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Flow Monitoring Supports Collection System Model; Lays Groundwork for Capacity, O&M Benefits

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April03

Without waiting for promulgation of USEPA’s impending SSO Rule or regulation on capacity, management, operations, and maintenance (CMOM), the Metropolitan Sewer District of Greater Cincinnati (MSDGC) has taken the proactive approach to implementing Best Management Practices (BMPs). MSDGC teamed with lead consultant CDM, engineering firm R.D. Zande and Associates, and other project partners to create a computerized model of the majority of its collection system that serves more than 800,000 customers across Hamilton County, Ohio.

After three years and $14 million, MSDGC’s system wide model (SWM) is demonstrating immediate returns and promises a multitude of long-term management benefits. Key among them, according to Susan Moisio, leader of the SWM project and member of WEF’s Collection Systems Committee, is the ability to use real-time controls within the system. In addition to improved operations, the MSDGC model lays the foundation for capacity evaluation and assurance, will support preventive maintenance, assist in evaluation of growth and planning scenarios, and help the system meet higher customer service expectations.

Accurate Flow Monitoring a Key Tool

The computerized hydraulic model is based on data collected using well-defined field procedures and hundreds of flow meters and rain gauges. John Barton, Zande team project leader, explained the field team very carefully evaluated each potential monitoring site, more than 1500 sites overall for each half of the system, against a host of criteria to make sure each manhole was practical to access, would yield meaningful data, and would support unimpaired probe operation. He indicated the team standardized on American Sigma flow meters from Hach Company, because “these meters are easy to program, and built-in data handling software actually makes it hard to lose data during download.” The meters utilize submerged depth/velocity sensors but offer the flexibility of ultrasonic detection in the few situations where levels rise above the limits of the submerged pressure transducer.

The meters successfully yielded velocity and level measurements every five minutes from nearly all sites, from January through June 2001. The data team carefully evaluated readings as they came in from the field, using scatter graphs and hydrographs, watching for a consistent flow/level relationship that signaled good data appropriate for model calibration. The entire study was repeated in a similar manner, the following year, for the second half of the system. MSDGC anticipates finalizing the model in April 2003.

Steve Donovan, MSDGC team project leader, continued to explain the role of reliable flow monitoring, “This dynamic model is not a static snapshot in time. We are continuing flow and level data collection to update the model, since the system changes daily with cleanouts and other O&M activity. We rely on about 130 flow meters in place now across the system for baseline resolution and additional meters in areas warranting more focused assessment.”

Accurate Flow Monitoring a Key Tool The computerized hydraulic model is based on data collected using well-defined field procedures and hundreds of flow meters and rain gauges. John Barton, Zande team project leader, explained the field team very carefully evaluated each potential monitoring site, more than 1500 sites overall for each half of the system, against a host of criteria to make sure each manhole was practical to access, would yield meaningful data, and would support unimpaired probe operation. He indicated the team standardized on American Sigma flow meters from Hach Company, because “these meters are easy to program, and built-in data handling software actually makes it hard to lose data during download.” The meters utilize submerged depth/velocity sensors but offer the flexibility of ultrasonic detection in the few situations where levels rise above the limits of the submerged pressure transducer. The meters successfully yielded velocity and level measurements every five minutes from nearly all sites, from January through June 2001. The data team carefully evaluated readings as they came in from the field, using scatter graphs and hydrographs, watching for a consistent flow/level relationship that signaled good data appropriate for model calibration. The entire study was repeated in a similar manner, the following year, for the second half of the system. MSDGC anticipates finalizing the model in April 2003. Steve Donovan, MSDGC team project leader, continued to explain the role of reliable flow monitoring, “This dynamic model is not a static snapshot in time. We are continuing flow and level data collection to update the model, since the system changes daily with cleanouts and other O&M activity. We rely on about 130 flow meters in place now across the system for baseline resolution and additional meters in areas warranting more focused assessment.” Knowing the Problem is Half the Solution As Pat Karney, Director of MSD of Greater Cincinnati sees it, the very least a system should do is implement some level of real-time control using flow meters installed in strategic locations. Output to a PLC or other control mechanism would permit timely changes in overflow regulator settings and automatic activation of temporary, inflatable diversions, all to take advantage of a system’s inherent storage capacity when needed. But he feels strongly that, to have an adequate MOM program, any system of reasonable size should have a computerized model accurately calibrated with carefully collected data. With a model, he suggested, system staff can simulate transfer between collection basins, for example, and predict if such a strategy is a reasonable assumption, then properly design and install the pump station to realize the strategy. Added Donovan, “We anticipate repeated situations where we will use the model to support cost-effective decisions when assessing small capital improvement projects.” Donovan continued, “We’ve immediately realized a better understanding of the collection system, through all the rigorous site inspection and evaluation by John’s team. Many O&M issues were indirectly addressed during the meter installation and data collection process of the modeling project. We’ve discovered some I/I and constraint situations and have a good start on capacity evaluation. We’ve even realized some missing pipe and elevation information in our very good GIS system. One of the first applications of our dry weather data was in helping specify pumps needed for diversion during temporary projects.”

Knowing the Problem is Half the Solution

As Pat Karney, Director of MSD of Greater Cincinnati sees it, the very least a system should do is implement some level of real-time control using flow meters installed in strategic locations. Output to a PLC or other control mechanism would permit timely changes in overflow regulator settings and automatic activation of temporary, inflatable diversions, all to take advantage of a system’s inherent storage capacity when needed.

But he feels strongly that, to have an adequate MOM program, any system of reasonable size should have a computerized model accurately calibrated with carefully collected data. With a model, he suggested, system staff can simulate transfer between collection basins, for example, and predict if such a strategy is a reasonable assumption, then properly design and install the pump station to realize the strategy. Added Donovan, “We anticipate repeated situations where we will use the model to support cost-effective decisions when assessing small capital improvement projects.”

Donovan continued, “We’ve immediately realized a better understanding of the collection system, through all the rigorous site inspection and evaluation by John’s team. Many O&M issues were indirectly addressed during the meter installation and data collection process of the modeling project. We’ve discovered some I/I and constraint situations and have a good start on capacity evaluation. We’ve even realized some missing pipe and elevation information in our very good GIS system. One of the first applications of our dry weather data was in helping specify pumps needed for diversion during temporary projects.”Knowing the Problem is Half the Solution

As Pat Karney, Director of MSD of Greater Cincinnati sees it, the very least a system should do is implement some level of real-time control using flow meters installed in strategic locations. Output to a PLC or other control mechanism would permit timely changes in overflow regulator settings and automatic activation of temporary, inflatable diversions, all to take advantage of a system’s inherent storage capacity when needed.

But he feels strongly that, to have an adequate MOM program, any system of reasonable size should have a computerized model accurately calibrated with carefully collected data. With a model, he suggested, system staff can simulate transfer between collection basins, for example, and predict if such a strategy is a reasonable assumption, then properly design and install the pump station to realize the strategy. Added Donovan, “We anticipate repeated situations where we will use the model to support cost-effective decisions when assessing small capital improvement projects.”

Donovan continued, “We’ve immediately realized a better understanding of the collection system, through all the rigorous site inspection and evaluation by John’s team. Many O&M issues were indirectly addressed during the meter installation and data collection process of the modeling project. We’ve discovered some I/I and constraint situations and have a good start on capacity evaluation. We’ve even realized some missing pipe and elevation information in our very good GIS system. One of the first applications of our dry weather data was in helping specify pumps needed for diversion during temporary projects.”

Yet MSDGC anticipates the ability to accurately predict system response and implement appropriate operations measures will be the most significant benefit of the SWM. Real-time response capability will help control sanitary sewer overflows (SSOs), combined sewer overflows (CSOs), the health and environmental risks they pose, and support affirmative defense. Doing the Right Thing Creation and application of the SWM is what Karney considers Best Management Practices for his system. “We’re not waiting for a regulator’s definition of BMPs,” emphasized Karney. “Every system is different and has a unique topography, personnel and resources, and history of problems. We strongly believe a critical self-assessment that focuses on our system, and not a system six states from here, is the best way to determine our BMPs. We scrutinize what the Ôbest of the best’ are doing, steal what we can that suits our system, and create customized solutions where we need to. Brown and Caldwell environmental consultants are helping us do that. We’re doing the right thing for MSDGC, and we’re positioning ourselves well for anyone else’s definition of BMPs, too.” For more on the MSDGC system wide model.

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