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... 1'"0 , .. ') Stronlia Springs Dam and Reservoir. A sophisticated computer system operates Foothills, one of the world's most modern treatment plants. It will control most plant processes, gather data and scheduie maintenance, with an analog system providing backup. Virtually all necessary underground piping for the eventual 500 mgd plant was installed during first phase construction. This allowed the first addition, boosting capacity to 285 mgd, to be constructed during 1983-86 without plant shutdown. Additional increments can be constructed similarly when needed. A 3 megawatt (3,000 kilowatt) hydroelectric turbine installed at the plant headworks generates electricity for heating, ventilating and equipment operation, with surplus sold to a local utility. A second 3 megawatt unit is planned for the third and fourth plant increments. The hydroelectric power utilizes the pressure head generated by Strontia Springs reservoir, converting it to electrical energy for operation of the treatment plant and sale of surplus. Otherwise this force would have to be dissipated at the headworks. From the headworks water enters the chemical building where polymers, alum, lime, activated carbon and chlorine may be added as required. In eight flocculation and sedimentation basins, particles of suspended material, more abundant during spring runoff, are agglomerated by chemical flocculation and removed through sedimentation. The basins feature three-stage mechanical flocculators and continuous mechanical sludge collectors. After the particles settle, the water enters 16 dual media rapid sand filters, which can treat 285 million gallons a day. From the filter beds water flows by gravity to two 25- million-gallon underground storage reservoirs, or it is directed into a 108"-diameter conduit more than nine miles long, continuing in a 90"-diameter conduit for the remainder of the nearly 16 miles to the Denver area. At the plant, water used for backwashing (cleansing) the filters is recycled, making the plant relatively free of waste discharge. The plant was designed by CH2M-Hill, Denver and constructed by Martin K. Eby Construction Co., Englewood, Colo. Pipe for the first nine miles of conduit was supplied by ITT Grinnell, Denver, and installed by Eby; the second section was supplied by Thompson Pipe & Steel Co., Denver and installed by C.R. Fedrick lnc./Kasler Ine/jY, San Bernardino, Calif.