Named “America’s Finest City” for its beauty and ideal climate, San Diego is a popular tourist destination, particularly because of its 70 miles of sandy beaches. However, many people don’t realize what is required to maintain the pristine ocean water lining the beaches.
THE NEED FOR CLEAN
Sewage flowing from Tijuana into the US Tijuana river valley and ultimately the nearby ocean has caused contamination of the water since the early 1900s. To address this growing environmental concern, the International Boundary & Water Commission (IBWC), a joint Mexico-US effort, created the South Bay International Wastewater Treatment plant.
Constructed in the 1990s, the original plant provided only primary treatment. To meet current EPA regulations, PCL was contracted to build the secondary treatment facility. The plant treats 25 million gallons per day (MGD), with expansion capability up to 100 MGD. PCL self-performed a vast majority of the work, and the civil site work included deep dynamic compaction and construction of two large cast-in-place concrete tanks, the activated sludge tank (AST), and the secondary sedimentation tank (SST).
When the PCL team began mobilizing onsite, they discovered that underground utilities had created a need for shoring on the AST structure. Through the use of virtual construction, the project team determined that, by minimally moving the AST structure, the excavation could be sloped, thus eliminating the need for shoring and saving time and money. This early and open communication led to a strong partnership between PCL and the IBWC. “PCL was proactive and forward-thinking about issues they saw, and quick to respond,” said Steve Smullen, area manager for IBWC.
As unique design challenges developed, PCL was able to provide the IBWC with solutions by using virtual construction tools. This commitment to collaborative workflows ensured few design overruns. The expansion was completed two months ahead of schedule, allowing the IBWC to meet their vision of providing acceptable water quality essential to the region and maintaining the quality of the beaches.