Reso 2009-115 - Laserfiche WebLink

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City of San Leandro Sewer System Management Plan Volume I capacity of key sewer system elements under peak flaw conditions. The following are the program components: • Evaluation -Evaluate portions of the collection system experiencing SSOs due to hydraulic deficiency. • Capacity Enhancement Measures - Establish a short- and long-term capital improvement program to address identified hydraulic deficiencies. • Plan updates -Update the plan on a regular basis as specified in the SSMP. Capital improvement requirements will be consistent with current planning objectives. Capacity assurance and modeling will be done periodically. Flow Projections Flow projections are based on historical flow rate data combined with calculated flow rates for growth areas, septic tank conversions and infill development. To estimate the sanitary flow impact of these areas, the results of actual metering and flow monitoring are used to define base sanitary flow, groundwater infiltration and RDI/I values of the tributary sub basins. To see the effect of development over time, the flow impacts were added into the model in three equal five-year phases until built out. In this manner an allotment for UI is also incorporated for new laterals and mains in the new areas. Residential infill UI assumes that existing sewers will be used to convey wastewater flows to the treatment plants, without added UI volumes for new work. The City currently specifies allowances of 1000 gpd/acre for pipes installed since 1975, 2500 gpd/acre for installations between 1962 and 1975, and 6000 gpd/acre for pipes installed prior to 1962. Non-residential UI were calculated based on the City standard of 1000 gpd/acre.l Hydraulic Analysis The hydraulic model evaluates the primary "back bone" of the system, i.e. lines greater than or equal to 10" in diameter. The City's GIS files are used to spatially define the system topology including geometry and network connectivity. Each individual structure data is maintained in the system database. The data maintained includes pipe types (gravity or pressure pipe), manhole types (split, diversion, outfall or standard manhole), pipe diameters, rim and invert elevations, pipe lengths and slopes. Diversion manholes are also incorporated into the model. Diversion manholes split the incoming flow into two components -one that continues through the main line and another that is diverted to an overflow line. Flow is divided according to predicted performance curves that should be calibrated as more flow data becomes available in the future. ~~~e ~z