Condition Assessment and Rehabilitation of the Interplant Digester Gas Line

The interplant High-Pressure Digester Gas Line (HDGL) allows Orange County Sanitation District (OCSD) the flexibility to move digester gas between two wastewater treatment plants (which are about four miles apart)for waste-to-energy conversion. Portions of the pipeline are located in public right-of-ways. The pipeline was designed and constructed in 1993 and operated for about 20 years without incident. During a master planning effort in 2004, the pipeline was assessed using standard gas pipeline indirect methodologies. Subsequent investigations identified deficiencies and the need for rehabilitation to bring the pipeline into compliance with changing regulatory requirements and District maintenance and design restrictions. This paper documents the projects and design decisions made along the way to rehabilitate the pipeline using high density polyethylene (HDPE) slip lining materials. The decision process that led from considerations of replacement in kind to the final selection of HDPE as a lining material are discussed and the lessons learned are documented.