To ensure the compliance of an Edison S.p.A. hydroelectric power plant already existing in the territory it was necessary to redefine the urban planning and acoustic profiles of the area in which the plant is located. To this end, we designed a detailed modification to the Local Strategic Plan and Acoustic Classification Plan of the municipality of Arba. As required by the Administration, the modifications were supported by a preliminary environmental report to assess any significant impacts on the environment and its cultural heritage. The results of the assessment excluded negative environmental effects being caused by implementation of the modification, so full application of the SEA procedure was not necessary.