Establishing Pipe-By-Pipe Rehabilitation and Re-Inspection Schedules Using Years Remaining Service Life

Many sewer asset management plans function at the 10,000 foot level, providing broad program planning guidance to rehabilitation needs, but failing to specify exactly when to rehabilitate which pipes, when to partially repair versus holistically rehabilitate or replace, and which technology offers the best life cycle cost for a given pipe segment. Arcadis developed a method to do this using the Town of Sullivan’s Island, South Carolina sewer system as full-scale proof of concept.The Town of Sullivan’s Island, South Carolina awarded Arcadis a contract to provide Construction Management at Risk (CMAR) construction services for their 2015 Phase 1 Sewer Pipeline Rehabilitation Project; including the development of a long-term sewer replacement and rehabilitation capital program. Arcadis created a 50-year rehabilitation and replacement capital program for each individual pipe segment based on the actual mix of physical defects found in each sewer segment. Four different rehabilitation technologies (pipeline testing and sealing, cured in place mainline linings, cured in place point repairs, and excavate and replace) were considered on each asset. Arcadis developed a rehabilitation decision matrix to determine the most economical technology or mix of technologies to use for the rehabilitation of each sewer segment.Central to the decision matrix logic is the concept of Years Remaining Service Life (YRSL). This concept starts with the assumption that a pipe is serviceable until it collapses. The rate of deterioration from Crack to Collapse varies widely and is subject to very localized conditions. The structural defects and their predicted worsening rate determines the YRSL. The more defects, and the more severe the defect, the lower the predicted YRSL. As structural pipe defects follow a set order of progression from cracks to fractures to breaks to collapses, a pipe does not suddenly collapse without going through this progression.For Sullivan’s Island, VCP pipe with no defects (i.e., like new, regardless of actual life) was assigned a remaining service life of 50 years. If a pipe contains defects, the YRSL would be lowered depending on the severity and number of defects within the segment. YRSL can be improved by repairing or rehabilitating some or all of the defects on a given asset.Deciding which defects to repair, when, and with what technology, represents an actionable asset management plan. The variety of sewer pipe rehabilitation technologies on the market gives engineers and system owners multiple options for rehabilitating deteriorating sewers. Each technology has certain strengths, costs, longevity, and defect applicability that make them more or less suitable for certain pipe conditions (e.g., defects, depth, location, number of taps). Because sewer pipe defect conditions are highly localized, using all the available rehab technologies at one’s disposal on a defect by defect and pipe by pipe basis reduces the overall price of a rehabilitation project and increases the usefulness of the project vs. using only one technology per project in a broad-brush approach. This same thinking can also be applied to optimize the reinspection frequency to prevent potential loss of pipe service before deferred pipeline rehabilitation can be completed.The decision matrix Arcadis created used inputs such as basic pipe information, PACP codes pulled from the preconstruction CCTV inspections, unit costs of the rehabilitation technologies, unit costs of reinspection, and the reinspection and contingency costs of non-action to calculate the initial capital costs of using each technology, the reinspection and reimplementation schedule for each pipe, and the life cycle cost of each technology.By implementing multiple rehabilitation technologies and determining which technology to use on a pipe by pipe basis by prioritizing YRSL, the capital program cost was optimized, and a 25-year pipe specific reinspection frequency program was laid out. System rehabilitation costs during the year 50 to year 60 life of the system was reduced by approximately 75% from its original generic risk-based asset management rubric. Using this pipe-based method, only 8% of the 50-year old system was found to require action within 5 years, with 85% of the system found to have >25 YRSL, and fully 56% have >40 YRSL. Both the capital rehabilitation and the pipe reinspection were programed into the utility’s GIS-based work order system and the costs of these programs inserted into both the long-term and short-term CIP programs/budgets.The capital plan was adopted in 2016 and is being successfully implemented now.