CIPP in Paradise — Large Diameter Gravity Interceptor Sewer Rehabilitation by lining with UV Cured-in-Place Pipe

This presentation is intended to convey the design concepts, efficacy of rehabilitation methods, and construction challenges for the Guam Waterworks Authority (GWA) Interceptor Sewer Refurbishment Project. The project included the rehabilitation of a large diameter interceptor sewer by UV cured-in-place pipe (UV CIPP). Design of the UV CIPP was based on ASTM F2019 - Rehabilitation of Existing Pipelines and Conduits by the Pulled in Place Installation of Glass Reinforced Plastic (GRP) Cured-in-Place Thermosetting Resin Pipe (CIPP). Design criteria for the project included the calculation of dead loads based on the actual depths of cover above the top of the existing pipes as well as live loads based on AASHTO HS25 for sewers both inside and outside of the roadways. Guam is a U.S. Territory in the Western Pacific with a population of almost 170,000. The island is approximately 10 miles wide by 32 miles long. It is located about a quarter of the way between the Philippines and Hawaii, approximately 900 miles north of the equator, and it sits atop the western rim of the Marianas Trench. The island is strategically important to U.S. military operations because of its location, its land areas suitable for major airports, and its naturally deep harbor is a safe port for ships and submarines. U.S. military bases, including Naval Base Guam and Andersen Air Force Base cover approximately 39,000 acres or 29% of Guam's total land area. To accommodate the increased wastewater flows expected with the transfer of 5,000 or more U.S. Marine Corps families from Okinawa to Guam in late 2024, the Guam Water Authority assessed the condition of about 8.4 miles of 18-inch through 42-inch diameter interceptor sewer to reliably carry wastewater. The interceptor sewer extends from Andersen Air Force Base on the north end of the island along Guam Route 9 and thence along Guam Route 3 to the Northern District Wastewater Treatment Plant. The existing interceptor sewer was constructed in the 1970s. An assessment of the condition of the sewer was conducted in 2010, and a report of the findings was completed in 2015. The report noted significant corrosion of the inner walls of the sewer and recommended rehabilitation of its entire length. Additional assessment in 2017 noted that most of the sewer was constructed using Techite Reinforced Polymer Mortar Pipe and Asbestos Cement Pipe. Both materials can be problematic. Techite pipe is a thin-walled fiberglass composite pipe that was manufactured in the 1970s. It was removed from the market in about 1980, because it was found to be subject to catastrophic failures. Because of the concerns to health caused by the handling of AC pipe- especially the risks of inhaling asbestos dust when cutting the pipes - it is no longer produced or allowed in many countries, including the United States. Guam Waterworks Authority utilized a progressive design-build delivery process to procure a contractor (design-builder) for the project and contracted with our design-build team in September 2019. The design-build team included Core Tech-Hawaiian Dredging (CT-HD), as the general contractor; Michels for the UV CIPP lining; Mocon Construction for manhole rehabilitation; Dueñas, Camacho and Associates for bypass pumping and civil design; and Gresham Smith for rehabilitation design. The project was funded by the Department of Defense (DoD) for the U.S. Marine Corps redeployment of families from Okinawa to Guam. GWA and CT-HD determined that UV CIPP was the best solution for the pipeline rehabilitation. Previous attempts to install conventional CIPP on Guam USA had achieved mixed results at best. This was partially due to the remote location of the island, which makes the installation of conventional CIPP logistically difficult. Essentially, the conventional liner manufacturer must either build a wet-out facility on the island, or the installation crews must wet out the liner on the job site. On-site wet-out is difficult for even small pipe diameters. It is impractical if not impossible for larger diameter liners. Therefore, UV CIPP was selected because the liners could be impregnated at the manufacturer's wet-out facility, then properly stored and transported by container ship to the island. The obvious conclusion is that UV CIPP is ideally suited for sewer rehabilitation in a remote location such as the island of Guam. Almost all the existing manholes on the interceptor were PVC lined precast concrete. Significant portions of the PVC manhole liners were defective and in need of repair. In lieu of repairing the PVC liners with similar products, our Design-Build team proposed rehabilitating the defective manholes using an epoxy lining system. The $23 million project, which included the rehabilitation of approximately 44,350 LF of 18-inch through 42-inch diameter sewers, necessary pre-lining point repairs, and the refurbishment of approximately 100 manholes, was successfully completed in July 2020. Although the project was completed on schedule and with minimal change order costs, our team had to overcome significant challenges. These challenges included: - Scheduling of all phases of the work, including long delivery times for the liners from the manufacturer. - Numerous bypass pumping setups, which were complicated by required minimum cure times for cementitious repairs before lining the existing manholes with Raven epoxy. - Detailed traffic control plans and coordination with highway construction along Guam Route 3. - Scheduling and permitting work on Federal Lands. - Protection of Endangered Species such as the Common Mariana Moorhen. - Archeological Review. - Constructability issues such as:
a manhole and sewer segment that were partially under a multistory apartment building.
removal of jagged edges of failed
Techite pipe without a robotic cutter, which was not available on the island. It is felt that the information provided in this presentation will be of value to the engineering community, especially for future projects with large diameter sewers, extensive bypass pumping, remote installations, and stringent design requirements.