PCCP Sewerage Force Main Structural Condition Assessment and Asset Management Approach

Abstract

The Greater Lawrence Sanitary District (GLSD) learned in 2002 that Prestressed Concrete Cylinder Pipe (PCCP) supplied to GLSD in 1974, was similar to pipelines experiencing a high rate of catastrophic failures throughout the United States. The District began an assessment program in 2005 to assess the structural condition of one of its PCCP lines. This paper discusses the approach GLSD used to assess the structural condition of the pipeline, including finite element analysis, acoustic and transient pressure monitoring, electromagnetic inspection, visual and sounding inspection, and material testing. This paper also discusses the emergency structural repair that was accomplished when one pipe section was found to be in imminent danger of failure. GLSD treats wastewater from Lawrence, Methuen, Andover and North Andover Massachusetts and Salem New Hampshire. The design capacity of the GLSD treatment plant is 52 MGD. During wet weather, the flow is increased to 110 MGD. Current plans involve raising the peak wet weather capacity of the plant to 135 MGD and in the future to 165 MGD. GLSD owns over 4 miles of PCCP ranging from 48 to 102 inches in diameter, which was manufactured by Interpace Corporation in 1973 and 1974. Much of this pipe is used in lower pressure applications. However, one GLSD pipeline, the Riverside Pump Station (RPS) 2700 foot long 72 inch diameter force main operates at higher pressures. Virtually all sewage received by GLSD is pumped to the treatment plant through the RPS force main. The force main route is through a residential neighborhood and crosses under an active railroad track that is used by Amtrak, commuter trains and freight trains. The majority of the force main is between 200 feet and 1000 feet from the Merrimack River, a major recreational, water supply and fisheries resource. Failure of this pipeline would have significant financial, environmental and operational consequences. The GLSD learned of the issues with its Interpace Class IV PCCP in June of 2002 while engaged in planning for combined sewer overflow abatement. In March 2003, the Middlesex County Utility Authority (MCUA) in New Jersey experienced a catastrophic failure of a similar 102 inch PCCP sewer force main. Representatives of the GLSD subsequently visited MCUA to learn about MCUA's response to the failure. MCUA's response included instituting a PCCP condition assessment program. Based on the uncertain structural condition of the GLSD force main, the District, in 2004 determined that it would be prudent to begin a program which would allow it to assess the current structural condition of its 72 inch PCCP force main. GLSD advertised and received proposals from engineering consultants and began its condition assessment program in 2005. GLSD hired CDM to lead the assessment program and they engaged specialty sub-contractors Openaka Corporation and Pure Technologies to conduct the condition assessment program.