A rectangular chlorine contact chamber measures 80 ft long, 25 ft wide, and operates at a water depth of 10 ft. At a peak flow rate of 2.00 MGD, what is the detention time in minutes?

Formula Used: Detention Time (min) = [Volume (gal) × 1,440 min/day] ÷ Daily Flow (gpd)

Step-by-Step Mathematical Derivation:

1. Calculate rectangular volume in cu ft = 80 ft × 25 ft × 10 ft = 20,000 cu ft.
2. Convert volume to gallons = 20,000 cu ft × 7.48 gal/cu ft = 149,600 gallons.
3. Calculate flow in GPM = 2,000,000 gpd ÷ 1,440 min/day = 1,388.89 gpm.
4. Detention Time = 149,600 gal ÷ 1,388.89 gpm = 107.7 minutes.

⚠️ Common Exam Trap: State exams frequently ask for detention time in MINUTES for contact basins and flash mix chambers, but in HOURS for sedimentation basins.