The Central Station project is NCC’s largest contract ever, one stage as part of the major West Link infrastructure construction project in Gothenburg. Swedish Hydro Solutions has been contracted for its water management. At the hight of the operation, as many as seven individual treatment systems have been running simultaneously.

The so-called “West Link” (Västlänken) is a multi billion Euro project, is to deliver a rail tunnel for commuter trains that will run right underneath the whole city centre of Gothenburg. The project is divided into five stages, with NCC being responsible for two of these: “Korsvägen” and “Central Station”.

The latter part (also the largest) stretches from the Kanaltorget square, situated next to the Nordstan shopping center, all the way to “Skansen Lejonet” and terminates with a bridge over the E6 highway. This working area is about two kilometers long and one hundred meters wide.

Several hundred people are working every day on this section, with operations expected to continue until around 2026. A large and complicated planning puzzle is being executed, with many stakeholders involved in a central location that is undergoing rapid change.

A major challenge is that the area is very elongated and that it is crisscrossed by roads to ensure that traffic in the city center still can function, says Ellen Samuelsson, NCC Environmental Manager for the Centralen section

Careful monitoring of the groundwater level

The West Link is not the only construction project underway in the area. Nearby, the E45 highway is being lowered underground and the new Hising Bridge is being built. The area has certainly earned its nickname of the “Gothenburg Pit”.

Ellen Samuelsson explains that the many large construction projects, the muddy ground conditions and the proximity to the river have meant that there are strict requirements not to lower the groundwater level during construction, as this could cause the buildings in the vicinity to subside. NCC is excavating soil and clay masses down to a depth of more than twenty meters, well below the groundwater level.

There is pressure from the river, which risks getting into the shafts, so we need to have water treatment with good capacity. We must pump the water away – but at the same time not too much, since that would risk lowering the groundwater, level, says Ellen Samuelsson.

The soil is not only muddy, but also contaminated by more than a century of industrial activity. In the terminal area, oil has leaked, and multi-layers of railway sleepers has contaminated the soil with tars. Even longer ago, there was seabed here, so the entire train yard is built on fill material containing both heavy metals and tars.

Flexible multi-system treatment

NCC had expected to need two major water treatment systems. But that turned out to not work in practice. Since the construction area is fragmented, six systems are now in operation, and a seventh has just been decommissioned. Consumables and services are also provided by Swedish Hydro Solutions.

Swedish Hydro Solution’s water treatment handles both particles and dissolved contaminants. The chitosan causes the particles to flocculate and settle. Dissolved organic pollutants and metals such as oil, solvents, zinc, lead and copper are filtered out in BioMedia filters. Ellen Samuelsson is pleased that the treatment method is free from the chemicals that are often associated with more traditional water treatment.

It is incredibly positive that it is environmentally sustainable. It is also a robust system that is easy to maintain. We can manage much of it ourselves.

A designated NCC staff member takes care of sampling on a regular basis and a team takes care of the daily inspection and cleaning of the chitosan systems. The automatic and internet connected monitoring systems keep track of water flow, pH, conductivity and turbidity. An alarm is also connected, which quickly issues an alert if any values are exceeded. The chitosan socks are changed every two or three days, depending on the water flow-through.

Hassan Daher, a member of the team managing water treatment system operation.

Mobile units increase flexibility

Water treatment is a major budget item for NCC, and extremely important for production, explains Ellen Samuelsson. Failure to do so would halt the flow of production, which would result in high costs. The choice to hire Swedish Hydro Solutions was very much about capacity and flexibility. The small size and space efficiency of the treatment units are an advantage in a large construction project, where space is at a premium and a lot is going on at the same time. NCC has already taken advantage of the ability to move the treatment equipment a couple of times.

It may seem expensive, but Swedish Hydro Solutions’ solution is the best choice in the long run, says Ellen Samuelsson.