Establishing a land-fill dump for contaminated material which is suitable for biological treatment comprises (a) excavating the soil in the contaminated region and immediately sepg. it in accordance with its degree and type of contamination, (b) segregating the material which can be treated by a microbiological process is from that which can be disposed of without treatment or which needs special treatment, (c) transporting the segregated material to a remote waste material tipping area in the form of a depression (2) in the ground, which has been provided with floor and side wall sealing membranes (3), and which has a seepage water collection and drainage system (5) for the controlled removal of seepage water and gas, (d) classifying the material to be dumped according to particle size by sieving out larger particles, (e) mixing the material with nutrient substrates and loosening agents such as bark, wood shavings, compost etc. and placing it in the dumping area in thin layers (6, 11), (f) intensively microbiologically treating the material in sections by regular turning, chopping and/or mulching, (g) levelling off the area and prepg. it for the dumping of further layers of soil, (h) removing or adding gas, nutrient solution and moisture to the various layers in a controlled manner, and (i) degassing and dewatering all of the layers when the topmost layer (13) is in position.    The material in the dump may be injected with oxygen from below. Each layer is covered by a separate sealing membrane (13), below which is placed a degassing layer (7) contg. a system by which gas and moisture can be removed from or added to the dumped material. All of the layers are de-gassed and de-watered together via rising pipes (9, 10, 14) when it is no longer required to add gas or moisture into any of the layers.    USE/ADVANTAGE -   Used in the disposal of contaminated soil and waste material which can be treated by a biological process. The contaminated earth, which may have to be removed because of construction or de-contaminating operations, is biologically treated in a reliable and dependable manner.