the 1,500 gph WPU; 1/4 Ib per gal for the 3,000 gph WPU) and placed in the lower left
hand chemical solution tank. Never mix the two chemicals as they produce a greenish
yellow chlorine gas that is irritating, disagreeable, and toxic. WhiIe the WPU is in
operation, the chemical solutions are fed to the erdlator tank by means of the chemical
solution feeder at a rate prescribed in the TM (see para 5-10). The rate of feed is set on
the chemical solution feeder controls (see figure 5-8). The operator may have to vary
the rate from time to time, depending on the quality of the treated water. The operator
must also monitor the amount of solution in the tanks and recharge each one when the
solution level drops to about 4 1/2 inches from the bottom of the tank. Each chemical
solution tank holds approximately 5 gallons.
Figure 5-8. Chemical solution feeder controls.
b. Pulverized Limestone. An initial charge of Iimestone slurry is prepared in
the right hand compartment of the chemical slurry feeder. The concentration is 1 pound
of pulverized Iimestone per gallon of water. Since the compartment holds
approximately 14 gallons, the initial charge is 14 pounds of Iimestone to a full
compartment of water. Raw water is continuously supplied to the compartment from the
raw water influent Iine. The operator sets the rate of feed variator (see figure 5-9) on
the right hand side of the chemical slurry feeder at the setting prescribed in the TM.
The water level remains constant in the slurry compartment, but the slurry becomes
more diluted; therefore, it must be recharged with dry chemical every hour.