Inspecting a Submerged Effluent Outfall System, Inside and Out

This paper describes the planning, preparations, equipment and procedures that were necessary to successfully inspect a submerged treatment facility effluent diffuser system. The system is owned by Niagara County Sewer District No. 1 and located in the Upper Niagara River in New York State. An external inspection of the diffuser system was performed by launching a remotely operated vehicle (ROV) from a vessel anchored upriver from the diffusers. Three attempts were made using a progression of equipment and procedures. The successful inspection had the ROV equipped with a forward looking tilting camera, a stationary downward looking camera, imaging sonar, and GPS locator equipment. The key to success was marking diffuser locations by GPS as each one was inspected, then extrapolating the expected position of the next. A shore-based internal inspection of the effluent header pipe was performed with a different ROV model. This unit was equipped with a forward looking camera, twin laser distance measuring equipment, imaging sonar, and profiling sonar. The diffuser header was visually inspected and invert sediment was quantified at regular stations using the profiling sonar. The inspection found the system to be in good physical condition with only minor damage to the outlet elbows and internal sedimentation at the far end of the system, equaling half a pipe at the far outlet. The lessons learned and GPS inventory of outlet locations are expected to make the next inspection quicker and easier.