Water Treatment Plant 3
The withdrawal of water for Water Treatment Plant #3 is accomplished by twenty shallow gravel pack type of production wells pumping from the surficial aquifer. Phase 1 of the wellfield was constructed in 2006 & 2007 and consists of six wells. Two of the wells previously utilized at Water Treatment Plant #1 have been redirected to supply water to WTP#3. Phase 2 has been constructed and consists of twelve wells to allow WTP#3 to produce 3.0 million gallons of water per day.
The pretreatment process begins with a sand separator designed to eliminate sand production that could foul subsequent treatment processes. A chemical pretreatment with the application of a scale inhibitor has been established to reduce potential scale. Following chemical pretreatment, physical pretreatment is accomplished using 5-micron sediment filters to trap particulates, mainly fine sediment and sand particles. Subsequent to pretreatment is membrane filtration.
After the pretreatment process, the source water is treated through the membrane system. There are two membrane treatment trains, each with a rated permeate production capacity of 1.125 million gallons per day for a total of 2.25 million gallons per day. Each pressure vessel contains seven membrane modules. The membranes are 8 inches in diameter with an individual rating capacity of 12,700 gallons per day and a salt rejection of 99.0 %. The water entering the pressure vessels is called feedwater. Most of the feedwater is recovered as Permeate water which is the water that has passed through the membranes. The rejected dissolved solids in the feedwater stream are concentrated as it passes from the feed end of the pressure vessel to the back end. The concentrate is the waste product and it is discharge to Water Treatment Plant #1 for final treatment.
The next step in the treatment process is degasification. The Permeate and Concentrate water flow through separate Degassers. The permeate water flows into the chlorine contact chamber for disinfection. The method of disinfection is chloramination. Ammonium sulfate is applied downstream of the sodium hypochlorite and will react with the free chlorine residual to produce a chloramination residual. The contact chamber consists of an area of interconnected weaving paths that is designed to slow the flow and create enough contact time to provide a positive disinfection action. Transfer pumps operate based on water level in the chamber, and transfer the chlorinated water from the contact chamber to the 2 million gallon storage tank. Four High Service Pumps are controlled to pump a desired flow rate and pressure to the Distribution System based on system demand. The plant is controlled and monitored by a programmable logic controller (PLC) and an operator interface terminal (OIT) located in both control rooms, the Chemical and the Generator Buildings.