In this step of the treatment process, polymers are also added so that most of the hardness and particulates in the water can settle out in the softening units in the form of solids. After water leaves the softening units, it passes through filter media consisting of 10 inches of sand and 20 inches of anthracite coal to remove any remaining particulate matter and calcium carbonate, which further clarifies the water. The filters are operated for approximately 80 to 100 hours before they are backwashed to remove collected particles. Backwash water is sent to a recovery basin and is eventually recycled to the beginning of the plant. To handle peak system demands and demands for fighting fires, three ground storage tanks with a combined capacity of 6.5 million gallons are located at Water Treatment Plant 2A. Treated water is stored in these tanks before it is pumped through the distribution system by the high service pumps which pressurize the system.
Disinfection is accomplished by the addition of chlorine and ammonia.
The chlorine and ammonia residual continues to work throughout the distribution system to prevent bacterial regrowth. Solids, which settle out in the softening unit, are collected and pumped to a settling basin where they are thickened. The thickened solids are then pumped to a dewatering facility where a vacuum filter removes excess water. Dewatered solids are hauled away for disposal by land application. Filtrate water from the vacuum filter is recycled back to the head of the plant for treatment.