During a transfer step involving used oil tanks at a conventional power plant, the oil level reached the tank’s overflow, which was directly connected to the dripping recovery pit for both the transfer zone and pumps. The oil level rose in the recovery pit above the level of the oil intake pipe coming from the oil trap, which was recovering all of the transfer zone’s runoff rainwater. The oil trap filled and the oil level rose into the transfer zone’s gutter. When the employee assigned to oversee transfer operations saw oil in the gutter, he immediately stopped the pump. The oil remained confined within the transfer zone, meaning that no contamination reached any other zone at the plant or the natural environment. The driver responsible for material transfers had completed three shifts, even though the plant had informed him the day before that only two shifts were possible given the site’s oil storage capacities. The used oil that spread into the gutter was pumped out. Immediately after this incident, an operating protocol addressed to power plant technicians was drafted to ensure that technicians did not validate a transfer step whenever the tank’s oil level had exceeded 150 m³. Over the medium term, a study was conducted to introduce safety measures that would shut down the power supply to transfer pumps once the oil level neared the overflow threshold in either of the two tanks or when the level had risen in the dripping recovery pit.