Surprise leaks lead to short-term rehab of a 90 year-old water reservoir

PUC undertook immediate action to empty the reservoir so that RVA could complete a visual condition assessment. The primary focus was to evaluate the structural integrity of the reservoir and provide repair recommendations to recommission it as soon as possible. CCT#1 and CW#3 were emptied while the influent and effluent chambers remained in use under emergency bypass operations.

Condition assessment

The leak was thought to have originated from some of the 320 linear metres of small to large cracks (<1 mm to 25 mm) scattered across the floor slab. When the reservoir was in operation, and varying liquid levels were present in the CCT#1 and CW#3, water leaked through the floor cracks. It travelled laterally, creating an interconnected network of voids underneath the slab. Fortunately, the reservoir had been built on native silty clay which provided some resistance against erosion when subjected to leaking water. Once the excavation for the new reservoir was complete, the water found a path through the southern berm and was no longer contained by the silty clay.

The majority of cracks were found to be in the floor slab and were parallel to column grid lines. They ran from wall to wall in both directions and at regular intervals. Many of the cracks coincided with construction joints that were not properly prepared and likely did not include a waterstop. Some of the floor cracks were diagonal to the grid which indicated concrete shrinkage during construction.

Deterioration of the concrete walls and columns was present throughout the reservoir, probably due to the combined effects of concrete segregation during construction and chemical attack throughout its extended lifespan. Segregation allowed chlorinated water to attack the concrete which reduced its strength and further accelerated deterioration. Several columns had previously been repaired by the installation of concrete jackets around their bases. This was probably done as a result of heavy segregation during construction.