Calexico operates its own wastewater collection and treatment system. The current wastewater collection system consists of pipes ranging in size from six inches to 30 inches in diameter. Lateral and truck, sewer lines discharge into one of two major interceptor sewer mains. The South Interceptor Sewer main primarily serves east of the Southern Pacific Railroad and south of Highway 98. Wastewater flows from the north and west portions of the City discharge into the North Interceptor Sewer Mains.
Due to the flat topography, most of the sewer lines have been constructed at minimum slopes and the interceptors are relatively deep, some as much as 20 feet. A series of small pump stations have also been constructed to provide service to new developments.
The wastewater treatment plant (WWTP) is located in the southwest part of the City. The wastewater treatment plant (WWTP) is bound by the Calexico International Airport to the south and the New River to the north. Treatment effluent is discharged to the New River. The plant uses activated sludge technology and has an average daily flow capacity of 4.3 million gallons per day (MGD) and peak daily flow capacity of 5.5 million gallons per day (MDG). The process consists of a head works structure, primary clarifier, aeration tanks, secondary clarifiers and sludge drying beds.