The investigation found that the level gauge had stuck at random times after a tank service in August 2005, but it did not concern maintenance contractors or site management. The independent shut-off switch was not fitted with a critical padlock to allow its check lever to work. Secondary containment (meant to trap the petrol in a retaining wall around the tank) failed and allowed petrol to flow out. Tertiary containment (drains and catchment areas to prevent release of spilled chemicals to the environment) also failed, and fuel and firefighting foam entered groundwater supplies. The investigation found secondary and tertiary containment to be inadequately designed and poorly maintained.