A tank which catches drain oil at a service station overflows, allowing the products to leak into the boiler room of a neighbouring building. A water officer on site notices that the spill is coming through cracks in the wall and flowing into a sump equipped with a drain pump for the building’s wastewater. Given that this water is released directly into the storm water and then into the Seine river, the building manager suspends operation of the pump. Two weeks later, specialised companies clean out the oil pit and the boiler room basement. The station operator checks the tank’s tightness and conducts an analysis of the ground in which it is buried. The building manager installs a separate drainage system, which will prevent their waterborne sewage system from being released directly into the storm water.