The South Bay International Wastewater Treatment Plant (SBIWWTP) is owned and operated by the United States section of the International Boundary and Water Commission (IBWC) , and is located near the United States/Mexico border on a 100-acre site south of San Diego. Its purpose is to treat wastewater from Tijuana, Mexico, before discharging it into the Pacific Ocean. Waste water currently flows via several pump stations through a 96-inch pipe from Mexico into the plant. Originally constructed in 1996, the SBIWWTP provided only primary sewage treatment. With the need to provide higher levels of treatment, the IBWC chose PCL through a best-value selection process to construct this most recent phase. This expansion and upgrade, completed in 2011, added secondary treatment to the process. The project consisted primarily of constructing two large cast-in-place concrete tanks, the activated sludge tank (AST), and the secondary sedimentation tank. Other features were new gravity thickeners, a new chlorine injection system, and a new non-potable water system for the plant.