Minimizing CSOs Using Hydraulic Modeling with Real-Time Controls and Optimization Technology at the City of Hamilton

Chris Gainham and Patrick Delaney — Jun 01, 2009

he City of Hamilton owns and operates one of the largest and most complex combined sewer systems (CSSs) on the Great Lakes. The overall wastewater collection system includes three wastewater treatment plants, approximately 65 wastewater outstations, eight combined sewer overflow (CSO) tanks, one equalization tank and approximately 1,600 kilometers (1,000 miles) of sanitary and combined sewers.

The area is blessed with a large natural harbor providing for a wide range of industrial and recreational uses and also contains sensitive receiving waters, most notably Cootes Paradise Marsh. This area is the site of one of the largest wetland rehabilitation projects in North America. Three large interceptor sewers collect combined sewage from an area of approximately 54 square kilometers (21 square miles) and convey it to a wastewater treatment plant (WWTP). During dry weather and small storm events, all combined sewage is conveyed to the WWTP where it receives treatment before being discharged into the eastern end of Hamilton Harbour. During larger storm events, 21 combined sewer overflow outfalls are active, discharging untreated combined sewage to receiving waters to avert sewer system surcharging, basement flooding, and to avoid over capacitating the WWTP.

The City’s CSS employs a number of motorized sluice gates which can be opened or closed by the operators at the WWTP to dynamically regulate the amount of flow entering the sanitary interceptors. However, historically, there was no specific operational plan for when and by how much the gates should be adjusted in order to optimize existing storage capacity in the sewer system while maintaining manageable inflows to the WWTP.

To improve the situation, the City worked with AWS Engineers and Planners (now Hatch Mott McDonald) to develop a preliminary design of a computer-based real-time control (RTC) system including hydrologic and hydraulic simulation models to predict resulting flows at key points within the CSS, CSO control optimization model and flow conversion modes to determine the desired optimum flows at each controllable device in the CSS and determine the required gate or pump set-points required to achieve these optimum flows.

The Phase 1 RTC models were then used to evaluate the long-term benefits of RTC in terms of CSO control and potential capital cost savings for future CSO control efforts. The planned RTC system would continually adjust the levels of existing regulator gates and storage facilities according to measured rainfall and flow conditions, striving to optimize the flow in the system by maintaining a manageable inflow to the WWTP, minimize CSOs and maximize existing storage (in-line and off-line) in the system.
The proposed RTC system also included a network of rainfall gauges and flow sensors located throughout the system, providing a continuous stream of real-time information. This information would be displayed to the operators, and used by a central computer to apply existing or forecasted conditions to a model of the system in order to evaluate the system response at critical locations, and make any necessary adjustments to the operational scenarios (AWS Planners and Engineers, 2005).

The implementation of this system was commissioned in two phases. Phase 1 involved updating the components of the existing RTC system, including the hydrologic and hydraulic simulation models, the real time rainfall forecast model, the CSO control optimization model, and the flow conversion model, so they accurately represent the operation and performance of Hamilton’s existing combined sewer system, and accurately define the City’s objectives with respect to CSO control (AWS Engineers and Planners, 2005).

An updated hydrologic and hydraulic simulation model was needed in order to:

Better understand the various processes contributing to flows in the system, including rainfall runoff, inflow and infiltration, and dry weather wastewater loading from residential, industrial and commercial land uses.
Evaluate scenarios to optimize the operation of existing structures according to the following objectives;

maximize storage in the system,
maintain a manageable inflow to the wastewater treatment plant, and
minimize CSO volumes.

Serve as a design tool for evaluating the effectiveness and benefits of additional structural and/or operational improvements to the system.
Serve as a planning tool to evaluate alternatives for system expansion and upgrades to accommodate future growth.

In light of the multiple objectives of the model and the need to evaluate a complex, dynamic system with real-time control and operation of structures, the City selected DHI’s MOUSE modeling software for the project. The MOUSE model (stands for modeling of urban sewers) is widely used in major municipalities throughout North America and around the world. It was selected because it met all of the requirements for this challenging project including:

Ease of use: Engineers and operators need to be able to be trained to run the model under different scenarios and interpret the results to help make critical operational decisions.
Real-time controls: The model needs to be able handle complex, rule-based operational controls for structures.
Numerical stability: When running in a real-time environment it is imperative the model will produce meaningful and reliable results with minimal supervision and user-intervention.
SCADA integration: The model will need to be able to capture, process and manage real-time data via SCADA systems.
Support: The RTC system will be operational for many years to come so it is important that the product be supported by a reputable organization that can be counted on to continue to develop and support the product for the foreseeable future.

The updated models were used to evaluate different operational scenarios on existing structures and storage facilities to estimate the long-term benefits of RTC to the City of Hamilton in terms of CSO pollutant reduction and potential cost savings for future CSO control efforts. Phase 1 also included a preliminary investigation of alternative strategies and approaches to RTC in Hamilton, and recommendations for possible enhancements to the RTC system.

Based on the results of the Phase 1 report, it was clearly demonstrated that an operational RTC system can be effectively implemented for optimizing the operation and sizing of the wastewater and CSO facilities in order to best manage wet weather flows in the combined system. The ability of the models to effectively demonstrate the response of the system to various RTC strategies under different system stresses was one of the key determining factors in the decision to move forward with the next phase of the project.

The City has been using the calibrated trunk sewer model to support hydraulic analyses of its combined and sanitary trunk system. The existing wastewater model in MOUSE is a fully dynamic model capable of continuous simulation of sewer hydraulics including sewer surcharging and backwater effects, complex control structures, and rule-based real-time controls. The rules-based RTC strategies evaluated with the model have been implemented for operation of the regulator gates, CSO tanks and pump facilities. The existing model functions as a cornerstone tool for the RTC system and is also utilized in many ways to support related City activities such as:

Supporting the City’s water and wastewater master plan beyond 2031
Collection system performance analysis for capital planning and budgeting
Operational planning and support (post-flood event forensics and evaluating short-term, non-standard operating scenarios)
Water quality and loading calculations; and
Ultimately, flow frequency-based system design and performance monitoring.

Since the completion of the Phase 1 report, the City has been implementing upgrades to the existing wastewater system and CSO facilities to improve operation of the system and provide additional capacity to support growth-related flows and minimize bypasses/overflows during wet weather events. The operational and structural improvements implemented thus far have continued to reduce CSOs, but in order to reach the ultimate goal of achieving 90 percent capture of wet weather flows in an average year, the City has recently initiated Phase 2 of the RTC system implementation.

The water and wastewater master plan followed by the class environmental assessment for wastewater treatment and CSO control were prepared to identify and evaluate infrastructure requirements, costs and impacts associated with growth and meeting regulatory performance targets. In conjunction with significant end-of-pipe infrastructure and expansions, the need for Phase 2 RTC was reiterated in the master plan, the WWTP environmental study report and the recommendations of the Phase 1 RTC study were verified in terms of the future preferred servicing strategy.

Phase 2 (initiated November 2008) involves full-scale design and on-line implementation of a comprehensive state-of-the art RTC system that is fail-safe, reliable, flexible, robust and user friendly. The consulting team for the Phase 2 works is being led by Stantec and BPR-CSO, who together bring a strong understanding of how to apply the operational capabilities of RTC to a complex collection/treatment system so that performance targets are achieved and capital investments are reduced. The planned system integrates with the City’s SCADA systems, asset management systems, and computerized maintenance management system (CMMS) and is being developed concurrently by the same consulting team with an expanded sanitary and combined sewer model to provide real-time information and decision support at all times during dry and wet weather conditions.

Some of the major challenges to the success of Phase 2 and the realization of a fully operational RTC system include using the refined MIKE URBAN model to assess planned capital infrastructure and upgrades, completion of the project in a phased manner so that the target of 90 percent wet weather capture is achieved as soon as possible and in conjunction with planned WWTP primary clarifier upgrades. Other goals for this second phase of RTC implementations include maximizing CSO tank use while minimizing interceptor use, providing a pre-defined constant flow to the WWTP, reducing the impact of the peak flow factor on secondary treatment design and providing opportunity for water quality based RTC. In addition, there is a significant human component of change management that must be applied in order to develop a system that wastewater operators will trust, utilize during intense storm events and a system in which they have pride of ownership.

One of the first major tasks in the implementation of Phase 2 was an overall assessment of the existing MIKE URBAN trunk system model to identify missing and erroneous data and make corrections using actual elevation and geometry of weirs and regulators with field verified measurements. This initial exercise also required adding structures and operating rules that were not included in the original model. The refinement of the model to suit the assessment of master plan capital works and the development of a preferred RTC and CSO control strategy also required the construction of a five-minute resolution synthetic rainfall time series from City raingauge records. This time series was required to replace the rather coarse 30-year, 1-hour resolution rainfall series that had been used as an input to the original model. Currently the model is being used to flag collection system regulators requiring upgrades necessary to make use of residual system capacity.

The City of Hamilton has been hit with an increasing frequency of severe storms in recent years and, like many other urban centers, is dealing with urban flooding with increasing frequency. The development of the all pipes model and introduction of RTC is also being leveraged to assess options for reducing urban flooding risk, some of which may also be leveraged for further CSO control.

Currently the baseline assessment and RTC approach are scheduled for completion summer 2009 with development of RTC systems design for spring 2010. The initial implementation of RTC and pilot testing of the system is planned out to summer 2011 with substantial completion and implementation of the fully functional RTC system by spring 2012.

Chris Gainham is Senior Project Manager - Water & Wastewater Infrastructure Planning at City of Hamilton, Ontario. Patrick Delaney is vice president, software, for DHI, Cambridge, Ontario.

Software Showcase

DHI Integrated GIS and Urban Water Modeling

MIKE URBAN combines DHI’s 30 years of excellence and innovation in water modeling with ESRI’s world leading GIS technology. The result is a complete urban water modeling and GIS system that is setting a new industry standard for GIS integration, productivity, ease-of-use and visualization.
The concept behind MIKE URBAN is to have one software package for all urban water modeling activities. This allows you to maximize your productivity and fully leverage your investment in GIS and water modeling software tools. MIKE URBAN uses an ArcGIS GeoDatabase for storage of all network and catchment data, allowing you to view and edit your data with ArcMap or any other compatible application.

CUES Inspection/Management Software

In conjunction with NASSCO, the Manhole Assessment and Certification Program (MACP) will be released in CUES’ flagship software called Granite XP. Certified inspectors will be able to collect MACP-compliant inspection data and GPS coordinates for the manholes to verify and update the community’s GIS maps. CUES has released the Granite XP “Cleaning Inspection” module that allows any sewer cleaning vehicle to record/update pipeline inspection and cleaning status information, and the Granite XP “Smoke Test” module will be released that allows for the systematic identification of Inflow & Infiltration sources. Additionally, CUES, in partnership with IBM Maximo, is releasing a bidirectional Work Order integration module between Granite XP and Maximo version 7 and newer.

Wallingford’s InfoNet Software

Wallingford Software offers InfoNet, the water industry’s first purpose-built data and asset management system for the water supply, water distribution, wastewater collection, sewers and storm water sectors.
InfoNet is designed to: integrate water network infrastructure survey data; manage, clean and analyze water network data; access up-to-date information; and report on network infrastructure. The InfoNet user has access to single user, multi-user and portable databases, all with in-built data models for water, wastewater and storm water infrastructure, a GIS type user-interface and an in-built report generator.

InfoNet has now gone mobile with the acquisition of InfoStream, a leading mobile information software developer and systems integrator. InfoStream’s tools provide users with a complete ‘office to field and field to office’ solution.

POSM Laser Measurement Utility

While determining the overall condition and current state of a pipeline, it is crucial to have an accurate measurement of cracks and joints. POSM (Pipeline Observation System Management) software utilizes a laser measurement utility for precise measurements of pipeline defects.

The POSM laser measurement utility makes possible high precession measurements and greater accuracy in verifying the actual size of defects. The measurement utility will work with multiple CCTV equipment manufacturers and can be used in the field during a live run or in the office with POSM Office.
To use POSM’s measurement tool the user must first input the known distance between the laser points. The user will then right click on the mouse and drag a blue line between the laser points. The laser measurement utility will then count the amount of pixels that exist within the blue line to accurately measure the distance of any joints, cracks or various defects.

GIS Module for flexidata by PipeLogix

Exporting your infrastructure survey conditions and displaying them on maps with correlated exact footage is now easily accomplished with the GIS module from flexidata.

Outstanding features include: ability to import asset details from shape files, personal geodatabases, enterprise geodatabases and visual layers, including raster files; user can select assets to inspect from displayed maps in the survey form, surveyed pipes are automatically highlighted so the viewer can see what has been completed; select groups of assets to create survey projects; flow direction of the pipe can be viewed easily with the build flow layer option and numerous import and export options to enable the user to perform an endless variety of analyses and generate reports.

The module provides a handy toolbar to use inside ESRI Arcmap to allow quick viewing access to pictures and movies files associated with the survey and the DVS Player calls up the video when the user selects the condition. This module’s powerful tools make data that was seen in the field now accessible, organized and conveniently viewable in the office directly from your maps to save you time.

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