Field testing and numerical modeling conducted on two nearly identical 60-foot diameter, 10-ft side water depth circular clarifiers at Incline Village, Nevada provided an understanding of how subtle factors affect clarifier performance. The studied clarifiers differed only in feedwell diameter: 10-foot and 20-foot. Clarifier testing complied with the protocols of the American Society of Civil Engineers (ASCE) Clarifier Research Technical Committee (CRTC) and included settling tests, dispersed suspended solids/flocculated suspended solids tests, and hydraulic stress tests.