Sonja Leinonen

Associate, Master of Laws

Services

  1. Environment, Energy & Green Transition
  2. International Construction & Projects

Contact details

I advise our clients in matters related to the environment, infrastructure and natural resources as well as industrial projects and energy law assignments.

Initially I joined Castrén & Snellman as a trainee. Prior to graduating, I also worked at another major law firm on questions related to energy law and wind power and in the Unit for Sustainable Development and Climate Policy of the Ministry for Foreign Affairs of Finland.

I graduated from the University of Helsinki where I wrote my master’s thesis on the international regulation of underwater noise caused by shipping.

Latest references

Fortum – Sale of recycling and waste business
We acted as the lead counsel to Fortum in a cross-border transaction in which Fortum sold its recycling and waste business. The business was sold to thematic impact investing firm Summa Equity through its portfolio company NG Group. The debt-free purchase price is approximately EUR 800 million.  Fortum’s recycling and waste business to be sold comprises municipal and industrial waste management and end-to-end plastics, metals, ash, slag and hazardous waste treatment and recycling services. These businesses are located in Finland, Sweden, Denmark and Norway and currently employ approximately 900 employees.
Case published 18.7.2024
Kemijoki – Major construction project for pumped storage hydropower plants that enable safe energy transition
We are advising Kemijoki Oy as the company is exploring the possibility of building pumped storage hydropower plants as part of its existing production infrastructure in Northern Finland. The socially significant project enables safe energy transition and would have a significant role in mitigating climate change. The 200–600 MW pumped storage power plants explored by Kemijoki Oy would increase the regulating capacity of hydropower in Finland by up to 4,000 MW. The increase is exceptionally significant since Finland’s current hydropower capacity, which is mainly regulatable, is 3,100 MW. The scale of the project is also reflected in the fact that the nominal capacity of the company’s largest operating hydropower plant, Petäjäskoski hydropower plant, is 182 MW. The scale of the possible investment totals up to 3 billion euros. The production of weather-dependent wind and solar power will increase significantly in Finland. This requires ensuring sufficient production capacity that can be regulated, and hydropower is the most important form of such production. The overall generating capacity of pumped storage hydropower is on the rise in Europe and elsewhere in the world, reducing the need of fossil fuels. The pumped storage plant consists of two reservoirs that will help the plant to produce power when demand is high by running water through turbines down from the upper reservoir to the lower reservoir. When demand for electricity is low, the pumped storage plant will pump water back up into the upper reservoir.
Case published 29.5.2023
Nevel – Acquisition of Veitsiluoto’s Energy Infrastructure, and Utility Supply for Infinited Fiber Company
We are advising Nevel Oy in the implementation of energy infrastructure services in Veitsiluoto in Kemi, northern Finland. Nevel will purchase the area’s district heating business from Stora Enso. The acquisition will ensure the continuity of the service for the local households and real estate. Nevel has signed a contract to supply the energy to the Stora Enso Veitsiluoto sawmill and plans to invest in a new 11 MW biofuel boiler plant and flue gas condenser at the Veitsiluoto sawmill, which will reduce emissions from heat production. Nevel has also agreed to supply renewable textile and fashion technology company Infinited Fiber Company with energy and water utilities for their new processing plant at the Veitsiluoto site. Infinited Fiber Company is planning to convert a paper factory previously operated by Stora Enso on the site into a textile fiber production plant. This will be the company’s first commercial-scale plant. The fiber production processes require steam energy and water purification. Among other services, Nevel is set to supply Infinited Fiber Company with energy and water utilities. Energy provided will be renewable, reducing emissions from heat production. Nevel is a utility infrastructure company offering advanced industrial and municipal infrastructure solutions that are fit-for-purpose and future-proof. Nevel operates more than 130 energy production sites and manages over 40 district heating networks. The company has an annual turnover of EUR 100 M, and employs 150 experts in Finland, Sweden, and Estonia. Infinited Fiber Company is a fashion and textile technology company. Its breakthrough innovation turns cellulose-rich materials – like worn-out clothes – into InfinnaTM, a premium textile fiber.
Case published 23.6.2022
Rudus – Acquisition of stone aggregates business
We advised Rudus Oy in the acquisition of TerraWise Oy’s stone aggregates business. Rudus Oy is the leading specialist in the market of stone-based building materials and solutions operating in Finland’s building product industry. This business acquisition supplements the stone aggregates business of Rudus while strengthening and expanding its offering, particularly in the Helsinki Metropolitan Area. Since 1999, Rudus has been a part of the Irish CRH Group, a global operator in the building materials industry. CRH operates in 28 countries and has 71,000 employees in approximately 3,155 locations. CRH is the largest building materials company in North America and the second largest in the world.
Case published 13.6.2022
Keva – Acquisition of 50% Ownership in Stockholm Exergi by Investor Consortium
We advised Keva in a transaction in which a 50% ownership stake in the Swedish district heating and cooling company Stockholm Exergi Holding AB (publ) will be acquired by a group of long-term European institutional investors. The consortium comprises APG, Alecta, PGGM, Keva and AXA. The total consideration is approximately EUR 2.9 billion based on a 100% enterprise value of approximately EUR 7.1 billion. In 2020, Stockholm Exergi’s heating and cooling sales were 7.6 TWh and power sales 0.7 TWh. The consortium’s investment in Stockholm Exergi represents a significant milestone in their commitment to significantly reduce CO2 emissions. Stockholm Exergi has a fantastic track record of growth, leadership in ESG and delivering and developing customer centric solutions like Carbon Capture and Storage, all of which are driving the long-term sustainable energy transition of Stockholm and the region. The consortium intends to grow the Company by investing significant capital, targeting to enhance the environmental sustainability and efficiency of its heating plants and district heating networks.
Case published 1.7.2021
Nomios – Acquisition of Intragen Group
We advised Nomios, a portfolio company of the European growth buyout investor Keensight Capital, with its cross-border acquisition of Intragen Group, a leading European expert in digital identity and access management. The acquisition marks a major milestone in Nomios’ growth strategy and further strengthens its position as the global trusted partner for cybersecurity across Europe. Nomios is one of Europe’s leading providers of cybersecurity services. Keensight Capital is a European growth buyout investor with deep expertise in technology and healthcare.  
Case published 17.11.2025
Ministry of the Environment – Report on the promotion of circular economy aspects in public procurement
Castrén & Snellman was commissioned by the Ministry of the Environment to carry out a study on how the Circular Economy Act could be used to promote circular economy aspects in public procurement. Our report provides valuable information to the working group tasked with preparing the new Circular Economy Act. The report includes an overview of relevant strategies, action programmes and policies, a look at relevant legislation and case law, an assessment of the current state of circular economy procurement and examples of integrating circular economy aspects into public procurement from around the world. We end the report with concrete conclusions and a proposal for a new circular economy provision with justification. The proposal aims to maximise the regulation’s effectiveness and minimise any adverse side effects. The final report is available on the Circular Economy Act project’s Gateway to Information (in Finnish). The study was carried out by Anna Kuusniemi-Laine, Sanna Aalto-Setälä, Lotta Huhtamäki, Marja Ollila, Laura Vuorinen, Paavo Heinonen and Anna Ylitalo.
Case published 11.11.2025
CapMan Real Estate – Acquisition of a High-Quality Residential Asset
We advised CapMan Real Estate in the acquisition and financing of a high-quality residential asset located in Katajanokka, Helsinki.  The asset was acquired from the Finnish Seamen’s Service Bureau (MEPA).  The property consisting of 38 modern rental apartments with a parking garage was completed in 2017. The building features high-quality construction, modern floorplans, and well-designed communal areas including a gym and rooftop sauna premises, and blends with the area’s historic maritime character. The residential asset is located in the prestigious Katajanokka seaside district of central Helsinki, known for its architectural heritage and proximity to the city centre. The property has a high ESG profile which will be further improved by CapMan Real Estate.
Case published 6.11.2025

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