The Bee Slough System is one of the major sewer systems in Evansville Water and Sewer Utility’s East Service Area. It is a concrete-lined drainage channel that conveys the wet weather overflows to the Ohio River. It is specifically referenced in the consent decree, and remedying the associated health, odor, and aesthetic issues is the Utility’s highest priority. One of the mitigating measures includes two wet weather treatment facilities to treat the overflows exceeding the East WWTP’s treatment capacity. The proposed two wet weather treatment facilities are one CSO Treatment Wetland and one Vertical Treatment Unit (VTU).
A detailed dynamic hydraulic model was built to better understand how the wetland, the VTU, and the WWTP would perform together to treat wet‐weather flows in the Typical Year. It also assessed the feasibility/effect of minimizing primary effluent (PE) bypasses of the WWTP secondary treatment by changing the proposed operating scheme.
For simplification, the Wetland Model did not include the rest of the whole East Sewer System. The simulated Typical Year flow time series from the Whole model served as the flow inputs to the Wetland Model, at the corresponding boundary conditions. In addition to existing facilities, the Wetland Model also included components and controls representing the proposed systems and operating strategies for the East WWTP, wetland, VTU, WWTP Effluent Pump Station and connecting piping. Real time control rules were in place to dictate how, when, and where flow is to be conveyed.
Activations and treatment volumes were evaluated for all the three treatment facilities. Additional detailed wetland performances were evaluated for flow duration, max depth, average flow, drainage, and volumes exceeding its treatment capacity. The results of the modeling showed that altering the operating scheme could reduce the number of PE bypasses in a typical year from 38 events to 8 events with no negative impact on the wetland or vertical treatment unit (VTU) performance.