Outfall Inspection and Rehabilitation

Hampton Roads Sanitation District (HRSD), Virginia Beach, Virginia developed an underwater inspection program for nine wastewater treatment plant outfalls. These outfalls are used to convey treated effluent using large diameter pipelines to adjacent rivers, the Chesapeake Bay and the Atlantic Ocean. A baseline underwater inspection of the nine outfalls was conducted in 2000 by a team of engineer divers. From inspection findings, guidelines on inspection intervals and repair recommendations were developed. Of the nine outfall facilities, four were found to have significant deficiencies. Three outfalls, the Boat Harbor Outfall, the James River Outfall and the Williamsburg Outfall, required immediate repairs. The Boat Harbor Outfall had serious damage to the main barrel and the James River and Williamsburg Outfalls were observed to have blocked diffuser ports. Repairs of the Boat Harbor Outfall, James River Outfall and Williamsburg Outfall were completed in 2001 and 2002. The fourth outfall found to have deficiencies was the Atlantic Plant Outfall. The multiport diffuser showed significant loss of sediment cover over a 732-meter (2400-foot) section 3 kilometers offshore in the Atlantic Ocean. The consequences of the loss of cover on the structural stability and durability of the Atlantic Plant Outfall was unknown. The primary concern was structural stability during heavy weather events. A study analyzed the overturning/rotational sliding of the multiport diffuser under heavy weather. This paper provides a synopsis of a program management approach to maintaining outfalls, a case study of the Atlantic Plant Outfall and an overview of repairs to the Boat Harbor and Williamsburg Outfalls. It also includes a checklist for the inspection of outfalls.