Abstract: In a process for detoxifying a coal-tar deposit, effective amounts of carbon and a calcium oxide containing substance are added at a mixing station to at least a portion of the coal-tar deposit. The reaction mixture thus formed is mixed at a temperature of about 70.degree. F. to 130.degree. F. for a time sufficient to detoxify it and convert it into a non-hazardous reaction product. The coal-tar deposit may be either a substantially homogeneous coal-tar or a heterogeneous coal-tar contaminated substrate. The mixing station site may be either subsurface or surface and may include a container. The non-hazardous reaction product may be separated into small particles, suitable as fuel, and large particles, suitable as safe fill.