At 6 a.m., during a shift inspection, the upstream shift crew of an oil-fired power plant located on the seafront detected hydrocarbons in the rainwater and industrial water discharge channel downstream of the decanter. The operations manager ordered the immediate closure of the valves in the downstream part of the canal to contain the pollution, as well as the verification of all the installations. At 7:30 am, the shift supervisor reported coastal oil pollution around the wharf downstream of the discharge channel.
At 7:50 am, on the orders of the operations manager, the site personnel redeployed a floating boom already in place for the unloading of a heavy fuel oil vessel scheduled for the day. As soon as they arrived, the emergency services were supported by two of the operator’s clean-up experts who had taken part in an exercise on the site the previous day. Absorbents were placed all around the discharge area, which was delimited by the mouth of the canal, the floating boom and the riprap of the wharf. A private company recovered and disposed of 70 m³ of polluted water, as well as the soiled sorbents.
On the morning of the accident, the operator issued a press release and gave interviews to local radio and television.
The site’s wastewater treatment facility consists of settling tanks, treatment ponds and a discharge channel from upstream to downstream. A chain of material and human failures was observed. The lift pump of a diesel unit drip sump failed to stop at its low level, continuing to operate until it was unplugged by the shift workers. A centrifuge also malfunctioned and discharged massive amounts of fuel oil. These two incidents led to a massive influx of hydrocarbons into the decanting basins, whose water/oil separators were saturated, allowing pollutants to flow into the treatment basins. The treatment basins have 2 independent devices: 2 oil filters on the one hand and 1 aeroflocculator on the other hand. At around 4:00 a.m., during a surveillance round carried out every 2 hours and when the oil filters were not operating, an employee noticed that the aeroflocculator was discharging hydrocarbons into the discharge channel. He stopped the equipment pump but, contrary to the instructions, failed to inform the head of the block, to close the valves between the aeroflocculator and the discharge channel and to carry out a visual inspection of the latter.
Furthermore, no anomaly was detected in the control room because the two cabins for monitoring the continuous measurement of hydrocarbon levels in the discharge channel had been inoperative since 15/09 (the breakdown notice was being processed). The material and human malfunctions were finally aggravated by heavy rainfall (1 m of water in 24 hours).
The operator repaired the defective equipment, carried out an audit of the industrial water treatment plant, treated the discharge channel, analysed its monitoring procedures and raised the awareness of all its personnel. An exercise involving the state services is planned for the following year.
