City of San Carlos. Sewer Collection System Master Plan. Water and Environment

Transcription

1 City of San Carlos Sewer Collection System Master Plan January 2013 Final Report Water and Environment

2 January 2, 2013 Mr. Jay Walter, P.E. Public Works Director/City Engineer City of San Carlos 600 Elm Street San Carlos, CA Re: Sewer Collection System Master Plan Dear Mr. Walter: RMC Water and Environment is pleased to submit this Final Report for the City of San Carlos Sewer Collection System Master Plan. The report presents the results of a comprehensive analysis the capacity and condition of the City s sanitary sewer collection system to support the City s ongoing efforts to upgrade its sewer infrastructure and minimize the risk of sanitary sewer overflows. The capacity assessment has been based on a detailed study methodology encompassing use of sewer system flow monitoring data, water use and land use planning data, coupled with state-of-the art hydraulic modeling to quantify flows in the system and identify existing and future capacity requirements. The condition assessment has utilized data from closed-circuit television inspection of the City s sewer pipes and application of a systematic decision process to identify sewer repair, rehabilitation, and replacement needs. The information presented in the report will help inform City decisions on providing additional hydraulic capacity where needed and/or targeting sewer system rehabilitation to address structural and maintenance problems in the system and reduce wet weather infiltration/inflow. The report also supports the City s compliance with its Consent Decree with San Francisco Baykeeper, as well as the Sewer System Management Plan requirements of the Statewide General Waste Discharge Requirements for Sanitary Sewer Systems. We appreciate the opportunity to have worked with the City on this challenging project and thank City staff for their assistance and guidance throughout the study. Sincerely, Gisa M. Ju, P.E. Project Manager

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4 Table of Contents Executive Summary. 1 Existing Sewer System and Service Area... 1 Capacity Assessment and Capacity Improvement Program... 2 Condition Assessment and Rehabilitation/Replacement Program... 8 Recommended Capital Improvement Program Chapter 1 Introduction Background and Study Objectives Study Area Existing Sewer System Scope of Study Report Organization Chapter 2 Hydraulic Model Development Modeling Terminology Modeled System Network Data and Data Validation Flow Monitoring Program Flow Estimating Methodology Wastewater Flow Components Base Wastewater Flow Groundwater Infiltration Rainfall-Dependent I/I Model Calibration Dry Weather Calibration Wet Weather Calibration Chapter 3 Capacity Assessment and Capacity Improvement Program Design Flow and Performance Criteria Design Storm Condition Capacity Deficiency Criteria Capacity Analysis Results Gravity Sewer System Deficiencies Pump Stations Capacity Improvement Projects Project Sizing Criteria Cost Criteria Detailed Project Descriptions Coordination with SBSA Infiltration/Inflow I/I Source Detection and Control Methods Chapter 4 Condition Assessment and Rehabilitation/ Replacement Program Sewer Condition Assessment Methodology CCTV Inspection Program Condition Grading and Rating Rehabilitation/Replacement Decision Process Defect Categorization and Terminology Decision Process Recommendations Condition Assessment and Renewal Decision Results Projected Sewer Renewal Requirements Projected Costs for Sewer Rehabilitation and Replacement January 2013 i

5 Chapter 5 Recommended Capital Improvement Program Recommended Capital Improvement Program Implementation Recommendations Flow Verification Parallel vs. Replacement Pipes Alternative Alignments Diversions Pre-Design Activities Model and Master Plan Updates Appendices Appendix A - Appendix B - Appendix C - Appendix D - Appendix E - Plots of Monitored Flow and Rainfall Data Model Calibration Plots Capacity Improvement Project Details Technical Memorandum on Pump Station Condition Assessment Sewer Renewal Decision Analysis Results for Inspected Sewers January 2013 ii

6 List of Tables Table ES- 1: Capacity Improvement Projects... 5 Table ES-2: Projected Sewer Renewal Requirements... 8 Table ES-3: Estimated Costs for Sewer Rehabilitation and Replacement... 9 Table ES- 4: Anticipated Schedule for Implementation of High-Priority Capacity Improvement Projects Table ES-5: Recommended Collection System Capital Improvement Program Table 1-1: Collection System Inventory Table 1-2: Gravity Sewer Pipe Materials Table 2-1: Flow Meter Locations Table 2-2 Planned Development Areas Table 2-3: Dry Weather Flow Summary Table 3-1: Pump Station Capacity Results Table 3-2: Capacity Improvement Projects Table 3-3: Peak I/I by Sewer Basin Table 4-1: Sewer Renewal Decision Process Explanations Table 4-2: Sewer Renewal Decision Analysis Results Table 4-3: Projected Sewer Renewal Requirements Table 4-4: Unit Construction Costs for Sewer Rehabilitation Table 4-5: Estimated Costs for Sewer Rehabilitation and Replacement Table 5-1: Recommended Collection System Capital Improvement Program Table 5-2: Anticipated Schedule for Implementation of High-Priority Capacity Improvement Projects List of Figures Figure ES-1: Existing Wastewater Collection System... 3 Figure ES-2: Overview of Capacity Improvement Projects... 7 Figure ES-3: Recommended Sewer Rehabilitation Figure 1-1: Study Area Figure 1-2: Existing Collection System Figure 2-1: Modeled Sewer Network Figure 2-2: Flow Monitoring Sites & Tributary Areas Figure 2-3: Plot of Typical Flow Data for Flow Monitoring Period (Meter 12) Figure 2-4: Wastewater Flow Components Figure 2-5: Anticipated Development Areas Figure 2-6: Diurnal Profiles Figure 2-7: RDI/I Hydrograph Components Figure 3-1: Design Rainfall Event Figure 3-2: Predicted Areas of Sewer Surcharge Under Design Storm Peak Wet Weather Flow Figure 3-3: Overview of Capacity Improvement Projects Figure 3-4: Wet Weather Peaking Factors Figure 3-5: Peak RDI/I Rates for Flow Meter Basins Figure 4-1: Sewer Renewal Decision Process Flow Diagram Figure 4-2: Highest Structural Grade of Inspected Sewers Figure 4-3: Sewer Renewal Decision Analysis Results January 2013 iii

7 Acknowledgements CITY OF SAN CARLOS DEPARTMENT OF PUBLIC WORKS Jay Walter, Public Works Director/City Engineer Ray Chan, Senior Engineer Keith Hanna, Civil Engineer Technician Paul Baker, Public Works Superintendent Chris Zanoni, Public Works Supervisor Frank Amoroso, Public Works Supervisor Albert Savay, Community Development Director RMC WATER AND ENVIRONMENT Gisa Ju, Project Manager Catherine Greenman, Project Engineer Glenn Hermanson Michael Flores Tony Valdivia Javier de la Cruz Winola Cheong Aaron Hope Subconsultants V&A Consulting Engineers (Flow Monitoring) January 2013 iv

8 List of Abbreviations ADWF Average Dry Weather Flow APN Assessor Parcel Number Baykeeper San Francisco Baykeeper BWF Base Wastewater Flow CalCAD California CAD Solutions CAR Capacity Assurance Report CCTV Closed-Circuit Television CIP Capital Improvement Program or Capital Improvement Plan CIPP Cured-in-Place Pipe City City of San Carlos CMMS Computerized Maintenance Management System d/d Ratio of flow depth to pipe diameter DEM Digital Elevation Model DWF Dry Weather Flow ENR CCI Engineering News Record Construction Cost Index FOG Fats, Oils, and Grease fps Feet per second FY Fiscal Year GIS Geographic Information System gpd Gallons per day GWI Groundwater Infiltration HDPE High Density Polyethylene (Pipe) I/I Infiltration and Inflow LPR Lining Point Repair MFR Multi-Family Residential MG Million Gallons mgd Million gallons per day MH Manhole MPR Major Point Repair NASSCO National Association of Sewer Service Companies NAVD88 North American Vertical Datum 1988 NGVD29 National Geodetic Vertical Datum 1929 January 2013 v

9 PACP PDWF PE PR PS PVC PWWF QA/QC RDI/I RMC R/R RWQCB SBSA SFR SQR SSMP SSO SWRCB V&A VCP WWF WWPF WWTP Pipeline Assessment and Certification Program Peak Dry Weather Flow Polyethylene (Pipe) Point Repair Pump Station Polyvinyl Chloride (Pipe) Peak Wet Weather Flow Quality Assurance/Quality Control Rainfall Dependent Infiltration and Inflow RMC Water and Environment Rehabilitation/Replacement Regional Water Quality Control Board, San Francisco Bay Region South Bay System Authority Single Family Residential Structural Quick Rating Sewer System Management Plan Sanitary Sewer Overflow State Water Resources Control Board V&A Consulting Engineers Vitrified Clay Pipe Wet Weather Flow Wet Weather Peaking Factor Wastewater Treatment Plant January 2013 vi

10 Executive Summary City of San Carlos Sewer Collection System Master Plan

11 Executive Summary Executive Summary This report presents the results and recommendations of the Sewer Collection System Master Plan for the City of San Carlos (City). The report was prepared by RMC Water and Environment (RMC) under an agreement with the City dated August 25, The objective of this Master Plan is to prepare a comprehensive assessment of the City s sewer collection system in order to identify system capital improvement needs. The Master Plan will also meet the requirements of the Statewide General Waste Discharge Requirements for Sanitary Sewer Systems, which require that every collection system agency in California prepare a Sewer System Management Plan (SSMP) which includes a System Evaluation and Capacity Assurance Plan and a plan for rehabilitation and replacement of sewers based on their condition. The City is subject to infiltration and inflow (I/I) of extraneous groundwater and stormwater into the collection system, resulting in high wet weather flows during storm events. As a result, sanitary sewer overflows (SSOs) have occurred at several locations in the system during large storms. In 2010 the City entered into a Consent Decree with San Francisco Baykeeper (Baykeeper), a non-governmental organization, which requires the City to implement a number of measures targeted at reducing SSOs. This Master Plan report is also intended to satisfy the specific requirements of the Consent Decree related to sewer system condition assessment, preparation of a capacity assurance plan, and development of Capital Improvement Program (CIP) for the wastewater collection system. Existing Sewer System and Service Area The City s sewer collection system serves a population of about 28,000 within the San Carlos city limits, plus adjacent areas in unincorporated San Mateo County (Devonshire County Sanitation District, Harbor Industrial Sewer Maintenance District, Scenic Heights County Sanitation District, and a portion of Emerald Lakes Heights Sewer Maintenance District) and a small portion of the City of Belmont that are tributary to the City s sewer system. All wastewater is conveyed to the South Bayside System Authority (SBSA) San Carlos Pump Station, from where it is pumped to the SBSA Wastewater Treatment Plant (WWTP) in Redwood Shores. Figure ES-1 shows the existing collection system. The system includes approximately 103 miles of gravity sewer mains, about 1 mile of pressure (force) mains, and 7 sewage pump stations. The major of the gravity system (almost 70 percent) consists of 6- inch pipe, and over 85 percent is less than 10 inches in diameter. The oldest portions of the system date to the 1920s, with a large portion of the system constructed in the 1940s and 1950s and newer areas in the hills developed later. The primary sewer pipe material in the collection system is vitrified clay pipe, with plastic materials used for newer sewer construction and rehabilitation. The collection system also includes approximately 11,000 private sewer laterals. The City assumes responsibility for the maintenance and repair of the lower portion of the laterals located within the public right-of-way. January

12 Executive Summary Capacity Assessment and Capacity Improvement Program The capacity of the collection system was assessed using a hydraulic model. The assessment focused on the trunk sewer network, the system of pipes that convey flow generated throughout the area to the San Carlos Pump Station. The modeled network includes all gravity sewers 15 inches in diameter and larger, over 90 percent of the 10- and 12-inch pipes, and about 10 percent of the 6- and 8-inch pipes, totaling about 22 percent of the length of sewers in the collection system, plus three of the system pump stations. The modeled network is shown in Figure ES-1. Flow loads to the model were developed from customer water use data provided by the water purveyors that serve the City (California Water Service Company and Mid-Peninsula Water District); estimates of additional flows from potential future development as determined from the City s General Plan and Housing Element and lists of near-term planned developments provided by the City s Planning Department; and from a flow monitoring program conducted for this study. Winter water use data typically provides a very accurate estimate of base wastewater flow (BWF), as outside water use is minimal during that time of year. Flow monitoring was conducted at 17 sites in the collection system during the winter 2010/11, with rainfall data also collected by three temporary rain gauges. The purpose of the monitoring was to obtain data to confirm base wastewater flows and to quantify the I/I response of the system to rainfall. The flow monitoring data was used to estimate the amount of I/I for various areas of the system and to confirm, through model calibration, that the hydraulic model reasonably simulates the actual performance of the system during both dry and wet weather conditions. Design Storm The capacity of the system was assessed with respect to a design rainfall event, defined as a 10-year recurrence frequency, 24-hour duration storm with a temporal rainfall distribution based on guidelines established in the U.S. Department of Agriculture Natural Resources Conservation Service publication Technical Release 55, Urban Hydrology for Small Watersheds. This document defines a particular synthetic rainfall distribution, called an SCS Type 1A storm, which is applicable to areas in northwestern California. The SCS Type 1A rainfall distribution was applied to rainfall data specific to the San Carlos area to develop a specific Design Storm for this study. The 24-hour Design Storm rainfall ranges from 3.3 to 3.7 inches, depending on location, with a peak intensity ranging from 0.52 to 0.58 inches per hour. The design storm is comparable in size to notable large rainfall events that have occurred in the San Francisco Bay Area over the past several years, including the storms of December 31, 2005, and January 25, Capacity Analysis Results The hydraulic model was run with the 10-year Design Storm to identify areas of the collection system that would not have adequate capacity to convey the peak wet weather flows generated by that event. Capacity was considered inadequate whenever the model predicted that the peak flows would result in overflows from the system or surcharge (flow above the crown of sewer pipes) to within four feet of manhole rims. However, areas where the risk of overflow was greatest, as defined by surcharging to within one foot of the ground, were considered highest priority for near-term capital improvements to be included in the five-year capacity CIP required by the Consent Decree. Pump station capacity was considered inadequate if the peak flows exceeded the station s firm capacity (capacity with the largest pump not in operation). The modeling indicated gravity pipeline capacity deficiencies in a number of areas of the collection system, including locations along Brittan Avenue, Belmont Avenue, Arroyo Avenue, Industrial Road, and Cedar Street. Several of the deficiencies are locations of historical wet weather overflows. January

13 «82 City of Belmont Harbor Industrial Sewer Maintenance District El Camino Real (State Hwy 82) 101 Alameda De Las Pulgas Ralston Ave Holly St Associate PS ") ") SBSA San Carlos PS Lower Crestview PS ") ") Upper Crestview PS Tierra Linda PS ") Devonshire County Sanitation District Devonshire Blvd San Carlos Ave Brittan Ave Industrial Rd Booster PS ") Kelly Moore PS I & II ") ") Crestview Dr Whipple Ave 280 Unincorporated Palomar Park (Septic Systems) Alameda De Las Pulgas Scenic Heights County Sanitation District Edgewood Rd City of Redwood City Jefferson Ave - Emerald Lake Heights Sewer Maintenance District Miles ") Modeled Pump Station ") Other Pump Station Modeled Manhole San Carlos City Boundary Modeled Sewer Unmodeled City Sewer County Sewer City of San Carlos Sewer Collection System Master Plan Existing Wastewater Collection System Figure ES San Carlos Sewer Master Plan\G. GIS\MXDs\Figures for Report\ES-1_Existing Wastewater Collection System.mxd

14 Executive Summary Based on the model results, improvement projects to address the predicted capacity deficiencies were developed. The projects primarily involve replacing existing deficient sewers with larger diameter pipes, or diverting flows to other existing sewers with available capacity or to proposed new pipes. Proposed sewer improvements were tested in the model to confirm that they would eliminate the identified capacity deficiencies and to confirm that sewers and pump stations downstream of the upsized pipes could handle the higher peak flows. Eleven capacity improvement projects were identified for the near-term capacity improvement program. These projects include a total of about 14,000 feet of new or replacement (upsized) gravity sewers, as well as construction of a new wet weather pump station on Industrial Road (at the location of the current booster pump station) with a force main extending to the San Carlos Pump Station. Five additional projects were identified as lower priority, but are still needed to alleviate potentially risky surcharge conditions under the Design Storm. Table ES- 1 lists all of the identified capacity improvement projects, including location, description of proposed improvements, and estimated planning level costs. The projects are shown on Figure ES-2. Estimated costs for capacity improvements were based on cost data compiled by RMC from similar projects. The costs are conceptual level estimates, considered to have an estimated accuracy range of -30 to +50 percent, suitable for use for budget forecasting, CIP development, and project evaluations, with the understanding that refinements to the project details and costs would be necessary as projects proceed to design and construction. All costs are presented in current (2012) dollars and include a 30 percent allowance for contingencies for unknown conditions, as well as an allowance of 25 percent of estimated construction cost for engineering, administration, and legal costs. The results of the modeling of proposed pipe capacity improvements indicated that peak flows reaching the San Carlos Pump Station during the Design Storm, after construction of the recommended capacity improvement projects, would be about 25.4 million gallons per day (mgd) under existing development conditions and 26.6 mgd with future development included. These flows exceed the City s current capacity allocation in the SBSA system. SBSA is currently implementing a capital improvement program to significantly upgrade its system, including capacity increases to the San Carlos Pump Station and downstream force mains. It is recommended that the City work closely with SBSA to ensure that the capacity improvement programs of the two agencies are coordinated. Infiltration/Inflow The City s collection system is subject to significant amounts of I/I, resulting in high peak flows during wet weather events, and capacity deficiencies as described above. Wet weather peaking factors (ratio of Design Storm peak wet weather flow to average dry weather flow) range from about 4 to over 25, with many areas having peaking factors exceeding 10. However, even reducing peak I/I in the worst areas by a reasonably achievable amount (e.g., 30 percent) would not be sufficient to eliminate the immediate need for capacity improvement projects to reduce the risk of wet weather SSOs. However, the City recognizes the benefit of reducing I/I in the long-term, as reducing I/I also reduces the costs for pumping and treatment, and provides the added benefit of further improving the condition of the sewer system, which in turn can reduce maintenance requirements and the risk of dry weather blockages and overflows. Through its sewer condition assessment and rehabilitation/replacement program, discussed in the next subsection, the City will be able to implement gradual improvements to the sewer system, which will help reduce I/I. Sewer rehabilitation can also be supplemented with other targeted programs, such as smoke testing and enforcement to eliminate sources of direct stormwater inflow (through illegal connections such as roof and area drains, or unknown cross-connections to the storm drain system), as well as programs that facilitate replacement of private sewer laterals. January

15 Executive Summary Table ES- 1: Capacity Improvement Projects Project No. Project Name Description Estimated Construction Cost Estimated Capital Cost 1 2 San Carlos Avenue/Beverly Drive Cedar Street/Manzanita Avenue Upsize 400 ft. of 6 sewer to 8 pipe in San Carlos Ave. north of Beverly Dr. Upsize 2,000 ft. of 6 & 8 sewer to 8, 10 & 12 pipe in Cedar St. and Manzanita Ave.; construct 500 ft. of new 12 pipe to divert flows to exist. 18 sewer in Cedar St. $ 138,000 $ 173,000 $ 722,000 $ 903,000 3 Brittan Avenue (Hewitt) Upsize 500 ft. of 8 sewer to 10 pipe in Brittan Ave. west of Hewitt Dr. $ 143,000 $ 178,000 4 Brittan Avenue Diversion 5 Arroyo Avenue 6 De Anza/Alameda De Las Pulgas/Edgewood 7 Orange Avenue Diversion 8 Belmont Avenue 9 Brittan Avenue Parallel to Industrial Road 10 Industrial Road South 11 New Industrial Road Pump Station and Force Main Upsize 2,500 ft. of 12 sewer to 15 pipe in Brittan Ave. from Orange Ave. to east of Laurel St; construct new 12 pipe to divert flows from 6 to 15 sewers in Brittan Ave. at Alameda De Las Pulgas. Upsize 1,100 ft. of 6 sewer to 8 pipe from west of Woodland Ave. to Walnut St.; construct 700 ft. of new 10 sewer between Walnut St. and exist. 12 trunk sewer at El Camino Real. Upsize 600 ft. of 6 sewer to 8 pipe in De Anza Ave. from Robin Way to east of Maple Way; upsize 1,100 ft. of 8 sewer to 10 pipe in Alameda De Las Pulgas and Edgewood Dr. east of Wildwood Ave. Construct 200 ft. of new 10 sewer in Orange Ave. from easement sewer parallel to Belmont Ave. to exist. 10 sewer in Belmont Ave. Upsize 1,100 ft. of 12 sewer to 15 pipe in Belmont Ave. from west of Rosewood Ave. to east of Laurel St. Construct 1,200 ft. of new 18 parallel sewer in Brittan Ave. from Old County Rd. to east of Industrial Rd. Construct 1,600 ft. of new 12 parallel sewer in Industrial Rd. from American St. to Brittan Ave. Construct 400 ft. of new 15 parallel sewer in Industrial Rd. from Brittan Ave. to exist. Booster PS site; construct new 5.3-mgd pump station and 4,400 ft. of 12 force main in Industrial Rd., Bransted Rd., and Skyway Rd. to the exist. San Carlos PS in Monte Vista Rd. $ 410,000 $ 513,000 $ 378,000 $ 472,000 $ 504,000 $ 630,000 $ 53,000 $ 66,000 $ 229,000 $ 286,000 $ 341,000 $ 426,000 $ 338,000 $ 422,000 $3,755,000 $4,733,000 Subtotal Near-Term Projects $7,011,000 $8,802,000 January

16 Executive Summary Project No. Project Name Description Estimated Construction Cost Estimated Capital Cost M1 M2 M3 Devonshire Boulevard/ Windsor Drive Pearl Avenue Alberta Avenue Diversion Upsize 700 ft. of 8 sewer to 10 pipe in Devonshire Blvd. west of Windsor Dr. and Windsor Dr. south of Devonshire Blvd. Upsize 1,300 ft. of 12 sewer to 15 pipe in Pearl Ave. from Eaton Ave. to Alberta Ave. and Alberta Ave. west of Pearl Ave. Construct new 12 pipe to divert flows from 8 sewer in easement parallel to Cedar St. to 15 sewer in Alberta Ave. $ 183,000 $ 229,000 $ 216,000 $ 270,000 $ 48,000 $ 61,000 M4 Elm Street Upsize 400 ft. of 8 sewer to 10 pipe in Elm St. south of Belmont Ave. $ 99,000 $ 124,000 M5 Tierra Linda Pump Station Upgrade Replace two existing pumps with larger (20 HP) pumps. 1 $ 75,000 $ 95,000 Subtotal Additional Projects $ 621,000 $ 779,000 Total All Capacity Improvement Projects $7,632,000 $9,581, Feasibility of pump replacement would need to be assessed based on analysis of pump curves and size of wet well; generator upgrade might also be required. January

17 « City of Belmont Harbor Industrial Sewer Maintenance District El Camino Real (State Hwy 82) Alameda De Las Pulgas Industrial Rd Ralston Ave SBSA San Carlos PS ") Holly St ' M5 ") Tierra Linda PS Upgrade (Project M5) ' 1 ' 2 San Carlos Ave ' 11 New Industrial Rd PS (Project 11) ") Devonshire County Sanitation District ' M1 Devonshire Blvd ' 5 ' 4 Brittan Ave ' 7 ' 8 ' 9 ' M4 ' 10 Crestview Dr ' 4 ' 3 ' 6 ' M3 ' M2 Alameda De Las Pulgas Whipple Ave 280 Unincorporated Palomar Park (Septic Systems) Scenic Heights County Sanitation District Edgewood Rd City of Redwood City Jefferson Ave Miles Emerald Lake Heights Sewer Maintenance District ' # ' # High Priority Capacity Improvement Project and ID Other Capacity Improvement Project and ID ") Pump Station Project Modeled Sewer Unmodeled City Sewer County Sewer City of San Carlos Sewer Collection System Master Plan Overview of Capacity Improvement Projects Figure ES San Carlos Sewer Master Plan\G. GIS\MXDs\Figures for Report\ES-2_Overview of Capacity Improvement Projects.mxd

18 Executive Summary Condition Assessment and Rehabilitation/Replacement Program The condition of the gravity collection system was evaluated through review of closed-circuit television (CCTV) inspection data collected in 2011 by a CCTV inspection contractor employed by the City. As of the end of 2011, the over 60 percent of the sewers in the system had been inspected (the City plans to complete inspection of the remainder of the sewers by the end of 2012). For recording CCTV data, the City uses the Pipeline Assessment and Certification Program (PACP) guidelines developed by the National Association of Sewer Service Companies (NASSCO), which are considered the current standard of the industry. Condition ratings were developed for the inspected sewers using the PACP system, which assigns grades (from 1 to 5) to all observed defects based on their type and severity. Grades are assigned to both structural defects (e.g., cracks, broken pipe, offset pipe joints) and maintenance-related defects (e.g., grease, debris, root intrusion). To utilize the condition rating and defect information, RMC, in conjunction with City staff, developed a decision process to determine the appropriate sewer renewal method for sewers with defects warranting near-term repair. The focus of the analysis was on pipes with major defects that could result in structural failures; large offset joints, which can impede inspection and cleaning equipment; and significant root intrusion, which can cause blockages resulting in SSOs. Each inspected pipe was analyzed, and video reviewed as necessary, to identify the apparent most costeffective method of renewal (e.g., localized point repair, lining, or replacement) to address these issues; or if renewal was not considered necessary at this time, the pipe was identified for continued maintenance. Figure ES-3 shows the results of the renewal decision process in terms of the recommended renewal method for the sewers inspected as of The results from the rehabilitation decision analysis of the inspected sewers were extrapolated to the remaining 40 percent of the system based on the size and material of those pipes. This enabled estimates of sewer renewal quantities to be developed for the entire system, as shown in Table ES-2. As indicated in the table, is it estimated that about 40 percent of the system requires repair, rehabilitation, or replacement due to structural defects in the pipes. For the as-yet-uninspected portion of the system, the specific pipes requiring rehabilitation or replacement will be determined based on subsequent CCTV inspection results. Table ES-2: Projected Sewer Renewal Requirements Sewer Renewal Reason and Decision Length of Pipe Segments (ft.) Percentage of Total Pipe Length Number of Localized Repairs Major Structural Defects 206, % 606 Replace 124, % 0 Line 4, % 24 Localized Repair 78, % 582 Large Offset Joints 11, % 62 Replace 2, % 0 Localized Repair 8, % 62 Significant Root Intrusion 23, % 0 Replace 19, % 0 Line 4, % 0 Renewal Subtotal 241, % 668 Maintain (Reinspect in Future) 305, % 0 TOTAL 546, % 668 January

19 Executive Summary Table ES-3 presents the estimated cost of the required sewer repair, rehabilitation, and replacement based on the quantities shown in Table ES-2. Note that since over 60 percent of the recommended sewer renewal is replacement or lining of entire manhole-to-manhole segments, and it is assumed that lower laterals would be replaced whenever a sewer is replaced or lined, a significant portion (over 40 percent) of the total estimated sewer renewal cost is for replacement of lower laterals. Table ES-3: Estimated Costs for Sewer Rehabilitation and Replacement Reason for Renewal Estimated Construction Cost 1 Estimated Capital Cost 2 Major Structural Defects $41,725,000 $52,157,000 Large Offset Joints $1,247,000 $1,558,000 Significant Root Intrusion $6,610,000 $8,262,000 Total $49,582,000 $61,977, Includes 30% allowance for contingencies. 2. Includes 25% allowance for engineering, administration, and legal costs. The costs presented in Table ES-3 represent the estimated capital investment in the system required to address significant existing structural deficiencies and root problems. Over the long-term, additional sewer renewal will be needed to continue to maintain the structural integrity of the system as it ages, as determined through future sewer inspection. The recommended sewer rehabilitation and replacement program described above is intended to restore the condition of existing sewers to a reasonably good condition and maximize their remaining useful service lives. However, it is recognized that this program may require significant increases in sewer rates in order to provide the necessary funding to sustain this level of sewer rehabilitation. At a minimum, the City is obligated to address identified sewer defects in accordance with its Consent Decree, which requires that all Grade 5 (most severe) structural defects must be repaired within 2 years (or 90 days if imminent failure is likely), and all Grade 4 structural defects must be repaired within 5 years. If repairs are not made within those timeframes, the pipes must be re-inspected at specified regular intervals to confirm that their condition has not worsened. Virtually all of the inspected pipe segments identified for some type of renewal have Grade 4 or 5 defects. For many of these pipes, the recommended sewer renewal method is pipe replacement rather than point repair. Replacing or even lining the entire pipe segment would not only address the most severe defects but would also eliminate smaller defects and help address other issues such as I/I, and ultimately would extend the service life of the pipe for a much longer period than if only the minimum required defects were repaired. Implementing only the minimum-required point repairs would be less expensive for the City in the shortterm, but would undoubtedly increase the City s long-term costs for sewer rehabilitation, as many pipes that have undergone point repairs would likely need complete replacement in the future. However, for purposes of bracketing the potential costs of the sewer rehabilitation program, an estimate for a minimum point repair approach has been developed. Based on these assumptions, the total capital cost for sewer point repairs to address existing sewers (based on their current condition) would be about $32 million, or about half that of the program developed based on the renewal decision analysis process applied in this Master Plan. January

20 «82 City of Belmont 101 El Camino Real (State Hwy 82) Alameda De Las Pulgas Ralston Ave Holly St Industrial Rd San Carlos Ave Devonshire Blvd Brittan Ave Crestview Dr Whipple Ave Alameda De Las Pulgas 280 Edgewood Rd City of Redwood City Jefferson Ave Miles Replace or Line Localized Repair Maintain (Rehabilitation Not Needed) Condition Not Yet Evaluated City of San Carlos Sewer Collection System Master Plan Recommended Sewer Rehabilitation Figure ES-3 \\rmcla\rmcla\projects GIS\San Carlos Sewer Master Plan\2 MXD\ES-3 Recommended Sewer Rehabilitation.mxd

21 Executive Summary Recommended Capital Improvement Program The recommended CIP includes 16 capacity improvement projects and sewer repair, rehabilitation, and replacement to address significant structural and maintenance issues. The schedule for the 11 high priority capacity improvement projects, as presented in the Capacity Assurance Report submitted to Baykeeper in compliance with the Consent Decree, are listed in Table ES-4. These projects have been prioritized based on relative severity of existing capacity deficiencies and the location of historical wet weather overflows, and have been phased to accommodate the City s anticipated financial resources over a five-year construction period. Other capacity projects have been assigned lower priorities because the potential risk of overflows is lower. Sewer repairs and replacements to address major structural defects are considered the highest priority with respect to sewer rehabilitation because the present the greatest risk of structural failure, followed by projects to address large offset joints (which do not present a risk of structural failure but may impede inspection or cleaning equipment) and significant root intrusion. Root intrusion increases the risk of SSOs due to blockages, but can be controlled by effective maintenance (rodding and/or root foaming) in the interim period before the sewers are rehabilitated. The City has developed a root control plan as part of its overall maintenance program. In addition to addressing the capital project needs identified in the capacity assurance and near-term sewer rehabilitation plans, the City intends to continue efforts for overall rehabilitation of the sewer system to reduce I/I, focusing on those areas identified as having the highest I/I contributions to the system. In implementing its structural rehabilitation program, the City may choose to conduct more extensive rehabilitation (e.g., manhole-to-manhole pipe replacement or lining rather than just localized point repairs of major defects, or including additional adjacent pipe segments in the rehabilitation work) to match these objectives and will prioritize its structural rehabilitation program accordingly. Therefore the rehabilitation/replacement component of the recommended CIP is formulated as an budget allocation rather than a list of specific projects, to allow the City flexibility to tailor the program to meet both structural rehabilitation and long-term I/I reduction objectives and/or take an area-by-area approach to the sewer rehabilitation and replacement work. Table ES-5 presents the recommended 20-year collection system CIP, including the specific capacity improvement projects recommended for implementation during the first six years of the program, as listed in Table ES-4. A portion of the sewer rehabilitation work would also be targeted for completion during this initial phase. The table shows both the recommended sewer renewal program based on the rehabilitation/replacement decision analysis methodology that was applied to the CCTV inspection data, as well as the minimum point repair approach discussed previously. It is expected that the City will decide on its approach to the sewer rehabilitation program after consideration of its long-term goals, as well as financial constraints and impact on sewer rates. The City will update the long-range CIP in 2013 based on additional sewer inspections and development of a financial plan to be completed subsequent to this Master Plan report. January

22 Executive Summary Table ES-4: Anticipated Schedule for Implementation of High-Priority Capacity Improvement Projects Priority Project No. 1 4 Project Name Brittan Avenue Diversion Estimated Capital Cost FY2012/13 1 FY2013/14 FY2014/15 FY2015/16 FY2016/17 FY2017/18 $ 513,000 $ 62,000 $ 451, Arroyo Avenue $ 472,000 $ 57,000 $ 415, Brittan Avenue Parallel to Industrial Road New Industrial Road Pump Station and Force Main $ 426,000 $ 51,000 $ 375,000 $ 4,733,000 $ 563,000 $2,085,000 $2,085, Industrial Road South $ 422,000 $ 51,000 $ 371, Cedar Street & Manzanita Avenue San Carlos Avenue/Beverly Drive De Anza/Alameda De Las Pulgas/Edgewood $ 903,000 $ 108,000 $ 795,000 $ 173,000 $ 21,000 $ 152,000 $ 630,000 $ 76,000 $ 554, Belmont Avenue $ 286,000 $ 34,000 $ 252, Orange Avenue Diversion $ 66,000 $ 8,000 $ 58, Brittan Avenue (Hewitt) $ 178,000 $ 21,000 $ 157,000 Total $ 8,802,000 $ 170,000 $1,804,000 $2,085,000 $2,244,000 $1,326,000 $1,173, The City expects to request a one-year extension for completion of the capacity improvement projects in order to implement a fee increase and obtain required funding, but may elect to begin design of the highest priority projects using existing funding sources. January

23 Executive Summary Project ID Years 1-6 Table ES-5: Recommended Collection System Capital Improvement Program Project Name R/R Decision Analysis Approach Est. Capital Cost ($) Minimum Point Repair Approach 4 Brittan Avenue Diversion 513, ,000 5 Arroyo Avenue 472, ,000 9 Brittan Avenue Parallel to Industrial Road 426, , New Industrial Road Pump Station and Force Main 4,733,000 4,733, Industrial Road South 422, ,000 2 Cedar Street & Manzanita Avenue 903, ,000 1 San Carlos Avenue/Beverly Drive 173, ,000 6 De Anza/Alameda De Las Pulgas/ Edgewood 630, ,000 8 Belmont Avenue 286, ,000 7 Orange Avenue Diversion 66,000 66,000 3 Brittan Avenue (Hewitt) 178, ,000 Years 7-20 Sewer Rehabilitation 12,000,000 3,000,000 Subtotal - Years ,802,000 11,802,000 M1 Devonshire Boulevard/ Windsor Drive 229, ,000 M2 Pearl Avenue 270, ,000 M3 Alberta Avenue Diversion 61,000 61,000 M4 Elm Street 124, ,000 M5 Tierra Linda Pump Station Upgrade 95,000 95,000 Sewer Rehabilitation 49,977,000 29,000,000 Subtotal - Years ,756,000 29,779,000 TOTAL CIP 71,558,000 41,581,000 January

24 Chapter 1 Introduction City of San Carlos Sewer Collection System Master Plan

25 Chapter 1 Introduction Chapter 1 Introduction This report presents the results and recommendations of the Sewer Collection System Master Plan for the City of San Carlos (City). The report was prepared by RMC Water and Environment (RMC) under an agreement with the City dated August 25, This introductory chapter provides background information on the objectives and scope of the Master Plan, the City s sewer system and service area, and the contents and organization of the Master Plan report. 1.1 Background and Study Objectives Over the past 10 to 15 years, the City has conducted various studies related to flows and capacity requirements in its sewer collection system, but has not prepared a comprehensive master plan for its overall system. During the past few years, several improvements to the sewer system have been constructed, including the Tierra Linda Pump Station, which diverted flows back to San Carlos that had previously been conveyed into the City of Belmont s sewer system, and the Industrial Road Booster Pump Station, which was designed to help alleviate severe surcharging in the Industrial Road trunk sewer. The City also developed mapping of the system in a geographic information system (GIS) and implemented a new computerized maintenance management system (CMMS). In January 2011, the City initiated a closed-circuit television (CCTV) inspection program to assess the condition of its entire gravity sewer system. The City has been required to monitor and report occurrences of sanitary sewer overflows (SSOs) since 2004, initially to the San Francisco Bay Regional Water Quality Control Board (RWQCB or Regional Board), and later (since 2007) to the State Water Resources Control Board (SWRCB) under the Statewide General Waste Discharge Requirements for Sanitary Sewer Systems adopted in Under the Regional and State regulations, the City was also required to prepare and adopt a Sewer System Management Plan (SSMP), including plans and programs for addressing the operation and maintenance of the system and assessing its condition and capacity. The City is required to audit and update its SSMP regularly. As a result of SSOs that have occurred in the system over the past few years, the City entered into a Consent Decree with San Francisco Baykeeper (Baykeeper), requiring it to implement a number of measures targeted at reducing SSOs. The requirements of the Consent Decree include developing procedures for determining causes of SSOs; preparing a Capacity Assurance Report (CAR) and constructing required capacity improvement projects; conducting sewer inspection and condition assessment in order to prioritize sewer repair, rehabilitation and replacement; implementing sewer cleaning, root control, and fats, oils and grease (FOG) control programs; and adopting standards and requirements for inspection and repair of private sewer laterals. The Consent Decree also contains SSO performance standards with decreasing maximum allowable number of SSOs specified for each year through This Master Plan report specifically addresses the capacity assessment of the system to develop required capacity improvement projects, and the condition assessment of the system based on inspection data collected to date to identify sewer rehabilitation needs. 1.2 Study Area The study area for this Master Plan consists of the City of San Carlos and areas outside the city that are tributary to the City s wastewater collection system, as shown in Figure 1-1. The city is bounded on the north by the City of Belmont, on the west by unincorporated areas of San Mateo County, on the south by the City of Redwood City, and on the east by the Redwood Shores area of Redwood City, the Bair Island Ecological Preserve and San Francisco Bay. January

26 Chapter 1 Introduction The oldest parts of San Carlos were developed starting in the 1920s, with significant growth in the 1940s and 1950s, and later development in the western hills. The city is largely single-family residential in nature, with a traditional downtown area including adjacent multi-family development located along El Camino Real, Laurel Street, and San Carlos Avenue. Industrial areas and retail centers are located east of the Caltrain right-of-way. The city is now largely built out, with only a few areas of potential new development, although there are redevelopment plans for areas along the El Camino Real and Caltrain transit corridor and in the industrial/commercial areas to the east. The collection system serves a population of about 28,000 within the city limits and also conveys flows from unincorporated areas served by the Devonshire County Sanitation District, Harbor Industrial Sewer Maintenance District, Scenic Heights County Sanitation District, and a portion of the Emerald Lakes Heights Sewer Maintenance District (all owned and operated by San Mateo County), as well as a small portion of the City of Belmont. Sewers serving a few parcels within the city along Hartford and Buckland Avenues near the northern boundary with Belmont discharge to Belmont s sewer system. 1.3 Existing Sewer System The City s sanitary sewer system includes approximately 103 miles of gravity sewer mains, about 1 mile of pressure (force) mains, and seven sewage pump stations. All sewage is conveyed to the San Carlos Pump Station, owned and operated by the South Bayside System Authority (SBSA), from where it is pumped to the SBSA Wastewater Treatment Plant (WWTP) in Redwood Shores. SBSA is a joint powers authority of the Cities of Belmont, San Carlos, and Redwood City and the West Bay Sanitary District. Figure 1-2 shows the existing collection system layout. Table 1-1 tabulates the footage of pipe by diameter. As noted in the table, almost 70 percent of the gravity sewer mains are 6 inches in diameter, and over 85 percent are likely less than 10 inches. Pipe Diameter Table 1-1: Collection System Inventory Total Pipe Length (miles) Percent of System % % % % % % % % % % Unknown % Gravity Sewers % Force Mains % Number of Pipes 2 2, Likely 6-inch or 8-inch pipe 2. Rounded to the nearest 10 January

27 «82 Harbor Industrial Sewer Maintenance District City of Belmont 101 Alameda De Las Pulgas Ralston Ave San Carlos Airport Holly St Industrial Rd Devonshire County Sanitation District Devonshire Blvd San Carlos Ave City of San Carlos El Camino Real (State Hwy 82) Brittan Ave Crestview Dr Alameda De Las Pulgas Whipple Ave 280 Edgewood Rd Unincorporated Palomar Park (Septic Systems) Scenic Heights County Sanitation District City of Redwood City Jefferson Ave Emerald Lake Heights Sewer Maintenance District Miles Study Area San Carlos City Boundary County Sewer Maintenance/Sanitation District City of San Carlos Sewer Collection System Master Plan Study Area Figure San Carlos Sewer Master Plan\G. GIS\MXDs\Figures for Report\1-1_Study Area.mxd

28 «82 Harbor Industrial Sewer Maintenance District City of Belmont 101 Alameda De Las Pulgas El Camino Real (State Hwy 82) Ralston Ave Holly St Associate PS ") ") SBSA San Carlos PS Industrial Rd Lower Crestview PS ") Upper Crestview PS ") ") Tierra Linda PS Devonshire County Sanitation District Devonshire Blvd San Carlos Ave Brittan Ave Booster PS ") Kelly Moore PS ") ") I & II Crestview Dr Alameda De Las Pulgas Whipple Ave 280 Unincorporated Palomar Park (Septic Systems) Scenic Heights County Sanitation District Edgewood Rd City of Redwood City Jefferson Ave - Emerald Lake Heights Sewer Maintenance District Miles ") Pump Station City Sewer County Sewer San Carlos City Boundary City of San Carlos Sewer Collection System Master Plan Existing Collection System Figure San Carlos Sewer Master Plan\G. GIS\MXDs\Figures for Report\1-2_Existing Collection System.mxd

29 Chapter 1 Introduction As is common in most San Francisco Bay Area communities, the primary pipe material in the gravity collection system is vitrified clay pipe (VCP), which comprises 60 to 70 percent of the system. Newer and/or rehabilitated sewers have been constructed of plastic materials such as high density polyethylene (HDPE or PE) or polyvinyl chloride (PVC) pipe, which now comprise over 25 percent of the system. Table 1-2 shows a breakdown of pipe materials in the system. Pipe Material Table 1-2: Gravity Sewer Pipe Materials Total Pipe Length (miles) Percent of System Asbestos Cement % Cast Iron/Ductile Iron % Concrete (non-reinforced) % Polyethylene % Polyvinyl Chloride % Reinforced Concrete % Vitrified Clay % Other % Unknown % 1. Likely mostly VCP. The collection system also includes approximately 11,000 private sewer laterals. The City assumes responsibility for the maintenance and repair of the lower portion of the sewer laterals located within the public right-of-way. 1.4 Scope of Study The scope of the Master Plan, as well as a brief discussion of work conducted under each task, is described below. Task 1 Project Coordination. Periodic progress meetings and teleconferences were held with City staff to review project status and discuss project issues, and monthly status reports were prepared to document the work completed. Task 2 Data Collection and Review. This task involved assembling, organizing, and reviewing maps, documents, and data related to the sewer system, including previous reports; maps and drawings of sewer system facilities and recent sewer improvement projects; pump curves and operating data; water use and customer account data; the City s General Plan and other relevant planning information; sewer CCTV inspection data; and sewer design standards and specifications. Task 3 Flow Monitoring. A plan for flow and rainfall monitoring in the collection system during the 2010/11 wet weather season was developed. The program included 17 flow meters and three rain gauges installed for a period of approximately two months. The monitoring was conducted by RMC s subconsultant, V&A Consulting Engineers. Task 4 Hydraulic Model Development. A Hydraulic Modeling Work Plan was prepared for submittal to Baykeeper as required under the Consent Decree. Based on the Work Plan, a hydraulic model of the City s trunk sewer system was developed using InfoWorks CS software. Sewersheds were delineated to define areas loading to the model, and flow loads to the model were compiled using water use and land use data and flow factors representing unit base wastewater flow (BWF) January

30 Chapter 1 Introduction rates, diurnal BWF patterns, and infiltration/inflow (I/I). The model was calibrated for dry and wet weather conditions using the flow monitoring data collected under Task 3. Task 5 System Performance Evaluation and Improvement Needs. The model was used to determine sewer system capacity requirements and identify capacity deficiencies under peak wet weather flow conditions, defined based on a design storm and system performance criteria. Areas of the system with high rates of I/I were identified, and the potential effectiveness of reducing peak flows by reduction of I/I through sewer system rehabilitation was assessed. Potential solutions to capacity deficiencies were identified and tested in the model, and capacity improvement projects and associated costs were developed based on these analyses. Task 6 Condition Assessment and Rehabilitation/Replacement Program. In this task, assistance was provided to the City in developing standards and quality assurance/quality control (QA/QC) guidelines for CCTV inspection. The CCTV inspection data collected by the City during the first year of its program were reviewed, and a process was developed to utilize the data to develop preliminary rehabilitation/replacement (R/R) decisions. The R/R decision process was implemented by developing a set of database queries with the results linked to the sewer pipes in GIS. Estimated costs for sewer R/R were developed for incorporation into the long-range capital improvement program (CIP) in Task 8, including an estimate of budget needs for sewer rehabilitation based on extrapolation of the condition assessment results for the portion of the system that has not yet been inspected. In addition to the sewer condition assessment, a pump station condition assessment was prepared based on review of existing information and field visits to each of the seven system pump stations. Task 7 Prioritized Capital Improvement Plan Development. The recommended capacity and rehabilitation projects were prioritized for incorporation into near-term and long-term CIPs. Task 8 Master Plan and Capacity Assurance Report Preparation. The Capacity Assurance Report was prepared for submittal to Baykeeper as required under the Consent Decree, and this Master Plan report was prepared to present the results and recommendations of the study. 1.5 Report Organization The contents of each of the chapters and appendices of this Master Plan report are described below. Executive Summary The Executive Summary provides a brief, stand-alone summary of the Master Plan report, with emphasis on the major findings and recommendations. Chapter 1- Introduction This introductory chapter provides background information on the objectives and scope of the Master Plan, the City s sewer system and service area, and the contents and organization of this report. Chapter 2 Hydraulic Model Development This chapter describes the modeled sewer system, development of the model network and sewershed areas, the flow monitoring program and basis for estimating model flows, and the calibration of the model for dry and wet weather conditions. Chapter 3 Capacity Assessment and Capacity Improvement Program This chapter defines the basis for the capacity assessment of the system, including the selected design storm and performance criteria; describes the identified capacity deficiencies based on the model results; presents the design criteria used to develop capacity improvements; and presents the recommended capacity improvement projects. Each project is documented with a general description and planning level January

31 Chapter 1 Introduction cost estimate. The chapter also identifies areas of the system with high I/I and discusses the potential benefits of I/I reduction and the methods for detecting and reducing I/I. Chapter 4 Condition Assessment and Rehabilitation/Replacement Program This chapter describes the City s CCTV data and the R/R decision process developed and applied to the data. The results of the R/R decision analysis and recommended rehabilitation program and estimated costs are presented. Chapter 5 Prioritized Capital Improvement Program This chapter presents the sewer projects that are recommended for inclusion in the City s near-term and long-term CIPs based on the results of the capacity and condition assessments. The CIP includes a recommended schedule for project implementation and associated capital costs that will form the basis for the City s financial plan for the wastewater collection system. Recommendations for project implementation are also provided. The appendices to the report provide additional detailed information to support the findings and recommendations presented in the report chapters, including plots of flow monitoring data and model calibrations, detailed project descriptions and cost estimates for improvement projects, recommended rehabilitation/replacement decisions for inspected sewers, and a Technical Memorandum on the Pump Station Condition Assessment. January

32 Chapter 2 Hydraulic Model Development City of San Carlos Sewer Collection System Master Plan

33 Chapter 2 Hydraulic Model Development Chapter 2 Hydraulic Model Development This chapter documents the development of the hydraulic model that was used to assess the capacity of the City s sewer system. The chapter provides an overview of the model development process, including descriptions of the modeled sewer network and sewersheds, the flow monitoring program conducted for this study, the basis for estimating wastewater flows, and the calibration of the model. A Hydraulic Modeling Work Plan was prepared at the beginning of the study for submittal to Baykeeper to document the overall approach for model development and capacity assessment. The modeling utilized InfoWorks CS, a fully-dynamic hydraulic modeling software supported by a GIS-based modeling interface. 2.1 Modeling Terminology Key modeling terminology is defined below. Network refers to the representation of the physical facilities being modeled. Modeled network components include pipes, manholes, and pump stations. Nodes are primarily manholes, but also include pump station wet wells and outfalls (discharge points from the modeled system). Key data associated with nodes include manhole ground elevations and pump station wet well elevations and cross-sectional areas. Pipes or conduits are connections between nodes, and include both gravity sewers and force mains. Key data associated with pipes are upstream and downstream node IDs, pipe length, diameter, roughness factor, and upstream and downstream invert elevations. Pumps are modeled individually, connecting pump station wet wells with the upstream node of associated force mains. Data associated with pumps include type (e.g., fixed or variable speed), on and off levels, pump capacities, and pump discharge curves. Subcatchments (also called sewersheds) are areas that contribute flow to the modeled sewer network and represent the unmodeled sewers in the collection system. Data associated with subcatchments include sanitary flow (computed based on population, water use, or other available data), type of diurnal sanitary flow profile (which is a function of land use), infiltration/inflow (I/I) parameters, and the node at which the flow from the subcatchment enters the modeled system. Model loads are the flows entering the modeled sewer system from each subcatchment. Model loads include residential and commercial sanitary or base wastewater flow (BWF), groundwater infiltration (GWI), and rainfall-dependent I/I (RDI/I). As a sum, they represent the total wastewater flow applied to the model. Models are the combination of a modeled network, its associated subcatchments and loads, and other data files (e.g., rainfall, diurnal profiles, inflows from other areas, etc.) that comprise a specific model scenario. 2.2 Modeled System The modeled network includes all 15-inch and larger diameter pipes, over 90 percent of the 10- and 12-inch pipes, and additional 6- and 8-inch lines that effectively serve as trunk sewers. In total, the network includes approximately 23 miles of pipelines (over 500 manhole-to-manhole segments), or about 22 percent of total length of sewers in the system, including about 10 miles of 6- and 8-inch sewers. The model includes three of the system pump stations (Tierra Linda, the Associate, and the Industrial Road booster pump station). The network has a single model outfall at the discharge point to the SBSA San Carlos Pump Station. The model network is shown in Figure 2-1. January

34 Chapter 2 Hydraulic Model Development The City s sewered area was divided into 210 sewersheds, called subcatchments in InfoWorks, with an overall average size of about 20 acres per subcatchment. Each subcatchment loads to a manhole in the modeled network Network Data and Data Validation The data used to define the model network and associated attributes were derived from a variety of sources, as listed below: Sewer GIS files. The City s GIS consultant, California CAD Solutions (CalCAD), provided GIS files containing the locations and IDs for the sewers and manholes. The model was originally developed based on the October 2010 version of these files. Through ongoing field inspections and CCTV work, the City identified several differences between these files and the actual sewer system and periodically asked CalCAD to update the GIS files while the model development work was on-going. In general, changes identified through November 2011 that affected the model system or flow inputs into the model system were incorporated into the model network. Hansen data. CalCAD provided this database file with the initial delivery of the sewer GIS files in October According to CalCAD, the data in this file came from the City s old Hansen database. This data file includes information needed for the model, including pipe diameter, upstream and downstream invert elevations, and pipe length. The data were not complete, however, and appeared to be inconsistent or erroneous in some areas. BKF data. The City provided a set of Excel files containing additional pipe data originating from about These files also included pipe data needed for modeling, including pipe diameter, upstream and downstream invert elevations, pipe length, and manhole rim elevations. Like the Hansen data, these data were also incomplete and appeared inconsistent in areas, but provided more information than available through the Hansen data alone. Note that the Hansen data includes a BKF ID, which corresponds to the pipe IDs in the BKF Excel files and allowed an initial linking of the two datasets. The BKF ID in the Hansen data was incompletely populated, however, so additional linking was achieved based on upstream and downstream manhole IDs, as well as old City mapbooks. In some areas, the pipe data included in the BKF data were different than that included in the Hansen data. City staff noted that, in general, the BKF data was more likely to be accurate than the Hansen data. Old Sewer Mapbooks. The City provided two old mapbooks. The first mapbook, City of San Carlos Sewer Block Maps, was originally developed in 1973 by McCandless, Boone & Cook, with the latest revision dated January The second mapbook, City of San Carlos Digital Map Atlas, was produced by Towill, Inc, dated These mapbooks provided information that allowed additional linking of the BKF data to pipes and manholes in the model (the BKF data includes references to map numbers and old manhole IDs in the 1973 mapbook, as well as new manhole IDs in the newer 1994 mapbook). These mapbooks also provided some additional information on pipe diameters in selected locations. San Mateo County Digital Elevation Model (DEM). The County DEM was used to populate ground elevations for manholes that did not have elevations in the BKF data. The ground elevations in the County DEM were adjusted by -2.8 feet to account for the approximate difference in the vertical datum between the County DEM (NAVD88 datum) and the sewer data available (typically NGVD29 datum). Record Drawings. In a few selected areas, the City was able to provide record drawings showing pipeline profiles, elevations, and pipe diameters. January

35 «82 City of Belmont Harbor Industrial Sewer Maintenance District El Camino Real (State Hwy 82) Alameda De Las Pulgas Ralston Ave 101 Holly St Associate PS ") ") SBSA San Carlos PS Tierra Linda PS ") San Carlos Ave Industrial Rd Booster PS ") Devonshire County Sanitation District Devonshire Blvd Brittan Ave Crestview Dr Whipple Ave 280 Edgewood Rd Unincorporated Palomar Park (Septic Systems) Alameda De Las Pulgas Scenic Heights County Sanitation District City of Redwood City Jefferson Ave - Emerald Lake Heights Sewer Maintenance District Miles ") Modeled Pump Station ") SBSA Pump Station Modeled Manhole Modeled Sewer Unmodeled City Sewer County Sewer City of San Carlos Sewer Collection System Master Plan Modeled Sewer Network Figure San Carlos Sewer Master Plan\G. GIS\MXDs\Figures for Report\2-1_Modeled Sewer Network.mxd

36 Chapter 2 Hydraulic Model Development Manhole Field Investigations. At RMC s request, City maintenance staff inspected 31 manholes at flow split locations (manholes with more than one outgoing pipe, where flow could potentially split into more than one direction). City staff measured the depths to the incoming and outgoing pipes and noted if there were any special structures in the manholes (such as weirs) that would route flow in a particular direction. Staff performed additional field investigations to confirm pipe diameters in selected locations. Easement Manhole Depth Measurements. For a separate project, City maintenance staff had measured depths at several manholes in sewer easements. These additional depth measurements were used in the model in areas where no other pipe invert data were available. Manhole Surveys. At RMC s request, the City had 45 manholes surveyed to fill in additional gaps where no manhole invert data were available, or where the various sources of data conflicted. Manholes rims were surveyed by MacCloud & Associates, and depths were measured by City staff. Inference. Where reasonable, pipe data (diameters and invert elevations) were inferred or interpolated to fill in missing data. Data for modeled pump stations includes pump types, wet well dimensions and elevations, and pump operating levels and head-discharge curves. This information was provided by City staff. After the model network was defined, a procedure was followed to fill in missing information, validate the network data, and create a fully connected network, as follows: The modeled network was checked for connectivity. This means that all manholes are connected by pipes, and that pipes are generally connected in the correct direction (from upstream to downstream) to create a fully-connected system. Connectivity was corrected in several locations based on record drawings and field inspection information from City maintenance staff. Manhole and pipe attribute data were populated based on the best available rim, invert, and diameter data from the sources listed above. Pipe lengths were based on graphical length from the GIS sewer map. After filling in missing data, modeled pipeline profiles were reviewed, and areas with suspect data were discussed with City staff. Subcatchments were delineated to define areas tributary to the modeled pipe network. Each subcatchment was assigned to a manhole in the modeled system to define where the model load from that subcatchment enters the modeled sewer system. Global parameters which are required by the model were populated, such as manhole diameters (assumed to be 4 feet), Manning s n (assumed to be for all pipes), and headloss factors. January

37 Chapter 2 Hydraulic Model Development 2.3 Flow Monitoring Program As part of the Master Plan, 17 temporary meters and 3 recording rain gauges were installed by V&A Engineers (V&A), subcontractor to RMC, from December 17, 2010 to February 21, Figure 2-2 shows the locations of the flow meters and rain gauges. The figure also shows the associated tributary area (basin) for each flow meter. Note that five of the meters (Meters FM 3, 4, 11, 13, and 16) were located downstream of other meters; therefore, the tributary areas shown for these meters in Figure 2-2 are the incremental areas between the flow meter and tributary basins of the upstream flow meters. Table 2-1 lists the flow meter locations, pipe diameters, and upstream meters. Sixteen of the meters were area-velocity type gravity flow meters, which record flow depth and velocity and compute flow rate based on average flow velocity and the cross-sectional area of flow (a function of flow depth and pipe diameter), and one of the meters was a pump logger installed at the Tierra Linda Pump Station. In addition to the data from the temporary meters, SBSA provided flow data for the San Carlos Pump Station. Meter ID Location Table 2-1: Flow Meter Locations Meter Manhole ID 1 Pipe Upstream Manhole ID Pipe Dia. (in.) 2 Upstream Meters FM1 Old County Rd. n/o Inverness Dr. AA/15 AD/ FM2 San Carlos Ave. w/o Arundel Rd. AF2/11 AW/ FM3 San Carlos Ave. w/o Arundel Rd. AF2/10 BE/01 15 Tierra Linda FM4 Cherry St. at El Camino Real AG/02 AG/ ,3 FM5 Industrial Way n/o Holly St. DA/02 DA/ FM6 Brittan Ave. at Greenwood Ave. AI/55 AI/ FM7 Brittan Ave. at Brook St. AI/64 AI/ FM8 Brittan Ave. at El Camino Real AC/15 AH/ FM9 Belmont Ave. w/o Elm St. AP/12 BA/ FM10 Belmont Ave. w/o Elm St. AQ/06A BA/ FM11 Brittan Ave. w/o Industrial Rd. AC/04 AC/ ,7,8,9,10,14,15 FM12 Francis Way w/o Elm St. AQ/55 AQ/ FM13 Industrial Rd. s/o Brittan Ave. AC/22 AC/ FM14 Orange Ave. n/o Brittan Ave. AI/28 AI/ FM15 Elm St. at Belvedere Ave. AQ/07 AQ/ FM16 Industrial Rd. at Holly St. MT/03 AA/01c 36 1,4,5,11,13 Tierra Tierra Linda Pump Station PS/05 B-1/01A NA -- Linda 1. Meter installed in inlet pipe to manhole (i.e., at downstream manhole of pipe). 2. Measured diameter. The purpose of the flow monitoring program was to quantify the flows in the system to provide data with which to calibrate the hydraulic model (discussed later in this chapter), and to quantify the I/I response to storm events in various areas of the system. Approximately 9 inches of rainfall (ranging from about 8.5 inches in the south to 9.5 inches in the northwest) fell during the two month flow monitoring period. Approximately 50 percent of the rainfall occurred during the latter part of December 2010 and approximately 40 percent during mid-february Figure 2-3 shows a typical plot of measured flow and rainfall for one flow meter. Appendix A includes plots of the rainfall and flow data for all of the rain gauges and meters. January

38 City of Belmont El Camino Real (State Hwy 82) Alameda De Las Pulgas Basin 5 Ralston Ave 101 FM 5 RG 2 SBSA RG 1 Tierra Linda Tierra Linda Basin Basin 2 Devonshire Blvd Basin 4 FM 2 FM 3 Basin 1 FM 1 San Carlos Ave Holly St FM 4 Basin 8 FM 16 Basin 16 FM 8 FM 11 Industrial Rd Basin 13 FM 13 Basin 3 Basin 6 Basin 14 FM 6 FM 14 Basin 11 FM 9 FM 10 FM 15 Crestview Dr FM 7 Basin 9 FM 12 Basin 7 Brittan Ave RG 3 Basin 12 Basin 15 Basin 10 Whipple Ave Basin 12 Alameda De Las Pulgas 280 Edgewood Rd City of Redwood City Jefferson Ave Basin Miles Emerald Lake Heights (most flow to Redwood City) #* Flow Meter ÔÕ Rain Gauge Modeled Sewer Unmodeled City Sewer County Sewer Meter Basin City of San Carlos Sewer Collection System Master Plan Flow Monitoring Sites & Tributary Areas Figure San Carlos Sewer Master Plan\G. GIS\MXDs\Figures for Report\2-2_Flow Monitoring Sites & Tributary Areas.mxd

39 Chapter 2 Hydraulic Model Development Figure 2-3: Plot of Typical Flow Data for Flow Monitoring Period (Meter 12) 2.4 Flow Estimating Methodology This section describes the methodology for estimating wastewater flows for loading to the hydraulic model Wastewater Flow Components Wastewater flows typically include three components: base wastewater flow (BWF), groundwater infiltration (GWI), and rainfall-dependent infiltration/inflow (RDI/I). BWF represents the sanitary and process flow contributions from residential, commercial, institutional, and industrial users of the system. GWI is groundwater that infiltrates into the sewer through defects in pipes and manholes. GWI is typically seasonal in nature and remains relatively constant during specific periods of the year. RDI/I is storm water inflow and infiltration that enter the system in direct response to rainfall events. RDI/I can occur through direct connections such as holes in manhole covers or illegally connected roof leaders or area drains (called direct inflow ), or through defects in sewer pipes, manholes, and service laterals. RDI/I typically results in short term peak flows that recede quickly after the rainfall ends. These three flow components are illustrated conceptually in Figure 2-4. Dry weather flow (DWF) consists of BWF plus GWI, while wet weather flow (WWF) adds the RDI/I component. January

40 Chapter 2 Hydraulic Model Development Figure 2-4: Wastewater Flow Components Base Wastewater Flow Existing residential and non-residential base wastewater flows were estimated using information compiled at the parcel level (approximately 10,300 parcels) and then aggregated into the 210 model subcatchments. The total residential and non-residential BWF for each model subcatchment were calculated by summing the BWF for all parcels within that subcatchment. Existing Flows Existing BWF was determined based on winter water use data by parcel obtained from the water purveyors that serve the City (California Water Service Company and Mid-Peninsula Water District). Metered water use during the winter months most closely approximates wastewater generation, since outdoor water use is at a minimum. Therefore, meter readings taken in the winter of 2010/2011 were used as the basis for estimating BWF. In some cases where water use data were not available, BWF was estimated based on typical unit flow factors for the type of parcel use (primarily single family dwellings). Future Flows Although the City is largely built out, there are several identified near-term planned development projects, as well as anticipated intensification consistent with the City s General Plan. Figure 2-5 shows the location of these areas of potential future development. January

41 «82 City of Belmont 101 El Camino Real (State Hwy 82) Alameda De Las Pulgas Ralston Ave 301 Industrial (PAMF) 285 Old County Rd 144/150 Elm Street Transit Village Holly St 501 Industrial Rd San Carlos Airport Devonshire Blvd San Carlos Ave 500 Walnut St 657/665 Prospect St Wheeler Plaza Transit Village 777 Walnut St 700 Chestnut/ 1501 Cherry 1001 Laurel St Industrial Rd Brittan Ave 1580 Laurel St Crestview Dr Alameda De Las Pulgas Whipple Ave 280 Edgewood Rd City of Redwood City Jefferson Ave « Miles General Plan Planning Areas Parcel with Potential Development/Redevelopment Near-Term Planned Development Projects San Carlos City Boundary City of San Carlos Sewer Collection System Master Plan Anticipated Development Areas Figure San Carlos Sewer Master Plan\G. GIS\MXDs\Figures for Report\2-5_Anticipated Dvpt Areas.mxd

42 Chapter 2 Hydraulic Model Development Table 2-2 lists each of the planned development projects and the type and quantity of proposed land uses. In addition to these specific projects, the General Plan identifies the potential for 3.4 million square feet of additional commercial, office, and light industrial development in the downtown area, along El Camino Real and the Caltrain corridor, and in the area to the east; and City s Housing Element lists vacant and underutilized residential sites with potential for 1,476 new housing units. Table 2-2 Planned Development Areas Area Planned Development Wheeler Plaza 139 multi-family units 14,355 sq. ft. retail 4,000 sq. ft. office 700 Chestnut/1501 Cherry Street 34 multi-family units 301 Industrial Road (Palo Alto Medical Foundation) 224,223 sq. ft. medical office 97-bed hospital 144/150 Elm Street 8 multi-family units 500 Walnut Street 4 multi-family units 1580 Laurel Street 4 dwelling units 2,100 sq. ft. commercial Transit Village 280 multi-family units 14,000 sq. ft. retail 16,000 sq. ft. office 285 Old County Road 26,840 sq. ft. light industrial 665 Prospect Street 7 clustered, detached units 501 Industrial Road 180-room hotel 220,565 sq. ft. office 1001 Laurel Street 90 multi-family units 657 Prospect Street 5 dwelling units 777 Walnut Street 28 dwelling units In addition to this potential development within the City, the unincorporated area adjacent to the Devonshire County Sanitation District, which is tributary to the City s sewer system, has several single family home parcels that are currently vacant. These sites were assumed to be developed for the future scenario (84 new single family homes assumed). The following flow factors were used to calculate BWF from future developments. These flow factors are based on an analysis of the City s water consumption data, as well as factors commonly used at the master planning level for similar communities. For residential properties: - Single family residential (SFR) = 190 gpd/unit - Multi-family residential (MFR) = 120 gpd/unit Hotels = 150 gpd/room January

43 Chapter 2 Hydraulic Model Development Non-residential properties = 0.12 gpd/sq.ft of building floor space Hospitals = 165 gpd/bed For developed parcels which are not included in any planned development or redevelopment areas, the estimated current flow was assumed to characterize their BWF in the future. BWF Diurnal Profiles In domestic wastewater systems, BWF varies throughout the day, typically peaking early on weekday mornings (later on weekends) and again in the evening hours in residential areas. BWF patterns in commercial and industrial areas depend on specific land use types but are typically characterized by a more uniform flow that lasts throughout working hours. The variations in BWF on a typical day are represented by diurnal profiles. Diurnal profiles are defined by a set of hourly factors that are applied to the average BWF for each subcatchment. For San Carlos, separate sets of diurnal profiles were defined for weekdays and weekends and for residential and non-residential development. Profiles were developed based on monitored flows for smaller meter areas that isolated specific land use types, and are similar to those observed in other similar communities. Figure 2-6 shows the diurnal profiles used in the model. Figure 2-6: Diurnal Profiles January

44 Chapter 2 Hydraulic Model Development Groundwater Infiltration GWI is typically applied in the model as a constant load in addition to the BWF. The amount of GWI in any particular area is determined during model calibration by comparing the modeled flows to actual observed dry weather flows at points in the system where flow meter data are available. Where modeled BWF is less than monitored dry weather flow, the difference is assumed to represent GWI. The GWI determined at the monitoring location is then distributed to the meter tributary area on a peracre basis. Note that because GWI is seasonal in nature, the modeled GWI represents a typical GWI rate during the wet weather season rather than a dry season (summertime) GWI Rainfall-Dependent I/I RDI/I flows result from rainfall events that produce infiltration and inflow of storm water runoff into the sewer system. RDI/I flows are defined by the magnitude, shape, and timing of the RDI/I response. RDI/I varies depending on many factors, including the magnitude and intensity of the storm event, area topography, type of soil, and the condition of the sewers, manholes, and sewer service laterals. In a dynamic model, RDI/I is typically computed as a percentage of the rainfall (sometimes referred to as the R value ) falling on the contributing area of a subcatchment for each of three or more hydrograph components, representing different response times to rainfall, e.g., fast, medium, and slow, as illustrated in Figure 2-7. (The contributing area is assumed to be the sum of the area of all developed parcels, except for large open areas such as parks and parking lots.) Summing all of the component hydrographs for the entire duration of the rainfall event results in the total RDI/I hydrograph for the event for that subcatchment. Note that although the slow RDI/I component can contribute significantly to the total RDI/I volume, the fast component has the biggest impact on the magnitude of the peak wet weather flow. Figure 2-7: RDI/I Hydrograph Components Fast Flow Medium Slow Time January

45 Chapter 2 Hydraulic Model Development The model parameters defining the RDI/I flows to the system within a given meter area are determined by comparing modeled wastewater flow at the meter location to the measured wastewater flow during one or more rainfall events, as discussed in the model calibration section later in this chapter. The same calibrated parameters are generally applied to all subcatchments within each meter area. 2.5 Model Calibration Model calibration is the process of comparing model-computed flows to observed (monitored) flows and adjusting various model parameters until the model is accurately simulating flows in the sewer system. The model was calibrated for both dry and wet weather conditions Dry Weather Calibration The 7-day dry period from January 23 to 29, 2011 was used as the dry weather calibration period for comparing flow data to the model results. This period was selected because it was not impacted by previous rainfall and a majority of the meters showed consistent readings. The primary focus of the dry weather calibration was to confirm that the calculated average BWF based on winter water consumption was consistent with the measured flows at the meter locations. The other objectives of the dry weather calibration were to confirm the flow routing in the system, particularly in areas where flow can be diverted in more than one direction (flow splits), as well as to confirm the diurnal profiles used to represent the hourly variations in BWF. The diurnal curves shown in Figure 2-6 were developed based on the calibration. Finally, GWI was added when the observed (metered) dry weather hydrographs were greater than the model-simulated hydrographs by a relatively constant value throughout the day. GWI was applied to seven of the meter basins, with rates ranging from 80 to 650 gpd/acre. The additional flow seen at the meters was distributed to upstream subcatchments on an area-weighted basis. It should be noted that it may be difficult to assess the actual amount of GWI, as the relative accuracy of the flow monitoring data, water consumption data, and other model assumptions will affect the amount of flow attributed to GWI. However, this methodology is considered adequate for modeling purposes. Table 2-3 summarizes the existing and future average BWF and DWF for the City s sewer system (including flow from outside tributary areas). In this table, DWF represents a dry (non-rainfall) period during the wet weather season, as was used for the dry weather model calibration. Table 2-3: Dry Weather Flow Summary Flow (mgd) Flow Component Existing Future (2010) Residential BWF Non-Residential BWF Total Average BWF Estimated Wet Season GWI Total Wet Season Average DWF Calculated based on difference between metered non-rainfall period flows and estimated BWF calculated from winter water use data. January

46 Chapter 2 Hydraulic Model Development Wet Weather Calibration During wet weather calibration, parameters are adjusted to accurately simulate the volume and timing of RDI/I for monitored storm events. The two-week period from December 17 through 30, 2010, was used as the primary period for wet weather calibration, with specific attention paid to the large storm on December 19, which generated an average of 1.7 inches of rainfall over a 12-hour period and an average peak hour intensity of 0.45 inches. Subsequent events in late December and in February were used for further verification of model calibration. Rainfall was assigned to subcatchments using data from the closest of three rain gages maintained by V&A during the monitoring period. The wet weather calibration resulted in a good match between modeled and metered flows for both peak and volume. Plots of model vs. metered flow for the December wet weather period are included in Appendix B. Total wet weather flows in the San Carlos system are also presented in the following section in the context of a Design Storm that is used for analysis and planning of sewer system capacity improvements (see Table 3-3, footnote 11). January

47 Chapter 3 Capacity Assessment and Capacity Improvement Program City of San Carlos Sewer Collection System Master Plan

48 Chapter 3 Capacity Assessment and Capacity Improvement Program Chapter 3 Program Capacity Assessment and Capacity Improvement The capacity performance of the system and need for capacity improvements were evaluated using the calibrated hydraulic model described in Chapter 2. This chapter discusses the criteria on which the capacity assessment was based and presents the model results and proposed capacity improvement projects. The potential benefits of reducing I/I in the system are also discussed. 3.1 Design Flow and Performance Criteria Sewer system capacity is assessed with respect to the system s performance under a design flow condition. The subsections below define the design flow criteria used for the capacity assessment and the criteria for assessing system performance and identifying system capacity deficiencies Design Storm Condition The use of wet weather design events as the basis for sewer capacity evaluation is a well-accepted practice. The approach is to first calibrate a hydraulic model of the system to match wet weather flows from observed storm(s), and then apply the calibrated model to a design rainfall event to identify capacity deficiencies and size improvement projects. The design event may be synthesized from rainfall statistics, or may be an actual historical rainfall event of appropriate duration and intensity. Other considerations for the design event include the spatial variation of the rainfall and the timing of the storm relative to the diurnal base wastewater flow pattern. Selection of a design rainfall event is typically based on an allowable level of risk, often expressed as the return period. It is recognized that while wet weather overflows are highly undesirable, it is not cost-effective to provide capacity for the largest possible storm event. Regulatory agencies have not adopted standard criteria for return periods, so each agency must choose a target return period based on desired level of service, potential impacts of overflows, and cost. As specified in the Consent Decree with Baykeeper, the City has used a synthetic 10-year recurrence frequency, 24-hour duration Design Storm for assessing the hydraulic capacity of its collection system. The 24-hour Design Storm rainfall for San Carlos ranges from 3.3 to 3.7 inches, depending on location, as determined from NOAA Atlas 14 Point Precipitation Frequency Estimates. 1 The Design Storm includes shorter durations of intense rainfall as determined by the distribution curve for a Type IA storm as referenced in Appendix B of the USDA guidance document Urban Hydrology for Small Watersheds TR-55 (June 1986), with a peak hour intensity ranging from 0.52 to 0.58 inches. The timing of the design storm also affects the resultant peak wet weather flows. If the design storm is timed such that the peak RDI/I occurs at the same time as the peak BWF ( peak-on-peak ), the total PWWF will be higher than if the design storm occurs under average or minimum BWF conditions. The City has elected to set the timing of the design storm rainfall such that the peak RDI/I resulting from the design storm occurs at or near the time of peak BWF flow (which typically occurs around 7 a.m. on a weekday) for most areas of the system. Timing the storm to produce peak-on-peak results is generally thought to create a return period of the peak wastewater flow that is greater than the return period of the design rainfall event. Figure 3-1 shows a histogram of the Design Storm rainfall at the location of the Tierra Linda Pump Station. The design storm is comparable in size to other notable large rainfall events that have occurred over the past several years, such as the storms of December 31, 2005 and January 25, January

49 Chapter 3 Capacity Assessment and Capacity Improvement Program Figure 3-1: Design Rainfall Event 0.70 Design Storm SCS 10 Yr, 24 Hr, Type IA (at Tierra Linda PS) Rainfall (in/hr) Time For future scenarios, the sewer system s response to rainfall is assumed to remain the same as existing conditions (other than for alternative scenarios in which targeted I/I reduction is considered). This implies that any increase in I/I due to deterioration of existing sewers will be offset by a decrease due to sewer rehabilitation or replacement, and that new sewers and laterals will contribute minimal I/I flows Capacity Deficiency Criteria Capacity deficiency or performance criteria are used to determine when the capacity of a sewer pipeline or pumping facility is exceeded to the extent that a capacity improvement project (e.g., a relief sewer, larger replacement sewer, or pump station capacity expansion) is required. Capacity deficiency criteria are sometimes called trigger criteria in that they trigger the need for a capacity improvement project. These criteria may differ from design criteria that are applied to determine the size of a new facility, which may be more conservative than the performance criteria. It is important that the capacity deficiency criteria be coordinated with the peak design flow criteria. For example, if the peak design flow considers only peak dry weather flow and little or no I/I, the deficiency criteria should be conservative (e.g., require pipes to flow less than full under dry weather flow to allow capacity for I/I that may increase the flow under a wet weather condition). On the other hand, if the peak design flow includes I/I from a large, relatively infrequent design storm event, it is appropriate to allow the sewers to flow full or even surcharged to some extent, since the peak flows will be infrequent and brief in duration. For San Carlos, since the design storm PWWF represents an infrequent, 10-year return period event coinciding with a conservative BWF condition, the City considers it acceptable to allow surcharging over the pipe crown, provided the hydraulic grade line (water level) remains at least four feet below the ground surface. However, areas where the risk of overflow is greatest, as defined by surcharging January

50 Chapter 3 Capacity Assessment and Capacity Improvement Program to within one foot of the ground, would be considered the highest priority for near-term capital improvements. Under peak dry weather conditions, sewers should be able to convey the peak flow without surcharge. Performance criteria for pump stations are based on their firm capacity, defined as pumping capacity with the largest pumping unit out of service. Force mains are considered to be capacity deficient if maximum velocity exceeds 8 feet per second (fps) under design peak wet weather flow or 6 fps under normal peak dry weather flow. 3.2 Capacity Analysis Results The calibrated model was run for existing and future conditions to identify areas of the system that fail to meet the specified performance criteria under design storm peak wet weather flows. No capacity deficiencies in the system were identified for dry weather conditions Gravity Sewer System Deficiencies Figure 3-2 shows the location of model-predicted surcharged sewers and potential overflows under future Design Storm peak wet weather flow conditions. Pipes shown in red are predicted to be surcharged due to throttle conditions, indicating that the full pipe capacity of the pipe is less than the predicted peak flow. Pipes shown in orange are predicted to be surcharged due to backwater from a downstream throttle condition. The locations of model-predicted overflows under the Design Storm are shown as blue circles in the figure. It should be noted that the location of model-predicted overflows may not reflect the actual locations where overflows would occur or have occurred in the past, due to other physical conditions (e.g., root intrusion or debris) that are not reflected in the model, or system storage that is available in the smaller diameter, unmodeled pipes. However, historical wet weather overflows have occurred in the vicinity of several of the locations where overflows are predicted by the model. As noted above, predicted surcharge in a particular pipe does not necessarily indicate a capacity deficiency at that particular location, as flows can back up due to a downstream capacity deficiency and cause extensive surcharging or even overflows upstream due to backwater effects. However, relieving upstream deficiencies can also create additional or more severe capacity deficiencies downstream of the relieved pipe. For example, providing relief for the capacity deficiencies identified along Brittan Avenue would increase the flows to the downstream sewers in Industrial Road, thereby increasing the peak flow and predicted surcharge and potential overflows in those lines. These effects were considered in developing the capacity improvement projects described later in this chapter. Based on the model calibration runs, the predicted surcharged conditions along Brittan Avenue, Belmont Avenue, Industrial Road, and Elm St (near Belmont Ave) were also predicted to occur under the December 19, 2010 storm observed during the flow monitoring period, and were confirmed by flow monitoring data for several of the meters that were located along those reaches. Wet weather overflows have, in fact, occurred at or near many of these locations during past large storm events. Other locations with model-predicted surcharge that have experienced historical overflows include the areas around Arroyo Avenue and Elm Street, Windsor Drive near Devonshire Boulevard, and De Anza Avenue near Maple Way. January

51 «82 City of Belmont 101 El Camino Real (State Hwy 82) Alameda De Las Pulgas Ralston Ave SBSA San Carlos PS ") Holly St San Carlos Airport!(!(!(!(!(!(!( San Carlos Ave Industrial Rd!( Devonshire Blvd!(!(!(!(!( Brittan Ave!(!(!( Crestview Dr!(!( Alameda De Las Pulgas Whipple Ave 280 Edgewood Rd City of Redwood City Jefferson Ave « Miles!( Modeled SSO Modeled Manhole Modeled Sewer Surcharge (backwater) Surcharge (throttle) Unmodeled City Sewer County Sewer City of San Carlos Sewer Collection System Master Plan Predicted Areas of Sewer Surcharge Under Design Storm Peak Wet Weather Flow Figure San Carlos Sewer Master Plan\G. GIS\MXDs\Figures for Report\3-2_Model Results.mxd

52 Chapter 3 Capacity Assessment and Capacity Improvement Program Pump Stations The City operates seven sewer pump stations, three of which (Tierra Linda, the Associate, and the Industrial Road wet weather booster station) are included in the modeled network. The modeled pump stations were evaluated as part of the capacity assessment to determine if they had adequate capacity to convey future design peak wet weather flows. The four unmodeled pump stations in the City s system serve small areas; two of them (Kelly Moore I and II) serve a single commercial customer, and the other two pump stations together (Upper and Lower Crestview) serve fewer than 60 single family homes. Except for Kelly Moore II, all of these pump stations are equipped with duty and standby pumps, and City operators report that only one pump is needed during rainfall events. Additional information about the City s pump stations is summarized in the Technical Memorandum on Sewer Pump Station Condition Assessment included in Appendix D. The total and firm capacities for the modeled pump stations were determined using manufacturer pump curves and information from pump station surveys prepared by City staff compared to system curves estimated based on required lift and force main headlosses. Table 3-1 compares the total and firm capacity of the Tierra Linda and Associate Pump Stations to the modeled flows under existing and future flow conditions. The table indicates that both stations have sufficient total capacity to convey design storm peak wet weather flows, but the Tierra Linda Pump Station does not have sufficient firm capacity. However, that pump station has a high-level gravity overflow line that would allow flow to be bypassed to the City of Belmont sewer system if one pump were to go out of service during a peak wet weather event. Pump Station Table 3-1: Pump Station Capacity Results No. of Pumps Total Capacity (mgd) Firm Capacity 1 (mgd) Existing PWWF (mgd) Future PWWF (mgd) Tierra Linda The Associate Capacity with largest pump out of service. The Industrial Road booster pump station has a single pump designed to operate only during high wet weather flows to help alleviate surcharge in the Industrial Road trunk sewer. However, the model results indicate this facility would be ineffective for preventing potential overflows under a design storm event. 3.3 Capacity Improvement Projects This section describes the sewer improvement projects that would be needed to reduce the risk of overflows in the collection system due to insufficient capacity for design peak wet weather flows. The assumptions that were used to define the projects are also discussed. Each project is documented in further detail in Appendix C with an individual plan map and project information sheet that provides project details, key considerations, and planning-level construction and capital cost estimates. Capacity improvement projects were identified to address the potential deficiencies identified through the capacity analysis. For each identified gravity sewer capacity deficiency, a project was developed to replace the existing pipe with a larger pipe, or to divert flow to a new pipe or to another existing pipe with available capacity. January

53 Chapter 3 Capacity Assessment and Capacity Improvement Program Figure 3-3 shows an overview of the collection system capacity project locations, and Table 3-2 lists all of the identified capacity improvement projects, including location, description of proposed improvements, and estimated planning level costs. Eleven of the projects are considered high priority (model-predicted overflow or surcharge to less than 1 foot below ground under design storm PWWF conditions) and would be included in the City s 5-year capacity improvement program as required under the Consent Decree. The remaining five projects (identified with a prefix M ) include relief for sewers in which the model-predicted surcharge level under design storm PWWF is between 1 and 4 feet below ground; and a pump upgrade for the Tierra Linda Pump Station to provide additional firm capacity. Explanation of project sizing criteria and basis of cost estimates is provided in the following subsections. Prioritization of projects as part of the overall sewer system capital improvement program is discussed in Chapter Project Sizing Criteria For gravity sewer capacity improvement projects identified as part of this Master Plan, replacement or new pipes were sized to convey the future Design Storm PWWF with no (or only minimal) surcharge. Existing pipe slopes and depths were preserved when upsizing sewers in-place. Model runs with all capacity projects in place were made to determine the impact of increased capacity from upstream projects on peak flows in pipes downstream of those projects to verify that no additional collection system capacity deficiencies would result Cost Criteria Costs for capacity improvement projects were estimated based on input from the City and RMC experience with similar projects. These cost estimates are planning or conceptual level estimates, and are considered to have an estimated accuracy range of -30 to +50 percent. This level of accuracy corresponds to an order of magnitude or Class 5 cost estimate as defined by the American Association of Cost Estimators. These estimates are suitable for use for budget forecasting, CIP development, and project evaluations, with the understanding that refinements to the project details and costs would be necessary as projects proceed into the design and construction phases. All costs have been adjusted to an Engineering News Record Construction Cost Index (ENR CCI) of approximately 10,208, which represents the January 2012 ENR CCI for the San Francisco Area. Cost criteria include baseline unit construction costs for gravity sewers using open-cut and trenchless (e.g., pipe bursting) methods. Pipe bursting is assumed for most projects that involve upsizing existing sewers to 15-inch diameter or smaller; construction of new sewers or pipes larger than 15 inches assumes open cut construction, except where trenchless construction would be required for major crossings (e.g., of Highway 101). Costs for gravity trunk sewers vary with pipe diameter and depth (in the case of open-cut construction), and include replacement of lower laterals and installation of cleanouts at the property line. Allowances added to the baseline construction cost include mobilization/demobilization and project-specific costs for bypass pumping for pipe bursting and remove and replace construction, traffic control for work in roadways, and a delay factor (additional construction time) for remove and replace projects. A 30 percent allowance for contingencies for unknown conditions was also included for all projects, as well as an allowance of 25 percent of construction cost for engineering, administration, and legal costs. January

54 « City of Belmont Harbor Industrial Sewer Maintenance District El Camino Real (State Hwy 82) Alameda De Las Pulgas Industrial Rd Ralston Ave SBSA San Carlos PS ") Holly St ' M5 ") Tierra Linda PS Upgrade (Project M5) ' 1 ' 2 San Carlos Ave ' 11 New Industrial Rd PS (Project 11) ") Devonshire County Sanitation District ' M1 Devonshire Blvd ' 5 ' 4 Brittan Ave ' 7 ' 8 ' 9 ' M4 ' 10 Crestview Dr ' 4 ' 3 ' 6 ' M3 ' M2 Alameda De Las Pulgas Whipple Ave 280 Unincorporated Palomar Park (Septic Systems) Scenic Heights County Sanitation District Edgewood Rd City of Redwood City Jefferson Ave Miles Emerald Lake Heights Sewer Maintenance District ' # ' # High Priority Capacity Improvement Project and ID Other Capacity Improvement Project and ID ") Pump Station Project Modeled Sewer Unmodeled City Sewer County Sewer City of San Carlos Sewer Collection System Master Plan Overview of Capacity Improvement Projects Figure San Carlos Sewer Master Plan\G. GIS\MXDs\Figures for Report\3-3_Overview of Capacity Improvement Projects.mxd

55 Chapter 3 Capacity Assessment and Capacity Improvement Program Table 3-2: Capacity Improvement Projects Project No. Project Name Description Estimated Construction Cost Estimated Capital Cost 1 2 San Carlos Avenue/Beverly Drive Cedar Street/Manzanita Avenue Upsize 400 ft. of 6 sewer to 8 pipe in San Carlos Ave. north of Beverly Dr. Upsize 2,000 ft. of 6 & 8 sewer to 8, 10 & 12 pipe in Cedar St. and Manzanita Ave.; construct 500 ft. of new 12 pipe to divert flows to exist. 18 sewer in Cedar St. $ 138,000 $ 173,000 $ 722,000 $ 903,000 3 Brittan Avenue (Hewitt) Upsize 500 ft. of 8 sewer to 10 pipe in Brittan Ave. west of Hewitt Dr. $ 143,000 $ 178,000 4 Brittan Avenue Diversion 5 Arroyo Avenue 6 De Anza/Alameda De Las Pulgas/Edgewood 7 Orange Avenue Diversion 8 Belmont Avenue 9 Brittan Avenue Parallel to Industrial Road 10 Industrial Road South Upsize 2,500 ft. of 12 sewer to 15 pipe in Brittan Ave. from Orange Ave. to east of Laurel St; construct new 12 pipe to divert flows from 6 to 15 sewers in Brittan Ave. at Alameda De Las Pulgas. Upsize 1,100 ft. of 6 sewer to 8 pipe from west of Woodland Ave. to Walnut St.; construct 700 ft. of new 10 sewer between Walnut St. and exist. 12 trunk sewer at El Camino Real. Upsize 600 ft. of 6 sewer to 8 pipe in De Anza Ave. from Robin Way to east of Maple Way; upsize 1,100 ft. of 8 sewer to 10 pipe in Alameda De Las Pulgas and Edgewood Dr. east of Wildwood Ave. Construct 200 ft. of new 10 sewer in Orange Ave. from easement sewer parallel to Belmont Ave. to exist. 10 sewer in Belmont Ave. Upsize 1,100 ft. of 12 sewer to 15 pipe in Belmont Ave. from west of Rosewood Ave. to east of Laurel St. Construct 1,200 ft. of new 18 parallel sewer in Brittan Ave. from Old County Rd. to east of Industrial Rd. Construct 1,600 ft. of new 12 parallel sewer in Industrial Rd. from American St. to Brittan Ave. $ 410,000 $ 513,000 $ 378,000 $ 472,000 $ 504,000 $ 630,000 $ 53,000 $ 66,000 $ 229,000 $ 286,000 $ 341,000 $ 426,000 $ 338,000 $ 422,000 January

56 Chapter 3 Capacity Assessment and Capacity Improvement Program Project No. Project Name Description Estimated Construction Cost Estimated Capital Cost 11 New Industrial Road Pump Station and Force Main Construct 400 ft. of new 15 parallel sewer in Industrial Rd. from Brittan Ave. to exist. Booster PS site; construct new 5.3-mgd pump station and 4,400 ft. of 12 force main in Industrial Rd., Bransted Rd., and Skyway Rd. to the exist. San Carlos PS in Monte Vista Rd. $3,755,000 $4,733,000 Subtotal Near-Term Projects $7,011,000 $8,802,000 M1 M2 M3 Devonshire Boulevard/ Windsor Drive Pearl Avenue Alberta Avenue Diversion Upsize 700 ft. of 8 sewer to 10 pipe in Devonshire Blvd. west of Windsor Dr. and Windsor Dr. south of Devonshire Blvd. Upsize 1,300 ft. of 12 sewer to 15 pipe in Pearl Ave. from Eaton Ave. to Alberta Ave. and Alberta Ave. west of Pearl Ave. Construct new 12 pipe to divert flows from 8 sewer in easement parallel to Cedar St. to 15 sewer in Alberta Ave. $ 183,000 $ 229,000 $ 216,000 $ 270,000 $ 48,000 $ 61,000 M4 Elm Street Upsize 400 ft. of 8 sewer to 10 pipe in Elm St. south of Belmont Ave. $ 99,000 $ 124,000 M5 Tierra Linda Pump Station Upgrade Replace two existing pumps with larger (20 HP) pumps. 1 $ 75,000 $ 95,000 Subtotal Additional Projects $ 621,000 $ 779,000 Total All Capacity Improvement Projects $7,632,000 $9,581, Feasibility of pump replacement would need to be assessed based on analysis of pump curves and size of wet well; generator upgrade might also be required. January

57 Chapter 3 Capacity Assessment and Capacity Improvement Program Detailed Project Descriptions Detailed descriptions and maps of the collection system capacity improvement projects are presented in Appendix C. The descriptions are each contained on a single page and follow a standard format that consists of a summary project description (project location, length, pipe sizes, estimated capital cost, and discussion of any specific project assumptions, issues, or other considerations) followed by a detailed planning level cost breakdown. The maps show the projects on an aerial photo background, indicating the project pipe segments, manhole IDs, and existing and proposed pipe sizes Coordination with SBSA The results of the modeling of proposed pipe capacity improvements indicate that peak flows reaching the San Carlos Pump Station during the Design Storm, after construction of the recommended capacity improvement projects, would be about 25.4 million gallons per day (mgd) under existing development conditions and 26.6 mgd with future development included. These flows exceed the City s current capacity allocation in the SBSA system. SBSA is currently implementing a capital improvement program to significantly upgrade its system, including capacity increases to the San Carlos Pump Station and downstream force mains. It is recommended that the City work closely with SBSA to ensure that the capacity improvement programs of the two agencies are coordinated. 3.4 Infiltration/Inflow The San Carlos wastewater collection system is subject to significant amounts of I/I, resulting in high peak flows during wet weather events. As described previously, the flow monitoring data and hydraulic model were used to characterize the I/I response in various areas of the system and to quantify the peak I/I and peak wet weather flows generated in each area. Table 3-3 summarizes the I/I response in each meter basin in terms of peak RDI/I per acre of contributing sewered area, and the ratio of PWWF to ADWF, referred to as the wet weather peaking factor, for the Design Storm. Wet weather peaking factors based on the model-predicted flow for the 10-year Design Storm range from about 4 to over 25. Figure 3-4 shows the range of wet weather peaking factors by area, and Figure 3-5 shows peak RDI/I per acre. The highest peaking factors (greater than 15) occur in Basins 5 and 14. However, the flow data for Basin 5, which includes the Harbor Industrial Sewer Maintenance District, indicated sporadic spikes, not all of which were associated with rainfall (it is also suspected that there may be a sewer connection from the City of Belmont collection system that is impacting the flows in this basin), and no capacity deficiencies were identified in this area. Many other parts of the system exhibit wet weather peaking factors exceeding 10. Areas with particularly high peaking factors and peak RDI/I rates include Basins 1, 2, 8, 9, 10, 12, and 14. Many of the capacity deficiencies in the system were found in the trunk sewers serving these areas with high I/I. Field investigations, such as smoke testing and closed-circuit television (CCTV) inspection, would help confirm the potential sources of the I/I in these areas. Based on experience in similar communities, it is likely that the primary sources are defects in sewer pipes, manholes, and service laterals. A cursory analysis was conducted to determine if reducing peak RDI/I in targeted areas of the system could eliminate the need for some capacity improvement projects. Specifically, RDI/I reductions of 30 percent were applied to the fast and medium response components of RDI/I (see Figure 2-7) in Basins 1, 8, and 14, which would have the greatest impact on the Cedar Street, Arroyo Avenue, and Brittan Avenue capacity improvement projects. The results indicated that this level of RDI/I reduction would have little impact on the need for the identified capacity improvements. Higher levels of RDI/I reduction would require much more aggressive and costly programs, and would not be practical nor cost-effective to implement in the near-term. January

58 Chapter 3 Capacity Assessment and Capacity Improvement Program Sewer Basin 1 Contributing Area (ac.) 6 Table 3-3: Peak I/I by Sewer Basin ADWF (mgd) 7 Peak RDI/I (mgd) 8 PWWF (mgd) 9 Unit Peak RDI/I Rate (gpd/ac) Wet Weather Peaking Factor 10 Tierra Linda , , , , , , , , , , , , , , , , , Total 5 3, , Note: Basin flows based on existing development (not including future growth). mgd = million gallons per day. 1. For meters with upstream basins, represents the incremental meter basin area, as shown on Figure Basin 3 includes the Devonshire County Sanitation District. 3. Basin 5 includes the Harbor Industrial Sewer Maintenance District. Flow data indicated sporadic spikes, not all of which were associated with rainfall. It is also suspected that there may be a sewer connection from the City of Belmont collection system that is impacting the flows in this basin. 4. Basin 12 includes the Scenic Heights County Sanitation District and a portion of the Emerald Lakes Sewer Maintenance District. 5. Includes small unmetered area (approximately 100 acres). 6. Net area of developed parcels. 7. Average dry weather flow. Includes groundwater infiltration during non-rainfall periods, representing approximately 10 to 15 percent of ADWF. 8. Peak rainfall-dependent I/I flow for Design Storm. Represents sum of peak flows for individual subcatchments within each basin. 9. Peak wet weather flow for Design Storm. Represents sum of peak flows for individual subcatchments within each basin; does not reflect flow routing through the system (which would typically reduce the peak flows). 10. Ratio of PWWF to ADWF for Design Storm. 11. Sum of basin flows; does not reflect flow routing through system. Total estimated PWWF to San Carlos Pump Station without collection system capacity improvements is 23.1 mgd; with capacity improvements, estimated PWWF is 25.4 mgd under existing conditions and 26.6 mgd with future development included. January

59 101 City of Belmont El Camino Real (State Hwy 82) Alameda De Las Pulgas Basin 5 Unmetered Ralston Ave Basin 1 Holly St Tierra Linda Basin Basin 16 Basin 2 San Carlos Ave Industrial Rd Devonshire Blvd Basin 4 Basin 8 Basin 13 Basin 14 Brittan Ave Basin 11 Basin 3 Basin 6 Crestview Dr Basin 9 Basin 7 Basin 10 Basin 12 Alameda De Las Pulgas Basin 15 Whipple Ave 280 Edgewood Rd Basin 12 City of Redwood City Jefferson Ave « Miles Wet Weather Peaking Factor < >15 Modeled Sewer Unmodeled City Sewer County Sewer City of San Carlos Sewer Collection System Master Plan Wet Weather Peaking Factors for Design Storm Figure San Carlos Sewer Master Plan\G. GIS\MXDs\Figures for Report\3-4_Wet Weather Peaking Factors.mxd

60 City of Belmont El Camino Real (State Hwy 82) 101 Alameda De Las Pulgas Basin 5 Unmetered Ralston Ave Basin 1 Holly St Tierra Linda Basin Basin 16 Basin 2 San Carlos Ave Industrial Rd Devonshire Blvd Basin 4 Basin 8 Basin 13 Basin 14 Brittan Ave Basin 11 Basin 3 Basin 6 Crestview Dr Basin 9 Basin 12 Basin 15 Basin 7 Basin 10 Alameda De Las Pulgas Whipple Ave 280 Edgewood Rd Basin 12 City of Redwood City Jefferson Ave « Miles Peak RDI/I Rates (gpd/acre) < 3,000 3,000-5,000 5,000-10,000 > 10,000 Modeled Sewer Unmodeled City Sewer County Sewer City of San Carlos Sewer Collection System Master Plan Peak RDI/I Rates for Flow Meter Basins for Design Storm Figure San Carlos Sewer Master Plan\G. GIS\MXDs\Figures for Report\3-5_RDII Rates.mxd

61 Chapter 3 Capacity Assessment and Capacity Improvement Program That said, however, the City recognizes the benefit of reducing I/I in the long-term, as reducing I/I also reduces the costs for pumping and treatment. If achieved through sewer rehabilitation and replacement, I/I reduction provides the added benefit of further improving the condition of the sewer system, which in turn could reduce maintenance requirements and the risk of dry weather blockages and overflows. Therefore, it is in the City s best interest to construct needed capacity improvements in order to minimize the potential near-term risks of wet weather overflows from the collection system, but at the same time, continue a long-term program of sewer rehabilitation to improve the overall condition of the system and reduce I/I systemwide. Potential methods of I/I source detection and control are described below. Specific I/I reduction approaches recommended for the City are discussed in Chapter I/I Source Detection and Control Methods A necessary step in identifying potential I/I control measures is a realistic assessment of the actual sources of I/I in the collection system. Based on the pattern and magnitude of flows in the City s collection system, the likely sources of RDI/I flows are defects in sewers and service laterals, and possibly some direct connections (e.g., illegally connected roof and area drains, direct connections from the storm drain system, etc.). Appropriate I/I control methods depend on the type and sources of I/I. Control methods must include detection as well as correction. Potential methods are described in the following paragraphs. Direct Inflow Sources Direct inflow sources can contribute significantly to both volume and peak rates of I/I, and have the greatest probability of being cost effective to eliminate. The main methods used to detect and locate direct inflow sources are smoke and dye testing (dye testing is used primarily as a confirmatory test). Smoke testing is considered to be a relatively easy and inexpensive method (cost is approximately $0.50 per foot if a substantial length of pipe is tested), and discovery of just a few direct storm drain cross-connections, for example, can make the effort worthwhile. However, unless there is some indication or knowledge of the existence of direct connections in the system, finding them may require an extensive smoke testing program, which requires public notification measures and access onto private property to document the smoke returns. For this reason, smoke testing is generally targeted at specific areas with high peak RDI/I rates. Elimination of direct inflow connections requires disconnection of the source and re-direction of the drainage to an appropriate location. This may simply be to the ground surface (as in the case of roof drains), or connection to a nearby storm drain or street gutter. In general, each identified source needs to be evaluated on a case-by-case basis to identify the appropriate corrective measure. Generally the most numerous type of sources found during smoke testing are not direct inflow connections but defects in shallow pipes, primarily laterals. Rehabilitation of laterals may be a challenging institutional issue (see discussion below on correction of private property I/I sources). Manholes subject to ponding or located in drainage courses are also considered to be sources of direct inflow. The amount of I/I depends on the manhole location, type of manhole cover (number and size of holes), and the condition of the cover and frame. Physical inspection of manholes is the most effective way to identify such conditions, and correction is relatively straightforward (replace cover, realign frame, raise manhole to grade, remove or relocate manhole in watercourse, etc.). Physical inspection can be conducted in conjunction with sewer inspection or routine cleaning work, or as a separate activity. Infiltration Sources in Sewer Mains and Manholes Infiltration sources are defects in sewer pipes or manholes caused by defective materials or construction, general deterioration, or damage caused by physical conditions such as ground January

62 Chapter 3 Capacity Assessment and Capacity Improvement Program movement or settlement, traffic loads, or root intrusion. Infiltration sources (defects) are detected by inspection: visual inspection in the case of manholes and CCTV inspection for sewer mains. However, visual observation of active I/I is generally not feasible since the RDI/I generally occurs for only short periods during rainfall events, and the pipes may fill up during those periods, making CCTV inspection difficult or impossible. Infiltration correction methods involve rehabilitation or replacement of entire pipe segments or manholes or spot repair of localized defects. There are numerous materials and methods used for this type of rehabilitation. In general, however, the cost per unit amount of I/I removed is relatively high, since the defects individually contribute relatively small amounts of flow. It is recognized that infiltration in the sewer system will migrate to other nearby defects that are left un-repaired. Therefore, a fairly extensive area of the system may need to be included in the rehabilitation effort in order to achieve substantial flow reduction. Furthermore, reductions greater than about 30 percent can rarely be achieved without also addressing the infiltration from private laterals. Generally, rehabilitation to reduce infiltration is cost effective only if a significant amount of infiltration can be isolated to a relatively small area, or there are extremely costly improvements required downstream to convey, treat, and dispose of the excess flow. I/I Sources on Private Property I/I sources on private property are primarily defective laterals, but may also include broken cleanouts or cleanout caps, or directly connected roof and area drains. Smoke testing is the primary method for detecting private property I/I sources. For more aggressive programs, building or property inspections can be conducted, and/or laterals can be CCTV inspected or tested for leaks using air or water pressure tests. These types of inspections and tests generally require that the lateral have cleanout access, ideally at both the connection to the building plumbing and at or near the property line. However, new technologies are now available, such as cameras that can be launched up the lateral during CCTV inspection of the mainline, that make it easier to inspect private laterals. One method that has been implemented by a number of sewerage agencies is an ordinance requiring testing or inspection of the sewer lateral at the sale of the property (and/or other triggers such as change in property use or major remodel). If the lateral fails to pass the inspection or test, then appropriate repairs must be made before the sale can close or as a condition of the building permit. In many areas where the problems caused by I/I and the need for sewer and lateral rehabilitation was effectively communicated to the community, a lateral ordinance was found to be an effective way to implement a private property rehabilitation program with the least financial impact on the public agency. Grant or loan programs can also reduce the financial impact on property owners, or the City may be able to negotiate reduced prices for lateral rehabilitation with contractors, for example, in an area where the sewer mains are also being rehabilitated or replaced as part of a City project.. January

63 Chapter 4 Condition Assessment and Rehabilitation/ Replacement Program City of San Carlos Sewer Collection System Master Plan

64 Chapter 4 Condition Assessment and Rehabilitation/ Replacement Program Chapter 4 Condition Assessment and Rehabilitation/ Replacement Program This chapter describes the process used to assess the condition of the gravity sewer system by closedcircuit television (CCTV) inspection, the methods used to analyze the data to identify needed repairs and rehabilitation/replacement (R/R) needs, and presents the recommended sewer system R/R program. The recommended gravity sewer R/R projects are included in the capital improvement program presented in Chapter 5. The program is based on characteristics of the City s sewer system and results of sewer inspections performed in As the City continues its inspection program to include the remaining portions of the system, the R/R program will be updated to reflect additional information. An assessment of the condition of the system pump stations, based on site visits, interviews with City staff, and review of available documents, was also conducted as part of this project. However, no significant capital improvement projects were identified based on the assessment. A copy of the Technical Memorandum on the Sewer Pump Station Condition Assessment is included in Appendix D. 4.1 Sewer Condition Assessment Methodology CCTV inspection is the basic method used by the City to assess gravity sewer condition. This section describes the City s program, including data documentation standards and condition grading CCTV Inspection Program The City initiated its CCTV inspection program in 2010 with the development of standards, specifications and contract documents for a City-Wide Sanitary Sewer Cleaning and Inspection Program. An inspection contractor, Advanced Sewer Technologies, was hired to perform the initial work under the program. Over 60 percent of the system was inspected from January through September The data collected in 2011 was used to perform the condition assessment and develop the R/R program presented in this report. The City has hired National Plant Services for the second phase of the program to inspect the remaining portion of the system. This work is anticipated to be completed by the end of Following completion of this phase of the work, City will update the condition assessment to incorporate the additional inspection data. Effective use of CCTV inspection data requires that the data recorded be consistent, complete, and of high quality; and that it is captured in a format that can be readily accessed for analysis. Current industry best practice is to use Pipeline Assessment and Certification Program (PACP) standards developed by the National Association of Sewer Service Companies (NASSCO), which specifies observation codes and grades to be applied to all structural and maintenance-related defects. The City s CCTV program utilizes PACP standards and WinCan CCTV software to capture the data, video, and still images. During the CCTV inspection work, City staff conducted quality control/quality assurance (QA/QC) review of the data delivered by the contractor to ensure that pipe segments were accurately identified by upstream and downstream manhole IDs, that observed defects were properly coded, and that the quality of the video provided was acceptable. The contractor was required to correct deficiencies in the data identified by the City s review. In addition, any critical defects discovered through the inspection were immediately assessed to identify the need for near-term repairs. Specifically, in accordance with its Consent Decree with Baykeeper, the City was required to repair certain types of severe defects (e.g., collapsed or broken pipe) within 30 days (this timeframe has since been relaxed based on a subsequent stipulated agreement with Baykeeper) Condition Grading and Rating Under the PACP standard, all structural defects are assigned a condition grade of 1 to 5, with Grade 5 representing severe defects that require attention in the short-term and Grade 1 representing minor January

65 Chapter 4 Condition Assessment and Rehabilitation/ Replacement Program defects. The grades for individual defects observed on a manhole-to-manhole pipe segment can be combined in various ways to determine an overall structural condition rating for the pipe. The PACP manual suggests several formulas for this purpose, including summing the grades of all defects or averaging the grades. While such formulas may be useful for screening pipes in terms of overall condition, they are not particularly useful for deciding which pipes require immediate or near-term attention. What is most important in such decisions is the presence of major defects and the number of such defects. For example, a single Grade 5 defect in a pipe requires action, while five Grade 1 defects do not, even though they have a PACP Segment Grade Score of 5. The number of major defects is significant since it helps determine whether point repair(s) or manhole-to-manhole rehabilitation (e.g., lining) or replacement would be most appropriate. Because it provides the best overall rating method for the purposes of decision making, the PACP Structural Quick Rating (SQR) has been used in this report as the primary rating system for condition assessment. The rating is a four-digit code that indicates the number of defects having the two highest grades. For example, a SQR of 5132 indicates the worst defect was a Grade 5 defect (of which there was only one occurrence), and the next worst defect was Grade 3 (of which there were 2 occurrences). 4.2 Rehabilitation/Replacement Decision Process Based on the inspection data collected under the City s CCTV inspection program, a formal decision process was developed to facilitate the use of the data in determining appropriate actions to repair, rehabilitate, or replace defective sewers pipes or to continue to monitor and maintain sewers that are not in need of renewal in the near future. In the context of the discussion in this report, the terms renewal and rehabilitation/replacement are used to designate any type of action that results in a structural improvement to the sewer pipe, including a point repair, short-segment lining, or lining or replacement of an entire manhole-to-manhole pipe reach. The decision process is designed to set clear criteria for pipes requiring accelerated actions, pipes requiring renewal, and selection of an appropriate repair, rehabilitation, or replacement method. The process is illustrated in the flow diagram in Figure 4-1. The diagram depicts how the data for each pipe segment is systematically evaluated using decision points to drive an objective preliminary decision outcome based on its condition, the types of defects it contains, and the estimated cost-effectiveness of various renewal methods. The input, decision points, and potential decision outcomes are described in Table 4-1 and discussed in more detail below. The decision outcomes resulting from the decision process are intended to support review of the CCTV inspection data. Outcomes from the decision process recommending a renewal action are further reviewed to validate the decision. The review consists of detailed review of CCTV inspection defect data as well as viewing of selected video or defect photo images and CCTV reports as required. In addition, other factors such as pipe capacity, location, maintenance history, and constructability issues might be assessed and considered. Finally, other considerations, such as a goal of reducing infiltration, could also influence the choice of renewal method for a particular pipe or area of the system Defect Categorization and Terminology Under the PACP system, pipeline defects are categorized by type (e.g., structural or operation & maintenance) and severity (Grade 1 to 5). Defects of certain type and severity can be considered major defects, requiring some type of renewal action. Examples of major defects include collapsed, broken or fractured pipe, holes, obstacles or laterals ( taps ) intruding significantly into the pipe, and significant corrosion in concrete or asbestos cement pipes. January

66 Chapter 4 Condition Assessment and Rehabilitation/ Replacement Program Figure 4-1: Sewer Renewal Decision Process Flow Diagram January