The E6 over Kvænangsfjellet in Finnmark is one of Norway's most weather-prone road sections. In winter, polar low pressure leads to large amounts of snow, drifting snow and a high risk of avalanches. During the 2020-2021 winter season, Norway was split in two almost 80 times. The only detour between Troms and Finnmark is almost 70 miles via Finland.

Soon it will be possible to drive the route all year round, without the risk of avalanches. Two tunnels are being built to make the mountain crossing more predictable in winter: the 3470 m Kvænangsfjelltunnel, which will lead the E6 away from a very weather-prone area, and the 2430 m Mettevoll Tunnel, which is an avalanche screening measure.

Focus on the environment

Nye Veier sets strict environmental requirements for the contractors with the aim of ensuring that the project has the lowest possible impact on nature. Among other things, both tunnels have requirements for the treatment of wash water, and the system in the tunnels is built up with a separate system for wastewater. The wash water is led into sedimentation tanks where the wash water is purified and sludge is collected for further handling.

The dimensioning requirements for the sedimentation tanks are that the tank must receive all wash water from the tunnel and store it for a period of time for decomposition and sedimentation. In addition, the tank must have space to take up to ^40m3 of liquid from a possible tank truck overturn in the tunnel. When the contractor had to choose a solution for the sedimentation tanks, the choice fell on polyethylene (PE) tanks from Haplast.

Haplast supplies 100% sealed sedimentation systems for roads and railways, helping the contractor to meet today's requirements for the treatment of wash water and sludge. Johannes Grønnvoll, Sales Manager at Haplast explains the solution:

• We manufacture polyethylene tanks based on ^KRAHTM technology. Polyethylene (PE) is a flexible and strong material that will stand the test of time. The tanks are made with double walls that provide good insulation. Smooth and bright interior surfaces simplify cleaning and inspection. We fully weld all our pipe penetrations, thus ensuring tensile strength and tight joints. It is essential that we avoid leaks when washing water from the tunnels must be handled properly.

For the project, tanks with an internal diameter of 3 meters were chosen. Both dry-installed and wet-installed pumping solutions were considered. The choice fell on the wet-installed pump solution. This does not require a separate chamber and is the most cost-effective option. 

Plug and play

The first two tanks were delivered to Kvænangsfjellet in the summer of 2023. For the Kvænangsfjellet tunnel, one tank was delivered completely prefabricated, ready to connect power, signals and pipe. For the Mettevoll tunnel, the tank had to be delivered in two parts due to its length of 27 meters.

• In principle, we can deliver tanks as large as required. If they are too long to be delivered completely finished by road transport, we can deliver the tanks as a construction system, after which the modules are joined and welded together at the plant. We have skilled colleagues who can assist with the welding work to ensure a good result. The tanks come with pre-assembled pumps and valves, so all that remains is to connect pipe and power once the tank is in place. This is a quick and easy solution that saves contractors a lot of time," says Johannes.

Quick installation - long lifespan

The contractor spent approximately two days installing each tank. The first day was spent preparing the trench with foundations, and the next day the tank was hoisted into place and connected to other infrastructure. The tanks are lightweight, and if logistics allow, they can be hoisted directly from the truck to the trench. So it only takes a couple of days to install a solution that can last for over 100 years.

The PE plastic does not corrode and is chemically resistant to most acids and alkalis. When you break down the price by lifespan, it's clear that a PE sedimentation tank of this type is a very sustainable choice in terms of both the environment and the economy. Snorre Leth-Olsen VA Engineer at Asplan Viak agrees.

• The total cost of delivering and installing such a tank is low when you look at the lifetime of the product. The short installation time also gives us a gain in HSE and environmental footprint," says Snorre.