The Fix factory once manufactured window fittings and espagnolettes. There were concerns that oils from boiler rooms and pipes, as well as fluids from surface treatments, might have ended up in the soil. However, soil samples provided reassuring information. On the other hand, fill materials with elevated levels of heavy metals and PAHs (polycyclic aromatic hydrocarbons) were found. A three-meter-thick layer of soil has was transported away. In some places, where archaeologists conducted their investigations, digging went as deep as five meters.

– There's a lot of stuff in the ground. And a lot of water. The deeper we dig, the damper and muddier it gets, says Alexander Furubrink, site manager at HTE Production, responsible for the groundwork, remediation, and material handling after the buildings were demolished.

In the construction of the new residential area, the decision was made to reuse clean structural concrete. It is crushed, the reinforcement is separated, and the crushed concrete is placed back as fill material under what will become streets. Avoiding the transport and purchase of new crushed material is both an economic and environmental gain.

– We reuse about 4,000 cubic meters of clean concrete - 10,000 tons, says environmental consultant Lena Bergdén.

Both soil contamination and concrete recycling impose high demands on water treatment. All the water that comes into contact with the crushed concrete must undergo pH adjustment and particle separation. Turbidity and pollutants risk harming plant and animal life if released into stormwater drains. According to the City of Gothenburg’s guidelines, the particle concentration in the local water must be below 25 mg/l, with a pH value between 6 and 9 before being discharged from the construction site. At Fixfabriken, the water has sometimes had a particle content of several hundred mg/l and a pH of over 11.

In the initial weeks, before Swedish Hydro was on-site, the water was pumped between various basins within the area. When the contaminated local water obstructed an excavation, it had to be pumped to the next location. And so on.

– We had no opportunity to infiltrate it; eventually, there were no areas left, Lena Bergdén explains.

Since the installation of Swedish Hydro Solutions' mobile treatment plant, the process has been significantly smoother. Now, the contaminated water is first pumped through a pre-dosing station, adjusting the pH using carbon dioxide. Here, a small dose of polyaluminum chloride is also added to facilitate flocculation. Then, the water passes through the dosing station with the flocculating agent chitosan, causing the particles in the water to aggregate.

The water is then pumped to two containers where the flocked particles settle at the bottom and are separated from the water. As a final step, the water is gravity-filtered through two Biomedia boxes, ensuring that dissolved contaminants and organic particles are removed. After this, the water is clean enough to be discharged into the stormwater.

– There have been many checks and controls, both of the concrete and the water, says Lena Bergdén. But it has always looked good. Swedish Hydro Solutions made some adjustments for the pH value only.

The water treatment is essentially self-managing. Felix Kihle at HTE Production is tasked with the daily inspection of the plant, and Swedish Hydro Solutions conducts site visits every two weeks or as needed. The treatment will run for three months, after which the groundwork should be complete - all contaminated soil removed, and the recycled concrete in place under the new streets. The area is set for occupancy in 2021. And by then, the Fix sign should be up again.