The City of Hamilton, located 70 km west of Toronto, owns, operates, and maintains a large underground network of sewers. Three separate large diameter combined sewer systems (The Eastern Sanitary Interceptor, The Western Sanitary Interceptor, and the Red Hill Trunk Sewer) collect combined storm and sanitary flows from the City’s vast sewer network and conveys them through these above sewers to Hamilton’s only treatment plant – the Woodward Avenue Wastewater Treatment Plant.

The City’s Asset Management Group, with a mandate to carry out sewer inspections, determine rehabilitation needs, and manage the entire sewer system, has deemed that large diameter combined trunk sewers, as ‘Critical Assets’, have a zero tolerance for failure.

The Western Sanitary Interceptor (WSI) CSO is a hand mined sanitary sewer tunnel that collects and conveys more than 35 per cent of the city’s total sewage flow from outlying suburbs; winds its way underground through heavily populated and environmentally sensitive areas in the western core of the City.

Accurate condition assessments of large diameter, deep, high-flowing interceptors remain one of the most significant challenges facing Hamilton’s Asset Management Group. In 1998, the City commissioned a combined CCTV/Sonar inspection of the WSI. Of the 15 km stretch, approximately 1.5 km was strategically selected for inspection. A 270 m segment of the inspected sewer running under Locke Street, from York Boulevard to Barton Street (a heavily populated area) showed significant cracking and infiltration.

This particular segment of sewer is approximately 28 m deep, has an internal diameter of 1,525 mm and is located within 1 km of Hamilton Harbor, which is an environmentally sensitive area that would be greatly affected by discharges resulting from a sewer failure. Given the criticality of this sewer, the City had deemed it to have a zero tolerance for failure, and as such, a proactive management strategy and intervention practice was implemented.

Building the team

Due to the extreme depth, consistent high flow, and limited access, it was determined that the inspection and rehabilitation of this 270 m long sewer segment would be a difficult process, and would have to be undertaken in several phases. It would require a team with diverse skills and extensive experience in Trenchless Technology, sewer rehabilitation, and confined space entry procedures who could work together as an integrated and cohesive unit.

This team was made up of the City of Hamilton Engineering Services Group, who are leaders in the industry in assessing and determining the need to rehabilitate their critical infrastructure, and R.V. Anderson Associates Limited (RVA), who have worked closely with the City to rehabilitate and replace its underground services for nearly a decade. The team also included PipeFlo Contracting Corp. (PipeFlo), who are the local expert in confined space entry and deep sewer inspection and have significant experience working on the City’s sewer system.

As a result of the team’s combined effort, an approach was developed to address a number of challenges that expanded the project’s complexity far beyond a typical sewer rehabilitation project.

Project objectives

The ultimate goal of this project was to undertake a thorough investigation to determine the scope of rehabilitation that would be required for the section of sewer identified in the 1998 CCTV/Sonar report as having significant cracking and infiltration problems.

The complexity of this project demanded a lengthy planning period to ensure that the project could be executed safely and successfully. A significant portion of the two-year planning phase was spent developing contractor pre-qualification documents that would address the significant risks associated with undertaking this work.

These included: working around scheduling limitations due to rain events and their effect on the sewer’s flows, the anticipated hazardous working environment within the sewer, and the operational/management challenges inherent in co-ordinating project activities.

Once the pre-qualification documents were created, a public expression of interest (EOI) was issued by the City to be responded to by all and any interested parties. Upon completion of the EOI, two contractors were prequalified to bid. Upon review of the subsequent bid submissions received by the City, the contract was awarded to PipeFlo, and Phase One of the project was initiated.

In order to carry-out continuous man-entry inspections for a deep high-flowing large diameter sewer, a number of activities needed to be addressed including safety documents and training, manhole modifications

Team planning and project planning

In order to carry-out continuous man-entry inspections for a deep high-flowing large diameter sewer, a number of activities needed to be addressed.

Safety documents and training

Due to the nature of the environment within pipe, extensive safety procedures were documented and training was undertaken for all team members, including confined space entry, fall arrest, specialised equipment, and mock rescue scenarios.

Manhole modification

Two existing manhole shafts were modified to provide access for workers and equipment during detailed inspection and rehabilitation. The work included removing the top 3 m cone section of both manholes, and removing existing ladders and safety platforms. Modifications also included installing a temporary shaft extension (for equipment access), which was subsequently replaced with a continuous concrete shaft extension to street level and installing a large, custom, rectangular shaped manhole cover to accommodate future maintenance.

A temporary scaffold ‘man-lift’ was set up over one of the shafts to lower personnel and equipment into the sewer.

Flow diversion plan

During the initial planning stage, it was identified that a large portion of the flow could be diverted temporarily into a nearby CSO tank (the City’s Main-King CSO) in order to allow for person-entry inspections during low flow periods and to eliminate the need for an expensive mechanical bypass.

The team developed and implemented a detailed flow diversion plan and lock out procedure, while an access road was constructed to one of several flow diversion chambers located in a remote valley underneath a highway overpass.

Strategy and logistics planning

Creation of the Execution Documents was undertaken as a team effort between RVA, PipeFlo and City of Hamilton Operational staff. The team had to determine the limitations, characteristics and logistics of diverting the flow to the Main-King CSO Tank in a safe and effective manner, and develop lockout procedures and an overall plan for the completion of the work. Because the pipe involved two 45-degree bends, special consideration had to be made for the use of equipment and the safety of man-entry.

Creation of MAThW Vehicle

To assist the technicians working in a 1,524 mm diameter sewer, PipeFlo designed and built a Modular Apparatus Three-Wheeled (MAThW) vehicle that would carry various types of equipment and would be used for the third phase of cleaning as well as during the grouting operations. The MAThW would also have enough space for two technicians to sit and operate the equipment in relative comfort. A replica segment of the pipe was set up in PipeFlo’s equipment yard in order to allow the team to practice using the MAThW vehicle and fine tune its construction.

Dry run practice

A full scale dry run operation was undertaken in order to confirm and evaluate PipeFlo Contracting’s ability to safely lower and raise both man and equipment down the 28 m deep manhole shaft. This dry run was monitored by team members from the City/RVA and by an outside safety consultant. The results of the dry run were reviewed in a post dry run debrief meeting. Minor issues that were identified during the dry run were addressed at the meeting and solutions were implemented into PipeFlo’s confined space entry and rescue plan.

Sewer cleaning operations

Heavy debris cleaning was required prior to carrying out the inspection and rehabilitation work. As standard cleaning operations would not be effective due to the depth of the sewer and high flow levels, specialised equipment was created to suit the required depth, flow and distance.

The cleaning was completed in three stages:

• Heavy debris cleaning – A specialised high velocity nozzle head was used to flush heavy debris, which was then removed using a custom-made air assist vacuum tube to lift it to the surface for disposal.
• Man entry for calcite cleaning – A man entry team manually removed calcite deposits from the pipe walls.
• Spray cleaning – the MAThW vehicle was lowered in to the sewer to spray the pipe walls using a custom made arm with rotating spray nozzles to further clean the pipe wall.

Man-entry inspections

Once the cleaning was complete, the inspection of the sewer-Phase II of the project could proceed. Initially, the City planned only to conduct an inspection to verify data from the 1998 report; however, the City decided to include an assessment of the sewer’s structural integrity as well.

This included exploration of:

• Pipe wall thickness and concrete strength verification – concrete cores were extracted from the pipe walls inside the sewer to confirm concrete thickness and strength.
• External void detection – Ground Penetrating Radar (GPR) was used to detect voids outside of the pipe walls, the first time this procedure had been undertaken locally.
• Pipe wall void detection – while using GPR to locate external voids, the team discovered voids within the pipe wall as well, likely a result of the concrete pouring practices used in the 1960s when the sewer was constructed. These voids were located and sealed.
• Boreholes – boreholes were drilled from the surface to confirm soil strata around the pipe, and to determine the ground water table level and the hydraulic head that would be present during grouting.
• Groundwater infiltration – water samples were collected from the ongoing infiltration to determine sediment accumulation and rate of ground water infiltration.

The inspections confirmed that debris was entering the pipe, which would require immediate rehabilitation. While the man-entry team completed their inspection, the technicians created a detailed location map for each crack requiring injection and sealing.

Based on the information retrieved from the inspection, PipeFlo made modifications to the MAThW vehicle to accommodate sealing operations, and completed further dry-land training with the replica pipe to ensure that all man-entry team members were proficient in the use of the refitted MAThW vehicle and equipment.

The final phase of the project involved sealing the cracks, which was carried out by several man-entry shifts, using the MAThW vehicle and location map created during the inspection phase.

Project challenges and solutions

To overcome various challenges dealing with deep high-flowing sewers, the project team used a multi-phased planning process prior to the implementation of the project.

Planning

Putting together a project of this magnitude, the likes of which had never previously been attempted by the City, required the team to think creatively in the planning and development of solutions to overcome challenges as they were identified.

The entire planning process took over two years, given that the team had to work to identify the scope of work required, the operational and communication challenges, and address the risks inherent in the sewer environment.

Contract documents

One main challenge was to determine the specific qualifications required of the contractor in order to carry out the work. Because of the uncertainty surrounding the condition of the sewer and contractor’s preparedness to execute the work, the contract itself was structured using a phased approach. This would allow the City to terminate the contract at specific milestones if the working conditions in the sewer were too hazardous, if a significant change in scope was required, or if the contractor could not demonstrate adequate capability to execute the work.

Team development

One of the major factors in the success of this project was the ability of the City, RVA and PipeFlo to communicate efficiently and to work collaboratively towards a common objective. This ensured the effective management of risks associated with undertaking the work.

The focal point of this communication occurred around the use of the City’s Main-King CSO tank. In order to establish this communication protocol, a number of meetings were established between team members and stakeholders. Once a communications protocol was established, cross training was implemented to ensure continuity in project implementation.

Diverting flow

In addition to the use of the CSO tank, an inflatable flow-through plug was installed to act as a temporary weir wall in an up-stream flow diversion chamber to divert flow away from the CSO tank and to gain additional working time. However there were still a number of conditions that had to be met in order to make use of the CSO Tank:

• The tank had to be dry prior to beginning the shift.
• The team could only fill the tank to approximately 25 per cent of the total capacity. This would reduce the likelihood of overflow should there be any unexpected need for the tank.
• Work could only be done during “dry” weather periods. City staff needed to be able to drain fully the tank before the next rain event, a process that can take up to twelve hours.

To accommodate these conditions, the team developed a 72 hour go/no-go checklist to determine if a shift would be feasible.

Accessibility

There were a number of factors affecting accessibility:

• Depth – at 28 m deep, team members had to undergo specialised training to safely enter/work in the sewer.
• Manholes – manholes had to be modified in order to allow access of equipment and men.
• Pipe configuration – with two 45-degree bends in the pipe, line-of-sight was compromised and special considerations were required with regards to the visual surveillance of the team.

During the planning stage, it was decided that the teams could only enter the pipe up to 150 m before compromising safety due to the risk of tangled ropes, loss of visual surveillance, and difficulty of rescue. This meant that the teams had to complete the setup twice, once from each manhole, to allow work to take place along the entire length of the pipe.

Health and safety

Lockout procedures – under the initially developed lockout procedures, the team members in the pipe were required to hold the keys for the gates and vehicles being used, in order to prevent the accidental opening of the gates.

However, due to the time constraints surrounding the setup, these team members were not able to physically attend to the lockout of the gates, which were 4 km and 1 km away, respectively. A solution was developed where the ground team did the lockout, placed all of the keys in a lockbox and the team in the pipes held the key to the lockbox. This allowed for a safe and secure shift, while conforming to the time restraints that were a part of the entry logistics.

Exhaustion

With a diameter of only 1,525 mm, the sewer was not large enough for a person of average height to stand upright. This meant that two teams were needed to switch out periodically over the eight hour shift in order to avoid exhaustion and physical strain. With the work initially scheduled overnight to take advantage of lower flow levels, crew members had the added challenge of acclimatizing themselves between day and night schedules.

Confined space entry – all team members were required to undergo specialised, advanced confined space entry training. This included vertical and horizontal access rescue training, which involved several field practices, as well as training and certification in the use of Scott air-packs and re-breathers and the use of the military grade communication system employed during the project.

Flow levels – working at night during low flow periods allowed for the maximum reduction of risk to the man-entry teams.

Developing technology

Working in constant flow and penetrating the sewer to a distance of up to 150 m at a time presented technical challenges for the contractor. As a result, PipeFlo developed innovative equipment to assist the teams in carrying out the work, including the MAThW vehicle that was designed with space for team members to be seated while working, a rotating sprayer unit for pipe wall cleaning and outfitted with containers to carry equipment and grout pumps.

Communication

In order to ensure the safety of the crew below, a live communication link between the command truck and the technicians working in the sewer needed to be established. This included the use of military-quality rescue ropes containing a communication line, which provided a continuous two-way communication between technicians and the command truck through the use of throat microphones and ear pieces.

Simultaneously, a video camera and additional lighting were deployed from a downstream manhole, providing the camera truck with a constant view of the technicians in the pipe, creating a record of the work being done, and providing additional lighting for the team. A wireless system was set up to transmit the visual data 300 m back to the command truck located the upstream manhole, visual and auditory data were monitored simultaneously.

The magnitude of repair to a sewer and the selection of rehabilitation methods are dependent on the pipe size and depth. The deeper the pipe is buried, the greater the degree of difficulty in accessing it for rehabilitation and inspection. However, the consequence of failure of a sanitary sewer resulting in a CSO discharge in to the environment is greater than a storm sewer drain, regardless of size.

Historically, the industry did not use a forward thinking process with regards to the management of critical infrastructure – assets were repaired when they broke, or added when a need became apparent. A proactive approach, like the one adopted by the City of Hamilton, allows for better management and sustainment of assets.

Engineering staff are now understanding and applying broader financial management and governance principles within their organisation, which helps to allocate funding with regards to their infrastructure. This approach defers outright replacement of assets and lowers overall management costs. Benefits of a more proactive approach include:

• Enhanced life expectancy of assets
• Improved risk management
• Improved service level management.

Environmentally, proactive asset management represents a significant contribution to sustainability because of the extension of the life cycle of the asset, and avoidance of the need to expend resources and energy renewing the infrastructure prematurely. It maintains infrastructure in better operating condition, which allows it to properly perform its role in protecting the environment.