Pipeline Rehabilitation amidst Environmentally Sensitive Location

The District of Columbia Water and Sewer Authority (DC Water) was faced with repair of a degrading aerial sewer located in an environmentally sensitive area. The sewer is located over Klingle Creek in US National Park Service land. The sewer is an 18-in sanitary terra cotta line encased in 30-in wide by 30-in deep degrading concrete with support columns and footings position in the steam bed and banks. Significant erosion at the stream bed undermined the stream bed footings. This caused the design span to double and put the aerial sewer in jeopardy. Mitigation options included realignment, replacement, renewal, and footing support updates. The importance of the sewer to accommodate public demand was not well supported by options requiring environmental impact reports or special permits, such as replacement, realignment, and stream bed alterations. Although initial project discussions considered realignment and replacement as viable options, DC Water recognized the urgency for an alternative that did not require extended planning and permitting. The pipe owner contacted Analytical Engineering to provide an FRP (fiber reinforced polymer) repair alternative. Analytical recommend the use of the Tyfo CFRP (carbon fiber reinforced polymer) system for strengthening the exiting encased crossing while eliminating the need for stream bed supports and alterations. The use of the Tyfo CFRP system for external rehabilitation of the crossing also eliminated the need for dewatering the pipeline, which provided significant cost and time savings to the owner. Additionally, the CFRP system is environmentally compliant with no impacts on high water flows contacting the crossing. The work was completed by Fibrwrap Construction with no spillage and no incidents which would have negatively affected the creek area. This renewal option not only solved the environmental issues and extended schedules required of other options, but was did so at a fraction of their costs.