5-1 Waste Disposal

The volume and composition of our domestic waste is discussed in section 14.1 of the textbook. Canadians and Americans are undisputed world leaders in waste production, and efforts to encourage us to cut back on the stuff that we consume and then later throw away have not been particularly successful. As shown on Figure 14.1.3 in the textbook, the largest single component of a typical waste stream is organic matter (mostly food waste), followed by paper, plastic and hygiene products. This course includes a section on waste disposal because waste is inevitable with our existing lifestyle (although we can change that) and because disposal of waste on the land is a geological problem that has connections to many aspects of environmental geology, including climate change.

Most of these materials (except the plastic) are putrescible, meaning that they will be broken down by microorganisms within a waste pile, resulting in the production of gases (especially carbon dioxide and methane) and contaminated water. Those gases are one of the major issues with the waste in our landfills, because of their climate implications, but their production can be significantly limited with diversion programs.

Section 14.2 of the textbook includes a discussion of landfill siting criteria that are based on environmental, social, safety, and other issues. Please complete Exercise 14.2 Does Your Landfill Meet the Siting Criteria for British Columbia? which is about the specific landfill where your waste goes. An important consideration in landfill siting that is not discussed there is the permeability of the geological material underneath the landfill. This is critical because no matter how careful we are in constructing landfill liners, some leakage is almost inevitable. If the natural material of the region is relatively impermeable the opportunity for leachate to be dispersed offsite will be minimized. As described in section 14.2 landfills are designed to minimize the environmental and social impacts of solid waste disposal. That includes preventing the waste itself from leaving the site, landfill leachate liquids from getting into surface and groundwater systems, and landfill gases from getting into the atmosphere.

The contaminated water (leachate) and gases that are emitted by landfills are discussed in section 14.3. Leachate compositions are summarized in Table 14.3.1. An important thing to observe there is the difference in composition between typical leachate (the “30-UK-Irish” column would be a good one to use) and typical drinking water (the last column). Typical leachate has from tens to many hundreds of times higher levels than are common in drinking water, so there is a high risk that leakage from a landfill would contaminate surface or groundwater. Please complete Exercise 14.3 Visualizing Leachate Composition in the textbook.

Figure 14.3.2 shows the evolution of leachate within a typical landfill. An important thing to note is that while it is evident that leachate concentrations decrease over time, contaminated leachates will continue to be generated throughout the life of landfill as new waste is added, and for decades after a landfill is closed.

Landfill gas compositions also evolve over time. Carbon dioxide is dominant in the early stages while oxygen is still present, and then increasing amounts of methane are produced in the later stages (Figure 14.3.3). A mature landfill will produce approximately equal proportions of carbon dioxide and methane. Methane is the really critical gas from a climate change perspective because it is a much more potent greenhouse gas than carbon dioxide.

Many of the components of our waste stream are sources of energy, and, as described in section 14.4, there is good potential to convert waste to energy, and to thus avoid some of the negative aspects of landfills, such as water and air contamination and land use. North Americans are quite far behind other places in this regard.