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<br />In the filters, the water flows by gravity through the <br />anthracite coal and sand that filter out the very tiny <br />suspended solids left in the water. The dual media gravity <br />filters consist of 28 filter cells. Each cell filters <br />approximately 4 million gallons of water per day. The tiny <br />solids that are filtered out of the water are left behind in the <br />sand and anthracite coal; and these tiny solids are cleaned <br />out periodically by "backwashing" the filters. <br /> <br />From the dual media gravity filters, the filtered water flows <br />by gravity to a large underground storage tank called the <br />clearwell. As the water flows into the clearwell, additional <br />chlorine can be transported from the chlorine building <br />through a pipeline to the clearwell to stop the growth of <br />micro-organisms and algae in the clearwell. <br /> <br />Also, from the "shmp" silos, sodium hexametaphosphate is <br />added to the water to help prevent scale buildup in the <br />reverse osmosis desalting membranes, and here the pH of <br />the water is again lowered (to about 5.5). <br /> <br />The clearwell holds about 4 million gallons of water. The <br />concrete that covers the top of the clearwell keeps dust <br />from blowing into the cleaned water. <br /> <br />To produce desalted water, the reverse osmosis desalting <br />process requires an average pressure of 400 pounds per <br />square inch. That pressure is provided by more than a <br />dozen large pumps at the clearwell~ <br /> <br />C:'j:r8al8d\Oa1pl1\mOdel.cI1p (model.sty) 5 <br />