A third source, neither the ministry census nor OpenStreetMap: what the town itself publishes. It is the only one that says where a facility came from, who built it and what it cost.
Chaumes-en-Retz's pumptrack is in the parc de loisirs de Chéméré, rue de la Blanche: an asphalt track, bumps and loops, with a skatepark right next to it, a playground and a car park. Access is free year-round. What is known here comes from the department and regional tourist boards, not the town.1, 2