Optimal Sanitary Sewer Overflow Management ...

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Optimal Sanitary Sewer Overflow Management Strategies Considering Reliability, Scheduling, and Permitting Restrictions Len Wright, Ph.D., P.E. Carollo Engineers 380 Interlocken Crescent, Ste 780 Broomfield, CO 80021 (303) 635-1220 [email protected] Shawn Dent, P.E. Carollo Engineers 2700 Ygnacio Valley Road, Suite 300 Walnut Creek CA, 94598 978-510-1046 [email protected] Rolf Ohlemuetz Ph.D., P.E. Vallejo Sanitation and Flood Control District The long-term management of wet-weather SSOs may involve some combination of increased capacity of conveyance, storage, and treatment systems along with flow reduction through collection system rehabilitation. The amount of flow reduction attained by rehabilitation has been difficult to predict during project planning phases because many unknown variables affect rehabilitation performance. Post-auditing of rehabilitation efforts has shown widely varying results. Rehabilitation as an SSO control does show promise as part of a long-term management plan, especially when the longterm rehabilitation strategies may be revised based on interim, mid-project performance data. However this form of adaptive management plan may not be amenable to shortterm performance goals that must be met to avoid permit violations and subsequent enforcement actions. The trade-offs between short-term permit enforcement, reliability of the management plan and long-term level-of-service performance goals must be balanced in a cost-effective manner. Centralized, downstream storage and treatment controls tend to be more reliable solutions for meeting SSO goals and permit requirements in the short term because they are more controlled and the effect of these controls on the wet-weather response hydrograph is well understood. Rehabilitation is a decentralized solution and it is difficult to predict performance for SSO management through RDII reduction. However, when the problem is approached from a long-term perspective, that of an infrastructure maintenance problem, rehabilitation becomes more attractive. It is likely that persistent maintenance efforts that are fine-tuned by adaptive management strategies based on measured performance data will pay off in a cost effective manner over the life cycle of the infrastructure. This is because pipes that are deteriorated and leak RDII into the system will eventually fail structurally and will require repair or replacement to maintain service. This expense will occur regardless of the downstream SSO controls that are installed. The time frame for meeting performance goals becomes a critical factor in SSO management decision-making. In the long-term, it

Impacts of Global Climate Change

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may be approached as an asset management problem, minimizing the life-cycle costs while meeting a level of service that prevents SSOs to some defined frequency. In the short term the variability

Impacts of Global Climate Change