Seismic Resilience: Orange County Sanitation District Is Planning for 2030 and beyond through a Risk-Based Evaluation of Their Process Facilities

Seismic resiliency is a major concern for the stewards of our wastewater infrastructure throughout California. This includes the Orange County Sanitation District (OC San), who provides wastewater collection, treatment, and disposal services for approximately 2.6 million people in Southern California. Because OC San’s facilities are exposed to local seismic hazards, including potential for surface fault rupture, liquefaction, and liquefaction-induced differential settlement and lateral spread, the risk of earthquake damage and associated service disruptions is a significant threat to their $11 billion infrastructure. With this realization, OC San has taken a proactive approach and conducted a study to evaluate structures at their two treatment plants for potential seismic hazards, including identification of mitigation strategies to improve operational resiliency following a major earthquake. Based on the findings from this study, a plan was developed to identify and prioritize mitigation projects using a risk-based methodology that serves as the foundation for integrating seismic resilience into OC San’s overall capital improvements program.