Promises bind only those who believe in them. And promises, in the case of the ballast pits of Braqueville, in Toulouse, there have been dozens over the past two decades. And dozens of others over the past century. The ballast pits are four lakes where more than 4,200 tons of nitrocellulose have been buried since the 1920s, an explosive product that was used in the manufacture of shells produced during the First World War, in the nearby gunpowder factory. This installation gave way to the southern chemical zone which lasted until the explosion of the AZF factory on September 21, 2001.
The biggest post-war industrial disaster had put this cumbersome file back on the table, with local residents demanding the evacuation of these strips, an estimated time of 46,000 tonnes, then reassessed at 5,000 tonnes, then 4,200 tonnes now. Today, 20 years later, the Oncopôle and its cancer patients have taken up residence near the gravel pits, which the cable car flies over daily.
If the immersion of nitrocellulose in water renders it inert, the outcry from residents pushed the State services a few years ago to relaunch the reflection on the depollution of this military site. Already in 2017, Bernard Cazeneuve, the Prime Minister at the time, announced that the work would be started by 2022. Three years later, one of his successors, Jean Castex, made a commitment by letter to the mayor of Toulouse to the establishment of a working group responsible for studying the file.
Two years later, a meeting of the monitoring committee dedicated to the rehabilitation project was held on 29 November. “The first results of the naturalist studies launched in the spring of 2021 have shown that beyond the presence of new species on the site, the environmental richness is growing rapidly. These studies have also made it possible to specify the potential methods of intervention for destocking operations”, indicate the prefecture of Haute-Garonne and the metropolis of Toulouse in a press release.
Depollution processes known mid-2023?
The site being classified Natura 2000, the flora and the fauna took back their rights there for a long time. What Geneviève Darrieussecq, then Minister Delegate to the Minister for the Armed Forces, had already noted in 2020 during a response to the National Assembly addressed to her by the deputy for the constituency at the time.
As for the rehabilitation processes that will be used, they are currently still being studied, indicate the State services. As early as 2013, the Directorate General for Armaments had proposed several hypotheses to treat this nitrocellulose. Firstly, that of thermal energy, which consists of burning it outside the site and the cost of which was then estimated at 40 million euros. The option of on-site biodegradation by bacteria had been considered, but it required setting up a Seveso site and the use of 9 kg of sand for one kilo of nitrocellulose. Difficult to set up with a hospital located right next door.
Nearly ten years later, the prefecture indicates on Tuesday that “three tests are currently being carried out over a short period” and that a “reduced volume of powder samples has been taken in order to compare these innovative processes with more conventional solutions. , such as the heat treatment of powders. Full results are expected in the first half of 2023.” And to conclude in its press release that “the work phase should start in 2024”. A conditional rigor in this file which looks like a real Arlesian.