Risk Assessment and Capital Planning of Gravity Sewers at the Los Angeles County Sanitation Districts

Presentation Description: The Los Angeles County Sanitation Districts (LACSD) manages over 1,400 miles of wastewater trunk sewers, serving a population of more than 5.6 million in Los Angeles County. These trunk sewers primarily consist of large-diameter pipes, with around 50% having diameters of 20 inches or larger. About 37% of LACSD's trunk sewers are constructed with corrodible materials, such as bricks, reinforced concrete, and non-reinforced concrete. Historically, LACSD used its own customized pipe condition rating system to identify and prioritize sewer rehabilitation projects. To eliminate sewer overflows and minimize emergency repairs throughout its aging infrastructure, LACSD has proactively worked towards lining all corrodible sewers within the next 20 years. To help achieve this goal, a more comprehensive risk model became essential for prioritizing rehabilitation projects.

Since July 2022, LACSD, in collaboration with West Yost consultants, developed a comprehensive risk assessment framework for its collection system. This framework, specifically for gravity sewers, now provides risk assessment scores for over 22,000 gravity assets. The project was completed in February 2024, and transitioned to LACSD engineering staff for further updates and improvements.

The risk assessment is based on the likelihood of failure and consequence of failure for each asset. After evaluating nearly 30 potential factors, LACSD selected three “likelihood of failure” factors (condition rating, pipe material, and flow capacity) and three “consequence of failure” factors (asset proximity to critical areas, environmentally sensitive areas, and potential spill volume). GIS and other business intelligence tools were utilized to calculate these factors. This risk assessment framework enables LACSD to optimize its capital planning processes.

This presentation will discuss LACSD's experience in developing the risk assessment framework, covering geospatial data collection, data quality evaluation, GIS risk assessment modeling, and the use of business intelligence applications for model results analysis. It will also highlight collaboration between departments and consultants, and the training and transition of the project to LACSD staff. Attendees will have opportunities to engage and share their experiences related to sewer asset management, GIS data integration, and capital planning processes.