The lignite waste heap named Le Défens, located on the territory of the OHM Bassin Minier de Provence, is subject to hazards related to the nature of this mining waste deposit: superficial landslide hazard, non-negligible fire risk and risk of contamination transfer by erosion of the substrate. However, today it is accessible to the public and is the place of many practices despite the potential dangers. The objective of this study was to analyze the effect of the various types of vegetation present on the heap on the quality and the stability of the substrate of the heap slopes, on the fire risk and to assess the quality of the runoff water. on the slag heap in order to recommend the most appropriate actions to limit the risks. The substrate of the heap is of mediocre quality and not very stable. However, vegetation is maintained there. Some vegetation strata characterized by a dense and relatively homogeneous vegetation cover seem more appropriate for slope stabilization. The use of pioneer local, nurses and engineers plant species could be an interesting solution to stabilize the unvegetated slopes of the heap. On the other hand, the water content of soils and plants, the composition and structure of vegetation can play a role in fire prevention. The gradual conversion of the Aleppo pine stand to a non-coniferous woody stand could limit the risks of fire spread and landslides. The facies of erosion observed on the heap represent preferential paths of water flow. However, only a tiny fraction of the substrate elements appears to be transferred to water. The proposed conversion of the pine forest to a non-coniferous shrub formation with herbaceous and diverse undergrowth could also limit these risks.