Sweetwater Authority treats its surface water supplies at the Robert A. Perdue Water Treatment Plant at Sweetwater Reservoir in Spring Valley, CA. There, particles are removed from the water through a four-step cleaning process, and the water is disinfected with chlorine and ammonia, chemically bound together to form chloramine.
The water is also treated to improve its taste, color and odor. The Perdue Water Treatment Plant can process 30 million gallons of water each day. After the water is tested, treated and ready to drink, it is delivered to customers through more than 400 miles of pipelines.
Sweetwater Reservoir
Built in 1888, Sweetwater Dam is 127 feet high and allows the reservoir to hold up to nine billion gallons of water. The reservoir is protected by a diversion system which traps polluted and low-quality local runoff.
Disinfection
Chlorine dioxide is added to untreated water to kill bacteria and viruses in the water.
Coagulation
Ferric chloride and cationic polymer are quickly added and mixed into the water to begin the process of removing dirt and particles.
Flocculation
During the flocculation process, polymers and ferric gently mix, causing the dirt particles to stick together to form clumps. The iron in the ferric causes the floc clumps to turn an orange, rusty color.
Dissolved Air Flotation (DAF) System
The DAF basins provide a reaction zone where tiny bubbles are added into the water. The air bubbles catch onto the coagulated particles causing them to rise and float; this forms a sludge blanket on top of the water. The sludge blanket hydraulically floats to a desludging basin, where it is removed. Meanwhile, the clarified water travels below the sludge blanket to the sediment basins.
Sedimentation
The sedimentation basin is where most of the remaining particles sink to the bottom. By the end of this stage, 85 to 90% of the particulate matter will have been removed.
Filtration
The sedimentation water travels to gravity filters where it flows downward through a layer of anthracite coal and sand (to remove fine particles). The filters are periodically cleaned by a backwash procedure.
Clear Well
The clear well stores ten million gallons of clear, clean drinking water until it enters the distribution system which delivers it to our homes, schools, and businesses. The Clear Well and other enclosed "reservoirs" in the system help assure that Sweetwater Authority can meet customers' demands even during peak use times which exceed the Perdue Water Treatment Plant's 30 million gallons a day capacity.