Northumbrian Water Ltd v Sir Robert McAlpine Ltd

An occupier or contractor is required to take reasonable care when investigating utility services and carrying out works; the obligation is not absolute. In an isolated escape case, ordinary nuisance does not impose strict liability merely because damage results. Strict liability for an isolated escape depends on the rule in Rylands v Fletcher, including the applicable danger or mischief requirement. Damage must also be reasonably foreseeable. A party alleging failure to mitigate must identify the reasonable steps that should have been taken and show that they would have reduced the loss.

The claimant, a statutory sewerage undertaker, sought recovery of the cost of removing concrete from a public sewer. The concrete had escaped during piling works carried out for the defendant’s construction project. The defendant denied that the concrete came from its works and disputed liability in negligence and nuisance. It also alleged failure to mitigate.

The court determined the source of the concrete, whether the investigation and piling works were negligent, whether an isolated escape could found liability in nuisance without reliance on Rylands v Fletcher, and whether the claimant had failed to mitigate its loss.

1. Source of the concrete. On the balance of probabilities, the concrete found in the sewer was the concrete poured by the defendant’s piling subcontractor. The circumstantial evidence, including the location of the pile, the loss of concrete during piling, the timing of the escape and the location of the concrete, outweighed the equivocal expert evidence.
2. Negligence. The defendant’s obligation was to take reasonable care in investigating utility services and executing the works. It was not an absolute obligation. The claimant had not pleaded or proved a specific failure in the investigations or piling operation, and there was no expert evidence establishing the level of investigation reasonably expected for the development. The negligence claim therefore failed.
3. Damage. Concrete adhering to the invert of the sewer and materially reducing its efficiency constituted damage. Its removal could not properly be characterised merely as cleaning.
4. Nuisance and isolated escape. The court considered Cambridge Water Co v Eastern Counties Leather plc and Transco plc v Stockport MBC. The rule in Rylands v Fletcher is a sub-species of nuisance. An isolated escape does not create strict liability in ordinary nuisance where the claimant does not rely on that rule. Strict liability under the rule requires satisfaction of the mischief or danger test, which is not easily met. The nuisance claim therefore failed.
5. Foreseeability. The relevant question was whether the damage was reasonably foreseeable. The existence of a connecting drain was necessary for the concrete to reach the sewer, but its existence was not shown to have been reasonably foreseeable. The alternative foreseeability argument would therefore also have failed.
6. Mitigation. The duty to mitigate is not onerous, but the defendant bore the burden of identifying the precise steps that should have been taken and proving that they would have reduced the loss. That burden was not discharged.

The action was dismissed.