ADEQ Wastewater Treatment 1 Practice Test

Surface overflow rate is the flow per unit area of the clarifier surface. For a circular clarifier, use the area πr^2. With a 60 ft diameter, the radius is 30 ft, so the surface area is π × 30^2 = 900π ft^2 ≈ 2,827 ft^2. Convert the flow to gallons per day: 2,000 gpm × 1,440 minutes per day = 2,880,000 gpd. Divide the daily flow by the surface area: 2,880,000 gpd ÷ 2,827 ft^2 ≈ 1,018 gpd/ft^2. Therefore, the surface overflow rate is about 1,018 gpd/ft^2.