In the chlorine contact tank example, the CT value is 100 mg·min/L.

• A. True
• B. False
• C. Cannot be determined
• D. Not enough data

Answer: (A)

CT value is the disinfection exposure, calculated as the chlorine concentration (C) in mg/L multiplied by the contact time (t) in minutes, with units of mg·min/L. In a chlorine contact tank, this product shows how much disinfectant exposure the water has received. If the example states a CT value of 100 mg·min/L, that is exactly the measured or targeted exposure expressed in the standard units. Different C and t combinations can yield the same CT; for instance, 1 mg/L held for 100 minutes or 2 mg/L for 50 minutes both give 100 mg·min/L. Since the value is provided directly and the units are correct, the statement is true.