A dual-media rapid sand filter measures 18.0 ft wide by 24.0 ft long. At an inflow rate of 1,500 GPM, what is the hydraulic filter loading rate in gpm/sq ft?

Formula Used: Loading Rate (gpm/sq ft) = Influent Flow (GPM) ÷ Filter Surface Area (sq ft)

Step-by-Step Mathematical Derivation:

1. Calculate filter bed surface area: 18.0 ft × 24.0 ft = 432.0 sq ft.
2. Divide flow by filter surface area: 1,500 GPM ÷ 432.0 sq ft = 3.47 gpm/sq ft.

⚠️ Common Exam Trap: Ensure flow is in GPM (gallons per minute), not MGD or GPD. If flow is in MGD, convert by dividing by 1,440 first.