One PCCP Transmission Main, Three Inspection Cycles

WSSC Water (WSSC) is among the largest water and wastewater utilities in the United States, serving approximately 1.8 million residents in Montgomery County and Prince George’s County, Maryland. The backbone of WSSC’s potable water transmission system is 145 mi of large diameter (36-in. and greater) prestressed concrete cylinder pipe (PCCP). For over ten years, WSSC implemented a condition assessment and asset management program to ensure the reliability of their PCCP transmission mains. WSSC Water employs a proactive approach to manage the condition of their PCCP transmission mains with a five year cycle multi-approach inspection followed by near-real-time pipeline acoustic fiber optic (AFO) monitoring. Inspection data and structural analysis together with AFO provide to WSSC up-to-date condition assessment information of each monitored PCCP to make informed proactive decisions. This paper will compare and discuss the results of four condition assessments performed in 2008, 2009, 2014, and 2020 on the same 48-in. PCCP Rockville Montgomery County High Zone transmission main. The 48-in. PCCP transmission main is comprised of approximately 31,895 ft of embedded cylinder PCCP (ECP) and approximately 517 ft of ductile iron pipe (DIP). The main connects the system from east to west providing redundancy between two WSSC’s water treatment plants. A failure occurred in June 2008 resulting in an interruption of the service affecting residences and businesses primarily north of Randolph Road in Montgomery County. As a result, WSSC contracted Pure Technologies (Pure) to conduct a condition assessment of the transmission main. After the first condition assessment was completed in 2008 and the subsequent AFO monitoring technology installed for ongoing monitoring, this PCCP transmission main has been reinspected in 2014 and 2020 utilizing Pure’s electromagnetic inspection technology. This paper will also evaluate the progression of deterioration, review the frequency of reinspection, analyze how repairs extended the service life of the 48-in. PCCP transmission main, share the lessons learned by WSSC’s engineers executing the condition assessment every five years, and discuss what changes are ahead to improve the continuous success of the WSSC’s PCCP program.