If a water tank has a volume of 3.25 MG and the flow from the tank is 6.10 mgd, what is the detention time in hours?

• A. 6.5 hours
• B. 12.8 hours
• C. 24 hours
• D. 52.0 hours

Answer: (B)

Detention time is how long water stays in a tank, calculated by dividing the tank volume by the flow rate. With 3.25 million gallons in the tank and a discharge of 6.10 million gallons per day, the time equals 3.25 / 6.10 days, which is about 0.5328 days. Converting to hours by multiplying by 24 gives 0.5328 × 24 ≈ 12.8 hours. So the water stays in the tank for roughly 12.8 hours at that flow.