As early as the 1890s, industries were present at Ringön - an industrial area on Hisingen in Gothenburg. It housed everything from metal industries, car scrapyards, and shipbuilding facilities to railway depots and airfields. Around the turn of the century, a ring canal was dug around the area, hence the name Ringön. The canal was later filled in – with any available materials.

When the Västra Götaland Region decided to build a new tram depot on the site in the 2010s, replacing an old depot, there were many soil contaminations to consider. The region's real estate company, Västfastigheter, assigned Skanska the task of building the tram depot. When the company started excavation in early 2021, they found a mix of materials, ranging from brick and asbestos to coal, oil, and car wrecks.

Despite this, no treatment of the drainage water was needed as the levels of all substances were below the limits. Therefore, the Environmental Department of Gothenburg City approved the re-infiltration of water from the excavations back into the ground. But, at the end of the summer, an analysis result brought the construction to a total stop: High levels of the carcinogenic aromatic hydrocarbon benzene.

Found a Solution

The elevated levels of benzene meant that the drainage water could no longer be re-infiltrated. Simultaneously, the substance posed a workplace risk. As a result, work had to be suspended. To avoid falling far behind schedule, Skanska had to quickly find a solution.

– It was crucial to quickly initiate water treatment since we were in a critical stage of production and needed to move forward, says Elin Elfwering, site manager for remediation and soil at the Ringön project with Skanska.

Skanska's environmental consultant then recommended Swedish Hydro Solutions. It was a name also known to the project's production manager.

– With those recommendations, we knew we had found a good partner for the task, says Elin Elfwering.

Swift Implementation

Just two weeks after the first contact between the project and Swedish Hydro Solutions, a facility with a treatment capacity of 20 cubic meters per hour was ready: equipment for chitosan dosing and other flocculation and precipitation chemistry, lamella separators, and BioMedia filtration. Besides benzene, the facility also handled suspended material, dissolved zinc, and various oil contaminations.

Since the facility achieved excellent treatment results for more contaminants than benzene, approval was granted to discharge water directly into the stormwater network without re-infiltration.

– It was good because we treated large volumes. The re-infiltrated water would have eventually come back to our excavations since they are well below the groundwater level, says Elin Elfwering.

Swift Adjustments

Water treatment, however, was not without its challenges. Contaminant levels varied significantly at different locations in the excavations. Thus, the load on the treatment facility varied over time. To monitor these changes, the project conducted continuous analyses -sampling outgoing water every fourth day and incoming water every seventh day.

– The changes in the amount of contaminants have been a challenge. On two occasions, we had to stop the discharge to the stormwater because we needed to adjust water treatment.

To enable swift adjustments in water treatment, Skanska's environmental consultant directly communicated the analysis results to Swedish Hydro Solutions. As soon as results indicating elevated levels arrived, Swedish Hydro Solutions could adjust the facility - for example, increase the addition of precipitation chemicals to meet an increased zinc contamination.

Elin Elfwering is satisfied with the company's efforts.

– Swedish Hydro Solutions has done a great job, and the collaboration has worked well. They have been keen on ensuring the facility operates all the time and have conducted checks a couple of times a week.

Work Continues

Apart from the two adjustments caused by changes in contaminant levels, the treatment facility has done its job.

– The compilation of the treatment results has been very good. We have met the limits to discharge into the stormwater network.

However, benzene never caused any problems.

– We have always managed to handle benzene, which was the reason the treatment facility ended up here in the first place, says Elin Elfwering, pleased with the treatment.

– Thanks to the treatment facility, we have been able to maintain a healthy working environment and carry on with the work all the time.

After about two months on-site, the treatment facility was decommissioned.