Landfill sites are a necessary part of modern life, but they’re also responsible for releasing a vast number of gases into the atmosphere. Depending on the site in question, methane and carbon dioxide make up around 90 to 98% of landfill gas, with the remaining 2 to 10% coming from nitrogen, oxygen, ammonia, hydrogen, and sulfides, amongst others. In order to ensure safety for humans and ecological life, landfill gas monitoring is necessary to determine air quality and migration of gases, alongside other potential gases.

Types of landfill gas monitoring

There are currently five main types of landfill gas monitoring that take place, these include:

1. Soil/ground gas monitoring

Soil or ground gas monitoring is necessary for measuring the concentration of chemicals and gases such as methane, oxygen, carbon dioxide and nitrogen in the vapor space of soils. These measurements are taken at depth using probes or wells and are useful for reviewing the potential risk of explosions and ensuring landfill gases are not migrating into soils surrounding the site.

2. Near-surface gas monitoring

Near-surface gas monitoring measures the concentrations of gases no higher than four inches above the ground’s surface. This is done to determine whether high levels of landfill gases such as methane are escaping the surface and is also helpful in checking landfill gas collection and control systems are performing correctly. Near-surface gas monitoring is usually done with a portable instrument known as an organic vapor analyzer flame ionization detector (OVA/FID).

3. Emissions monitoring

Emissions monitoring measures the rate at which chemicals are released from a specific location such as landfill surfaces, stacks, or flares. These gases are sampled using a variety of techniques, depending on the source of the emissions and the chemicals in question.

4. Ambient air monitoring

Ambient air monitoring measures the levels of pollution in outdoor ambient air or the air people breathe. Sampling is generally carried out in the vicinity of landfills, then this data is sent to be critically evaluated by environmental health professionals to check air exposure concentrations.

5. Indoor air monitoring

This type of monitoring measures levels of contamination in indoor air spaces and is typically carried out at structures on or surrounding landfill sites. This is useful for evaluating the risk of explosions and exposure to certain contaminants.

Where are landfill gas analyzers placed?

Landfill gas analyzers and systems can be placed at several different locations, depending on the type of monitoring that needs to take place and the data that needs to be collected.

• Subsurface: used for analyzing concentrations of contaminants in soil gas below the soil-air interface. The depth of sampling can range from a few inches to several feet.

• Surface systems: these measure concentrations of gas a couple of inches above the soil-air interface.

• Enclosed space systems: responsible for monitoring gases in indoor air or confined areas such as buildings, vaults, and utilities near landfill sites.

Methods for landfill gas monitoring

Landfill gas is collected and analyzed using a range of different techniques and equipment. Some of the most common ways it’s collected are as follows:

Portable monitors

These are hand-held instruments that are easy to carry around the site. Portable monitors are most useful for locating the source of methane leaks or for the initial screening of landfill gas migration pathways.

Stationary monitors

Stationary monitors are installed at fixed locations and are not moved throughout the entire monitoring process. Typically, they produce higher quality data than portable devices and are particularly useful for measuring gases at a set location.

Grab sampling

Grab sampling is a one-time measurement of gas concentrations and can provide a quick overview of landfill gas composition at a set place and time. This method is not useful for evaluating changes in the long term unless it’s carried out regularly in reference to a more detailed plan.

Continuous monitoring devices

As the name suggests, these devices continuously analyze and sample gas concentrations. Some have the ability to document fluctuations over short intervals, whereas others will provide an average of concentrations. Continuous monitoring devices are generally better at providing insight into gas composition in the long term.

How are gas samples analyzed?

Once the gas samples have been collected, there are two main ways in which they’re analyzed. For more detailed and accurate results, samples may be sent to a laboratory for further analysis which may take some time and be more expensive. Alternatively, samples may be evaluated right away in the field which is referred to as real-time monitoring. Real-time monitoring generally isn’t as sensitive and does not look for a range of pollutants like laboratories can, but they do provide data as soon as it’s measured, which may be useful for obtaining a quick snapshot.