How to Find Underground Water Leaks

Water lines are often buried underground. This keeps pipelines from freezing, helps prevent physical damage, and keeps them out of sight. Unfortunately, this invisibility means that when a break or leak occurs it can be difficult to diagnose, locate, and repair. In this article, we address common reasons for underground leaks, damage prevention techniques, how to diagnose an pipeline with an underground leak, how to locate the leak, and steps taken to repair or replace a damaged pipeline.

What Causes Underground Leaks

Below are some of the most common causes of underground pipeline leaks along with methods for their prevention.

• Freezing: Unlike other liquids, water expands when it freezes. When this occurs inside a pipeline it can cause enormous stress on the walls, joints, and valves which can cause cracks and breaks. Freeze prevention methods can include deeper burial or heating elements placed along the length of the pipeline. Another method is to allow a small amount of flow to occur on pipelines in extremely cold weather. This is usually accomplished by allowing a faucet or valve to slowly drip.
• Drought: Soils can expand and shrink with changing moisture levels. This is particularly the case in soils with a high clay content. If drought conditions are severe enough, large amounts of soil can shift over the course of a few days. This can be enough to cause pipelines to move and break. Prevention methods include burying pipelines below the drought line and keeping soils moist with irrigation.
• Tree Roots: Tree roots grow slowly, but given time they can break up asphalt, concrete, and even bedrock. If tree roots push against or through a pipeline, they can easily cause significant damage. If there is a small leak already present on the line, roots may seek out the water and clog the line entirely. Prevention methods can include placing pipelines away from large trees or removing existing trees that could cause potential problems.
  
• Construction/Excavation: Most contractors will call 811 to locate utilities before breaking ground. Unfortunately, the marks can sometimes be in the wrong place and an accident can occur. Usually, the contractor is immediately aware of the issue and takes steps to start the repair process. Sometimes, however, the line is damaged without the knowledge of the contractor and can be reburied without a repair being made. Double checking all 811 marks with personal utility locators prior to excavation can help prevent these line strikes.
• Water Hammer: Water is heavy and large amounts of water moving through a pipeline system carry a lot of inertia. If a valve is closed too suddenly and the water comes to a quick stop, the momentum can cause large pressures to build up against pipeline walls, valves, or joints. The best water hammer prevention technique is to close valves slowly. Alternatively, some valves are manufactured specifically to prevent water hammer situations from occurring.
• Municipal Work: Many water supply systems are owned and operated by city and town managers. When repair or upgrade work is being performed on the line, damage can be occur and may not be recognized before restoration. The best prevention for this damage is to test repaired pipelines before reburial.

Determining if an Underground Pipeline is Leaking

Sometimes a leaking underground pipeline causes pooling on the ground surface or sink holes to appear. In these cases, diagnosing the problem is usually straightforward. However, water can travel long distances below the ground and may not reach the surface at all near the actual leak location.

Other signs of leaks can include abnormally high water bills, loss of water pressure, or a water meter that with rapidly increasing readouts.

To help determine if a system is leaking, all outlets such as faucets and hoses are first closed. After closing all potential water outlets, the system water meter or pressure gauge are checked. If the meter is still running, or if pressure is below where it should be, there is likely a leak on the line. If parts of the system can be isolated, doing so may make it easier to narrow down the section with damage.

Locating an underground water leak

If a leak is diagnosed, locating the underground water leak is the next step. Water supply professionals have used water line leak detectors for decades to help identify which buried lines are leaking and to pinpoint individual leak locations. Identification of which line is leaking is made during water leak surveys. Once the damaged line has been identified, the pinpointing of individual leaks can occur.

Water Leak Surveys: Water leak surveys are performed by utility professionals to determine which lines on their system are leaking. These are generally conducted on a street-by-street, or line-by-line basis. During these surveys, the ground microphone of an acoustic leak detector is put into direct contact with hydrants, valves, or pipelines and the operator listens for leak sounds conducted down the pipeline.

Since solids such as metal or plastic conduct sound better than soils this direct connection is an effective way to listen for leaks along long stretches of pipeline. The connection is generally made with a contact rod threaded directly to the microphone, or with a powerful magnet that allows the microphone to attach to an iron or steel valve or hydrant.

Water Leak Pinpointing: Once a leaking pipeline has been identified, the operator uses the leak detector’s microphone and walks the length of the line, placing the microphone on the ground every few feet. As the operator gets closer to the leak location, the leak noises become louder. After passing the leak location, the sound will begin to decrease.

Choosing the right underground water leak detector

If a water line leak detector is to be used, it is important to consider what type of locating activities will be conducted, the type of environment they are likely to be used in, and the amount of training required for the operator.

If a leaking pipeline has already been identified, a leak pinpointing device may be adequate for the job. If leak survey and pinpointing functions are both necessary, a unit with both capabilities should be considered.

Some water line leak detectors have noise frequency filters that can be useful in urban environments, but if the leak locating activities are primarily going to be focused in remote or rural areas, background noise filters may be unnecessary.

Repairing an Underground Water Leak

Repairs of underground leaks on public water lines should only be conducted by water service professionals or licensed plumbers. A repair process generally proceeds through the following steps.

General Steps for Repairing a Water Leak on an Underground Pipeline

• Identification: Using leak survey and pinpointing equipment such as an acoustic leak detector, the leaking pipeline is identified.
• Isolation: Many municipal water supply systems are designed as a grid to allow damaged portions of the system to be isolated. This minimizes the water service disruption and allows service for many customers to be restored before or during repair operations.
• Excavation: The damaged pipeline is excavated and exposed.
• Draining: If a leak is major or has been running for some time, the excavation may require pumping of excess water to expose the damaged line.
• Inspection: The damaged line is inspected to identify the leak and potential cause of the break. The cause of the line damage should be resolved before repairs begin.
• Repair/Replacement: The damaged line is repaired or replaced. If the owner of the system is currently working on upgrades, they may take the opportunity to upgrade the damaged section of line entirely.
• Cleaning/Flushing: Contaminants may enter the water supply system during the repair process. The repaired line should be flushed and sanitized before service is restored.
• Initial Testing: Pressure testing may happen during or after flushing to ensure that joints and welds are installed correctly and that the new line is watertight at pressure.
• Restoration: Once the line has been repaired and tested, the excavated area is backfilled and restored. This may include reburial of the pipeline, rebuilding of sidewalks or streets, and the planting of new grass.
• Monitoring/Testing: Testing and monitoring should be conducted on newly repaired pipelines at regular intervals to ensure that repairs are holding, and that all contamination has been removed from the system.

Routine Monitoring for Underground Water Leaks

Water supply organizations are usually aware of water main breaks almost immediately. Most suppliers have pressure monitors throughout their systems and operators are immediately notified of any pressure loss. However, the pressure monitoring systems may not be functioning properly, or small leaks may slowly grow into large leaks and large pressure drops may not occur.

Due to this, large water supply systems should have a leak monitoring regime that is routinely implemented. Water leak surveys can be conducted on a monthly or quarterly basis or after weather events such as deep freezes and droughts.

In conclusion, city and municipal water supply systems are large and may encompass hundreds of miles of pipeline. At any given time, multiple leaks can be present on these systems. Routine monitoring can be a useful tool for identifying minor or small water leaks before they become larger problems. They can also help prevent large numbers of small leaks from becoming a major systemwide issue on a water supply system.