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The prioritization of municipal sewer system rehabilitation work to reduce inflow and infiltration (I&I) is based largely on the selection of projects that will most quickly provide the largest return on investment. Strategies to determine this vary from municipality to municipality; however, performing service lateral rehabilitation work first is critical to the success of any comprehensive municipal rehabilitation program.
Failure to do this will allow groundwater to travel around any repairs. To expeditiously locate areas within the system that are in need of rehab work, reliable flowmeters that provide accurate flow data are a critical component.
When the Cutting Edge Group, LLC (CEG), a design-build firm located in Lake George, N.Y., was contracted to provide flow services for the village of Whitehall, N.Y., its first task in the pilot study was to monitor the flow of the village’s service laterals.
The village of Whitehall is located on the Vermont border at the south end of Lake Champlain. Records indicate that portions of the system were replaced in the mid-1970s, mid-1980s and early 1990s.
Much of the municipal collection system is the original vitrified clay pipe, which is estimated to be more than 75 years old. As with many villages, the private side of the collection system receives very little maintenance. Based on a detailed study of the methodologies associated with the village’s most successful rehabilitation project, it was suspected that the laterals or other private sources of inflow may be contributing significantly to the problem.
Work done for the pilot study would provide scientifically defendable data explaining this phenomenon. To determine the most cost-effective method of collecting the flow data required for its study, CEG performed a thorough investigation to compare the costs of flowmeter purchase versus rental and consider the use of available outside services to collect the flow data. This evaluation placed an emphasis on establishing an approach that would minimize the number of costly trips to the site and the number of confined space entries needed to ensure proper operation of the meter.
During this search, CEG was introduced to Hach Co.’s Data Delivery Services (DDS). Web-enabled Flo-Dar flowmeters provide 24/7 access to flow data via any Web browser, eliminating the need for site visits to collect flow data or maintain the meters. They utilize a non-contact radar velocity/area sensor when performing open-channel and sewer flow monitoring. Flo-Dar’s unique non-contact measuring technology eliminates sensor fouling associated with submerged sensors. The sensor utilizes digital doppler radar velocity sensing technology with ultrasonic pulse echo level sensing.
The flexibility of DDS allows for either a totally hands-off approach to flow monitoring by providing installation and any maintenance requirements or in the case of CEG, allows the experienced flow service providers the ability to install and maintain the meters themselves for additional cost savings.
“The conclusion that we came to was to select DDS based on the pricing structure. It’s definitely a cost savings,” said Tom Davey, member of CEG. “We did a very thorough investigation of what was out there and the costs associated with each. We started out by pricing the purchase of several meters, and then we went back and looked at rental fees. When we compared the prices provided by Hach with every other company out there, and when you really look at the big picture, we found that DDS was the most cost-effective way to go.”
Meters in Action
Line sizes to be monitored in the village’s collection system were primarily 8-in. lines, with an occasional larger or smaller pipe size.
The first task of the pilot study performed with the meters was to monitor the flow of the service laterals prior to scheduled rehabilitation work. Pipe bursting and sliplining were performed, and the meters were reinstalled to determine the effects of the rehab work.
“We took the service laterals up to the property line and what we found out was that the expenditures associated with mainline rehabilitation at these locations didn’t have any effect on the I&I. In essence, private side laterals are what was contributing most of the I&I on those streets,” Davey said.
Based on the results of the pilot study, the village expanded CEG’s contract to allow for a more thorough I&I program for other areas within the jurisdiction. DDS meters have been relocated several times and at the time of print, the contract is still being extended.
Now very familiar with the meters’ capability, CEG has come to rely on them for various tasks. When a water main break occurred and the actual location in a large tract could not be pinpointed, the meters were installed and indicated a large spike in flow, quickly isolating the water main break.
Internet access to flow data is a feature that has allowed CEG to monitor its flows right from staff members’ desks rather than performing site visits to ensure that the meters are fully operational.
“The ability to get the information online was very helpful,” Davey added. “From the online data, users can get a good indication while reviewing that data if there’s some type of problem. If you are regularly looking at that data, you can detect problems and react to them versus having to radically go out and respond and do an inspection from site to site.”
While submerged sensor-style meters had been used in prior years to monitor open-channel flow in the village, they were plagued with sensor maintenance issues such as fouling, which now is eliminated with the use of the non-contact flowmeters.
“I feel that DDS is a very reliable and user-friendly program that is in place,”Davey said. “We’re absolutely on board with using the latest and greatest technology, particularly having Internet and cell phone access to the meters. We’re a real advocate for programs like that.”
Appropriately named, CEG’s name represents its desire to provide customers with results that are based on the use of the most cutting-edge technology. Moving forward, CEG has said that it “absolutely” plans on the continued use of DDS.
Dave Baker, DDS business development manager for Hach Co., added: “What started out to be a short-term flow study has turned into Cutting Edge using our DDS meters for nearly two years. When we can see our customers benefit from this service to the degree we’ve seen CEG benefit from it, we know we are doing something right.”