Skredet Stenungsund

The Landslide in Stenungsund

On the night of September 23, 2023, a major landslide occurred in Stenungsund, causing significant damage to infrastructure, including parts of the E6 highway and the nearby Ucklumsvägen. Since then, the Swedish Transport Administration has been responsible for the reconstruction of the E6, while the municipality of Stenungsund is handling the restoration of Ucklumsvägen. Peab is the contractor for both of these parallel projects, and Swedish Hydro Solutions has provided equipment and expertise for water treatment.

On May 30, 2024, the Swedish Transport Administration announced that the E6 in Stenungsund would reopen for traffic on July 5. Swedish Hydro Solutions has been on-site with water treatment since February 2024, and our work will continue until the project is completed.

Originally, the forecast for the E6 reopening was initially set for early autumn, and no later than the end of 2024 or early 2025. However, since the work has progressed well and the foundation work at the landslide area has been completed, the Swedish Transport Administration has been able to revise their timeline, as stated on their social media in April 2024.

– Our water treatment systems will remain in place for a while even after the E6 has opened, as there is still work to be done in the roadside areas, says Andreas Pettersson, project manager at Swedish Hydro Solutions.

The municipality of Stenungsund mentions on their website that they currently do not have an official completion date for Ucklumsvägen.

Skredet Stenungsund

Background

Just one week after the landslide, the Swedish Transport Administration established a project organization and dispatched geotechnicians to understand the extent of the landslide. Test drilling was conducted for geotechnical investigations and to determine which foundation methods would be needed for the road's reconstruction.

In the initial phase, the Swedish Transport Administration's top priority was to minimize the risks for the upcoming reconstruction, prevent further landslides, and ensure that personnel could work safely on site.

Ucklumsvägen, which runs parallel to the E6, was also affected by the landslide, but Stenungsund municipality has been responsible for the road's restoration. However, the Swedish Transport Administration and the municipality have worked closely together, and both projects have proceeded in parallel. The Swedish Transport Administration appointed Peab Anläggning as the contractor about a month after the landslide, and shortly thereafter, Peab was also assigned the contract for Stenungsund municipality.

The ground would be stabilized using lime-cement columns, which increases the pH level. Therefore, we began by delivering equipment consisting of our pH adjustment system and online water monitoring to assess its condition before discharge.

— Andreas Pettersson, Project Manager, Swedish Hydro Solutions

Skredet Stenungsund

Soil stabilization led to the need for water treatment

As the soil stabilization work was about to begin, Peab contacted Swedish Hydro Solutions for assistance with water treatment.

– The soil was to be stabilized using lime-cement columns, which increases the pH level. We started by providing equipment consisting of our pH adjustment system and online water monitoring to assess its quality before discharge, says Andreas Pettersson, project manager at Swedish Hydro Solutions.

– Later, the system was supplemented with our flocculation and precipitation system, including chitosan dosing and sedimentation, to address the particle content, Andreas continues.

We then integrated our HydroBox into the E6 installation, with the capacity to handle approximately 40 cubic meters of water per hour, with the possibility of increasing to an additional 40 cubic meters if needed.

– Shortly after we installed the chitosan treatment in the HydroBox, we observed a significant improvement in the quality of the outgoing water. The chitosan worked exceptionally well in this context, adds Andreas.

Since we, for obvious reasons, did not have the opportunity to design a technical solution for water treatment in advance, we had to develop the installation as the project progressed. The good dialogue with Swedish Hydro Solutions has been crucial for the successful outcome.

— Jonas Astonson, Environmental Coordinator, Peab

Skredet Stenungsund

The facility has been adapted and scaled over time

One challenge with the project has been the need to design and build simultaneously, which also affected water treatment.

– Since we, for obvious reasons, did not have the opportunity to design a technical solution for water treatment in advance, we had to develop the installation as the project progressed. The good dialogue with Swedish Hydro Solutions has been crucial for the successful outcome, says Jonas Astonson, environmental coordinator at Peab.

In addition to pH adjustment and chitosan treatment in the HydroBox, two lamella separators and a collection container were installed for effective sedimentation and sludge management.

At the start of the water treatment at the E6 site, the municipality of Stenungsund also required water treatment. After the installation at the E6 site was developed, a similar system was established at Ucklumsvägen, consisting of pH adjustment, a HydroBox, and lamella separators.

– Given the conditions of the projects, both installations needed to be as space-efficient as possible. They had to be modular to allow for ongoing process adjustments without affecting the completion timeline or compromising the quality of the outgoing water. This worked perfectly in close collaboration with Jonas at Peab, adds Andreas, project manager at Swedish Hydro Solutions.

Skredet Stenungsund

Fish are still spawning in the river

Norumsån, which runs alongside Ucklumsvägen, has shifted to a new course following the landslide. A bit downstream, it serves as a recipient for both treatment facilities. This is evident at the Ucklumsvägen installation, where a pipe leads directly from the facility and discharges the treated water into the stream.

– Sometimes we can discharge water directly into a recipient, and here it was very convenient that the stream flowed right below the facility, says Andreas.

During a site visit, a construction worker mentioned how he had seen fish jumping in the stream, despite its new path.

Jonas from Peab adds that there are trout in the stream.

Andreas from Swedish Hydro Solutions hasn’t seen the activity himself but notes that the fish likely use the brook as a spawning ground.

– Before the project, Peab anticipated that the pH levels could be high, and the equipment on-site has worked well to manage this. We have maintained very high quality in the water we’ve discharged into Norumsån. The strong cooperation and prioritization of water treatment have protected Norumsån from further damage after the landslide and helped preserve its environment, especially for the fish, concludes Andreas.

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