Merck-Saint-Liévin is a commune in the Pas-de-Calais department in the Hauts-de-France region of France about 10 miles southwest of Saint …Merck-Saint-Liévin is a commune in the Pas-de-Calais department in the Hauts-de-France region of France about 10 miles southwest of Saint-Omer. The river Aa flows through the village. The Chemin de fer d'Anvin à Calais opened a railway station at Merck-Saint-Lièvin in 1881. The railway was closed in 1955.