The effects of mining on land surface can be controlled by injecting filling materials or waste into the underground cavities. However, disposal of industrial byproducts in underground mines is not always feasible. This particularly regards waste which due to its chemical composition can contaminate underground water or the cases when the method of disposal is itself hampered by mining and geological considerations. The author gives a general verview of mining waste and PFA, and discusses conditions for waste disposal on the land surface or under it.