The environmental risk assessment of wastewater pumping stations in the Turku region aims to protect the Baltic Sea 

Turun seudun puhdistamo Oy is responsible for wastewater treatment in 14 municipalities. There are hundreds of wastewater pumping stations in the area, and the risk of overflow for many of them increases as a result of climate change. The geospatial environmental risk assessment carried out by Sweco highlighted the most critical points for the Baltic Sea.

Turun seudun puhdistamo Oy (TSP) is responsible for the wastewater treatment of nearly 300,000 residents and industry in 14 municipalities. Regional cooperation works well in Southwest Finland, and people are used to developing responsibility in wastewater treatment together. 

“We regularly engage in cooperation with our shareholder associations aimed at better preparedness and reducing overflows, such as exercises and seminars,” says Jarkko Laanti, Quality and Environment Manager at Turun seudun puhdistamo Oy. TSP has also developed a system for reporting overflows, in which each municipality transparently records overflows that have occurred in its area to other municipalities and authorities.  

From the point of view of the Baltic Sea, the operation of the region’s wastewater pumping stations is of great importance. Most of the pumping stations are located in the catchment area of the Archipelago Sea, so overflows from wastewater sewers may eventually end up in the Baltic Sea. The goal is to avoid overflows and to end up all wastewater in the right place: the Kakolanmäki wastewater treatment plant.  

“Our wastewater is treated much more efficiently than required by the environmental permit, which reduces the nutrient load of the Baltic Sea,” says Suvi Venho, Network Engineer at TSP. For example, wastewater leaving the treatment plant is hygienised in a separate UV plant. In addition, TSP complies with the Green Deal commitment for urban wastewater treatment.  

Climate change increases overflow risks

In the fall of 2022, TSP wanted to update the environmental risk assessment of sewer overflows carried out five years ago. The aim was to reduce stormwater ending up in the wastewater network and thus also reduce sewer overflows, even though precipitation, heavy rainfall and flooding will increase as a result of climate change. 

“We wanted to identify pumping stations that are located in particularly sensitive places, such as groundwater areas or near beaches or waters of high fish value,” Laanti says. Based on the location, criticality classes were defined for the pumping stations. “The more criteria a pumping station is located in, the higher its criticality rating and the more important it is to minimise overflows from that pumping station.” 

The project is coordinated by Valonia, a sustainable development expert organisation belonging to the Regional Council of Southwest Finland. It relied on Sweco’s water management experts in the risk assessment. “We were particularly looking for experience in assessing overflow risks related to climate change, and Sweco has developed a suitable GIS method for this,” says Katariina Yli-Heikkilä, Environmental Specialist at Valonia. 

In his opinion, the good local knowledge of Sweco’s experts and, on the other hand, knowledge of the most nationally effective methods of preventing environmental risks speeded up the implementation of the project. 

Extensive environmental risk assessment of 500 pumping stations

Overflow risks were assessed at approximately 500 wastewater pumping stations.  According to  Jaana Pulkkinen, Sweco’s Planning Manager, the most significant difference from the previous risk assessment was that the analysis was expanded to include the local impacts of a particular pumping station on the entire catchment area. 

“We analysed the environmental risks of the entire overflow route, from the flood ditch through rivers all the way to the sea. It gave a truer and more accurate picture of the risks.” 

The geospatial risk analysis took into account the impact of rising seawater on the risk of flooding pumping stations. In addition, stormwater-related risks were addressed by assessing which pumping stations are located low relative to flood ditches.  

The workshop brought municipal representatives together

At the end of the project, a joint workshop was organised for representatives of water utilities, municipal decision-makers and authorities. It presented the results and interview data collected by Sweco on best practices from different parts of Finland. The root causes of the problems were also discussed together. 

“The workshop was really useful because it gave municipalities yet another opportunity to discuss and think together about where resources should be invested in the future,” Venho says. 

He and Laanti are satisfied with the consultant’s expertise and new perspectives. The results presented on the map confirmed the preconceptions of TSP’s experts, but now the most critical overflow points have also been computationally identified. “I believe that the results will give a hand longer, for example, to apply for funding for wastewater network development projects,” Laanti says. 

The environmental risk assessment received funding from the Ministry of the Environment’s Water Protection Enhancement Programme (2019–2023).