Drammen, Lier and Asker municipalities have all treatment facilities that do not currently fulfil the requirements set by the Government Manager in the discharge permits. In addition, the contracting authority has notified the implementation of purification requirements from the EU through the establishment of a new sewage directive. Although the directive has not yet been adopted, the Norwegian Environment Agency/Government Manager has already implemented significant sharpening of cleaning requirements. The reason for this is the poor condition of the Oslo fjord.In 2020 – 2022 a concept choice study (KVU) was carried out. The concept choice review included both alternative solutions for treatment facilities and the necessary transfer pipelines to the alternative concept alternatives. Based on recommendations from the KVU, identical decisions were made in the municipal councils of Drammen, Lier and Asker municipalities (February/March 2023) that the concept of a regional treatment facility in Nordbykollen should be further reviewed in a preliminary project phase. The preliminary project and external quality assurance of this for the treatment plant have been carried out in the period 4 quarter 2023 up to and including the four quarters of 2025. The preparation of the development plan has been ongoing parallel to the preliminary project.