Facts
During excavation work for the MITTIM development near Wallisellen train station, the release of tetrachloroethylene (PCE), which belongs to the group of chlorinated hydrocarbons (CHCs), was detected on November 11, 2008. The property owner and developer, [B. AG], then commissioned [C. AG] to conduct investigations into the contaminated site and provide construction management services. The Office of Waste, Water, Energy and Air of the Canton of Zurich (AWEL) approved the proposed containment and remediation measures.
Based on the investigations by [C. AG], it became apparent that the contamination was not limited to the MITTIM development, but had also extended to the adjacent Schwarzackerstrasse. The municipality of Wallisellen then commissioned [D. AG] to conduct additional investigations. The site was entered in the Cadastre of Contaminated Sites (KbS).
By order dated June 19, 2013, AWEL allocated the costs, assigning 55% to [A. AG], 20% to [B. AG], and 25% to the municipality of Wallisellen, of the total eligible remediation costs of CHF 600,127.30. Both [B. AG] and [A. AG] appealed against this order.
In a judgment dated May 12, 2016, the Administrative Court of the Canton of Zurich consolidated the two proceedings. It dismissed the appeal of [B. AG] but upheld that of [A. AG]. It reallocated the remediation costs, with 35% to be borne by [B. AG] and 65% by the municipality of Wallisellen.
Considerations
The Federal Supreme Court overturned the judgment of the Administrative Court and remanded the case for a new assessment. It concluded that there was no need for remediation within the meaning of Art. 32d(1) of the Environmental Protection Act (USG), as the affected groundwater was "perched groundwater" that was not usable. Therefore, the costs could not be distributed according to the rules for the remediation of contaminated sites.
However, a cost allocation under Art. 32d(1) USG was considered appropriate for the costs of…