WHAT ARE THE REAL RISKS OF SSOs?

When the collection system experiences a performance exception event such as a release of wastewater to the surrounding environment, the release can pose health and environmental risks. The realrisk of a sanitary sewer overflow (SSO) is complex and depends on whether the concern is directedtoward, for example, human health, the environment, or customer services. Municipalities recognize that the strict regulatory interpretation of the Clean Water Act (CWA) regarding SSOs puts municipalities in a difficult situation given the number of system flow issues that are not under thedirect control of the municipality. Municipalities have difficulty balancing capacity versus system flows, particularly wet weather flows. At the urging of a number of municipalities, the U.S. Environmental Protection Agency (EPA) established a Federal Advisory Committee (FAC) of key stakeholders to make recommendations about how the National Pollutant Discharge Elimination System (NPDES) should address SSOs. In 1995, EPA chartered an Urban Wet Weather Flows Federal Advisory Committee that formed an SSO Subcommittee, and later, the FAC produced a framework to address SSOs that formed the basis for EPA's proposed SSO Rule. The proposed SSO Rule provided a consensus approach to strategic planning to address SSOs. It did not provide a clear approach about how to setthecapacity of a system. Wastewater planners traditionally have used approaches that addressed primarily dry weather, steady-state conditions and often did not coordinate flows between the collection and treatment systems. EPA has held several dialogues regarding the management of wet weatherflows, and with the possible exception of the Combined Sewer Overflow (CSO) Control Policy there has been no definitive national guidance on planning for wet weather and selecting feasible andinfeasible capacity strategies. The recent Water Environment Federation (WEF) publication,Guide to Managing Peak Wet Weather Flows in Municipal Wastewater Systems (Guide), presentsa wastewater collection and treatment system capacity sizing approach for planning. The Guide introducesa Risk Management Approach for selecting the system capacity that supports community values an strategies. The Risk Management Approach includes a six-step structured process that uses stakeholder input to develop and compare competing community values. The six-step process is modeled afterthe risk-based model developed by the American Water Works Association Research Foundation (AWWARF). The planning outcome of the Risk Management Approach is a regulatory compliance approach thatleads to the selection of a defendable system capacity that measures risks (such asSSOs) to community values.