An 80-foot diameter circular primary clarifier treats a wastewater flow of 3.00 MGD. What is the Surface Overflow Rate (SOR) in gallons per day per square foot (gpd/sq ft)?

Formula Used: Surface Overflow Rate (gpd/sq ft) = Daily Flow (gpd) ÷ Clarifier Surface Area (sq ft)

Step-by-Step Mathematical Derivation:

1. Calculate surface area: 0.7854 × (80 ft)² = 5,026.55 sq ft.
2. Daily wastewater flow: 3.00 MGD = 3,000,000 gpd.
3. SOR = 3,000,000 gpd ÷ 5,026.55 sq ft = 596.8 gpd/sq ft (~597 gpd/sq ft).

⚠️ Common Exam Trap: Surface settling rate depends solely on horizontal SURFACE AREA, not side water depth.