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$ - Shift operators 3 - Relief Operators 1 - Ohemist 1 - Superintendent The chemicals used for treatment are as follows: Caustic Soda Sulfate of Alumina Sodium Hexametaphosphate Activated Carbon - (occasionally) Caustic soda is mixed with the incoming water to the reaction tanks for the purpose of converting the calcium and magnesium bec&rbonates to an insoluable state, thus permitting its removal by sedimentation* The caustic soda used is produced on this project at the chlorine plant and pumped to the water treatment plant through 13,100 lineal feet of 2 inch pipe line. About 1000 pounds of H&QH is required for the treatment of one million gallons of water. No addition of soda ash is made. For coagulation, sulfate of alumina is added to the water ahead of the reaotio tanks. Floo is built up in the lower part of the tanks by a mechanical slow stirring device. The incoming raw water is distributed at the bottom of the tank and reses vertically through a floe blanket. The precipitated sludge is thickened on the floor of the tanks and swept to a sludge pocket near the center from whidiit is pumped to waste on the desert. About midway between the bottom and the water serface is located a large receiver to which the excess sludge overflows. The sludge pumps operating on program switch con­trol pump sludge from these receivers periodically. From the reaction tanks the water passes directly to the battery of eight rapid sand filters. Before entering the filters it is dosed with sodium hexametaphosphate at the rate of about five pounds per million gallons. This dls&ge is to stabilize the water sufficiently to prevent calcium car­bonate scaling of the filter sand. Rate of flow controllers regulate the flow of water from the filters to the stabilized water clear well in pro­portion to the deman. All gates and valves connected with the operation and backwashing of the filters are hydraulically operated by pilot switches from the operating tables. Filters are b&ck-washed from the stabilized water clear well by two 12» 50-HP, **000 G-.P.M. centrifugal pumps, at the rate of 15 gallons per square foot per minute. Backwash water is reclaimed and retreated. At this point the total hardness of the water has undergone about ©7$ reduction, and it is distributed for general use at the Magnesium Plant, and Into the fire protection system. A portion of the water leaving the filters is admitted through controllers to four Zeolite softening beds. The controllers are actuated from floats on the water surface of the Zeolite treated water clear well, and admit enough water through the beds to always satisfy the demand. The synthetic Zeolites are hydrous silicates of sodium and aluminum. They absorb the calcium and mag­nesium from the water and release an equal amount of sodium. When the capac­ity of the Zeolite to absorb calcium and magnesium is exhausted the beds @,re regenerated with salt brine to restore the sodium and carry off the absorbed calcium and magnesium. Balt brine for regeneration is pumped through m 3 inch pipe line a distance of 13,100 feet from the Chlorine Plant. At the Water Treatment Plant the brine is passed through a pressure filter and 10