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DE 
Environmental remediation is a key part of protecting ecosystems and public health - especially at sites that have historically been used for industrial purposes. One outstanding example is the remediation of a former gasworks site in Lower Saxony, which was operated by a municipal utility company. Due to the hazardous contaminated sites, the responsible authorities categorised the site as contaminated, which required immediate action to prevent further environmental damage.
Detailed investigations carried out between 1999 and 2024 revealed significant groundwater and soil contamination. Extensive contamination by polycyclic aromatic hydrocarbons (PAHs) and cyanides was found - the pollutant concentrations reached up to 50 mg/kg and 30 mg/kg respectively and penetrated deep into the saturated groundwater zone.
In addition, two areas were identified as the main sources of contamination: an old tar and ammonia pit and a separate tar pit. Both areas contained pollutants such as BTEX (benzene, toluene, ethylbenzene, xylene), mineral oil hydrocarbons (MKW) and phenols, which pose a significant risk to the environment - especially to the groundwater resources, which serve as a source of drinking water for almost 15,000 inhabitants in the region.
Planning and strategy of the refurbishment project
In view of the extent of the contamination, a comprehensive remediation project was initiated as part of a public-law remediation contract. The main objective was to stop the release of pollutants from the identified "hotspots" into the groundwater and to minimise long-term environmental risks. To achieve this goal, the remediation strategy focussed on soil replacement, the removal of contaminated material and in-situ measures to protect the groundwater.
The project involved the excavation and disposal of a total of 800 tonnes of contaminated soil - 600 tonnes from the former tar and ammonia pit and a further 200 tonnes from the adjacent tar pit. These materials were classified according to the hazardous waste categories, predominantly as DK I (soil with moderate contamination), and treated in accordance with the strict regulations for the disposal of hazardous waste. In addition, monitoring wells were installed along the site to continuously monitor and evaluate the effectiveness of the groundwater protection measures.
Key phases of the refurbishment project
The first phase of remediation began in May 2024 and covered an 85 square metre area of the former tar and ammonia pit. The initial measures included locating and removing existing supply lines and demolishing the old pit walls. A single-track corner shoring system (approx. 3 x 3 metres) was installed in stages, reaching a depth of 3.5 metres below ground level. This careful approach allowed the surrounding infrastructure to remain largely intact while the excavation process was efficiently controlled.
During this phase, construction supervision played a crucial role in ensuring that all procedures complied with strict safety and environmental regulations. During the excavation, 600 tonnes of contaminated material was removed and transported to certified disposal sites for proper removal and treatment. By removing the contaminated soil, the risk of pollutants entering the groundwater was significantly reduced. A protective sealing layer is then applied to prevent the penetration of pollutants from the surface in the long term.
Groundwater protection and risk management
Groundwater contamination is a particularly critical problem at this site, as the region is heavily reliant on groundwater resources. In view of the fact that the concentrations of the pollutants found exceeded the permissible limits for environmental safety, immediate action was required to stop the migration of these pollutants into the aquifer. The remediation project not only aimed to remove the contaminated soil, but also integrated advanced environmental risk management techniques for the sustainable protection of groundwater.
A further 200 cubic metres of soil will be removed from the second hotspot - the tar pit - by June 2024, which will complete the main phase of remediation. The site will then be monitored in the long term to ensure that the measures taken to protect the groundwater remain effective in the long term. The aim of the entire project is to reduce contamination levels by over 95 % and ensure that pollutant concentrations are well below the legal limits for safe groundwater.
Long-term effects and forecasts
The remediation of this industrial site serves as a model for future environmental protection projects, not only in Germany but also in other contaminated regions throughout Europe. With almost 800 tonnes of contaminated soil removed and hazardous pollutants successfully contained, the site is expected to be fully remediated by early 2025. Completion of the remediation measures will not only protect the local groundwater supply, but also pave the way for the potential reutilisation of the site, bringing both economic and environmental benefits to the region.
In terms of financial aspects, the total budget for the project is expected to be 1.5 million euros. Of this, 50 % of the funds are earmarked for the disposal of hazardous substances, while the remainder will be used for excavation work, soil treatment and post-remediation monitoring. The cost of remediation appears to be justified given the long-term benefits, such as improved groundwater quality and the potential to repurpose the site.
In addition, the knowledge gained from this remediation process will serve as a valuable basis for the management of future underground contamination and remediation projects at industrial sites. The successful collaboration between STRABAG Environmental Technology GmbH and M&P Ingenieurgesellschaft GmbH illustrates the importance of combining expertise in the fields of construction supervision and environmental engineering for the success of such remediation projects.
Conclusion
The former gasworks in Lower Saxony is a prime example of the environmental problems that can arise from contaminated industrial sites. Through careful planning, competent monitoring and comprehensive remediation of contaminated sites, the project team has impressively demonstrated how natural resources can be protected and public health safeguarded through targeted removal of pollutants. This successful project provides valuable lessons for further remediation efforts addressing groundwater contamination and the restoration of contaminated sites across Europe.
As the project enters its final phase, it is expected that the site will not only fulfil the strict environmental standards of the local authorities, but also serve as a model for future environmental protection measures. This will make an important contribution to ensuring a cleaner and safer future for generations to come.