Wet Weather Testing and Verification - The Challenges Ahead

Communities throughout the United States are spending billions to manage wet weather flows. Regulatory programs now address the full range of wet weather issues, including combined sewer overflows (CSO), sanitary sewer overflows (SSO), stormwater and wet weather effluents from wastewater treatment plants (WWTPs). In some cases, such as the management of stormwater quality, specific performance requirements e.g. effluent limits have not as yet been broadly applied. In other instances, such as CSO satellite treatment or treatment of wet weather flows at WWTPs, the facility operating permit specifies capacity and treatment requirements. Both facility designers and operating authorities face considerable challenges in this environment. One such challenge is the uncertainties associated with wet weather facilities design and sizing. Another is the need for post-implementation monitoring to assess facility performance aimed at meeting requirements stipulated by regulatory authorities in operating permits. Wet weather testing and verification when conducted in advance of design is employed to predict performance under various operating conditions, to the set appropriate limits for the range of operating conditions and to facilitate the development of a design meeting desired objectives. Wet weather testing and verification can serve a second purpose, that of compliance assessment. This activity addresses the evaluation of facilities under actual operating conditions and is every bit as challenging than pre-design evaluation. The purpose of this paper is, therefore, to present a systematic, scientifically based approach for compliance assessment with specific reference to CSO and WWTP wet weather treatment facilities.