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Wastewater Collection Infrastructure Renewal Strategy

City of San Luis Obispo

WSC is currently working with the City of San Luis Obispo to create a hydraulic model for its collection system, evaluate the capacity and condition of its sewer pipelines, and develop an Infrastructure Renewal Strategy (IRS) that will guide future capital improvement projects.  The City of San Luis Obispo’s wastewater collection system, of which portions are over 100 years old, includes approximately 138 miles of gravity sewer mains and 3 miles of force mains.  The pipeline materials consist of terra cotta salt glazed pipe, vitrified clay pipe, polyvinyl chloride, high density polyethylene, steel, cast iron, and asbestos cement.  Additionally, the collection system includes approximately 2,100 manholes, 800 cleanouts, 20 inverted siphons, and 9 lift stations.

While the City possesses a comprehensive GIS dataset for its collection system, it does not have reliable invert elevation data.  To prioritize the invert data collection and avoid having to survey the entire system, WSC will utilize a methodology called “Flattening” that will focus the City’s data collection and free up budget to incorporate condition assessment and risk based project prioritization into the IRS.  A key component of the Flattening process includes the development of an all-pipes hydraulic model and spatially allocated sewer flow loading to improve the accuracy of the sewer flow routing. The spatially allocated sewer flow loading will additionally enable WSC to develop land use based flow factors that can be used to predict future flows under various growth scenarios.

WSC will incorporate the capacity results from the hydraulic model with condition data from the City’s existing data management systems, including GIS, Cityworks, IT pipes, and Infrastructure Optimization (IO).  Using this combined dataset, WSC will develop an asset management toolset that uses a “business risk exposure” rating system to prioritize repair, rehabilitation, and replacement projects and will enable analysis of multiple future capital investment scenarios to develop a risk-based IRS the integrates capacity and condition assessment for the City of San Luis Obispo.

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