallons a day instead. The problem was resolved June 23, Neinhuis said.

Flows typically don’t exceed 40 million gallons a day, Smullen said.

“There were some days when it was five MGD but most of the time it was 1/5 MGD, or 1/10 of an MGD,” Smullen said about the amount of sewage released as a result.

Among other changes made since the plant opened, engineers increased depleted oxygen concentrations in aeration tanks to better support the bacteria population.

Toxins and heavy metals like lead and chromium have been detected in the water at times, Neinhaus said. Additional meters were installed to better detect toxins and conditions in aeration tanks.

Launders which capture water at the top of the clarifier tanks originally weren’t given a sufficient coat of a paint to prevent corrosion and had to be shut down for a month earlier this year .

The California Regional Water Quality Control Board sued the U.S. IBWC in 2001 over Clean Water Act violations. In 2003 the court sided with the WQCB and in 2004 a federal judge ordered the plant come up with a scheduled to reach Clean Water Act standards which means a fully operational secondary plant.

On Sept. 27, a federal judge granted requests by the state attorney general’s office on behalf of the California Regional Water Quality Control Board for a continuance of four months to monitor the facility and report their findings to the court in February 2012. If there are no violations before February, a new National Pollutant Discharge Elimination System permit may be granted, Smullen said.

“We’ve done what was required but we have to make sure the effluent meets the standards. There may be some additional things that we need to do after clarifier gets solved. We just don’t know yet,” Smullen said.

Among other topics discussed at the meeting, to offset the environmental impact of building the secondary treatment plant, the Goat Canyon sediment basin was cleaned and Southwest Wetland Interpretive Association conducted five acres of native plant reclamation.

In all, 15 tons of solid waste and 1,000 waste tires were removed from the Goat Canyon sediment basin near Monument Road, said Rob Stroop with URS Corporation, the company who carried out the project.

The results of the Tijuana River Action Month results were also announced at the citizen forum by Danielle Litke, volunteer coordinator for the .

In its second year, the action month took place from mid September to mid October and centered around making a difference in trash collection around the Tijuana River before the start of the wet season. Altogether there were 50 hours of activities and more than 8,000 volunteer hours, Litke said. 

Last year the event was primarily focused on cleanups but this year more events were added like habitat restoration, informative workshops and water quality training.

Of 2,647 people who took part in action month cleanups, more than 2,000 were from Mexico. In 35 cleanups that took place from Tecate to Tijuana on Beach Cleanup Day, more than 63,000 pounds of trash was collected.

Tijuana River Action Month is organized by members of the Tijuana River Action Network, a collective of organizations passionate about the Tijuana River watershed in the U.S. and Mexico. 

Comments are closed.