Gregoire sanitary sewer project helps sustain Fort McMurray’s growth

By Jason Lueke and Jeff Fetter

The Regional Municipality of Wood Buffalo in Northern Alberta continues to experience unprecedented economic expansion, arising from the area’s natural energy and oil industries. The Municipality comprises ten communities, of which the City of Fort McMurray is the largest. It has a population of about 120,000 residents, including over 76,000 in Fort McMurray and a large workforce population. The burgeoning population and growing economy is causing increased pressure and higher levels of risk to municipal infrastructure.

In response, the local government is investing hundreds of millions of dollars in new infrastructure projects, including sewer and water systems, wastewater and water treatment facilities, and roads and bridges. As part of their infrastructure planning efforts, Wood Buffalo identified the Gregoire Sanitary Sewer project as a key priority in their 2009 Wastewater Master Plan. Without an upgrade, the Region predicted a higher risk of sewer back-ups and development restrictions, thus hampering future growth.

Selection of innovative solution

Associated Engineering worked closely with the Municipality to develop a design and construction methodology that addressed challenging site geology, minimized impact on the environment, reduced construction risk and reduced impact on the public. Using horizontal directional drilling, which requires no digging, the sewer was installed in varying and steep terrain within an environmentally sensitive valley. This included a 50-metre deep section of sewer situated under an actively sliding slope and protected waterway.

The sewer route crosses developed urban areas, including a busy roadway, soccer field, children’s play park and Highway 63, a major transportation route. Therefore, safeguarding the public and minimizing impact to businesses and residents were important. While safety was paramount, existing development also placed constraints on construction staging areas.

To confirm the appropriateness of horizontal directional drilling, the project team performed a detailed field investigation along the preliminary drill path. Based on borehole data from the field investigation, it was anticipated the majority of the crossing would primarily traverse through limestone bedrock. The thickest subsurface layer above bedrock was found to be oil-bearing sands of a medium-to-fine grain and possessing a medium-to-rich oil content. This meant drilling to deep depths through the oil sands formation, complicating environmental issues with drill mud disposal.

Based on the field investigation, and the need to reduce the environmental impact during construction, while also mitigating the risk of slope instability along the very steep embankment, horizontal directional drilling was selected as the most suitable method for installing the pipeline. While horizontal directional drilling reduced impact on the environment and the public, the selected technique presented greater uncertainty due to the actual ground conditions that would be encountered. This technology originated in the oilfield drilling and extraction sector many decades ago and was not typically used for such a long sewer main at significant depths.

The drill path was extremely unusual in that it required a long, complex curve under a creek and up through an active slope-failure zone, including a 50-metre deep section under the active sliding slope and creek. Construction traversed both privately-owned and public land parcels.

During construction, assembly and welding activities for the steel pipeline had to be confined to a very narrow corridor within the Highway 63 road right-of-way. This required coordination with private, municipal and provincial authorities, to permit the uninterrupted peak-hour use of very busy roads located inside the workspace. Working closely with the contractor and Municipality, the team helped to coordinate the complex roadside erection of steel A-frame structures. These provided support for the pipe string over Gregoire Drive at the Highway 63 intersection.

Risks such as drill mud escaping to the surface through hydraulic fractures, disposal of the drill mud and reclamation of staging areas, were mitigated by conducting extensive pre-disturbance assessments before construction. These were followed by monitoring and a drilling mud disposal plan during construction. Monitoring confirmed there was no drilling mud seepage or related fluids coming back up through to the surface. There was no adverse impact to the environmentally sensitive Saline Creek valley embankment and nearby creek areas.

At one point in construction, the continuous 1.6 kilometre long steel pipe string was suspended overtop of a busy intersection by industrial cranes, with ongoing use of the road by commercial and industrial traffic during pipe installation. Traditionally, the roadway would have been closed during pull-back of the pipe string, but this method would have greater costs and impact on all stakeholders and the public.

The project team identified a small area for staging of entry-side operations within an existing public soccer field, and adjacent to the children’s play park. To maintain the project schedule, the team coordinated with the Municipality to allow 24-hour
construction operation in a residential area. This required the use of noise reducing equipment during construction, and design and construction of extensive sound barriers. Afterwards, the soccer field and play park were restored and improved for the community.

Added value

Drill mud from the horizontal directional drilling operation needed to be collected and disposed of. During construction, the team identified that drill mud could be combined with drilling fluids from other horizontal directional drilling projects in the area, and disposed of at a common site. Typical disposal sites required hauling waste nearly four hours away.

Working with the Municipality, the team identified an old cement plant site on municipal land that would accept the drilling mud to accommodate a mix bury cover disposal method. This would also help restore and reclaim the site. Disposal of drill fluids in this manner minimized cost for offsite disposal and time for hauling. Combining disposal of drill mud with other drilling operations and using it to help restoration of a former cement plant site, was a sustainable use of the construction waste.

Project completion

Completed in 2012, the $16.1 million Gregoire Sanitary Sewer project demonstrates how major infrastructure can be designed and constructed cost-effectively, and in an environmentally sustainable manner. The Regional Municipality of Wood Buffalo and the City of Fort McMurray benefits from increased infrastructure capacity and reduced risks to their sewer system.

Awards

Since completion, the Gregoire Sanitary Sewer project has received a number of awards from prominent technical organizations for the unique technical methodology used and overall project management. These include:

• Consulting Engineers of Alberta: 2014 Award of Excellence in Environmental category.
• Alberta Construction Magazine: Top 2012 Project, Civil Under $50 Million.
• Northwest Chapter of North American Society for Trenchless Technology: Runner-up for 2012 Trenchless Project of the Year.

Jason Lueke, Ph.D, P.Eng., and Jeff Fetter, P.Eng.,are with Associated Engineering. This article appeared in ES&S’s July/August Issue.