Leak Detection and Repair

Leak detection has long been a vital part of system operations for all conscientious water providers; however the methods for detecting leaks vary widely.    In that leaks will always be a part of a water distribution system, given the complexity and age of our water utility infrastructure, best management practices need to be employed to detect and facilitate leak repair, based on the requirements of the utility, the economics of the efforts, and the operational limitations of the organization (see the discussion of "recoverable real losses" in the introductory section of the Water Distribution BMPs). 

Leak detection can be supported through various programs and practices; however the most effective practices are those that are performed with precise regularity.  Leak detection programs can vary widely in terms of costs and efforts, depending on the size and complexity of the distribution system.  Therefore, care should be taken when selecting programs and practices for consideration and ultimately implementation at a utility.

The specific methodology that a water utility selects for leak detection is based on available resources.  Most effective leak detection programs utilize a number of programs and practices.  Many water utility managers employ an analysis of leak records to predict areas of concern.  However, leak surveys are the single most popular leak detection method whereby those appurtenances that are accessible such as valves, fire hydrants, service connection curb stops and other access points are accessed and sounded. It is not unusual for utilities to emply more than one leak detection method to search for and locate active system leaks. For example, transducers can be deployed and programmed to “awaken” at minimum noise hours (using leak noise loggers (LNL)), as one way to assist in manual leak detection efforts.  However, all leak detection methods require that data is collected in an orderly manner, and that the data is cleansed, assessed and evaluated to support the utility's overall water loss control efforts.

For those water utilities that do not have the resources, the Colorado Rural Water Association has equipment that may be leased to perform acoustic leak detection testing.  Otherwise, small and medium utilities should implement regular practices to detect and track leaks using the following methods described above an in the water distribution system data collection and management BMP:

  • Track leaks and repair leak reports.
  • Collect instantaneous water production measurements (at least daily) for comparison to previous days and past years of record.
  • Install meters in various locations within the distribution system (creating district metered areas) and collect flow measurements instantaneously (or at least daily) from these locations for comparison to previous days and past years of record.
  • Conduct regular field surveys to look for surface expression of leaks.
  • Conduct acoustic leak testing whenever practical, especially in areas of high concern.

Once a leak has been detected, the leak should be repaired as soon as possible and practical.   Typical leak repair techniques include (based on AWWA, 2009):

  • For small leaks, simply tightening a few bolts on valve or pump packing may alleviate the problem.
  • Service line leaks are very common for all water utilities.  The repair team/contractor will have to determine if the service line can be repaired or replaced completely, depending on the nature of the leak and the age of the service line.  Another consideration may be whether or not the utility is scheduled to replace or upgrade the water meter, yoke and/or backflow prevention device.  Replacing any or all of these items may dictate whether or not the entre service line is replaced.  Note that there are trenchless methods for service line replacement.
  • For small to medium water lines, repair clamps are commonly used to quickly repair a ruptured or broken water line; however, clamps may not be applicable to some kinds of plastic pipe (e.g., ABS) that has a tendency to split.
  • Pipe joints are often the site of smaller leaks caused by worn joint material, uneven settlement of pipe, age, or other impacts.  For split bell-ends of pipe, replacement may need to occur, whereas there are clamps that can be used to encapsulate the bell without its removal.  Some joints can simply be re-caulked.
  • Larger ruptures or splits in pipe, the faulty section may need to be removed and replaced.  Care should be taken when replacing a pipe of one material with another.  For example, ABS pipe is known for splitting.  It is also known for not being commercially available.  Therefore, ABS it is commonly replaced with other plastic pipe (e.g., PVC); however, special attention is needed when coupling PVC to ABS pipe, for proper joints must be maintained.  Similarly, if one type of metallic pipe is replaced with another metallic pipe, consideration should be made for the potential of accelerated corrosion when different metals are coupled.

Regardless of the repair needed, often special tools and skills are needed to repair and/or replace pipe and related appurtenances.  Therefore, leak repairs must be undertaken by only trained professionals that have experience with the pipe materials at hand.

 

Tracking of Water Production

Instantaneous and/or daily tracking of water production and comparing the trend from day to day and year to year (for the same day each year) can be a very effective practice for identifying certain types of leaks.  This is especially effective for leaks that are new and are of a large enough size that they can be detected within the total water delivery of the water utility.  Tracking water use through meters dispersed within the distribution system can also help identify whether or not a leak may exist if the data is collected daily, or preferably more often.  Instantaneous night time readings of system water production and use can be very helpful in characterizing water leaks.

Although this is a simple method that can be readily implemented by any water utility, it is limited in its effectiveness in locating a leak.  Other leak detection methods are needed to support this effort; however, it is possible to use this method of water production tracking as a trigger for implementing more rigorous field programs.

 

Field Observations

Most water utilities have many eyes in the field, for their staff and customers will report the presence of abnormally wet ground or other indication of a water line leak to the utility.  For some utilities, field observations (e.g., riding the lines) is triggered if water production increases without known cause.  In this way field observations can be very helpful in locating and ultimately repairing leaks. 

Unfortunately, there are many natural conditions that may limit the effectiveness of field observation.  Examples include the leak is too small to surface, the soils underlying the leak is porous and allows the leaking water to infiltrate down into the ground (as opposed to coming up to the surface where it could be spotted), the ground is covered with snow, the ground is wet from precipitation, the leak surfaces in a location that cannot be readily observed, etc.  Therefore, field observations, while important and typically cost-effective, are not as proactive as other leak detection programs can be.  

 

Shocking the System

Some water utility operators of small systems have utilized a method of “shocking the system” to identify leaks.  This method involves turning off production from surface or groundwater supplies, then turning the system back on to send a transient, or water hammer, through the distribution piping.  This transient may help to exacerbate a leak and thus help bring water to the surface for field observation.

This method, while it can support helping to find a leak, is not recommended, since transient pressure waves sent through a distribution system can create new leaks, and increase the effect of existing leaks.  Water utility operators using this method should proceed cautiously.

 

Acoustic Leak Detection

Acoustic leak detection is a technique for locating an unreported water distribution system leak based on the noise leaks generate underground.  To conduct acoustic leak detection testing, the equipment (listening devices) must be able to be placed in direct contact with the pipe.  Therefore, it may be necessary to excavate access holes to allow for the testing equipment to be deployed.  In addition, acoustic leak detection equipment, which can be used on any pipe material, is best on metallic pipe, since sound travels more efficiently in metallic versus non-metallic materials.  More access holes will need to be created to test PVC, plastic and/or other non-metallic pipe as compared to metallic pipe.  In addition, soil conditions may influence the effectiveness of acoustic methods to detect some leaks.  For example, sandy soils transmit sound better than clayey soils.  System pressure and ground cover impact the effectiveness of acoustic testing.  Systems under higher pressures (at least greater than 15 psi) tend to generate more noise, than lower pressure systems.  Paved ground surfaces also tend to amplify the noise of leaking pipes in comparison to sod or natural terrain, which can act to muffle sound.

 

Non-Accoustic Leak Detection Methods

Acoustic leak detection is one means of detecting leaks in pressurized water distribution and delivery systems.  There are however several other methods that are available to identify leaks in piping and related appurtenances.  While each method may have certain advantages, it may also have limitations related to availability, accuracy, and applicability to specific conditions.  The following methods are currently in limited use commercially, although research continuous on these and other new methods (AWWA, 2009). 

Gas Tracer Method – this method involves the use of tracer gas to pinpoint small and hard to detect leaks in empty and full pipe systems.  Helium is used as a tracer gas in empty pipe sections, whereas hydrogen can be injected into full pipes, since it can be injected in liquid form (noting that handling hydrogen gas can be a highly hazardous operation that should only be undertaken by trained professionals).  The injected helium or hydrogen leaves the pipeline at a leak in the gaseous state and it detected on the ground surface using highly sensitive instrumentation.

Ground-Penetrating Radar (GPR) – this method could potentially be used to detect voids in the ground caused by leaks, or by variations in saturated depth to water.  GPR is implemented at the ground surface using sound waves to penetrate the ground.  As the sound waves bounce back to the surface, they are detected and recorded identifying anomalies. 

Thermography – this method detects thermal infrared radiation and displays it in visible images.  In an infrared radiation image, water leaks may appear as areas of cooler or warmer areas within the soil, or may appear as a result of some other discontinuity identifying a potential area of concern. 

 

Resources

Colorado Water Utilities Council (to track training opportunities)

Colorado Rural Water Authority (for training)

American Water Works Association, M-36 (for methods)