A process for the removal of slag and other residual solid material from a coal gasification process as a suspension in water free from noxious gases normally associated therewith wherein water is drawn off from the quench section of a coal gasifier with the slag into lock hopper and is displaced by introducing cold fresh water into the lower portion of the lock hopper displacing the sour water from an exit in the upper portion of the lock hopper back into the quench section of the coal gasification system. In an alternate embodiment, noxious gases are stripped from the quench water in the lock hopper with a stripping gas. Solid waste and clean or decontaminated water are discharged from the system without pollution of the environment.