When drinking water treatment plants chlorinate water, the chlorine must remain in contact with the water for at least 30 minutes before being delivered to customers. A water plant operator wishes to know if his existing 10,000-gallon storage tank can provide this HRT. He does a wash-out tracer test with fluoride salt (conservative). The initial concentration is 12 mg/L and after an hour of feeding non-fluoridated water through the tank at 20 gpm, the concentration has dropped to 2 mg/L. Does the tank have the required HRT? [Yes, the HRT is 33.5 minutes]?