MORE CSO CONTROL FOR LESS DOLLARS!

Many communities face a significant financial impact to comply with regulatory requirements for Combined Sewer Overflow (CSO) control. Implementation of the required level of control brings an immediate capital cost impact as well as significant long term operations and maintenance (O&M) requirements. Therefore, the selection of CSO controls must take into consideration both the capital, as well as the operations and maintenance requirements.The regulatory requirement for CSO control varies by state. The State of Michigan requires a community to either take a demonstrative approach to assure their level of CSO control meets water quality standards at the time of discharge or take a presumptive approach requiring a higher level of CSO control, which is presumed to meet water quality standards at the time of discharge. The additional effort required to demonstrate that a control meets water quality standards, along with the risk of a failed demonstration, usually leads a community to follow a more costly presumptive approach. However, if the presumptive CSO control does not result in the facility meeting water quality standards (WQS) then retrofitting is required. Hence, both design approaches involve a risk of not meeting WQS.This paper presents a third approach in the development of the required CSO control that was utilized for a project being considered by the Detroit Water and Sewerage Department (DWSD). The approach involves the use of extensive monitoring information and analysis to allow the community to work with the regulatory authority in the development of a design criteria which addresses the needs of CSO control by focusing the CSO control alternative: on the specific water quality impairments; the effectiveness of CSO controls to eliminate these impairments; capital cost; and the operational and maintenance requirements. Using this approach, DWSD has worked with the Michigan Department of Environmental Quality (MDEQ) to jointly develop a new CSO control standard to be used for a proposed CSO control project. DWSD is proceeding with the implementation of a CSO capture tunnel for the CSO outfalls along the Rouge River. This project is expected to save DWSD 877 million dollars in capital costs and 3.2 million dollars in annual operations and maintenance costs as compared to a project designed using the presumptive approach. In addition, the utilization of the new sizing standard reduced the frequency of overflows from a presumptive approach yielding four overflows per year to less than one overflow per year. The approach taken by DWSD during their planning of this treatment facility has demonstrated the concept of providing more CSO control for less dollars.