Dynamic computational fluid dynamic (CFD) modeling for secondary clarifiers was used as part of a recent facilities plan for a Midwest treatment plant to assess the performance and capacity of existing clarifiers. Modeling was also used to assess the benefits of physical and/or process modifications on sustained peak wet weather flow (PWWF) capacity. The modeling results showed that significant improvement in sustained PWWF capacity could be achieved. Clarifier modeling as part of an overall secondary treatment optimization identifies cost-effective modifications to increase sustained PWWF capacity of existing treatment facilities and minimizes the cost of new wet weather treatment facilities.