Large volumes of transborder flows of wastewater mixed with stormwater entered the United States early in the morning on March 9 and the U.S. section of the International Boundary and Water Commission (IBWC) said it met with Mexican officials to troubleshoot the issue.
According to Dr. Maria-Elena Giner, U.S. commissioner of the IBWC, multiple unforeseen construction issues with a wastewater collector resulted in the excessive flows entering the U.S. via the Tijuana River.
Construction problems included complications installing two inflatable plugs into pipes. That diverted wastewater flows to the river for about four hours.
In addition, the statement explained that unexpected flows from two pipes that were previously unknown to the Tijuana utility sent large amounts of rainwater into a drain system, which ultimately clogged it.
The flow, estimated to be more than three million gallons, exceeded the capacity of an international collector, according to Giner.
Accumulated debris also obstructed a junction box at the South Bay International Wastewater Treatment Plant (SBIWTP), resulting in minimal flows reaching the plant early March 9.
USIBWC contractor Veolia cleaned the debris so flow could resume to the plant and, by that afternoon, normal operations had resumed.
“I have made it very clear to Mexico the importance of avoiding future transboundary flows to the greatest extent possible during this very complicated construction project,” Giner said.
However, she said, Mexico told the IBWC that construction challenges and heavy rains may delay completion of the international collector, a key component of the treatment system.
“I ask everyone to keep in mind that getting the new international collector in operation as soon as possible is a crucial milestone and will bring more resiliency to the sewage infrastructure in Tijuana and reduce transboundary flows,” Giner said.
However despite heavy rain on March 13, there were no structural problems with the Tijuana River levees or the SBIWTP, said Giner in an update.
Mexico placed sandbags around the international collector bypass to prevent street flooding and keep sewage out of the river, and real-time monitoring of the river indicated very low concentrations of sewage in the river due to dilution by the rainfall.
The USIBWC and the Environmental Protection Agency continued to hold daily calls with Mexico as of March 14 to get updates on the international collector project.
“I just would like to reiterate: The existing international collector manages average flows of 32 million gallons a day and has had portions of the line fail due to age and disrepair,” Giner said. “Given the amount of flow conveyed by this line, any failures would be catastrophic for the region.
“Getting the new international collector up and running as soon as possible is a crucial milestone and will bring more resiliency to the sewage infrastructure in Tijuana,” Giner expressed.
The collector, the largest wastewater conveyance pipe in Tijuana, has been plagued by leaks that have caused transboundary flows, according to the statement. After expansion, it will have the capacity to carry up to 60 million gallons per day of raw sewage to the SBIWTP for treatment.
