Repairing History: DC Water’s Experience Designing the Rehabilitation of a 150-Year-Old Sewer

The Northeast Boundary Trunk Sewer (NEBTS) was constructed between 1879 and 1894 and ranges from approximately 6 ft (1.8 m) to 23 ft (7 m) in diameter and is approximately 28,800 linear feet (LF) (8,778 m) in length. In 2018, DC Water commissioned a report on the condition of various sections of the sewer. Based on the results of the report, two sections/segments of the sewer required rehabilitation. Segment 1 has a circular cross section with a diameter of 22 ft (6.7 m). Segment 2 has a 9 ft (2.7 m) by 6 ft (1.8 m) wide egg-shaped cross section. DC Water tasked the Greeley and Hansen/Ramboll Joint Venture with analysis of rehabilitation alternatives. Once geopolymer was selected, the Joint Venture was tasked with a Finite Element Analysis to determine the thickness of the liner. Construction is anticipated to begin in Spring 2024 and finish in Summer 2025.