Returning Impaired Marine Outfall Diffusers to Full Service

Abstract

This paper considers the troubled diffusers of four major U.S. outfalls, one in Hawaii and three on the West Coast. All four of these facilities had damaged and/or blocked outflow devices, and contained deposits that were responsible for flow obstruction. The difficult and expensive rehabilitation measures are described on a case by case basis. In one instance, a pipe in deep water was simply flushed following port-clearing operations. In other instances, nonhazardous materials were vacuumed into shallow local waters, and risers were returned to full service. In the fourth case, the hazardous deposits were carefully pumped from deep water to a barge and treated; the liquid and solid fractions were disposed of separately. This paper concludes with a pair of sections: a summary of the important lessons learned from the case studies, and a list of vital considerations for the whole outfall inspection-operation-maintenance-repair process. Full realization of the potential pitfalls should help engineers and coastal wastewater agencies prevent their recurrence.