Alternative Condition Score for Large-Diameter Pipe Rehabilitation and Inspection Prioritization

The Potomac Interceptor (PI) is a gravity sewer system that takes wastewater from Virginia and Maryland and delivers it to DC Waters’ Blue Plains Advanced Wastewater Treatment Plant in Washington, DC. DC Water has been performing condition assessments on these pipes and found that a number of reinforced concrete pipeline reaches had experienced various levels of corrosion. The problem DC Water faced was determining which portions should be included in the capital improvement plan (CIP) for rehabilitation. The condition assessments indicated many of the impacted pipes had the same National Association of Sewer Service Companies’ (NASSCO) Pipeline Assessment Certification Program (PACP) ratings 4 and 5. Rehabilitation of all the pipes with these high PACP ratings was prohibitively expensive. This paper will discuss the methodology used in detail, and benefits of this type of alternative condition analysis. Also, the paper will cover how this methodology, if applied by the industry, could potentially allow utilities to spread their CIP costs over longer periods to help ease the financial burden on rate paying customers.