Landfill Odors: I See, Therefore I Smell

Written by Neal Bolton 

Landfill gas emissions come in two varieties: those you can smell…and those you can’t.  By a wide margin, the majority of landfill gas falls into the “can’t smell” category; it is odorless. 

The gas generated at a typical landfill consists of an approximate 50-50 ratio of methane and carbon dioxide-both are odorless, tasteless, and invisible gases. While nearly all landfill emissions are made up of these two gases, there are other compounds-and it’s these other compounds that cause the bad smell associated with landfills.

Here’s something interesting about landfill odors. We typically think of odors being detected first by someone’s sense of smell. The more sensitive their sense of smell, the more likely they are to detect landfill odors. But in some cases, it’s a person’s sense of sight that will first make them aware of the presence or potential presence of landfill odors. In other words, for many people, landfill odors will be so slight or so far in the background of their subconscious that they won’t really notice it until they see a sign that tells them a landfill is nearby…or see the landfill itself.

In the same way that a placebo drug has sometimes been shown to improve how a person feels, experts have also identified a nocebo response-where an inert drug can create negative expectations (and negative responses). These two words come from the Latin words placebo (I will please) and nocebo (I will harm).

Landfills are often blamed as the cause of odor when the odors actually originate from somewhere else-perhaps a wastewater treatment plant, feed lot, manufacturing operation, or other source. Why is that? I think it comes from the long-standing notion of landfills as dumps. So, when it comes to landfill odors, there is some truth to the statement: “We get-or rather, smell-what we are looking for.”

Does this mean that all landfill odor complaints are a fictitious bad rap against landfills? It certainly does not. Landfills can-and sometimes do-smell bad.

Though the presence of odors doesn’t necessarily indicate a poorly run landfill. It’s simply related to the decomposition process that occurs at virtually all landfills. When organic waste materials, such as foodwaste, paper, greenwaste, or other organics are landfilled, decomposition will occur and landfill gas will be generated.

So, what should you do when you receive offsite complaints of odors? The same thing you do if you received a hit in your groundwater-monitoring network: retest.

First, make sure the odors are actually coming from the landfill. Go to the location of the complaint and see if you can smell something. Then, make sure that something is, in fact, the landfill.

One way to do this is to note the wind direction at the time of the complaint. This is one of the many reasons for having a data-logging weather station at your landfill-it provides a continuous record of onsite climate-specifically wind speed and direction.

If you determine that, “Yes, landfill odors are being detected onsite,” the next step should be to identify the specific source. It’s not enough to simply recognize that the landfill smells bad, you need to be specific. In the same way that a conscientious doctor will research and ask lots of questions to find out why you don’t feel well, so too will a responsible landfill manager seek to understand the source of odors.

Odors can originate from a variety of sources at a landfill, most often they are a result of decomposition of the waste mass within the landfill. These odors can be broader and more generalized across the landfill and may vary considerably depending on weather conditions, type of soil, and the presence and effectiveness of a landfill-gas collection system.

Options for odor mitigation include simply not receiving specific types of odorous loads, changing the operation in regard to when odorous loads are accepted, and how they are handled, repairing leachate seeps, or eliminating leachate storage ponds or other sources of odor not related to waste.

Of course, if the odor is originating from the waste mass within the landfill, a landfill-gas collection will often be the most effective solution.

During the interim, or sometimes as a long-term solution, perimeter or onsite misters that emit odor-destroying enzymes that will neutralize the odors can be installed. Another option is to use some type of masking scent.

Most landfills have the potential to create odors, but there are also many ways to effectively mitigate them. The key to successfully dealing with landfill odors is to first understand their origin and movement and then-and only then-identify practical solutions.

Consultant and contributing columnist Neal Bolton specializes in landfill operations and management.