The Sewer Rehabilitation of the Denver Federal Center and the Utilization of Trenchless Technologies
Background: The Denver Federal Center (DFC) is one of the largest concentrations of federal agencies in the United States, second only to Washington D.C. For the sanitary sewer rehabilitation portion of the contract, PCL contracted C&L Water Solutions, Inc. (C&L) to provide a complete project solution operation. The scope of work included:
- Approximately 21,000 linear feet of CIPP, or cured in place pipe, sized six to twelve inch;
- 3,500 linear feet of pipe bursting, upsizing four to six inch, six to eight inch, and ten to twelve inch;
- Miscellaneous point repairs, manhole removal and replacements, 48 manhole rehabilitations, cleanout installations, and minor mainline removal and replacement.
Due to the unique nature of the DFC facility, these methods were preferred over traditional open cut removal and replacement. According to Steve Kovach, the Senior Project Manager for PCL, trenchless technology practically guarantees that there will be minimal disturbance and few disruptions to the everyday functions of the DFC.
The Problem: As the DFC has been an operable facility for nearly 70 years, the underground utilities had fallen into disrepair and were in serious need of rehabilitation. The facility provides a perfect example of the effectiveness and relevance of trenchless technology in sewer rehabilitation, repair, and replacement. The DFC had undergone many years of “undocumented maintenance,” according to Steve Kovach. Utilities were installed, abandoned, and rerouted with no prior as-build history.
Challenges: One problem that C&L encountered was the age of some of the existing water line utilities that were in close proximity to the sewer line segments that were scheduled for bursting. The DFC’s valve locations and operability is unknown and limited at best. In the event of a water break, the damage could be costly and disruptive. The vibration from the pneumatic system could have posed a problem for aging lines. However, a static system was chosen to mitigate this potential issue. The static system uses brute pulling force to burst the new pipe into place, whereas pneumatic uses air pressure to “hammer” the missile through the existing line. 90 percent of the facility’s sewer mains and lateral pipes were replaced or rehabilitated using either pipe bursting or cured in place pipe.
The Solution: Trenchless technologies allowed the contractor to rehabilitate, replace, and repair pre-existing utilities with little to no risk of disturbance to existing structures, facilities, and tenants in a cost effective manner.
An important aspect of trenchless at the DFC is the minimal cost to the customer when compared to traditional open cut excavation. In particular, the Saertex CIPP liner offers best value through its innovative design. Saertex liners are UV cured, fiberglass reinforced cured in place liners with superior structural characteristics. The liner’s structural strength allows it to be installed with thinner wall structure, thereby retaining flow capacity. Additionally, the strengths allow the liner to be successfully tested beyond a 70-year design life.
Mark Hallett, the Vice President of Saertex Multicom USA, has said that due to the nature of this project, it became a project designed on value engineering. C&L was able to provide a technologically advanced product at the best value. “Saertex is pleased to offer our customer a product with a 70 year design life,” Mark Hallett remarked, “and we were thrilled to work with a quality contractor on a project with such a high profile.” While CIPP was important in the successful completion of this project, pipe bursting is another trenchless technology that provided an additional solution.
Lines that required additional capacity were upsized and replaced utilizing both static and pneumatic pipe bursting. Fuse welded HDPE was chosen for the replacement pipe and TT Technologies Grundocrack® and Grundoburst® systems were used to pull the pipe into place. This method was very effective, especially considering there were no service connections in the runs that were replaced. Only two excavation pits were required for each pull and the piping could be pulled through intermediate manholes with no difficulty.
In addition to the sewer utilities being rehabilitated, 48 manholes were rehabilitated using Sewpercoat PG. C&L contracted DRC Construction Services to install the Sewpercoat PG product at the DFC. The product was chosen for its superb corrosion resistance, quick and effective application, and structural properties. The DRC crew could clean, install steps, and spray one to two manholes per day. The corbel, wall, and bench portions were all rehabilitated into one monolithic structure. The end product was a rehabilitated manhole that looked new.
Final Thoughts: The successful sewer utility rehabilitation at the DFC was due in large part to the effectiveness of the crews, but also the advanced technologies that were used. Had PCL opted to use traditional excavation practices, the project undoubtedly would have been more expensive, and certainly would have disrupted the general order of the facility and its employees. Because trenchless technology is generally not disruptive, the employees were able to continue working, and buildings were kept open during the process.