It is impossible to be sure without better context, but I think that it is likely that "cabecera" here refers to a slope somewhere on or in the vicinity of the landfill. "Head of the slope" (the top of a slope), & its companion term "toe of the slope" (the bottom of a slope), are common terms in drainage engineering. Because erosion of the slope by runoff from rainfall may be unacceptable, sometimes a drainage ditch is constructed across the top of the area of interest on a slope. This ditch intercepts surface runoff and sends it off to the sides of the slope, not permitting it to flow down the slope where it could cause erosion.
The problem is "vertedero": it can mean landfill or garbage dump; slope or hillside; weir or dike.
We don't normally speak of the head of a landfill - the head of something is a geometric feature, the highest point. But landfills generally have almost flat top surfaces during operation - the landfill is typically built up in near-horizontal layers using heavy equipment to dump, spread & compact the refuse. However, after closure, the top surface of the landfill mass is typically sloped to promote drainage & prevent ponding of water on the surface that could infiltrate into the mass & cause unacceptable chemical reactions within the mass; but the slope of the top surface has to be carefully designed so that water flowing across it & moving away from the landfill doesn't achieve velocities high enough to cause erosion.