Sainte-Anne-sur-Brivet

The incident

On 5th April 2016, earthmoving work to bury power lines in Tragouët, in the municipality of Sainte-Anne-sur-Brivet in north-western France, caused a leak from the pipeline which runs from Donges refinery (Loire-Atlantique) to the storage facility at Vern-sur-Seiche (Ille-et-Vilaine). An estimated 400 m³ of diesel fuel containing an additive (FAME - Fatty Acid Methyl Ester) was released from the pipeline, affecting a residential area then the natural environment.

The spill started by trickling through the roadside ditches before reaching a stream which flows successively into two ponds surrounded by wetlands. The fuel then flowed towards the confluence with the Brivet, some 3 km downstream, which drains the Brière marshes and is of great environmental importance.

The pipeline pumps were shut down as soon as the drop in pressure was detected, and the pipeline section was isolated after the company reported the leak’s location. The refinery’s internal emergency plan was activated; the refinery’s firefighters and an emergency response vehicle were mobilised immediately, as was the Loire-Atlantique fire and rescue service (SDIS 44). Pumping and containment equipment was sent to the site of the leak, and containment measures were put in place at the ponds to prevent the pollutant from spreading downstream.

 

Measures were rapidly implemented to protect the area and local inhabitants by the command centre, which was set up within hours of the spill under the auspices of the local authority (Préfecture de Loire-Atlantique):

• evacuation of the inhabitants of around ten affected houses along the edge of the road,
• cordoning off of affected area and ban on traffic,
• preventive ban on water consumption (streams and wells)
• bans and specific monitoring of the pollution of houses, several wells, gardens and individual sanitation systems (septic tanks, etc.),
• various response actions immediately implemented at the source of the leak.

Pollution response

Alongside the immediate response implemented by the fire-fighters from Donges refinery and the Loire-Atlantique fire brigade (SDIS 44), two specialised companies were contracted on the very first evening to carry out clean-up operations.

Clean-up sites were set up for three specific types of affected areas: ditches, ponds and surrounding wetlands, and streams. At the height of the response, 200 people were involved in operations each day.

Ditches

As the incident occurred at the edge of road, the fuel collected in and flowed through several hundred metres of roadside ditches. In the village, the ditches were drained using vacuum trucks, then scraped out. Downstream, to avoid the need for dredging, facilitate self-cleaning and slow the progress of residual pollutants towards the ponds, small accumulations of fuel at the base of the vegetation were recovered by pumping. Sorbents and filter barriers were placed in the entire length of ditches, where rinsing and fuel recovery operations were latterly carried out to compensate for the low rainfall at the time.

Ponds and surrounding wetlands

The largest quantities of fuel collected in the ponds and surrounding wetland areas. At the downstream end of the ponds, large amounts of fuel accumulated along the walls and weirs, after the structure’s outfall was closed to prevent the oil from spreading. In the first few days following the leak, the layer of diesel floating at the surface was several centimetres thick in these areas. It was at these sites that the greatest clean-up efforts, in terms of the workforce and equipment deployed, were concentrated.

During the initial clean-up phase, containment, pumping, storage and transfer operations were set up. The fuel was contained by light-weight floating booms, used in conjunction with manufactured sorbents (mainly skirted booms, simple booms and pads), bunds with pipes and bales of straw. To recover the oil from the banks, weir skimmers connected to diaphragm pumps were initially used. This solution was then replaced by oleophilic skimmers (disc and grooved drum) connected to centrifugal screw pumps, offering a more selective system which was less sensitive to oiled plant debris. This helped to optimise the quantities recovered by only collecting a small proportion of water. Along the flooded wooded banks of one of the ponds, access was impossible for vacuum tankers and space was extremely limited for the installation of temporary storage areas. Floating hoses were therefore set up over considerable distances to transfer the oil to an accessible area.

During the final clean-up phase, operations in the ponds were difficult due to the complex morphology of the banks and the dense vegetation (damp woodland, wet grassland, reed beds), in particular with the presence of a remarkable stretch of water horsetail upstream of one of the ponds. To remobilise the fuel trapped in vegetation on the banks without damaging the environment or potentially burying the fuel, a low pressure rinsing system was set up to flush the fuel towards recovery points in areas of open water. These rinsing operations were carried out either from small boats on the water body using medium pressure jets or from the banks using a sprinkler system (variable droplet size and reach). The arrangement is completed by a low pressure flow at ground level created by perforated pipes. Simultaneously, the flow rate of the stream which irrigates the wetlands surrounding the first pond was increased by pumping water from the pond (100 m³/h) and reinjecting it further upstream. The residual fuel released by these operations was recovered on the water using skimmers, by trawling and occasionally using water suction systems. In difficult access areas, the fuel was pushed towards the banks by operators in the water, wearing waders and carrying blowers. It was then recovered or collecting using floating sorbents. In a few oiled areas, surfaces (pond walls) were manually scraped and oiled vegetation was cut back in places.

Streams

Upstream of the ponds, in between them, and downstream towards the River Brivet, many sorbent booms were deployed at the surface of the streams and filter dams were built in the water column. Makeshift barriers  were built using wire mesh and loose sorbents or bales of straw. These systems were alternated or reinforced with manufactured sorbent booms and pads. Whether in easy access areas, such as bridges, or in wooded banks which were difficult to access, these installations required very regular maintenance to ensure they remained effective. Meanwhile, oiled plant debris and oily sheen was recovered manually.

Site-related difficulties

The regulation of the water level in the ponds raised a two-fold issue during the first weeks. It was important to:

• prevent overspill of the fuel if the pond were to overflow downstream in the event of heavy rain, by deploying considerable pumping equipment — four high flow rate centrifugal pumps and mobilising a duty team around the clock,
• restrict the drop in water level in the ponds to prevent oiling of the banks by prolonging the floating oil recovery phase.

Changes in wind direction meant that several recovery areas had to be set up and containment systems had to be frequently readjusted to prevent recontamination of areas that had already been cleaned.

 
Given this fragile environment and the site access difficulties, particular efforts had to be made in terms of traffic channelling and reduction (transport of equipment and movement of personnel), by marking out, building and consolidating pathways (e.g. walkways).

Environmental sensitivity

The ponds, riparian wetlands and streams form a patchwork of environments of ecological interest, justifying the introduction of precautionary measures during the response and influencing technical choices (in particular the implementation of major rinsing operations).

 
Preliminary surveys of wildlife contamination and mortality (in particular aquatic invertebrates, amphibians, fish and birds), as well as preliminary vegetation surveys, were carried out by the French agency for water and aquatic environments, ONEMA (now OFB), throughout the response. A system of perforated hose pipes, supplied with compressed air, was set up to compensate for a potential oxygen depletion.

 

In terms of vegetation, burns caused by the fuel were seen on the aerial parts of certain aquatic plants, in particular horsetail. No mowing operations were recommended so as to avoid trampling the roots; after a few weeks, new shoots began to appear, as was the case for other species in the reedbeds. Spring growth of aquatic plants was also observed. The mortalities recorded were restricted to certain clumps of rushes which trapped the fuel.

  

Contamination assessment and monitoring

Very soon after the spill occurred, measurement networks were established to assess the degree of contamination of the environment. These measurements were taken in the water (river, ponds and wells) and the sediment, but also in the air at the homes directly affected by the spill. The quality of the drinking water supply was also tested. The tests measured the total hydrocarbon content, the PAH (Polycyclic Aromatic Hydrocarbon) content and the VOC (Volatile Organic Compound) content. 

 
Once response operations had come to completion, this measurement network was supplemented and reinforced to offer a comprehensive post-spill environmental monitoring programme so as to assess the spontaneous rehabilitation dynamics of the environment and the different compartments affected: sediment, surface waters (chemical analysis and biological indices), aquatic macroinvertebrates (standardized global biological index), fish populations, amphibians, odonates and birds.

These monitoring results showed that, by the end of the year of the spill (2016), hydrocarbon concentrations in the waters of the streams and the ponds were no longer detectable or were very low, while the sediments remained locally contaminated in the recovery areas along the dykes, where the largest accumulations of oil had been concentrated and which had been trampled by operators. The impact on flora and fauna was minor and localised, as the environment was already naturally constrained by significant fluctuations in water levels, with parts of the streams drying up in summer.

In 2017, monitoring data showed a return to ‘normal’ levels, in line with what was expected in this type of environment, as well as the presence of two emblematic species: the southern damselfly and the otter. However, in order for the owners to recover full use of their site (particularly for fishing), the ponds were drained at the end of January 2018 and a sediment sampling and analysis programme was carried out, which led, in the following October, to the dredging of an area of approximately 600 m² to a depth of 20 cm. The abundant terrestrial vegetation that grew during this dry spell was mown. Following these operations, the ponds were refilled with water and restocked with fish in early 2019.

Two and a half years after the incident, more than 5,000 tonnes of contaminated soil from the area, close to the nearby homes, had been excavated and replaced with clean soil. The contaminated soil was treated at Donges refinery for subsequent reuse.

Clean-up operations reached completion at the end of 2017 around the homes in the area and in October 2018 at the ponds.

In 2019, the Nantes administrative court dismissed the application to be exempted from all liability filed by the company that had commissioned the works, despite the fact that two €1,500 administrative fines had been issued by the Prefect of Loire-Atlantique.

Cedre's role

Cedre was called on from day one by the Loire-Atlantique authorities. Several staff members from Cedre were present on a rota throughout operations to assist the State services - in particular Onema (now OFB), SDIS 44, DREAL - as well as Total, responsible for coordinating operations, as well as the clean-up contractors.

Cedre provided its expertise in terms of surveys, recommendations on implementing the appropriate clean-up techniques and equipment, clean-up site monitoring and advice relating to the area's environmental sensitivity. Sampling and testing programmes were also implemented.
Furthermore, Cedre assisted the municipality of Sainte-Anne-sur-Brivet with its communication and information actions geared towards the local inhabitants.

Within hours of the spill, a chemist from Cedre was sent on site to answer the questions which soon arose on the product, its behaviour and its persistence in the environment. Several on-site missions were then organised to monitor, with figures in hand, the evolution of the water contamination and the behaviour of the fuel.
In addition to the samples regularly taken by Cedre's agents in the field and the analyses performed in our laboratory, two missions were carried out with the use of mobile analytical equipment on site.

The first aimed to ascertain the nature of the orange particles in suspension in the water.

The second, initiated as soon as the bulk of the fuel had been removed from the ponds, sought to determine the PAH levels in the ponds and streams. The stir bar sorptive extraction (SBSE) technique for PAHs was proven useful for field missions.

Cedre was then tasked with monitoring sediment contamination as part of the environmental monitoring programme; Cedre’s laboratory was able to distinguish between biogenic hydrocarbons naturally present in the organic sediments at the bottom of the ponds and samples showing residual contamination linked to the oil spill.

This was the first significant spill of biodiesel for which Cedre was involved in the response. During this spill, we observed specific behaviour as the product weathered, with gradual phase separation, the formation of an oily supernatant and sticky aggregates, leading to technical difficulties during recovery operations in the ponds. Cedre took advantage of these observations to expand its knowledge and, in the years that followed, carried out tests on the behaviour of biodiesel in its Polludrome®. These tests confirmed the behaviour observed in the natural environment.