Up for Rehab: Proactive Pipeline Rehabilitation to Prevent Failure in SAWS’ Largest Lift Station

A deteriorated pipe can lead to a community out of service and an operations group on standby for repairs. Hence, rehabilitation methods are vital in keeping a pipe in service, more so for a 30″ ductile iron effluent force main for the largest lift station in the San Antonio Water Systems (SAWS). Analysis of the main in preparation for a hot tap revealed up to 90% loss of its wall thickness. Given the corrosion, the hot tap was not completed. Given the high potential of failure, SAWS pursued improvements to the lift station to mitigate risk and increase operational redundancy for the critical lift station. The lift station is in an “environmentally sensitive” area within the San Antonio Missions National Historical Park, which is designated as a United Nations Educational, Scientific, and Cultural Organization (UNESCO) World Heritage Site, owned by the San Antonio River Authority (SARA), and managed by the National Park Service (NPS). As a result, a plan was developed to have archeological monitoring to occur during the construction effort to collect archaeological materials should they be encountered. Given the criticality and location of the lift station, various improvements to the effluent force main were analyzed to improve the redundancy in the system. Cured-in-place pipe (CIPP), pipe bursting rehabilitation, and open cut replacement were analyzed to determine the feasibility of restoring the force main. Cost, lead time, feasibility, and materials were all considered as part of the analysis. Additionally, a parallel force main alignment with a future bypass connection was studied to improve the resiliency of the lift station. Rehabilitation methods were ruled out due to work zone availability and regulation requirements. HDPE, PVC, and ductile iron pipe materials were analyzed for both parallel and replacement force mains. Based on maintenance, cost, and lead time, HDPE was selected as the preferred pipe material. Availability of large diameter plug valves was determined to have an impact in replacing the force main. Thus, plug valve procurement was initiated during the design phase. Knife gate valves and swing check valve replacements were also necessary inside the lift station to avoid future maintenance.