Chaumox Landfill Final Closure

Our design solution and process

Our first objective was to develop a closure system for the landfill that included environmental controls to contain the waste, minimize leachate, control the run-off of surface water, vent methane gas and minimize odours.

Our six-layer cover system is designed to minimize infiltration, vent gas and support native plant growth, turning the landfill into a green landscape. 

It includes a gas collection layer, a clay barrier, a gravel drainage layer, common fill subsoil, organic topsoil and vegetation. Selecting an appropriate vegetation layer required us to research root depths of common tree species that could thrive at the site. We chose western hemlock as it has shallow roots and is native to the area. 

The landfill uses natural attenuation to remediate the leachate and protect the groundwater from contamination. We used contour data from the site and ran a hydrologic evaluation to estimate annual leachate generation and then used this information to size our trenches. 

We designed a natural attenuation trench at the eastern slope, and to ensure that the leachate doesn’t migrate further, we proposed a one metre thick clay barrier to the east of the trench. The leachate will seep down into the gravel pathway and can then be managed by the existing natural attenuation system.

The site generates less than 1,000 tonnes of methane annually. We’ve designed a system to passively vent the gas in a controlled manner. The gas collection layer includes a network of perforated HDPE pipes and eight vertical vent stacks that extend two metres above ground to safely vent the gas. 

Surface water was another consideration we needed to manage. To prevent issues of flooding and erosion, we designed an infiltration swale that uses previously excavated soil as backfill to minimize costs. This swale collects water and a small perforated pipe underneath the trench drains water. We designed our system to be able to manage a 1-in-100-year storm and also incorporated a 20 per cent climate change factor to ensure our system is future resilient.

The challenges we faced

Before we started this project, we knew extremely little about landfills! 

None of us had worked on comparable projects in our courses or co-op experiences and we knew very little about technical issues like leachate management. This meant we had a lot to learn about a complex subject area over a short period of time. 

What we’re most proud of

We’ve learned so much since September and gained new expertise in so many different areas of landfill design. Landfills are particularly interesting to work on because they require you to integrate virtually every subdiscipline of civil engineering, as well as other areas of engineering and science, including botany (such as selecting vegetation that will be appropriate for the site).

It was extremely rewarding to have gone from knowing very little about landfills to completing a detailed design for a closure plan. 

There were other highlights along the way as well, including having the opportunity to learn and work with AutoCAD and Civil3D and to have the time to work on each drawing and/or calculation. 

This capstone project shows us how valuable it can be to step out of your comfort zone to work in a new area – as well as just how much can be accomplished in eight months.