Damage caused by mineral oil products within the scope of a construction measure uncovered and remediated

In northern Lower Saxony, odorous and visually conspicuous soil areas were encountered in the course of a construction project.

The approx. 3,000 m² property in a medium-sized town north of Hanover has several buildings of different ages and uses. The majority of the buildings are small businesses and offices. The aim was to modernise the existing buildings. In the course of this, dilapidated buildings were to be demolished and the supply lines renewed.

During the unsealing of the surface after the deconstruction work, areas were encountered in the subsoil that smelled strongly of mineral oil. The owners then informed the responsible authorities. On the part of the local lower soil protection authority, it was recommended to the property owner to call in an expert office to accompany the remediation of the contaminated soil areas.

M&P Ingenieurgesellschaft mbH was commissioned in September 2022 with the expert monitoring of the construction work.

Various commercial uses have taken place on the project site over the last 100 years. The highest environmental relevance was shown by the use of the site as a car repair shop and car wash. Pollutant groups such as CHCs and PAHs were released into the subsoil. The contaminated areas were to be excavated as part of the current construction project and disposed of in accordance with the applicable regulations.

Due to the proximity of a receiving watercourse and the peaty layers there, the level of the stratum water was approx. 0.80 m below the ground surface, so that dewatering had to be carried out. The stratum water was pumped out and treated using an activated carbon filter system. The treated water was regularly examined and, with the approval of the local water authority, discharged into the municipal wastewater sewer system.

In the course of this project, a total of 30 heaps or containers were sampled by the employees of M&P Nord. In addition, in situ sampling was carried out several times, as it was not possible to stockpile the excavated soil for the purpose of sampling and waste declaration due to the limited space available.

All work was carried out in close coordination with the local authorities. After completion of this measure, a comprehensive project report will be prepared documenting a fundamental upgrading of this property.