How Diligence With Data Can Help You Overcome I&I

A South Carolina district puts heavy emphasis on monitoring and data in its fight against I&I.

How Diligence With Data Can Help You Overcome I&I

Ray Childs (left) and Trent Bowles install a Hach FL901 Flow Logger in a manhole.

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Fighting inflow and infiltration is a never-ending challenge, but that doesn’t mean it’s a hopeless endeavor. Taylors (South Carolina) Fire and Sewer District officials pin their hopes on data — lots and lots of data. The data-driven approach is identifying problem areas, saving money and improving the integrity of the sewer system.

Taylors Fire and Sewer is a special-purpose district in Northeast South Carolina and principally serves the unincorporated Taylors area and surrounding county properties. It is solely a satellite collection system, delivering wastewater from more than 11,000 customers to a nearby, independently operated sewer treatment plant. The fire protection component is a separate division of the district.

Because it’s a satellite system, the district is subject to external pressures. Interaction with adjacent collection systems can spark disputes about I&I sources. Overlaying jurisdictions periodically make noises about taking over the district. These tensions slowed the district’s I&I efforts that began 15 years ago.

But a half-dozen years ago, district Director Samantha Babb, her supervisors, crew and a technical adviser began to mitigate stormwater and groundwater infiltration in earnest. It happened after they implemented a comprehensive data-driven program that focuses on the performance and condition of the sewer infrastructure across the district.

Mini-system assessment

In its painstaking collection of data, the district meticulously assesses the performance of an individual line and the condition of the line. Only after that information is cataloged and evaluated is a specific course of action decided upon to rehabilitate the line. Federal, state and internal standards are used in evaluating the functionality of each tributary.

To systematize data collection, the sewer district was divided into nine mini-systems, or sub-basins, that flow into the treatment plant. In each mini-system, determining the performance of feeder lines can involve as many as 60 different operational and maintenance criteria. That’s a lot of detailed information.

“When we complete an assessment, we can discuss with an engineering group the exact condition of a mini-system and its tributaries,” Babb says.

The district has completed assessments of six of the nine mini-systems. A 10th sub-basin is comprised of pass-through lines and residential septic tank systems.

A look at District Mini-System No. 3 (MS-3) illustrates the level of scrutiny involved. The sub-basin was originally scheduled for evaluation next July, but a wet-weather study by an outside environmental consulting firm identified MS-3 as the biggest offender in the service area. So, its evaluation was moved up to January of this year.

MS-3 is comprised of 889 acres within the overall district and contains more than 400 developed parcels of land, including residences and restaurants, slightly fewer than 14 miles of pipe and 367 manholes. As in every case, the process of assessing the performance of the mini-system was carefully documented. Its history was noted, objectives of the assessment stipulated, data collection procedures and dates spelled out, profiles of three recorded rainfall events recorded, and so on.

All in all, the performance assessment of MS-3 consumed 94 workdays. It would be followed by an assessment of the mini-system’s infrastructure and, ultimately, consideration of how best to rehab the sub-basin to reduce groundwater and stormwater infiltration.

District officials say nothing “super critical” was uncovered during the MS-3 performance assessment, though significant infiltration of water into the sub-basin from an external source was discovered. An old industrial wastewater treatment plant in another district is suspected as the likely source. However, finding the point of infiltration and having the adjacent district correct the issues are problematic.

All of this preliminary evaluation and documentation in each mini-system obviously is time-consuming. Aside from data, there really is nothing to show for it. Yet, like the footings and foundation of a house, the cumulative data is what a tighter, more efficient collection system is built upon.

Babb was asked if gathering I&I information is harder work than fixing the problem. “It’s about 50-50,” the director says. “Figuring out the magnitude and identity of the I&I is about half the effort. Once you’ve identified it, then it’s about prioritizing the problem and selecting the most cost-effective solutions. It lets you focus on where the real problem is, which saves money and time.”

Ensuring accuracy

The district uses flowmeters by both Hach and ADS Environmental Services, along with a portable flow test stand built by the utility’s technical consultant with assistance from TRI Environmental. The stand ensures its flowmeters are working properly and validates their accuracy. The portable stand can be carried to a field site on a trailer so district officials can replicate conditions below ground and evaluate performance.

The stand includes a length of PVC pipe with access ports cut into it, a holding tank, a generator, an electric pump and a flow control gate valve. A known flow rate is achieved in the test-stand pipe using a calibrated-flow rotameter. The test-stand gpm flow is compared to the gpm flow reading in the below-ground collection pipe. “The improved precision and accuracy using the test stand has proven very beneficial in accurately determining inflow and infiltration volumes,” Babb says.

Flowmeters in the system are of two kinds. The first are meters that communicate via cellular network receivers, which are used in major tributaries in the system. The district is required to monitor the flow of its collection system as part of an intergovernment agreement. 

Besides area/velocity flowmeters, level recorders can be inserted in key locations to document flow levels at a particular point of interest. “They give you a quick 24-hour assessment. We generally put them in place and leave them for a week, Monday to Monday,” Babb says.

An aging sewer network

Taylors Fire and Sewer District reached a point of unsustainable I&I the same way any collection system does: Its 147 tributaries or feeder lines were getting older, and not enough attention was paid to maintaining them. The area’s natural springs are also a factor in the situation. “We have a number of natural springs nearby,” Babb says, “that can contribute to I&I in older pipes if they are not well maintained.”

The mostly clay pipe network was laid primarily in the late 1960s, which makes many of the pipes more than 50 years old. Not until 2015 or so did the district — under the direction of Babb — begin to systematically address I&I in its 134 miles of pipe. “We had some previous consultants and contractors, but we determined they weren’t doing what was best for Taylors. So, we have our hands on it now, doing it in-house,” says the director. As for the fruit of the data-driven approach? The current number of sanitary sewer overflows is 0.76 events per 100 miles of pipe.

Taking initiative

Because an estimated 70% of I&I occurs on private property, part of the solution to invasive water is working with homeowners and commercial property owners. When an issue is spotted — a broken pipe, tree roots — owners of the property are made aware of the problem. Babb says the vast majority of those contacted by the district end up working to resolve an issue, which says something positive about the district’s relationship with its customers.

District budgeting to battle I&I varies from year to year. Some $1.4 million has been set aside in the upcoming budget. Almost as important as the money, however, are the initiatives the Taylors Fire and Sewer District takes to get its money’s worth.

Babb and colleagues have a successful strategy going to I&I mitigation, and it begins with doing the necessary work to get accurate information about what’s happening inside the pipes. Collecting large amounts of data may not be an especially satisfying task day after day, but when the numbers are totaled up, they tell the story. “Let the numbers tell you where the problems are. Otherwise, you’re just throwing money into the dark,” Babb says.

Babb also emphasizes to trust the instruments. Properly calibrated and monitored meters — positioned at the optimum points in a pipe to catch the full flow — dependably record what is happening out of sight, day and night. “Let them tell you where to go to correct the problems.”  



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