The project comprised the construction of two outfalls: a main outfall and an emergency outfall. The main outfall consists of several sections, including a 505-metre pipe-jacked section reaching a depth of -10.37 metres, a 3,020-metre subsea section extending to -35.00 metres, and a final diffuser section equipped with 20 discharge diffusers designed to optimise the dispersion of treated effluent.

The emergency outfall, running parallel to the main pipeline along the entire pipe-jacked section, provides additional operational reliability and ends in a 45-degree bend fitted with a control valve.

The Santoña Marshes constitute one of Spain’s most important natural ecosystems and represent a unique environmental enclave along the Cantabrian coast. Their estuarine environment supports a rich biodiversity and plays a vital role in the ecological balance of the region.

The sustained growth of the local population, together with the expansion of industrial, recreational and urban activities, has increased pressure on this sensitive environment. In response to the challenge of preserving the marshes’ ecological value while supporting the region’s socio-economic development, the Santoña Marshes General Sanitation Plan was implemented, with the Berria submarine outfall serving as a cornerstone of the strategy.

As a result, the project has significantly improved wastewater management in the area, enhanced the protection of coastal and estuarine waters, and contributed to the long-term conservation of one of the most important wetland ecosystems in Spain.