Preserving Casper's Infrastructure: A Large Diameter Pipeline Trenchless Rehabilitation Project

This presents an overview of the successful construction of a large diameter using trenchless technologies for renewal in Casper, a region with few large-scale projects. This project preserved and enhanced the City's aging wastewater infrastructure for an additional 100+ years. The pipeline, known as the North Platte Sanitary Sewer Interceptor (NPSSI) represents a nine-mile conveyance system that was initially constructed in four phases between 1980 and 1983 as part of a wastewater regionalization effort in the Casper metropolitan service area. The pipe material for the interceptor was unlined reinforced concrete pipe (RCP). Due to elevated levels of H2S within the pipeline, associated sulfuric acid formation became problematic along the entire interceptor alignment, causing serious deterioration of the NPSSI. The project team of CEPI, BlueWater, and Jacobs utilized a series of internal inspections and investigations of the entire interceptor over a three-year period to assess its condition and requirements for rehabilitation. This led to the first phase of strategic rehabilitation utilizing cured-in-place pipeline (CIPP) by Aegion/Insituform. Construction of the most critical portions of the NPSSI began in mid-2022 and was completed in early 2023. The project scope consisted of 7,600’ of 48-54” pipe rehabilitation along with numerous deep-bury point repairs, junction structures, river siphons, and inlet/outlet structures. Despite record cold winter weather and numerous site challenges encountered, Insituform Technologies delivered the project to the City of Casper with only a single time extension. The total cost of the project was below the original contracted amount, or $8.1M. The Casper NPSSI demonstrates who the successful renewal of a deteriorating wastewater interceptor within a stream-sensitive aquafer can be done using trenchless renewal in the best way possible. Added value was provided from the collaboration by all stakeholders, careful planning, and executing innovative technologies, to achieve an outcome beyond expectation.