Facts
Parties and procedural history:
The Swisscom (Schweiz) AG (appellant) operates three adaptive mobile radio systems (WIAB, WITZ, WIBR) in the political municipality of Wil, which were equipped with adaptive antennas in 2019. At that time, the assessment was carried out according to the so-called "worst-case scenario" without taking a correction factor into account. On 2 and 3 June 2021 and on 5 July 2022, Swisscom submitted updated site data sheets applying a correction factor, which the political municipality of Wil classified as a modification of the systems and required an ordinary building permit procedure. The municipality ordered the discontinuation of the deviating operation. Swisscom appealed against these orders to the Building and Environmental Department of the Canton of St. Gallen, which dismissed the appeals on 10 January 2023. The Administrative Court of the Canton of St. Gallen confirmed this decision on 17 August 2023. Swisscom then filed an appeal in public law matters with the Federal Supreme Court.
Relevant legal bases:
The dispute concerns the question of whether the application of a correction factor to existing adaptive mobile radio systems requires a building permit under Art. 22 para. 1 SPA. The NIRO (Ordinance on Protection against Non-Ionising Radiation) regulates in Annex 1 No. 62 para. 5bis and No. 63 paras. 2 and 3 the application of correction factors for adaptive antennas. No. 62 para. 5 NIRO defines the modification of a system, while No. 62 para. 5bis NIRO clarifies that the application of a correction factor to existing adaptive antennas does not constitute a modification. No. 63 para. 4 NIRO requires the submission of an updated site data sheet when applying the correction factor.
Considerations
1. Building permit requirement under Art. 22 SPA:
The Federal Supreme Court examines whether the application of the correction factor to existing adaptive mobile radio systems requires a building permit under Art. 22 para. 1 SPA. The decisive factor is whether the measure has such significant consequences for space and the environment that there is a public or neighbourly interest in prior control. The court refers to case law according to which even operational changes may require a building permit if they have significant environmental impacts (ATF 139 II 134 para. 5.2).
2. Effects of applying the correction factor:
The application of the correction factor means that the maximum transmission power only has to be complied with on average over 6 minutes, while short-term power peaks may significantly exceed the previously approved maximum transmission power. This may lead to an exceedance of the system limit values (SLV) at locations with sensitive use (LSU). The court emphasises that these power peaks cause concern among the population and justify an interest in prior control. The previous approval according to the "worst-case scenario" does not cover these new operating conditions.
3. No exhaustive regulation in the NIRO:
No. 62 para. 5bis NIRO merely regulates that the application of a correction factor does not constitute a modification of the system within the meaning of the NIRO. The question of the building permit requirement under Art. 22 SPA is not affected by this. The court points out that the NIRO does not address the building permit requirement and that this issue is regulated at federal level in Art. 22 SPA. The cantons may specify the building permit requirement but may not restrict it. The mere submission of an updated site data sheet is not sufficient to safeguard the public and neighbours' interest in prior control.
4. Right to be heard and legal protection:
The court emphasises that an ordinary building permit procedure is…