Background

In coordination with NADBank, the U.S. Environmental Protection Agency (EPA), the Mexican National Water Commission (CONAGUA) and the U.S. and Mexican Sections of the International Boundary and Water Commission (IBWC/CILA), CESPT and the State of Baja California have been working to address incidents of untreated wastewater discharges to the Tijuana River basin and the Pacific Ocean. As part of a binational commitment formalized through the Statement of Intent (SOI) signed by EPA and CONAGUA, as well as IBWC Minute 328, specific wastewater infrastructure rehabilitation and replacement projects are scheduled for implementation over the next few years with cost-share commitments from both countries.

The project proposed for certification is included in the SOI and will address two key components of the wastewater collection and conveyance system in Tijuana: (i) replacement and abandonment of the old sewer main known as the International Collector and rehabilitation of the PB1B lift station; and (ii) rehabilitation of the Tijuana River diversion system, which includes works to improve the operation and increase the capacity of the PBCILA lift station and rehabilitate the PB1A lift station.

On July 30, 2022, the parallel conveyance system related to PB1A and PB1B, which convey Tijuana River water to the Pacific Ocean and wastewater to the San Antonio de los Buenos Wastewater Treatment Plant (WWTP), respectively, experienced major breaks in both force mains, which caused both lift stations to be shut down. While the PB1B force main has been replaced and regular operations have resumed, repairs on the PB1A force main have not been completed, impairing the operations at the PB1A lift station. As a result, excess wastewater flows have been conveyed to the South Bay International WWTP, severely impacting its operation. Moreover, due to the condition of the PBCILA lift station and its river intake, the diversion system was not functioning adequately to prevent transboundary flows in dry-weather seasons.

Description

The project consists of replacing and abandoning the deteriorated International Collector, rehabilitating PB1A, PB1B and PBCILA lifts stations, increasing the capacity of PBCILA from 1,008 to 1,490 liters per second (lps) or 23 million to 34 million gallons a day (mgd) and constructing a new intake from the Tijuana River channel to PBCILA. The improvements to each of these components are described below:

• Tijuana River Diversion System – construction completed by CONAGUA
  • Tijuana River in-take: Installation of 289 ft of 48-inch fiberglass reinforced
  • PBCILA Lift Station improvements: Sand and grit removal (Vortex), fine and coarse mechanized screen, effluent flow meter, conveyor belts for automatic trash and debris collection, a new 125-HP Chopper pump, and 300-kVA transformer replacement.
• International Collector – under construction by Mexican Ministry of Defense (SEDENA): 8,356 ft of 60-inch high-density polyethylene (HDPE) pipe, 656 ft of 72-inch HDPE pipe, smart ultrasonic flow meter and SCADA system.
• Improvements in the PB1A & PB1B Lift Stations – pending construction BEIF/ CESPT: Sand and grit removal (Vortex), two fine and coarse mechanized screens, two motor control centers, four new pumping trains (two 700-HP / 500 lps (11.4 mgd) per train), 13 flow control gates of various sizes, electric substation maintenance, and two flow meters. Due to the location of the PB1A and PB1B lift stations, the final designs also include flood protection measures.

As a result of the project, the PBCILA lift station will convey dry-weather flows from the Tijuana River to the PB1A lift station and discharge directly to the ocean through one of the parallel lines. With the new system, PBCILA will not be connected to the International Collector. 

The new International Collector will convey wastewater from the downtown and northwest areas of the city of Tijuana to the South Bay plant. With the installation of a smart ultrasonic flow meter in the International Collector and traditional flow meters at both PB1A and PB1B, CESPT will be able to better manage flows to the appropriate infrastructure. Once flows reach the capacity of the South Bay plant, the remaining flows will be sent to PB1B and conveyed through the second parallel line to the San Antonio de los Buenos WWTP, which will be rehabilitated.

Benefits

Replacing the International Collector and rehabilitating the PB1B lift station will improve wastewater infrastructure serving up to 208,360 existing residential connections, by reducing the risk of pipeline failure and preventing the potential discharge of up to 1,400 liters per second (lps) or 32 million gallons per day (mgd) of wastewater from spills and leaks that could impact the Tijuana River. The rehabilitation of the PBCILA and PB1A lift stations will allow CESPT to divert approximately 1,120 lps or 25.6 mgd of dry-weather flows in the Tijuana River and discharge them to the Pacific Ocean. Therefore, the project will also benefit the U.S. by eliminating transboundary flows of water through the Tijuana River