ARQUES Wastewater Treatment Plant, Arques, Hauts-de-France, France

The ARQUES wastewater treatment plant is located in Arques, a commune in the Pas-de-Calais department of Hauts-de-France, France. It serves a population of approximately 42,117, classifying it as a medium-sized agglomeration under the EU Urban Waste Water Treatment Directive (UWWTD). The plant is situated in the historic region of French Flanders, near the city of Saint-Omer. As a French facility, the plant operates under the EU UWWTD (91/271/EEC), which requires secondary treatment for agglomerations between 10,000 and 150,000 population equivalent (PE). French regulations, enforced by the Agences de l'Eau, mandate compliance with national standards derived from the directive. The plant discharges treated wastewater into the local watershed, which ultimately drains into the North Sea via the Aa River and the English Channel. The region is characterized by low-lying terrain and extensive canal networks, supporting diverse aquatic habitats. The downstream environment includes the Marais Audomarois, a large wetland area of ecological importance, providing habitat for migratory birds and rare plant species.

The ARQUES plant discharges into the Aa River basin, which flows through the Marais Audomarois, a vast wetland and biosphere reserve. This area supports a rich diversity of birdlife and aquatic plants. The river eventually reaches the North Sea via the English Channel, making the plant's effluent quality critical for both local and coastal ecosystems.