Identifying the Difficulties in Locating Leaks in Non-Metallic Watermains
How do we define a leak?
Merriam-Webster’s (MW) definition of “LEAK” is 1 a: to enter or escape through an opening usually by a fault or mistake — fumes leak in; b: to let substance or light in or out through an opening — the roof was leaking. MW also has the term “SPRING A LEAK” which is: to suddenly let water in or out through a crack or break — the pipe suddenly sprung a leak.”
In our industry, the second terminology rings true. How do we find these leaks? A National Research Council “Construction Technology Update No. 40”, written by Mr. Hunaidi in October 2000 identifies the following tools for leak detection: Water Audits, Leak Detection Surveys (using listening rods, geophones and ground microphones), Leak Noise Correlators, Tracer Gas Technology (helium or hydrogen), and Ground-penetrating Radar.
This article also identifies the difficulties in locating leaks in non-metallic watermains. Since the year 2000, leak detection technologies mentioned above have improved and newer technologies have emerged, such as live leak detection from inside the watermain. GAME Trenchless Consultants has been involved in using live watermain leak detection tools since 2012 across North America. Some of our clients have called us in as a last resort, after they have exhausted conventional leak detection methods. Other clients have called on our Watermain Condition Assessment services to confirm existing status of the pipe prior to replacement or rehabilitation of their watermains.
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The tools that GAME Consultants uses for pressurized leak detection, not only pin point leaks, but also provide a high definition video inspection. We own and operate JD7 leak detection tools for both small and large diameter watermains. Since 2012, we have inspected more than 21.1 miles (34.1 km) of small diameter pipes (less than 12-in. or 300 mm) using approximately 550 access points. In the same period, we have completed 37 inspections covering approximately 8 miles (13.0 km) of large diameter pipe, ranging from 14- to 60-in. (350 mm to 1,500 mm).
We will present some specific situations where GAME was called in to find a specific leak after the client had used conventional leak detection tools but still had some additional leaks that were not successfully located. The tools we employ are not standard leak detection tools as they internally identify acoustic signatures and therefore can be used in all types of watermain pipes. Standard leak detection methods are at times less reliable in non-metallic pipes due to differences in acoustic transmission through the material.
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Access for small diameter leak detection is done through existing fire hydrants, direct taps onto the watermain or through test caps. Although there are numerous different types of fire hydrants throughout North America, there are three different operating styles: Compression, Gate or Wet Barrel. Similarities between the styles allows for the system to be modified whenever a new hydrant model is encountered. Once inside the pipe, the Investigator+™ tool gets pushed through the main as far as the conditions will allow and provides visual and acoustic footage.
For the larger diameter pipes, a LDS1000 tool enters directly into the main through pressure fittings. Being a long-distance range tool, the device can either travel throughout the network using a parachute while it is in service or it can be towed within an out of service main between two access points.
Since both tools are capable of operating in watermains that are in service or out of service, it is important to note that leak detection can only be performed while the main is under pressure. Leak detection using an internal acoustic tool is not as simple as having a computer algorithm identify noise within the environment since the moving tool also produces noise during the inspection. Operators are trained in the art of leak identification since differences in material, operating pressure, magnitude, diameter, etc will directly affect how a leak sounds. Contrary to what many people believe, a leak rarely produces any visual identifiers. Occasionally, an operator may get a break and catch a leak at an exposed or pinched gasket. On the rare occasion where a leak is more than just a pin-hole, you may be able to see the suspended particles lead through a joint or hole and the camera may even get drawn to the opening.
When it comes to the leaks themselves, similarities can be observed between situations on site. For new constructions, a pressure test which fails to hold 125 psi but stabilizes at 70 psi is most likely a gasket either rolled or damaged but that has not completely failed; a test which slowly drops from the testing pressure could be slightly opened joint which was overworked during installation; if pressure can’t reach testing pressure, a service connection may be opened or a gasket may have completely failed. When working on an aged network, an operator must listen for particular sounds while inspecting a section of main. Distinctive differences in sound between different pipe materials makes it easier to confirm a leak vs. background noise. Metallic pipes have the largest audible zone for a leak. Depending on the pressure, a leak may be heard a few feet (between 3 to 4 ft) before and after the actual source of the leak (in these situation, the leak is identified as being the location where the sound is at its peak). Leaks on plastic pipes on the other hand can only heard within a foot of the source therefore an operator must take extra care during the inspection to make sure it is not missed.
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In the past few years, we have been called in on projects that were failing tests because of leaks in the range of 0.5 gpm at 125 psi. As long as the leak is only at one location and not spread out between 2 or 3 different locations, we may still be able to locate it assuming it produces an audible sound. If a site has too much surrounding sound (vehicles, trucks, etc.) and a leak is not found on site at the time of the inspection, the recordings are then re-analyzed in house in a more sound-isolated environment.
Therefore, if you are looking for an overall condition assessment or require help locating a specific leak — GAME will be able to help out. Can you hear me now?
Piero Salvo, P. Eng., is president of GAME Trenchless Consultants and David Gosselin, Ing., is project engineer at GAME Trenchless Consultants.