8. system evaluation & capacity assurance

City of San Mateo Public Works Department Environmental Services Division SYSTEM EVALUATION & CAPACITY ASSURANCE 8. SYSTEM EVALUATION & CAPACITY ASSURANCE Because the City of San Mateo collection system service area is essentially built-out, the primary capacity concern is the accommodation of rainfall dependent inflow and infiltration. 8.1 HISTORIC I&I EFFORTS The City’s infiltration and inflow (I&I) Program began in the early 1980’s with a Citywide flow monitoring program and I&I report prepared by ADS Consulting (1982). Results indicated that the area of the system with the most significant rainfall dependent I&I was a residential community located south of Hillsdale Boulevard between Hwy 101 and the Laurel Creek drainage channel. This area, referred to as San Mateo Village, had historically been plagued with excessive surcharging and overflows during periods of rainy weather. In September of 1985, at the request of the City, WWI Consulting Engineers completed the “San Mateo Village Infiltration/Inflow Isolation Study.” The objective of the study was to complete a comprehensive investigation to determine the levels of I&I into the San Mateo Village system, a system consisting of approximately 50,000 lineal feet of clay sewer mainline and 37,000 lineal feet of service laterals. The study included short and long-term flow monitoring, smoke testing, CCTV lateral inspection, pump station capacity analysis, hydrograph generation and formulation of alternatives and recommendations. The report identified only 21 direct inflow sources which were disconnected. The major findings of the report included:

• Low number of defects identified through smoke testing was due to high groundwater and sagging lines

• Deterioration of house laterals were the major defect found

• Sewers in the street were better than those in backyards

• Root intrusion at pipeline joints and lateral to main connections was

extensive in backyards

• 80% of lateral to mainline connections in backyards were of break-in type

• Laterals are large source of I&I

• Groundwater table is above sewer inverts in many areas The final report recommended that the City rehabilitate collection system sub areas with greater than 10,000 gallons/in mile/day of I&I and increase existing pump station capacity. From 1986 through 1992, the recommended improvements were implemented via a mainline and manhole grouting program. City personnel upgraded the pumps and VFD’s at the Santa Clara Sewage Pump Station.

Last update: 11-15-2009 City of San Mateo SSMP Element 8: SYSTEM EVALUATION & CAPACITY ASSURANCE

8 - 1

City of San Mateo Public Works Department Environmental Services Division SYSTEM EVALUATION & CAPACITY ASSURANCE An upgrade of the Casanova Storm Water Pump Station was identified as necessary to adequately drain rainfall away from the area. This project was designed in the late 1990’s with construction completion in 2004. In another part of the City, a major storm sewer/sanitary sewer cross connect was identified in 2002. During rain events, the entire storm drainage along 17th Avenue at the railroad was directed into the sanitary sewer. Over the next year, the drainage was re-established by removing a building that blocked the natural channel and the storm water flow was directed away from the sanitary sewer to the drainage channel at 16th Avenue. 8.2 RECENT I&I EFFORTS In 1998, the Environmental Services Division contracted with consultants Montgomery Watson Harza (MWH) to begin a thorough evaluation of the hydraulic performance of San Mateo’s sanitary sewer collection system and develop cost-effective solutions to wet weather problems. The Los Prados-South Shoreview area, a hydraulically independent sewer network, was evaluated first. Hydraulic evaluation of the City’s sewer collection system west of the Marina Lagoon was completed in June, 2005. The Mariners Island area, another hydraulically independent sewer network, was excluded from the study given its relatively newer infrastructure, effective series of six pumping stations and forcemains that carry flow directly to the treatment plant, and lack of inflow and infiltration issues. The City-Wide Sewer Study (Study) confirmed that San Mateo’s sanitary sewer collection system experiences heavy infiltration during storm events. Flow monitoring performed between 1997 and 2002 for the Study identified which neighborhoods are the worst I&I offenders. The report identified 35 sewer improvement projects targeting current and future capacity issues related to I&I. Results were based on flow monitoring analysis, population and land use information. Currently, the Environmental Services Division is under contract with Brown & Caldwell to take the results of the MWH hydraulic analysis and complete an overall study that incorporates the volume constraints of treatment and outfall capacity and identify projects necessary to tighten the system and provide for overflow storage to allow future collection system expansion. See exhibit C for the Scope of Work for this contract. The contract was awarded in November of 2007 with an anticipated completion date of February 2009. Exhibit D to this section includes a letter to the California Regional Water Quality Control Board describing how the Wet Weather Capacity Analysis ties into the completion of the upsizing of the Hillsborough portion of the El Cerrito Trunk Line. The City determined that it was necessary to identify a plan to deal with the entire drainage basin prior to moving forward with isolated improvements. Completion of the El Cerrito trunk line prior to the upgrade of downstream systems would merely transfer sanitary sewer overflows from Hillsborough to San Mateo.


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City of San Mateo Public Works Department Environmental Services Division SYSTEM EVALUATION & CAPACITY ASSURANCE


8.3 CURRENT 5 YEAR CAPACITY PROGRAM PLAN

SHORT-TERM CAPACITY IMPROVEMENT PROJECTS Project Title Implementation

Date (Initiate Construction)

Estimated Cost*

Est’d Time* (years)

Annual Collection System Rehabilitation Program

December 2010 $ 2,000,000 2

Los Prados Trunk Relief (LPS-1, LPS-2) December 2010 $ 8,500,000 5 Total $ 10,500,000


December 2011 $ 2,200,000 2

Flint Pump Station Upgrade (LPS-7) December 2011 $ 6,300,000 4 Kingridge Rehabilitation December 2011 $ 3,600,000 6 Total $ 12,100,000


December 2012 $ 2,310,000 2

SST-8

24th Ave Relief (SST-8) December 2012 $ 2,330,000 4

Total $ 4,640,000


December 2013 $ 2,426,000 2

El Cerrito Trunk Relief (SNT-1, SNT-4) March 2013 $19,000,000 7 SST-4

25th Ave Relief (SST-4) December 2013 $ 2,338,000 4

South Trunk Relief (SAT-1, SST-1, SST-2) December 2013 $15,000,000 6 Total $ 38,764,000


December 2014 $ 2,547,000 2

LPS-4

Dale Ave Relief (LPS-4) December 2014 $ 602,000 4

Total $ 3,149,000 GRAND TOTAL $ 69,153,000 * Estimated Cost is total project cost, escalated to year of implementation * Estimated Time is total project duration

City of San Mateo Los Prados-South Shoreview Sewer Study

This report presents the results of a study of the sewers in the Los Prados-South Shoreview area of the City of San Mateo. This report was prepared by Montgomery Watson under an agreement with the City dated February 16, 1999. BACKGROUND AND PURPOSE OF STUDY The purpose of the Los Prados-South Shoreview Sewer Study is evaluate the hydraulic performance of the existing sewer system, identify capacity deficiencies in the system, and recommend potential sewer improvement projects to correct the identified problems. The Los Prados-South Shoreview area was selected by the City as a “pilot” study area to evaluate the use of hydraulic modeling for gaining a better understanding of sewer system performance and developing cost-effective solutions to wet weather problems. This area of the City is known to be subject to high flows during wet weather periods, which have resulted in sewer overflows during rainfall events. The Los Prados-South Shoreview area is also a “hydraulically independent” area of the City’s sewer system, that is, it does not receive flows from any upstream areas and it discharges directly to the City’s Dale Avenue Pump Station, which pumps flow to the Wastewater Treatment Plant (WWTP). Therefore, it was considered to be a good candidate for such a pilot study. Prior to the initiation of this study, the City selected and purchased a hydraulic modeling program called HydroWorks to use for modeling of the wastewater collection system. HydroWorks is a fully dynamic hydraulic model that can be used to simulate the performance of both gravity and pumped systems and provide an accurate representation of flow rates, velocities, and water levels in the system under a variety of flow conditions. Montgomery Watson was selected by the City to perform the modeling study and system evaluation. The report is organized into the following sections:

• Study Area and Sewer System Model • Flow Monitoring • Base Wastewater Flow Estimates • Model Calibration • Design Storm • Design Storm Model Results • Recommended Improvements

Montgomery Watson EXHIBIT A 8 - 4

Los Prados-South Shoreview Sewer Study Recommendations The following recommendations are made for the Los Prados-South Shoreview sewer system: • Highest priority for construction should be given to the Norfolk Relief Phase 1 and Dale Relief

projects. The City should budget for construction of these projects as soon as possible and initiate predesign studies to confirm the viability of the proposed alignments and estimated construction costs.

• Conduct smoke testing to identify potential direct inflow connections to the sewer system. Smoke testing is a technique by which non-toxic smoke is blown into the sewers to detect potential entry points for I/I. The smoke emerges from directly connected storm drains catch basins, building roof leaders or area drains, or from the soil above defects (cracks and open joints) in sewers and laterals. In area of high groundwater, like the Los Proados-South Shoreview area, the effectiveness of smoke tsting to detect pipe defects is limited because the smoke cannot easily travel through the soil. However, direct inflow sources, which are potentially large sources of I/I, can still be identified. Smoke testing should be followed by dye flooding to confirm suspected storm drain cross connections and concurrent television inspection of the sewer reaches where the suspected direct connections are observed.

• Survey the influent sewers and wet well elevations of the Flint-Norfolk and Los Prados pump stations to confirm the elevations of the hydraulic model. Evaluate the operations of the Flint-Norfolk Pump Station, particularly the setting for pump on-off levels with respect to the elevation of the influent sewers to minimize potential backup in the sewers.


City of San Mateo City-Wide Sewer System Study

This report presents the results of the City-Wide Sewer System Study for the City of San Mateo (City). This report was prepared by MWH under an agreement with the City dated June 2001. BACKGROUND AND PURPOSE OF STUDY The purpose of the City-Wide Sewer System Study is to evaluate the hydraulic performance of the existing sewer system, identify capacity deficiencies in the system, and recommend potential sewer improvement projects to correct the identified problems. The study also evaluated impacts on the City’s collection system of proposed development of the former Bay Meadows racetrack. Prior to this study, MWH conducted a separate capacity study for the Los Prados-South Shoreview area of the City. This area was selected by the City as a “pilot” study area to evaluate the use of hydraulic modeling for gaining a better understanding of sewer system performance and developing cost-effective solutions to wet weather problems. The Los Prados-South Shoreview area was selected for this initial study because it is known to be subject to high flows during wet weather periods. It is also a “hydraulically independent” area of the City’s sewer system; that is, it does not receive flows from any upstream areas and discharges directly to the City’s Dale Avenue Pump Station, which pumps flow to the Wastewater Treatment Plant (WWTP). The results of the Los Prados-South Shoreview sewer study, including recommendations developed by MWH to provide additional capacity for sewer system in this area, are summarized in a report entitled “Los Prados-South Shoreview Sewer Study” dated January 2001. The results of the City-Wide Sewer System Study summarized in this report do not include the Los Prados-South Shoreview area. However, the recommended sewer improvement projects for that area are incorporated into the recommended sewer system capacity improvement program at the end of this report. The report is organized into the following sections:

• Study Area and Sewer System • Sewer System Model Development • Flow Monitoring • Model Flows • Model Calibration • Design Storm • Design Storm Model Results • Recommended Improvements • Conclusion and Recommendations

MWH EXHIBIT B 8 - 11

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CITY OF SAN MATEOCITY-WIDE SEWER SYSTEM STUDY

Rainfall Dependent I&I% of Total Rainfall

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INFLOW & INFILTRATION ANALYSISFlow Monitoring Results for Rainfall Dependent Inflow & Infiltration

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City of San Mateo City-Wide Sewer System Study CONCLUSIONS AND RECOMMENDATIONS The results of the flow monitoring and hydraulic modeling of the City of San Mateo trunk sewer system indicate that the system has substantial capacity deficiencies that could potentially result in sanitary sewer overflows during large storm events. This study identifies trunk sewer improvement projects (relief sewers and pump station capacity expansions) which, if constructed, would increase system capacity and thereby reduce the risks of wet weather overflows. Although the focus of this study has been on expanding trunk conveyance capacity, other alternatives for mitigating the risk of wet weather flow do exist, including sewer rehabilitation to reduce I/I or construction of storage basins upstream in the system to temporarily retain flows during peak storm periods. The cost and viability of these alternatives would need to be closely evaluated to determine if they could be cost-effective solutions to wet weather problems in the City’s sewer system. As noted previously, construction of the capacity relief projects identified in this report could substantially increase the potential peak wet weather flows reaching the City’s Dale Avenue Pump Station and Wastewater Treatment Plant. The issues and costs relating to increasing downstream pumping, treatment, and effluent discharge capacity were not evaluated as part of this study, but would likely be significant. When considered in conjunction with the need to expand these downstream facilities, sewer system rehabilitation and / or wet weather storage could become viable components of the City’s overall wastewater planning strategy. The following recommendations are made based on the results and conclusions of this City-Wide Sewer System Study: • The City should budget for construction of the highest projects as soon as possible

and initiate predesign studies to confirm the viability of proposed alignments and estimated construction costs.

• The alignments and sizes of all recommended projects should be verified with detailed predesign analysis, including topographic surveys, geotechnical investigations, utility research, and constructability reviews. Viable alternative alignments should be considered during predesign.

• The decision to parallel or replace existing sewers should consider the physical condition and remaining useful life of the existing pipelines; the availability of pipeline corridors for new sewer construction; and operation and maintenance concerns.

• The City should work with the Town of Hillsborough to develop equitable cost sharing for construction of common relief facilities needed to convey flows from both jurisdictions.


• The City should review the capacity requirements of downstream facilities (i.e. Dale Avenue Pump Station and wastewater treatment plant) to handle increased flows that will likely result from construction of significant relief improvements in the collection system. Studies to evaluate options to handle increased flows at these downstream facilities should be initiated as soon as possible.

• The City should address I/I on an area-specific basis. Targeted I/I source detection and correction should be considered in areas with particularly high I/I flows, such as the San Mateo Village. In any areas with suspected direct inflow connections to the sewer system (directly connected roof or area drains or storm drain cross-connections), smoke testing should be conducted to identify potential sources. Smoke testing is a technique by which a non-toxic smoke is blown into the sewers to detect potential entry points for I/I. The smoke emerges from directly connected storm drain catch basins, building roof leaders or area drains, or from the soil above defects (cracks and open joints) in sewers and laterals.

• The City should continue its on-going program of closed-circuit television inspection

of the sewer system to identify sewers with structural defects and potential sources of I/I, and implement a long-term renewal and replacement program to preserve the City’s sewer pipeline assets and address identified problems before they become more severe.

• The City should take steps to develop a comprehensive Sewer System Management

Plan (SSMP) following the guidelines recently developed by the San Francisco Bay Regional Water Quality Control Board. The SSMP includes a number of components to ensure proper and effective management, operation, and maintenance of wastewater collection systems. The work conducted for this City-Wide Sewer System Study provides a foundation for preparation of a System Evaluation and capacity Assurance Plan, one of the key components of the SSMP.


8. system evaluation & capacity assurance

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