What we do

Challenge

Second World War and rebuilt in the early 1950s. With the exception of the former administration building and warehouse, all refinery-related structures were demolished and oil-related activities at the site were discontinued by 2001.

Following the closure of the refinery, cleaning and demolition works took place, after which the site was thoroughly investigated and widespread soil contamination was discovered which needed to be remediated.

Various fuels and petroleum-related products were produced during the refinery operations, including (but not limited to) transformer and lube oils. These oils were produced through vacuum distillation and cleaned via acid treatment and filtration. The production process resulted in waste materials such as acid tar and Fuller’s Earth being found within the eastern portion of the site (eastern coast of the Vallø peninsula, facing Oslo fjord). Remediation was required to comply with the ‘Miljødirektoratet’ (Norwegian Environment Agency) criteria, whereby the land has to be suitable for commercial and residential use.

Construction workers on the construction site of Valloy, Norway

Solution

DEME was awarded this complex remediation project in a joint venture with Veidekke ASA. Based on our fields of expertise, DEME took the lead regarding activities related to waste treatment and disposal, and Veidekke ASA was responsible for the civil and excavation works.

This challenging project highlights the close cooperation required between DEME, ExxonMobil and the Norwegian Environment Agency. Given the extremely strict health, safety and environmental standards, it was crucial that we had the most stringent data management system in place. Data capture and a thorough measurement campaign formed a vital part of the project.

Our soil remediation activities consisted of the removal of the most heavily impacted soil materials and any free-phase oil products encountered during the excavations. Our solution for the proposed two site areas, Area A and B, would remove the most important active sources that would impact the groundwater within the two Areas and, in the long-term, groundwater quality would also further improve through natural attenuation. We also monitored the groundwater during and after the remediation to verify that the natural attenuation was taking place.

Used technology

Environmental technology

UXO removal

DEME also examined the site for the likely presence of UXO and we discovered four, intact Second World War bombs ranging between 500 lbs and 1,000 lbs, as well as other UXO. Each bomb had to be cleared by the Norwegian army with the strictest safety procedures in place. The nearby village was evacuated and we built protective layers around the bombs to limit their impact when they were detonated.

Sorted and segregated waste streams

We removed all the waste above ‘Site Specific Acceptance Criteria’ (SSAC) by a careful, layer wise excavation in 25 x 25 m grids because of the possibility of the presence of UXO. We then sorted and segregated all the waste streams (hazardous and non-hazardous), if feasible, and the different waste fractions (soil, bricks, concrete, metal) were delivered to ExxonMobil approved landfills, if it was not possible to reuse them on site. In Area B, we first conditioned the removed hazardous Acid Tar in a mixing plant by using lime and wood fibre. This neutralised and stabilised material was stored on site until it was accepted at an approved waste (co)incineration plant or site. We transported all of the material off site by trucks and vessels.

Boulders, with a surface contamination requiring treatment, were cleaned mechanically using a surface scrubbing process (impact crushing), resulting in a reduction in the size of the boulders. We removed the contaminated fines fraction from the coarse fraction by segregation and this was subjected to chemical analysis to determine the appropriate treatment/disposal option. After verification of its quality through chemical analysis, the coarse fraction could be reused on site.

Eventually, we treated over 75,000 tonnes of acid tar and more than 650,000 tonnes of contaminated soil. The excavated acid tar was also turned into good quality, usable secondary fuel.

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