The project began with a phase of careful planning, during which we, in close cooperation with the client Implenia, designed and developed two comprehensive and separate water treatment solutions. Maintaining good communication both before and during the project has been crucial to ensuring everything runs smoothly, as significant coordination is required with the tunnel being excavated from both the north and the south simultaneously.

Old landfill and groundwater infiltration

Work on the Ersmark Tunnel involves two tunnel portals on either side of Ersmarksberget, with each drilling rig equipped with three drill heads. In addition to the water used during drilling, groundwater was also expected to leak into the tunnel. Furthermore, the bedrock was assessed to contain traces of an old landfill, posing a potential risk of contaminants entering the tunnel along with the groundwater if the protective membrane between the rock and the landfill was not sufficiently sealed.

Complete facilities for strict requirements

To manage both the expected groundwater infiltration and potential contaminants, we developed an efficient and flexible water treatment solution. After the water has been treated, it is discharged onto an infiltration bed with biological fauna, and strict discharge regulations apply since the water could potentially come into contact with groundwater. To minimize environmental impact around the tunnel, such as the construction of large sedimentation ponds, a container-based solution was therefore chosen.

Both treatment systems include pre-sedimentation, oil separation, pH adjustment, Swedish Hydro Solutions' patented dosing system HydroBox, mixers, lamella separators for efficient particle separation, and a final filtration system. If hexavalent chromium appears during cement work, the RedOx3 reducing agent can be added to the HydroBox to neutralize it.

– The design and development phase went very well in the early stages of the project, which is great. The discharge requirements are strict, and the tunnel is being excavated through rock with an old landfill on top. At the outset, we didn’t fully know what contaminants we would encounter, says Carl-William Kalholm at Swedish Hydro Solutions.

– The excellent cooperation with Implenia has resulted in two highly capable treatment facilities that we trust and that can handle very large volumes of water, he continues.

Now that the treatment has been running for nearly a year, the most prominent contaminants have consisted of suspended solids, oil, and metals such as cadmium, copper, and zinc. Chromium has also been prevalent due to the concrete casting in the tunnel, leading to elevated levels.

In addition to the 1.6-kilometer-long main tunnel, an 800-meter-long service and rescue tunnel is also being constructed, equipped with concrete structures, drainage mats, and service roads. After drilling sludge and other contaminants have been removed through the advanced treatment facilities, the water can either be recirculated to the tunnel rigs or discharged into the recipient.

An important part of the project is the ability to reuse the treated water in the drilling machines, reducing the need for fresh water and contributing to more sustainable water management.

– In many of our tunnel projects, including this one, water reuse is a crucial factor. It ensures that Implenia does not need to use as much fresh water in their processes, adds Erik Tholén, project manager for the Ersmark Tunnel at Swedish Hydro Solutions.

– Water recirculation is very straightforward. After the final treatment stage, the water is pumped into two buffer containers, where Implenia can use it in their processes. If they do not need the water, it can instead be pumped for discharge, adds Erik.

About the Norrbotniabanan

Norrbotniabanan is a 270-kilometer-long new coastal railway between Umeå and Luleå, designed for faster, safer, and more environmentally friendly travel and transport. It strengthens community development and enhances the competitiveness of businesses across Sweden. Once completed, Norrbotniabanan will connect what is currently Sweden’s most densely populated region without daytime train services.