Pilot Study uses Acoustic Technology to Evaluate Sewer Lines for Blockages and Breaks

Everything we flush, pour and rinse down the drain makes its way into our extensive network of sewage pipes below the ground. The system is designed to move wastewater away from houses and commercial buildings to massive sewage treatment plants. But in order to keep these networks functioning properly, it’s essential that utility and maintenance crews regularly inspect and clean the lines. Yet, the challenge often faced is where and when to perform these activities. KCI worked closely with officials in New Castle County, Delaware, to test a new inspection tool that can help prioritize resources and operations.

Residents in the county generate over 50 million gallons of wastewater each day. To service this need, the sewer maintenance department is responsible for ensuring that approximately 1,800 miles of sanitary sewer pipe and roughly 55 thousand manholes remain in proper working order. Mandated by their environmental regulator, the Delaware Department of Natural Resources and Environmental Control (DNREC), the county is required to clean 500 miles of sewer each year. This routine maintenance helps to remove debris, deposits, roots and grease from the sewer lines and reduce frequency and severity of sanitary sewer overflows and main line stoppages.

Looking at past problem areas, the county uses this data to determine how often a segment needs to be cleaned. Based on the total miles of pipe and the required amount of cleaning, the sewer maintenance department set their target cleaning frequency to every three years. Often, pipes in newer neighborhoods can be pushed out four to six years without having to be cleaned as frequently, but older infrastructure or areas with root or grease issues may need attention as often as once a year.

KCI has been managing sanitary sewer investigations for New Castle County for the last decade. Under an open-end contract, our team is responsible for identifying, evaluating and implementing new and emerging technologies that can help the sewer maintenance department operate more efficiently. Project manager Thomas Wyatt Sr. recognized that the pre-determined routine maintenance plan wasn’t effectively maximizing the county’s resources. While cleaning and inspecting pipes is essential, without knowing in advance whether the system is blocked, crews could be spending time in areas that don’t need to be cleaned. So when Wyatt attended an industry conference, he was intrigued to learn about a recently developed low-cost tool, the Sewer Line Rapid Assessment Tool, or SL-RAT, which provides a quick blockage assessment.

New-Castle-County-Sewer-Inspections-Running Test
The basic premise behind the SL-RAT is that if sound waves can travel unimpeded from one manhole to another, then the pipe between has no blockages or debris that could significantly affect the flow.

Manufactured by InfoSense Inc., the portable on-site assessment tool uses acoustic-based technology to detect blockage conditions in gravity-fed sewers. Originally developed for a specific municipal customer, the technology is best suited for pipes with a six- to 12-inch diameter, where the majority of blockages occur. Placed over top of two adjacent open manholes, a transmitter sends an acoustic signal down the pipe, and a receiver listens and interprets the sound. The technology measures the dissipation of sound energy in the airspace between the two units. Any obstructions within the pipe such as roots or grease will block the sound waves and create an energy gap.

Courtesy of InfoSense Inc.
Courtesy of InfoSense Inc.

One of the benefits of using sound energy is that it can easily navigate around bends and obstacles in the pipe, and the type of pipe material doesn’t affect the results. In less than three minutes, the device produces a numerical output on a zero to 10 scale, which relates to the segment’s blockage condition. This rating is based on years of experience and research and is designed to be conservatively cautious. Zero signifies that the pipe has multiple obstructions affecting the flow while a 10 indicates that the pipe is completely unobstructed.

In one day, a typical two man crew is able to inspect anywhere from 8,000 to 10,000 linear feet of pipe depending on the terrain. Crews essentially leap frog down a sewer line, moving one unit at time to the next manhole to inspect multiple segments. The only piece of information field technicians are required to input is the approximate length of the pipe segment.

One of the greatest benefits of this inspection tool is it helps to quickly prioritize where to focus cleaning operations. If a blockage is detected, crews can perform a more detailed inspection method, like closed-circuit television (CCTV) or move forward with cleaning the pipe. “It does not replace cleaning; it does not replace CCTV,” said George Selembo, CEO of InfoSense Inc. “This is something you do in front of those more expensive operations so you can spend the time cleaning the pipes that actually need it.”

Using cameras to validate and confirm the condition of a pipe is very costly and time consuming. The SL-RAT allows technicians to quickly and inexpensively go through the system ahead of cleaning crews to determine where pipes are clogged.

A municipality or utility can tailor the rating system to their own needs. When KCI began using the technology, crews would perform an assessment with the SL-RAT and then validate the results with CCTV video to gather visual evidence of what each rating represented. Based on these evaluations, the county decided that any pipe receiving a score of seven or above was in good condition and would require no current action, while a rating between four and six was considered fair and would need to be cleaned within three months, and a pipe with a score of three or below was in poor condition and required immediate action. KCI then conducted a pilot study to determine what percentage of the county’s pipes were actually in need of cleaning.

In the pilot study area, our team assessed over 56,000 linear feet of sewer lines. Without the acoustic analysis, the county would have spent time and money cleaning all of these pipes, but based on the SL-RAT assessments, the ratings revealed that only ten percent of the pipes required immediate action. “We’ve always suspected a lot of pipe doesn’t need to be cleaned, so that is what attracted us to the SL-RAT technology,” said New Castle County Operations Service Manager Robert Roff. “Instead of having an entire sub-basin that is supposed to be cleaned every three years from top to bottom, the SL-RAT is going to enable us to go through the whole system ahead of the cleaning crews and determine what pipes actually need to be cleaned and which ones don’t.” In addition to time and cost savings this technology is also helping cities meet their compliance efforts.

Since results are immediately displayed in the field, crews are quickly able to determine what areas need attention. Courtesy of Infosense

The Environmental Protection Agency (EPA) conducted a study evaluating the effectiveness of using the SL-RAT. Their results concluded that application of the tool can enhance a sewer cleaning maintenance program. The formal study is helping many cities streamline the process of gaining approval to use the technology to meet environmental regulations. In New Castle County, DNREC agreed and approved that assessments produced by the SL-RAT would count towards the county’s annual 500 miles of required cleaning. Whether crews are cleaning the pipes or proving them to be clean, New Castle County will be meeting their compliance efforts while saving time and using taxpayer dollars more efficiently. Recognizing the importance of providing the best service available to their residents, New Castle County is planning to put their projected savings right back into their maintenance program.

By introducing new tools like the SL-RAT to our clients, we can help them become more efficient and better serve their customers.

Thomas G. Wyatt Sr., Senior Construction Manager

Although, most of us don’t think about where our wastewater goes after it disappears down the drain, KCI is constantly evaluating new methods that can help improve sewer maintenance programs. By using the SL-RAT, New Castle County can easily determine where they need to focus their resources and operations, and eliminate unnecessary cleaning.