Impacts of Sewer Capacity Assessment in Los Angeles

Authors: Lau, Rowena; Danishwar, Abdulsamad; Gonzalez, Fernando; Poosti, Ali

Source: Proceedings of the Water Environment Federation, WEFTEC 2011: Session 21 through Session 30 , pp. 1122-1134(13)

Publisher: Water Environment Federation

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Abstract:

The City of Los Angeles (City) owns and operates one of the largest wastewater collection systems in the country. It is made up of 6,700 miles of public sewers that serves over four (4) million residents and 29 contract agencies. As the City continues to grow and develop, a sewer capacity review process was created to ensure that no future developments will risk overtaxing the collection system.

The sewer capacity review process evaluates the existing sewer flow conditions to determine if there is adequate capacity to safely convey sewage from proposed development projects, construction dewatering projects, and proposed redevelopments from existing facilities. This procedure is used for both the planning and construction phases of any project. Request for Wastewater Service Information and request for comments as part of the California Environmental Quality Act (CEQA) process are capacity reviews received during the planning phase. A Sewer Capacity Availability Review (SCAR) application is received through the construction phase as a clearance requirement for a sewer connection permit. The proposed sewage flows may range from 2,000 gallons per day (GPD) to 1.5 million gallons per day (MGD), depending on the size of the project.

The sewer capacity review process requires several GIS databases. The databases collect and track all the approved developments, hydraulic gauging data, and closed-circuit television (CCTV) data. Sewer capacity is determined by establishing the existing flow conditions of the sewer system, estimating proposed flows of the project, and tracing the downstream sewer system. With that information, a wastewater engineer can evaluate if the additional flow from the proposed project will adversely impact the collection system. When the GIS database shows a large number of approved developments within a location or the proposed project consists of a large area, a hydrodynamic model may be used to provide a more detailed capacity analysis of the sewer system, including a future flow analysis.

The sewer capacity review process is a great asset for the City. The extensive GIS database allows engineers to graphically view all the new and future developments with their estimated sewage flows. If a large number of approved projects are shown, the planning departments can inform developers of conditions that may be required early in the project planning phase, such as the construction of a new sewer line. This will aid developers in their planning and construction process.

The sewer capacity review process is one of the essential tools to aid in the protection of public health and safety and reducing sanitary sewer overflows. This procedure serves not only as a predicted hydraulic analysis of the City's sewer system due to developments, and as a management system to track all development projects. This procedure is easily changed to fit any type of sewer capacity requests and help the City maintain a high level of service to its residents. The City also collects a fee for this service which constitutes a source of revenue for the City. The SCAR program was initiated in 2002 and to date has processed over 1,700 Sewer Capacity Reviews.
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