According to a study conducted in Kerava, filter wells remove up to 94 percent of the solids in stormwater. The efficiency is comparable to traditional above-ground stormwater systems, which filter wells have come to complement – especially in densely built urban environments.
Text: Kaisa Salminen | Photos: Uponor Infra Oy
As cities become denser and climate change brings increasingly heavy rainfall, stormwater causes urban flooding and puts a strain on waterways.
"Quantitative management of stormwater has become increasingly important. At the same time, interest in qualitative stormwater treatment has grown, as heavy rains wash away pollutants from streets and yards, which can end up directly in waterways," says Teemu Salminen, Sales Manager of the GF Industry and Infrastructure Flow Solutions division (formerly Uponor Infra Oy).
Traditionally, stormwater has been treated using above-ground, nature-based methods such as wetlands, filter ponds, and settling tanks. These have been shown to be effective in removing both solids and pollutants bound to them in many studies.
More technical solutions installed underground, such as filter wells, are also increasingly being used – especially if there is not enough space above ground for traditional solutions.
Tested under field conditions
In 2024, the performance of a filter well was studied in field conditions in Kerava. Based on the measurements, up to 94 percent of solids were removed. According to Sitowise, which carried out the study, the result is comparable to above-ground systems.
The study was commissioned by GF and used a vertical well with a diameter of 1,6 meters and two filters. Filter wells usually contain 1–4 replaceable filters depending on the capacity. The filters are designed to remove impurities from stormwater before it is discharged.
Stormwater contains several pollutants, such as heavy metals, phosphorus, nitrogen and other harmful substances. They are mainly bound to solids. The transport of pollutants is strongly linked to particle size: the larger the particles, the easier they are to settle and separate.
Filter wells utilize this principle combined with mechanical filtration, making them a promising solution, especially in dense urban environments.
"Filter wells combine two big benefits: they do not require valuable surface space, and the solution is an inconspicuous part of the infrastructure. They also increase safety, especially in areas with large families with children, where traditional solutions can be a safety risk," says Teemu Salminen.
Responsible solutions are interesting
GF offers complete solutions, including comprehensive design support for system selection. We work closely with both public actors and companies in the industry.
For example, we are currently participating in the University of Eastern Finland's Hydrocarbon project, together with GRK, which is developing biocarbon filters, especially for purifying stormwater and nutrient-rich agricultural waters.
"Although there are no official limit values for the concentration of pollutants in stormwater in Finland, many progressive customers and organizations already want to invest in responsible solutions. We are developing them together," Salminen sums up.
Uponor Infra Oy is now part of the GF Industry and Infrastructure Flow Solutions business unit, which has over 60 years of experience in plastic systems. It offers products and solutions for the safe transport of liquids and gases for industry and infrastructure needs worldwide.