(8)Where archaeologically valuable sites are encountered during infrastructural works, such as the building of collecting systems or urban wastewater treatment plants, such works are often delayed due to the need to perform archaeological studies on the site in accordance with national law. It is therefore appropriate to adapt the implementation deadlines in those specific cases. More specifically, where a Member State establishes that, due to the necessity to preserve cultural heritage, the construction of the required infrastructure is particularly difficult, it should be allowed to adapt the implementation deadlines in specific areas, and update accordingly its national implementation programme. The extensions of the deadlines should be set for each area and kept as short as possible, not exceeding 8 years. Cultural heritage should be understood within the meaning of Article 1 of the 1972 UNESCO World Heritage Convention.