One site in the city of Zurich is contaminated with chromate, chlorinated hydrocarbons (CHCs) and perfluorinated and polyfluorinated alkyl substances (PFAS) in the subsoil, with some of the contaminants overlapping. All three contaminated sites are in need of remediation in terms of groundwater protection.
The pollutants originate from different sources, on the one hand from galvanic operations in two buildings and on the other hand from a suspected chemical cleaning operation. Due to the different polluters and sources of contamination, the chromate and CHC sites were treated and documented separately from the investigations through to the remediation project. The remediation was planned jointly for both sites as part of a construction project using excavation, and a joint implementation concept was drawn up. Prior to its approval, the authorities requested extensive additional investigations into the PFAS group of pollutants, which had come into focus for the first time at the time. It turned out that between the chromate and CHC contamination, there was also a PFAS site in need of remediation.
Following the demolition of the building, excavation work was carried out simultaneously over several months in the various areas. In some cases, excavation down to around 7 m below ground level and thus in the saturated zone was necessary for the remediation, which was made possible with sheet pile boxes and dewatering. One building had to remain standing, which is why underpinning and the installation of a sealing wall using the jetting method (as a vertical excavation pit closure) were necessary to enable decontamination. Pumped-out groundwater was purified on site using activated carbon filters and ion exchangers. Areas with additional excavated material for the remediation of contaminated sites were backfilled with gravel after the base was cleared.
Following the preliminary and detailed investigation of the contaminated site, Ecosens AG worked with all stakeholders to develop a feasible remediation project. During the remediation phase, Ecosens AG was responsible for the specialist construction management and also coordinated third-party services (contractors, laboratory, etc.) as well as ongoing adjustments to the remediation process, monitoring the achievement of objectives and documenting the work for the client and the authorities. Groundwater monitoring is currently underway as part of the aftercare.
