Clean ballast means the tank in which, since oil was last carried therein has been so cleaned that effluent there from if it were discharged from the ship which is stationary, into clean calm water on a clear day would not produce visible traces of oil on the surface of the water or on adjoining shore lines or cause a sludge or emulsion to be deposited beneath the surface of water or upon adjoining shorelines.
If the ballast is discharged through an oil discharge monitoring system, approved by the administration, the oil content of the effluent did not exceed 15 ppm