The water supplying the St. Helens filtration plant is taken from groundwater wells located along the west bank of the Columbia River.  The wells are called Ranney Collectors. (Pictured at Left) As the raw, or untreated well water,  arrives at the filtration plant the initial part of the filtration process begins.  A very strong concentration of Sodium Hypochlorite, a 12.5% solution of chlorine bleach, is injected into the 20 inch raw water main just before it enters the 113,000 gallon raw water tank. (pictured at right)    Note: Household "Clorox" bleach is a 5.25% concentration.                                                                                                                                       Inside the raw water tank is a series of three baffle curtains.  The baffles provide two very important functions.  First, they prevent the flow of water from “short circuiting” or entering the large tank through one pipe, finding the quickest and shortest way through the tank, and into the outlet pipe supplying the raw water pumps. 

The water now enters the filtration plant by gravity flow from the raw water tank through a 20” service header, which supplies 4 - 500 gallon wet well basins located directly under each of the raw water pumps. (left)  The water is then drawn up and pumped through fine mesh mechanical strainers. (right) The strainers remove any small particles such as twigs and leaves that can damage, plug or foul the micro filtration hollow fiber membranes. 

The complete module assembly is what is referred to as a rack. (See the picture at the top center of the page) The raw water pumps supply pressure to the racks at 30 psi. There are five "racks" of membrane modules.   Four of the racks consist of 52 individual modules. A fifth rack of membrane modules has only 19 modules. The short rack of modules is used exclusively to recycle the reverse filtration water, so that that a minimum amount of water is wasted in the filtration process.  The filtration process recovers 99.8% of the water flowing through the treatment plant which becomes drinking water.  To help you understand how efficient our filtration process is, typically, 2,000,000 gallons of water flows through the filtration plant every day. Of that 2 million gallons that flowed through the filtration plant, 1,994,000 gallons was captured as fresh drinking water and only 6,000 gallons was wasted in the filtration process. 

                AFTER THE STRAINERS, HOW DOES THE WATER FLOW THROUGH THE FILTRATION PLANT?     

After the strainers, the raw water is then evenly distributed to four pairs of parallel, stainless steel headers on which the modules are directly mounted. (See picture to the left) The raw water enters the bottom of each of the module casings through 32 ports that are molded through a solid fiberglass plug. Once the water is inside the module casing the water continues flowing upward into the module and floods around the outside of thousands (6,350) tiny membrane fibers that are bundled together inside the module housing.  Raw, chlorinated water continues flowing through the modules by being forced through the tiny pores (0.1 micron) of the “skin” of the membranes and into the center of the hollow fibers.  The pore size of the fibers is so small that it is able to filter out Giardia, Cyrptosporidium even E. Coli bacteria.  

Clean, filtered water continues it’s upward flow through the center of the hollow fibers and exits through the top of the membrane as filtrate or water that is ready for drinking. Each module has a flow rate of 27 gallons per minute and an entire rack of 52 modules can produce 2 million gallons of clean, fresh, filtered water per day!  The water filtration plant is designed to produce 6 million gallons of water per day.   Since the water plant came on line in February of 2006 we have only seen a peak of 4 million gallons of water per day being produced during the summer months.  The water plant was designed for expansion so that we can add two more racks to our existing system and produce 10 million gallons per day to meet water demands in the future as St. Helens grows in population.   

The filtrate is collected in a 455,000 gallon reservoir or clearwell.  The clearwell also has baffle curtains which provide an additional 3 to 4 hours of contact time in the disinfection process before the water is delivered to the distribution main supplying drinking water to the City of St. Helens.   As the water leaves the filtration plant, a pH buffer is added to raise the pH level of your drinking water from the “acidic” side of the pH scale (6.8)  to the “neutral” zone (7.4 - 7.6) for corrosion control.  After this final adjustment, a continuous, fresh, high quality, filtered drinking water is delivered to your tap, ready to serve you.  The City of St. Helens maintains, stores and delivers 5.5 million gallons of fresh, filtered drinking water from high elevation reservoirs. 

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This page was last updated on 7/20/2010 by Howard (Howie) Burton