Local historian Yves le Maner was charged with the task of developing the project while a feasibility study was conducted into the possibility of completing some of the original excavation work to make the site safe for public access. The plans were approved in 1993 and the site was purchased by the Commune de Helfaut. The following year, the Conseil Général du Pas-de-Calais acquired the site. The 69-million-franc project (£7.5 million at 1997 prices) was largely underwritten by the Conseil Général, which provided 35 million francs, with another 17 million coming from the regional council. The European Union provided a further 12 million, the French State provided 3 million and the Saint-Omer municipal administration funded the remaining 1 million francs; a number of private shareholders were also involved. The Societé d'Equipement du Pas-de-Calais was contracted to carry out the development work, which involved excavating a further two metres (six feet) beneath the dome, clearing out and completing the unfinished concreting of some of the tunnels, building an exhibition centre and car park in the quarry floor and installing a lift to carry visitors up from the octagon to the dome.