The Vall d’en Joan is situated in the Natural Park of Garraf, in the municipalities of Begues and Gavà , in the county of Baix Llobregat. Originally, this spot was one of the many closed, winding valleys that form the foothills of the Garraf massif. Its use as a landfill dates back to 1974, since when it has been the destination of most of the urban waste produced by Barcelona and its metropolitan area. When closure of the site began, it occupied an approximate extension of 85 hectares and had been filled to two-thirds of its original level. Before restoration, the landfill was a vast extent of steep slopes where a layer of 20 centimeters of earth covered the waste beneath, but with no definitive capping. This huge sloping tract covered the entire valley, the top part of which was still functioning as a landfill. The image of the valley occupied by the dump contrasted with the variety of relief and vegetation of the landscapes in the natural park in which it was set.
The landfill restoration project aimed to use a single operation to address the three basic aspects identified: solving a complex technical problem, creating a new public space and constructing a new landscape. The multidisciplinary technical team that carried out restoration brought to this single intervention knowledge from different disciplines (environmental engineering, geology, landscape architecture and agronomy) to create this new place. The complex technical problems that derived from closing and capping the landfill served to outline a working strategy based on rationalization. The organization of stabilizing terraces and retaining embankments, and the track providing access marked out the geometry of the landfill, and structured the layout of piping to collect and conduct biogas to the transformation plant where it is turned into electrical energy and the draining and storage of leachates. This organization is complemented by the construction of channels to divert runoff.
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