A Comprehensive Approach

Work smarter against inflow and infiltration with better infrastructure intelligence.

A Comprehensive Approach

A crew prepares to launch an Envirosight camera and crawler. Video inspection can pinpoint I&I sources after flow monitoring has established the most heavily impacted sections of your system.

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Finding and removing excessive inflow and infiltration isn’t easy, and it’s not cheap. With shrinking budgets and continued deterioration of aging infrastructure, there are compelling reasons to support a proactive and intelligent approach to combating I&I. 

Municipalities often decide to focus their financial resources “in the ground” (i.e. rehabilitation) instead of into planning and investigating. Yet, an analysis-driven strategy can dramatically increase the amount of I&I resolved for a given budget.

Financial impact

A recent study of all municipal sewer systems in the state of Tennessee showed that I&I represents approximately 104.6 billion gallons per year. This amount accounts for 45 percent of the annual flow to treatment plants. Processing this extra water is estimated to cost at least $188 million annually statewide. This figure is conservative compared to the Environmental Protection Agency’s recommendation in 2014 for using an operations and maintenance rate of $2 to $5 per 1,000 gallons — resulting in a cost estimate between $208 million and $522 million. 

The Clean Water Act (CWA) establishes the basic structure for regulating discharges into the waterways of the U.S. and setting wastewater standards for the industry. The cost of consent decree penalties can surpass the cost of establishing a comprehensive inspection program.

In 2012, Memphis, Tennessee, was cited for violations against the CWA. The EPA entered into a consent decree with the city requiring them to pay a total of $1.29 million in civil penalties to resolve the CWA violations. In some cases, the EPA can waive these fines if municipalities demonstrate that they have a strategy in place to address I&I. In either case, the failure to address I&I can have catastrophic environmental and financial implications.

Impact on capacity

In 1999, publicly owned wastewater treatment plants served 189.7 million people and treated 32.1 billion gpd. Today, that number is higher. The quality of our water sources depends on the capacity of wastewater treatment plants and ensuring that extraneous water entering the system is minimized. This extraneous water includes water entering the system through I&I. 

According to an article published by the Chalmers University of Technology’s Division of Water Environment Technology, 35 percent of flow entering wastewater treatment plants comes from I&I, another 35 percent is stormwater, and the remaining 30 percent is sewage. In other words, 70 percent of total flow into treatment facilities is water that wouldn’t need treatment had it not entered a sewer line. It robs valuable capacity from treatment plants, and such capacity shortfalls can lead to damaging and costly sanitary sewer overflows.

Total system approach

As early as 1981, the EPA documented problems with sewer rehabilitation programs. Reducing I&I through rehabilitation was often found to be ineffective because of inadequate system knowledge and the arbitrary application of fixes. When rehabilitating indiscriminately, municipalities run the risk of fixing what’s not broken. In the long run, this approach may be strategically catastrophic. A more effective, data-driven approach must be implemented to combat I&I. 

Rehabilitation shouldn’t focus solely on sewer mains, but also on laterals, manholes, and the connections between these structures. A study of several municipalities suggests that I&I reductions of just 10 to 30 percent are achieved when solely rehabilitating pipes. When pipes are rehabilitated, infiltration simply finds a new path into the sewer by migrating through service laterals and manholes. The same study suggests that when high-priority areas are targeted for a combination of main, lateral and manhole rehabilitation, municipalities can realize I&I reductions of up to 50 to 65 percent. The sewer system can be likened to a boat. If only some of the leaks are fixed, the boat will still sink. Likewise, groundwater doesn’t discriminate where it enters the system. 

When creating a strategy to address I&I, significant emphasis should be placed on detecting I&I and preparing corrective rehabilitation actions. George Kurz, P.E., DEE, introduces the concept of a total system approach in his paper, “Sewer Renewal — A Strategic Plan” as part of the EPA’s Capacity, Management, Operations, and Maintenance (CMOM) Program. Kurz points out that accurate flow monitoring, visual inspection and interpretation are essential for success. Kurz researched 31 project areas that included 126 miles of lining — and associated laterals and manholes — in Nashville and Brentwood, Tennessee. Pre- and post-flow monitoring showed that more than 50 percent of the annual I&I and peak I&I was eliminated when the total system approach was implemented.

Locate and identify

Flow monitoring is usually one of the first steps taken to better understand the problem areas within a collections system. Electronic velocity and depth recording devices, or flowmeters, are strategically placed throughout the collections system. Flow monitoring studies generally last from 60 to 120 days, and compare wastewater flow in the system with a baseline flow estimate to determine the amount of I&I in the sewer system. 

Flow monitoring can be used as a tool in condition assessment to identify and prioritize areas for further inspection to quantify the severity of I&I problems. Once target areas have been identified, municipalities should further inspect using a sewer crawler to detect the I&I culprits. 

Segments of the sewer system should never be designated for pipe lining or rehabilitation without completing a video inspection first. A comprehensive approach to locating defects involves inspecting all aspects of a collections system, including manholes, sewer mains and laterals. 

Manholes —The EPA estimates that there are about 20 million manholes in the U.S. — one manhole for every 400 feet of pavement. Many of these manholes are seriously decayed or in need of immediate rehabilitation or replacement. Manholes generate a disproportionate amount of I&I and play a unique role in the structural integrity of roadways. Field inspectors should evaluate the manhole lid, frame condition and the frame connection for any defects or leak sources.

After manually inspecting the manhole cover, the field inspector can employ a manhole inspection camera or a zoom survey (pole) camera to inspect within the manhole. A manhole inspection camera captures visual and dimensional data, and presents the operator with deliverables such as a flat scan with detailed image data covering every inch of the manhole wall, a dense point cloud for 3-D visualization of the manhole structure, and a virtual view inside the manhole. A zoom camera uses a video camera mounted on a telescopic pole, making inspection inside the manhole possible. During inspection the operator should document all cracks and deficiencies found and make a decision about whether findings are a source of I&I.

Sewer main — Groundwater seeps into sewer pipes through cracks, leaky joints and other defects. A CCTV inspection is by far the most detailed method of pinpointing and characterizing I&I in pipelines. An operator watching the footage can stop to study any observed defect. The video can identify cracks, fractures or breaks, root intrusions, leaking water (usually infiltration from groundwater), and general deterioration. CCTV inspection can determine the specific location and cause of infiltration. Furthermore, CCTV inspection can be very economical when compared to other I&I inspection methods because it is accurate in pinpointing infiltration sources without requiring other inspection methods. 

Laterals — Solely inspecting and rehabilitating sewer mains is not enough when addressing I&I. Service laterals are often culprits of heavy I&I, particularly where a lateral connects to the sewer main. Careful inspection of private laterals can help identify sources of I&I. One study reports that when service laterals are renewed following sewer lining, an additional reduction of 20 to 25 percent of I&I is expected.

Make an impact

With deteriorating sewer systems and increasing need for capacity, mitigating I&I is essential. The city of Brentwood implemented a comprehensive program to address I&I that resulted in positive financial and environmental results. Brentwood rehabilitated 21 percent of its sewage collections system after carefully studying the location of pipe defects and I&I entry points. Rehabilitation efforts have resulted in an approximate reduction of 713.3 million gallons of I&I per year, or 42 percent. Additionally, the city is saving approximately $1.3 million each year. 

By implementing a total system approach of inspecting for sources of I&I and then planning rehabilitation efforts accordingly, municipalities can achieve a significant reduction of I&I. Once municipalities identify I&I problem areas, they can create a plan to address the defects found in a comprehensive manner, thereby adding to their success rate.

Only after a thorough understanding of the sewer system is achieved can a prioritized set of improvements be planned, designed and constructed. In this way, visual inspection tools are imperative to the success of minimizing I&I.

Venay Sehgal Bhatia is the digital marketing manager for Envirosight.

Moving beyond traditional video inspection

If the number, size and type of defects observed by video inspection do not appear to justify the volume of I&I identified in the flow monitoring, further investigation may be needed. In these situations, employing other technologies can help identify previously undetected defects. 

Sewer Scanning Evaluation Technology is an alternative technology to CCTV that removes the responsibility of rating the structural integrity of the sewer from the camera operator and gives it to the engineer. The 360-degree visual scan enables the entire surface of the pipe to be observed in flat view, giving the engineer the capability to measure the opening of joints and cracks as well as pinpoint telltale staining and deposits. 

Electrical leak location identifies pipe defects by measuring the electrical resistance of the pipe wall. Most sewer pipes are electrical insulators and will have high resistance to electrical currents. A defect in the pipe that leaks water will also leak electrical current, whether or not water infiltration is visually apparent at the time of the test.

Acoustic, or sonar, detection is increasingly being used to find leaks. Acoustic sensors use measuring devices to detect vibrations and sound waves emitted by defects and leaks. The sensors can be stopped during the inspection and pulled back and forth to reinspect a section of pipe or confirm a reading. This process provides utilities with real-time verification of potential problems. 


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