At 2:30 pm inside a paper mill located 5 km east of Arcachon Bay, a 5,000-m³ black liquor tank ruptured. Black liquor is a highly alkaline paper manufacturing residue composed of organic matter, soda and other chemical products; it serves as a fuel for boilers used in the paper pulp production process. 4,000 m³ of this product at 85°C spilled over a 2 to 3-ha area within the mill. After destroying a low retaining wall, 100 m³ of product overflowed into the LACANAU and then the LEYRE Rivers. The rest of the liquor was channelled into a backup pond. The mill operator plugged a stormwater pit connecting the site with the LACANAU River using earth in 2 spots, in addition to shutting down installations, activating the internal emergency plan and ordering personnel to evacuate. Assistance was requested from an agency specialised in emergency situations and a measurement network set up along the 2 affected watercourses. According to the press, 300 kg of dead fish were recovered on the banks, while aerial surveys estimated the pollution had spread along a 2-km length. The Prefecture banned swimming and boating on the two rivers. The gendarmerie was assigned to enforce these measures. Local drinking water supplies were not threatened, since no extraction point was located within the affected zone. Arcachon Bay oyster farmers were informed of the pollution incident. The Prefecture held a press conference at 10 pm that evening.
The next day, as analyses indicated no further traces of pollution, the swimming and boating restrictions were lifted. A series of emergency Prefecture orders were enacted so as to:
– recover and dispose of the product released (6th July, 9th July, 3rd August);
– authorise the partial start-up of installations, with the aim of draining a digester to allow performance of maintenance on a black liquor injection pipe (20th July, 14th August);
– conduct an impact study on the surface water, sediments, groundwater and soils due to the accident, focusing on conditions in the designated Natura 2000 nature zone in the valleys of the wider and narrower arms of the LEYRE River (6th July), and then propose appropriate remediation measures (6th July);
– identify the causes of this accident (6th July);
– authorise restart of the entire facility, extending to all controls, repair work and measures adopted by the company (23rd August).
The operator proceeded to treat all pollution confined to the site by transfer to authorised waste handling facilities, with one mobile treatment unit being delivered by lorry and another in situ batch processing operation. The residual effluent from these two on-site treatment streams was then discharged into the physicochemical sedimentation tank at the mill’s water purification plant.
To ensure a successful restart of operations, the operator inspected 107 of the site’s 194 tanks, all of which contained black liquor. 16 tanks were deactivated at the request of company executives (12 had already been removed from service before the accident); moreover, the filling capacity on some containers was limited. Another black liquor tank, built the year prior to the damaged one, was to be replaced by new equipment. The firm also made plans to rebuild the backup pond in 2014. Production losses due to the accident were considerable; the company’s Managing Director estimated for the press that a day of downtime cost €200,000, i.e. in excess of €6 million since the 5th July accident. Nonetheless, many maintenance operations were prepared to avoid the maintenance shutdown scheduled for 9th through 21st September 2012.
The tank in question showed signs of aging and corrosion. The mill operator had scheduled complementary inspections on this tank for the end of July 2012 specifically to ensure its suitability for continued service.
As part of the judicial hearing, an initial appraisal was conducted on a tank fragment, in order to determine the accident cause. These investigations are still underway.
Three months after the accident, 3 individuals were still receiving psychological treatment. Production losses had topped €10 million and pollution cleanup costs had been valued at over €1 million. Property damage at the mill has been estimated at between €2 and €10 million.
Measures relating to environmental responsibility law have been put in place with the operator required to continue monitoring impacts until 2014 with respect to groundwater, surface water as well as flora, fauna and habitats.

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