Hespeler Trunk Sanitary Sewer Case Study: A Proactive Municipality Benefits From The Use Of CIPP
By Brad Marin and Aaron Bruce, GHD
Trenchless technologies are a rapidly evolving set of construction methods, which are continuously improving in efficiency, effectiveness and availability across the globe. Cured-In-Place Pipe (CIPP) is one of the most popular rehabilitation methods available for restoring aging infrastructure such as sanitary sewers and watermains. This case study highlights how one municipality in Ontario, Canada had the foresight to use CIPP to rehabilitate a part of its critical collection system that was reaching the end of its design life. The successful results offer proof of how this trenchless technology minimized disruption to a community while saving tax dollars from the higher costs associated with more traditional open cut-and-cover methods.
The City of Cambridge (City) is responsible for the operation and maintenance of the Hespeler Trunk Sanitary Sewer. This project consisted of the structural rehabilitation of one-thousand-sixty-nine meters of six-hundred-millimeter diameter, three-hundred-ten meters of six-hundred-seventy-five-millimeter diameter and sixteen sanitary maintenance holes.
The sewer line conveys wastewater from north Hespeler under the Speed River to the Hespeler Wastewater Treatment Plant, servicing over thirty-five-thousand residents within the local community. The City’s asset management department routinely inspects the sewer by using a closed-circuit television camera. This proactive inspection approach illuminated points of serious concern including structural and maintenance defects, infiltration, and inflow.
GHD prepared a feasibility report that evaluated a series of four separate rehabilitation options for the aging sewer system. CIPP was selected as the preferred construction technique due to its multiple benefits, which included reduced environmental impacts (no excavation, less dewatering requirements, reduced greenhouse gas emissions and minimal vegetation removal), the ability to meet all technical requirements, the ease and speed of constructability, reduced impacts on the built and social environments, and cost advantages.
Traditional replacement methods would have resulted in significant costs and approval challenges for the City, including the requirement to cut the surrounding forestry within an environmentally sensitive area to provide adequate access and laydown area needed for construction. Greater lead-time would have been required to secure approvals from the Ministry of Natural Resources and Department of Fisheries and Oceans for the crossing of the Speed River, and fill alterations permits from the Grand River Conservation Authority. In addition, the City was concerned about the risks of operating a collection system in a compromised state of service.
Following the recommendations from the feasibility report, GHD completed the detailed design, secured necessary approvals and provided recommendations for a comprehensive request for proposal (RFP) tender package. The RFP documents laid out the requirements for contractor experience, qualifications, and constraints that would form the basis of the proposed construction work plans prepared by each of the bidders.
The team provided overall project management planning including the following components:
- Data collection and background study
- Conceptual design and feasibility report
- Detailed design and RFP documents
- Permitting and approval coordination
- Contract administration and site inspection services including daily and weekly reporting, and general overview of the Contractor’s performance
- Quality assurance testing and resolution of all technical matters and public concerns
- As-built drawings
In September 2017, the contractor’s team started constructing the temporary access road, bridge and sewer bypass system. This construction technique uses a woven felt liner wetted in a polyester-based epoxy/resin, which is installed by compressed air from maintenance hole to maintenance hole. Once the liner is in place and properly inflated, it is cured by either using water or steam over a period of hours. Real time, full-length temperature measurements were taken throughout the curing process. Samples were then collected to confirm the quality of the materials and properties of the final placement. In December 2017, the project was substantially complete. The CIPP rehabilitation restored the structural integrity of the sewer system and extended its life cycle by an additional fifty years, allowing for contiguous pipe repair without joints.
To complete the proposed work plan, a fully redundant sewer bypass system was implemented to carry flows around the length of the sewer for the duration of the rehabilitation work, using a temporary modular bridge that crossed the bypass piping over the Speed River, also allowing for continuous inspection of the bypass piping throughout the project.
- The planning of a fully redundant bypass system over the entire length of the rehabilitation project was a challenging endeavor. This planning system fostered a significantly improved delivery schedule, reducing the overall cost of the project. This process proves that mains of this size can be rehabilitated cost effectively.
- Due to the proximity of the sewer to the Hespeler Wastewater Treatment Plant, restrictions were stipulated that styrene levels of any water-cured CIPP condensate used in the process had to meet Provincial Water Quality Objectives of four micrograms per liter. Therefore, requirements were set in the contract for a separate, metered and controlled discharge line from which the CIPP condensate was tested, confirming compliance with the Region’s permit requirements, prior to discharge into the trunk.
- To install an inline sump at the head of the sanitary bypass system, the City required a permit to take water due to high ground water levels. GHD worked with the City and Ministry of the Environment and Climate Change to secure the required permit prior to the tendering of the construction contract, in case it was needed.
- An aerial crossing of the Speed River was needed to eliminate approvals from several agencies such as the Department of Fisheries and Oceans and Ministry of Natural Resources and Forestry. To achieve this, the Contractor proposed a suspended pipe system (temporary bridge) to keep the bypass pipes over the river.
- The sewer system and sixteen maintenance holes were brought from a grade condition three-and-four standard (needs repair), to a grade condition one standard, or new.
- Using an open-cut installation would have increased the need for approvals and consultation, taking more time to coordinate and costing more money. Using CIPP reduced the schedule and capital expenditure for the City. The Hespeler Trunk Sanitary Sewer rehabilitation project was completed on time and under budget with the Contractor’s warranty period extending through 2018, and yielded a cost savings of approximately one-million dollars
- The use of the North American Society of Trenchless Technology greenhouse gas carbon emissions calculator showed an overall reduction of seven-hundred to nine-hundred tonnes of greenhouse gas were eliminated from entering the atmosphere.
- Noise pollution was lessened through the silenced generators and pumps, reducing the effect on nearby residents and communities.
- Closure of the recreational multi-use Mill Run Trail (which has a high volume of pedestrian traffic) was limited to weeks instead of months, strengthening community ties. This is evidenced in the overwhelming public support of the project directed to the team by verbal compliments.
Because of the City’s diligent maintenance of their assets and uncompromising data collection process, the Hespeler Trunk Sanitary Sewer was rehabilitated before any occurrences of extreme structural defect, environmental spill, or emergency dig repairs were needed.
These results show how trenchless technology can be used to minimize disruption to a community while saving tax dollars from the higher costs associated with more traditional excavating and backfilling.
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