System Evaluation and Capacity Assurance Plan (SECAP) The WDR requires owners and operators of sewer collection systems to have a (SECAP). This component involves preparing and implementing a Capital Improvement Program (CIP) that will provide hydraulic capacity of key sewer system elements for dry weather peak flow conditions, as well as the appropriate design storm or wet weather event. At a minimum, the SECAP must include: Steps to evaluate those portions of the sanitary sewer system, which are experiencing or contributing to an SSO discharge caused by hydraulic deficiency. The evaluation must provide estimates of peak flows (including flows from SSOs that escape from the system) associated with conditions similar to those causing overflow events, estimates of the capacity of key system components, hydraulic deficiencies (including components of the system with limiting capacity) and the major sources that contribute to the peak flows associated with overflow events; Establishing a short- and long-term CIP to address identified hydraulic deficiencies including prioritization, alternatives analysis, and schedules. The CIP may include increases in pipe size, I&I reduction programs, increases and redundancy in pumping capacity, and storage facilities. 8.1 Capacity Evaluation The capacity of a sewer collection system should be regularly evaluated to ensure that all areas of the system have sufficient capacity for existing and future flow conditions. It is especially critical to evaluate capacity when adding new connections or developments to the existing system. Several tools exist to aid in the assessment of sewer system capacity, including flow monitoring, Inflow & Infiltration (I&I) study and hydraulic modeling. 8.1.1 Flow Monitoring System capacity is also evaluated using real-time flow monitoring data. EVWD occasionally contracts with flow monitoring contractors to measure actual flows in mainline trunks. The flow monitoring data is used to verify possible areas of the system that are experiencing capacity problems. For fiscal year 8-1
2014-15, the District budgeted money to purchase flow monitors in order to monitor flows on a yearly basis. In the past, flow monitoring data was limited to 4-6 weeks a year. By purchasing flow monitors the District has the flexibility to monitor different types of scenarios. The data will also help with calibrating the Districts existing model. 8.1.2 Hydraulic Modeling Measured flow monitoring data and evaluation of current City and County land use plan information was used in developing a dry weather and wet weather hydraulic models for the 2013 Wastewater Collection System Master Plan. Wet weather storm events were monitored to as best as could be to further develop and evaluate the capacity within the existing trunk sewer lines and to help calibrate the model. 8.1.3 Sewer Master Planning EVWD completed a comprehensive Wastewater Collection System Master Plan in 2013. This Master Plan includes a capacity analysis and provided a capital improvement program that identifies capacity related improvement projects. The Districts goal is to revise the plan every 5 years to maintain an accurate capital improvement program and to maintain an updated model which can be used to analyze developments as needed. 8.1.4 Identification of Capacity Needs The capacity assessment of the entire sewer collection system has been evaluated through the development of EVWD s Wastewater Collection System Master Plan. The capacity analysis used the calibrated dry weather and wet weather wastewater collection system model to evaluate existing and projected 2035 conditions. The District s sewer collection system lines range from 6- inches to 24-inches in diameter. There are 4,500 manholes and 215 miles of gravity sewer pipes that were included in the hydraulic model which was used to develop the2013 master plan. The hydraulic model includes all pipes 10 inches in diameter and larger, as well as 6 inch and 8 inch lines that were considered hydraulically necessary or important to evaluate the wastewater collection system. The model also includes the entire East Trunk Sewer. 8-2
The ratio of flow depth to pipe diameter (d/d ratio) was used to identify pipe capacity issues. The District s criteria is d/d = 0.50 (peak dry weather) for pipes equal to or less than 12 inches in diameter and d/d = 0.75 (peak dry weather) for pipes greater than 12 inches in diameter and d/d=1.0 (peak wet weather) for all gravity sewer pipelines. 8.1.5 Identification of Rehabilitation Needs EVWD has developed and implemented a Closed Circuit Television (CCTV) inspection program of the sewer system as part of their Operation and Management (O&M) Program. Inspection of sewer lines follows National Associating of Sewer Services Companies (NASSCO) Pipeline Assessment and Certification Program (PACP) standards. This program has allowed EVWD to identify and verify some of the hydraulic deficiencies as identified in the model and also deficiencies that exist in the system due to structural, operations, construction, or other miscellaneous issues. This program has provided a standardized comprehensive reservoir of data that is used for the prioritization, planning and renovation of wastewater collection improvement projects. The CIP schedule will be determined according to the prioritization as determined by the PACP grading system. Deficient pipes will be ranked and prioritized and incorporated into the short-term or long-term CIPs. 8.2 Design Criteria EVWD has a well established set of standards and criteria for the design and construction of sewer lines within their system. These include: Standard Specifications for the Furnishing of Materials and the Construction of Sanitary Sewers, revised Standard Drawings for Sewer Systems, Approved General Notes & Certificates, Table 8-1 shows the design criteria used by EVWD for sewer lines. It is important to note that EVWD does not own or operate any lift stations or force mains; thus they have not developed specific design criteria for these facilities. 8-3
Table 8-1 Hydraulic Criteria for the Design of EVWD Sewer Collection System Lines Element Value Manning s n Factor Minimum Pipe Size (for gravity sewers) Maximum Allowable Flow Depth 0.013 for all materials 8 inches Under peak design dry weather flow conditions: d/d = 0.50 for pipes 12-inches in diameter and smaller d/d = 0.75 for pipes larger than 12-inches in diameter The remaining capacity is assumed to be available for wet weather flows. Minimum Velocity/Slope Maximum Velocity Gravity lines: 2 ft/sec at peak dry weather flow at build-out (2.5 ft/sec is preferred). Gravity lines: 10 ft/sec 8.3 Capital Improvement Program The 2013 Master Plan presented recommendations to the District to address existing and future hydraulic and capacity deficiencies found in the compilation of data and analysis of the primary wastewater system using a hydraulic model. This section presents the recommendations to meet the primary objectives of this report. The 2013 Wastewater Collection System Master Plan contains a more detailed discussion of the capacity evaluation recommendations. A copy of the plan is located on the Districts website at www.eastvalley.org. Recommended Master Plan Programs Two wastewater collection system programs designed to meet various operational needs are recommended for implementation: 1. Short-Term Capital Improvements for immediate consideration. 2. Long-Term Capital Improvements for development and implementation These recommendations will be updated as EVWD s CCTV program is being implemented. 8-4
8.3.1 Short-Term CIPs As part of the update of the wastewater collection system master plan, EVWD will develop a Short-Term CIP to correct hydraulic deficient primary sewers in the existing system or to identify potential deficiencies that may occur at these locations. The short-term CIP will identify the deficient locations, costs associated with the improvement needs, and a time line for implementation of the projects. The deficient pipe(s) will be sized to accommodate system flows at build out as well as to correct existing deficiencies. 8.3.2 Long-Term CIPs As part of the update of the wastewater collection system master plan, EVWD will develop a Long-Term CIP to correct hydraulic deficient sewers using a phasing system that allows the District to evaluate the improvements to accommodate system flows for build-out conditions. The long-term CIP will identify the deficient locations, costs associated with the improvement needs, and a time line for implementation of the projects. 8.4 CIP Schedule As stated above, the short-term and long-term CIPs will include a time line for implementation of the projects. It is important to note that the CIPs will be living documents that will be adjusted as the District gathers additional information of their system as the CCTV program continues to be implemented and as their master plan is updated. 8-5