Underground Water Mains Leak Detection in Brackley

Symptoms

The property in NN13 had a suspected leak on the external mains supply. Initial conditions complicated matters from the outset: the road stopcock, which had not been updated by the water company, was found to have water present around the head, suggesting the gland nut was weeping.

When this was shut off to aid investigation, an outside tap was removed to allow further isolation but the stop valve on this had failed and was letting water by, meaning the supply could not be fully isolated.

Methods Used

Once the concrete was broken out and the ground exposed, the steel mains pipe was uncovered between a gas pipe to the right and a drain to the left. Water was found flowing from beneath the pipe.

The steel was cut out at the leak location and inspected at both ends. Although the pipe was generally in good condition, it had corroded through at two distinct points where the leak was occurring.

Investigation Process

1. 1
   Road stopcock shut off

   The road stopcock was closed as the first isolation step. Water was noted around the head, indicating a weeping gland nut on this fitting, which had not been replaced by the water company.

2. 2
   Outside tap removed; stop valve failure identified

   The outside tap was removed to allow further investigation, but the associated stop valve was found to be letting by, preventing full isolation of the supply.

3. 3
   Acoustic testing carried out

   Acoustic correlation was deployed along the external mains route. Anomalies were detected approximately two metres from the drain cover.

4. 4
   Concrete broken out and ground exposed

   Excavation began at the acoustic target area. The gas pipe was located to the right and the drain to the left, with constant water coming up from the ground during digging.

5. 5
   Drain condition noted

   An 18-inch section of drain was visible with a crack present. The water company advised the drain is misaligned; this was observed but was not confirmed as the source of the water.

6. 6
   Steel mains pipe exposed and leak confirmed

   The steel mains pipe was uncovered with water clearly flowing from beneath it. Two corrosion-through points were identified on the pipe where it had failed.

7. 7
   Steel pipe cut out and repaired

   The corroded section was cut out, the steel cleaned up at both ends, and the repair carried out using specialist UTC repair fittings and 25mm MDPE.

Result & Outcome

The corroded section of steel was cut out and replaced using specialist UTC repair fittings and 25mm MDPE pipe. The steel at both cut ends was in acceptable condition, confirming the corrosion was localised to the leak area. For a water mains leak detection job of this nature — where isolation is partially compromised and multiple underground services are present — the acoustic-led approach was the decisive factor in keeping groundworks controlled.