How Landfills Work
Modern landfills are highly engineered structures — far more than just holes in the ground. They are designed and operated under strict provincial and federal environmental regulations to contain waste, capture byproducts, and eventually return the land to safe use.
1. Site Selection and Preparation
Before any waste is deposited, the site undergoes extensive geological and hydrological assessment. Engineers evaluate soil composition, groundwater depth, proximity to water bodies, and prevailing wind patterns. An ideal landfill site has a thick layer of low-permeability natural clay beneath it. If the natural geology is insufficient, additional barriers are constructed.
2. The Liner System
At the base of every modern engineered landfill is a composite liner — a multi-layer barrier designed to prevent any liquids from escaping into the surrounding soil and groundwater. A typical liner system includes:
- Compacted clay layer (minimum 60 cm) — provides the primary hydraulic barrier
- Geomembrane (HDPE plastic liner) — a flexible, high-density polyethylene sheet resistant to chemical attack
- Geotextile protection layer — cushions the geomembrane from punctures
- Leachate collection pipes — perforated pipes embedded in gravel that collect liquid (leachate) that percolates through the waste
3. How Waste is Placed
Waste is deposited in compacted layers called cells. Each cell is typically one day's worth of waste. At the end of each day, the working face is covered with 15-30 cm of soil or an approved alternative daily cover (ADC) like tarps, foam, or compost. This controls odour, prevents windblown litter, and deters scavenging animals and birds. Once a section reaches its permitted height, it is capped with a final cover system.
4. Leachate Management
As rainwater filters through waste, it dissolves and carries contaminants, forming leachate — a dark, odorous liquid that can contain heavy metals, organic compounds, and pathogens. Leachate is captured by the drainage layer at the base of the landfill and pumped to treatment facilities. Depending on the site, leachate may be treated on-site or hauled to a municipal wastewater treatment plant.
5. Landfill Gas (Methane) Collection
As organic waste decomposes anaerobically (without oxygen), it produces landfill gas — roughly 50% methane and 50% carbon dioxide, with trace amounts of other volatile organic compounds. Methane is a potent greenhouse gas (25-28x more powerful than CO₂). Modern landfills install vertical and horizontal gas collection wells connected to a vacuum system. The captured gas is either:
- Flared — burned off to convert methane to less harmful CO₂
- Used for energy — fed to engines or turbines to generate electricity
- Upgraded to pipeline quality — purified and injected into natural gas networks (renewable natural gas / RNG)
6. Groundwater Monitoring
A network of monitoring wells is installed around the landfill perimeter, both up-gradient and down-gradient. These wells are sampled regularly (monthly to quarterly) to detect any leakage through the liner system. Parameters tested include pH, conductivity, heavy metals, volatile organic compounds, and biological indicators. Any exceedance triggers immediate investigation and remediation.
7. Closure and Post-Closure Care
When a landfill reaches capacity, it enters closure. A final cover system is installed: a composite cap similar to the bottom liner, covered with topsoil and vegetation. The closed landfill enters a post-closure care period (typically 25-30 years in Canada), during which the operator must continue monitoring groundwater, maintaining caps, and managing gas. After post-closure care, the land may be repurposed — many closed landfills become parks, golf courses, or wildlife habitat.