Abstract: A system and process for treating oil well discharge pit liquors mixes successive portions of the watery layer of such liquors with surface active agents and sprays the resultant mixture in the air so that a large portion thereof is rapidly evaporated and the non-evaporated portion is applied to one or more of the walls of the pit as a spray. The watery spray particles so applied reversibly enter the interparticulate spaces in the pit walls without disturbing the capillary characteristics thereof and are subsequently evaporated. The penetration of such liquor from the spray into the pit wall is monitored to control (a) the amount of surface active agent added to the liquor, (b) the amount and rate of the spray of the liquid to the walls and (c) avoid contamination of water-bearing earth strata below the pit walls.